EFFECTS OF LIGAND TOPOLOGY ON THE PROPERTIES OF DINUCLEAR RUTHENIUM COMPLEXES OF BIS-SEMIQUINONE BRIDGING LIGANDS

The two ligands H4L1 and H4L2 were prepared in which two catechol dono r groups are linked by vinyl groups to a central phenyl ring which is 1,3-substituted (for H4L1) or 1,4-substituted (for H4L2). These were u sed to prepare dinuclear complexes [{Ru((t)Bu(2)bipy)(2)}(2)(mu-L)](2) (L=L-1, complex 1; or L-2, complex 2) in which aerial oxidation of t he catecholate ligands to the semiquinone state has occurred. In 2 the two unpaired electrons that would be expected for two semiquinones ca n pair up to give a diamagnetic complex with a quinonoidal bridge, due to the 1,4-substitution pattern of the phenyl spacer; in 1 this canno t occur due to the 1,3 substitution pattern and the complex is a dirad ical as shown by EPR, spectroscopy. (C) 1998 Elsevier Science S.A.