Physical Organic Chemistry of Transition Metal Carbene Complexes. 26. Kinetics and Mechanism of the Reactions of [Phenyl(thiomethyl)carbene]pentacarbonylchromium(0) with Amines in Aqueous Acetonitrile

The kinetics of the reactions of (CO)5CrC(SMe)Ph (4-Cr) with five primary aliphatic and four secondary alicyclic amines have been investigated in 50% MeCN−50% water (v/v) at 25 °C. With n-butylamine, 2-methoxyethylamine, 2-chloroethylamine, glycinamide, piperidine, piperazine, and 1-(2-hydroxyethyl)piperazine, the reaction is strictly second order, i.e., first order in 4-Cr and first order in the amine. With morpholine, base catalysis by the amine and by OH- was observed while with aminoacetonitrile, OH- catalysis but no amine catalysis was detected. These results are interpreted in terms of a three-step reaction mechanism (Scheme 1): the first step is nucleophilic attachment of the amine to the carbene complex, to form a zwitterionic intermediate, ; the second step is a fast equilibrium deprotonation of to generate the anionic intermediate ; the third step is MeS- expulsion by two concurrent pathways, one being spontaneous (solvent catalyzed) expulsion of MeS-, the other being RR‘NH2+ catalyzed loss of ...