Theoretical investigation of the gas-phase reactions of CF2ClC(O)OCH3 with the hydroxyl radical and the chlorine atom at 298 K

A Theoretical study on the mechanism of the reactions of CF₂ClC(O)OCH₃ with the OH radical and Cl atom is presented. Geometry optimization and frequency calculations have been performed at the MPWB1K/6-31+G(d,p) level of theory and energetic information is further refined by calculating the energy of the species using G2(MP2) theory. Transition states are searched on the potential energy surface involved during the reaction channels and each of the transition states are characterized by presence of only one imaginary frequency. The existence of transition states on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation. Theoretically calculated rate constants at 298 K and atmospheric pressure using the canonical transition state theory (CTST) are found to be in good agreement with the experimentally measured ones. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF₂ClC(O)OCH_3, CF₂ClC(O)OCH₂ and CF₃C(O)OCH₃ are also reported for the first time.     

Ab initio studies on the reactivity of the CF3OCH2O radical: Thermal decomposition vs. reaction with O2

Hydrofluoroethers are being considered as potential candidates for third generation refrigerants. The present investigation involves the ab initio quantum mechanical study of the decomposition mechanism of CF₃OCH₂O radical formed from a hydrofluoroether, CF₃OCH₃ (HFE-143a) in the atmosphere. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at the DFT (B3LYP) level of theory using 6-311G(d,p) basis set. Energy calculations have been performed at the G2(MP2) and G2M(CC,MP2) level of theory. Two prominent decomposition channels, C-O bond scission and reaction with atmospheric O₂ have been considered for detailed investigation. Studies performed at the G2(MP2) level reveals that the decomposition channel involving C-O bond scission occurs with a barrier height of 23.8 kcal mol⁻¹ whereas the oxidative pathway occurring with O₂ proceeds with an energy barrier of 7.2 kcal mol⁻¹. On the other hand the corresponding values at G2M(CC,MP2) are 24.5 and 5.9 kcal mol⁻¹ respectively. Using canonical transition state theory (CTST) rate constants for the two pathways considered are calculated at 298 K and 1 atm pressure and found to be 5.9 × 10⁻⁶ s⁻¹ and 2.3 × 10⁻⁵ s⁻¹ respectively. The present study concludes that reaction with O₂ is the dominant path for the consumption of CF₃OCH₂O in the atmosphere. Transition states are searched and characterized on the potential energy surfaces involved in both of the reaction channels. The existence of transition state on the corresponding potential energy surface is ascertained by performing intrinsic reaction coordinate (IRC) calculation.     

Synthesis, structure and solution chemistry of quaternary oxovanadium(V) complexes incorporating hydrazone ligands

[V^IVO(acac)₂] reacts with an equimolar amount of benzoyl hydrazone of 2-hydroxyacetophenone (H₂L¹) or 5-chloro-2-hydroxyacetophenone (H₂L²) in the presence of excess pyridine (py) in methanol to produce the quaternary [V^VO(L¹)(OCH₃)(py)] (1) and [V^VO(L²)(OCH₃)(py)] (2) complexes, respectively, while under similar condition, the benzoyl hydrazones of 2-hydroxy-5-methylacetophenone (H₂L³) and 2-hydroxy-5-methoxyacetophenone (H₂L⁴) afforded only the methoxy bridged dimeric [V^VO(L³/L⁴)(OCH₃)]₂ complexes. The X-ray structural analysis of 1 and 2 indicates that the geometry around the metal is distorted octahedral where the three equatorial positions are occupied by the phenolate-O, enolate-O and the imine-N of the fully deprotonated hydrazone ligand in its enolic form and the fourth one by a methoxide-O atom. An oxo-O and a pyridine-N atom occupy two axial positions. Quaternary complexes exhibit one quasi-reversible one-electron reduction peak near 0.25 V versus SCE in CH₂Cl₂ and they decompose appreciably to the corresponding methoxy bridged dimeric complex in CDCl₃ solution as indicated by their ¹H NMR spectra. These quaternary VO³⁺ complexes are converted to the corresponding -complexes simply on refluxing them in acetone and to the -complexes on reaction with KOH in methanol. An equimolar amount of 8-hydroxyquinoline (Hhq) converts these quaternary complexes to the ternary [V^VO(L)(hq)] complexes in CHCl₃.     

