Photoactive Chromium(III)–Cyclam Complexes with Axially Bound geminal‐Diethynylethenes

Reported herein are the preparation and characterization of trans‐[Cr(cyclam)(X‐gem‐DEE)2]OTf compounds (gem‐DEE = σ‐geminal‐diethynylethene, OTf = trifluoromethanesulfonate) 1 and 2, which are the first examples of 3d metal complexes containing gem‐DEE ligands. All compounds reported herein were characterized by visible, emission, and infrared spectroscopy, electrochemistry (CV and DPV), and high‐resolution mass spectrometry, and compound 2 was further studied by single‐crystal X‐ray diffraction. Both the photophyiscal data and the structural data indicate that the gem‐DEE ligands are similar to simple linear alkynyls in their coordination to the CrIII core. DFT calculations revealed that π delocalization is the most extensive within the SOMO and SOMO–1, in which both the vinyl and free ethynyl groups of the gem‐DEE ligand contribute significantly to the π⟂ orbital that mixes intimately with both the dyz and dxz orbitals of the Cr core.