Complex hydndes

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

There are few structures known with coordination numbers larger than 8. The existence of coordination number 12 in some crystal lattices was mentioned above. Discrete nine-coordinate structures are known for complexes such as (LnlH.O) )1 and for the hydnde complexes [MHJ2- (where M = Tc or Re). These structures are formed by adding a ligand to each of the rectangular feces of a trigonal prism (Fig. 12.40). 

ZIEGLER CATALYST. A type of stereospedfie catalyst, usually a chemical complex derived from a transition metal halide and a metal hydride oi a metal alkyl. The tiansition metal may be any of those in gioups IV to VIII of the periodic table the hydnde or alkyl metals are those of groups I, II, and III. Typical, titanium chloride is added to aluminum alkyl in a hydrocarbon solvent to form a dispersion or precipitate of the catalyst complex. These catalysts usually operate at atmospheric pressure and are 1773... 

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