Transition metal complexes with sulfur ligands, CXXXIII - Synthesis, structure, and properties of new Fe-II complexes with [FeN2S2] cores

In order to obtain suitable precursors for iron complexes that model the re activity 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. 4H(2)O with the tetradentate amine-thiolate ligand 'N2H2S2'(2-) and CO, PR3, or P(OR)(3) yielded the complexes [Fe(CO)(2)('N2H2S2')] (1), [Fe(C O)(PR3)('N2H2S2')] (R = Et (2), Pr (3), Bu (4)), [Fe(PMe3)(2)('N2H2S2')] (7 ), [Fe(dppe)('N2H2S2')] (8, dppe = 1,2-bis(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 synth esized by PMe3/P(OPr)(3) exchange of the labile complexes [Fe(PMe3)(2)('N2H 2S2')] (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 subst itution. They exhibit characteristic low-frequency nu(CO) bands (approximat e to 1925 cm(-1)), and their remaining CO ligand proved photolytically iner t. 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 obt ained with monodentate phosphanes other than PMe3. The corresponding N-meth ylated 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(dipheny lphosphino)methane), and 12 . 0,5'N2H2S2' HZ 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 inst ability 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 dehydrog enation of the 'N2H2S2'(2-) ligand and yields the dinuclear Schiff-Base com plex [Fe('gma')](2) ('gma'(2-) = glyoxal-bis(2-mercaptoanil)(2-)). In contr ast, oxidation of [Fe(CO)(PR3)('N2H2S2')], [Fe(PR3)(2)('N2H2S2')] and [Fe(P (OR)(3))(2)('N2H2S2')] complexes by dioxygen occurs metal-centered and give s the Fe(IV) complexes [Fe(PR3)('N2S2')] (R = Me, Pr), [Fe(P(OR)(3))('N2S2' )] (R = Me) and [Fe('N2S2')](2) that contain the tetraanionic thiolate amid e ligand 'N2S2'(4-).