GROUP MEMBERS: NG MEI XIANG NOOR HIDAYAH MOHD JUSOH LEE YEE VOON NORADILA AWANG  MOHD NORULAKMAL AB MALIK  EXPERIMENT 5: I...
<ul><li>Complex [Mo(CO) 4 (pip) 2 ] can be synthesized from the reflux reaction between molybdenum hexacarbonyl, Mo(CO) 6 ...
<ul><li>After the thermal isomerization, the trans-[Mo(CO) 4 (PPh 3 ) 2 ] formed was brownish-off white in colour.  </li><...
<ul><li>Three molybdenum tetracarbonyl complexes and the molecular geometry of the complexes was determined by using infra...
<ul><li>Most of the organometallic compounds are air sensitive and tend to decompose if not handled properly.  </li></ul><...
 
Mo(CO) 6 (1.0g)Weighted  + 40ml dry heptane  + 5ml piperidine  + few pieces boiling stones & magnetic stirring bar Filter ...
0.5g Mo(CO 4 )(pip) 2   + 20ml dichloromethane in N 2  + 0.75g PPh 3   ->  Reflux for 20 mins Cool to room temperature  Fi...
0.5g molybdenum carbonyl  complex+ 10ml dry toluene  under N 2 -> Reflux for 30 minutes  Cool to room temperature  Reduce ...
 
(A) Synthesis of [Mo(CO) 4 (HNC 5 H 10 ) 2 ] Table 1: Data from Infrared Spectrum [Mo(CO) 4 (HNC 5 H 10 ) 2 ] Weight of pr...
( B) Synthesis of cis-[Mo(CO) 4 (PPh 3 ) 2 ] Table 2: Data from Infrared Spectrum cis-[Mo(CO) 4 (PPh 3 ) 2 ] Weight of pro...
(C) Synthesis of trans-[Mo(CO) 4 (PPh 3 ) 2 ] Table 3: Data from Infrared Spectrum trans-[Mo(CO) 4 (PPh 3 ) 2 ] Weight of ...
<ul><li>All the apparatus used in this experiment must totally dry. </li></ul><ul><li>Piperidine is a reagent for the reac...
<ul><li>Reflux </li></ul><ul><li>Paraffin oil </li></ul><ul><ul><li>its boiling point (>110.6  0 C) was higher than heptan...
<ul><li>Precipitate was filtered while it was still hot  </li></ul><ul><ul><li>to prevent the formation of impurities  </l...
 
<ul><li>Physical change of colour product, because organometallic compound is ease oxidized and sensitivity to oxygen and ...
<ul><li>The reaction is carried out dissolve in dry heptane, so the CO ligand is highly solvated. </li></ul><ul><li>One of...
The S N 2  mechanism of formation  [Mo(CO) 4 (HNC 5 H 10 ) 2 ] is shown as following : intermediate   Cis-[Mo(CO) 4 (HNC 5...
<ul><li>Mixture(0.5g of  [Mo(CO) 4 (pip) 2 ] + 20 mL </li></ul><ul><li>of dry dichloromethane + 0.75 g of PPh 3  ) was hea...
<ul><li>Rotary evaporator  </li></ul><ul><ul><li>to remove the solvent from the product formed </li></ul></ul><ul><li>8 dr...
Pale yellow precipitate formed
<ul><li>For the synthesis of [Mo(CO) 4 (PPh 3 ) 2 ], dry dichloromethane was used as a solvent. Since piperidine was highl...
The reaction for the formation of cis-[Mo(CO) 4 (PPh 3 ) 2 ] complex by using S N 1 mechanism.    Cis-isomer Mo CO CO OC O...
<ul><li>Solution (0.5 g of [Mo(CO) 4 (PPh 3 ) 2 ] + 10 mL of dry toluene under N 2 ) was heat at reflux temperature for 30...
<ul><li>The solution was heat at reflux temperature for 30 minutes to make sure that the reaction was completed.  </li></u...
<ul><li>This showed that the reaction does not go to completion in this part and there is a mix of cis and trans isomers i...
Brownish off-white precipitate was [Mo(CO) 4 (PPh 3 ) 2 ]
<ul><li>For the trans synthesis of [Mo(CO) 4 (PPh 3 ) 2 ], toluene was used as a solvent. The PPh 3  was first dissolved i...
