Efficient Synthesis of Titanium Complexes Bearing Tridentate [N–,N,O

Article pubs.acs.org/Organometallics

Efficient Synthesis of Titanium Complexes Bearing Tridentate [N−,N,O−] Anilido-Imine Ligands and Their Catalytic Properties for Ethylene Polymerization Lei Zhang, Xuyang Luo, Wei Gao,* Jingshun Zhang, and Ying Mu* State Key Laboratory of Supramolecular Structure and Materials, School of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, People’s Republic of China S Supporting Information *

ABSTRACT: A series of tridentate anilido-imine [N,N,O] ligands 2-(2(R12-2,6-C6H3NH)C6H4)HCN(4-tBu-6-R2-C6H2OH) [R1 = Me, R2 = tBu (LaH2); R1 = Et, R2 = tBu (LbH2); R1 = iPr, R2 = tBu (LcH2); R1 = Me, R2 = Ad (LdH2); R1 = Et, R2 = Ad (LeH2); R1 = iPr, R2 = Ad (LfH2)] were synthesized and characterized. Reaction of the free ligand LdH2 with TiCl4 in toluene at low temperature affords the zwitterionic complex Ld+H2Ti−Cl4 (1d). The zwitterionic complex can be dissolved in THF to form THF-solvated complex 1d′. Heating 1d in toluene at 40 °C affords the neutral complex LdHTiCl3 (2d) by losing a HCl. Complex 2d can be fully converted to the final complex LdTiCl2 (3d) at 140 °C under vacuum by losing another HCl. Complexes 3a−3c, 3e, and 3f were also synthesized in high yields in the same one-pot procedure. All complexes were characterized by 1H and 13C NMR spectroscopy, and the molecular structures of 1d′, 3b, 3d, and 3e were determined by singlecrystal X-ray diffraction analysis. The titanium centers in complexes 3b, 3d, and 3e are five-coordinated with a geometry situated between trigonal bipyramid and square pyramid. Upon activation with alkylaluminum and Ph3C+B(C6F5)4−, complexes 3a−3f exhibit moderate catalytic activity for ethylene polymerization.

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INTRODUCTION Group IV transition metal olefin polymerization catalysts bearing noncyclopentadidenyl ligands have attracted considerable attention in recent years due to their feasible preparation and easy modification of their steric and electronic properties.1−9 A large number of titanium or zirconium complexes with ligands bearing N, O, P, and S donors have been investigated.6−9 Titanium or zirconium complexes bearing phenoxy-imine bidentate ligands (FI catalysts) have been extensively studied. Some of these complexes were found to show high catalytic activity for ethylene and propylene polymerization and produce polymers with high molecular weight and narrow molecular weight distribution. Some of bis(phenoxyimine)titanium(IV) complexes even were found to be active catalysts for copolymerization of ethylene with acetyl protected hex-5-en-1-ol with moderate comonomer incorporation.6b Similar titanium complexes supported by β-enaminoketonato bidentate ligands were also reported to be efficient catalysts for ethylene (co)polymerization.8 In recent years, titanium and zirconium di- or trichlorides bearing a tridentated chelating ligand were also extensively investigated as ethylene polymerization catalysts. Complexes of titanium trichlorides with a [O−,N,S] or [O−,N,P] chelating ligand were found to show high catalytic activity in ethylene (co)polymerization.10 Complexes of titanium trichlorides bearing a pyridinyl decorated phenoxyimine [N,N,O−] ligand were also reported to show good activity in ethylene polymerization and copolymerization with 1-hexene.3a Besides the complexes with a monoanion tridentate ligand, some titanium and zirconium © XXXX American Chemical Society

complexes chelated by a dianion tridentate ligand were studied too. It was reported that titanium complexes with a [O−,N,S−] dianion tridentate ligand exhibit good catalytic activity for ethylene polymerization,2a and zirconium complexes with a [O−,N,O−] dianion tridentate ligand show moderate catalytic activity and more than 99% 2,1-regioselectivity for 1-hexane polymerization.11 So far, the group IV transition metal complexes with a tridentate ligand studied as olefin polymerization catalysts are mainly the complexes supported by a phenoxyimine-based ligand. It should be interesting to develop new catalysts carrying different types of tridentate ligands. We have synthesized a series of new [N−,N,O−] dianion tridentate ligands by incorporating a hydroxyl group into the known anilido-imine ligands.12 With these new ligands, a number of titanium complexes have been prepared by a new one-pot procedure from the HCl elimination reaction of TiCl4 with the free ligands. In these titanium complexes, the substituent on the amido nitrogen atom is close to the metal center, which would bring a bulkier coordination environment around the central metal and thus will have an impact on the catalytic performance of these complexes. In this paper we report the synthesis and characterization of the new free ligands 2-(2-(R12-2,6C6H3NH)C6H4)HCN(4-tBu-6-R2-C6H2OH) [R1 = Me, R2 = tBu (LaH2); R1 = Et, R2 = tBu (LbH2); R1 = iPr, R2 = tBu (LcH2); R1 = Me, R2 = Ad (LdH2); R1 = Et, R2 = Ad (LeH2); R1 Received: June 17, 2013

A

dx.doi.org/10.1021/om400562p | Organometallics XXXX, XXX, XXX−XXX

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TiCl4 with the cooresponding free ligands LaH2−LfH2. However, it was found that the complexes with halfdeprotonated ligands or undeprotonated zwitterionic ligands were always obtained at low or ambient temperatures. As shown in Scheme 2, the reaction of TiCl4 with the free ligand

= iPr, R2 = Ad (LfH2)] and their titanium complexes LTiCl2 [L = La (3a); Lb (3b); Lc (3c); Ld (3d); Le (3e); Lf (3f)], as well as the catalytic performance of the new titanium complexes in ethylene polymerization.

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RESULTS AND DISCUSSION Synthesis and Characterization of Free Ligands. The free ligands LaH2−LfH2 were synthesized in moderate to high yields by refluxing a 2-(arylamino)benzaldehyde derivative with a 2-amino-4-tert-butyl-6-alkylphenol compound in methanol in the presence of a few drops of formic acid, as illustrated in Scheme 1. The 2-(arylamino)benzaldehyde derivatives were

Scheme 2. Proposed Mechanism for the Reaction of TiCl4 with the Ligand LdH2

Scheme 1. Synthetic Route for the Free Ligands LaH2−LfH2

LdH2 in toluene at low temperature (−78 °C) results in the formation of a red precipitate (1d), which shows low solubility in toluene and is almost insoluble in hexane. The poor solubility of 1d suggests that it might be a complex with an undeprotonated zwitterionic ligand in dimeric form as reported previously for the reaction of Ti(OiPr)Cl3 with 2-aminophenol.17 Removal of the solvent from the red precipatate under vacuum gives a mixture of 1d and 2d (identified by 1H NMR) due to partial conversion of 1d to 2d by losing a HCl molecule under vacuum conditions. The 1H NMR spectrum of 1d was therefore obtained with an in situ reaction mixture of TiCl4 with LdH2 in CDCl3. In the 1H NMR spectrum of 1d, the broad signal at 12.65 ppm can be tentatively assigned to the HCNH+ proton. When complex 1d was dissolved in THF, the THF-solvated complex 1d′ (as shown in Scheme 3) was formed, and its single crystals suitable for X-ray diffraction analysis were obtained. Crystal structural analysis on 1d′ confirms that it is a THF-solvated zwitterionic titanium complex with an undeprotonated ligand coordinating to the central metal titanium only through the aryloxy O atom. The 1 H NMR spectrum of 1d′ shows a doublet resonance (3J = 15 Hz) for the HCNH+ proton at 8.58 ppm and consequently a doublet resonance (3J = 15 Hz) for the HCNH+ proton at 14.23 ppm, which further confirms the assignment for the resonance of the HCNH+ proton in 1d at 12.65 ppm. When the reaction of LdH2 and TiCl4 in toluene was carried out at 40 °C, the red complex 1d precipitated out at the beginning of the reaction, which dissolved gradually with time to form the complex 2d. In the 1H NMR spectrum of 2d in CDCl3 as shown in Figure 1c, two characteristic singlets at 8.76 and 8.71 ppm for the resonances of the NH and HCN protons can be observed. The presence of the NH resonance indicates that the amine group is not bonded to the metal center and the complex 2d is not the expected final product. When reactions were run at 60−100 °C, mixtures of 2d and a new product (3d) were obtained. 1H NMR spectra of the obtained crude products show that the ratio of 3d/2d increases with elevation of the reaction temperature, as seen in Figure 1d,e. However, it was

