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.