NCN-Pincer Metal Complexes (Ti, Cr, V, Zr, Hf, and Nb) of the Phebox

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NCN-Pincer Metal Complexes (Ti, Cr, V, Zr, Hf, and Nb) of the Phebox Ligand (S,S)-2,6-Bis(40 -isopropyl-20-oxazolinyl)phenyl Alexey V. Chuchuryukin,†,‡ Rubin Huang,‡,^ Martin Lutz,§,|| John C. Chadwick,‡,^ Anthony L. Spek,§ and Gerard van Koten*,† †

Debye Institute for Nanomaterials Research, Organic Chemistry and Catalysis, and §Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands ‡ Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands ^ Laboratory of Polymer Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands

bS Supporting Information ABSTRACT: Reaction of (S,S)-2,6-bis(40 -isopropyl-20 -oxazolinyl)phenyllithium (i-Pr-Phebox-Li) (2a) with 4,40 -bis[P(chlorogold(I))diphenylphosphino]biphenyl [(dppbp)(AuCl)2] (5) afforded the new, bimetallic gold complex 4,40 -bis[P-(η1-Ci-Pr-Phebox-gold)diphenylphosphino]biphenyl [(P-Au(η1-Ci-Pr-Phebox))2(dppbp)] (6). Transmetalation of 6 with 2 equiv of Cl3MX (MX = TiOi-Pr, VCl, CrPy, ZrCl, HfCl, NbO) afforded the corresponding monopincer compounds [MCl2X(i-Pr-Phebox)] (M = Ti, V, Cr) (7) and [MCl2X(i-Pr-Phebox)]2 (M = Zr, Hf, Nb) (8) in high yields and the gold starting material 5, which could be quantitatively recovered and reused. The structures in the solid state of the digold compound 6, the monopincer compounds R-PheboxAu(PPh3) (R = i-Pr, t-Bu), and a number of Phebox-ETM complexes (7a, 7b, 7c, 8a, 8b, and 8c) were obtained. In each of these structures the i-Pr-Phebox monoanion is mer-N,C,N-tridentate bonded. The monopincer Phebox-Zr and -Hf compounds are dimeric because of two bridging chlorides, while the corresponding Nb compound has bridging oxygen atoms. Reaction of 6 with iron(III) chloride resulted in the formation of a N4(FeCl2)2 complex, characterized by X-ray crystal structure determination, comprising a bridging, tetradentate N4 ligand formed by CC coupling of two Phebox anions to a biphenyl species. The new Phebox complexes 7 and 8 have been tested as olefin polymerization precatalysts. Rapid catalyst deactivation was observed in ethene polymerization under homogeneous conditions, whereas stable activity was obtained after immobilization on MgCl2-based supports. From preliminary investigations on the reaction of 8a with either methylmagnesium chloride or methyllithium we assume that the low reactivity in homogeneous polymerization is due to the alkylation of the Phebox ligand.

’ INTRODUCTION Design and application of novel olefin polymerization catalysts based on pincer-type transition metal compounds has attracted considerable attention over the past decade. In particular a large number of NNN-pincer-type complexes of middle and late transition metals have been reported due to the relative ease of their preparation, accompanied in some cases by remarkable catalytic properties.1 Much less work has concerned the synthesis of ECE-pincer-type early transition metal (ETM) compounds containing a σ-aryl donor ligand with two ortho-chelating substituents with neutral E (N, O, P) donor atoms. Some NCN-type pincer metal compounds of early and middle transition metals have been reported and tested with some success as olefin polymerization precatalysts.2 CNN-pincer-type organozirconium and organohafnium compounds have also been applied as olefin polymerization precatalysts.3 It is well known that chiral catalysts can be particularly useful for the stereospecific synthesis of polymers. As a relatively simple chiral, monoanionic, NCN-type ligand, which can be prepared from inexpensive natural chiral precursors, 2,6-bis(20 -oxazolinyl)phenyl r 2011 American Chemical Society

(Phebox)4 was chosen. A large number of Phebox complexes of late transition metals have already been reported, which commonly were synthesized by either direct cyclometalation5a or transmetalation reaction from the corresponding organolithium5b or organotin precursors.5c,d However, in a number of cases we were unsuccessful in preparing NCN-pincer metal complexes of higher oxidation state ETMs from the corresponding Li or Mg precursor reagents because of the occurrence of uncontrollable reductive side reactions. Recently, we found that aryl gold compounds, because of their lower nucleophilicity than the organolithium reagents, can be convenient precursors for the synthesis of corresponding mono-ECE-pincer metal complexes of other transition metals via a direct transmetalation reaction.6 In particular, the use of the bimetallic gold complexes synthesized from 4,40 -bis(diphenylphosphino)biphenyl bis(gold(I) chloride) (5, (AuCl)2(dppbp), vide infra Scheme 3) is particularly useful, due to the fact that 5, which is quantitatively re-formed as a product of the transmetalation process, is poorly soluble in many Received: February 22, 2011 Published: April 20, 2011 2819

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Scheme 1. Lithiation of 1a

Conditions: (i) THF, 78 C, 10 min, yield of 3 99%, [R]25589 = 91.3; (ii) pentane, 78 C to rt, 4 h, yield of 3 96%, [R]25589 = 79.7.

Scheme 2. Synthesis of (S,S)-Phebox-gold(I) Triphenylphosphine Complexes 4a and 4b

Figure 1. Displacement ellipsoid plot of 4a (50% probability). Only one of two independent molecules is shown. Hydrogen atoms are omitted for clarity.

organic solvents and can be easily separated and recycled.2d In this paper we report the successful synthesis of a series of mono-Phebox ETM complexes that otherwise are difficult to obtain via the common Grignard or organolithium transmetalation reactions. These complexes appear to have low catalytic activity in ethene polymerization under homogeneous conditions, most likely because they are highly reactive to alkyl metal cocatalysts such as methylaluminoxane (MAO), as was concluded from the results of preliminary reactions of (i-Pr-PheboxCl2ZrCl)2, 8a, with MeMgCl or MeLi.

’ RESULTS AND DISCUSSION For the lithiation of (S,S)-R,H-PheboxBr (R= i-Pr 1a, t-Bu 1b) a modified literature procedure was used.5d Lithiation of 1a with n-BuLi was performed in THF at 78 C. The in situ formed (i-Pr,H-Phebox)Li (2a) was used at the same temperature within 10 min of its preparation in subsequent experiments. In one of these experiments the Phebox-lithium product was hydrolyzed by water, affording i-Pr,H-PheboxH (3) in 99% yield as a white solid (Scheme 1). The optical rotation measured for this product in dichloromethane ([R]25589 = 91.3) was identical to that previously reported in the literature,4 confirming that the lithiation procedure followed leaves the chiral centers in the Phebox ligand unaffected. In a further experiment lithiation of 1a was carried out in pentane at 78 C. The resulting solution was stirred at room temperature for 4 h followed by hydrolysis. The yield of 3 was 96% (yellow oil slowly solidifying at room temperature), but the optical rotation of the product in dichloromethane, [R]25589 = 79.7, was somewhat lower than that of 3 obtained from the reaction in THF, vide supra. These results show that in this case the lithiation reaction caused partial racemization of the Phebox ligand. Reasons for the lower selectivity of the lithiation reaction in pentane are the low solubility of 1a in this solvent at 78 C, thus requiring longer reaction times (4 h) and higher reaction temperatures (78 C to room temperature) to achieve complete conversion of the starting Phebox-aryl bromide ligand.

