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Bio-inspired iron-catalyzed cis-dihydroxylation of an arene

Recent research from the group of Professor Lawrence Que.

In a paper just published in Chemical Communications (Chem. Commun. 2009, 50-52) and designated as a HOT article by the RCS journal, graduate student Yan Feng and coworkers reported the first example of a synthetic iron complex that activates H2O2 to effect the cis-dihydroxylation of naphthalene. In Nature, the bio-degradation of aromatic compounds is initiated by Rieske dioxygenases, which catalyze the cis-dihydroxylation of an arene double bond. As found for naphthalene 1,2-dioxygenase (NDO), the best structurally characterized of this class, these enzymes have a mononuclear non-heme iron active site where O2 activation occurs. To mimic enzyme function, the complex [FeII(TPA)(NCMe)2](OTf)2 (1) was used as catalyst and H2O2 as oxidant to convert naphthalene to its cis-1,2-dihydrodiol derivative, demonstrating this transformation for the first time by an iron complex (Figure 1). 18O labeling studies showed that one oxygen atom in the cis-diol product derived from H2O2 and the other from H2O. This unique labeling pattern required the postulation of an cis-HO-Fe(V)=O oxidant that is formed from the water-assisted cleavage of an Fe(III)-OOH intermediate (Figure 2). The proposed oxidant is analogous to the OsO4 reagent that is well established to carry out the cis-dihydroxylation of olefins (but not arenes). This research effort is supported by the US Department of Energy and aimed at developing oxidation catalysts with economical and environmentally friendly metal centers.

Figure 1. Naphthalene cis-dihydroxylation catalyzed by 1


Figure 2. Proposed mechanism for naphthalene cis-dihydroxylation by 1.

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