Carbenic nitrile imines: Properties and reactivity

Structures and properties of nitrile imines were investigated computationally at B3LYP and CCSD(T) levels. Whereas NBO analysis at the B3LYP DFT level invariably predicts a propargylic electronic structure, CCSD(T) calculations permit a clear distinction between propargylic, allenic, and carbenic structures. Nitrile imines with strong IR absorptions above ca. 2150 cm-1 have propargylic structures with a CN triple bond (RCNNSiMe 3 and R2BCNNBR2), and those with IR absorptions below ca. 2150 cm-1 are allenic (HCNNH, PhCNNH, and HCNNPh). Nitrile imines lacking significant cumulenic IR absorptions at 1900-2200 cm -1 are carbenic (R-(C:)-N=N-R′). Electronegative but lone pair-donating groups NR2, OR, and F stabilize the carbenic form of nitrile imines in the same way they stabilize "normal" singlet carbenes, including N-heterocyclic carbenes. NBO analyses at the CCSD(T) level confirm the classification into propargylic, allenic, and carbenic reactivity types. Carbenic nitrile imines are predicted to form azoketenes 21 with CO, to form [2+2] and [2+4] cycloadducts and borane adducts, and to cyclize to 1H-diazirenes of the type 24 in mildly exothermic reactions with activation energies in the range 29-38 kcal/mol. Such reactions will be readily accessible photochemically and thermally, e.g., under the conditions of matrix photolysis and flash vacuum thermolysis

NUCLEOPHILIC REACTIVITY -Changing the gold standard

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Carbyne anions get to work

International audienceThe isolation of a rare example of a highly reactive low-valent carbon compound-a carbyne anion complex-enables the discovery of low-valent carbon transfer reactions. Carbon reactive species are key intermediates in several CC and C-X bond forming reactions-the basic transformations chemists use to build complex molecules with control of structure and functionality. Over the years, a variety of highly reactive carbon species have been isolated, or at least characterized, enabling progress in synthesis. While trivalent and divalent compounds are now well-known and quite common (Fig. 1a), related monovalent species remain extremely scant. The high degree of unsaturation further enhances the reactivity of anionic, cationic and radical centres, making them attractive species but also challenging compounds to synthesize and stabilize. In 2018, carbyne equivalents 1 (monovalent carbon species with three non-bonded electrons) were generated and their dual radical-carbene reactivity exploited to forge three covalent bonds

Introduction: Frontiers in Main Group Chemistry

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Stabilised Phosphazides

The Staudinger reaction between phosphines and azides provides a straightforward route to azaylides. Until the 1980s, it was thought that the putative intermediates of this reaction, namely phosphazides, were merely transient species that could be detected only by spectroscopic methods. This review summarises the achievements reported over the last 25 years on the preparation, structure and properties of phosphazides stabilised by substitution effects and/or coordination to transition metals or main group elements. Relevant computational studies on the Staudinger reaction are included

Pi-Alkene/Alkyne and Carbene Complexes of Gold(I) Stabilized by Chelating Ligands

International audienceLong overlooked, chelating ligands have garnered recently increasing interest in gold chemistry. They enforce bending at gold(I) and thereby, noticeably modify its electronic properties. This review focuses on -complexes with alkenes and alkynes side-on coordinated to gold(I), as well as gold(I) carbene complexes. The influence of the chelating ligand on the structure, bonding and reactivity of these species is thoroughly discussed