Boratranes with all six-membered rings or with two different ring sizes: Synthesis, characterization, and X-ray crystal structures

摘要

New types of boratranes B[(O-o-ArCH_2)_(3-n)N(CH_2CH_2O)_n] (Ar = 2,4-di-MeC _6H_2; n = 0, 1; n = 1, 2; n = 2, 3) featuring three six-membered chelating ring (1) to two five-membered chelating rings (3) in a stepwise fashion through 2 have been synthesized by the reaction of B(OMe) _3 with a series of tetradentate ligands such as (HO-o-ArCH _2)_(3-n)N(CH_2CHOH)_n (Ar = 2,4-di-MeC_6H_2; n = 0, L1H_3; n = 1, L2H _3; n = 2, L3H_3). Compounds 1-3 have been characterized by solution ~1H, ~(13)C{~1H} and, ~(11)B NMR and the crystal structures of 1 and 3 have been determined by single crystal X-ray diffraction. Compounds 1 and 3 are the first structurally characterized boratrane derivatives bearing all six-membered rings and mixed ring systems in the atrane cage, respectively. Especially, the molecular structures of 1 revealed that its transannular N-B bond length of 1.6322(19) is the shortest among the previously reported boratrane and its derivatives.