Boron Trifluoride Complexes Research Articles

Synthetic utility and mechanistic implications of the Fries rearrangement of hydroquinone diesters in boron trifluoride complexes

Reactions of boron trifluoride methyl and ethyl etherate complexes with hydroquinone diesters yield monomethyl and monoethyl derivatives of acetylhydroquinones. The use of sterically hindered boron trifluoride etherate complexes results in acetylhydroquinone derivatives. This procedure represents a one-step synthesis of acetylhydroquinone derivatives, important building blocks for a variety of synthetic applications.

Carbene Complexes of Pnictogen Pentafluorides and Boron Trifluoride

Synthesis, characterization, and solid state X-ray crystallographic structures for 12-Pn-6 complexes derived from carbene 4,5-dichloro-1,3-dimesitylimidazol-2-ylidene and phosphorus, arsenic, or antimony pentafluoride are reported. The adducts show octahedral geometries at the pnictogen centers with C-Pn bond distances of 189.8 (P), 199.9 (As), and 217.5 (Sb) pm. The structures are those of internal zwitterions with imidazolium ion character in the heterocyclic ring and a pentafluoropnictanide anion bonded to C2. Adducts of BF3 with 1,3-dimesitylimidazol-2-ylidene and 4,5-dichloro-1,3-dimesitylimidazol-2-ylidene are also reported for comparison. Although the reactivity of chlorinated and non-chlorinated carbenes varies considerably, the spectroscopic and structural properties of analogous adducts are remarkably similar.

The vibrational spectra of the boron halides and their molecular complexes: Part 7. Ab initio predictions of the infrared spectra of the complexes of boron trifluoride with some linear nitrogen donors

The infrared spectra of the 1:1 molecular complexes of boron trifluoride with five linear nitrogen-containing electron donors (nitrogen, hydrogen cyanide, cyanogen fluoride, cyanogen and cyanoacetylene) have been computed by means of a series of ab initio molecular orbital calculations, at the second order level of Møller–Plesset perturbation theory, using the 6-31G∗∗ basis set. This work extends the calculations of the structures, energetics and Mulliken atomic charges of the same series of complexes, reported earlier. The vibrational properties, specifically the complex–monomer wavenumber shifts and the B⋯N stretching and BF3 librational wavenumbers and their associated force constants, have been correlated with the computed interaction energies, corrected for basis set superposition error and for zero-point energy difference.

Cationic Polymerization of Benzoxazine Monomers by Boron Trifluoride Complex

Cationic Polymerization of Benzoxazine Monomers by Boron Trifluoride Complex

Strength of Lewis acid–Lewis base interactions. A 13C NMR study of the ether interchange in boron trifluoride complexes

The intramolecular chemical shift difference previously used for calibration of Bronsted acid strengths (the Δδ method) has been extended to the study of Lewis acid–base interactions. The exchange between an ether complexed with boron trifluoride and another ester is fast on the 13C NMR timescale (75.4 MHz, 22 °C) and allows the determination of the equilibrium constant by interpolation of chemical shifts. Using boron trifluoride diethyl etherate as the standard, equilibrium constants for the reaction (Et2O·BF3 + ROR′⇌Et2O + RR′O·BF3) have been measured both in dichloromethane and without solvent for R, R′: Bu, Bu; Me2CH, Me2CH; Me, CH2CH2Cl; CH2CH2Cl, CH2CH2Cl; Me, C6H5; Et, C6H5. The values agree in some cases with literature values obtained by other methods and do not agree in other cases. The electronic and steric effects of substituents upon the stability of complexes are evidenced in the results.

The vibrational spectra of the boron halides and their molecular complexes. Part 4. Ab initio predictions of the structures and vibrational spectra of the complexes of boron trifluoride with dimethyl ether and dimethyl sulphide

The optimized structures and vibrational spectra of the 1:1 complexes of boron trifluoride with dimethyl ether and dimethyl sulphide have been determined by means of a series of ab initio calculations using the gaussian-90 computer program at the Hartree-Fock level with the 6–31G ∗∗ basis set. The results have been rationalized on the basis of the interactions of the Lewis acid (BF 3) with a hard ((CH 3) 2O) and a soft ((CH 3) 2S) base. The magnitudes of the wavenumber shifts, both for the acid and the base fragments, are far larger for the complex with the hard than with the soft base. The computed results have been used as aids in the interpretation of the infrared spectra of BF 3 co-condensed with (CH 3) 2O and with (CH 3) 2S in cryogenic matrices, to be reported in a forthcoming publication.

