Cis–trans Isomerism in mixed-ligand ruthenium(II) complexes containing bis(phosphine) and azoimine ligands

Abstract

This study presents the syntheses and characterization of mixed-ligand azoimine-diphosphine ruthenium complexes of the general formula [RuCl2(Azo)(P–P)] (C1–C5) {Azo=C6H5NNC(COCH3)NC6H5; P–P=1,2-bis(dimethylphosphino)ethane (dmpe) (C1), cis-1,2-bis(diphenylphosphino)ethylene (depe) (C2), 1.1′-bis(diphenylphosphino)methane (dppm) (C3), 1,2-bis(diphenylphosphino)benzene (dbpe) (C4), 1,2-bis(di(pentaflurophenyl)phosphino)ethane (F-dppe) (C5)}. These complexes were synthesized via the reaction of RuCl3, azoimine and the diphosphine ligands in ethanol solutions. The X-ray structure of C2 reveals a cis-dichloro geometry, in spite of the bulky P–P ligand, and this is attributed to the presence of an intramolecular π–π interaction between benzene rings (on the Azo and P–P ligands) [centroid–centroid distances=3.596 and 3.654Å; dihedral angle between ring planes=13.2(3) and 15.4(4)° for the two independent molecules]. In contrast, the X-ray structure of C1, with a less bulky dmpe ligand in which no Ph rings are available for π–π bonding, revealed a trans-dichloro geometry. In addition to the X-ray structures of C1 and C2, this work presents and discusses the spectroscopic (IR, UV–Vis, 1H NMR and 31P NMR) and electrochemical (cyclic voltammetry) behavior of C1–C5.