Enantioselective carbonylation reactions of para-substituted 2-phenylpropenes

The enantioselective hydroformylation catalyzed by [(R,R)-Diop]Pt(SnCl₃)Cl7 and the enantioselective hydroisopropoxycarbonylation catalyzed by [(R,R)-Diop]PdCl₂8 or by [(R,R)-Diop-dbp]PdCl₂9 of some para-substituted 2-phenylpropenes (para substituents = NO₂, H, CH₃O, Cl, CF₃) was investigated in order to recognize possible electronic influences on the regioselectivity and on the enantioface selection which take place in such carbonylation reactions. The catalytic systems used gave no carbonylation products when the nitro compound was the substrate. 7 and 8 show similar regioselectivities, the less branched isomer being exclusively formed for all substrates except p-methoxy-2-phenylpropene which gave small amounts of the alternative regioisomer. The enantioselectivity depends on the σ_p effect of the substituent in both cases; the differences are, however, rather small and the trend is opposite in the two cases. The regioselectivity displayed by 9 is still in favour of the less branched isomer but it is high only in the case of p-trifluoromethyl-2-phenylpropene. Larger differences with respect to the other catalytic systems were also observed for enantioselectivity but the trend for both regioselectivity and enantioselectivity is not linear.     

Effects of substituent and temperature on enantioselectivity for lipase-catalyzed esterification of 2-(4-substituted phenoxy) propionic acids in organic solvents

Substituent effects on the enantioselectivity for the lipase-catalyzed esterifications in organic solvents were studied by use of 2-(4-substituted phenoxy)propionic acids as the substrates with various substituents of H, F, Cl, CF(3), CH(3), CH(3)CH(2), and CH(3)O. The distinction in the behavior of their enantioselectivity was primarily responsible for the size effects of the substituents, although the substituents are far away from the stereocenter of the substrates. For the similar substituents in size, CH(3) and CF(3), however, their electronic effects played an important role in controlling the enantioselectivity. This variation of the enantioselectivity due to the electronic effects is also supported by the discussion based on the value of the Michaelis constant (K(m)) obtained. In addition, by raising the reaction temperature with enough water added to isopropyl ether as the reaction medium, the enantioselectivity is found to be dramatically enhanced for the substrate bearing CH(3)O group due to the strong electron-donating effect.     

Comparative properties of fluorous phosphine ligand complexes: W(CO)5L. Crystal structure of W(CO)5P(C6H4-4-CH2CH2(CF2)7CF3)3

The compounds W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ (1) and W(CO)₅P(CH₂CH₂(CF₂)₅CF₃)₃ (2) were synthesized in order to probe the electronic and physical effects of ligation by perfluorocarbon substituted tertiary phosphine ligands in a W(CO)₅L complex. The π-accepting ability of the fluorous phosphines was found to rank with non-fluorous comparators as P(CH₂CH₂(CF₂)₅CF₃)₃ > P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ > PPh₃ > P(p-tolyl)₃ > P(n-octyl)₃. The X-ray crystal structure of W(CO)₅P(C₆H₄-4-CH₂CH₂(CF₂)₇CF₃)₃ shows strong intermolecular association of fluorous components but confirms that the para fluorocarbon subtituents have an insignificant effect on the tungsten coordination environment. Partition coefficients (toluene/perfluoromethylcyclohexane) were measured for compounds 1 and 2.     

ETS-NOCV description of σ-hole bonding

The ETS-NOCV analysis was applied to describe the σ-hole in a systematic way in a series of halogen compounds, CF₃-X (X?=?I, Br, Cl, F), CH₃I, and C(CH3)_nH_3-n-I (n?=?1,2,3), as well as for the example germanium-based systems. GeXH₃, X?=?F, Cl, H. Further, the ETS-NOCV analysis was used to characterize bonding with ammonia for these systems. The results show that the dominating contribution to the deformation density, Δρ ₁ , exhibits the negative-value area with a minimum, corresponding to σ-hole. The “size” (spatial extension of negative value) and “depth” (minium value) of the σ-hole varies for different X in CF₃-X, and is influenced by the carbon substituents (fluorine atoms, hydrogen atoms, methyl groups). The size and depth of σ-hole decreases in the order: I, Br, Cl, F in CF₃-X. In CH₃-I and C(CH3)_nH_3-n-I, compared to CF₃-I, introduction of hydrogen atoms and their subsequent replacements by methyl groups lead to the systematic decrease in the σ-hole size and depth. The ETS-NOCV σ-hole picture is consistent with the existence the positive MEP area at the extension of σ-hole generating bond. Finally, the NOCV deformation density contours as well as by the ETS orbital-interaction energy indicate that the σ-hole-based bond with ammonia contains a degree of covalent contribution. In all analyzed systems, it was found that the electrostatic energy is approximately two times larger than the orbital-interaction term, confirming the indisputable role of the electrostatic stabilization in halogen bonding and σ-hole bonding.

