Chiral Diphosphine Research Articles

A chiral diphosphine as trans-chelate ligand and its relevance to catalysis

The chiral diphosphine ligand R,R-trans-1,2-C(6)H(10)(NHCOC(6)H(4)PPh(2))(2), 1, gives the fluxional trans-chelate complexes [M(1)]X, 2a-2c, M = Au or Ag. It is suggested that a similar trans-chelate conformation may be present in the catalytic intermediate [Pd(1)].

Asymmetric hydrogenation of ketones: tactics to achieve high reactivity, enantioselectivity, and wide scope.

Ru complexes with chiral diphosphines and amine-based ligands achieve high catalytic activity and enantioselectivity for the hydrogenation of ketones under neutral to slightly basic conditions. The chiral environment is controllable by changing the combination of these two ligands. A concerted six-membered transition state is proposed to be the origin of the high reactivity. The η6-arene/TsDPEN–Ru and MsDPEN–Cp*Ir catalysts effect the asymmetric reaction under slightly acidic conditions. A variety of chiral secondary alcohols are obtained in high enantiomeric excess.

Chiral undecagold clusters: synthesis, characterization and investigation in catalysis

Enantiopure undecagold clusters protected by chiral atropisomeric diphosphine ligands (P^P) have been synthesized by the stoichiometric reduction of the corresponding (P^P)(AuCl)(2) complexes with NaBH(4). The molecular mono-disperse [Au(11)(P^P)(4)Cl(2)]Cl species have been thoroughly characterized using an array of analytical techniques. (31)P NMR experiments suggested the presence of a slow intramolecular ligand exchange process. Circular dichroism measurements showed that enantiomeric clusters display mirror-image chiroptical activity. Such undecagold clusters containing two chloride ligands bound to the peripheral Au(I) atoms were expected to display a carbophilic Lewis acidity similar to the well-documented molecular Au(I) complex catalysts. Chloride abstraction, performed to generate active Au(+) sites, induced the Au(11) cluster evolution to larger gold clusters and nanoparticles, together with Au(I) complexes, which, in fact, perform the catalysis. This result was corroborated by running an asymmetric tandem hydroarylation-carbocyclization reaction, for which the enantiomeric excesses obtained with Au(11) clusters are similar to those reported using Au(I) complexes.

Interrogation of a dynamic multi-catalyst ensemble in asymmetric catalysis

The ‘Trost Standard Ligand’ (2) is a chiral diphosphine ligand that distinguishes itself by the high selectivity it induces in the Pd-catalysed reactions of allylic substrates that generate slim cyclic or small linear intermediates. However, a range of unusual features, including memory effects, inverse dependence of selectivity and rate on catalyst concentration, high sensitivity to counter-ion, particularly chloride, and decreasing enantioselectivities at lower temperatures, are often encountered, thus requiring considerable optimisation of reaction conditions to attain optimum selectivity. These features can be accounted for by a model involving a dynamic multi-catalyst ensemble. To gain evidence for this model, the manner in which diphosphine 2 interacts with Pd–allyl cations, and in particular the higher-order systems it generates, has been investigated by use of NMR, isotopic labelling, polarimetry, UV, neutron scattering, X-ray crystallography and molecular modeling. Ligand 2 coordinates to Pd–allyl cations to generate a mononuclear P,P-chelate. This is found to readily form non-chelate oligomers, present in a range of forms, including rings, for which high homochiral selectivity in oligomerisation is demonstrated by the technique of pseudoenantiomers. All of these species are in relatively rapid equilibrium, with half-lives for interconversion in the range 2–6 s. Higher-order aggregation is also detected, and thus at even moderate concentrations (>50 mM) large rod-like aggregates are formed.

Palladium-Catalyzed Tandem Annulation of 2-Formylarylboronic Acids with Allenoates

The cationic palladium complex was shown to be a good catalyst for the tandem annulation of 2-formylarylboronic acid and allen­oates to produce indenol derivatives with good yield and diastereoselectivity. The use of chiral diphosphine ligands also provided good enantio­selectivities for this novel transformation.

