Dimerization of Propylene by Nickel （II） and Cobalt （II） Catalysts Based on Bidentate Nitrogen-phosphino Chelating Ligands

The catalytic property of propylene dimerization by several nickel (II), cobalt (II) complexes containing N-P bidentate ligands was studied in combination with organoaluminum co-catalysts. The effects of the type of aluminum co-catalysts and its relative amount, the nature of precursors in terms of ligand backbone and metal center were investigated. The results indicated that precursor I (N,-N-dimethyl-2-(diphenylphosphino)aniline nickel (II) dichloride)exhibited high activity in propylene dimerization in the presence of the strong Lewis acid Et3A12Cl3, whereas low productivity by its cobalt analogues was observed under identical reaction conditions.     

Dimerization of Propylene by Nickel (Ⅱ) and Cobalt (Ⅱ) Catalysts Based on Bidentate Nitrogen-phosphino Chelating Ligands

The catalytic property of propylene dimerization by several nickel (Ⅱ), cobalt (Ⅱ) complexes containing N-P bidentate ligands was studied in combination with organoaluminum co-catalysts. The effects of the type of aluminum co-catalysts and its relative amount, the nature of precursors in terms of ligand backbone and metal center were investigated. The results indicated that precursor I (N,N-dimethyl-2-(diphenylphosphino)aniline nickel (Ⅱ) dichloride) exhibited high activity in propylene dimerization in the presence of the strong Lewis acid Et3Al2Cl3, whereas low productivity by its cobalt analogues was observed under identical reaction conditions.     

Optically active helical polyisocyanides bearing chiral phosphine pendants: Facile synthesis and application in enantioselective Rauhut-Currier reaction

Three novel enantiopure phenyl isocyanide monomers with BH3-protected phosphine functional group were designed and synthesized.Polymerization of these monomers using a alkyne-Pd(Ⅱ) complex as a catalyst led to the formation of respective helical polyisocyanides in high yields with controlled molecular weights (Mns) and narrow molecular weight distributions (Mw/Mns).Removing the protecting BH3 groups afforded helical poly(phenyl isocyanide)s bearing phosphine pendants.Thanks to the chiral induction of monomer,the isolated helical polyisocyanides showed high optical activity,as revealed by circular dichroism (CD) and absorption spectroscopies and polarimetry.The helical structures of these polymers were quite stable in various organic solvents with different polarities and in a wide temperature range.Moreover,these helical polymers could be used as organocatalysts and showed good performance in enantioselective cross Rauhut-Currier reaction.The enantiomeric excess (ee) values of the isolated products of cross Rauhut-Currier reaction could be up to 90％.The polymer organocatalysts could be easily recovered from the reaction mixtures and reused at least five times in the reaction without significant loss of their enantioselectivities and catalytic activities.     

Eco-friendly co-catalyst-free cycloaddition of CO_2 and aziridines activated by a porous MOF catalyst

Cycloaddition of CO_2 with aziridines is an important reaction to obtain high-value products.Porous MOFs can catalyze this reaction,but co-catalysts are still necessary to improve the catalytic performance.Such a reaction catalyzed by MOFs-based materials without co-catalyst has not been reported hitherto.Herein,a porous and stable three-dimensional(3 D) framework{[Ni(DCTP)]·6.5 DMF}_n(1) with a large Langmuir surface area of 3,789 m~2/g was synthesized,which displayed high I_2 adsorption ability up to 731.0 mg/g and could release it reversibly.Additionally,it exhibited a high CO_2 adsorption capacity of104.0 cm~3/g at 273 K.The investigation results revealed 1 could effectively catalyze the cycloaddition of CO_2 and aziridines in the absence of additional co-catalyst,and it could maintain the catalytic activity after five cycles.Furthermore,1 also exhibited high catalytic activity for the gram-scale experiment.Importantly,it is the first MOF material as a heterogeneous catalyst for the conversion of CO_2 and aziridines without co-catalyst.     

