115509-09-6Relevant articles and documents
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.
B-halogenated pyrazaboles
Clarke,Das,Hanecker,Mariategui,Niedenzu,Niedenzu,N?th,Warner
, p. 2310 - 2317 (2008/10/08)
A series of 4,4,8,8-tetrahalopyrazaboles of the type X2B(μ-pz*)2BX2 (Hpz* = C-substituted pyrazole; X = Cl, Br) has been prepared by reaction of the corresponding B-tetrahydro derivatives with elemental halogen. The reaction of (C2H5)2O·BF3 with pyrazabole, H2B(μ-pz)2BH2, has been used for the preparation of both F2B(μ-pz)2BF2 and F2B(μ-pz)2BH2 (Hpz = pyrazole). The latter was chlorinated to yield the unsymmetrical B-tetrahalopyrazabole Cl2B(μ-pz)2BF2. 4,8-Dihalopyrazaboles, XRB(μ-pz)2BXR, have been obtained (as isomer mixtures) by the reaction of RBX2 with (CH3)3Si(pz). In addition, the 4,4-dihalopyrazaboles X2B(μ-pz)2B(C6H5)2 (X = F, Cl) have been prepared. Representative reactions of the cited types of B-halogenated pyrazaboles, e.g., with organometallics, carboxylic acid anhydrides, and alcohols, are described. New types of B-substituted pyrazaboles include the first example of a pyrazabole where each boron atom is bonded to two different terminal hydrocarbon substituents. The structures of three species have been determined. F2B(μ-pz)2BF2 crystallizes in the monoclinic system in space group P21/c with a = 7.636 (1) A?, b = 19.729 (5) A?, c = 7.213 (3) A?, β = 117.64 (28)°, and Z = 4. cis-(C2H5)ClB(μ-pz)2BCl(C2H 5) crystallizes in the orthorhombic system in space group Pbcn with a = 12.344 (8) A?, b = 7.794 (6) A?, c= 15.091 (10) A?, and Z = 4. Cl2B(μ-pz)2B(C6H5)2 crystallizes in the orthorhombic system in space group Pbca with a = 7.940 (3) A?, b = 15.270 (4) A?, c = 31.064 (9) A?, and Z = 8.
