Transition Metal Complexes with Sulfur Ligands, CXXXIII [1]. Synthesis, Structure, and Properties of New FeII Complexes with [FeN2S2] Cores

In order to obtain suitable precursors for iron complexes that model the reactivity of the active sites of nitrogenases, the coordination chemistry of the [Fe('N2H2S2')] fragment was systematically investigated ('N2H2S2' 2 = 1,2-ethanediamine-N,N'-bis(2-benzenethiolate)(2-)). One-pot reactions of FeCl2 4H2O with the tetradentate amine-thiolate ligand 'N2H2S2' 2 and CO, PR3, or P(OR)3 yielded the complexes [Fe(CO)2('N2H2S2')] (1), [Fe(CO)(PR3)('N2H2S2')] (R = Et (2), Pr (3), Bu (4)), [Fe(PMe3)2('N2H2S2')] (7), [Fe(dppe)('N2H2S2')] (8, dppe = 1,2bis(diphenylphosphine)ethane), and [Fe(P(OR)3)2('N2H2S2')] (R = Me (9), Pr (10)). Mixed phosphane/phosphite complexes [Fe(PMe3)(P(OR)3)('N2H2S2')] (R = Me (11), Pr (12)) were synthesized by PMe3/P(OPr)3 exchange of the labile complexes [Fe(PMe3)2('N2H2S2')] (7) and [Fe(P(OPr)3)2('N2H2S2')] (10). The [Fe(CO)(PR3)('N2H2S2')] complexes 3 and 4 also resulted from 1 and PR3 by photochemical CO substitution. They exhibit characteristic low-frequency (CO) bands ( 1925 cm ), and their remaining CO ligand proved photolytically inert. Reaction of 3 or 4 with NOBF4 yielded the dinuclear NO complex [Fe(NO)('N2HS2')]2 (6) which contains two amide functions. Contrary to expectations, [Fe(PR3)2('N2H2S2')] complexes could not be obtained with monodentate phosphanes other than PMe3. The corresponding N-methylated ligand 'N2Me2S2' 2 yielded only the complexes [Fe(CO)2('N2Me2S2')] (15) and [Fe('N2Me2S2')] (16). X-ray structure analyses of complexes 7, 8 MeOH, 3, [Fe(CO)(dppm)('N2H2S2')] 0,5THF (5 0,5THF, dppm = bis(diphenylphosphino)methane), and 12 0,5'N2H2S2'-H2 confirm the pseudo-octahedral coordination of the Fe centers by two trans-S and two cis-N donors and two cis-coligands. The structural data further suggest that the unexpected instability of the [Fe(PR3)2('N2H2S2')] complexes is not caused by steric but by electronic effects. The cyclic voltammograms and the reactivity of the [Fe(L)(L')('N2H2S2')] complexes corroborate this assumption. The oxidation behaviour of the [Fe(L)(L')('N2H2S2')] complexes depends critically on the coligands L and L'. Reaction of 1 with dioxygen leads to oxidative dehydrogenation of the 'N2H2S2' 2