Catalytic Asymmetric Michael Additions of α-Cyanoacetates

Enantiopure Michael addition products of α-cyanoacetatesconstitute attractive precursors for functionalised quaternary aminoacids and other biologically interesting compounds. Since the pioneeringwork by Ito et al. in 1992 using rhodium(I) in combination witha TRANS-chelating planar chiral diphosphine,various complementary approaches have been reported; these are critically discussedand compared in this review. The most efficient recent methodologiesutilise a bifunctional activation mode; for example, by dinuclearLewis acid catalysis or by a well-defined hydrogen-bonding network.This strategy can overcome the difficulty that α-cyanoacetatesare incapable of two-point binding to a Lewis acid thus hamperingthe differentiation of prochiral enol(ate) faces. 1 Introduction 2 Rhodium, Iridium and Ruthenium Catalysts 3 Palladium and Platinum Catalysts 4 Aluminium Catalysts 5 Organocatalysis 5.1 Cinchona Alkaloids 5.2 Thiourea-Derived Catalysts 5.3 Cinchona Alkaloid-(Thio)Urea Hybrids 5.4 Iminium Catalysis 6 Phase-Transfer Catalysis 7 Conclusions

ChemInform Abstract: Enantioselective Rh‐Catalyzed Hydrogenation of 3‐Aryl‐2‐phosphonomethylpropenoates by a New Class of Chiral Ferrocenyl Diphosphine Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric Hydrogenation of Heteroaromatic Ketones and Cyclic and Acyclic Enones Mediated by Cu(I)-Chiral Diphosphine Catalysts

Copper(I)-catalyzed asymmetric hydrogenation of heteroaromatic ketones, cyclic and acyclic enones is reported. The choice of the chiral diphosphine ligand highly influenced enantioselectivity as well as chemoselectivity. Highly enantioselective hydrogenation of ortho-substituted heteroaromatic ketones was achieved using BDPP as the ligand. In the 1,2-selective hydrogenation of acylic enone, SEGPHOS gave higher enantioselectivity than BDPP. On the other hand, the bulky ligand DTBM-SEGPHOS had a 1,4-selective nature, leading to the first highly 1,4-selective and enantioselective hydrogenation of cyclic enones.

Axial Chirality Control by 2,4‐Pentanediol for the Alternative Synthesis of C3*‐TunePhos Chiral Diphosphine Ligands and Their Applications in Highly Enantioselective Ruthenium‐Catalyzed Hydrogenation of β‐Keto Esters

AbstractA highly efficient strategy for the synthesis of a series of C3*‐TunePhos chiral diphosphine ligands was well established with several remarkable features. The synthetic utility of these ligands was explored for the ruthenium‐catalyzed asymmetric hydrogenation of β‐keto esters. Up to 99% ee values were achieved for the enantioselective synthesis of β‐hydroxy acid derivatives, which are very important chiral building blocks for the synthesis of a variety of natural products and biologically active molecules.

ChemInform Abstract: Electron‐Poor Chiral Diphosphine Ligands: High Performance for Rh‐Catalyzed Asymmetric 1,4‐Addition of Arylboronic Acids at Room Temperature.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Chiral Chelating Diphosphines with Stereogenic C‐Centers in the Interconnecting Spacer — History, Current Developments and Impact on Asymmetric Catalysis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and application of peripherally alkyl-functionalized dendritic pyrphos ligands: Homogeneous-supported catalysts for enantioselective hydrogenation

A new series of dendritic ligands with a chiral diphosphine located at the focal point have been synthesized through coupling of (R,R)-3,4-bis(biphenylphosphino)pyrrolidine (pyrphos) with peripherally alkyl-functionalized benzoic acid dendrons. These ligands were employed in the Rh-catalyzed asymmetric hydrogenation of prochiral dehydroamino acids, exhibiting excellent catalytic activities and enantioselectivities. The second-generation dendritic catalyst could be recovered by simple liquid–liquid biphasic separation and reused four times without serious loss of its activity and selectivity.