Synthesis and characterization of palladium(II) complexes with aryl tellurols and diaryl ditellurides

Polymeric complexes of formula [PdCl(TeAr)]_n (I) and [Pd(TeAr)₂]_n (II) are readily obtained by the reaction between Na₂[PdCl₄] and NaTeAr (ArC₆H₅, C₆H₄OCH₃−4 and C₆H₄OCH₂CH₃−4) in ethanol at room temperature. Chemical and far infrared spectral evidences support alternating chloride and tellurol bridges in I and tellurol bridges in II. While the reaction of I (AtC₆H₄OCH₃−4) with PPh₃ in stoichiometric amount results in splitting of chloride bridges and formation of a tellurol bridged dimeric complex [PdCl(TeC₆H₄OCH₃−4)(PPh₃)]₂ (III), with excess of PPh₃, cleavage of both chloride and tellurol bridges leads to the formation of a monomeric compound [PdCl(TeC₆H₄OCH₃−4)(PPh₃)₂] (IV). Furthermore, the reaction of I (Ar C₆H₄OCH₂CH₃−4) with 1,2-bis(diphenyl phosphino)ethane in equimolar ratio also resulted in a monomeric compound [(PdCl(TeC₆H₄OCH₂CH₃−4)(diphos)] (V). The complex III (ArC₆H₄OCH₂CH₃−4) is also prepared by the reaction between Pd(PPh₃)₂Cl₂ and Ph₃SnTeC₆H₄OCH₂CH₃−4 in 1:1 molar ratio or between Pd₂Cl₄(PPh₃)₂ and Ph₃SnTeC₆H₄OCH₂CH₃−4 in 1:2 molar ratio in benzene at room temperature. Sodium tetrachloropalladate reacts readily with diarylditellurides in ethanol at 0 °C to form dimeric complexes [PdCl₂(ArTeTeAr)]₂ (VI). However, at 40 °C or above the same ditellurides form polymeric complexes I with Na₂[PdCl₄] in ethanol. The complex VI is also obtained by the reaction of Pd(PhCN)₂Cl₂ with Te₂Ar₂ in benzene at room temperature. The complexes were characterized by elemental analysis, IR, Raman and ¹H NMR spectra and, where possible, by conductivity measurements and molecular weight determinations.     

The preparation and electrochemistry of cysteine-ester oxovanadium(IV) complexes

An improved synthesis of VO(CysOCH₃)₂, (CysOCH₃  the anion of cysteine methyl ester), is reported, as is an analogous preparation of VO(CysOCH₂CH₃)₂, (CysOCH₂CH₃  the anion of cysteine ethyl ester). These are the first two examples of isolated vanadium-cysteine compounds. The oxidation of VO(CysOCH₃)₂ in DMSO is a reversible one electron change at 0.24 V versus SCE followed by a rapid chemical reaction which produces a stable vanadium(V) species. This species is reduced back to the vanadium(IV) complex at −1.30 V. The electrochemistry of VO(Cys-OCH₂CH₃)₂ is nearly identical to that of the methyl ester compound.     

Oxidative addition of methyl iodide to [Rh(CH3COCHCOCH3)(CO)(P(OCH2)3CCH3)]

The reaction rate of the oxidative addition and the following CO insertion step of methyl iodide with [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] is determined. The key finding is that while [Rh(acac)(CO)(P(OCH₂)₃CCH₃)] oxidatively adds methyl iodide ca 300 times faster than the Monsanto catalyst, the CO insertion step is much slower. However, the rate-determining step of the oxidative addition reaction of the phosphorus-containing acetylacetonato-rhodium(I) complex, the carbonyl insertion step, is still in the same order or faster than the rate-determining oxidative addition step of iodomethane to [Rh(CO)₂I₂]⁻.     

Tetra-, penta- and hexacoordinate copper(II) complexes with N3 donor isoindoline-based ligands: Characterization and SOD-like activity

Reaction of 1,3-bis(2′-Ar-imino)isoindolines (HLⁿ, n = 1-7, Ar = benzimidazolyl, N-methylbenzimidazolyl, thiazolyl, pyridyl, 3-methylpyridyl, 4-methylpyridyl, and benzthiazolyl, respectively) with Cu(OCH₃)₂ yields mononuclear hexacoordinate complexes with Cu(Lⁿ)₂ composition. With cupric perchlorate square-pyramidal [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes (n = 1, 3, 4) were isolated as perchlorate salts, whereas with chloride Cu^II(HLⁿ)Cl₂ (n = 1, 4), or square-planar Cu^IICl₂(HLⁿ) (n = 2, 3, 7) complexes are formed. The X-ray crystal structures of Cu(L³)₂, Cu(L⁵)₂, [Cu^II(HL⁴)(NCCH₃)(OClO₃)]ClO₄, Cu^IICl(L²) and Cu^IICl(L⁷) are presented along with electrochemical and spectral (UV-Vis, FT-IR and X-band EPR) characterization for each compound. When combined with base, the isoindoline ligands in the [Cu^II(HLⁿ)(NCCH₃)(OClO₃)]ClO₄ complexes undergo deprotonation in solution that is reversible and induces UV-Vis spectral changes. Equilibrium constants for the dissociation are calculated. X-band EPR measurements in frozen solution show that the geometry of the complexes is similar to the corresponding X-ray crystallographic structures. The superoxide scavenging activity of the compounds determined from the McCord-Fridovich experiment show dependence on structural features and reduction potentials.     