The Vibrational Spectra of the Boron Halides and Their Molecular Complexes. 3. Ab Initio Predictions of the Structures, Energetics, and Mulliken Atomic Charges of the Complexes of Boron Trifluoride with Some Linear Nitrogen Donors

The structures of the 1:1 electron donor−acceptor complexes of boron trifluoride with a number of linear nitrogen bases (N2, N2O, HCN, FCN, C2N2, and HCCCN) have been optimized by means of a series...

ChemInform Abstract: Electrophilic Reaction of Pyridine, Quinoline, Isoquinoline, Their N‐ Oxides and Their Boron Trifluoride Complexes Through Base‐Induced Deprotonation

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Electrophilic Reaction of Pyridine, Quinoline, Isoquinoline, Their N-Oxides and Their Boron Trifluoride Complexes through Base-induced Deprotonation

Electrophilic Reaction of Pyridine, Quinoline, Isoquinoline, Their N-Oxides and Their Boron Trifluoride Complexes through Base-induced Deprotonation

The structure of the 2-methylacrolein boron trifluoride complex in the crystalline phase and in solution

A crystalline 1:1 complex of BF 3 and 2-methylacrolein has been isolated and shown to have molecular structure 1. 1H NMR molecular dynamics and NOE studies have demonstrated that the same s-trans structure of the complex predominates at 185 K in CD 2Cl 2 solution. The relevance of these results to the enantioselectivity of Diels-Alder reactions with chiral Lewis acids is discussed.

A study of the electronic structures of boron trifluoride complexes with carbonyl compounds by ab initio MO methods

The syn-CH 3 CHO-BF 3 complex is only 1.22 kcal mol -1 less stable than the corresponding anti-CH 3 CHO-BF 3 complex at the MP2/6-31G* level of theory. The corresponding difference in syn- and anti-PhCHO-BF 3 complexes is 5.31 kcal mol -1 . The calculated C-C=O (129 o ) and C-O-B (156 o ) angles for syn-PhCHO-BF 3 complexes have a much greater deviation from the standard geometries of a sp2 orbital than that (123.9 o and 125.4 o ) calculated for syn-CH 3 CHO-BF 3 complexes

A UV photoelectron spectroscopic study of addition compounds of boron trifluoride with methyl-substituted pyridines

Vertical ionization energies of the 1 : 1 molecular complexes of boron trifluoride with the three picolines and 3,5-lutidine are reported along with assignments based on their HeI photoelectron spectra and semi-empirical molecular orbital calculations. The shift in the lone pair (n N) orbital of the donor molecules towards a higher ionization energy (IE) upon complexation is found to be essentially constant in all the complexes (nearly 2.8 eV) except in 3,5-lutidine·BF 3 where the shift is 3.3 eV. Such shifts in the IEs of the π orbital are about 1.1 eV for the 2- and 3-picoline complexes and 1.3 eV for the complexes of 4-picoline and 3,5-lutidine. These shifts reflect the relative stabilities of the complexes. The complex 2,6-lutidine·BF 3 undergoes dissociation into the free donor and acceptor molecules under the conditions of our experiment. A comparison of the shifts is made with the experimental heats of reaction of the pyridine bases with boron trifluoride. Relative stabilities of the complexes as deduced from ab initio and AM1 calculations are compared with predictions of gas-phase basicities of the bases.

Intramolecular electron transfer in the novel photoreaction of some β,γ-unsaturated oxime–boron trifluoride complexes. A new synthetic path to dihydroisoxazoles

β, γ-Unsaturated oximes are photochemically reactive in benzene solution when irradiated in the presence of boron trifluoride–diethyl ether; typically 2,2-dimethyl-4,4-diphenylbut-3-enal oxime affords a low yield of 2,2-diphenyl-3,3-dimethylcyclopropanecarboxaldehyde by the aza-di-π-methane rearrangement, and a principal product (48%) identified by X-ray diffraction analysis as 4, 4-dimethyl-5-(diphenylhydroxymethyl)-4,5-dihydroisoxazole.

ChemInform Abstract: Synthesis, Stereochemistry, and Isomerization of 4‐Aryl‐5‐aroyl‐2‐methyl‐2‐imidazolines.

AbstractTreatment of the trans‐ (I) or cis‐arylaroylaziridine boron trifluoride complexes (V) with methyl thiocyanate (II) gives regio‐ and stereoselectively the cis‐ (III) or trans‐imidazolines (VI) which are converted to the free bases (IV) or (VII) upon treatment with triethylamine.

ChemInform Abstract: Synthesis of Azetidin‐3‐ones by Heterocyclization of α‐Cyclohexylamino‐α′,β′‐epoxy Ketones.

AbstractThermal treatment of the boron trifluoride complexes (I) of amino epoxy ketones gives hydroxymethylazetidinones (II) which are converted to the derivatives (III), (V), and (VI).

ChemInform Abstract: Synthesis of Pyrrolidine Derivatives by Improved Aminoselenation via Addition of Boron Trifluoride Complex of Dihomoallylcuprate to Aldimines Containing α‐Hydrogen.

