Reactions of substituted pyridines with electrophilic boranes

Abstract

The lutidine derivative (2,6-Me₂)(4-Bpin)C₅H₂N when combined with B(C₆F₅)₃ yields a frustrated Lewis pair (FLP) which reacts with H₂ to give the salt [(2,6-Me₂)(4-Bpin)C₅H₂NH][HB(C₆F₅)₃] (1). Similarly 2,2′-(C₅H₂(4,6-Me₂)N)₂ and (4,4′-(C₅H₂(4,6-Me₂)N)₂ were also combined with B(C₆F₅)₃ and exposed to H₂ to give [(2,2′-HN(2,6-Me₂)C₅H₂C₅H₂(4,6-Me₂)N][HB(C₆F₅)₃] (2) and [(4,4′-HN(2,6-Me₂)C₅H₂C₅H₂(2,6-Me₂)N] [HB(C₆F₅)₃] (3), respectively. The mono-pyridine-N-oxide 4,4′-N(2,6-Me₂)C₅H₂C₅H₂(2,6-Me₂)NO formed the adduct (4,4′-N(2,6-Me₂)C₅H₂C₅H₂(2,6-Me₂)NO)(B(C₆F₅)₃) (4) which reacts further with B(C₆F₅)₃ and H₂ to give [(4,4′-HN(2,6-Me₂)C₅H₂C₅H₂(2,6-Me₂)NO)B(C₆F₅)₃] [HB(C₆F₅)₃] (5). In a related sense, 2-amino-6-CF₃-C₅H₃N reacts with B(C₆F₅)₃ to give (C₅H₃(6-CF₃)NH)(2-NH(B(C₆F₅)₃)) (6). Similarly, the species, 2-amino-quinoline, 8-amino-quinoline and 2-hydroxy-6-methyl-pyridine were reacted with B(C₆F₅)₃ to give the products as (C₉H₆NH)(2-NHB(C₆F₅)₃) (7), (C₉H₆N)(8-NH₂B(C₆F₅)₃) (8) and (C₅H₃(6-Me)NH)(2-OB(C₆F₅)₃) (9), respectively; while 2-amino-6-picoline, 2-amino-6-CF₃-pyridine, 2-amino-quinoline, 8-amino-quinoline and 2-hydroxy-6-methyl-pyridine react with ClB(C₆F₅)₂ to give the species (C₅H₃(6-R)NH)(2-NH(ClB(C₆F₅)₂)) (R = Me (10), R = CF₃ (11)) (C₉H₆NH)(2-NH(ClB(C₆F₅)₂)) (12), (C₉H₆N)(8-NH₂ClB(C₆F₅)₂) (13) and (C₅H₃(6-Me)NH)(2-OClB(C₆F₅)₂) (14), respectively. In a similar manner, 2-amino-6-picoline and 2-amino-quinoline react with B(C₆F₅)₂H to give (C₅H₃(6-Me)NH)(2-NH(HB(C₆F₅)₂)) (15) and (C₉H₆NH)(2-NH(HB(C₆F₅)₂)) (16). The corresponding reaction of 8-amino-quinoline yields (C₉H₆N)(8-NHB(C₆F₅)₂) (17). In a similar fashion, reaction of 2-amino-6-CF₃-pyridine resulted in the formation of (18) formulated as (C₅H₃(6-CF₃)N)(2-NH(B(C₆F₅)₂). Finally, treatment of 15 with iPrMgCl gave (C₉H₆N)(2-NH(B(C₆F₅)₂)) (19). Crystallographic studies of 1, 2, 4, 6, 7, 10, 11, 12 and 15 are reported.