Complex groups, oxides

A number of investigations of the copper-group oxides and dioxygen complexes have been reported. The electronic spectra of CuO, AgO, and AuO were recorded in rare-gas matrices (9), and it was found that the three oxides could be formed effectively by cocondensation of the metal atoms with a dilute, oxygen matrix, followed by near-ultraviolet excitation. The effective wavelengths for CuO or AgO formation were X > 300 nm and for AuO was X > 200 nm. In addition, the laser fluorescence spectrum of CuO in solid Ar has been recorded (97). 

The reaction of tetraalkyltin complexes with oxide surfaces was studied244,245 but no description at the molecular level has been reported. The low-temperature reactivity of tetraalkyltin (SnR4, where R=Me, Et, i-Pr, Bu) complexes toward the surface of silica was studied in detail.246 At room temperature, the complex is physisorbed. Above 100°C, the adsorbed molecules react with the OH groups and the evolution of alkanes is observed (Scheme 7.15). 

Asymmetric alkylation. Deprotonation of (-)-l provides exclusively an (E)-enolate, which is alkylated to provide a single diastereomeric product. De-complexation by oxidation [Br, I2, Ce(IV)] in the presence of water provides the corresponding acid with the same configuration. This sequence has been used for synthesis of the drug (- )-captopril (3). In this case liberation of the acyl group in the presence of the amine provides the amide 2. 

Bolm et al. (130) reported the asymmetric Baeyer-Villiger reaction catalyzed by Cu(II) complexes. Aerobic oxidation of racemic cyclic ketones in the presence of pivalaldehyde effects a kinetic resolution to afford lactones in moderate enan-tioselectivity. Aryloxide oxazolines are the most effective ligands among those examined. Sterically demanding substituents ortho to the phenoxide are necessary for high yields. Several neutral bis(oxazolines) provide poor selectivities and yields in this reaction. Cycloheptanones and cyclohexanones lacking an aryl group on the a carbon do not react under these conditions. 

Electrochemical complexation studies of [5], disappointingly, revealed that the reversible ferrocenoyl oxidation wave was not perturbed on addition of either sodium or potassium cations, implying that the complexed group 1... 

The starting material is an 18 electron nickel zero complex which is protonated forming a divalent nickel hydride. This can react further with alkenes to give alkyl groups, but it also reacts as an acid with hard bases to regenerate the nickel zero complex. Similar oxidative addition reactions have been recorded for phenols, water, amines, carboxylic acids, mineral acids (HCN), etc. 

Caulton and coworkers found that fluoride ligands in certain Ir complexes promote oxidative addition reactions [44]. This group s results showed that the fluoride complex lr(H)2F(P Bu2Ph)2 rapidly activated C—H bonds under dehydrogenation conditions. The reactive intermediate in these reactions may be a fluoro-bridged analogue of compounds 4-12, namely [lr(p-F)(P Bu2Ph)2]2. This would explain the improved reactivity in the Ir-catalyzed OHA reaction in the presence of cocatalytic naked fluoride . 

The imidazole complexes are unstable in aqueous solution and decompose rapidly to TCO2. At lower pH the complexes undergo acid-catalyzed decomposition. None of the complexes exhibited oxidation or reduction processes by cyclic voltammetry. However, it was chemically possible to reduce the imidazole complex with Zn in IM HCl. A defined complex formed that did not contain the Tc=0 group probably reduction to Tc complexes occurred. " ... 

Copper forms practically aU its stable compounds in -i-l and +2 valence states. The metal oxidizes readily to -i-l state in the presence of various com-plexing or precipitating reactants. However, in aqueous solutions +2 state is more stable than -i-l. Only in the presence of ammonia, cyanide ion, chloride ion, or some other complexing group in aqueous solution, is the +1 valence state (cuprous form) more stable then the +2 (cupric form). Water-soluble copper compounds are, therefore, mostly cupric unless complexing ions or molecules are present in the system. The conversion of cuprous to cupric state and metalhc copper in aqueous media (ionic reaction, 2Cu+ — Cu° -i- Cu2+) has a Kvalue of 1.2x106 at 25°C. 

The ability to harness alkynes as effective precursors of reactive metal vinylidenes in catalysis depends on rapid alkyne-to-vinylidene interconversion [1]. This process has been studied experimentally and computationally for [MC1(PR3)2] (M = Rh, Ir, Scheme 9.1) [2]. Starting from the 7t-alkyne complex 1, oxidative addition is proposed to give a transient hydridoacetylide complex (3) vhich can undergo intramolecular 1,3-H-shift to provide a vinylidene complex (S). Main-group atoms presumably migrate via a similar mechanism. For iridium, intermediates of type 3 have been directly observed [3]. Section 9.3 describes the use of an alternate alkylative approach for the formation of rhodium vinylidene intermediates bearing two carbon-substituents (alkenylidenes). 

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