Coumarinyl azoimidazolyl complexes of osmium(II) hydridocarbonyls: spectroscopic and structural characterization, oxidation catalysis , photovoltaic effect and density functional theory computation

Os(II) hydridocarbonyl complexes of coumarinyl azoimidazoles, [ Osh (CO)(PPh 3 ) 2 (CZ‐4R‐R′)] 0/+ ( 3 , 4 ) (CZ‐R‐H = 2‐(coumarinyl‐6‐azo)‐4‐substituted imidazole or 1‐alkyl‐2‐(coumarinyl‐6‐azo)‐4‐substituted imidazole), were characterized from spectroscopic data and the single‐crystal X‐ray data for one of the complexes, [ Osh (CO)(PPh 3 ) 2 (CZ‐4‐Ph)] ( 3c ) (CZ‐4‐Ph = 2‐(coumarinyl‐6‐azo)‐4‐phenylimidazolate), confirmed the structure. The complexes show higher emission (quantum yield ϕ  = 0.0163–0.16) and longer lifetime ( τ  = 1.4–10.3 ns) than free ligands ( ϕ  = 0.0012–0.0185 and τ  = 0.685–1.306 ns). Cyclic voltammetry shows quasi‐reversible metal oxidation at 0.67–0.94 V for [Os(III)/Os(II)] and 1.21–1.36 V for [Os(IV)/Os(III)] and subsequent azo reductions (−0.68 to −0.95 V for [NN]/[N N] − and irreversible < −1.2 V for [N N] − /[NN] 2− ) of the chelated coumarinyl azoimidazole. The complexes are photostable and show better photovoltaic power conversion efficiency than free ligands. Also, the complexes were used as catalysts for the oxidation of primary/secondary alcohols to aldehydes/ketones using oxidizing agents like N ‐methylmorpholine N ‐oxide, t ‐BuOOH and H 2 O 2 . Density functional theory computation was carried out from the optimized structures and the data obtained were used to interpret the electronic and photovoltaic properties. Copyright © 2016 John Wiley & Sons, Ltd.