Enantioselective reduction of fluorenones in surfactant-aqueous solution by fruits and vegetables

Various fruits and vegetables have been evaluated as biocatalysts in the enantioselective reduction of substituted fluorenones under mild and eco-friendly conditions. Grape exhibited the best results with 99% ee and 97% conversion. The conversion rate varies in the presence of different surfactants, but the enantioselectivity remains unchanged. That is, enantiomeric selectivity is from biocatalysts and the conversion is related to the aqueous solubility of substrates. The surfactant, Triton X-100, is the best for improving the biotransformation and behaved in a concentration-dependent manner. The high enantioselectivity of halogen substituents is attributed to halogen electron-withdrawing effects rather than electron-donating effects like –CH₃, but the yield is not dependent on the size of the halogens. It is interesting that the absolute configuration of the product, 2-chloro-fluorenol, is R not S, indicating its biocatalytic reduction following anti-Prelog's rule. This study provided a useful method for the reduction of rigid macro-cyclic aromatic ketones.     

Kinetics and mechanism of alkali-induced decomposition of 2-alkoxyethylcobaloximes

Kinetics of the base-induced decomposition of five 2-alkoxyethyl(aquo)cobaloximes, ROCH₂CH₂- Co(D₂H₂)OH₂ (R = C₆H₅, CF₃CH₂, CH₃, CH₃CH₂, (CH₃)₂CH), have been studied manometrically in aqueous base, ionic strength 1.0 M (KC1) at 25.0± 0.1 °C under an argon atmosphere. For the complexes with good leaving group alkoxide substituents (R = C₆H₅ and CF₃CH₂) the reactions are first- order in cobaloxime and first-order in hydroxide ion and produce stoichiometric amounts of ethylene and leaving group alcohol (ROH). NMR observation of decomposing solutions and workup of cobalt chelate products show that the reaction is initiated by hydroxide ion attack on an equatorial quaternary carbon leading to formation of an altered cobal- oxime product in which one of the Schiff's base linkages has become hydrated. For the remainer of the complexes the yield of ethylene is less than stoichiometric and pH-dependent, and the ethylene evolving reaction is second-order in hydroxide ion activity. The yield-limiting side reaction is shown to be base-catalyzed formation of a base-stable but photolabile alkoxyethylcobaloxime analog in which a Schiff's base linkage of the chelate has become hydrated, β-Elimination to form alkyl vinyl ethers was not observed for any of the alkoxyethylcobal- oximes. The second-order dependence of ethylene formation on hydroxide ion activity for R = CH₃, CH₂CH₃, and CH(CH₃)₂ is discussed at some length, but is not well understood at present.     

Tuning iridium(III) complexes containing 2-benzo[b]thiophen-2-yl-pyridine based ligands in the red region

Synthesis and characterization of four iridium(III) complexes containing 2-benzo[b]thiophen-2-yl-pyridine based ligands are reported. The absorption, emission, electrochemistry, and thermostability of the complexes were systematically investigated. The (btmp)₂Ir(acac) (btmp = 2-benzo[b]thiophen-2-yl-4-methyl-pyridyl, acac = acetyl acetone) was characterized using X-ray crystallography. Calculation on the electronic ground state for (btmp)₂Ir(acac) was carried out using B3LYP density functional theory, HOMO levels are a mixture of Ir and btmp ligand orbitals, while the LUMO is predominantly btmp ligand based. Introduction of substituents (CH₃, CF₃) into pyridyl ring in a typical red emitter (btp)₂Ir(acac) leads to a marked decrease in the sublimation temperature, which is more suitable for OLEDs process. Electrochemical studies showed that (btmp)₂Ir(acac) has a slightly lower oxidation potential, but (btfmp)₂Ir(acac), (btfmp)₂Ir(dbm), and (btfmp)₂Ir(pic) (btfmp = 2-benzo[b]thiophen-2-yl-5-trifluoromethyl-pyridine, dbm = dibenzoylmethane, pic = 2-picolinic acid) containing CF₃ group are much difficult to oxidate than (btp)₂Ir(acac). The emission characteristics of these complexes can be tuned by either changing the substituents and their position on 2-benzo[b]thiophen-2-yl-pyridine or using different monoanionic ligands, showing emission λ_max values from 604 to 638 nm in CH₂Cl₂ solution at room temperature.     