The structure of U3(O)(OCMe3)10, and unusual trinuclear U(IV) oxo-alkoxide

In an attempt to prepared tetrakis(tert-butoxy)uranium(IV) a trinuclear oxo-alkoxide of uranium(IV) was obtained instead. The compound has the formula U₃O[(CH₃)₃CO]₁₀ and it crystallizes in the hexagonal space group P6₃mc with a = b = 18.256(4) Å, c = 10.013(2) Å, Z = 2. The trinuclear unit is strikingly reminiscent of that in Mo₃O(OCH₂CMe₃)₁₀. In contrast to the molybdenum compound where there is metal-metal bonding, the U?U distance of 3.574(1) Å indicates a non-bonded interaction.     

Biocatalytic,Enantioselective Preparations of (R)- and (S)-Ethyl 4-Chloro-3-Hydroxybutanoate,a Useful Chiral Synthon

The synthesis of optically active ethyl 4-chloro-3-X-butanoate derivatives la-d (X = OH, a; OCOCH₃, b; OCOC₃H₇, c; OCH₂C₆H₅, d) was realized using various biocatalytic approaches such as microbiological reduction of ethyl 4-chloro-3-oxobutanoate 2 with lactic acid bacteria, hydrolysis of lb-d by the hydrolytic enzymes PLE and BChE and the transesterification of la catalyzed by a lipase from Pseudomonas fluorescens (PFL).     

Palladium complexes with hydrophosphorane ligands (HP∼O and HP∼N), catalysts for Heck cross-coupling reactions

The synthesis and structural characterization of palladium complexes 1-3 incorporating H-spirophosphorane HP(OCMe₂CMe₂O)₂ and H-phosphonate congener HP(O)(OCMe₂CMe₂O) ligands are reported. The chemical composition of the complexes [PdCl(μ-Cl){P(OCMe₂CMe₂O)OCMe₂CMe₂OH}]₂ (1), [Pd{P(O)(OCMe₂CMe₂O)}₂]_n (2), and [Pd(μ-Cl){P(OCMe₂CMe₂O)OH}{P(OCMe₂CMe₂O)O}]₂ (3) was established by means of NMR, IR, ESI-MS spectroscopic methods. The relative stereochemistry of 1 and 3 was unambiguously determined by single X-ray diffraction studies. It was proved that complexes 1-3, and complex [PdCl₂P(OCH₂CMe₂NH)OCH₂CMe₂NH₂] (4) previously described in the literature, are very efficient catalysts for the Heck cross-coupling of bromobenzene with n-butyl acrylate. Moreover, they were also found to be effective catalysts in the stereoselective synthesis of trans-stilbenes.     

Palladium(II) and platinum(II) complexes with polypyridylbenzene ligands

The ligands 1,3-bis(3-pyridyl)benzene (1), 1,3-bis(4-pyridyl)benzene (2) and 1,3,5-tris(4-pyridyl)benzene (3) have been prepared by Stille coupling of 3- or 4-trimethylstannylpyridine with the appropriate bromoarene. Ligands 1 and 2 react with [M(OTf)₂(dppp)] (M=Pd, Pt) to produce the dipalladium- or diplatinum-containing macrocycles [M₂(μ-1)₂(dppp)₂](OTf)₄ or [M₂(μ-2)₂(dppp)₂](OTf)₄. These have been characterized by NMR spectroscopy and mass spectrometry and, in the case of [Pd₂(μ-1)₂(dppp)₂](OTf)₄, by X-ray crystallography. The molecular structure of the [Pd₂(μ-1)₂(dppp)₂]⁴⁺ cation reveals a shallow arrangement of the aromatic rings, with the palladium atoms lying above and below. The tridentate ligand 3 reacts with [Pd(OTf)₂(dppp)] to produce a trimetallic species of the form [Pd₃(μ₃-3)₂(dppp)₃](OTf)₆.     

