Search

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.

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 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.

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.

Studies novel rhodium-catalyzed cycloisomerization of 1,6-enynes with an intramolecular halogen shift. Omission of phosphine ligands; Cycloisomerization catalyzed by RhC(PPh[sub3])[sub3].

The article presents a study on the unprotected nitrogen—hydrogen (N—H) imines' enantioselective hydrogenation. It defines the hydrogenation process of imines as a fundamental step in the direct asymmetric reductive amination development of ketones. It examines a variety of N—H substrates with the use of Ir-f-binaphane catalyst system. It also evaluates electron-rich chiral Ir-phosphine complexes.

Chiral amino alcohol is a key function group in biologically active molecules. Consequently, the construction of this structural motif attracts extensive efforts by organic chemists. Developing highly enantioselective methods to prepare amino alcohols with efficiency remains one of the major challenges. Without any doubt, asymmetric hydrogenation is the most powerful method to make chiral molecules. For example, asymmetric hydrogenation of ketones is regarded as the most successful method to form chiral alcohols.

Homogeneous asymmetric hydrogenation of unprotected benzophenone N-H imines 1a-r using Ir-(S)-N-benzyl-N-methyl-MonoPhos as a catalyst provides chiral amines 2a-r in 80-96% yield with enantioselectivities up to 98% ee (18 examples) for ortho-substituted substrates.

A general protocol for the rhodium-catalyzed oxidative carbonylation of arenes to form esters has been developed. A broad substrate scope has been demonstrated allowing carbonylation of electron-rich, electron-poor, and heterocyclic arenes, and the reaction shows wide functional group tolerance and excellent regioselectivities. Up to 96% yield of ortho-substituted aryl or heteroaryl carboxylic esters were obtained with this methodology. The possible mechanism for the rhodium-catalyzed oxidative carbonylation reaction was proposed in this article. Studies show that Oxone play an important role in the transformation.

A new pyrrole-based tetraphosphorus ligand capable of forming multiple chelating modes has been prepared. Higher regioselectivity has been achieved in the rhodium-catalyzed isomerization-hydroformylations of internal olefins compared with its bisphosphorus analogue.