Catalyst 1a Research Articles

Assessing the ligand properties of 1,3-dimesitylbenzimidazol-2-ylidene in ruthenium-catalyzed olefin metathesis

The deprotonation of 1,3-dimesitylbenzimidazolium tetrafluoroborate with a strong base afforded 1,3-dimesitylbenzimidazol-2-ylidene (BMes), which was further reacted in situ with rhodium or ruthenium complexes to afford three new organometallic products. The compounds [RhCl(COD)(BMes)] (COD is 1,5-cyclooctadiene) and cis-[RhCl(CO)2(BMes)] were used to probe the steric and electronic parameters of BMes. Comparison of the percentage of buried volume (%V(Bur)) and of the Tolman electronic parameter (TEP) of BMes with those determined previously for 1,3-dimesitylimidazol-2-ylidene (IMes) and 1,3-dimesitylimidazolin-2-ylidene (SIMes) revealed that the three N-heterocyclic carbenes (NHCs) had very similar profiles. Nonetheless, changes in the hydrocarbon backbone subtly affected the stereoelectronic properties of these ligands. Accordingly, the corresponding [RuCl2(PCy3)(NHC)(=CHPh)] complexes displayed different catalytic behaviors in the ring-closing metathesis (RCM) of α,ω-dienes. In the benchmark cyclization of diethyl 2,2-diallylmalonate, the new [RuCl2(PCy3)(BMes)(=CHPh)] compound (1d) performed slightly better than the Grubbs second-generation catalyst (1a), which was in turn significantly more active than the related [RuCl2(PCy3)(IMes)(=CHPh)] initiator (1b). For the formation of a model trisubstituted cycloolefin, complex 1d ranked in-between catalyst precursors 1a and 1b, whereas in the RCM of tetrasubstituted cycloalkenes it lost its catalytic efficiency much more rapidly.

Recyclable Cyclohexanediamine Derivatives as Organocatalysts: Organocatalytic Reduction with Trichlorosilane and Aldol Reaction

Reduction of ketimine with trichlorosilane was carried out using bisformamide catalyst 1a derived from cyclohexanediamine to give the corresponding product in 81% yield with 39% ee. Deprotection of the formyl groups of the catalysts 1 gave the corresponding diamines 2 which were utilized in aldol reaction of acetone with 4-nitrobenzaldehyde. The reaction using 2b in brine afforded the aldol adduct in 81% yield with 29% ee.

Anchored [RuCl2(p-cymene)]2 in hybrid zirconium phosphate–phosphonate coated and pillared with double-stranded hydrophobic linear polystyrene as heterogeneous catalyst suitable for aqueous asymmetric transfer hydrogenation

A novel type of phosphonate-containing polystyrene copolymers 1a-e bearing an N'-alkylated TsDPEN chiral ligand and double-stranded polystyrene chains were prepared for the first time using simple radical copolymerization of 1-phosphonate styrene with (R,R)-N'-4'-vinylbenzyl-N-4-vinylbenzenesulfonyl-1,2-diphenylethylene-1,2-diamine. Through the coprecipitation of their supported Ru polystyrene copolymers 2a-e and NaH2PO4 with ZrOCl2, pillared hybrid zirconium phosphate-phosphonate-anchored Ru catalysts 3a-e and 4d1-d5 were obtained as heterogeneous catalysts suitable for aqueous asymmetric transfer hydrogenation. In the aqueous asymmetric transfer hydrogenation of aromatic ketones, the anchored Ru catalysts showed good catalytic activities, chemoselectivities (~100%), and enantioselectivities (73.6% ee to 95.6% ee). The Ru catalysts retained their catalytic properties even at the fifth recycle time (92.2% conv., 92.1% ee). However, corresponding supported Ru catalyst 3d' resulted in disappointing reusability because of the loss of ruthenium in every recycle process. The conversions of aromatic ketones were closely related to the o-, m- or p-positions of the substituents on the aromatic ring caused by shape-selective matching.

