Divergent Reactivity of an Isolable Nickelacyclobutane

Nickelacyclobutanes are mostly invoked as reactive intermediates in the reaction of nickel carbenes and olefins to yield cyclopropanes. Nevertheless, early work suggested that other decomposition routes such as β‐hydride elimination and even metathesis could be accessible. Herein, we report the isolation and characterization of a stable pentacoordinated nickelacyclobutane incorporated in a pincer complex. The coordination of different coligands to the nickelacyclobutane determines its selective decomposition along cyclopropanation, metathesis or apparent β‐hydride elimination pathways. DFT calculations shed light on the mechanism of these different pathways.

Cycloaddition Chemistry of a Silylene-Nickel Complex toward Organic π-Systems: From Reversibility to C-H Activation

The versatile cycloaddition chemistry of the Si-Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMS L)ClSi→Ni(NHC)2 ] (TMS L=N(SiMe3 )Dipp; Dipp=2,6-iPr2 C6 H4 ; 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.

Gold(I) Carbenoids: On-Demand Access to Gold(I) Carbenes in Solution

Chloromethylgold(I) complexes of phosphine, phosphite, and N-heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors. Activation of these gold(I) carbenoids with a variety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene, olefin cyclopropanation, and Buchner ring expansion of benzene.

Reductive Cyclopropanations Catalyzed by Dinuclear Nickel Complexes

Dinuclear Ni complexes supported by naphthyridine-diimine (NDI) ligands catalyze the reductive cyclopropanation of alkenes with CH2 Cl2 as the methylene source. The use of mild terminal reductants (Zn or Et2 Zn) confers significant functional-group tolerance, and the catalyst accommodates structurally and electronically diverse alkenes. Mononickel catalysts bearing related N chelates afford comparatively low cyclopropane yields (≤20 %). These results constitute an entry into catalytic carbene transformations from oxidized methylene precursors.