Copper complexes carbon ligands

The ability of cobalt(II), nickel(II), and copper(II) to exhibit a greater tendency than Zn(II) towards bidentate coordination is further illustrated by structural comparisons within a series of bridging carbonate complexes (188). For example, of the complexes [TpPr 2]M 2(/x-C03) (M = Mn, Fe, Co, Ni, Cu, Zn), only the zinc derivative does not exhibit bidentate coordination at both metal centers (151,153). Furthermore, the carbonate ligand in the complexes [TpPr 2]M 2(/x-C03) (M = Mn, Fe, Co, Ni, Cu) also exhibits varying degrees of asymmetry that closely parallel the series of nitrate complexes described earlier (Fig. 47 and Table IX). 

Many examples of asymmetric reactions catalyzed by copper complexes with chiral ligand systems have been reported. In particular, various copper-bis(oxazoline) catalysts (e.g., complexes (H) to (L), Scheme 48) are effective for carbon-carbon bond-forming reactions such as aldol,204 Mukaiyama-Michael, Diels-Alder,206 hetero Diels-Alder,207,208 dipolar cycloaddition,209,210... 

The X-ray crystallographic analysis of 2 -Cu reveals a dimeric structure, where two copper ions are coordinated to two ligand molecules (Fig. 8). Each copper ion is situated in a trigonal planar carbene/alkenyl carbon ligand environment, coordinated to two carbene arms from one chelator and a third carbon from the pendant arm of a second chelator. The average Cu—C bond distance is 1.996 (1)A, consistent with that of other reported Cu(I) carbene complexes (29). 

The p3-bridged carbonato complex posseses a pseudo-3-fold molecular symmetry. Each of the Cu atoms is five coordinate with the four nitrogen atoms of tren and one oxygen atom of the carbonate ligand (C). The coordination polyhedron of the Cu atom can be described as almost (TBP), the copper ions being slightly out of the plane (0.15 A) of the three primary amine groups (Fig. 5). 

Heterocyclic thiones have been extensively studied because of their facility to yield coordination complexes. All the ligands contain thione and occasionally thiol (mer-capto) groups directly attached to the carbon atoms of heterocyclic molecules. They have been previously reviewed by Raper in 1985576, and very recently the same author has reviewed28 the copper complexes of heterocyclic thioamides and related ligands. 

Chemical Speciation Models. Using the stability constants derived by us for copper complexes with hydroxo and carbonate ligands (Table I) and for natural organic ligands (Table II), the Newport and Neuse Rivers were modeled for copper speciation as a function of pH, total copper, carbonate alkalinity and total dissolved organic matter. Speciation models were calculated from the equation ... 

On the basis of these observations and the known structures of a few polynuclear copper complexes, we suppose that CuC=CR is a part of a soluble complex, e.g. structure 26 . The coordination number of the copper is probably 4 and the ligands (L) may be amine, alkyne, etc. In the coupling reaction, the slow step is the release or transfer of X from carbon. These speculations lead to something like the progression in equation (271). 

Bis- and tris(hexafluoro-2,4-pentanedionato) (hexafluoroacetyl-acetonate, hfa) complexes of 23 different metal(II), (III), and (IV) ions have been prepared.1 5 Most of these have been isolated as low-melting solids, which can be readily sublimed unchanged between 25 and 150°. Most methods of synthesis of this class of complexes in different solvents have resulted in incomplete conversion to the chelate. For example, the copper complex Cu(hfa)2 has been prepared in 80% yield using excess ligand as the solvent. Several solvents having various polarities (water, ethanol, carbon tetrachloride, acetone) have been used. 

Tarkhanova IG, Smirnov VV, Rostovshchikova TN (2001) Distinctive characteristics of carbon tetrachloride addition to olefins in the presence of copper complexes with donor ligands. Kinet Katal 42(2) 216-222... 

Displacement of the mesyloxy group is formally a Sn2 process. The hydride reaction with the bromo compounds probably involves electron transfer, capture of bromine, and back-donation of hydrogen (deuterium) to the substrates within the ligand sphere of the copper complexes. The reason for the dichotomy must be hinged on the acceptor characteristics of bromine vis-d-vis the harder carbon. 

Alkynyl complexes contain metal-carbon bonds in which the metal is bound to the sp-hybridized carbon at the terminus of a metal-carbon triple bond. The materials properties of these complexes have been investigated extensively. The properties of these complexes include luminescence, optical nonlinearity, electrical conductivity, and liquid crystallinity. These properties derive largely from the extensive overlap of the metal orbitals with the ir-orbitals on the alkynyl ligand. The M-C bonds in alkynyl complexes appear to be considerably stronger than those in methyl, phenyl, or vinyl complexes. Alkynyl complexes are sometimes prepared from acetylide anions generated from terminal alkynes and lithium bases (e.g., method A in Equation 3.42), but the acidity of alkynyl C-H bonds, particularly after coordination of the alkyne to the transition metal, makes it possible to form alkynyl complexes from alkynes and relatively weak bases (e.g., method B in Equation 3.42). Alkynyl copper complexes are easily prepared and often used to make alkynylnickel, -palladium, or -platinum complexes by transmetallation (Equation 3.43). This reaction is a step in the preparation of Ni, Pd, or Pt alkynyl complexes from an alkyne, base, and a catalytic amoimt of Cul (Equation 3.44). This protocol for... 

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