Asymmetric epoxidation of unsaturated hydrocarbons catalyzed by ruthenium complexes

Development of a ruthenium–aquo complex for utilization in synthesis and catalysis for selective hydration of nitriles and alkynes

A ruthenium(ii)–aquo complex serves as a precursor for the synthesis of new ternary complexes and also as an efficient catalyst for selective hydration of aryl nitriles to aryl amides and aryl alkynes to aryl aldehydes.

A Chimeric Styrene Monooxygenase with Increased Efficiency in Asymmetric Biocatalytic Epoxidation

The styrene monooxygenase (SMO) system from Pseudomonas sp. consists of two enzymes (StyA and StyB). StyB catalyses the reduction of FAD at the expense of NADH. After the transfer of FADH2 from StyB to StyA, reaction with O2 generates FAD-OOH, which is the epoxidising agent. The wastage of redox equivalents due to partial diffusive transfer of FADH2 , the insolubility of recombinant StyB and the impossibility of expressing StyA and StyB in a 1:1 molar ratio reduce the catalytic efficiency of the natural system. Herein we present a chimeric SMO (Fus-SMO) that was obtained by genetic fusion of StyA and StyB through a flexible linker. Thanks to a combination of: 1) balanced and improved expression levels of reductase and epoxidase units, and 2) intrinsically higher specific epoxidation activity of Fus-SMO in some cases, Escherichia coli cells expressing Fus-SMO possess about 50 % higher activity for the epoxidation of styrene derivatives than E. coli cells coexpressing StyA and StyB as discrete enzymes. The epoxidation activity of purified Fus-SMO was up to three times higher than that of the two-component StyA/StyB (1:1, molar ratio) system and up to 110 times higher than that of the natural fused SMO. Determination of coupling efficiency and study of the influence of O2 pressure were also performed. Finally, Fus-SMO and formate dehydrogenase were coexpressed in E. coli and applied as a self-sufficient biocatalytic system for epoxidation on greater than 500 mg scale.

A new diphosphine-carbonyl complex of ruthenium: an efficient precursor for C–C and C–N bond coupling catalysis

Reaction of 1,2-bis(diphenylphosphino)benzene (dppbz) with [{Ru(CO)₂Cl₂}_n] affords [Ru(dppbz)(CO)₂Cl₂], which serves as an excellent pre-catalyst for Suzuki-type C–C coupling and Buchwald-type C–N coupling reactions.

Halogenated tetraphenyl porphyrin; iodosylbenzene an efficient catalytic system for olefin epoxidation

Olefin epoxidation using o-phenyl and [Formula: see text]-pyrrole substituted tetraphenyl porphyrin complexes of Fe(III) and Mn(III) as catalysts and [Formula: see text]Iodosylbenzene as oxidant was studied. Excellent yields of epoxide and secondary oxidation products were observed. Effect of pyridine, imadizole, sodium lauryl sulphate, and solvent variation was also studied. Effect of substituents on catalytic activity of the porphyrin complex is also explained. o-phenyl substituted complexes gave better yield of epoxide as compared to [Formula: see text]-pyrrole substituted complexes.

Comparative Assessment of DFT Performances in Ru- and Rh-Promoted σ-Bond Activations

In this work, the performances of 19 density functional theory (DFT) methods are calibrated comparatively on Ru- and Rh-promoted σ-bond (C-H, O-H, and H-H) activations. DFT calibration reference is generated from explicitly correlated coupled cluster CCSD(T)-F12 calculations, and the 4s4p core-valence correlation effect of the two 4d platinum group transition metals is also included. Generally, the errors of DFT methods for calculating energetics of Ru-/Rh-mediated reactions appear to correlate more with the magnitude of energetics itself than other factors such as metal identity. For activation energy calculations, the best performing functionals for both Ru and Rh systems are MN12SX < CAM-B3LYP < M06-L < MN12L < M06 < ωB97X < B3LYP < LC-ωPBE (in the order of increasing mean unsigned deviations, MUDs, of less than 2 kcal/mol). For reaction energy calculations, best functionals with MUDs less than 2 kcal/mol are PBE0 < CAM-B3LYP ≈ N12SX. The effect of the DFT empirical dispersion correction on the performance of the DFT methods is beneficial for most density functionals tested in this work, reducing their MUDs to different extents. After including empirical dispersion correction, ωB97XD, B3LYP-D3, and CAM-B3LYP-D3 (PBE0-D3, B3LYP-D3, and ωB97XD) are the three best performing DFs for activation energy (reaction energy) calculations, from which B3LYP-D3 and ωB97XD can notably be recommended uniformly for both the reaction energy and reaction barrier calculations. The good performance of B3LYP-D3 in quantitative description of the energetic trends further adds value to B3LYP-D3 and singles this functional out as a reasonable choice in the Ru/Rh-promoted σ-bond activation processes.

