A series of mono-alkynyl CoIII(TIM) complexes, where TIM is 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene, has recently been synthesized and characterized. The trans-[Co(TIM)(C2R)Cl]+ type complexes (R = phenyl (Ph), naphthalene (Np), and -C6F5) were readily obtained by the addition of HC2R to trans-[Co(TIM)Cl2]PF6 in the presence of Et3N. Upon further exploration, it was found that the addition of an electron-rich terminal alkyne (R = 4-N,N-dimethylaniline (DMAP), ferrocene (Fc), and N,N-bis(4-methoxyphenyl)aniline (TPA)) in the presence of KOH selectively yielded trans-[Co(TIM′)((HC=C)R)Cl]+ type complexes, where TIM′ is the resulting derivative of TIM. As discussed in this poster, molecular structures of these latter complexes have been established through X-ray diffraction studies to reveal the formation of a 1-aza-2-cobalt-cyclobutene. Additional verification via FT-IR and 1H NMR confirmed the lack of a ν(C≡C) stretching frequency and the presence of two δ(=CH2) proton signals, respectively. Supplementary 1H NMR studies suggest that the noninnocent behavior of the TIM ligand is enabled by a formal two-electron donation stemming from the deprotonation of a TIM methyl group. Electrochemical studies demonstrated that the aza-cobalt-cyclobutene constitutional isomers display an irreversible Co3+/2+ reduction that is cathodically shifted relative to those displayed by the s-coordinated mono-alkynyl Co(TIM) analogues.

CoIII(TIM) complexes bearing aza-cobalt-cyclobutenes: Revealing the hidden non-innocence of TIM

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