Oxidative Addition of Dihydrogen, Boron Compounds, and Aryl Halides to a Cobalt(I) Cation Supported by a Strong-Field Pincer Ligand

Abstract

Cationic cobalt(I) dinitrogen complexes with a strong-field tridentate pincer ligand were prepared and the oxidative addition of polar and non-polar bonds was studied. Addition of H₂ to [(^iPrPNP)Co(N₂)]⁺ (^iPrPNP = 2,6-bis((diisopropylphosphaneyl)methyl)pyridine) in THF-<i>d8</i> resulted in rapid oxidative addition and formation of the <i>cis</i>-Co(III) dihydride complex, <i>cis</i>-[(^iPrPNP)Co(H)₂L]⁺ where L = THF or N₂. The addition of H₂ was reversible as evidenced by the dynamics observed by variable temperature ¹H NMR spectroscopy and the regeneration of [(^iPrPNP)Co(N₂)]⁺ upon exposure to dinitrogen. In contrast, addition of HBPin, (Pin = pinacolato) B₂Pin₂ and aryl halides resulted in the formation of net one-electron oxidation products: cationic Co(II)-boryl and Co(II)-halide/aryl complexes, respectively. All products were structurally characterized by X-ray crystallography and the electronic structures were determined by a combination of magnetic moment measurements, EPR spectroscopy and DFT calculations. Monitoring the addition of HBPin to [(^iPrPNP)Co(N₂)]⁺ provided evidence for a transient Co(III) oxidative addition product that likely undergoes comproportionation with the cobalt(I) starting material to generate the observed Co(II) products.