Preparation of fructone catalyzed by water-soluble Brφnsted acid ionic liquids

Fructone(2-methyl-2-ethylacetoacetate-1,3-dioxolane),a flavouring material,has been synthesized from ethyl acetoacetate and glycol using five water-soluble Br(?)nsted acid ionic liquids as catalysts for the first time.The used Br(?)nsted acid ionic liquids include [Hmim]Tfa,[Hmim]Tsa,[Hmim]BF_4,[Bmim]HSO4,[Bmim]H_2PO_4,and[Hmim]BF_4 showed the highest catalytic activity for the preparation of fructone.After reaction,the product could be isolated from the reaction system automatically,and the ionic liquid could be directly reused without dehydration.     

An efficient procedure for protection of carbonyls in Brønsted acidic ionic liquid [Hmim]BF4

Protection of carbonyls as acetals or ketals using Brønsted acidic ionic liquid [Hmim]BF₄ as catalyst as well as solvent was investigated. Satisfactory results were obtained for the protection of carbonyls as cycloacetals or ketals with diols. The product can be separated conveniently from the reaction system, and the ionic liquid can be reused after removal of water.     

1-Methylimidazolium tetrafluoroborate [Hmim][BF4]: an efficient acidic ionic liquid catalyst for insertion of α-diazo compounds into the N–H bonds of amines

The reusable acidic ionic liquid, 1-methylimidazolium tetrafluoroborate [Hmim][BF₄], was found to be an effective catalyst for the insertion of α-diazoacetate into the N–H bonds of amines. The corresponding products were obtained in good yields and short reaction times via a simple procedure. The catalyst could be recycled and reused without any noticeable decrease in its activity.     

Selectfluor-mediated mild oxidative halogenation and thiocyanation of 1-aryl-allenes with TMSX (X = Cl,Br, I,NCS) and NH4SCN

Presence of TMSX (X = Cl, Br, I) unleashes the oxidative character of Selectfluor and provides a mild dihalogenation method for 1-arylallenes. Preference for 2,3-addition was observed with TMSCl in MeCN irrespective of the nature of the substituent on the aryl moiety, whereas 1,2-addition was preferred in [BMIM][BF₄]. With TMSBr and TMSI only products corresponding to 2,3-addition were observed. Reactions carried out with TMSBr in IL solvents gave the corresponding monobromoalkenes as a major product along with the isomeric dibromo-alkenes. Reaction with NH₄SCN provided convenient access to dithiocyanate derivatives. The same products were formed via TMS-NCS/Selectfluor. Formation of common products via TMSNCS and NH₄SCN points to the formation and interplay of SCN⁺/NCS⁺ as incipient electrophiles.     

Temperature-controlled highly selective dimerization of α-methylstyrene catalyzed by Brönsted acidic ionic liquid under solvent-free conditions

A temperature-controlled highly selective dimerization of α-methylstyrene to produce 2,4-diphenyl-4-methyl-1-pentene and 1,1,3-trimethyl-3-phenylindan was catalyzed by Brönsted acidic ionic liquid [Hmim]⁺BF₄⁻. At 60 °C, 2,4-diphenyl-4-methyl-1-pentene was formed in 93% selectivity with >92% conversion under a solvent-free condition while 1,1,3-trimethyl-3-phenylindan could be obtained in 100% selectivity when the reaction temperature was increased to 170 °C. The ionic liquid [Hmim]⁺BF₄⁻ could be reused with almost no loss of activity.     

