Synthesis and characterization of (N→B) phenyl[N-alkyl-N-(2-alkyl)aminodiacetate-O,O′,N]boranes and phenyl[N-alkyl-N-(2-alkyl) aminodiacetate-O,O′,N]boranes

The reaction of boron heterocycles 1 and 2 with n-butyl lithium and alkyl halides led to (N→B) phenyl[N-alky-N-(2-alkyl)aminodiacetate-O,O′,N]boranes 3–6(a–b), 7(b) and 9(b), where alkyl can be in exo and/or endo position, and phenyl[N-alkyl-N-(2-alkyl)aminodiacetate-O,O′,N]boranes 7(c) and 8(c) isomers, which do not display the intramolecular N→B coordination bond. The existence of steric interactions between N-benzyl and the alkyl group at 2 position was indicated by 1H and 13C NMR, while, the δ(11B) values confirm the tetrahedral and trigonal environment of the 11B nucleus in these compounds. Moreover, the compounds were characterized by COSY, HETCOR and homonuclear proton decoupling experiment. The study of the intramolecular N→B coordination by dynamic NMR afforded a ΔG‡ value of 81.09 kJ/mol for compound 6(b).

Graphical abstractThe reaction of boron heterocycles 1 and 2 with n-butyl lithium and alkyl halides led to (N→B) phenyl[N-alky-N-(2-alkyl)aminodiacetate-O,O′,N]boranes, where alkyl can be in exo (a) and/ or endo (b) position, and phenyl[N-alkyl-N-(2-alkyl)aminodiacetate-O,O′,N]boranes (c) isomers, which do not display the intramolecular N→B coordination. The existence of steric interactions between N-benzyl and the alkyl group at 2 position was indicated by 1H and 13C NMR, while, the δ(11B) values confirm the tetrahedral and trigonal environment of the 11B nucleus in these compounds. Moreover, the compounds were characterized by COSY, HETCOR and homonuclear proton decoupling experiment. The study of the intramolecular N→B coordination by dynamic NMR afforded a ΔG‡ value of 81.09 kJ/mol for compound (N→B) phenyl[N-benzyl-N-(2-methyl)aminodiacetate-O,O′,N]borane.Figure optionsDownload full-size imageDownload as PowerPoint slide