Mixed-ligand complexes transfer

As shown in Scheme 4-6, the reaction proceeds via a Ti(IV) mixed-ligand complex A bearing allyl alkoxide and TBHP anions as ligands. The alkyl peroxide is electrophilically activated by bidentate coordination to the Ti(IV) center. Oxygen transfer to the olefinic bond occurs to provide the complex B, in which Ti(IV) is coordinated by epoxy alkoxide and r-butoxide. In complex B,... 

In the (—)-DAIB-catalyzed reaction of diethylzinc and benzaldehyde, the rate is first-order in the amino alcohol. The initial alkylation rate is influenced by the concentration of diethylzinc and benzaldehyde but soon becomes unaffected by increased concentration. Thus, under the standard catalytic reaction conditions, the reaction shows saturation kinetics the rate is zeroth order with respect to both dialkylzinc reagent and aldehyde substrate. These data support the presence of the equilibrium of A-D, and alkyl transfer occurs intramolecularly from the dinuclear mixed-ligand complex D. This is the stereo-determining and also turnover-limiting step. 

Finally it should be pointed out that there is an alternate mechanism for the two successive electron transfer processes indicated by the sequence 14-> 15 -> 16- 13 a. It is quite possible that the ascorbate radical anion dissociates from the mixed ligand complex 15, prior to reoxidation of the Cu(I) ion, and recombines with another Cu(II) chelate prior to the final electron transfer step indicated by 16 17 +... 

The mixed-ligand complexes [M(CO)x(PR3)7] with M = Cr, Mn, Mo, W were prepared by CO or ligand substitution by electron transfer chain catalysis (ETC catalysis),47- 9 such as ... 

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