Novel One-Pot Synthesis of Alkaline Earth Species
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Novel One-Pot Synthesis of Alkaline Earth Species
- 1. I. Novel, One-Pot Reactions towards Molecular Alkaline Earth Species Yuriko Takahashi Ruhlandt Group Syracuse University II. Exploring Weak Interactions as Structure Determining Factors in MOCVD volatility
- 2. 1 Education and Research Experience Dept. of Engineering, Applied Chemistry, Saitam University, Japan (April 2005 - March 2007 ) B.A. Chemistry, Augustana College, SD (May 2009) Summer Research Program at Lehigh University, PA (2008 Summer) Summer Research Program at Syracuse University, NY (2009 Summer) Ph.D. Candidate, Syracuse University, NY (2009 - ) I. Exploration of a benign, efficient synthetic route for alkaline earth metal compounds II. Evaluation of influence of weak interactions on thermal properties of target compounds
- 3. 2 What is involved? Inert gas synthetic techniques NMR (mechanistic) studies Structural studies, crystallography Thermogravimetric analysis (TGA) Ligand synthesis
- 4. 3 Inert Gas Synthetic Techniques ◆ All reactions are carried out under inert gas condition ◆ Solvents – dried, and degassed prior to use ◆ Starting materials - dried over CaH2 and distilled under vacuum or inert gas prior to use Dry box Schlenk line Solvent system
- 5. 4 What is involved? Inert gas synthetic techniques NMR (mechanistic) studies Structural studies, crystallography Thermogravimetric analysis (TGA) Ligand synthesis
- 6. 5 Highly attractive reagents Inexpensive Earth abundant Mg and Ca are biocompatible Sr and Ba are found in electronic materials Attractive substitutes for selected rare-earth metals H AcRaFr LaBaCs YSrRb ScCaK MgNa BeLi H AcRaFr LaBaCs YSrRb ScCaK Na BeLi Mg Why Alkaline Earth Metals?
- 7. 6 Applications Synthetic Chemistry Catalysis • Hydroamination, Hydrophosphination, Hydrosilylation Selective deprotonation agents Polymer Chemistry Polymerization initiators • Lactides, Caprolactone , Styrene Material Chemistry Hydrogen storage Synthetic bone scaffolds MOCVD (Metal Organic Chemical Vapor Deposition) precursors The Chemistry of Organolithium Compounds. Wiley: New York, 2004. Elschenbroich, C., Organometallics. Wiley-VCH Verlag GmbH & Co,: KGaA, Weinheim, 2006. Crimmin, M. R.; Casely, I. J.;Hill, M. S., J. Am. Chem. Soc. 2005, 127, 2042 Westerhausen, M., Coord. Chem. Rev. 1998, 176, 157. Yanagisawa, A.; Habaue, S.; Yamamoto, H., J. Am. Chem. Soc. 1991, 113, 8955. Otway, D. J.; Rees, W . S., Jr., Coord. Chem. Rev. 2000, 210, 279. Harder, S.; Feil, F.; Weeber, A., Organometallics 2001, 20, 1044.
- 8. 7 H AcRaFr LaBaCs YSrRb ScCaK MgNa BeLi H AcRaFr LaBaCs YSrRb ScCaK Na BeLi Mg Ba Mg Sr Ca size Ionic Radii (Å) 0.72 1.00 1.18 1.35 CN = 4 CN = 6 CN = 6 CN = 6 High oxo- and hydrophilicity Tendency towards aggregation and subsequently poor volatility Challenges Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.
