Super Lewis Acid Research Articles

Ab initio investigation on the mechanism of SO2 activation by P/B intermolecular frustrated Lewis pairs.

In silico study investigates the activation of sulfur dioxide by newly designed frustrated Lewis pairs, i.e., [P(tBu)3…B(C2NBSHF2)3], where the Lewis acid part is a super Lewis acid. The activation process involves the making of P-S and B-O bonds, leading to the formation of an FLP-SO2 adduct. The calculated results demonstrate that the activation of SO2 by the FLP is almost barrierless and exothermic. Exploration of the impact of the solvent environment on the feasibility and energetics of the reaction has been investigated. The exothermicity is increasing in nonpolar solvents. This study focuses on understanding the electronic activity of SO2 activation by FLP with the help of the Minnesota 06 functional, M06-2X (global hybrid functional with 54% HF exchange) along with Pople's basis set, 6-311G (d, p). Principal interacting orbital and extended transition state-natural orbitals for chemical valence studies, giving impactful insight into the favorable orbital interaction and electron transfer in this reaction. Furthermore, useful CDFT descriptors such as reaction force constant and reaction electronic flux profiles along the intrinsic reaction coordinate give insights into the synchronicity and total electronic activity of the reaction.

Regioselective Functionalization of Arenes Using Iron Triflimide Catalysis

AbstractHere we present our development of the super Lewis acid, iron(III) triflimide as an activating agent of N-halo- and N-thioaryl succinimides for the regioselective functionalization of arenes. We also describe how the iron(III)-catalyzed halogenation reactions were further exploited by combination with copper(I)-catalyzed Ullmann-type coupling reactions for the development of one-pot, multistep processes, including intermolecular aryl C–H amination. This Account also illustrates intramolecular versions of these one-pot processes for the preparation of benzannulated heterocycles, as well as the application of these methods for the synthesis of biologically active compounds and natural products.1 Introduction2 Iron(III)-Catalyzed Halogenation of Arenes3 One-Pot Intermolecular Aryl C–H Amination4 One-Pot Intramolecular C–N, C–O, and C–S Bond-Forming Processes5 Iron(III)-Catalyzed Thioarylation of Arenes6 Synthesis of Phenoxathiins and Phenothiazines Using Lewis Acid and Lewis Base Catalysis7 Conclusions

One-Pot Synthesis of Diaryl Sulfonamides using an Iron- and Copper-Catalyzed Aryl C–H Amidation Process

AbstractA one-pot, two-stage synthesis of diaryl sulfonamides using sequential iron and copper catalysis is developed. Regioselective para-iodination of activated arenes by the super Lewis acid, iron triflimide and N-iodosuccinimide (NIS), is followed by a copper(I)-catalyzed N-arylation reaction. The process is found to be applicable for the coupling of a range of anisoles, anilines and acetanilides with primary sulfonamides and is used for the one-pot synthesis of biologically important compounds.

Thioarylation of anilines using dual catalysis: two-step synthesis of phenothiazines.

A two-step synthesis of phenothiazines has been developed using a dual-catalytic ortho-thioarylation reaction of anilines as the key step. Activation of N-(2-bromophenylthio)succinimide was achieved using the super Lewis acid, iron(III) triflimide and the Lewis base, diphenyl selenide, resulting in an accelerated and efficient ortho-thioarylation reaction of various protected aniline derivatives and less reactive, unprotected analogues. The thioarylated adducts were then cyclised to the desired phenothiazines using either an Ullmann-Goldberg or Buchwald-Hartwig coupling reaction. The dual catalytic thioarylation and copper(I)-catalysed cyclisation approach was used for the four-step synthesis of methopromazine, a neuroleptic agent with antipsychotic activity.

Oxathiaborolium-Catalyzed Enantioselective [4 + 2] Cycloaddition and Its Application in Lewis Acid Coordinated and Chiral Lewis Acid Catalyzed [4 + 2] Cycloaddition.

The nascency of second-generation sulfur-stabilized borenium cations by halophilic Lewis acid SnCl4 leads to highly active chiral Lewis acids that are very effective catalysts for [4 + 2] cycloaddition. Oxathiaborolium pentachlorostannate (5-10 mol %) successfully catalyzed cycloaddition of various dienes and dienophiles to afford cycloadducts with excellent enantioselectivity (20 examples, up to 99% ee). This super Lewis acid also exhibited good enantioselectivity for the first Lewis acid coordinated and chiral Lewis acid catalyzed [4 + 2] cycloaddition to α,β-unsaturated mixed ester amide.

Superhalogens as Building Blocks of Super Lewis Acids.

Lewis acids play an important role in synthetic chemistry. Using first-principle calculations on some newly designed molecules containing boron and organic heterocyclic superhalogen ligands, we show that the acid strength depends on the charge of the central atom as well as on the ligands attached to it. In particular, the strength of the Lewis acid increases with increasing electron withdrawing power of the ligand. With this insight, we highlight the importance of superhalogen-based ligands in the design of strong Lewis acids. Calculated fluoride ion affinity (FIA) values of B[C2 BNO(CN)3 ]3 and B[C2 BNS(CN)3 ]3 show that these are super Lewis acids.

Production of Jet Fuel-Range Hydrocarbons from Hydrodeoxygenation of Lignin over Super Lewis Acid Combined with Metal Catalysts.