Immobilization of chiral cationic diphosphine rhodium complexes in nanopores of mesoporous silica and application in asymmetric hydrogenation

Heterogeneous chiral cationic rhodium complexes bearing bidentate phosphine derived from (−)-2,2-dimethyl-4,5-bis(diphenylphosphino)methyl)-1,3-dioxolane (DIOP) were prepared by covalent immobilization onto SBA type silica. In order to introduce the tether to the surface, it was necessary to modify chemically the DIOP ligand through a reaction sequence consisting of hydrolysis and condensation with organosiloxane precursor. Two types of cationic rhodium hybrid materials based on SBA-15 and partially capped SBA-3 type silica were prepared under classical grafting procedures. The catalytic solids were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. The performances of these latter were then evaluated in the hydrogenation of methyl ( Z)-2- N-acetylaminocinnamate under various reaction conditions (pressure and temperature). Generally, the activity of supported catalysts was high as full conversions were obtained but immobilization of the system leads to significant loss of enantioselectivity. The best ee (20%) was observed in the case of the catalyst whose surface had been passivated prior to the grafting but the enantiomeric excesses were fairly below the values of the homogeneous catalysis.

Fengphos, a Ferrocene‐Based Chiral Diphosphine: Synthesis and Applications

Fengphos is a type of ferrocenyl diphosphine incorporating axial as well as central chirality, which is synthesized in three steps from Ugi amine (see scheme). Acting as ligands, they are effective in the Rh-catalyzed hydrogenation of a wide range of substrates, including dimethyl itaconate (ee values greater than 99 %) and ethyl β-acetamido acrylate (ee values up to 95 %).

Catalytic Asymmetric Baeyer–Villiger Oxidation in Water by Using PtII Catalysts and Hydrogen Peroxide: Supramolecular Control of Enantioselectivity

The enantioselective Baeyer-Villiger oxidation of cyclic ketones is a challenging reaction, especially when using environmentally friendly oxidants. The reaction was carried out in water by using soft Lewis acid Pt(II) complexes that have chiral diphosphines as well as monophosphines. Addition of a surfactant is crucial, which leads to the formation of micelles that act as nanoreactors in which the substrate and catalyst encounter each other in an ordered medium that in several cases positively influences both the conversion and the selectivity of the reactions. This is due to the combination of the hydrophobic effect (which confines the components of the reaction in the micelles), together with supramolecular interactions between the partners within the ordered palisade provided by the alkyl chains of the surfactant. For the oxidation of meso-cyclobutanones, addition of surfactant allowed the reaction to proceed in high yields and the enantiometic excess (ee; 56%) was higher than in organic solvents. Subsequent extension to meso-cyclohexanones resulted in a general decrease in yields but an enhancement of enantioselectivity (ee up to 92%) moving from organic to water-surfactant media, regardless of the substrate or the catalyst employed. Different behaviour was observed with chiral cyclobutanones 7 and 10: with 7 the best catalyst was 1 g, whereas with the larger substrate, 10, complexes 1 a-b performed better in terms of enantioselectivity. Each combination of substrate, catalyst and surfactant is a new system and supramolecular reciprocal interactions together with the hydrophobic character of the counterparts play crucial roles. The asymmetric Baeyer-Villiger oxidation in water catalyzed by 1 a-h in the presence of micelles is a viable reaction that often benefits from the hydrophobic effect, leading to substantial increases in enantioselectivity.