The platinum-olefin binding energy in series of (PH<Subscript>3</Subscript>)<Subscript>2</Subscript>Pt(olefin) complexes - a theoretical study

Theoretical investigation of Pt(0)-olefin organometallic complexes containing tertiary phosphine ligands was focused on the strength of platinum-olefin electronic interaction. DFT theoretical study of electronic effects in a substantial number of ethylene derivatives was evaluated in terms of the Pt-olefin binding energy using MP2 correlation theory. Organometallics bearing coordinated olefins with general formula (R¹R²C = CR³R⁴)Pt(PH₃)₂ [R = various substituents] had been selected, including olefins containing both electron-donor substituents as well as electron-withdrawing groups. The stability of the corresponding complexes increases with a strengthening electron-withdrawal ability of the olefin substituents. Figure Representation of (CH₂ = CHR)Pt(PPh₃)₂ and the stability chart     

Screening Schiff-base complexes for activity in dehalogenation of chloroform

The metal-chelate assisted dehalogenation of chloroform was studied using bis(salicylaldimine)nickel(II) compounds of the type (5-ZC₆H₃-2-0-1-CHNR)₂ Ni in the presence of (CH₃)₂NCH₂CH₂N(CH₃)₂. The nickel compounds were screened for activity in terms of percent chlorine converted to chloride ion following a 6 h reflux period. The conversion was insensitive to the nature of Z, but sensitive to the nature of R (=H, alkyl, and substituted phenyl). Chloride conversion was related to the electronic effects of substituents on substituted phenyls that affected two competing effects in the transition state: (1) increase in electron density on the coordinated nitrogen to enhance the basicity and ease of proton removal from chloroform vs. (2) reduction in the formal charge of nickel that would reduce the tendency of chlorine from chloroform to be coordinated. Effects of other structural changes are considered.     

Tandem crystallization strategies for resolution of 3,3,3‐trifluorolactic acid [CF3CH(OH)COOH] by chiral benzylamines

Resolution of rac‐3,3,3‐trifluorolactic acid by diastereomeric salt formation was reinvestigated. The use of (S)‐1‐phenylethylamine gives coprecipitation of two diastereomeric phases, 1 (S)‐[NH₃CH(CH₃)Ph](S)‐[CF₃CH(OH)COO] and 2 (S)‐[NH₃CH(CH₃)Ph](R)‐[CF₃CH(OH)COO]·H₂O. Pure phase 1 may be obtained using molecular sieves as desiccants. Resolution by (S,S)‐2‐amino‐1‐phenylpropan‐1,3‐diol gives monoclinic (S,S)‐[NH₃CH(CH₂OH)CHOHPh] (R)‐[CF₃CH(OH)‐COO] 3 with minor (S)‐3,3,3‐trifluorolactate contamination, which is precluded in the recrystallized orthorhombic form 4 . A new resolution using inexpensive phenylglycinol gives pure phase 5 (S)‐[NH₃CH(CH₂OH)Ph] (S)‐[CF₃CH(OH)COO] in 76% yield, 94% ee in a single step, in preference to its (S)‐(R) diastereomer 6 . Overall efficient resolution for both enantiomers of the trifluorolactic acid (each ca. 70% yield, 99% ee) may be achieved by various two‐step “tandem” crystallizations, involving direct addition of either water or a second base to the filtrate from the initial reaction.     

1,1′-Bis(3-hydroxypropyl)ferrocene: Preparation and substitution with polyfluoroalkyl groups

SiMe₃CH₂CH₂ was demonstrated as a robust and convenient OH protecting group in the preparation of 1,1′-bis(3-hydroxypropyl)ferrocene (1). The OH groups were used to introduce polyfluorinated alkyl chains by acylation of 1 with (C₂F₅CO)₂O and alkylation with CF₃(CF₂)₆CH₂OH under Mitsunobu reaction conditions. This demonstrates a new method for introduction of an ω-hydroxyalkyl group to the Cp unit as a synthetic handle for modification of molecular properties.     

The reactivity of affinity labels: A kinetic study of the reaction of alkyl halides with thiolate anions—a model reaction for protein alkylation

Factors have been investigated which govern the electrophilic reactivity of alkyl halides with thiolate anions in aqueous solution. In the series of alkyl halides studied, some are potential metal-directed affinity labels, while others are frequently used in protein modification. Previous data on the kinetics of this type of alkylation are compared with the present results. The influence of electronic, polar, and steric factors on alkyl halide reactivity is seen. The following order of reactivity for alkyl halides bearing different α substituents was observed: RCH₂CH(X)COOCH₃ > RCH₂CH(X)CONH₂ > RCH₂CH(X)COOH > RCH₂CH₂X > RCH₂CH(X)CH₂OH. The metal-directed affinity labels are imidazole derivatives, some of which have substituents in their imidazole ring. The effect of the imidazole ring and of ring substitution on reactivity is seen. The nucleophilic reactivity of thiols is highly pH dependent since the thiolate anion (RS^?) is the reactive species, but only minor differences emerged between different free thiolates.     

