Spin-state-dependent oxygen sensitivity of iron dithiolates: sulfur oxygenation or disulfide formation

The oxygen sensitivity of two related iron(III) dithiolate complexes of the ligand [4,7-bis-(2′-methyl-2′-mercatopropyl)-1-thia-4,7-diazacyclononane], (bmmp-TASN)FeCN (1) and (bmmp-TASN)FeCl (2), has been examined. Oxygen exposure of the low-spin complex 1 yields the disulfonate complex (bmmp-O₆-TASN)FeCN (3) as an olive-green solid with characteristic peaks in the IR spectrum at 1262, 1221, 1111, 1021, 947, 800, and 477 cm⁻¹. The corresponding nickel dithiolate, (bmmp-TASN)Ni (4), yields the related disulfonato derivative, (bmmp-O₆-TASN)Ni (5) upon addition of H₂O₂ (IR bands at 1258, 1143, 1106, 1012, 800, and 694 cm⁻¹. Oxygen exposure of the high-spin complex 2 results in disulfide formation and decomplexation of the metal with subsequent iron-oxo cluster formation. Complexes 1 and 2 were examined using density functional theory calculations. A natural bond order/natural localized molecular orbital covalency analysis reveals that the low-spin complex 1 contains Fe–S_thiolate bonds with calculated covalencies of 75 and 86%, while the high-spin complex 2 contains Fe–S_thiolate bonds with calculated covalencies of 11 and 40%. The results indicate the degree of covalency of the Fe–S bonds plays a major role in determining the reaction pathway associated with oxygen exposure of iron thiolates. The X-ray structures of 1, 4, and 5 are reported. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nitrile- and Amide-converting Microbial Enzymes: Stereo-, Regio- and Chemoselectivity

Biotransformations using microbial nitrile- and amide-converting enzymes have developed considerably in the recent years. Most processes profited from the stereo-, regio- and chemoselectivity of nitrile hydratases, nitrilases and amidases specific for primary or secondary amides. The aim of this review is to discuss the developments in this branch of biotransformations in the last ca. 5 years by taking highlights from research journals, patents and industrial applications.