Figure 2. Displacement ellipsoid plot of 4b (50% probability). Only one of two independent molecules is shown. Hydrogen atoms are omitted for clarity.

Monometallic NCN-Phebox gold(I) complexes (4a and 4b) were synthesized by reacting the corresponding organolithium compounds (2a and 2b) with (triphenylphosphino)gold chloride. These (S,S)-Phebox-gold(I) complexes were isolated in good yields as pure, colorless solids (Scheme 2) after recrystallization from diethyl ether solution. Structures in the solid state of both 4a and 4b were determined by X-ray crystallography (Figure 1, Figure 2). The (S,S)-Phebox anions in both complexes are η1-C-bound to the gold cations via Cipso without additional NAu coordination of the ortho-oxazolinyl N-substituents, which is similar to the bonding motifs found for (η1-C-Me,Me-Phebox)AuPPh32d and for earlier synthesized (η1-C-NCN)AuPPh3 (NCN is 2,6-(Me2NCH2)2C6H3-anion)6 in the solid state. Reaction of 4,40 -bis(diphenylphosphino)biphenylbis(gold(I) chloride) (5, (AuCl)2(dppbp))2d with 2 equiv of 2a in THF resulted in the formation of bis{(S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl) 2820

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phenyl]gold(I) (dppbp) (6, P,P0 -(η1-C-i-Pr-PheboxAu(I))2(dppbp)) in 88% yield (Scheme 3). Initially, crude 6 was crystallized from methanol. A crystallographic study, however, indicated that 6 crystallized as 6 3 3MeOH, having three methanol molecules in the lattice bound via hydrogen bonds to each molecule of 6 (Figure 3A, SI). It is important to note that the presence of methanol would hamper the further use of 6 in transmetalation experiments to synthesize the corresponding ETM complexes. Whereas major amounts of methanol could be removed from 6 3 3MeOH by drying the samples under vacuum at 20100 C, this treatment also caused melting and partial decomposition of 6 with formation of a red glassy substance. Complete removal of residual amounts of methanol still present in pure, predried samples of 6 could be achieved by subsequent recrystallization from benzene. Table 1. Selected Distances [Å] and Angles [deg] in the Crystal Structures of 4a and 4ba 4a

a

4b

Au1C11

2.060(2)

2.057(7)

Au1P1

2.2758(6)

2.2807(18)

Au1N11

3.049(2)

3.046(4)

Au1N12

3.053(2)

4.285(3)

Au1O11 Au1O12

4.5425(18) 4.6108(19)

4.721(7) 3.163(3)

C11Au1P1

172.72(7)

178.1(2)

Only one of the two independent molecules is listed, respectively. For full data see the SI.

Finally 6 was obtained as a benzene solvate (see Figure 3 for its structure in the solid state), and this material was used in the further experiments reported below. The bis-organogold compound 6 3 C6H6 reacted smoothly at room temperature with a variety of transition metal chlorides, affording the corresponding i-Pr,H-Phebox transition metal complexes 7 and 8, with (dppbp)gold(I) chloride (5) being formed as coproduct (Scheme 4). Reaction of 6 with titanium isopropoxide trichloride in THF resulted in formation of (S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl) phenyl]titanium(IV) isopropoxide dichloride (7a) in 73% yield. X-ray crystal structure determination was performed for a single crystal of 7a grown from ether/pentane (Figure 4). The geometry of the titanium center in this compound is similar to that of nonchiral [2,6-bis(40 -dimethyl-20 -oxazolinyl)phenyl]titanium isopropoxide dichloride.2d An attempt to synthesize (S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl)phenyl]titanium trichloride using titanium(IV) tetrachloride in a similar way failed, although reaction of 6 3 C6H6 with titanium(IV) chloride did occur and precipitation of the expected (dppbp)gold(I) chloride (5) from the reaction mixture was observed. Obviously, together with the anticipated metal exchange reaction, other side reactions between the starting materials occurred. A possible reaction is cleavage of the oxazoline ring by the highly Lewis-acidic and oxophilic titanium(IV) chloride, which is known to cleave some ethers (e.g., diisopropyl ether, anisole).7 Moreover, 2-oxazolines are also susceptible to cleavage in acidic media.5a Reaction of 6 3 C6H6 with vanadium(IV) tetrachloride in benzene resulted in formation of (S,S)-[2,6-bis(40 -isopropyl-20 oxazolinyl)phenyl]vanadium(IV) trichloride (7b) in 82% yield

Scheme 3. Synthesis of Bimetallic Bis-Phebox-gold(I) dppbp Complex 6

Figure 3. Displacement ellipsoid plot of 6 3 C6H6 (50% probability). Hydrogen atoms and benzene solvent molecule are omitted for clarity. Selected distances [Å], angles [deg], and torsion angles [deg] of 6 3 C6H6: Au1C11 2.070(6), Au2C21 2.059(7), Au1P1 2.2795(17), Au2P2 2.2740(16), C34C44 1.494(4), C11Au1P1 177.28(19), C21Au2P2 173.66(19), C33C34C44C45 1.3(7). (For the full data and for 6 3 3MeOH see the SI.) 2821


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Scheme 4. Transmetalation Reaction of Bimetallic Organogold Compound 6 3 C6H6

Figure 4. Displacement ellipsoid plot of 7a (50% probability). Hydrogen atoms are omitted for clarity.

and precipitation of 5 (99%), which could be easily separated by filtration. Compound 7b crystallized from benzene/pentane solution as a benzene solvate (Figure 5). Interestingly, upon reacting 6 with V(THF)3Cl3 in THF, not a single product separated from the solution, again indicating that a competing reaction had occurred. In this case a disproportionation of the vanadium(III) compound into vanadium(II) and vanadium(IV) compounds could be responsible. EPR spectra of 1 mM solutions of 7b in benzene and toluene were measured. Spectra in both solvents were identical and revealed the presence of two different species in solution with Aiso = 101 and 111 G, respectively. This could indicate the presence of species with either N- or O-coordination of the oxazoline rings in solution.8

Figure 5. Displacement ellipsoid plot of 7b (50% probability). Hydrogen atoms and benzene solvent molecule are omitted for clarity.

Reaction of 6 with Cr(THF)3Cl3 in THF resulted in formation of the corresponding pincer chromium compound, which was isolated as a pyridine adduct in 75% yield (Figure 6). Attempts to crystallize the reaction product (S,S)-[2,6-bis(40 isopropyl-20 -oxazolinyl)phenyl]chromium(III) dichloride itself from dichloromethane/pentane, i.e., in the absence of pyridine, resulted in the formation of an insoluble solid that, however, could be redissolved in pyridine. From the latter solution crystals of 7c were obtained. These observations suggest that the primary transmetalation reaction indeed afforded (S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl)phenyl]chromium dichloride, but that attempts to crystallize it resulted in the formation of a coordination polymer that can be broken up into mononuclear species by coordination with pyridine, affording 7c. The broad applicability of the gold transmetalation method is underlined, as zirconium(IV) and hafnium(IV) chlorides also reacted smoothly with 6 3 C6H6 in THF to give the corresponding 2822


