New Fe(III)(cyclam) Complexes Bearing Axially Bound geminal-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.