AbstractThe unsaturated amines (III) derived from the imines (I) are cyclized and selenenylated to give the phenylselenenylmethylpyrrolidines (V) which are reduced, forming the methylpyrrolidines (VI).

ChemInform Abstract: The Molecular Structures of Complexes of Pyridine with Boron Trifluoride, Boron Trichloride and Boron Tribromide as Studied by Gas Phase Electron Diffraction.

Abstract The molecular structures of pyridine complexes with boron trifluoride, boron trichloride and boron tribromide have been determined from gas electron-diffraction data. The molecular parameters of the boron trifluoride complex are r g (NB) = 1.669(7) A, r g (BF) = 1.366(2) A, ∠FBF = 113.3(4)°, r g (CN) = 1.345(6) A and r g (CC) = 1.382(4) A. The corresponding values for the boron trichloride complex are 1.706(12) A, 1.830(3) A, 112.5(3)°, 1.360(10) A and 1.390(6) A, and those of boron tribromide complex are 1.694(17) A, 1.986(3) A, 111.9(3)°, 1.362(12) A and 1.392(8) A. On complex formation the structure change of the acceptor molecules is much larger than that of the donor molecule and increases with the increase of atomic number of the halogen atoms.

The molecular structures of complexes of pyridine with boron trifluoride, boron trichloride and boron tribromide as studied by gas phase electron diffraction

The molecular structures of pyridine complexes with boron trifluoride, boron trichloride and boron tribromide have been determined from gas electron-diffraction data. The molecular parameters of the boron trifluoride complex are r g(NB) = 1.669(7) Å, r g(BF) = 1.366(2) Å, ∠FBF = 113.3(4)°, r g(CN) = 1.345(6) Å and r g(CC) = 1.382(4) Å. The corresponding values for the boron trichloride complex are 1.706(12) Å, 1.830(3) Å, 112.5(3)°, 1.360(10) Å and 1.390(6) Å, and those of boron tribromide complex are 1.694(17) Å, 1.986(3) Å, 111.9(3)°, 1.362(12) Å and 1.392(8) Å. On complex formation the structure change of the acceptor molecules is much larger than that of the donor molecule and increases with the increase of atomic number of the halogen atoms.

Epoxy resin cure III: Boron trifluoride catalysts

AbstractBoron trifluoride forms complexes with nitrogen‐and oxygen‐containing Lewis bases. These acid–base complexes are sometimes added to epoxy resins to accelerate their cure at elevated temperature (120°C–160°C). Several possible processing concerns with the use of boron trifluoride complexes have been investigated. It was shown that each complex can be readily identified by its distinct fluorine‐19 NMR spectrum. All of the boron trifluoride complexes are converted to fluoroboric acid under normal epoxy resin cure conditions. The fluoroboric acid is the true catalyst for epoxy resins. Experimental results show that fluoroboric acid does not catalyze the polymerization of an epoxy resin at room temperature. Finally, it was shown that fluoroboric acid is not hydrolyzed to hydrofluoric acid.

1H, 19F and 11B nuclear magnetic resonance characterization of BF 3: amine catalysts used in the cure of C fibre-epoxy prepregs

1H, 19F and 11B nuclear magnetic resonance studies are reported which characterize the complexes of boron trifluoride with monoethylamine and with piperidine, BF 3:NH 2C 2H 5 and BF 3:NHC 5H 10, respectively. These complexes are used as catalysts for the cure of high performance C fibre-epoxy composities from prepregs. The chemical compositions of commercial BF 3:amine complexes are variable and contain BF 4 − and BF 3(OH) − salts together with other unidentified highly reactive species. The BF 3:amine complexes, which are susceptible to hydrolysis, also partially convert to the BF 4 − salt (i.e. BF 4 −NH 3 +C 2H 5) upon heating. This salt formation is accelerated in dimethyl sulphoxide solution and in the presence of the epoxides that are present in commercial prepregs. Commercial C fibre-epoxy prepregs are shown to contain either BF 3:NH 2C 2H 5 or BF 3:NHC 5H 10 species together with their BF 4 − salts and a variety of boron-fluorine or carbon-fluorine prepreg species. Considerable variation in the relative quantities of BF 3:amine to its BF 4 − salt was observed from prepreg lot to lot, which will cause variable viscosity-time-temperature prepreg cure profiles. It is concluded that the chemically stable and mobile BF 4 − salt is the predominant catalytic species, acting as a cationic catalyst for the prepreg cure reactions. During the early stages of cure the BF 3:amine catalysts convert to the BF 4 − salts in the presence of epoxides, whereas the BF 3-prepreg species are susceptible to catalytic deactivation and immobilization.