Immobilization of chiral ferrocenyl ligands on silica gel and their testing in Pd-catalyzed allylic substitution and Rh-catalyzed hydrogenation

Five different silica gels containing two chiral ferrocenyl ligands were prepared by various synthetic routes and tested in an enantioselective Pd(0)-catalyzed allylic substitution and Rh-catalyzed hydrogenation. All the prepared anchored ligands were characterized by porosimetry data, DRIFTS spectra, thermal data and AAS. The aim of the work was to compare the influence of the carrier, surface properties and immobilization strategy on the performance of the catalyst.     

C2-Symmetric bisphosphinites and a bisaminophosphine as new chiral ligands for Pd-catalyzed asymmetric allylic substitution

A family of C₂-symmetric bisphosphinites 3, 5, 7, 9 and bisaminophosphine 11 were prepared and were probed in the prototypical reaction system of palladium-catalyzed asymmetric allylic substitution. The highest ee of 86% was achieved by employing ligand 3.     

Preparation and use of MeO-PEG-supported chiral diphosphine ligands: soluble polymer-supported catalysts for asymmetric hydrogenation

Two new chiral MeO-PEG-supported (R)-BINAP and (3R,4R)-Pyrphos ligands were synthesized and employed in the Ru(II)- and Rh(I)-catalyzed asymmetric hydrogenation of 2-(6′-methoxy-2′-naphthyl)propenoic acid 5 and prochiral enamides 10. The results showed that these new soluble polymeric catalysts exhibited high catalytic activity and enantioselectivity. Enantiomeric excesses (e.e.s) in the ranges 90–96% and 86–96% were achieved in the hydrogenation of 5 and 10, respectively. Furthermore, these catalysts could be recovered easily and the recycled catalysts were shown to maintain their efficiency in subsequent reactions.     

Synthesis of new chiral monodentate phosphite ligands and their use in catalytic asymmetric hydrogenation

[reaction: see text] New monodentate phosphite ligands have been developed from axially chiral biphenols, which show excellent enantioselectivity in the Rh(I)-catalyzed hydrogenation of dimethyl itaconate. The new chiral ligand system is suitable to create libraries and possesses fine-tuning capability.     

Novel chiral ferrocenyl-imino phosphine ligands and their use in palladium catalyzed allylic alkylations

New chiral P,N-ferrocenyl imino-phosphine ligands have been synthesized and the absolute configuration of the stereocenters in each molecule has been determined by a single-crystal X-ray analysis of a common intermediate. Pd^II-allyl complexes of the new ligands have been isolated and tested as catalyst precursors in the asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl acetate with dimethyl malonate in different solvents. Quantitative yields and enantiomeric excesses as high as 80% have been obtained.     

Synthesis of iridium complexes with new planar chiral chelating phosphinyl-imidazolylidene ligands and their application in asymmetric hydrogenation

The synthesis of planar chiral phosphinoimidazolium salts such as (R_p)-3-(4-diphenyl-phosphino[2.2]paracyclophan-12-ylmethyl)-1-(2,6-diisopropylphenyl)imidazolium bromide (R_p)-11c starting from enantiopure 4,12-dibromo[2.2]paracyclophane (R_p)-6 is reported. After deprotonation of these salts and a subsequent reaction with [Ir(COD)Cl]₂, chelating iridium imidazolylidene complexes (R_p)-5a–c are obtained. These complexes catalyze the asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee.     

Recent advances in the application of chiral phosphine ligands in Pd-catalysed asymmetric allylic alkylation

One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has promoted the synthesis of new chiral ligands to be evaluated as asymmetric inductors. Although the mechanism as well as the active species equilibria are known, the performance of the catalytic system depends on the fine tuning of factors such as type of substrate, nucleophile nature, reaction medium, catalytic precursor and type of ligand used. Particularly interesting are chiral phosphines which have proved to be effective asymmetric inductors in several such reactions. The present review covers the application of phosphine-donor ligands in Pd-catalysed asymmetric allylic alkylation in the last decade.     

新的手性膦配体的合成及其在苯乙烯不对称氢酯基化中的应用

近年来,糖衍生的手性膦配体在不同的催化反应中转化率较高,对映选择性极好,三苯膦氧配体催化效果好,膦硫配体在氢甲酰化反应中也具有一定的催化活性。本文从价廉易得的甘露醇出发合成了两个手性膦配体,作了^1HNMR,^31PNMR,MS和元素分析结构表征。以苯乙     

First chiral phosphoroamidite-phosphite ligands for highly enantioselective and versatile Pd-catalyzed asymmetric allylic substitution reactions

[reaction: see text] A series of phosphite-phosphoroamidite ligands, derived from readily available d-xylose, has been successfully applied for the first time in the Pd-catalyzed allylic substitution of several substrates with different steric and electronic properties, with high enantioselectivities (ee's up to 98) and activities in standard conditions.     

Palladium/chiral phosphine–olefin complexes: X-ray crystallographic analysis and the use in catalytic asymmetric allylic alkylation

X-ray crystallographic studies on π-allylpalladium complexes coordinated with a chiral phosphine–olefin ligand (−)-1b demonstrate that the phosphine ligand shows a larger trans-influence than the π-bound olefin. The palladium/chiral phosphine–olefin complex efficiently catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with 96% enantioselectivity.     