ADDUCT FORMATION BETWEEN BISCYCLOPENTADIENYL TITANIUMDIFLUORIDE AND BORON TRIFLUORIDE AND PHOSPHORUS PENTAFLUORIDE

Abstract

The reactions of organoplatinum cations have been investigated over the past few years in this laboratory.¹ As part of a general program, we recently tried to synthesize the biscyclopentadienyltitanium dication, Cp₂Ti²⁺ (where Cp =pentahaptocyclopentadienyl). Reaction of Cp₂TiCl₂ with two equivalents of AgBF₄ (or AgPF₆) in acetone gave, after filtering and evaporating the reaction solution, a red oil. Treatment of this red oil with methanol caused immediate precipitation of yellow Cp₂TiF₂. The isolation of Cp₂TiF₂ has been reported previously from reactions involving fluorine-containing reagents such as silver salts of CF₃S^?2, BF₄ ^?, PF₆ ^?, SbF₆ ^? and AsF₆ ^?3. Methanolysis of bis(cyclopentadienyl) (ethyl-3-ketobutyrato)titanium hexafluorophosphate also yields Cp₂TiF₂ ⁴. This sort of transfer of fluorine from counter-ion to metal has recently been observed in the reactions of metal bistetrafluoroborates (M =Co²⁺, Ni²⁺ and Cu²⁺) with triethylenediamine and quinuclidene⁵ in refluxing tetrahydrofurandimethoxypropane azeotrope. The products in these cases were the metal difluorides and BF₃ adducts of the strong nitrogen bases. The phenomenon is not confined to transition metals. (CH₃)₂SnF₂ is formed in the reaction of (CH₃)₂SnCl₂ with two equivalents of AgBF₄ or AgPF₆ in methanol.⁶     

Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

Reaction of (TBBP)AlMe ? THF with [Cp*₂Zr(Me)OH] gave [(TBBP)Al(THF)?O?Zr(Me)Cp*₂] (TBBP=3,3’,5,5’‐tetra‐tBu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)?O?Zr(Me)Cp₂] with [PhMe₂NH]⁺[B(C₆F₅)₄]^? gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)?O?Zr(THF)Cp₂]⁺[B(C₆F₅)₄]^? (DIPPnacnac=HC[(Me)C=N(2,6‐iPr₂?C₆H₃)]₂). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40–47 kcal mol^?1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six‐membered‐ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal‐Me‐C angle that prevents synchronized bond‐breaking and making. A more‐likely pathway is dissociation of the Al‐O‐Zr complex into an aluminate and the active polymerization catalyst [Cp*₂ZrMe]⁺.     

Heck Reaction of Iodoarenes with Methyl Acrylate Catalyzed by Cyciopalladated Complexes of Tertiary Arylamines Immobilized in Ionic Liquid[ Bmim ] ^＋ BF4^-

Heck reaction of iodoarenes with methyl acrylate, catalyzed by cyclolmlladated complexes of tertiary arylamines, was investi-gated in ionic liquid 1-butyl-3-metylimidazolium tetratluorobo-rate ([Bmim] BF4^- ). The products can be isolated convenient-ly from the ionic liquid-catalyst system. The catalysts could be reused for more than 10 times still with satisfactory catalytic ac-tivity.     

Theoretical study of interactions between 1-alkyl-3-methyimidazolium tetrafluoroborate and dibenzothiophene: DFT,NBO, and AIM analysis

Density functional theory is employed to study the interaction energies between dibenzothiophene (DBT) and 1-alkyl-3-methylimidazolium tetrafluoroborate ([C _n mim]⁺[BF₄]^?). The structures of DBT, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim]⁺[BF₄]^?), 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]+[BF₄]?), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C₆mim]⁺[BF₄]^?), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]⁺[BF₄]^?), [C₂mim]⁺[BF₄]^?–DBT, [C₄mim]⁺[BF₄]^?–DBT, [C₆mim]⁺[BF₄]^?–DBT and [C₈mim]⁺[BF₄]^?–DBT systems are optimized systematically at the B3LYP/6-31G(d,p) level, and the most stable geometries are obtained by NBO and AIM analyses. The results indicate that DBT and imidazolium rings of ionic liquids are parallel to each other. It is found that the [BF₄]^? anion prefers to be located close to a C1–H9 proton ring in the vicinity of the imidazolium ring and the most stable gas-phase structure of [C _n mim]⁺[BF₄]^? has four hydrogen bonds between [C _n mim]+ and [BF₄]?. There are hydrogen bonding interactions, π–π and C–H–π interactions between [C₈mim]⁺[BF₄]^? and DBT, which is confirmed by NBO and AIM analyses. The calculated interaction energies for the studied ionic liquids can be used to interpret a better extracting ability of [C₈mim]⁺[BF₄]^? to remove DBT, due to stronger interactions between [C₈mim]⁺[BF₄]^? and DBT, in agreement with the experimental results of dibenzothiophene extraction by [C _n mim]⁺[BF₄]^?.     

