Kinetics and mechanism of styrene hydrocarboalkoxylation catalyzed by Pd0 complex in the presence of toluenesulfonic acid

The kinetics of the catalytic reaction of styrene with CO and n-butanol in the Pd(dba)₂—TsOH—Ph₃P system in dioxane (383 Ê) was studied. The initial rates of accumulation of regioisomeric products (butyl 2- and 3-phenylpropionates) were measured as functions of the CO pressure, reactant concentrations, and the catalytic system components. A kinetic model of the process and a hydride mechanism with the HPd(Ph₃P)₃ ⁺ cationic complex acting as a key intermediate were proposed.     

Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl—PdCl₂ (1 : 0.04) system in acetonitrile.     

Palladium-Catalyzed C-Phenylation of Methyl Acrylate with Triphenylbismuth Dicarboxylates

A new catalytic reaction of C-phenylation of methyl acrylate with bismuth derivatives Ph₃Bi(O₂CR)₂ (R = H, Me, Et, Bu, CF₃, Ph) or Ph₃BiCl₂ in a 3 : 1 ratio was studied. The reaction was performed in the presence of 4 mol % palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and PdLCl₂ (L = dppm, dppe, dppp, dppb, dppf, binap, xantphos) at 50°C in CH₃CN, DMF, THF, or CH₂Cl₂ and gave methyl cinnamate (yield up to 85% based on the starting bismuth compound), diphenyl (up to 138%), and benzene (up to 59%).     

Kinetics and Mechanism of a Reaction of Phenylacetylene with Carbon Monoxide and Butanol in Toluene Catalyzed by a Palladium(0) Complex in the Presence of Trifluoroacetic Acid and Triphenylphosphine

The reaction of phenylacetylene with CO and n-butanol in toluene (363 K) catalyzed by the Pd(dba)₂/m(CF₃COOH)/n(Ph₃P) system (dba is dibenzylideneacetone; 2 m 8; 10 n 30) is studied. The initial rate of the main product (butyl 2-phenylpropenoate) buildup is found to depend on the pressure of CO and the concentrations of reactants and system components. The state of the catalyst under reaction conditions is studied in situby IR spectroscopy. A kinetic model is developed based on the experimental results. This model corresponds to the mechanism that resembles the hydride mechanism in the type of main intermediates in the catalytic cycle.     

Modification of polymethylhydrosiloxane by dehydrocoupling reactions catalyzed by transition metal complexes: Evidence for the preservation of linear siloxane structures

Polysiloxanes with pendant poly(ethylene oxide) side chains (4 were prepared by the dehydrocoupling reaction of poly(methylhydrosiloxane) (PMHS, 3 with 2-(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethoxy)ethanol (1 and poly(ethylene glycol) methyl ether (2 using a metal catalyst. Catalysts investigated were tin(II) 2-ethylhexanoate, Rh(Ph₃P)₃Cl, and Pd₂(dba)₃. The reaction of a cyclic siloxane, D₄^H, with 1 catalyzed by Pd₂(dba)₃ was also carried out to synthesize siloxane 6. The polysiloxanes were characterized by ¹H NMR, ²⁹Si NMR, FT-IR, and GPC. ²⁹Si NMR study of these comb-like polysiloxanes revealed that there is a significant difference in the structure of the siloxane polymers prepared depending upon the catalyst. M, D, and T units were observed when tin(II) was used as a catalyst, but only M and D units were detected when Rh(Ph₃P)₃Cl or Pd₂(dba)₃ was employed. Furthermore, M and T units are negligible for the cyclic siloxane 3 using Pd₂(dba)₃. A mechanism is proposed to account for these observations.     

Catalytic C-phenylation of methyl acrylate with triphenylantimony(v) dicarboxylates

Triphenylantimony dicarboxylates Ph₃Sb(OAc)₂ and Ph₃Sb(O₂CEt)₂ are efficient C-phenylating agents for methyl acrylate. In the presence of the Pd(OAc)₂, Li₂PdCl₄ or Pd₂(dba)₃(CHCl₃) catalysts in MeCN at 50 °C, methyl cinnamate forms in 70—150% yield with respect to Sb^V. Copper(ii) salts do not increase the reaction yield.     

