Question

[3] A sample of trans-Mo(PPh3)4Cl2 was reduced under an atmosphere of carbon monoxide with sodium amalgam at low temperature. Product “A” was isolated from this reaction. It was found that compound “A” reacted to turn into compound “B” when it was refluxed in toluene (b.p = 109°C). A reasonable estimate of the data for compounds A and B is given below. Please identify these two species and give your reasons. Justify the transformation which occurs when A is heated in terms of orbital or trans-effect considerations.

Compound A:

1H NMR δ (CDCl3): Three multiplets between 7 and 8 ppm, integrate in a ratio of 2:1:2.

13C{1H} NMR δ (CDCl3): 200 ppm (triplet), and 4 signals in aromatic region (115-140 ppm), some with

doublet splitting.

31P{1H} NMR δ (CDCl3): 20 ppm (s)

IR ν (CH2Cl2): 1950 (v. weak), 1875 (v. strong)

EI-MS (m/z): 1202(P+), 1174 (P+ - CO), 1146 (P+ - 2CO)

Compound B:

1H NMR δ (CDCl3): A mess which boils down to 6 overlapping multiplets between 7 and 8 ppm.

13C{1H} NMR δ (CDCl3): 203 ppm (doublet of triplet of doublets), and 8 other signals in aromatic region,

some with couplings. 31P{1H} NMR δ (CDCl3): 28 ppm (t), 25 ppm (t) IR ν (CH2Cl2): 1925 (strong), 1850 (strong) EI-MS (m/z): 1202(P+), 1174 (P+ - CO), 1146 (P+ - 2CO)