Mono- and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis-1,4-([3]Cumulene)-p-carboquinoid System.

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.

Comment on "crystallographic snapshot of an arrested intermediate in the biomimetic activation of CO2 ".

Out of focus: A recent Communication published in this journal describes the synthesis of [nBu4 N]HCO3 . The authors performed a single-crystal X-ray study that revealed a putative species described as an incipient hydroxide ion engaging in a long, and presumably weak, interaction with CO2 . Our recent exploration of the coordination chemistry of CO2 with small ions leads us to believe that such an exceptional bonding situation is unlikely. Instead, we argue that the crystal structure is that of [nBu4 N]O2 CCH3 and therefore not representative of the bulk powder from the synthesis.

Synthesis and characterisation of p-block complexes of biquinoline at different ligand charge states.

The first examples of p-block coordination complexes of biquinoline, namely [(biq)BCl2]Cl and [(biq)BCl2]˙, were synthesized and structurally characterized. The acquired data allowed the estimation of the ligand charge state based on its metrical parameters. The subsequent use of this protocol, augmented with theoretical calculations, revealed ambiguities in the published data for transition metal complexes of biquinoline.

Synthesis of new hybrid 1,4-thiazinyl-1,2,3-dithiazolyl radicals via Smiles rearrangement.

The condensation reaction of 2-aminobenzenethiols and 3-aminopyrazinethiols with 2-amino-6-fluoro-N-methylpyridinium triflate afforded thioether derivatives that were found to undergo Smiles rearrangement and cyclocondensation with sulphur monochloride to yield new hybrid 1,4-thiazine-1,2,3-dithiazolylium cations. The synthesized cations were readily reduced to the corresponding stable neutral radicals with spin densities delocalized over both 1,4-thiazinyl and 1,2,3-dithiazolyl moieties.

Direct observation of a borane-silane complex involved in frustrated Lewis-pair-mediated hydrosilylations.

Perfluorarylborane Lewis acids catalyse the addition of silicon-hydrogen bonds across C=C, C=N and C=O double bonds. This 'metal-free' hydrosilylation has been proposed to occur via borane activation of the silane Si-H bond, rather than through classical Lewis acid/base adducts with the substrate. However, the key borane/silane adduct had not been observed experimentally. Here it is shown that the strongly Lewis acidic, antiaromatic 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene forms an observable, isolable adduct with triethylsilane. The equilibrium for adduct formation was studied quantitatively through variable-temperature NMR spectroscopic investigations. The interaction of the silane with the borane occurs through the Si-H bond, as evidenced by trends in the Si-H coupling constant and the infrared stretching frequency of the Si-H bond, as well as by X-ray crystallography and theoretical calculations. The adduct's reactivity with nucleophiles demonstrates conclusively the role of this species in metal-free 'frustrated-Lewis-pair' hydrosilylation reactions.