synthesized following a published procedure13 by coupling 1,3dioxolane-protected 2-bromobenzaldehyde with the corresponding 2,6-dialkylaniline in toluene using Pd(OAc)2 as the catalyst. The free ligands LaH2−LfH2 were characterized by 1H and 13C NMR spectroscopy. All these compounds show the characteristic resonances for HCN (8.75−8.76 ppm) and Ar−OH (6.47−6.54 ppm) in similar patterns. The Ar−NH resonances were observed in the region 9.81−9.88 ppm, suggesting the existence of a hydrogen bond between the NH and imine groups. The hydrogen bond interaction has been previously observed in similar bidentate anilido-amine free ligands.12 Synthesis and Characterization of Titanium Complexes. The titanium complexes bearing a mono- or dianion tridentate ligand were generally synthesized by a salt metathesis reaction, in which the ligands were first deprotonated with n BuLi or KH followed by the reaction with TiCl4. However, our attempts to synthesize new titanium complexes by reactions of TiCl4 with the bilithium salt of the cooresponding ligand (LaLi2−LfLi2) were unsuccessful. No identifiable product has been obtained from the reactions except for a mixture of polymeric materials featuring broadened 1H NMR signals. It has been reported that some titanium complexes with a bidentate or tridentate ligand containing O− or S− coordinating atom(s) can be synthesized by direct reaction of TiCl4 with cooresponding −OH- or −SH-containing ligands.2a,10c,14 Jin’s group has reported that titanium complexes with a [N−,N−,S] ligand can also be synthesized by direct reaction of TiCl4 with the −NH-containing ligands at room temperature.15 However, they did not get any crystal structural evidence to confirm that the proton of the −NH group in the ligands of these complexes has been removed. Very recently, Tang et al. demonstrated that the reactions of TiCl4 with phenoxy-amine ligands at 50 °C afford only complexes with half-deprotonated ligands [O − ,NH,S] or [O − ,NH,P], not deprotonated ligands [O−,N−,S] or [O−,N−,P].16 Referring to these literature procedures, we tried to synthesize our new titanium complexes by direct reactions of B

dx.doi.org/10.1021/om400562p | Organometallics XXXX, XXX, XXX−XXX

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Scheme 3. Formation of 1d′ by Coordination of THF to 1d

Figure 1. 1H NMR spectra of (a) free ligand LdH2, (b) complex 1d, (c) product from reaction of LdH2 with TiCl4 at 40 °C for 12 h, (d) product from reaction of LdH2 with TiCl4 at 60 °C for 12 h, (e) product from reaction of LdH2 with TiCl4 at 100 °C for 12 h, (f) complex 3d.

the 2,6-iPr2Ph group in 3c and 3f are observed, indicating that the rotation of the Ar group around the C−N bond is inhibited in these complexes.12c,18 Crystallographic Analysis on Complexes 1d′, 3b, 3d, and 3e. The molecular structures of complexes 1d′, 3b, 3d, and 3e were determined by single-crystal X-ray diffraction analysis. Their molecular structures together with selected bond distances and angles are shown in Figures 2−5, respectively. The crystallographic analysis reveals that 1d′ is a zwitterionic six-coordinated titanium complex with the central titanium atom carrying a negative charge and the iminium N atom in the ligand carrying a positive charge. Another thing worth noting is that a hydrogen bond between the hydrogen atom in CNH+ and one chloride (Cl2) at the central titanium atom with a H··· Cl bond distance of 2.363 Å is formed as observed previously for a similar complex, [Ti(OiPr)Cl3(THF)(2-OC6H4NH3)](THF).17 The Ti−Cl and Ti−O bond lengths are all comparable to the corresponding ones in [Ti(OiPr)Cl3(THF)(2-OC6H4NH3)](THF).17 Complexes 3b, 3d, and 3e are isostructural, and they all have a molecular geometry about their titanium centers situated between trigonal bipyramid and square pyramid with the trigonality index parameters τ of 0.49 in 3b, 0.46 in 3d, and 0.50 in 3e, respectively. If they were

found that the reaction cannot go to completion even though the reaction was carried out at 110 °C. Finally, we tried to heat the crude product at 140 °C under vacuum and found that 2d can be almost completely converted to 3d. The 1H NMR spectrum of the new product 3d shows only one singlet (9.40 ppm) in the low-field region that can be assigned to the HC N proton. The disappearence of the resonance of the NH proton demonstrates that complex 3d is the expected final product with the amide N atom being attached to the central metal atom. The structure of 3d was further confirmed by single-crystal X-ray diffraction analysis. On the basis of the above investigation, complexes 3a−3f were synthesized in high yields by carrying out the reactions of TiCl4 with the corresponding free ligands LaH2−LfH2 in toluene at 110 °C and then heating the crude products at 140 °C for a couple of hours. All complexes 3a−3f were characterized with 1H and 13C NMR spectroscopy, as well as elemental analyses. Structures of complexes 3b, 3d, and 3e were determined by single-crystal X-ray crystallography. In their 1H NMR spectra, all complexes show the characteristic resonance of the HCN proton at 9.40−9.41 ppm. Two sets of multiplets for the methylene protons in the 2,6-Et2Ph group in 3b and 3e and two sets of doublets for the methyl protons in C

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Figure 4. Perspective view of complex 3d with thermal ellipsoids drawn at the 30% probability level. Hydrogens and uncoordinated solvent are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N1 2.148(2), Ti1−N2 1.964(3), Ti1−O1 1.852(2), Ti1− Cl1 2.2663(9), Ti1−Cl2 2.242(1); Cl1−Ti1−Cl2 103.2(1), O1−Ti1− N1 75.73(9), O1−Ti1−N2 134.8(1), Cl1−Ti1−N1 162.59(8), O1− Ti1−Cl2 113.03(9), Cl2−Ti1−N2 106.23(8), Cl2−Ti1−N1 91.05(8).

Figure 2. Perspective view of complex 1d′ with thermal ellipsoids drawn at the 30% probability level. Hydrogens and uncoordinated solvent are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ti1−O1 1.811(2), Ti1−O2 2.163(3), Ti1−Cl1 2.3545(11), Ti1−Cl2 2.4221(11), Ti1−Cl3 2.3133(11), Ti1−Cl4 2.2951(11); O1−Ti1−O2 174.82(11).

