Synthesis and structures of new 1,3,6,2-dioxazaborocanes containing substituents in the ocane fragment

Abstract

New 1,3,6,2-dioxazaborocanes R1N(CHR3CR4R2O)(CHR6CHR5O)BX (1–11, X = Ph, 4-MeC6H4, Me; R1 = Me, PhCH2; R2, R3, R4, R5, R6 = H, Ph) were synthesized by the reactions of aryl- or methylboronic acids with dialkanolamines. The treatment of (Me2NCH2CH2O)3B (15) with MeN(CH2CH2OH)(CH2CPh2OH) afforded 2-[2-(dime-thylamino)ethoxy]-1,3,6,2-dioxazaborocane (12). 2-Fluoro-1,3,6,2-dioxazaborocanes R1N(CHR3CHR2O)(CH2CH2O)BF (13: R1 = PhCH2, R2 = R3 = H; 14: R1 = Me, R2 = R3 = Ph, threo) were synthesized by the reaction of bis(trimethylsilyl) ethers of the corresponding dialkanolamines with BF3·Et2O. The new borocanes can be used for the synthesis of the corre-sponding germanium derivatives PhCH2N(CH2CH2O)2GeX2 (16, X = OEt; 17, X = Cl), as exemplified by the reaction of compound 6. The structures of erythro-MeN(CH2CH2O)(CHPhCHPhO)BPh (3), threo-MeN(CH2CH2O)(CHPhCHPhO)BPh (4), erythro-MeN(CH2CH2O)(CHPhCHPhO)B(4-MeC6H4) (8), and PhCH2N(CH2CH2O)2BF (13) were established by X-ray diffraction. The coordination polyhedra of the boron atoms in these complexes can be described as distorted tetrahedra. The boron-nitrogen distances (1.705(7)–1.723(3) A) provide unambiguous evidence for the presence of the B←N transannular interaction in these compounds. The structures of the resulting borocanes containing phenyl substituents at the carbon atoms of the ocane skeleton were studied by NMR spectroscopy and quantum chemical density functional theory calculations.