Intramolecular pyridine-based frustrated Lewis-pairs

Abstract

Deprotonation of the methylpyridines 2,6-lutidine, 2-picoline, 4-dimethylamino-2,6-dimethylpyridine as well as 2,6-dimethyl-4-(piperidine-1-yl)pyridine with n-butyllithium or n-butyllithium/KO-t-Bu at the methyl positions led to the corresponding organolithium or -potassium compounds. Treatment with ClB(C₆F₅)₂ resulted in formation of the 2-borylmethylpyridines py-CH₂-B(C₆F₅)₂. They are monomeric and form intramolecular B–N bonds and four-membered rings. A short intramolecular B–N distance was observed in the crystal structure of the dimethylamino-functionalized derivative and proposed to be responsible for the low reactivity of the products towards hydrogen, thf, acetonitrile and CO₂. Hydroboration of 6-tert-butyl-2-but-4′-enylpyridine with HB(C₆F₅)₂ led to the corresponding hydroboration product t-Bu-py-(CH₂)₄-B(C₆F₅)₂ which shows no intramolecular B–N bond formation due to steric crowding. H/D-scrambling experiments with a H₂/D₂ mixture revealed its reactivity towards hydrogen.