Nucleophilic Substitution in Ionizable Fischer Thiocarbene Complexes: Steric Effect of the Alkyl Substituent on the Heteroatom.

DIEGO M. ANDRADA; MARTÍN E. ZOLOFF MICHOFF; RITA H. DE ROSSI; ALEJANDRO M. GRANADOS

Royal Chemical Society

Año: 2015 vol. 44 p. 5520 - 5520

detailed kinetic study has been carried out for the aminolysis of ionizable Fischer thiocarbene complexes (CO)5M=C(SR)CH3 (M = Cr, W; R = iPr, nBu, cHex, tBu) with five primary amines and one secondary amine in aqueous acetonitrile solutions (50% MeCN-50% water (v/v)). The observed rate constants for the reaction with primary amines showed a first-order dependence on the amine concentration, while with morpholine the rate constant has second-order dependence. The general base catalysis process was confirmed by the variation of the rate constants with the concentration of an external catalyst and the pH. The results agree with an stepwise mechanism where the nucleophilic addition to the carbene carbon to produce a tetrahedral intermediate (T) is the first step, followed by a rapid deprotonation of T to form the anion T- which leads to the products by general-acid catalysed leaving group (?SR) expulsion. In general, it was found that the chromium complexes are less reac