Tris-(1,3-diaryltriazenide) complexes of rhodium - Synthesis, structure and, spectral and electrochemical properties

Abstract

Reaction of 1,3-diaryltriazenes (abbreviated in general as HL-R, where R stands for the para-substituent in the aryl fragment and H stands for the dissociable hydrogen atom, R = OCH₃, CH₃, H, Cl, NO₂) with [Rh(PPh₃)₂(CO)Cl] in ethanol in the presence of NEt₃ produces a series of tris-diaryltriazenide complexes of rhodium of type [Rh(L-R)₃], where the triazenes are coordinated to rhodium as monoanionic, bidentate N,N-donors. Structure of the [Rh(L-OCH₃)₃] complex has been determined by X-ray crystallography. The complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. They also fluoresce in the visible region under ambient condition while excited at around 400 nm. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation (within 0.84-1.67 V vs SCE), followed by an oxidation of the coordinated triazene ligand (except the R = NO₂ complex). An irreversible reduction of the coordinated triazene is also observed for all the complexes below -1.03 V vs SCE.