Transition metal complexes with sulphur ligands, part 151 [1]. Ligand enforced configurations and low-spin states of [FeNS4] cores in [Fe-II(L)('pyS(4)')] complexes with sigma and sigma-pi ligands (L = N2H4, pyridine, PMe3, PnPr(3); 'pyS(4)'(2-)=2,6-bis(2-mercaptophenylthiomethyl)pyridine (2-))

The reactions of [Fe('pyS(4)')](2) with PMe3, PnPr(3), N2H4 and pyridine af forded mononuclear [Fe(L)('pyS(4)')] complexes with L = PMe3 (1), PnPr(3) ( 2), N2H4 (3) and pyridine (4). NMR spectroscopy, magnetic measurements and X-ray structure determinations revealed that all complexes exhibit trans-th iolate donors and low-spin Fe-II centres, irrespective of the sigma-pi or o r ligand character of L. In this regard, the properties of [Fe(L)('pyS(4)') ] complexes strongly contrast with those of [Fe(L)('NHS4')] Complexes ('NHS 4'(2-) = 2,2'-bis(2-mercaptophenylthio)diethylamine(2-)) and indicate that the rigid py(CH2)(2) entity of the 'pyS(4)'(2-) ligand is able to enforce t rans configurations and low-spin states of complexes with [FeNS4] cores. In spite of their diamagnetism, confirming the absence of antibonding electro ns, all complexes 1 to 4 are highly reactive and rapidly exchange their L l igands for CO to give [Fe(CO)('pyS(4)')]. Evidence was obtained that the ox idation of [Fe(N2H4)('pyS(4)')] (3) yields the diazene complex [mu -N2H2{Fe ('pyS(4)')}(2)] (5).