The reaction of dissociation mechanism for the formation of trans-[Mo(CO) 4 (PPh 3 ) 2 ] complex by using S N 1 mechanism.
<ul><li>Through the infrared spectrum obtained, we found that the tetracarbonyldipiperidine molybdenum,[Mo(CO) 4 (HNC 5 H ...
<ul><li>1) By interpreting the absorption bands of the CO group in the infrared spectra, determine the stereochemistry of ...
<ul><li>2 .  Write a reaction scheme to show clearly the  stereochemistry of isomers formed in the complexes. </li></ul><u...
<ul><li>(ii)  The reaction for the formation of cis-  [Mo(CO) 4 (PPh 3 ) 2 ] complex </li></ul>CO CO OC H 10 C 5 HN Mo Mo ...
<ul><li>(iii) The reaction for the formation of trans    [Mo(CO) 4 (PPh 3 ) 2 ] complex </li></ul>CO OC OC CO Mo CO Mo OC ...
<ul><li>State the type of mechanism involved in the carbonyl substitution reaction. </li></ul><ul><li>Answer: </li></ul><u...
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Kto Lab Presentation

  1. 1. GROUP MEMBERS: NG MEI XIANG NOOR HIDAYAH MOHD JUSOH LEE YEE VOON NORADILA AWANG MOHD NORULAKMAL AB MALIK EXPERIMENT 5: IDENTIFICATION OF STEREOCHEMICAL ISOMERS OF [Mo(CO) 4 (L) 2 ] BY INFRARED SPECTROSCOPY
  2. 2.
  3. 3. <ul><li>Complex [Mo(CO) 4 (pip) 2 ] can be synthesized from the reflux reaction between molybdenum hexacarbonyl, Mo(CO) 6 with piperidine. </li></ul><ul><li>The yellow brownish precipitate formed was then react with triphenylphosphine (PPh3) with reflux and the cis-[Mo(CO) 4 (PPh 3 ) 2 ] formed was pale yellow in colour. </li></ul>
  4. 4. <ul><li>After the thermal isomerization, the trans-[Mo(CO) 4 (PPh 3 ) 2 ] formed was brownish-off white in colour. </li></ul><ul><li>The infrared spectrum have few sharp absorbance at about 2100-1750 cm -1 as the C=O bond present in the complex. </li></ul><ul><li>The structure of [Mo(CO) 4 (pip) 2 ] and [Mo(CO) 4 (PPh 3 ) 2 ] were cis and in thermal isomerization, the structure of [Mo(CO) 4 (PPh 3 ) 2 ] was trans. Trans- structure was more stable than Cis- structure. </li></ul>
  5. 5.
  6. 6. <ul><li>Three molybdenum tetracarbonyl complexes and the molecular geometry of the complexes was determined by using infrared spectroscopy. </li></ul><ul><li>Metal carbonyls and their derivatives display sharp, intense CO stretching vibrations in the 1750 - 2100 cm -1 region. </li></ul><ul><li>Intensity data for the CO stretching motion in substituted metal carbonyls are presented for compound of the types [Mo(CO) 4 (L) 2 ] , trans-[Mo(CO) 4 (L) 2 ]and cis-[Mo(CO) 4 (L) 2 ]. </li></ul><ul><li>Four carbonyl absorption bands are to be expected from a cis-[Mo(CO)4(L)2] complex whereas only one band is expected from trans isomer. </li></ul>
  7. 7. <ul><li>Most of the organometallic compounds are air sensitive and tend to decompose if not handled properly. </li></ul><ul><li>Those compounds can be oxidized easily, especially when they are in solution, because of their sensitivity to oxygen and water. </li></ul><ul><li>Consequently, handling of organometallic compounds should be carried out under dry and deoxygenated atmosphere or under vacuum. </li></ul><ul><li>Mo(CO) 6 is a popular reagent in organometallic synthesis because one or more CO ligands can be displaced by other donor ligands. </li></ul>
  8. 9. Mo(CO) 6 (1.0g)Weighted + 40ml dry heptane + 5ml piperidine + few pieces boiling stones & magnetic stirring bar Filter precipitate while hot Wash twice with 10 ml (60-80  C) petroleum ether that has been cooled 1)Weight 2)Calculate the % yield 3) Record IR Heated for two hours (reflux temp= 110 o C-120 o C) with stirring. Suck dry by vacuum pump
