Summary Of Post Doc Synthetic Procedures 2003


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Summary Of Post Doc Synthetic Procedures 2003

  1. 1. 1 FINAL REPORT SUBMITTED BY Dr. FRANK E. INSCORE DECEMBER 18, 2002. POSTDOCTORAL RESEARCH ASSOCIATE IN ENEMARK RESEARCH GROUP THE UNIVERSITY OF ARIZONA, DEPARTMENT OF CHEMISTRYSUMMARIZING AND POINTING OUT KEY SYNTHETIC ASPECTS ON SYSTEMS STUDIED MAY 2000 TO DECEMBER 2002This report focuses on the 4 major high-valent TM dithiolate (and thiolate) systems that were studied as apostdoctoral fellow for JHE. These include 1). Tp*ME(S-S), where M=Mo: E=O,S,NO and M=W: E=O;2). [MoO(S-S)2]-; 3). Tp*MoO2SR; and 4). Cp2M(S-S), where M = Mo, W. The following report, which isfar from being complete, is an attempt to bring closure to the study of these systems regarding mycontributions and purpose. The goals and objectives of these studies and interest are an extension andcontinuation of ideas/postulates initially developed from my PhD work as a spectroscopist, and here aswell, which has provided the motivation to balance out my knowledge of these systems by obtainingextensive synthetic experience. Thus, this report primarily serves to present key synthetic aspects andmethodologies developed that are described in some detail for specific examples, and therefore shouldprovide additional assistance to others interested in the syntheses, chemistry and the structural, electronicand electrochemical properties of these systems. The majority of the spectroscopic sampling I have left forothers in the group, thereby coupling them into the research and providing projects and material for theirtheses and dissertations. In addition, I have made it a point to also couple as much as possible others in thegroup into these synthetic aspects so they can obtain valuable experience and balance, and thusindependence in their future works. I have therefore included in the report praise and credit to thoseinvolved and their specific contributions to these previous and on going studies. It has certainly been anhonor and valuable learning experience to serve as a senior research associate in the NIH funded worldclass group of Prof. John H. Enemark. Special praise and professional respect go to Julien Schirilin , PabloBernardson (both undergraduates) and Hemant Joshi (graduate student), all of whom I have had the honorof directing and participating in their research here at the University of Arizona (Dept of Chem), as well asmy wife (Kristie) who put up with my long and sometimes weird hours. The most praise goes to JohnEnemark, who allowed me the freedom and independence to develop my own projects of interest, whichhave resulted in papers published and new ideas that has motivated others in the group to pursue further.
  2. 2. 2Works past, in progress, contributions and future responsibilities w/r to model studies.Synthetic Systems from May 2000 to December 2002.FeTTP Porphirin complex (with Hiroshi) for EPR std for Arnold.KTp*Ultra pure H2bdt (white crystals) from vac.distil.under Ar from H2bdt from Na2bdt/from protected formand/or Li2bdt from S8/ HSPh(vac distilled under Ar) ; using reported synthetic methods.Na2bdt from H2bdt/NaOMe/MeOH; H2bdt being commercial or synthesized. Note one can also use Na(K).similarly NaSPh from HSPh/Na2EDT from H2EDT/Na2PDT from H2PDT using commercial dithiols(Com.dithiols, that are liquids at RTcan also and easily be distilled under vac/Ar, e.g H2bdt,EDT, HSPH)H2qdt/ /Na2qdt/H2qdt from reported synthetic method.MoO(Cl)3THF2 from purified: MoCl5 (Aldrich)+THF// WO(Cl)3THF2 from purified: WCl6 (Aldrich)+THF (Tp*)MoOCl2 // Other potential precursors as reported: (Tp*)MoO(OMe)2, (Tp*)MoO(OEt)2, (Tp*)MoO(EDO) (Tp*)MoO(bdo), (Tp*)MoO(bdo,s), (Tp*)MoO(OPh)2 (Tp*)MoO(SPhMe)2 (Tp*)MoO(tdt), (Tp*)MoO(bdt), (Tp*)MoO(bdtCl2) (Tp*),MoO(qdt), (Tp*)MoO(edt) (Tp*)MoO(EDT), (Tp*)MoO(EDTMe2), (Tp*)MoO(PDT) (Tp*)MoSCl2 from (Tp*)MoOCl2 (Tp*)MoS(tdt), (Tp*)MoS(bdt)(Tp*)WOCl2(Tp*)Mo(CO)3 from Mo(CO)6 (Aldrich) // (Tp*)W(CO)3 from W(CO)6 (Aldrich) (Tp*)MoNO(CO)2 (Tp*)MoNOI2 // (Tp*)MoNO(OEt)2/ “ (Tp*)MoNO(EDO)” “semi-isolated/ and identified by MS” (Tp*)MoNO(tdt) (Tp*)MoNO(bdt) (Tp*)MoNO(bdtCl2) “(Tp*)MoNO(qdt)” “identified in crude react. mixture by MS, very unstable for separating on collumn”(Tp*)WO(CO)2 // (Tp*)WI(CO)2 (Tp*)WOI2 (Tp*)WO(bdt) (Tp*)WO(tdt)[MoO(CL)4]- from MoCl5 (Aldrich) // [MoO(Cl)4H2O]-[MoO(SPh)4]- from HSPh and MoOCL3THF2 // [MoO(SPhCl)4]- from HSPhCl and MoOCL3THF2 [MoO(EDT)2]- [MoO(bdt)2]- [MoO(bdtCl2)2]- “[MoO(SPh)2(bdtCl2)]-“ “unstable intermediate semi-isolated and identified from MS”Mo2O2Cl2 from // Mo2O2Br2 from//(Tp*)MoO2Cl // (Tp*)MoO2Br// (Tp*)MoO2SPh (Tp*)MoO2SCH2PhCp2MoCl2 (Aldrich)/Cp2WCl2 (Aldrich)Cp2Mo(tdt), Cp2Mo(bdt), Cp2Mo(bdtCl2), Cp2Mo(qdt), Cp2Mo(edt) from Cp2MoCl2“CpMo(bdt)]2-“ “unexpected side product isolated/ identified by MS” Direct synth from CpMo(CO)3I too.Cp2W(bdt), Cp2W(bdtCl2) from Cp2WCl2
  3. 3. 3 KTp* WOCl3THF2 MoOCl3THF2 (Tp*)MoNO(CO)2 (Tp*)MoVS(Cl)2 (Tp*)WVO(I)2 (Tp*)MoIINO(I)2 (Tp*)MoVO(Cl)2 (Tp*)MoIINO(I)2 (Tp*)MoVS(Cl)2 (Tp*)WVO(Cl)2 H2(S-S) Na2(S-S) 2:NEt3 (Tp*)MoIINO(OEt)2 2:NEt3 (Tp*)MoIINO(Cl)2(Tp*)MoVO(qdt) “(Tp*)MoIINO(qdt)” H2(S,S) Na2(S,S) H2(S,S) H2(S-S) IINO (S-S) 2:NEt3 (Tp*)MoVS(S-S) (Tp*)Mo(Tp*)MoVO(bdtCl2 ) (Tp*)MoIINO(bdtCl2 ) Na2(S,S)(Tp*)MoVO(tdt) (Tp*)MoIINO(tdt) (Tp*)MoVS(tdt) (Tp*)WVO(tdt) (Tp*)MoIINO(OMe)2 (Tp*)MoVO(bdt) (Tp*)MoIINO(bdt) (Tp*)MoVS(bdt) (Tp*)WVO(bdt) (Tp*)MoVO(edt) (Tp*)WVO(I)2 (Tp*)MoVO(I)2 (Tp*)MoVO(EDO)(Tp*)MoVO(SPhMe)2 H2(S-S) (Tp*)MoVO(OR)2 2:NEt3 Na2(S-S) 2Na(OR)2Na(SR)(Tp*)MoVO(EDT)(Tp*)MoVO(EDTMe2)(Tp*)MoVO(PDT) (Tp*)MoVO(S-S) (Tp*)WVO(S-S) (Tp*)WVO(OR)2(Tp*)MoVO(bdo) (Tp*)WVO(SR)2(Tp*)MoVO(bdo,s) 2:NEt3 2:NEt3 H2(S,S) Na2(S,S) H2(S,S) Na2(S,S)(Tp*)MoVO(EDO) “(Tp*)MoIINO(EDO)” (Tp*)MoVO(Cl)2 (Tp*)WVO(Cl)2(Tp*)MoVO(OPh)2(Tp*)MoVO(OMe)2 Na2(qdt) H2(qdt) Aldrich H2(bdt) H2(tdt) H2(bdtCl2) MoOCl3THF2 WOCl3THF2 (Tp*)MoNO(CO)2 Na2(bdt) H2(bdt) Na2(edt) H2(edt) Mo(Cl)5 W(Cl)6 (Tp*)W(CO)2 (Tp*)Mo(CO)2 W(CO)6 Mo(CO)6 KTp* (Tp*)MoVIO2(SCH2Ph) (Tp*)MoVIO2(Cl) (Tp*)MoVIO2(SPh) (Tp*)MoVIO2(Br) [MoO(EDT)2]- rt [MoO(SPh)4]- THF(excess) [MoO(bdt)2]- 4H(SPhR) MoCl5 MoOCl3THF2 H2(S-S) 4Net3 [MoO(bdtCl2)2]- [MoO(SPhCl)4]- [MoO(Cl)4]- [CpMoIV(bdt)2]- Cp2 MoIV(bdt) Benz// 2Net3// H2O reflux 1hr Cp2 MoIV(tdt) Cp2 MoIVCl2 Cp2 MoIV(bdtCl2) H2(S-S) Cp2 MoIV(qdt) Benz// H2O reflux 1hr Cp2 MoIV(edt) Na2(edt) Cp2 WIV(bdt) Benz// Net3// H2O reflux 1hr Cp2 WIVCl2 H2(S-S) Cp2 WIV(bdtCl2)
  4. 4. 4 (Tp*)ME(S-S) Precursors// Potential (Tp*)MO(S-S) Precursors (Tp*)MoVO(Cl)2 (Tp*)MoIINO(I)2 (Tp*)MoVS(Cl)2 (Tp*)WVO(I)2 (Cp2 MoIVCl2) (Cp2 WIVCl2) [MoO(SPh)4]- (Tp*)MoVIO2(Cl) (Tp*)MoVO(OMe)2 (Tp*)MoIINO(OEt)2 (Tp*)WVO(Cl)2 (Tp*)MoVIO2(Br) (Tp*)MoVO(EDO) (Tp*)MoVO(tdt) (Tp*)MoIINO(tdt) (Tp*)MoVS(tdt) (Tp*)WVO(tdt) Cp2 MoIV(tdt) (Tp*)MoVO(bdt) (Tp*)MoIINO(bdt) (Tp*)MoVS(bdt) (Tp*)WVO(bdt) [MoO(bdt)2]- Cp2 MoIV(bdt) Cp2 WIV(bdt) (Tp*)MoVO(bdtCl2) (Tp*)MoIINO(bdtCl2) Cp2MoIV(bdtCl2) Cp2WIV(bdtCl2) [MoO(bdtCl2)2]- (Tp*)MoVO(qdt) Cp2 MoIV(qdt) (Tp*)MoVO(edt) Cp2 MoIV(edt) Submitted for: -Studies char prod identity/purity//chemical//physical properties//eval syn/pur route. Reactivity studies MS MS/NMR -CV studies in DCE,identical conds. comparison; red/ox pots, rev, behavior ect. Char;(MS/NMR) -Hetrogenous ET rates -CV -CV -structural studies/ comparison (XRD) -electronic studies/ comparison (IR(KBr-DCM)//EA(DCE)//EPR(Tol)//) -XRD -XRD -PES(GP-HeI/II) (NeI) studies/ comparison -IR/EA -IR/EA -IR/EA -rR(solid-solution(Ben)) vibrational studies/ comparison -PES (HeI/II) -Anionic PES -DFT comp studies for structurally defined complexes;MO descript/basis elec struct. -rR -Generation-isolation of 1e- red/ox species; parallel studies-struct-elec char of/comp. -DFT -DFT calcs -DFT DITHIOLATE COMPLEXES (with (-SC-CS-)n n=1,2; (-SCCCS-))•(Tp*)MoVO(EDT) saturation effects: SC-CS vs SC=CS; compare to edt complex. •[MoO(EDT)2]- (Tp*)MoVO(EDTMe2) compare to edtMe2 complex, in case cant make edt complex.•(Tp*)MoVO(PDT) chelate ring size effects THIOLATE COMPLEXES (with (-SR)n n=1,2,4) •[MoO(SPh)4]- •(Tp*)MoVIO2(SPh)•(Tp*)MoVO(SPhMe)2 chelate effects:monodentate vs bidentate (Tp*)MoO(S2) systems •[MoO(SPhCl)4]- ADDITIONAL COMPLEXES •(Tp*)MoVIO2(SCH2Ph) (Tp*)MoVO(bdo,s) donor atom type effects (1O vs 1S)•(Tp*)MoVO(bdo) donor atom type effects (O vs S)(Tp*)MoVO(EDO) •[MoO(Cl)4]-(Tp*)MoVO(OPh)2 donor atom effects. These were also synthesized for comparison with potential Tp*MoNO analogs. Sent to Kirk group for additional vibrational database etc.
