Search

A detailed study on ligand preparation and their applications to the amination reactions of unactivated aryl chlorides and Suzuki-Miyaura coupling reactions of different substrates including ortho-substituted aryl chlorides to form hindered biaryls is discussed. A cache model for the Pd/7i complex shows that the likelihood of a Pd-arene interaction might be a rationale for its high catalytic activity.

Research has been conducted on 1,4-diphenylphosphines and thioethers. The synthesis of these compounds has been carried out starting from tartrates via the use of Ley's BDA and Dispoke methods and the results demonstrate that the 1,4-dioxane backbone in general structure ligands is important for the stabilization of metal-ligand chelate conformation.

Results describe methodology for synthesizing chiral bisphosphines for Ru-catalyzed asymmetric hydrogenation of beta-ketoesters. Data indicate that changing ligand dihedral angles of the bisphosphines produces variations in their enantioselectivity.

Research has been conducted on the chiral phosphine ligands.The development of the bisphosphine ligand as an effective ligand for the Rh-catalyzed enamides hydrogenation in the chiral amine preparation is described.

A practical synthetic route for chiral hydroxyl mono- and bisphospholane synthesis is described. Data suggest that the hydroxyl phospholanes accelerate the Baylis-Hillman reaction. Further, the Rh(I) complexes of bisphospholanes serve as catalysts for the enantioselective hydrogenation of unsaturated substrates.

A study concerning the hydrogenation of beta-(acylamino)acrylates for the synthesis of beta-amino acid derivatives is presented. The use of Rh-BICP and Rh-DuPhos catalytic systems is described.

A study was conducted to analyze the asymmetric rhodium-catalyzed hydrogenation of enamides with a chiral 1,4-bisphosphine bearing diphenylphosphino groups. Reactions were performed using a nitrogen-filled glovebox or standard Schelnk methods. Experimental results indicated that bis(diphenylphosphino)-1(R),1'(R)-dicyclopentane is one of the best chiral diphenylphosphino ligands for the rhodium-catalyzed asymmetric hydrogenation of electron-rich olefin substrates.

Research was conducted to examine the asymmetric formation of quaternary carbon centers catalyzed by novel chiral 2,5-dialkyl-7-phenyl-7-phosphabicyclo-(2.2.1)heptanes. Results indicate that phosphine 2,5-diakyl-7-phenyl-7-phosphabicyclo-(2.2.1)heptanes are one of the most effective catalysts for the asymmetric gamma-addition reaction. However, a rationale for the asymmetric C-C forming reaction could not be found.

The process of asymmetric hydrogenation of dehydroamino acids was thoroughly investigated. A new set of phosphinites, which could possibly produce nine-membered chelated complexes with rhodium, had remarkably high selectivities for the hydrogenation of dehydroamino acids. The main element in this process was that the two cyclopentane in the backbone restrict the conformational flexibility of the nine-membered ring and the four stereogenic carbon centers in the backbone determine the orientation of the four P-phenyl groups.

Aromatic aldehydes were utilized as a substrate for the Ti-catalyzed enantioselective addition of Et2Zn in the presence of a titanate complex with a tetradentate helical ligand. The asymmetric addition of diethylzinc to aldehydes for the synthesis of chiral secondary alcohols was dependent on (1R, 2R)-(+)-1,2-bis(3,5-dichloro-2-hydroxybenzenesulfonamido)(cyclohexane). The catalyst containing phenolic aromatic sulfonamide acted as monomeric titanate species during the asymmetric bond forming process.

A class of iron(II) porphyrins with unusually low CO to O2 affinity ratio was synthesized via the congruent multiple Michael addition method. Analysis of the nuclear magnetic resonance spectra of the myoglobin active site analogues indicated the role of steric interactions in reducing their CO to O2 affinity ratio. Furthermore, the low CO to O2 ratio was influenced by the structure of the porphyrin cavity and the steric effects of the axial ligand on Fe.