BiMo基复合氧化物催化剂丙烷直接氧化至丙烯醛研究

The effects of the available zoon above the catalyst bed on the performance of the catalyst were investigated. It has been suggested that propylene is an intermediate species in the reaction of propane to acrolein， and a two-step reaction scheme is proposed， the first step is oxidative dehydrogenation of propane to propylene in the gas phase then followed by the second step， the selective oxidation of propylene to acrolein on the surface of the catalyst. The performance of the catalyst depends on both the oxidative dehydrogenation of propane to propylene in the gas phase and the selective oxidation of propylene to acrolein on the catalyst surface. The thermal cracking， homogeneous oxidative dehydrogenation and heterogeneous catalytic dehydrogenation of propane as well as the selective catalytic oxidation of propane to acrolein over BiMoO based mixed oxides catalysts were studied. Under the optimum reaction conditions of propane dehydrogenation and selective oxidation of propylene， the selectivity and the yield of acrolein approached to 45mol% and 14mol%， respectively under about 30mol% propane conversion.     

Improved catalytic performance of Ni catalysts for steam methane reforming in a micro-channel reactor

Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon （SIC） was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.     

A Novel Tripyridyldiamine Nickel Complex:Synthesis,Structure and Characterization

A novel nickel(II)complex[Ni(H2 tpda)(NCS)2(CH3 OH)]was synthesized by using tripyridyldiamine as ligand and Ni(NCS)2 as starting materials,and characterized by a variety of techniques including single-crystal X-ray diffraction,IR spectroscopy and TG-DSC.The single-crystal structure reveals that the complex exhibits as a neutral molecule and that the central atom Ni(II)is octahedrally coordinated by an H2 tpda,two NCS-ions and a ligand molecule CH3 OH.The 3 D supramolecular network is formed through hydrogen bonds andπ-πinteractions.The complex can catalyze the addition reaction of carbon dioxide and propylene oxide.     

Microwave assisted,ligand free,copper catalyzed reaction of aryl halides with phenyl urea

The ligand free coupling reaction of phenyl urea with different functionalized aryl halides in the presence of air stable Cu₂O and t-BuOK as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.This method is milder than the palladium catalyzed arylation and avoids the use of toxic phosphine ligand.     

Hydrogenation of Toluidines Catalyzed by Silica-supported Carboxymethylcellulose-platinum Complex

The hydrogenation of toluidines catalyzed by silica-supported carboxymethyl cellulose platinum complex forms methylcyclohexlamines in high yields, such as m-toluidine to 3-methylcyclohexylamine, o-toluidine to 2-methylcyclohexylamine, and p-toluidine to 4-methylcyclohexylamine in 97%, 96. 7% and 98. 2% yields,respectively, at 30℃ and under atmospheric hydrogen pressure. The yields were remarkably affected by the Pt content in the complex, the kind of solvent and the reaction temperature. The catalyst was very stable and could be reused several times without remarkable change in the catalytic activity.     

Steric hindrance ligand strategy to aluminum porphyrin catalyst for completely alternative copolymerization of CO2 and propylene oxide

Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide (PO),but they suffer from relatively poor poly(propylene carbonate) (PPC) selectivity.Herein,steric hindrance porphyrin ligand was used to enhance the PPC selectivity.Typically,a bulky anthracene-like group was incorporated into the porphyrin ring to form 5,10,15,20-tetra(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl)porphyrin,the aluminum porphyrin complex with this ligand,in combination with bis(triphenylphosphine)iminium chloride as a co-catalyst,produced completely alternate PPC.Additionally,the obtained PPC showed high regioselectivity,with a head-to-tail linkage content (HT) of 92％.Therefore,we demonstrated that introduction of bulky steric ligand into the porphyrin ring could reduce the propylene oxide homopolymerization activity leading to excellent PPC selectivity,and improve regioselectivity for the PO ring-opening during the copolymerization.     

Novel polymer‐supported β‐dithioketonate nickel catalysts for selective propylene dimerization

Brominated and chloromethylated styrene–divinylbenzene resins were used for the synthesis of polymer‐bound dithio‐β‐diketones, obtained by anchoring the chelate ligand through the central position. The heterogenized dithio‐β‐diketone ligand was subsequently reacted either as sodium salt with a Ni(II) phosphino derivative or directly with a Ni(0) complex in the presence of a free phosphine and activated in situ with an aluminum co‐catalyst for the selective dimerization of propylene to 2,3‐dimethylbutenes. The hetetogenized catalysts so obtained showed, particulary when prepared starting from chloromethylated styrene/divinylbenzene resins, very high activity and selectivity towards 2,3‐dimethylbutenes. Moreover, the above catalysts, at least under the adopted reaction conditions, did not display any appreciable metal leaching during the catalytic cycle, thus working as really heterogeneous systems. Copyright © 1999 John Wiley & Sons, Ltd.     