  5. 5. 5 Na2(qdt) H2(qdt) (Tp*)MoVO(qdt) H2(bdtCl2) (Tp*)MoVO(bdtCl2 ) Aldrich H2(bdt) H2(tdt) Tol (Tp*)MoVO(tdt) (Li2(bdt)//K2(bdt)) 70°C Na2(bdt) H2(bdt) (Tp*)MoVO(bdt) Solv? Tol -2 Cl- H+:NEt Na2(edt) H (edt) 3 (Tp*)MoVO(edt) -2 I- H+:NEt3 2:NEt3 2:NEt3 Na2(mnt) H22 (mnt) (Tp*)MoVO(mnt) H2(S-S) H2(S-S) (Tp*)MoVO(S-S) ? (Tp*)MoVO(S-S) Na2(S-S) Na2(S-S) ? (Tp*)MoVO(bdt) -2 NaI 2HSR/NEt3 Solv? (Tp*)MoVO(SR) ?? Tol -2 NaCl 2 Tol (Tp*)MoVO(edt) 2NaSR/(KSR)Tol -2NaCl Tol(Ben) Ligand Exchange: K2(S-S) -2 KCl (Tp*)MoVO(EDT) //(SC-CS) (Tp*)MoVO(Cl)2 at elevated T(>rt) (Tp*)MoVO(I)2 ? (Tp*)MoVO(EDO) ? in np Solv Tol(Ben) Tol Tol (Tol?) +H2(bdo) H2(S-S) (Tp*)MoVO(edt) 2:NEt3 -2 Cl- H+:NEt3 H2(O-O) (Tp*)MoO(O-O) (Tp*)MoO(bdo) (Tp*)MoVO(S-S) ? Na2(O-O) -2 NaCl Tol -H2(EDO) (Tp*)MoVO(bdt) Tol(Ben) Tol(Ben) 2NEt3 Tol Alc/solvl 2NEt3? 2HOR (Tp*)MoVO(OR)2 Tol (Tp*)MoVO(bdt) 2NaOR -2 NaCl (Tp*)MoVO(OEt)2 ? (2KOR) 2NaOMe Solv? H2(S-S) -2H(OMe) (Tp*)MoVO(edt) Tol ? (Tp*)MoVO(S-S) ? (Tp*)MoVO(OMe)2 MeOH Na2(S-S) -2NaOMe Tol (Tp*)MoVO(edt) 2NaOMe /MeOH Solv? MeOH (Tp*)MoVO(bdt) MoOCl3THF2 MoCl5 KTp* Mo(CO)6 AldrichI.Complexes of the{(Tp*)MoO}2+ System TypeA.Preparation of Ligands1. KTp*-There was some of this ligand already availlable in the lab; synthesized and commercial grade. Also,precursors for making this ligand were also availlable in the lab.-However, as this is the Enemark group and we specialize in stabilizing a wide variety of complexes withthis ligand, KTp* was also freshly prepared and purified by following well established procedures asreported and further developed in this lab. This provides a better feel for the chemistry of this ligand, itsproperties, behavior and how to obtain in ultra pure form and handle, subsequent to using in various stagesof reactions that ultimately involve metallation with Mo (W) forming 6-coordinatecomplexes.NOTE:-There is literature precedent for making Na salts of Tp*, and appears to change the reactivity somewhat vsKTp*, this was thought about but never got around to trying. Mike Arven (grad.stud) has taken mysuggestion and is making both salts in his attempt to further stabilize a reaction route to making the(Tp’)MoOCl2 precursor with Tp’=Tp(F) vs Tp(Me) = Tp*.-It is apparent that the e- donating capabilities of the remote substituents on the Pz rings has a direct impacton the e- density of the metal and hence electronic structure as evident by the literature of various Tp’Mcomplexes (w/r to structure; Tp’, Tp’-M, and M-L metrics, also different electronic and redox properties).The Lit needs to be scoured as there are a substantial number of papers with Tp’M that look at the effects or
  6. 6. 6report the effects of Tp’ =H,Me,F, and other such variations etc in an isostructural environment w/r to themetal and other coordinated ligands. This is important as the question now to address is how the Tp ligandand the nature of it affects the electronic structure of Tp’ME(S-S) complexes, as we have now probed theeffects of the metal, axial changes, and nature of the equatorial (dithiolate) ligand with Tp’(=Tp*)remaining invariant. Furthermore, changing from Tp(Me) to Tp(F) with its expected different e- donatingability (due to e- withdrawing property of F substituents) is anticipated to shift Tp ionizations in PES andmay deconvolute S based ionizations lying under the envelope in the Tp* systems aiding in bandassignments. Mike is attempting to address these issues as directed by JHE.--Mike and I on our 1st attempt to make Tp(F)MoOCl2 witnessed firsthand the difference that the nature ofTp’ has on making this precursor, and hence reflecting the reactivity/stability of the KTp’ ligand. This isnot an easy problem or syntheses, but I believe it can be done with perseverence. HeI(II?)PES (Hemant) ofKTp(F) showed significant shifts in the ionizations vs KTp(Me) consistent with e- withdrawing nature of Fand also consistent with Mikes calc shifts in energy with this substitution. The goal here was to make thehalide precursor and subsequent ligand exchange for preparing Tp(F)MoO(bdt) and comparing to theprevious well characterized Tp(Me)MoO(bdt). This should significantly change the electronic structure(and metrics) such that would help in elucidating the PES of the Tp*MoO(S-S) complexes. The differencesin the Tp(F) ligand valence MO energies and e- withdrawing properties, upon interacting with the metalshould have an affect on the electronic structure of the Mo complex, and more importantly shift the Tp’ionizations in PES so that can resolve out additional L bands.Side Note: w/r to above applications, problems with initial synthesis may be due to presence of water inKTp(F), I have suggested this as possible reason for decomposition for various reasons (e.g. hydrolysis ofprecursor) and it is evident that the initial salt was wet. Mike is trying ways to eliminate any water fromKTp’ prep.Mike may also consider utilizing a different precursor other than Tp’MoOCl2, e.g. such as the Tp’ analogof (Tp*)MoOI2, the latter has been made/reported in the literature but yet to be isolated in our lab or evenknown whether it will undergo ligand exchange. Whether this would work or not for Mike remains to beseen.-In fact the use of (Tp*)MoOI2 as an alternative precursor for the target dithiolate complexes afforded bythe di-Cl analog in this particular system has yet to be applied. I have suggested the use of (Tp*)MoOI2 asa potential precursor for ligand exchange reactions to make Tp*MoO(S-S) based on our success foremploying this type of precursor (Tp*)MEI2 (M=W,E=O; M=Mo, E=NO) in making the correspondingdithiolene complexes, whereas the Cl analogue in these latter systems could be isolated it did not affect thedesired reaction. The use of this complex as a potential precursor is certainly worth pursuing.-(Hemant has tried to make the (Tp*)MoOI2, from reported procedure, for comparison with the PES of theother halides (F,Cl,Br) but it appears to be unstable and not isolated as shown when Hemant and I ranabsorption on his ambiguous and still not pure sample, there being no evidence of low energy CT whichshould be the case, overlapping the dxy to dxz,yz and dx2-y2 LF transitions as one goes from F to I in theF,Cl,Br,I series). Also it appears to be very sensitive to presence of air (O2 /Water ) especially in solution,and this may be the reason for his difficulties. This sensitivity I have previously observed also with theTp*Mo(NO)I2 analog e.g., used as our precursor for making dithiolene complexes via ligand exchange andrequired special precautions that must be employed (and as has been suggested in the literature, w/r toadvantages and disadvantages of di-iodo precursor vs using the di-Cl analog in this {Tp*MoNO}2+ system),which Hemant must buckle down and employ here as well in order to isolate and stabilize this complex.The take home message from preparing and purifying the Tp*Mo(NO)I2 analog that Julien Schirlin and Iboth learned the hard way is that it must be preped under extremely dry-deoxygenated conditions beforeusing, as it is already extremely difficult to purify all the way; this being evident even with a silica gelcollumn dried and deoxy w/r to gel and solvents used, side products/decomposition still occurr on thecollumn as a result of minute traces of water ect that reduce the amt of initial pure precursor resolved uponbeing eluted. Thus, pure compound can be obtained, but is subsequently and easily decomposed uponsolvation. This unevitable complicated decomposition upon solvation and/or use of collumnchromatography must also be considered for the oxo-Mo-di-iodo system as well, and neccesitates the use ofvery dry/deoxy conditions be employed and not taken lightly. Another caveat is that there are severalvariations on making a (Tp*)MEI2 from M(CO)6 involving the various intermediates that can be isolated
  7. 7. 7along this reaction route (i.e.May need to try different route, e.g. see Tp*MoNO(CO)2 directly toTp*MoNOI2).(the reported procedure for Tp*MoO(I)2 is: in situ prep of Tp*Mo(CO)3 by refluxing Mo(CO)6 (2.63g,10.0mmol)+KTp*(3.36g,10.0mmol) +THF(85ml) -- Tp*Mo(CO)3 / then +I2 (2.54g, 10.0mmol) atRT/24hrs/conc to 20ml -- (50ml n-heptane crashed out red/brown ppt/filtered of and washed withheptane/dried in vacuo) Tp*MoI(CO)2 / . Tp*MoI(CO)2 (.542g/.941mmol)+I2 (.239g,9.42mmol) in 30mlTol/RT-24hr/evap to dryness -- (Tp*)MoOI2 ) (XRD from residue tol/heptane layer –dk purple/blackTp*MoO(I)2 •C7H8) IR is used to monitor reaction progress by appearance/dissappearance of COvibrational modes between 2025-1922 cm-1. Need to check stoichiometry and IR reported for reactants asthis paper has lots of discrepencies, also as can see the crystal obtained for xrd came from a solution of rawresidue obtained that was considered pure with respect to monitoring the absence of v(CO) in the IR,however there may be other leftover reactants and/or sideproducts that may be present ).Note: See synthetic methods to all other precursors below.2.a.Dithiols: The H2(S-S) dithiol ligands (protonated forms of the corresponding dithiolate S-S2- dianion),commercialy availlable are S-S = tdt, bdt, bdtCl2 (of dithiolene SC=CS type; and EDT,PDT ect. ofdithiolate SC-CS type; and diols of both types H2bdo, H2EDO ect, diolates being unprotonated dianions;and thiols HSR/SPh, SPhR R=H, Me,Cl ect, thiolates being nonprotonated monoanions). Other dithioleneligands e.g., such as qdt2- and edt2- dithiolate dianions, must be synthesized from availlable precursors(generally non S containing) that can be converted to some form from the corresponding dianion (dithiolate salt of dithiolate dianion or protonation of dithiolate dianion to dithiol.).Note: These 1,2-dithiolenes S-S2- (dithiolate dianions) are designated as ene-1,2-dithiolates. However, theedt2- ligand is a true ene-1,2-dithiolate (able to undergo facil redox changes), while bdt2- and similar ligandswhich do possess a -SC=CS- chelate, are really an aromatic 1,2-dithiolate instead, due to being conjugated–delocalized with the benzene ring. However, to a 1st approximation, such aromatic dithiolates areconsidered in general to represent the ene-1,2-dithiolate w/r to the SC=CS portion, and has been found tobe reasonable. (see valence bond approach w/r to S-C/C=C metrics).