Maria B. Ezhova

Bio: Maria B. Ezhova is an academic researcher from University of British Columbia. The author has contributed to research in topics: Catalysis & Imine. The author has an hindex of 9, co-authored 18 publications receiving 292 citations.

Direct, Catalytic α-Alkylation of N-Heterocycles by Hydroaminoalkylation: Substrate Effects for Regiodivergent Product Formation.

Abstract: Saturated N-heterocycles are prevalent in pharmaceutical and agrochemical industries, yet remain challenging to catalytically alkylate. Most strategies for C-H activation of these challenging substrates use protected amines or high loadings of precious metal catalysts. We report an early transition-metal system for the broad, robust, and direct alkylation of unprotected amine heterocycles with simple alkenes. Short reaction times are achieved using an in situ generated tantalum catalyst that avoids the use of bases, excess substrate, or additives. In most cases, this catalyst system is selective for the branched reaction product, including examples of products that are generated with excellent diastereoselectivity. Alkene electronic properties can be exploited for substrate-modified regioselectivity to access the alternative linear amine alkylation product with a group 5 catalyst. This method allows for the facile isolation of unprotected N-heterocyclic products, as useful substrates for further reactivity.

A new class of bleaching and brightness stabilizing agents. Part I: Bleaching of mechanical pulps

Abstract: Nous avons decouvert une nouvelle classe d'agents de blanchiment et de stabilisation de la blancheur pour les pâtes chimiques et mecaniques. Les nouveaux agents sont des sels de phosphine tertiaire et des sels d'hydroxymethylphosphonium quartenaire, comme le tris(hydro-xymethyl)phosphine (THP), le P(CH 2 OH) 3 , et le chlorure de tetrakis(hydroxymethyl)-phosphonium (THPC) ou [P(CH 2 OH) 4 ]Cl. Pour le blanchiment des pâtes mecaniques, ces composes phosphores sont dotes d'une puissance de blanchiment similaire a celle de l'hydrosulfite de sodium, mais ils peuvent etre employes sur une plus grande echelle de pH (4,3 a 9,3), de temperature (20 a 130 °C) et de teneur (par ex. 1,5 a 20 % Cs.) sans qu'il ne soit necessaire d'eliminer l'oxygene ou les ions metalliques de transition. En outre, les pâtes blanchies avec ces nouveaux agents sont plus stables a la chaleur et a l'humidite que celles ayant ete blanchies avec de l'hydrosulfite de sodium ou du peroxyde alcalin. Le blanchiment des pâtes mecaniques avec du THP ou du THPC est accompagne d'une reduction du coefficient d'absorption des pâtes.

New chiral N, P-oxazolines, and their Ir complexes in asymmetric hydrogenation of an imine

Abstract: (+) (1S,2S)-2-Amino-1-phenyl-1,3-propanediol reacts with ortho-esters to form 4-hydroxymethyl-5-phenyl-1,3-oxazolines. Subsequent reaction of their toluenesulfonyl derivatives with diphenylphosphinolithium yields the N,P-ligands, (4S,5S)-2-R-4-diphenylphosphinomethyl-5-phenyl-1,3-oxazoline (R = Me, Et, Ph). X-ray analyses of (4S,5S)-2-methyl-4-toluenesulfonylmethyl-5-phenyl-1,3-oxazoline and (4S,5S)-2,5-diphenyl-4-diphenylphosphinomethyl-1,3-oxazoline reveal retention of absolute configuration throughout the synthesis. The [Ir(COD)(N,P-oxazoline)]PF6 systems in CH2Cl2 effect catalytic hydrogenation of N-(1-phenylethylidene)benzylamine, PhCH2N = C(Me)Ph, to the corresponding amine with upto 63% e.e. with the R = Et ligand.

Transition Metal-Catalyzed Enantioselective Hydrogenation of Enamines and Imines

Abstract: Transition metal-catalyzed enantioselective hydrogenation of enamides and enamines is one of the most important methods for the preparation of optically active amines. This review describes the recent developments of highly efficient catalytic asymmetric hydrogenation of enamides, and enamines. It specifically focuses on the substrates because hydrogenation of enamides and enamines is highly dependent on the substrates although the chiral metal catalysts play a significant role.

Recent applications of oxazoline-containing ligands in asymmetric catalysis.

