Fluoroalkyldistannoxane Catalysts for Transesterification in Fluorous Biphase Technology

Novel, practical protocols of transesterification have been advanced with recourse to fluorous biphase technology. The fluoroalkyldistannoxane catalysts enable transesterification in FC‐72 solvent to furnish 100% yields of the desired esters by use of reactants ester and alcohol in a 1 : 1 ratio. The catalysts also work in FC‐72/organic solvent system as well as in toluene alone. A number of esters and alcohols bearing various functional groups are employable. The catalysts can be totally recovered and reused. More conveniently, the catalyst solution in FC‐72 which is separated from the reaction mixture is directly used for the next reaction.     

Rhodium‐Catalyzed Hydrogenation of Alkenes by Rhodium/Tris(fluoroalkoxy)phosphane Complexes in Fluorous Biphasic System

The reaction of [Ir(μ‐Cl)(COD)]₂ with various fluorous derivatives of triphenylphosphane containing a para‐, meta‐, or ortho‐(1H,1H‐perfluoroalkoxy)‐substituted fluorous phosphane P(C₆H₄‐ORf)₃ (Rf=CH₂C₇F₁₅, CH₂CH₂CH₂C₈F₁₇) and CO (1 atm) gives the corresponding trans‐[Ir(μ‐Cl)(CO){P(C₆H₄ORf)₃}₂]. The IR ν_CO values of these complexes give some information on the donor/acceptor properties of the phosphanes. These fluorous derivatives of triphenylphosphane, as well as a phosphane bearing two (1H,1H‐perfluoroalkyloxy) chains at the 3,5‐positions, were used in association with [Rh(μ‐Cl)(COD)]₂ or [Rh(COD)₂]PF₆ in the reduction of methyl cinnamate, 2‐cyclohexen‐1‐one, cinnamaldehyde, and methyl α‐acetamidocinnamate in a two‐phase system D‐100/ethanol under 1 bar hydrogen at room temperature. Some differences in catalytic activity were observed in the reduction of methyl cinnamate, the most active catalyst being the rhodium complex containing the phosphane with the p‐fluorous ponytail. Recycling of the fluorous catalyst was possible, particularly using the p‐substituted phosphane, where no significant loss of catalyst or activity was observed, and generally with very low leaching of rhodium or phosphane in the organic phase.     

3,5‐Bis(n‐perfluorooctyl)benzyltriethylammonium Bromide (F‐TEBA): An Efficient,Easily Recoverable Fluorous Catalyst for Solid‐Liquid PTC Reactions

A readily available 3,5‐bis(perfluorooctyl)benzyl bromide and triethylamine were reacted under mild conditions to give 3,5‐bis(n‐perfluorooctyl)benzyltriethylammonium bromide ( F‐TEBA ), an analogue of the versatile phase‐transfer catalyst, benzyltriethylammonium chloride (TEBA), containing two fluorous ponytails. This perfluoroalkylated quaternary ammonium salt was successfully employed as a catalyst in a variety of reactions run under solid‐liquid phase‐transfer catalysis (SL‐PTC) conditions. Thus, being both hydrophobic and lipophobic, F‐TEBA could be quickly recovered in quantitative yields, and reused without loss of activity over several reaction cycles.     

The Addition Reaction of Samarium Enolates and 2‐Haloenolates Derived from Esters,and Amides to Imines. Totally Stereoselective Synthesis of Enantiopure 3,4‐Diamino Esters or Amides

The addition reaction of samarium enolates and 2‐haloenolates derived from esters and amides to imines takes place in an efficient manner. A novel protocol to perform the addition reaction of samarium enolates derived from esters or amides to chiral 2‐aminoimines, with total stereoselectivity and without racemization, is also reported. The use of samarium enolates in place of other classic metallic enolates (lithium, magnesium, etc.) could be a valuable alternative to obtain enantiopure 3,4‐diamino esters or amides, when enolates of low basicity are necessary.     

Enhanced Hydrogenation Activity and Recycling of Cationic Rhodium Diphosphine Complexes through the Use of Highly Fluorous and Weakly‐Coordinating Tetraphenylborate Anions

