Transition Metal Complexes with Sulphur Ligands , Part 151 [ 1 ] . Ligand Enforced Configurations and Low - Spin States of [ FeNS 4 ] Cores in

Z. Naturforsch. 56 b, 581-588 (2001); received April 6 , 2001 Iron Sulphur Complexes, Nitrogenase The reactions of [Fe('pyS4 ')l2 with PMe3 , P«Pr3 , N2 H4 and pyridine afforded mononuclear [Fe(L)('pyS4 ')] complexes with L = PMe3 ( 1 ), PnPr3 (2 ), N2 H4 (3) and pyridine (4). NMR spectroscopy, magnetic measurements and X-ray structure determinations revealed that all complexes exhibit frans-thiolate donors and low-spin Fe11 centres, irrespective of the a-ir or a ligand character of L. In this regard, the properties of [Fe(L)('pyS4 ')] complexes strongly contrast with those of [Fe(L)('NHS4 ')] complexes ('NhS4 i2~ = 2 ,2 '-bis(2 -mercaptophenylthio)diethylamine(2 -)) and indicate that the rigid py(CH2 ) 2 entity of the 'pyS4 ,2~ ligand is able to enforce trans configurations and low-spin states of complexes with [FeNS4 ] cores. In spite of their diamagnetism, confirming the absence of antibonding electrons, all complexes 1 to 4 are highly reactive and rapidly exchange their L ligands for CO to give [Fe(CO)('pyS4 ')]. Evidence was obtained that the oxidation of [Fe(N'-H4 )('pyS4 ')] (3) yields the diazene complex [/x-N2 H2 {Fe('pyS4 ’)}2 ] (5).