The synthesis, molecular structure and supramolecular architecture of complexes between the ammonia adduct of tris(pentafluorophenyl)boron and a series of mono and polydentate hydrogen-bond acceptors.
The ammonia adduct of tris(pentafluorophenyl)boron, (C6F5)3B.NH3, is a potentially tri-functional hydrogen-bond donor. Co-crystallisation with the bases acetonitrile, pyridine, tetrahydrofuran, tetramethylethylenediamine, 15-crown-5, 1,4-diazabicyclo[2.2.2]octane (DABCO), pyrazine and 4,4'-bipyridine results, not in donor exchange, but in the formation of supermolecules assembled through hydrogen bonding to second coordination sphere acceptors. The complexes have been characterised by elemental analysis, multinuclear NMR and single-crystal diffraction methods. The solid-state architectures range in complexity, from the hydrogen bonded pairing of (C6F5)3B.NH3, with a single monodentate acceptor molecule (e.g. MeCN to form (C6F5)3B.NH3.NCMe), through complexation with all three N-H groups to the macrocycle 15-crown-5, to the formation of infinite one-dimensional chains with pyrazine and DABCO, and to two-dimensional networks with the divergent acceptor 4,4'-bipyridine.
Reaction of the Lewis Acid Tris(pentafluorophenyl)borane with a Phosphorus Ylide: Competition between Adduct Formation and Electrophilic and Nucleophilic Aromatic Substitution Pathways
Treatment of the phosphorus ylide Ph3PCH2 (2a) with B(C6F5)3 (1) yields the adduct Ph3P+−CH2−B(C6F5)3- (3a), which was characterized by X-ray crystal structure analysis. The ylide Ph3PCHPh (2b) reacts analogously with B(C6F5)3 at 0 °C to form Ph3P+−CHPh−B(C6F5)3- (3b), but this adduct formation is reversible. Increasing the temperature leads to the formation of Ph3P+−CH2−(p-C6H4)−B(C6F5)3- (4), which is formed by an electrophilic aromatic substitution reaction of the electron-deficient borane reagent at the ylidic phenyl group. Compound 4 is also cleaved upon prolonged thermolysis to eventually yield Ph3P+−CHPh−(p-C6F4)−BF(C6F5)2- (5), which is the product of thermodynamic control in this series. Compound 5 arises from a nucleophilic aromatic substitution reaction of the nonstabilized phosphorus ylide at a −C6F5 ring of the B(C6F5)3 reagent. Compound 5 was also characterized by an X-ray crystal structure analysis.
Identification of Dihydroxy Aromatic Compounds in a Low-Temperature Pyrolysis Coal Tar by Gas Chromatography−Mass Spectrometry (GC−MS) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS)
Dihydroxy aromatics in coal tar undergo rapid coupling reactions with each other and with some coal-derived species during coal pyrolysis and liquefaction. However, only limited information on the structure of dihydroxy aromatics is known. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and gas chromatography−mass spectrometry (GC−MS) were used to characterize the dihydroxy aromatics in a low-temperature pyrolyzed coal tar and its distillate and residue fractions. Negative-ion electrospray ionization (ESI) FT-ICR MS spectra of coal-tar-derived samples had low molecular masses and narrow mass ranges. Negative-ion ESI is extremely selective for the dihydroxy aromatics present in coal tar. The O2 class species had the highest ion intensity among the species in the negative-ion FT-ICR mass spectrum for each sample. Dihydroxy compounds with an aromatic core structure of benzene, indan, biphenyl (and/or acenaphthene), and naphthalene were identified in the distillate fract...