Halide donors

In the polymerization of dienes with Ziegler/Natta catalyst systems it is a well-established fact that the presence of halide donors is essential in order to achieve high catalytic activities and high cis-1,4-contents [360,361]. The halide free catalyst system NdO/TIBA is a good example for a catalyst with a poor performance and a high trans- 1,4-specificity [362,363]. For various binary and ternary catalyst systems the qualitative impact of chlorides on the stereochemistry of BR is demonstrated in a series of fundamental experiments the results of which are summarized in (Table 5) [364], 

Nd(COOR)3/Mg(Allyl)2 Nd(COOR)3/Mg(Allyl)2/halide-donor 

In Nd-based catalyst systems there are only small differences between bromide and chloride donors regarding polymerization activities and cis-1,4-contents. Chlorine-containing donors are preferred, especially in large-scale production, as chlorine donors are readily available and have a modest price. 

Quite evidently, for binary catalyst systems of the type NdCl3 D/A1R3 an additional catalyst component which acts as a halide source is not required. NdCb constitutes an appropriate halide source which provides halogen at a fixed molar ratio of nx/ Nd = 3. 

For ternary catalyst systems a vast number of halide donors was investigated which renders a complete quotation impossible. It is important to note, however, that for a given halide, the actual halide source neither has a strong influence on catalyst activity nor on cis- 1,4-contents. As halogen sources which are found in the literature cover the whole range from ionic halides to covalently bound halogen atoms the strength by which the halide is bound to the donor is not a critical factor. 

668 Harland, S. Cradock, and J. C. J. Thynne, Inorg. Nuclear Chem. Letters, 1973, 

Vande Vondel and G. P. Vander Kelen,/. Organometallic Chem., 1973,55,85. 

Davidovich, T. F. Levchishina, and T. A. Kaidalova, Zhur. neorg. Khim., 1973, 

Cl-----H—hydrogen-bonding between cation and anion, and accounts 

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Preparation of ionic liquids by treatment of amines with halide donors in the presence of metal halides [HNR3]C1/A1C13 Akzo Nobel NV, Netherlands 2000 31... 

X-ray structural analyses reveal that the jt-bonding of dihalogens, halocar-bons and halides to arene donors and acceptors are characterized mostly by over-the-rim coordination in which the dihalogen acceptor generally follows the position of highest electron density on the aromatic donor, and the arrangement of halide donor mostly follows the LUMO shape of the aromatic acceptor. 

Oxidative addition occurs readily with allylic halides. Donor ligands (tertiary phosphines, bipyridyl, halide ions) and anionic complexes are required for activation of aromatic and vinyl halides (4, 70). Certain aliphatic halides are also reactive. The intermediate species R—Ni—X... 

Ruthenium(ii).—Group VII Donors. Halide donor ligands. A study has shown that the blue complexes obtained by electrolytic reduction of H2[RuCl5H20] in acidic solution are further examples of mixed Ru"-Ru " complexes. They were previously assumed to contain only Ru . Dimers of the type Ru2Ch3Vi," (n = 0,1, or 2) were separated and isolated using ion-exchange chromatography. 

One of the more notable features of antimony(V) halide chemistry is the tendency to achieve a CN of six, thus resulting in the facile formation of complex anions, particularly with halide donors (Table 21) the d(Sb—F) depends on the nature of the cation. Their structures are related to the F—Sb- -F interactions between crystal structure units, which is dependent upon the potential field of the cation. 

From the early 1960s onwards, the use of lanthanide (Ln) based catalysts for the polymerization of conjugated dienes came to be the focus of fundamental studies [31]. The first patent on the use of lanthanides for diene polymerization originates from 1964 and was submitted by Union Carbide Corporation (UCC) [32,33]. In this patent the use of binary lanthanum and cerium catalysts is claimed. Soon after this discovery by UCC, Throckmorton (Goodyear) revealed the superiority of ternary lanthanide catalyst systems over binary catalyst systems. The ternary systems introduced by Throckmorton comprise a lanthanide compound, an aluminum alkyl cocatalyst and a halide donor [34], Out of the whole series of lanthanides Throckmorton... 

It is speculated that the use of heterogeneous or partially heterogeneous Nd catalyst systems results in gel formation. Due to this reason, Nd-systems which are soluble in hydrocarbon solvents are preferred today, especially in large-scale operations. The soluble catalysts are usually based on ternary systems which consist of Nd salts with anions bearing long-chain aliphatic groups, an alkyl aluminum cocatalyst and a halide donor. 

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

Obviously, the addition of halide donors is not an issue in NdX3-based systems since halides are already present in sufficiently high quantities. A representative selection of Nd-halide-based catalyst systems is given in Table 2. 

Neodymium carboxylate Cocatalyst Halide donor cis-1,4-Content/% Refs. 

It has to be mentioned that as early as in 1991 Porri et al. reported on the reaction of NdCl3 with Mg(C3H5)Cl in THF yielding an undefined Nd allyl compound which was successfully tested in diene polymerizations [141, 167,294]. For the polymerization experiments the cocatalysts TIBA, TMA, TIBAO and MAO were used and no halide donor was added. The undefined Nd allyl compound + TIBA yields a catalyst system that is reported to be at least three times more active than the system NdzO/TIBA/DEAC. The application of MAO with the Nd allyl compound increases catalytic activity 30-fold. 

Activation of Nd carboxylates and Nd alcoholates by alumoxanes provides the option to omit halide donors. By the use of alumoxanes high activity levels are accomplished but cis-1,4-contents are considerably reduced as opposed to the use of AIR3 with which very high cis- 1,4-contents are accessible [175]. 

