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While azides do not react with simple alkenes except under harsh conditions, a diboron alkene analogue, the doubly cyclic alkyl(amino)carbene (CAAC)‐stabilized dicyanodiborene 1, reacts spontaneously with organic azides (7–10 equiv.) at room temperature to yield two equivalents of stable CAAC‐imino(cyano)boranes (2‐R). NMR‐spectroscopic monitoring of the reaction mixtures shows the initial formation of a 1 : 1 mixture of 2‐R and a relatively long‐lived intermediate (Int), which in the presence of excess azide is converted into a second equivalent of 2‐R. In the absence of excess azide, however, Int decomposes to 3, the product of an intramolecular C−H activation by a putative dicoordinate borylene intermediate "(CAAC)B(CN)". Mechanistic insights from trapping experiments, NMR‐spectroscopic and high‐resolution mass spectrometry data, as well as DFT computations reveal that Int is the terminal borylene end‐on‐dinitrogen adduct [(CAAC)B(CN)(η1‐N2)]. The formation of the iminoboranes 2‐R from diborene 1 and RN3 proceeds via an azide‐diborene Huisgen‐type [3+2] cycloaddition reaction, followed by a retro‐[3+2] cycloaddition, yielding 2‐R and [(CAAC)B(CN)(η1‐N2)]. The latter then undergoes either N2 extrusion and intramolecular C−H activation to generate 3, or a Staudinger‐type reaction with a second equivalent of azide to generate a second equivalent of the iminoborane 2‐R. [ABSTRACT FROM AUTHOR]

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2‐azaborinines, it was diverted to the formation of a 1,2,3‐diazaborinine by changing the electronic characteristics of the reagents. The isolable azo‐azaborinine intermediate initially formed from the reaction of 1‐(2,3,4,5‐tetraphenylborolyl)ferrocene with 4‐azido‐N,N‐dimethylaniline gradually decomposed to a 1,2,3‐diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation. Nitrile & error: A new pathway for the ring expansion reaction of boroles with organic azides is presented, leading to a 1,2,3‐diazaborinine instead of the expected 1,2‐azaborinine. Mechanistic DFT calculations provided insight into the mechanism of formation of the BN2C3 heterocycle, and spectroscopic and reactivity studies demonstrated the analogies of the 1,2,3‐diazaborinine to pyridine. [ABSTRACT FROM AUTHOR]

Abstract: The room‐temperature, ambient‐pressure reactions of CO2 with two species containing boron–boron multiple bonds led to the incorporation of either one or two CO2 molecules. The structural characterization of a thermally unstable intermediate in one case indicates that an initial [2+2] cycloaddition is the key step in the reaction mechanism. [ABSTRACT FROM AUTHOR]