Styrene as substrate

Using styrene as substrate both 6 and 7 could be recycled four times, apparently without loss in activity or selectivity (>99% conversion after 20 hours b l ratio i 18 1). When p-methoxystyrene was used as a substrate the first three cycles did not suffer... 

Use of chiral ligands allows asymmetric synthesis of optically active branched aldehydes. In the early 1970s, two groups independently reported the first examples of asymmetric hydroformylation (109). Optical yields of less than 2 % were obtained by using styrene as substrate and a chiral Schiff base-Co or phosphine-Rh complex as catalyst. 

Scheme 9.32 Synthesis of aziridines with styrene as substrate...

The work of Nakamura (Tatsuno et al., 1974 Nakamura et al., 1978a, 1978b) is not only interesting because he used a cobalt complex (8.161) as cyclopropanation catalyst, but also because of enantiomeric selectivity. The latter was high when using dienes and styrene as substrate (8-73), but low with simple alkenes. 

P450 enzymes activate substrates with C=C double bonds, for instance from monounsaturated fatty acids, to form epoxides as an initial step in their metabolism. Quite a few biochemical studies focused on the products observed from double-bond activation using, for example, propene, cyclohexene, and styrene as substrates (82-86). Subsequent computational studies provided... 

In a seminal paper in Nature in 2005, Hughes et al. [165] reported catalytic activity of supported Au nanoparticles in the epoxidation of aUcenes using small amounts of peroxide initiators. Strong solvent effects were estabhshed, yet, wide particle size distributions (5-50 nm) did not allow pinpointing any size effects. Medium-to-high selectivity toward epoxide formation was achieved by careful tuning. For example, in the case of styrene as substrate with a 1% Au/C catalyst, a selectivity toward partial oxidation products (cf. the complete oxidation product, COj) of 97% was achieved with an epoxide selectivity of about 23%. 

Using water soluble 2,5-dihydrofuran and water insoluble styrene as substrates, 8 turnovers/h were achieved with this system. While the vesicle preparation successfully models all steps in the enzymatic cycle, the presence of both oxygen and hydrogen in the system caused water molecules to form on the surface of the platinum, thereby decreasing the efficiency of the system. 

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