Co^III(cyclam) Oligoynyls: Monomeric Oligoynyl Complexes and Dimeric Complexes with an Oligoyn-diyl Bridge

Described in this work are the preparation and characterization of an extensive family of Co^III(cyclam)-oligoynyl compounds (cyclam = 1,4,8,11-tetraazacyclotetradecane) and elucidation of their electronic structures through DFT calculations. Monomeric Co compounds bearing one oligoynyl, namely, [Co­(cyclam)­(C_2nR)­Cl]⁺ with n = 1–3, and two butadiynyls [Co­(cyclam)­(C₄H)₂]⁺ were prepared from the reactions between [Co­(cyclam)­Cl₂]­Cl, Et₃N or Et₂NH, and the corresponding alkynes. The oligoyndiyl-bridged (μ-C_2m) dimers of Co^III(cyclam)Cl with m = 2 and 3 were prepared via the same process by varying alkyne stoichiometry, while those with m = 4 and 6 were prepared using the Glaser coupling reaction. The complexes were prepared in moderate yield (with the exception of m = 6) under mild conditions without requiring an anaerobic or anhydrous environment and are generally stable toward ambient atmosphere. Voltammetric analysis of the dimeric complexes revealed a weak Co–Co interaction through the bridge, which is attenuated by the length of the oligoyne. The orbital origin of the Co–Co interaction is rationalized through DFT analysis.