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.