(see reported dithiolene ligands, where for the exceptions mentioned above must all be synthesized).A recognized problem with HSR thiols and H2(S-S) dithiols (dithiolene/dithiolate type) are their propensityto be decomposed in air. A particular problem is their sensitivity to air, being oxidized facily by oxygen todisulfides; the extent of this sensitivity appears to be dependent upon the nature of the dithiol; e.g. PDTdecomposes by 30% within 30 min upon exposure to air while much larger chelate rings are lesssusceptable and may take weeks to exhibit signs of decomposition, also S rich dithiolenes (e.g. (HS)4Benz)are extremely susceptable to air oxidation, in particular in solution (and especially in the presence of a basewhich deprotonates the dithiol and subsequently forms the dithiolate dianion in solution, being more proneto decomposition ), as compared to a less S rich dithiol such as (HS)2Benz (=H2bdt). The increasedpotential for decomposition upon base addition which acts to deprotonate the dithiol in solution to a freedianion dithiolate ligand reflects the greater sensitivity of this resulting dianion in solution vs theprotonated dithiol free ligand whether in solution or not. Further, the external appearance of the dithiol insolid may over a periode of time not reveal the presence or extent of oxidation even when isolated fromthis, thus even minute changes can upon char reveal decomposition. The presence of water w/r to thisligand at this point is not problematic here, and in fact can be used as a solvent. However, H2S-S exposureto O2 must be minimized at all times.Thus, to ensure the purity of the dithiols (commercial or synthesized), we have routinely employed aspecial vacuum distillation setup for this purpose, in particular for collecting the purified thiol/dithiolligands that are liquids at RT/1 atm (HSPh/ H2(bdt)/ H2EDT) under Ar, free from water/oxygen/disulfidesand other contaminants. The H2tdt and H2bdtCl2 ligands commercially availlable are solids at RT, and aregenerally used as received (but are dried/deoxy by gentle purging cycles under vacuum prior to use atslightly elevated temperature). This setup is similar to that previously employed by Julian Schirilin/JonMcmaster for the final purification of synthesized H2bdt proligand following a specific lit procedure fromHSPh that reported the highest yield and purity of all methods published. This brings up another issue,especially with respect to commercial H2bdt which is obtained in 100 or 500mg sample vials (~1ml- )rather expensive and of such small quantity making it difficult to purify this way (note: pure synthesized
  8. 8. 8H2bdt is obtained from this method is relatively clear crystalline material when maintained in fridge,turning yellow/brown upon exposure to air or time; while commercial H2bdt is brown liquid at RT uponpurchase, thus distilling of commercial H2bdt requires a large (and expensive) investment making itspurification by direct synthesis more convenient than purifying commercial material. Julian and Isubsequently used the synthesized H2bdt ligand in all of our synthysis employing it while the supply andintegrity lasted; the ligand being stored in fridge, would over time turn brownish, and hence prior toadding to reactions we would again redistill the parent H2bdt synthesized/purified by this method to obtainultra pure proligand prior to adding it in our reactions. This was so for the Tp*MoNO(bdt) synthesis.Eventually, this material was used up before Julian left, and required me to make additional ligand by thismethod. I was able to use this new material (distilling prior to use) in subsequent reactions to make moreTp*MoNObdt, Tp*MoO(bdt) and also for making Tp*WObdt, and [MoO(bdt)2]-, but unfortunately thismaterial was unknowingly left out in the air exposed by others,and was subsequently unuseable afterwards.This required that commercial H2bdt be employed in making additional Tp*MoE(bdt) complexes and laterthe Cp2M(bdt) complexes, which was initially distilled from the commercial material at great effort prior touse.However, the success of purifying commercial/ and presynthesized H2bdt by this distillation setupsuggested that HSPh and H2EDT, which are commercially availlable in large cheap quantities (100ml orgreater) making purification by this setup affordable for these latter dithiol ligands obtained commercially,possible. This was initially applied with HSPh in the synthesis of ~10g of the [MoO(SPh)4]- precursor,which was used in subsequent reactions with purified H2bdt to make MoO(bdt)2]-. This precursor isextremely sensitive in solution to air, and difficult to handle, and decomposes rapidly unless precautions aretaken. Using an anaerobic cell, the progress of the reaction is easily monitored by EA with thedissapaerance of the precursor low energy CT band () followed by the concommitant appearance of thelower energy CT band () upon substitutiion of 4SPh ligands for 2 bdt bidentate chelating ligands. EPR canalso be used to monitor the reaction progress. A similar synthesis from this precursor using commercialH2bdtCl2 was employed to make the new complex [MoO(bdtCl2)2]- (note that longer reaction time isrequired for full conversion of this precursor ~2x as long else get a mixture including complex with partialconversion 1bdtCl2 and 2SPh ligands confirmed by MS (also HSPhCl commercial ligand to makecorresponding SPh analog as previously reported). Further reactions with this precursor included makingMoO(EDT)2]-, where H2EDT, obtained commercially possessed significant contaminants, and if notdistilled resulted in a very difficult reaction mixture to separate (usually an oil) also a problem in theTp*MoO(EDT) system. Thus, Pablo Bernardson was directed by me to distill this commercially purchasedH2EDT ligand using this method. This was successful and the ligand was subsequently used to make theMoO(EDT)2]- complex.Note: Here is a point for digression. This was the time where I took Pablo under my wing to show him andto demonstrate how to synthesize air sensitive complexes using the appropriate schlenk methods andequipment (in this case, an extreme synthetic example requiring very rigorous exclusion; and futherconsider that not many could take these lessons to heart and eventually apply successfully on their on,which is the goal all teachers/mentors hope/ (or should) for their proteges). This was necessary as hisprevious attempts to synthesize less sensitive complexes had been difficult under the direction of himselfand others (no clear understanding of adv. synthetic techniques whatsoever at this point) and such being thecase could have clearly demoralized to such an extent that future progress (as those for certain littlesetbacks in any research project eventually occur) could have been retarded. A similar situation (lack ofconfidence due to misinterpretation of limited success; which was nothing more than the absence of properguidance and positive experience) was also apparent with a previous undergrad student and several recentgraduate students. All that is needed is to take a little time, interest and initiative to motivate an individual,who we sometimes forget is there to learn and aspire to self sufficiency. As a postdoc, I firmly believe thatit is our responsibility to facilitate both grad and undergrad research, even at the expense of relinquishingfull credit of a project well in progress upon the inclusion of those with very little experience and in thelatter exp stages. This direct participation of postdocs has a high payoff; this is I believe is the success ofJHE research, and results in the well known world class quality of students fortunate enough to beinvolved; specifically the highest caliber of grad/undergrad students availlable and in my direct experienceand good fortune these are Hemant K. Joshi(G)/Pablo Bernardson(ug)/ Julien Schirilin (ug) along withothers I was less involved with. The latter part of this synthesis I introduced eventually to Pablo, although
  9. 9. 9simple in theory, involving a direct ligand exchange of H2(S-S) with the previously prepared and purifiedMoO(SPh)4]- precursor, however presented very difficult challenges w/r to maintaining total exclusion ofwater and air, and thus provided the perfect system for him to learn schlenk techniques and master the artof air free synthetic methods that are applicable for any system, especially regarding how to develop andexperimentally setup a reaction route with total control of the environment (minimizing all potentialextraneous variables in the process). This voluntary tutoring (of which I allways give freely for those whowant to learn) with detailed explanation of each step has served him well, allowing him to pursue andachieve independently other projects later. Specifically, he assisted me in the 2nd synthetic batch ofMoO(bdt)2]-, watching and learning, which was further remphasized by assisting me in the final synthesesof the MoO(EDT)2]- compound (the most difficult to obtain in purified form, being isolated as a salt of, buthighly susceptible to decomposition even under conditions that generally were accepted as rigorous , thatwould occur nonetheless unless very extreme conditions and precautions were employed ) . As a resultofhis desire to learn and willingness to participate, he was directed to write up his observations of thissynthesis and methodology experience in a report submitted for his undergraduate research. This was animportant learning experience imparted. I was fully aware that this reaction could go various ways for anumber of reasons and thus even the best laid plans do not always give you the desired results, and as inthis case rather than giving up or starting over, it is best to think why, and what can be done to overcomethe problems even though they appear insurrmountable, i.e. adapt/ never give up so easily. I have seenother graduate students involved with this