Iron Catalyst Alkene dihydroxylation

In addition, also nonheme iron catalysts containing BPMEN 1 and TPA 2 as ligands are known to activate hydrogen peroxide for the epoxidation of olefins (Scheme 1) [20-26]. More recently, especially Que and coworkers were able to improve the catalyst productivity to nearly quantitative conversion of the alkene by using an acetonitrile/acetic acid solution [27-29]. The carboxylic acid is required to increase the efficiency of the reaction and the epoxide/diol product ratio. The competitive dihydroxylation reaction suggested the participation of different active species in these oxidations (Scheme 2). 

For alkene dihydroxylations, heavy metal oxides such as 0s04 and Ru04 can be applied. They are efficient catalysts but their toxitity makes their use less desirable and there is a dear need for non-toxic metal catalysts. Nevertheless, only a few reports have focused on the use of iron catalysts for alkene dihydroxylations. All systems described so far try to model the naturally occurring Rieske dioxygenase, an enzyme responsible for the biodegradation of arenes via cis-dihydroxylation by soil baderia [66]. 

The iron-carbonyl complexes can be viewed as a protected form of the diene, as the complexes do not undergo typical diene or alkene reactions. Complexation to iron-tricarbonyl fragments has been used in dendralene chemistry in this way. When the [3]dendralene 10.14 was complexed to iron tricarbonyl, employing a cinnamaldehyde imine as a catalyst, the two complexed alkenes lost typical alkene reactivity, while the uncomplexed alkene retained it (Scheme 10.6). Cyclopropanation, dihydroxylation and crossmetathesis of the uncomplexed alkene proceeded as expected. The monocomplexed [4]dendralene 10.19 underwent Diels-Alder reactions at the uncomplexed alkenes (Scheme 10.7). ... 

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