生物擬態{Fe(NO)2}9雙亞硝基鐵含[S,S]/ [O,O]/ [N,O]/ [S,O]配位基化合物:化合物結構、穩定性、反應性與相互轉換的探討

Abstract

Reaction of complex [Fe(CO)2(NO)2] with phosphorus or nitrogen-containing ligands such as PPh3, ethylenediamine, TMEDA and sparteine, led to the formation of the neutral {Fe(NO)2}10 [(PPh3)2Fe(NO)2] (3)、[(ethylenediamine)Fe(NO)2] (5)、[(TMEDA)Fe(NO)2] (4) and [(sparteine)Fe(NO)2] (15). Reaction of complex 3 with thiol and thiolate at 45 ℃ lead to the formation of the anionic {Fe(NO)2}9 DNICs [(SPh)2Fe(NO)2]- (1) and [(4-ClC6H4S)2Fe(NO)2]- (2). These two complexes can be converted to the complex 3 by addition of PPh3 and sodium biphenyl. This study demonstrates that the anionic {Fe(NO)2}9 and the neutral {Fe(NO)2}10 DNICs are interconvertable. Furthermore, the neutral {Fe(NO)2}10 complex 4 or 5 can also be converted to the neutral {Fe(NO)2}10 complex 3 under the presence of 2 equiv of PPh3 at ambient temperature. Presumably, the electronic configuration of the neutral {Fe(NO)2}10 DNICs could be described as {Fe-2(NO+)2}10. According to HSAB rule, triphenylphosphine (compared to TMEDA and ethylenediamine) tends to be softer ligand favorably binding to {Fe(NO)2}10 motif. The neutral {Fe(NO)2}10 complex 5 can be generated from reaction of the neutral {Fe(NO)2}10 complex 4 with 1 equiv of ethylenediamine ligand. The driving force of the ligand substitution reaction might be due to the fact that the steric hindrance of ethylenediamine ligand is less than TMEDA. The biomimetic [2Fe-2S] cluster [PPN]2[(S(CH2)nS)Fe(μ-S)2Fe(S(CH2)nS)] (n = 2(7), 3(8), 4(9), 6(10)) were synthesized by reaction of [PPN]2[S5Fe(μ-S)2FeS5] (6) and 2 equiv of different chain-length thiolates and 8 equiv of thiol. Compared to the other [PPN]2[(S(CH2)nS)Fe(μ-S)2Fe(S(CH2)nS)] (n = 2, 3, 4, 6), complex [PPN]2[(S(CH2)6S)Fe(μ-S)2Fe(S(CH2)6S)] is the most stable. The bidentate alkyl DNICs (( n = 2(11), 3(12), 4(13), 6(14)) are synthesized from either reaction of complex 7, 8, 9 and 10 with PPh3 and NO(g) or the reaction of cationic [(sparteine)Fe(NO)2]+ (16) (the complex 16 was synthesized by adding one equiv of oxidant agent [NO][BF4] to the complex 15) with 1 equiv of [S(CH2)nS]2–. RRE [Fe2(μ-SPh)2(NO)4] (17) could be synthesized by reaction of complex 1 and complex 16 serving as {Fe(NO)2}9-donor reagent. Complexes 2, 8, 12, 15 were characterized by IR, UV-vis, and single-crystal X-ray diffraction. The presence of the anionic {Fe(NO)2}9 [(Cl)(p-FPhO)(Fe(NO)2]- (21)、 [(p-FPhO)2(Fe(NO)2]- (26) and [(OPh)2Fe(NO)2]- (23) implicated the possible existence of the protein-bound tyrosine-coordinate DNICs. Reaction of [Fe(Cl)3(NO)]- with 3 equiv of [Na][p-FOPh] led to the formation of complex 21. Reaction of complex 21 with [Na][NO2] and [Na][p-FOPh] gives rise to complex 26. It is presumed that the better binding ability between [Na]+ and [Cl]- promotes the formation of intermediate [(NO2)(p-FOPh)Fe(NO)2]-. Addition of theσ-donor and π-donor [Na][p-FOPh] ligand triggers the ligand substitution reaction of [(NO2)(p-FOPh)Fe(NO)2]- yielding the complex 26. The synthetic process of the complex 23 is similar to that of complex 26. Addition of the strong electron-donating thiolate groups such as [SPh]- and [-SC4H3S]- to complex 23 led to the formation of [(OPh)(SPh)FeNO)2]- (27) and [(OPh)(-SC4H3S)Fe(NO)2]- (28), respectively. However, addition of the strongσ-donor and π-donor [C3H3N2]- ligand to complex 23 in 1:1 and 1:2 via ligand substitution led to the formation of complex [(OPh)(C3H3N2)FeNO)2]- (25) and [(C3H3N2)2FeNO)2]- (29), respectively. EPR spectrum of complexes 21, 23, 26, 27,and 28 exhibit the well-resolved five-line EPR signal, and complexes 25and 29 exhibit the well-resolved nine-line EPR signal at gav = 2.03 ± 0.004. Compared to the thermodynamical stability of the series of complexes 1, 23, 25, 27, 29, [(SPh)(C3H3N2)Fe(NO)2]- and [(NO2)2Fe(NO)2]-, this study shows that complex 1 is the most thermodynamically stable, followed by complexes [(SPh)(C3H3N2)Fe(NO)2]-、29、27、25、23 and complex [(NO2)2Fe(NO)2]- (22). Complexes 21, 23, 26, 27 and 28 were characterized by IR, UV-vis, and single-crystal X-ray diffraction. On the basis of the electron-donating ability, we can conclude that the bond distance decreases in the trend of Fe-Se, Fe-S, and Fe-O from the X-ray data of complexes 1, 23, 26 and [(SePh)2Fe(NO)2]-. The separation in NO stretching frequency (△νNO is 65 cm-1, 45 cm-1, and 55 cm-1) could be used to distinguish the O/Cl, O/O or N/O ligation modes of complexes 21, 23, 25 and 26； S/S or Se/Se coordinated to {Fe(NO)2}9 core of complex 1/[(SePh)2Fe(NO)2]-； and the S/O coordination of complexes 27/28.