synthetic system of complexes give up. The confidence obtainedwith a successful preparation and continued perserverence, imploying clearly defined systematicmethodologies is evident, and should provide a catalyst for further independent studies on his own merit, asindeed he has shown and proven. In fact, I wish to state that his understanding and appreciation is nowsuch that he is approaching developed skills and techniques that never takes the short cut for expediency forany case, but rather looks for additonal ways, even if more time consuming for such small details to bettercontrol and reduce the variables involved in a synthetic reaction. This is a characteristic required for anexceptional experimental synthesist. The same can be said for Hemant, who also has this potential, but atthe present time is more focused on spectroscopically studying the samples giving to him; note that I wasalso the same way being a hardcore spectroscopist when an undergraduate and most of my graduate studies,and finally at the end reallized this is great but unfortunately as one cant depend always on someone else toprovide the things you wish to study (and with reliable purity) it becomes very obvious and necessary forone to be self suffient and reliant in order for obtaining the necessary samples for rigorous spectroscopicstudy with confidence and reproducibility. Hemant I believe can if pushed, excell at the highest levels asboth a synthesist and spectroscopist, this being the best situation for providing clear and innovating insightinto both fields, and thus the ability to carry out very independent and well rounded bioinorganic/inorganicresearch without being handicapped/limited. Thus the ability for a spectroscopist to achieve excellence inboth fields is important; we are chemist after all, even though we may be a theoretician at heart.Q.What are the properties of these ligands (mp/bp/d/mwt ect). The properties of these ligands in solution,and/or isolated as free dithiols or salts of the dithiolate are important .-Na2bdt can be prepared directly from H2bdt (commercial or synth) in MeOH/ + NaOMe/MeOH, or fromdeprotection of a protected precursor synthesized, and subsequently can be isolated (sol?), then acidified byHCl to its dithiol form and extracted by (sol?) to be distilled in vac. JS has also provided me synth H2bdt.In a similar manner, HSPh, H2EDT(and related dithiolates such as PDT etc) can be converted into their Na(or K) salts. H2tdt can also be converted into its K salt.-It is known that the salts of dithiolates vs protonated dithiol forms are more stable, and thus more readilypurified, and can be stored for longer periodes.b.H2qdt was preped by lit methods from its Na2qdt form. Sol diffs? Hemant has also provided me H2qdt.c.Na2edt was prepared and purified by Pablo using a multistep procedure shown below, similar to thesynthetic route reported previously in the literature.Note:Any char? Can we try to submit a sample of it (and its protected precursor) prepared prior to reaction,say for H1NMR/13C-NMR and compare to reported, and ensure purity of it?Note:What happens to it in reaction solvent and subsequent exposure to air etc, so can use as control formonitoring presence or similar decomp products in reaction product. Can we remove excess or decompproducts based on its behavior from reaction prod mixture?Note:Can we protonate edt dithiolate, if not why etc?
  10. 10. 10Preparation of Disodium Ethylene Dithiolate: as obtained using reported procedure. Taken from PablosSyntheses and Report.Part 1. Preparation of cis-1,2-bis(benzylthio)-ethylene Compound Amt. needed mmol FW mp (ºC) bp (ºC) density cis-1,2- 10 g 104 96.94 -80 60 1.284 dichloroethylene Toluene-α-thiol 17.7 ml 151 124.21 194-195 1.058 KOH 40.38 g 727 56.11 Ethanol 160 ml 46.07 Cl SH S + KOH Cl ethanol SToluene-α-thiol + cis-1,2-dichloroethylene cis-1,2-bis(benzylthio)-ethyleneToluene-α-thiol was distilled and stored in a refrigerator prior to use.In a 250 ml round bottom flask, KOH (40.38g, 727 mmol), ethanol (160 ml, absolute) and distilled toluene-α-thiol (17.7 ml, 151 mmol) were stirred and refluxed under an atmosphere of dry Argon gas for 3 hours.See Figure 1. After 1 hour, all of the KOH should have dissolve and the solution turned to a very darkbrown almost black color.Figure Reaction Apparatus
  11. 11. 11FEI Note: see safety note below as this setup wrong. The Ar flow on bottom must be turned off, insteadflow from top with Ar and close the bottom valve. Set flow such that backflow/press minimized.Cis-1,2-dichloroethylene (10g, 104 mmol) was then added drop-wise to the solution at the boiling pointover 30 min. After adding only 1 ml of cis-1,2-dichloroethylene a precipitate began to form and the colorof the solution appeared light brown. The formation of cis-1,2-bis(benzylthio)-ethylene is highlyexothermic, therefore, cis-1,2-dichloroethylene must not be added too quickly.Safety Note: The above reflux setup needs to be modified, w/r to this reaction. By the top being open, anda pos flow of Ar introduced through the bottom flask, the point and whole ideal of doing reflux can bethwarted; as this open sytem under pos flow (motivated by the misguided idea that this is reflux and airfree) can push/carry the volatils out the exit, with loss resulting in conc reaction mixture. However, this notonly defeats the purpose of reflux (be better to close system with septa under Ar) but is dangerous as itresults in a fire hazard/exposure from solvents; but here it is more dangerous as the reaction at temp(bp)produces volatils that upon exposure to air ignite, which was the case for Pablo observed by the fire at thetop/exit point of his reflux condenser open to the air, as a result of pos Ar flow making this occur even withcooled condenser (cooling –condensation of volatils is overcome by sufficient enough Ar flow.) Turningoff the bottom Ar flow stopped the fire immediately, as cooling could now prevent escape of volatils. Thepoint being, reflux can be done under Ar in a nonclosed system by applying a slight Ar flow to top ofcondenser -as we do in flash chromatography- (where overpressurizing is eliminated by external mineral oilbubbler system with pos Ar excess directed back through and out to open air access , that can be connectedto a trap for volatils if they escape reflux condenser)/ where the bottom reflux schlenk flask sidearms areclosed w/r to any flow in or out in this specific case. The possibility of fire was mentioned in reportedprocedure but not where, why and specific precautions taken ( just that don’t expose to air fordecomposition of target and fire hazards implied w/r to target product isolated). Point is make sure coolingflow or coolant temp (water vs isoprop) is suffient at bp of mixture such that efficient reflux occurs andhence no volatils escape from top. Such reflux can also occur with above Ar setup described above , suchthat no volatils exit the reaction flask at bottom/condenser at top. For efficient reflux, flow of Ar throughcondensor from bottom flask must be capped off , and if still worry about exposure toair and need to ensurethat complete dry/deoxy conditions are maintained use the apparatus described above designed to maintaina system semi-closed under a constant blanket of dry/pure Ar introduced at top of condenser, but asrequired for refluxing, still open, which occurs when system becomes overpressurized yet remains closedw/r to introduction and subsequent exposure to air.The product was filtered and dissolved in boiling ethanol. Insoluble impurities were filtered off while hot.The majority of medium-length, white crystals crash out by cooling the solution to room temperature.Additional crops were obtained by adding cold water to the mother liquors. During this process an oil had
  12. 12. 12formed, which was separated from the solid product, and recrystalized by dissolving in boiling ethanol,cooling, and adding water. This was repeated until all of the oil has disappeared.Part 2. Deprotection upon Sodium Substitution (from Pablos report, following above published procedure)Compound Amt. needed mmol FW mp (ºC) bp (ºC) densitycis-1,2-bis(benzylthio)ethylene 7.643 g 28 272.43Na metal 5.6 g 43 124.21 194-195 1.058ethanol 30 ml, 50 ml 46.07toluene 50 ml +Na-S S Na ethanol +Na-S Scis-1,2-bis(benzylthio)-ethylene disodium ethylenedithiolate Cis-1,2-bis(benzylthio)ethylene (7.643g, 28 mmol) was placed in a 250 ml round bottom flaskover an argon atmosphere using the apparatus shown in Figure 1. Ethanol (30ml, absolute) was added andthe solution was stirred and heated at 105º (oil bath temperature) until all of the Cis-1,2-bis(benzylthio)ethylene had dissolved . Next, Na metal (5.6g, 43 mmol) was added over a period of 20 minat which point a fluffy, white precipitate began to form. As more Na metal was added, the solution becamevery thick with precipitate, therefore 5 additional 10 ml aliquots of ethanol were added during this time tofacilitate stirring. After all the Na had been added, the temperature was raised to 130º and the solution waslet stir for 45 min. It then was cooled to room temperature and brought into the glove box. Additionalcrops of disodium ethylene dithiolate were obtained by the addition of 50 ml of toluene (dry, degassed).The remaining solid was filtered and washed several times with diethyl ether (50 ml).C6H4 (SH)2 As reported, in a 1L three-necked round bottomed flask, under a constant argon pressure, wereadded through a septum 75 ml of hexane with a syringe followed by the TMEDA (24.2 ml) followed by acareful dropwise addition of 200 ml of butyl lithium, at first, to avoid any overheating due to potentialtraces of water in hexane. The mixture being thoroughly stirred, while thiophenol (15.1 ml) was carefullyadded dropwise. To control any overheating the flask was cooled down by an ice/water bath. The mixturewas then left and stirred during two days under continuous argon pressure. Sulfur (4.65 g), previously putunder argon pressure, was then carefully added to the fairly creamy yellowish mixture. The reaction flaskwas even cooled down with an ice bath. The reaction mixture was then stirred for one more day. Themixture was quite thick and yellowish. Careful and dropwise addition of 3M HCl solution (100 ml) wasperformed. Quenching of the solution was done with water (50 ml) plus ice. The solution was extractedthree times with ethyl ether. The combined ethyl ether layers were then evaporated. The resulting thickyellowish oil was then distilled at atmospheric pressure and at a temperature of 78°C. A clean whitedistillate was obtained and conserved in the fridge where it crystallized. 9 - 10.5 ml of pure H2bdt wereobtained (55 % -62% yield; reported ~95%)3.Preparation of precursors
