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Polymer 54 (2013) 4455e4462

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Polymer

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Titanium (IV) and zirconium (IV) chloride complexes on the baseof chiral tetraaryl-1,3-dioxolane-4,5-dimetanol ligands in thepolymerization of ethylene: The promoting role of lithium andmagnesium chloride

Vladislav A. Tuskaev a,*, Svetlana C. Gagieva a, Victor I. Maleev b, Alexandra O. Borissova b,Mikhail V. Solov’ev a, Zoya A. Starikova b, Boris M. Bulychev a

aDepartment of Chemistry, M. V. Lomonosov Moscow State University,1 Leninskie Gory, 119992 Moscow, Russian FederationbA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow, Russian Federation

a r t i c l e i n f o

Article history:Received 13 April 2013Received in revised form16 June 2013Accepted 17 June 2013Available online 25 June 2013

Keywords:ZieglereNatta catalystTitaniumZirconium

* Corresponding author. Fax: þ7 495 932 8846.E-mail addresses: sgagieva@yandex.ru, tuskaev@y

0032-3861/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.polymer.2013.06.041

a b s t r a c t

Coordination compounds of titanium (IV) and zirconium (IV) with tetra-aryl-1,3-dioxolan-4,5-dimethanol (1,2) derivatives were synthesized and characterized by NMR- and IR-spectroscopy and X-ray crystallography. It was demonstrated that titanium dichloride complexes (5e6, 9e12) when treatedwith MAO, TMA or TIBA are inactive in ethylene polymerization catalysis. However, these compoundsbecome catalytically active in presence of lithium or magnesium chlorides. It was found that themagnitude of the resulting catalytic activity correlates with the following factors: mode of non-transitionmetals chlorides introduction to the reaction mixture, the nature of activator, and its overall amount.Resulting catalytic activity varied between 54 and 3500 kg PE/mole Ti٠h٠bar. Formed polymer was alinear polyethylene of high and ultrahigh molecular weight (over 5.95 105 g/mole) with high poly-dispersity index. Possible mechanisms of lithium and magnesium chlorides ability to promote the cat-alytic process were proposed.

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1. Introduction

The quest for new, inexpensive, highly efficient, and stereo-specific catalysts for olefin polymerization, capable of combiningthe benefits of homogeneous as well as classic heterogeneousZieglereNatta catalysts, has resulted in an increased interest ininvestigation of post-metallocene catalysis. There are very few re-ports related to the chiral post-metallocene catalytic systemscapable of synthesis stereoregular polyolefins [1e8]. Theoretically,such systems can compete with currently used metallocene cata-lysts which are expensive and hard to synthesize [9,10].

Tetra-aryl-1,3-dioxolan-4,5-dimethanol derivatives (TADDOLs)are chiral ligands widely used in asymmetric organic synthesis.Their complexes with Ti(IV) have unique catalytic properties inreactions requiring the CeC bond formation (nucleophilic additionto electrophiles and DielseAlder reactions [11]). Similarity of thesereactions to olefin polymerization process suggests that abovecomplexes can effectively catalyze polyolefin synthesis as well;

andex.ru (V.A. Tuskaev).

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while modification of ligand steric hindrance might alter chaintransfer rate and therefore regulate the molecular weight ofresulting polymer.

Original reports of chiral TADDOLecontaining complexesapplication for olefin polymerization [12,13] have indicated that(R,R)-TADDOL∙TiCl2 complexes when treated with methyl-alumoxane (MAO), demonstrate catalytic activity in ethylenepolymerization at 3e530 kg PE/mol Ti٠h٠bar level and result inpolymer products with molecular weights ranging from 300,000to 600,000. It was noted, however, that this catalytic activity canbe observed only in presence of synthesis byproduct e lithiumchloride [14]. It was demonstrated that once LiCl is removed fromreaction mixture, catalytic properties of complex disappear aswell. Hence, it was assumed that catalytic activity of [(R,R)-TAD-DOL∙TiCl2 e LiCl e NAP] system is due to the products of sec-ondary coordination. Recently [14,15], we have observed a similareffect of MgCl2 on ethylene and propylene polymerization cata-lyzed by titanium dichloride complex with a TADDOL ligandactivated with MAO.

This work summarizes the results of our studies of individualTi(IV) complexes with TADDOL ligands and their catalytic proper-ties, upon activation with aluminum- and magnesium-organic

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e44624456

compounds and comparison of their catalytic activities to the sys-tems that contain byproducts of complex formation in ethylenepolymerization reactions.

2. Results and discussion

Synthesis of (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraaryl-1,3-dioxolan-4,5-dimethanol derivatives (ligands 1 and 2) was performedaccording to reported methods [16,17]. As previously reported,direct interaction of TADDOLs (1,2) with Ti(OiPr)4 results in di-isopropylate complexes of titanium 3 and 4 [18]. Once reactedwith Me3SiCl or SiCl4 they yield dichloride derivatives 5 and 6(Fig. 1, Reaction 1) [19]. The same compounds were synthesized bysymmetrization reaction occurring when spiro-complexes (7 and8) interact with titanium (IV) chloride (Reaction 2) [20]. Com-pounds 5 and 6 obtained by either method matched the reportedcharacteristics.

