CH* complex

The main advantages of the Cosorb process over the older copper ammonium salt process are low corrosion rate, abiHty to work in carbon dioxide atmospheres, and low energy consumption. The active CuAlCl C H CH complex is considerably more stable than the cuprous ammonium salt, and solvent toluene losses are much lower than the ammonia losses of the older process (94). 

Although the crystal structure of CODH or CODH/ACS has not yet been solved, a great deal of work has been done on these enzymes and plausible catalytic mechanisms have been proposed. Concerted action between the Ni ion and one of the Fe centers of a 4Fe-4S cluster are thought to elicit the formation of CO2 from CO. But perhaps the most extraordinary reaction is the one catalyzed by Cluster A the insertion of CO to a Ni-CHs complex. Through the two reactions catalyzed by CODH/ACS, the highly toxic, CO is not only removed, but is used as a source of carbon and electrons. 

For the (Cp)M(Ch) complexes therefore orbital occupation of the S(e2) level will be more favoured than in the M(Bz)2 and M(Cp)2 systems, so that it is therefore no surprise... 

The leading NBO Lewis structure of the less strongly bound Au(HCCH)+ complex does indeed correspond to separated Au+ HCCH reactants. Figure 4.89 illustrates the principal NBO donor-acceptor interactions for the Au(HC=CH)+ complex, which are seen to be rather similar to those for the long-range Ti(H2C=CH2) complex (Fig. 4.72). Thus, for a transition metal with only one vacant valence orbital, acetylene and ethylene 7tCc bonds function rather similarly as two-electron donors, and the p2, two-electron complex description is apt. 

Structures of CHS complexed with different Coenzyme A (CoA) thioesters and product analogs (i.e., naringenin and resveratrol) demonstrate that the active site is buried within an interior cavity located in the cleft between the upper and lower domains of each monomer (Fig. 12.3). Considering the complexity of the reaction... 

Ni(l 11) shows a clear di-rr spectrum at low temperatures (195-197, 201) but is exceptional among fee (111) surfaces in not showing a conversion to ethyli-dyne at higher temperatures. The spectrum observed at 300 K is clearly from a (di-other hand, as will be seen in the next section, the ethylidyne species is readily... 

The main difference between mononuclear complexes containing either a M—H—C or a M—H—Si three-center bond is that most tj2-CH complexes correspond to an earlier stage of the addition reaction than do the 7j2-SiH complexes 7(CMH) coupling constants are usually closer to the values for /(OH), while /(SiMH) values are closer to 2/(SiMH), and the relative lengthening of the C—H distance on 172 coordination is usually smaller than that of coordinated Si—H bonds. For example, in the representative iron complex 21 [the structure of which was determined by neutron diffraction analysis (74)], the coordinated C—H bond... 

Fig. 12. SiHj —CH, complexes IGLO/II//MP2(FC)/6-3 IG 5 si NMR vs TMS number of imaginary frequencies (NIMAG) in parentheses NIMAG = 0 (minimum), 1 (transition state), 2 (second order)...

Some lanthanide /3-diketonate complexes (11, M = Pr, Eu, Dy, R = n-Pr, R = f-Bu) have selectivity for further coordination with Cl ions, over F , Br , I , C104, SCN , OH, AcO , HCOs, N03 and SOa ", and are the active component of ion-selective electrodes (ISE) for CG. It was proposed to take advantage of the luminescence in the visible range associated with CH complexation, for the development of specific naked eye optodes (M = Eu) for this ion . A sensitive fiuorescence enhancement system for the determination of terbium was developed and studied. This method was applied to... 

Koeller KM, Wong CH. Complex carbohydrate synthesis tools for glycobiologists enzyme-based approach and programmable one-pot strategies. Glycobiology 2000 10 1157-1169. 

When the olefin has the configuration (207) and Z = CHs, complex formation results in an upfield change in the olefinic proton shielding in the order AH > AH > AH, the values for propene being 0.69, 0.64, and 0.63 ppm, respectively (326). The Pt coupling constants with... 

Lone pair Z Base and Adjacent CH Complex Metal Hydride MH4- Organo- metallic R-M Allylic Z-C=C Simple Pi Bonds C=C CsC Aromatics 0... 

Fig. 13. Lindahl s model for the reaction depicted in Eq. (5) and catalyzed by the A-cluster of CODH/ACS. This model proposes the insertion of Ni-bound CO into the Ni-CH, complex. The special pair of cysteines (the D-center) is shown. Arrows are meant to indicate that the actual coordination position (axial or equatorial) is not known. This figure is based on [70]...

The electronic structure of U(cp")2X2 (X Cl, CH) complexes [2a,34] has been studied both by gas-phase p.e. and by theoretical Xa calculations. In this context, a recent p.e. study has reported on the electronic structure of similar complexes [35] and, in particular, on complexes where the X ligands are -BH4, -NEt2,... 

SCHEME 15.3 Proposed mechanism for trans-1,3-insertion of CPE via indirect isomerization through a o-CH complex (P = polymer chain). (Reprinted with permission from Kelly, W. M. Wang, S. CoUins, S. Macromolecules 1997, 30, 3151-3158. Copyright 1997 American Chemical Society.)... 

Figure 7. Conrotation and disrotation CH2 = CH - CH complexes. In (a),reactants are converted to excited products, while,in (b),there is smooth conversion of reactants to products. Also compare Figure 7 with Figure 3.

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