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

Abstract

Thev ersatile cycloaddition chemistry of the SiÀ Ni multiple bond in the acyclic( amido)(chloro)silylene! Ni 0 complex 1,[ ( TMS L)ClSi!Ni(NHC) 2 ]( TMS L = N(SiMe 3 )Dipp; Dipp = 2,6-iPr 2 C 6 H 4 ;N HC = C[(iPr)NC(Me)] 2 ), towardu nsaturated organic substrates is reported, which is both reminiscento fa nd expanding on the reactivity patternso f classical Fischer and Schrock carbene-metal complexes. Thus, 1:1r eactiono f1 with aldehydes,i mines, alkynes, and even alkenes proceed to yield [2+ +2] cycloaddition products, leading to ar ange of four-membered metallasilacycles. This cycloaddition is in factr eversible for ethylene, whereas addition of an excesso ft his olefin leads to quantitative sp 2 -CH bond activation, via a1 -nickela-4-silacyclohexanei ntermediate.T hese results have been supported by DFT calculations giving insights into key mechanistic aspects.

Macrocyclic “tet a”-Derived Cobalt(III) Complex with a N,N′-Disubstituted Hexadentate Ligand: Crystal Structure, Photonuclease Activity, and as a Photosensitizer

“…In general, the tiny distances of five-membered and six-membered chelate rings are 2.6–2.7 and 2.8–2.9 Å, respectively, while the biting angles are 84–88 and 92–96°, respectively. 14 The N–Co–N bond angles (88.13 and 87.71°) and N···N bond distances (2.813 and 2.808 Å) in the current study depart somewhat from the standard value of six- and five-membered chelate rings. Similarly, the bond distances and bond angles of N···N (2.882 and 3.013 Å) and N–Co–N (90.13 and 96.89°) varied slightly from the usual range for the six-membered ring octahedral coordination and chelate rings on the metal.…”

“…The phenolic (C–O) lengths [1.321 Å] in complex 1 are significantly longer than those [1.302 Å] in the precursor. In general, the tiny distances of five-membered and six-membered chelate rings are 2.6–2.7 and 2.8–2.9 Å, respectively, while the biting angles are 84–88 and 92–96°, respectively . The N–Co–N bond angles (88.13 and 87.71°) and N···N bond distances (2.813 and 2.808 Å) in the current study depart somewhat from the standard value of six- and five-membered chelate rings.…”

Bimetallic, Silylene‐Mediated Multielectron Reductions of Carbon Dioxide and Ethylene

“…Based on our findings with carbon dioxide, the reactions with [2] + with ethylene to afford [4] 2+ may also occur via initial [2+2]‐cycloaddition [12b] . However, at this point the intimate mechanism is not entirely clear and will be the subject of further studies.…”

“…Complete scission of CO 2 at a metal silylene has not previously been reported, though we have previously demonstrated silylene-assisted hydride delivery to CO 2 [8] and CO 2 splitting at metal silyl units (SiÀM) has been reported to afford siloxide complexes. [6e, 10] Cycloadditions of organoisocyanates [11] and benzaldehydes [12] have been demonstrated at metal silylenes, though without C À O cleavage. The [2+2]cycloaddition of CO 2 at metal carbenes (M = C) can lead to net C = O cleavage.…”

Cooperativity in Transition Metal Tetrylene Complexes

“…Similar [2+2] cycloaddition reactions between nickel silylene complex 6 and a range of unsaturated compounds were studied (Scheme 14 ). [80] In the case of phenylacetylene its acidic C−H bond led to C−H activation across the Ni=Si bond ( 35 ), while internal alkynes led to the corresponding [2+2] cycloaddition product ( 36 ).…”