Figure 5. Perspective view of complex 3e with thermal ellipsoids drawn at the 30% probability level. Hydrogens and uncoordinated solvent are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N1 2.143(2), Ti1−N2 1.996(2), Ti1−O1 1.850(2), Ti1− Cl1 2.257(1), Ti1−Cl2 2.245(1); Cl1−Ti1−Cl2 101.35(4), O1−Ti1− N1 75.90(9), O1−Ti1−N2 135.0(1), Cl1−Ti1−N1 165.27(7), O1− Ti1−Cl2 111.07(8), Cl2−Ti1−N2 107.82(8), Cl2−Ti1−N1 89.77(7).

Figure 3. Perspective view of complex 3b with thermal ellipsoids drawn at the 30% probability level. Hydrogens and uncoordinated solvent are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ti1−N1 2.137(2), Ti1−N2 1.968(2), Ti1−O1 1.858(2), Ti1− Cl1 2.263(1), Ti1−Cl2 2.248(1); Cl1−Ti1−Cl2 103.07(3), O1−Ti1− N1 76.10(9), O1−Ti1−N2 134.69(10), Cl1−Ti1−N1 164.01(7), O1−Ti1−Cl2 113.99(7), Cl2−Ti1−N2 105.40(7), Cl2−Ti1−N1 90.34(7).

N2(amido) bond lengths (1.964(2)−1.996(2) Å) in these complexes are shorter than the Ti−Namido bond length (2.305(2) Å) in [ONN] titanium complexes.2b Ethylene Polymerization. All new titanium complexes 3a−3f were evaluated as precatalysts for ethylene polymerization. The polymerization reactions were carried out at 70 °C in toluene, and the preliminary results are summarized in Table 1. Upon activation with alkylaluminum and Ph3C+B(C6F5)4−, all these complexes show moderate catalytic activities. The complexes with an adamantyl-substituted ligand (3d−3f) were found to show relatively high catalytic activity in comparion to those with a tert-butyl-substituted ligand (3a−3c). For all these catalyst systems, the catalytic activity increases with the increase

considered as distorted square pyramidal molecules with one chloride atom (Cl2) occupying the apical position, the titanium atoms deviate significantly from the basal planes in the direction of Cl2 with a deviation of ca. 0.215 Å in 3b, 0.228 Å in 3d, and 0.203 Å in 3e. The Ti−O bond lengths of 1.850(2)−1.852(2) Å in these complexes are comparable to those in bis(phenoxyimino)titanium(IV) complexes.6b Their Ti−N1(imine) bond distances of 2.137(2)−2.148(2) Å are close to the corresponding ones in related complexes [NNO]TiCl33a and [ONO]TiCl211 but much longer than those in bis(phenoxyimino)titanium(IV) complexes.6 The Ti− D

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titanium complex and trialkylaluminum,19 partial4a or full20 transfer of the chelated ligand from titanium to aluminum, or reduction of the CN double bond in the chelated ligand by alkylaluminum.6c To understand the reason for our catalytic system to show relatively low activity, we studied the reactions of 3a with different amounts of AlMe3 in an NMR tube. The 1H NMR spectrum for the reaction mixture of 3a with 1 equiv of AlMe3 shows that 3a was partially converted to a new complex with three singlet resonances, at −0.53, 0.41, and 1.91 ppm, caused obviously by three methyl groups on the titanium or aluminum atoms. Upon increasing the amount of AlMe3 to 5 equivalents, complex 3a was fully converted to the new complex, indicated by the displacement of the signal at 8.82 ppm by a signal at 8.55 ppm for the HCN proton. The resonances for the Me and tBu groups in the chelated ligand can also be clearly observed in the 1H NMR spectrum of the new complex. With these observations, the new complex could be tentatively assigned to 4a, as shown in Figure 6. Further increase in the amount of AlMe3 to 30 and 50 equivalents resulted in decomposition of 4a, and a complicated mixture was formed, demonstrating that the chelated ligand has been partially or fully displaced from the central titanium atom. Such transfer reactions of the ligand from the central titanium to aluminum were also found in some bis(phenoxyimine) titanium complexes and bis(pyrrolylaldiminato) titanium complexes.21 Careful hydrolysis of the reaction mixture of 3a with 30 equivalents of AlMe3 leads to the recovery of the free ligand LaH2. No product from addition reaction of the HCN double bond was obtained.

Table 1. Ethylene Polymerization with N,N,O Tridentate Titanium Complexesa entry

catalyst

Al/Ti ratio

1 2 3 4 5 6 7 8 9 10 11 12 13d 14e 15f 16g

3a 3b 3c 3d 3e 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f 3f

100 100 100 100 100 100 50 200 300 100 100 100 100 100 100 1000

T/°C yield/g 70 70 70 70 70 70 70 70 70 30 50 90 70 70 70 70

0.20 0.24 0.31 0.28 0.34 0.62 0.38 0.56 0.53 0.40 0.43 0.45 0.75 0.10 0.40 0.38

activityb

Mnc × 10−4

PDIc

32.0 38.4 49.6 44.8 54.4 99.2 60.8 89.6 84.8 64.0 68.8 72.0 60.0 16.0 64.0 60.8

1.9 3.0 4.1 3.1 4.8 6.2 7.6 5.2 4.2 15.9 8.5 4.2 6.5 1.2 4.7 4.3

2.7 2.4 2.6 3.0 3.2 2.7 2.9 2.5 2.8 3.0 2.7 3.3 2.8 3.7 2.8 3.0

a

Polymerization conditions: 60 mL of toluene, 15 min; catalyst 5 μmol; Al = Al(iBu)3; B/Ti molar ratio 1.2, B = Ph3C+B(C6F5)4−; ethylene pressure 5 atm. bUnits of kg PE (mol Ti)−1 h−1 atm−1. c Determined by GPC relative to polystyrene standards. d30 min. e AlMe3 was used. fAlEt3 was used. gMAO was used as cocatalyst.

in the size of the 2,6-R2Ar group at the amido N atom (entries 1−3 and 4−6 in Table 1). These results may be attributed to bulky substiuents on the ligand shielding the metal center and therefore preventing the catalytically active species from deactivation. Detailed studies on other factors influencing the polymerization reaction were carried out with the 3f/AlR3/ Ph3C+B(C6F5)4− systems. It was found that the catalytic activity is strongly affected by the nature of the trialkylaluminum activator. The catalyst system shows the highest activity with AliBu3 as the activator and the lowest activity with AlMe3 as the activator (see entries 6, 14, and 15 in Table 1). The catalytic activity is also influenced by the Al/Ti ratio. It was found that the catalytic activity increases with an increase in Al/Ti ratio from 50 to 100 and then decreases slowly with a further increase in the Al/Ti ratio. It was also observed that the catalytic activity significantly increases with an increase in polymerization temperature from 30 °C to 70 °C and decreases obviously with an increase in polymerization time from 15 min to 30 min. As observed in other catalyst systems,3a the molecular weight of the resulting polymers in the present system decreases with an increase in the Al/Ti ratio from 50 to 300 due to the increased probability of chain transfer from titanium to aluminum at high Al/Ti ratios. Upon activation with MAO, complex 3f shows similar catalytic activity to the 3f/AlR3/Ph3C+B(C6F5)4− system. Gel permeation chromatography (GPC) analysis on the resultant polymers exhibits a relatively narrow polydispersity index (PDI) of 2.45−3.75, indicating the single-site nature of these catalyst systems. The polymers were also characterized by 13C NMR, which indicates that the resultant polymers are linear with a characteristic resonance at 30.2 ppm. The melting points of the obtained polyethylenes range from 138 to 142 °C, which is typical for linear polyethylene. It has been known that many non-metallocene types of titanium complexes show relatively low catalytic activity for olefin polymerization due to formation of a Ti−Al heterobinuclear complex with Me or Cl bridges by combination of the

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CONCLUSION In summary, several anilido-imine-based [N,N,O] tridentate ligands and their titanium complexes 3a−3f have been synthesized and structurally characterized. The titanium complexes were synthesized in high yields by direct reactions of TiCl4 with the corresponding free ligands LaH2−LfH2 in toluene at 110 °C and then heating the crude products at 140 °C. Reactions carried out at room or low temperatures give zwitterionic complexes L+H2Ti−Cl4 with a protonated ligand coordinating to the central metal titanium only through the aryloxy O atom. Neutral complexes LHTiCl3 can be obtained by heating the zwitterionic complexes in toluene at 40 °C with the loss of 1 equivalent of HCl. Upon further heating at 140 °C under vacuum, the neutral complexes can be fully converted to the expected titanium(IV) dicholoride complexes LTiCl2 (3a− 3f) by losing another equivalent of HCl. Upon activation with alkylaluminum and Ph3C+B(C6F5)4−, these complexes show moderate catalytic activity for ethylene polymerization.