- 9. I. Novel, one-pot reactions towards molecular alkaline earth species Safe Inexpensive Simple Available starting materials Minimize environmental impact
- 10. Classic Synthetic Routes 9 Direct metallation via anhydrous NH3(l) activation Ae[N(SiMe3)2]2(thf)2 + 2 HL 2 KL + AeI2 Ae + 2 HL NH3(l) Ae = Ca, Sr, Ba HL = Protonated ligand Salt Elimination Transamination Ae(L)2 •Limited surface area of metal slows reaction •Work with condensed NH3 •Poor for bulky HL •Require highly acidic HL •Prior synthesis of Ae[N(SiMe3)2]2(thf)2 •Highest quality AeI2 •Preparation of KL Gillett-Kunnath, M. M. Doctoral Dissertation, Syracuse University, 2007
- 11. Redox Transmetallation/ 10 pKa (Benzene) = 43 (in DMSO) Ae + HgPh2 {AePh2(thf)n} + Hg {AePh2(thf)n} + 2 HL AeL2(thf)n + 2 C6H6 Ae = Ca, Sr, Ba THF THF Redox transmetallation Ligand exchange Torvisco, A., et al. Coord. Chem. Rev., 2011, 255, 1268. Hitzbleck, J., et al. Chem. Eur. J. 2004, 10, 3315. Deacon, G. B., et al. Dalton Trans, 2009, 4878. Deacon, G. B., et al. Organometallics, 2008, 27, 4772. Deacon, G. B., et al. Dalton Trans, 2011, 40, 1601. Hauber, S-O., et al. Angew. Chem. Int. Ed., 2005, 44, 5871. Cole, M.L., et al. Dalton Trans, 2006, 3360. Deacon, G. B., et al. N J Chem, 2010, 34, 1731. Ligand Exchange (RTLE) Toxicity of mercurial limits the use of this route L = cyclopentadienide, pyrazolate, formamidinate, aryloxide HgPh2 LD50 = 50-400 mg kg-1 oral, rat
- 12. 11 HgPh2 BiPh3 LD50 = 50-400 mg kg-1 LD50 = 180 g kg-1 oral, rat oral, dog Environmental Friendly Hg2+/Hg Bi3+/Bi E0(V) 0.852 0.30 Eo (V) M2+ (aq) + 2e- → M(s)) Ca2+ -2.87 Sr2+ -2.89 Ba2+ -2.90 An alternative to HgPh2
- 13. Attractive alternative synthetic route Redox Transmetallation/ 12Gillett-Kunnath, M. M.; MacLellan, J. G.; Forsyth, C. M.; Andrews, P. C.; Deacon, G. B.; Ruhlandt-Senge, K. Chem. Commun. 2008, 37, 4490. Ligand Exchange (RTLE) using BiPh3 3 Ae(xs) + 2 BiPh3 + 6 HL 3 Ae(L)2(thf)n + 2 Bi + 6 C6H6 THF Sonication Advantages of RTLE utilizing BiPh3 Commercially available starting materials One-pot; time and cost effective Environmentally benign Easy work-up Good product yields BiPh3 LD50 = 180 g kg-1 oral, dog Ae = Ca, Sr, Ba
- 14. N NH H 13 Objectives SiMe3 NH SiMe3 N H SiMe3 OH Explore mechanism of RTLE reaction utilizing BiPh3 Demonstrate feasibility of RTLE utilizing BiPh3 for the synthesis of alkaline earth metal organometallics Investigate/examine influence of ligands acidity (pKa) on the reaction rate
- 15. Experimental Procedure 14 NMR tube sealed with a J-Young tap •Ba metal filings (0.50 mmol, excess) • BiPh3 (0.15 mmol) • HL (0.45 mmol) • Cyclohexane (internal standard) • D8-THF (0.6 mL) anhydrous •All reactions carried out under inert gas conditions •Sonication, T = 60 oC •Monitored by1H-NMR spectroscopy
- 16. Example of NMR data 15 0 h 2 h 10 h BiPh3 C6H6 Cyclohexane (internal standard) SiMe3 NH SiMe3 SiMe3 N SiMe3 HMDS 3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6 THF Sonication
- 17. 0 20 40 60 80 100 0 5 10 15 Concentration(%) Time (h) Free ligand Deprotonated ligand BiPh3 Mechanistic Considerations 16 3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6 THF, N2 Sonication SiMe3 NH SiMe3
- 18. Kinetic Investigation 17 Heterogeneous nature of the reactions Active area of the metal surface is unknown and is continuously changing We get kinetic data from indirect measurements of the chemical composition of the bulk solution Kinetic results are certainly sufficient for surveying average trends Rogers, H. R., et al. J. Am. Chem. Soc. 1980, 102, 217. Olson, I. A., et al. J. Phys. Chem. A 2011, 115, 11001.
- 19. 0 20 40 60 80 100 0 5 10 15 Concentration(%) Time (h) Free ligand Deprotonated ligand BiPh3 Mechanistic Considerations 18 20% of BiPh3 left over 3 Ba(xs) + 2 BiPh3 + 6 HN(SiMe3)2 3 Ba[N(SiMe3)2]2(thf)2 + 2 Bi + 6 C6H6 THF, N2 Sonication 50 % of product: t50%conv = ca. 5h SiMe3 NH SiMe3
- 20. Direct Metallation 19 3 Ba(xs) + 6 HN(SiMe3)2 THF, N2 Sonication 0 20 40 60 80 100 0 5 10 15 20 25 30 Concentration(%) Time (days) Free ligand Deprotonated ligand Direct metallation and RTLE based BiPh3 occur simultaneously Direct metallation was not complete Rate for RTLE (t50%conv = 5h ) is much faster than that for direct metallation SiMe3 NH SiMe3 ca. 26 days After t50%conv product decomposition
- 21. 0 20 40 60 80 100 0 50 100 150 200 250 300 350 400 450 500 Concentration(%) Time (h) DM RTLE vs. Direct Metallation – HCp* 20 ca. 21 days
- 22. 0 20 40 60 80 100 0 50 100 150 200 250 300 350 400 450 500 Concentration(%) Time (h) RTLE + DM DM RTLE vs. Direct Metallation – HCp* 21 ca. 22 h ca. 21 days
- 23. RTLE vs. Direct Metallation – Ph2pzH 22 0 20 40 60 80 100 0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 Concentration(%) Time (h) RTLE + DM DM N NH H 1 h 2.5 h Reactions between Ba metal and the pyrazole ligand are not enhanced by the BiPh3.