Direct interaction of ligands 1 and 2 with titanium dichlorodiisopropylate (TiCl2(O-iPr)2) results in formation of dichlor-idotitanium(IV) complexes (9, 10) in one step (Scheme 1, Reaction3) [21]. However, in this case complex will include two additionalsolvating molecules of isopropanol. Solvation takes place duringthe interaction of either 1 or 2 with TiCl4 in ether or THF, as well(Reaction 4, complexes 11 and 12). In either case, reaction yieldscoordination saturated compounds LTiCl2∙L20, where L0 ¼ THF,iPrOH (Scheme 1).

Resulting complexes were characterized by NMR- and IR-spec-troscopy’s, as well as element analysis. Structure of 10 was deter-mined by X-ray and presented in Fig. 1. The lengths of main bondsand the bond angles for this compound are presented in Table 1.

Titanium atom in 10 has distorted octahedral surrounding,created by atoms of chlorine and oxygen of the initial ligand, as wellas oxygen atoms of isopropanol. Chlorine atoms are positionedapically on either side of the plane formed by oxygen atoms P(3)eP(4)eP(5)eP(6). The Cl(1)eTi(1)eCl(2) angle is equal to162.04(3)�. The Ti(1)eO(3) and Ti(1)eO(4) distances are essentiallyidentical and equal to 2.16 �A. Similarly, Ti(1)eO(1) and Ti(1)eO(2)bonds lengths are nearly identical, both about 1.79�A. Interestingly,

Fig. 1. The structure of complex 10 according to single-crystal X-ray diffraction study(hydrogen atoms are not shown, PfPH e C6F5).

Scheme 1. Methods of Ti(IV) e TADDOL complexes synthesis.

lengths of Ti(1)eCl(1) and Ti(1)eCl(2) bonds differ from each otherand are equal to 2.298(1) and 2.370(1)�A, respectively. According tothe structural analysis, complex 10 has the symmetry close to thatof S2, disregarding the conformation of isopropanol moleculespresent in the titanium coordination sphere.

NMR experiments have confirmed that similar coordination isretained in solution as well. It was demonstrated from NMR ex-periments that complex 9 has the same overall structure as 10.

Table 1Selected bond lengths (�A) and angles (deg.) for 10.

Ti(1)eO(1) 1.7930(17) Ti(1)eO(4) 2.1619(18)Ti(1)eO(2) 1.7858(17) Ti(1)eCl(1) 2.2976(8)Ti(1)eO(3) 2.1637(19) Ti(1)eCl(2) 2.3696(7)O(1)eTi(1)eO(2) 95.32(8) O(2)eTi(1)eCl(1) 98.20(6)O(1)eTi(1)eO(3) 90.93(8) O(3)eTi(1)eCl(1) 87.94(6)O(1)eTi(1)eO(4) 173.66(8) O(4)eTi(1)eCl(1) 86.16(6)O(2)eTi(1)eO(3) 170.80(8) O(1)eTi(1)eCl(2) 96.35(6)O(2)eTi(1)eO(4) 90.64(7) O(2)eTi(1)eCl(2) 94.46(5)O(3)eTi(1)eO(4) 82.90(7) O(3)eTi(1)eCl(2) 78.11(6)O(1)eTi(1)eCl(1) 95.11(6) O(4)eTi(1)eCl(2) 80.99(5)

Cl(1)eTi(1)eCl(2) 96.68(6)

Scheme 2. Reaction products of the lithium salt of the ligand 2 and TiCl4.

Table 2Selected bond lengths (�A) and angles (deg.) for 17.

Ti(1)eO(1) 2.464(2) Ti(1)eCl(1) 2.2694(9)Ti(1)eO(2) 1.829(2) Ti(1)eCl(2) 2.2219(10)Ti(1)eO(3) 2.165(2) Ti(1)eCl(3) 2.2032(10)O(1)eTi(1)eO(2) 70.44(8) O(2)eTi(1)eCl(2) 101.61(8)O(1)eTi(1)eO(3) 71.00(8) O(2)eTi(1)eCl(3) 97.95(8)O(2)eTi(1)eO(3) 75.24(8) O(3)eTi(1)eCl(1) 80.37(6)O(1)eTi(1)eCl(1) 81.20(5) O(3)eTi(1)eCl(2) 92.04(6)O(1)eTi(1)eCl(2) 162.48(6) O(3)eTi(1)eCl(3) 167.26(6)O(1)eTi(1)eCl(3) 96.68(6) Cl(1)eTi(1)eCl(2) 100.77(4)O(2)-Ti(1)-Cl(1) 147.25(7) Cl(1)eTi(1)eCl(3) 101.38(4)

Cl(2)eTi(1)eCl(3) 99.95(4)

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e4462 4457

It should be noted that complexes 5 and 6 can not be obtained inpure form by traditional method that utilizes lithium- ormagnesium-organic derivatives (according to Reactions 5 and 6,Scheme 1) as reaction byproducts (lithium and magnesium chlo-rides) can not be completely removed from reaction mixture; smallamounts of these salts are still found in the target products evenafter 4e5 cycles of recrystalization. This observation is an indirectevidence of the secondary complex formation. Regrettably, wecould not obtain these adducts in the sufficient purity to confirmtheir structure.

