3. Variable crystallinity polyethylene nanoparticles
3.3. Summary and conclusions
3.4.3. Polymerization procedure
Polymerizations were carried out in a 300 mL stainless steel mechanically stirred (750 rpm) pressure reactor equipped with a heating/cooling jacket supplied by a thermostat controlled by a thermocouple dipping into the polymerization mixture. A valve controlled by a pressure transducer allowed for applying and keeping up a constant ethylene pressure. The required flow of ethylene, corresponding to ethylene consumed by polymerization, was monitored by a mass flow meter and recorded digitally. Prior to a polymerization experiment, the reactor was heated under vacuum to the desired reaction temperature for 30 to 60 min, and then back-filled with argon. To a mixture of SDS and the respective Ni-methyl complex 100 mL of distilled and degassed water were added at room temperature via a teflon cannula in a 150 ml Schlenk-flask.
The mixture was stirred for 2 min to afford a homogeneous solution. The solution was cannula-transferred to the argon-flushed reactor and the reactor was closed. The reactor was pressurized to 40 bar with constant ethylene feeding under stirring. The final pressure was obtained within less than 3 min. After the desired reaction time, the reactor was carefully vented, and the obtained dispersion was filtrated through a plug of glass-wool. For determination of yields and for further polymer analysis a specified portion of the dispersion was precipitated by pouring into excess methanol. The polymer was washed three times with methanol and dried in vacuo at 50 °C.
Chapter 4
Extremely narrow-dispersed high molecular weight polyethylene and block copolymers of
ethylene/propylene from living polymerization at elevated temperatures with o-F substituted Ti
enolatoimines
Abstract: A series of new titanium complexes with imineenolato ligands (3a –c) has been synthesized and characterized. The catalyst systems display high activities and produce high molecular weight polyethylenes with MAO as a cocatalyst at room temperature under atmospheric pressure. With a new ortho-fluorinated titanium imineenolato complex (3a), ethylene is polymerized in an unprecedented living fashion affording polymer with a high molecular weight (Mn > 105 g mol-1) and an extremely narrow distribution (Mw/Mn = 1.01) at the same time; the living character is also retained even at an elevated temperature of 75°C (Mw/Mn
= 1.15 after 15 min) and even after 1h of polymerization time (Mn = 9.9 x 105 g mol-1, Mw/Mn = 1.17 at 25 ºC). Ethylene/propylene block copolymers were also accessible. Living behavior was further corroborated by a linear increase of number average molecular weight (Mn) with reaction time. In contrast, complexes 3b and 3c lacking fluorine atoms in the ortho-position did not promote any living ethylene polymerization. The catalyst precursors are incompletely activated.
4.1. Introduction
Living polymerization techniques are an essential tool for the synthesis of polymers with controlled architectures, such as monodisperse polymers or blockcopolymers.93 Polymerization in a living fashion requires the essential absence of chain termination and irreversible transfer.
