1073-07-0

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A homogenous metal hydride (M?H) catalyst for isomerization normally requires rigorous air-free techniques. Here, we demonstrate a highly efficient protocol in which simple non-redox metal ions as Lewis acids can promote olefin isomerization dramatically with a commercially available RuH2(CO)(PPh3)3 complex in an open-flask system. Isomerization can be accomplished within a short time, and a satisfactory selectivity for different types of unsaturated compounds can be obtained. Meanwhile, an excellent turnover number up to 17208 was achieved under air, and open-flask gram-scale experiments further demonstrated the efficiency of the RuH2(CO)(PPh3)3/non-redox-metals system. We used FTIR spectroscopy, GC–MS, NMR spectroscopy and kinetics studies to evidence that in the sluggish RuH2(CO)(PPh3)3 catalyst, bloated PPh3 ligands cause steric hindrance for the coordination of the free alkene. Alternatively, the addition of non-redox metal ions could induce the dissociation of the PPh3 ligand to offer unoccupied coordination sites for the alkene and to form the Mg-bridged adduct OC?Ru?H2?Mg2+ as the highly active species, which benefited the isomerization significantly through the metal hydride addition–elimination pathway. Finally, this strategy was demonstrated as an impactful approach for hydride catalysts of other transition metals such as Os.

Three isomeric cyclooctadienes (1.5-, 1.4-, and 1.3-COD) were hydrogenated with phenylacetaldehyde (PAA)- or carbon monoxide (CO)-treated palladium black in tetrahydrofuran at 25 deg C and atmospheric pressure of hydrogen.A complete depression of the hydrogenation of cyclooctene (COE) to cyclooctane (COA) was attained with both of the poisoned catalysts.By PAA the hydrogenation of 1,5-COD to COE was not hindered and the isomerization of 1,5-COD to 1,4-COD was greatly promoted, while the rate of hydrogenation of 1,4- and 1,3-COD decreased in the presence of PAA.By CO the hydrogenation and isomerization of 1,5-COD, as well as the hydrogenation of 1,4- and 1,3-COD, was suppressed.In the hydrogenation of 1,5-COD the PAA-treated palladium was more active and selective than was the CO-treated palladium for the formation of COE.The differences in the effects of these catalyst poisons are discussed on the basis of kinetic data concerning the individual and competitive hydrogenation of the three isomeric cyclooctadienes.

The isomerization of 1,5-cyclooctadiene (1,5-COD) with Ni(acac)2-Et3Al2Cl3-phosphorus ligand (Ni:Al2:P = 1:10:3) was first examined with varying P ligands in toluene in order to find suitable conditions for the formation of 1,4-COD.The product distribution depended largely on the P ligands.For several phosphites possessing very strong ?-acceptor properties, the main product was 1,4-COD.In particular, the less-bulky bicyclic phosphite, 4-ethyl-2,6,7-trioxa-1-phosphabicyclooctane (L-3) was very effective and gave 1,4-COD in a high selectivity of 93 percent at 66 percent conversion (1,5-COD/Ni = 500, molar ratio) by employing a low temperature of -30 deg C.However, the reaction stopped before reaching completion because the catalyst was deactivated by the accumulation of 1,4-COD product.The conversion, depending on the 1,5-COD/toluene ratio (volume) rather than the 1,5-COD/Ni ratio, increased with a decrease in the 1,5-COD/toluene ratio and was 66-69 percent at a ratio of 0.19.On the other hand, the catalyst (P: L-3) was much less active for 1,4-COD than for 1,5-COD and was deactivated quickly under the same reaction conditions.This appeared to result in a high selectivity of 1,4-COD in the isomerization of 1,5-COD.The mechanistic implications of the experimental results are discussed.

A NiII polymer-bound catalyst was prepared by anchoring anthranilic acid to chloromethylated, highly crosslinked polystyrene beads and then equilibrating with NiCl2*6H2O.By treating this catalyst with sodium borohydride, a second catalyst was prepared.Both nickel catalysts are active in the hydrogenation of alkenes and dienes and in the reduction of nitrobenzene.The structures of the catalysts were probed by XPS studies.