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dimeric, monopincer i-Pr,H-Phebox compounds (8a,b), which were separated as benzene solvates by crystallization from benzene/hexane in 82% and 83% yield, respectively (Figures 7 and 8). An attempt to synthesize heptacoordinate, monomeric (S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl)phenyl]niobium(V) tetrachloride in a similar manner, starting from niobium(V) chloride in THF, resulted in formation of dimeric (S,S)-[2,6bis(40 -isopropyl-20 -oxazolinyl)phenyl]niobium dichloride oxide (8c). This is probably a result of a primary reaction of niobium(V) chloride with THF affording niobium trichloride oxide,9 then followed by its transmetalation with 6 3 C6H6. No reaction occurred when tantalum(V) chloride was used instead of niobium(V) chloride, possibly because of the low stability of tantalum trichloride oxide.9 Organoniobium compound 8c was crystallized from benzene/pentane. X-ray crystal structure determination revealed the presence of one molecule of benzene and one molecule of pentane in the asymmetric unit. The molecular structure of 8c is presented in Figure 9. Interestingly, no reaction of 6 3 C6H6 with iron(II) chloride in THF was observed. At room temperature, reaction of 6 3 C6H6 with iron(III) chloride in benzene did not occur either. However, on refluxing the reaction mixture for 6 h, a complex mixture of products was formed (Scheme 5), from which a number of products could be isolated and identified. The di-iron(II) complex 9 and recovered 5 (99%) were isolated from the reaction mixture. Complex 9 was identified by X-ray

crystallography (Figure 10). The organic components Phebox-H and Phebox-Cl could be identified via GC-MS analysis of the reaction mixture after hydrolysis. Complex 9 could be characterized by X-ray crystal structure determination. A similar product mixture (except compound 5) was formed when the Phebox-Li compound 2a instead of the organogold reagent was used in the reaction with iron(III) chloride at 78 C, followed by warming to room temperature. Complex 9 comprises a newly formed neutral, tetradentate di(Phebox) ligand, resulting from the oxidative CC coupling reaction of two Phebox anions, that is N,N0 -chelate bonded with oxazonilyl groupings of different aryl groupings to one FeCl2 and from the other side of the diaryl moiety again N,N0 -chelate bonded to the second FeCl2 entity. The formation of diPhebox, Phebox-H, and Phebox-Cl indicates that the reaction of 6 with iron(III) chloride resulted in the formation of Phebox radicals that either dimerized, thus forming the tetradentate neutral N4 ligand present in 9, underwent H-abstraction, e.g., from the solvent, forming the Phebox-H compound, or reacted by atom transfer oxidation with iron(III) trichloride to produce Phebox-Cl. Compounds 7 (ac) and 8 (ac) were tested as precatalysts in ethene polymerization. It appeared that in homogeneous polymerization experiments in toluene using PMAO as activator only compound 7b was active. The results are summarized in Table 4. In both experiments an initial rapid rise in temperature was observed. However, rapid catalyst deactivation occurred when

Figure 6. Displacement ellipsoid plot of 7c (50% probability). Only one of two independent molecules is shown. Hydrogen atoms are omitted for clarity.

Figure 7. Displacement ellipsoid plot of 8a (50% probability). Hydrogen atoms and benzene solvent molecules are omitted for clarity.

Table 2. Selected Distances [Å] and Angles [deg] in the Crystal Structures of 7a, 7b, and 7ca 7a (M = Ti)

7b (M = V)

MC1

2.141(3)

2.0906(17)

1.9973(19)

MN1

2.177(2)

2.0926(14)

2.1110(16)

MN2

2.190(2)

2.0932(15)

2.1075(17)

MCl

2.3610(9)2.4223(8)

2.2258(6)2.3034(5)

2.3354(6)2.3414(6)

MO1

1.774(2)

MN3

a

7c (M = Cr)

2.2025(16)

C1MN1

72.63(10)

73.95(6)

77.58(7)

C1MN2

73.26(10)

74.55(7)

76.97(7)

In 7c only one of the two independent molecules is shown; for full data see the SI. 2823


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Table 3. Selected Distances [Å] and Angles [deg] in the Crystal Structures of 8a, 8b, and 8ca 8a (M = Zr)

Figure 8. Displacement ellipsoid plot of 8b (50% probability). Only one of two independent molecules is shown. Hydrogen atoms and benzene solvent molecules are omitted for clarity.

8b (M = Hf)

8c (M = Nb)

M1C11

2.2948(16)

2.275(6)

2.295(3)

M2C21 M1N11

2.2893(15) 2.3759(14)

2.259(5) 2.350(5)

2.287(2) 2.286(2)

M1N12

2.3521(13)

2.347(6)

2.301(2)

M2N21

2.3827(14)

2.359(5)

2.287(2)

M2N22

2.3690(13)

2.343(5)

2.315(2)

M1Cl11

2.4347(4)

2.3927(17)

2.3787(7)

M1Cl12

2.4256(5)

2.4176(17)

2.3943(7)

M2Cl21

2.4244(4)

2.4060(17)

2.3841(7)

M2Cl22 M1Cl13

2.4423(4) 2.6199(4)

2.4060(16) 2.6352(17)

2.3910(7)

M1Cl23

2.6819(4)

2.6108(15)

M2Cl13

2.6205(4)

2.6431(15)

M2Cl23

2.6583(4)

2.6183(17)

M1O1

1.9459(18)

M1O2

1.9572(18)

M2O1

1.9468(17)

M2O2 C11M1N11

68.27(5)

69.5(2)

1.9478(17) 68.24(9)

C11M1N12

68.80(5)

69.3(2)

67.88(9)

C21M2N21

68.85(5)

69.3(2)

68.42(9)

C21M2N22

68.48(5)

68.9(2)

67.98(9)

M1Cl13M2

109.133(15)

106.23(6)

M1Cl23M2

106.176(14)

107.68(6)

M1O1M2

103.24(8)

M1O2M2

102.78(8)

a

In 8b only one of the two independent molecules is shown; for full data see the SI.

Scheme 5. Reaction of Bis-organogold(I) dppbp Compound 6 with Iron(III) Chloride Figure 9. Displacement ellipsoid plot of 8c (50% probability). Hydrogen atoms, disordered pentane, and benzene solvent molecules are omitted for clarity.

the temperature inside the reactor reached ca. 65 C (Figure 11). The data presented in Table 4 represent average activities during 15 min of polymerization. Rapid catalyst deactivation, leading to low polymer yield, is a common feature in olefin polymerization with many homogeneous transition metal catalysts, including those based on titanium and vanadium. In the case of vanadium-catalyzed polymerization, this is generally ascribed to the transformation of active species to inactive V(II).10 A potential solution to this problem is immobilization of the catalyst on a magnesium chloride support. This approach is effective for titanium-based catalysts, which are less susceptible to (over)reduction on contact with aluminum alkyls when immobilized on MgCl2.11 Metallocenes such as Cp2TiCl2 undergo rapid deactivation under homogeneous polymerization conditions, whereas their immobilization on MgCl2 leads to stable activity.12 Examples of highly stable MgCl2-supported vanadium catalysts have also been reported.13 Particularly effective supports, with almost

perfectly spherical particle morphology and having the composition MgCl2/AlEtn(OEt)3n, can be obtained by reaction of AlEt3 with MgCl2 3 nEtOH adducts.14 In the present work, the effect of immobilizing the titanium and vanadium complexes 7a and 7b on such supports was investigated. Immobilization was carried out at 50 C by contacting the support overnight with a toluene solution containing the desired quantity of the Phebox complex. It was observed that the yellow (7a) or olive green (7b) color of the starting solutions was transferred to the supports, giving sandy red and brown colored solids. The slurry of immobilized 2824


