The reduction chemistry of cobalt complexes with HPNP (HPNP = HN((CH2CH2PPr2)-Pr-i)(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)(mu-PNP)(mu-(Pr2PCH2CH2NCHCH2PPr2)-Pr-i-Pr-i)Co] (6). We also observed the oxidative addition of H-Si bond to complex 3 to form [(HPNP)CoCl(H)SiH2Ph] (7). H-1 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.