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

(N-heterocyclic carbene)2-Pd(0) catalyzed silaboration of internal and terminal alkynes: scope and mechanistic studies

Pd(ITMe)2(PhC≡CPh) acts as a highly reactive precatalyst in the silaboration of terminal and internal alkynes to yield a number of known and novel 1-silyl-2-boryl alkenes. Unprecedented mild reaction temperatures for terminal alkynes, short reaction times, and low catalytic loadings are reported. During mechanistic studies, cis-Pd(ITMe)2(SiMe2Ph)(Bpin) was directly synthesized by oxidative addition of PhMe2SiBpin to Pd(ITMe)2(PhC≡CPh). This represents a very rare example of a (silyl)(boryl)palladium complex. A plausible catalyst decomposition route was also examined

Synthesis, characterization and catalytic activity of stable [(NHC)H][ZnXY2] (NHC = N-Heterocyclic carbene, X, Y = Cl, Br) species

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C) and the EPSRC (EP/J500549/1, EP/K00445X/1) for funding. S.P. N. acknowledges support from KSU.The synthesis and characterization of imidazol(in)ium-based zinc(II) halide salts are reported. These compounds present interesting structural features and exhibit high stability. Their catalytic activity was explored in the methylation of amines with CO2 and PhSiH3.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

Generalization of the copper to late-transition-metal transmetallation to carbenes beyond N-heterocyclic carbenes

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), the EPSRC (EP/J500549/1) and the DOE (DE-FG02-13ER16370) for financial support.Carbene transition-metal complexes have become a prevalent family of catalysts enabling numerous organic transformations. Their facile synthetic access is a matter of great importance. To this end, the CuI-NHC transfer methodology has emerged as a powerful alternative presenting attractive advantages over other methods. Herein, we report the remarkable ability of copper to transfer not only NHCs but also other types of carbenes such as abnormal NHCs (aNHCs), cyclic (alkyl)(amino)carbenes (CAACs), and mesoionic carbenes (MICs) to various transition metal precursors.PostprintPeer reviewe

Electronic effects in mixed N-heterocyclic carbene/phosphite indenylidene ruthenium metathesis catalysts

The authors gratefully acknowledge the Royal Society (University Research Fellowship to CSJC), the EC (CP-FP 211468-2 EUMET and CIG09-GA-2011-293900) and the MICINN (PGC2018-097722-B-I00 to AP) for funding.Five new complexes [RuCl2(SIMes)(Ind)(O-pXC5H4)] bearing different para-substituted triphenylphosphites (X = H, OCH3, CF3, Cl, SF5 and CN) were synthesised and used to study the effect of the electronic properties of the phosphite on olefin metathesis activity. Investigations of the physical properties of the new ligands and complexes were performed using physicochemical and DFT calculations. The catalytic activity of the complexes was benchmarked in challenging ring closing metathesis transformations featuring the formation of tetra-substituted double bonds. Complex [RuCl2(SIMes)(Ind)P(O-pCF3C5H4)3] (3c) exhibited a particularly high catalytic activity, superior to state-of-the-art catalysts, and was further tested on a wide range of substrates.PostprintPeer reviewe

Comparison of the reactivity of the low buried-volume carbene complexes (ITMe)2Pd(PhC≡CPh) and (ITMe)2Pd(PhN=NPh)

The novel Pd(0)-azobenzene complex (ITMe)2Pd(PhN=NPh) (5) (ITMe = 1,3,4,5-tetramethylimidazol 2-ylidene) has been isolated and characterized in the solid state and by cyclic voltammetry. Its reactivity towards E-E’ bonds (E, E’= Si, B, Ge) has been compared with that of the known palladium carbene complex (ITMe)2Pd(PhC≡CPh) (2). Whereas 2 reacts with all E-E’ bonds studied, 5 only reacted with B-B and B-Si moieties, echoing our previous catalytic studies on azobenzenes