Übergangsmetallkomplexe mit Schwefelliganden, C*. Unerwartet einfache Bildung von Diazen-Komplexen und ein neuer Typ von Diastereomerie: [µ-N2H2{Fe(PPr3)('S4')}2] und analoge Komplexe mit [FeS]-Zentren. ( 'S4'2-= 1,2-Bis(2-mercaptophenylthio)ethan(2-)) / Transition Metal Complexes with Sulfur Ligands, C*. Unexpectedly Facile Formation of Diazene Complexes and a New Type of Diastereomerism: [µ-N2H2{Fe(PPr3)('S4')}2] and Analogous Complexes with [FeS]-Centers. ('S4'2- = 1,2-Bis(2-mercaptophenylthio)ethane(2-))

Abstract

Abstract Single pot reactions of FeCl2∙4H2O with the tetradentate thioether-thiol 'S4-H2' = 1,2-bis(2-mercaptophenylthio)ethane, phosphines such as PEt3, PPr3 or PBu3, and a ca. 40-fold excess of N2H4∙H2O yield, in the presence of air, diazene complexes of the general formula [µ-N2H2{Fe(PR3)('S4')}2]. In contrast to previous syntheses of diazene complexes, the yields can excel 80%, and the syntheses can be carried out on a 10 g scale. [µ-N2H2{Fe(PPr3)('S4')}2], 1 and [µ-N2H2{Fe(PEt3)('buS4')}2], 2 were characterized by X-ray structure analysis. 2 contains 'buS4'2−= 1,2-bis(3,5-ditertiarybutyl-2-mercaptophenylthio)-ethane(2-), which is the tertiary-butyl derivative of 'S4'2−. 1 and 2 contain trans-HN=NH which bridges enantiomeric [Fe(PPr3)('S4')] or [Fe(PEt3)('buS4')] fragments. HN=NH is stabilized by 4c - 6 e− - π bonds, strong tricentric N − H∙∙∙(S)2 bridges, and steric shielding. NMR studies show that centrosymmetric 1 isomerizes in solution at temperatures around 0 °C in order to give a diastereomerie diazene complex which is also centrosymmetric. The diastereomerism is traced back to bridging the chiral [Fe(PPr3)('S4')] fragments by trans-HN=NH in a different way. The two different bridging modes are verified by X-ray structure analyses of analogous ruthenium complexes. Because this new type of diastereomerism is basically caused by a different position only of the N − H∙∙∙(S)2 bridges, it is termed hydrogen bridge diastereomerism. A mechanism for the isomerization is suggested. 1 exhibits three anodic waves in the cyclovoltammogram. The second wave indicates formation of the dication [1]2+, which is a redox isomer of the diprotonated (and as yet hypothetical) dinitrogen complex [µ-N2{Fe(PPr3)('S4')}2]. The significance of [1]2+ and of its Lewis basic thiolate donors with respect to electrochemical reduction of molecular dinitrogen under mild conditions is discussed.