Dinitrosyl Iron Complexes (DNICs) Containing S/N/O Ligation: Transformation of Roussin's Red Ester into the Neutral {Fe(NO)₂}¹⁰ DNICs

Addition of the Lewis base [OPh]- to the THF solution of Roussin's red ester [Fe(μ-SC6H4-o-NHCOPh)(NO)2]2 (1) and [Fe(μ-SC6H4-o-COOH)(NO)2]2 (2), respectively, yielded the EPR-active, anionic {Fe(NO)2}9, [(SC6H4-o-NCOPh)Fe(NO)2]- (3) with the anionic [SC6H4-o-NCOPh]2- ligand bound to the {Fe(NO)2} core in a bidentate manner (S,N-bonded) and [(SC6H4-o-COO)Fe(NO)2]- (4) with the anionic [SC6H4-o-COO]2- ligand bound to the {Fe(NO)2} core in a bidentate manner (S,O-bonded), characterized by IR, UV−vis, EPR, and single-crystal X-ray diffraction. In contrast to the bridged-thiolate cleavage yielding the neutral {Fe(NO)2}9, [(SC6H4-o-NHCOPh)(Im)Fe(NO)2] (Im = imidazole), by addition of 2 equiv of imidazole to complex 1 observed in the previous study, the addition of the stronger σ-donating and π-accepting PPh3 ligand triggered the reductive elimination of bridged thiolates of complex 1 to yield the neutral {Fe(NO)2}10, [(PPh3)2Fe(NO)2]. These results unambiguously illustrate one aspect of how the nucleophile L (L = imidazole, PPh3, [OPh]-) functions to control the reaction pathways (bridged-thiolate cleavage, reductive elimination, and deprotonation) upon the reaction of complex 1 and the nucleophile L. The EPR-active, dimeric {Fe(NO)2}9 dinitrosyl iron complex (DNIC) [Fe(μ-SC7H4SN)(NO)2]2 (6), with S and N atoms of the anionic [−SC7H4SN−]- (2-benzothiozolyl thiolate) ligands bound to two separate {Fe(NO)2}9 cores, was also synthesized from reaction of bis(2-benzothiozolyl) disulfide and [(NO)2Fe(PPh3)2]. A straightforward reaction of complex 6 and 4 equiv of [N3]- conducted in THF led to the anionic {Fe(NO)2}9, [(N3)2Fe(NO)2]- (7). Conclusively, the EPR-active, {Fe(NO)2}9 DNICs can be classified into the anionic {Fe(NO)2}9 DNICs with S/N/O ligation, the neutral {Fe(NO)2}9 DNIC with one thiolate and one neutral imidazole ligation, and the cationic {Fe(NO)2}9 DNICs with the neutral N-/P-containing coordinated ligands.将路易斯碱（Lewis base）[OPh]-分别加入鲁西红酯（Roussin's red ester）的四氢呋喃（THF）溶液中，两种底物分别为[Fe(μ-SC6H4-o-NHCOPh)(NO)2]2（络合物1）与[Fe(μ-SC6H4-o-COOH)(NO)2]2（络合物2），反应分别得到具有电子顺磁共振（EPR）活性的阴离子型{Fe(NO)2}9配合物：[(SC6H4-o-NCOPh)Fe(NO)2]-（配合物3）与[(SC6H4-o-COO)Fe(NO)2]-（配合物4）。其中，阴离子配体[SC6H4-o-NCOPh]2-以双齿（S、N配位）形式结合于{Fe(NO)2}核，而[SC6H4-o-COO]2-则以双齿（S、O配位）形式结合于该核，相关产物通过红外光谱（IR）、紫外-可见光谱（UV−vis）、电子顺磁共振（EPR）以及单晶X射线衍射完成表征。与此前研究中向络合物1加入2当量咪唑（Imidazole，Im）得到桥连硫醇盐断裂产物——中性{Fe(NO)2}9配合物[(SC6H4-o-NHCOPh)(Im)Fe(NO)2]不同，向络合物1加入σ给体与π受体能力更强的三苯基膦（PPh3）配体，会触发络合物1的桥连硫醇盐还原消除反应，得到中性{Fe(NO)2}10配合物[(PPh3)2Fe(NO)2]。上述结果清晰阐明了亲核试剂L（L=咪唑、三苯基膦、[OPh]-）在络合物1与亲核试剂L的反应中，如何通过桥连硫醇盐断裂、还原消除以及去质子化这三类路径调控反应进程。此外，通过双(2-苯并噻唑基)二硫醚与[(NO)2Fe(PPh3)2]的反应，还合成了具有EPR活性的二聚体{Fe(NO)2}9型二亚硝酰铁配合物（dinitrosyl iron complex, DNIC）[Fe(μ-SC7H4SN)(NO)2]2（配合物6），该配合物中阴离子配体[-SC7H4SN-]-（2-苯并噻唑硫醇盐）的S、N原子分别结合于两个独立的{Fe(NO)2}9核。将配合物6与4当量的叠氮负离子[N3]-在四氢呋喃中进行简单反应，得到阴离子型{Fe(NO)2}9配合物[(N3)2Fe(NO)2]-（配合物7）。综上，具有EPR活性的{Fe(NO)2}9型二亚硝酰铁配合物可分为三类：带有S/N/O配位的阴离子型{Fe(NO)2}9二亚硝酰铁配合物、带有一个硫醇盐与一个中性咪唑配位的中性{Fe(NO)2}9二亚硝酰铁配合物，以及带有中性含N/P配位配体的阳离子型{Fe(NO)2}9二亚硝酰铁配合物。