Polypyrrole-functionalized ruthenium carbene catalysts as efficient heterogeneous systems for olefin epoxidation

New Ru complexes containing the bpea-pyr ligand (bpea-pyr stands for N,N-bis(pyridin-2-ylmethyl)-3-(1H-pyrrol-1-yl)propan-1-amine), with the formula [RuCl2(bpea-pyr)(dmso)] (isomeric complexes 2a and 2b) or [Ru(CN-Me)(bpea-pyr)X)](n+) (CN-Me = 3-methyl-1-(pyridin-2-yl)-1H-imidazol-3-ium-2-ide; X = Cl, 3, or X = H2O, 4), have been prepared and fully characterized. Complexes 3 and 4 have been anchored onto an electrode surface through electropolymerization of the attached pyrrole group, yielding stable polypyrrole films. The electrochemical behaviour of 4, which displays a bielectronic Ru(IV/II) redox pair in solution, is dramatically affected by the electropolymerization process leading to the occurrence of two monoelectronic Ru(IV/III) and Ru(III/II) redox pairs in the heterogeneous system. A carbon felt modified electrode containing complex 4 (C-felt/poly-4) has been evaluated as a heterogeneous catalyst in the epoxidation of various olefin substrates using PhI(OAc)2 as an oxidant, displaying TON values of several thousands in all cases and good selectivity for the epoxide product.

Bis[(2-methyl-benz-yl)bis-(pyridin-2-ylmethyl-κN)amine-κN]manganese(II) bis-(perchlorate)

In the title complex, [Mn(C20H21N3)2](ClO4)2, two tridentate (2-methyl-benz-yl)bis-(pyridin-2-ylmeth-yl)amine (L) ligands form the Mn(II) complex [MnL 2](ClO4)2. The Mn(II) ion lies on a twofold axis and the complex cation is significantly distorted from regular octa-hedral geometry. The packing is stabilized by weak C-H⋯O inter-actions between the cations and anions, which link them into a zigzag ribbon along [101]. The perchlorate anion is disordered and was constrained to be tetra-hedral with two orientations having occupancies of 0.768 (4) and 0.232 (4). The 2-methylbenzyl moiety is also disordered over two sets of sites, with occupancies of 0.508 (15) and 0.492 (15).

A one-dimensional coordination polymer formed from the reaction of 1,1-diphenyl-3,3'-[(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)]dibut-2-en-1-one with MnCl2·4H2O

In the title coordination polymer, catena-poly[[dichloridomanganese(II)]-μ-1,1-diphenyl-3,3'-[(1R,2R)-cyclohexane-1,2-diylbis(azaniumylylidene)]dibut-1-en-1-olate-κ(2)O:O'], [MnCl2(C26H30N2)]n, synthesized by the reaction of the chiral Schiff base ligand 1,1-diphenyl-3,3'-[(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)]dibut-2-en-1-one (L) with MnCl2·4H2O, the asymmetric unit contains one crystallographically unique Mn(II) ion, one unique spacer ligand, L, and two chloride ions. Each Mn(II) ion is four-coordinated in a distorted tetrahedral coordination environment by two O atoms from two L ligands and by two chloride ligands. The Mn(II) ions are bridged by L ligands to form a one-dimensional chain structure along the a axis. The chloride ligands are monodentate (terminal). The ligand is in the zwitterionic enol form and displays intramolecular ionic N(+)-H...O(-) hydrogen bonding and π-π interactions between pairs of phenyl rings which strengthen the chains.

