Oligomerization mechanism

The active catalytic species appears to involve a metal hydride complex, as added H2 enhances the reaction rate. Additionally, H4Ru4(CO)12 is observed during the course of the reaction and may also be used as an effective entry into the catalytic system. The oligomerization mechanism may proceed via a nucleophilic attack of the amine on a metal-activated Si-H bond, resulting in Si-N bond formation. 

Saito, J., Hara, J., Toda, S., and Tanaka, S., Analysis for the oligomerization mechanism of styrene by field desorption mass spectrometry. Bull. Chem. Soc. Japan, 56, 748, 1983. 

S. Ando and M. Ueda. Density functional theory calculations of the local spin densities of 3-suhstituted thiophenes and the oligomerization mechanism of 3-methylsulfanyl thiophene. Synth. Met. 129(2), 207-213 (2002). 

Scheme 6.16.5 Relevance of the insertion step for the different ethylene oligomerization mechanisms (a) and (b) showing ethylene insertion into a Ni-hydride and a Ni—all

The olefin oligomerization mechanism on a bimetallic center proposed by Rodriguez, van Looy, and Gabant [37-41] for ethylene oligomerization on the (MeOl Ti/EtjAl system is as follows ... 

Urbane, B., Betnel, M., Cruz, L., Bitan, G., 8c Teplow, D. B. (2010). Elucidation of amyloid beta-protein oligomerization mechanisms Discrete molecular dynamics study. Journal of the American Chemical Society, 132, 4266. 

The principal organs involved in the peripheral clearance of hGH from the plasma are the kidney and fiver. hGH is cleared via glomerular filtration at the kidney and by a receptor-mediated mechanism at the fiver (58,59). In animal models, derivatives of hGH such as the 20,000 mol wt variant, oligomeric forms, and hGH complexed with GH-binding protein have been shown to be cleared from the semm at significandy lower rates than 22,000 mol wt hGH (60—62). The prolonged plasma half-life of these derivatives probably reflects a combination of decreased receptor affinity and size constraints on glomerular filtration. 

Structure and Mechanism of Formation. Thermal dimerization of unsaturated fatty acids has been explaiaed both by a Diels-Alder mechanism and by a free-radical route involving hydrogen transfer. The Diels-Alder reaction appears to apply to starting materials high ia linoleic acid content satisfactorily, but oleic acid oligomerization seems better rationalized by a free-radical reaction (8—10). 

Examples of the unique insights obtained by solid state NMR applications to materials science include the Si/Al distribution in zeolites, the hydrogen microstructure in amorphous films of hydrogenated silicon, and the mechanism for the zeolite-catalyzed oligomerization of olefins. ... 

An EB-curable struetural adhesive formulation usually eonsists of one or more crosslinkable oligomeric resins or prepolymers, along with such additives as reactive diluents, plasticizers, and wetting agents. The oligomer is an important component in terms of the development of mechanical properties. The adhesive and cohesive properties depend on the crosslink density, chemical group substitution, and molecular organization within the polymer matrix. Adhesion is achieved... 

The cationic polymerization of cardanol under acidic conditions has been referred to earlier [170,171], NMR studies [16] indicated a carbonium ion initiated mechanism for oligomerization. PCP was found to be highly reactive with aldehydes, amines, and isocyates. Highly insoluble and infusible thermoset products could be obtained. Hexamine-cured PCP showed much superior thermal stability (Fig. 12) at temperatures above 500°C to that of the unmodified cardanol-formaldehyde resins. However, it was definitely inferior to phenolic resins at all temperatures. The difference in thermal stability between phenolic and PCP resins could be understood from the presence of the libile hydrocarbon segment in PCP. 

Oligomerization of ethylene using a Ziegler catalyst produces unbranched alpha olefins in the C12-C16 range by an insertion mechanism. A similar reaction using triethylaluminum produces linear alcohols for the production of biodegradable detergents. 

Of course in solution such an intermediate, if formed at all, would be very shortlived and could be the species responsible for the side reaction which produces some oligomerization of the furan ring. However, any interpretation of the mechanism of oligomerization must be regarded at this point as highly speculative since there is an obvious need for more experimental evidence, particularly concerning the structure of the products. 

The proposed polymerization mechanism is shown in Scheme 9.12. Thermal decomposition of the hexasubstituted ethane derivative yields hindered tertiary radicals that can initiate polymerization or combine with propagating species (primary radical termination) to form an oligomeric macroinitiator. The addition of the diphenylalkyl radicals to monomer is slow (e.g. k[ for 34 is reported as KT M"1 s l at 80 °C84) and the polymerization is characterized by an inhibition period during which the initiator is consumed and an oligomeric macroinitiator is formed. The bond to the Cl I formed by addition to monomer is comparatively thermally stable. 

Investigations of silicon-metal systems are of fundamental interest, since stable coordination compounds with low valent silicon are still rare [64], and furthermore, silicon transition-metal complexes have a high potential for technical applications. For instance, coordination compounds of Ti, Zr, and Hf are effective catalysts for the polymerization of silanes to oligomeric chain-silanes. The mechanism of this polymerization reaction has not yet been fully elucidated, but silylene complexes as intermediates have been the subject of discussion. Polysilanes find wide use in important applications, e.g., as preceramics [65-67] or as photoresists [68-83],... 

The issue of nucleation and growth is complicated by the formation of oligomeric and polymeric species in solution and their precipitation onto the electrode surface, which may be the primary mechanism for nuclei formation.62 The expansion of nuclei and film growth arise both from the precipitation of oligomeric intermediates formed in solution and... 

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