Homo- and Co-Polymerization of Ethylene with Cyclic Olefins

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

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Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes Giorgia Zanchin,†,‡ Laure Vendier,∥,# Ivana Pierro,†,§ Fabio Bertini,† Giovanni Ricci,† Christian Lorber,*,∥,# and Giuseppe Leone*,† †

CNR-Istituto per lo Studio delle Macromolecole (ISMAC), via A. Corti 12, I-20133 Milano, Italy Dipartimento di Chimica, Università degli Studi di Milano, via C. Golgi 19, I-20133 Milano, Italy § Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy ∥ CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP44099, 31077 Toulouse, France # Université de Toulouse, UPS, INPT, LCC, 31077 Toulouse, France

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‡

S Supporting Information *

ABSTRACT: The synthesis and the characterization of a series of phosphine adducts of (imido)vanadium(IV) dichloride complexes of the type V(NR)Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V( NtBu)Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N−V−C bond. Complexes 1−3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1−3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly(ethylene)s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V−N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand.

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INTRODUCTION The polymerization of olefins mediated by transition metal catalysts is a mature field and a well-established technology.1 A constant subject is the development of efficient catalysts, which provide the opportunity to fabricate new polyolefin materials to meet the growing needs of people’s everyday life. In the 1980s, the discovery of metallocene catalysts, a combination of group 4 metallocene and methylaluminoxane (MAO), allowed great control over stereochemistry, molecular weight, molecular weight distribution, and comonomer incorporation, thus providing a wide range of high performance polyolefins.2 In addition, metallocenes opened the door for designing catalysts on a molecular level. The search for new highly reactive metal complexes has led to the exploration of ancillary ligands beyond Cp (Cp = cyclopentadienyl) and its derivatives and © XXXX American Chemical Society

demonstrated that post-metallocenes not only expanded the commercially useful metals across the transition series but also broadened the range of polymers accessible by insertion polymerization.3 In this context, ligands with nitrogen donor atoms have received much attention.4 One promising set of nitrogen ligands is the family of imido ligands. Transition metal imido complexes attracted particular interest for their potential for “metallocene-like” reactivity. From an electronic point of view, there is an isolobal analogy between transition metal imido complexes and the monoanionic Cp moiety, since they can bind to a metal using a combination of 1σ and 2π orbital Received: July 17, 2018

A

DOI: 10.1021/acs.organomet.8b00502 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 1. Generic Synthesis Leading to V(NR)Cl2(PMe2Ph)2a

a

R = 2,6-Cl2-C6H3 (1), 2,6-iPr2-C6H3 (2), tBu (3).

interaction.5 Moreover, as a π-donor ligand, the imido group is able to promote high oxidation state coordination chemistry.6 Early transition metal imido complexes are generally envisioned as containing metal−imido triple (or double) bond and a nucleophilic imido nitrogen. The potential of imido ligands is correlated to the ease with which steric and electronic properties can be tuned by virtue of the number of alternative substituents. Extensive studies have been carried out with first row metals (particularly Ti, V, and Cr). Several examples of (imido)Ti(IV) complexes have been reported.6,7 Cr(VI) complexes bearing two dianionic supporting imido ligands have been also investigated6,8 for the possibility of developing a homogeneous, well-defined catalytic system, analogous to the widespread heterogeneous Phillips catalyst. Dianionic imido ligands have been employed also with group 5 metals;6 for these metals in the +5 oxidation state, the isolobal analogy with group 4 metallocenes is reached with a monoanionic supporting ligand in addition to the dianionic imido ligand. In particular, the imido function has proven to stabilize alkyl groups in both V(IV) and V(V) complexes.9 The use of imido ligands in V(V) chemistry is well documented.10 Great improvement in this field was achieved by Gibson, who reported the first example of an (imido)vanadium complex, that is CpV(N-4-Me-C6H4)Cl2, to be used as catalysts for the polymerization of olefins,5b,c and Nomura, who developed several examples of V(V) complexes of the type V(NAr)Cl2(L) containing both 2,6-disubstituted aryl−imido ligands (NAr) and anionic ancillary donor ligands (L) such as aryloxo,9,11c,e imidazolin-2-iminato and imidazolidin-2-iminato,11d N-heterocyclic carbenes,11b 2-(2′-benz-imidazolyl)pyridine,11a and chelated (2-anilidomethyl)pyridine, 12a and (anilido)methylimine ligands.12b Many of such vanadium(V) complexes, in combination with aluminum alkyls, proved to be highly active in the (co)polymerization of ethylene, giving high molecular weight (co)polymers,11 with the exception of those complexes containing chelated ligands that proved to be highly efficient catalysts for ethylene dimerization.12 Compared to V(V), terminal (imido)V(IV) complexes are still rare.13 A possible explanation is connected with the difficulties associated with the isolation of single crystals useful for Xray structural characterization, which proves to be of fundamental importance dealing with the paramagnetism of d1 vanadium(IV). In 2000, Lorber et al. reported the synthesis and the structural characterization of the first Cp-free (d1imido)V(IV) complex ([V(NAr)Cl2(NHMe2)2]),14 followed by a systematic investigation of the synthetic and structural chemistry of aryl−imido V(IV) complexes bearing neutral nitrogen, V(NAr)X2(NHMe2)2 (X = Cl, NHMe2; Ar

