New Synthetic Routes to Biscarbonylbipyridinerhenium(I) Complexes <i>cis,trans</i>-[Re(X<sub>2</sub>bpy)(CO)<sub>2</sub>(PR<sub>3</sub>)(Y)]<i><sup>n</sup></i><sup>+</sup> (X<sub>2</sub>bpy = 4,4‘-X<sub>2</sub>-2,2‘-bipyridine) via Photochemical Ligand Substitution Reactions, and Their Photophysical and Electrochemical Properties
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Photochemical ligand substitution of fac-[Re(X2bpy)(CO)3(PR3)]+ (X2bpy = 4,4‘-X2-2,2‘-bipyridine; X = Me, H, CF3; R = OEt, Ph) with acetonitrile quantitatively gave a new class of biscarbonyl complexes, cis,trans-[Re(X2bpy)(CO)2(PR3)(MeCN)]+, coordinated with four different kinds of ligands. Similarly, other biscarbonylrhenium complexes, cis,trans-[Re(X2bpy)(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(Me2bpy)(CO)2{P(OEt)3}(PPh3)](PF6) was determined by X-ray analysis. Crystal data: C38H42N2O5F6P3Re, monoclinic, P21/a, a = 11.592(1) Å, b = 30.953(4) Å, c = 11.799(2) Å, V = 4221.6(1) Å3, Z = 4, 7813 reflections, R = 0.066. The biscarbonyl complexes with two phosphorus ligands were strongly emissive from their 3MLCT 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(X2bpy)(CO)2(PR3)(MeCN)]+.
