CoIII(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 = 1,4,8,1 1-tetraazacyclotetradecane) and elucidation of their electronic structures through DFT calculations. Monomeric Co compounds bearing one oligoynyl, namely, [Co-(cyclam)(C2nR)Cl](+) with n = 1-3, and two butadiynyls [Co(cyclarn)-(C4H)(2)](+) were prepared from the reactions between [Co(cyclam)-Cl-2]Cl, Et3N or Et2NH, and the corresponding alkynes. The oligoyndiyl-bridged (mu-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.