Counterion Dynamics in an Interpenetrated Coordination Cage Capable of Dissolving AgCl

In solution, the eight BF₄^? counterions of a positively charged D₄‐symmetric interpenetrated [Pd₄ligand₈]⁸⁺ double cage ( 1 ) are localized in distinct positions. At low temperatures, one BF₄^? ion is encapsulated inside the central pocket of the supramolecular structure, two BF₄^? ions are bound inside the equivalent outer pockets, and the remaining five BF₄^? ions are located outside the cage structure (expressed by the formula [3 BF₄@ 1 ][BF₄]₅). On warming, the two BF₄^? ions in the outer pockets are found to exchange with the exterior ions in solution whereas the central BF₄^? ion stays locked inside the central cavity (here written as [BF₄@ 1 ][BF₄]₇). The exchange kinetics were determined by exchange spectroscopy (EXSY) NMR experiments and line‐shape fitting in different solvents. The tremendously high affinity of this double cage for the binding of two chloride ions inside the outer pockets allows for complete exchange of two BF₄^? ions by the addition of solid AgCl to give [2 Cl+BF₄@ 1 ][BF₄]₅. The uptake of the two chloride ions is allosteric and is thus accompanied by a structural rearrangement (compression along the Pd₄ axis) of the double cage structure. An analysis by using 900 MHz NOESY NMR spectroscopy shows that this compression of about 3.3 % is associated with a helical twist of 8°, which together resemble a screw motion. As a consequence of squeezing each of the outer two pockets by 53 %, the volume of the central pocket is increased by 43 %, which results in an increase of 36 % in the ¹⁹F spin‐lattice relaxation time (T₁) of the central BF₄^? ion. The packing coefficients (PC) for the ions in the outer pockets (103 % for BF₄^? and 96 % for Cl^?) were calculated.     

Chemical Transformations of 4,6-Dimethyl-2β-hydroxy-8-oxo-3,5,7-trioxatetracyclo[7.2.1.04,11.06,10]dodecane

Reactions of 4,6-dimethyl-2β-hydroxy-8-oxo-3,5,7-trioxatetracyclo-[7.2.1.0.^4,11.0^6,10]dodecane 1 with nucleophiles have been studied. Reaction of 1 with alcohols, triethylsilane, allyltrimethylsilane, and methylthiotrimethylsilane in CH₂Cl₂ in the presence of TiCL₄, gave the substitution products 2,7a, 7b, and 7c in 80-90% yields. The substitution reaction took place chemoselectively on the hemiacetal group of I. Reaction of 1 with cyanotrimethylsilane in CH₂C1₂ in the presence of TiCL₄, gave compound 8 and the rearranged product 9. The structure of 9 was proven by X-ray analysis.     

Expanded‐Ring N‐Heterocyclic Carbenes Efficiently Stabilize Gold(I) Cations,Leading to High Activity in π‐Acid‐Catalyzed Cyclizations

A series of six‐ and seven‐membered expanded‐ring N‐heterocyclic carbene (er‐NHC) gold(I) complexes has been synthesized using different synthetic approaches. Complexes with weakly coordinating anions [(er‐NHC)AuX] (X^?=BF₄^?, NTf₂^?, OTf^?) were generated in solution. According to their ¹³C NMR spectra, the ionic character of the complexes increases in the order X^?=Cl^?<NTf₂^?<OTf^?<BF₄^?. Additional factors for stabilization of the cationic complexes are expansion of the NHC ring and the attachment of bulky substituents at the nitrogen atoms. These er‐NHCs are bulkier ligands and stronger electron donors than conventional NHCs as well as phosphines and sulfides and provide more stabilization of [(L)Au⁺] cations. A comparative study has been carried out of the catalytic activities of five‐, six‐, and seven‐membered carbene complexes [(NHC)AuX], [(Ph₃P)AuX], [(Me₂S)AuX], and inorganic compounds of gold in model reactions of indole and benzofuran synthesis. It was found that increased ionic character of the complexes was correlated with increased catalytic activity in the cyclization reactions. As a result, we developed an unprecedentedly active monoligand cationic [(THD‐Dipp)Au]BF₄ (1,3‐bis(2,6‐diisopropylphenyl)‐3,4,5,6‐tetrahydrodiazepin‐2‐ylidene gold(I) tetrafluoroborate) catalyst bearing seven‐membered‐ring carbene and bulky Dipp substituents. Quantitative yields of cyclized products were attained in several minutes at room temperature at 1 mol % catalyst loadings. The experimental observations were rationalized and fully supported by DFT calculations.     

