Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
J Am Chem Soc. 2010 Apr 14;132(14):5290-9. doi: 10.1021/ja100849r.
Nitrosylation of PPN[(ONO)(2)Fe(eta(2)-ONO)(2)] [1; PPN = bis(triphenylphosphoranylidene)ammonium] yields the nitrite-containing {Fe(NO)}(7) mononitrosyliron complex (MNIC) PPN[(NO)Fe(ONO)(3)(eta(2)-ONO)] (2). At 4 K, complex 2 exhibits an S = (3)/(2) axial EPR spectrum with principal g values of g( perpendicular) = 3.971 and g( parallel) = 2.000, suggestive of the {Fe(III)(NO(-))}(7) electronic structure. Addition of 1 equiv of PPh(3) to complex 2 triggers O-atom transfer of the chelating nitrito ligand under mild conditions to yield the {Fe(NO)(2)}(9) dinitrosyliron complex (DNIC) [PPN][(ONO)(2)Fe(NO)(2)] (3). These results demonstrate that both electronic structure [{Fe(III)(NO(-))}(7), S = (3)/(2)] and redox-active ligands (RS for (RS)(3)Fe(NO) and [NO(-)] for complex 2) are required for the transformation of {Fe(NO)}(7) MNICs into {Fe(NO)(2)}(9) DNICs. In comparison with the PPh(3)-triggered O-atom abstraction of the chelating nitrito ligand of the {Fe(NO)(2)}(9) DNIC [(1-MeIm)(2)(eta(2)-ONO)Fe(NO)(2)] (5; 1-MeIm = 1-methylimidazole) to generate the {Fe(NO)(2)}(10) DNIC [(1-MeIm)(PPh(3))Fe(NO)(2)] (6), glacial acetic acid protonation of the N-bound nitro ligand in the {Fe(NO)(2)}(10) DNIC [PPN][(eta(1)-NO(2))(PPh(3))Fe(NO)(2)] (7) produced the {Fe(NO)(2)}(9) DNIC [PPN][(OAc)(2)Fe(NO)(2)] (8), nitric oxide, and H(2)O. These results demonstrate that the distinct electronic structures of {Fe(NO)(2)}(9/10) motifs [{Fe(NO)(2)}(9) vs {Fe(NO)(2)}(10)] play crucial roles in modulating nitrite binding modes (O-bound chelating/monodentate nitrito for {Fe(NO)(2)}(9) DNICs vs N-bound nitro as a pi acceptor for {Fe(NO)(2)}(10) DNICs) and regulating nitrite activation pathways (O-atom abstraction by PPh(3) leading to the intermediate with a nitroxyl-coordinated ligand vs protonation accompanied by dehydration leading to the intermediate with a nitrosonium-coordinated ligand). That is, the redox shuttling between the {Fe(NO)(2)}(9) and {Fe(NO)(2)}(10) DNICs modulates the nitrite binding modes and then triggers nitrite activation to generate nitric oxide.
PPN[(ONO)(2)Fe(eta(2)-ONO)(2)] [1; PPN = 双(三苯基膦亚基)铵] 的亚硝酰化生成含亚硝酸盐的 {Fe(NO)}(7) 单核亚硝酰铁配合物 (MNIC) PPN[(NO)Fe(ONO)(3)(eta(2)-ONO)] (2)。在 4 K 下，配合物 2 表现出 S = (3)/(2) 轴向 EPR 谱，主要 g 值为 g( perpendicular) = 3.971 和 g( parallel) = 2.000，表明 {Fe(III)(NO(-))}(7) 电子结构。向配合物 2 中加入 1 当量的 PPh(3)，在温和条件下引发螯合亚硝酰配体的氧原子转移，生成 {Fe(NO)(2)}(9) 双亚硝酰铁配合物 (DNIC) [PPN][(ONO)(2)Fe(NO)(2)] (3)。这些结果表明，电子结构 [{Fe(III)(NO(-))}(7)，S = (3)/(2)] 和氧化还原活性配体 (RS 用于 (RS)(3)Fe(NO) 和 [NO(-)] 用于配合物 2) 对于将 {Fe(NO)}(7) MNIC 转化为 {Fe(NO)(2)}(9) DNIC 都是必需的。与 PPh(3)引发的螯合亚硝酰配体的氧原子摘取代反应相比，{Fe(NO)(2)}(9) DNIC [(1-MeIm)(2)(eta(2)-ONO)Fe(NO)(2)] (5; 1-MeIm = 1-甲基咪唑)中的 [Fe(NO)(2)}(9) DNIC 生成 {Fe(NO)(2)}(10) DNIC [(1-MeIm)(PPh(3))Fe(NO)(2)] (6)，在 {Fe(NO)(2)}(10) DNIC [PPN][(eta(1)-NO(2))(PPh(3))Fe(NO)(2)] (7) 中，冰醋酸质子化 N 键合的硝基配体生成 {Fe(NO)(2)}(9) DNIC [PPN][(OAc)(2)Fe(NO)(2)] (8)、一氧化氮和水。这些结果表明，{Fe(NO)(2)}(9/10) 基序的不同电子结构 [{Fe(NO)(2)}(9) 与 {Fe(NO)(2)}(10)] 在调节亚硝酸盐结合模式 (O-键合螯合/单齿亚硝酰基用于 {Fe(NO)(2)}(9) DNICs 与 N-键合硝基作为 {Fe(NO)(2)}(10) DNICs 的π受体) 和调节亚硝酸盐活化途径 (PPh(3) 的氧原子摘取代导致配体带有硝酰基配位，质子化伴随脱水导致配体带有硝鎓基配位)方面起着至关重要的作用。也就是说，{Fe(NO)(2)}(9) 和 {Fe(NO)(2)}(10) DNIC 之间的氧化还原穿梭调节亚硝酸盐的结合模式，然后触发亚硝酸盐的活化以生成一氧化氮。
