Formation of Octameric Methylaluminoxanes by Hydrolysis of Trimethylaluminum and the Mechanisms of Catalyst Activation in Single‐Site α‐Olefin Polymerization Catalysis

Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO)_n(AlMe₃)_m. The thermodynamically favored pathway of MAO formation is followed up to n=8, showing the major impact of associated TMA on the structural characteristics of the MAOs. The MAOs bind up to five TMA molecules, thereby inducing transition from cages into rings and sheets. Zirconocene catalyst activation studies using model MAO co‐catalysts show the decisive role of the associated TMA in forming the catalytically active sites. Catalyst activation can take place either by Lewis‐acidic abstraction of an alkyl or halide ligand from the precatalyst or by reaction of the precatalyst with an MAO‐derived AlMe₂⁺ cation. Thermodynamics suggest that activation through AlMe₂⁺ transfer is the dominant mechanism because sites that are able to release AlMe₂⁺ are more abundant than Lewis‐acidic sites. The model catalyst system is demonstrated to polymerize ethene.     

High‐Throughput Screening in Olefin‐Polymerization Catalysis: From Serendipitous Discovery Towards Rational Understanding

High–throughput‐screening (HTS) tools and methods are used more and more, especially in industry, in the search for new, selective organometallic catalysts. In most cases, the approach is, in essence, empirical, and the strategy is to increase the number of experiments that can be run at a given place in a given time. Highly miniaturized, parallel reaction setups have been implemented for the rapid assessment of whether novel catalysts resulting from the structural amplification of a basic framework are “good” or “bad” with respect to the properties of interest, and, depending on the response, worthy of a subsequent, more‐careful evaluation. In this article, we demonstrate that it is possible to utilize these state‐of‐the‐art HTS platforms with a different strategy: the rapid generation of reliable kinetic data for mechanistic studies in view of a thorough understanding and rational catalyst design. Ziegler–Natta‐type catalytic olefin polymerization will be used throughout as an example.

     

新型取代硅桥联茂稀土化合物的合成及在纳米级氢化钠助催化剂作用下高活性催化甲基丙烯酸甲酯聚合的研究

The synthesis and characterization of four new silicon-linked lanthanocene complexes with pendant phenyl groups on cyclopentadiene were reported. Based on the data of elemental analyses, MS and IR, the complexes were presumed to be unsolvated and dimeric complexes [Me2Si(C5H3CMe2C6H5)2LnC1]2 [Ln=Er (1), Gd (2), Sm (3), Dy (4)]. In conjunction with AlEt3 or sodium hydride as the co-catalyst, these complexes could efficiently catalyze the polymerization of methyl methacrylate (MMA). When the nanometric sodium hydride was used as a co-catalyst, the complexes were highly effective for the polymerization of MMA. At low temperature and in short time, in [MeESi(C5H3CMe2C6H5)2LnC1]2/NaH (nanometric) system, the polymer was obtained in more than 80% yield and the molecular weight was greater than 105. The activity reached that of organolanthanide hydride as a single-component catalyst. In ]MeESi(C5H3CMe2C6H5)2ErC1]2/Nail (nanometric) system, the effects of the molar ratio of MMA/catalyst and catalyst/co-catalyst, and the temperature on polymerization were studied.     

Heterobi‐ and ‐trimetallic Ion Pairs of Zirconocene‐Based Isoselective Olefin Polymerization Catalysts with AlMe3

The reactivity towards AlMe₃ of discrete cationic ansa‐zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6‐tBu₂‐Flu)(3‐tBu‐5‐Et‐Cp)}ZrMe₂)] {Cp‐Flu} and rac‐[{Me₂Si‐(2‐Me‐4‐Ph‐Ind)₂}ZrMe₂] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe₃ adduct ( 3 b ) is reported. In the presence of excess AlMe₃, the {SBI}‐based AlMe₃ adduct 3 b undergoes a slow decomposition via C? H activation in a bridging methyl unit to yield a new species ( 4 b ) with a trimetallic {Zr(μ‐CH₂)(μ‐Me)AlMe(μ‐Me)AlMe₂} core. EXSY NMR data for the process 2 b ? 3 b → 4 b suggest very rapid and reversible binding of an additional AlMe₃ molecule onto AlMe₃ adduct 3 b . The resulting heterotrimetallic species intermediates exchange of methyl groups between different metal centers and slowly undergoes the C? H activation reaction towards 4 b .     