Syntheses, crystal structures and fluorescent properties of R, R-DIOP based copper (I) and cadmium (II) complexes { R, R-DIOP = (4 R,5 R)- trans-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxalane}

Two chiral complexes, [CuCl( R, R-DIOP)] 2 ( 1) and [CdCl 2( R, R-DIOP)] n ( 2), have been synthesized by reaction of CuCl or CdCl 2 with chiral diphosphine ligand R, R-DIOP under argon. They were characterized by elemental analysis, IR, UV–vis, fluorescence spectra and single-crystal X-ray diffraction. X-ray analysis indicates that the metal centers (Cu I for 1 and Cd II for 2) are both in distorted tetrahedral environment, but 1 is a binuclear complex in which Cu I ions are surrounded by two μ 2-bridging chloride ions and two bismonodentate coordinated R, R-DIOP ligands; while 2 is a helical polymer along b axis and each Cd II ion is coordinated with two chloride ions and two P atoms of two μ 2-bridging R, R-DIOP ligands. Both of them crystallize in monoclinic system, space group P 21, with a = 9.8855(7) Å, b = 37.857(3) Å, c = 23.9585(16) Å, β = 92.0920(10)°, Z = 6 for ( 1) and a = 10.1740(8) Å, b = 13.9899(11) Å, c = 11.4007(9) Å, β = 108.3690(10)°, Z = 2 for ( 2). Fluorescence measurements show that complex 1 can emits much strong blue emission than 2 at room temperature in the solid state.

Enantioselective Rh-Catalyzed Hydrogenation of 3-Aryl-2-phosphonomethylpropenoates by a New Class of Chiral Ferrocenyl Diphosphine Ligands

A new class of chiral ferrocenyl diphosphine ligands with an imidazole ring, (R(c),S(Fc))-ImiFerroPhos, has been prepared from acylferrocenes through a five-step transformation and successfully applied in the Rh-catalyzed asymmetric hydrogenation of various 3-aryl-substituted 2-phosphonomethylpropenoates, in which a series of chiral 3-phosphono-2-arylmethylpropanoic acid derivatives were achieved in ee values of up to 98%.

Electron-Poor Chiral Diphosphine Ligands: High Performance for Rh-Catalyzed Asymmetric 1,4-Addition of Arylboronic Acids at Room Temperature

Electron-poor chiral diphosphine ligands, MeO-F(28)-BIPHEP (1a) and MeO-F(12)-BIPHEP (1b), were synthesized for controlling a transition-metal catalyst electronically. The 1b-ligated Rh catalyst showed excellent catalytic activity with high % ee for asymmetric 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyls at 20 degrees C. The strong pi-acceptor ability of 1b induces transmetalation of arylboronic acid to catalyst precursor [RhCl(1b)](2) directly in the first step of the catalytic cycle.

Bridged silsesquioxanes containing a chiral diphosphine substructure. Catalytic properties in asymmetric hydrogenation

Bridged silsesquioxanes with asymmetric catalytic properties are described. These new silica-based materials are obtained by the sol-gel hydrolysis of an organosilylated chiral compound bearing rhodium-complexed diphosphine ligands. The incorporation of the organometallic species in various hybrid networks was achieved upon co-hydrolysis of the latter silylated ligands with TEOS or with 1,4-bis(trimethoxysilyl)benzene. These amorphous hybrids have been tested as enantioselective catalysts for the hydrogenation of (Z)α-(acetamido)cinnamic acid to the corresponding aminoacid and the results were compared with that obtained from the complexed precursor in homogeneous medium and related grafted silica. Enantioselectivities slightly higher than for homogeneous reaction were obtained in the case of the heterogeneous catalysts prepared by the direct hydrolysis of the rhodium-complexed diphosphine compound or by its co-hydrolysis with 1,4-bis(trimethoxysilyl)benzene. Conversely, a significant decrease in selectivity was observed when the organometallic species was immobilised in silica or grafted at the surface of silica.

ChemInform Abstract: Highly Enantioselective Synthesis of Pseudo‐C2‐Symmetric Axially Chiral Biaryl Diphosphines via Rhodium‐Catalyzed Double [2 + 2 + 2] Cycloaddition.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.