Isomerization of alkenes in the presence of Pd(acac)2-BF3OEt2 catalytic system

Positional isomerization of alkenes was studied in the presence of Pd(acac)₂ + 20BF₃OEt₂ catalytic system. The reactivity of alkenes decreases in the following order: 1-hexene > 1-heptene > 2-methyl-1-pentene > 4-methyl-2-pentene (cis + trans).     

Spectroscopic Study of the Interaction of the Pd(acac)(C3-acac)PPh3Complex with BF3OEt2 in the Presence of PPh3

The interaction between the components of a catalytic system Pd(acac)(C³-acac)PPh₃+nPPh₃+ mBF₃OEt₂(where n= 1–4, m= 0.25–4, and acac is the acetylacetonate ligand) in benzene is examined by UV and IR spectroscopy. With a relative excess of PPh₃(n> m), acacH and [Pd(acac)(PPh₃)₂]⁺BF^– ₄were the main products, whereas BF₂acac and a polynuclear complex of PdF₂with PPh₃also containing Pd²⁺(BF^– ₄)₂units were formed with a relative excess of BF₃OEt₂(n< m).     

Palladium - catalyzed dimerization of propene

Summary The insertion of the previously coordinated second molecule of propene into the Pd-C bond is the rate-determining step in the dimerization of propene with the Pd(acac)₂ + BF₃OEt₂ catalyst system. Tetracoordinated square planar Pd hydrides bearing two vacant coordination sites are likely to be catalytically active species in the dimerization of propene. The simplicity of the catalyst system composition might be of industrial importance.     

Characterization of acid sites on the external surface of zeolites

Styrene oligomerization in the presence of Pd(acac)₂+PPh₃+BF₃OEt₂ catalytic system (acac—acetylacetonate) has been studied. Styrene conversion at optimum conditons (T=343 K, B/Pd=7, P/Pd=2) was as high as 75,000 mol of C₃H₃ per mol of Pd in 7 h with a selectivity to dimers, mostly 1,3-diphenylbut-1-ene, up to 93%.     

High-efficiency catalysts for norbornene polymerization, based on palladium carboxylates and boron trifluoride

Catalytic systems based on palladium carboxylates and boron trifluoride etherate were studied in the reaction of additive polymerization of nonbornene. The system Pd(OAc)₂ + 25BF₃OEt₂ exhibits a high activity, up to 154 100 kg of nonbornene per mole of Pd per hour.     

Fluoroaziridines as novel substrates in the modified Petasis reaction: synthesis of monofluorinated propargyl amines

Reaction of 2-fluoroaziridines with potassium alkynyltrifluoroborates in the presence of BF₃·OEt₂ leads to fluorinated propargyl amines in moderate to good yields. The reaction proceeds as an in situ isomerization of 2-fluoroaziridines to α-fluorinated imines, followed by the reaction of the imine with alkynyldifluoroborane, which is generated in situ from the potassium alkynyltrifluoroborates and BF₃·OEt₂.     

The Structure of Pd2(CH≡CC6H5)2(C5H7O2)3(BF3)2BF4

IR and NMR data showed that the ionic complex Pd₂(CHCC₆H₅)₂(C₅H₇O₂)₃(BF₃)₂BF₄ isolated in the reaction Pd(Acac)₂ + PA + 5BF₃OEt₂ (Acac is C₅H₇O₂, PA is phenylacetylene) is an adduct of two complexes, namely, (Acac)PdBF₄ and [(PA)₂Pd(C³-Acac · BF₃)]⁺(Acac · BF₃)^– (coordinatively unsaturated). On dissolution in deuteroacetone or deuteromethanol, the [(Acac)PdF₂BF₂Pd(C³-Acac · BF₃)(PA)₂]⁺(Acac · BF₃)^– adduct decomposed to Pd(Acac)₂, 2BF₃ · L (L = (CD₃)₂CO, CD₃OD) and the [L(PA)₂Pd(C³-Acac]⁺BF₄ ^– complex.     

Synthesis and structure of (acetylacetonato-κ<Superscript>2</Superscript>-O,O′)(bistriphenylphosphine)palladium tetrafluoroborate as a precursor of catalysts active in the conversion of unsaturated hydrocarbons

An X-ray diffraction analysis is carried out for the complex [Pd(Acac)(PPh₃)₂]BF₄ (I), which is a precursor of the active complexes of styrene dimerization and norbornene additive polymerization in the system [(Acac)Pd(PPh₃)₂]BF₄-BF₃ · OEt₂. In complex I the palladium atom is coordinated by two oxygen atoms of the acetylacetonate ligand and two phosphorus atoms of the triphenylphosphine ligands at the vertices of the distorted square.     

