Organozinc alkoxides

Organozinc Alkoxides Derived From Diols, Triols, and Related Compounds 369... 

Organozinc Alkoxides Bearing Chelating Mixed Donor Ligands 375... 

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]. 

Organozinc Compounds Bearing Alkoxides, Siloxides, Boryloxides,... 

Organozinc Compounds Bearing Simple Alkoxides and Related Monodentate... 

Because of their ease of crystallization, alkylzinc alkoxides are often isolated as decomposition products in reactions involving organozinc compounds. The methylzinc lithium tert- butoxide heterocubes [ (THF)LiOBut 2-(MeZnOBu1 ]182 (Figure 58, 123) and [(LiOBu MeZnOBu1 ]183 124 were isolated as hydrolysis products from reactions involving amines, amidines, /< //-butyllithium, and dimethylzinc. 

Synthetic routes include anionic, cationic, zwitterionic, and coordination polymerization. A wide range of organometallic compounds has been proven as effective initiators/catalysts for ROP of lactones Lewis acids (e.g., A1C13, BF3, and ZnCl2) [150], alkali metal compounds [160], organozinc compounds [161], tin compounds of which stannous octoate [also referred to as stannous-2-ethylhexanoate or tin(II) octoate] is the most well known [162-164], organo-acid rare earth compounds such as lanthanide complexes [165-168], and aluminum alkoxides [169]. Stannous-2-ethylhexanoate is one of the most extensively used initiators for the coordination polymerization of biomaterials, thanks to the ease of polymerization and because it has been approved by the FDA [170]. 

The organozinc intermediate thus formed reacts with aldehydes as Grig-nard reagents do to form alcohols. In the presence of aluminum chloride, elimination of chlorine and fluorine from the vicinal carbons of the dichlorotrifluoroethyl group generates halogenated allylic alkoxides that are protonated to allylic alcohols, in the present case J, 2-chloro-3,3-difluoro-1 -phenylpropen-2-ol [114]. 

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