Janus POCOP Pincer Complexes of Nickel

A phosphinite-based dinickel pincer complex, {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂Cl₂, is synthesized by heating a mixture of 1,2,4,5-tetrahydroxybenzene, ⁱPr₂PCl, NiCl₂, and Et₃N at 150 °C in a microwave reactor or refluxing 1,2,4,5-(ⁱPr₂PO)₄C₆H₂ with NiCl₂ and Et₃N at 175–250 °C in a flask. Substitution of chlorides by hydrides (from LiAlH₄ or LiEt₃BH) and methyl groups (from MeLi) generates {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂H₂ and {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂Me₂, respectively. Protonation of the methyl complex with HCO₂H gives {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂(OCHO)₂. Spectroscopic and crystallographic data of these Janus POCOP pincer complexes are compared to those of the analogous mononuclear complexes {2,6-(ⁱPr₂PO)₂C₆H₃}­NiX (X = Cl, H, Me, and OCHO). The hydride complex {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂H₂ reacts with phenylacetylene and CO₂ to give insertion products. It also catalyzes the reduction of CO₂ with catecholborane (HBcat) to yield CH₃OBcat and catBOBcat with a turnover frequency of 7.5 min^–1. The stoichiometric and catalytic activities of {2,3,5,6-(ⁱPr₂PO)₄C₆}­Ni₂H₂ are compared to those of {2,6-(ⁱPr₂PO)₂C₆H₃}­NiH.