Ionic liquids with natural organic derived anions (l-lactate, l-tartrate, malonate, succinate, l-malate, pyruvate, d-glucuronate, d-galacturonate) were easily prepared from tetrabutylammonium hydroxide and an excess of the corresponding acid with good yields. Their characterization was realized through classical NMR, IR, and elemental analysis techniques; their viscosity and TGA (thermogravimetric analysis) parameters were also determined. These ionic liquids showed good performance and recyclability in the selective catalytic hydrogenation of 1,5-cyclooctadiene (1,5-COD) into cyclooctene (COD) at room temperature under atmospheric H2 pressure. Antimicrobial toxicity assays toward a large panel of bacteria and fungi strains were also completed and biodegradation studies (Closed Bottle test, 28 days) were also performed.

Evidence for a radical process in the reaction of lithium alkoxides with alkyl iodides was obtained by observation of cyclization of appropriate radical probes, by the trapping of radicals, and by EPR spectroscopic observations relating to the one electron donor properties of alkoxides.

Displacement of piperidine from Ru(COD)(piperidine)-trans-(H)Cl (I) by 1,4-diaza-1,3-dienes (DAD: RN=CR'CR'=NR) gives the complexes cis-Ru(COD)(DAD)(H)Cl (III).With relatively bulky DAD ligands the complexes III are unstable and are converted into compounds IV, which are also formed from III on heating.Complexes III are not accessible from Ru(COD)(DAD)Cl2(V).If the analogous starting material involving a cycloheptatriene Ib in place of the COD ligand is used, a piperidide anion is preserved as a ligand instead of a hydride.In the room temperature 1H NMR spectra of rigid asymmetric III all twelve hydrogen atoms of the COD ligand can be seen separately.A full assignment has been made by use of 2D-H/H-correlated spectra.The highest field resonance (1.2 ppm) is assigned to an olefinic H atom, shielded by the DAD chelate.Complexes III catalyse the isomerization of terminal alkenes to a cis/trans mixture (20/80) of internal alkenes.During the catalytic hydrosilylation of 1-alkenes this isomerization is a competing side reaction.Thermal decomposition of III gives free 1,3-COD; the decomposition under hydrogen gives cyclooctane stoichiometrically.In catalytic experiments III is found to catlyse the isomerization of 1,5-COD to 1,3-COD via 1,4-COD.Under hydrogen pressure (20 bar), III catalyses the hydrogenation of 1-hexene and cyclohexene.Four different ways in which one, two,or three 'vacant site' can be generated starting from III are discussed.

1,5-Cyclooctadiene and 1,5-hexadiene are selectively reduced by hydrogen transfer from i-PrOH using Rh6(CO)16 as procatalyst.The first step of the reaction appears to be the formation of conjugated diene isomers, which are subsequently reduced to monoenes.Carbonyl clusters of Os, Ru and Ir can also be used, but their activities are lower and they predominantly catalyze isomerization.

This work reports on the redox and acid–base properties of binuclear complexes of nickel from 1,4-terphenyldithiophenol ligands. The results provide insight into the cooperative electronic interaction between a dinickel core and its ligand. Donor/acceptor contributions flexibly adjust to stabilize different redox states at the metals, which is relevant for redox reactions like proton reduction. Proton transfer to the [S2Ni2] core and Ni?H bond formation are kinetically favored over the thermodynamically favored yet unproductive proton transfer to ligand.

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Selective hydrogenation of 1,3-, 1,4-, and 1,5-cyclooctadiene to cyclooctene was carried out at 30 deg C under atmospheric hydrogen pressure using colloidal palladium which was prepared by reducing palladium(II) chloride with refluxing methanol in the presence of poly(N-vinyl-2-pyrrolidone).The yields of cyclooctene were 99.9percent and 97.8percent for hydrogenation of 1,3- and 1,5-cyclooctadiene, respectively at the point that an equimolar hydrogen was uptaken by cyclooctadienes.The hydrogenation rate of 1,3- and 1,4- cyclooctadiene (R1) is expressed as R1=k1, and that of 1,5-cyclooctadiene (R2) is expressed as R2=k20.7, where k1 and k2 are the rate constants.Alcohols were found to be good solvents for hydrogenation.In particular the fastest rate and the highest selectivity for monoene were observed in methanol among the solvents examined.Effect of bases on the monoene selectivity has also been investigated.

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Methyl linoleate and 1,5-cyclooctadiene are hydrogenated with high selectivity to the corresponding monoenes over palladium catalysts in the presence of added phenylacetaldehyde, with almost complete depression of the hydrogenation to the saturates.

