A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

A novel Co(II) hydroxo complex Co{HB(3-tBu-5-iPrpz)3}(OH) 4 {where HB(3-tBu-5-iPrpz)3 = hydrotris(3-tert-butyl-5-isopropylpyrazol-l-yl)borate} has been prepared and its molecular structure has been determined by X-ray crystallography. This complex is mononuclear with distorted tetrahedral geometry. The reaction of CO2 with Co{HB(3-tBu-5-iPrpz)3}(OH) resulted in the formation of a μ-carbonato bridged binuclear complex [Co{HB(3-tBu-5-iPrpz)3}]2(CO3) wherein the carbonate group is bound to both metal centers in an asymmetrical manner. In order to explore the role of labile metal complexes in promoting ester hydrolysis, complexes [Co{HB(3,5-iPr2pz)3}]2(OH)2 and Co{HB(3-tBu-5-iPrpz)3}(OH) have been used as catalysts in the hydrolysis of both carboxylate as well as phosphate esters. The product of 4-nitrophenylacetate hydrolysis with Co{HB(3-tBu-5-iPrpz)3}(OH) was isolated as four coordinate Co{HB(3-tBu-5-iPrpz)3}(OC6H4-4-NO2) 6, whereas the reaction of 4-nitrophenyltrifluoroacetate with [Co{HB(3,5-iPr2pz)3}]2(OH)2 resulted the formation of the six coordinate Co{HB(3,5-iPr2pz)3}(OC6H4-4-NO2)(MeCN)2 species.