The mechanism of catalyst formation from tungsten hexachloride and cocatalyst in olefin metathesis

Summary The mechanism of the catalyst formation in hept-2-ene metathesis was investigated by gas chromatographic analysis of the products from reactions of tungsten hexachloride with R₄Sn(R = Ph, n-Bu), RLi, RMgl (R = n-Bu) or R₃Al(R = Et) as cocatalyst. The products are chiefly RH, RCl and RR species, and the highest catalytic activity is observed for an equimolar ratio of products to tungsten hexachloride. The facts suggested that the active catalyst, a WCl₄ species, is formed by the elimination of two R groups from R₂WCl₄ and/or one R group and chlorine from RWCl₅. The total quantity and composition of the products varies with the cocatalyst:WCl₆ ratio, and the difference between the behavior of tetra-n-butylstannane and n-butyllithium in the catalyst formation is explainable on the basis of their relative nucleophilicities. Gas chromatographic analysis of the organotin compounds resulting from the WCl₆:: Bu₄Sn system shows that tetra-n-butylstannane provides only one butyl group per mole of WCl₆.     

Etudes sur le mecanisme de la metathese des olefines : II. Coupure des alkyltungstenes,amorçages anormaux

With a view to elucidating the mode of action of tungsten containing catalyst of the olefin metathesis, the thermal decomposition of various alkyltungsten derivatives was examined. It was shown that n-alkyltungsten derivatives (i.e. n-alkylmagnesium halides + WCl₆) are decomposed to lighter alkenes and alkanes (i.e. propyl to ethylene, ethane and methane). With methyl or neopentyl derivatives of tungsten, alkenes are observed, which derive from alkylation and fission of the metathesis substrate (i.e. Me₃CCH₂MgBr + WCl₆ + 2-pentene give inter alia 2,2-dimethyl-4 hexene). Metathesis of tetramethylethylene was also observed, as evidenced by the formation of 2-methyl-2-pentene in the presence of 3-hexene.All these facts agree with the intermediacy of a tungsten hydride as the key step in the formation of a metathesis catalyst, intermediacy which is linked with the formation of tungstacarbene (alkylidene tungsten).     

Influence of the order of introduction of protonic acids on the formation of active complexes in the Ni(PPh3)4/BF3 · OEt2 catalytic system

The influence of the order of introduction of promoters (complex protonic acids) on the formation of active complexes in the Ni(PPh₃)₄/BF₃ · OEt₂ catalytic system and the activity of these systems in ethylene oligomerization have been studied. The activity of the systems in which nickel exists mainly as cationic Ni(I) complexes is more than one order of magnitude higher than the activity of the systems where nickel exists mainly in the form of Ni(II) hydride complexes. The role of alcohols as promoters in the Ni(PPh₃)₄/BF₃ · OEt₂ catalytic system is elucidated. The alcohols are the source of Ni(II) hydrides and, more importantly, the source of strong Brønsted acids, which efficiently ensure the coordinative unsaturation of the cationic Ni(I) complexes.     

Halo-nitrosyl-carbonyl-tungsten complexes and their triphenylphosphine derivatives as olefin methathesis catalysts

The tungsten complexes W(CO)₄(NO)X, W(CO)₃(NO)(PPh₃)X and W(CO)₂(NO)(PPh₃)₂X (X = Cl, Br and I) have been shown to be effective catalysts for the metathesis of 1,7-octadiene.     

Formation and nature of catalysts based on nickel(0) phosphine complexes active in lower alkene dimerization and oligomerization

The catalytic properties and formation mechanism of alkene dimerization-active complexes in systems based on Ni(PPh₃)₄ and boron trifluoride etherate are considered. The nature of the modifying action of Brønsted acids on the properties of metal complex catalysts for propylene dimerization is reported. The interaction between Ni(PPh₃)₄ and BF₃ · OEt₂ is influenced by water. Depending on the water concentration, the reaction can proceed via formally one-electron oxidation to yield cationic Ni(I) complexes or via two-electron oxidation to yield Ni(II) hydrides. The catalytically active species in alkene dimerization and oligomerization in these systems are Ni(II) hydrido complexes.     