In olefin polymerization, chain transfer (occurring by β-hydride transfer or transfer to cocatalyst) and termination can be suppressed by polymerization at low temperatures.56,94 This, however, results in low catalyst activities and limited molecular weights attainable especially for semicrystalline polymers. Therefore, considerable effort has been directed at the development of new catalysts. Albeit a significant number of catalyst systems with living polymerization characteristics at ambient or elevated temperature have been reported,60,67,70,72-75,77a,b,95,96,97,98
the synthesis of linear polyethylene (PE) with a high molecular weight and truly narrow distribution remains a challenge. Phenoxyimine Ti complexes with o-fluorine substitution of the N-aryl moiety, discovered by Fujita et al., are highly active versatile catalysts for, e.g., the synthesis of narrowly distributed (ultra high molecular weight) PE and of block copolymers.73-75,95 The o-F substituents have been suggested to suppress chain transfer by interaction with the β-hydrogen atoms of the growing PE chain.73-75,95,,99
At 25 °C linear PE with Mw/Mn as low as 1.05 was obtained, when a short reaction time (3 min) and diluted ethylene (0.04 atm) were employed for this very reactive system. The PE formed with this narrow distribution has a molecular weight of several 104 g mol-1.74,75a-b Living characteristics can be retained for longer reaction times also at 50 °C, as evidenced by a linear increase of molecular weight with time to afford PE with, e.g., Mw/Mn = 1.19, Mn = 1.4 × 105 g mol-1 after 15 min of polymerization.73 For complexes with other N,O-chelating ligands, however, no living polymerization was observed to result from o-F substitution,100 , 101 and living polymerization occurs also for nonfluorinated N,O-chelated Ti complexes.60,95b This prompted us to study the effect of o-F substitution in a different type of
4.2. Results and discussion
4.2.1. Synthesis of Ti complexes
Ti(IV) enolatoimine complexes [(N^O)2TiCl2] substituted in the 2,6-position of the N-aryl moiety were prepared in good yields (70%) by reaction of the corresponding ketoenamines with [Ti(NMe2)2Cl2] and chlorination of the resulting mixed amidochloro intermediate with
In the solid state, 3a possesses a C2-symmetric, distorted octahedral geometry (Figure 4-1). The two oxygen atoms are oriented trans to one another (O-Ti-O angle 164°), while the two nitrogen atoms (N-Ti-N 92°) and the two chlorine atoms are positioned in a cis fashion. The latter is a prerequisite for polymerization catalysis.
Figure 4-1. ORTEP plot of the molecular structure of 3a. Ellipsoids are shown with 50%
probability. The H-atoms are not shown for clarity.
4.2.2. Ethylene homopolymerization
Activation of 3a-c with an MAO cocatalyst affords ethylene polymerization catalysts (Table 4-1). Astonishingly, 3a affords high molecular weight linear PE with an extremely narrow molecular weight distribution of Mw/Mn = 1.01 at room temperature (entry 2; cf.
Experimental Section for details of molecular weight determination and Addendum for GPC trace). The polymer molecular weight determined agrees within experimental error with the theoretical value calculated from the amount of polymer obtained and catalyst precursor employed. This shows that the catalyst precursor is rapidly converted to a single type of active species, chains are initiated simultaneously, and essentially no chain transfer or termination occurs. The catalyst is highly stable during ethylene polymerization. After 1 h of living polymerization, narrowly distributed ultrahigh molecular weight polyethylene is obtained (entry 7).102 By contrast, a comparatively much broader polydispersity (Mw/Mn = 1.45) is observed with the nonfluorinated 3c (entry 1). The even broader molecular weight distribution obtained with 3b (R= CH3, entry 3) supports the fact that the living behavior of 3a is not due to a steric effect of the o-fluorine substituents. Interestingly, relatively high molecular weights are obtained
polymerization was living (vide infra). Considering also the broad molecular weight distributions, this suggests that by contrast to the o-fluorinated 3a the catalyst precursors 3b and 3c are inefficiently converted to the active species and that actually, by comparison to the o-fluorinated analogue, the intrinsic rate of chain growth is higher in the active species, which are prone to chain transfer.
bDetermined by GPC referenced to linear PE (cf. addendum for details).
The effect of polymerization temperature was studied (entries 2, 4, 5, and 6). The extremely narrow molecular weight distribution is retained at an elevated temperature of 50 °C.
PE with Mw/Mn = 1.03 and Mn = 3.2 × 105 g mol-1 is obtained after 15 min of polymerization (entry 5). Remarkably, molecular weight control is retained even at 75 °C in polymerization with 3a (entry 6). To further confirm the living nature of the polymerization with 3a, the development of Mn and Mw/Mn over time was studied at 25, 50, and 75 °C (Figure 4-2 and Figure S14 in Addendum). A linear increase of Mn with polymerization time and narrow molecular weight distributions were observed for all runs, thus corroborating the highly controlled nature of the polymerization. By comparison to the well studied highly active
phenoxyimine catalysts,73-75,95 the lower insertion rates with 3a facilitate control of the polymerization reactions. A generally lower reactivity may also contribute to the stability over time at higher temperatures.