The effect of the nature of the anion on the performance of ionic rhodium catalysts has received little attention. Herein it is shown that the use of highly fluorous tetraphenylborate anions can enhance catalyst activity in both conventional and fluorous media. For hydrogenation catalysts of the type [Rh(COD)(dppb)][X] {COD=1,5‐cis,cis‐cyclooctadiene; dppb=1,4‐bis(diphenylphosphino)butane; X=BF₄⁻ ( 1a ), [BPh₄]⁻ ( 1b ), [B{C₆H₄(SiMe₃)‐4}₄]⁻ ( 1c ), [B{C₆H₃(CF₃)₂‐3,5}₄]⁻ ( 1d ), [B{C₆H₄(SiMe₂CH₂CH₂C₆F₁₃)‐4}₄]⁻ ( 1e ), [B{C₆H₄(C₆F₁₃)‐4}₄]⁻ ( 1f ) and [B{C₆H₃(C₆F₁₃)₂‐3,5}₄]⁻ ( 1 g )} the activity towards the hydrogenation of 1‐octene in acetone increased in the order 1c < 1b < 1e < 1a < 1d ~ 1f < 1g with 1g being twice as active as the commonly applied 1a . Despite the fluorophilic character introduced by the substituted tetraarylborate anions, the presence of some perfluoroalkyl‐substituents in the cation was still required for achieving high partition coefficients. Therefore, [Rh(COD)(Ar₂PCH₂CH₂PAr₂)][X] {Ar=C₆H₄(SiMe₂CH₂CH₂C₆F₁₃)‐4, X=[B{C₆H₃(C₆F₁₃)₂‐3,5}₄]⁻ ( 3f ); Ar=C₆H₄(SiMe(CH₂CH₂C₆F₁₃)₂)‐4 and X=[B{C₆H₄(C₆F₁₃)‐4}₄]⁻ ( 2g )} were prepared, which were active in the hydrogenation of 1‐octene, 2g even more so than 3f . Both these highly fluorous catalysts could be recycled with 99% efficiency through fluorous biphasic separation, whereas the corresponding BF₄⁻ complex of 2g ( 2a ) did not show any affinity for the fluorous phase.     

An Efficient and Selective Epoxidation of Olefins with Novel Methyltrioxorhenium/(Fluorous Ponytailed) 2,2′‐Bipyridine Catalysts

Novel complexes between methyltrioxorhenium (MTO) and bis(fluorous‐ponytailed) 2,2′‐bipyridines (bpy‐F_n) were synthesized and used for the oxidation of alkenes with hydrogen peroxide under fluorous catalysis. High conversions and yields of the corresponding epoxides were obtained.     

Oligomerization of n‐Butenes in a Two‐Phase Reaction System with Homogeneous Ni/Al‐Catalysts

The oligomerization of n‐butenes in a two‐phase catalyst system consisting of a Lewis acidic ionic liquid (IL) and a nonpolar phase is described. A highly active catalyst system with NiCl₂(PMe₃)₂ was investigated, resulting in 91 % dimers with N‐methylpyrrole as a buffer. The reaction was found to be dependent on the molar ratio of the IL to the catalyst. Additionally, the influence of the Lewis acid was investigated and AlCl₃ was determined as the most suitable for activating the nickel complex. The concentration of AlCl₃ played an important role in achieving high catalyst activity and dimer selectivity. Several reactions with different pyrrole derivatives demonstrated that the use of a buffer with low steric hindrance was also important with regard to increased dimer selectivity.     

Chiral Cyclopentadienyl‐Iron and ‐Ruthenium Lewis Acids Containing the Electron‐Poor BIPHOP‐F Ligand: a Comparison as Catalysts in an Asymmetric Diels‐Alder Reaction

Chiral iron and ruthenium Lewis acids: analogies and differences between the catalysts and the role of the anion in catalytic Diels‐Alder reaction. In short: Fe catalysts are faster but Ru analogues are more stable and can be recovered quantitatively. Rational ligand design is shown to result in a large increase in chiral induction.     

A Polystyrene‐Supported,Highly Recyclable Squaramide Organocatalyst for the Enantioselective Michael Addition of 1,3‐Dicarbonyl Compounds to β‐Nitrostyrenes

A chiral squaramide has been supported onto a polystyrene (PS) resin through a copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction and used as a very active, easily recoverable and highly reusable organocatalyst for the asymmetric Michael addition of 1,3‐dicarbonyl compounds to β‐nitrostyrenes. The PS‐supported squaramide could be recycled up to 10 times.     

从废催化剂中回收镍的技术经济分析

根据废催化剂原料的组成情况 ,介绍了分离回收镍的工艺原理、工艺参数、设备类型以及相应的操作方法 ,同时进行了扼要的经济分析。     

Cyanation of N‐Acylhydrazones with Trimethylsilyl Cyanide Promoted by a Brønsted Base and a Lewis Acid

Cyanation of N‐acylhydrazones using trimethylsilyl cyanide (TMSCN) proceeded well in the presence of an amine to afford the corresponding α‐hydrazinonitriles in high yields. For less reactive substrates, the combined use of an amine and a catalytic amount of scandium triflate [Sc(OTf)₃] was effective to promote the reactions. The mechanistic study suggested that the amine worked as a Brønsted base.     

Diastereoselective Synthesis of Substituted Tetrahydroisoquinolines and Isoindolines via a Silver(I) Triflate‐Promoted Tandem Reaction

A new silver(I) triflate‐promoted tandem reaction comprising the ring opening of aziridines and a Michael reaction has been developed. Using secondary amines or primary amines as nucleophiles, this methodology allows for the synthesis of cis‐1‐alkyl‐4‐aminotetrahydroisoquinolines or cis‐1,3‐disubstituted isoindolines in good yields with excellent diastereoselectivities, respectively. Besides, easy operation and mild reaction conditions are also notable features of this tandem reaction.

