trans-[Fe(cyclam)(C2R)2]+: A New Family of Iron(III) Bis-Alkynyl Compounds

We previously communicated the preparation and characterization of two trans-[Fe­(cyclam)­(CCR)2]­OTf compounds, 2b and 2c (where cyclam = 1,4,8,11-tetraazacyclotetradecane, R = −SiiPr3 (2b) or −Ph (2c), and OTf = trifluoromethanesulfonate), which were the first examples of Fe­(III) bis-alkynyl complexes. In this work, the series has been expanded to include R = −H (2a), −C2SiMe3 (2d), −C4SiMe3 (2e), and −Fc (2f), which were prepared from the reaction between cis/trans-[Fe­(cyclam)­(OTf)2]­OTf (1) and LiCCR (NaCCH for 2a). Compounds 2a–2f were characterized by spectroscopic/voltammetric techniques as well as high-resolution mass spectrometry (HR-MS). The trans-orientation of the alkynyl ligands were established from the single-crystal X-ray diffraction studies of 2b–2d. Furthermore, the electronic structures of the model compounds 2a′+, 2d′+, and 2e′+ were analyzed with density-functional calculations, which revealed significant dπ–π­(CC) interactions.