The influence of hydrophobic/hydrophilic balance of the mesoporous solid acid catalysts in the selective dehydration of fructose into HMF

The application of a number of mesoporous sulfonic acids including MCM-41–PrSO3H (1a), MCM-41–Ph–PrSO3H (1b), SBA-15–PrSO3H (2a), SBA-15–Ph–PrSO3H (2b), SBA-15–EtPhSO3H (3a), and SBA-15–Ph–EtPhSO3H (3b) with different surface hydrophobicity in acid-catalyzed dehydration of fructose into 5-hydroxymethylfurfural (HMF) in a water–nitromethane solvent mixture was investigated. Among the studied mesoporous solid acids, the catalysts with lower surface hydrophobicity and relative acidity were found to be more selective and efficient catalytic system for HMF production. Our studies showed that the hydrophilic surface of the employed solid acids might indeed provide a means of faster departure of HMF from the system mesopores as soon as it forms, thus retarding the rehydration of HMF to unwanted by-products and improving the HMF selectivity. HMF selectivity of 75% was reached in 93% fructose conversion in a water–NM system at 140 °C within 30 min in the presence of catalyst 2a, which is comparable or even superior to other systems which employ MIBK–2-butanol or other organic co-solvents.

Total replacement of solvent in polyurethane synthesis using carbon dioxide soluble 1,3‐dichlorodistannoxane catalysts

AbstractThis work demonstrates catalytic synthesis of polyurethanes using 1,3‐dichlorodistannoxane catalysts (1) in carbon dioxide (CO2) and carbon dioxide expanded liquids (CXL). Catalytic polyurethane synthesis was also performed in pure organic solvent (dimethylformamide) for comparison. In this study, mainly, 4, 4′‐methylene‐bis‐(phenyl isocyanate) (MDI) as the diisocyanate precursor and ethylene glycol (EG) as the diol precursor were used for polyurethane synthesis. In addition to MDI, hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and p‐isocyanatobenzylisocyanate (PIBI) were also used for polyurethane synthesis with different diols or triol in CO2. Polyurethanes with a molecular weight ranging from 3000 to 70,000 were synthesized depending upon the combination of diisocyanate and diol used. Comparable yields of polyurethanes were obtained using an all butyl group substituted (1a) catalyst in CO2 (55 bars, 50°C) and in DMF (50°C). Additionally, the yield and polydispersity index (PDI) of polymer formed in neat CO2 was comparable with those synthesized in the largely used organic solvent DMF. Interestingly, catalyst 1a in CXL (55 bars, 50°C) gave higher yields, and polymers with lower PDI (1.19). Reactions carried out in scCO2 at 145 bars using PIBI and EG were found to be about three times faster than the reaction carried out in DMF. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Direct Amidation of Carboxylic Acids Catalyzed by ortho-Iodo Arylboronic Acids: Catalyst Optimization, Scope, and Preliminary Mechanistic Study Supporting a Peculiar Halogen Acceleration Effect

The importance of amides as a component of biomolecules and synthetic products motivates the development of catalytic, direct amidation methods employing free carboxylic acids and amines that circumvent the need for stoichiometric activation or coupling reagents. ortho-Iodophenylboronic acid 4a has recently been shown to catalyze direct amidation reactions at room temperature in the presence of 4A molecular sieves as dehydrating agent. Herein, the arene core of ortho-iodoarylboronic acid catalysts has been optimized with regards to the electronic effects of ring substitution. Contrary to the expectation, it was found that electron-donating substituents are preferable, in particular, an alkoxy substituent positioned para to the iodide. The optimal new catalyst, 5-methoxy-2-iodophenylboronic acid (MIBA, 4f), was demonstrated to be kinetically more active than the parent des-methoxy catalyst 4a, providing higher yields of amide products in shorter reaction times under mild conditions at ambient temperature. Catalyst 4f is recyclable and promotes the formation of amides from aliphatic carboxylic acids and amines, and from heteroaromatic carboxylic acids and other functionalized substrates containing moieties like a free phenol, indole and pyridine. Mechanistic studies demonstrated the essential role of molecular sieves in this complex amidation process. The effect of substrate stoichiometry, concentration, and measurement of the catalyst order led to a possible catalytic cycle based on the presumed formation of an acylborate intermediate. The need for an electronically enriched ortho-iodo substituent in catalyst 4f supports a recent theoretical study (Marcelli, T. Angew. Chem. Int. Ed.2010, 49, 6840-6843) with a purported role for the iodide as a hydrogen-bond acceptor in the orthoaminal transition state.

