Cobalt catalysts active sites generation

One such example that has appeared recently features the central pyridine as the site for attachment. For example, Kim et al. have exploited the 4-substituted O-aUyl group in LI (Ar = 2,6-Me2CsH3) as a means of generating silica-supported iron and cobalt systems (31) (Scheme 5.13) [58]. On activation with MAO these immobihzed catalysts exhibited about 100-fold lower activity when compared to their homogeneous counterparts. This lowering in activity has been attributed to either diffusion Umitation of monomer into the interior pores of the supported catalyst or to the result of reduced active sites present in the heterogeneous variant. 

Another new catalyst generation based on iron and cobalt. The direct iron analogs of the nickel-diimine catalysts derived from structures (25) and (26) did not seem to be very active in olefin polymerization at all. The electronic and steric structure analysis shows why the nickel d -system favors a square planar coordination sphere but the iron d -system favors a tetrahedral one. It is very likely that these tetrahedral coordination sites are not available for olefin insertion, and hence no polymerization can take place. 

A water-soluble hydroformylation catalyst was developed by Xi and co-workers [65]. Third generation PAMAM dendritic ligands, with hydrophilic amine or sulfonic acid end groups, were phosphonated and the rhodium complexes thus formed were found to catalyse efficiently the hydroformylation of 1-octene and styrene, under very mild conditions. Water-soluble dendritic cobalt phthalocyanines that exhibited catalytic activities and oxidised thiols in the presence of oxygen, have been synthesised by Kimura and co-workers [66]. The catalytic activity of the phthalocyanines was influenced by a egation of the catalytic sites that results fi om strong intermolecular cohesive forces. It was proposed that steric isolation, enforced by the addition of a bulky dendritic coaf around the active phthalocyanine unit, could improve the catalytic activity. Acid terminated polyamide dendrimers were coupled to a phthalocyanine core to produce the desired water-soluble cobalt phthalocyanines, which were tested subsequently for catalytic activity and stability. The results obtained showed that the aggregation of phthalocyanines was reduced the catalytic activity was improved and the stability of the catalyst was improved by addition of the dendritic substituents. 

Nanba T, Uemura A., Ueno A., Haneda M., Hamada H., Kakuta N., Miura H., Ofune H., Udagawa Y. Studies on active species for selective catalytic reduction of NO on alumina-supported cobalt oxide catalysts. Bull. Chem. Soc. Jpn. 1998 71 2331-2337 Nishiwaki K., Kakuta N., Ueno A., Nakabayashi H. Generation of acid sites on finly divided Ti02. J. Catal. 1989 118 498-501... 

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