  9. 10. 0.5g Mo(CO 4 )(pip) 2 + 20ml dichloromethane in N 2 + 0.75g PPh 3 -> Reflux for 20 mins Cool to room temperature Filter orange solution by gravity filtration Concentrate filtrate by rotary evaporator Collect by pump filtration Add 8 drops methanol Solution put in ice bath first, then cooled in freezer (<0 o C) for 15 minutes 1)Weight 2)Calculate the % yield 3) Record IR
  10. 11. 0.5g molybdenum carbonyl complex+ 10ml dry toluene under N 2 -> Reflux for 30 minutes Cool to room temperature Reduce volume on rotary evaporator Purify the product by 10ml dichloromethane Collect product by gravity filtration Concentrate the filtrate, collect precipitate Weight product, calculate % yield, and record IR
  11. 13. (A) Synthesis of [Mo(CO) 4 (HNC 5 H 10 ) 2 ] Table 1: Data from Infrared Spectrum [Mo(CO) 4 (HNC 5 H 10 ) 2 ] Weight of product = 1.14g Colour of product = Yellow colour Melting point = 125 0 C Percentage yield = 79.72% Functional Group Wavenumber, cm -1 N-H (°2 amine) 3264.59 C-H (sp 3 stretching) 2926.20, 2855.26 C = O stretching 1839.16, 1890.44,1995.98, 2011.68
  12. 14. ( B) Synthesis of cis-[Mo(CO) 4 (PPh 3 ) 2 ] Table 2: Data from Infrared Spectrum cis-[Mo(CO) 4 (PPh 3 ) 2 ] Weight of product = 0.84g Colour of product = Pale yellow Melting point = 160 0 C– 165 0 C Percentage yield = 86.60% Functional Group Wavenumber, cm -1 C-H (sp 2 stretching) 2925.34 C = O stretching 1827.84,1871.46, 2012.45 C=C stretching 1461.50
  13. 15. (C) Synthesis of trans-[Mo(CO) 4 (PPh 3 ) 2 ] Table 3: Data from Infrared Spectrum trans-[Mo(CO) 4 (PPh 3 ) 2 ] Weight of product = 0.44g Colour of product = Brownish off-white Melting point = 163 0 C-168 0 C Percentage yield = 88% Functional Group Wavenumber, cm -1 C-H (sp 2 stretching) 2924.79 C = O stretching 1889.17, 1947.80,2021.88,2071.59 C=C stretching 1463.91, 1585.12
  14. 16.
  15. 17. <ul><li>All the apparatus used in this experiment must totally dry. </li></ul><ul><li>Piperidine is a reagent for the reaction to occur while dry heptane acted as a catalyst. </li></ul>1) Mo(CO) 6 is very sensitive to water 2) has high tendency to form complex with aqua ligand if water was present
  16. 18. <ul><li>Reflux </li></ul><ul><li>Paraffin oil </li></ul><ul><ul><li>its boiling point (>110.6 0 C) was higher than heptanes </li></ul></ul><ul><ul><li>suitable for heat transfer </li></ul></ul><ul><li>The temperature should not be too high (slightly above 110.6 0 C) to avoid the solution turn to brown color </li></ul><ul><li>After reflux for 2 hours, a yellow brownish </li></ul><ul><li>precipitate was formed. </li></ul>to allow the mixture to undergo complete reaction
  17. 19. <ul><li>Precipitate was filtered while it was still hot </li></ul><ul><ul><li>to prevent the formation of impurities </li></ul></ul><ul><ul><li>interferences on the surface of precipitate </li></ul></ul><ul><li>Wash with cool ether petroleum </li></ul><ul><ul><li>Avoid the precipitate to dissolve </li></ul></ul><ul><li>Ether petroleum </li></ul><ul><ul><li>Good eluent which did not dissolve most of the organic compounds </li></ul></ul><ul><ul><li>Acted as washing agent </li></ul></ul><ul><ul><li>Has low dissolution in water </li></ul></ul>