Synthesis and Rearrangement of P‐Nitroxyl‐Substituted PIII and PV Phosphanes: A Combined Experimental and Theoretical Case Study

Low‐temperature generation of P‐nitroxyl phosphane 2 (Ph₂POTEMP), which was obtained by the reaction of Ph₂PH ( 1 ) with two equivalents of TEMPO, is presented. Upon warming, phosphane 2 decomposed to give P‐nitroxyl phosphane P‐oxide 3 (Ph₂P(O)OTEMP) as one of the final products. This facile synthetic protocol also enabled access to P‐sulfide and P‐borane derivatives 7 and 13 , respectively, by using Ph₂P(S)H ( 6 ) or Ph₂P(BH₃)H ( 11 ) and TEMPO. Phosphane sulfide 7 revealed a rearrangement to phosphane oxide 8 (Ph₂P(O)STEMP) in CDCl₃ at ambient temperature, whereas in THF, thermal decomposition of sulfide 7 yielded salt 10 ([TEMP‐H₂][Ph₂P(S)O]). As well as EPR and detailed NMR kinetic studies, indepth theoretical studies provided an insight into the reaction pathways and spin‐density distributions of the reactive intermediates.     

Synthesis,structure, and catalytic properties of heteroelement carbene tungsten complexes Ph<Subscript>3</Subscript>ECH=W(OBu-<Emphasis Type="Italic">t</Emphasis>)<Subscript>2</Subscript>(OPh)<Subscript>2</Subscript> (E = Si,Ge)

Novel silicon- and germanium-containing tungsten complexes Ph₃ECH=W(OBu-t)₂(OPh)₂ were synthesized by the reaction of carbyne derivatives Ph₃EC≡W(OBu-t)₃ (E = Si, Ge) with phenol and isolated in high yields. Their structure was determined by X-ray diffraction. Individual complexes do not exhibit catalytic activity, whereas in the presence of AlBr₃ they initiate metathesis polymerization of cyclooctene.     

Palladium- and platinum-catalyzed coupling reactions of allyloxy aromatics with hydridosilanes and hydridosiloxanes: Novel liquid crystalline/organosilane materials

Pt-and Pd-catalyzed reactions of a set of allyloxyaromatic mono-and diesters with selected silanes were examined to develop simple, mild methods of forming liquid crystal (LC)/ siloxane and LC/silsesquioxane polymers. Pt complexes catalyze hydrosilylation to give primarily (≤ 80% selectivity at 100% conversion) terminal silylation of the allyloxys. The catalyst, platinum-1,3-divinyltetramethyldisiloxane [Pt (dvs), gives the cleanest reactions, fewest side products, under the mildest conditions. Model studies of Pt(dvs) catalyzed hydrosilylation of 4-allyloxy methylbenzoate gave relative reactivities (HSiO_1.5)₈ ? Et₃SiH > HMe₂Si? O? SiMe₂H > Ph₂SiH2. The cubic silsesquioxane, (HSiO_1.5)₈, is so reactive hydrosilylation is over in 1–3 h at 0°C. All other reactions required > 40°C and longer reaction times. Initial efforts to form high polymers by Pt-catalyzed reactions of bis-allyloxy aromatics with Ph₂SiH₂ provide polymers with bimodal MW distributions (polystyrene), M_ws ≈ 30 kDa, and PDIs ≈ 5. Pd catalysis gives quite different products resulting from loss of propene with coincident formation of Si? O bonds, “oxysilylation.” The same products appear (10–15%) in some Pt catalyzed reactions. Palladium dibenzylideneacetone/ Ph₃P[Pd(dba)₂/Ph₃P], gives the cleanest oxysilylation reactions. Relative oxysilylation activities are: Ph₂SiH₂ > HMe₂SiOSiMe₂H > Et₃SiH. Polymerization with Pd catalysts provides polymers with M_ws ≈ 11 kDa, and PDIs ≈ 2. Reaction of 1 equiv. of (HSiO_1.5)₈ with 4 equiv. of 4-(4-allyloxy-benzoyloxy) biphenyl gives relatively pure tetrasubstituted LC/silsesquioxane [M_n ≈ 1860 Da, PDI ≈ 1.09 (styrene equiv.) vs. 1746 Da caled.] A detailed analysis of the products formed, the catalytic reactivity patterns of the his (allyloxy) aromatic diesters and their LC transitions is presented. © 1994 John Wiley & Sons, Inc.     

