Abstract
The versatile cycloaddition chemistry of the Si−Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMSL)ClSi→Ni(NHC)2] (TMSL=N(SiMe3)Dipp; Dipp=2,6‐iPr2C6H4; NHC=C[(iPr)NC(Me)]2), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four‐membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2‐CH bond activation, via a 1‐nickela‐4‐silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects.
Highlights
The versatile cycloaddition chemistry of the SiÀ Ni multiple bond in the acyclic(chloro)silylene! Ni0 complex 1, [(TMSL)ClSi!Ni(NHC)2] (TMSL = N(SiMe3)Dipp; Dipp = 2,6-iPr2C6H4; N-heterocyclic carbenes (NHCs) = C[(iPr)NC(Me)]2), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes
Highly reactive carbon–metal multiple bonds can undergo formal [2+2] cycloaddition reactions with carbon– carbon or carbon–heteroatom multiple bonds, typically through a [2+1] addition of the unsaturated species at the metal center, with subsequent chemistry leading to cyclopropyl or metathesized products.[1d,2] such systems have been studied extensively since the seminal discovery of a stable carbene–metal complex by Fischer et al.[1a,3] Notably, N-heterocyclic carbenes (NHCs), as well as other stable carbene systems, are broadly utilized as ligands in transition-metal chemistry, but their carbene–metal bonds are typically unreactive toward CÀX p-bonds (X = C, heteroatoms).[4]
Of alkynes and benzonitrile to a Si=Ti bond.[13]. These remarkable reports are reminiscent of key steps in the metathesis reactions of classical Schrock-type carbene complexes.[2]
Summary
Structural analysis of the products from these reaction mixtures confirmed that cycloaddition of acetylene and ethylene had occurred, forming nickelasila-cyclobutene and -cyclobutane derivatives 6 and 7, respectively (Scheme 2, Figure 2).
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