  13. 13. 13a. MOCl3THF2 from MoCl5 (or WCl6)A modification of a reported procedure was used for isolating: MoCl5(s) /CCl4 +THF1).(Tp*)MoOCl2 prepared as reported by adding KTp* to a solution containing MoOCl3THF2 generated insitu (or isolated) from MoCL5 and THF (reaction being highly exothermic and thus must be cooled).Purification followed procedures well established in this lab.In a 250 ml round bottomed flask, 6.50 g (23.831 mmol) of MoCl5, sitting in a dry ice bath with acetone (-70ºC), was vigorously stirred under argon while 60 ml of dry tetrahydrofuran was slowly syringed in. Onaddition of the first couple of drops into the flask, under constant argon pressure a thick white fume wasobserved. The mixture was brought slowly to room temperature, with constant stirring. Near roomtemperature the color changed from a brownish color to a greenish color, which is the color of theprecipitate. To this mixture was added 10 g (23.81 mmol) of KL, and the mixture was heated to 45ºC andstirred for about 12 hours. By filtration the greenish precipitate was separated from the dark redsupernatant. The precipitate was washed three times with 50ml of acetonitrile and dried in vacuo. Thecrude product was dissolved in 1L of boiling dichloromethane and filtered to remove potassium chlorideand evaporated to dryness. Finally the green product was washed with 250 ml of acetonitrile.7.98 g are recovered and confirmed by mass spec and TLC plate which showed no impurities.(a).(Tp*)MoO(OMe)2 prepared by Pablo from (Tp*)MoOCl2 by new more efficient method (Pablos) inMeOH with NaOMe. This is similar to the reported method I had employed previously specifically usingToluene and NaOMe instead.(b) (Tp*)MoSCl2 prepared from (Tp*)MoOCl2from reported procedure: A suspension of (Tp*)MoOCl2 ) (1.5g, 3.1mmol) and B2S3 (0.9g, 7.6mmol) indry/deoygenated DCM (80ml) was stirred under Ar for 24hr. The reaction mixture was filteredanaerobically,and the filtrate collected was evaporated to dryness in vacuo. The resulting residue wasresolvated with 50ml of DCM and subsequently filtered at RT (this step is equivalent to reducing thevolume in vacuo and subsequent filtration of the concentrated mixture). The addition of MeOH (200mL)to this solution was employed to ppt out the complex; and upon standing for 30 min , the brown solid wasfiltered off and washed with MeOH. Recrystallization from DCM/MeOH yielded orange-brown crystals.(EI-MS; parent ion m/z 497 vs 481 for oxo analog)2). MoO(SPh)4]- from MoOCl3THF2b.Tp*MECO2 from Tp*M(CO)3 from MCO61).Tp*MoNOI22). Tp*WOI2c.Mo2O2Cl2/Br2 from1).Tp*MoO2(Cl)2). Tp*MoO2(Br)d.Cp2MCl2 (Commercial; from Cp2MH2)
  14. 14. 14(Tp*)MoO(bdt) (1)/(Tp*)MoO(tdt) (2) synthesis/isolation/purification/general characterization/ specificcharacterizationThe preparation and characterization of the related (Tp*)MoO(S2) compounds, compounds(Tp*)MoVO(bdt) (1),262,273 and (Tp*)MoVO(tdt) (2),295 were prepared from highly purified (Tp*)MoOCl2following previously reported procedures, where the proligands (H2bdt and H2tdt) in the presence of base(TEA) afforded ligand exchange in a stirring dry/deoxygenated toluene solution under Ar at 70°C over aperiode of 18-24hrs .18,29,30 All reactions and manipulations were carried out under an inert atmosphere ofpure dry argon by using Schlenk techniques. Purification of organic solvents and reagents employed in thesynthesis followed standard procedures. All solvents (OmniSolv and DriSolv; EM Science) were dried bydistillation under nitrogen, and thoroughly deoxygenated prior to use via a combination of repeated freezepump thaw cycling and argon saturation; solid reagents/reactants were dried in vacuo prior to use.Structural, spectroscopic and electrochemical samples were prepared under conditions (including allreagents/solvents) designed for the rigorous exclusion of oxygen and water in a glove bag under a positivepressure of argon to maintain and to ensure sample integrity. Upon conversion, the reaction mixture wasfiltered, and evap to dryness in vacuo. Collumn chromatography using tol(or benz) as eluant affordedrelatively pure compounds. However, due to fact that precursor elutes somewhat in front of bdt complexand elutes right on the tail of tdt complex if present that results in trace amts of this lime green compoundin the targets, and as we require very pure samples for subsequent spectroscopic and electrochemicalcharacterization that are quiet sensitive to trace amts of the precursor, a 2nd collumn was employed inbenzene where small fractions were collected and monitored for trace precursos by IR (Mo=O; 961 vs932/926 cm-1) and subsequently combined and dried, following extracting the dry sample withtoluene/filtering/conc/and layering with pentane/collecting and washing the filtered ppt/ resolvating withDCM –filtered ,dried in vacuo/stored .The following study was initiated prior to joining JHE group, but has provided the catalyst for additionalstudies to further address the results and postulates presented here. Also this is where the synthesis of(Tp*)MoO(qdt) was first published.Spectroscopic Evidence for a Unique Bonding Interaction in Oxo-Molybdenum Dithiolate Complexes:Implications for Electron Transfer Pathways in the Pyranopterin Dithiolate Centers of EnzymesInscore, F. E.; McNaughton, R.; Westcott, B. L.; Helton, M. E.; Jones, R.; Dhawan, I. K.; Enemark, J. H.;Kirk, M. L.Solution and solid state electronic absorption (EA), magnetic circular dichroism (MCD) and resonanceRaman (rR) spectroscopies have been used to probe in detail the excited state electronic structure ofLMoO(bdt) and LMoO(tdt) (L=hydrotris(3,5-dimethyl-1-pyrazolyl)borate; bdt=1,2-benzenedithiolate; tdt =3,4-toluenedithiolate). The observed energies, intensities, and MCD band patterns are found to becharacteristic of the low-symmetry paramagnetic d1 LMoVO(S-S) dithiolate compounds, where (S-S) is a1,2-dithiolene or 1,2-dithiolate ligand forming a five-membered chelate ring with the Mo(V) ion. Grouptheoretical arguments, in conjunction with available spectroscopic data show that the low energy S→Mocharge transfer transitions which dominate the spectral region below 28,000 cm-1 result from one-electronpromotions originating from an isolated set of four filled dithiolate orbitals that are primarily sulfur incharacter. Resonance Raman intensity enhancement profiles constructed for observed vibrational modesbelow 1,000 cm-1 with laser excitation between ~930 – 400 nm have allowed for the definitive assignmentof the ene-1,2-dithiolate Sin-plane→Mo dxy charge transfer transition at ~19,000 cm-1. This is a bonding toantibonding transition and its intensity directly probes sulfur covalency contributions to the redox activeorbital (Mo dxy ). Raman spectroscopy has identified three totally symmetric vibrational modes at 362 cm-1
  15. 15. 15(S-Mo-S bend), 393 cm-1 (S-Mo-S stretch), and 932 cm-1 (Mo ≡ O stretch), in contrast to the large numberof low frequency vibrational modes observed in the resonance Raman spectra of Rhodobacter sphaeroidesDMSO reductase (DR). The results acquired from the electronic structure studies on the LMoVO(S-S)complexes are interpreted in the context of the mechanism of sulfite oxidase (SO), the modulation ofreduction potentials by a coordinated ene-1,2-dithiolate, the origin of the intense low energy absorptioncharge transfer (CT) feature in R. sphaeroides and R. capsulatus (DR), and the nature of the orbitalpathway for electron transfer (ET) regeneration of pyranopterin ene-1,2-dithiolate Mo enzyme active sites.(Tp*)MoO(bdtCl2) (3); new model synthesis/isolation/purification/general characterization/ specificcharacterizationRemote Ligand Substituent Effects on the Properties of Oxo-Mo(V)Centers with a Single Ene-1,2-Dithiolate LigandFrank E. Inscore, Hemant K. Joshi, Anne E. McElhaney, and John H. Enemark*The synthesis of (Tp*)MoO(bdtCl2) was achieved by a ligand exchange reaction between the precursorcomplex (Tp*)MoOCl2 and free ligand H2bdtCl2 in the presence of a strong base (Et3N), as with otherrelated compounds.16,18,20,21,27,28 The identity of the reaction product was confirmed by its high resolutionmass spectrum, which shows an [M + H]+ peak that gives m/z = 619.0063 (calculated, 619.0059) andcorresponds to the formula [12C21H25N611B32S235Cl2O97Mo] (97or 98Mo?). The product is soluble indichloromethane, dichloroethane, toluene and benzene. This compound appeared to be relatively stable inair; however, to ensure structural integrity and sample purity, the product was stored under argon prior touse.All reactions, synthetic operations and manipulations followed strict anaerobic procedures and wereperformed under a dry blanket of pre-purified argon gas using standard Schlenk techniques, a high-vacuum/gas double line manifold, and an inert atmospheric glove bag. Synthetic operations were alsocarried out in an inert atmosphere glove box filled with pure dinitrogen gas. The argon was predried bypassing the high-purity-grade inert gas through a series of drying towers. Dinitrogen was obtained directlyfrom a pressurized liquid nitrogen cryogenic transfer/storage dewar. All glassware was oven dried at150°C and Schlenk ware was further purged by repeated evacuation and inert gas flushes prior to use.Tetrahydrofuran (THF) and toluene were distilled from Na/benzophenone; triethylamine was distilled fromNa/K amalgam.25 The prepurified solvents were subsequently transferred and stored