Steric influence of salicylaldehyde-based Schiff base ligands on the formation of trans-[Re(PR 3 ) 2 (Schiff base)] + complexes

Complexes of the type trans-[Re(PR ) (Schiff base)] (R = ethyl and/or phenyl) 2-7 were prepared by the reaction of (nBu N)[ReOCl ] with H sal en or H sal ibn followed by addition of a tertiary phosphine. The trans-[Re(PR ) (sal en)] complexes 2-4 were stable in solution, whereas the trans-[Re(PR ) (sal ibn)] complexes 6-7 were observed to convert to their corresponding cis-[ReO(PR )(sal ibn)] products through a process involving ligand dissociation, metal oxidation, and Schiff base ligand rearrangement. The conversion of the trans-[Re(PR ) (sal ibn)] complexes is likely driven by steric interactions between the bulky backbone gem-dimethyl groups of the sal ibn ligand and the phosphine ligands. These complexes were isolated and characterized by H and C NMR, FT-IR spectroscopy, cyclic voltammetry, and single crystal X-ray diffraction. The results reported herein provide insight into the factors that drive trans-[Re(PR ) (Schiff base)] complex formation. This will aid in the development of novel Re therapeutic agents and the design of novel bifunctional N O Schiff base ligands.