1,2-Metallotropic shifts in tricarbonylrhenium(I) complexes of pyridazine (pydz): a dynamic NMR investigation of the effects of cis-chelating ligands

Abstract

Complexes of general formula fac-[Re(CO) 3(L–L)(pydz)][BF 4] (L–L=neutral bidentate chelate ligand; pydz=pyridazine) were prepared in high yield from fac-[ReBr(CO) 3(L–L)]. The pyridazine ligand coordinates to the metal moiety in a monodentate fashion, and undergoes a facile intramolecular 1,2-Re–N shift. The kinetics of the 1,2-metallotropic shift were measured by either one-dimensional NMR bandshape analysis or two-dimensional exchange spectroscopy. The free energies of activation, Δ G ≠ (298 K), were found to be dependent on the nature of the chelate ligand, and were in the range 77–87 kJ mol −1. The origins of the chelate ligand effects are discussed.