Super Lewis acids containing the triflate anion [e.g., Hf(OTf)4 , Ln(OTf)3 , In(OTf)3 , Al(OTf)3 ] and noble metal catalysts (e.g., Ru/C, Ru/Al2 O3 ) formed efficient catalytic systems to generate saturated hydrocarbons from lignin in high yields. In such catalytic systems, the metal triflates mediated rapid ether bond cleavage through selective bonding to etheric oxygens while the noble metal catalyzed subsequent hydrodeoxygenation (HDO) reactions. Near theoretical yields of hydrocarbons were produced from lignin model compounds by the combined catalysis of Hf(OTf)4 and ruthenium-based catalysts. When a technical lignin derived from a pilot-scale biorefinery was used, more than 30 wt % of the hydrocarbons produced with this catalytic system were cyclohexane and alkylcyclohexanes in the jet fuel range. Super Lewis acids are postulated to strongly interact with lignin substrates by protonating hydroxyl groups and ether linkages, forming intermediate species that enhance hydrogenation catalysis by supported noble metal catalysts. Meanwhile, the hydrogenation of aromatic rings by the noble metal catalysts can promote deoxygenation reactions catalyzed by super Lewis acids.

Design of stereoelectronically promoted super lewis acids and unprecedented chemistry of their complexes.

A new family of stereoelectronically promoted aluminum and scandium super Lewis acids is introduced on the basis of state-of-the-art computations. Structures of these molecules are designed to minimize resonance electron donation to central metal atoms in the Lewis acids. Acidity of these species is evaluated on the basis of their fluoride-ion affinities relative to the antimony pentafluoride reference system. It is demonstrated that introduced changes in the stereochemistry of the designed ligands increase acidity considerably relative to Al and Sc complexes with analogous monodentate ligands. The high stability of fluoride complexes of these species makes them ideal candidates to be used as weakly coordinating anions in combination with highly reactive cations instead of conventional Lewis acid-fluoride complexes. Further, the interaction of all designed molecules with methane is investigated. All studied acids form stable pentavalent-carbon complexes with methane. In addition, interactions of the strongest acid of this family with very weak bases, namely, H2, N2, carbon oxides, and noble gases were investigated; it is demonstrated that this compound can form considerably stable complexes with the aforementioned molecules. To the best of our knowledge, carbonyl and nitrogen complexes of this species are the first hypothetical four-coordinated carbonyl and nitrogen complexes of aluminum. The nature of bonding in these systems is studied in detail by various bonding analysis approaches.

Synthesis of Sulfated Pt/ZrO2 Catalysts Using Different Precipitants for n-Hexane Hydroisomerization

AbstractAmmonia (AOH), dimethylamine (DME) and triethanolamine (TEA) as precipitants were used to prepare Pt-SO42-/ZrO2 catalysts, and the crystalline structures, textural structures and surface acid properties of the catalyst samples were characterized and n-hexane hydroisomerization activity over the samples were investigated. DME and TEA as the precipitants would delay the crystallization process. The organic amines were difficult to remove during the washing process, leading to the rinsing times increase, which probably decreased the catalyst BET area. Super Lewis acid sites in SZ catalysts would play very important roles in catalytic hydroisomerization activity.

Trimethylsilyl Pentafluorophenylbis(trifluoromethanesulfonyl)methide as a Super Lewis Acid Catalyst for the Condensation of Trimethylhydroquinone with Isophytol.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Trimethylsilyl pentafluorophenylbis(trifluoromethanesulfonyl)methide as a super Lewis acid catalyst for the condensation of trimethylhydroquinone with isophytol.

Acid and vitamin E: Trimethylsilyl super Lewis acids, such as [C6F5C(Tf)2]− Me3Si+ and Tf3CSiMe3, are extremely active and highly effective catalysts for the regioselective condensation of trimethylhydroquinone with isophthyol to afford (±)-α-tocopherol (vitamin E; see scheme, Tf=CF3SO2.

Trimethylsilyl Pentafluorophenylbis(trifluoromethanesulfonyl)methide as a Super Lewis Acid Catalyst for the Condensation of Trimethylhydroquinone with Isophytol

Trimethylsilyl Pentafluorophenylbis(trifluoromethanesulfonyl)methide as a Super Lewis Acid Catalyst for the Condensation of Trimethylhydroquinone with Isophytol

A New Type of Silicon Super Lewis Acids for Polymerization of Silyl Vinyl Ethers

A New Type of Silicon Super Lewis Acids for Polymerization of Silyl Vinyl Ethers

Complexes of CO2, COS, and CS2 with the Super Lewis Acid BH4+ Contrasted with Extremely Weak Complexations with BH3: Theoretical Calculations and Experimental Relevance1

Structures and energies of the complexes of CO2, COS, and CS2 with BH4+, a super Lewis acid (1−4a), were calculated with the density functional theory (DFT) at the B3LYP/6-311+G** level. Each of the complexes 1−4a contains a hypercoordinate boron with a three-center two-electron (3c-2e) bond. Formation of 1−4a from the complexation of CO2, COS, and CS2 with BH4+ was calculated to be exothermic by 26−42 kcal/mol. At the same B3LYP/6-311+G** level calculations indicate that complexation of CO2, COS, and CS2 with neutral BH3 leads only to very weak complexes (1−4c) with relatively long B−O or B−S bonds. The computational results shed new light on related experimental studies of the ready and extremely mild superacid induced ionic hydrogenation of CO2, COS, and CS2 with NaBH4 to methane.

Enantioselective Diels-Alder reactions between cyclopentadiene and α,β-acetylenic aldehydes catalyzed by a chiral super Lewis acid

The first examples of catalytic enantioselective Diels-Alder reactions of cyclopentadiene and α,β-acetylenic aldehydes such as Bu 3SnCCCHO are described.