Synthesis of Novel Bis(β‐enaminoketonato)titanium Catalyst with High Activity and Excellent Ability to Copolymerize Olefins

AbstractA new titanium complex [PhN=C(Ph)CHC(CF3)O]2TiCl2 (2a), with an asymmetric β‐enaminoketonato [N,O] ligand, has been synthesized and fully characterized. With modified methylaluminoxane as a cocatalyst, the behaviors of ethylene polymerization, and ethylene/α‐olefin and ethylene/norbornene copolymerization have been explored in detail. Relative to its regioisomer 2b ([PhN=C(CF3)CHC(Ph)O]2TiCl2), the present catalyst exhibits significant predominance. The catalytic activity in 2a‐catalyzed homo‐ and copolymerization are much higher than those in 2b‐catalyzed (co)polymerization. Furthermore, compared with 2b, catalyst 2a possesses an obviously stronger ability towards copolymerization, due to a wide coordination space caused by exchanging the position of the phenyl group and trifluoromethyl group on the framework.

Enantioselective Synthesis of 3,4-Dihydropyran Derivatives via Organocatalytic Michael Reaction of α,β-Unsaturated Enones

A simple chiral diamine catalyst (1a) was successfully applied in the asymmetric Michael reaction between cyclic dimedone and α,β-unsaturated ketones. Both acyclic enones with aryl or alkyl β-substituents and cyclic enones were tolerated well in the reaction. The desired adducts were obtained in high yields (up to 98%) with excellent enantioselectivities (up to 97% ee). The additives were found to increase the reactivity dramatically. The biologically active 2,4-disubstituted polyhydroquinoline scaffold was conveniently prepared through an ammoniation from the generated 3,4-dihydropyran product.

Asymmetric Epoxidation of Chromenes Using Manganese(III) Complexes with Novel Chiral Salen-like Schiff Base Ligands

Three novel chiral salen-like schiff base ligands and their Mn(III) complexes containing different amino acid unit have been synthesized and characterized. Asymmetric epoxidation reactions show these complexes are effective catalysts for the chromenes with buffer NaOCl as terminal oxidant and pyridine N-oxide as co-catalyst in the presence of ionic liquid. Good-to -excellent enantioselectivity and acceptable yields can be obtained under optimum reaction conditions. Catalyst 4c gives the highest ee (95%) for 6-chloro-2,2-dimethylchromene among these catalytic performances. Furthermore, compared the enantioselectivity of catalyst 4c with the other two catalysts 4a and 4b, the positive experimental results suggest that the steric effect of the ligands plays an important role in the asymmetric catalysis. Asymmetric epoxidation of chromenes with Mn (III) complex containing amino acid moiety

ChemInform Abstract: C3‐Symmetrical Cinchonine‐Squaramide as New Highly Efficient, and Recyclable Organocatalyst for Enantioselective Michael Addition.

A novel and recyclable catalyst, a C3-symmetrical cinchonine-squaramide, has been developed for the asymmetric Michael addition of 1,3-dicarbonyl compounds to nitroalkenes. When using only 1 mol% of catalyst 1a for the reaction, high reaction yields with excellent enantioselectivities and diastereoselectivities (up to 96% yield,>99% ee,>99:1 dr) were achieved, in which the results for cyclic keto esters are the best ever achieved. Moreover, 1a can be easily recovered by simple precipitation and was used for six cycles without losing any selectivity and activity.

ChemInform Abstract: Chiral Amine Organocatalysts for the syn‐Aldol Reaction Involving Substituted Benzaldehydes and Hydroxyacetone.