A Copper(I)–Arene Complex With an Unsupported η6 Interaction

Addition of PR₃ (R=Ph or OPh) to [Cu(η²‐Me₆C₆)₂][PF₆] results in the formation of [(η⁶‐Me₆C₆)Cu(PR₃)][PF₆], the first copper–arene complexes to feature an unsupported η⁶ arene interaction. A DFT analysis reveals that the preference for the η⁶ binding mode is enforced by the steric clash between the methyl groups of the arene ligand and the phenyl rings of the phosphine co‐ligand.     

Dinuclear Rare‐Earth Metal Alkyl Complexes Supported by Indolyl Ligands in μ‐η2:η1:η1 Hapticities and their High Catalytic Activity for Isoprene 1,4‐cis‐Polymerization

Two series of new dinuclear rare‐earth metal alkyl complexes supported by indolyl ligands in novel μ‐η²:η¹:η¹ hapticities are synthesized and characterized. Treatment of [RE(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of 3‐(tBuN?CH)C₈H₅NH ( L₁ ) in THF gives the dinuclear rare‐earth metal alkyl complexes trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH(CH₂SiMe₃)}Ind)RE(thf)(CH₂SiMe₃)]₂ (Ind=indolyl, RE=Y, Dy, or Yb) in good yields. In the process, the indole unit of L₁ is deprotonated by the metal alkyl species and the imino C?N group is transferred to the amido group by alkyl CH₂SiMe₃ insertion, affording a new dianionic ligand that bridges two metal alkyl units in μ‐η²:η¹:η¹ bonding modes, forming the dinuclear rare‐earth metal alkyl complexes. When L₁ is reduced to 3‐(tBuNHCH₂)C₈H₅NH ( L₂ ), the reaction of [Yb(CH₂SiMe₃)₃(thf)₂] with 1 equivalent of L₂ in THF, interestingly, generated the trans‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (major) and cis‐[(μ‐η²:η¹:η¹‐3‐{tBuNCH₂}Ind)Yb(thf)(CH₂SiMe₃)]₂ (minor) complexes. The catalytic activities of these dinuclear rare‐earth metal alkyl complexes for isoprene polymerization were investigated; the yttrium and dysprosium complexes exhibited high catalytic activities and high regio‐ and stereoselectivities for isoprene 1,4‐cis‐polymerization.     

A Mononuclear η2‐Bonded Phosphaalkyne Nickel(0) Complex

The synthesis and characterization of the new complex [Ni(Im^iPr)₂(η²‐P≡C‐tBu)] ( 1 ) is reported. Compound 1 represents the first structurally characterized example of a mononuclear nickel(0) complex with a side on coordinated phophaalkyne ligand.     

Nickel(I) Monomers and Dimers with Cyclopentadienyl and Indenyl Ligands

The reaction of (μ‐Cl)₂Ni₂(NHC)₂ (NHC=1,3‐bis(2,6‐diisopropylphenyl)‐1,3‐dihydro‐2H‐imidazol‐2‐ylidene (IPr) or 1,3‐bis(2,6‐diisopropylphenyl)imidazolidin‐2‐ylidene (SIPr)) with either one equivalent of sodium cyclopentadienyl (NaCp) or lithium indenyl (LiInd) results in the formation of diamagnetic NHC supported Ni^I dimers of the form (μ‐Cp)(μ‐Cl)Ni₂(NHC)₂ (NHC=IPr ( 1 a ) or SIPr ( 1 b ); Cp=C₅H₅) or (μ‐Ind)(μ‐Cl)Ni₂(NHC)₂ (NHC=IPr ( 2 a ) or SIPr ( 2 b ); Ind=C₇H₉), which contain bridging Cp and indenyl ligands. The corresponding reaction between two equivalents of NaCp or LiInd and (μ‐Cl)₂Ni₂(NHC)₂ (NHC=IPr or SIPr) generates unusual 17 valence electron Ni^I monomers of the form (η⁵‐Cp)Ni(NHC) (NHC=IPr ( 3 a ) or SIPr ( 3 b )) or (η⁵‐Ind)Ni(NHC) (NHC=IPr ( 4 a ) or SIPr ( 4 b )), which have nonlinear geometries. A combination of DFT calculations and NBO analysis suggests that the Ni^I monomers are more strongly stabilized by the Cp ligand than by the indenyl ligand, which is consistent with experimental results. These calculations also show that the monomers have a lone unpaired‐single‐electron in their valence shell, which is the reason for the nonlinear structures. At room temperature the Cp bridged dimer (μ‐Cp)(μ‐Cl)Ni₂(NHC)₂ undergoes homolytic cleavage of the Ni?Ni bond and is in equilibrium with (η⁵‐Cp)Ni(NHC) and (μ‐Cl)₂Ni₂(NHC)₂. There is no evidence that this equilibrium occurs for (μ‐Ind)(μ‐Cl)Ni₂(NHC)₂. DFT calculations suggest that a thermally accessible triplet state facilitates the homolytic dissociation of the Cp bridged dimers, whereas for bridging indenyl species this excited triplet state is significantly higher in energy. In stoichiometric reactions, the Ni^I monomers (η⁵‐Cp)Ni(NHC) or (η⁵‐Ind)Ni(NHC) undergo both oxidative and reductive processes with mild reagents. Furthermore, they are rare examples of active Ni^I precatalysts for the Suzuki–Miyaura reaction. Complexes 1 a , 2 b , 3 a , 4 a and 4 b have been characterized by X‐ray crystallography.     

