Structure and reactivity of vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkyl hydroperoxides. To the mechanism of selective epoxidation of olefins

Vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkylhydroperoxides are characterized according to their¹H and⁵¹V NMR spectra and the reactivity of these complexes towards cyclohexene is studied.

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¹H ⁵¹V , .

     

Studies of immobilized V?P/SiO2 catalysts

It has been revealed by the ESR method that complexes of O ₂ ^– with palladium compounds are formed during the interaction of H₂O₂ with palladium acetate in various solutions.

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H₂O₂ O ₂ ^– .

     

EPR Detection and Characterization of High-Valent Manganese Complexes in MnIII(Salen) Catalyzed Aerobic Olefin Epoxidation

Using EPR, high-valent Mn^IV complexes have been detected in Mukaiyama's catalytic system, Mn^III(Salen)/Isobutyraldehyde/O₂, and shown to form also in the model system Mn^III(Salen)/Peroxyisobutyric acid. Their possible role in alkene epoxidation is discussed.     

Modular,Homochiral, Porous Coordination Polymers: Rational Design,Enantioselective Guest Exchange Sorption and Ab Initio Calculations of Host–Guest Interactions

Two new, homochiral, porous metal–organic coordination polymers [Zn₂(ndc){(R)‐man}(dmf)]?3DMF and [Zn₂(bpdc){(R)‐man}(dmf)]?2DMF (ndc=2,6‐naphthalenedicarboxylate; bpdc=4,4′‐biphenyldicarboxylate; man=mandelate; dmf=N,N′‐dimethylformamide) have been synthesized by heating Zn^II nitrate, H₂ndc or H₂bpdc and chiral (R)‐mandelic acid (H₂man) in DMF. The colorless crystals were obtained and their structures were established by single‐crystal X‐ray diffraction. These isoreticular structures share the same topological features as the previously reported zinc(II) terephthalate lactate [Zn₂(bdc){(S)‐lac}(dmf)]?DMF framework, but have larger pores and opposite absolute configuration of the chiral centers. The enhanced pores size results in differing stereoselective sorption properties: the new metal–organic frameworks effectively and stereoselectively (ee up to 62 %) accommodate bulkier guest molecules (alkyl aryl sulfoxides) than the parent [Zn₂(bdc){(S)‐lac}(dmf)]?DMF, while the latter demonstrates decent enantioselectivity toward precursor of chiral anticancer drug sulforaphane, CH₃SO(CH₂)₄OH. The new homochiral porous metal–organic coordination polymers are capable of catalyzing a highly selective oxidation of bulkier sulfides (2‐NaphSMe (2‐C₁₀H₇SMe) and PhSCH₂Ph) that could not be achieved by the smaller‐pore [Zn₂(bdc){(S)‐lac}(dmf)]?DMF. The sorption of different guest molecules (both R and S isomers) into the chiral pores of [Zn₂(bdc){(S)‐lac}(dmf)]?DMF was modeled by using ab initio calculations that provided a qualitative explanation for the observed sorption enantioselectivity. The high stereo‐preference is accounted for by the presence of coordinated inner‐pore DMF molecule that forms a weak C? H???O bond between the DMF methyl group and the (S)‐PhSOCH₃ sulfinyl group.     

Formation and Evolution of Chain‐Propagating Species Upon Ethylene Polymerization with Neutral Salicylaldiminato Nickel(II) Catalysts