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catalyst was diluted with light petroleum and used directly in polymerization. In addition to ethene homopolymerization, ethene/1-hexene copolymerizations were carried out in order to gain a first indication of the ability of these complexes to incorporate a co-monomer and to identify differences between the titanium and vanadium catalysts in this respect. The results of polymerizations with the immobilized Ti complex 7a are shown in Table 5, from which it is apparent that, in contrast to the lack of activity observed in homogeneous polymerization, good activity is observed when the catalyst is immobilized on a MgCl2 support. Essentially constant activity was observed in these experiments, illustrating the stabilizing effect of the support. The presence of co-monomer (1-hexene) resulted in some decrease in catalyst

Figure 10. Displacement ellipsoid plot of 9 (50% probability). Only one of two independent molecules is shown. Hydrogen atoms and disordered solvent molecules are omitted for clarity. Selected distances [Å], angles [deg], and torsion angles [deg] in the crystal structure of 9: Fe1N11 2.097(3), Fe1N21 2.096(3), Fe2N12 2.085(3), Fe2N22 2.095(4), Fe1Cl11 2.2680(11), Fe1Cl12 2.2377(14), Fe2Cl21 2.2666(13), Fe2Cl22 2.2622(15), C11C21 1.492(5), N11Fe1N21 111.98(12), N12Fe2N22 108.39(12), Cl11Fe1Cl12 123.91(5), Cl21Fe2Cl22 120.54(6), C12C11C21C22 101.6(5) (for full data see the SI).

activity and polyethylene molecular weight, particularly in the Mw values, giving somewhat narrower molecular weight distributions in copolymerization. Acceleration of chain transfer in the presence of a co-monomer is a frequently observed phenomenon in ethene polymerization with both homogeneous and immobilized catalysts.15 Slightly lower polymer melting temperatures and crystallinities were also obtained, consistent with incorporation of a small quantity of co-monomer into the polyethylene chain. 13 C NMR analysis revealed hexene contents of approximately 0.1 and 0.2 mol % in the copolymers prepared at 50 and 70 C, respectively, confirming the relatively poor copolymerization ability of this catalyst. Polymerizations with the vanadium complex 7b immobilized on a MgCl2/AlEtn(OEt)3n support gave the results shown in Table 6. The activities obtained are lower than those obtained with 7a, but around an order of magnitude higher than those measured under homogeneous polymerization conditions. Again, the presence of 1-hexene is seen to lead to decreased activity, but the significantly lower melting temperatures of the polymers prepared in ethylene/1-hexene copolymerization indicate greater co-monomer incorporation with the vanadium complex than was obtained with the titanium complex 7a. This was confirmed by 13C NMR analysis, which revealed hexene contents of 0.25 and 1.0 mol % in the copolymers prepared at 50 and 70 C, respectively.

Figure 11. Temperature profiles of polymerizations carried out under homogeneous conditions with precatalyst 7b.

Table 4. Homogeneous Polymerization Experiments with Precatalyst 7b

a

entry no.

start temp, C

activity, kg PE/mol 3 h 3 bar

Mw, g/mol

Mn, g/mol

Mw/Mn

Tm, C

χc,a %

1 2

50

72

785 000

395 000

2.0

135.0

39

20

118

673 000

340 000

2.0

135.4

43

Crystallinity (χc) calculated from melting enthalpy (ΔH), taking a ΔH value of 293 J/g for 100% crystalline polyethylene.

Table 5. Ethene (Co-)polymerization Using Complex 7a on a MgCl2-Based Supporta entry

temp, C

1

50

2

50

3

70

4

70

activity, kg/mol 3 h 3 bar

Mw, g/mol

Mn, g/mol

Mw/Mn

Tm, C

χc, %

0

4600

1 400 000

450 000

3.1

136.6

48

20

3900

870 000

380 000

2.3

133.2

45

0

4100

1 280 000

280 000

4.6

136.7

51

20

3200

980 000

270 000

3.6

131.4

45

1-hexene, mL

Support composition: MgCl2 3 0.21AlEt2.38(OEt)0.62. Polymerization conditions: 500 mL of light petroleum, immobilized catalyst 100 mg (4 μmol Ti), AliBu3 1 mmol, ethene pressure 5 bar, time 1 h. a

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Table 6. Ethene (Co-)polymerization Using Complex 7b on a MgCl2-Based Supporta AlR3

temp, C

1-hexene, mL

Mn, g/mol

Mw/Mn

Tm, C

χc, %

Ali-Bu3

50

0

520

Ali-Bu3 AlEt3

70 50

0 0

1800 1200

740 000

360 000

2.0

136.9

52

690 000 1 480 000

360 000 850 000

1.9 1.7

136.0 135.6

42 40

AlEt3

50

20

AlEt3

70

0

580

980 000

450 000

2.2

126.7

34

1600

1 010 000

500 000

2.0

135.2

AlEt3

70

20

920

42

730 000

290 000

2.5

123.9

30

Mw, g/mol

activity, kg/mol 3 h 3 bar

Support composition: MgCl2 3 0.17AlEt2.21(OEt)0.89. Polymerization conditions: 500 mL of light petroleum, immobilized catalyst 100 mg (2 μmol V), AlR3 1 mmol, ethene pressure 5 bar, time 1 h. a

Figure 12. Possible structures of products anticipated in methylation reactions of 8a after subsequent reaction of the alkylation mixture with water.

The molecular weight data for the polyethylenes synthesized with the vanadium complex 7b indicate a narrow (Schulz Flory) distribution, indicative of single-center catalysis, although the Mw/Mn values show some broadening in distribution in the copolymerizations, carried out with AlEt3 as cocatalyst. The broader copolymer distribution appears to arise from a more significant decrease in Mn than in Mw, in contrast to what was observed with the Ti-Phebox complex 7a. Confirmation of the single-center characteristics of the vanadium complex in ethene homopolymerization with Ali-Bu3 as cocatalyst has been obtained from an investigation of the polymer melt rheological properties.16 Comparison of a range of different MgCl2-supported titanium and vanadium catalysts revealed that single-center behavior was consistently retained in the case of vanadium, but not with analogous titanium complexes. To study possible reasons for the low activity of both 7 (ac) and 8 (ac) as precatalysts in homogeneous polymerization, reactions of 8a with either MeLi or MeMgCl were carried out. In both cases it appeared impossible to separate pure products of alkylation from these reaction mixtures. Subsequently these crude product mixtures were hydrolyzed with water. The organic products were extracted with ether, and the ether extracts analyzed by GC-MS analysis. This revealed in each case the presence of a complex mixture of products with m/z values of 314, 329, 347, and 406. Structures proposed for these products are presented in Figure 12. It is noteworthy that the arene product for the ligand with m/z 300 was absent in the mixture. This indicates complete alkylation of the ligand. The product with m/z 406 is probably the result of a reaction of 8a with THF with subsequent hydrolysis.