under N2 over freshdrying agents. These solvents were freshly distilled under nitrogen prior to use, thoroughly degassed byrepeated freeze-thaw-pump cycles, and transferred to reaction vessels via steel cannulae techniques under apositive pressure of inert gas. Dichloromethane, 1,2-dichloroethane, cyclohexene, toluene (EM Science,Omnisolv), n-hexane and n-pentane (Burdick and Jackson) were used as received and deoxygenated byargon saturation prior to use. Solvents employed in the spectroscopic characterization studies weredegassed by freeze-thaw pump cycling before use. The 1,2-dichloroethane used in the electrochemicalstudies was of anhydrous grade (EM Science; Drisolv) and required no further purification. Reagents weregenerally used as received. Molybdenum pentachloride (MoCl5, Aldrich) was dried in vacuo and storedunder dinitrogen prior to use. Potassium hydrotris(3,5-dimethyl-1-pyrazolyl)borate (KTp*) and theprecursor complex, (Tp*)MoVOCl2, were prepared according to literature procedures.18 The ligands H2bdt(1,2-benzenedithiol) and H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol) employed in the syntheses of the(Tp*)MoVO(S-S) compounds (1, 3) were used as received from Aldrich. The preparation of(Tp*)MoO(bdt) (1) followed from published procedures.20,21 The synthesis, isolation, purification andcharacterization of (Tp*)MoO(bdtCl2) (3) is described below.Highly purified (Tp*)MoOCl2 (500 mg, ) was added to an evacuated Schlenk flask and dissolved in 50 mlof dry degassed toluene. The mixture was deoxygenated thoroughly with argon saturation while beingstirred at ~80°C. Solid H2bdtCl2 (220 mg, 1.1 equiv) was added in slight excess to the suspension under a
  16. 16. 16positive pressure of argon. The resulting solution was purged with argon for 20 minutes. Dry degassedEt3N (0.40 ml, 2.2 equiv) was added slowly dropwise via gas tight syringe to this rigorously stirringsolution. The mildly refluxing reaction solution was observed to change gradually from an emerald greento a dark red-brown color after 4 hours of stirring. The reaction progress, and hence optimal yield, wasmonitored by TLC analysis (silica gel 60 F254 plastic sheets, EM Science). The reaction was stopped uponobserving the near disappearance of the green (Tp*)MoOCl2 precursor concomitant with the maximalformation of the red-brown product. Upon completion of the reaction, the blue-green precipitate, primarilyEt3N⋅HCl resulting from the hydrogen abstraction and ligand exchange processes, was filtered off the hotsolution under dry argon. The filtrate was cooled to room temperature and evaporated to dryness with arotorary evaporator. The solid red-brown residue was re-dissolved in toluene, concentrated under vacuum,and layered with n-pentane. The red-brown powder precipitate was collected by filtration and washed withn-pentane until the eluant was clear. The powder was then dissolved in dichloromethane, filtered toremove any insoluble materials, and evaporated to dryness in vacuo. The solid was pumped on for severalhours to ensure dryness and the complete removal of excess triethylamine (Et3N). The solid material wasre-dissolved in dichloromethane, concentrated, and loaded on a silica gel chromatographic column (70-230mesh, pore diameter 60 Å, Aldrich) under a positive pressure of argon. A red-brown fraction (band #2)eluted off the column using dichloromethane: cyclohexene (1:3) as the eluant. The purity of(Tp*)MoO(bdtCl2) was confirmed by TLC analysis. The red-brown powder was evaporated to dryness invacuo. The compound was re-dissolved in dichloromethane, and layered with n-pentane to yield a darkred-brown crystalline material. The crystalline material was filtered, washed and then dried in vacuum.The product was characterized by IR, UV/VIS, EPR and mass spectroscopy. Suitable crystals (burgandyplate) for X-ray diffraction studies were obtained by a slow diffusion of n-pentane (or n-hexane) into aconcentrated dichloromethane solution of purified 3.Mass spectra were recorded on a JEOL HX110 high-resolution sector instrument utilizing fast atombombardment (FAB) ionization in a matrix of 3-nitrobenzyl alcohol (NBA). Infrared (IR) vibrationalspectroscopic data were collected on a Nicolet Avatar ESP 360 FT-IR spectrophotometer. The IR spectra(4000-400 cm-1) were measured in KBr disks or as dichloromethane solutions (between NaCl plates) atroom temperature. Electronic absorption spectra of samples solvated in 1,2-dichloroethane solutions wererecorded with a 1-cm pathlength Helma quartz cell equipped with a teflon stopper, on a modified Cary 14(with OLIS interface, 250-2600 nm) spectrophotometer. Quantitative absorption spectra were acquired at2.0 nm resolution using a dual-beam Hitachi U-3501 UV-vis NIR spectrophotometer calibrated with knownmercury lines and a 6% neodymium doped laser glass standard (Schott Glass). Absorption spectra wereanalyzed using Hitachi supplied Grams software. Electron paramagnetic resonance (EPR) spectra at X-band frequency (~9.1 GHz) of solution (298 K) and frozen glasses (77 K) were obtained on a Bruker ESP300 spectrometer. The EPR samples were prepared as 1.0 or 2.0 mM solutions in dry degassed toluene.Cyclic voltammetric (CV) data were collected on a Bioanalytical Systems (BAS) CV-50W system. BASsupplied software provided scan acquisition control and data analysis/graphics capabilities. Theelectrochemical cell employed was based on a normal three-electrode configuration. This cell consists of aplatinum disk working electrode (1.6 mm diameter, BAS), a platinum wire counter electrode (BAS) and aNaCl saturated Ag/AgCl reference electrode (BAS). Prior to each experiment, the electrode was polishedusing 0.05 µm alumina (Buehler) and electrochemically cleaned in dilute sulfuric acid. Cyclicvoltammetric measurements of (Tp*)MoO(bdtCl2) and related (Tp*)MoO(S-S) complexes were performedin dry degassed 1,2-dichloroethane solutions (10 ml, ~1mM, 25°C) over a potential window of ± 1.5 V vs.Ag/AgCl with 0.1 – 0.2 M dried tetra-n-butylammonium tetrafluoroborate [n-Bu4N][BF4] (Aldrich) as thesupporting electrolyte. The background scans of dry/deoxygenated DCE with the [n-Bu4N][BF4]supporting electrolyte exhibited no electroactive impurities or solvent decomposition within the potentialwindow employed. Ferrocene was utilized as an internal standard, and all potentials were referencedrelative to the Fc/Fc+ couple. He I gas-phase photoelectron spectra (PES) were collected on a spectrometerwith a 36-cm radius hemispherical analyzer (8 cm gap, McPherson), sample cells, excitation sources, anddetection and control electronics using methods that have been previously described in detail.22 Theabsolute ionization energy scale for the He I experiments was calibrated by using the 2E1/2 ionization ofmethyl iodide (9.538 eV), with the argon 2P3/2 ionization (15.759 eV) used as an internal calibration lockduring the experiment. During data collection the instrument resolution (measured using the FWHM of theargon 2P3/2 ionization peak) was 0.020 – 0.023 eV. All data were intensity corrected with an experimentallydetermined instrument analyzer sensitivity function. The He I spectra were corrected for the presence of
  17. 17. 17ionizations from other lines (He Iβ line, 1.9 eV higher in energy and 3% the intensity of the He Iα line).All samples sublimed cleanly with no detectable evidence of decomposition products in the gas phase or asa solid residue. The sublimation temperatures were monitored using a “K” type thermocouple passedthrough a vacuum feed and attached directly to the aluminum ionization sample cell. The sublimationtemperatures (in °C, 10-4 Torr) were as follows: (Tp*)MoO(bdtCl2), 198°; and (Tp*)MoO(bdt), 183°.(Tp*)MoO(qdt) (4);synthesis/isolation/purification/general characterization/ specific characterizationA new purification procedure allowed this previously reported complex to be isolated with ultra purity andsuitable crystals obtained for XRD char. Previously, considerable effort to do this over 2 years had failedfor original authors. Not untill a procedure was developed producing ultra pure sample was this finallypossible. The same solvent choice det here for XRD crystals applied to sample prepared by previousmethods did not result in crystal formation. Molecular Structure and Vibrational Studies of an Oxomolybdenum Complex with a ChargeDeficient Dithiolate [Hydrotris(3,5-Dimethyl-1-Pyrazolyl)-Borato](Quinoxaline-2,3-Dithiolato)-Oxomolybdenum(V): Remote Ligand Effects on Geometric and Electronic Structure of Oxo-Mo Ene-1,2-Dithiolates.Frank . E. Inscore†, Nick. D. Rubie‡, Hemant. K. Joshi†, Martin. L. Kirk‡* and John. H. Enemark†*General. Unless otherwise stated, all reactions and manipulations were carried out under an inertatmosphere of pure dry argon by using Schlenk techniques. Structural, spectroscopic and electrochemicalsamples were prepared under conditions (including all reagents/solvents) designed for the rigorousexclusion of oxygen and water in a glove bag under a positive pressure of argon to maintain and to ensuresample integrity. Purification of organic solvents followed standard procedures. All solvents (OmniSolvand DriSolv; EM Science) were dried by distillation under nitrogen, and thoroughly deoxygenated prior touse via a combination of repeated freeze pump thaw cycling and argon saturation. The preparation andcharacterization of the quinoxaline-2,3-dithiol (H2qdt) ligand followed previous reported methods.41-4428(Tp*)MoVO(qdt) (4) was prepared by published methods.16,17 The compound (Tp)*MoO(qdt) dissolved ina minimum amount of toluene was chromatographed on silica gel (70-230 mesh) and eluted in a binarymixture of toluene: 1,2-dichloroethane (1:1) as a red band. The red fraction was collected and evaporatedto dryness in vacuo. The solid residue was resolvated in a minimal amount of dichloromethane, and theaddition of hexane, layered on the concentrated solution (1:1), induced a deep red-brown powder to form,which was subsequently washed and dried upon collection. The (Tp*)MoVO(qdt) (4)18,19,36 and related(Tp*)MoO(S2) compounds