Table 5 clearly demonstrates that cis-l,4-BR is only obtained if chloride is present in the catalyst system. In the absence of chloride BR with a high transit-content is obtained. These features were recently confirmed by Evans et al. who used well-defined Nd carboxylates for the polymerization of dienes [365]. According to Evans et al. halide atoms are transferred from the halide donor to Nd [366]. The role of halides for the achievement of high cis-1,4-contents was also demonstrated by Kwag et al. On the basis of density... 

In alkyl aluminum chlorides of the type RxAlyClz two different chemical moieties which cause alkylation as well as chlorination are present in one molecule. Therefore, RAAL,Clz-type activators do not require the separate addition of other halide donors in order to achieve high cis-1,4-contents. In Nd-based catalyst-systems the dual role of RXA1 C1Z compounds is demonstrated by Watanabe and Masuda [364], These findings only hold true for Nd-based catalyst systems. For lanthanum-based catalyst systems Lee et al. found that the use of alkyl aluminum chlorides results in trans- 1,4-polymerization (93-94%) [371]. However, usually, in Nd catalysts the alkylating power of RxAlyClz is not sufficient at the applied amounts of RXA1 C1Z. Thus, an additional standard cocatalyst has to be added for the activation of the Nd precursor. 

Examples of halide donors with a C-Cl-bond are (BuCl [175,232], CCI4 [157,372-375] and CHC13 [376,377]. Examples for Si-containing Cl-donors are SiCLi [157,187] and RSiCl3 [157,378,379]. TiCl4 [157], PC13 and other halide donors can also be beneficially used but are less often referenced. Even tin halides have recently been mentioned by Kumho [380,381]. 

In Nd alcoholate-catalyzed polymerizations, as a rule of thumb, the same halide donors are applied at the same molar ratios as with Nd-carboxylate-based catalyst systems. In the literature, hydrocarbon soluble as well as hydrocarbon insoluble halide donors are combined with Nd-alcoholates. Examples are benzyl chloride (BzCl) [37,38], AlBr3 [224,225], AlEtCl2 [226,227], Et2AlCl [231], fBuCl [231,232] and Me3SiCl [231]. 

To our knowledge, only one example is known in which the addition of halide donors (Et2AlCl,1 BuCl and McjSiCl) was not beneficial for catalyst activity. Dong et al. studied the polymerization of IP with the catalyst system Nd(0 Pr)3/MMA0. Addition of the halide donors reduced catalyst activity in the following order Et2AlCl > (BuCl > MejSiCl [231]. 

Halide donors constitute an essential component of ternary catalyst systems (Sect. 2.1.3). In these systems variations of the molar ratios x/ Nd (X = halide) affect catalyst activities, molar masses, MMDs and the microstructures of the poly(diene)s. 

For Nd-based catalyst systems the quantitative range of halide donors investigated falls between 0 < x/ Nd < 10. A maximum in catalyst activity is usually observed at molar nx/ Nd-rali°s between 2 and 4, e.g. [49,89,168, 178,187,232,272,318]. Various factors such as addition order of the catalyst components, catalyst preformation and catalyst aging have an influence on the location of the optimum molar nx/n -xdXio (Sect. 2.1.6). 

Increase of the fraction of active Nd with increasing amounts of halide donor. 

With the MMAO-activated catalyst system Nd( OPr)3/MMAO/halide donor a unique dependence of molar mass on the ratio of ftci/ Nd was obtained. Molar mass steadily decreases with increasing nci/nN(j-ratios (between 0.5 to 2.0) regardless of the type of chlorine source (Et2AlCl, fBuCl and Me3SiCl) [231]. 

As can be seen from Table 9 an increase in the ( i/ Nd-ralio from 0.5 to 3.0 results in an increase of the cis- 1,4-content. A further increase of the ci/ Nd-ratio to 4.0 and 10.0 decreases the cis- 1,4-content. BR which is obtained without halide donor (at a very low catalyst activity) exhibits a unique mi-crostructural composition 71.9% czs-1,4, 21.2% trans-1,4 and 6.9% 1,2. This observation corroborates the fact that high-czs-l,4-poly(butadiene) products only can be obtained in the presence of halide donors. 

Systematic studies on the addition order of catalyst components focused on the catalyst system NdV/DIBAHTBuCl. The variations included all six conceivable addition orders. It was found that the order in which the halide donor (BuCl was added plays a decisive role concerning the heterogeneity of the catalyst and its activity [158] ... 

BR with narrow MMDs (Mw/Mn > 3.5) and a low solution viscosity can also be obtained by the use of a multi-component catalyst system which comprises the following six components (1) Nd-salt, (2) additive for the improvement of Nd-solubility, (3) aluminum-based halide donor, (4) alumoxane, (5) aluminum (hydrido) alkyl, and (6) diene. The solubility of the Nd-salt is improved by acetylacetone, tetrahydrofuran, pyridine, N,N-dimethylformamide, thiophene, diphenylether, triethylamine, organo-phosphoric compounds and mono- or bivalent alcohols (component 2). The catalyst components are prereacted for at least 30 seconds at 20 - 80 °C. Catalyst aging is preferably performed in the presence of a small amount of diene [397,398 ]. As the additives employed for the increase of the solubility of Nd salts exhibit electron-donating properties it can be equally well speculated that poisoning of selective catalyst sites favors the formation of polymers with a low PDI. 

The solubility of neodymium carboxylates in organic solvents is also improved by the addition of electron donors such as acetylacetone, tetrahy-drofuran, N,N -dimethylformamide, thiophene, diphenylether, triethylamine, pyridine, organic phosphorus compounds etc. Also the storage stability of neodymium carboxylates in organic solutions (reduction of sediment formation) is increased by these additives. Mixtures of the Nd-precursor and the respective additives are reacted in the temperature range 0-80 °C. The sequential addition of Al-compound and halide donor yield the active polymerization catalysts [409,410]. 

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