Carbonylation-decarbonylation reactions of the carbomethoxymethylcobalt complexes CH3O2CCHRCO(CO)3l (R = H, CH2CO2CH3; L = CO, PPh3) and their acyl derivatives

Article abstract of DOI:10.1016/S0022-328X(96)06405-4

The primary and secondary alkyl- and acylcobalt carbonyl complexes CH₃O₂CCHRCo(CO)₃L and CH₃O₂CCHRC(O)Co(CO)₃L (R = H or CH₂CO₂CH₃; L = CO, PPh₃) (1-8) have been prepared and studied by a variety of IR and ¹H, ¹³C{¹H}, ³¹P{¹H} and ¹⁷O{¹H} NMR spectroscopic methods. Unlike their primary analogues, all the secondary complexes readily undergo a reversible carbonylation-decarbonylation reaction. The new alkyl complex trans-CH₃O₂CCH₂Co(CO)₃PPh₃ (3) was characterized in solution, and exhibited remarkably different properties from the well-known homologue trans-CH₃CH₂O₂CCH₂Co(CO)₃PPh₃, i.e. it readily decomposes to [Co(CO)₃PPh₃]₂, suggesting homolytic dissociation of the carbon-cobalt bond, and its IR spectrum exhibits an organic ν(CO) absorbance at an unusually low frequency, pointing to an oxygen-cobalt interaction. The corresponding acyl complex trans-CH₃O₂CCH₂C(O)Co(CO)₃PPh₃ (4) was isolated as a stable solid, but smoothly decarbonylated in solution to 3. Multinuclear NMR spectroscopic monitoring of this reaction suggested the intermediate formation of cis-CH₃O₂CCH₂Co(CO)₃PPh₃, providing the first direct evidence for alkyl migration in cobalt carbonyl complexes.