Convenient syntheses of unsymmetrically B-substituted borazines

Abstract

Literally hundreds of borazines, (RBNR')3, are known, but only relatively few unsymmetrically substituted derivatives of the six-membered B3N3 heterocycle have been characterized and their chemistry has hardly been explored.1 The most readily available

Preparation and Characterization of Some Polyborazines

“…The cited formation of polyborazinyls as byproducts in the described condensation reactions may suggest that an initially formed diborazinyl of type 1 can rearrange with the formation of (C 2 H 5 BNH) 3 and the observed additional polyborazinyls. Alternatively, the polyborazinyls could be formed during the principal condensation reaction.…”

“…This latter assumption would imply that the original condensations proceed via substantial cleavage of borazine rings. In view of the observed thermal stabilities of the diborazinyls of type 1, this latter interpretation appears to have more credence, especially since a simple proton transfer within a given diborazinyl can be excluded in view of the formation of a considerable -14-amount of (C 2 H 5 BNH) 3 , and a third fraction consisting of the latter diborazinyl and the desired lb. This reaction was not further pursued, since the N-lithiation did not appear to be sufficiently selective and yielded mixtures of similar species, rendering the isolation of individual compounds difficult.…”

“…NMR spectra were recorded for solutions in CDCI 3 (unless otherwise noted) on a Varian VXR-400 or XL-200 ("1B) or GEMINI-200 ('H, 1 3 C) instrument. Chemical shift data are given in ppm with positive values indicating a downfield shift from the reference (internal (CH 3 ) 4 Si for IH and 1 3 C NMR, external (C 2 H 5 ) 2 0.BF 3 for "1B NMR); s = singlet, d = doublet, t = triplet, q = quartet, m = unresolved multiplet, sh = shoulder, and an asterisk denotes a broad signal.…”

“…The 12--eV mass spectrum of this material exhibited an ion cluster at m/z 654 to indicate a species 7 with n = 4. The sublimation residue, mp 158-180 'C, exhibited -9- -10-(CH 3 SBNCH 3 ) 3 . A stirred mixture of 6.80 g (30.1 mmol) of (ClBNCH 3 ) 3 ,1 27 g (90 mmol) of Pb(SCH 3 ) 2 , and 75 mL of hexane was heated to reflux for 32 h. The mixture was filtered, the residue was washed with hexane, and solvent was evaporated from the combined solutions under reduced pressure.…”

“…Such species have recently become available in good yield and purity by the reaction of symmetrically substituted 2,4,6-triorganylborazines with boron trihalides, which proceeds by successive displacement of the organic boron substituents by halogen. This work was initially performed with (C 2 H 5 BNCH 3 ) 3 , 3 but the method later was also found useful for the preparation of unsymmetrically B-substituted borazines containing annular N-groups. 4 The present report describes a study on the preparation and characterization of selected types of polyborazines utilizing such unsymmetrically substituted borazines.…”