Three-Coordinate Ni^II: Tracing the Origin of an Unusual, Facile Si−C(sp³) Bond Cleavage in [(^tBu₂PCH₂SiMe₂)₂N]Ni⁺

All attempts to synthesize (PNP)Ni(OTf) form instead (^tBu₂PCH₂SiMe₂NSiMe₂OTf)Ni(CH₂P^tBu₂). Abstraction of F⁻ from (PNP)NiF by even a catalytic amount of BF₃ causes rearrangement of the (transient) (PNP)Ni⁺ to analogous ring-opened [(^tBu₂PCH₂SiMe₂NSiMe₂F)]Ni(CH₂P^tBu₂). Abstraction of Cl⁻ from (PNP)NiCl with NaB(C₆H₃(CF₃)₂)₄ in CH₂Cl₂ or C₆H₅F gives (PNP)NiB(C₆H₃(CF₃)₂)₄, the key intermediate in these reactions is (PNP)Ni⁺, [(PNP)Ni]⁺, in which one Si−C bond (together with N and two P) donates to Ni. This makes this Si−C bond subject to nucleophilic attack by F⁻, triflate, and alkoxide/ether (from THF). This σ_Si−C complex binds CO in the time of mixing and also binds chloride, both at nickel. Evidence is offered of a “self-healing” process, where the broken Si−C bond can be reformed in an equilibrium process. (PNP)Ni⁺ reacts rapidly with H₂ to give (PN(H)P)NiH⁺, which can be deprotonated to form (PNP)NiH. A variety of nucleophilic attacks (and THF polymerization) on the coordinated Si−C bond are envisioned to occur perpendicular to the Si−C bond, based on the character of the LUMO of (PNP)Ni⁺.