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EXPERIMENTAL SECTION

General Considerations. All manipulations involving air- and moisture-sensitive compounds were carried out under an atmosphere of dried and purified nitrogen using standard Schlenk or drybox techniques. Toluene and hexane were dried over sodium/benzophenone and distilled under nitrogen prior to use. Polymerization grade ethylene was further purified by passage through columns of 5 Å molecular sieves and MnO. NMR spectra were recorded on a Varian Mercury-300 MHz at room temperature in CDCl3. The elemental analysis was performed on an Elementar model Vario EL cube analyzer. The molecular weights (MWs) and polydispersity indices (PDIs) of the polymer samples were determined at 150 °C by a PLGPC 220 type high-temperature gel permeation chromatograph. 1,2,4Trichlorobenzene was employed as the solvent at a flow rate of 1.0 mL/min. The calibration was made by polystyrene standard Easi-Cal E

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Figure 6. 1H NMR spectra of 3a (a) and 3a/AlMe3 mixtures (b−f): Al:Ti = 1 (b); Al:Ti = 2 (c); Al:Ti = 5 (d); Al:Ti = 30 (e); Al:Ti = 50 (f). PS-1 (PL Ltd.). The differential scanning calorimetry (DSC) measurements were performed on a Netzsch DSC 204 instrument under N2 atmosphere. The samples were heated at a rate of 10 °C/min and cooled at a rate of 10 °C/min. 2,6-Dimethylaniline, 2,6diethylaniline, and 2,6-diisopropylaniline were purchased from Aldrich. 2-(2,6-Diisopropylphenylamino)benzaldehyde was prepared according to the literature procedure.13 Preparation of Ligands. 2-(2,6-Dimethylphenylamino)benzaldehyde. 2,6-Dimethylaniline (3.00 g, 24.8 mmol), Pd(OAc)2 (43.6 mg, 0.198 mmol), NaOtBu (2.86 g, 29.7 mmol), bis[2-

(diphenylphosphino)phenyl] ether (DPEphos) (160.5 mg, 0.298 mmol), 1,3-dioxolane-protected 2-bromobenzaldehyde (6.27 g, 27.3 mmol), and degassed toluene (50 mL) were added into a flask. After stirring at 100 °C for 10 h, water (40 mL) and toluene (100 mL) were added, and the toluene phase was collected. p-TsOH (2.08 g) was added, and the solution was stirred for 2 h and washed with concentrated aqueous NaHCO3 (30 mL). The organic solution was dried with anhydrous MgSO4, and the solvent was removed by rotary evaporation to give a residue, which was purified by column chromatography on silica gel eluting with ethyl acetate and petroleum F

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ether (v/v, 1:30). Yield: 3.91 g, 70%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.96 (s, 1H, Ar-NH), 9.55 (s, 1H, Ar-CHO), 7.56 (dd, JH−H = 7.8 Hz, J = 1.6 Hz, 1H, Ar-H), 7.29−7.22 (m, 1H, Ar-H), 7.16 (s, 3H, Ar-H), 6.76 (m, 1H, Ar-H), 6.21 (d, J = 8.4 Hz, 1H, Ar-H), 2.19 (s, 6H, CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 194.3 (s, 1C, CH N), 149.6, 136.7, 136.4, 135.8, 128.6, 127.0, 118.4, 116.0, 112.3, 18.3 (s, 2C, ArCH3) ppm. 2-(2,6-Diethylphenylamino)benzaldehyde. A procedure analogous to that used to prepare 2-(2,6-dimethylphenylamino)benzaldehyde was used, but starting from 2,6-diethylaniline (3.00 g, 20.1 mmol). Yield: 3.36 g, 66%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.96 (s, 1H, Ar-NH), 9.59 (s, 1H, Ar-CHO), 7.55 (dd, JH−H = 7.8 Hz, J = 1.6 Hz, 1H, Ar-H), 7.24−7.06 (m, 4H, Ar-H), 6.73 (m, 1H, Ar-H), 6.21 (d, J = 8.4 Hz, 1H, Ar-H), 2.63−2.53 (m, 4H, CH2CH3), 1.12 (t, J = 7.5 Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 193.8 (s, 1C, CHN), 150.1, 137.0, 136.7, 136.2, 128.2, 127.5, 118.8, 116.3, 112.1, 25.1 (s, 2C, CH2CH3), 14.4 (s, 2C, CH2CH3) ppm 2-(2-(2,6-Dimethylphenylamino)benzylideneamino)-4,6-di-tertbutylphenol (LaH2). To a solution of 2-(2,6-dimethylphenylamino)benzaldehyde (2.25 g, 10.0 mmol) and 2-amino-4,6-di-tert-butylphenol (2.21 g, 10.0 mmol) in methanol was added two drops of formic acid at room temperature. After refluxing for 12 h, the resulting mixture was cooled to room temperature, affording a yellow solid. The solid was recrystallized from methanol to give LaH2 as yellow crystals. Yield: 3.64 g (85%). 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.88 (s, 1H, ArNH-Ar), 8.75 (s, 1H, CHN), 7.49 (dd, JH−H = 7.8 Hz, J = 3 Hz, 1H, Ar-H), 7.23 (d, J = 2.1 Hz, 1H, Ar-H), 7.20−7.14 (m, 4H, Ar-H), 7.06 (d, J = 2.4 Hz, 1H, Ar-H), 6.79−6.73 (m, 1H, Ar-H), 6.53 (s, 1H, ArOH), 6.27 (d, J = 6 Hz, 1H, Ar-H), 2.26 (s, 6H, CH3), 1.45 (s, 9H, C(CH3)3), 1.38 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 164.6 (s, 1C, CHN), 149.0, 147.1, 143.1, 138.4, 138.0, 137.5, 136.1, 135.9, 133.6, 129.5, 127.6, 123.2, 118.4, 117.1, 113.1, 113.0, 35.9 (s, 1C, C(CH3)3), 35.6 (s, 1C, C(CH3)3), 32.7 (s, 3C, C(CH3)3), 30.5 (s, 3C, C(CH3)3), 19.4 (s, 2C, ArCH3) ppm. 2-(2-(2,6-Diethylphenylamino)benzylideneamino)-4,6-di-tert-butylphenol (LbH2). A procedure analogous to that used to prepare LaH2 was used, but starting from a 2-(2,6-diethylphenylamino)benzaldehyde ligand (2.53 g, 10.0 mmol). Yield: 3.65 g, 80%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.96 (s, 1H, Ar-NH-Ar), 8.68 (s, 1H, CHN), 7.47 (dd, JH−H = 7.8 Hz, J = 1.5 Hz, 1H, Ar-H), 7.18 (d, J = 1.2 Hz, 1H, ArH), 7.13−7.06 (m, 4H, Ar-H), 7.02 (d, J = 2.1 Hz, 1H, Ar-H), 6.69− 6.63 (m, 1H, Ar-H), 6.54 (s, 1H, Ar-OH), 6.20 (d, J = 6 Hz, 1H, ArH), 2.63−2.40 (m, 4H, CH2CH3), 1.35 (s, 9H, C(CH3)3), 1.28 (s, 9H, C(CH3)3), 1.08 (t, J = 7.5 Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 163.9 (s, 1C, CHN), 149.1, 146.3, 142.9, 142.3, 137.8, 135.9, 135.2, 135.1, 132.8, 127.4, 126.9, 122.3, 117.4, 116.2, 112.4, 112.1, 35.1 (s, 1C, C(CH3)3), 34.8 (s, 1C, C(CH3)3), 31.9 (s, 3C, C(CH3)3), 29.7 (s, 3C, C(CH3)3), 25.0 (s, 2C, CH2CH3), 15.0 (s, 2C, CH2CH3) ppm. 2-(2-(2,6-Diisopropylphenylamino)benzylideneamino)-4,6-ditert-butylphenol (LcH2). A procedure analogous to that used to prepare L a H 2 was used, but starting from a 2-(2,6diisopropylphenylamino)benzaldehyde ligand (2.81 g, 10.0 mmol). Yield: 4.21 g, 87%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.94 (s, 1H, Ar-NH-Ar), 8.75 (s, 1H, CHN), 7.52 (dd, JH−H = 7.8 Hz, J = 1.5 Hz, Ar-H), 7.35 (dd, JH−H = 8.7 Hz, J = 6.4 Hz, 1H, Ar-H), 7.24−7.26 (m, 4H, Ar-H), 7.23 (d, J = 2.4 Hz, 1H, Ar-H), 6.77−6.69 (m, 1H, Ar-H), 6.54 (s, 1H, Ar-OH), 6.28 (d, J = 7.8 Hz, 1H, Ar-H), 3.15 (m, 2H, CH(CH3)2), 1.42 (s, 9H, C(CH3)3), 1.36 (s, 9H, C(CH3)3), 1.18 (d, JH−H = 9.0 Hz, 6H, CH(CH3)2), 1.13 (d, JH−H = 6.0 Hz, 6H, CH(CH3)2). 13C NMR (75 MHz, CDCl3, 25 °C): δ 164.0 (s, 1C, CHN), 149.8, 147.7, 146.3, 142.2, 137.8, 135.2, 135.1, 134.2, 132.8, 128.0, 124.1, 122.3, 117.2, 116.1, 112.6, 112.2, 35.1 (s, 1C, C(CH3)3), 34.8 (s, 1C, C(CH3)3), 31.9 (s, 3C, C(CH3)3), 29.7 (s, 3C, C(CH3)3), 28.7 (s, 2C, CH(CH3)2), 25.0 (s, 2C, CH(CH3)2), 23.3 (s, 2C, CH(CH3)2) ppm. 2-(2-(2,6-Dimethylphenylamino)benzylideneamino)-4-tert-butyl6-adamantylphenol (L d H 2 ). To a solution of 2-(2,6dimethylphenylamino)benzaldehyde (2.25 g, 10.0 mmol) and 2amino-4-tert-butyl-6-adamantylphenol (2.99 g, 10.0 mmol) in

