Abstract
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(′N 2 H 2 S 2 ′)] fragment was systematically investigated(′N 2 H 2 S 2 ′ 2- = 1,2-ethanediamine-N,N′-bis(2-benzenethiolate)(2-)). One-pot reactions of FeCl 2 -4H 2 O with the tetradentate amine-thiolate ligand ′N 2 H 2 S 2 ′ 2- and CO, PR 3 or P(OR) 3 yielded the complexes [Fe(CO) 2 (′N 2 H 2 S2′)] (1), [Fe(CO)(PR 3 )(′N 2 H 2 S 2 ′)] (R = Et (2), Pr (3), Bu (4)), [Fe(PMe 3 ) 2 (′N 2 H 2 S 2 ′)] (7), [Fe(dppe)(′N 2 H 2 S 2 ′)] (8 , dppe = 1,2- bis(diphenylphosphine)ethane), and [Fe(P(ÖR) 3 ) 2 (′N 2 H 2 S 2 ′)l (R = Me (9), Pr (10)). Mixed phosphane/phosphite complexes [Fe(PMe 3 )(P(OR) 3 )(′N 2 H 2 S 2 ′)] (R = Me (11), Pr (12)) were synthesized by PMe 3 /P(OPr) 3 exchange of the labile complexes [Fe(PMe 3 ) 2 (′N 2 H 2 S 2 ′)] (7) and [Fe(P(OPr) 3 ) 2 (′N 2 H 2 S2′)] (10). The [Fe(CO)(PR 3 )(′N 2 H 2 S 2 ′)l complexes 3 and 4 also resulted from 1 and PR 3 by photochemical CO substitution. They exhibit characteristic low-frequency v (CO) bands ( ≈1925 cm -1 ), and their remaining CO ligand proved photolytically inert. Reaction of 3 or 4 with NOBF 4 yielded the dinuclear NO complex [Fe(NO)(′N 2 HS 2 ′)] 2 (6 ) which contains two amide functions. Contrary to expectations, [Fe(PR 3 ) 2 (′N 2 H 2 S 2 ′)l complexes could not be obtained with monodentate phosphanes other than PMe 3 . The corresponding N-methylated ligand ′N 2 Me 2 S 2 ,2 - yielded only the complexes [Fe(CO) 2 (′N 2 Me 2 S 2 ′)] (15) and [Fe(′N 2 Me 2 S 2 ′)] (16). X-ray structure analyses of complexes 7, 8 -MeOH, 3, [Fe(CO)(dppm)(′N 2 H 2 S 2 ′)]·0,5 THF (5 ·0,5THF, dppm = bis(diphenylphosphino)methane), and 12·0,5′N2 H 2 S 2 ′-H 2 confirm the pseudo-octahedral coordination of the Fe centers by two trans-S and two cis-N donors and two c/s-coligands. The structural data further suggest that the unexpected instability of the [Fe(PR 3 ) 2 (′N 1 H 2 S 2 ′)] complexes is not caused by steric but by electronic effects. The cyclic voltammograms and the reactivity of the [Fe(L)(L′)(′N 2 H 2 S 2 ′)] complexes corroborate this assumption. The oxidation behaviour of the [Fe(L)(L′)(′N 2 H 2 S 2 ′)] complexes depends critically on the coligands L and L′. Reaction of 1 with dioxygen leads to oxidative dehydrogenation of the ′N 2 H 2 S 2 ′2- ligand and yields the dinuclear Schiff-Base complex [Fe(′gma′ )] 2 (′gma′ 2- = glyoxal-bis(2- mercaptoanil)(2-)). In contrast, oxidation of [Fe(CO)(PR 3 )(′N 2 H 2 S 2 ′)], [Fe(PR 3 ) 2 (′N 2 H 2 S 2 ′)] and [Fe(P(OR) 3 ) 2 (′N 2 H 2 S 2 )] complexes by dioxygen occurs metal-centered and gives the Fe(IV) complexes [Fe(PR 3 )(′N 2 S 2 ′)] (R = Me, Pr), [Fe(P(OR) 3 )(′N 2 S 2 ′)] (R = Me) and [Fe(′N 2 S 2 ′)] 2 that contain the tetraanionic thiolate-amide ligand ′N 2 S 2 ′ 4- .