Synthesis of Re(I) Rings Comprising Different Re(I) Units and Their Light-Harvesting Abilities

Trimethylamine N-oxide (Me3NO) could selectively remove only one CO ligand from fac-[Re­(N^N)­(CO)3(PR2R′)]+ (N^N = diimine ligand), whereby only the CO ligand in the trans position to the phosphorus ligand was selectively removed to give cis,trans-[ReI(N^N)­(CO)2(PR2R′)­(L)]n+ in good yields. This decarbonylation reaction using Me3NO was found to be especially useful for synthesizing biscarbonyl Re­(I) complexes with electron-withdrawing groups in the diimine ligand, which could not be synthesized or were obtained only in low yields by the photochemical method. Me3NO also selectively removed the carbonyl ligands in the trans position to the phosphorus ligands from the edge Re­(I) complex units, which have the fac-[Re­(N^N)­(CO)3(PR2R′)]+ structure, in linear-shaped Re­(I) multinuclear complexes. This reaction was successfully applied to synthesize a novel precursor with ring-shaped multinuclear Re complexes (Re-rings) comprising different kinds of Re­(I) units. The newly synthesized Re-rings, which consist of one Re unit with a 4,4′-bis­(trifluoromethyl)-2,2′-bipyridine (CF3bpy) ligand and one or two Re unit(s) with a 2,2′-bipyridine (bpy) ligand, showed almost quantitative excitation-energy harvesting ability from the Re unit(s) with bpy to that with CF3bpy