- 24. RTLE vs. Direct Metallation 23 pKa 5.60 ± 0.38[1] 11[2] 13.03[3] 14[4] 22.6[4] 26.1[4] t50 % conv. 3.5 h 4 h 2.5 h 5 h 6 h 22 h D M t50 % conv. 25 h 4 h 1 h 26 days 19 days 21 days SiMe3 NH SiMe3 N H SiMe3 N NH H OH D M R T L E [1]Estimated pKa values of silylamides was calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (© 1994- 2012 ACD/Labs). [2]Sinha, A., et al. Organometallics, 2006, 25, 1412. [3]Aggarwal, V. K., et al. J. Org. Chem., 2003, 68, 5381. [4]Bordwell, F.A.; Bausch, M.J. Am. Chem. Soc. 1983, 105, 6188.
- 25. RTLE vs. Direct Metallation -Pyrazoles 24 [Sr(Me2pz)2(Me2pzH)4][Ca(Me2pz)2(Me2pzH)4] Hitzbleck, J.; O'Brien, A.Y.; Forsyth, C.M.; Deacon, G.B.; Ruhlandt-Senge, K. Chem., Eur. J. 2004, 10, 3315. Form stable complexes through hydrogen bonding
- 26. Conclusions 25 RTLE utilizing environmentally benign BiPh3 provides an excellent alternative for synthesis of organoalkaline earth complexes Replaces organomercury One-pot, convenient Variety of ligands Dramatically improves reaction rates over direct metallation
- 27. II. Exploring Weak Interactions as Structure Determining Factors in MOCVD Volatility MOCVD process deposits thin films on a substrate Semiconductor High temperature super conductors Computer memory
- 28. 27 H AcRaFr LaBaCs YSrRb ScCaK MgNa BeLi H AcRaFr LaBaCs YSrRb ScCaK Na BeLi Mg Ba Mg Sr Ca size Ionic Radii (Å) 0.72 1.00 1.18 1.35 CN = 4 CN = 6 CN = 6 CN = 6 High oxo- and hydrophilicity Tendency towards aggregation and subsequently poor volatility Challenges Shannon, R.D. Acta Crystallogr., 1976, A32, 751; Elschenbroich, C. Organometallics, 3 ed., Wiley-VCH, Weinheim, 2006.
- 29. 28 Coordinative Saturation Ligand bulk Neutral co-ligands Non-covalent interactions (secondary interactions) Metal∙∙∙π (arene) Agostic (M∙∙∙H－C) Metal∙∙∙F providing a major factor in the reactivity and physical properties of the alkaline earth organometallics
- 30. 29 Metal∙∙∙F Metal∙∙∙π Agostic H-Bond Free energies of rotation (kcal/mol) 18.7 - 19.1 19.0 13.6 - 14.6 15.0 – 40.0 Metal-ligand bonding Secondary interactions Transition metals Strong Much smaller role Alkaline earth metals Weak Significant role Importance of Secondary Interactions As alkaline earth metal compounds frequently display weak, highly polar metal-ligand bonding, secondary interactions are an important means to provide steric saturation to the metal center Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Ruhlandt-Senge, K. in prep. Szatylowicz, H. J. Phys. Org. Chem. 2008, 21, 897-914. Gillett-Kunnath, M.; Teng, W.; Vargas, W.; Ruhlandt-Senge, K., Inorg. Chem. 2005, 44, 4862.
