A Series of Mono- and Bis-Alkynyl Co(III) Complexes Supported by a Tetra-imine Macrocyclic Ligand (TIM)

Abstract

Reported herein is the synthesis and characterization of a series of mono- and bis-alkynyl CoIII(TIM) complexes, where TIM is 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene. The trans-[Co(TIM)(C2Ar)Cl]+ type complexes (Ar = phenyl (Ph, 1a), naphthalene (Np, 1b), and -C6F5 (1c)) were prepared by the addition of HC2Ar to trans-[Co(TIM)Cl2]PF6 in the presence of Et3N. Treatment of the mono-alkynyl complexes with AgOTf in MeCN resulted in the trans-[Co(TIM)(C2Ar)(NCMe)](OTf)2 complexes (Ar = Ph (2a), Np (2b), and -C6F5 (2c)). Complexes 2a and 2b react with the respective HC2Ar ligand in the presence of Et3N to afford the symmetrical bis-alkynyl complexes trans-[Co(TIM)(C2Ar)2]+ (Ar = Ph (3a) and Np (3b)). trans-[Co(TIM)(C2C6F5)2]+ (3c) was obtained directly from the prolonged reaction of trans-[Co(TIM)Cl2]PF6 with HC2C6F5. Furthermore, the addition of HC2Ph to 2c in the presence of a weak base yielded the unsymmetrical bis-alkynyl complex trans-[Co(TIM)(C2C6F5)(C2Ph)]OTf (4). Molecular structures of complexes 1a/b, 2a/b, [3a]PF6, 3b, and 4 were established through single crystal X-ray diffraction. The absorption spectra for 1–4 display d–d bands between 380 and 470 nm. Complexes 1b–3b exhibited Np-based fluorescence. Electrochemical studies revealed that all complexes display an irreversible reduction characteristic of the CoIII center, as well as up to two irreversible reduction(s) localized on the TIM macrocycle.