’ CONCLUSION A number of novel R-Phebox metal complexes of some early and middle transition metals were successfully synthesized via a transmetalation reaction of the respective transition metal

chlorides with a bimetallic Phebox-gold compound 6. In contrast to reactions with Phebox lithium compounds, which often lead to the formation of mono-, di-, and tri-Phebox complexes, the use of the corresponding gold(I) compounds resulted in the selective transfer of a single Phebox group to each metal center. This lower selectivity was very apparent in experiments with titanium isopropoxide trichloride that afforded the mono-Phebox titanium compound 7a with the gold reagent 6, whereas the reaction with the Phebox-lithium reagent provided an intractable mixture of mono-, di-, and tri-Phebox products. An obvious advantage of this synthetic method is the almost quantitative reformation of the insoluble dimeric gold chloride material 5 at the end of the reaction, which is easily separable and can be reused in another reaction. However, in cases where the gold reagent is not active enough, as is most likely the case for both iron(II) and -(III) salts, heating of the reaction mixture caused oxidative coupling of the Phebox ligand from the in situ formed Phebox iron complex. Structures of the new compounds in the solid state were established by X-ray crystallography. The enantiopurity of the crystal was confirmed by absolute structure determination using the Flack x parameter;24 see the SI, Table 6. In all cases the R-Phebox ligand appears to be mer-NCN bonded to the metal center. These i-Pr,H-Phebox metal complexes of early and middle transition metals were tested as precatalysts in ethene polymerization. Low stability was observed under homogeneous polymerization conditions, using methylaluminoxane as cocatalyst, but immobilization of the titanium and vanadium Phebox complexes 7a and 7b on MgCl2-based supports and ethene polymerization in the presence of Ali-Bu3 or AlEt3 led to stable catalyst activity and more than an order of magnitude increase in polymer yield. The immobilized vanadium complex 7b retained single-center behavior after immobilization, producing polyethylene with narrow (SchulzFlory) molecular weight distribution. 2826


Organometallics

’ EXPERIMENTAL SECTION All experiments were carried out in a dry, oxygen-free nitrogen atmosphere, using standard Schlenk techniques. Solvents were dried and distilled from sodium (pentane, toluene), sodium/benzophenone (diethyl ether, tetrahydrofuran, and hexane), or CaH2 (pyridine) prior to use. n-BuLi (1.6 M in hexanes) was supplied by Acros and used as received. 1H and 13C NMR spectra were recorded on a Varian Inova 300 spectrometer. (S,S)-(R,H-Phebox)Br (1a, 1b)5d and 4,40 -bis[P-(chlorogold(I))diphenylphosphino]biphenyl [(dppbp)(AuCl)2] (5)2d were synthesized according to literature procedures. All other chemicals were purchased from either Acros or Aldrich and used as received. Elemental analyses were performed by H. Kolbe Mikroanalytisches Laboratorium, M€ulheim an der Ruhr, Germany.

Triphenylphosphine (S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl) phenyl]gold (4a). To a solution of (S,S)-2,6-bis(40 -isopropyl-20 -

oxazolinyl)phenyl bromide (1a) (760 mg, 2 mmol) in THF (10 mL) at 78 C was added via a syringe 1.3 mL (2 mmol) of n-BuL(1.6 M) in hexane. The resulting solution containing in situ prepared 2a was stirred for 10 min. Subsequently (triphenylphosphine)gold chloride (1.03 g, 2.08 mmol) was added. The reaction mixture was allowed to warm to room temperature and stirred for 1 h. Water (1 mL) was added. The resulting reaction mixture was stirred for 10 min. The organic layer was separated, and the aqueous layer was extracted with diethyl ether (2 10 mL). The combined organic extracts were separated from water, dried over magnesium sulfate, and then concentrated in vacuo. The residue was dried in vacuo, redissolved in benzene, and again made dry in vacuo. This treatment was performed to convert crystalline product into an amorphous state. It precipitated from diethyl ether in a crystalline state. The resulting amorphous mass was dissolved in diethyl ether (20 mL). The clear solution was decanted from the precipitate and then left for crystallization at room temperature. Crystals were filtered off and washed with a small amount of diethyl ether. An additional amount of the product was obtained by recrystallization of the residue obtained after concentration of the mother liquor. Yield: 1.17 g of 4c (77%). 1H NMR (300 MHz, CDCl3): δ 0.72 (d, 6H, 3JHH = 6.7 Hz), 0.81 (d, 6H, 3 JHH = 6.7 Hz), 1.58 (septet, 2H, 3JHH = 6.6 Hz), 3.893.99 (m, 4H), 4.134.24 (m, 2H), 7.14 (t, 1H, 3JHH = 7.6 Hz), 7.407.50 (m, 9H), 7.617.73 (m, 6H), 7.90 (d, 2H, 3JHH = 7.6 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 17.8, 19.1, 32.6, 69.7, 72.7, 124.8, 128.7 (d, 3JPC = 11 Hz), 130.5, 130.8, 134.4 (d, 2JPC = 14 Hz), 138.1, 168.7. 31P{1H} NMR (121 MHz, CDCl3): δ 42.6 ppm.

Triphenylphosphine (S,S)-[2,6-Bis(40 -tert-butyl-20 -oxazolinyl) phenyl]gold (4b). (Triphenylphosphine)gold chloride (0.3 g, 0.6 mmol)

was added to a solution of 2a (vide supra) (0.6 mmol) in THF/hexanes at 78 C. The resulting reaction mixture was allowed to warm to room temperature and stirred for 1 h. Water (0.5 mL) was added, and the reaction mixture was stirred for 10 min, which was followed by separation of the organic layer. This layer was dried over magnesium sulfate, then filtered, and the filtrate was concentrated to dryness in vacuo. Subsequent workup as described for 4a resulted in the formation of crystals, which were filtered off and washed with a small amount of ether. An additional amount of the product was separated from the mother liquor. Yield: 350 mg (72%). 1H NMR (300 MHz, CDCl3): δ 0.76 (s, 18H), 3.86 (dd, 2H, 3JHH = 10.1 Hz, 3 JHH = 7.5 Hz), 3.994.13 (m, 4H), 7.14 (t, 1H, 3JHH = 7.6 Hz), 7.397.50 (m, 9H), 7.617.71 (m, 6H), 7.90 (d, 2H, 3JHH = 7.6 Hz). 13 C{1H} NMR (75 MHz, CDCl3): δ 25.9, 34.0, 68.5, 76.4, 128.8 (d, 3JPC = 11 Hz), 130.8, 134.5 (d, 2JPC = 14 Hz) 138.2. 31P{1H} NMR (121 MHz, CDCl3): δ 42.6 ppm. Anal. Calcd for C38H42AuN2O2P: C, 58.02; H, 5.38; N, 3.56. Found: C, 57.97; H, 5.46; N, 3.55.

4,40 -Bis{P-((S,S)-[2,6-bis(40 -isopropyl-20 -oxazolinyl)phenyl] gold)(diphenylphosphino)}biphenyl (6). 4,40 -Bis(diphenyl-

phosphino)biphenylgold chloride (5) (6.16 g, 6.24 mmol) was added to a solution of 2a (vide supra) (13 mmol) in THF/hexanes at 78 C.

