By the use of an N-heterocyclic carbene copper(I) complex as a catalyst, the boracarboxylation of various alkynes (e.g., diaryl alkynes, aryl/alkyl alkynes, and phenylacetylene) with a diborane compound and carbon dioxide has been achieved for the first time, affording the α,β-unsaturated β-boralactone derivatives regio- and stereoselectively via a borylcupration/carboxylation cascade. Some important reaction intermediates were isolated and structurally characterized to clarify the reaction mechanism.

Cooking with gas: Copper complexes serve as excellent catalysts for the direct carboxylation of aromatic heterocyclic CH bonds with CO2, thereby offering an economical and environmentally benign process for the synthesis of heterocyclic carboxylic esters (see scheme; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene). Some active intermediates of this reaction have been isolated and structurally characterized.

The N-heterocyclic carbene-copper alkoxide complex [(IPr)Cu(OtBu)] acts as a highly efficient catalyst for the hydrosilylation of carbon dioxide with a hydrosilane. The desired product, silyl formate could be isolated in multigram quantity under solvent free conditions. A copper formate catalyst intermediate was successfully isolated and structurally characterized, thus offering important insight into the mechanistic details.

This minireview gives an overview of the chemical transformations of carbon dioxide (CO 2 ) catalysed by N-heterocyclic carbene (NHC)-copper complexes. NHC-copper complexes can serve as excellent catalysts for the carboxylation of various substrates with CO 2 and the reduction of CO 2 to CO or formic acid derivatives. In addition, NHC ligands enable the isolation of structurally characterisable key reaction intermediates, thus helping in understanding the mechanistic details of the catalytic processes. The related reactions catalysed by other metal complexes with NHC ligands are also briefly described.

Metal-free catalytic C-H silylation of a series of aromatic compounds such as N,N-disubstituted anilines with various hydrosilanes has been achieved for the first time using commercially available B(C6F5)3 as a catalyst. This protocol features simple and neutral reaction conditions, high regioselectivity, wide substrate scope (up to 40 examples), Si-Cl bond compatibility, and no requirement for a hydrogen acceptor.

Caught in the act: N-Heterocyclic carbene copper(I) complexes (1; IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) serve as an excellent catalyst for the carboxylation of alkylboranes (2; R=alkyl) with CO(2) to afford a variety of functionalized carboxylic acids (3) in high yields. A novel copper methoxide/alkylborane adduct (A) and its subsequent CO(2) insertion product (B) have been isolated and shown to be true active catalyst species.

Integration of distinct substrate activation modes in a catalytic circle is critical for the development of new, powerful synthetic methodologies toward complex and value-added chemicals from simple and readily available feedstocks. Here, we describe a highly selective difunctionalization of imines through incorporation of activation of CO 2 by intramolecular N/B Lewis pairs into a copper catalytic cycle. Experimental and computational studies on the mechanistic aspect revealed an α-borylalkylamido intermediate, a metal amide-based Lewis pair formed by borylation of a C−N double bond, and enabled an unprecedented CO 2 fixation pattern that is in sharp contrast to the traditional CO 2 insertion into transition-metal-element bonds. The unique lithium cyclic boracarbamate products could be easily transformed into multifunctional N-carboxylated α-amino boronates. The highly diastereoselective reactions of chiral N-tert-butanesulfinyl aldimines were also achieved. We hope that our findings may inspire further development of selective multicomponent reactions by incorporation of Lewis pair chemistry into transition-metal catalysis.

We report a general strategy for the catalytic umpolung of imines, which was enabled by an unprecedented 1,2-boryl carbon-to-nitrogen migration. Based on the discovery of a rearrangement of an α-borylalkylamido copper intermediate to an α-borylaminoalkyl copper species through 1,2-migration of a boryl group from carbon to nitrogen and copper migration from nitrogen to carbon, we have developed a copper-catalyzed selective allylation of a wide range of aldimines and ketimines with allyl electrophiles in the presence of B2(pin)2 and LiOtBu. We expect this catalytic imine-umpolung strategy may derive useful methodologies for the synthesis of various functionalized amines.