Abstract A new series of cyclohexanediamine organocatalysts that contain the primary amine functionality has been designed, synthesized and tested as catalysts for the asymmetric aldol reaction involving hydroxyacetone and a variety of substituted benzaldehydes. High enantioselectivites and diasteroselectivites were obtained using catalyst 1a for these reactions. A key step in this reaction for the formation of the syn -product is the formation of a stable intramolecular hydrogen bonded Z -enamine isomer, which in addition to the steric bulk of the catalyst, serve to dictate the course of the stereochemical outcome of the reaction.

Chiral salen Mn(III) immobilized onto sulfoalkyl-modified zinc poly(styrene-phenylvinylphosphonate)-phosphate as effective catalysts for epoxidation of unfunctionalized olefins

The heterogeneous catalysts 3a–3c immobilized chiral salen Mn(III) onto sulfoalkyl-modified zinc poly(styrene-phenylvinylphosphonate)phosphate (ZnPSPPP) were prepared and used for the enantioselective epoxidation of unfunctionalized olefins. The catalysts were characterized with FT-IR, UV–vis, XRD, SEM, TEM. All the prepared heterogeneous catalysts exhibited much higher chiral induction than the homogeneous Jacobsen’s catalyst did and could be reused six times without significant loss of activity and enantioselectivity. Surprisedly, the conversions and enantiomeric excess (ee) values increased in the absence of axial base N-methylmorpholine N-oxide (NMO), which were different to what most literatures reported. Meanwhile, the role of axial ligand NMO in the asymmetric epoxidation of unfunctional olefin was also discussed here. Furthermore, this novel type of catalyst can also be validly used in large-scale reactions with superior catalytic disposition being maintained at the same level, which possessed the potentiality for application in industry.

C3‐Symmetrical Cinchonine‐Squaramide as New Highly Efficient, and Recyclable Organocatalyst for Enantioselective Michael Addition

AbstractA novel and recyclable catalyst, a C3‐symmetrical cinchonine‐squaramide, has been developed for the asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes. When using only 1 mol% of catalyst 1a for the reaction, high reaction yields with excellent enantioselectivities and diastereoselectivities (up to 96% yield,>99% ee,>99:1 dr) were achieved, in which the results for cyclic keto esters are the best ever achieved. Moreover, 1a can be easily recovered by simple precipitation and was used for six cycles without losing any selectivity and activity.

A novel C3-symmetric prolinol-squaramide catalyst for the asymmetric reduction of ketones by borane

A novel C 3-symmetric prolinol-squaramide has been developed for the asymmetric reduction of ketones by borane. By using only 5 mol % catalyst 1a for the reaction, high yields and excellent enantioselectivities (up to 95% yield, 93% ee) were obtained. Moreover, 1a can be easily recovered by simple precipitation and re-used for four cycles without losing the selectivity.

Binaphthol-Derived Bisphosphoric Acids Serve as Efficient Organocatalysts for Highly Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylides to Electron-Deficient Olefins

A variety of chiral bisphosphoric acids derived from binaphthols have been evaluated for enantioselective 1,3-dipolar cycloaddition reactions, revealing that the feature of the linker in the catalysts exerted great impact on the stereoselectivity. Among them, the oxygen-linked bisphosphoric acid 1a provided the highest level of stereoselectivity for the 1,3-dipolar cycloaddition reaction tolerating a wide range of substrates including azomethine ylides, generated in situ from a broad scope of aldehydes and α-amino esters, and various electron-deficient dipolarophiles such as maleates, fumarates, vinyl ketones, and esters. This reaction actually represents one of the most enantioselective catalytic approaches to access structurally diverse pyrrolidines with excellent optical purity. Theoretical calculations with DFT method on the formation of azomethine ylides and on the transition states of the 1,3-dipolar cycloaddition step showed that the dipole and dipolarophile were simultaneously activated by the bifunctional chiral bisphosphoric acids through the formation of hydrogen bonds. The effect of the bisphosphoric acids on reactivity and stereochemistry of the three-component 1,3-dipolar cycloaddition reaction was also theoretically rationalized. The bisphosphoric acid catalyst 1a may take on a half-moon shape with the two phosphoric acid groups forming two intramolecular hydrogen bonds. In the case of maleates, one phosphate acts as a base to activate the 1,3-dipole, and simultaneously, the two hydroxyl groups in the catalyst 1a may respectively form two hydrogen bonds with the two ester groups of maleate to make it more electronically deficient as a much stronger dipolarophile to participate in a concerted 1,3-dipolar cycloaddition with azomethine ylide. However, in the cases involving acrylate and fumarate dipolarophiles, only one hydroxyl group forms a hydrogen bond with the ester functional group to lower the LUMO of the C-C double bond and another one is remained to adjust the acidity and basicity of two phosphoric acids to activate the dipole and dipolarophile more effectively.

