Alkylzinc alkoxides, structure

The formation of tetrameric aggregates with a hetero-cubane structure is a structural motif that is observed for several alkylzinc alkoxides in the solid state (Figure 80). In these structures the alkoxy group is -bonded with its oxygen atom to three zinc atoms. The structural elucidation of [MeZnOMe]4 (152) represented the first example of such a structural motif in organozinc alkoxide chemistry . Later, similar structures were observed for alkylzinc alkoxides containing other alkoxy groups (153, = f-... 

More complicated structures of alkylzinc alkoxides have been observed in the solid state with the stoichiometry R eZn7(OR )8. These compounds have a hetero-di-cubane structure (two hetero-cubanes sharing a corner), and have been observed for Me6Zn7(OMe)g (159)240,241 Et6Zu7(OMe)8 (160)242 (ICH2)6Zu7(OMe)8 (161)2 (Figure 80). 

FIGURE 80. Alkylzinc alkoxides having a hetero-cubane structure... 

A series of alkylzinc alkoxides in which the alkoxide is an a-substituted 2-pyridinemeth-anol group has been prepared. Based on aggregation-state studies by cryoscopy in benzene, it appeared that depending on the particular a-substituent these compounds exist in solution either as dimers or as trimers. An X-ray crystal structure determination of one of these compounds, i.e. Mc3SiCH2ZnOCH2-2-Pyr, showed that this compound exists in the solid state as a cyclic tetramer. The four alkylzinc alkoxide units are linked via... 

The amino alcohol-catalyzed enantioselective addition of dialkylzincs to aldehydes, detailed in Chapter 5 (27), is accomplished with polymer catalysts containing DAIB, a camphor-derived auxiliary, and other chiral amino alcohols (28). Reactions that involve matrix isolation of the catalyst not only result in operational simplicity but also greatly facilitate understanding of the reaction mechanism. In solution, the catalytic chiral alkylzinc alkoxide derived from a dialkylzinc and DAIB exists primarily as dimer (27) however, when immobilized, its monomeric structure can be maintained. 

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