- 31. 30 Weak interaction of a coordinately unsaturated metal with a C—H bond Ca[N(SiMe3)(Mes)]2(thf)2 CN = 4 + 1 Ba2(Odpp)4 Deacon, G. B., et al. Chem. Eur. J. 2009, 15, 5503. Gillett-Kunnath, M. et al., Inorg. Chem., 2005, 44, 4862 Secondary Interactions Agostic (M∙∙∙H—C) Metal―π (arene) Ba2: CN = 4 +4Ba1: CN = 3 + 9
- 32. 31 Secondary Interactions Metal∙∙∙F KBa(PFTB)3(thf)4 C CF3F3C OH CF3 Perfluoro-t-butanol H(PFTB) Stabilized via M-F interaction Excellent thermal properties Previous work with Buchanan, W. D.; Ruhlandt-Senge, K. U.S. Pat. Appl. 12/471,776. 2009.; Buchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55. Ba1
- 33. C CF3F3C OH 32 C CF3F3C OH CF3 1,1,1,3,3,3-Hexafluoro- 2-phenyl-2-propanol Detailed analysis of strategies to achieve steric saturation Studies of its effect on: Coordination pattern Thermal properties Possible interactions Metal∙∙∙F Metal∙∙∙F, Metal―π, M∙∙∙H—C H(PFTB) H(HFPP) Evaluation of Secondary Interactions
- 34. Direct metallation via ammonia activation Moderate to good yields with high purity 33 C CF3F3C OH Ae + 2 THF -78 oC, NH3 (l) Monometallic Complexes -Synthesis Ae = Ca, Sr, Ba [Ae(HFPP)2(thf)4] + H2
- 35. Partial loss of THF co-ligands induced dimerization and extensive M∙∙∙F interactions to achieve coordinative saturation 34 Crystallization from THF Crystallization from toluene CN = 6 Sr1: CN = 6 Sr2: CN = 4 + 6 Monometallic Complexes -Structures [Sr(HFPP)2(thf)4] [Sr2(HFPP)4(thf)3]
- 36. 35 Heterobimetallic Complexes -Synthesis KH + H(HFPP) [K(HFPP)(thf)]4 THF [BaK(HFPP)3(thf)]24 [Ba(HFPP)2(thf)4] + [K(HFPP)(thf)]4 THF Combination of the two solutions of homometallic complex leads to heterobimetallic formation
- 37. 36 Heterobimetallic Complexes -Structure Ba1 36 C CF3F3C OH CF3 C CF3F3C OH KBa(HFPP)3(thf)4 KBa(PFTB)3(thf)4 1 Ba∙∙∙F 3 K∙∙∙F 0 Ba∙∙∙F 6 K∙∙∙F Buchanan, W. D.; Guino-o, M. A.; Ruhlandt-Senge, K. Inorg. Chem. 2010, 49, 7144-55.
- 38. 37 Magnitude of metal∙∙∙F interactions may potentially effect volatility of alkaline earth metal compounds Comparison of Thermal Properties by TGA C CF3F3C OH CF3 C CF3F3C OH 1 Ba∙∙∙F 3 K∙∙∙F 6 K∙∙∙F PFTB HFPP
- 39. 38 Conclusion/Future work Secondary non-covalent interactions are an important stabilizing factors Metal∙∙∙F Agostic → Isolated heterobimetallic alkaline earth metal HFPP complexes Secondary non-covalent interactions are likely to be a key factor in volatility Synthesis of another alkali/alkaline earth metal combination complexes is in process for direct comparison of structural features and thermal properties of two groups of compounds based on HFTB and HFPP Extend the work to divalent lanthanide metals
- 40. Dr. Karin Ruhlandt Dr. Glen B. Deacon Dr. Anna O’Brien Dr. Miriam M. Gillett-Kunnath Dr. Ana Torvisco Melanie Wolf Ruhlandt Group Members Syracuse University Department of Chemistry NSF Acknowledgements 39
Editor's Notes
- Hello, I’m Yuriko Takahashi. Thank you for inviting me to Houston Technology Center. It is my pleasure to talk to you today about my research project in Dr. Ruhlandt group at Syracuse University. Before start to talk about my research, I would like to introduce myself briefly. I would like to introduce them by way of acknowledging them for the work you are going to hear about today.Dr. Ruhlandt is a distinguished professor and Chair of the department of Chemistry at SU. She was also my Ph.D. advisor. I am grateful for her continued support, and allowing me to work in her lab again.Doctoral Candidate Yuriko Takahashi is a current member of the Ruhlandt group and she deserves special mention for her work on this project. I am very grateful to you for all that you have done. I would also like to acknowledge Dr. Gillett-Kunnath, LMC graduate, who earned her Ph.D. in the Ruhlandt Group. It was her doctoral work that began systematically investigating the synthetic route I will talk about today. This project is built upon her initial findings.Half the fun of working in the group is getting to know those who share your love of chemistry. So to graduate students Alan, Peter, Catherine, Andrew and Valerie – I am grateful that you have all come today.Others who have contributed to this project in various ways include summer research students and their mentors, as well as international collaborators from Germany and Australia.
