Intramolecular pyridine-based frustrated Lewis-pairs

Körte LA, Warner R, Vishnevskiy Y, Neumann B, Stammler H-G, Mitzel NW. Intramolecular pyridine-based frustrated Lewis-pairs. Dalton Transactions. 2015;44(21):9992-10002.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)-(C6F5)(2) which shows no intramolecular B-N bond formation due to steric crowding. H/D-scrambling experiments with a H-2/D-2 mixture revealed its reactivity towards hydrogen