Cyclometalated Osmium-Amine Electronic Communication through the p-Oligophenylene Wire.

Abstract

A series of bis-tridentate cyclometalated osmium complexes with a redox-active triarylamine substituent have been prepared, where the amine substituent is separated from the osmium ion by a p-oligophenylene wire of various lengths. X-ray crystallographic data of complexes 3(PF6) and 4(PF6) with three or four repeating phenyl units between the osmium ion and the amine substituent are presented. These complexes show two consecutive anodic redox couples between +0.1 and +0.9 V vs Ag/AgCl, with the potential splitting in the range of 300-390 mV. A combined experimental and theoretical study suggests that, in the one-electron-oxidized state, the odd electron is delocalized for short congeners and localized on the osmium component for long congeners. The electronic coupling parameter (Vab) was estimated by the Marcus-Hush analysis. The distance dependence plot of ln(Vab) versus the osmium-amine geometrical distance (Rab) gives a negative linear relationship with a decay slope of -0.19 Å(-1), which is slightly steeper with respect to the previously reported ruthenium-amine series with the same molecular wire. DFT calculations with the long-range-corrected UCAM-B3LYP functional gave more reasonable results for the osmium complexes with respect to those with UB3LYP.