Copper N-heterocyclic carbene complexe

Copper N-heterocyclic carbene complexes in catalysis 13CST912. Cyclopentadienyl-, indenyl- and fluorenyl-fimctionalized N-hetero-cyclic carbene metal complexes Synthesis and catalytic applications 12EJI1309. 

Bis(pyrazolyl)borate copper complex 902 has been employed as a catalyst in homogeneous and heterogeneous styrene epoxidation reactions <2000CC1653>. Pyrazole palladacycles 903 have proved to be stable and efficient catalysts for Heck vinylations of aryl iodides <2000CG2053>. A hemilabile pyrazolyl-functionalized N-heterocyclic carbene complex of palladium(ll) such as 904 has been found to be an excellent catalyst for Heck and Suzuki crosscoupling reactions in ionic liquids <2006JOC426>. 

Ellul CE, Reed G, Mahon MF, Pascu SI, Whitdesey MK. Tripodal N-heterocyclic carbene complexes of palladium and copper syntheses, characterization, and catalytic... 

Matsumoto K, Matsnmoto N, Ishii A, Tsukuda T, Hasegawa M, TsubomuraT. Sttnc-tural and spectroscopic properties of a copper(l)-bis(N-heterocyclic)carbene complex. Dalton Trans. 2009 6795-6801. 

Ito, Kawakami and Sawamura recently described the borylation of al-lylic carbonates by B2pin2, catalyzed by bis(phosphine)copper(I) alkox-ides. It was proposed that bis(phosphine)copper(I) boryl species formed by alkoxide/boryl a-bond metathesis are key intermediates in the catalytic cycle [231]. Making use of related N-heterocyclic carbene stabilized precursors, Sadighi and co-workers have very recently isolated the thermally labile copper boryl complex (IPr)CuBpin (11.1) together with the products of oxygen atom, styrene and aldehyde insertion into the Cu-B bond (11.2-11.5 Scheme 24) [232,233,237]. The structure of 11.1 in the solid state reveals an approximately linear Cu(I) coordination geometry [ZB-Cu-C 168.1(2)°] and a Cu-B distance [2.002(3) A] which is somewhat shorter than the sum of the expected covalent radii [2.05 A] [106]. Yet further evidence for the... 

Boehme and Frenking181 applied AIM to characterise bonds in complexes containing copper, silver and gold, warranting the use of relativistic ECPs and large valence basis sets (at MP2 level). Their work on N-heterocyclic carbene,... 

N-Heterocyclic carbene-copper(I) complexes in homogeneous catalysis, particularly, of [3 + 2] cycloaddition of azides and alkynes 07SL2158. 

Several Cu(I) complexes with N-heterocyclic carbene ligands have been described as CuAAC catalysts at elevated temperature in organic solvents, under heterogeneous aqueous conditions (when both reactants are not soluble in water), and under neat conditions [75]. These catalyst show high activity under the solvent-free conditions, achieving turnover numbers as high as 20 000. However, their activity in solution-phase reactions is significantly lower than that of other catalytic systems (for example, a stoichiometric reaction of the isolated copper(I) acetylide/NHC complex with benzhydryl azide required 12 h to obtain 65% yield of the product [76], whereas under standard solution conditions even a catalytic reaction would proceed to completion within 1 h). 

A bidentate N-heterocyclic carbene (NHC) ligand was found to be efficient for the asymmetric allylic alleviation employing diethylzinc (Scheme 15.22). In the reaction, a binuclear silver complex undergoes facile ligand exchange with a copper salt to afford an effective copper catalyst. y-Selective allylic alleviation is realised with allevlboranes as nucleophiles that are easily... 

Similar to rhodium, copper mediates retro-allylation when it is complexed with an N-heterocyclic carbene ligand [31]. The allyl transfer takes place not only to aromatic aldehydes but also to aromatic imines (Scheme 5.43). Notably, secondary homoallylic alcohols transfer their allyl groups, retro-allylation dominating over P-hydride elimination from the copper alkoxide intermediates. 

In this review, the applications in homogeneous catalysis of N-heterocyclic carbene-containing copper, silver and gold complexes will be presented. N-Heterocyclic carbenes (NHCs) are two-electron a-donor ligands that share a... 

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