- I spent my first two years of college at Saitam University in Japan, majoring in chemical engineering. And then I transferred to Augustana College, South Dakota where I’ve obtained Bachelor degree in chemistry. During my undergraduate studies, I participated in the summer research program at Lehigh University, Pennsylvania and also at Syracuse University, New York. I started my graduate studies in 2009 at Syracuse University. I’ve engaged two projects, one is the investigation of a new, benign, efficient synthetic route for synthesizing highly reactive alkaline earth metal compounds and the other is the development of new heterobimetallic species as single-source CVD precursors including the evaluation of the influence of weak interactions on the thermal properties of the target compounds.In addition to research, I’ve teaching general chemistry laboratory courses for four years and I am currently working on course development for various undergraduate laboratories.Two projects I will talk about today are quite different, but the focus of my research is making alkaline earth metal organometallic compounds. Characterized self-assembly of organic-inorganic hybrid amphiphilic surfactants using static and dynamic laser light scatteringHave done extensive ligand synthesis
- My first project for mechanistic studies involved NMR to evaluate kinetic trends. Current project includes a study of the structures of the compounds, using X-ray crystallography. I am well-experienced in the operation of the single-crystal and powder x-ray diffractometers.TGA is used to evaluate thermal stabilities and volatilities of compounds.I also have done ligand synthesis. Ligand shown here is one of ligands I’ve synthesized for undergraduate research project where I supervised an undergraduate student coming from Austria
- My projects also involve the use of inert gas synthetic techniques. These techniques include using a glove box and double manifold vacuum lines, or Schlenk lines. Any solvents used were taken from solvent system and have to be distilled and degassed. Also starting materials were dried and distilled using Schlenk line techniques.
- My first project for mechanistic studies involved NMR to evaluate kinetic trends. Current project includes a study of the structures of the compounds, using X-ray crystallography. I am well-experienced in the operation of the single-crystal and powder x-ray diffractometers.TGA is used to evaluate thermal stabilities and volatilities of compounds.I also have done ligand synthesis. Ligand shown here is one of ligands I’ve synthesized for undergraduate research project where I supervised an undergraduate student coming from Austria
- As I mentioned in my introduction,my research focus is synthesis of heavy alkaline earth organometallic compounds. As you know, the Alkaline Earth metals are the elements of group 2 on the periodic table. Specifically, we are interested in Mg and Ca which are biocompatible.We are also interested in Sr and Ba, which are found in electronic materials.We do not study Beryllium because it is highly toxic and also we do not use Radium because it is radioactive. The alkaline earth metals are abundant on the earth, inexpensive, and specifically calcium is nontoxic, providing a highly attractive reagent. Since calcium and strontium offer quit similar charge size ratios to the divalent rare-earth metals europium, samarium, and ytterbium, they can be attractive substitutes for the more difficult to obtain rare-earth metals.
- bAlkaline earth metal organometallic complexes have the wide range of applications including synthetic, polymer and material chemistry.Alkaline earth metal complexes have been investigated as effective catalysts in a wide range of organic transformation including intramolecularhydroaminations, hydrophosphinations, andhydrosilyations.Compounds can also be used to initiate polymerization reactions Hydrogen Storage is of great interest for energy applications. Metals and ligands can be arranged in 3-Dimentional arrays with empty spaces that can store and release hydrogen gas. Another class of coordination compounds, calcium phosphonates, are being investigated as synthetic bone scaffolds for the treatment of bone defects and fractures.My current project is the development of new heterobimetallic species as single source CVD precursors. Most of complexes for these applications are extremely difficult to make. Therefore the detailed examination of synthetic methodologies and the exploration of novel reaction routes has been critical to the growth of alkaline-earth metal chemistry. The focus of my first project is the examination and development of synthetic routes that allows the facile preparation and isolation of target compounds that can then be employed in a variety of applications.
- As I mentioned previously, synthetic challenges are related to their high oxo and hydrophilicity and tendency towards aggregation and consequent solubility challenges.In order to prevent aggregation of alkaline earth species, there are three significant factors in the stabilization of alkaline earth complexes.
- Hello, I’m Yuriko Takahashi. Thank you for inviting me to Houston Technology Center. It is my pleasure to talk to you today about my research project in Dr. Ruhlandt group at Syracuse University. Before start to talk about my research, I would like to introduce myself briefly. I would like to introduce them by way of acknowledging them for the work you are going to hear about today.Dr. Ruhlandt is a distinguished professor and Chair of the department of Chemistry at SU. She was also my Ph.D. advisor. I am grateful for her continued support, and allowing me to work in her lab again.Doctoral Candidate Yuriko Takahashi is a current member of the Ruhlandt group and she deserves special mention for her work on this project. I am very grateful to you for all that you have done. I would also like to acknowledge Dr. Gillett-Kunnath, LMC graduate, who earned her Ph.D. in the Ruhlandt Group. It was her doctoral work that began systematically investigating the synthetic route I will talk about today. This project is built upon her initial findings.Half the fun of working in the group is getting to know those who share your love of chemistry. So to graduate students Alan, Peter, Catherine, Andrew and Valerie – I am grateful that you have all come today.Others who have contributed to this project in various ways include summer research students and their mentors, as well as international collaborators from Germany and Australia.
