A crystalline doubly oxidized carbene

Abstract

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Carbones (–C2−–), carbenes (–C:–) and carbodications (–C2+–) on the magnetic criterion

“…These initial results of the model carbenes, carbones and carbo2+ structures brings us significantly forward in answering the initial question: as Guy Bertrand and coworkers suggested, 10 due to the higher electronegativity of nitrogen compared to carbon and the distinctive lone pair donation (+M effect) of the amino groups, the positive charges are not mainly located on the central carbon of the carbon2+ compound 6 but on the neighboring nitrogen atoms in exact allene structures; the direct comparison of the spatial magnetic properties with the allene CH 2 CCH 2 7 in Fig. 3 proves to be unequivocal.…”

“…Now to the recently synthesized carbo2+ structure 8 , 10 two analogues ( 9 , 10 ) and [4]cumulene 11 that are intended to support the generality of the former conclusions from the model compounds 1–7 on the magnetic criterion: the TSNMRS values as ICSSs of different size and direction are given in Fig. 4., and structural and magnetic data for 8–11 are given in Table 2.…”

“…The main goal hereby was to identify the predominant mesomeric contributor and, from this, to assign the existing π-electron distribution and thus the electronic structure of the novel carbo2+ compound. 10 This is the main object of this paper.…”

“…Finally, another carbon species was very recently discovered by Bertrand and coworkers 10 with a mesomeric contributor of two positive charges on the central carbon atom (carbo2+, doubly oxidized carbene); however, it can stabilize itself in a number of allene-like, cumulene-like canonical structures, and even a higher degree of multiple bond character on the central carbon atom is suspected (Scheme 3). 10…”

Synthesis and reactivity of N-heterocyclic carbene (NHC)-supported heavier nitrile ylides

“…6–10 Noteworthy, among these are nitrile ylides possessing allyl-zwitterionic ( V ) and carbenic character ( VI ), exhibiting dual ambiphilicity reminiscent of the ‘imino carbene’ concept. 11,12 This unique characteristic allows these species to engage in both 1,3-dipolar additions and carbene-type reactivity, including [3 + 2] cycloaddition, σ-bond activation, or dimerization via the carbene carbon (Scheme 1b). 10–12 However, the isolation of the elusive free carbenic nitrile ylide (type VI , Scheme 1a) remains a formidable task, with only one structurally characterized nitrile ylide known, possessing a propargylic structure.…”