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The photochemical properties of Ru(II) mono(bipyridine) complexes Ru(L)(CO) 2 Cl 2 [L ) 2,2′-bipyridine (1, 2) or 4,4′-dimethyl-2,2′-bipyridine (3)] were studied in CH 3 CN and CH 2 Cl 2 . Photochemical ligand substitution reactions occurring in CH 3 CN were followed by infrared and 1 H NMR spectroscopies and cyclic voltammetry. The structures of the photolysis products Ru(bpy)(CO)(CH 3 CN)Cl 2 (4), mer-(CH 3 CN) Ru(bpy)(CH 3 CN) 3 Cl + (6), and fac-(CH 3 CN) Ru(dmbpy)(CH 3 CN) 3 Cl + (8) were determined by single-crystal X-ray crystallography. Photosubstitution of the trans (1) and cis (2) Cl isomers of Ru(bpy)(CO) 2 Cl 2 (bpy ) 2,2′-bipyridine) led to the same monosubstituted Ru(bpy)(CO)(CH 3 CN)Cl 2 complex (4). Probably some isomerization occurs from the trans Cl isomer. Irradiation in CH 2 Cl 2 led mainly to the dichloro-bridged [Ru(bpy)(CO)Cl 2 ] 2 (5) dimer starting from either the trans (1) or cis (2) isomer of Ru(bpy)(CO) 2 Cl 2 .

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The complex cis(CO),trans(Cl)‐[Ru(bpy)(CO)2Cl2] (1) (bpy = 2,2′‐bipyridine) complex was photoirradiated with visible light in methanol. Light‐induced ligand substitution and alcohol coordination was observed under these conditions. The replacement of a carbonyl ligand with methanol is proposed to be the initial reaction step. The reaction product was characterized by NMR spectroscopy and cyclic voltammetry. The substitution of weakly bound alcohol occurred readily in acetonitrile, leading to the formation of more stable [Ru(bpy)(CO)(CH3CN)Cl2]. Extended (24 h) irradiation of cis(CO),trans(Cl)‐[Ru(bpy)(CO)2Cl2] in methanol resulted in the formation of the dinuclear, mixed‐valence complex [{Ru(bpy)}2(μ‐OMe)2(CO)Cl3] (2). The structure of 2 consists of two Ru(bpy) moieties, which are linked by two methoxide bridges. These results showed that photoirradiation can be utilized in the synthesis of alkoxide‐bridged ruthenium complexes. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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