The importance of living polymerization catalysts is considerably dependent on their ability to form block copolymers from common commercial monomers such as ethylene and propylene since these materials have applications as compatibilizers and elastomers.103 Although individual catalyst systems have been reported which achieve some characteristics of a living polymerization, the preparation of olefin block copolymers having both “hard” (semicrystalline or high glass transition temperature) and “soft” (amorphous and low glass transition temperature) segments remains a major challenges in the field of polymerization catalysis. Despite the high melting temperatures exhibited by isotactic or syndiotactic polypropylenes (PPs), the relatively high glass transition temperatures of these materials (Tg ~ 0 °C) limits their utility in elastomeric applications. On the other hand, ethylene-based polymers that incorporate varying fractions of α-olefin can meet this criterion. Polyethylenes (PE) with low comonomer content are
transition temperatures (Tg < -40 °C).
To lay out the general conditions for the block copolymerization, propylene homopolymerizations were investigated initially. Upon treatment with 1 000 equiv of MAO, complex 3a (5 µmol) was found to be active for the polymerization of propylene. At 25 °C in toluene (250 mL), high molecular weight polypropylene (Mn = 1 x 106 g/mol) was obtained after a reaction time of 3h under 2 bar of monomer pressure. The molecular weight distribution is relatively broad (Mw/Mn = 1.80). The broadening of the polydispersity is probably due to the slow initiation of the active species (vide infra). The fraction of titanium centers producing polymer chains is less than 1 (~0.73) which means that not all the catalysts applied were active.
Microstructure analysis by 13C NMR revealed incorporation by 1,2-insertion as the major chain growth mode, and an atacticity of the polymer. The glass transition temperature Tg, determined by DSC, was around -6 °C. In contrast to the relatively high productivity in ethylene homopolymerization, complex 3a showed only a turn over number (TON) of 2 x 103 mol(C3H6) mol (Ti)-1 in the propylene polymerization, indicating a distinctive monomer selectivity.
When catalyst precursor 3a was added to a solution of MAO ([Al]/[Ti] 1000) in toluene at 50 °C in the presence of ethylene (1 bar), a living polyethylene (A block) was formed after 3 min (Mn = 101 000 g/mol, Mw/Mn = 1.00). Subsequently, ethylene was removed from the reactor by several cycles of applying vacuum and backfilling with argon. The reactor was then backfilled with propylene (2 bar) and the polymerization was continued for growth of the second block. After 90 min of additional polymerization time, a higher molecular weight diblock polymer (AB diblock) was formed (Mn = 200 000 g/mol, Mw/Mn = 1.13) (Table 4-2;
entry 3). 13C NMR spectroscopy revealed a polyethylene-block-polypropylene microstructure with a total propylene content of 25 mol %. The Tm of this polymer is 137 °C, while the Tg of the aPP block is around -10 °C. The overall crystallinity, as determined by DSC, decreased from 67% (only the PE block) to 41% (block copolymer), in accordance with the composition determined by 13C NMR. That is the degree of crystallinity of the PE part which is not hindered
or altered by the introduction of the PP block.
Comparing the molecular weight distributions of the aforementioned polypropylene (Mw/Mn = 1.80) and the block copolymer (see Table 4-2, Figure 4-3) indicates that the first insertion of propylene by 1/MAO is not initiated rapidly and simultaneously which led to the broad polydispersity of the homopolymer. In case that a longer alkyl chain (originated by the insertion of ethylene) is linked to the metal center, the incorporation appeared to be facilitated.
Thus, the living character is retained in the block copolymerization.
