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.