HALOGENOTRICARBONYLRHENIUM(I) COMPLEXES OF 2,6-BIS-(THIOALKYL)-PYRIDINES AND 2,6-BIS-(THIOARYL)-PYRIDINES, THEIR SYNTHESES AND SOLUTION STEREODYNAMICS

Reactions of pentacarbonylhalogenorhenium(I) with 2,6-bis(rho-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.