金鸡纳碱季铵盐促进的 CO2 与环氧化合物的不对称环加成反应

 开发了钴配合物/金鸡纳碱季铵盐催化剂体系用于催化 CO2 与环氧化合物的不对称环加成反应, 考察了催化剂和助催化剂中阴离子对反应的影响. 结果表明, 该反应可在 667 kPa CO2 压力和室温下进行. 催化剂中不同阴离子的活性次序为 2-硝基苯氧基 > 2,4,6-三硝基苯氧基 > NO3? > OAc? > 三氟乙酸根 ≈ B ? > Cl? >对甲苯磺酸根. 当助催化剂阴离子为 Cl?时反应的 ee 值较高, 而为 Br? 时反应速度较快. 当以 (S,S)-1,2-环己二胺缩 (N,N-双 (3,5-二-叔丁基水杨醛) 钴 (III) 乙酸盐 ((S,S)-A) 结合 N,O-二苄基氯化奎宁 (1a) 作助催化剂时, 得到了 ee 值为 73% 的手性丙烯环碳酸酯.     

Palladium-catalyzed isomerization of 1-hexene

The isomerization of 1-hexene over Pd(acac)₂ + BF₃OEt₂ and Pd(acac)₂ + PPh₃ + BF₃OEt₂ catalyst systems proceeds by the consecutive-parallel scheme. Tetracoordinate square-planar Pd hydrides bearing two vacant coordination sites are likely to be catalytically active species for the isomerization of hexene-1. This revised version was published online in June 2006 with corrections to the Cover Date.     

Studies of η5-cyclichydrocarbon ruthenium(II) complexes containing para-amino-N-(pyrid-2-ylmethylene)phenylamine ligand: molecular structure of [(η5-C5H5)Ru(PPh3)(C5H4NCH=N-C6H4-p-NH2)]BF4

Reaction of [(η⁵-Cp)Ru(PPh₃)₂Cl] (1) with excess para-amino-N-(pyrid-2-ylmethylene)-phenylamine ligand (app) in methanol in the presence of NH₄BF₄ leads to the formation of [η⁵-CpRu(PPh₃)(aap)]BF₄ (6BF₄). Similarly, [(η⁵-ind)Ru(PPh₃)₂(CH₃CN)]BF₄ (4BF₄) and [(η⁵-Cp*)Ru(PPh₃)₂(CH₃CN)]BF₄ (5BF₄) react with app to yield the cationic complexes [(η⁵-ind)Ru(PPh₃)(app)]BF₄ (7BF₄) and [(η⁵-Cp*)Ru(PPh₃)(app)]BF₄ (8BF₄), respectively. The complexes were characterized by analysis and spectroscopic data. The structure of a representative complex (6BF₄) was established by single-crystal X-ray methods.     

The analysis of inorganic and organometallic antimony,arsenic and tin compounds using an on-column hydride generation method

A novel method of analysis of inorganic and organometallic compounds is reported. Essentially this utilizes the well-documented hydride generation technique, but in the present method the hydrides are generated from their involatile precursors (e.g. chlorides) on a GC column and separated from each other and from extraneous materials on the same GC column in a single process. Using the method, a solution of butyltin chlorides can be directly injected into a GC AA system to yield the volatile hydrides for separation, detection and quantification. To date, species analysed by this method include inorganic As(III), Me₂AsOOH, inorganic Sb(III) and Sb(V), MeSnCl₃, Me₂SnCl₂, Me₃SnCl, Et₂SnCl₂, Et₃SnCl, BuSnCl₃, Bu₂SnCl₂, Bu₃SnCl and Pr₃SnCl. With the use of the internal standard Pr₃SnCl and with the almost complete hydridization afforded by the technique, the procedure is shown to eliminate errors and to reduce the time involved in the analysis. The use of on-column derivatization also allows for the possibility that, in some cases, organotin hydrides reported to be found in the natural environment may, in fact, be organotin chlorides being reported as hydrides owing to inadvertent hydride production on the column. Some reports of successful gas chromatography for organotin halides could also conceivably be due to on-column hydride generation.     

