Ruthenium picolinates. Synthesis, characterization and reactivities of some picolinate complexes of ruthenium(II)

Reaction of Ru(PPh<SUB>3</SUB>)<SUB>3</SUB>X<SUB>2</SUB> (X = Cl, Br) with equimolar picolinic acid (Hpic) in dichloromethane solution at ambient temperature gave diamagnetic [Ru(PPh<SUB>3</SUB>)<SUB>2</SUB>(pic)(H<SUB>2</SUB>O)X], which in solution showed intense absorption bands in the visible region assigned to MLCT transitions. Each complex displayed a reversible ruthenium(II)-ruthenium(III) oxidation near 0.60 V vs SCE. Reaction of [Ru(PPh<SUB>3</SUB>)<SUB>2</SUB>(pic)(H<SUB>2</SUB>O)X] with base eliminated a molecule of HX and then dimerized to produce the hydroxo-bridged [{Ru(PPh<SUB>3</SUB>)<SUB>2</SUB>(pic)(OH)}<SUB>2</SUB>] complex. In solution it showed intense MLCT transitions in the visible region. Two successive quasi-reversible ruthenium(II)-ruthenium(III) oxidations were observed in this dimer at 0.75 V and 1.01 V vs SCE. Reaction of Ru(PPh<SUB>3</SUB>)<SUB>3</SUB>X<SUB>2</SUB> with two equivalents of Hpic in refluxing ethanol afforded [Ru(PPh<SUB>3</SUB>)<SUB>2</SUB>(pic)<SUB>2</SUB>]. This diamagnetic complex exhibited several intense MLCT transitions in solution. The ruthenium(II)-ruthenium(III) oxidation took place reversibly at 0.54 V vs SCE in this complex