Doubly functionalized, hierarchical-porosity silica monoliths were synthesized by postgrafting of sulfonic groups and in situ growth of Pd nanoparticles in that order. PdNP of 3.1 nm size located in the mesopores of the material showed to be evenly distributed within 4.6 % wt Pd monoliths. The system was explored in the continuous-flow, catalytic partial hydrogenation reaction of 3-halogeno-nitrobenzenes and 3-hexyn-1-ol in the liquid phase, showing remarkable conversion, selectivity, and resistance under very mild conditions.

Phosphonium-based Ionic Liquids (PhosILs) with natural organic derived anions (l-lactate, l-tartrate, malonate, succinate, l-malate, pyruvate, d-glucuronate, d-galacturonate, ferulate, p-coumarate) were easily prepared by acid-base method from tetrabutylphosphonium hydroxide and an excess of the corresponding acid with good yields. Their characterization was realized through classical NMR, IR and elemental analysis techniques; their viscosity and ATG parameters were also determined. These ionic liquids showed good performance and recyclability in the selective Pd-catalyzed hydrogenation of alkenes, polyenes like linoleic acid and enantioselective hydrogenation of unsaturated ketones such as isophorone at room temperature under atmospheric H2 pressure. Furthermore, NMR studies leading to computational calculations were performed to establish easily the composition of the resulting mixture obtained through the hydrogenation of linoleic acid.

In Wacker oxidation and inspired Pd(ii)/Cu(ii)-catalyzed C-H activations, copper(ii) is believed to serve in re-oxidizing of Pd(0) in the catalytic cycle. Herein we report that non-redox metal ions like Sc(iii) can promote Wacker-type oxidations even better than Cu(ii); both Sc(iii) and Cu(ii) can greatly promote Pd(ii)-catalyzed olefin isomerization in which the redox properties of Cu(ii) are not essential, indicating that the Lewis acid properties of Cu(ii) can play a significant role in Pd(ii)-catalyzed C-H activations in addition to its redox properties. Characterization of catalysts using UV-Vis and NMR indicated that adding Sc(OTf)3 to the acetonitrile solution of Pd(OAc)2 generates a new Pd(ii)/Sc(iii) bimetallic complex having a diacetate bridge which serves as the key active species for Wacker-type oxidation and olefin isomerization. Linkage of trivalent Sc(iii) to the Pd(ii) species makes it more electron-deficient, thus facilitating the coordination of olefin to the Pd(ii) cation. Due to the improved electron transfer from olefin to the Pd(ii) cation, it benefits the nucleophilic attack of water on the olefinic double bond, leading to efficient olefin oxidation. The presence of excess Sc(iii) prevents the palladium(0) black formation, which has been rationalized by the formation of the Sc(iii)...H-Pd(ii) intermediate. This intermediate inhibits the reductive elimination of the H-Pd(ii) bond, and facilitates the oxygen insertion to form the HOO-Pd(ii) intermediate, and thus avoids the formation of the inactive palladium(0) black. The Lewis acid promoted Wacker-type oxidation and olefin isomerization demonstrated here may open up a new opportunity in catalyst design for versatile C-H activations.

The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable-temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side-arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal-hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru0 coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined. The catalyst tested positive! A dearomatised ruthenium PNN (2-di-tert-butylphosphinomethyl-6-diethylaminomethylpyridine) pincer complex, [Ru(CO)H(PNN)], was evaluated as an alkene isomerisation catalyst. The isomerisation reaction was greatly accelerated by the addition of alcohols, in particular isopropanol. Isomerisation of terminal to internal alkenes took place at room temperature. A mechanism was proposed based on variable-temperature NMR spectroscopy.

In this work, it has been investigated a membrane-like effect of ionic liquid (IL) in the multistep catalytic hydrogenation of trans-cinnamaldehyde (CALD) and 1,5-ciclooctadiene (1,5-COD). A commercial Pd/C catalyst was impregnated with 1-hexyl-3-methyl-imidazolium at 0.5-10 wt%. SEM, EDS, XRD, TG and BET data suggested that the IL penetrates the carbon pore structure coating the catalyst, especially at 5 and 10% concentration. The presence of the IL layer strongly affected the selectivities of the hydrogenations of CALD and 1,5-COD. In the case of CALD, the IL favored the formation of the fully hydrogenated product (hydrocinnamyl alcohol). This result is discussed in terms of a membrane-like effect, in which the small H2 molecule diffuses more easily from toluene through the IL layer as compared to the larger cinnamaldehyde. This effect results in the production of comparatively higher concentrations of the Pd-H species, which favors the double hydrogenation. On the other hand, the IL layer during the 1,5-COD hydrogenation favored the intermediate product COE (cyclooctene). In this case, a membrane-like effect was also used to discuss the result, where the IL layer has the effect to expel the intermediate COE hindering its contact with the Pd surface.

