TRANSITION-METAL COMPLEXES WITH SULFUR LIGANDS PART CXXIX - RETENTIONAND REACTIVITY OF THE [FE-NH-NH-FE] CHROMOPHORE IN THE IRON-SULFUR DIAZENE COMPLEX [MU-N2H2(FE(PPR3)(S-4))(2)] IN EXCHANGE AND OXIDATION PROCESSES - (S-4(2-) = 1,2-BIS(2-MERCAPTOPHENYLTHIO)ETHANE(2-))

The [Fe - NH - NH - Fe] chromophore of [mu-N2H2{Fe(PPr3) ('S-4')}(2)] (1) [D. Sellmann, H. Friedrich, F. Knoch, M. Moll, Z. Naturforsch., Te ll B 48 (1994) 76] is retained in phosphine and H+/D+ exchange reactio ns. 1 exchanges the PPr3 ligand for PBu3 to give the analogous [mu-N2H 2{Fe(PBu3) ('S-4')}(2)] (2). Treatment of 1 with CO, however, leads to cleavage of the chromophore and the formation of [Fe(CO) (PPr3) ('S-4 ')] (3) as major product and of [Fe(CO)(2)('S-4')] and [Fe(CO) ('S-4') ](2) as by-products. The substitution reactions are suggested to be in itiated by a primary reversible dissociation of one PPr3 ligand in 1. Complex 1 exchanges the diazene NH protons for D+ from D2O or CD3OD vi a a base-catalyzed mechanism that involves the reversible formation of the [mu-N2H{Fe(PPr3) ('S-4')}(2)](-) anion. Cyclic voltammetry showed that 1 in CH2Cl2 solution can be oxidized in four consecutive steps, three of which are quasi-reversible. The redox waves are influenced by temperature changes and the presence of MeOH or NaOMe, indicating tha t the redox steps involve also reversible deprotonations of 1 and its oxidation products. Chemical oxidation of 1 by O-2, BuOOH or I-2 resul ted in nitrogen-free products. Oxidation of 1 by two equivalents of [C p2Fe]PF6 gave [mu-N2H2{Fe(PPr3) ('S-4')}(2)] (PF6)(2) (9). 9 is extrem ely unstable and decomposes above temperatures of - 20 degrees C with release of N-2. The properties of 9 are compatible with the mu-N-2 com plex [mu-N-2{Fe(PPr3) ('S-4')(2)] that has been twofold protonated by HPF6. 2H- and N-15-labeled isotopomers of 1 have been synthesized and completely characterized. The molecular structures of [Fe[CO] (PPr3) ( 'S-4')] (3), [Fe(CO) (PPh3) ('S-4')] (5) and [Fe(PPr3)(2)('S-4')] (11) have been elucidated by X-ray structure determination. (C) 1998 Elsev ier Science S.A. All rights reserved.