Synthesis, structural characterization, and reactivity of a dinuclear cobalt(II) (μ-hydroxo)(μ-pyrazolato) complex based on a hydrotris(pyrazolyl)borate ligand

A dinuclear (μ-hydroxo)(μ-pyrazolato)dicobalt(II) complex with hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (TpiPr), [CoII(TpiPr)]2(μ-OH)(μ-Pz) (8), was synthesized and structurally characterized, showing that the metal-hydroxide moiety acts as a nucleophile toward 4-nitrophenyl acetate and CO2, similarly to metalloenzymes. The X-ray analysis revealed that the complex 8 has a symmetry plane and that its two cobalt ions present distorted five-coordinated structures, that is, each of them is coordinated to one oxygen atom from the bridging μ-OH ligand and four nitrogen atoms from the TpiPr ligand and the bridging μ-Pz ligand. The Co1–O1 (1.966(2) Å) and Co1–N3 (2.085(4) Å, where N3 is from μ-Pz) bond lengths are shorter than the Mn–O (2.075(5) and 2.047(5) Å) and Mn–N (2.160(5) and 2.215(6) Å) ones of the previously reported dimanganese(II) analog complex due to the stronger Lewis acidity of cobalt(II). Upon reaction of the complex 8 with CO2, a dinuclear cobalt(II) μ-carbonato complex 7 was obtained. In case of reaction with 4-nitrophenyl acetate, a mononuclear cobalt(II) 4-nitrophenoxo complex with 3,5-diisopropylpyrazole (PzH) on the cobalt(II) center, [CoII(PzH)(TpiPr)(OC6H4-4NO2)] (9), was generated, thus serving as an important model for hydrolase enzyme.