Formation of Ni–polymeryl propagating species upon the interaction of three salicylaldiminato nickel(II) complexes of the type [(N,O)Ni(CH₃)(Py)] (where (N,O)=salicylaldimine ligands, Py=pyridine) with ethylene (C₂H₄/Ni=10:30) has been studied by ¹H and ¹³C NMR spectroscopy. Typically, the ethylene/catalyst mixtures in [D₈]toluene were stored for short periods of time at +60 °C to generate the [(N,O)Ni(polymeryl)] species, then quickly cooled, and the NMR measurements were conducted at ?20 °C. At that temperature, the [(N,O)Ni(polymeryl)] species are stable for days; diffusion ¹H NMR measurements provide an estimate of the average length of polymeryl chain (polymeryl=(C₂H₄)_nH, n=6–18). At high ethylene consumptions, the [(N,O)Ni(polymeryl)] intermediates decline, releasing free polymer chains and yielding [(N,O)Ni(Et)(Py)] species, which also further decompose to form the ultimate catalyst degradation product, a paramagnetic [(N,O)₂Ni(Py)] complex. In [(N,O)₂Ni(Py)], the pyridine ligand is labile (with activation energy for its dissociation of (12.3±0.5) kcal mol^?1, ΔH^≠₂₉₈=(11.7±0.5) kcal mol^?1, ΔS^≠₂₉₈ =(?7±1) cal K^?1 mol^?1). Upon the addition of nonpolar solvent (pentane), the pyridine ligand is lost completely to yield the crystals of diamagnetic [(N,O)₂Ni] complex. NMR spectroscopic analysis of the polyethylenes formed suggests that the evolution of chain‐propagating species ends up with formation of polyethylene with predominately internal and terminal vinylene groups rather than vinyl groups.     

Complexes of O2? radical ions with palladium and platinum compounds in solutions

Coordination of O ₂ ^– radical ions with palladium and platinum compounds in solutions has been detected by the ESR technique.

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- O ₂ ^– .

     

The nature of active species in catalytic systems based on non-heme iron complexes, hydrogen peroxide, and acetic acid for selective olefin epoxidation

The catalytic systems [(BPMEN)Fe^II(CH₃CN)₂](ClO₄)₂/H₂O₂/CH₃OOH and [(TPA)Fe^II(CH₃CN)₂](ClO₄)₂/H₂O₂/CH₃OOH, where BPMEN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane and TPA = tris(2-pyridylmethyl)amine, provide selective olefin epoxidation. Proton NMR studies showed that the mononuclear iron(IV) oxo complexes [(L)Fe^IV=O]²⁺, with L = BPMEN or TPA, are present in the cited catalytic systems. These intermediates are the decomposition products of the acylperoxo complexes [(L)Fe^III-O₃CCH₃]²⁺. Such a complex was observed by the ²H NMR technique at low temperatures. The [(L)Fe^IV=O]²⁺ and [(L)Fe^V=O]³⁺ oxo complexes are possible active species in the studied catalytic systems.     

Titanium–salan‐catalyzed asymmetric sulfoxidations with H2O2: design of more versatile catalysts

Titanium–salan complexes with 3,3’‐diphenyl substituents in the salicylidene rings of the salan ligand are efficient sulfoxidation catalysts, capable of catalyzing the asymmetric oxidation of bulky aryl benzyl sulfides with H₂O₂ with good to high enantioselectivities. In this paper, substituent effects on titanium‐salan‐catalyzed enantioselective oxidation of sulfides to sulfoxides have been systematically investigated. Titanium–salan catalysts with halogen substituents at the 5,5’‐positions (3,3’‐H₂dihydrogen substituted) have been found to catalyze the oxidation of both bulky aryl benzyl sulfides and small alkyl phenyl sulfides with good to high enantioselectivities. Kinetic data witness a direct attack of the sulfide to the electrophilic active oxygen species; a consistent reaction mechanism is proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

The origin of living polymerization with an o-fluorinated catalyst: NMR spectroscopic characterization of chain-carrying species

To characterize the origin of living polymerization with nonmetallocene titanium-based catalysts containing o-fluoroaryl substituents, ethene polymerization by an o-fluorinated bis(enolatoimine) titanium catalyst and its nonfluorinated counterpart has been studied by multinuclear NMR spectroscopy by using methylaluminoxane (MAO) or AlMe(3)/CPh(3)B(C(6)F(5))(4) as activators. Formation of ion pairs of the type [TiL(2)Me][MeMAO] and [TiL(2)Me][B(C(6)F(5))(4)] has been observed for both catalysts. These ion pairs react with ethene to afford the chain-propagating species [TiL(2)P][MeMAO] and [TiL(2)P][B(C(6)F(5))(4)], respectively (P = growing polymeryl chain). For the o-F-substituted catalyst species of the second type, NMR spectroscopy provides evidence that the o-F substituents interact with the metal center. This interaction is proposed to keep the polymerization catalysis living by suppressing chain transfer to AlMe(3) and β-hydrogen transfer processes.