Pergamon 0277%5387(94)00181-2 Polyhe&on Vol. 13, No. 21, pp. 2999-3004, 1994 Copyright 0 1994 Elswier Science Ltd Printed in Great Britain. All rights reserved 0277-5387/N 57.00 + 0.00 RUTHENIUM PICOLINATES. SYNTHESIS, CHARACTERIZATION AND REACTIVITIES OF SOME PICOLINATE COMPLEXES OF RUTHENIUM(I1) NATUN GHATAK and SAMARESH BHA’ITACHARYA* Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Calcutta 700032, India (Received 8 March 1994; accepted 5 May 1994) Abstract-Reaction of Ru(PPh3)3X2 (X = Cl, Br) with equimolar picolinic acid (Hpic) in dichloromethane solution at ambient temperature gave diamagnetic [Ru(P Ph,),(pic)(H,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(II1) oxidation near 0.60 V us SCE. Reaction of [Ru(PPh,),(pic)(H,O)X] with base eliminated a molecule of HX and then dimerized to produce the hydroxo-bridged ]{Ru(PPh3)2(pic)(DH)) 1 2 complex. In solution it showed intense MLCT transitions in the visible region. Two successive quasi-reversible ruthenium(II)-ruthenium(II1) oxidations were observed in this dimer at 0.75 V and 1.01 V us SCE. Reaction of Ru(PPh3)3X2 with two equivalents of Hpic in refluxing ethanol afforded [Ru(PPh,),(pic)J. This diamagnetic complex exhibited several intense MLCT transitions in solution. The ruthenium(II)- ruthenium(II1) oxidation took place reversibly at 0.54 V us SCE in this complex. The chemistry of ruthenium complexes, with special reference to their electron-transfer properties, has been receiving continuous attention.’ Ruthenium offers a wide range of oxidation states which are accessible chemically and electrochemically. There- fore, the complexes of ruthenium are redox-active and their application as redox reagents in different chemical reactions is of much current interest.’ Redox activity of any complex obviously depends on the nature of ligands bound to the central metal ion. Coordination of ruthenium by different types of ligands has thus been of significant importance with regard to the tunability of redox potentials by ligand variation. In the present study, which has originated from our interest in the chemistry of ruthenium,3 we have chosen picolinic acid [Hpic (1); H stands for the dissociable acidic hydrogen) as the principal ligand to coordinate ruthenium. The picolinate ion (pit-) binds metal ions as an N,O-coordinator forming five-membered chelate * Author to whom correspondence should be addressed. Picolinic acid (Hpic) M 1 z rings (2, M = metal ion). It is interesting to note that the chemistry of ruthenium picolinates has not been much explored so far.4 The goal of this present work has been to prepare and study mixed-ligand ruthenium picolinate complexes incorporating one and two picolinate ligands, respectively. Tri- phenylphosphine, water, hydroxide ion (OH-) and halide ions (X-; X = Cl, Br) have been used as co- ligands. The synthesis, characterization, electron- transfer properties and reactivities of a few such complexes are reported in this paper. EXPERIMENTAL Materials Commercial ruthenium trichloride (Arora Matthey, Calcutta, India) was converted to 2999