Table 4-2: Results of ethylene/propylene block copolymerization experiments with 1.[a]
Entry temp.
aGeneral conditions: 5 µmol complex 3a, 1 000 eq. MAO, 250 mL toluene, 1 bar of ethylene, 2 bar of propylene. bDetermined using gel permeation chromatography in 1,2,4-C6H3Cl3 at 140 °C versus polyethylene standards. cDetermined using quantitative
13C NMR at 130 °C. dDetermined using differential scanning calorimetry (second heating). e10 µmol complex, 500 eq. MAO. f1 bar of ethylene for the 1. block, then reduction of ethylene pressure to 0.3 bar, addition of 2 bar of propylene and polymerization at constant pressure by feeding ethylene (0.3 bar).
The effect of temperature on polymerization behaviour was investigated (Table 4-2).
temperature, and molecular weight distributions remained narrow. To our best knowledge, complex 3a is the first catalyst which is able to promote block copolymerization at such elevated temperatures (above 50 °C).
In addition, triblock copolymers were of interest, as these materials can have enhanced mechanical properties relative to the related diblock copolymers. A triblock copolymer was synthesized using an analogous approach (Table 4-2, entry 5). As described previously, catalyst 3a was added to a solution of MAO ([Al]/[Ti] 1000) in toluene at 25 °C in the presence of ethylene (1 bar), giving a monodisperse polyethylene (A-block) after 3 min (Mn = 79 000 g/mol, Mw/Mn = 1.03). Ethylene was removed from the reactor by several cycles of applying vacuum and backfilling with argon. The reactor was pressurized with 2 bar of propylene, and the second block started to grow for 180 min yielding a polyethylene-block-polypropylene diblock (AB-diblock) copolymer (Mn = 254 000 g/mol, Mw/Mn = 1.03, Tm= 135 °C, Tg= -7 °C). Finally, the reactor was evacuated and backfilled with argon again in several cycles and ethylene was added to the reactor. The polymerization was continued for further 3 min, giving a copolymer with Mn
= 298 000 g/mol and Mw/Mn = 1.17. The shift of GPC traces after each step in the synthesis of the ABC triblock copolymer strongly suggests that this process proceeds in a living fashion, even that the molecular weight distribution became broader (1.03 vs 1.17). The resulting polymer is an ABC-triblock composed of one pure polypropylene (B block) domain and two polyethylene segments (A and C block, respectively). DSC analysis of the final triblock copolymer revealed a glass transition temperature of -18 °C and a melting transition around 137
°C with a total crystallinity of 38 %, determined by DSC (cf. Figure S15 in Addendum).
Figure 4-3. GPC profile of poly(ethylene-block-a-propylene) obtained with complex 1 at 50 ºC (Table 4-2, entry 3, Mn = 2.0×105, Mw/Mn = 1.13).
In view of the fact that the Tg of a PP block can be lowered by incorporation of ethylene, attempts to synthesize PE-EPR block copolymer were undertaken at 25 °C. The first block was formed within 3 min under 1 bar of ethylene (Mn = 79 000 g/mol). Afterwards, the ethylene pressure was reduced to 0.3 bar, and 2 bar of propylene was added to the reactor. Due to the higher incorporation rate of ethylene, the total pressure was then kept constant at 2.3 bar by feeding ethylene (~ 0.3 bar). After 90 min, a second block featuring random copolymers of ethylene and propylene is formed (Mn = 651 000 g/mol calculated from the Mn (PE) and Mn (PE-EPR) determined by GPC). The molecular weight of PE-EPR (Mn = 731 000 g/mol, Mw/Mn = 1.24) as well as the yield are much higher than those of the PE-PP block copolymer as a result of the preferred incorporation of ethylene. 13C NMR spectroscopy was consistent with a polyethylene-block-poly(ethylene-ran-propylene) microstructure with a total propylene content of 46 mol %. On the basis of this value and the number average molecular weights of the A block and AB diblock, it can be estimated that the propylene content of the B-block is 52 mol%.
