Kinetics and mechamisms of CO substitution of M 4(CO) 11L(M = Co, Ir; L = PPh 3 P nBu 3, P(OMe) 3, P(OEt) 3) with L in the presence of the Me 3NO

Abstract

Reported are rates of CO substitution by L of M 4(CO) 11L(M = Co, Ir; L = PPh 3, P nBu 3, P(OMe) 3, P(OEt) 3) in the presence of added Me 3NO. The rate law is the same as that found earlier on such reactions, being first-order in the concentrations of metal carbonyl and of Me 3NO but zero-order in ligand concentration. The Ir compounds react from 2 to 7 times faster than do the corresponding Co compounds, and for each the rates of reaction with changes in ligand decrease in the order P(OMe) 3> P(OEt) 3> P nBu 3. The results are compared with earlier studies in the M 3(CO) 12 and M 3(CO) 11L (M = Fe, Ru, Os) clusters, where it was found that the reactivities decrease in the order Fe > Ru > Os. That this order differs from that now reported (Co < Ir) for the M 4(CO) 11L clusters is discussed in terms of the presumed important contribution of CO bridging to the rates of associative reactions in metal carbonyl clusters.