the polarographic reduction of aromatic carbodiimides in anhydrous aprotic solvents goes through a carbene intermediate by a diffusion controlled process in two one-electron steps. the first step is the rate-determining step and converts the carbodiirnide to a radical anion (6) that reduces further by a fast one-electron step to a carbene dianion intermediate (7). this abstracts an oxygen, alon...

The polarographic reduction of aromatic carbodiimides in anhydrous aprotic solvents goes through a carbene intermediate by a diffusion controlled process in two one-electron steps. The first step is the rate-determining step and converts the carbodiirnide to a radical anion (6) that reduces further by a fast one-electron step to a carbene dianion intermediate (7). This abstracts an oxygen, ...

Metal carbenes are often proposed as reactive intermediates in the late transition metal-catalysed transformations of alkynes. Owing to their high reactivity, however, isolation and structural characterization of metal carbene intermediates in these transformations has remained unknown. Herein, we report the isolation of two acyclic gold and copper carbene intermediates in either Au(I)- or Cu(I...

The synthesis of the first four-membered N-heterocyclic carbene is described. Depending on the substituents on the nitrogen atoms, it is possible to characterize at room temperature the carbene dimer or the free carbene. Crystallographic analyses are provided for these carbene species.

An enantioselective conjugate addition of boron to α,β-unsaturated ketones catalysed by either a N-heterocyclic carbene or a copper-carbene complex generated in situ from a new chiral bicyclic triazolium based on [2.2]paracyclophane is presented. The dual chiral carbene-copper catalyst has significant advantages over its carbene counterpart as an organocatalyst in asymmetric β-boration of acycl...

Rh(CO)2Cl(NHC) complexes of dipyrido-annelated N-heterocyclic carbenes were prepared. From the C-H coupling constant of the respective imidazolium salts and the N-C-N angle of the N-heterocyclic carbene (NHC), a weaker σ-donor character than that of typical unsaturated NHCs is expected. However, the IR stretching frequencies of their Rh(CO)2Cl complexes suggest an electron-donor character even ...

An (amino)(phosphino) carbene can be transformed into (amino)(phosphonio) carbenes, which undergo nucleophilic intermolecular as well as intramolecular substitution reactions at the carbene center. A variety of carbenes can be synthesized starting from a single carbene precursor. The resulting gamut of electronic and steric effects possible should open the way not only to a detailed study of th...

Exciting new variations in Fischer-type carbene complex composition and reactivity have been realised by following or modifying well-established synthetic approaches such as metal carbonyl functionalization and modification of existing carbene ligands. The formation of targeted complexes for organic synthesis, carbene-containing chelates, and polynuclear carbene complexes, by employing 'click c...

By reviewing the recent progress on the elucidation of the structure of gold carbenes and the definitions of metal carbenes and carbenoids, we recommend to use the term gold carbene to describe gold carbene-like intermediates, regardless of whether the carbene or carbocation extreme resonance dominates. Gold carbenes, because of the weak metal-to-carbene π-back-donation and their strongly elect...

Carbene species are grafted onto Mo(100) by the thermal decomposition of methylene iodide, where the decomposition is followed using ultraviolet photoelectron spectroscopy. Carbenes hydrogenate to methane by reaction with surface hydrogen via a secondorder reaction with an activation energy of 21 ___ 2 kJ mol1. Experiments with deuterium show that there appears to be no hydrogendeuterium exchan...