Chemistry of Reduced Monomeric and Dimeric Cobalt Complexes Supported by a PNP Pincer Ligand RozenelSergio S. PadillaRosa ArnoldJohn 2016 The reduction chemistry of cobalt complexes with HPNP (HPNP = HN­(CH<sub>2</sub>CH<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)<sub>2</sub>) as a supporting ligand is described. Reaction of [(HPNP)­CoCl<sub>2</sub>] (<b>1</b>) with <i>n</i>-BuLi generated both the deprotonated Co­(II) species [(PNP)­CoCl] (<b>2</b>) along with the Co­(I) complex [(HPNP)­CoCl] (<b>3</b>). Products resulting from reduction of <b>2</b> with KC<sub>8</sub> vary depending upon the atmosphere under which the reduction is performed. Monomeric square planar [(PNP)­CoN<sub>2</sub>] (<b>4</b>) is obtained under dinitrogen, whereas dimeric [(PNP)­Co]<sub>2</sub> (<b>5</b>) is formed under argon. Over time, <b>5</b> activates a C–H bond in the PNP ligand to form the species [Co­(H)­(μ-PNP)­(μ-<sup><i>i</i></sup>Pr<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>NCHCH<sub>2</sub>P<sup><i>i</i></sup>Pr<sub>2</sub>)­Co] (<b>6</b>). We also observed the oxidative addition of H–Si bond to complex <b>3</b> to form [(HPNP)­CoCl­(H)­SiH<sub>2</sub>Ph] (<b>7</b>). <sup>1</sup>H NMR studies showed that species <b>7</b> is in equilibrium with <b>3</b> and silane in solution. Complex <b>3</b> can be oxidized with AgBPh<sub>4</sub> to generate {(HPNP)­CoCl}­BPh<sub>4</sub> (<b>8</b>), a square planar species with a formal electron count of 15 electrons.