Indolyl Phosphine Nickel(II) Fluorido Complexes: Synthesis and Intermediates in Suzuki–Miyaura Cross-Coupling Reactions

The C−F bond activation of pentafluoropyridine and 2,3,5,6-tetrafluoropyridine at [Ni(cod)₂] (cod=1,5-cyclooctadiene) in the presence of the phosphine PPh₂(Ind) (Ind=3-methyl-2-indolyl) led to the formation of the nickel(II) fluorido bis(phosphine) complexes trans-[Ni(F)(2-C₅NF₄){PPh₂(Ind)}₂] and trans-[Ni(F)(2-C₅HNF₃){PPh₂(Ind)}₂]. The complexes are characterized by the presence of intramolecular hydrogen bonds between the NH group of the phosphine ligands and the fluorido ligand. Stochiometric model reactions of nickel(II) fluorido complexes with PhB(OH)₂ revealed that the former can be considered as intermediates in Suzuki–Miyaura cross coupling reactions. Catalytic experiments were attempted using 10 mol-% of trans-[Ni(F)(2-C₅NF₄){PPh₂(Ind)}₂] as catalyst and the activities of the PPh₂(Ind) complex were compared to the ones of an analogous nickel(II) fluorido complex, bearing PPh₃ instead of PPh₂(Ind) as ligands. The latter exhibited a somewhat lower catalytic activity suggesting a slight influence of the H-bonds in the outer coordination sphere.     

η3-Allylnickel alkoxides and their use as homogeneous and heterogeneous catalysts for the dimerization of olefins

η³-Allylnickel alkoxides {η³-C₃H₅NiOR}₂ (R = Me, Et, i-Pr, Ph, SiPh₃) may be activated by gaseous boron trifluoride (BF₃) to give active catalysts for the dimerization of propene in homogeneous phase. In CH₂Cl₂ at ?20 °C catalytic turnover numbers of 5000 mol propene(mol Ni)^?1h^?1 were measured. The nature of the OR group influences both the catalytic activity and the oligomerization product distribution. The ratio of methylpentenes to dimethylbutenes in the dimer fraction may be controlled by the presence of additional phosphine ligands at the nickel atom. The nickel alkoxide precursor was heterogenized on alumina to give {Al₂O₃}–O–Ni–(η³-C₃H₅). Subsequent activation using gaseous BF₃ generates a powerful heterogeneous olefin dimerization catalyst which converts 50 × 10³ mol propene (mol Ni)^?1 at ?10° to ?5°C in a batchwise process and 143 × 10³ mol propene (mol Ni)^?1 continuously to give 75% dimers and 25% higher oligomers. The solvent-free treatment of oxide supports, e.g. alumina or silica, with gaseous BF₃ produces strong ‘solid acids’. The activated hydroxyl groups on the support surface serve as effective anchor sites for organometallic complexes to form heterogenous catalysts. By reaction of Ni(cod)₂ with {Al₂O₃}O(BF₃)H or {SiO₂}O(BF₃)H, η¹, η²-cyclo-octenylnickel–O fragments may be fixed to the surface. In the absence of halogenated solvents, the resulting catalysts, e.g. {SiO₂}O–(BF₃)–Ni–(η¹, η²-C₈H₁₃), dimerize propene continuously at +5°C at the rate of 800 × 10³ mol liquid propene (mol Ni)^?1.     

