New synthetic routes to biscarbonylbipyridinerhenium(I) complexes cis,trans-[Re(X2bpy)(CO)2(PR3)(Y)]n+ (X2bpy=4,4′-X2-2,2′-bipyridine) via photochemical ligand substitution reactions, and their photophysical and electrochemical properties

Photochemical ligand substitution of fac-[Re(X(2)bpy)(CO)(3)(PR3)](+) (X(2)bpy = 4,4'-X-2-2,2'-bipyridine; X = Me, H, CF3; R = OEt, Ph) with acetonitrile quantitatively gave a new class of biscarbonyl complexes, cis,trans[Re(X(2)bpy)(CO)(2)(PR3)(MeCN)](+), coordinated with four different kinds of ligands. Similarly, other biscarbonylrhenium complexes, cis, trans-[Re(X(2)bpy)(CO)(2)(PR3)(Y)](n+) (n = 0, Y = Cl-; n = 1, Y = pyridine, PR'(3)), were synthesized in good yields via photochemical ligand substitution reactions. The structure of cis,trans-[Re(Me(2)bpy)(CO)(2){P(OEt)(3)}(PPh3)] (PF6) was determined by X-ray analysis. Crystal data: C38H42N2O5F6P3Re, monoclinic P2(1)/a, a = 11.592(1) Angstrom, b = 30.953(4) Angstrom, c = 11.799(2) Angstrom, V = 4221.6(1) Angstrom(3), Z = 4, 7813 reflections, R = 0.066. The biscarbonyl complexes with two phosphorus ligands were strongly emissive from their (MLCT)-M-3 state with lifetimes of 20-640 ns in fluid solutions at room temperature. Only weak or no emission was observed in the cases Y = Cl-, MeCN, and pyridine. Electrochemical reduction of the biscarbonyl complexes with Y = Cl- and pyridine in MeCN resulted in efficient ligand substitution to give the solvento complexes cis,trans-[Re(X(2)bpy)(CO)(2)(PR3)(MeCN)](+).