Redox Chemistry of the Triplet Complex (PNP)Co^I

Reaction of PNPCo, where PNP is (^tBu₂PCH₂SiMe₂)₂N^-, with the persistent radical galvinoxyl, G, gives PNPCo^IIG, a nonplanar S = ³/₂ species. Reaction with PhCH₂Cl or with 0.5 mol I₂ gives PNPCoX (X = Cl or I, respectively), but additional I₂, seeking Co^III, gives instead oxidation at phosphorus:  (^tBu₂P(I)CH₂SiMe₂NSiMe₂CH₂P^tBu₂)CoI₂. Hydrogen-atom transfer reagents fail to give PNPCoH, but H₂ gives instead PNPCo(H)₂, a result rationalized thermodynamically based on DFT calculations. Multiple equiv of PhSiH₃ give a product of Co(V), where N/SiPh and P/Si bonds have formed. N₂CH(SiMe₃) gives a 1:1 adduct of PNPCo, whose metric parameters suggest partial oxidation above Co^I; N₂CHPh gives a 1:1 adduct but with very different spectroscopic features. PhN₃ reacts fast, via several intermediates detected below 0 °C, to finally release N₂ and form a Co^I product where one phosphorus has been oxidized, PN(PNPh)Co. Whereas PNPCo(N₃) resists loss of N₂ on heating, one electron oxidation gives a rapid loss of N₂, and the remaining nitride nitrogen is quickly incorporated into the chelate ligand, giving [^tBu₂PCH₂SiMe₂NSiMe₂NP(^tBu₂)CH₂Co]. O₂ or PhIO generally gives products where one or both phosphorus centers are converted to its oxide, bonded to cobalt.