Reducing power of three-coordinate cobalt(I)

Carbon monoxide adds easily to (PNP)Co, PNP = N(SiMe2CH2PtBu2)2, to give (PNP)Co(CO), whose nuco value of 1885 cm-1 suggests much back-donation, and thus an easily oxidized Co(I) in (PNP)Co. However, Co(III) is inaccessible from (PNP)Co by oxidation with I2, the products being first (PNP)CoI, then the zwitterion ItBu2PCH2SiMe2NSiMe2CH2PtBu2]CoI2. The potential two-electron oxidant N2CH(SiMe3) reacts with (PNP)Co to form a 1:1 "adduct", whose crystal structure is most consistent with oxidation of Co(I), but not fully to Co(III).