     

Transition‐metal trifluoromethane‐sulphonates‐recyclable catalysts for the synthesis of branched fatty derivatives by Diels‐Alder reactions at unsaturated fatty esters

Diels‐Alder reactions of conjugated linoleic acid ethyl ester (1) with different quinones and with a variety of α/βunsaturated aldehydes and ketones are described in this paper. Using Sc(OTf)₃ or Cu(OTf)₂ as catalysts the reactions can be carried out at 25—40 °C with good yields. For the first time in oleochemistry it is possible to prepare Diels‐Alder cycloadditions with catalyst concentrations of 10 mol‐% instead of stoichiometric amounts of Lewis acids. Furthermore, the reaction time was partly shortened drastically. The catalyst Sc(OTf)₃ can be removed by a simple extraction of the organic layer with water. After evaporation of the aqueous phase to dryness the catalyst can be reused without loss of yield.     

Extended Lifetimes of Gold(III) Chloride Catalysts using Copper(II) Chloride and 2,2,6,6‐Tetramethylpiperidine 1‐Oxyl (TEMPO)

The turnovers of a gold(III) chloride catalyst were increased by 3,300% with the addition of several equivalents of 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO) and catalytic amounts of copper(II) chloride. A three‐component coupling reaction between piperidine, phenylacetylene, and benzaldehyde yielded a propargylic amine in quantitative conversions and isolated yields when gold(III) chloride was added in catalytic amounts, but the gold catalyst decomposed and had little to no reactivity when a second set of piperidine, phenylacetylene, and benzaldehyde was added after the reaction was complete. Thus, only one cycle was possible with gold(III) chloride. The addition of TEMPO and copper(II) chloride to reactions with gold(III) chloride maintained the catalytic activity of gold for up to 33 cycles. This result demonstrates a new way to greatly increase the turnovers of a gold(III) chloride catalyst with the addition of inexpensive, commercially available reagents.     

Ligand‐Free Nickel‐Catalysed 1,4‐Addition of Arylboronic Acids to α,β‐Unsaturated Carbonyl Compounds

A simple and efficient ligand‐free nickel‐based catalytic system has been developed for the 1,4‐addition of arylboronic acids to α,β‐unsaturated carbonyl compounds. With catalyst loadings of 1–2 mol%, a series of 1,4‐adducts from chalcones and cinnamates was obtained in moderate to excellent yields within 5–30 min under a nitrogen atmosphere and microwave irradiation. The 1,4‐addition of arylboronic acids to acrylates is less efficient.

     

Disperse Amphiphilic Submicron Particles as Non‐Covalent Supports for Cationic Homogeneous Catalysts

A simple method for the effective immobilization of homogeneous catalysts on polystyrene colloids via non‐covalent binding is demonstrated. Stable latices with sufficiently high loading of accessible borate anions are prepared via emulsion polymerization. Incorporation of cationic rhodium complexes, supported via their borate counter‐anion is efficient, and these supported homogeneous catalysts maintain constant catalytic activity for CC hydrogenation during several recycles, with very low metal leaching.     

Robust and Recyclable Self‐Supported Chiral Nickel Catalyst for the Enantioselective Michael Addition

A simple chemical modification of a chiral diamine ligand may produce a robust and recyclable enantioselective catalyst. Metallopolymers based on chiral cyclohexyldiamine‐containing ditopic ligands and nickel(II) complexes have been readily prepared and applied in catalytic enantioselective Michael additions of 1,3‐dicarbonyl compounds to nitroalkenes. High yields and good enantioselectivities have been obtained and the catalytic systems have been recycled up to 11 times without loss of either activity or enantioselectivity at a low catalyst loading of 0.75 mol%. Moreover, the nickel metallopolymers were found to be air‐ and moisture‐stable, which enabled this chemistry to be carried out on the bench without the use of any air‐free techniques and with non‐degassed solvents. Finally, the nature of the catalyst was studied by non‐linear effect experiments, giving a negative non‐linear effect (NLE) as a consequence of an in situ decrease in the ee of the active species consistent with the trapping of homochiral aggregates.

     

Water‐Tolerant and Reusable Catalysts for Direct Ester Condensation between Equimolar Amounts of Carboxylic Acids and Alcohols

ZrOCl₂⋅8 H₂O and HfOCl₂⋅8 H₂O are highly effective, water‐tolerant, and reusable homogeneous catalysts for direct ester condensation between equimolar amounts of carboxylic acids and alcohols. Notably, zirconium(IV) salts such as ZrOCl₂⋅8 H₂O and Zr(OAc)_x(OH)_y are potential green catalysts due to their low toxicity, commercial availability at low cost, ease of handling, high catalytic activity, and reusability.