1H和19F NMR研究镍系催化丁二烯聚合中醇类对BF3·Oet2的增溶作用

The solubility of BF₃OEt₂ in hydrogenated gasoline was improved greatly by means of premixing BF₃OEt₂ with C₃H₁₇OH in nickel catalyst system, so that the effeciency of fluorine in the system was increased markedly. It is confirmed that there was a intermolecular hydrogen bond between alcohol and BF₃OEt₂ molecules by using ¹H NMR, which was a vital factor to lead the solubilization of BF₃OEt₂ in hydrogenated gasoline. Otherwise, the caculation formula of the chemical shift ofproton in hydroxy, ¹H = xipi,was suggested in hydrogen bond system.     

Monomer-isomerization oligomerization of 2-ethyl-1,3-butadiene by acid catalysts

The cationic oligomerization of 2-ethyl-1,3-butadiene (2EBD) by a superacid (CF₃SO₃H) and a superacid derivative (CH₃COClO₄) accompanied monomer isomerization to 3-methyl-1,3-pentadiene (3MPD) before propagation to yield oligomers of the isomerized monomer as main products in benzene at 50°C. Detection of 3MPD in the reaction mixture and ¹H-NMR structural analysis of the produced oligomers confirmed the occurrence of this “monomer-isomerization oligomerization.” On the other hand, in the presence of a metal halide catalyst (BF₃OEt₂) 2EBD reacted without isomerization and yielded oligomers that were different from those produced by the foregoing superacid catalysts. Monomer isomerization was suppressed in a polar solvent [(CH₂Cl)₂] or at lower temperatures. The mechanism of the oligomerization with monomer isomerization was discussed.     

Palladium‐Catalyzed Direct C2 Arylation of N‐Substituted Indoles with 1‐Aryltriazenes

A novel and efficient palladium‐catalyzed C2 arylation of N‐substituted indoles with 1‐aryltriazenes for the synthesis of 2‐arylindoles was developed. In the presence of BF₃ ? OEt₂ and palladium(II) acetate (Pd(OAc)₂), N‐substituted indoles reacted with 1‐aryltriazenes in N,N‐dimethylacetamide (DMAC) to afford the corresponding aryl–indole‐type products in good to excellent yields.     

Cationic palladium(II)–acetylacetonate complexes bearing pyridinyl imine ligands as catalysts for the hydroamination of phenylacetylene and polymerization of norbornene

Acetylacetonate palladium(II) complexes bearing pyridinyl imine ligands [Pd(acac)(L)]BF₄ were synthesized via nitrile displacement in [Pd(acac)(MeCN)₂]BF₄ by the bidentate ligands L of type 2-C₅H₄N–CH=N–(CH₂)_nOMe or 2-C₅H₄N–CH=N–Ar. The structures of complexes were analyzed by X-ray diffractometry, NMR, and DFT. The complexes catalyze hydroamination of phenylacetylene with aniline to give the Markovnikov imine product as well as polymerization of norbornene.     

Regioselective synthesis of trifluoromethyl group containing allylic amines by palladium-catalyzed allylic amination and sequential isomerization

The palladium-catalyzed regioselective allylic amination of the α-trifluoromethyl group-substituted allyl acetate has been accomplished using Pd(OAc)₂/DPPE and [Pd(π-allyl)(cod)]BF₄/DPPF as catalysts. The selective formation of the γ-product was attained in the presence of Pd(OAc)₂/DPPE, while the α-product was obtained using [Pd(π-allyl)(cod)]BF₄/DPPF. We also succeeded in the regioselective synthesis of the enantiomerically enriched aminated product from chiral allyl acetate using Pd(OAc)₂/DPPE and [Pd(π-allyl)(cod)]BF₄/(S)-BINAP. Furthermore, we found that kinetic resolution had occurred during the isomerization step from the γ-type product to the α-type product by the [Pd(π-allyl)(cod)]BF₄/(S)-BINAP catalyst.     

