Amine adducts of (4-ClC6H4)3B3O3, Lewis acidity of triarylboroxines, and an XRD study on the related tetraphenylboroxinate(1-) salt, [C6H11NMe3][Ph4B3O3]

The stoichiometric reactions of amines with tri(4-chlorophenyl)boroxine (CPB) led to the formation of adducts CPB.L {L = morpholine (1a), benzylamine (1b) cyclohexylamine (1c), 2-picoline (1d), 4-picoline (1e), piperidine (1f)} and (CPB)2.(4,4’-trimethylenedipiperidine) (1g). Compounds 1a-1g have been characterised by NMR (11B, 1H, 13C), IR spectroscopy and powder-XRD. VT 1H NMR spectra on 1a and 1d-1g were consistent with a ligand exchange/recombination process and activation energies of 49 – 58 kJmol-1 were obtained. The synthesis of [C6H11NMe3][Ph4B3O3] (2) from Ph2BOBPh2, PhB(OH)2 and [C6H11NMe3][OH] in a 1:4:2 ratio in MeOH/H2O is also reported. Compound 2 was characterized by thermal analysis (TGA/DSC), spectroscopy (IR, NMR) and 1a, 1b and 2 were further characterized by single-crystal XRD studies.