It appears that purification of the labile LTiCl2�MCln products isfurther complicated by continuing structural rearrangementswithin the complex. It was observed that after 2 weeks of incuba-tion of dilithium salt of the ligand with TiCl4, instead of expected 6,small amounts of 17 (Scheme 2) are precipitating from the reactionmixture. Structure of 17 is presented in Fig. 2; the main bondlengths and angles are presented in Table 2

The coordination polyhedron of the titanium atom in 17 (Fig. 2)can be described as a distorted trigonal antiprism; the angle be-tween Cl(1)Cl(3)O(1) and Cl(2)O(2)O(3) planes is 14�; other bondlengths and angles are presented in Table 2. Such coordinationpolyhedra are characteristic for spatially constrained complexes, forexample Schiff base polydental complexes [22]. All TieCl bondshave very similar lengths, which is signifies their overall similarity.Meanwhile, the differences in TieO bond lengths are more

Fig. 2. The structure of complex 17 according to single-crystal X-ray diffraction study(hydrogen atoms are not shown, PfPH e C6F5).

dramatic: Ti(1)eO(2) 1.829(2) (formally covalent bond), Ti(1)eO(1)2.464(2), Ti(1)eO(3) 2.165(2) �A (dative bonds).

All attempts to synthesize the dichloride TADDOL complex ofzirconium have failed to yield desired product. All tested combi-nations of starting materials and/or reaction conditions have yiel-ded a very stable neutral tris-adduct (TADDOL)3Zr (Fig. 3). Bondlengths and angles for this complex are presented in Table 3.

The coordination polyhedron of zirconium can be described as anearly perfect antiprism; the angle between O(1)O(1A)O(1B) andO(2)O(2A)O(2B) planes is 2.2�; ZreO bond lengths vary in prettywide range of 2.033(8)e2.142(9) �A, which is typical for complexeswith high coordination number [23].

Chemical behavior of 18 is quite different from that of the Tispiro-complex. When 18 is treated with the excess of ZrCl4 or SiCl4,no traces of dichloride complex can be detected.

It was found that the TADDOL dichloride complexes can beobtained only from Ti tetraisopropylate with subsequent treatmentof the di-isopropoxy intermediate with either silicon chlorides orby symmetrization reaction from spiro-complexes 7 or 8. All otherreaction conditions result in either the respective adduct productsof isopropanol, THF, lithium or magnesium chlorides; the productof ligand rearrangement (17); or unidentifiable product. In case ofzirconium, the only resulting product was stable tris-TADDOLcomplex.

We have evaluated catalytic activity of these compounds inethylene polymerization. Results of these studies are summarizedin Table 4. Some findings are somewhat unexpected. All individualdichlorides or respective isopropanol or THF complexes (3e10),when treated with standard Ziegler cocatalysts e triisobutylalu-minum (TIBA), trimethylaluminum (TMA) or methylalumoxane

Fig. 3. The structure of complex 18 according to single-crystal X-ray diffraction study(hydrogen atoms are not shown).

Table 3Selected bond lengths (�A) and angles (deg.) for 18.

Zr(1)eO(1) 2.070(8) Zr(1)eO(1B) 2.047(8)Zr(1)eO(2) 2.033(8) Zr(1)eO(2A) 2.061(8)Zr(1)eO(1A) 2.096(8) Zr(1)eO(2B) 2.152(9)O(1)eZr(1)eO(2) 88.6(3) O(2)eZr(1)eO(1B) 107.0(3)O(1)eZr(1)eO(1A) 82.5(3) O(2)eZr(1)eO(2B) 85.1(3)O(1)eZr(1)eO(2A) 107.6(3) O(1A)eZr(1)eO(2A) 88.4(4)O(1)eZr(1)eO(1B) 85.7(3) O(1A)eZr(1)eO(1B) 83.6(3)O(1)eZr(1)eO(2B) 168.7(3) O(1A)eZr(1)eO(2B) 105.4(3)O(2)eZr(1)eO(1A) 165.7(3) O(2A)eZr(1)eO(1B) 163.5(3)O(2)eZr(1)eO(2A) 83.6(3) O(2A)eZr(1)eO(2B) 81.1(3)

O(1B)eZr(1)eO(2B) 87.1(3)

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e44624458

(MAO), were either completely inactive or demonstrated a very lowcatalytic activity.

However, it was found that dichloride complexes 13 and 14,synthesized according to Reaction 5 (Scheme 1) via lithium salt ofTADDOL derivatives and containing residual amounts of lithiumupon recrystallization, do possess a notable catalytic activity in

Table 4Ethylene polymerization results using complexes 3e18 (ethylene pressure 1 bar, time of

Run Complex Activator Al/Ti Aa

1 3 MAO 300 e

2 3 DEAC/Bu2Mgd 300 11093 4 NAP 300 e

4 5 NAP 300 Traces5 5 MAO 400 e

6 5 þ LiClb NAP 400 547 5 þ LiClb TNA 400 Traces8 5 þ MgCl2b MAO 400 Traces9 5 þ MgCl2b TMA 400 7210 5 þ MgCl2b TIBA 400 Traces11 6 NAP 300 Traces12 7 NAP 300 Traces13 8 NAP 300 Traces14 9 NAP 400 Traces15 9 TNA 400 Traces16 9 DEAC/Bu2Mgd 300 168717 9 DEAC/Bu2Mgd 500 305718 10 MAO 300 e

