Interconversion of phosphido-bridged polynuclear cobalt carbonyl complexes. Cleavage of the phosphido bridge during hydroformylation catalysis

Article abstract of DOI:10.1021/om00073a011

The interconversions of a series of phosphido-bridged cobalt carbonyl complexes have been examined. The oligomeric complex [Co(μ-PPh₂)(CO)₃]_x, 1, originally prepared by Hayter¹ but incorrectly given the binuclear formulation Co₂(μ-PPh₂)₂(CO)₆, 2, was found to lose CO upon heating to form trinuclear Co₃-(μ-PPh₂)₃(CO)₆, 3, in near quantitative yield. Both 1 and 3 react with PEt₂Ph upon heating to yield the new binuclear complex Co₂(μ-PPh₂)₂(CO)₂(PEt ₂Ph)₂, 4, which has been spectroscopically characterized. Under milder conditions, trinuclear 3 reacts with PEt₂Ph to produce mono- and disubstituted clusters Co₃(μ-PPh₂)₃(CO)₂(PEt ₂Ph), 5, and Co₃(μ-PPh₂)₃(CO)₄(PEt ₂Ph)₂, 6. Binuclear 4 was observed to react with CO to displace PEt₂Ph and reform trinuclear 3. An authentic sample of binuclear Co₂(μ-PPh₂)₂(CO)₆, 2, was prepared by heating either 1 or 3 under CO pressure (1000 psi). This compound has been spectroscopically characterized and was shown to be distinct from Hayter's oligomeric species 1. Complex 1 functions as a catalyst/catalyst precursor for the hydroformylation of 1-hexene (1000 psi of H₂/CO (1:1), 110°C). However, it is irreversibly transformed into Co₂(CO)₆(P(n-C₆H₁₃)Ph ₂)₂ under hydroformylation conditions.