A simply accessible organometallic system to gauge electronic properties of N-heterocyclic carbenes.

The intricate σ and π-bonding of N-heterocyclic carbenes (NHCs) to metals and the need to quantify their electronic properties to rationalize reactivity of complexes have resulted in the creation of numerous methodologies to understand the NHC-metal interaction which are, as we now show, flawed. Our search for a unified, easily accessible system to gauge these fundamental properties has resulted in the discovery of two systems that highlight the flaws present in existing systems and provide a more accurate measure of the NHC ligand electronic properties.

Copper(I) Catalysed Diboron(4) Reduction of Nitrous Oxide.

A process for the catalytic reduction of nitrous oxide using NHC-ligated copper(I) tert-butoxide precatalysts and Bpin as the reductant is reported. These reactions proceed under mild conditions via copper(I)-boryl intermediates which react with NO by facile O-atom insertion into the Cu-B bond and liberate N. Turnover numbers >800 can be achieved at 80 °C under 1 bar NO.

Dial-a-base mechanochemical synthesis of N-heterocyclic carbene copper complexes.

Liquid assisted ball milling of [NHC]HBr (NHC = N-heterocyclic carbene) salts with copper(I) chloride, and a range of alkali metal complexes was shown to efficiently produce (NHC)CuX (NHC = normal or RE-NHC, X = halide, alkoxide, amide, alkyl, aryl; RE-NHC = ring-expanded NHC).

The structures and reactivity of NHC-supported copper(i) triphenylgermyls.

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh complexes. Of these, (IPr)CuGePh (IPr = :C{N(2,6-iPrCH)CH}) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [PhGe].

Acyclic Boryl Complexes of Copper(I).

Reaction of (6-Dipp)CuOtBu (6-Dipp=C{NDippCH } CH , Dipp=2,6-iPr C H ) with B (OMe) provided access to (6-Dipp)CuB(OMe) via σ-bond metathesis. (6-Dipp)CuB(OMe) was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe) reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter.

The structures of ring-expanded NHC supported copper(I) triphenylstannyls and their phenyl transfer reactivity towards heterocumulenes.

Three ring-expanded N-heterocyclic carbene-supported copper(I) triphenylstannyls have been synthesised by the reaction of (RE-NHC)CuOBu with triphenylstannane (RE-NHC = 6-Mes, 6-Dipp, 7-Dipp). The compounds were characterised by NMR spectroscopy and X-ray crystallography. Reaction of (6-Mes)CuSnPh with di--tolyl carbodiimide, phenyl isocyanate and phenylisothiocyanate gives access to a copper(I) benzamidinate, benzamide and benzothiamide respectively phenyl transfer from the triphenylstannyl anion with concomitant formation of (PhSn).

A stable ring-expanded NHC-supported copper boryl and its reactivity towards heterocumulenes.

Reaction of bis(pinacolato)diboron with (6-Dipp)CuOBu generates a ring-expanded N-heterocyclic carbene supported copper(I) boryl, (6-Dipp)CuBpin. This compound showed remarkable stability and was characterised by NMR spectroscopy and X-ray crystallography. (6-Dipp)CuBpin readily dechalcogenated a range of heterocumulenes such as CO, isocyanates and isothiocyanates to yield (6-Dipp)CuXBpin (X = O, S).