Half‐metallocene diene complexes of niobium and tantalum catalyzed three‐types of polymerization: (1) the living polymerization of ethylene by niobium and tantalum complexes, MCl2(η4‐1,3‐diene)(η5‐C5R5) ( 1‐4 ; M = Nb, Ta; R = H, Me) combined with an excess of methylaluminoxane; (2) the stereoselective ring opening metathesis polymerization of norbornene by bis(benzyl) tantalum complexes, Ta(CH2Ph)2(η4‐1,3‐butadiene)(η5‐C5R5) ( 11 : R = Me; 12 : R = H) and Ta(CH2Ph)2(η4‐o‐xylylene)(η5‐C5Me5) ( 16 ); and (3) the polymerization of methyl methacrylate by butadiene‐diazabutadiene complexes of tantalum, Ta(η2‐RN=CHCH=NR)(η4‐1,3‐butadiene)(η5‐C5Me5) ( 25 : R = p‐methoxyphenyl; 26 : R = cyclohexyl) in the presence of an aluminum compound ( 24 ) as an activator of the monomer. 相似文献
A series of ortho or meta Lewis base functionalized unbridged zirconocenes, [{1‐(En‐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. 相似文献
Reaction of tetraphosphine complex [Mo(κ4‐P4)(Ph2PCH2CH2PPh2)] (1; P4 = meso‐o‐C6H4‐(PPhCH2CH2PPh2)2) with E‐1,3‐pentadiene in toluene at 60 °C gave the η4‐diene complex [Mo(η4‐E‐1,3‐pentadiene)(κ4‐P4)] (2), which is present as a mixture of two isomers due to the orientation of the Me group in the diene ligand. Treatment of 1 with Z‐1,3‐pentadien also resulted in the formation of 2 as the sole product after heating the reaction mixture at 90 °C. Whereas the reaction of 1 with 1,3‐cyclohexadiene at 60 °C afforded the η4‐diene complex [Mo(η4‐cyclohexadiene)(κ4‐P4)] (6), that with cyclopentadiene led to the C‐H bond scission product [η5‐C5H5)MoH(κ3‐P4)] (7). Detailed structures were determined by X‐ray crystallography for 2, 6,and 7, and fluxional feature of 6 in solution was clarified based on the VT‐NMR studies. 相似文献
The synthesis and characterization of copolymers from styrene and 1,3‐pentadiene (two isomers) are reported. Styrene/1,3‐pentadiene (1:1) copolymerization with carbanion initiator yield living, well‐defined, alternating (r1 = 0.037, r2 = 0.056), and highly stereoregular copolymers with 90%–100% trans‐1,4 units, designed Mns and low ÐMs (1.07–1.17). The first‐order kinetic resolution and NMR spectra demonstrate that the copolymers obtained possess strictly alternating structure containing both 1,4‐ and 4,1‐enchaiments. Also a series of copolymers with varying degrees of alternation are synthesized from para‐alkyl substituted styrene derivatives and 1,3‐pentadiene. The degree of alternation is strongly dependent on the polarity of solvent, reaction temperature, type of trans‐cis isomer of 1,3‐pentadiene and para‐substituted group in styrene. The macro zwitterion forms (SPC) through the distribution of electronic charges from the donor (1,3‐pentadiene) to the acceptor (styrenes) are proposed to interpret the carbanion alternating copolymerization mechanism. Owing to the versatility of the carbanion‐initiating reaction, the present alternating strategy based on 1,3‐pentadiene (especially cis isomer) can serve as a powerful tool for precise control of polymer chain microstructure, architecture, and functionalities in one‐pot polymerization.
