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.