19 10 TMA 300 e

20 10 TIBA 300 e

21 10 DEAC/Bu2Mgd 500 168522 10 DEAC/Bu2Mgd 300 306623 11 MAO 300 Traces24 11 DEAC/Bu2Mgd 500 195025 12 NAP 300 Traces26 12 DEAC/Bu2Mgd 500 215527 13 MAO 400 58428 13 MAO 1000 71829 13 DEAC/Bu2Mgd 500 229030 14 MAO 1000 78631 14 DEAC/Bu2Mgd 500 289632 15 MAO 100 5833 15 MAO 400 57134 15 MAO 1000 137335 15 MAO 2000 114536 15 TMA 300 74437 15 TIBA 300 137438 15 DEAC/Bu2Mgd 300 314339 16 NAP 300 62940 16 NAP 1000 268841 16 TNA 300 165742 16 TIBA 300 70043 16 DEAC/Bu2Mgd 500 350244 17 NAP 1000 Traces45 18 NAP 1000 Traces

a A e activity is expressed as kg PE/mole Ti٠h٠bar.b Ready forms of the chlorides were introduced to the system as Ti/Li ¼ 2 j Ti/Mg¼ 2.c Ins. in TCB e insoluble in 1,2,4-trichlorobenzene.d The molar ratio Al:Mg in the binary activator is 3:1.

ethylene polymerization reaction. Moreover, addition of fine sus-pension of LiCl orMgCl2 to the catalytically inert complex 5 resultedin a minor resurgence of catalytic activity (runs 6e10, Table 4).Above suspensions can be obtained by mixing butyllithium ordibutylmagnesium with HCl solution in toluene.

These results provide an evidence of Li or Mg chlorides directinvolvement in formation of active catalytic systems. Indeed, if Ticomplexes 13e16 are not purified from the reaction byproducts eLiCl or MgCl2, and used “as is”, instead of repurified individualcompounds, catalytic activity of such systems increases dramati-cally when pretreated with any of traditional activators.

As outlined in Table 4, systems containing LiCl are overall lessactive than the ones containing MgCl2. When MAO is used as cat-alytic activator, the peak of activity is observed at Al/Ti ratio of 1000(runs 32e35, pre-catalyst 15, Table 4). Further increase of this ratioleads to the decrease of catalytic activity.

It was reported earlier that catalytic activity increases signifi-cantly when perfluoroorganic compounds are used as ligands(possible mechanism of this effect was discussed in Ref. [24]).

polymerization 30 min, S(Ti) ¼ 5.00 10�6 mol/L, temperature 300 �S, toluene).

Mw Mn Mw/Mn Mp, �C

6.71 105 1.27 105 5.3 140

Ins. in TCBc 145

7.50 105 1.10 105 6.8 141

1.12 106 1.95 105 5.8 143Ins. in TCBc Ins. in TCBc Ins. in TCBc 147

9.89 105 1.16 105 8.5 142Ins. in TCBc Ins. in TCBc Ins. in TCBc 145

1.08 106 1.40 105 7.7 143

9.98 105 1.45 105 6.9 1417.90 105 1.61 105 4.9 140Ins. in TCBc Ins. in TCBc Ins. in TCBc 145

Ins. in TCBc Ins. in TCBc Ins. in TCBc 1471.14 106 1.58 105 7.2 1425.95 105 1.24 105 4.8 139Ins. in TCBc Ins. in TCBc Ins. in TCBc 146Ins. in TCBc Ins. in TCBc Ins. in TCBc 147Ins. in TCBc Ins. in TCBc Ins. in TCBc 145Ins. in TCBc Ins. in TCBc Ins. in TCBc 148Ins. in TCBc Ins. in TCBc Ins. in TCBc 1466.86 105 8.2 104 8.4 1429.96 105 1.54 105 6.4 143Ins. in TCBc Ins. in TCBc Ins. in TCBc 145Ins. in TCBc Ins. in TCBc Ins. in TCBc 148

Ins. in TCBc Ins. in TCBc Ins. in TCBc 148Ins. in TCBc Ins. in TCBc Ins. in TCBc 148

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e4462 4459

In LiCl-containing systems reported herein (13, 14), substitution ofphenyl moieties of the ligand by perfluorophenyl ones during MAOactivation of the system had no significant impact on catalytic ac-tivity (runs 27, 28, 30). Interestingly, MgCl2-containing complexesdisplay a different pattern of behavior; when ratio of AlMAO/Ti islow. Perfluoro-containing complexes are notably less active thantheir analogs lacking the fluorine moieties (runs 32, 33, 36, 37 vs.39, 41e43). However when the AlMAO/Ti ratio reaches 1000, theactivity of fluorine-containing complexes increases approximatelytwo times (runs 30 and 34, 35).

The differences in catalytic activities of systems 15 and 16 can bedemonstrated evenmore profoundlywhen TNA or TIBA is used forthe activation. System 15, containing non-fluorinated ligand 1,reaches the maximum of catalytic activity when 300 equivalents ofTIBA are used. If TMA is used instead, activity of the resulting sys-tem decreases 2 times. Notably, the monomer consumption by thelater system stays the same through the entire process, signifyingthe TMA doesn’t cause catalyst degradation as observed with FIcatalysts [25e27]. Fluorine-containing system 16 displays theopposite character; its activity is fairly low in presence of TIBA,while addition of 300 eq. of TMA results in reasonably high catalyticactivity (1657 kg PE/mol Ti٠hr).

