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

The reduction chemistry of cobalt complexes with HPNP (HPNP = HN­(CH₂CH₂PⁱPr₂)₂) as a supporting ligand is described. Reaction of [(HPNP)­CoCl₂] (1) with n-BuLi generated both the deprotonated Co­(II) species [(PNP)­CoCl] (2) along with the Co­(I) complex [(HPNP)­CoCl] (3). Products resulting from reduction of 2 with KC₈ vary depending upon the atmosphere under which the reduction is performed. Monomeric square planar [(PNP)­CoN₂] (4) is obtained under dinitrogen, whereas dimeric [(PNP)­Co]₂ (5) is formed under argon. Over time, 5 activates a C–H bond in the PNP ligand to form the species [Co­(H)­(μ-PNP)­(μ-ⁱPr₂PCH₂CH₂NCHCH₂PⁱPr₂)­Co] (6). We also observed the oxidative addition of H–Si bond to complex 3 to form [(HPNP)­CoCl­(H)­SiH₂Ph] (7). ¹H NMR studies showed that species 7 is in equilibrium with 3 and silane in solution. Complex 3 can be oxidized with AgBPh₄ to generate {(HPNP)­CoCl}­BPh₄ (8), a square planar species with a formal electron count of 15 electrons.