In the block copolymer PE-EPR, the benefits of both high Tm (132 °C and 124 °C) and low Tg (-51 °C) are retained. The presence of two melting peaks is likely due to the slight decrease of the
4.3. Summary and conclusion
In conclusion, the conveniently accessible novel enolatoimine Ti complex 3a upon MAO activation polymerizes ethylene in a living fashion with unprecedented molecular weight control and temperature stability. This provides viable access to high molecular weight PE with an extremely narrow molecular weight distribution (Mw/Mn = 1.01) and corresponding block copolymers. In addition to phenoxyimine Ti complexes, this is another example of a system in which o-F substitution appears beneficial for living polymerization of ethylene as well as propylene. Our studies indicate that these substituents also affect the activation reaction, which is effective only for 3a but not for analogues lacking o-fluorine substitution.
Moreover, narrowly distributed polyethylene-block-polypropylene block copolymers have also been prepared. The catalyst proceeds without appreciable chain termination or transfer to produce high molecular weight copolymers. The living nature of the catalyst allows the synthesis of monodisperse ethylene and propylene block copolymers with regioregular, atactic amorphous domains. Furthermore, PE-EPR block copolymers displaying a low Tg and a high Tm at the same time are accessible.
4.4. Experimental section
4.4.1. Materials and general considerations
All manipulations of air- and/or water-sensitive compounds were carried out under an inert atmosphere using standard glove box or Schlenk techniques. All glassware was flame-dried under vacuum before use. Toluene and benzene-d6 were distilled from sodium.
[Cl2Ti(NMe2)2]104 was prepared by comproportionation from TiCl4 and [Ti(NMe2)4], which were purchased from Aldrich. 1,1,1-trifluoro-2,4-pentanedione and 2,6-difluoroaniline (98%
purity) were obtained from ABCR. Aniline (99.5% purity), 2,6-dimethylaniline (99%) and BCl3 in toluenic solution (1M) were supplied by Aldrich. Methylalumoxane (MAO), purchased from
Crompton as a 10 wt.-% solution in toluene, was evaporated to dryness at room temperature in vacuo, and stored as a solid white powder. Complex 3c was prepared according to [78].
NMR spectra were recorded on a Varian Unity INOVA 400 spectrometer. 1H and 13C NMR chemical shifts were referenced to the solvent signal. Elemental analyses were performed up to 950 °C on an Elementar Vario EL. Differential scanning calorimetry (DSC) was performed on a Netzsch Phoenix 204 F1 at a heating/cooling rate of 10 K min-1. DSC data reported are from second heating cycles. Polymer crystallinities were calculated based on a melt enthalpy of 293 J g-1 for 100% crystalline polyethylene. Gel permeation chromatography (GPC) was carried out in 1,2,4-trichlorobenzene at 160 °C at a flow rate of 1 mL min-1 on a Polymer Laboratories 220 instrument equipped with Olexis columns with differential refractive index, viscosity and light scattering (15° and 90°) detectors. Data reported were determined via triple detection employing the PL GPC-220 software algorithm. As the instrument records light scattering at only two angles, data analysis involves an iteration for the calculation of molecular weights and form factors for each measured interval. The instrument was calibrated with narrow polystyrene and polyethylene standards. Data given is referenced to linear polyethylene.
Selected samples (amongst others entries 2, 5 and 7, Table 4-1) were analyzed independently by Dieter Lilge at Basell Polyolefine GmbH, Frankfurt. A Polymer Laboratories 210 instrument was used with 1,2,4-trichlorobenzene at 135°C and a flow rate of 0.6 mL min-1 employing 4 Shodex UT (3×806, 1×807) columns. Analysis were performed with infrared detection by a PolymerChar IR4 in conjunction with a Wyatt Dawn EOS 17 angle MALLS detector with a lasersource of 120 mW at λ = 658 nm. Data analysis employed Wyatt ASTRA 4.7.3 and CORONA 1.4 software. The absolute molecular weights where established by Zimm type extrapolation at each elution volume, as this procedure requires no dispersion correction.
