Nitrosylated Iron−Thiolate−Sulfinate Complexes with {Fe(NO)}^6/7 Electronic Cores: Relevance to the Transformation between the Active and Inactive NO-Bound Forms of Iron-Containing Nitrile Hydratases

The five-coordinated iron−thiolate nitrosyl complexes [(NO)Fe(S,S-C6H3R)2]- (R = H (1), m-CH3 (2)), [(NO)Fe(S,S-C6H2-3,6-Cl2)2]- (3), [(NO)Fe(S,S-C6H3R)2]2- (R = H (10), m-CH3 (11)), and [(NO)Fe(S,S-C6H2-3,6-Cl2)2]2- (12) have been isolated and structurally characterized. Sulfur oxygenation of iron−thiolate nitrosyl complexes 1−3 containing the {Fe(NO)}6 core was triggered by O2 to yield the S-bonded monosulfinate iron species [(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]- (R = H (4), m-CH3 (5)) and [(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]22- (6), respectively. In contrast, attack of O2 on the {Fe(NO)}7 complex 10 led to the formation of complex 1 accompanied by the minor products, [Fe(S,S-C6H4)2]22- and [NO3]- (yield 9%). Reduction of complexes 4−6 by [EtS]- in CH3CN−THF yielded [(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]2- (R = H (7), m-CH3 (8)) and [(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]2- (9) along with (EtS)2 identified by 1H NMR. Compared to complex 10, complexes 7−9 with the less electron-donating sulfinate ligand coordinated to the {Fe(NO)}7 core were oxidized by O2 to yield complexes 4−6. Obviously, the electronic perturbation of the {Fe(NO)}7 core caused by the coordinated sulfinate in complexes 7−9 may serve to regulate the reactivity of complexes 7−9 toward O2. The iron−sulfinate nitrosyl species with the {Fe(NO)}6/7 core exhibit the photolabilization of sulfur-bound [O] moiety. Complexes 1−4−7−10 (or 2−5−8−11 and 3−6−9−12) are interconvertible under sulfur oxygenation, redox processes, and photolysis, respectively.已分离并完成结构表征的五配位铁-硫醇盐亚硝酰配合物（five-coordinated iron−thiolate nitrosyl complexes）包括：[(NO)Fe(S,S-C6H3R)2]-（R = H（1）、m-CH3（2））、[(NO)Fe(S,S-C6H2-3,6-Cl2)2]-（3）、[(NO)Fe(S,S-C6H3R)2]2-（R = H（10）、m-CH3（11））以及[(NO)Fe(S,S-C6H2-3,6-Cl2)2]2-（12）。以{Fe(NO)}6为核的铁-硫醇盐亚硝酰配合物1~3可被氧气（O2）触发硫氧合反应，生成对应的S键合单亚磺酸盐铁物种（S-bonded monosulfinate iron species）：[(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]-（R = H（4）、m-CH3（5））与[(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]22-（6）。与之相反，氧气进攻{Fe(NO)}7型配合物10时，会生成配合物1，同时伴随副产物[Fe(S,S-C6H4)2]22-与硝酸根([NO3]-)，产率为9%。以乙腈-四氢呋喃（CH3CN−THF）为溶剂，用乙硫醇根负离子([EtS]-)还原配合物4~6，可得到[(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]2-（R = H（7）、m-CH3（8））与[(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]2-（9），同时通过氢核磁共振波谱法（1H NMR）检测到二乙基二硫醚((EtS)2)的生成。相较于配合物10，带有给电子能力更弱的亚磺酸盐配体且配位于{Fe(NO)}7核上的配合物7~9可被氧气氧化，生成配合物4~6。显然，配合物7~9中配位的亚磺酸盐对{Fe(NO)}7核产生的电子微扰，可调控此类配合物与氧气的反应活性。带有{Fe(NO)}6/7核的铁-亚磺酸盐亚硝酰物种，表现出硫键合[O]基团的光致解离特性（photolabilization）。配合物1−4−7−10（或2−5−8−11与3−6−9−12）可分别在硫氧合反应、氧化还原过程与光解作用下实现相互转化。