Chemistry of Reduced Monomeric and Dimeric Cobalt Complexes Supported by a PNP Pincer Ligand

The reduction chemistry of cobalt complexes with HPNP (HPNP = HN­(CH₂CH₂P^<i>i</i>Pr₂)₂) as a supporting ligand is described. Reaction of [(HPNP)­CoCl₂] (<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 KC₈ vary depending upon the atmosphere under which the reduction is performed. Monomeric square planar [(PNP)­CoN₂] (<b>4</b>) is obtained under dinitrogen, whereas dimeric [(PNP)­Co]₂ (<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-^<i>i</i>Pr₂PCH₂CH₂NCHCH₂P^<i>i</i>Pr₂)­Co] (<b>6</b>). We also observed the oxidative addition of H–Si bond to complex <b>3</b> to form [(HPNP)­CoCl­(H)­SiH₂Ph] (<b>7</b>). ¹H 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 AgBPh₄ to generate {(HPNP)­CoCl}­BPh₄ (<b>8</b>), a square planar species with a formal electron count of 15 electrons