Cyclometallation on platinum(ii) complexes; the role of the solvent and added base donor capability on the reaction mechanisms

Abstract

The reaction of PhCHNCH₂CH₂NMe₂ with [PtCl₂S₂] (S = SMe₂ or dmso) produces [PtCl₂(PhCHNCH₂CH₂NMe₂)] (1) in which the imine acts as a bidentate [N,N′] ligand. The cyclometallated [C,N,N′] platinum(II) complex [PtCl(C₆H₄CHNCH₂CH₂NMe₂)] (2) has been obtained by refluxing a methanol solution of complex 1 in the presence of base; both complexes 1 and 2 have been characterized crystallographically. The cyclometallation process has been studied kinetically at variable temperature and pressure as a function of the base added in methanol and ethanol solutions. In all cases, the actual C–H bond activation is preceded by the Z to E isomerization of the imine; detection of this species by proton NMR has also been achieved. The kinetic, thermal and baric activation parameters associated with the two processes are indicative of a different reaction mechanism operating for the reactions when the “external” base added (NaCH₃CO₂) can, in fact, react with the starting material to form a new acetato complex which allows for the reactions to be intramolecular.