methanol was added two drops of formic acid at room temperature. After refluxing for 12 h, the resulting mixture was cooled to room temperature to afford a yellow solid. The solid was recrystallized from methanol to give yellow crystals as the desired product ligand LdH2. Yield: 4.20 g (83%). 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.87 (s, 1H, Ar-NH-Ar), 8.76 (s, 1H, CHN), 7.67 (dd, JH−H = 7.8 Hz, J = 1.5 Hz, 1H, Ar-H), 7.23−7.13 (m, 6H, Ar-H), 6.76−6.66 (m, 1H, ArH), 6.53 (s, 1H, Ar-OH), 6.30 (d, J = 8.1 Hz, 1H, Ar-H), 2.26 (s, 6H, CH3), 2.20−1.72 (m, 15H, Ad), 1.32 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 163.7 (s, 1C, CHN), 148.2, 146.5, 142.4, 137.6, 137.2, 136.7, 135.4, 135.3, 132.8, 128.6, 126.8, 122.3, 117.5, 116.3, 112.2, 111.9, 40.5 (s, 3C, Ad), 35.1 (s, 3C, Ad), 34.8 (s, 1C, C(CH3)3), 31.8 (s, 3C, C(CH3)3), 29.2 (s, 3C, Ad), 18.6 (s, 2C, ArCH3) ppm. 2-(2-(2,6-Diethylphenylamino)benzylideneamino)-4-tert-butyl-6adamantylphenol (LeH2). A procedure analogous to that used to prepare L d H 2 was used, but starting from a 2-(2,6diethylphenylamino)benzaldehyde ligand (2.53 g, 10.0 mmol). Yield: 4.22 g, 79%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.86 (s, 1H, ArNH-Ar), 8.76 (s, 1H, CHN), 7.48 (dd, JH−H = 7.8 Hz, J = 1.5 Hz, 1H, Ar-H), 7.26−7.09 (m, 5H, Ar-H), 7.05 (d, J = 2.3 Hz, 1H, Ar-H), 6.80−6.68 (m, 1H, Ar-H), 6.50 (s, 1H, Ar-OH), 6.27 (d, J = 8.5 Hz, 1H, Ar-H), 2.68−2.48 (m, 4H, CH2CH3), 2.21−1.75 (m, 15H, Ad), 1.36 (s, 9H, C(CH3)3), 1.14 (t, J = 7.5 Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 163.8 (s, 1C, CHN), 149.0, 146.5, 142.8, 142.3, 137.7, 135.9, 135.4, 135.2, 132.7, 127.4, 126.8, 122.2, 117.3, 116.2, 112.4, 111.9, 40.5 (s, 3C, Ad), 37.2 (s, 3C, Ad), 34.8 (s, 1C, C(CH3)3), 31.9 (s, 3C, C(CH3)3), 29.2 (s, 3C, Ad), 25.0 (s, 2C, CH2CH3), 15.0 (s, 2C, CH2CH3) ppm. 2-(2-(2,6-Diisopropylphenylamino)benzylideneamino)-4-tertbutyl-6-adamantylphenol (LfH2). A procedure analogous to that used to prepare L d H 2 was used, but starting from a 2-(2,6diisopropylphenylamino)benzaldehyde ligand (2.81 g, 10.0 mmol). Yield: 4.95 g, 88%. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.82 (s, 1H, Ar-NH-Ar), 8.76 (s, 1H, CHN), 7.48 (dd, JH−H = 7.8 Hz, J = 1.5 Hz, 1H, Ar-H), 7.37−7.32 (m, 1H, Ar-H), 7.27 (s, 1H, Ar-H), 7.25 (d, J = 1.6 Hz, 1H, Ar-H), 7.18−7.13 (m, 2H, Ar-H), 7.07 (d, J = 2.2 Hz, 1H, Ar-H), 6.77−6.71 (m, 1H, Ar-H), 6.48 (s, 1H, Ar-OH), 6.28 (d, J = 8.0 Hz, 1H, Ar-H), 3.15 (m, 2H, CH(CH3)2), 2.19−1.74 (m, 15H, Ad), 1.36 (s, 9H, C(CH3)3), 1.17 (d, JH−H = 9.0 Hz, 6H, CH(CH3)2), 1.13 (d, JH−H = 6.0 Hz, 6H, CH(CH3)2). 13C NMR (75 MHz, CDCl3, 25 °C): δ 163.8 (s, 1C, CHN), 149.8, 147.6, 146.5, 142.3, 137.7, 135.5, 135.2, 134.2, 132.7, 127.9, 124.1, 122.2, 117.2, 116.1, 112.6, 112.0, 40.5 (s, 3C, Ad), 37.2 (s, 3C, Ad), 34.8 (s, 1C, C(CH3)3), 31.9 (s, 1C, C(CH3)3), 29.2 (s, 3C, Ad), 28.7 (s, 2C, CH(CH3)2), 25.0 (s, 2C, CH(CH3)2), 23.3 (s, 2C, CH(CH3)2) ppm. Preparation of N,N,O Tridentate Titanium Complexes. Complex 1d. To a stirred solution of LdH2 (1.01 g, 2 mmol) in 30 mL of toluene was added TiCl4 (0.22 mL, 2 mmol) in toluene (10 mL) at 0 °C. A red suspension formed immediately. The mixture was allowed to warm to room temperature and keep stirring for 2 h at room temperature. The red product 1d was obtained by filtration and washed twice with 10 mL of hexane and dried under vacuum (1.18 g, 85%). The 1H NMR of the red powder was revealed to be a mixture of 1d and 2d probably due to the partial conversion of 1d to 2d under vacuum in the preparation of the sample. Good 1H NMR and 13C NMR spectra were obtained by in situ addition of TiCl4 in the CDCl3 solution of ligand in an NMR tube. 1H NMR (300 MHz, CDCl3, 25 °C): δ 12.86 (bs, 1H, Ar-NH-Ar), 8.72 (bs, 1H, CHN), 7.85 (d, JH−H = 6.0 Hz, 1H, Ar-H), 7.58−7.53 (m, 2H, Ar-H), 7.21−7.16 (m, 4H, Ar-H), 7.03 (t, JH−H = 6.0 Hz, 1H, Ar-H), 6.52 (d, JH−H = 6.0 Hz, 1H, Ar-H), 2.23 (s, 6H, CH3), 2.38−1.72 (m, 15H), 1.37 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 162.4, 161.2, 158.1, 153.6, 149.9, 141.9, 135.5, 133.7, 132.2, 129.5, 127.5, 126.5, 121.5, 118.7, 117.4, 115.2, 111.1, 42.1 (s, 3C, Ad), 36.8 (s, 3C, Ad), 35.6 (s, 1C, C(CH3)3), 31.5 (s, 3C, C(CH3)3), 29.3 (s, 3C, Ad), 18.8 (s, 2C, ArCH3) ppm. Complex 1d′. To a solution of 1d (1.18 g, 0.85 mmol) in THF (2 mL) was added slowly hexane (20 mL), and the precipitate was collected by filtration. The pale red powder was washed with 10 mL of G