Abstract: Compounds containing a chiral oxazoline ring have become one of the most successful, versatile, and commonly used classes of ligands for asymmetric catalysis due to their ready accessibility, modular nature, and applicability in a wide range of metal-catalyzed transformations. The large majority of these ligands are derived from readily available chiral amino alcohols in short, high yielding synthetic sequences. As a consequence, the enantiocontrolling stereocenter resides on the carbon atom neighboring the coordinating nitrogen of the oxazoline ring and, therefore, in close proximity to the metal active site, thus having a direct influence on the stereochemical outcome of the reaction. Since the first report in 1986 of the use of chiral oxazolinebased ligands in asymmetric catalysis, a diverse range of ligands with one, two, or more oxazoline rings incorporating various heteroatoms, additional chiral elements, and specific structural features have been used with great success in a wide range of asymmetric reactions. This review reports on the use of such ligands in homogeneous metal-catalyzed asymmetric synthesis since 2004, when the area was last reviewed.1 We cover, to the best of our knowledge, all applications of oxazolinecontaining ligands reported in the literature until the end of 2007. This review will be structured in the same manner as our 2004 review, as we classify ligands not by the reaction to which their metal complexes have been applied but by the nature of the denticity, chirality, and donor atoms involved. In this manner, the continued development of ligand architectural design can be more easily monitored.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

Abstract: This Review gives a comprehensive overview of the most topical weakly coordinating anions (WCAs) and contains information on WCA design, stability, and applications. As an update to the 2004 review, developments in common classes of WCA are included. Methods for the incorporation of WCAs into a given system are discussed and advice given on how to best choose a method for the introduction of a particular WCA. A series of starting materials for a large number of WCA precursors and references are tabulated as a useful resource when looking for procedures to prepare WCAs. Furthermore, a collection of scales that allow the performance of a WCA, or its underlying Lewis acid, to be judged is collated with some advice on how to use them. The examples chosen to illustrate WCA developments are taken from a broad selection of topics where WCAs play a role. In addition a section focusing on transition metal and catalysis applications as well as supporting electrolytes is also included.

Well-defined chiral spiro iridium/phosphine-oxazoline cationic complexes for highly enantioselective hydrogenation of imines at ambient pressure.

Abstract: New chiral phosphine-oxazoline ligands (7, SIPHOX) with a rigid and bulky spirobiindane scaffold were synthesized, starting with optically pure 7-diphenylphosphino-7'-trifluoromethanesulfonyloxyl-1,1'-spirobiindane, in four steps in 40-64% overall yield. Iridium complexes of 7, the chiral analogues of the Crabtree catalyst, were generated by coordination of ligands 7 and [Ir(COD)Cl](2) in the presence of sodium tetrakis-3,5-bis(trifluoromethyl)phenylborate. The complexes were characterized by NMR, ESI-MS, and X-ray diffraction analysis. The Ir-SIPHOX complexes can catalyze the hydrogenation of acyclic N-aryl ketimines under ambient pressure with excellent enantioselectivities (up to 97% ee) and full conversions. This result represents the highest enantioselectivity and the first example of the hydrogenation of imines catalyzed by chiral analogues of the Crabtree catalyst at ambient pressure. Studies on the stability of the catalysts revealed that the catalysts Ir-SIPHOX are very stable and resistant to the formation of inactive trimers under hydrogenation conditions. On the basis of the X-ray diffraction analysis of the structures of catalysts and amine products, a rational explanation for the enantiocontrol of the chiral catalysts in the hydrogenation of imines is proposed.

Ring-Opening Polymerization of Lactides Catalyzed by Natural Amino-Acid Based Zinc Catalysts

Abstract: A series of chiral NNO-tridentate Schiff base ligands derived from natural amino acids were reacted with zinc(bis-trimethylsilylamide)2 to provide metal complexes which have been fully characterized. One of these derivatives was further reacted with p-fluorophenol to yield a phenoxide complex. X-ray crystallographic studies reveal the zinc Schiff base amide complexes to be monomeric, whereas, the p-fluorophenolate complex was shown to be dimeric with bridging phenoxide ligands. All zinc complexes were shown to be very effective catalysts for the ring-opening polymerization (ROP) of lactides at ambient temperature, producing polymers with controlled and narrow molecular weight distributions. These enantiomerically pure zinc complexes did not show selectivity toward either l- or d-lactide, that is, kd(obsd)/kl(obsd) ≈ 1. However, steric substituents on the Schiff base ligands exhibited moderate to excellent stereocontrol for the ROP of rac-lactide. Heterotactic polylactides were produced from rac-lactide wi...