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The reaction mixture was allowed to warm to room temperature and stirred for 1 h. Water (5 mL) was added, and the resulting reaction mixture was stirred for 10 min. The organic layer was separated from the aqueous layer, which was extracted with dichloromethane (2 20 mL). The combined organic extracts were dried over magnesium sulfate and filtered, and the filtrate was concentrated to dryness in vacuo. The crude product was dissolved in boiling methanol (70 mL) and crystallized overnight as a methanol solvate. The mother liquor was evaporated to dryness, and the residue was recrystallized from methanol once again to give additional amounts of the product. The product, 6, was dried in vacuo at 100 C until constant pressure (0.1 mbar) for 6 h to remove most of the methanol. The product was then dissolved in boiling benzene, and 6 crystallized as a benzene solvate by slow evaporation of the solvent. Yield: 8.3 g (88%). 1H NMR (300 MHz, CDCl3): δ 0.72 (d, 12H, 3JHH = 6.7 Hz), 0.81 (d, 12H, 3JHH = 6.7 Hz), 1.66 (m, 4H), 3.904.00 (m, 8H), 4.154.25 (m, 4H), 7.15 (t, 2H, 3JHH = 7.8 Hz), 7.407.52 (m, 12H), 7.607.82 (m, 16H), 7.90 (dd, 4H, 3JHH = 7.7 Hz, 5JPH = 1.5 Hz). 13C{1H} NMR (75 MHz, CDCl3): δ 17.8, 19.1, 32.6, 69.7, 72.7, 100.7, 124.9, 127.4 (d, 3JPC = 12 Hz), 128.8 (d, 3JPC = 11 Hz), 130.6 (d, 4JPC = 5.8 Hz), 131.0, 131.3 (d, 4JPC = 5.5 Hz), 132.0 (d, 3JPC = 5.8 Hz), 134.5 (d, 2JPC = 14 Hz), 135.1 (d, 2JPC = 14 Hz), 138.0, 168.7 (d, 5JPC = 3 Hz). 31P{1H} NMR (121 MHz, CDCl3): δ 42.2 ppm. Anal. Calcd for C72H74Au2N4O4P2: C, 57.07; H, 4.92; N, 3.70. Found: C, 56.88; H, 4.65; N, 3.79.

(S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl]titanium Isopropoxide Dichloride (7a). A solution of 6 (1.85 g, 1.16 mmol)

in THF (30 mL) was added in one portion to solid titanium isopropoxide trichloride (507 mg, 2.38 mmol). The reaction mixture was stirred for 16 h at room temperature and centrifuged to remove insoluble 5. The precipitate (5) was collected by decantation and was washed with THF (15 mL). The THF was removed in vacuo. Diethyl ether (10 mL) was added to the sticky amorphous residue, and the mixture was left to crystallize for 60 h. The diethyl ether solution was decanted from the crystals, which were filtered off and dried in vacuo. Yield: 0.83 g (73%). Single crystals for X-ray crystallography were grown by vapor diffusion of pentane into a diethyl ether solution of the product 7a. Yield of recovered 5 was 1.14 g (99%). 1H NMR (300 MHz, C6D6): δ 0.580.80 (m, 8H), 0.921.16 (m, 10H), 1.341.65 (m, 1H), 2.382.62 (m, 1H), 2.883.12 (m, 1H), 3.654.10 (m, 4H), 4.26 (m, 1H), 4.434.66 (m, 1H), 6.67 (t, 1H, 3JHH = 7.5 Hz), 7.26 (d, 2H, 3JHH = 7.3 Hz). 13 C{1H} NMR (75 MHz, C6D6): δ 15.5, 15.6, 15.7, 15.9, 18.7, 18.9, 19.1, 19.2, 19.4, 24.6, 24.9, 25.6, 30.2, 30.5, 33.3, 65.9, 69.8, 70.5, 70.7, 71.0, 72.7, 73.0, 73.3, 73.6, 81.6, 126.6, 129.0, 131.1. Anal. Calcd for C21H30Cl2N2O3Ti: C, 52.85; H, 6.34; N, 5.87. Found: C, 52.66; H, 6.48; N, 5.69.

(S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl]vanadium Trichloride (7b). A solution of 6 (1.0 g, 0.628 mmol) in benzene

(30 mL) was added to liquid neat vanadium(IV) tetrachloride (0.245 g, 1.27 mmol). The reaction mixture was stirred overnight. The resulting mixture was centrifuged (removal of insoluble 5) and the solution decanted. The solution was concentrated in vacuo. The residue was crystallized from a benzene/pentane mixture, affording a benzene solvate of 7b as dark green needles. Yield: 550 mg (82%). Yield of recovered 5 was 615 mg (99%). Anal. Calcd for C24H29Cl3N2O2V: C, 53.90; H, 5.47; N, 5.24. Found: C, 53.77; H, 5.53; N, 5.18.

Pyridino (S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl] chromium Dichloride (7c). A solution of 6 (525 mg, 0.33 mmol)

in THF (15 mL) was added to solid CrCl3(THF)3 (245 mg, 0.66 mmol). The reaction mixture was stirred for 16 h at room temperature. Solvent was evaporated under vacuum. The residue was dissolved in benzene (50 mL), and the solids (5) were removed by centrifugation and decantation of the supernatant. This solution was evaporated in vacuo. After evaporation of benzene pyridine (0.5 mL) was added to the 2827


Organometallics residue. The resulting mixture was dissolved in dichloromethane and crystallized by diffusion of pentane into this solution. Yield of 7c was 0.250 g (75%), dark purple crystals. Yield of recovered 5 was 320 mg (98%). Anal. Calcd for C23H28Cl2CrN3O2: C, 55.10; H, 5.63; N, 8.38. Found: C, 54.95; H, 5.70; N, 8.29.

(S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl]zirconium Trichloride Dimer (8a). A solution of 6 (0.525 g, 0.33 mmol) in THF

(15 mL) was added to solid ZrCl4 (154 mg, 0.66 mmol). The reaction mixture was stirred for 16 h at room temperature. Volatiles were removed in vacuo. The residue was extracted with benzene (50 mL) and centrifuged. The precipitate (5) obtained after centrifugation was flushed with a second portion of benzene (50 mL) and stirred overnight, and the supernatant was separated from the precipitate by centrifugation. The combined benzene extracts were concentrated in vacuo. The residue was crystallized from benzene/hexane, affording 8a as a solvate with benzene. Colorless crystals (312 mg, 82%) were obtained. Yield of recovered 5 was 320 mg (98%). 1H NMR (300 MHz, C6D6): δ 0.76 (d, 12H, 3JHH = 7.0 Hz), 0.86 (d, 12H, 3JHH = 6.7 Hz), 3.21 (m, 4H), 3.79 (t, 4H, 3JHH = 9.0 Hz), 4.17 (dd, 4H, 2JHH = 9.0 Hz, 3JHH = 3.4 Hz), 4.96 (d, 4H, 2JHH = 8.8 Hz), 6.86 (t, 2H, 3JHH = 7.6 Hz), 7.56 (d, 4H, 3JHH = 7.6 Hz). 13C{1H} NMR (75 MHz, C6D6): δ 14.1, 19.4, 29.9, 69.8, 71.4, 100.4, 127.5, 128.9, 130.6, 178.0. Anal. Calcd for C48H58Cl6Zr2N4O4: C, 50.12; H, 5.08; N, 4.87. Found: C, 50.21; H, 5.05; N, 4.80.

