Non-heme Iron Complexes For Stereoselective Oxidation: Tuning Of The Selectivity In Dihydroxylation Using Different Solvents

A new class of functional models for non-heme iron-based dioxygenases, including [(N3Py-Me)Fe(CH3 CN)2 ](ClO4 )2 and [(N3Py-Bn)Fe(CH3 CN)2 ](ClO4 )2 {N3Py-Me = [di(2-pyrid-yl) methyl]methyl(2-pyridyl)methylamine; N3Py-Bn = [di(2- pyridyl)methyl]benzyl(2-pyridyl)methylamine}, is presented here. NMR, UV and X-ray analyses revealed that six-coord-inate low-spin Fe II complexes with the pyridine N-atoms and the tertiary amine functionality of the ligand bound to Fe are formed. The two remaining coordination sites located cis to each other are occupied by labile CH3 CN groups that are easily exchanged by other ligands. We demonstrate that the reactivity and stereoselectivity of the complexes investigated depend on the choice of the solvent. The complexes have been examined as catalysts for the oxidation of both alkanes and olefins in CH3 CN. In this solvent alkanes are oxidized to alcohols and ketones and olefins to the corresponding cis- epoxides and cis-diols. In acetone as solvent a different react-ivity pattern was found, with, as the most striking example, the trans-dihydroxylation of cis-olefins. 18 O-labeling studies in CH3 CN establish incorporation of 18 O from H2 18 O2 and H2 18 O in both the epoxide and the diol implicating an HO-Fe V = 18 O active intermediate originating from an H2 18 O-Fe III OOH species. These results are in full agreement with mechanistic schemes derived for other dioxygenase model systems. Based on labeling studies in acetone an additional oxidation mechanism is proposed for this solvent, in which the solvent acetone is involved. This is the first example of a catalyst that can give cis- or trans-dihydroxylation products, just by changing the solvent.