1,4-Dihydropyridine/BF3OEt2 for the reduction of imines: Influences of the amount of added BF3OEt2 and the substitution at N-1 and C-4 of the dihydropyridine ring

We have evaluated four 1,4-dihydropyridines (DHPs 1a, 1b, 1c and 1d) as reducing agents, which presented free (hydrogenated) or phenyl-substituted N-1 and C-4 positions of the DHP ring. Reactions combining each of the DHP and different amounts of BF₃OEt₂ were evaluated for the reduction of imine 2a (N-benzylideneaniline). DHP simultaneously substituted at N-1 and C-4 (1a), and DHP substituted at C-4 (1b) gave lower yields for reduction of 2a in comparison with DHPs 1c and 1d (both unsubstituted at the C-4 position). By evaluating the amount of added BF₃OEt₂ to the reaction mixture, we have found that DHP 1c (substituted at N-1) provided its best yield for amine 3a (82%) when associated with stoichiometric amounts BF₃OEt₂, while DHP 1d (N-1- and C-4-unsubstituted derivative) was more effective (90% yield) with catalytic quantities of the Lewis acid. The reaction system using DHP 1c under stoichiometric BF₃OEt₂ could also be successfully applied with additional imine examples and under reductive amination conditions.     

A short and stereoselective synthesis of the (±) Prelog-Djerassi lactonic acid

Reaction of meso-4-carbomethoxy-2-methylpentanal ($\text{1}$) with crotyltri-n-butyltin at ?78°C in the presence of 1 eq BF₃·OEt₂, followed by the lactonization with BF₃·OEt₂, gave 6-(1-methylallyl)-3,4,5,6-tetrahydro-3,5-dimethyl-2-pyranone ($\text{2a}$) with the correct stereochemistry (erythro, anti-Cram) in 92% yield, which was converted to the title compound ($\text{3}$) in 85% yield upon the ozonolytic cleavage of the double bond.     

Concerning reversal of diastereoselectivity in the BF3 promoted addition of crotyl—organometallic compounds to aldehydes

The addition of a mixture of benzaldehyde and BF₃·OEt₂ to crotyl-organometallic reagents C₄H₇MLn (1) (M = Cu, Cd, Hg, Tl, Ti, Zr and V) produces predominantly the erythro homoallyl alcohol as well as the α-adduct, while without BF₃·OEt₂ the threo isomer is formed preferentially.     

PEG-400 as green reaction medium for Lewis acid-promoted cycloaddition reactions with isoeugenol and anethole

A simple and efficient one-pot method for the synthesis of new 2,4-diaryl-1,2,3,4-tetrahydroquinolines using a three-component imino Diels-Alder cycloaddition between trans-isoeugenol or trans-anethole, anilines, and benzaldehyde in the presence of BF₃·OEt₂ in PEG-400, a green and reusable solvent, has been developed. Also, BF₃·OEt₂-catalyzed formal [3+2] cycloaddition reaction of trans-isoeugenol or trans-anethole with 1,4-benzoquinone in PEG-400 to give dihydrobenzo[b]furan derivatives has been described.     

BF3·OEt2-initiated polymerization of 2-methylene-1,3-dioxepanes

BF₃·OEt₂-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF₃·OEt₂-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF₃·OEt₂-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873–881, 1998     

Controlled/living cationic polymerization of styrene with BF3OEt2 as a coinitiator in the presence of water: Improvements and limitations

The controlled/living cationic polymerization of styrene using R-OH/BF₃OEt₂ (R-OH = 1-phenylethanol (1), 2-phenyl-2-propanol (2) and 1-(4-methoxyphenyl)ethanol (3)) at 0 °C in CH₂Cl₂ and in the presence of water was investigated. With 1/BF₃OEt₂, the poor control over molecular weight and molecular weight distribution was ascribed to a competitive protonic initiation induced by water. The molecular weight of the polymers obtained with 2/BF₃OEt₂ and 3/BF₃OEt₂ at low water content ([H₂O] ? 0.11 M) increased in direct proportion to the monomer conversion in agreement with the calculated values, assuming that one initiator molecule generates one polymer chain, but the molecular weight distribution was found relatively broad (M_w/M_n ∼ 1.8). ¹H NMR analyses confirmed that polymerization proceeds via reversible activation of C-OH terminus, but some loss of hydroxyl functionality was revealed. Some trials using high water contents in the recipe ([H₂O] ? 1.6 M) produced only traces of polymer due to catalyst decomposition.     

Lewis acid-mediated [3+2] cycloaddition between hydrazones and olefins

[3+2] Cycloaddition between hydrazones and olefins was accelerated in the presence of a stoichiometric amount of BF₃·OEt₂ or a catalytic amount of Zr(OTf)₄, Hf(OTf)₄, or Sc(OTf)₃ under mild conditions. The corresponding pyrazolidine derivatives were obtained in moderate to high yields using this novel [3+2] Lewis acid catalysis.