Synthesis and Structure of 1—Cyclopentylindenyl Lanthanide（Ⅱ）Complexes and Their Catalytic Behavior for Polymerization of Acrylonitrile

The reaction between K(1‐C₅H₉C₉H₆) and anhydrous LnCl₃ (Ln=Sm, Yb) in the molar ratio of 2:1 in THF with subsequent treatment by Na‐K alloy afforded (1‐C₅H₉C₉H₆)₂Ln‐(THF)_n(Ln=Sm, n=1; Ln=Yb, n=2), while the reaction of Sml₂ with K(1‐C₅H₉C₉H₆) in the molar ratio of 1:2 in THF gave the anionic complex K(1‐C₅H₉C₉H₆)₃Sm(THF)₃. The X‐ray structure of (1‐C₅H₉C₉H₆)₂Yb(THF)₂ showed that central metal Yb is coordinated by two cyclopentadienyl rings of 1‐cyclopentylindenyls and two oxygen atoms from two tetrahydrofuran molecules to form pseudo‐tetrahedral coordinate geometry. All these complexes are active for the polymerization of acrylonitrile.     

钙对铝水解聚合反应及聚合铝物化特性的影响

The polyaluminum chloride containing Ca was prepared by adding Ca before and after the aluminium polymerization, respectively. The effects of Ca on the hydrolysis and polymerization of aluminum, the characteristic of aluminum species, the ζ potential and viscosity of PAC were also studied. The experimental results show that the introduction of Ca retards the formation of Al precipitates during the hydrolysis and polymerization of aluminum and increases the contents of Al_m and Al₁₃ in PAC. Aluminum species can complex with Ca to form heteronuclear hydroxo complexes, which decreases the chemical shifts of Al_m and Al₁₃ in NMR. The ζ potential and the viscosity of PAC increase with the rise of Ca/Al molar ratio. Comparing with adding Ca after the aluminium polymerization, there are much more Al-Ca heteronuclear hydroxo complexes formed by adding Ca before the polymerization, which leads to a more obvious influence of Ca/Al molar ratio on the ζ potential and the viscosity of PAC.     

Elaboration of rac‐Like Active Species from Lewis Base Functionalized Unbridged Zirconocenes for Isospecific Propylene Polymerization

A series of ortho or meta Lewis base functionalized unbridged zirconocenes, [{1‐(E_n‐Ph)‐3,4‐Me₂C₅H₂}₂ZrCl₂] (E=NMe₂, OMe; n=1, 2), and a half‐functionalized zirconocene, [{1‐(p‐Me₂NC₆H₄)‐3,4‐Me₂C₅H₂}{1‐(p‐tolyl)‐3,4‐Me₂C₅H₂}ZrCl₂], were prepared. The crystal structures of these compounds determined by X‐ray diffraction revealed the presence of only C₂‐symmetric rac‐like isomers in the asymmetric units. In combination with methylaluminoxane (MAO) cocatalyst, the meta‐functionalized complexes afforded mixtures of polymers that exhibit multimelting transition temperatures and broad molecular‐weight distributions (MWDs) in propylene polymerization at atmospheric monomer pressure, whereas the ortho‐functionalized complexes did not give rise to polymerization. Stepwise solvent extraction of the polymer mixtures showed that the polymers consist of amorphous, moderately isotactic, and highly isotactic portions, the weight ratio of which is dependent on the reaction temperature. ¹³C NMR spectral analysis indicated that the [mmmm] methyl pentad value of the isotactic portion reached around 90 %. Among the meta‐functionalized zirconocenes, the di‐OMe‐substituted one afforded the largest amount of the isotactic portion at all temperatures, and the portion comprised 82 wt % of the crude polymer obtained at 25 °C. In contrast, propylene polymerization with the half‐functionalized unbridged zirconocene resulted in the formation of nearly atactic polypropylene with a narrow MWD of around 2. These results corroborate the proposition that the rigid rac‐like cation–anion ion pair of type [rac‐L₂ZrP]⁺[Me‐MAO]^? generated in situ, through Lewis acid–base interactions between the functional groups and [Me‐MAO]^?, is responsible for the isospecific propylene polymerization with the given class of functionalized unbridged zirconocenes and further indicate that the formation of such ion pairs can be favored by difunctionalization at the meta position of the phenyl ring with OMe groups.     

Absolute Configuration of Small Molecules by Co‐Crystallization

The most reliable method to determine the absolute configuration of chiral molecules is X‐ray crystallography, but small molecules can be difficult to crystallize. We report rapid co‐crystallization of tetraaryladamantanes with small molecules as different as n‐decane to nicotine to produce crystals for X‐ray analysis and the assignment of absolute configuration when the molecules are chiral. A screen of 52 diverse compounds gave inclusion in co‐crystals for 88 % of all cases and a high‐resolution structure in 77 % of cases. Furthermore, starting from three milligrams of analyte, a combination of NMR spectroscopy and X‐ray crystallography produced a full structure in less than three days using an adamantane crystallization chaperone that encapsulates the analyte at room temperature.     