Crystalline titanium dichloride—an active catalyst in ethylene polymerization. I. Catalyst activation

Crystalline titanium dichloride, in the absence of organometallic cocatalyst, is a very poor catalyst for the polymerization of ethylene. It is transformed into a very active catalyst through mechanical activation (ball-milling). This catalyst is active in the absence not only of organometallic cocatalysts, but also metals and compounds (such as aluminium and AlCl₃) capable of forming organometallic compounds in situ (i.e., with ethylene, before polymerization starts). Ball-milling causes not only the expected increase in surface area but also disproportionation of Ti⁺⁺ to Ti⁺⁺⁺ and metallic titanium, as well as a crystal phase change to a structure not previously identified with those of TiCl₂ or TiCl₃. Catalyst activity (polymerization rate) is shown to be proportional to surface area and a direct function of Ti⁺⁺ content of the catalyst; an empirical equation relates catalyst activity to surface area and to Ti⁺⁺ lost through disproportionation. Titanium trichloride was found to be inactive in the absence of organometallic cocatalyst, even after ball-milling. The difference in structure of the catalytically active species in the conventional Ziegler (organometallic cocatalyst) and in the titanium dichloride catalyst are discussed. The mechanism of polymerization is compared with that of the supported (CrO₃ on SiO₂/Al₂O₃ and MoO₃ on Al₂O₃) catalyst systems.     

Preparation and reactivity with azo-species of hydride and dihydrogen complexes of osmium stabilised by tris(pyrazolyl)borate and phosphite ligands

Mixed-ligand OsCl(Tp)L(PPh₃) complexes 1 [Tp = hydridotris(pyrazolyl)borate; L = P(OMe)₃, P(OEt)₃ and PPh(OEt)₂] were prepared by allowing OsCl(Tp)(PPh₃)₂ to react with an excess of phosphite. Treatment of chlorocomplexes 1 with NaBH₄ in ethanol afforded hydride OsH(Tp)L(PPh₃) derivatives 2. Stable dihydrogen [Os(η²-H₂)(Tp)L(PPh₃)]BPh₄ derivatives 3 were prepared by protonation of hydrides 2 with HBF₄ · Et₂O at −80 °C. The presence of the η²-H₂ ligand is supported by short T_1 min values and J_HD measurements on the partially deuterated derivatives. Treatment of the hydride OsH(Tp)[P(OEt)₃](PPh₃) complex with the aryldiazonium salt [4-CH₃C₆H₄N₂]BF₄ afforded aryldiazene [Os(4-CH₃C₆H₄NNH)(Tp){P(OEt)₃}(PPh₃)]BPh₄ derivative 4. Instead, aryldiazenido [Os(4-CH₃C₆H₄N₂)(Tp)[P(OEt)₃](PPh₃)](BF₄)₂ derivative 5 was obtained by reacting the hydride OsH(Tp)[P(OEt)₃](PPh₃) first with methyltriflate and then with aryldiazonium [4-CH₃C₆H₄N₂]BF₄ salt. Spectroscopic characterisation (IR, ¹⁵N NMR) by the ¹⁵N-labelled derivative strongly supports the presence of a near-linear Os-NN-Ar aryldiazenido group. Imine [Os{η¹-NHC(H)Ar}(Tp){P(OEt)₃}(PPh₃)]BPh₄ complexes 6 and 7 (Ar = C₆H₅, 4-CH₃C₆H₄) were also prepared by allowing the hydride OsH(Tp)[P(OEt)₃](PPh₃) to react first with methyltriflate and then with alkylazides.     

