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Co(cyclam) Complexes of Triarylamine-acetylide: Structural and Spectroscopic Properties and DFT Analysis

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journal contribution
posted on 25.08.2020, 12:40 by Susannah D. Banziger, Adharsh Raghavan, Matthias Zeller, Tong Ren
Reported herein are the syntheses of mono- and bis-C2TPA (HC2TPA = 4-ethynyl-N,N-bis­(4-methoxyphenyl)­aniline) complexes of CoIII(cyclam) (cyclam = 1,4,8,11-tetraazacyclotetradecane) complexes, and the formation of η2-adducts of Cu­(I)/Ag­(I) to the acetylenic bond of TPAC2 ligand. The reaction between trans-[Co­(cyclam)­Cl2]Cl and HC2TPA in the presence of Et2NH yielded trans-[Co­(cyclam)­(C2TPA)­Cl]Cl ([1]­Cl) and subsequent treatment of [1]Cl with CuCl or AgNO3 afforded trans-[Co­(cyclam)­(C2TPA-η2-CuCl2)­Cl] (2a) or trans-[Co­(cyclam)­(C2TPA-η2-Ag­(NO3)2)­(NO3)] (2b), respectively. The reaction between [Co­(cyclam)­Cl2]Cl and 3 equiv of LiC2TPA afforded trans-[Co­(cyclam)­(C2TPA)2]Cl ([3]­Cl). X-ray diffraction studies of compounds [1]­Cl, 2a/b, and [3]Cl established their molecular structures. All four compounds display redox couples that are characteristic of TPA (reversible oxidation) and CoIII (irreversible reduction) center. The reversible TPA oxidation in compounds [1]­Cl and [3]Cl enables further UV–vis/near-IR spectroelectrochemical studies to elucidate the change of electronic structures upon oxidation. The electronic spectra of both compounds [1]Cl and [3]Cl and their oxidized derivatives have been rationalized based on DFT and TD-DFT analysis.