Precursor, Chel

These considerations led to the choice of trans-l,2-diaminocyclohex-ane (DACH) as the optimum initial Chel precursor since both (R,R)-(—)-DACH and (S,S)-(-f )-DACH may be obtained from the racemic mixture via the (-f)-tartrate and ( + )-bitartrate salts, respectively (7,... 

Mo(CNR)7]2+ [Mo(CNR)s(chel)]2+ (chel = dppm, dppe, bipy, etc.)-, [MoCl(CNBut)4(bipy)]+ Mo(CNC6H11)s(bipy)]2+ [Mo(CNR)3(bipy)2]2+. They are generally prepared by displacement of CO, bipy, OAc, NO or other ligands from a suitable precursor by RNC and have capped octahedral or capped trigonal prismatic structures.10,70... 

The reaction is sensitive to steric hinderance. Aromatic ketones are reduced to hydrocarbons. Unsaturated ketones are fully reduced and with no selectivity. Complexes of the type Ir(Chel)(CH2=CH2)2Cl, with Chel = 2,2 -bipyridine or phenantholine derivatives, behave as catalyst precursors for hydrogen transfer from isopropanol to ketones and Schiff bases. Potassium hydroxide is required as cocatalyst to convert the isopropanol coordinated to the Ir(I) ion, in the neutral isopropoxy derivative. Enolates that are present would act as inhibitors when coordinated to the cationic derivative. Ethylene complexes are better precursors than the corresponding cyclooctadiene derivatives, because they are activated more easily and more completely, and they show high catalytic activity. The most active complexes is the 3,4,7,8-Me4 phen derivative, which, at 83°C, gives turnovers of up to 2850 cycles/min. Reduction of 4-r-butylcyclohexanone affords 97% of the tra/u-alcohol. 

Table 2. Reduction of PhN02 by CO/H2O in the presence of Ru3(CO)i2 and a chelating ligand (chel) as catalyst precursors. (Data from [22]).

In addition to conventional aikoxide-based syntheses, Williams and Interrante [177] and Pouxviel et al. [175] investigated aluminosilicate gels prepared from organometallic precursors. Williams and Interrante reacted diketonate (chel) aluminum alkoxides with trimethylacetoxysilane forming heterocondensed products according to the following scheme ... 

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