New Fe(III)(cyclam) Complexes Bearing Axially Bound <i>geminal</i>-Diethynylethenes

Reported herein are the preparation and characterization of trans-[Fe­(cyclam)­(X-gem-DEE)2]­OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane, gem-DEE = σ-geminal-diethynylethene, and OTf = trifluoromethanesulfonate) compounds 2a, 2b, and 2c (X = −Ph (2a), −SiiPr3 (2b), and −Fc (2c)), which are the first examples of redox-active 3d metal complexes containing gem-DEE ligands. These compounds were prepared from the reaction between cis/trans-[Fe­(cyclam)­(OTf)2]­OTf (1) and X-gem-DEE-Li. Compounds 2a–2c were characterized by spectroscopic/voltammetric techniques. The trans-orientation of the gem-DEE ligands was established from the single-crystal X-ray diffraction study of 2a. Furthermore, the electronic structures of the model compounds 2a′+ and 2b′+ were analyzed with density-functional-theory calculations, which revealed significant dπ­(Fe)−π­(gem-DEE) interactions.本文报道了反式-[Fe(cyclam)(X-gem-DEE)₂]OTf类化合物2a、2b和2c的合成与表征，其中cyclam=1,4,8,11-四氮杂环十四烷（cyclam），gem-DEE=σ-偕二乙炔基乙烯（gem-DEE），OTf=三氟甲磺酸盐（trifluoromethanesulfonate）；该系列化合物中X分别为−Ph（2a）、−SiiPr₃（2b）与−Fc（2c），它们是首例含gem-DEE配体的氧化还原活性3d金属配合物。上述化合物通过顺式/反式-[Fe(cyclam)(OTf)₂]OTf（1）与X-gem-DEE-Li的反应制备得到。采用光谱学与伏安法对化合物2a~2c进行了表征，并通过2a的单晶X射线衍射分析确证了gem-DEE配体的反式配位取向。此外，借助密度泛函理论（density-functional-theory）计算对模型化合物2a′+与2b′+的电子结构进行了分析，结果揭示出Fe的dπ轨道与gem-DEE配体的π轨道之间存在显著的相互作用。