Ethylene polymerization by the chromium catalysts based on bidentate [O,PO] or [S,P] ligands

Novel chromium catalysts based on bidentate phenoxy‐phosphinoyl (HO‐2R₁‐4R₂‐6(Ph₂P?O)C₆H₂: R₁ = R₂ = H, 3a ; R₁ = tBu, R₂ = H, 3b ; R₁ = R₂ = tBu, 3c ; R₁ = R₂ = cumyl, 3d ; R₁ = anthracenyl, R₂ = H, 3e ) and thiophenol‐phosphine (HS‐2R₁‐4R₂‐6(Ph₂P)C₆H₂: R₁ = R₂ = H, 4a ; R₁ = SiMe₃, R₂ = H, 4b ) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high‐catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy‐phosphine ligands. Both the coordinated donors and the ortho‐substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b /CrCl₃(thf)₃ and 4b /CrCl₃(thf)₃. Catalyst 4b /CrCl₃(thf)₃ displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b /CrCl₃(thf)₃. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 311–319, 2010     

Nature of the modifying action of white phosphorus on the properties of nanosized hydrogenation catalysts based on bis(dibenzylideneacetone)palladium(0)

The catalytic properties and nature of the nanoparticles forming in the system based on Pd(dba)₂ and white phosphorus are reported. A schematic mechanism is suggested for the formation of nanosized palladium-based hydrogenation catalysts. The mechanism includes the formation of palladium nanoclusters via the interaction of Pd(dba)₂ with the solvent (N,N-dimethylformamide) and substrate and the formation of palladium phosphide nanoparticles. The inhibiting effect exerted by elemental phosphorus on the catalytic process is due to the conversion of part of the Pd(0) into palladium phosphides, which are inactive in hydrogenation under mild conditions, and the formation of mainly segregated palladium nanoclusters and palladium phosphide nanoparticles. By investigating the interaction between Pd(dba)₂ and white phosphorus in benzene, it has been established that the formation of palladium phosphides under mild conditions consists of the following consecutive steps: Pd(0) → PdP₂ → Pd₅P₂ → Pd₃P. It is explained why white phosphorus can produce diametrically opposite effects of on the catalytic properties of nanosized palladium-based hydrogenation catalysts, depending on the nature of the palladium precursor.     

High-Yield Synthesis of the Novel E,E-2,5-Dimethoxy-1,4-bis[2-(4-ethylcarboxylatestyril)]benzene by the Heck Reaction

The novel E,E-2,5-dimethoxy-1,4-bis[2-(4-ethylcarboxylatestyril)]benzene, 4, was obtained in good yield (92%), by the Heck cross-coupling reaction using Pd(dba)₂ and P(OPh)₃ like catalytic system. The high trans specificity of the product produced by the Heck reaction was confirmed by Fourier Transform–infrared and NMR. The methodology reported can be used as synthetic route for precursors to phenylenevinylene target systems with highly desired functional groups in their molecular structure, such as carboxylic, to build metal–organic frameworks and other applications within the supramolecular chemistry.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

N2-to-NH3 Conversion by a triphos–Iron Catalyst and Enhanced Turnover under Photolysis

Bridging iron hydrides are proposed to form at the active site of MoFe-nitrogenase during catalytic dinitrogen reduction to ammonia and may be key in the binding and activation of N₂ via reductive elimination of H₂. This possibility inspires the investigation of well-defined molecular iron hydrides as precursors for catalytic N₂-to-NH₃ conversion. Herein, we describe the synthesis and characterization of new P₂^P′PhFe(N₂)(H)_x systems that are active for catalytic N₂-to-NH₃ conversion. Most interestingly, we show that the yields of ammonia can be significantly increased if the catalysis is performed in the presence of mercury lamp irradiation. Evidence is provided to suggest that photo-elimination of H₂ is one means by which the enhanced activity may arise.     

Synthesis and crystal structure of triphenyl[tris(tetrahydrofuran)]ytterbium, Ph3Yb(THF)3

Triphenyl[tris(tetrahydrofuran)]ytterbium, Ph₃Yb(THF)₃ (1), was synthesized in high yields by the reaction of Yb with an excess of Ph₂Hg or Ph₃Bi in the presence of catalytic amounts of YbI₂(THF)₄ as well as by the reaction of Ph₂Yb(THF)₂ (2) with Ph₂Hg or Ph₃Bi. The crystal structure of complex1 was studied by X-ray structural analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 163–166, January, 1998.     

Hyperbranched bisphosphinoamine ligands: synthesis,characterization and application in ethylene oligomerization

Two hyperbranched bisphosphinoamine (PNP) ligands and chromium complexes were synthesized in good yield with 1.0 generation (1.0 G) hyperbranched macromolecules, chlorodiphenylphosphine (Ph₂PCl) and CrCl₃(THF)₃ as raw materials. The hyperbranched PNP ligands and chromium complexes were characterized by FT-IR, ¹H NMR, ³¹P NMR, UV and ESI-MS. Comparing with the chromium complexes, the hyperbranched PNP ligands, in combination with Cr(III), and activation by methylaluminoxane (MAO) in situ generated species with better catalytic performance for ethylene oligomerization. The effect of solvent, chromium source, ligand/Cr molar ratio, reaction temperature, Al/Cr molar ratio and reaction pressure on the catalytic activity and product selectivity were studied. The results showed that with increase of ligand/Cr molar ratio, reaction temperature and Al/Cr molar ratio, the catalytic activity increased at first and then decreased. However, the catalytic activity continuously increased with increase of reaction pressure. Under the optimized conditions, the catalytic system of hyperbranched PNP/Cr(III)/MAO led to catalytic activity of 2.68 × 10⁵ g/(mol Cr·h) and 37.71% selectivity for C₆ and C₈.     