Synthesis and characterization of cobalamines with anionic and neutral phosphorous donor ligands

In dimethyl formamide as solvent aquacobalamine reacts with the triorganyl phosphites 3–7 to give the corresponding (diorganylphosphito-P)cobalamines, their new β-axial ligands [P(O)(OR)₂]⁻ (3a–7a) being formed by partial hydrolysis. In methanol, however, additional methanolysis normally leads to (dimethylphosphito-P)cobalamine with the axial ligand [P(O)-(OMe)₂]⁻ (2a). Exceptions are P(OCH₂CH₂NMe₂)₃ (4) giving a complex with the only partially methanolized chiral ligand [P(O)(OCH₂CH₂NMe₂)- (OMe)]⁻ (4b), too, and the bicyclic phosphite 5 which is also coordinated in the unchanged, nonhydrolyzed form. All complexes are characterized by elementary analysis, electrophoresis, UVVis and ¹H, ³¹P NMR spectra. The chirality of the cobalamine moiety causes diatropism of the two organyl groups in the prochiral ligands [P(O)(OR)₂]⁻ which is well seen in the NMR spectra of the complexes with the methyl and phenyl derivatives 2a and 6a, whereas the spectra with ligands 3a and (in part) 4a are not resolved well enough to distinguish the two forms. With the chiral ligand 4b two diastereomers are obtained in different yields; this asymmetric induction is indicated by the intensities of the respective signals in the NMR spectra.     

Triaryl (Z)-olefins suitable for radiolabeling with carbon-11 or fluorine-18 radionuclides for positron emission tomography imaging of cyclooxygenase-2 expression in pathological disease

A group of (Z)-1,1-diphenyl-2-(4-methylsulfonylphenyl)alk-1-enes were synthesized using methodologies that will allow incorporation of a [¹¹C]OCH₃ substituent at the para-position of the C-1 phenyl ring, a [¹¹C]SO₂CH₃ substituent at the para-position of the C-2 phenyl ring, a [¹⁸F]OCH₂CH₂F substituent at the para-position of the C-1 phenyl ring, and a [¹⁸F]CH₂CH₂F substituent at the C-2 position of the olefinic bond. The [¹¹C] and [¹⁸F] radiotracers are designed as potential radiopharmaceuticals to image cyclooxygenase-2 (COX-2) expression in any organ where COX-2 is upregulated. The COX-1/COX-2 inhibition data acquired suggest that compounds having a [¹¹C]OMe or [¹⁸F]OCH₂CH₂F substituent at the para-position of the C-1 phenyl ring may be more suitable for imaging COX-2 expression in view of their ability to exclusively inhibit the COX-2 isozyme.     

Supported organometallic complexes part 39: cationic diamine(ether-phosphine)ruthenium(II) complexes as precursors for the hydrogenation of trans-4-phenyl-3-butene-2-one

Treatment of RuCl₂(η¹-Ph₂PCH₂CH₂OCH₃)₂(diamine) (1L₁-1L₇) with one equivalent of AgX (X=OTf, BF₄) in CH₂Cl₂ results in the formation of the monocationic ruthenium(II) complexes [RuCl(η¹-Ph₂PCH₂CH₂OCH₃)(η²-Ph₂PCH₂CH₂OCH₃)(diamine)]⁺X⁻ (2L₁-2L₇). These complexes were characterized by NMR, and mass spectroscopy as well as by elemental analyses, 2L₁ additionally by an X-ray structural analysis. Complex 2L₁ crystallizes in the monoclinic space group C2/c with Z=8. The monocationic and neutral complexes were applied as catalysts in the selective hydrogenation of trans-4-phenyl-3-butene-2-one. With the exception of 1L₃/1L₇ and 2L₃/2L₇ all catalysts showed high activities and selectivities toward the hydrogenation of the carbonyl group under mild conditions. However, the activity of the cationic catalysts is only half of that of their neutral congeners.     

Acylated cyanidin 3-sambubioside-5-glucosides in the red-purple flowers of Arabis blepharophylla Hook. & Arn. (Brassicaceae)

Acylated anthocyanins from the red-purple flowers of Arabis blepharophylla 1: pigment 1, R₁ = H, trans, R₂ = malonic acid 2: pigment 2, R₁ = OCH₃, trans, R₂ = malonic acid 3: pigment 3, R₁ = H, cis, R₂ = malonic acid 4: pigment 4, R₁ = H, trans, R₂ = H 5: pigment 5, R₁ = OCH₃, trans, R₂ = H.

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Highlights► Five anthocyanins were isolated from the flowers of Arabis blepharophylla. ► Anthocyanins were identified as acylated cyanidin 3-sambubioside-5-glucoside. ► Anthocyanins were acylated by p-coumaric acid, sinapic acid and/or malonic acid.     

