Olefin disproportionation catalysts

The application of these catalysts in the initial state (without any special treatment of the surface organometallic complexes of such cata-lysts) for ethylene polymerization has been described above. The catalysts formed by the reaction of 7r-allyl compounds with Si02 and AUOj were found to be active in the polymerization of butadiene as well (8, 142). The stereospecificity of the supported catalyst differed from that of the initial ir-allyl compounds. n-Allyl complexes of Mo and W supported on silica were found to be active in olefin disproportionation (142a). 

Olefin disproportionation Catalyst system, MoClg/E ALCL/ 44... 

Olefin disproportionation 02/CH3C00H, caused a higher catalyst stability and activity. Catalysts based on Mo or W, especially 45... 

Olefin disproportionation order to have an increased ration of P-olefins. This caused higher catalyst lifetime. Mo or W03 and alumosilicate as a carrier. 47... 

Olefin metathesis (olefin disproportionation) is the reaction of two alkenes in which the redistribution of the olelinic bonds takes place with the aid of transition metal catalysts (Scheme 7.7). The reaction proceeds with an intermediate formation of a metallacyclobutene. This may either break down to provide two new olefins, or open up to generate a metal alkylidene species which -by multiple alkene insertion- may lead to formation of alkylidenes with a polymeric moiety [21]. Ring-opening metathesis polymerization (ROMP) is the reaction of cyclic olefins in which backbone-unsaturated polymers are obtained. The driving force of this process is obviously in the relief of the ring strain of the monomers. 

The variety of transformations possible and the availability of both soluble and supported catalysts should make the industrial future of olefin disproportionation a bright one. 

Many organometallic compounds are moisture sensitive, a particularly important class from the catalytic viewpoint being transition metal hydrocarbyl derivatives (Mn+Rn). These compounds have been used as catalysts for or have been postulated as catalytic intermediates in many olefin reactions such as polymerization, oligomerization, and olefin disproportionation (23). Recent work has shown that compounds containing... 

The reactions chosen for study in this work were olefin polymerization and olefin disproportionation. Catalysts for the former reaction are, in the majority of cases, metal derivatives of Groups IVB-VIB whereas compounds of molybdenum, tungsten, and rhenium are recognized as catalysts for olefin disproportionation. 

We report here a study of Zr, Nb, Cr, and Mo hydrocarbyl compounds grafted onto oxide supports as potential olefin polymerization catalysts and oxide-supported Mo and W 7r-allyl derivatives in olefin disproportionation catalyses. The interaction of these compounds with silica and alumina supports has been examined using ESR and IR, analyses to define the catalytic materials that result. Finally, we consider why chemical support of these organometallic compounds confers on them an enhanced catalytic activity. 

The disproportionation activity in the supported species is parallel to the increased activity of ethylene polymerization on supported catalysts. Many of the steps in the reaction may be identical for example, the initial coordination of olefin to the metal center will be common to both systems. Indeed, some of these catalysts are also ethylene polymerization catalysts (see Table IV) although their activities are much less than the corresponding zirconium derivatives. A possible intermediate common to both disproportionation and polymerization could be the hydrocarbyl-olefin species (Structure I). Olefin disproportionation would result if the metal favored /3-hydrogen elimination to give the diolefin intermediate (Structure II) which is thought to be necessary for olefin disproportionation. Thus, the similarity between the mechanism and activation of olefin disproportionation and polymerization is suggested. 

The alkene metathesis reaction arose serendipitously from the exploration of transition-metal-catalysed alkene polymerisation. Due to the complexity of the polymeric products, the metathetic nature of the reaction seems to have been overlooked in early reports. However, in 1964, Banks and Bailey reported on what was described as the olefin disproportionation of acyclic alkenes where exchange was evident due to the monomeric nature of the products [8]. The reaction was actually a combination of isomerisation and metathesis, leading to complex mixtures, but by 1966 Calderon and co-workers had reported on the preparation of a homogeneous W/Al-based catalyst system that effected extraordinarily rapid alkylidene... 

Moffat and Clark 84> found that a Langmuir-Hinshelwood model applied to a heterogeneous surface can be used to describe both the general kinetics and the rate-temperature maxima reported by Banks and Bailey (Fig. 2) for olefin disproportionation on cobalt molybdate-alumina catalyst. They conclude that the rate-temperature maximum was caused by the reversible deactivation of sites superimposed on the irreversible poisoning of sites. 

A decrease in 1-butene yield indicated that double-bond isomerization activity of the catalyst decreased more rapidly than disproportionation activity. Patents to Wilson and Larson 90-92) relate to the start-up and operation of olefin disproportionation processes. 

Heterogeneous catalyst studies and factors that contributed to the discovery of the olefin disproportionation (metathesis) reaction are described. Also provided is a personal commentary on the developments of heterogeneous catalyst technology associated with this intriguing reaction and its commercialization. 

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