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Transition Metal Complexes with Sulfur Ligands, C. Unexpectedly Facile Formation of Diazene Complexes and a New Type of Diastereomerism: 2> and Analogous Complexes with -Centers. ('S4'(2-) = 1,2-Bis(2-mercaptophenylthio)ethane(2-))
Sellmann, Dieter,Friedrich, Helge,Knoch, Falk,Moll, Matthias
, p. 76 - 88 (2007/10/02)
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 2>.In contrast to previous syntheses of diazene complexes, the yields can excel 80percent, and the syntheses can be carried out on a 10 g scale. 2>, 1 and t-buS4')>2>, 2 were characterized by X-ray structure analysis. 2 contains 't-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 or t-buS4')> fragments.HN=NH is stabilized by 4c-6 e(-)-? bonds, strong tricentric N-H...(S)2 bridges, and steric shielding.NMR studies show that centrosymmetric 1 isomerizes in solution at temperatures around 0 deg C in order to give a diastereomeric diazene complex which is also centrosymmetric.The diastereomerism is traced back to bridging the chiral 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 (2+), which is a redox isomer of the diprotonated (and as yet hypothetical) dinitrogen complex 2>.The significance of (2+) and of its Lewis basic thiolate donors with respect to electrochemical reduction of molecular dinitrogen under mild conditions is discussed. - Keywords: Diazene, Iron Sulfur Complexes, Synthesis, X-Ray