Coordination modes of polydentate ligands. 4. The crystal and molecular structure of an oxo-bridged iron(III) complex containing a pentadentate imino-alkoxy ligand

In the presence of Fe³⁺, template condensation of the fluorinated keto-alcohol CH₃C(O)CH₂C- (CF₃)₂OH with the triamine CH₃C(CH₂NH₂)₃ leads to two products: a fully condensed, imino-alkoxy, iron(III) complex, Fe{CH₃C[CH₂NC(CH₃)CH₂C(CF₃)₂O]₃}, and a partially condensed iron(III) complex, O{FeCH₃C[CH₂NC(CH₃)CH₂C(CF₃)₂O]₂(CH₂NH₂)}₂, in which two six-coordinate iron(III) centers are linked by an oxide ion. A complete crystal and molecular structure determination of the latter has been made.Crystals are monoclinic, space group C2/c, a= 13.886(4); b=23.206(5); c=15.241(4) Å; β= 106.55(2)°; V=4708 ų; Z=4. Least-squares refinement on F of 322 variables using 2627 observations converged at a conventional agreement factor of 3.8%. The Fe to bridging oxide distance is 1.811(1) Å, the FeFe distance 3.468 Å, and the FeOFe angle 146.6(2)°. A comparison is made between this structure and those of natural hemerythrin systems.     

The surface properties of some silicone and fluorosilicone coating materials immersed in seawater

Changes in the surface properties of some silicone elastomers (General Electric RTV11, RTV160 and RTV655) and fluorosilicones (‐(Si(CH₃)((CH₂)₃‐O(CH₂)₂(CF₂)_XCF₃)‐O)_n‐, x = 5,7,9) on prolonged immersion in water (distilled water, artificial seawater, filtered and unfiltered seawater) have been investigated using measurements of advancing and receding contact angles, of surface roughness and of water uptake. Considerable increases in hydrophilicity and surface rugosity are attributed mainly to surface structural rearrangements accompanying absorption of water; these effects are greater for the fluorosilicones and the rugosity of RTV160 also increased considerably. Observations of early marine settlement (up to 16 weeks in flowing seawater), visualised by scanning electron microscopy, showed patchy attachment mainly of bacteria and microalgae while mature biofilms were formed on the poly(methylmethacrylate) controls. Although settlement was least on RTV11 and greatest on the fluorosilicones, the range of variation was small relative to the differences in the long‐term fouling resistance of the materials. The design requirements for fouling resistance of a smooth, soft, uniform surface are supported.     

Potassium-controlled synthesis of heterotopic macrocycles based on isothiosemicarbazide

The macrocyclisation reaction of 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)-bis(2-hydroxybenzaldehyde) (1) with S-methylisothiosemicarbazide hydroiodide (H₂NNC(SCH₃)NH₂·HI) in the presence of potassium triflate, followed by addition of M(CH₃COO)₂·nH₂O, where M=Ni, Cu, Zn, afforded [NiLKI₃] (2), [NiLK(CF₃SO₃)] (3), [CuLK(CF₃SO₃)(CH₃OH)] (4) and [(ZnILK)₂CH₃OH] (5), respectively. Compounds 2-5 have been characterised by X-ray crystallography. IR, electronic, mass, ¹H, ¹³C{¹H} and ¹⁹F{¹H} NMR spectra are reported. Magnetic susceptibility measurements and ESR spectra of 4 indicate weak intermolecular spin-spin interactions, which are mostly dipolar in origin.     

Theoretical study on rate constants for the reactions of CF3CH2NH2 (TFEA) with the hydroxyl radical at 298 K and atmospheric pressure

Theoretical investigations are carried out on reaction mechanism of the reactions of CF₃CH₂NH₂ (TFEA) with the OH radical by means of ab initio and DFT methods. The electronic structure information on the potential energy surface for each reaction is obtained at MPWB1K/6-31+G(d,p) level and energetic information is further refined by calculating the energy of the species with a Gaussian-2 method, G2(MP2). The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation. Our calculation indicates that the H abstraction from –NH₂ group is the dominant reaction channel because of lower energy barrier. The rate constants of the reaction calculated using canonical transition state theory (CTST) utilizing the ab initio data. The agreement between the theoretical and experimental rate constants is good at the measured temperature. From the comparison with CH₃CH₂NH₂, it is shown that the fluorine substution decreases the reactivity of the C-H bond.     

