Palladate precatalysts for the formation of C-N and C-C bonds

A series of imidazolium-based palladate precatalysts has been synthesized and the catalytic activity of these air- and moisture-stable complexes evaluated as a function of the nature of the imidazolium counterion. These precatalysts can be converted under catalytic conditions to Pd-NHC species capable of enabling the Buchwald-Hartwig aryl amination and the alpha-arylation of ketones. Both reactions can be carried out efficiently under very mild operating conditions. The effectiveness of the protocol was tested on functionality-laden substrates

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

Synthesis and reactivity of [Au(NHC)(Bpin)] complexes

The authors gratefully acknowledge the Royal Society (University Research Fellowship to C.S.J.C.), AstraZeneca (Studenship to C.M.Z) and VLAIO (CO2PERATE) for support of this work. We thank King Saud University (DSF Program) and KAUST (Award No.OSR-2015-CCF-1974-03) for support.A new class of [Au(NHC)(Bpin)] complexes has been synthesized and their unusual reactivity was investigated using computational and experimental methods. The gold-boryl complexes exhibit unexpected high stability and reactivity.PostprintPeer reviewe

Synthesis of gold(I)-trifluoromethyl complexes and their role in generating spectroscopic evidence for a gold(I)-difluorocarbene species

We thank the Ghent University (IoF), the Special Research Fund (BOF) starting (SPN, CSJC) and advanced (SPN, KVH) grants and Research Foundation Flanders (FWO) (fellowship to SVB and grant to CSJC and KVH) for funding.Readily-prepared and bench-stable [Au(CF3)(NHC)] compounds were synthesized using new methodologies, starting from [Au(OH)(NHC)], [Au(Cl)(NHC)] or [Au(L)(NHC)]HF2 precursors (NHC = N-heterocyclic carbene). The mechanism of formation of these species was investigated. Consequently, a new and straightforward strategy for the mild and selective cleavage of a single carbon-fluorine bond from [Au(CF3)(NHC)] complexes was attempted and found to be reversible in the presence of an additional nucleophilic fluoride source. This straightforward technique has led to the unprecedented spectroscopic observation of a gold(I)-NHC difluorocarbene species.PostprintPeer reviewe

Shallow flow over a bed with a lateral change of roughness

River beds frequently exhibit a lateral variation of roughness. For example, in the case of an overflowing river, the main channel has a smoother topography compared to the adjacent floodplains where vegetation and land occupation yield an important hydraulic roughness. The lateral difference in roughness can induce a high lateral velocity gradient within the river crosssection that gives birth to a mixing layer. This mixing layer leads to fluid and momentum transfers between the two adjacent beds. To understand such mixing processes in rivers is important for predicting stage-discharge relationships and the velocity distribution within the cross-section. In order to address these issues in the context of a shallow water flow with a water depth h of the same order as the roughness elements of the bed, experiments were undertaken in a 26 m long and 1.1 m wide glass-walled open-channel flume. One half-side of the bed was covered with an array of cubes of height k arranged in a square configuration, the other side with smooth glass. Three different levels of cube submergence h/k were examined (h/k = 0.8, 1.5 and 2). The experiments and measurements were designed to yield the flow in the complete volume of the interstices across the cube array. To achieve this, 2C-3D linear-scanning PIV measurements with zero-parallax optics were developed and set up. The measurements revealed the complexity of the flow structure around the interface between the rough and smooth beds. The results show that the ability of the mixing layer to exchange momentum is highly dependent on the level of the cube submergence h/k