compounds (Tp*)MoVO(bdt) (1),262,273 (Tp*)MoVO(tdt) (2),295(Tp*)MoVO(bdtCl2) (3),306 and (Tp*)MoVO(SPhMe)2 (5) 295 were prepared from (Tp*)MoOCl2 followingpreviously reported procedures.18,29,30 (Tp)*MoO(qdt) was further purified under argon by a combinationof multiple extraction (toluene/pentane; dichloromethane/hexane) and flash chromatographic steps (silicagel 230-400 mesh, Aldrich; eluted in binary mixtures of toluene: 1,2-dichloroethane (1:1) anddichloromethane: cyclohexane (1:2) as a red band). The final red fraction was collected and evaporated todryness in vacuo. The solid residue was resolvated in a minimal amount of dichloromethane, and theaddition of hexane, layered on the concentrated solution (1:1), induced a deep red-brown powder to form,which was subsequently washed and dried upon collection. Highly purified samples of 4 submitted forphysical characterization were obtained by a slow diffusion of n-pentane into a saturated dichloromethanesolution. The (Tp*)MoO(qdt) complex and other compounds investigated were identified by theircharacteristic UV/VIS and IR spectroscopic features.16,22,25-27 Reaction progress and purity of isolatedcompounds were monitored by thin-layer chromatography (silica gel 60 F254 plastic sheets; EM Science)and mass spectrometry. High resolution mass spectrometry showed (Tp*)MoO(qdt) (4) to have an [M+H]+experimental mass of 604.0889 with respect to the most abundant 98Mo isotope (calculated: 604.0902).The reduction potential (relative to the Fc/Fc+ couple in 1,2-dichloroethane) of (Tp*)MoO(qdt) (-461 mV) isconsistent with that previously reported19,36 for 4 and follows trends in the quasi-reversible Mo(V)/Mo(IV)couples observed for 4-1 in 1,2-dichloroethane.30,33 The (Tp*)MoO(qdt) complex and other compoundsinvestigated in this study were further identified by their characteristic IR, EPR and UV/VIS spectroscopic
  18. 18. 18features.18,19,26,27,29,30,36 The identity of the (Tp*)MoO(qdt) complex (4) was confirmed by an X-raycrystal structure analysis.Suitable crystals of the The (Tp*)MoO(qdt) (4) complex (4)were obtained as listed in Table 1 wasstructurally characterized by X-ray crystallography. Suitable crystals (dark-red blocks ) were obtained byslow vapor diffusion of pentane into a dichloromethane solution at room temperature.Physical Measurements. 1H- NMR spectra of the H2qdt ligand (in DMSO-d6) were obtained with aBruker AM 500 spectrometer. Mass spectra were recorded on a JEOL HX110 high-resolution sectorinstrument utilizing fast atom bombardment (FAB) in 3-nitrobenzyl alcohol solutions. Cyclic voltammetric(CV) data were collected on a Bioanalytical Systems (BAS) CV-50W system with an electrochemical cellconsisting of a platinum disk working electrode (1.6 mm diameter, BAS), a platinum wire counter electrode(BAS) and a NaCl saturated Ag/AgCl reference electrode (BAS). Cyclic voltammetric measurements wereperformed in 1,2-dichloroethane solutions (10 ml, ~1mM, 25°C) with 0.1 – 0.2 M dried tetra-n-butylammonium tetrafluoroborate [n-Bu4N][BF4] (Aldrich) as the supporting electrolyte. Ferrocene wasutilized as an internal standard, and all potentials were referenced relative to the Fc/Fc+ couple. IR spectrawere measured on solid (KBr disks) and solution (dichloromethane between NaCl plates) samples on aNicolet Avatar ESP 360 FT-IR spectrophotometer. .Electron paramagnetic resonance (EPR) spectra at X-band frequency (~9.1 GHz) of solution (298 K) and frozen toluene glasses (77 K) were obtained on aBruker ESP 300 spectrometer. Electronic absorption spectra of samples solvated in 1,2-dichloroethanesolutions were recorded on a Cary 300 (250-900 nm) or a modified Cary 14 (with OLIS interface, 250-2600 nm) spectrophotometer. Details of the electrochemical and spectroscopic he IR and UV-visiblemeasurements for these complexes have been described previously.186,19,262,295,30-,3627 (Tp*)MoO(edt) (5) new model synthesis/isolation/purification/general characterization/ specificcharacterization/DFT calcPaper in Progress:Note: This is the final complex synthesized in my research here. The success of this syntheses lies in theextreme dry/anaerobic setup and rigorous conditions employed in all aspects of the reaction, and I do meanextreme for every step as I will discuss and why(complete control) . I have included Pablo and Hemant ascollaborators. Pablo provided the Na2edt ligand from a previously reported procedure. This ligandrequired deprotection and purification prior to addition to reaction flask, this ligand was pablos primarycontribution to the 1st synthesis/purification/characterization, but still a very important component and thisclearly warrants his name on this paper, and as he has been coupled into what is going on in this synthesisand has and will continue to provide assistance w/r to this preparation, for him also to write the synthesis ofTp*MoOedt up in his thesis. Unfortunately, he had to depart to Japan that afternoon (the next day) and sowas not present in the isolation/purification/char steps that followed for the next several weeks. Also I havehad him working on a new precursor to try and make the the target of this study by a different route. I havealso coupled Hemant as usual for some characterization. Specifically, after isolation,purification andrecrystallization steps I generally supply suitable crystals for XRD to facility and hemant does the structurerefinement. In this particular case I have had hemant under my direct supervision prepare samplesanaerobically, for possible crystals using a variety of solvents (recently purchased by me for this purpose),chosen based on my previous solubility profiles. This XRD if obtainable, puts Hemant on the paper. Afterobtaining pure samples, they are characterized by MS,IR,EPR,EA,CV, and then afterwards some aresubmitted to PES facility(usally to Hemant). This and some additional characterization that I cannot finishor that needing repeated will now in this case be some of Hemants responsibility, and will subsequentlyinclude this characterization in his dissertation. However, it is one thing to be giving pure sample, prepedand ready for characterization. In this case, sample prep requires careful exclusion of air and water untillwe obtain purityand know the stability, and all of this will now have to be done by Hemant, and there are
  19. 19. 19no shortcuts. Furthermore, additional compound will be needed, and if they follow my methodology andsuggestions it should be no problem.The Synthesis and Characterization of (Tp*)MoO(cis-ethene-1,2-dithiolate): A New MinimalStructural Model and Effective Spectroscopic Benchmark for Probing Contributions to GeometricDistortions Observed in Folding of the Dithiolate Chelate Ring and Effect on Electronic StructureThe synthesis of (Tp*)MoO(edt) was achieved under an inert atm of Ar by a ligand exchange (substitution)reaction between the highly purified precursor complex (Tp*)MoOCl2 and sodium salt of the dithiolateligand Na2edt employing rigorously dry oxygen free conditions in a nonpolar solvent(Tol) at elevated temp.This is in contrast to the synthetic route reported for other related (Tp*)MoO(dithiolene) compoundsavaillable in this isostructural series, which employed similar reaction conditions, but utilized instead thedithiol proligand (H2(S-S), S-S = tdt,bdt bdtCl2,qdt) in the presence of a strong base(TEA). This is the 1stdithiolene in this series prepared/reported in such a manner, showing that this is a viable route to other(Tp*)MoO(dithiolene) complexes. However, the (Tp*)MoO(EDT) complex possessing a saturated 5-membered chelate ring (SC-CS) coord to Mo (as was several other related dithiolate complexes)r waspreviously prepared from both the Na and K salt of the dithiolate ligand.r The identity of the reactionproduct was confirmed by its high resolution mass spectrum, which shows an [M + H]+ peak that gives m/z= (calculated, ) and corresponds to the formula [12C17H25N611B32S2O98Mo]. The product is soluble indichloromethane, 1,2-dichlorethane, toluene and benzene. This compound appeared to be relatively stablein air for a short time, however, to ensure structural integrity and sample purity, the product (dried andpurged in vacuo) was stored in a schlenk flask under Ar and transferred to an inert atm glove box untillneeded. Subsequent manipulations and sample preparations were performed under a dry Ar atm withsolvents employed being relatively dry and thoroughly deoxygenated.Preparation of CompoundsGeneral: Materials and MethodsPreparation of Ligands1. KTp* was prepared and purified by following well established procedures as reported and furtherdeveloped in this lab.2. Na2edt was prepared and purified by a multistep procedure, similar to a synthetic route reportedpreviously in the literature.Note:Any char? Can we try to submit a sample of it (and its protected precursor) prepared prior to reaction,say for H1NMR/13C-NMR and compare to reported, and ensure purity of it?Note:What happens to it in reaction solvent and subsequent exposure to air etc, so can use as control formonitoring presence or similar decomp products in reaction product. Can we remove excess or decompproducts based on its behavior from reaction prod mixture?Note:Can we protonate edt dithiolate, if not why etc?3. other ligands that may be used? H2(S-S), Na2(S-S); where S-S = bdt (others tdt,bdtcl2,qdt,mnt; EDT)Preparation of precursors1.(Tp*)MoOCl2 prepared as reported by adding KTp* to a solution containing MoOCl3THF2 generated insitu from MoCL5 and THF. Purification followed procedures well established in this lab.2.(Tp*)MoO(OMe)2 prepared from halide precursor by new methods in MeOH with NaOMe, but similarto that reported using Toluene and NaOMe.Note: make sure char(MS/IR/EA/CV/EPR) and TLC to ensure purity of both precursors prior to reaction,and to provide controls for determining reaction progress and their presence in isolated products. Any sideproducts of these should we be aware of? Based on properties and behavior can we remove excess or sideproducts from reaction mixture containing target dithiolene complexes?
