Copper complexes halide ligands

The most common catalysts for ATRP are complexes based on a copper(T) halide and nitrogen based ligand(s). Various ligands have been employed and those most frequently encountered are summarized in Table 9.5. Typically, four nitrogens coordinate to copper. The bidentate bipyridyl (bpy) ligands 132-133 are known to form a 2 1 complex. The tetradentate ligands are expected to form a 1 1 complex. 

Copper-catalyzed ATRP is a multicomponent system, consisting of a monomer, an initiator with a transferable (pseudo)halogen, and a copper complex (composed of a copper (pseudo)halide and nitrogen-based complexing ligand). For a successful... 

ARGET ATRP has been successfully applied for polymerization of methyl methacrylate, ft-butyl acrylate and styrene in the presence of Sn(EH)2 (10 mol% vs. alkyl halide initiator or 0.07 mol% vs. monomer) [164,165]. For all monomers, polymerizations were well controlled using between 10 and 50 ppm of copper complexes with highly active TPMA and Me6TREN ligands. ARGET ATRP has also been utilized in the synthesis of block copolymers (poly(n-butyl acrylate)— -polystyrene and polystyrene-Z -poly(n-butyl acrylate) [164,165] and grafting... 

The remarkable variety in the permutations of the R2 Dtc ligands, various oxidation states of copper, and halide ions was again demonstrated in the synthesis of the Cu2(R2Dtc)3X2 complexes with copper in the oxidation states II and III. These paramagnetic compounds (1.77-1.86 BM per formula weight, R = Me, Et X = Br, Cl) were obtained by the reaction of CuCl or CuBr and R4Tds in CHC13 (598). 

To relieve the strain of sterically demanding ligands, a metal often remains coordinatively unsaturated. Copper(I) halides and phosphines form cubane-like metal cluster compounds, Lm(CuX) ,12 With the bulky trimesitylphosphine, a monomeric two-coordinate [CuBr(Pmes)3] is formed, Br—Cu—P = 173.7°.252 The d(Cu—P) of 2.193 A is comparable to that in normal tet-rameric complexes, but d(Cu—Br) at 2.225 A is shorter, no doubt due to the reduced coordination number. Heating crowded complexes can also result in a reduction in coordination number (see equation 65). 

Since Cu1 has no d—d transitions, its complexes are usually colorless, but there are some that are red or orange because of charge transfer transitions (both LMCT and MLCT).1 Copper(I) halide and other complexes are usually obtained by (a) direct interaction of ligands (which includes additional halide ions) with cop-per(I) halides or the triflate, (b) reduction of corresponding copper(II) compounds, or (c) reduction of Cu2+ in the presence of, or by, the ligand. 

Two complexes are known definitely to be monomeric—the triphenylphosphine sulfide complexes, CuX(Ph3PS) (X = Cl, Br). They were prepared by reacting the ligand with copper(I) halide in chloroform, and molecular weight determinations in this solvent show them to be monomeric (93). 

There remains a variety of unstable, insoluble, or incompletely characterized complexes whose true formulas remain open to speculation. Many unstable 1 1 complexes between copper (I) halides and ammonia (31) or the lower aliphatic amines (71, 281, 336) have been studied manometrically, but the compounds formed have high dissociation pressures, and attempts to isolate them have been unsuccessful owing to loss of ligand or to oxidation. Complexes with higher amines (348) or with pyridine (334) and its oligomers (178, 229, 230) are, in... 

To correlate the structural features of a specific copper or cuprate reagent with its reactivity, a better understanding of the interaction of such species with metal halides, ligands, solvents, and, last but not least, substrates is required. Such investigations have already begun and seem to have a promising future. In an elegant NMR study by Krause et al. [23] it was demonstrated that the reaction between t-BuCu(CN)Li and methyl propiolate (see Scheme 1.25) could be monitored by NMR. At -100 C, resonances attributable to the presence of a complex between the oi anocuprate and the substrate were observed. After the temperature had been raised to -40 C, the NMR spectrum of a vinylcopper intermediate... 

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