SOLVENT ASSISTANCE IN REACTIONS INVOLVING CARBON-MONOXIDE INSERTION INTO MANGANESE CARBON BONDS

Infrared spectroscopy in the carbonyl stretching region and H-1 NMR spectroscopy indicate that solvent (S)-coordinated acyl complexes [(CO)4(S)MnCOR] form in the reactions of manganese carbonyl alkyls [(CO)5MnR] with polar solvents. The extent of reaction is ethyl >> methyl > 2,3,4,5,6-pentamethylbenzyl > 2,4,6-trimethylbenzyl >> 4-methylbenzyl approximately phenyl and DMSO > DMF > pyridine > acetonitrile. The solvent-coordinated acyl complexes slowly decompose to yield, first, [(CO)5Mn(COR)] and then [(CO)5Mn]-. Further evidence for solvent involvement in ligand-induced CO insertion reactions has been obtained from kinetic analysis of the reaction of [(CO)5MnCH2C6H4CH3-4] with PPh3 in toluene solutions containing known amounts of polar solvents or solid promoters, such as OPPh3 and dibenzyl sulfoxide.