16243-58-6Relevant articles and documents
Pyrazole complexes of three-coordinated boranes
Komorowski,Maringgele,Meller,Niedenzu,Serwatowski
, p. 3845 - 3849 (2008/10/08)
Both BF3 and B(C2H5)3 form 1:1 molar complexes with pyrazole (=Hpz) and C-substituted derivatives thereof (=Hpz*). Provided the pyrazole is a relatively strong base, the BF3 complexes slowly decompose on prolonged standing at room temperature with the elimination of HF to form the corresponding dimeric 1-pyrazolylboranes = pyrazaboles, e.g., F2B(μ-pz)2BF2. Deprotonation of Hpz·B(C2H5)3 with NaH yields the ion [(C2H5)3B(pz)]-, and the salt K[(C2H5)2B(pz)2] is obtained on heating of an equimolar mixture of Hpz·B(C2H5)3 and Kpz in Hpz. Species of the type K[R2B(pz)2] are also obtained by the reaction of (dimethylamino)diorganylboranes, (CH3)2NBR2, with Kpz and Hpz; they were converted to the representative Pd complexes Pd[(μ-pz)2B(C2H5)2]2 and R2B(μ-pz)2Pd(π-CH2CHCH2) (R = C2H5, n-C3H7, C6H5), respectively. Interaction of (CH3)2NBR2 with 1 molar equiv of Hpz gives 1:1 complexes of the type (CH3)2HN·BR2(pz), which can react with an additional molar equivalent of Hpz at elevated temperatures to form Hpz·BR2(pz) = R2B(pz)2H, or form mixtures of the desired compound with the pyrazabole relative R2B(μ-pz)[μ-N(CH3)2]BR2. Steric factors may prevent the intermediate formation of the 1:1 complexes to lead directly to Hpz·BR2(pz). The complexes Hpz·BR2(pz) can be thermolyzed to yield the pyrazaboles R2B(μ-pz)2BR2. However, whereas the reaction of [(CH3)2NBF2]2 with Hpz ultimately yields the pyrazabole F2B(μ-pz)2BF2, the reaction of the cited aminoborane with Hpz and Kpz causes redistribution of fluorine and K[F3B(pz)] is obtained as the only product containing B-F bonds. The complex (pz)2B(C2H5)(H2NCH3) is formed on reaction of the borazine (C2H5BNCH3)3 with a large excess of Hpz, and H-(pz)3B(NHCH3) is obtained in analogous fashion originating from the borazine [(CH3)2NBNCH3]3. The reaction of [(C-H3)2NNH]3B with excess of Hpz yields the complex (CH3)2NNH2·B(pz)3.
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. XCVIII. PREPARATION AND REACTIONS OF 2-(AZOL-1'-YL)-1,3,2-DIAZABORACYCLOALKANES
Alam, Fazlul,Niedenzu, Kurt
, p. 19 - 30 (2007/10/02)
The preparation of several 1,3-dimethyl-2-(azol-1'-yl)-1,3,2-diazaboracyclohexanes is described and their NMR spectra are interpreted.The reaction of 2-(pyrazol-1'-yl)-1,3,2-diazaboracyclohexanes with pyrazoles was found to lead to 1/1 molar adducts which
