Stepwise Synthesis of Bis-Alkynyl Co^III(cyclam) Complexes under Ambient Conditions

Reported herein is a new synthetic method for the synthesis of Co^III(cyclam) bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic conditions. Upon the treatment of AgOTf in acetonitrile, complex trans-[Co­(cyclam)­(C₂C₆H₄NMe₂)­Cl]Cl (1) was converted to trans-[Co­(cyclam)­(C₂C₆H₄NMe₂) (NCMe)]­(OTf)₂ (2), and 2 was in turn reacted with HC₂Ar under weakly basic conditions to afford the novel bis-alkynyls trans-[Co­(cyclam)­(C₂C₆H₄NMe₂)­(C₂Ar)]­(OTf) (Ar = C₆H₄NMe₂ (3) and C₆F₅ (4)) in reasonable yields. Voltammetric analysis revealed a modest NMe₂/NMe₂ coupling across the Co-alkynyl backbone in 3, while DFT calculations identified the HOMO in 3 as the superexchange pathway for such coupling.