Mononuclear Schiff Base Boron Halides: Synthesis, Characterization, and Dealkylation of Trimethyl Phosphate

A series of mononuclear boron halides of the type LBX2 [LH = N-phenyl-3,5-di-tert-butylsalicylaldimine, X = Cl
(2), Br (3)] and LBX [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (7), Br (8); LH2 = N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (9), Br (10); and LH2= N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (11), Br (12)] were synthesized from their borate precursors LB(OMe)2 (1) (LH =
N-phenyl-3,5-di-tert-butylsalicylaldimine) and LB(OMe) [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine
(4), N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (5), N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (6)]. The
boron halide compounds were air and moisture sensitive, and upon hydrolysis, compound 7 resulted in the oxo-bridged compound 13 that contained two seven-membered boron heterocycles. The boron halide compounds
dealkylated trimethyl phosphate in stoichiometric reactions to produce methyl halide and unidentified phosphate
materials. Compounds 8 and 12 were found to be the most effective dealkylating agents. On reaction with tert-butyl diphenyl phosphinate, compound 8 produced a unique boron phosphinate compound LB(O)OPPh2 (14)
containing a terminal phosphinate group. Compounds 1−14 were characterized by 1H, 13C, 11B, 31P NMR, IR, MS,
EA, and MP. Compounds 5, 6, and 11−14 also were characterized by single-crystal X-ray diffraction.