Catalytic Asymmetric Conjugate Addition of NaHSO3to Chalcones

The first catalytic enantioselective 1,4-addition of the hydrogen sulfite ion to α,β-unsaturated ketones has been reported. Chalcones 2 were identified as suitable substrates for a highly enantioselective reaction catalyzed by cinchona-based thiourea catalyst 1a. The use of pseudo-enantiomeric catalyst 1b enabled the preparation of compounds ent-3 with comparable selectivity.

ChemInform Abstract: A Chiral N‐Phosphinyl Phosphoramide: Another Offspring for the Sage Phosphoric Acid Progenitor.

AbstractReview: 24 refs.

Chiral amine organocatalysts for the syn-aldol reaction involving substituted benzaldehydes and hydroxyacetone

A new series of cyclohexanediamine organocatalysts that contain the primary amine functionality has been designed, synthesized and tested as catalysts for the asymmetric aldol reaction involving hydroxyacetone and a variety of substituted benzaldehydes. High enantioselectivites and diasteroselectivites were obtained using catalyst 1a for these reactions. A key step in this reaction for the formation of the syn-product is the formation of a stable intramolecular hydrogen bonded Z-enamine isomer, which in addition to the steric bulk of the catalyst, serve to dictate the course of the stereochemical outcome of the reaction.

Simple and Facile l-Prolinamides Derived from Achiral Cycloalkylamines as Organocatalysts for the Highly Efficient Large-Scale Asymmetric Direct Aldol Reactions

A series of N-cycloalkylprolinamides have been designed and synthesized from achiral cycloalkylamines in a facile manner. They promoted high stereoselectivity in the cross-aldol reaction. N-cyclopropylprolinamide performed best with a smallest carbocyclic ring, and the anti-aldol products could be obtained with up to 99:1 anti/syn and 99% ee. Carbocyclic ring was found to play a significant role in the formation of the aldol products. This simple catalyst can be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which offers great possibility for applications in industry. All of the catalysts 1a–e synthesized from achiral cycloalkylamines in a facile manner and their catalytic properties were studied in depth for the first time. All of the catalysts 1a–e exhibited great catalytic activity in the asymmetric aldol reaction in m-xylene using acetic acid as cocatalyst at −20 °C with only 5 mol% catalyst loading in 4 equivalents ketone, and the anti-aldol products could be obtained with up to 99:1 anti/syn and 99% ee. Compared with proline and prolinamide 1f, it is easily found that the carbocyclic ring of N-cycloalkyl-l-prolinamide could be anticipated in some way to enhance the enantioselectivity in m-xylene at low temperature. The results observed for 1a surpass those reported so far for simple prolinamide derivatives and are comparable to those for organocatalysts of much more structural complexity. Catalyst 1a can be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which offers great possibility for applications in industry.

Reusable and Durable Immobilized‐Cationic Gold(I) Catalysts for Environmentally Benign Bond‐Forming Reactions

AbstractPolystyrene‐immobilized cationic gold catalysts 2a and 2b were synthesized for the first time and found to be highly effective catalysts for the bond‐forming reactions via the activation of the CC triple bonds. The immobilized 2a was easily and quantitatively recovered from the reaction mixture and reused at least seven times while maintaining the original catalytic activity. Furthermore, a flow reactor containing 2a was developed for a larger scale continuous production.