Hey i need help between part B & C which one is CIS and which one is TRANS B. Pr
ID: 812719 • Letter: H
Question
Hey i need help between part B & C which one is CIS and which one is TRANS
B. Preparation of [Mo(CO)4(PPh3)2] - isomer I (week 1)
Add 0.3 g molybdenumhexacarbonyl (Mo(CO)6) , 0.1 g sodium borohydride
(NaBH4) and 0.65 g triphenylphosphine (PPh3) to 15 mL of 2-methoxyethanol (deoxygenated as earlier) in a 100 mL two-necked flask. On heating (oil bath), all the solids should dissolve. Heat the mixture at reflux point for one hour and then filter the solid that has separated from the hot solution. Wash with cold water (3 x 10 mL) and using a Pasteur pipette wash with cold ethanol (5 mL). Allow the product to dry in air.
C. Preparation of [Mo(CO)4(PPh3)2] - isomer II (week 2)
Repeat the procedure described above in section B except using deoxygenated
ethanol as the solvent. Heat the mixture for about one hour in an oil-bath maintained at 650C. It is important that the solution must not reflux. Filter hot and wash well with water and cold ethanol.
For each of your three products note the physical appearance of the compound, record its melting point, record the yield (and calculate percentage yield) and measure its infrared spectrum (as KBr pellets) (see a demonstrator). Also record the infrared spectrum of the starting material, molybdenum hexacarbonyl (Mo(CO)6).
Explanation / Answer
Thermal analysis of cis-Mo(CO)4L2 [L = PPh2Et, PPh3, PPh2Me and P(m-tolyl)3] revealed that they undergo cis to trans isomerisation under solventless conditions.
in 2nd case, deoxygenated solvent was NOT used [solvent less conditions]. So 2nd product prtepared is a Trans isomer
Hope it helps !