A cooperative Pd-Cu system for direct C-H bond arylation

The authors are grateful to the Royal Society (University Research Fellowship to CSJC) for financial support.A novel and efficient method for C-H arylation using well-defined Pd- and Cu-NHC systems has been developed. This process promotes the challenging construction of C-C bonds from arenes or heteroarenes using aryl bromides and chlorides. Mechanistic studies show that [Cu(OH)(NHC)] plays a key role in the C-H activation and is involved in the transmetallation with the Pd-NHC co-catalyst.Publisher PDFPeer reviewe

A straightforward metal-free synthesis of 2-substituted thiazolines in air

The authors are grateful to the Royal Society (University Research Fellowship to CSJC) for financial support.A base-catalysed procedure for the synthesis of 2-substituted thiazolines from nitriles and cysteamine hydrochloride under solvent-free conditions is presented. This straightforward approach allows high conversion for a broad range of nitriles and an easy isolation of the desired products.PostprintPeer reviewe

Neutral dinuclear copper(I)-NHC complexes : synthesis and application in the hydrosilylation of ketones

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.) for funding.The synthesis of a class of highly stable neutral dinuclear Cu(I)-NHC complexes using 1,2,4-triazole as a bridging ligand is described. Various NHCs were used to generate a library of [Cu(μ-trz)(NHC)]2, complexes. Interestingly, [Cu(μ-trz)(IPr)]2 was found to be highly active in the hydrosilylation of ketones, without the need for an external base or any other additive. A wide range of aryl and alkyl ketones, as well as sterically hindered ketones, was successfully reduced to alcohols using the lowest catalyst loading reported to date.PostprintPeer reviewe

Copper-NHC complexes in catalysis

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.) for funding.Although the chemistry of copper has a long history [1a-d], the relatively recent discovery of N-heterocyclic carbene (NHC) as transition-metal supporting ligands has permitted novel vistas to be explored in copper reactivity and catalysis [1e,f]. Shortly after the seminal discovery of Arduengo, Raubenheimer reported a neutral copper carbene complex [1] and [2]. However, the field remained dormant for almost ten years. In the early 2000s, new breakthroughs were achieved: first, the synthesis of NHC–copper using Cu2O was reported by Danopoulos and followed by the first application in catalysis by Woodward [3] and [4]. The work by Buchwald and Sadighi appeared next, where the first catalysis using a well-defined complex was described [5]. The first reports in this field were based on systems used to mimic their phosphine relatives. NHCs have become ligands of significant interest due to their steric and electronic properties [6], [7] and [8]. Combining the NHC ligand family and copper became, for some, an obvious and productive area [6]. Over the last decade alone, numerous systems have been developed. Copper–NHC complexes can be divided into two major classes: neutral mono-NHC and cationic bis-NHC derivatives: [Cu(X)(NHC)] [9] (X = halide, acetate, hydroxide, hydride, etc.) and [Cu(NHC)(L)][Y] (L = NHC or PR3; Y = PF6, BF4) [10]. The neutral-halide-bearing complexes have been widely used in catalysis, mainly due to their ease of synthesis [9]. In addition to halide-bearing complexes, notable important related compounds have been reported: Nolan and co-workers disclosed the first hydroxide derivative [Cu(OH)(IPr)] (IPr = N,N’-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene) and Sadighi published alkoxides, hydrides and borate species, which permitted novel reactivity to be explored [9g-i]. With respect to cationic derivatives, homoleptic and heteroleptic bis-NHC complexes have been reported and have been efficiently used in catalysis allowing important improvements [10]. In this review, an overview of the two classes and their respective catalytic performance will be presented.PostprintPeer reviewe

N-Heterocyclic carbene copper(I) catalysed N-methylation of amines using CO2

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), the EPSRC (DTG011 EP/J500549/1) and the King Abdullah University of Science and Technology for funding, and the EPSRC National Mass Spectrometry Service Centre at Swansea University for HMRS analyses.The N-methylation of amines using CO2 and PhSiH3 as source of CH3 was efficiently performed using a N-heterocyclic carbene copper(I) complex. The methodology was found compatible with aromatic and aliphatic primary and secondary amines. Synthetic and computational studies have been carried out to support the proposed reaction mechanism for this transformation.Publisher PDFPeer reviewe

Copper-catalyzed regioselective formation of tri- and tetrasubstituted vinylboronates in air

