Pacman and hangman metal tetraazamacrocycles

Metal complexes of derivatized 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11. 3.1]heptadeca-1(17),2,11,13,15-pentane (bapa) ligands were prepared from 4-substituted diacetylpyridine derivatives by templated condensation with 3,3′-diaminodipropylamine in the presence of a metal halide or nitrate. The diacetylpyridine derivatives with Pacman and Hangman scaffolds are delivered from borylation of the 4-postion of diacetylpyridine and subsequent Suzuki coupling with the appropriate Hangman or Pacman backbone. Electrochemical examination of the parent [Co(bapa)]²⁺ scaffold reveals it to be a catalyst for the hydrogen evolution reaction (HER) in acetonitrile. Similar studies of the Hangman complex appear to be obscured by trace amounts of residual palladium remaining from the Suzuki coupling reaction to provide a cautionary note for the use of such cross-coupling methodologies in the preparation of HER catalysts. Man the gallows! Metal complexes of derivatized tetraazamacrocyclic ligands (see picture) are synthesized by metal-templated condensation between 3,3′-diaminodipropylamine and 4-substituted diacetylpyridine derivatives, which are prepared by palladium-catalyzed cross-coupling reactions. An electrochemical study on a Hangman complex prepared this way provides a cautionary note that residual amounts of palladium can support H₂ generation.