Nickel(II) complexes bearing pyrazolylimine ligands: Synthesis, characterization, and catalytic properties for ethylene oligomerization

Four phenyl-substituted pyrazolylimine ligands 2-(C₃HN₂Me₂-3,5)(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6)) (L1: R₁ = ⁱPr, R₂ = H; L2: R₁ = H, R₂ = NO₂; L3: R₁ = R₂ = H; L4: R₁ = H, R₂ = OCH₃) were synthesized. The influences of steric bulk and electronic effect of pyrazolylimine ligands on the structures of their corresponding nickel complexes were investigated. Ligands with more bulky and electron withdrawing substituents on N-phenyl ring produced four-coordinate nickel complexes (2-(C₃HN₂Me₂-3,5))(C(Ph)(4-R₂C₆H₂(R₁)₂-2,6)NiBr₂ (1, R₁ = ⁱPr, R₂ = H; 2, R₁ = H, R₂ = NO₂)), whereas the ligands with less bulky and electron donating substituents on N-phenyl ring formed bis-pyrazolylimine dinickel tetrahalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂ (R₁)₂-2,6)Ni₂Br₄ (3, R₁ = R₂ = H; 4, R₁ = H, R₂ = OCH₃)) and six-coordinate nickel dihalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6) NiBr₂ (5, R₁ = R₂ = H;6, R₁ = H, R₂ = OCH₃)). The solid-state structures of complexes 1, 4 and 5 have been confirmed by X-ray single-crystal analyses. Activated by methylaluminoxane (MAO), complexes 1, 2, 5 and 6 showed moderate to high activity for ethylene oligomerization, and complex 5 revealed the highest activity up to 8.96 × 10⁵ g oligomer/(mol Ni · h). The proportions of resultant oligomers were mainly C4-C8 and a little C10-C14 determined by gas chromatography/mass spectrometry.     

Group 3 complexes incorporating (furyl)-substituted disilazide ligands

A series of mono- and bis-amide scandium and yttrium compounds incorporating the furyl-substituted disilazide ligand, [N{SiMe₂R}₂]⁻ {i} (where R = 2-methylfuryl) have been synthesized. The compounds Sc{i}Cl₂ (1), Sc{i}(CH₂SiMe₃)₂ (2) and Sc{i}(OAr)₂ (3) were made from suitable scandium starting materials employing either a salt metathesis protocol with Li{i} or via protonolysis of Sc-C bonds by the neutral amine H{i}. The thermally unstable bis-alkyl yttrium compound, ‘Y{i}(CH₂SiMe₃)₂^’ was isolated as the bis-THF adduct (4) and the bis-aryloxide Y{i}(OAr)₂ (5) was synthesized by elimination of LiOAr from Y(OAr)₃. The bis-amide complex Y{i}₂Cl (6) and conversion to a rare example of an yttrium benzyl compound Y{i}₂(CH₂Ph) (7) are described. The yttrium cation, [Y{i}₂]⁺, was synthesized by benzyl abstraction from 7 using B(C₆F₅)₃. Structural characterization of representative examples show variation in the coordination modes for amide ligand {i}, differing primarily in the number of furyl groups that coordinate to the metal, with examples in which zero, one or two M-O_furyl bonds are present. Preliminary investigation in two areas of catalysis are presented.     

Synthesis and structural studies of mixed-ligand rhenium(V) complexes anchored by tridentate pyrazole-based ligands

The novel oxorhenium dichlorides mer-[ReO(L1)Cl₂] (1) and fac-[ReO(L2)Cl₂] (2) (L1 = 2-[2-(pyrazol-1-yl)ethyliminomethyl]phenolate; L2 = 2-[2-(pyrazol-1-yl)ethylaminomethyl]phenolate) were synthesized by reacting [NBu₄][ReOCl₄] with L1H and L2H, respectively. X-ray structural analysis of 1 and 2 has shown that L1 and L2 act as (N,N,O)-tridentate chelators coordinating to the Re(V) centre in a meridional and in a facial fashion, respectively. The reactivity of 2 towards potential bidentate/dianionic substrates is strongly dependent on the donor atom set, being observed that the presence of sulphur favours the displacement of the ancillary ligand (L2). By contrast, complex 2 reacted with (O,O)-bidentate substrates (1,2-ethanediol and oxalic acid) providing the mixed-ligand complexes fac-[ReO(L2)(OCH₂CH₂O)] (3) and fac-[ReO(L2)(C₂O₄)] (4). Complexes 3 and 4 are air and water-stable and have been characterized by the common spectroscopic techniques (IR, ¹H and ¹³C NMR) and by X-ray diffraction analysis.