- Common synthetic pathways employed for the synthesis of alkaline earth metal organometallics include salt elimination, transamination, and direct metallation via anhydrous ammonia activation.Salt elimination involves treatment of the alkaline earth metal halide with alkali metal salt of the ligand.Transamination involves a reaction between the alkaline earth metal amides and a more acidic substrate.Alkaline earth metal complexes can be also prepared by direct metallation which involves a reaction of a metal with an acidic ligand.While sucessful for the preparation of a large number of compounds, each of these methodologies pose a variety of drawbacks.For salt elimination, highest quality of alkaline earth metal iodides are required which tend to be quite expensive.Transamination requires the preparation of high reactive reactants.Direct metallation requires an oxide-free metal surface and metal activation. Typically this can be accomplished by the dissolutino of the metals in anhydrous liquid ammonia. However, reaction proceed slowly because of limited surface area of metal and also keeping reactions below -35oC to condense NH3 gas. Moreover, working with condensed ammonia is very dangerous, and the options for scaling up are rather limited.These disadvantages associated with current synthtic methodologies promoted efforts to use redox transmetallation/ligand exchange RTLE reaction for the synthesis of the alkaline earth organometallics.
- The mercury-based route that is known is a RTLE reaction.RTLE reaction proposes two steps: the first step is redo reaction between the alkaline earth metal and organomercury compounds, typically diphenylmercury as a transmetallating agent, resulting in the formation of a reactive alkaline earth organometallic intermediate and deposition of mercury. Second step is ligand exchange where a more acidic ligand reacts with the high reactive intermediate to form a stable product under the release of benzene.In order for this reaction to work, pKa of the ligand has to be lower than that of benzene which is around 43. The high pKa of benzens allows a possibility of using a variety of ligands for the synthesis of corresponding organoalkaline earth metal complexes. Organomertcurials have been used extensively in this methodology for the preparation of alkaline earth metal organometallics including cyclopentadienides, pyrazolates, formamidinate, and aryloxides. However the high toxicity of mercury and its compound make this route less attractive.
- Recent advances to this synthetic strategy have been made by replacing this toxiorganomercurial with the benign Ph3Bi. The redox reaction depends on the difference in lidox potential between the alkaline earth metal and mercury. And high negative redox potential of heavy alakline earth metals allows replacing mercury with the less positive bismuth.
- RTLE reaction utilizing Ph3Bi can be run one-pot allowing this reaction to be both time and cost effective. In addition to benign less toxic than the classic organomercurials, Ph3Bi offers several advantages.It is commercially available and inexpensive, air and moisture stable, and allows an easy work up of the target compounds while providing good product yields.
- We have been exploring mechanism of RTLE reaction utilizing BiPh3 in order to demonstrate the feasibility of RTLE based on BiPh3 for the synthesis of alkaline earth metal organometallics.Also we want to investigate and examine the influence of the pKa of the ligands on the reaction rate.To accomplish this study, we have used a series of silylated amines, cyclopentadienyls, pyrazoles, and aryoxyligands of varied acidity.
- In order to better understand how the RTLE reaction proceeds and monitor the reaction rate, each one-pot reaction was cariied out in a J-Young tab NMR tube.Because alkaline earth metals are highly hydrophilic and oxophilic, all reactions were prepared under inert gas using drybox.In a typical reaction, the metal fillings used to increase the surface area of the metal, trypenylbismuth, ligand, cyclohexane as internal standard, deutratedthf were placed in an NMR tube saeld with a J-Young tap. They were sonicated and monitored by proton NMR spectroscopy.
- The following are select spectra for the RTLE reaction between Ba, Ph3Bi, andhexamethyldisilazane, HMDS.For each experiments, proton NMR spectra were obtained at regular intervals until free ligand was consumed.The consumption of free ligand and Ph3Bi and increase in deprotonated ligand were monitored by intergrating the corresponding peaks in the presence of the internal standard. As you can see in the reaction between barium and HMDS already at 2 hour we see increase of deprotonated ligand which indicates product formation and at approximately 10 hour we see complete conversion to benzene.
- Using these proton NMR spectra, the percent concentration of each of the three species were calculated at each time point and plotted as a function of time. Identical reactions were repeated multiple times to verify results. Percent concentration values for a given time were averaged over duplicate runs and error bars represent the standard deviation of these average values.
- As you may notice from large error bars, the reproducibility of duplicate run is difficult to achieve despite careful technique.This is due to the heterogeneous nature of the reactions. A central difficulty in studying the heterogeneous reaction mechanism is obtaining reliable kinetics infromation.Also complications lie at the metal surface. The active area of the metal surface is unknown and continuously changing.Even if the metal surface appears uniform, it doesn’t mean it is reacting uniformly.Furthermore, we are getting kinetic data on reactions that happen at the metal surface by indirect measurements of the chemical composition of the bulk solution.We need to be careful about over mechanistic interpretation of the data, but still our data is sufficient for surveying average trends.
