Structural Similarities in Dinuclear, Tetranuclear, and Pentanuclear Nickel Silyl and Silylene Complexes Obtained via Si-H and Si-C Activation

The reactions of ((Pr3P)-Pr-i)(2)Ni-0 precursors with Ph2SiHCl, Ph2SiH2, PhSiH3, and Ph3SiH provide mononuclear, dinuclear, tetranuclear, and pentanuclear complexes with silyl and silylene ligands. Reaction of the dinuclear Ni(0) dinitrogen complex [((Pr3P)-Pr-i)(2)Ni](2)(mu-eta(1):eta(1)-N-2) with Ph2SiHCl afforded the thermally sensitive mononuclear complex ((Pr3P)-Pr-i)(2)Ni(H)SiClPh2 (1), which displays considerable hydridic character in the Ni-H-Si interaction. This species thermally converts to the dinuclear complex [((Pr3P)-Pr-i)Ni(mu-SiHPh2)](2) (2.), where the silyl ligand bridges via an agostic Si-H interaction. Alternate higher-yield routes to 2 include the rapid room-temperature reaction of Ph2SiH2 with [((Pr3P)-Pr-i)(2)Ni](2)(mu-eta(1):eta(1)-N-2) and the reaction of Ph2SiH2 with Ni(1,5-cyclooctadiene)2 and (Pr3P)-Pr-i at elevated temperatures. Double Si-H activations are observed in the reaction of PhSiH3 with [((Pr3P)-Pr-i)(2)Ni](2)(mu-eta(1):eta(1)-N-2), which provides the tetranuclear C-3-symmetric complex ((Pr3P)-Pr-i)Ni[((Pr3P)-Pr-i)Ni(mu(3)-SiHPh)](3) (3) as the major product and the pentanuclear S-4-symmetric complex Ni[((Pr3P)-Pr-i)Ni(mu(3)-SiHPh)](4) (4) as a minor product. Density functional theory (DFT) geometry optimizations of model complexes support the presence of agostic Ni H Si interactions within the tetra- and pentanuclear cores of 3 and 4. The reaction of Ph3SiH with [((Pr3P)-Pr-i)(2)Ni](2)(mu-eta(1):eta(1)-N-2) results in Si-C bond cleavage to provide the asymmetric dinuclear complex [((Pr3P)-Pr-i)(2)Ni](2)(mu-C6H5)(mu-SiHPh2) (5), where the phenyl moiety is asymmetrically bridging. Complexes 2-5 all display similar coordination environments at one of the nickel centers, suggestive of formal oxidation state assignments of Ni(III)-Ni(I) in tetranuclear 3 and Ni(IV)-Ni(I) in pentanuclear 4.