Catalyst ethylene complex

The inhibitor effectively suppresses the formation of MA homopolymer, which decreases the catalyst activity and incorporation of MA into the polymer [42]. The incorporation of MA in the copolymer is approximately twice as large in CO2 at the same monomer ratio. Therefore, less MA is needed for similar incorporation of MA in the copolymer. The rate-determining step in the polymerization is the insertion of the monomers. As a consequence, the incorporation of MA and ethylene is determined by the ratio of the catalyst-ethylene complex and catalyst-MA complex (see Fig. 8.15). Apparently, the polymerization temperature does not influence the incorporation of MA in the polymer, because the polymerization performed by Brookhart et aL [14] at 298 K follows the same trend as the polymerizations at 308 K. 

The difference in solvent properties can affect the chemical potential of the catalyst complexes and monomers. The latter effect is expected to be small because of the absence of strong interactions between MA, CO2, and ethylene. A higher incorporation of MA in the copolymer in CO2 can be caused by an energetically more favorable catalyst-MA complex compared to the catalyst-ethylene complex. Another effect of the non-polar CO2 is that the local concentration of the polar MA is probably higher around the catalyst than in the bulk to stabihze the electrical charge of the cationic palladium complex and the counterion in... 

In conclusion, copolymerizations of MA and ethylene can be carried out in compressed CO2. In comparison with dichloromethane, similar molecular weights are obtained. The incorporation of MA in the copolymer at the same monomer ratio is approximately twice as large in compressed CO2, which can be attributed to a higher MA concentration near the catalyst or to an energetically more favorable catalyst-MA complex as compared to the catalyst-ethylene complex. 

Fig. 2. Time-evolution of the methyl/ethyl C-C distances for both the zirconocene and the corresponding titanocene catalyst. The two curves starting at around 3.2 A represent the distance between the methyl carbon atom and the nearest-by ethylene carbon atom in the zirconocene-ethylene and the titanocene-ethylene complex, respectively. The two curves starting at around 1.35 A reflect the ethylene internal C-C bond lengths in the two complexes.

Pentapyrrolic macrocycles, 2,888 2,1,2-Pen tathiadiazol e-4,7-dicarbonitrile in hydrogen production from water, 6, 508 Pentatungstobis(organophosphonates), 3, 1053 4-Penten-l-al reaction with ethylene catalysts, rhodium complexes, 6, 300... 

Nishiyama et al. introduced a new catalyst, the chiral tr<2 i -RuCl2(Pybox-i-Pr)(ethylene) complex (91), which showed for the first time both enantio- and diastereoselectivity (trans-selectivity) at excellent levels in the reactions of terminal olefins (Scheme 66).251-253 With 4-substituted Ru(Pybox-i-Pr) complexes (92), they studied the substituent effect on enantioselectivity... 

The course of stereospecific olefin polymerization was studied by using the molecular mechanics programs, MM-2 and Biograph, based on the optimized geometries of the ethylene complex and the transition state [13,203]. Interestingly, the steric interaction at the transition state mainly controls the stereochemistry in polymerization, which proceeds specifically isotactic or syndiotactic depending on the kind of catalyst. 

Figure 4. Structures resulting from ethylene insertion and chain termination due to the generic catalyst (HN=C(H)-C(H)=NH)PdC3H7+. Ethylene complex (3a) insertion transition state (TS[ 3a-4a]) termination transition state (TS[3a-5a) new olefin product from termination process (5a).

Ethylene is commonly chosen to illustrate homogeneous hydrogenation with Wilkinson s catalyst, but the process is actually very slow with this aJkene. The explanation lies with the formation of a stable rhodium ethylene complex, which does not readily undergo reaction with H,. Ethylene competes effectively with the solvent for the vacant coordination site created when triphcnylphosphinc dissociates from Wilkinson s catalyst and thus serves as an inhibitor to hydrogenation. 

Acetylene hydrogenation. Selective hydrogenation of acetylene to ethylene is performed at 200°C over sulfided nickel catalysts or carbon-monoxide-poisoned palladium on alumina catalyst. Without the correct amount of poisoning, ethane would be the product. Continuous feed of sulfur or carbon monoxide must occur or too much hydrogen is chemisorbed on the catalyst surface. Complex control systems analyze the amount of acetylene in an ethylene cracker effluent and automatically adjust the poisoning level to prepare the catalyst surface for removing various quantities of acetylene with maximum selectivity. 

The catalyst-hydroperoxide complexes are more stable for the metals of Group B than for those of Group A. Epoxidation of the olefins proceeds more easily and more selectively. " They are particularly significant in the industrially important epoxidation of propylene. Reference should be made to the very selective epoxidation of cyclohexene with a Mo complex and to publications relating to the epoxidation of ethylene, hexene-1, and octene-1 with a Cr complex. 

In the presence of CS the reaction did not begin at 25,40, 50, 60, or 70 °C. At 80 - 85 °C instant catalyst conversion from yellow insoluble salt to brown solution, evidently of a Pt(0) complex, takes place. On this catalyst, ethylene was adsorbed to frill tiiethoxysilane conversion. The catalyst proved to be stable in the presence of ethylene, thus testifying to the combined character of the compound. The next day, when a new portion of triethoxysilane was added to the previous synthesis, the reaction proceeded quantitatively, but a little more slowly (lower platinum concentration). In the absence of ethylene on the next day a black residue of platinum metal precipitated where synthesis did not proceed. 

RhCl(C2H4)pip2] is formed as the actual catalyst. The complex, whose structure is established by X-ray crystal structure analysis [18], can be easily prepared by piperidine addition to the well-known [Rh(C2H4)2Cl]2, which shows identical catalytic properties. The catalytic efficiency is limited by the thermal instability of the bis(piperidine) ethylene complex at higher temperatures. The thermal decomposition proceeds with formation of metallic rhodium, presumably according to eq. (5). 

The phosphine-stabilized ethylene complex of zirconocene(n) reacts with 1 equiv. of B(G6F5)3 to form the girdle-type zwitterionic complex 754 (Equation (49)).574 Both the solution and solid-state structures of 754 feature a strong f3-CH agostic interaction. The zwitterion 754 is a single-component catalyst for the polymerization of ethylene under ambient conditions, although for optimal activity an additional equivalent of B(G6F5)3 is needed. 

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