Ruthenium (II) complexes bearing thioether‐appended α‐iminopyridine ligands: Arene precursors permit access to κ2‐N,N and κ3‐N,N,S complexes

Abstract

Herein we report the preparation of a series of Ru(II) complexes featuring α‐iminopyridine ligands bearing thioether functionality (NNSR, where R = Me, CH2Ph, Ph). Metallation using [(p‐cymene)RuCl]2 permits access to Ru complexes with a κ2‐N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p‐cymene moiety is displaced, and the ligand adopts a κ3‐N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNSMe)Ru (NCMe)2Cl]Cl. The κ2‐N,N‐Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec‐phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S‐Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.