Stepwise Synthesis of Bis-Alkynyl Co<sup>III</sup>(cyclam) Complexes under Ambient Conditions

Reported herein is a new synthetic method for the synthesis of Co<sup>III</sup>(cyclam) bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic conditions. Upon the treatment of AgOTf in acetonitrile, complex <i>trans</i>-[Co­(cyclam)­(C<sub>2</sub>C<sub>6</sub>H<sub>4</sub>NMe<sub>2</sub>)­Cl]Cl (<b>1</b>) was converted to <i>trans</i>-[Co­(cyclam)­(C<sub>2</sub>C<sub>6</sub>H<sub>4</sub>NMe<sub>2</sub>) (NCMe)]­(OTf)<sub>2</sub> (<b>2</b>), and <b>2</b> was in turn reacted with HC<sub>2</sub>Ar under weakly basic conditions to afford the novel bis-alkynyls <i>trans</i>-[Co­(cyclam)­(C<sub>2</sub>C<sub>6</sub>H<sub>4</sub>NMe<sub>2</sub>)­(C<sub>2</sub>Ar)]­(OTf) (Ar = C<sub>6</sub>H<sub>4</sub>NMe<sub>2</sub> (<b>3</b>) and C<sub>6</sub>F<sub>5</sub> (<b>4</b>)) in reasonable yields. Voltammetric analysis revealed a modest NMe<sub>2</sub>/NMe<sub>2</sub> coupling across the Co-alkynyl backbone in <b>3</b>, while DFT calculations identified the HOMO in <b>3</b> as the superexchange pathway for such coupling.