Molecular weights and molecular weight distributions Mw/Mn are in good agreement with the
To provide a direct comparison of this analysis method with molecular weight data reported in [73], a typical polymerization run was repeated and the PE analyzed (catalyst precursor [{κ2 -N,O-6-C(H)=N(C6F5)-2-tBu-C6H3O}2TiCl2], 25 °C, 1 atm ethylene pressure, polymerization time 1 min. Conditions corresponded to entry 4 in Table 2 of [73]). A molecular weight Mn = 4.6×105 g mol-1 and Mw/Mn = 1.17 were determined. This corresponds well with Mn = 4.2×105 g mol-1 and Mw/Mn = 1.13 (referenced to linear polyethylene, detectors employed not given) previously determined [73].
4.4.2. Synthesis of ketoenamines
To a stirred solution of 1,1,1-trifluoro-2,4-pentanedione (3.0 g, 19.5 mmol) in dry toluene were added 23.4 mmol of the aniline component and a small amount of p-toluenesulfonic acid as a catalyst. The mixture was refluxed for ca. 24 h in the presence of molecular sieves. After evaporation of the solvent, the crude product was recrystallized from ethanol to afford pure compounds 1a-c.
4-(2,6-Difluorophenylamino)-1,1,1,-trifluoropent-3-en-2-one (1a)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 12.00 (br, 1H, NH), 6.44 (m, 1H, para H to NH), 6.30 (t, 3JHH = 7.9 Hz, 2H, meta H to NH), 5.40 (s, 1H, vinylic HC=C), 1.23 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C): δ/ppm = 178.21 (q, 2JCF = 33.5 Hz, CF3CO), 168.92 (vinylic C), 157.98 (dd, 1JCF = 251.2 Hz and 3JCF = 3.8 Hz, ortho C), 128.88 (t, 3JCF = 9.8 Hz, para C), 118.12 (q, 1JCF = 288.9 Hz, CF3), 114.92 (t, 2JCF = 16.5 Hz, ipso C), 111.82 (dd, 2JCF = 18.4 Hz and 4JCF = 5.4 Hz, meta C), 91.85 (vinylic CH), 18.78 (t, 5JCF = 2.3 Hz, CH3). 19F NMR (376 MHz, C6D6, 25 °C): δ/ppm = -76.97 (s, 3F, CF3CO) and -118.89 (t, 3JFH = 6.6 Hz, 2F, aromatic F). Anal. calcd. (%) for C11H8F5NO: C, 49.82; H, 3.04; N, 5.28; Found: C, 49.96; H, 3.09; N, 5.32. MS (m/z, %): 265.1 (31.2, M+). Yield: 75 %.
4-(2,6-Dimethylphenylamino)-1,1,1,-trifluoropent-3-en-2-one (1b)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 12.13 (br, 1H, NH), 6.85 (t, 3JHH = 7.5 Hz, 1H, para H to NH), 6.71 (d, 3JHH= 7.5 Hz, 2H, meta H to NH), 5.45 (s, 1H, vinylic HC=C), 1.72 (s, 6H, aryl CH3), 1.08 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C): δ/ppm = 177.04 (q, 2JCF = 32.6 Hz, CF3CO), 169.63 (vinylic C), 135.40 (ortho C), 135.32 (ipso C), 128.51 (meta C), 128.27 (para C), 118.57 (q, 1JCF = 289.2 Hz, CF3), 89.67 (vinylic CH), 18.55 (CH3), 17.67 (aryl CH3).
19F NMR (376 MHz, C6D6, 25 °C): δ/ppm = -76.62 (s, CF3CO). Anal. calcd. (%) for C13H14F3NO: C, 60.70; H, 5.49; N, 5.44; Found: C, 60.71; H, 5.43; N, 5.49. MS (m/z, %): 257.2 (90.5, M+). Yield: 70 %.