dx.doi.org/10.1021/om400562p | Organometallics XXXX, XXX, XXX−XXX

Organometallics

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hexane and dried under vacuum (1.24 g, 95%). Crystals suitable for Xray diffraction analysis were grown from a mixed solution of THF and hexane. Anal. Calcd for C39H50N2O2TiCl4 (768.51): C 60.95; H 6.56; N 3.65. Found: C 60.93; H 6.59; N 3.63. 1H NMR (300 MHz, CDCl3, 25 °C): δ 14.23 (d, JH−H = 15 Hz, 1H, HCNH+-Ar), 8.58 (d, JH−H = 15 Hz, 1H, HCNH+-Ar), 8.03 (d, JH−H = 9 Hz, 1H, Ar-H), 7.51− 7.45 (m, 2H, Ar-H), 7.15 (bs, 3H, Ar-H), 7.07 (bs, 1H, NH), 6.95− 7.00 (m, 2H, Ar-H), 3.86 (bs, 4H, THF), 6.30 (d, J = 8.1 Hz, 1H, ArH), 2.43 (s, 6H, CH3), 2.17−1.73 (m, 15H), 1.88 (m, 4H, THF), 1.34 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 160.7, 152.2, 147.6, 144.6, 140.0, 136.2, 136.1, 135.6, 134.4, 133.8, 129.3, 127.7, 127.1, 120.2, 117.7, 116.4, 115.8, 70.3 (s, 2C, THF), 42.5 (s, 3C, Ad), 36.9 (s, 3C, Ad), 35.3 (s, 1C, C(CH3)3), 31.5 (s, 3C, C(CH3)3), 29.5 (s, 3C, Ad), 25.8 (s, 2C, THF), 18.6 (s, 2C, ArCH3)ppm. Complex 2d. To a stirred solution of LdH2 (1.01 g, 2 mmol) in 60 mL of toluene was added TiCl4 (0.22 mL, 2 mmol) in toluene (40 mL) at −78 °C. A red suspension formed immediately. The mixture was allowed to warm to room temperature, and then the mixture was heated to 40 °C and keeped stirring for 18 h. During the reaction period, the red suspension dissolved gradually, and the solution turned to black-red. After the solvent was removed under vacuum, the residue was recrystallized with a mixed solution of CH2Cl2 (2 mL) and hexane (15 mL), affording complex 2d as brown-red crystals (1.20 g, 91%). Anal. Calcd for C35H41N2OTiCl3 (659.94): C 63.70; H 6.56; N 4.27. Found: C 63.73; H 6.54; N 4.29. 1H NMR (300 MHz, CDCl3, 25 °C): δ 8.7 (s, 1H, Ar-NH-Ar), 8.72 (s, 1H, CHN), 7.74 (d, J = 7.2 Hz, 1H, Ar-H), 7.56−7.16 (m, 7H, Ar-H), 6.85 (d, J = 8.1 Hz, 1H, Ar-H), 2.60 (s, 3H, CH3), 2.20−1.72 (m, 18H), 1.38 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 163.5, 148.0, 146.4, 142.2, 137.4, 137.0, 136.6, 135.3, 135.1, 132. 6, 128.5, 126.6, 122.1, 117.4, 116.1, 112.1, 111.8, 40.4 (s, 3C, Ad), 37.1 (s, 3C, Ad), 34.7 (s, 1C, C(CH3)3), 31.7 (s, 3C, C(CH3)3), 29.1 (s, 3C, Ad), 18.5 (s, 2C, ArCH3) ppm. Complex 3a. To a stirred solution of LaH2 (0.86 g, 2 mmol) in 30 mL of toluene was added TiCl4 (0.22 mL, 2 mmol) in toluene (10 mL) at −78 °C. A red suspension formed immediately. The mixture was allowed to warm to room temperature and then heated to 110 °C to remove the solvent. The residue was heated to 140 °C under vacuum for 3 h. Pure complex 3a (1.00 g, 92%) was obtained as dark red crystals. Anal. Calcd for C29H34N2OTiCl2 (545.37): C 63.87; H 6.28; N 5.14. Found: C 63.90; H 6.30; N 5.10. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.42 (s, 1H, CHN), 7.99 (dd, JH−H = 8.0 Hz, J = 1.5 Hz, 1H, Ar-H), 7.53−7.42 (m, 3H, Ar-H), 7.33−7.27 (m, 2H, ArH), 7.26−7.14 (m, 2H, Ar-H), 6.38 (d, J = 8.8 Hz, 1H, Ar-H), 2.02 (s, 6H, CH3), 1.44 (s, 9H, C(CH3)3), 1.40 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 160.6 (s, 1C, HCN), 154.3, 153.4, 147.6, 144.6, 139.9, 136.4, 135.3, 134.8, 134.6, 129.6, 128.8, 123.8, 122.7, 122.2, 114.1, 108.5, 35.2 (s, 1C, C(CH3)3), 35.1 (s, 1C, C(CH3)3), 31.9 (s, 3C, C(CH3)3), 29.3 (s, 3C, C(CH3)3), 18.9 (s, 2c, Ar-CH3) ppm. Complex 3b. Complex 3b was synthesized in the same way as described above for the synthesis of complex 3a with ligand LbH2 (0.91 g, 2.0 mmol) as starting material. Pure complex 3b (1.07 g, 93%) was obtained as dark red crystals. A single crystal suitable for X-ray crystallographic analysis was obtained from a mixed solution of CH2Cl2/hexane (v/v = 1−2:10). Anal. Calcd for C31H38N2OTiCl2 (573.42): C 64.93; H 6.68; N 4.89. Found: C 64.90; H 6.65; N 4.91. 1 H NMR (300 MHz, CDCl3, 25 °C): δ 9.42 (s, 1H, CHN), 7.98 (dd, JH−H = 8.0 Hz, J = 1.5 Hz, 1H, Ar-H), 7.54−7.40 (m, 3H, Ar-H), 7.34−7.28 (m, 3H, Ar-H), 7.22−7.14 (m, 1H, Ar-H), 6.35 (d, J = 8.8 Hz, 1H, Ar-H), 2.56−2.41 (m, 2H, CH2CH3), 2.30−2.15 (m, 2H, CH2CH3), 1.42 (s, 9H, C(CH3)3), 1.41 (s, 9H, C(CH3)3), 1.07 (t, J = 7.5 Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 161.1 (s, 1C, HCN), 155.6, 153.4, 146.3, 144.4, 140.2, 140.1, 136.3, 135.3, 134.4, 129.2, 127.2, 123.7, 122.4, 122.0, 114.6, 108.5, 35.2 (s, 1C, C(CH3)3), 35.1 (s, 1C, C(CH3)3), 31.9 (s, 3C, C(CH3)3), 29.6 (s, 3C, C(CH3)3), 24.4 (s, 2C, CH2CH3), 14.3 (s, 2C, CH2CH3) ppm. Complex 3c. Complex 3c was synthesized in the same way as described above for the synthesis of complex 3a with ligand LcH2 (0.97 g, 2 mmol) as starting material. Pure complex 3c (1.14 g, 95%) was obtained as dark red crystals. Anal. Calcd for C33H42N2OTiCl2