A detailed study investigating the mechanism of the hydrosilylation of 4-F-acetophenone by N-heterocyclic biscarbene rhodium(I) complexes was performed, delivering substantial experimental evidence for a recently proposed catalytic cycle and explaining the observed side-product formation. Labeling experiments, silylene trapping reactions, and specific catalytic reactions were employed to substantiate each step of the catalytic cycle and explain the differences observed for different types of chiral catalysts. It is further shown that hydrosilylation and dehydrocoupling reactions with dihydrosilanes are mechanistically related.

A direct synthetic route to cationic N-heterocyclic carbene (NHC) complexes of rhodium and iridium from neat dialkyl-imidazolium ionic liquids (ILs) has been found. The method uses complexes bearing basic anionic ligands, [M(COD)(PPh3)X], X = OEt, MeCO2, which react with the inactivated imidazolium cation in the absence of external bases yielding one M-NHC moiety and the free protonated base. This new one-pot synthesis leaving pure, catalytically active IL solutions is faster, cleaner and more efficient than traditional syntheses of such NHC complexes. The observed reactivity also gives insight into NHC incorporation of rhodium and iridium catalyzed reactions performed in common dialkyl-imidazolium ILs. The complexes synthesised in this manner are compared with their bis-phosphine analogues in terms of activity for catalytic dehydrogenation of 1,5-cyclooctadiene and 1,3-cyclooctadiene in neat [BMIM][NTf2] as solvent. Even at high temperature, no ligand exchange reaction is observed with [(COD)M(PPh3)2] [NTf2] catalysts. As expected, the yields of all the reactions were low, iridium was much more active in C-H activation than rhodium and the NHC ligands were more stable than triphenylphosphine. For all catalysts, the isomerisation of 1,5-cyclooctadiene is the major reaction. However, the phosphine-NHC complex of iridium seems to be more selective for dehydrogenation than its bis-phosphine counterpart, which is more active in transfer-hydrogenation and less stable under the applied conditions. Different reaction conditions were tried in order to optimise selectivity for dehydrogenation over isomerisation and transfer-hydrogenation. Surprisingly, with 1,3-cyclooctadiene as substrate selectivity for dehydrogenation is much higher than with 1,5-cyclooctadiene for all catalysts.

The mixture of samarium diiodide, amine, and water (SmI2/H 2O/Et3N) is known to be a particularly powerful reductant, but until now the limiting reducing power has not been determined. A series of unsaturated hydrocarbons with varying half-wave reduction potentials (E 1/2 = -1.6 to -3.4 V, vs SCE) have been treated with SmI 2/H2O/Et3N and YbI2/H 2O/Et3N, respectively. All hydrocarbons with potentials of -2.8 V or more positive were readily reduced with SmI2/H 2O/Et3N, whereas all hydrocarbons with potentials of -2.3 V or more positive were readily reduced using YbI2/H 2O/Et3N. This defines limiting values of the chemical reducing power of SmI2/H2O/Et3N to -2.8 V and of YbI2/H2O/Et3N to -2.3 V vs SCE.

In benzene under an atmosphere of hydrogen, triplet excited-state xanthone or acetone sensitizes the photoreduction of bis(acetylacetonato)nickel(II), Ni(acac)2, to transient nickel(I) complexes which can be detected by ESR spectroscopy in the presence of stabilizing ligands.The kinetics of these ESR signal decays prove that these nickel(I) complexes are derived from moderately co-ordinating ligands, such as tetrahydrofuran and 1,5-cyclo-octadiene (1,5-COD), and react with hydrogen in the dark to form nickel hydride complexes.An excess of 1,5-COD in the photolysate was sequentially and catalytically isomerized and hydrogenated under the irradiation conditions; i.e., 1,5-COD -> 1,4-COD -> 1,3-COD -> COE -> COA.The nickel hydride complexes are proposed as the key species in the initiation of the catalytic cycle in which steps involving the addition and elimination of nickel hydride bonds and the hydrogenolysis of nickel complexes are assumed.As these alkene reactions cease in the dark and are quenched by a high concentration of 1,3-COD, it can be concluded that one or more steps in the catalytic cycle requires sensitized photoexcitation.