Activation of Strong Boron–Fluorine and Silicon–Fluorine σ‐Bonds: Theoretical Understanding and Prediction

The oxidative addition of BF₃ to a platinum(0) bis(phosphine) complex [Pt(PMe₃)₂] ( 1 ) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF₃ to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol^?1, respectively) and require large Gibbs activation energies (ΔG°^≠=56.3 and 38.9 kcal mol^?1, respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF₃ to 1 in the presence of a second BF₃ molecule occurs with ΔG°^≠ and ΔG° values of 10.1 and ?4.7 kcal mol^?1, respectively. ΔG°^≠ becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF₃, occurs from the dissociating fluoride to the second non‐coordinated BF₃. This CT interaction stabilizes both the transition state and the product. The B?F σ‐bond cleavage of BF₂Ar^F (Ar^F=3,5‐bis(trifluoromethyl)phenyl) and the B?Cl σ‐bond cleavage of BCl₃ by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF₄ to 1 easily occurs in the presence of a second SiF₄ molecule via the formation of a hypervalent Si species.     

Theoretical study on interactions between thiophene/dibenzothiophene/cyclohexane/toluene and 1-methyl-3-octylimidazolium tetrafluoroborate

It is critically important to understand the interactions between thiophene/dibenzothiophene/cyclohexane/toluene and 1-methyl-3-octylimidazolium tetrafluoroborate ([C8MIM]⁺[BF₄]^?) due to desulfurization by ionic liquids. In this work, the structures of thiophene, dibenzothiophene, cyclohexane, toluene, [C8MIM]⁺[BF₄]^?, [C8MIM]⁺[BF₄]^?-thiophene, [C8MIM]⁺[BF₄]^?-dibenzothiophene, [C8MIM]⁺[BF₄]^?-cyclohexane, and [C8MIM]⁺[BF₄]^?-toluene were optimized systematically at the GGA/PW91/DNP level, and the most stable geometries were performed by NBO and AIM analyses. It was found that [BF₄]^? anion tends to locate near C2–H2 and four hydrogen bonds between [C8MIM]⁺ and [BF₄]^? form in [C8MIM]⁺[BF₄]^?. There exist hydrogen bonds and C–H···π interactions between [C8MIM]⁺[BF₄]^? and thiophene/cyclohexane/toluene, while the hydrogen bonding interactions, π···π and C–H···π interactions occur between [C8MIM]⁺[BF₄]^? and dibenzothiophene confirmed by NBO and AIM analyses. The interaction energies between [C8MIM]⁺[BF₄]^? and thiophene, dibenzothiophene, cyclohexane, toluene are 18.83, 20.93, 6.83, 12.99 kcal/mol, showing the preferential adsorption of dibenzothiophene and thiophene by ionic liquid, in agreement with the experimental results of dibenzothiophene and thiophene extraction by [C8MIM]⁺[BF₄]^?.     

Halogen-Free Room-Temperature Brønsted Acidic Ionic Liquid [Hmim]+ HSO4 − as a Recyclable Green “Dual Reagent” Catalysis for the Synthesis of Triarylmethanes (TRAMs)

Abstract

The halogen-free Brønsted acidic ionic liquid methylimidazolium hydrogen sulfate ([Hmim]⁺ HSO₄ ^?) acts as a very efficient catalyst for the one-pot, two-component Baeyer condensation of a variety of aromatic aldehydes with dimethyl or diethyl aniline at room temperature. This “green” reagent behaves as both catalyst and solvent; that is, it exhibits “dual-reagent catalysis.” The room-temperature acidic ionic liquid could be recycled several times with almost no loss in the yield of the reaction. This is the first report of the Baeyer synthesis with a halogen-free ionic liquid.     