(601.47): C 65.90; H 7.04; N 4.66. Found: C 65.86; H 7.01; N 4.68. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.41 (s, 1H, CHN), 7.94 (dd, JH−H = 8.0 Hz, J = 1.5 Hz, 1H, Ar-H), 7.56−7.47 (m, 3H, ArH), 7.42−7.27 (m, 3H, Ar-H), 7.17−7.09 (m, 1H, Ar-H), 6.29 (d, J = 8.8 Hz, 1H, Ar-H), 2.65 (m, 2H, CH(CH3)2), 1.42 (s, 9H, C(CH3)3), 1.40 (s, 9H, C(CH3)3), 1.34 (d, J = 6.7 Hz, 6H, CH(CH3)2), 0.95 (d, J = 6.7 Hz, 6H, CH(CH3)2). 13C NMR (75 MHz, CDCl3, 25 °C): δ 161.8 (s, 1C, HCN), 156.8, 154.7, 145.3, 144.6, 143.7, 141.0, 136.2, 135.8, 134.3, 130.1, 125.7, 123.7, 122.6, 122.0, 115.9, 108.7, 35.3 (s, 1C, C(CH3)3), 35.2 (s, 1C, C(CH3)3), 32.1 (s, 3C, C(CH3)3), 29.7 (s, 3C, C(CH3)3), 28.9 (s, 2C, CH(CH3)2), 25.5 (s, 2C, CH(CH3)2), 24.6 (s, 2C, CH(CH3)2) ppm. Complex 3d. Complex 3d was synthesized in the same way as described above for the synthesis of complex 3a with ligand LdH2 (1.01 g, 2 mmol) as starting material. Pure complex 3d (1.17 g, 94%) was obtained as dark red crystals. A single crystal suitable for X-ray crystallographic analysis was obtained from a mixed solution of CH2Cl2/n-hexane (v/v = 1−2:10). Anal. Calcd for C35H40N2OTiCl2 (623.48): C 67.42; H 6.47; N 4.49. Found: C 67.45; H 6.51; N 4.47. 1 H NMR (300 MHz, CDCl3, 25 °C): δ 9.42 (s, 1H, CHN), 7.98 (dd, JH−H = 8.0 Hz, J = 1.5 Hz,, 1H, Ar-H), 7.51−7.41 (m, 2H, Ar-H), 7.33−7.27 (m, 2H, Ar-H), 7.26−7.14 (m, 3H, Ar-H), 6.37 (d, J = 8.8 Hz, 1H, Ar-H), 2.04 (s, 6H, CH3), 2.16−2.06 (m, 9H, Ad), 1.85−1.70 (m, 6H, Ad), 1.41 (s, 9H, C(CH3)3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 161.0 (s, 1C, HCN), 154.3, 153.0, 147.7, 144.3, 139.9, 136.4, 135.1, 134.4, 134.4, 129.3, 128.5, 123.4, 122.4, 122.0, 113.8, 108.1, 40.4 (s, 3C, Ad), 37.0 (s, 3C, Ad), 35.0 (s, 1C, C(CH3)3), 31.8 (s, 3C, C(CH3)3), 28.9 (s, 3C, Ad), 18.8 (s, 2C, CH3) ppm. Complex 3e. Complex 3e was synthesized in the same way as described above for the synthesis of complex 3a with ligand LeH2 (1.07 g, 2 mmol) as starting material. Pure complex 3e (1.21 g, 93%) was obtained as dark red crystals. A single crystal suitable for X-ray crystallographic analysis was obtained from a solution of CH2Cl2/nhexane (v/v = 1−2:10). Anal. Calcd for C37H44N2OTiCl2 (652.53): C 68.21; H 6.81; N 4.30. Found: C 68.19; H 6.85; N 4.33. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.42 (s, 1H, CHN), 7.97 (dd, JH−H = 8.0 Hz, J = 1.5 Hz, 1H, Ar-H), 7.52−7.39 (m, 2H, Ar-H), 7.35−7.29 (m, 2H, Ar-H), 7.25−7.13 (m, 3H, Ar-H), 6.35 (d, J = 8.8 Hz, 1H, ArH), 2.50−2.33 (m, 2H, CH2CH3), 2.22−2.10 (m, 2H, CH2CH3), 2.07−1.60 (m, 15H), 1.34 (s, 9H, C(CH3)3), 1.01 (t, J = 7.5 Hz, 6H, CH2CH3). 13C NMR (75 MHz, CDCl3, 25 °C): δ 161.2 (s, 1C, HC N), 155.5, 153.0, 146.5, 144.3, 140.2, 139.8, 135.1, 134.1, 128.8, 127.4, 126.9, 123.3, 122.1, 121.7, 114.4, 108.0, 40.5 (s, 3C, Ad), 37.0 (s, 3C, Ad), 35.0 (s, 1C, C(CH3)3), 31.7 (s, 3C, C(CH3)3), 28.9 (s, 3C, Ad), 24.2 (s, 2C, CH2CH3), 14.1 (s, 2C, CH2CH3) ppm. Complex 3f. Complex 3f was synthesized in the same way as described above for the synthesis of complex 3a with ligand LfH2 (1.13 g, 2.0 mmol) as starting material. Pure complex 3f (1.30 g, 96%) was obtained as dark red crystals. Anal. Calcd for C39H48N2OTiCl2 (679.58): C 68.93; H 7.12; N 4.12. Found: C 68.97; H 7.15; N 4.08. 1H NMR (300 MHz, CDCl3, 25 °C): δ 9.40 (s, 1H, CHN), 7.93 (dd, JH−H = 8.0 Hz, J = 1.5 Hz,, 1H, Ar-H), 7.56−7.47 (m, 2H, Ar-H), 7.44−7.32 (m, 3H, Ar-H), 7.25−7.08 (m, 2H, Ar-H), 6.31 (d, J = 8.8 Hz, 1H, Ar-H), 2.65 (sept, J = 6.7 Hz, 2H, CH(CH3)2), 2.20− 1.69 (m, 15H), 1.41 (s, 9H, C(CH3)3), 1.34 (d, J = 6.7 Hz, 6H, CH(CH3)2), 0.96 (d, J = 6.7 Hz, 6H, CH(CH3)2). 13C NMR (75 MHz, CDCl3, 25 °C): δ 161.7 (s, 1C, HCN), 156.5, 154.2, 145.0, 144.4, 143.3, 140.8, 136.2, 135.5, 133.9, 129.7, 125.3, 123.2, 122.2, 121.6, 115.5, 108.2, 40.5 (s, 3C, Ad), 37.0 (s, 3C, Ad), 35.2 (s, 1C, C(CH3)3), 31.8 (s, 3C, C(CH3)3), 29.2 (s, 3C, Ad), 28.5 (s, 2C, CH(CH3)2), 25.2 (s, 2C, CH(CH3)2), 24.3 (s, 2C, CH(CH3)2) ppm. Ethylene Polymerization Experiments. The ethylene polymerization experiments were carried out as follows: A dry 250 mL steel autoclave with a magnetic stirrer was charged with 50 mL of toluene, thermostated at the desired temperature, and saturated with ethylene (1.0 atm). The polymerization reaction was started by addition of a mixture of the catalyst and AliBu3 in toluene (5 mL) and a solution of Ph3C+B(C6F5)4− in toluene (5 mL) at the same time. The vessel was pressurized to 5 atm with ethylene immediately, and the pressure was maintained by continuous feeding of ethylene. The reaction mixture H

