6431-90-9

Upstream product

• 99593-93-8 C6H5B(μ-C3H3N2)2(μ-OBC6H5O)BC6H5 
• 3262-89-3 triphenylboroxine 
• 288-13-1 NH-pyrazole 
• 4426-21-5 oxybis(diphenylborane) 
• 960-71-4 triphenylborane 
• 10026-04-7 tetrachlorosilane 

Relevant academic research and scientific papers

Chemical behavior and structure of triply bridged pyrazaboles of the type RB(μ-pz)2(μ-OBRO)BR

Triply bridged pyrazaboles of the type RB(μ-pz)2(μ-OBRO)BR (1, R = C2H5, C6H5; Hpz = pyrazole) are thermally quite stable and can be sublimed without decomposition even under atmospheric pressure. At room temperature they are resistant to water but are not soluble. Dissolution of 1 in protonic solvents occurs with complete breakdown of the molecule. Halogenation of 1 (R = C2H5) with SOCl2 yields the pyrazabole RClB(μ-pz)2BRCl. The latter compound is a valuable material for the preparation of various other pyrazaboles. Thus, reaction with alkali-metal alkoxide or with alcohol in the presence of triethylamine gives access to R(R′O)B(μ-pz)2BR(OR′) (R′ = CH3, C2H5), the first examples of B-alkoxypyrazaboles; with (CX3CO)2O (X = H, F), the species with R′ = CX3CO are obtained. The crystal and molecular structures of 1 with R = C2H5 were determined. The molecule crystallizes in the monoclinic system in space group P21/c with a = 7.587 (2) A?, b = 12.415 (2) A?, c = 16.387 (3) A?, β = 90.50 (2)°, and Z = 4.

Boron-nitrogen compounds. 110. Reactions of boroxins and diboroxanes with pyrazole

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.

Syntheses and reactions of pyrazaboles

The unsymmetrical pyrazabole (C6H5)2B(μ-pz)2BH2 (pz = N2C3H3 = pyrazolyl) was prepared by the reaction of K[(C6H5)2B(pz)2] with (CH3)3N·BH2I; subsequent halogenation with Br2 yielded (C6H5)2B(μ-pz)2BBr2. Similarly, (C2H5)2B(μ-pz′)2BH 2 (Hpz′ = 3,5-dimethylpyrazole) was converted to (C2H5)2B(μ-pz′)2BBr 2. Reaction of H2B(μ-pz′)2BH2 with (even an excess of) BBr3 gave a mixture of cis and trans isomers of HBrB(μ-pz′)2BHBr, whereas reaction with Br2 afforded Br2B(μ-pz′)2BBr2. Reaction of the latter compound with K[pz] yielded (pz)2B(μ-pz′)2B(pz)2, the first characterized pyrazolylpyrazabole containing different pyrazolyl moieties bonded to the same boron atom. A second, polymeric modification of Hpz′B(μ-pz′)2BHpz′ was identified; it appears to be the one reacting with additional Hpz′ to form (pz′)2B(μ-pz′)2B(pz′)2. The latter forms a monohydrate in a reversible reaction, but no similar interaction occurs with NH3.