Diethylbis(2,2′‐bipyridine)Fe/MAO is an extremely active catalyst for the polymerization of 1,3‐dienes. Polymers with a 1,2 or 3,4 structure are formed from butadiene, isoprene, (E)‐1,3‐pentadiene and 3‐methyl‐1,3‐pentadiene, while cis‐1,4 polymers are derived from 2,3‐dimethyl‐1,3‐butadiene. The 1,2 (3,4) polymers obtained at 25°C are amorphous, while those obtained below 0°C are crystalline, as was determined by means of X‐ray diffraction. Mechanistic implications of the results are briefly discussed. 相似文献
The bis‐C‐glucoside 2 has been synthesised as the first representative of a series of templated glucosides and cellooligosaccharides that mimick part of the unit cell of cellulose I. As expected, there are, at best, weakly persistent H‐bonds between the two glucosyl residues in (D6)DMSO and (D7)DMF solution. The acetylated oct‐1‐ynitol 7 and deca‐1,3‐diynitol 12 were prepared from the gluconolactone 5 (Scheme 1). Coupling of 12 to PhI and 2‐iodothiophene yielded 13 and 14 , respectively, while dimerisation of the benzylated and acetylated deca‐1,3‐diynitols 10 and 12 afforded the bis‐C‐glucosyloctatetrayne 15 and the less stable 16 , respectively. The 2‐glucosylthiophene 17 was obtained by treating the C‐silylated deca‐1,3‐diynitol 9 with Na2S. Cross‐coupling of (trimethylsilyl)acetylene (TMSA) with 1,8‐bis(triflyloxy)‐9,10‐anthraquinone ( 20 ) at elevated temperature gave the dialkynylated 21 ; its structure was established by X‐ray analysis (Scheme 2). Sequential coupling of 6 or 7 and TMSA to 20 gave the symmetric dialkyne 21 , the mixed dialkynes 23 (from 6 ) and 25 (from 7 ), and the symmetric diglucoside 36 (from 7 ) in modest yields; a stepwise coupling to the acetylated monotriflate 28 proved advantageous. It led to the oct‐1‐ynitol 29 and the deca‐1,3‐diynitol 33 that were transformed into the triflates 30 and 34 , respectively. Coupling of the triflate 34 to the oct‐1‐ynitol 7 gave the unsymmetric bis‐C‐glucoside 35 ; this was obtained in higher yields by coupling the triflate 30 to the deca‐1,3‐diynitol 12 . Coupling of the bistriflate 20 with either 7 or 12 afforded the symmetric bis‐C‐glucosides 36 and 37 , respectively. Deacetylation (KCN in MeOH) of 35 – 37 provided the unsymmetric bis‐C‐glucoside 2 and the symmetric analogues 3 and 4 . 相似文献
The structures of dichloro{2‐[(5‐methyl‐1H‐pyrazol‐3‐yl‐κN2)methyl]‐1H‐1,3‐benzimidazole‐κN3}copper(II), [CuCl2(C12H12N4)], and di‐μ‐chloro‐bis(chloro{2‐[(5‐methyl‐1H‐pyrazol‐3‐yl‐κN2)methyl]‐1H‐1,3‐benzimidazole‐κN3}cadmium(II)), [Cd2Cl4(C12H12N4)2], show that these compounds have the structural formula [ML(Cl)2]n, where L is 2‐[(5‐methylpyrazolyl)methyl]benzimidazole. When M is copper, the complex is a monomer (n = 1), with a tetrahedral coordination for the Cu atom. When M is cadmium (n = 2), the complex lies about an inversion centre giving rise to a centrosymmetric dimer in which the Cd atoms are bridged by two chloride ions and are pentacoordinated. 相似文献
Sterically hindered olefins like norbornene, dimethanooctahydronaphthalene (DMON), 4‐methylpentene, and 3‐methylbutene can be copolymerised with ethene by metallocene/MAO catalysts. Different C2‐, Cs‐ and C1‐symmetric and meso‐zirconocenes were used. Only isolated and alternating norbornene sequences but no norbornene blocks are formed by substituted [Me2C(Cp‐R)(Flu)]ZrCl2 catalysts. The alternating microstructure leads to melting points up to 270°C for ethene‐norbornene copolymers and up to 380°C for the semi‐crystalline alternating copolymer of ethene and DMON. Other sterically hindered olefins such as 3‐methylpentene build more blocky structures with high glass transition temperatures. The mechanism for the insertion reaction of the different catalysts is discussed. 相似文献
The title compounds, [CuFe2(C5H5)2(C9H8O2)2], (I), and [CuFe4(C5H5)4(C13H9O2)2], (II), are four‐coordinate square‐planar copper(II) complexes with two bidentate 1‐ferrocenylbutane‐1,3‐dionate or 1,3‐diferrocenylpropane‐1,3‐dionate ligands, respectively. The copper ion in (I) lies on an inversion centre, with one‐half of the molecule in the asymmetric unit, while in (II), there are two independent half molecules in the asymmetric unit, with the copper ions also situated on inversion centres. The ferrocene substituents in (I) are in an anti arrangement. The molecules assemble in the crystal structure in layers with ferrocene groups at the surface. The pairs of ferrocene substituents on each ligand in complex (II) are syn and these adopt an anti arrangement with respect to the pair on the other diketonate ligand. As found in (I), complexes assemble in a layered structure with ferrocene‐coated surfaces. 相似文献