dx.doi.org/10.1021/om400562p | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

(8) (a) Yu, S.-M.; Mecking, S. J. Am. Chem. Soc. 2008, 130, 13204. (b) Li, X.-F.; Dai, K.; Ye, W.-P.; Pan, L.; Li, Y.-S. Organometallics 2004, 23, 1223. (9) Oakes, D.-C. H.; Kimberley, B.-S.; Gibson, V.-C.; Jones, D.-J.; White, A.-J. P.; Williams, D.-J. Chem. Commun. 2004, 23, 2174. (10) (a) Yang, X.-H.; Liu, C.-R.; Wang, C.; Sun, X.-L.; Guo, Y.-H.; Wang, X.-K.; Wang, Z.; Xie, Z.; Tang, Y. Angew. Chem., Int. Ed. 2009, 8099. (b) Wang, C.; Ma, Z.; Sun, X.-L.; Gao, Y.; Guo, Y.-H.; Tang, Y.; Shi, L.-P. Organometallics 2006, 25, 3259. (c) Yang, X.-H.; Sun, X.-L.; Han, F.-B.; Liu, B.; Tang, Y.; Wang, Z.; Gao, M.-L.; Xie, Z.; Bu, S.-Z. Organometallics 2008, 27, 4618. (d) Hu, W.-Q.; Sun, X.-L.; Wang, C.; Gao, Y.; Tang, Y.; Shi, L.-P.; Xia, W.; Sun, J.; Dai, H.-L.; Li, X.-Q.; Yao, X.-L.; Wang, X.-R. Organometallics 2004, 23, 1684. (11) Xu, T.; Liu, J.; Wu, G.-P.; Lu, X.-B. Inorg. Chem. 2011, 50, 10884. (12) (a) Yang, N.; Xin, L.; Gao, W.; Zhang, J.; Luo, X.; Liu, X.; Mu, Y. Dalton Trans. 2012, 41, 11454. (b) Gao, W.; Cui, D.; Liu, X.; Zhang, Y.; Mu, Y. Organometallics 2008, 27, 5889. (c) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren, Y.; Feng, S. Organometallics 2005, 24, 1614. (d) Yao, W.; Mu, Y.; Gao, A.; Gao, W.; Ye, L. Dalton Trans. 2008, 3199. (13) Sasamori, T.; Matsumoto, T.; Tokitoh, N. Polyhedron 2010, 29, 425. (14) Białek, M.; Czaja, K.; Szydło, E. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 565. (15) Jia, A.-Q.; Wang, J.-Q.; Hu, P.; Jin, G.-X. Dalton Trans. 2011, 7730. (16) Wan, D.-W.; Chen, Z.; Gao, Y.-S.; Shen, Q.; Sun, X.-L.; Tang, Y. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2495. (17) Ho, Y.-C.; Hwang, T.-Y.; Gau, H.-M. Inorg. Chim. Acta 1998, 278, 232. (18) (a) Hayes, P.-G.; Welch, G.-C.; Emslie, D.-J.-H.; Noack, C.-L.; Piers, W.-E.; Parvez, M. Organometallics 2003, 22, 1577. (b) Scollard, J.-D.; McConville, D.-H.; Payne, N.-C.; Vittal, J.-J. Macromolecules 1996, 29, 5241. (19) Makio, H.; Fujita, T. Macromol. Symp. 2004, 213, 221. (20) Zhang, D. Eur. J. Inorg. Chem. 2007, 19, 3077. (21) (a) Bryliakov, K.-P.; Kravtsov, E.-A.; Broomfield, L.; Talsi, E.-P.; Bochmann, M. Organometallics 2007, 26, 288. (b) Bryliakov, K.-P.; Kravtsov, E.-A.; Pennington, D.-A.; Lancaster, S.-J.; Bochmann, M.; Brintzinger, H.-H.; Talsi, E.-P. Organometallics 2005, 24, 5660.

was stirred at the desired temperature for 15 min. The polymerization was then quenched by injecting acidified ethanol containing HCl (3 M). The polymer was collected by filtration, washed with water and ethanol, and dried to a constant weight under vacuum. Crystal Structure Determination. The crystals were mounted on a glass fiber using the oil drop method. Data obtained with the ω−2θ scan mode were collected on a Bruker SMART 1000 CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods and refined with full-matrix least-squares on F2. All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were introduced in calculated positions with the displacement factors of the host carbon atoms. All calculations were performed using the SHELXTL crystallographic software packages.

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ASSOCIATED CONTENT

* Supporting Information S

X-ray crystallographic data and refinements for complexes 1d′, 3b, 3d, and 3e in CIF format are available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: (W. Gao) [email protected]. *E-mail: (Y. Mu) [email protected] Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Natural Science Foundation of China for financial support (Nos. 21074043, 51173061, and 21274050).

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REFERENCES

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dx.doi.org/10.1021/om400562p | Organometallics XXXX, XXX, XXX−XXX