Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire

The studies of long-range electronic communication are hampered by solubility and potential-splitting issues. A “hybridized redox-asymmetry” method using a combination of organic and inorganic redox species is proposed and exemplified to overcome these two issues. Complexes 1(PF(6))–6(PF(6)) (from short to long in length) with the organic redox-active amine and inorganic cyclometalated ruthenium termini bridged by the para-oligophenylene wire have been prepared. Complex 6 has the longest Ru-amine geometrical distance of 27.85 Å. Complexes 3(PF(6)) and 4(PF(6)) show lamellar crystal packing on the basis of a head-to-tail anti-parallelly aligned dimeric structure. Two redox waves are observed for all complexes in the potential region between +0.2 and +0.9 V vs Ag/AgCl. The electrochemical potential splitting is 410, 220, 143, 112, 107, and 105 mV for 1(PF(6)) through 6(PF(6)), respectively. Ruthenium (+2) to aminium (N(•+)) charge transfer transitions have been identified for the odd-electron compounds 1(2+)–6(2+) by spectroelectrochemical measurements. The electronic communication between amine and ruthenium decreases exponentially with a decay slope of −0.137 Å(−1). DFT calculations have been performed to complement these experimental results.