Carbonylation of the A-frame complex Rh2(.mu.-CO)(CH2C6H5)2(dppm)2. Formation of the dicarbonylated product via a radical pathway

The dibenzyl A-frame compound Rh2(mu-CO)-(CH2C6H5)2(dppm)2 is prepared by the reaction of benzylmagnesium chloride with Rh2Cl2(CO)2(dppm)2. The compound undergoes carbonylation leading to mono- and dicarbonylated products depending on CO pressure. At 300 Torr (0.4 atm) of CO, the major product is the monoketone 1,3-diphenylacetone, while, at 2.5 atm of CO, clean conversion to dicarbonylated product is observed. An intermolecular mechanism for dicarbonylation is shown by a crossover experiment, and radical involvement is demonstrated through the use of an H-atom donor during carbonylation, yielding phenylacetaldehyde as the major organic product.