Effect of tungsten oxide loading on metathesis activity of ethene and 2-butene over WO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> catalysts

The metathesis of ethene and 2-butene to propene was studied over WO₃/SiO₂ catalysts with various WO₃ loadings (2, 4, 8, 12, 16, and 24 wt%). The 2-butene conversion and propene selectivity increased greatly with WO₃ loading increasing from 2 to 8 wt%, reached maximum at 8–12 wt% WO₃ loading, and then decreased when the WO₃ loading was higher than 12 wt%. From the above results and taking the economics into account, the optimal amount of WO₃ loading was ~8 wt%. The catalysts were characterized by physico-chemical and spectroscopic techniques to elucidate the effect of different tungsten oxide loadings on the metathesis reactivity of ethene and 2-butene. The characterization data indicated that three types of tungsten species (i.e., surface tetrahedral tungsten species, surface octahedral polytungstate species, and WO₃ crystallites) were present in the catalysts. It was found that WO₃ was not the active centers, and surface tetrahedral tungsten species might be more active than octahedral polytungstate species in metathesis reaction. The reduced form of tungsten species [W⁺⁴, W⁺⁵, and W^+(6−y) (0 < y < 1)] may be the suitable state of W species acting as metathesis active centers.     

Synthesis and characterization of the bimetallic gold-iridium compoundscis-[IrH(AuPPh3)(dppe)2]PF6 andmer-[IrH(AuPPh3)(CO)(PPh3)3]PF6

Summary The bimetallic complexes [IrH(AuPPh₃)(dppe)₂]X(X=Cl, BPh₄, PF₆ or BF₄) and [IrH(AuPPh₃)(CO)(PPh₃)₃] PF₆ have been synthesized from the corresponding neutral iridium phosphine hydrides and [AuCl(PPh₃)]. The molecular structure of the latter compounds, determined by single-crystal x-ray crystallography, consists of an octahedrally co-ordinated iridium atom and an almost linear P–Au–Ir–P arrangement. The Au–Ir distance is 2.6628(4) Å. The position of the hydride ligand was located in the x-ray structural analysis and istrans to the carbonyl group, which is consistent with the i.r. and n.m.r. spectral data.     

Regulation of Catalytic Activity by Phosphine Ligand Design

Abstract

Starting with the catalytic complex [Rh(PPh₃)₃Cl], the influence of variation of phosphine ligand properties on the activity of rhodium phosphine complexes as catalysts for the hydrogenation of olefins was systematically studied. The following catalyst modifications were examined (a) varying the basicity of the triarylphosphine ligands, (b) replacing Cl^? by a non-coordinating anion (BF₄ ^?) to make the catalyst cationic, (c) substituting a chelating diphosphine for the monophosphine ligands to ensure cis-coordination, and (d) varying the chain length of the diphosphine ligand to vary the chelate ring size and flexibility. By systematic manipulation of these parameters, enhancements of catalytic activity by factors in excess of 10⁴ were achieved.     

Ring-opening polymerization of 2-azabicyclo-[2,2,1]-hept-5-en-3-one using metathesis catalysts

The ring-opening polymerization of an unsaturated bicyclic lactam, 2-azabicyclo-[2,2,1]-hept-5-en-3-one (ABHEO), was carried out using metathesis catalysts under various reaction conditions. It is observed that the best results (34% conversion and η_inh: 0.18 dL/g) were obtained when the mole ratios of ABHEO to WCl₆ as a catalyst and WCl₆ to AlEt₃ as a cocatalyst were 200 and 4, respectively. The infrared (IR) and nuclear magnetic resonance (¹H- and ¹³C-NMR) spectra of the polymer obtained indicated that the ABHEO was transformed to the ring-opened polymer, poly(2-pyrrolidone-3,5-diylvinylene) [poly(ABHEO)]. The resulting polymer was amorphous as determined by DSC analysis, which showed only secondary transition at 100°C.     

Catalytic dehydrogenation of cyclooctane with titanium, zirconium and hafnium metallocene complexes

