Ethylene coordination polymerisation

Coordination polymerisation was first proposed in 1956 for the unusual, at that time, low-pressure polymerisation of ethylene and polymerisation of propylene with the transition metal catalysts discovered by Ziegler in 1953 [1], and for the ferric chloride catalysed ring-opening polymerisation of propylene oxide to crystalline polymer reported by Pruitt et al. in a Dow patent [2]. 

Coordination polymerisation via re complexes comprises polymerisation and copolymerisation processes with transition metal-based catalysts of unsaturated hydrocarbon monomers such as olefins [11-19], vinylaromatic monomers such as styrene [13, 20, 21], conjugated dienes [22-29], cycloolefins [30-39] and alkynes [39-45]. The coordination polymerisation of olefins concerns mostly ethylene, propylene and higher a-olefins [46], although polymerisation of cumulated diolefins (allenes) [47, 48], isomerisation 2, co-polymerisation of a-olefins [49], isomerisation 1,2-polymerisation of /i-olcfins [50, 51] and cyclopolymerisation of non-conjugated a, eo-diolefins [52, 53] are also included among coordination polymerisations involving re complex formation. 

The same group of coordination polymerisations in which alkene undergoes re complex formation with the metal atom includes the copolymerisation of ethylene, a-olefins, cycloolefins and styrene with carbon monoxide in the presence of transition metal-based catalysts [54-58], In this case, however, the carbon monoxide comonomer is complexed with the transition metal via the carbon atom. Coordination bond formation involves the overlapping of the carbon monoxide weakly antibonding and localised mostly at the carbon atom a orbital (electron pair at the carbon atom) with the unoccupied hybridised metal orbitals and the overlapping of the filled metal dz orbitals with the carbon monoxide re -antibonding orbital (re-donor re bond) [59], The carbon monoxide coordination with the transition metal is shown in Figure 2.2. 

Such examples have shown that the role of the cationic group 4 metal complexes in the coordination polymerisation of ethylene and oc-olefins with homogeneous single-site Ziegler-Natta catalysts must not be limited to those containing cyclopentadienyl-like ligands. 

Figure 3.59 Life cycles of catalysts for olefin coordination polymerisation (a) early-generation Ziegler-Natta catalysts for ethylene and propylene polymerisation (b) Phillips catalysts for ethylene polymerisation (c) fourth-generation Ziegler-Natta catalysts for ethylene polymerisation (d) fourth-generation Ziegler-Natta catalysts for propylene polymerisation (e) metallocene-based catalysts for olefin polymerisation leading to polymers of various stereoregularity...

The coordination polymerisation and copolymerisation of heterocyclic monomers have been restricted in industry to a much smaller volume than the polymerisation and copolymerisation of hydrocarbon monomers polyether elastomers from epichlorohydrin and ethylene oxide or propylene oxide, and allyl glycidyl ether as the vulcanisable monomeric unit, are produced on a larger scale [4-7],... 

The metal thiolate species are more reactive towards the coordinating monothiocarbonate monomer during the polymerisation presented by scheme (20) than the corresponding metal alcoholate species operating in ethylene carbonate polymerisation [scheme (15)]. 

Simple monodentate NHCs are somewhat susceptible to dissociation when coordinated to early transition metals [6], so in most cases multidentate chelating hgands are employed in which the carbene is tethered to a strongly coordinating anchoring group. This is not universally the case however, and simple monodentate NHC complexes of Zr 1 (Fig. 4.1) have been studied [7]. The complexes were activated with MAO and tested for ethylene polymerisation, leading to moderate activities between 7 and 75 kg mol bar h for linear polyethylene. 

A consensus on or explanation for the influence of the oxidation state of titanium on olefin polymerisation activity has not been reached. The absence of any insertion of the coordinating ethylene into the Ti-C bond in Ti(II) species is noteworthy instead, two ethylene molecules, which coordinate at two coordination sites at Ti(II) species, undergo an oxidative addition, and thus the respective metallacycle, titanacyclopentane, is formed [305], Such a reaction for dimethyltitaniumcomplexed by l,2-bis(dimethylphosphione)ethane [Dmpe] is as follows [305] ... 

Semiempirical molecular orbital calculations on this model [309] suggest that, in the case of propylene polymerisation, equatorial 2,4-substitution of the metallacyclopentane ring is the most stable form this would lead to regiose-lective head-to-tail propagation during the polymerisation of propylene and, moreover, to the formation of isotactic polypropylene [51]. Such calculations concern a case, however, that has not been confirmed by experiments a coordination of propylene at Ti(II) species and subsequent reaction according to the above scheme is not as obvious as that of ethylene. 

This model would explain the inability of metallocene-alkylaluminium halide systems to promote the polymerisation of propylene and higher a-olefins [94] it is obvious that there is insufficient capability of the more weakly coordinating a-olefins to form reactive, olefin-separated ion pairs by displacement of an aluminate anion from the metal centre. At any rate, the limitation of homogeneous catalysts to the polymerisation of only ethylene was a crucial obstacle to progress in this field for many years. This impediment was fortunately overcome, however, by a series of serendipitous observations [90-95, 100,101,103] that led, around the 1980s, to the discovery by Kaminsky, Sinn et al. [90, 91,94,95,100,101] that metallocenes are activated for catalysing the polymerisation of propylene and other a-olefins (without a, a-disubstituted olefins) by methylaluminoxane [30],... 

Name and characterise coordination catalysts for the polymerisation of ethylene and a-olefins. 

In order to clarify the mechanism, the reaction of carbon disulphide with mercury bis(n-butanethiolate) was studied. On the basis of results obtained, it was suggested that this reaction involved the formation of a coordination complex, followed by the formation of active species containing the Hg-SC(S) bond. Moreover, the cyclic trithiocarbonate, ethylene trithiocarbonate, found to be present in trace amounts in copolymerisation products, was excluded as a possible intermediate for the copolymer formation, since it did not undergo any polymerisation under the given conditions [249],... 

Lawrence, S.C., Ward, B.D., Dubberley, S.R. et al. (2003) Highly efficient ethylene polymerisation by scandium alkyls supported by neutral fac-Ks coordinated N3 donor Ugands. Chemical Communications,... 

The application of organometallic compounds in medicine, pharmacy, agriculture and industry requires the accurate determination of these metals as part of their application. Most % complexes characterised by direct carbon-to-carbon metal bonding may be classified as organometallic and the nature and characteristics of the n ligands are similar to those in the coordination metal-ligand complexes. The -complex metals are the least satisfactorily described by crystal field theory (CFT) or valence bond theory (VBT). They are better treated by molecular orbital theory (MOT) and ligand field theory (LFT). There are several uses of metal 7i-complexes and metal catalysed reactions that proceed via substrate metal rc-complex intermediate. Examples of these are the polymerisation of ethylene and the hydration of olefins to form aldehydes as in the Wacker process of air oxidation of ethylene to produce acetaldehyde. 

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