Phenylethenyl-substituted silicones via Heck coupling reaction

Systematic studies of several palladium complexes (Pd(OAc)₂, [PdCl₂(cod)], [Pd₂(dba)₃], [Pd(PPh3)4], [PdCl(SnCl₃)(P{p-Tol}₃)₂], [Pd₂Cl₂(SnCl₃)₂(P{p-Tol}₃)₂]) as potential catalytic systems for arylation of vinylsiloxanes via Heck coupling reactions are described. Catalytic activity and selectivity were studied for a model reaction of trimethylvinylsilane with PhBr and m-ClC₆H₆Br and then the most effective systems were applied for functionalisation of tetramethyltetravinylcyclotetrasiloxane and poly(dimethylsiloxane-co-methylvinylsiloxane), leading to the silicone fluids having high refractive index (1.5–1.6).     

N2‐to‐NH3 Conversion by a triphos–Iron Catalyst and Enhanced Turnover under Photolysis

Bridging iron hydrides are proposed to form at the active site of MoFe‐nitrogenase during catalytic dinitrogen reduction to ammonia and may be key in the binding and activation of N₂ via reductive elimination of H₂. This possibility inspires the investigation of well‐defined molecular iron hydrides as precursors for catalytic N₂‐to‐NH₃ conversion. Herein, we describe the synthesis and characterization of new P₂^P′PhFe(N₂)(H)_x systems that are active for catalytic N₂‐to‐NH₃ conversion. Most interestingly, we show that the yields of ammonia can be significantly increased if the catalysis is performed in the presence of mercury lamp irradiation. Evidence is provided to suggest that photo‐elimination of H₂ is one means by which the enhanced activity may arise.     

The Preparation and X-Ray Structure of [AsPh4][Ph2P(S)NSiMe3] · 0.5 THF

The reaction of Ph₂P(S)N(SiMe₃)₂ with potassium tert-butoxide in a 1:1 molar ratio produces K[Ph₂P(S)NSiMe₃], which was converted to the AsPh₄⁺ salt by metathesis with [AsPh₄]Cl. The X-ray crystal structure of [AsPh₄][Ph₂P(S)NSiMe₃] · 0.5 THF consists of noninteracting AsPh₄⁺ and Ph₂P(S)NSiMe₃^? ions with d(P? S) = 1.980(4) Å and d(P? N) = 1.555(8) Å. The PNSi bite angle in the anion is 136.3(5)°. Electrophilic attack by Ph₂P(S)Cl occurs at the sulfur atom of Ph₂P(S)NSiMe₃^?. The oxidation of the anion with iodine produces a disulfide which regenerates K[Ph₂P(S)NSiMe₂] upon treatment with potassium tert-butoxide.     

Darstellung und Eigenschaften von Tris(diphenylamino)-phosphin

Preparation and Properties of Tris (diphenylamino) Phosphine The synthesis and some properties of tris(diphenylamino)phosphine are described. Displacement of the chlorine atom is readily achieved by reaction of (Ph₂N)₂PCl with Ph₂NSime₃. Thus tris(diarylamino)phosphine (Ph₂N)₃P is obtained almost in quantitativ yield. The aminolysis reaction of PCl₃ or (Ph₂N)₂PCl with Ph₂NH gives also (Ph₂N)₃P. The properties and structure of the phosphine on basis of spectroscopical and X-ray investigations are discussed.     

N-Isocyaniminotriphenylphosphorane (Ph3PNNC) as a metal-free catalyst for the synthesis of functionalized isoindoline-1-ones

A novel application in the field of N-isocyaniminotriphenylphosphorane (Ph₃PNNC) chemistry has been introduced in this work. A series of substituted isoindolin-1-one ring systems has been successfully synthesized through a novel and efficient multicomponent reaction of methyl 2-formylbenzoate and primary amines in the presence of N-isocyaniminotriphenylphosphorane (Ph₃PNNC) as a catalyst. This one-pot three component reaction (3-CR) gives high yield using N-isocyaniminotriphenylphosphorane (Ph₃PNNC) as a metal-free catalyst under mild conditions.