Syntheses, characterization and reactivity of Lewis acid–base adducts based on B–N dative bonds

Solid-State Synthesis of B←N Adducts by the Amine-Facilitated Trimerization of the Phenylboronic Acid

Stable boroxine-amine adducts comprising dative B←N bond(s) were prepared by mechanochemically-induced reactions of phenylboronic acid (PBA) and amines (pyridine, DMAP, 1H-pyrazole, piperidine, DABCO, hexamethylenetetramine, or 4,4'-bipyridine). In-situ Raman monitoring, ex-situ PXRD and DFT calculations were used for product identification. Stoichiometry of the product (3 : 1, 3 : 2 or 6 : 1 adduct) was controlled by the amine structure and the molar ratio of the reactants. The 1 : 2 H-bonded assembly of PBA and 4,4'-bipyridine (bpy) was confirmed as an intermediate in the adduct formation for bpy. Competitive binding experiments indicated that the exchange of the amines in the 3 : 1 adducts follows the computed adduct stabilities that increase with the amine basicity. Following the DFT prediction, the first adduct with two different amines, DMAP and pip, bound to one boroxine moiety was isolated and structurally characterized. Results show that calculations can be used to predict possible and preferred product(s) and their spectral characteristics.

From Stiba- and Bismaheteroboroxines to N,C,N-Chelated Diorganoantimony(III) and Bismuth(III) Cations-An Unexpected Case of Aryl Group Migration

An unprecedented transfer of an aryl group from boron to Sb and Bi is observed in the reaction of heteroboroxines of general formula ArM[(OBR)2O] [where M = Sb, Bi; Ar = C6H3-2,6-(CH2NMe2)2; R = Ph, 4-CF3C6H4, 4-BrC6H4] with corresponding boronic acid RB(OH)2. Using this procedure, ion pairs [ArMR](+)[R4B5O6](-) were obtained [where M = Sb and R = Ph (4), 4-CF3C6H4 (5), 4-BrC6H4 (6); where M = Bi and R = Ph (7), 4-CF3C6H4 (8), 4-BrC6H4 (9)]. All compounds were characterized using elemental analysis, electrospray ionization mass spectrometry, and multinuclear NMR spectroscopy, and molecular structures of 4 and 7 were determined by single-crystal X-ray diffraction analysis. The central metal atoms in 4-9 were arylated by respective boronic acids, which represents, to the best of our knowledge, unprecedented reaction path in the chemistry of heavier group 15 elements. Investigation of the mechanism of this transformation indicated that Lewis pairs consisting of monomeric oxides ArMO and boroxine rings are probably key intermediates. In this regard, molecular structures of ArSbO[(4-CF3C6H4)3B3O3]·(4-CF3C6H4)B(OH)2 (10) and {ArSbO[(3,5-(CF3)2C6H3)3B3O3]} (13) were established by single-crystal X-ray diffraction analysis, and compound 13 was also fully characterized in solution by multinuclear NMR spectroscopy. The bonding in 13 was analyzed in detail by using density functional theory and natural bond order calculations and compared with known adduct ArSbOB(C6F5)3 (14) and hypothetical ArSbO monomer.