B(C6F5)3- and HB(C6F5)2-mediated transformations of isothiocyanates

An Anionic Mesoionic Carbene (anMIC) and its Transformation to Metallo MIC-Boranes: Synthesis and Properties

Neutral mesoionic carbenes (MICs) based on a 1,2,3-triazole core have had a strong impact on various branches of chemistry such as homogeneous catalysis, electrocatalysis, and photochemistry/photophysics. We present here the first general synthesis of anionic mesoionic carbenes (anMICs, 2) based on a 1,2,3-triazole core and a borate backbone. The free anMIC is stable in solution under an inert atmosphere at low temperatures, and can be stored for several weeks. Analysis of donor properties shows that these anMICs are extremely strong σ-donors, bypassing the donor properties of strong donors such as MICs, NHCs, anionic NHCs and N-heterocyclic olefins. The room temperature conversion of the free anMICs leads to three equally interesting compound classes: an amide-coordinated borane based on a MIC-borane backbone (2BR3), a polymeric triazolide (1Li) and an amide-coordinated metallo-MIC-borane. The metallo-MIC-borane (3Li) is an interesting precursor for the synthesis of further amide-coordinated MIC-borane compounds. Quantum chemical calculations have been used to elucidate the mechanism of transformation of the anMICs. We thus introduce three new categories of mesoionic compounds here with potential for different branches of chemistry and beyond.

Selective hydroboration of electron-rich isocyanates by an NHC-copper(I) alkoxide

The (IPr)CuOtBu catalysed reduction of 11 aryl and alkyl isocyanates with pinacolborane gave only the boraformamides, pinBN(R)C(O)H, in most cases. Overreduction, which hampers almost all isocyanate hydroborations, was restricted to electron poor aryl isocyanates (4-NC-C₆H₄NCO, 4-F₃C-C₆H₄NCO, 3-O₂N-C₆H₄NCO). Computational analysis showed stability of [(IPr)CuH]2, which was proposed to be the catalyst resting state, drives selectivity, suggesting an approach to prevent overreduction in future work. In the case of iPrNCO, formation of this species renders overreduction kinetically inaccessible. For 4-NC-C₆H₄NCO, however, the barrier height for the first step of over-reduction is much lower, even relative to [(IPr)CuH]2, resulting in unselective reduction.

Reported Catalytic Hydrofunctionalizations that Proceed in the Absence of Catalysts: The Importance of Control Experiments

The enlarged landscape of catalysis lies in the heart of chemistry. As the journey has set a milestone in organic synthesis, its darker side has not entered into the limelight. Studies disclose that the reported reactions by using catalysts were also attainable in the absence of catalysts in many cases. This article presents a literature collection that includes the significance of control experiments in hydrofunctionalization reactions. Systematic analysis reveals that the catalysts are ambiguous and might be unessential in chemical reactions enlisted here.

On 1,3-phosphaazaallenes and their diverse reactivity

1,3-Phosphaazaallenes are heteroallenes of the type RP Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CNR′ and little is known about their reactivity. In here we describe the straightforward synthesis of ArPCNR (Ar = Mes*, 2,4,6-tBu-C₆H₂; ^MesTer, 2.6-(2,4,6-Me₃C₆H₂)–C₆H₃; ^DipTer, 2.6-(2,6-iPr₂C₆H₂)–C₆H₃; R = tBu; Xyl, 2,6-Me₂C₆H₃) starting from phospha-Wittig reagents ArPPMe₃ and isonitriles CNR. It is further shown that ArPCNtBu are thermally labile with respect to the loss of iso-butene and it is shown that the cyanophosphines ArP(H)CN are synthetically feasible and form the corresponding phosphanitrilium borates with B(C₆F₅)₃, whereas deprotonation of ^DipTerP(H)CN was shown to give an isolable cyanidophosphide. Lastly, the reactivity of ArPCNR towards Pier's borane was investigated, showing hydroboration of the CN bond in Mes*PCNtBu to give a hetero-butadiene, while with ^DipTerPCNXyl the formation of the Lewis acid–base adduct with a B–P linkage was observed.

The combination of phospha-Wittig reagents with isonitriles affords 1,3-phosphaazaallenes and their diverse reactivity has been studied in detail.