4-phenylamino-1,1,1,-trifluoropent-3-en-2-one (1c)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 12.70 (br, 1H, NH), 6.86 (br, 1H, para H to NH), 6.85 (br, meta H to NH), 6.45 (d, 3JHH = 6.4 Hz, 2H, ortho H to NH), 5.36 (s, 1H, vinylic HC=C), 1.27 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C): δ/ppm = 176.88 (q, 2JCF = 32.9 Hz, CF3CO), 167.32 (vinylic C), 137.20 (ipso C), 129.23 (para C), 126.85 (meta C), 124.93 (ortho C), 118.47 (q, 1JCF = 288.9 Hz, CF3), 91.11 (vinylic CH), 19.39 (CH3). 19F NMR (376 MHz, C6D6, 25 °C): δ/ppm = -76.72 (s, CF3CO). Anal. calcd. (%) for C11H10F3NO: C, 57.64; H, 4.40; N, 6.11; Found: C, 57.68; H, 4.42; N, 6.08. MS (m/z, %): 229 (67.3, M+). Yield: 55 %.
4.4.3. Synthesis of complexes
A solution of ketoenamine (0.1 mmol) in toluene was added dropwise to a toluene solution of [Ti(NMe)2Cl2] (0.05 mmol) at –30°C. A colour change was observed immediately. After removal of HNMe2·HCl by filtration through a glass frit at room temperature, solvent was evaporated in vacuo to afford 2a and 2b, respectively, in quantitative yield.
Chloro-(dimethylamido)-bis[κ2 -N,O-4-(2,6-difluorophenylimino)-1,1,1-trifluoropent-2-en-2-olato]titanium(IV) (2a)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 6.65-6.52 (m, 3H, aryl H), 6.52-6.40 (m, 3H, aryl H), 5.71 (s, 1H, vinylic CH), 5.67 (s, 1H, vinylic CH), 3.52 (br, 6H, N-(CH3)2), 1.40 (s, 3H, CH3), 1.29 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C): δ/ppm = 175.54 (imine C), 174.86 (imine C), 157.88 (q, 2JCF = 35.2 Hz, CF3CO), 157.06 (q, 2JCF = 33.6 Hz, CF3CO), 155.94 (dd,
1JCF = 253.9 Hz and 3JCF = 5.4 Hz, ortho C), 155.53 (dd, 1JCF = 249.3 Hz and 3JCF = 5.4 Hz, ortho C), 155.94 (t, 2JCF = 5.0 Hz, ipso C), 153.50 (t, 2JCF = 4.6 Hz, ipso C), 127.35 (t, 3JCF = 9.4 Hz, para C), 126.51 (t, 3JCF = 9.2 Hz, para C), 120.21 (q, 1JCF = 279.6 Hz, CF3), 119.55 (q, 1JCF
= 279.6 Hz, CF3), 113.04 (d, 2JCF = 20.7 Hz, meta C), 112.05 (d, 2JCF = 21.5 Hz, meta C), 111.38 (d, 2JCF = 21.5 Hz, meta C), 110.89 (d, 2JCF = 20.8 Hz, meta C), 103.72 (vinylic C=CH), 103.68 (vinylic C=CH), 52.00 (N-CH3), 24.28 (CH3), 23.64 (CH3). 19F NMR (376 MHz, C6D6, 25 °C): δ/ppm = -73.03 (s, 3F, CF3CO), -73.99 (s, 3F, CF3CO), -112.78 (m, 1F, aryl F), -118.33 (m, 1F, aryl F), -120.32 (m, 1F, aryl F), -122.31 (m, 1F, aryl F). Anal. calcd. (%) for C24H20F10N3O2ClTi: C, 43.96; H, 3.07; N, 6.41; Found: C, 44.19; H, 3.32; N, 6.32.