- Now let’s have a look at the result obtained from the reaction between barium and HMDS in presence of Ph3Bi.Light blue line shows percent concentration of deprotonated ligand, in other words, product. Pink line shows percent concentration of free ligand.Green line shows percent concentration Ph3Bi.50% of product was formed within 5 hours. We define this time as 50% conversion time. We noticed that many reactions had unreacted Ph3Bi after the RTLE reaction had completed, suggesting a possibility of alternative reaction mechanism or the second reaction route is occurring simultaneously alongside this RTLE route which doesn’t consume Ph3BiIt was believed that the second reaction occurring simultaneously alongside RTLE might in fact be direct metallation…
- In order to figure out alternative reaction mechanism, we conducted a control experiment which is a reaction between barium and HMDS without Ph3Bi.The result shows the reaction proceeds even without Ph3Bi, indicating when the reaction is carried out with Ph3Bi as a transmetallatin agent, direct metallation and RTLE based BiPh3 occur simultaneously.Direct metallation was not complete as you can see products were decomposed after the reaction reached 50% conversion.Although directmetallation and RTLE based Ph3Bi reaction occur simultaneously, RTLE reaction predominates since RTLE reaction is much faster than direct metallation.
- Similar result was observed for the HCp* ligand. As you can see a big difference in 50% conversion time, the addition of Ph3Bi to direct metallation speeds up reaction rate dramatically. When the reaction is run in the absence of BiPh3, it takes 21 days to reach 50% conversion of the product. When Ph3Bi are used, the 50% conversion time speeds up to only 22 hours
- Similar result was observed for the HCp* ligand. As you can see a big difference in 50% conversion time, the addition of Ph3Bi to direct metallation speeds up reaction rate dramatically. When the reaction is run in the absence of BiPh3, it takes 21 days to reach 50% conversion of the product. When Ph3Bi are used, the 50% conversion time speeds up to only 22 hours
- Unlike other ligands, Ph2pzH (3,5-diphenylpyrazole)shows slightly faster reaction rate for direct metallation, compared to RTLE based Ph3Bi reaction within the experimental error. These results suggest that reactions between Ba metal and the pyrazole ligand are not enhanced by the BiPh3, because in fact the DM route is very fast on its own.
- Theligands are arranged here from most acidic on the left to least acidic on the right in order to examine the influence of ligand acidity on reaction rates.The reaction rates for the RTLE reaction are shown on top, and DM shown on bottom in terms of 50% conversion times.Reactions with less acidic ligand (HN(SiMe3)2, Hflu, HCp*) have vividly demonstrated that utility of Ph3Bi as redox transmetallation agent can afford much shorter reaction time. For two ligands tested, addition of BiPh3 did not improve within error of measurement.Therefore we figured that they must be something else at play besides just acidity.
- We believe the tendency for the pyrazolate ligand to undergo direct metallation at such a fast rate likely due to its ability to form stable complexes through hydrogen bonding.Previously calcium and strontium metal pyrazolate complexes have been synthesized and these are two structures obtained from X-ray crystallography.Some of the pyrazoles coordinated to the metal center have hydrogens that bond to neighboring pyrazoles, in effect stabilizing the final product. Such stability may be a driving force speeding up the reaction rates we’ve seen here.
- RTLE utilizing enviromentally benign BiPh3 provide an excellent alternative for synthesis of organoalkaline earth complexes. RTLE can be utilized for a variety of ligand systems. The toxic organomercurial reagents previously required for RTLE reactions of alklaine earth metals can now be replaced with a greener reagent, Ph3Bi.All of the reagents can be added at once to one container and left to sonicate until the reaction completes. The reagents are inexpensive, can be purchased and used without purificationBy adding Ph3Bi, the reaction rate for many ligands goes from days, or even weeks to just hours. utilizing Ph3Bi has proven to be useful especially for reactions with less acidic ligands, providing great improvements of reaction rates.Currently, we are writing the manuscript for publication of these results.
- Hello, I’m Yuriko Takahashi. Thank you for inviting me to Houston Technology Center. It is my pleasure to talk to you today about my research project in Dr. Ruhlandt group at Syracuse University. Before start to talk about my research, I would like to introduce myself briefly. I would like to introduce them by way of acknowledging them for the work you are going to hear about today.Dr. Ruhlandt is a distinguished professor and Chair of the department of Chemistry at SU. She was also my Ph.D. advisor. I am grateful for her continued support, and allowing me to work in her lab again.Doctoral Candidate Yuriko Takahashi is a current member of the Ruhlandt group and she deserves special mention for her work on this project. I am very grateful to you for all that you have done. I would also like to acknowledge Dr. Gillett-Kunnath, LMC graduate, who earned her Ph.D. in the Ruhlandt Group. It was her doctoral work that began systematically investigating the synthetic route I will talk about today. This project is built upon her initial findings.Half the fun of working in the group is getting to know those who share your love of chemistry. So to graduate students Alan, Peter, Catherine, Andrew and Valerie – I am grateful that you have all come today.Others who have contributed to this project in various ways include summer research students and their mentors, as well as international collaborators from Germany and Australia.