Assuming the cationic nature of post metallocene catalyst activesite, such a behavior can be explained as following: to form a{LTi(þ4)R}þ{A}� type ion couple, 15 needs a voluminous, weak-coordinating counterions, such as in MAO or TIBA. To activate 16,containing sterically hindered C6F5-groups, a smaller TMA is moreefficient; while larger activators can not approach the core to forman ion pair.

Overall, presence of just 2 equivalents of Li or Mg chlorides inthe system leads to one to three orders of magnitude increase of itscatalytic activity. Time of introduction and the form of these chlo-rides plays an important role in the resulting catalytic activity.Addition of fine dispersion of these salts to purified TADDOLcomplexes results in only modest increase of catalytic activity,while their formation during reaction (in statu nascendi) results in asubstantially more notable catalytic activity of the resulting system.The highest catalytic activity (w3500 kg PE/mol٠h٠bar) was ach-ieved in 16 formed in statu nascendi as described above and acti-vated by MAO (run 40). This observation does indirectly confirmsthe formation of secondary complex, although other explanationsare also possible.

For example, magnesium-organic compounds themselves canserve as activators. Earlier works describe application of universalbinary activator, consisting of DEAC and Bu2Mg (usually in 3:1ratio) for all the types of Ziegler, metallocene, and post-metallocene catalysts [28,29]. The results of the ethylene poly-merization catalysis using complexes 9, 10 and binary activator aresummarized in Table 4. It is evident that purified complexes 9e12,that can not be activated by usual alumo-organic compounds,demonstrate reasonably high activity (1688e3064 kg PE/molTi٠h٠bar) when activated by mixture of DEAC and Bu2Mg (runs 16,17, 24, 25, 24, 26). It should be noted that in all the experimentswith Li and Mg salts present, the resulting polyethylene is char-acterized by very high molecular weight and insolubility in 1,2,4-trichlorobenzene at 135 �C. Resulting polymer is not branching,which is evident from the lack of 1378 cm�1 band in IR spectra,characteristic to the symmetric bending vibration of CH3e groups.Respectively, all resulting samples of polyethylene were charac-terized by high melting temperatures and degrees of crystallinity.PE obtained with 13/NAP system (run 28) has demonstrated amelting temperature of 145 �C and 55% of crystallinity at secondreheat. A PE obtained with the 15/NAP (1000 equivalents) systemhas demonstrated a melting temperature of 147 �C and 58% ofcrystallinity (run 34).

Thermodynamic calculations predict formation of Li and Mgchlorides as a result of the exchange Reactions 5e6 (Fig. 1), as well asthe interaction of binary activator components: MgBu2þ2AlEt2Cl ¼ MgCl2þ2AlEt2Bu. However, X-ray diffractometry could notidentify those species due to amorphous character of precipitate ob-tained from the reaction (either solution or suspension). That isdespite the fact that MgCl2 is de facto formed upon mixing of com-ponents of binary activator [28,29]. It should be noted that reportauthors [29] speculate that the unique properties of binary activatorwere the result of its ability to forman ionic salt {MgBu}þ{AlBuEt2Cl}�,which was expected to be a stronger Lewis Acid than the originalcomponents; and not due to the formation of MgCl2. However, wesuggest that Li orMg chlorides are equally important as theyappear tobe directly involved in catalyst formation. In other words we suggestthat thesechlorides arenotonlya structure formingelements,but alsoa structure modifying promoters of catalyst synthesis; not only theyare participating in the formation of catalytic centers, but they alsochanging the catalytic center intrinsic characteristics.

It should be emphasized that this kind of behavior is repre-sentative of only the Ti complexes with eOOe type of ligands.Additional experiments with phenoxyimine-based Ti complexestreated with different chlorides did not reveal any changes inresulting catalyst activity. This observation suggests that our pre-vious hypothesis [14] assuming the possibility of formation of ate-type bi-nuclear complexes Ti-mCl-Mg< or >Ti-mCl-Li< is incorrect.Although these are the well studied moieties common for the rareearth elements chemistry, it is more plausible that in the case oftitanium complexes, Mg or Li atoms are coordinated to the hydroxyloxygens of eOOe ligands. We deem the Mg coordination occurringthrough dioxolane moiety oxygen as much less probable since such5-member cyclic fragments would be much more constrained.

Each oxygen atom has 2 unshared electron pairs (Scheme 3) oneof which directed outside and another one inside the sevenmember ring. This arrangement of unshared electron pairs allowsthem to form a bimetallic binuclear “endo”-complex (Scheme 3). Itcan form even more complex structures in non-solvating environ-ments (Scheme 3).

Such assumption is reasonable as oxygen atoms with m3 coor-dination and MeO distances of 1.8e2.2 �A are quite common forcoordination complexes of transitional and non-transitional metalsand oxo-ligands. Also the presence of this kind of bonds in group 4metal complexes has been previously reported [30]. Formation of“exo”-complexes is still possible, but they should be substantiallyless stable, as complexes with eONe ligands (phenoxyimines, FI)have only one oxygen that can participate in formation of suchbond. Besides, we see no changes in complex catalytic activity uponaddition of MgCl2 which suggests that above can be correct.