(S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl]hafnium Trichloride Dimer (8b). A solution of 6 (1.59 g, 1 mmol) in THF

(20 mL) was added to solid hafnium(IV) chloride (640 mg, 2 mmol). The reaction mixture was stirred for 40 h at room temperature. The solvent of the reaction solution was evaporated in vacuo. Benzene (100 mL) was added to the residue, and the mixture was stirred for 50 h at room temperature and then centrifuged. The residue (5) obtained after decantation of the supernatant was flushed with a second portion of hot benzene (100 mL). The resulting mixture was centrifuged. Combined benzene extracts were concentrated in vacuo. The residue was crystallized from benzene/hexane, affording 8b as benzene solvate. Colorless crystals (1.03 g, 83%) were obtained. Yield of recovered 5 was 977 mg (99%). 1H NMR (300 MHz, C6D6): δ 0.75 (d, 12H, 3 JHH = 7.3 Hz), 0.85 (d, 12H, 3JHH = 6.7 Hz), 3.23 (m, 4H), 3.80 (t, 4H, 3JHH = 9.2 Hz), 4.18 (d, 4H, 3JHH = 7.6 Hz), 4.93 (d, 4H, 3 JHH = 7.0 Hz), 6.90 (t, 2H, 3JHH = 7.6 Hz), 7.65 (d, 4H, 3JHH = 7.6 Hz). 13C{1H} NMR (75 MHz, C6D6): δ 14.1, 19.4, 29.9, 69.7, 71.8, 100.4, 127.5, 128.6, 129.2, 179.2. Anal. Calcd for C42H52Cl6Hf2N4O4: C, 40.47; H, 4.20; N, 4.49. Found: C, 40.45; H, 4.42; N, 4.38.

(S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl]niobium Dichloride Oxide Dimer (8c). A solution of 6 (487 mg, 0.306 mmol) in

THF (10 mL) was added to solid NbCl5 (165 mg, 0.611 mmol). The reaction mixture was stirred overnight at room temperature. Volatiles of the reaction mixture were removed in vacuo. The residue was dissolved in benzene and centrifuged in order to remove insoluble 5. The decanted solution was concentrated in vacuo. The residue was crystallized from benzene/pentane, affording 8c as a benzene and pentane solvate (lemon-yellow needles). Yield of 8c was 256 mg (76%). Yield of recovered 5 was 300 mg (99%). 1H NMR (300 MHz, C6D6): δ 0.77 (d, 12H, 3JHH = 7.0 Hz), 0.94 (d, 12H, 3JHH = 6.7 Hz), 3.28 (septet of doublets, 4H, 3JHH = 6.9 Hz, 3JHH = 2.5 Hz), 4.10 (t, 4H, 3JHH = 9.5 Hz), 4.29 (dd, 4H, 2JHH = 8.7 Hz, 3JHH = 4.7 Hz), 5.09 (doublet of quadruplets, 4H, 3JHH = 9.9 Hz, 4JHH = 2.4 Hz), 6.86 (t, 2H, 3JHH = 7.5 Hz), 7.58 (d, 4H, 3JHH = 7.6 Hz). 13C{1H} NMR (75 MHz, C6D6): δ 14.8, 20.1, 28.7, 68.1, 71.8, 99.3, 127.5, 128.9, 129.4, 176.7. Anal. Calcd for C47H64Cl4N4Nb2O6: C, 50.92; H, 5.82; N, 5.05. Found: C, 50.69; H, 5.76; N, 4.95.

Reaction of Bis-pincer-gold Diphosphine 6 with Iron(III) Chloride. A solution of 6 (1.6 g, 1 mmol) in benzene (20 mL) was added to solid FeCl3 (340 mg, 2.1 mmol). The reaction mixture was

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stirred overnight at room temperature. No conversion was observed. Subsequently the reaction mixture was refluxed under stirring for 6 h. Formation of a white precipitate (5) and a change of color of the reaction mixture from dark brown to yellow-orange were observed. The reaction mixture was cooled to room temperature, and 5 removed by centrifugation. A small fraction of the supernatant was diluted with dichloromethane, washed with water, and analyzed by GC-MS. Solvent was evaporated in vacuo. The product was crystallized from acetonitrile/ ether and identified by X-ray crystallography as [9 3 2Et2O]. Yield of [9 3 2Et2O] was 110 mg (11%). Reaction of Pincer Lithium 2a with Iron(III) Chloride. A solution of in situ prepared 2a (910 mg, 2.4 mmol) in THF (10 mL) was added to solid iron(III) chloride (370 mg, 2.28 mmol) in THF (10 mL) at 78 C. The reaction mixture was allowed to warm to room temperature and was stirred for another 1 h. A small sample of the resulting reaction mixture was diluted with dichloromethane, washed with water, and analyzed by GC-MS. The result of this analysis is presented in Scheme 5. Solvent of the remaining reaction mixture was evaporated in vacuo. The residue was dissolved in benzene (50 mL; removal of LiBr), and the precipitate removed by centrifugation and decantation of the supernatant. The supernatant was concentrated in vacuo, and the residue was crystallized from ether/pentane, which afforded 9 as colorless needles. They were identified by X-ray crystallography as [9 3 2Et2O]. Yield of [9 3 2Et2O] was 114 mg (9.5%).

Reactions of (S,S)-[2,6-Bis(40 -isopropyl-20 -oxazolinyl)phenyl] zirconium Trichloride Dimer (8a) with Either Methylmagnesium Chloride or Methyllithium. To a solution of (S,S)-[2,6-bis

(40 -isopropyl-20 -oxazolinyl)phenyl]zirconium trichloride (8a) (200 mg, 0.4 mmol) in THF (10 mL) at 78 C was added the alkylating reagent (either methylmagnesium chloride in THF (22 wt %, d = 1.03) (90.3 mg, 0.4 mL, 1.21 mmol) or methyllithium in diethyl ether (1.6 M, 0.8 mL, 1.28 mmol)). The reaction mixture turned bright green, but after cooling ceased the color of the reaction mixture soon turned brown. The reaction mixture was allowed to warm to room temperature and was stirred at room temperature overnight. The reaction mixture was concentrated in vacuo. Attempts to crystallize the residue from various solvents failed. No pure, crystalline material was obtained. The remaining residue was then hydrolyzed with aqueous sodium hydroxide. The resulting aqueous solution was extracted with diethyl ether, and its contents were analyzed by GS-MS. GC-MS analysis revealed a complex mixture of products with m/z 314, 329, 347, 406. Polymerization Experiments. All manipulations were performed under an argon atmosphere using a glovebox (Braun MB-150 GI or LM-130) and Schlenk techniques. Light petroleum (bp 4060 C) and toluene were passed over columns containing activated alumina. All solvents were freezethawdegassed twice before use. AlEt3 (1.3 M in heptane), Ali-Bu3 (25 wt % in toluene), and polymeric methyl aluminoxane (PMAO, 10 wt % solution in toluene) were obtained from Acros, Akzo Nobel, and Crompton, respectively. Ethene (3.5 grade supplied by Air Liquide) was purified by passing over columns of BASF RS3-11supported Cu oxygen scavenger and 4 Å molecular sieves. Homogeneous Polymerization Experiments. Toluene (300 mL) was introduced into a 1 L stainless steel reactor maintained at the experiment temperature (see Table 4), after which ethene (20 bar) was introduced. PMAO (2.8 g, 10 wt % in toluene, 5.0 mmol Al) was added, followed by a solution of 7b benzene solvate (5.3 mg, 10 μmol) in toluene (5 mL). The reaction was stirred for 15 min, after which the polymerization was terminated by venting off the volatiles. The polymer was filtered off, washed with an aqueous HCl (1 M) solution and ethanol, dried, and weighed.

