Pergamon 0277-5387(94)EO141-Y Polyhedron Vol. 13, No. 18, pp. 265%266), 1994 Copyright 0 1994 Elsetier Science Ltd Printed in Great Britain. All rights reserved 0277-5387/94 $7.00+0.00 CATALYTIC OXIDATION OF TWO-ELECTRON DONORS BY DINUCLEAR COPPER(H), NICKEL(II) AND COBALT@) COMPLEXES AND EPOXIDATION OF OLEFINS USING IRON(II1) COMPLEXES CHEPURI R. K. RAO, H. ANEETHA, B. SRINIVAS and P. S. ZACI-IARIAS* School of Chemistry, University of Hyderabad, Hyderabad 500 134, India and A. RAMACHANDRAIAH Department of Chemistry, Regional Engineering College, Warangal506004, India zyxwvutsrqponm (Received 26 January 1994; accepted 29 March 1994) Abstract-Dinuclear copper( nickel(II), cobalt(l1) and iron(III) complexes derived from the Schiff base ligands obtained from the condensation of 3,3’-dimethyl-4,4’-diamino- biphenyl and pyridine-2-aldehyde and mononuclear iron(III) complexes of Schiff bases from substituted anilines and pyridine-2-aldehyde have been synthesised. Conductivity measurements on dilute solutions revealed that the dinuclear complexes are 1: 4 electrolytes while the mononuclear complexes are 1 : 2 electrolytes. The geometry of the complexes is assigned based on spectral and magnetic susceptibility values. Catalytic activity of these complexes for the oxidation of two-electron donors such as 3,5-di-t-butylcatechol (3,5- DTBC) and ascorbic acid is examined. Dinuclear iron(II1) complexes show greater activity than the mononuclear complexes for the epoxidation of olefins, namely cyclohexene and styrene using iodosyl benzene as oxygen source. A number of dinuclear transition metal complexes where the metal ions are in close proximity have been synthesised and characterised because of their interesting spectral, magnetic, electron transfer, and catalytic properties which are markedly different from the analogous mononuclear complexes.*-3 Out of the large number of bridged dinuclear systems, only a few biphenyl bridged systems are known.4T5 One such system is obtained from bis[3,3’-dime- thoxy-4,4’-bis(3-methyl-triazene-3-oxide)biphenyl] and the copper-copper distance in the dicopper complex is ca 12 A. The geometry at the copper(I1) centres is distorted square planar with DZd point group.6 The torsional angle between the two phenyl planes in each biphenyl bridge is ca 26” which *Author to whom correspondence should be addressed. results in an inclination of 70” between the coor- dination planes of the two copper centres. It has been shown that magnetically interacting dinuclear complexes are catalytically active for the oxidation of two-electron donors such as 3,5-di-t- butylcatechol(3,5-DTBC) and ascorbic acid.7-9 The proposed pathway for the electron transfer between ascorbic acid and dinuclear copper(I1) complex involves a ‘steric match’ between the donor and the acceptor7 which necessitates the metal-metal distance to be ca 34 A. While planar mononuclear copper(I1) complexes have little or no catalytic activity, dinuclear complexes are catalytically efficient. It becomes clear that dinuclear complexes of biphenyl bridged ligand systems will behave more like mononuclear complexes in catalysis experiments because of the large metal-metal distance. In addition, transition metal complexes 2659