Divalent Silicon-Assisted Activation of Dihydrogen in a Bis(N-heterocyclic silylene)xanthene Nickel(0) Complex for Efficient Catalytic Hydrogenation of Olefins.

The first chelating bis(N-heterocyclic silylene)xanthene ligand [Si(Xant)Si] as well as its Ni complexes [Si(Xant)Si]Ni(η-1,3-cod) and [Si(Xant)Si]Ni(PMe) were synthesized and fully characterized. Exposing [Si(Xant)Si]Ni(η-1,3-cod) to 1 bar H at room temperature quantitatively generated an unexpected dinuclear hydrido Ni complex with a four-membered planar NiSi core. Exchange of the 1,3-COD ligand by PMe led to [Si(Xant)Si]Ni(PMe), which could activate H reversibly to afford the first Si-stabilized mononuclear dihydrido Ni complex characterized by multinuclear NMR and single-crystal X-ray diffraction analysis. [Si(Xant)Si]Ni(η-1,3-cod) is a strikingly efficient precatalyst for homogeneous hydrogenation of olefins with a wide substrate scope under 1 bar H pressure at room temperature. DFT calculations reveal a novel mode of H activation, in which the Si atoms of the [Si(Xant)Si] ligand are involved in the key step of H cleavage and hydrogen transfer to the olefin.