Preparation and kinetics of acid, base and Hg(II)-induced hydrolysis of cis β

Abstract

The kinetics of aquation and base hydrolysis of cisgb₂ [CoCl(benzimidazole)(trien)]²⁺ cation are described. In the range [H⁺]=0.001-0.1 M (I=0.1 M) chloride is released from the complex via aquation and base hydrolysis paths. At 50°C k_H2O = 3.4 × 10^-5 sec^-1, δH^*=104±5 kJ mol^-1, δS^*=-11±16 JK ^-1 mol ^-1 and k_OH=2.19×10⁷ M^-1 sec ^-1, δH^*=66.4±4.3 kJ mol ^-1, δS^*=101±13 JK ^-1 mol ^-1. The site of deprotonation in the base hydrolysis path, generating the reactive conjugate base, is believed to be the planar secondary NH of the trien ligand trans to benzimidazole; chloride dissociation from the conjugate base is rate limiting (SN₁cb). The rate and activation parameters for the acid independent Hg(II)-induced aquation are 0.103 ± 0.002 M^-1 sec^-1(35°C), 72.4± 5.5 kJ mol^-1, and -29 ± 18 JK^-1 mol^-1 (I = 0.3 M) respectively. There is no evidence of release of benzimidazole from the chloro complex, but the OH group of cisβ₂ [CoOH(BzmH)(trien)]²⁺ is found to labilise benzimidazole from the Co(III) centre to yield the corresponding aquo product.