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

The reactions of (iPr3P)2Ni0 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 [(iPr3P)2Ni]2(μ-η1:η1-N2) with Ph2SiHCl afforded the thermally sensitive
mononuclear complex (iPr3P)2Ni­(H)­SiClPh2 (1), which displays considerable
hydridic character in the Ni–H–Si interaction. This
species thermally converts to the dinuclear complex [(iPr3P)­Ni­(μ-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 [(iPr3P)2Ni]2(μ-η1:η1-N2) and the reaction of Ph2SiH2 with Ni­(1,5-cyclooctadiene)2 and iPr3P at elevated temperatures. Double Si–H
activations are observed in the reaction of PhSiH3 with
[(iPr3P)2Ni]2(μ-η1:η1-N2), which provides the tetranuclear C3-symmetric complex (iPr3P)­Ni­[(iPr3P)­Ni­(μ3-SiHPh)]3 (3) as the major product and the pentanuclear S4-symmetric complex Ni­[(iPr3P)­Ni­(μ3-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 [(iPr3P)2Ni]2(μ-η1:η1-N2) results
in Si–C bond cleavage to provide the asymmetric dinuclear complex
[(iPr3P)2Ni]2(μ-C6H5)­(μ-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.