Cationic coordinated polymerizations homogeneous reactions

The dissociation of water coordinated to exchangeable cations of clays results in Brtfnsted acidity. At low moisture content, the Brrfnsted sites may produce extreme acidities at the clay surface-As a result, acid-catalyzed reactions, such as hydrolysis, addition, elimination, and hydrogen exchange, are promoted. Base-catalyzed reactions are inhibited and neutral reactions are not influenced. Metal oxides and primary minerals can promote the oxidative polymerization of some substituted phenols to humic acid-like products, probably through OH radicals formed from the reaction between dissolved oxygen and Fe + sites in silicates. In general, clay minerals promote many of the reactions that also occur in homogenous acid or oxidant solutions. However, rates and selectivity may be different and difficult to predict under environmental conditions. This problem merits further study. 

Sterically hindered Zr and Ti chelated phenoxide complexes represent a new class of homogeneous olefin oligomerization/polymerization catalysts when combined with cocatalysts such as MAO and FAB (eq 36).Spectroscopic investigations of the reaction between the Zr dibenzyl complex with FAB in toluene reveals the formation of the corresponding cationic complex associated with a benzylborate anion via Ph coordination (64 eq 36). Similar findings were obtained from bis(o-arylphenoxide)M(CH2Ph)2 complexes (M = Zr, Ti),2° while the corresponding dimethyl complexes yield unstable species after FAB activation. The products mediate the polymerization of ethylene and propylene. 

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