Electronic Effects of (N₂S₂)M(NO) Complexes (M = Fe, Co) as Metallodithiolate Ligands

Heterobimetallic complexes comprised of W(CO)4 adducts of (N2S2)M(NO) have been isolated and characterized by ν(CO) and ν(NO) IR spectroscopies and X-ray diffraction. The molecular structures of (N2S2)M(NO) compounds (bme-dach)Co(NO), [(bme-dach)Co(NO)]W(CO)4, and [(bme-dach)Fe(NO)]W(CO)4 [bme-dach = N,N′-bis(2-mercaptoethyl)-1,4-diazacycloheptane)] find the square-pyramidal (bme-dach)M(NO) unit to serve as a bidentate ligand via the cis-dithiolato sulfurs, with a hinge angle of the butterfly bimetallic structures of ca. 130°. The W(CO)4 moiety is used as a probe of the electron-donor ability of the nitrosyl complexes through CO stretching frequencies that display a minor increase as compared to analogous [(N2S2)Ni]W(CO)4 complexes. These findings are consistent with the electron-withdrawing influence of the {Co(NO)}8 and {Fe(NO)}7 units on the bridging thiolate sulfurs relative to Ni2+. Also sensitive to derivatization by W(CO)4 is the NO stretch, which blue shifts by ca. 30 and 50 cm−1 for the Co and Fe complexes, respectively. Cyclic voltammetry studies find similar reduction potentials (−1.08 V vs NHE in N,N-dimethylformamide solvent) of the (bme-dach)Co(NO) and (bme-dach)Fe(NO) free metalloligands, which are positively shifted by ca. 0.61 and 0.48 V, respectively, upon complexation to W(CO)4.本研究已分离得到由(N₂S₂)M(NO)的W(CO)₄加合物构成的异双金属配合物，并通过CO伸缩振动（ν(CO)）、NO伸缩振动（ν(NO)）红外光谱及X射线衍射对其完成表征。针对三类(N₂S₂)M(NO)化合物——(bme-dach)Co(NO)、[(bme-dach)Co(NO)]W(CO)₄以及[(bme-dach)Fe(NO)]W(CO)₄ [bme-dach = N,N'-双(2-巯基乙基)-1,4-二氮杂环庚烷]的分子结构解析结果显示：四方锥构型的(bme-dach)M(NO)单元通过其顺式二硫醇盐硫原子作为双齿配体，该蝴蝶状双金属结构的铰链角约为130°。W(CO)₄单元可作为探针，通过CO伸缩振动频率表征该亚硝酰配合物的给电子能力：相较于类似的[(N₂S₂)Ni]W(CO)₄配合物，本研究中配合物的CO伸缩振动频率仅出现小幅升高。上述结果与{Co(NO)}₈及{Fe(NO)}₇单元相较于Ni²+对桥联硫醇盐硫原子的吸电子效应相一致。NO伸缩振动同样对W(CO)₄的衍生化反应敏感：对于钴系与铁系配合物，其NO伸缩振动峰分别发生约30 cm⁻¹与50 cm⁻¹的蓝移。循环伏安法研究结果表明：游离的(bme-dach)Co(NO)与(bme-dach)Fe(NO)金属配体具有相近的还原电位（在N,N-二甲基甲酰胺溶剂中相对于标准氢电极（Normal Hydrogen Electrode, NHE）为-1.08 V）；当与W(CO)₄配位后，其还原电位分别正向偏移约0.61 V与0.48 V。