Organozinc alkoxides, structure

Because of the separation of this chapter into fundamental synthetic and structural aspects of organozinc compounds and the applications of these compounds in organic synthesis, many topics are treated twice, but with decidedly different emphases. By way of example, the important organozinc alkoxides are covered first in the inorganometallic section, where the emphasis is on their syntheses, structures, and applications other than in organic synthesis. Later, in Section 2.06.16.2, the uses of such compounds as chiral catalysts in asymmetric addition reactions are discussed. 

Heterobimetallic clusters (Figure 58,125 and 126) with solvent-dependent structures were also obtained upon mixing alkali metal tert-butoxides and -trimethylsiloxides in THF, TMEDA, and toluene.184 The common occurrence of heterocubes shows that there is a strong driving force for the formation of heterocubic structures in organozinc alkoxides. Solvent effects are important, however, as demonstrated by the formation of seeo-diheterocubic compounds in TMEDA. 

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-... 

Structure. The presence of an oxygen atom directly bound to zinc increases both the electron deficiency of the zinc and the donor character of the oxygen atom. This condition will inevitably result in intermolecular (see Intermolecular) association increasing the coordinative saturation of zinc and leading to high thermal stability and low sensitivity towards oxygen and moisture. Organozinc alkoxides and aryloxides... 

The remarkable structural diversity of supramolecular aggregates of organozinc alkoxides and related compounds is possible because of the variations in the coordination numbers and geometry of the metal it is favored by the relatively strong donor-acceptor bonds formed between oxygen and zinc. Most of the supramolecular aggregates are preserved in hydrocarbon solution (e.g. benzene), when there is no competition from the solvent for the vacant coordination sites of the metal. 

In the solid state pentafluorophenylcadmium hydroxide, CeFsCdOH, is a tetramer, 25, based on a Cd404 cubane skeleton (Cd-O 2.204-2.248 A), reminiscent of the structures of organozinc alkoxides [46]. An organocadmiiun-sulfur cubane supermolecule, [C6F5CdSCPPh3]4, and related self-assembled anionie species have also been reported [47]. 

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