Chloro-(dimethylamido)-bis[κ2 -N,O-4-(2,6-dimethylphenylimino)-1,1,1-trifluoropent-2-en-2-olato]titanium(IV) (2b)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 6.99 – 6.75 (m, 6 H, aryl H), 5.89 (s, 1H, vinylic CH), 5.56 (s, 1H, vinylic CH), 3.09 (q, 4JHH = 1.07 Hz, 3H, N-CH3), 2.94 (q, 4JHH = 1.07 Hz, 3H, N-CH3), 2.42 (s, 3H, aryl CH3), 2.31 (s, 6H, aryl CH3), 1.60 (s, 3H, aryl CH3), 1.24 (s, 3H, CH3), 1.14 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C): δ/ppm = 172.54 (imine C), 171.14 (imine C), 162.57 (q, 2JCF = 33.0 Hz, CF3CO), 154.81 (q, 2JCF = 34.1 Hz, CF3CO), 150.71, 150.65, 132.75, 130.70, 129.66, 129.00, 128.64, 127.62, 126.08, 125.54, 120.22 (q, 1JCF = 282.3 Hz, CF3), 120.19 (q, 1JCF = 277.7 Hz, CF3), 104.52 (vinylic C), 98.22 (vinylic C), 55.40 (N-CH3), 51.73 (N-CH3), 23.34 (CH3), 23.03 (CH3), 19.42 (aryl CH3), 19.29 (aryl CH3), 18.24 (aryl
CH3), 17.40 (aryl CH3). 19F NMR (376 MHz, C6D6, 25 °C): δ/ppm = -73.28 (s, CF3CO), -74.52 (s, CF3CO). Anal. calcd. (%) for C28H32F6N3O2ClTi: C, 52.56; H, 5.04; N, 6.57; Found: C, 52.62; H, 5.10; N, 6.48.
A solution of 1a (0.1 mmol) in toluene was added dropwise to a toluene solution of [Ti(NMe)2Cl2] (0.05 mmol) at –30°C. A colour change from red-brownish to dark-green (blackish) was observed immediately. After removal of HNMe2·HCl by filtration through a glass frit at room temperature, 1 eq. of BCl3 in toluene was added to the intermediate at -30°C. The reaction mixture was allowed to warm to room temperature. Within 30 min, the solution turned from blackish to red and precipitation was observed. The mixture was stirred for 3 hours. The solution was evaporated to dryness in vacuo. Slow recrystallization from toluene at room temperature afforded 3a in ca. 70 %.
Dichloro-bis[к2 -N,O-4-(2,6-difluorophenylimino)-1,1,1-trifluoropent-2-en-2-olato]titanium(IV) (3a)
The crystal employed for x-ray crystal structure determination was dissolved. Two isomers are obtained by NMR spectroscopy. 1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 6.64-6.44 (br, 3H, aryl H), 5.71 (br, 1H, vinylic CH), 1.18 (br, 3H, CH3). 19F NMR (376 MHz, C6D6, 25 °C):
δ/ppm = -73.38 (br), -73.81 (s) (overlap of signals, total integral 3F, CF3CO), -114.35 (br), 114.45 (br) (overlap of signals), -119.17 (br, total integral 2F, aryl F). 13C NMR analysis was hampered by the low solubility of the compound. Anal. calcd. (%) for C22H14F10N2O2Cl2Ti: C, 40.83; H, 2.18; N, 4.33; Found: C, 41.31; H, 2.49; N, 4.42.
For the preparation of compound 3b, a solution of 1b (0.1 mmol) in toluene was added dropwise
through a glass frit at room temperature, 2 eq. of BCl3 in toluene was added to the intermediate at -30 °C. The reaction was stirred for 2h at 50 °C. Evaporation in vacuo afforded 3b in quantitative yield.
Dichloro-bis[к2-N,O-4-(2,6-dimethylphenylimino)-1,1,1-trifluoropent-2-en-2-olato]titanium (IV) (3b)
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 6.88 (t, 1H, para H), 6.79 (d, 2H, meta H), 5.61 (s, 1H, vinylic CH), 2.01 (s, 6H, aryl CH3), 0.94 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C):
1H NMR (400 MHz, C6D6, 25 °C): δ/ppm = 6.88 (t, 1H, para H), 6.79 (d, 2H, meta H), 5.61 (s, 1H, vinylic CH), 2.01 (s, 6H, aryl CH3), 0.94 (s, 3H, CH3). 13C NMR (100 MHz, C6D6, 25 °C):