Ac yclic (alkyl)(amino)carbene (CAAC) has been shown to react with acovalentazide similar to the Staudinger reaction. The reaction of Me CAAC with trimethylsilyl azide afforded the N-silylated 2-iminopyrrolidine ( Me CAAC=NSiMe 3 ), which was fully characterized. This compound undergoes hydrolysis to afford the 2-iminopyrrolidine and trimethylsiloxane which co-crystallize as ah ydrogen-bonded adduct. The N-silylated 2-iminopyrrolidine was used to transfer the novel pyrrolidine-2-iminatol igand onto both main-group and transition-metal centers. The reactiono ft he tetrabromodiborane bis(dimethyl sulfide) adduct with two equivalents of Me CAAC=NSiMe 3 afforded the disubstituted diborane.

Sterically hindered, in situ generated 1,3,4-substituted 1,2,3-triazol-5-ylidene mesoionic carbenes (MICs) were employed to stabilize a number of aryl- and heteroaryldihaloboranes, as well as the first MIC-supported diborane. Reduction of borane adducts of the 1-(2,6-diisopropylphenyl)-3-methyl-4-tert-butyl-1,2,3-triazol-5-ylidene ligand with KC in non-coordinating solvents led to intramolecular C-H- and, C-C-activation at an isopropyl residue of the supporting ligand. DFT calculations showed that each of these activation reactions proceeds via a different isomer of a borylene intermediate.

Potent main-group Lewis acids are capable of activating element-hydrogen bonds. To probe the rivalry for hydride between silylium-and borenium-ion centers, a neutral precursor with the hydrosilane and hydroborane units in close proximity on a naphthalene-1,8-diyl platform was designed. Abstraction of one hydride leads to a hydroborane-stabilized silylium ion rather than a hydrosilane-coordinated borenium ion paired with [B(C 6 F 5 ) 4 ] À or [HCB 11 Cl 11 ] À as counteranions. Characterization by multinuclear NMR spectroscopy and X-ray diffraction supported by DFT calculations reveals a cationic, unsymmetrical open three-center, twoelectron (3c2e) SiÀ HÀ B linkage.

Strong electrophilicity of silylium ions is leveraged to probe an intramolecular Friedel–Crafts-type cyclization of aryl-substituted 1,1-difluoroalkenes. The reaction is presumed to be initiated by a preferential electrophilic silylation of the carbon–carbon double bond over the activation of one of the vinylic C(sp2)–F bonds. Subsequent cyclization followed by hydrodefluorination of the resulting C(sp3)–F bonds leads to the final product. The resulting tetraline derivatives were obtained in moderate to good yields. Distinct from earlier reports, the reaction proceeds with the perfluorinated tetraphenylborate counteranion under ambient condition without the prerequisite of carborate counteranion associated with the silylium-ion intermediates.