The binding of oxygen atom unshared electron pairs can lead tosubstantial distortion of Ti coordination geometry, and overallelectron structure of catalyst active center. Distortion can be strongenough to cause the improved activity of complexes pretreatedwith TMA or TIBA, although the latter ones have weak activatingpotential for most of metallocenes and some post-metallocenescomplexes.

3. Conclusions

Finally, we would like to drive the analogy of results reportedherein with most classic heterogeneous ZieglereNatta catalyticsystems [31]. Most modern ethylene and propylene polymerizationcatalysts utilize the heterogeneous systems formed by MgCl2 withapplied TiCl4 and so called “internal” (ethylbenzoate or methyl-p-toluate) and “external” (diamines, polyethers) donors. Althoughthe exact function of these organic components in catalytic systemsis yet to be explained, it is quite reasonable to assume that they

Table 5Details of the data collection and refinement of 4, 17 and 18.

Parameter 4 17 18

Formula C37H24Cl2F20O6Ti C38H17Cl3F20O4Ti C100H94O12ZrM 1063.33 1071.77 1578.97T 100(2) K 100(2) K 153(2) KSpace group P 212121 P21 P 212121a, �A 13.6693(9) 9.4280(5) 13.138(4)B, �A 14.3972(9) 21.4270(12) 24.267(8)c, �A 20.3128(13) 9.8049(6) 24.710(7)A, � 98.6320(10)V, �A3 3997.6(4) 1958.29(19) 7878(4)Z 4 2 4Density, gcm�3 1.763 1.818 1.331m (MoKa), mm�1 0.488 0.562 0.207F(000) 2120 1060 3320Diffractometer SMART APEX

DUO CCDSMARTAPEX2 CCD

Bruker SMART 1000

Absorptioncorrection(MoKa)

Semiempiricalfromequivalents

Semiempiricalfromequivalents

Semiempiricalfrom equivalents

Scan technique Scan with 0.5step

Scan with 0.5step

Scan with 0.3 step

q max, � 29 29 29Number of

collected reflns31,407 22,770 41,952

Number ofindependentrflns (Rint)

10,613 (0.0441) 10,367 (0.0383) 9820 (0.1383)

Number ofobserved rflnswith I > 2s(I)

8440 8689 3291

wR2 0.0940 0.1080 0.1615R1 0.0388 0.0449 0.0676GOF 1.005 1.005 1.005r max/r min, e�3 1.045/�0.386 0.356/�0.735 0.526/�0.310

Scheme 3. Probable structures of LTiCl2 and MgCl2 coordination products.

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e44624460

might convert the classic ZieglereNatta catalytic system to thepost-metallocene one. That can explain the increase of system ac-tivity and in some cases, stereospecificity.

4. Experimental section

All manipulations were carried out according to the standardSchlenk techniques. Solvents for air- and moisture-sensitive re-actions were dried over sodium benzophenone ketyl and storedover the 3 or 4�A molecular sieves. The NMR spectra were recordedby Bruker WP-600 and Bruker ANY-400 instruments. IR spectrawere recorded on Magna-IR 750 instrument. Element analysis wasperformed on Carlo Erba-1106 or Carlo Erba-1108 instruments.

X-ray diffraction data for the single crystals of 4 were collectedusing a “Bruker SMART APEX DUO” CCD diffractometer, for thesingle crystals of 17e using “Bruker SMARTAPEX II” diffractometer,for the single crystals of 18 e using “Bruker SMART 1000” diffrac-tometer. The resulting images were integrated [32]. Precise unit celldimensions and errors were determined. Absorption correctionwas applied semiempirically using the SADABS program [33]. De-tails of X-ray data collection and subsequent refinement are listedin Table 5. Initially spherical atom refinements were undertakenwith SHELXTL PLUS 5.0 using the full-matrix least-squares method[34]. All non-hydrogen atoms were allowed to have an anisotropicthermal motion. Atomic coordinates, bond lengths, angles, andthermal parameters have been deposited at the Cambridge Crys-tallographic Data Center (CCDC 923013e923015). Gel chromatog-raphy was performed on Waters GPCV-2000 LC system equippedwith PLgel 5 mmMIXED-C column using 1,2,4-trichlorobenzene as asolvent at 135 �C and with polystyrene calibration standards.

Thermogravimetric analysis was done using the NETZSCH-STAJupiter449 C. All experiments were performed under the argonflow (100 ml/min) at temperatures between 300 and 400 �C; thetemperature ramping was 5 �C/min.

(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethanol 1 [16], (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(penta-fluorophenyl)-1,3-dioxolane-4,5-dimethanol 2 [17] (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethanolato-dichloro-bis(isopropanol) titanium 9 [21] were prepared accordingto literature procedures.

4.1. [(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethanolato-O,O0] diisopropoxy titanium(IV) (3)

To a solution of TADDOL (0.233 g, 0.5 mmol) in 3 ml of toluene,Ti(OiPr)4 (0.15 ml, 0.5 mmol) was added with stirring at room

temperature. After a reaction time of 5 h, the mixture was dried invacuo completely to remove any volatile materials. The residue wasredissolved in 5 ml of toluene:hexane (1:2) mixture. Beige precipi-tate was filtered out and washed with 2 ml of toluene. Yield: 68%.

