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 (tBu(2)PCH(2)SiMe(2)NSiMe(2)OTf)Ni((CH2PBu2)-Bu-t). Abstraction of F- from (PINIP)NiF by even a catalytic amount of BF3 causes rearrangement of the (transient) (PNP)Ni+ to analogous ring-opened [((Bu2PCH2SiMe2NSiMe2F)-Bu-t)]Ni((CH2PBu2)-Bu-t). 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 reaction.; 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 sigma(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 envisionee to Dccur perpendicular to the Si-C bond, based on the character of the LUMO of (PNP)Ni+.