Asymmetric epoxidation with H2O2 by manipulating the electronic properties of non-heme iron catalysts

A non-heme iron complex that catalyzes highly enantioselective epoxidation of olefins with H2O2 is described. Improvement of enantiomeric excesses is attained by the use of catalytic amounts of carboxylic acid additives. Electronic effects imposed by the ligand on the iron center are shown to synergistically cooperate with catalytic amounts of carboxylic acids in promoting efficient O-O cleavage and creating highly chemo- and enantioselective epoxidizing species which provide a broad range of epoxides in synthetically valuable yields and short reaction times.

Syntheses and characterization of a series of asymmetric porphyrins containing an 8-ethoxycarbonyl-1-naphthyl group

Using aldehydes with different substituents of the aryl groups, we have synthesized a series of asymmetric porphyrins containing an 8-ethoxycarbonyl-1-naphthyl group by one-pot reactions. Our studies suggest the steric property of substituents is the major factor to affect the reaction yields, the steric hindrance is unfavorable for such reaction. Compared with those para-substituted species, NMR studies of 2,6-substituted species show upfield shifts for their NH and ethyl protons, downfield shifts for their pyrrole protons, which is probably due to the decrease of porphyrin ring current. Three of them have been characterized by X-ray crystallography. Structures show that the ester group is hanging over the porphyrin plane, compound 3 and 4 have much different core conformations from compound 2, which is probably due to the π–π interactions in the solid state.

Ruthenium complexes with chiral bis-pinene ligands: an array of subtle structural diversity

A new chiral derivative of the N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, Me-pinene[5,6]bpea [(-)-L1], has been prepared from a new aldehyde building block [Me-pinene-aldehyde, (-)-4] arising from the monoterpene chiral pool. The tridentate (-)-L1 ligand has been employed to prepare a new set of Ru-Cl complexes in combination with didentate 2,2'-bipyridine (bpy) with the general formula [RuCl((-)-L1)(bpy)](+). These complexes have been characterized in solution by cyclic voltammetry, UV-vis, and 1D and 2D NMR spectroscopy. Isomeric mixtures of trans,fac-C1a and anti,mer-C1c compounds are formed when (-)-L1 is reacted with a [Ru(bpy)(MeOH)Cl3] precursor. Density functional theory calculations of all of the potential isomers of this reaction have been performed in order to interpret the experimental results in terms of electronic and steric effects and also to unravel the observed isomerization pathway between anti,mer-C1c and trans,fac-C1a.

Ruthenium(II) hydrazone Schiff base complexes: synthesis, spectral study and catalytic applications

Ruthenium(II) hydrazone Schiff base complexes of the type [RuCl(CO)(B)(L)] (were B=PPh(3), AsPh(3) or Py; L=hydrazone Schiff base ligands) were synthesized from the reactions of hydrazone Schiff base ligand (obtained from isonicotinoylhydrazide and different hydroxy aldehydes) with [RuHCl(CO)(EPh(3))(2)(B)] (where E=P or As; B=PPh(3), AsPh(3) or Py) in 1:1 molar ratio. All the new complexes have been characterized by analytical and spectral (FT-IR, electronic, (1)H, (13)C and (31)P NMR) data. They have been tentatively assigned an octahedral structure. The synthesized complexes have exhibited catalytic activity for oxidation of benzyl alcohol to benzaldehyde and cyclohexanol to cyclohexanone in the presence of N-methyl morpholine N-oxide (NMO) as co-oxidant. They were also found to catalyze the transfer hydrogenation of aliphatic and aromatic ketones to alcohols in KOH/Isopropanol.

Recent advances in catalytic asymmetric epoxidation using the environmentally benign oxidant hydrogen peroxide and its derivatives

There has been a recent drive to develop asymmetric catalytic methods to produce epoxides using environmentally benign oxidants, especially hydrogen peroxide. This critical review discusses the advances that have been made using both metal-based and organocatalytic homogeneous catalysts (142 references).