1H NMR (CDCl3, d, J/Hz) 1.34 (s, 12H), 1.41 (s, 6H), 3.32 (s, 2H),3.86 (s, 2H). Calculated (%) for C37H42O6Ti: C, 70.47; H, 6.71; Ti, 7.60.Found (%): C, 70.18; H, 6.54; Ti, 7.18.

4.2. [(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(pentafluorophenyl)-1,3-dioxolane-4,5-dimethanolato-O,O’]-diisopropoxy titanium(IV) (4)

To a solution of ligand (2) (0.413 g, 0.5 mmol) in 5 ml of toluene,Ti(OiPr)4 (0.15 ml, 0.5 mmol) was added with stirring at room tem-perature. After a reaction time of 5 h, themixturewas dried in vacuo

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e4462 4461

completely to remove any volatile materials. The residue wasredissolved in 5 ml of toluene:hexane (1:2) mixture. Beige precipi-tate was filtered out and washed with 2 ml of toluene. Yield: 63%.

1H NMR (CDCl3, d, J/Hz) 1.34 (d, 12H), 1.41 (s, 6H), 3.32 (s, 2H),3.86 (s, 2H). Calculated (%) for C37H22F20O6Ti: C, 44.87; H, 2.24; Ti,4.84. Found (%): C, 44.30; H, 2.06; Ti, 4.76.

4.3. [(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethanolato-O,O0]dichlorotitanium (5)

To a solution of complex (3) (0.630 g, 1 mmol) in 25 ml oftoluene, SiCl4 (2 ml of 0.5 N solution in toluene; 1 mmol) wasadded. Mixture was stirred for 1 h at room temperature. Resultingsolution was evaporated; the residue was dried under vacuum.Yield: 0.570 g (95%).

1H NMR (CDCl3, d, J/Hz) 0.70 (s, 6H), 3.94 (s, 2H), 7.26e7.38 (m,12H), 7.39e7.47 (m, 4H), 7.47e7.55 (m, 4H). Calculated (%) forC31H28Cl2O4Ti: C, 63.83; H, 4.84; Cl, 12.15, Ti, 8.21. Found (%): C,64.30; H, 4.91; Cl, 11.94, Ti, 8.08.

4.4. (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(pentafluorophenyl)-1,3-dioxolane-4,5-dimethanolato-O,O0]-dichlorotitanium (6)

To a solution of complex (4) (0.990 g, 1 mmol) in 25 ml oftoluene, SiCl4 (2 ml of 0.5 N solution in toluene; 1 mmol) wasadded. Mixture was stirred for 1 h at room temperature. Resultingsolution was evaporated; the residue was dried under vacuum.Yield: 0.70 g (70%).

1H NMR (CDCl3, d, J/Hz) 0.96 (s, 6H), 5.34 (s, 2H). Calculated (%)for C31H8F20Cl2O4Ti: C, 39.48; H, 0.85; Cl, 7.52, Ti, 5.08. Found (%): C,39.33; H, 0.66; Cl, 7.38, Ti, 4.95.

4.5. Bis{(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethanolato -O,O0}-titanium (7)

To a solution of TADDOL (0.233 g, 0.5 mmol) in 2 ml of toluene,Ti(OiPr)4 (0.075 ml, 0.25 mmol) was added with stirring at 40 �C.After a reaction time of 10 h, the mixture was dried in vacuocompletely to remove any volatile materials. The residue wascrystallized from toluene:hexane (1:5) mixture. White precipitatewas filtered out and washed with 3 ml of hexane. Yield: 68%.

1H NMR (CDCl3, d, J/Hz) 1.52 (s, 12H), 3.24 (s, 4H), 7.18e7.40 (m,40H). Calculated (%) for C62H56O8Ti: C, 76.22; H, 5.78; Ti, 4.90.Found (%): C, 76.19; H, 5.70; Ti, 4.84.

4.6. Bis{(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(pentafluorophenyl)-1,3-dioxolane-4,5-dimethoxo}-Titanium (8)

To a solution of ligand (2) (0.413 g, 0.5 mmol) in 5 ml of toluene,Ti(OiPr)4 (0.075 ml, 0.25 mmol) was added with stirring at 40 �C.After a reaction time of 3 h, the mixture was dried in vacuocompletely to remove any volatile materials. The residue wascrystallized from toluene:pentane (1:7) mixture. White precipitatewas filtered out and washed with 2 ml of hexane. Yield: 60%.

1H NMR (CDCl3, d, J/Hz) 0.96 (s, 12H), 5.34 (s, 4H). Calculated (%)for C62H16F40O8Ti: C, 43.89; H, 0.95; Ti, 2.82. Found (%): C, 43.80; H,0.89; Ti, 2.77.

4.7. [(4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(pentafluorophenyl)-1,3-dioxolane-4,5-dimethanolato-O,O0]-dichloro-bis(isopropanol)titanium (10)

To a solution of ligand (2) (0.413 g, 0.5 mmol) in 5 ml of toluene,TiCl2(OiPr)2 (0.12 g, 0.5 mmol) in 2 ml of toluenewas added and left

unstirred for 1 h at room temperature. White precipitate wasfiltered out and washed with 2 ml of toluene. The yield was 82%. Toobtain the crystals suitable for X-ray crystallography, the productwas recrystallized from toluene:hexane (1:2) mixture.