Reaction of 5,10,15, 20-tetrakis(2-hydroxyphenyl)porphyrin with ditosylthretiol derivatives produces nine compounds, which are members of a family of new chiral porphyrins. 1H NMR spectra and X-ray studies enable the identification of the resultant isomers. A comparative study of the epoxidation of unfunctionalized olefins, using manganese derivatives of these chiral porphyrins as catalysts, reveals that a manganese porphyrin generates up to 88% ee in the epoxidation of 1,2-dihydronaphthalene.

A surface acoustic wave (SAW) device that responds to oxygen pressure was developed by coating a 158-MHz quartz SAW device with an oxygen-binding agent. Two types of coatings were used. One type was prepared by dissolving an oxygen-binding agent in a toluene solution of a copolymer containing the axial ligand. A second type was prepared with an oxygen-binding porphyrin in a toluen solution containing excess axial ligand without a polymer matrix. In the polymer-based coatings, the copolymer served to provide the axial ligand to the oxygen-binding agent and as a coating matrix on the surface of the SAW device. The oxygen-sensing SAW device has been shown to bind oxygen following a Langmui isotherm and may be used to measure the equilibrium constant of the oxygen-binding compound in the coating matrix.

1H NMR and oxygen affinity analysis of iron and cobalt picnic basket porphyrins (PBP) reveals that PBPs have high oxygen affinities. Increase in basket size decreases oxygen affinity. Interactions between terminally bound dioxygen and amide protons influence oxygen affinity. The oxygen ligand in Co(II)O2 adducts has a greater electron density than that in Fe(II)O2 adducts.

Research demonstrates a new palladium-catalyzed homocoupling pathway, which is initiated with ethyl bromoacetate. Data indicate that the palladium enolate intermediate undergoes double transmetalation with an alkynyl copper to form diynes in high yields.

Asymmetric hydrogenation of aromatic ketones was examined via s Ru-BICP catalytic system. The results suggested that a Ru-BICP-chiral-diamine KOH catalyst system is affective for hydrogenation of aromatic ketones, especially 2-acetyltiophene derivatives. Moreover, it was also suggested that multipoint interactions between the substrate and the catalysts might be responsible for high enantioselectinity in reduction of 2-acetylthiophene derivatives.

The novel synthesis of a family of chiral phosphines with a unique fused bicyclic {2.2.1} ring structure was developed. Pd-catalyzed allylic alkylations with single phosphine complex yielded good enantioselectivities. It was shown that modifying the size of the substituents on the chiral monophosphine affected the selectivity. Furthermore, mechanistic aspects of this reactions were investigated.

A cytochrome c oxidase model that consists of a cobalt(II) porphyrin with a copper(I) triazacyclononane macrocycle fastened on the distal face and an imidazole covalently attached to the proximal face has been synthesized and characterized. Redox titrations with molecular oxygen ([O.sub.2]) and cobaltocene were carried out, and [O.sub.2] was found to bind irreversibly in a 1:1 ratio to the model compound. This [O.sub.2] adduct (a bridged peroxide) can be fully reduced to the deoxygenated form with four equivalents of cobaltocene. The model compound was adsorbed on an edge-plane graphite electrode, and rotating ring-disk voltammetry was used to monitor the electrocatalytic reduction of [O.sub.2]. Four-electron reduction of [O.sub.2] was observed at physiological pH., Oxidative phosphorylation, a process required by all respiring organisms, involves four-electron ([4e.sup.-]) reduction of [O.sub.2] to [H.sub.2]O by the cytochrome c oxidase enzyme family (1-4). The active site of cytochrome [...]

The authors review the publications on asymmetric hydrogenation which utilizes molecular hydrogen to produce imines, olefines and ketones. The topics include the analysis of chiral phosphorus ligands, and the applications of these ligands in asymmetric hydrogenation.

