Catalysts, general activator pair

The CM of olefins bearing electron-withdrawing functionalities, such as a,/ -unsaturated aldehydes, ketones, amides, and esters, allows for the direct installment of olefin functionality, which can either be retained or utilized as a synthetic handle for further elaboration. The poor nucleophilicity of electron-deficient olefins makes them challenging substrates for olefin CM. As a result, these substrates must generally be paired with more electron-rich crosspartners to proceed. In one of the initial reports in this area, Crowe and Goldberg found that acrylonitrile could participate in CM reactions with various terminal olefins using catalyst 1 (Equation (2))." Acrylonitrile was found not to be active in secondary metathesis isomerization, and no homodimer formation was observed, making it a type III olefin. In addition, as mentioned in Section 11.06.3.2, this reaction represents one of the few examples of Z-selectivity in CM. Subsequent to this report, ruthenium complexes 6 and 7a were also observed to function as competent catalysts for acrylonitrile... 

The surface basicity of a solid catalyst can be defined in a way analogous to that applied to conventional bases. Thus, a surface Lewis base site is one that is able to donate an electron pair to an adsorbed molecule. If we take the definition of surface basicity in a more general way, it could be said that the active surface corresponds to sites with relatively high local electron densities. This general definition will include not only Lewis basicity but also single electron donor sites. We emphasize that the literature of heterogeneous catalysis often reports that both single-electron and electron-pair donor sites exist on basic catalysts. 

A large cationic radius generally increases the nucleophilic reactivity of the anion in an ion pair. A small cationic radius results in stronger electrostatic attraction and lesser reactivity of the anion. Catalysts with the active site separated from the polymer backbone by an aliphatic chain have higher activity than those prepared by quatemi-zation of a chloromethylpolystyrene with a tertiary amine or tertiary phosphine, leaving only one carbon atom between the active site and the aromatic ring. 

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