Three-coordinate NiII: 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 ((t)Bu(2)PCH(2)SiMe(2)NSiMe(2)OTf)Ni(CH(2)P(t)Bu(2)). Abstraction of F(-) from (PNP)NiF by even a catalytic amount of BF(3) causes rearrangement of the (transient) (PNP)Ni(+) to analogous ring-opened [((t)Bu(2)PCH(2)SiMe(2)NSiMe(2)F)]Ni(CH(2)P(t)Bu(2)). Abstraction of Cl(-) from (PNP)NiCl with NaB(C(6)H(3)(CF(3))(2))(4) in CH(2)Cl(2) or C(6)H(5)F gives (PNP)NiB(C(6)H(3)(CF(3))(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 H(2) 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(+).