99593-93-8Relevant academic research and scientific papers
On the Structures of the 1:1 Adducts of Triorganylboroxins and Pyrazole
Yalpani, Mohamed,Koester, Roland
, p. 1553 - 1556 (2007/10/02)
The structures of the 1:1 adducts 3, 4 of triorganylboroxins and pyrazole have been reinvestigated.Detailed NMR analyses reveal that, contrary to recent reports, they form a normal 1:1 adduct in which only one nitrogen and one boron atom are involved in bonding as our earlier studies had shown.
Pyrazaboles of the type RR′B(μ-pz)2BRR′ and related studies
Das,DeGraffenreid,Edwards,Komorowski,Mariategui,Miller,Mojesky,Niedenzu
, p. 3085 - 3089 (2008/10/08)
Boron-bonded hydrogen or organylthio groups of pyrazaboles, R2B(μ-pz*)2BR2 (Hpz* = pyrazole or C-substituted derivatives thereof), can be replaced by reaction with either (C2H5)2O·BF3 or CH3OH·BF3 to give the corresponding F2B(μ-pz*)2BF2 species. Attempts to replace boron-bonded hydrocarbon groups require much more forcing conditions and usually result in a complete breakdown of the molecule. However, under mild conditions the B-C bond is not attacked and (C6H5)FB(μ-pz)2B(C6H 5)F is readily obtained from the reaction of (C6H5)(C2H5S)B(μ-pz) 2B(C6H5)(SC2H5) with BF3. 4,8-Dihalopyrazaboles, RXB(μ-pz)2BRX, are also obtained from the reaction of dihaloboranes, RBX2, with N-(trimethylsilyl)pyrazole, (CH3)3Si(pz); the halogen of the pyrazabole can be displaced readily by reaction with a Grignard reagent or an alcohol. The compound [(C2H5)2N](pz)B(μ-pz)2B[N(C 2H5)2](pz) was also prepared by the cited procedure. The diethylamino group of the latter species is easily displaced by reaction with pyrazole. Several additional pyrazaboles of the type RR′B(μ-pz)2BRR′ have been prepared. (C6H5)(pz)B(μ-pz)2B(C6H 5)(pz), which is accessible by various preparative routes, was separated into isomers that exhibit distinctly different 1H NMR spectra. The mass spectral fragmentations of such (cis and trans) isomers are significantly different with respect to their loss of the first fragments from the parent ions.
Boron-nitrogen compounds. 110. Reactions of boroxins and diboroxanes with pyrazole
Bielawski,Niedenzu
, p. 1771 - 1774 (2008/10/08)
Tetraorganyldiboryl oxides (1,3-diboroxanes) (R2B)2O (R = C2H5, C6H5), react at elevated temperatures with excess pyrazole, Hpz, to give an essentially quantitative yield of the corresponding pyrazabole, R2B(μ-pz)2BR2. The 1,3-diboroxane [(CH3)2NBR]2O (R = C6H5) reacts with Hpz in refluxing toluene to form the triply bridged pyrazabole RBB(μ-pz)2(μ-OBRO)BR as the major product besides substantial quantities of the diboroxane derivative [(pz)RB(μ-pz)2BR]2O. In the latter, two pyrazabole moieties are linked by an oxygen bridge between boron atoms. The boroxin adduct (-BRO-)3·Hpz (R = C6H5) is obtained on direct interaction of triphenylboroxin with pyrazole at room temperature. As based on NMR data, two boron atoms of the boroxin ring are coordinated to pyrazole nitrogen atoms and the N-bonded proton is delocalized. In contrast, all three boron atoms are coordinated in 1:1 molar mixtures of the boroxin with either 3,5-dimethylpyrazole or imidazole. The adduct (-BRO-)3·3Hpz was identified as a transient species. It undergoes a slow condensation on standing in solution at room temperature. At elevated temperatures the reaction progresses readily to yield the triply bridged pyrazabole RB(μ-pz)2(μ-OBRO)BR. When a neat mixture of the two reagents is refluxed, the pyrazabole R2B(μ-pz)2BR2 is obtained. Triethylboroxin and pyrazole interact readily even at room temperature beyond mere complexation to form RB(μ-pz)2(μ-OBRO)BR with R = C2H5. Additional pyrazole and even minor increases in temperature promote the condensation process.