Insight into the gas phase dissociation of CF<Subscript>3</Subscript>CH<Subscript>2</Subscript>I and its reactions with H and OH by first principles

The Arrhenius kinetic parameters of dissociation reactions and reactions of CF₃CH₂I with radicals like H, O, and OH are determined using highly accurate first principles calculations. Thermophysical properties like molar heat capacity (C_p), thermal stability index, and the bond dissociation energies are also determined for the CF₃CH₂I molecule under the PBE/DNP formalism. Since, there are no theoretical study or experimental investigation reports available regarding the dissociation reactions of CF₃CH₂I and reactions of this molecule with the H and OH radical, a parallel comparative analysis is done with similar iodoalkanes to ascertain the precision of the results obtained. The atmospheric lifetime of 0.54 years is obtained for this molecule.     

Biodefluorination and biotransformation of fluorotelomer alcohols by two alkane‐degrading Pseudomonas strains

Fluorotelomer alcohols [FTOHs, F(CF₂)_nCH₂CH₂OH, n = 4, 6, and 8] are emerging environmental contaminants. Biotransformation of FTOHs by mixed bacterial cultures has been reported; however, little is known about the microorganisms responsible for the biotransformation. Here we reported biotransformation of FTOHs by two well‐studied Pseudomonas strains: Pseudomonas butanovora (butane oxidizer) and Pseudomonas oleovorans (octane oxidizer). Both strains could defluorinate 4:2, 6:2, and 8:2 FTOHs, with a higher degree of defluorination for 4:2 FTOH. According to the identified metabolites, P. oleovorans transformed FTOHs via two pathways I and II. The pathway I led to the production of x:2 ketone [dominant metabolite, F(CF₂)_xC(O)CH₃; x = n ? 1, n = 6 or 8], x:2 sFTOH [F(CF₂)_xCH(OH)CH₃], and perfluorinated carboxylic acids (PFCAs, perfluorohexanoic, or perfluorooctanoic acid). The pathway II resulted in the formation of x:3 polyfluorinated acid [F(CF₂)_xCH₂CH₂COOH] and relatively minor shorter‐chain PFCAs (perfluorobutyric or perfluorohexanoic acid). Conversely, P. butanovora transformed FTOHs by using the pathway I, leading to the production of x:2 ketone, x:2 sFTOH, and PFCAs. This is the first study to show that individual bacterium can bio‐transform FTOHs via different or preferred transformation pathways to remove multiple ? CF₂? groups from FTOHs to form shorter‐chain PFCAs. Biotechnol. Bioeng. 2012; 109: 3041–3048. © 2012 Wiley Periodicals, Inc.     

Optically active aromatic amino acids. part V: Some N-t-butyloxycarbonyl-O-methyl-L-tyrosine analogues with ring substitution at position 3

Six new derivatives of Boc-L -Tyr(Me)-OH have been prepared, with the following substituents at ring position 3: −CO₂Me, −CO₂Et, −CHO, −CH₂OH, −CH₂OBzl and −(E)−CH=NOH. © 1997 European Peptide Society and John Wiley & Sons, Ltd. J. Pep. Sci.3: 354–360 No. of Figures: 2. No. of Tables: 1. No. of References: 16     

Synthesis,crystal structure and magnetic behaviour of dimeric and polymeric gadolinium carboxylates with pentafluoropropionic acid

The three novel gadolinium(III) containing compounds (NH₃CH₃)[Gd(CF₃CF₂COO)₄(H₂O)] (1), (NH₃C₂H₅)[Gd(CF₃CF₂COO)₄(H₂O)] (2) and ((CH₃)₄N)[Gd(CF₃CF₂COO)₃(H₂O)₂]CF₃CF₂COO (3) were synthesized and structurally characterized by X-ray crystallography. In the crystal structures of 1 and 2, the gadolinium ions are bridged by carboxylate groups to dimers with a Gd³⁺–Gd³⁺ distance of 451.6(2) (1) and 451.8(3) pm (2), respectively. In the crystal structure of 3 the Gd³⁺ ions are bridged by carboxylate groups to chains with almost the same Gd³⁺–Gd³⁺ distances (494.0(8) and 503.4(7) pm). The magnetic behaviour of 1 and 2 was investigated in the temperature range of 1.76–300 K. The magnetic data indicate weak antiferromagnetic interactions within the dimeric unit.