Effect of substituents on amine N-oxides on the rates of O-atom transfer to metal carbonyls

The kinetics of CO substitution in Cr(CO) 6 to afford Cr(CO) 5PPh 3 in the presence of different alkyl amine N-oxides, R 3NO, and aryl amine N-oxides ( p-X-C 6H 4)(CH 3) 2NO, are reported. Within each type of amine N-oxide. the rates of reaction increase with increasing basicity of the amine N-oxide. However, even at lower basicities, the aryl reagents react more rapidly than do the alkyl reagents. Competition experiments between py (pyridine) and P(n-Bu) for the coordinatively unsaturated intermediates “M(CO) 5” show that the discrimination abilities increase in the order Cr