Synthesis and Catalytic Use of Gold(I) Complexes Containing a Hemilabile Phosphanylferrocene Nitrile Donor

Removal of the chloride ligand from [AuCl( 1 ‐κP)] ( 2 ) containing a P‐monodentate 1′‐(diphenylphosphanyl)‐1‐cyanoferrocene ligand ( 1 ), by using silver(I) salts affords cationic complexes of the type [Au( 1 )]X, which exist either as cyclic dimers [Au( 1 )]₂X₂ ( 3 a , X=SbF₆; 3 c , X=NTf₂) or linear coordination polymers [Au( 1 )]_nX_n ( 3 a′ , X=SbF₆; 3 b′ , X=ClO₄), depending on anion X and the isolation procedure. As demonstrated for 3 a′ , the polymers can be readily cleaved by the addition of donors, such as Cl^?, tetrahydrothiophene (tht) or 1 , giving rise to the parent compound 2 , [Au(tht)( 1 ‐κP)][SbF₆] ( 5 a ) or [Au( 1 ‐κP)₂][SbF₆] ( 4 a ), respectively, of which the last two compounds can also be prepared by stepwise replacement of tht in [Au( 1 ‐κP)₂][SbF₆]. The particular combination of a firmly coordinated (phosphane) and a dissociable (nitrile) donor moieties renders complexes 3/3′ attractive for catalysis because they can serve as shelf‐stable precursors of coordinatively unsaturated Au^I fragments, analogous to those that result from the widely used [Au(PR₃)(RCN)]X catalysts. The catalytic properties of the Au‐ 1 complexes were evaluated in model annulation reactions, such as the synthesis of 2,3‐dimethylfuran from (Z)‐3‐methylpent‐2‐en‐4‐yn‐1‐ol and oxidative cyclisation of alkynes with nitriles to produce 2,5‐disubstituted 1,3‐oxazoles. Of the compounds tested ( 2 , 3 a′ , 3 b′ , 3 a , 4 a and 5 a ), the best results were consistently achieved with dimer 3 c , which has good solubility in organic solvents and only one firmly bound donor at the gold atom. This compound was advantageously used in the key steps of annuloline and rosefuran syntheses.     

Synthesis and Characterization of Monomeric Salicylaldiminato Lanthanide Complexes and Their Catalytic Behavior for Polymerization of ε—Caprolactone

IntroductionSchiffbaseligandscanbeusedtoprovideastereochem icallyrigidligandframeworkinhomogenousprecatalystsofsomemetals,suchassalenCrcatalystsinasymmetricring openingreactionofepoxide1andsalenAlinring openingpolymerizationoflactideandrelatedcyclicesters .2 Recently ,itwasreportedthatthebidentateSchiffbasecomplexesofearlyandlatetransitionmetalscanserveaspromisingalterna tivestometallocenecatalystsforthepolymerizationofα olefins.3Therefore ,theapplicationsofSchiffbaseligandsinorganometallic…     

吡啶二亚胺Ni(Ⅱ)配合物的合成、晶体结构及其催化乙烯聚合的研究

由三齿配体2,6-二[1-(2-甲基苯基亚胺)乙基]吡啶(L₁)和2,6-二[(1-苯基亚胺)乙基]吡啶(L₂)分别与NiCl₂.6H₂O在乙腈中反应,合成了两个吡啶二亚胺基氯化镍配合物L₁Ni(Ⅱ)Cl₂.CH₃CN(1)和L₂Ni(Ⅱ)Cl₂(2).通过元素分析、IR和¹HNMR对配体和配合物进行了结构表征,并测定了配合物1和2的晶体结构.X射线衍射分析结果表明,两个配合物均为五配位扭曲三角双锥构型,属单斜晶系,C_c空间群.配合物1的晶胞参数a=2.5783(5)nm,b=1.4843(3)nm,c=1.5866(3)nm;β=122.82(3),°V=5.1024(18)nm³,Z=4,R₁=0.0708,配合物2的晶胞参数a=1.5772(1)nm,b=0.8594(1)nm,c=1.5459(1)nm;β=103.27(1),°V=2.039(2)nm³,Z=4,R₁=0.0375.配合物1和2经MAO活化后对乙烯聚合表现出较低的催化活性.     

Manganese‐Corrole Complexes as Versatile Catalysts for the Ring‐Opening Homo‐ and Co‐Polymerization of Epoxide

Manganese‐corrole complexes in combination with a co‐catalyst [PPN]X ([PPN]⁺=bis(triphenylphosphoranylidene)iminium) were found to be new versatile catalysts for the polymerization of epoxides, copolymerization of epoxides with CO₂, and copolymerization of epoxides with cyclic anhydrides affording a wide range of polymeric materials. This work should allow the synthesis of new types of improved innovative (co)polymers with original properties and would clearly increase the number of applications for polyesters, polycarbonates, and polyethers.     