  18. 21. <ul><li>Physical change of colour product, because organometallic compound is ease oxidized and sensitivity to oxygen and water. </li></ul><ul><li>Handling of these compounds suggest to be carried out under dry and deoxygenated atmosphere or under N 2 gas. </li></ul><ul><li>The function of N 2 gas was to eliminate oxygen gas and to prepare the suitable medium for chemical reaction. </li></ul><ul><li>The mechanism of formation [Mo(CO) 4 (HNC 5 H 10 ) 2 ] by reaction of Mo(CO) 6 and HNC 5 H 10 by using S N 2 mechanism. </li></ul>
  19. 22. <ul><li>The reaction is carried out dissolve in dry heptane, so the CO ligand is highly solvated. </li></ul><ul><li>One of the CO bond was weakening while the pip was coming to approach the metal. This complex is cis-complex due to the strong trans effect of CO bond. </li></ul><ul><li>Due to the Mo(CO) 6 complex is an inert complex because of CO has more electrons occupied in t 2g orbitals and prevent the pip easily approach to the central metal atom. </li></ul><ul><li>Therefore, the solution was refluxed for two hours with stirring to provide extra energy to complete the reaction. </li></ul>
  20. 23. The S N 2 mechanism of formation [Mo(CO) 4 (HNC 5 H 10 ) 2 ] is shown as following : intermediate   Cis-[Mo(CO) 4 (HNC 5 H 10 ) 2 ] Mo CO CO CO CO OC OC + pip pip------Mo(CO) 5 ----CO Mo CO CO CO OC OC pip slow + Mo CO CO CO OC OC pip pip Mo CO CO OC OC pip pip
  21. 24. <ul><li>Mixture(0.5g of [Mo(CO) 4 (pip) 2 ] + 20 mL </li></ul><ul><li>of dry dichloromethane + 0.75 g of PPh 3 ) was heated at reflux temperature for 20 minutes to make sure that the reaction was fully completed. </li></ul><ul><li>Orange solution was left to cool to room </li></ul><ul><li>temperature for the precipitation process </li></ul><ul><li>before filtered through gravity filtration. </li></ul>
  22. 25. <ul><li>Rotary evaporator </li></ul><ul><ul><li>to remove the solvent from the product formed </li></ul></ul><ul><li>8 drops of methanol was added and the solution was cooled in a freezer (<0 0 C) </li></ul><ul><ul><li>to induce the formation of the precipitate </li></ul></ul><ul><li>There are 4 absorption bands of C=O show that this complex has Cis- structure. </li></ul>
  23. 26. Pale yellow precipitate formed
  24. 27. <ul><li>For the synthesis of [Mo(CO) 4 (PPh 3 ) 2 ], dry dichloromethane was used as a solvent. Since piperidine was highly solvated in dichloromethane, the synthesis reaction became faster and undergoes dissociation process. </li></ul><ul><li>PPh 3 was a ∏ acceptor ligand which was a stronger ligand than pip which was only a σ donor ligand. Therefore, the reaction go more faster than the synthesis of [Mo(CO) 4 (pip) 2 ] from Mo(CO) 6 . </li></ul><ul><li>Moreover, this complex was is cis-complex which was kinetically stable because PPh 3 just substitutes the ligand of pip which had weak field ligand . </li></ul>
  25. 28. The reaction for the formation of cis-[Mo(CO) 4 (PPh 3 ) 2 ] complex by using S N 1 mechanism.   Cis-isomer Mo CO CO OC OC pip Mo CO CO OC OC + PPh 3 Mo CO CO OC OC PPh 3 PPh 3 PPh 3 PPh 3 Mo CO CO OC OC pip pip Mo CO CO OC OC pip + PPh 3 Mo CO CO OC OC pip PPh 3
  26. 29. <ul><li>Solution (0.5 g of [Mo(CO) 4 (PPh 3 ) 2 ] + 10 mL of dry toluene under N 2 ) was heat at reflux temperature for 30 minutes to obtained complete reaction. </li></ul><ul><li>The solvent volume was reduced through rotary evaporator to yield a product as a brownish off-white residue. </li></ul>