The behaviour of four different copper-based catalysts, CuO-Al2O3, CuO-SiO2, CuO-CuCr2O4, CuO-ZnO-Al2O3, has been tested in the hydrogenation of 1,3-cyclooectadiene and (Z,Z')-1,5-cyclooectadiene by using the Water Gas Shift Reaction (WGSR) as source of molecular hydrogen.The catalytic activity of these compounds was found to be influenced by their surface composition.The pre-reduced copper catalysts brought about hydrogenation of the conjugated diene even in the presence of massive amounts of water (molar ratio H2O/Cu = 170).In the case of (Z,Z')-1,5-cyclooectadiene the inhibiting effect of water resulted to be greater in the isomerization steps than in the addition of H2 to the double bonds.ESCA characterization of the catalyst surface was performed and used to determine the relative amounts of the species Cu(II), Cu(I) and Cu(0).

Xanthone-sensitized photoreduction of Ni(acac)2 in benzene under hydrogen, in the presence of cis,cis-1,5-cyclooctadiene (1,5-COD), causes isomerization and hydrogenation of the diene according to the consecutive transformation 1,5-COD -> 1,4-COD -> 1,3-COD -> cyclooctene -> cyclooctane.Evidence was provided that (i) a nickel hydride complex was generated, (ii) the sensitized excitation of this complex caused addition two the double bond, (iii) subsequent elimination caused isomerization, and (iv) triplet excited xanthone sensitized the transformations.

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In sharp contrast to the wavelength-dependent photobehaviour of simple mono-alkenes, the photochemistry of conjugated dienes was found to be independent of excitation wavelength in the region 185-254 nm.

Thiocyanatotris(triphenylphosphine)cobalt(I) prepared in situ from bis(thiocyanato)bis(triphenylphosphine)cobalt(II), triphenylphosphine, zinc bromide, selectively hydrogenated conjugated dienes to the corresponding cis-monomenes. The C//2-or/ and C//3-methyl substituted 1,3-butadienes enhance the reactivity by a factor of 2. 3 per one methyl group, while C//1- or/and C//4-methyl substituted 1,3-butadienes lower the reactivity by a factor of 1/23 per one methyl group. In the hydrogenation of cyclic conjugated dienes alpha -angle is closely related to the hydrogenation rate. The rates of hydrogenation in cyclic ethers are greater than those in acyclic ethers, but the cis-selectivity in acyclic ethers is much higher.

We report the synthesis of (η3-C8H13)((C6H 5)2PCH2COO)Ni (1), which proved to be an excellent one-component model catalyst for the oligomerization of ethylene as practiced in Shell's higher olefin process (SHOP). In toluene solution this complex exists in two isomeric forms, the C8H13 ligand being 60% 4-enyl and 40% η3-allyl. Under reaction conditions (75°C, 10-80 bar, ethylene in toluene) 1 catalyzed the highly selective oligomerization of ethylene to linear (99+%), α olefins (93-99%) at activities of 0.6 mol of ethylene/mol of Ni/s. The chain growth factor K ranges from 0.67 to 0.77 depending on reaction conditions. Kinetic activation parameters and reaction constants could be determined (Ea = 71 kJ mol-1; S? = -49 J mol-1 K-1; kinsert/348K = 0.81 s-1).

Visible or long-wavelength ultraviolet excitation of alkali metal salts of cyclooctadiene leads to electron exchange.Primary photoinduced electron transfer has been used to initiate the geometrical isomerization of cis-stilbene and the photosubstitution of aryl halides.Mechanistic details for these reactions are presented.Electron exchange so dominates the excited-state reactivity of this pentadienyl anion that neither potential pericyclic reaction (i.e., electrocyclization or sigmatropic shifts) nor photoinduced cis-trans isomerization can be detected.

The bis-mercuriated derivative (12) of 9,10-dioxabicyclodecane has been prepared by peroxymercuriation of cis,cis-octa-1,5-diene, but substantial amounts of bicyclic ethers are also formed in the reaction.The bicyclic peroxides (4) and (5) have been obtained from (12) by reduction and brominolysis respectively. 8,9-Dioxabicyclodecane (6) and the dibromo-derivative (7) have similarly been prepared by peroxymercuriation and demercuriation of cyclo-octa-1,4-diene.It is suggested that the isomeric purity of the peroxides and the concurrent formation of bicyclic ethers both result from equilibrium control of reversible (per)oxymercuriation-de(per)oxymercuriation.A low yield of the -peroxide (8) has been obtained by peroxymercuriation and brominolysis of cyclohexa-1,4-diene, but attempts to prepare -compounds from 5,5-disubstituted cyclopentadienes have been unsuccessful.