AbstractÐA kinetic study of the reactions of (CO) 5 CrvC(OMe)C 6 H 4 X (X4-Cl, 4-F, H, 4-Me, 4-OMe and 4-NMe 2 ) and the respective tungsten carbene complexes with primary aliphatic amines (mainly n-butylamine) in 50% MeCN±50% water (v/v) at 258C is reported. The rate law is complex and shows OH 2 and amine catalysis at low amine and OH 2 concentrations but not at high concentrations. The results are consistent with a three-step mechanism: the ®rst step is nucleophilic addition of the amine to the carbene complex to form a zwitterionic steady state intermediate, T Â ; which, in the second step, is followed by a rapid deprotonation of T Â to form the anionic steady state intermediate T 2
A ; while the third step involves water and RNH 1 3 catalyzed methoxide ion expulsion, respectively, to form the substitution product, (CO) 5 MvC(NHR)C 6 H 4 X (MCr or W). It is shown that the third step is rate limiting at low OH 2 and amine concentrations while the ®rst step is rate limiting at high OH 2 and/or amine concentrations. The reasons why T Â and T 2 A cannot be observed directly are discussed and a detailed analysis of the substituent effects on various kinetic parameters is presented.