- As I mentioned previously, synthetic challenges are related to their high oxo and hydrophilicity and tendency towards aggregation and consequent solubility challenges.In order to prevent aggregation of alkaline earth species, there are three significant factors in the stabilization of alkaline earth complexes.
- These include: use of sterically demanding ligands, coordination to neutral co-ligands and presence of secondary non-covalent interactions. Various secondary interactions such as M-π, agostic, and M-fluorine interaction are commonly observed in heavy alkaline earth metals.
- As the alkaline earth metal compounds frequently displayweak, highly polar metal-ligand bonding, secondary interactions play a significant role.
- Among the various secondary interactions, M-π interactions have been the most extensively studied. For alkaline earth metals, it is generally observed that the extent of M-π interactions increase as the metal size increases. As you can see in the left picture, the differences in coordination number leads to a significant difference in the number of M-π interactions to each metal center. The Ba2 with the terminal ligand has a coordination number of four with four metal-π interactions, while the Ba1 with only bridging ligands reaches a coordination number of three but attains nine M-Cp interactions.Another set of secondary interactions that provide further steric saturation are agostic interaction. These interactions are defined as weak interactions of a coordinatively unsaturated metal with a C-H bond. Agostic interactions have received comparatively little attention as they are frequently considered to be too weak to make a difference.
- The potential of M-F interactions to stabilize reactive metal centers has been an underutilized tool in organoalkaline earth chemistry. A family of alkaline earth perfluorotertbutoxide species have been synthesized by former group member. Importantly, the metal-fluorine interactions in PFTB compounds allow the preparation of the heterobimetallic species as shown in the picture here. The heterobimetallic compounds are remarkably volatile and sublime cleanly atlow temperatures. Having high volatility, these compounds can be utilized for CVD applications. My current project is extending these PFTB work to other fluorinated ligands
- A modification to the ligand systems is the replacement of one of the fluoromethyl groups in PFTB by a phenyl group. Introducing of metal…C(π) interactions provided by the HFPP ligand allows detailed analysis of strategies to achieve steric saturation and studies of its effect on the overall geometry and coordination patterns as well as thermal properties for heterobimetallic alkali/alkaline earth metal fuluoroalkoxides.
- Direct metallationvia anhydrous liquid ammonia activation was employed to prepare the target homometallic species. Ammonia activation of the alkaline earth metals allows their direct reaction with the HFPP under liberation of hydrogen gas affording a series of alkaline earth HFPP complexes in moderate to good yield and high purity. Among alkaline earth HFPP complexes I’ve synthesized, I will discuss strontium HFPP complexes.
- Strontium HFPP specie shows two types of structures. The monomeric structure in the left picture was obtained by crystallization from THF. The monomer exhibits a cis conformation of HFPP ligands with THF moleculers. it displays six-coordinate metal center involving two HFPP ligands and four THF contacts.Recrystallization of monomer from toluene afforded dimeric complex as shown in the right picture. Three HFPP ligans are birding two Sr2+ metal atoms, three THF donors on Sr1, and a terminal HFPP ligand on Sr2. Sr1 is six coordinate and No metal-fluorine interactions are evident in the Sr1 because THF co-ligand incorporation sufficiently provides the coordinative saturation. On the other hand, Sr2 is four-coordinate and The coordination spheres of Sr2 is supplemented by extensive metal…F-C interactions from trifluoromethyl groups of the bridging HFPP ligands. A total of six Sr…F interactions were observed. By contrast with monomeric structure, partial loss of THF co-ligands induced dimerization and extensive M-fluorine interactions to achieve coordinative saturation.
- heterobimetallic alkaline earth complex was prepared by treating the homometallic alkali complex with the homometallic alkaline earth compound in THF.The monometallic alkali compoundwas prepared by treating alkali hydride with HFPP in THF .
- Although secondary interactions are weaker than covalent interactions, they play a significant role in metal stabilizationHFPP complexes I’ve synthesized so far show poor volatilitiesCurrently I am synthesizing another metals combination such as Ca-Na, Sr-K, Ba-Na, for the direct comparison of structural features and thermal properties of two groups of compounds based on HFTB and HFPP that will be able to offers a better understanding of the role of secondary interactions and their influence on the coordination chemistry and thermal properties of the target compounds.I am planning to extend this work to divalent lanthanide metals.
- Thank you for your kind attention and I would be happy to answer any questions you might have.