Synthesis and Reactivity of Nickel(II) Hydroxycarbonyl Species, NiCOOH‑κ<i>C</i>

2013-12-09T00:00:00Z (GMT) by Changho Yoo Jin Kim Yunho Lee
Reactions of nickel complexes supported by an anionic PNP pincer ligand (PNP<sup>–</sup> = N­[2-P<sup><i>i</i></sup>Pr<sub>2</sub>-4-Me-C<sub>6</sub>H<sub>3</sub>]<sub>2</sub>) toward CO<sub>2</sub> and CO are investigated, particularly for interrogating their C–O bond formation/cleavage chemistry. The formation of a nickel formate species (<b>2</b>) was accomplished by the reaction of (PNP)­NiH with CO<sub>2</sub>, while the structural isomer complex (PNP)­NiCOOH-κ<i>C</i> (<b>4</b>) was successfully produced from the corresponding nickel hydroxyl compound by exposing it to CO­(g). Its structurally unique character was gleaned by obtaining two solid-state structures for (PNP)­NiCOOH-κ<i>C</i> (<b>4</b>) and {(PNP)­Ni}<sub>2</sub>-μ-CO<sub>2</sub>-κ<sup>2</sup><i>C</i>,<i>O</i> (<b>6</b>); the latter was obtained from the reaction of <b>4</b> with a nickel hydroxyl complex. Both species possess a NiCOO-κ<i>C</i> binding mode, which is reminiscent of the binding mode found at the carbon monoxide dehydrogenase (CODH) active site with its Ni–COO–Fe fragment. The cationic species {(PNP)­NiCO}<sup>+</sup> (<b>7</b>) was also prepared via the protonation of <b>4</b>, which then led to the investigation of the C–O bond formation in <b>7</b> by adding a nucleophile such as OH<sup>–</sup>.