Polymeric anions, four-coordinated metal

Polymeric anions, four-coordinated metal centers, halogenocuprate(I) and halogenoar-gentate(I) ions, 37 26-32 miscellaneous, 37 31-32... 

A metal coordination number of four is undoubtedly that most commonly exhibited in halogenocuprates(I) and halogenoargentates(I), vertex, edge, and face sharing of metal(I)-ligand tetrahedra leading to a wealth of structural motifs, especially where polymeric anions are concerned. 

Like their aluminum counterparts, gallium alkoxides are susceptible to hydrolysis, giving Ul-defined products. Methanolysis of hydrated Ga + ions produces Ga(OMe) + and Ga(OMe)2+ in solvated forms, as well as polymeric complexes. Ga(OPh)3 reacts with boiling MeOH or EtOH to form the corresponding alkoxide. Reaction of the trialkoxide compounds with other metal alkoxides, for example, LiOR, results in the formation of four-coordinate complex anions of the type [Ga(OR)4] A recent review of sesquihahdes/oxides... 

The mechanism for the stereoselective polymerization of a-olefins and other nonpolar alkenes is a Ti-complexation of monomer and transition metal (utilizing the latter s if-orbitals) followed by a four-center anionic coordination insertion process in which monomer is inserted into a metal-carbon bond as described in Fig. 8-10. Support for the initial Tt-com-plexation has come from ESR, NMR, and IR studies [Burfield, 1984], The insertion reaction has both cationic and anionic features. There is a concerted nucleophilic attack by the incipient carbanion polymer chain end on the a-carbon of the double bond together with an electrophilic attack by the cationic counterion on the alkene Ti-electrons. 

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