Hydrogen transfer to coordinated acyls

Hydrogen Transfer to Coordinated Acyls The Molecular Structure of (C,H ),Re [(C HyZrCHs] (OCHCH )... 

The eq. (ii) involves the b-hydrogen transfer to coordinated olefin, eq. (iii) the insertion of CO to form acyl and eq. (iv) the acyl cleavage by hydrogen. This process is frequently followed by reduction of the aldehyde to an alcohol. 

Under pressure of CO and H2, the cobalt catalyst precursor is transformed into cobalt carbonyl hydride, HCo(CO)4. The main steps of the reaction mechanism, first elucidated by D. S. Breslow and R. F. Heck, involve (a) /3-hydrogen transfer to the coordinated olefin, (b) the insertion of CO to form an acyl intermediate, and (c) the hydrogenolysis of the acyl, with formation of the aldehyde product ... 

Electrolytic oxidation of [NEt4][Cr(COPh)(CO)5] gives the hydroxycar-bene complex [Cr C(OH)Ph (CO)s] via hydrogen atom transfer from [NEt4] + to [Cr(COPh)(CO)5]. The reduction of coordinated acyls to... 

The last of these steps, which is the only one in the cycle that involves a change in oxidation state of the metal, is probably rate-determining. The final steps are another H transfer to the carbon atom of the acyl group in (D), followed by loss of aldehyde and regeneration of the 4-coordinate species (E). An excess of CO over H2 inhibits the hydroformylation reaction, probably through the formation of 5-coordinate dicarbonyl acyls (F), which cannot react with hydrogen. 

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