Chemical and electrochemical oxidation of metallocenes,reactions of metallocenes with mercury salts

The products of chemical and electrochemical oxidation of metallocenes, (C₅H₅)₂M (M  Fe, Ru, Os), were investigated. (C₅H₅)₂Fe on Pt and Hg anodes was oxidized to the ferricenium cation while the electrolysis of osmocene on Pt electrode led to the previously unknown (C₅H₅)₂Os^oBF₄^? salt and oxidation of ruthenocene yielded the unstable (C₅H₅)₂Ru²⁺ cation. On a mercury electrode Ru and Os metallocenes gave the adducts [(C₅H₅)₂M]₂Hg(BF₄)₂. The stability constants of mercury-containing complexes were calculated using the polarographic data. The chemical interaction of metallocenes with HgX₂ also gave mercury-containing adducts. Chemical oxidation of ruthenocene resulted in salts with the metal in the +4 formal oxidation state.     

Acetic acid functionalized ionic liquid systems: An efficient and recyclable catalyst for the regioselective ring opening of epoxides with NaN3

In the present study, an environmentally benign, efficient, and solvent-free procedure was developed for the synthesis of 1,2-azidoalcohols by the regioselective ring opening of some epoxides with sodium azide (NaN₃) in the presence of an acetic acid functionalized imidazolium salt [Cmmim]BF₄ or [Cmmim]Br as a green and Brønsted acidic ionic liquid (BAIL) catalyst under mild and neutral reaction conditions at 60 °C. The remarkable features of this procedure are excellent regioselectivity, simple work-up procedure, high yields of products, short reaction times, and ease of recyclability of ionic liquids.     

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH₃O₂CCH₂NH₃]⁺ (MeGlyH⁺) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonites [high‐purity montmorillonite (MMT)‐MeGlyH⁺] had larger interlayer spacing (12.69 Å) than montmorillonites without treatment (9.65 Å). The zirconocene catalyst system [Cp₂ZrCl₂/methylaluminoxane (MAO)/MMT‐MeGlyH⁺] had much higher Zr loading and higher activities than those of other zirconocene catalyst systems (Cp₂ZrCl₂/MMT, Cp₂ZrCl₂/MMT‐MeGlyH⁺, Cp₂ZrCl₂/MAO/MMT, [Cp₂ZrCl]⁺[BF₄]/MMT, [Cp₂ZrCl]⁺[BF₄]^?/MMT‐MeGlyH⁺, [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT‐MeGlyH⁺, and [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (Cp₂ZrCl₂/MAO/MMT‐MeGlyH⁺). MeGlyH⁺ and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1892–1898, 2002     

Ring opening of epoxides with alcohols using Fe(Cp)2BF4 as catalyst

Fe(Cp)₂BF₄ is an efficient catalyst for the alcoholysis of aromatic, aliphatic, and cyclic epoxides giving excellent yields of the corresponding β-alkoxy alcohols under ambient conditions. The methanolysis of styrene oxide using Fe(Cp)₂BF₄ as a catalyst (5 mol %) gave excellent yield of 2-methoxy-2-phenylethanol with complete regio-selectivity. The ring opening of cyclic epoxides gave 77–97% yields of trans-β-methoxy alcohols, in 0.5–6 h. The use of 1,2-epoxyhexane and 1,2-epoxydodecane as substrates gave both regioisomers in excellent yields. The first order rate of reaction with respect to catalyst was observed for the kinetics of ring opening of 1,2-epoxyhexane with methanol.     

Synthesis of 5-(perfluoroalkylmethyl)-1,3-dioxolan-4-ones

Acid catalysed condensation of F-alkyl α-hydroxy acids with simple aldehydes or ketones gave F-alkyl 1,3-dioxolan-4-ones. When BF₃,OEt₂ was used as the catalyst, the condensation products were obtained in moderate to good yields and the “cis” isomers are largely favoured, while with HOTs/H₂SO₄ as catalyst, poor yields and lower stereoselectivities were observed.