Supported Transition Metal Complexes as Catalysts

Other covalently bonded catalysts are those on inorganic supports such as silica, molecular sieves (zeolites), and alumina, the complexes being held either directly via the oxygen of surface hydroxy groups or via an intermediate functional group, again especially phosphino. 

Ionically bound complexes on sulfonated or aminated ion-exchange resins have been used, as have complexes adsorbed (van der Waals forces) onto silica gel and other supports. 

From the data available, Hartley and Vezey (27) discussed the variable parameters. The type of support material is important. On phosphinated silica, the complex is on the outside the surface and is more accessible 

Clearly, considering the number of variable parameters, the matching of substrates and catalysts to give high selectivity is at this stage somewhat of an empirical art and perhaps mimics in this respect its twin subject, asymmetric hydrogenation (Section III) they were both born in 1968- 1969. 

Deactivation of a homogeneous catalyst by dimerization can usefully be prevented by supporting the monomeric unit [note also that most multicenter catalysts require dissociation to an active monomeric form (/, p. 405 also Section VI)]. This concept has been used to maintain the hydrogenating activity of titanocene intermediates, which normally dimerize to inactive fulvalene complexes (334-336). Similarly maintained 

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Structures of Organolithium Compounds, 3, 365 Supported Transition Metal Complexes as Catalysts, 15, 189 Transition Metal-Carborane Complexes, 8, 87 Transition Metal-lsocyanide Complexes, 11, 21... 

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