Reduction of carbene-borane adduct [(cAAC)BBr (CN)] (cAAC=1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) cleanly yielded the tetra(cyanoborylene) species [(cAAC)B(CN)] presenting a 12-membered (BCN) ring. The analysis of the Kohn-Sham molecular orbitals showed significant borylene character of the B atoms. [(cAAC)B(CN)] was found to reduce two equivalents of AgCN per boron center to yield [(cAAC)B(CN) ] and fragmented into two-coordinate boron(I) units upon reaction with IMeMe (1,3,4,5-tetramethylimidazol-2-ylidene) to yield the corresponding tricoordinate mixed cAAC-NHC cyanoborylene. The analogous cAAC-phosphine cyanoborylene was obtained by reduction of [(cAAC)BBr (CN)] in the presence of excess phosphine.

Silylenes: Reaction of the donor-stabilized silylene 1 with elemental sulfur, selenium, or tellurium led to the formation of 2 a-c [SiN(4)X skeletons (X = S, Se, Te)], the first stable five-coordinate silicon(IV) compounds with silicon-chalcogen double bonds (see figure).

The base-stabilized borylene [Cp(OC) Mn=BtBu(IMe)] readily reacts with elemental chalcogens in an insertion reaction that yields borachalcone complexes [Cp(OC) Mn-E=BtBu(IMe)] (E=S, Se, Te). The tellurium example features the first double bond between boron and tellurium, making Te the heaviest main-group element to make multiple bonds with boron. This unprecedented interaction has been fully investigated both experimentally and computationally.

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This side-by-side reactivity study of a borylene and a diborene with the same empirical formula demonstrates their non-interconvertibility.