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Issue 28, 2014
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Si–H bond activation at {(NHC)2Ni0} leading to hydrido silyl and bis(silyl) complexes: a versatile tool for catalytic Si–H/D exchange, acceptorless dehydrogenative coupling of hydrosilanes, and hydrogenation of disilanes to hydrosilanes

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Abstract

The unique reactivity of the nickel(0) complex [Ni2(iPr2Im)4(COD)] (1) (iPr2Im = 1,3-di-isopropyl-imidazolin-2-ylidene) towards hydrosilanes in stoichiometric and catalytic reactions is reported. A series of nickel hydrido silyl complexes cis-[Ni(iPr2Im)2(H)(SiHn−1R4−n)] (n = 1, 2) and nickel bis(silyl) complexes cis-[Ni(iPr2Im)2(SiHn−1R4−n)2] (n = 1, 2, 3) were synthesized by stoichiometric reactions of 1 with hydrosilanes HnSiR4−n, and fully characterized by X-ray diffraction and spectroscopic methods. These hydrido silyl complexes are examples where the full oxidative addition step is hindered. They have, as a result of the remaining Si–H interactions, remarkably short Si–H distances and feature a unique dynamic behavior in solution. Cis-[Ni(iPr2Im)2(H)(SiMePh2)] (cis-5) shows in solution at room temperature a dynamic site exchange of the NHC ligands, H–D exchange with C6D6 to give the deuteride complex cis-[Ni(iPr2Im)2(D)(SiMePh2)] (cis-5-D), and at elevated temperatures an irreversible isomerization to trans-[Ni(iPr2Im)2(D)(SiMePh2)] (trans-5-D). Reactions with sterically less demanding silanes give cis-configured bis(silyl) complexes accompanied by the release of dihydrogen. These complexes display, similarly to the hydrido silyl complexes, interestingly short Si–Si distances. Complex 1 reacts with 4 eq. HSi(OEt)3, in contrast to all the other silanes used in this study, to give the trans-configured bis(silyl) complex trans-[Ni(iPr2Im)2Ni(Si(OEt)3)2] (trans-12). The addition of two equivalents of Ph2SiH2 to 1 results, at elevated temperatures, in the formation of the dinuclear complex [{(iPr2Im)Ni-μ2-(HSiPh2)}2] (6). This diamagnetic, formal Ni(I) complex exhibits a long Ni–Ni bond in the solid state, as established by X-ray diffraction. The capability of the electron rich {Ni(iPr2Im)2} complex fragment to activate Si–H bonds was applied catalytically in the deuteration of Et3Si–H to Et3Si–D employing C6D6 as a convenient deuterium source. Furthermore, we show that 1 serves as a catalyst for the acceptorless dehydrogenative coupling of Ph2SiH2 to the corresponding disilane Ph2HSi–SiHPh2 and trisilane Ph2HSi–Si(Ph)2–SiHPh2, and the coupling of PhSiH3 to give a mixture of cyclic and linear polysilanes with high polydispersity (Mw = 1119; Mn = 924; Mw/Mn = 1.2). The capability of 1 to catalyze the formal reverse reaction as well is demonstrated by the hydrogenation of disilanes. The hydrogenation of the disilanes Ph2MeSi–SiMePh2 and PhMe2Si–SiMe2Ph to the corresponding hydrosilanes Ph2MeSi–H and PhMe2Si–H, respectively, proceeds effectively in the presence of 1 under very mild conditions (room temperature, 1.8 bar H2 pressure).

Graphical abstract: Si–H bond activation at {(NHC)2Ni0} leading to hydrido silyl and bis(silyl) complexes: a versatile tool for catalytic Si–H/D exchange, acceptorless dehydrogenative coupling of hydrosilanes, and hydrogenation of disilanes to hydrosilanes

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Publication details

The article was received on 28 Apr 2014, accepted on 06 May 2014 and first published on 06 May 2014


Article type: Paper
DOI: 10.1039/C4DT01250J
Citation: Dalton Trans., 2014,43, 10816-10827
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    Si–H bond activation at {(NHC)2Ni0} leading to hydrido silyl and bis(silyl) complexes: a versatile tool for catalytic Si–H/D exchange, acceptorless dehydrogenative coupling of hydrosilanes, and hydrogenation of disilanes to hydrosilanes

    D. Schmidt, T. Zell, T. Schaub and U. Radius, Dalton Trans., 2014, 43, 10816
    DOI: 10.1039/C4DT01250J

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