1H NMR (CDCl3, d, J/Hz) 1.34 (s, 12H), 1.41 (s, 6H), 3.32 (s, 2H),4.51 (s, 2H), 5.65 (s, 2H). 19F NMR (CDCl3, d, J/Hz) �59.13 (br. s,4F), �61.33 (d, J ¼ 18.5 Hz, 4F), �73.62 (t, J ¼ 20.7 Hz, 2F), �74.21to �74.89 (m, 2F), �81.84 to �82.41 (m, 4F), �82.78 to �83.23 (m,4F). Calculated (%) for C37H22Cl2F20O6Ti: C, 41.87; H, 2.09; Cl, 6.68; F,35.80. Found (%): C, 42.48; H, 2.17; Cl, 6.60; F, 35.36.

4.8. (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetraphenyl-1,3-dioxolane-4,5-dimethoxo-dichloro-bis(tetrahydrofuran)titanium (11)

To a solution of TADDOL (0.466 g, 1.0 mmol) in 20 ml of ether,TiCl4 (0.14 ml, 1.30 mmol) was added with stirring at room tem-perature. After a reaction time of 30 min, 5 ml of THF was added tothe reaction mixture and reaction was stirred for another hour.Solvent was evaporated to the final volume of 10 ml and reactionwas cooled to �25 �C. Formed crystals were filtered out. Yield was0.45 g (56%). The mixture was dried in vacuo completely to removeany volatile materials. The residue was crystallized from toluene:-hexane (1:5) mixture. White precipitate was filtered out andwashed with 3 ml of hexane. The yield was 68%.

1H NMR (CDCl3, d, J/Hz) 0.66 (s, 3H), 1.88 (m, 8H), 4.09e3.86 (m,8H), 5.27 (s, 2H), 7.39e7.20 (m, 12H), 7.51e7.41 (m, 4H), 7.61e7.52(m, 4H). Calculated (%) for C39H44Cl2O6Ti: C, 64.38; H, 6.10; Cl, 9.75.Found (%): C, 64.39; H, 6.25; Cl, 9.55.

4.9. (4R,5R)-2,2-dimethyl-a,a,a0,a0-tetrakis(pentafluorophenyl)-1,3-dioxolane-4,5-dimethoxo-dichloro-bis(tetrahydrofuran)titanium (12)

To a solution of ligand 2 (0.826 g,1.0mmol) in 25ml of ether, TiCl4(0.14 ml, 1.30 mmol) was added with stirring at room temperature.After a reaction time of 30 min, 10 ml of THF was added to the re-actionmixture and reactionwas stirred for another hour. Solvent wasevaporated to the final volume of 10 ml and reaction was cooledto �25 �C. Formed crystals were filtered out. Yield: 0.49 g (52%).

1H NMR (CDCl3, d, J/Hz) 0.58 (s, 6H), 1.97 (m, 8H), 3.90e4.26 (m,8H), 5.10 (s, 2H). Calculated (%) for C39H24Cl2F20O6Ti: C, 43.09; H,2.20; Cl, 6.54, Ti, 4.33. Found (%): C, 42.89; H, 2.25; Cl, 6.40, Ti, 4.39.

Synthesisof13,14. A toluene solutionof the ligand (0.5mmol)wasplaced under argon in the flask equipped with a magnetic stirrer.Toluene solution of BuLi (1.05 mmol) was added dropwise whilestirring and cooling to�78 �C. Reactionmixturewas brought to roomtemperature and incubated for 30min. It was cooled again to�78 �Cand TiCl4 (0.50 mmol) was added. The reaction was brought to roomtemperature again and stirred for 12h. Resultingproductwasused forethylene polymerization without further purification.

Synthesis of 15,16. A 10-ml toluene solution of the ligand(0.50 mmol) was placed under argon in the flask equipped with amagnetic stirrer. n-Heptane solution of dibutylmagnesium(1.05 mmol) was added dropwise while stirring at �78 �C. Reactionmixturewas slowlybrought to roomtemperature and stirred for 4h.It was cooled again to �78 �C and TiCl4 (0.50 mmol) was added.Reactionwas brought to room temperature again. Resulting productwas used for ethylene polymerization without further purification.

5. Polymerization of ethylene

The polymerization of ethylene was performed in a 100-mlreactor (Parr Instrument Co.) equipped with a magnetic stirrer andinlets for loading components of catalytic systems and ethene at atotal pressure of ethene and toluene vapors of 1 bar. Toluene (50ml)

V.A. Tuskaev et al. / Polymer 54 (2013) 4455e44624462

and the necessary amount of a cocatalyst (Me3Al (TMA), (MeAlO)n(MAO), iBu3Al (TIBA), or Et2AlCl/Bu2Mg (DEAC/Bu2Mg)) were loadedin the reactor. The reactorwas heated to a specified temperature, andthe reaction mixture was saturated with ethylene. Polymerizationwas started by the addition of pre-catalyst to the reaction mixture.The pressure of ethylene was maintained constant during polymer-ization. Polymerizationwas stopped through the addition of 10%HClsolution in ethanol to the reactor. The polymer was filtered off,washed several times with watereethanol mixture, and dried undervacuum at 50e60 �C until a constant weight was achieved.

Acknowledgments

This study was supported by Russian Fund of FundamentalSciences (grants No’s 10-03-00926, 11-03-00297 and 11-03-12172)and The Ministry of education and science of Russian Federation(contract 8459).

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