  20. 20. 20Note: Consider properties of all the reactants/reagents and expected products (target/other prod/excessreactants/side prods etc for how to remove.Preparation of Model ComplexesSee reaction route scheme for making (Tp*)MoO(S-S) complexes, as 4 potential precursors, 4 generalroutes; and each can generally be subdivided into 2 sub routes depending if using dithiol (a) or salt ofdithiolate ligand (b). We only consider 2 of these 4 general routes here. Primary focus is on edt complex(Method 1 from halide precursor), however bdt system is also to be looked at for new route employed herefor 1st time using (Tp*)MoO(OMe)2 precursor (Method 2), and also to provide a reactivity comparison withthe edt complex and especially if can employ identical reaction conditions. Note:The syntheses and char.of the secondary dithiolene complexes (bdtcl2,tdt,qdt) and dithiolate complex (EDT) to be compared to areall ready reported. All of these complexes I have synthesized for additional comparison if needed inaddition to what has been already published. The chemical, geometric,electronic properties andelectrochemical behavior of the target are to be compared primarily w/r to those in the bdt system (a muchsimpler and less bulky dithiolene system that is a true ene-1,2-dithiolate vs. aromatic dithiolate withconjugated ring) and EDT system (a 5-membered chelate ring with SC=CS vs relatively isostructural SC-CS ring system as function of saturation effects/ less restricted rotation of S orbitals in EDT). Big Q is how much does these properties change, and what effects on the fold angle does the less stericallyhindered edt ligand have vs the bdt system?// how does the electronic structure change for edt vs EDT?1.Preparation of (Tp*)MoO(edt)Method1.Method 1a. was not tried due to the difficulties in protonation of edt dianion and its subsequent instability.Method1b.The highly air sensitive Disodium ethylene dithiolate (0.29g, 2.13 mmol) ligand was preparedand purified as previously described from its protected precursor immediately prior to the reaction andsubsequently dried under vacuum to avoid decomposition products. The observed sensitivity of this ligandto air is evident following deprotection and isolation, where exposure to air results in decomposition of thewhite powder, initially turning yellow-brown and then into a dark brown viscous semi-liquid within amatter of minutes. The purified, dry ligand was weighed, suspended in 12 ml tol and transfered slowly in aglove bag(pos press of dry Ar -flowed through drierite packed entry tube) to a green suspension (pre-purged) of highly purified dry (invacuo)Tp*MoOCl2 (0.90g, 1.87 mmol) in 25 ml of dry(distilled under Arover Na/benzophenone/collected and transferred anaerobically from still to prepurged/evac receivingschlenk flask connected directly to vac/inert gas manifold), deoxygenated(via Ar sat/FTP) toluene andsubsequently transferred to reaction flask anaerobically via steel cannula under Ar pres,s in bag, flask ofstirring mixture subsequently purged by Ar sat and vacuum, heated slowly to 50º C,under Ar blanket in oilbath(mineral) at which time the color of the solution changed slightly from green to brown. The reactionmixture was let stir for another 18 hours at 70 C under an inert atmosphere of dry Argon gasReaction mixture filtered anaerobically(hot), cooled to rt and conc to red solution, the filtrate char by MSFAB and ESI/MeCN both showed the presence of target in react.mixture(see analysis; also see presence oftrace precursor).Evap to dryness invacuo/ resolv/extracted with tol under Ar, conc (tlc profile in tol) and ran down silica gelcollumn anaerobically tol/tol eluant.(next time more anaerobic) note still have brown mat in flask, caked on sides etc pretty good, see someloose green evidence at bottom (residue from extraction, indicating other stuff not as sol in tol.3 bands pulled off for identity(still dk brn bands behind and on top1st green in schlenk flask, 2nd brown-red schlenk, 3rd left on bottom was purple; 1,2 submitted for esi ms;green showed to be target, slight halide precursor trace evident, neither in band 2 from ms.Tlc of left over green ms sample after submitted and identified as targ (or the subsequent dried greenfract)., only 1 spot in tol ,consistent with previous behavior of TLC profile prior to collumn separation asanticipated.Tlc control of cl2 prec vs green in tol or tol/dcm show they both elute the same , cl2 slightly tailing, thusthis and fact very minute amts of cl2 implies difficulties in sep excess cl2 from target.How to ensure verypure?Green fract conc/ and dried in vac anaerobically to remove tolResolv in dcm ,and transfer to smallerflask (vial) for storage, dry evap under Ar stream(septum sealed vialwith pos press and needle in septa,, seal vial, store in glove box.
  21. 21. 21Halide less sol in tol than edt, not sol in pentane, edt in tol/pent 1st 2 layers then becomes mixed over time;can we recrystal?Suggest: make sure cl2 is consumed completely, what is best temp and time for this, run ms sample to det ifneed to continue.(tlc not useful)Inc yield by ensuring all ops done anaerobically including collumn (evac gel for ox etc)Anaerobic Filtration of Reaction MixtureExternal Anaerobic Solvent Remover (slows breakdown of Apeizon-N grease on schlenk manifold)Designed and installed on my schlenk line by Pablo.
  22. 22. 22Taken out of glove box and transferred to glove bag under Ar, for preparing samples for growing crystalsand initial EA. Sat sample with DCM/ transfer small aliquots of sat dcm sample to 4 vials. Recrystall:Vap diff of new pentane into 1dcm sample in sealed jar; liq diff of pentane,heptane, and hexane layeredseparately onto 3 DCM samples sealed. (kept in bag with pos press/ note by accident ar turned off overnight. Q. is samples still ok? Also 1 dilute dcm sample preped in anaerobic quartz cell matched with cellwith DCM only. Abs ran, and sample put back in bag. Q is it still ok over course of exp and after nightwith ar off over time? After making samples original dried again by septum and needle, also left outovernight, is it still ok? All put in glove bag this next day under Ar. Is it still on? This was not good, loss ofcontrols-introduced new variables; poor technique and planning, now need to det if sensitive to air!!!!!However, the glove bag was not maintained as promised, thus potential for decomposition and loss ofvaluable product may have occurred.Q. also,did the original sample from tol change with dcm/method before storage , did dried sample changein box during storage? Need to TLC and MS to ensure.Q. also, redo ms Note: from EA, definite that the green fract is not just halide, as band at 16750 says it hassomething else. Could run 2nd band ea to see how it looks( does it look more like bdt complex than doesgreen, then maybe something got messed up.Q. thus from above, the stability of target in solution and solid should be addressed. Does ab samplechange over time and/or with exposure to air? With change in solvent dcm vs tol ; any possible way toknock of edt and replace with solvent or cl?Note: always control the exp, no extra variables introduced. Thus char each step, and maintain some origmaterials as a control to test each step and diff conditions.Exps to do:
  23. 23. 231.The synthesis with halide precursor should be repeated, as this appears to be viable route to target basedon fact that MS of crude product (and isolated fraction)says we made it for initial reaction(are we for sureabout MS identification? Need detailed analysis) Based on presence of halide precursor in crude filteredproduct by MS(FAB and ESI) and subsequent isolated component assumed to be target (green fraction,band 1) based on MS(ESI) of band 1 and band 2, appears incomplete conversion of precursor is suggestingneed to react for longer time (monitor dissappearance of halide by MS and IR) or higher temp to forceconsumption, or presence may be due to not enough ligand (or base) for some reason (dec by side react ornot enough added to start with relative to halide, or too much halide added to start with thus can make sureweight of precursor known and use slight excess of ligand and base w/r to this halide combined with longerreact time /higher temp and monitoring of progress to ensure complete conversion beforeproceeding/terminating reaction.The results/ char etc of initial reaction will be important for optimizing the 2nd reaction. Remember, retaincontrol and don’t introduce new variables.1. check MS (ESI in MeCN) of Green fracta. the redried septum sealed sample (solvent blown off by Ar via 2 needles in septa for several hours andthese subsequently removed, thus sample at least from this point on should be ok here even though notstored in box after taking off Ar line) in vial after solvating (in bag Ar pos press) with new drisolv dcm for2nd time for the EA and recrystall exps prepped in bag; as this is best we have left of original isolatedcomponent.-see if still observe target and halide/ compare to originalthis also sees if sensitive to DCM etc vs tol/ also is the green component the correct one for target identifiedby MS or was there a mixup between band 1 green and 2 brown? If appears mixup, still have browncomponent which can be tested, also have original crude tol prod in flask available that can be extractedand ran down small tol collumn. To get new green/brown fracts.If this green fract ok, then we can further test stability by opening to air for time, if not then have tobacktrack.Objective 1.Evaluate the reaction route and synthetic methods for preparing (Tp*)MoOV(edt)and viabil alternatives.Showing that the reaction route produced the desired target compound , identifying the target in the isolatedcomponents during purification, and determining the purity of the target is the initial experimental objectiveof this study. The next objective is can we and by what means obtain pure compound for furthercharacterization and studies?Then we can direct our focus to the primary issues and goals of specific interest regarding the study of thiscomplex(which is ? and by what means?).Thus;I.Q. How do we know that this reaction was successful?II.Q.Considering the initial separation/isolation/purification process following the reaction, how do wemonitor this and identify the target in a specific component?III.Q. How do we determine/monitor the purity/purification of the isolated target component upon beingidentified?NOTE:-MS combined with TLC are our primary/initial tools for monitoring the reaction progress, the nature andnumber of components in the reaction mixture –reactant/product, and in particular for MS, identifying thepresence or not of the target compound in the crude/final product. TLC profiling is useful for determininginitial conditions and methodologies to employ in isolation/purification steps,and for tracking results and
  24. 24. 24monitoring progress/behavior w/r to product formation//purification//purity and stability of productisolated/identified.-Additional spectroscopic techniques that can be employed similarly for monitoring reactionprogress/purification/ product purity,identity, and behavior include IR and NMR spectroscopy.EA, EPR spectroscopy and CV can also provide some insight into the nature and purity of isolated product.Once highly purified product isolated can be submitted for elemental analysis for insight into molecularformulation, and if obtain suitable crystals for XRD can get solid state geometric structure of molecule.-The combined results of these techniques ensure that we know the purity/stability of product isolated, itsidentity, electronic nature, and ultimately geometry/structure. The compound can now be used in furthercharacterization and specific studies.MS analysisGeneral:The identity of the target complex in the crude product reaction mixture was confirmed by MS; FAB andESI, which show the parent ion peak associated with a peak cluster characteristic of isotopic distributionpattern of Mo, and corresponding to the mwt, in addition to identifying char peak fragments associated withthe observed Mwt. The analysis of observed peak patterns is consistent with that observed for other relatedwell characterized complexes.The identity of the isolated target during the initial separation/isolation/purification was determined andmonitored by MS(ESI) following these general standard procedures. Specifically, upon filtration/removing solvents/-volatils by evaporation to dryness in vacuo /extraction and further drying// determiningsolubilty properties combined with subsequent TLC analysis for monitoring /determining theisolation/purification conditions for separating out the components by extraction/recrystallization and intialcollumn chromatography resulted in these isolated fractions being probed by MS, which determined the 1stband (green) isolated from collumn chromatography containing the target.The MS results of the crude product show that the reaction was not complete and that of the initial isolatedtarget component is not entirely pure as traces of the halide precursor is present. Modifications to thereaction procedure to ensure complete conversion and higher yield is suggested (e.g. longer reaction time/higher temp/solvent choice), or further purification becomes necessary as will be the case here for thisinitial synthesis.A.Q. Consider anticipated ideal structure/formulation and e- configuration of target complex:Can we identify the target with absolute certainty?If not, can we do so at least to some degree of certainty? To what extent and at what point?Analysis of certain peak fragmentation patterns and expected isotope distribution patterns could beassociated with Tp*MoO ion, etc that corresponded to diffs with respect to the [M+] and its Mwt for thetarget complex, and the presence of a Mo containing compound.q. Is the analysis of observed peak patterns/isotopic distributions consistent with that observed for otherrelated well characterized complexes of this system? Are we certain about this and the identity of target?B.Q. Consider reaction; reactants and products,:1. Can we determine the extent/progress of this route? Can we identify specific reactants/ products/ sidereaction and decomposition products?Any stability issues?Similar analysis of mass spectrum and comparison to previous MS data of anticipated/potentialcharacterized complexes, as above reveals in addition the presence of:- precursor (Tp*)MoOCl2. (what is specific evidence, How much is present relative to target?)q. What does this suggest?Reaction incomplete, the complete conversion of precursor to target requires its consumption during ligandexchange with dithiolate ligand. Assuming ideal conditions and stoichiometric conversion, the presence of