  27. 30. <ul><li>The solution was heat at reflux temperature for 30 minutes to make sure that the reaction was completed. </li></ul><ul><li>There are 4 absorption bands of C=O show that this complex has Cis- structure. </li></ul><ul><li>Theoretically, this was a complex with trans-isomer with one absorption peak in the spectrum. </li></ul><ul><li>This is because during the 30 minutes reflux, the cis isomer would convert to the trans-isomer due to the considerable steric hinderance inherent in using PPh3 as ligands, making the trans isomer thermodynamically more stable. </li></ul>
  28. 31. <ul><li>This showed that the reaction does not go to completion in this part and there is a mix of cis and trans isomers in our product. </li></ul><ul><li>The product was purified by dissolving in 10mL of dichloromethane and was collected by gravitational filtration. </li></ul>
  29. 32. Brownish off-white precipitate was [Mo(CO) 4 (PPh 3 ) 2 ]
  30. 33. <ul><li>For the trans synthesis of [Mo(CO) 4 (PPh 3 ) 2 ], toluene was used as a solvent. The PPh 3 was first dissolved in the toluene because PPh 3 was a bulky ligand. </li></ul><ul><li>Although PPh 3 dissociation occurs in this trans-[Mo(CO) 4 (PPh 3 ) 2 ] species, this dissociative process is less facile than in the cis-[Mo(CO) 4 (PPh 3 ) 2 ]. </li></ul><ul><li>After dissociation of PPh 3 , the PPh 3 will form back as in the trans position due to the steric repulsion in the PPh 3 compounds. </li></ul>
  31. 34. The reaction of dissociation mechanism for the formation of trans-[Mo(CO) 4 (PPh 3 ) 2 ] complex by using S N 1 mechanism.
  32. 35. <ul><li>Through the infrared spectrum obtained, we found that the tetracarbonyldipiperidine molybdenum,[Mo(CO) 4 (HNC 5 H 10 ) 2 ] complex formed has Cis structure, while [Mo(CO) 4 (PPh 3 ) 2 ] complex for part B has the Cis- structure and [Mo(CO) 4 (PPh 3 ) 2 ] complex for part C has the Trans- structure. </li></ul>
  33. 36.
  34. 37. <ul><li>1) By interpreting the absorption bands of the CO group in the infrared spectra, determine the stereochemistry of the complexes that you have prepared. </li></ul><ul><li>  </li></ul>Complexes C=O absorption band(cm -1 ) stereochemistry [Mo(CO) 4 (HNC 5 H 10 ) 2 ] 2011.68,1995.98,1890.44, 1839.16 Cis isomer [Mo(CO) 4 (PPh 3 ) 2 ], b 2012.45,1871.46, 1827.84 Cis isomer [Mo(CO) 4 (PPh 3 ) 2 ], c 1947.80 Trans isomer
  35. 38. <ul><li>2 . Write a reaction scheme to show clearly the stereochemistry of isomers formed in the complexes. </li></ul><ul><li>(i) The reaction for the formation of [Mo(CO) 4 (HNC 5 H 10 ) 2 ] complex. </li></ul>OC H 10 C 5 HN CO CO Mo Mo OC CO H 10 C 5 HN CO CO CO + 2 HNC 5 H 10 Cis-isomer
  36. 39. <ul><li>(ii) The reaction for the formation of cis- [Mo(CO) 4 (PPh 3 ) 2 ] complex </li></ul>CO CO OC H 10 C 5 HN Mo Mo OC CO H 10 C 5 HN PPh 3 PPh 3 CO + 2 PPh 3 CO OC cis-isomer
  37. 40. <ul><li>(iii) The reaction for the formation of trans [Mo(CO) 4 (PPh 3 ) 2 ] complex </li></ul>CO OC OC CO Mo CO Mo OC CO PPh 3 OC PPh 3 PPh 3 Thermal Isomerization PPh 3 cis-isomer trans-isomer
  38. 41. <ul><li>State the type of mechanism involved in the carbonyl substitution reaction. </li></ul><ul><li>Answer: </li></ul><ul><li>Type of mechanism involved in the carbonyl substitution reaction is outer sphere mechanism. </li></ul><ul><li>Name the isomer of complex [Mo(CO) 4 (PPh 3 ) 2 ] which is thermodynamically more stable. </li></ul><ul><li>Answer: </li></ul><ul><li>Trans isomer of complex [Mo(CO) 4 (PPh 3 ) 2 ] is more thermodynamically stable. </li></ul><ul><li>  </li></ul>

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