Modular synthesis of the ClickFerrophos ligand family and their use in rhodium- and ruthenium-catalyzed asymmetric hydrogenation

A series of diphosphine ClickFerrophos ligands (CF), based on a triazoleferrocene backbone, was synthesized in a four-step sequence via click chemistry methodology. In addition to the four previously synthesized ligands CF1, CF4, CF7 and CF10, six novel CF ligands CF2–3 and CF5–8 were prepared. Hydrogenation reactions of alkenes and ketones were significantly improved upon by using CF ligands as rhodium- or ruthenium-complexes in which the % ee values can be optimized by choosing the appropriate CF ligand depending on the substrate.     

Synthesis of chiral polydentate ligands and the use of their titanium complexes as pre-catalysts for the asymmetric trimethylsilylcyanation of benzaldehyde

A number of polydentate ligands based on enantiomerically pure binaphthol have been synthesized. The ligand complexes with titanium isopropoxide were used as catalysts for the asymmetric addition of trimethylsilyl cyanide to benzaldehyde. A fragment with axial chirality is responsible for the configuration of O-trimethylsilyl cyanohydrin product. In the case of the optimum ligand based on (R)-binaphthol and (S)-leucinol, an enantiomeric excess of 86% and quantitative yield were achieved in 4 h. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1946–1953, September, 2008.     

Screening of chiral ferrocenyl amino alcohols as ligands for ruthenium-catalysed transfer hydrogenation of ketones

A variety of ferrocenyl amino alcohols possessing central chirality have been screened as ligands for ruthenium(II)-catalysed transfer hydrogenation of acetophenone using 2-propanol in the presence of KOH as the hydrogen source. Enantiomerically enriched 1-phenylethanol was obtained in high yield and 70% e.e. using ligand 9. This ligand was employed in the asymmetric reduction of different arylalkyl ketones and the corresponding alcohols were obtained in up to 80% e.e. A comparison of the catalytic properties of ferrocenyl amino alcohols and their phenyl analogues is discussed briefly.     

Reversal in enantioselectivity for the palladium-catalyzed asymmetric allylic substitution with novel metallocene-based planar chiral diphosphine ligands

The novel C₂-symmetric metallocene-based ligands with only planar chirality were synthesized easily and applied in palladium-catalyzed asymmetric allylic substitution with excellent enantioselectivity and high catalytic activity. When two ester groups on Cp rings of the metallocene were replaced by hydroxymethyl groups, opposite configuration of the product was obtained with high catalytic activity and excellent enantioselectivity. The opposite configuration of products was also obtained when the hydroxyl groups were protected as esters or ethers. These results might be attributed to the different configuration of the diphosphine ligands-Pd(II) complexes.     

Developments in asymmetric catalysis by metal complexes of chiral chelating nitrogen-donor ligands

In part because of their straightforward and modular syntheses from readily available enantiopure starting materials, and their capacity to bind a wide variety of transition metals, chiral, chelating nitrogen-donor ligands have played a prominent role in asymmetric catalysis. A large number of highly enantioselective transformations rely upon these ligands whose reported classes are built around amine, imine, pyrrole, pyrrolidine, oxazoline and oxazolidine donor groups, among others. In this Perspective, we examine a selection of transformative developments in asymmetric catalysis by metal complexes of bi- and polydentate members of this ligand family. We describe approaches to ligand design and synthesis, structure and bonding in coordination complexes, and limitations and future challenges.     

Enantioselective Pd-catalyzed allylic alkylation of indoles by a new class of chiral ferrocenyl P/S ligands

Chiral ferrocenyl heterobidentate P/S ligands bearing both central and planar chirality were prepared from (S)-Ugi's amine via a three-step modular synthesis. Through systematic screening and optimization, L8 was found to be the best ligand for Pd-catalyzed asymmetric allylic alkylation of indoles with ee's up to 96% being attained.     

A new class of chiral P,N-ligands and their application in palladium-catalyzed asymmetric allylic substitution reactions

An efficient and modular synthesis of a series of chiral nonracemic P,N-ligands is reported. The P,N-ligands were prepared from 2-chloro-4-methyl-6,7-dihydro-5H-[1]pyrindine-7-one and a series of substituted chiral C(2)-symmetric 1,2-ethanediols (R = Me, i-Pr, and Ph). The ligands were evaluated for use in catalytic asymmetric synthesis in the palladium-catalyzed allylic substitution reactions of a racemic allylic acetate and dimethyl malonate. In the case of the P,N-ligand (R = Ph), the reaction was found to be highly stereoselective (90% ee).     

Synthesis of new chiral 2,2'-bipyridine ligands and their application in copper-catalyzed asymmetric allylic oxidation and cyclopropanation

A series of modular bipyridine-type ligands 1 and 3-9 has been synthesized via a de novo construction of the pyridine nucleus. The chiral moieties of these ligands originate from the isoprenoid chiral pool, namely, beta-pinene (10 --> 1), 3-carene (14 --> 3 and 5), 2-carene (28 --> 4), alpha-pinene (43 --> 6-8), and dehydropregnenolone acetate (48 --> 9), respectively. Copper(I) complexes, derived from these ligands and (TfO)(2)Cu (1 mol %) upon an in situ reduction with phenylhydrazine, exhibit good enantioselectivity (up to 82% ee) and unusually high reaction rate (typicaly 30 min at room temperature) in allylic oxidation of cyclic olefins (52 --> 53). Copper-catalyzed cyclopropanation proceeded with < or =76% enantioselectivity and approximately 3:1 to 99:1 trans/cis-diastereoselectivity (54 --> 55 + 56). The level of the asymmetric induction is discussed in terms of the ligand architecture that controls the stereochemical environment of the coordinated metal.