Photochemical isomerization of trans- to cis-[RuCl2(dppb) (4,4′-X2-2,2′-bipy)] (X=-H, -NO2, -Me, -COOH, -SMe, -O=SMe, -Cl, -OMe) complexes

A series of [RuCl2(dppb)(4,4'-X-2-2,2'-bipy)] complexes was synthesized from [RuCl2(dppb)(PPh3)] and 4,4'-X-2-2,2'-bipy [dppb = 1,4-bis(diphenylphosphino)butane and 4,4'-X-2-2,2'-bipy = 2,2'-bipyridine (bipy), 4,4'-dimethoxy-2,2'-bipyridine (MeO-bipy), 4,4'-dimethyl-2,2'-bipyridine (Me-bipy), 4,4'-dicarboxy-2,2'-bipyridine (COOH-bipy), 4,4'-dithiomethyl-2,2'-bipyridine (MeS-bipy), 4,4'-dichloro-2,2'-bipyridine (Cl-bipy), 4,4'-dinitro-2,2'-bipyridine (NO2-bipy), and 4,4'-dithiomethylsulphoxide-2, 2'-bipyridine (MeS=O-bipy)]. The complexes were characterized by elemental analysis, cyclic voltammetry and differential pulse voltammetry, and by UV-Vis and P-31{H-1}NMR spectroscopies. The pK(a) of the ligands were determined. The trans[RuCl2(dppb)(4,4'-X-2-2,2'-bipy)] complexes were photoisomerized under white light and the isomerization rate constants from trans to cis isomers were consistent with first order reactions and were correlated with the pK(a) of the ligands and with the E-1/2 of the complexes. The suggested mechanism of isomerization reactions is consistent with an intramolecular twist process. (C) 2003 Elsevier Ltd. All rights reserved.