Synthesis and Characterisation of Amine Adducts of Tri(4-bromophenyl)boroxine, Tri(3-nitrophenyl)boroxine, and Tri(3-aminopheny1)boroxine; Molecular Structure of 3-Picoline·tri(4-bromopheny1)boroxine
Affiliations: Chemistry Department, University of Wales, Bangor, LL57 ZUW, UK | Chemistry Department, University of Wales, Cardiff, PO Box 912, Cardiff, CF1 3TB, UK
Note: [] Authors for correspondence
Note: [] Authors for correspondence
Note: [] Current address: Pilkington Group Research, Pilkington Technology Centre, Lathom, Lancashire, L40 5UF, UK.
Abstract: Twenty five 1:l adducts of the triarylboroxines (4-BrC6H4)3B3O3(PBB) (3-NO2C6H4)3- B3O3 (MNB), and (3-NH2C6H4)3B3O3 (MAB) with N donor ligands (cyclohexylamine, 4- picoline, 3-picoline, piperidine, morpholine, isobutylamine, triethylamine, pyridine, isoquinoline, benzylamine) have been prepared by reaction of stoichiometric quantities of ligand and triarylboroxine in Et2O at room temperature. All 25 adducts have been characterised by elemental analysis, Mpt, IR and by 1H and 13C NMR. MNB and 4 of its adducts have been characterised by 1lB MAS NMR. In solution variable temperature 1H NMR of selected PBB derivatives and of MNB·cyclohexylamine indicate that a ligand dissociation-recombination process is occuring with ΔG+ of ca. 39–54 kJ·mol−1. The crystal and molecular structure of 3-picoline·PBB has been determined by a single-crystal X-ray diffraction study. The colourless compound crystallises in the orthorhombic space group (Pbca) with a = 14.1710(10), b = 15.446(5), and c = 22.418(7) A, with Z = 8, calculated density = 1.737 Mg/m3, and final R values [I > 2σ (I)] of R1 = 0.0376, and ωR2 = 0.0691 from 3786 independent reflections.