Metallocene complexes in combination with cocatalysts like methylalumoxane (MAO) are not only excellent catalysts for olefin polymerization but also appropriate catalysts for the activation of alkanes in homogeneous (autoclave) and heterogeneous (fixed bed reactor) reactions. The activities of the catalysts depend on the temperature, the cocatalysts, additives, the central metal and the ligand structure. Generally, complexes with low steric demands and MAO as cocatalyst gave the highest activities. The comparison of different π-ligands resulted in the following activity order: cyclopentadienyl > indenyl > fluorenyl. The influence of σ-ligands and n-donor ligands gave the following activity order: -Cl > -PMe₃ > -CH₂Ph > -(CH₂)₄CH₃ > -NPh₃. The activities depended on the nature of the cocatalyst and decreased in the following order: MAO ? AlMe₃ > AlEt₃. The addition of aluminum powder and the Lewis base NPh₃ increased the activity of the Cp₂ZrCl₂/MAO catalyst. The Cp₂ZrCl₂/MAO/NPh₃ catalyst showed the highest activity in homogeneous reactions with 458 turnovers in 16 h at 300 °C. The Cp₂ZrCl₂/MAO/NPh₃/SI1102 catalyst gave the highest activity in heterogeneous catalysis with 206 turnovers in 5 h at 350 °C. None of the catalysts required a hydrogen acceptor like an external olefin.     

Synthesis,Structure, and Reactivity of RuII Complexes with Trimethylsilylethinylamidinate Ligands

The mononuclear amidinate complexes [(η⁶‐cymene)‐RuCl( 1a )] ( 2 ) and [(η⁶‐C₆H₆)RuCl( 1b )] ( 3 ), with the trimethylsilyl‐ethinylamidinate ligands [Me₃SiC≡CC(N‐c‐C₆H₁₁)₂]^– ( 1a^– ) and[Me₃SiC≡CC(N‐i‐C₃H₇)₂]^– ( 1b^– ) were synthesized in high yields by salt metathesis. In addition, the related phosphane complexes[(η⁵‐C₅H₅)Ru(PPh₃)( 1b )] ( 4a ) [(η⁵‐C₅Me₅)Ru(PPh₃)( 1b )] ( 4b ), and [(η⁶‐C₆H₆)Ru(PPh₃)( 1b )](BF₄) ( 5 ‐BF₄) were prepared by ligand exchange reactions. Investigations on the removal of the trimethyl‐silyl group using [Bu₄N]F resulted in the isolation of [(η⁶‐C₆H₆)Ru(PPh₃){(N‐i‐C₃H₇)₂CC≡CH}](BF₄) ( 6 ‐BF₄) bearing a terminal alkynyl hydrogen atom, while 2 and 3 revealed to yield intricate reaction mixtures. Compounds 1a / b to 6 ‐BF₄ were characterized by multinuclear NMR (¹H, ¹³C, ³¹P) and IR spectroscopy and elemental analyses, including X‐ray diffraction analysis of 1b , 2 , and 3 .     

Spectroscopic Study of the Interaction of the Pd(acac)(C3-acac)PPh3Complex with BF3OEt2 in the Presence of PPh3

The interaction between the components of a catalytic system Pd(acac)(C³-acac)PPh₃+nPPh₃+ mBF₃OEt₂(where n= 1–4, m= 0.25–4, and acac is the acetylacetonate ligand) in benzene is examined by UV and IR spectroscopy. With a relative excess of PPh₃(n> m), acacH and [Pd(acac)(PPh₃)₂]⁺BF^– ₄were the main products, whereas BF₂acac and a polynuclear complex of PdF₂with PPh₃also containing Pd²⁺(BF^– ₄)₂units were formed with a relative excess of BF₃OEt₂(n< m).     

A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO2 Nanosheet

The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO₂ nanosheets doped with Rh at Ti sites as one‐atom cocatalysts. A hydride species adsorbed on the one‐atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo‐excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride.     

Gas-phase polymerization of ethylene over Ti-based Ziegler–Natta catalysts prepared from different magnesium sources

This study focuses on gas-phase polymerization of ethylene using the titanium-based Ziegler–Natta catalysts prepared from different magnesium sources including MgCl₂ (Cat A), magnesium powder (Cat B), and Mg(OEt)₂ (Cat C). During polymerization, different cocatalysts were also used. It was found that Cat C with triethylaluminum as a cocatalyst exhibited the highest activity. This was likely attributed to optimal distribution of active sites on the catalyst surface. It can be observed by increased temperature in the reactor due to highly exothermic reaction during polymerization. By the way, the morphologies of the polymer obtained from this catalyst were spherical, which is more preferable. Besides the catalytic activity, crystallinity and morphology were also affected by the different magnesium sources used to prepare the catalysts.