Polymerization Experiments with Supported Catalysts. a. Support Preparation and Catalyst Immobilization. The supports used in this work were prepared by addition of AlEt3 to the adduct MgCl2 3 1.1EtOH in light petroleum (AlEt3/EtOH = 2) at 0 C, after which the mixture was kept at room temperature for 2 days with 2828


Organometallics

Compound 7a. All hydrogen atoms were located in difference Fourier maps and refined with a riding model. Compound 7b 3 C6H6. All hydrogen atoms were located in difference Fourier maps and refined with a riding model. Compound 7c. All hydrogen atoms were located in difference Fourier maps and refined with a riding model. Compound 8a 3 2C6H6. Hydrogen atoms were introduced in calculated positions and refined with a riding model Compound 8b. The crystal was cracked with a 2.1 rotation about an arbitrary axis relating the two fragments. Refinement was performed on a HKLF5 file.23 The asymmetric unit contains two metal complexes and three cocrystallized benzene solvent molecules, of which two were refined with full and one with partial occupancy. Distance and flatness restraints were used for this benzene molecule. Hydrogen atoms were introduced in calculated positions and refined with a riding model. Compound 8c. Pentane and benzene molecules were refined with disorder models, respectively. Distance and angle restraints and additional restraints to approximate isotropic displacement parameters were used for these disordered molecules. Hydrogen atoms were introduced in calculated positions and refined with a riding model. Compound 9. The crystal structure contains voids filled with disordered solvent molecules (752 Å3/unit cell). Their contribution to the structure factors was secured by the SQUEEZE routine of the PLATON22 software, resulting in 198 electrons/unit cell. Hydrogen atoms were introduced in calculated positions and refined with a riding model.

’ ASSOCIATED CONTENT

bS

Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*Tel: þ3130 2533120. Fax: þ3130 2523615. E-mail: g.vankoten@ uu.nl. Address correspondence pertaining to crystallographic studies to this author. E-mail: [email protected].

)

occasional agitation. The resultant support was washed with light petroleum three times and dried under argon flow and subsequently under vacuum until free-flowing. The ethoxide contents in the MgCl2/ AlEtn(OEt)3n supports were determined by gas chromatographic (GC) analysis of the ethanol content of a solution obtained by dissolving 100 mg of support in 5 mL of BuOH containing a known quantity of PrOH as an internal standard. Immobilization was carried out by contacting the support (100 mg) with 24 mL of a toluene solution containing 24 μmol of the titanium (7a) or vanadium (7b) Phebox complex at 50 C for 16 h. The resulting slurry was, after dilution with light petroleum, used as such in polymerization. b. Polymerization Procedure. Polymerization was carried out in an l L Premex autoclave by charging the immobilized catalyst, slurried in approximately 100 mL of light petroleum, to a further 400 mL of light petroleum containing 1 mmol of AlEt3 or Ali-Bu3, at the desired temperature and at an ethene pressure of 5 bar. After catalyst injection, polymerization was continued at constant pressure for 1 h with a stirring rate of 1000 rpm. Copolymerization experiments were carried out under similar conditions after addition of 20 mL of 1-hexene. After venting the reactor, 20 mL of acidified ethanol was added, and stirring was continued for 30 min. The polymer was recovered by filtration, washed with water and ethanol, and dried in vacuo overnight at 60 C. c. Polymer Characterization. Molecular weight and molecular weight distributions of the resulting polymers were determined by means of gel permeation chromatography on a PL-GPC210 at 135 C using 1,2,4trichlorobenzene as solvent. Differential scanning calorimetry (DSC) was carried out with a Q100 differential scanning calorimeter (TA Instruments). The samples (1.52.5 mg) were heated to 160 C at a rate of 10 C/min and cooled at the same rate to 20 C. A second heating cycle at 10 C/min was used for data analysis. 13 C NMR analysis of ethene/1-hexene copolymers was kindly carried out by Prof. R. Cipullo at the University of Naples. Quantitative 13C NMR spectra were recorded at 120 C on 20 mg/mL solutions in tetrachloroethane-1,2-d2, with a Bruker DRX 400 Avance spectrometer operating at 100.6 MHz with a 5 mm probe, under the following conditions: 80 pulse; acquisition time 2.7 s; relaxation delay 2.5 s; >10K transients. Broad-band proton decoupling was achieved with a modified WALTZ16 sequence (BI_WALTZ16_32 by Bruker). X-ray Crystal Structure Determinations. X-ray intensities were measured on a Nonius KappaCCD diffractometer with rotating anode (λ = 0.71073 Å) at a temperature of 150(2) K. Integration was performed with HKL200017 (compounds 4a, 7b 3 C6H6, 8c) or EvalCCD18 (4b, 6 3 3MeOH, 6 3 C6H6, 7a, 7c, 8a 3 2C6H6, 8b, 9). The structures were solved with automated Patterson methods using DIRDIF-9919 (4a, 4b, 6 3 3MeOH, 6 3 C6H6, 8b, 9) or direct methods using SHELXS-9720 (7a, 7b 3 C6H6, 7c, 8a 3 2C6H6) and SIR-9721 (8c). Least-squares refinement was performed with SHELXL-9720 on F2 of all reflections. Structure calculations and checking for higher symmetry was performed with PLATON.22 Further details are given in the SI, Table 6. Compound 4a. The structure was refined as a pseudo-orthorhombic twin with a 2-fold rotation about the reciprocal c*-axis as twin operation. The twin fraction refined to 0.0168(2). All hydrogen atoms were located in difference Fourier maps and refined with a riding model. Compound 4b. The tert-butyl groups were refined with distance and angle restraints and additional restraints to approximate isotropic displacement parameters. Hydrogen atoms were introduced in calculated positions and refined with a riding model. Compound 6 3 3MeOH. The isopropyl groups were refined with distance and angle restraints and additional restraints to approximate isotropic displacement parameters. Hydrogen atoms were introduced in calculated positions and refined with a riding model Compound 6 3 C6H6. Hydrogen atoms were introduced in calculated positions and refined with a riding model

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’ ACKNOWLEDGMENT This research was supported in part (A.V.C., R.H.) by the Dutch Polymer Institute (DPI), projects 106 and 495, and (A.L.S.) by the Council for Chemical Sciences of The Netherlands Organisation for Scientific Research (CW-NWO). Prof. Dr. B. Hessen and Dr. G. P. M. van Klink are kindly acknowledged for their suggestions and stimulating discussions. Dr. E. van Faassen is thanked for recording the ESR spectra of 7b. O. Staal and Dr. W. P. Kretschmer and the COP-Center (RU Groningen) are kindly acknowledged for providing the opportunity and help during the homogeneous olefin polymerization experiments. ’ REFERENCES (1) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315. (2) (a) de Koster, A.; Kanters, J. A.; Spek, A. L.; van der Zeijden, A. A. H.; van Koten, G.; Vrieze, K. Acta Crystallogr. C 1985, 41, 893–895; (b) Donkervoort, J. G.; Jastrzebski, J. T. B. H.; Deelman, B.-J.; Kooijman, H.; Veldman, N.; Spek, A. L.; van Koten, G. Organometallics 1997, 16, 4174–4184; (c) Matsunaga, P. T. (Exxon Chemical Patents Inc., USA) PCT Int. Appl. WO99/57159, 1999. Chem. Abstr. 1999, 131, 351802. (d) Stol, M. Aryl Metal Complexes Stabilized by Intramolecular 2829


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NCN-Pincer Metal Complexes (Ti, Cr, V, Zr, Hf, and Nb) of the Phebox

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