MECHANISTIC STUDIES ON THE BRIDGE CLEAVAGE REACTION OF THE DINUCLEAR ETHYLENEDIBIGUANIDE COMPLEXES OF RUTHENIUM(III), COBALT(III), CHROMIUM(III) AND RHODIUM(III) IN ACIDIC MEDIUM

Acid-catalysed bridge cleavage reactions of four metal-ethylenedibigua nide (EDG) (metal = Ru-III, Co-III, Cr-III, Rh-III complexes have been investigated in perchloric acid and for Ru-III complex in nitric and paratoluenesulphonic acids also. The Com complex reacts both via acid- dependent and acid-free paths, while other complexes by acid-dependent path only. Rate law for the Rum and Crm complexes is k(obs) = k(1) [H +], that of the Co-III complex is k(obS) = k(2) [H+] + k(3) and for th e Rh-III complex is k(obs) = k(4)K/(K + H+), where K is the equilibriu m constant for protonation. The mechanism involves protonation equilib rium of respective complex, followed by a rate-determining bridge clea vage Activation parameters have also been calculated, Order of reactiv ity of complexes is : Cr-III > Co-III > Ru-III > Rh-III.