Theoretical study of OH− nucleophilic attack on cobalt(II)-verdoheme complex

Abstract

OH[Formula: see text] attack on a four, five and six-coordinated cobalt(II)-verdoheme-coordinated with imidazole (1 M) while the axial ligand was studied using B3LYP method. Different spin multiplicities were considered, namely doublet, quartet, and sextet. Results show the most positive charge to be concentrated at the cobalt and carbon atoms adjacent to the oxygen in the cobalt(II)-verdoheme complex. Data obtained show that a stable intermediate was formed by a nucleophilic attack on one of the latter carbon atoms. The intermediate is initially formed by a nucleophilic attack on one of the aforementioned carbon atoms. This intermediate is then directly converted to a helical open-ring complex by passing it through a transition state. It is specified that if every nucleophilic attack is considered separately, then the OH[Formula: see text] attack on cobalt(II)-verdoheme occurred at all spin multiplicity and coordination states, from a thermodynamics and kinetics point of view, all except an OH[Formula: see text] attack on five-coordinated cobalt(II)-verdoheme at quartet state. However, comparison of reaction paths with different spin in the same coordination show that such a nucleophilic attack is not proceeded, while the reactant is a four and six-coordinated cobalt(II)-verdoheme because the latter reaction spin state is not conserved. It is clear that OH[Formula: see text] attack on five-inatedcoordinated Co(II)-verdoheme at doublet spin multiplicity is the most stable reaction path. Moreover, these findings were confirmed by NBO analysis and molecular orbital calculations.