Research has been conducted on Ir-f-binaphane complex. The authors demonstrate that using this complex as a catalyst they could achieve conversions and enantioselectivities in the asymmetric aryl ketone reductive amination carried out in the presence of iodine and titanium(IV) isopropoxide.

Research has been conducted on the BINAPO ligands. The development of these ligands for the enantioselective Ru-catalyzed hydrogenation is discussed.

A highly enantioselective palladium-catalyzed asymmetric cyclocarbonylation of geminally disubstituted allylic alcohols was developed. The first highly enantioselective cyclocarbonylation of beta,gamma-substituted allylic alcohols without dialkyl substituents at the alpha position was demonstrated. These findings show that BICP is a novel chiral ligand for palladium-catalyzed asymmetric carbonylation.

A highly enantioselective Rh-PennPhos catalyst was developed for the asymmetric hyrdogenation of cyclic enamides. The enamide substrate used was the N-(3,4-dihydro-1-naphthyl)acetamide since it can be easily prepared by the reduction of the corresponding oxime with iron powder in the presence of acetic anhydride. Results indicated that the reaction has a strong potential for the synthesis of enantiomerically pure alpha-aminotetralins and alpha-aminoindanes.

The first practical asymmetric hydrogenation technique, which allows efficient syntheses of enantiomerically enriched beta-amino alcohols, is described. The transformation uses cationic BICP-Rh and Me-DuPhos-Rh complexes as catalysts. The method involves the synthesis of alpha-hydroxy ketones, a novel enamide formation process from oximes and high enantioselectivity in the hydrogenation. Asymmetric hydrogenations of a variety of alpha-arylenamides with a MOM-protected beta-hydroxy group are described.

The ligand system of bis(oxazolinylmethyl)amine was studied through the synthesis of bis[4-(R)-phenyloxazolin-2-yl-methyl]amine (1,(R)-ph-ambox) and the results correlated with asymmetric transfer hydrogenation of aromatic ketones. The Ru-ambox catalyst produced a similar enantioselectivity to the Ru-TsDPEN transfer hydrogenation system. The chiral tridentate ligand was capable of developing a highly effective and practical catalyst with RuCl2-(PPh3)3 for transfer hydrogenation of aryl alkyl ketones.

A method for the synthesis of new chiral monophosphines with novel fused bicyclic [2.2.1] ring structure was developed based on the utilization of chiral diols. The synthetic process was characterized by the formation of the target compounds based on the nucleophilic addition of Li2PPh to the chiral dimesylates. The resulting products also catalyzed [3+2] cycloaddition reactions between 2,3-butanedienoates and electron-deficient olefins to form cyclopentene products.

A new chiral 1,4-biphosphine, (2R,2'R)-bis(diphenylphosphino)-(1R,1'R)-dicyclopentane (1) in the rhodium-catalyzed asymmetric hydrogenation of alpha-(acylamino)acrylic acids has been synthesized. The main feature of the ligand is that it has two cyclopentane rings in its backbone which limit its conformational flexibility. Findings showed that the new chiral 1 is an excellent ligand for the Rh(I)-catalyzed asymmetric hydrogenation of several alpha-(acylamino)acrylic acids.

A short synthetic sequence involving metalation reactions enables the synthesis of a cytochrome c oxidase model which has structural similarity with the oxygen binding site of the native enzymes. UV-vis spectroscopic studies suggest that the model forms a 1:1 adduct with dioxygen and the titration of the adduct with cobaltocene followed by NMR and UV-vis spectroscopy reveals that the adduct oxidizes 4 equiv of cobaltocene. Resonance Raman's spectra helps analyze the model and electrospray mass spectroscopy confirms the formation of 1:1 dioxygen:porphyrin adduct.

A potent general procedure is proposed for the synthesis of analogues of various heme protein active regions. The convergent multiple Michael addition forms the basis of this methodology to prepare biomimetic model hemes. A Fe (II) porphyrin which binds dioxygen reversibly and a mercaptide Fe(II) carbonyl complex with the special spectral properties of cytochrome P-450.