Hydrophilic Modification of Microporous Polysulfone Membrane via Surface‐Initiated Atom Transfer Radical Polymerization and Hydrolysis of Poly(glycidylmethacrylate)

Poly(glycidylmethacrylate) (PGMA) brushes were grafted from chloromethylated polysulfone (CMPSF) membrane surface by surface‐initiated atom transfer radical polymerization (SI‐ATRP), and the grafting was followed by hydrolysis of epoxy groups in the grafting chains to improve the membrane's hydrophilic property. Fourier transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS) measurements confirmed the successful grafting and hydrolysis of PGMA. The grafting degree of the monomer, measured by periodic acid titration and gravimetric analysis, increased linearly with the polymerization time, while the static water contact angle of the membrane grafted with PGMA or hydrolyzed PGMA linearly decreased. In comparison with the PGMA‐grafted membranes, the hydrolyzed PGMA‐grafted membranes possess stronger hydrophilicity as indicated by their contact angle and hydration capacity, and as a result they have an improved antifouling property. Therefore, the control of the hydrophilicity of PSF membrane could be realized through adjusting the polymerization time and transforming the functional groups in the grafting chain.     

Chiral Salan Aluminium Ethyl Complexes and Their Application in Lactide Polymerization

Synthetic routes to aluminium ethyl complexes supported by chiral tetradentate phenoxyamine (salan‐type) ligands [Al(OC₆H₂(R‐6‐R‐4)CH₂)₂{CH₃N(C₆H₁₀)NCH₃}‐C₂H₅] ( 4 , 7 : R=H; 5 , 8 : R=Cl; 6 , 9 : R=CH₃) are reported. Enantiomerically pure salan ligands 1–3 with (R,R) configurations at their cyclohexane rings afforded the complexes 4 , 5 , and 6 as mixtures of two diastereoisomers ( a and b ). Each diastereoisomer a was, as determined by X‐ray analysis, monomeric with a five‐coordinated aluminium central core in the solid state, adopting a cis‐(O,O) and cis‐(Me,Me) ligand geometry. From the results of variable‐temperature (VT) ¹H NMR in the temperature range of 220–335 K, ¹H–¹H NOESY at 220 K, and diffusion‐ordered spectroscopy (DOSY), it is concluded that each diastereoisomer b is also monomeric with a five‐coordinated aluminium central core. The geometry is intermediate between square pyramidal with a cis‐(O,O), trans‐(Me,Me) ligand disposition and trigonal bipyramidal with a trans‐(O,O) and trans‐(Me,Me) disposition. A slow exchange between these two geometries at 220 K was indicated by ¹H–¹H NOESY NMR. In the presence of propan‐2‐ol as an initiator, enantiomerically pure (R,R) complexes 4 – 6 and their racemic mixtures 7 – 9 were efficient catalysts in the ring‐opening polymerization of lactide (LA). Polylactide materials ranging from isotactically biased (P_m up to 0.66) to medium heterotactic (P_r up to 0.73) were obtained from rac‐lactide, and syndiotactically biased polylactide (P_r up to 0.70) from meso‐lactide. Kinetic studies revealed that the polymerization of (S,S)‐LA in the presence of 4 /propan‐2‐ol had a much higher polymerization rate than (R,R)‐LA polymerization (k_SS/k_RR=10.1).     

Pd‐Iminocarboxylate Complexes and Their Behavior in Ethylene Polymerization

Designing co‐catalyst‐free late transition metal complexes for ethylene polymerization is a challenging task at the interface of organometallic and polymer chemistry. Herein, a set of new, co‐catalyst‐free, single‐component catalytic systems for ethylene polymerization have been unraveled. Treatment of anthranilic acid with various aldehydes produced four iminocarboxylate ligands ( L1 – L4 ) in very good to excellent yield (75–92 %). The existence of 2‐((2‐methoxybenzylidene)amino) benzoic acid ( L1 ) has been unambiguously demonstrated using NMR spectroscopy, MS and single‐crystal X‐ray diffraction. A neutral Pd‐iminocarboxylate complex [{N O}PdMe(L1)] (N O=κ²‐N,O‐ArCHNC₆H₄CO₂ with Ar=2‐MeOC₆H₄) C1 was prepared by treating stoichiometric amount of L1.Na with palladium precursor. The identity of C1 was confirmed by 1–2D NMR spectroscopy and single‐crystal X‐ray diffraction studies. Along the same lines, palladium complexes C2 – C4 were prepared from ligands L2 – L4 respectively. In‐situ high‐pressure NMR investigations revealed that these Pd complexes are amenable to ethylene insertion and undergo facile β‐H elimination to produce propylene. These palladium complexes were then evaluated in ethylene polymerization reaction and various reaction parameters were screened. When C1 – C4 were exposed to ethylene pressures of 10–50 bar, formation of low‐molecular‐weight polyethylene was observed.