Photoluminescence, photoredox properties and crystal structures of rhenium(V)-benzylidyne complexes with phosphine ligands

Abstract

Several rhenium(V)-benzylidyne complexes [Re(CR)(pdpp)2Cl]+ [R = C6H2Me3-2,4,6, pdpp = o-phenylenebis(diphenylphosphine)], [Re(CR)L2(CO)(H2O)Cl]+ [L = PPh3, P(C6H4OMe-p)3 or PMe2Ph] and trans-[Re(CR)(dppe)(CO)2Cl]+ [dppe = 1,2-bis(diphenylphosphino)ethane] have been prepared. The structures of trans-[Re(CR)(pdpp)2Cl]ClO4·CHCl 3·0.25MeOH and [Re(CR)(PPh3)2(CO)(H2O)Cl]ClO 4· 1.5MeOH have been determined by X-ray analyses. The Re≡C distances are 1.802(5) and 1.784(8) Å respectively. In acetonitrile and dichloromethane the complexes show intense absorption bands at 318-330 nm and weak ones at 405-450 nm, the latter being tentatively assigned to dxy → dπ* (dxz,dyz) transitions. Photoexcitation in the solution, solid or glassy state gives intense orange to red emissions, and the emitting states are tentatively assigned to 3[(dxy)1(dπ*)1]. The variation in non-radiative decay rate constants for the emissions of the rhenium(V)-benzylidyne complexes are consistent with a prediction from the energy-gap law. The excited states are better oxidants and reductants than the ground states. The values of Eo(ReV*-ReIV) and Eo(ReVI-ReV*) in acetonitrile have been determined using spectroscopic and electrochemical data as well as by Stern-Volmer quenching experiments.