The first "in air" copper-catalyzed method for the selective synthesis of tri- and tetrasubstituted vinylboronate derivatives is presented. Three different variants of the borylation of internal alkynes (alpha-hydroboration, beta-hydroboration, and carboboration) are described using a single catalyst: [Cu(Cl)(IMes)] (IMes = N,N'-bis-[2,4,6-(trimethyl)phenyl]-imidazol-2-ylidene) without taking any precaution to avoid the presence of air. Bis(pinacolato)diboron was used to afford beta-hydroborated products in the presence of methanol. Adding instead another electrophile allowed the formation of tetrasubstituted vinylboronate species. Finally, the alpha-products were obtained using pinacolborane as the boron source. All compounds were obtained in high yield with excellent regioselectivity at low catalyst loading (0.04-2, mol %). The protocol constitutes a very convenient route to access these highly valuable molecules

Copper-NHC complexes in catalysis

Although the chemistry of copper has a long history [1a-d], the relatively recent discovery of N-heterocyclic carbene (NHC) as transition-metal supporting ligands has permitted novel vistas to be explored in copper reactivity and catalysis [1e,f]. Shortly after the seminal discovery of Arduengo, Raubenheimer reported a neutral copper carbene complex [1] and [2]. However, the field remained dormant for almost ten years. In the early 2000s, new breakthroughs were achieved: first, the synthesis of NHC–copper using Cu2O was reported by Danopoulos and followed by the first application in catalysis by Woodward [3] and [4]. The work by Buchwald and Sadighi appeared next, where the first catalysis using a well-defined complex was described [5]. The first reports in this field were based on systems used to mimic their phosphine relatives. NHCs have become ligands of significant interest due to their steric and electronic properties [6], [7] and [8]. Combining the NHC ligand family and copper became, for some, an obvious and productive area [6]. Over the last decade alone, numerous systems have been developed. Copper–NHC complexes can be divided into two major classes: neutral mono-NHC and cationic bis-NHC derivatives: [Cu(X)(NHC)] [9] (X = halide, acetate, hydroxide, hydride, etc.) and [Cu(NHC)(L)][Y] (L = NHC or PR3; Y = PF6, BF4) [10]. The neutral-halide-bearing complexes have been widely used in catalysis, mainly due to their ease of synthesis [9]. In addition to halide-bearing complexes, notable important related compounds have been reported: Nolan and co-workers disclosed the first hydroxide derivative [Cu(OH)(IPr)] (IPr = N,N’-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene) and Sadighi published alkoxides, hydrides and borate species, which permitted novel reactivity to be explored [9g-i]. With respect to cationic derivatives, homoleptic and heteroleptic bis-NHC complexes have been reported and have been efficiently used in catalysis allowing important improvements [10]. In this review, an overview of the two classes and their respective catalytic performance will be presented.</p

Transition metal-catalyzed carboxylation of organic substrates with carbon dioxide

The development of sustainable chemical processes is a long-standing challenge. Carbon dioxide represents a renewable C1 building block for organic synthesis and industrial applications as an alternative to other common feedstocks which are based on natural gas, petroleum oil, or coal. Apart from the advantages associated with the nontoxicity and abundance of CO2, its utilization further enables the reduction in its atmospheric content, which contributes significantly to the greenhouse effect. Although widespread application of CO2 in organic synthesis - even on an industrial scale - will not be able to fully compensate for the steadily increasing atmospheric quantities produced (mainly by the combustion of fuels), ecological and economical factors make its usage highly desirable. Therefore, tremendous efforts toward activation and utilization of CO2 have been made by the scientific community over the last 30 years, and, as a result, the number of highly efficient transition metal-catalyzed CO2-incorporative reactions has increased dramatically, especially within the last decade. The achievements in the development of sustainable and economic chemical processes for the carboxylation of organic molecules with CO2 are presented in detail in this chapter

Heteroleptic bis(N-heterocyclic carbene)copper(I) complexes : highly efficient systems for the [3+2] cycloaddition of azides and alkynes

The first examples of heteroleptic bis-N-heterocyclic carbene (NHC) copper(I) complexes and a mixed NHC-phosphine Cu complex are reported. These complexes are easily synthesized from the reaction of [Cu(OH)(NHC)] with various imidazol(idin)ium or phosphonium tetrafluoroborate salts. These cationic heteroleptic bis-NHC Cu complexes are highly active systems for the azide-alkyne cycloaddition leading to the formation of 1,2,3-triazoles. The mechanism of this transformation was investigated, and information gathered suggests that only one NHC remains coordinated to the metal center during catalysis