Oxygen Coordinated Products

The latter method, the template method, involves a reaction to produce a transition state similar to the desired product using a template. The template should have a shape similar to the space of the product. The template interacts with the substrate by forming noncovalent bonds such as coordination bonds (Fig. 3). The representative and most successful examples are found in crown ether chemistry. In the chemistry, alkali metals act as templates to create a crown-ether-like transition state with an ethylene glycol substrate by using metal-oxygen coordination bonds. 

When an appropriate chiral phosphine ligand and proper reaction conditions are chosen, high enantioselectivity is achieved. If a diphosphine ligand of C2 symmetry is used, two diastereomers of the enamide coordination complex can be produced because the olefin can interact with either the re face or the si face. This interaction leads to enantiomeric phenylalanine products via diastereomeric Rh(III) complexes. The initial substrate-Rh complex formation is reversible, but interconversion of the diastereomeric olefin complexes may occur by an intramolecular mechanism involving an olefin-dissociated, oxygen-coordinated species (18h). Under ordinary conditions, this step has higher activation enthalpies than the subsequent oxidative addition of H2, which is the first... 

More recently, Apeloig and Nakash have studied diastereoselectivity in the reaction of (E)-5 with p-methoxyphenol53. In both benzene and THF, the stereochemistry of the products was independent of the phenol concentration. The syn/anti ratios of the addition products were 90 10 in benzene and 20 80 in THF. They have suggested that intramolecular proton transfer after rotation of the Si—Si bond of the phenol-coordinated intermediate is responsible for the formation of the anti-addition rather than intermolecular proton transfer. This must be a special case due to much slower (by a factor of 109-1012) rates of addition of phenol to (E)-5. Since phenolic oxygen is definitely less basic than alkyl alcoholic oxygen, coordination of oxygen in the zwitterionic intermediate in the reaction of (E)-5 with phenol must be loose and hence the intermediates should have much chance of rotation around the Si—Si bond. 

Sulfur dioxide can insert in various ways as shown in (21-XLVI). The usual product is the S-sulfinate (21-XLVIa), although the other isomers are known. The insertion of S02into M—OR bonds, e.g., of Ir(OR)(CO)L2, gives oxygen-coordinated sulfite complexes.211... 

The hydroperoxide formation on Pt(100) implies that at negative potentials, the remaining oxo-species (Figure 4.5) would be negatively charged and after the H+-ion coordination, water desorption would occur. The mechanism for this reaction is similar to that proposed on Pt(lll), and it justifies the simultaneous desorption of water from Pt(100) and the detection of the only oxygen reduction product from Pt(l 11). 

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