Exploration of Cobalt and Copper complexes of TIM Macrocycles

Reported herein is the synthesis and characterization of cobalt and copper complexes supported by a tetra-imine macrocycle, TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene. A new cobalt(I) intermediate, [Co(TIM)(thf)]PF₆, was isolated and characterized from the reaction between trans-[Co(TIM)Cl₂]PF₆ and NaBH₄. The UV-vis absorption spectrum showed that solvent coordination plays a role in different absorption bands. An extended period of time under a nitrogen atmosphere leads to a transition in the [Co(TIM)(thf)]PF₆ creating a Co(TIM)-radical species, [Co(TIM*)]PF₆. Single crystal X-ray diffraction studies of [Co(TIM*)]PF₆ located the radical on the TIM macrocycle along with the protonation of key imine nitrogen and carbon atoms. Two new Cu(TIM) complexes, [Cu(TIM)(MeCN)](PF₆)₂ and Cu(TIM)Cl₂, were also isolated and characterized. The crystal structures of these show that the copper metal center can occupy both square pyramidal and octahedral geometries. The desire to increase the solubility of Cu(TIM) in nonpolar solvents led to the attempt to make Cu(TEIM) (TEIM = 2,3,9,10-tetraethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene) containing longer hydrocarbon chains on the macrocycle. Instead, the macrocycle didn’t fully form, potentially due to steric bulk, and [Cu(N₄C₁₂H₂₆)Cl]PF₆ was isolated instead.