Halogenotricarbonylrhenium(I) complexes of 2,6-bis(thioalkyl)- and -(thioaryl)-pyridines, their syntheses and solution stereodynamics

Abstract

Reactions of pentacarbonylhalogenorhenium(I) with 2,6-bis(p-tolylthiomethyl)pyridine (L¹) or 2,6-bis(methylthiomethyl)pyridine (L²) afforded complexes of type fac-[ReX(CO)₃L](X = Cl, Br or I; L = L¹ or L²). These potentially tridentate ligands, L¹ and L², are here acting as bidentate N/S species forming five-membered ring chelate complexes. In an NMR study of both series of complexes, pyramidal inversion of the co-ordinated sulfur atoms was observed together with an intramolecular fluxional process which exchanges co-ordinated and unco-ordinated thioalkyl or thioaryl groups. The two processes have similar activation energies but were separately measurable in certain cases. Two possible mechanisms for the novel intramolecular exchange process are discussed.