Synthesis,Reactivity and Crystal Structures of the Palladium(II) Complexes with the Pyrimidine Containing Ligand: Crystal Structures of [Pd(PPh3)(η1‐C4H3N2)(η2‐S2CNC4H8)] and [Pd(PPh3)(η1‐C4H3N2)(η2‐Tp)]

Treatment of Pd(PPh₃)₄ with 5‐bromo‐pyrimidine [C₄H₃N₂Br] in dichloromethane at ambient temperature cause the oxidative addition reaction to produce the palladium complex [Pd(PPh₃)₂(η¹‐C₄H₃N₂)(Br)], 1 , by substituting two triphenylphosphine ligands. In acetonitrile solution of 1 in refluxing temperature for 1 day, it do not undergo displacement of the triphenylphosphine ligand to form the dipalladium complex [Pd(PPh₃)Br]₂{μ,η²‐(η¹‐C₄H₃N₂)}₂, or bromide ligand to form chelating pyrimidine complex [Pd(PPh₃)₂(η²‐C₄H₃N₂)]Br. Complex 1 reacted with bidentate ligand, NH₄S₂CNC₄H₈, and tridentate ligand, KTp {Tp = tris(pyrazoyl‐1‐yl)borate}, to obtain the η²‐dithiocarbamate η¹‐pyrimidine complex [Pd(PPh₃)(η¹‐C₄H₃N₂)(η²‐S₂CNC₄H₈)], 4 and η²‐Tp η¹‐pyrimidine complex [Pd(PPh₃)(η¹‐C₄H₃N₂)(η²‐Tp)], 5 , respectively. Complexes 4 and 5 are characterized by X‐ray diffraction analyses.     

μ3‐η2:η2:η2‐Coordination of Primary Silane on a Triruthenium Plane

A μ₃‐η²:η²:η²‐silane complex, [(Cp*Ru)₃(μ₃‐η²:η²:η²‐H₃SitBu)(μ‐H)₃] ( 2 a ; Cp*=η⁵‐C₅Me₅), was synthesized from the reaction of [{Cp*Ru(μ‐H)}₃(μ₃‐H)₂] ( 1 ) with tBuSiH₃. Complex 2 a is the first example of a silane ligand adopting a μ₃‐η²:η²:η² coordination mode. This unprecedented coordination mode was established by NMR and IR spectroscopy as well as X‐ray diffraction analysis and supported by a density functional study. Variable‐temperature NMR analysis implied that 2 a equilibrates with a tautomeric μ₃‐silyl complex ( 3 a ). Although 3 a was not isolated, the corresponding μ₃‐silyl complex, [(Cp*Ru)₃(μ₃‐η²:η²‐H₂SiPh)(H)(μ‐H)₃] ( 3 b ), was obtained from the reaction of 1 with PhSiH₃. Treatment of 2 a with PhSiH₃ resulted in a silane exchange reaction, leading to the formation of 3 b accompanied by the elimination of tBuSiH₃. This result indicates that the μ₃‐silane complex can be regarded as an “arrested” intermediate for the oxidative addition/reductive elimination of a primary silane to a trinuclear site.     

Chloro(1‐{3‐[2‐(di­phenyl­phos­phanyl‐κP)­ethyl]‐η6‐benzyl}‐3,5‐di­methyl‐1H‐pyrazole‐κN2)­ruthenium(II) tri­fluoro­methane­sulfonate

To address the question of the role of chirality at the metal in enantioselective catalysis, a pseudo‐tetrahedral three‐legged piano‐stool complex has been prepared, i.e. [RuCl(C₂₆H₂₇N₂P)](CF₃SO₃). Anchoring a phosphine and a pyrazole tether to an arene (PArN) yields, after η⁶:η¹:η¹ coordination to ruthenium, [{η⁶:η¹:η¹‐(PArN)}RuCl]⁺ as a 1:1 mixture of enantiomers. Unfortunately, all attempts to resolve the enantiomers failed. The structure solution revealed the presence of racemic crystals.