Solvent and nucleophile effects on the carbonyl insertion reaction into metal—carbon bonds

Abstract

The rate constant, k 3 , for the direct insertion of carbon monoxide induced by tertiary phosphines into [(η 5 -C 5 H 5 )(CO) 3 MoCH 2 C 6 H 5 ] in toluene solution decreases steadily with increasing cone angle of the phosphine. In contrast, for [(CO) 5 MnCH 2 C 6 H 5 ], k 3 increases with decrease in the Tolman electronic parameter, v , of the phosphine (i.e., with increasing electron donation) and does not correlate with the cone angle. However, k 3 reflects the size of the phosphine to a greater degree as the size of the benzyl substituent on manganese increases. An analysis of k 1 values in the solvent-assisted insertion pathway has been made for both the molybdenum and manganese systems in THF, 2-MeTHF and 2,5-Me 2 THF solutions. The general decrease in k 1 with increasing size of the solvent for the cyclopentadienyl-molybdenum system becomes less marked as the size of the benzyl substituent increases. The manganese complexes are relatively less sensitive to solvent size. A comparison has been made between the nucleophilic role of a solvent molecule in the k 1 step and that of a tertiary phosphine in the k 3 step.