= C6H5, C6F5, 2,6-iPr2-C6H3, 2,6-Me2-C6H3, 2,6-Cl2-C6H3),15 and phosphorus donor ligand V(N-2,6- i Pr 2 -C 6 H 3 )Cl2(PMe2Ph)2.16 In this connection, we became very interested in the polymerization of ethylene and copolymerization of ethylene with cyclic olefins catalyzed by phosphine adducts of (imido)VCl2. Cyclic olefin copolymers (COCs) have gained much attention as high-tech engineering plastics.17 High transparency in visible and near-ultraviolet region, high refraction index, glass transition temperature (Tg) up to 220 °C, heat-resistance, and good processability make these copolymers useful coatings for high-capacity CDs and DVDs,18a packaging,18b medical equipment,18c electronic devices,18d microfluidic devices,18e and microfluidic immobilized-enzyme reactors.18f COCs have been commercialized under the trade names of APEL by Mitsui Chemicals, Inc.19 and TOPAS by Topas Advanced Polymer.20 Herein, we report the synthesis and the characterization of a series of (imido)V(IV) dichloride complexes of the type V( NR)Cl2(PMe2Ph)2 [R = 2,6-Cl2-C6H3 (1), 2,6-iPr2-C6H3 (2),16 tBu (3)] and V(NtBu)Cl2(PMe3)2 (3′) having both aryl or alkyl imido moiety and a phosphine coligand. Complexes 1−3 were evaluated as catalyst precursors for the polymerization of ethylene and copolymerization with various cyclic olefins. We demonstrate that 1−3, in combination with Et2AlCl and Cl3CCO2Et (ETA),21 are versatile and promising catalysts for the synthesis of COCs. The effects of the structure of the investigated complexes, polymerization temperature and time, and NB/E (NB = norbornene, E = ethylene) and ETA/V mole ratio on the catalytic activity, reactivity toward the target comonomers, and (co)polymer structure and properties (i.e., molecular weight, comonomer incorporation, microstructure, and thermal behavior) are investigated and discussed.

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RESULTS AND DISCUSSION

Preparation and Characterization of the Complexes. The general synthetic pathway leading to the imido− phosphine complexes V(NR)Cl2(PMe2Ph)2 (1−3) is depicted in Scheme 1. It consists of a three step procedure from V(NMe2)4 via the initial formation of imido-bridged dimers [V(μ-NR)(NMe2)2]2 that are further converted into the oligomeric [V(NR)Cl2]n.15,22,23 Upon treatment with monophosphines, the oligomeric [V(NR)Cl2]n gives the bisphosphine imido adduct as already mentioned for the synthesis of the known V(N-2,6-iPr2−C6H3)Cl2(PMe2Ph)2 (2)16 and its analogous PMe 3 adduct V(N-2,6- i Pr 2 -C 6 H 3 )Cl2(PMe3)2.24 Overall, 1−3 were obtained in moderate yields after recrystallization. They are NMR silent (1H, 51V) and their B


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Organometallics d1 configuration (μeff = ca. 1.7−1.8 μB) make them EPR active (Figure S1−S3). The EPR spectra of 1−3 are in agreement with those previously reported and rare examples of such imido-bis(phosphines) V(IV) complexes:16,24 a pattern of eight overlapping 1:2:1 triplets due to coupling of the I = 7/2 51 V nucleus and two equivalent I = 1/2 31P nuclei and with giso = ca. 1.98, Aiso(51V) = ca. 85 G, and Aiso(31P) = ca. 30 G. Single crystal structure determination was used to compare the steric and electronic properties of the imido ligand in V( NR)Cl2(PMe2Ph)2 complexes. Crystals of 1 suitable for structure determination were obtained. Although we did not obtained suitable crystals of 3, we could solve the structure of its parent PMe3 adduct V(NtBu)Cl2(PMe3)2 (3′). ORTEP drawings of the molecules of 1 and 3′ are shown in Figures 1

Figure 2. Molecular structure of 3′. Thermal ellipsoids are drawn at the 50% probability level and partial atom-labeling schemes. Hydrogen atoms are omitted for clarity, and carbon atoms are drawn as spheres.

Figure 1. Molecular structure of 1. Thermal ellipsoids are drawn at the 50% probability level and partial atom-labeling schemes. Hydrogen atoms are omitted for clarity, and carbon atoms are drawn as spheres.

Figure 3. Molecular structure of 2. Thermal ellipsoids are drawn at the 50% probability level and partial atom-labeling schemes. Hydrogen atoms are omitted for clarity, and carbon atoms are drawn as spheres.

Table 1. Comparison of Average Interatomic Distances (Å) and Angles (deg) in 1, 2, and 3′

and 2, respectively. Both molecular structures allow a direct comparison with the know structure of 2 (Figure 3),16 and important metric parameters (interatomic bond distances and angles) are given in Table 1 for that purpose. The three compounds 1, 2, and 3′ exhibit similar features: a geometry around the metal center between a distorted trigonal-bipyramid (with equatorial aryl-imido and chlorine atoms) and a square pyramid (τ parameter = 0.54−0.62) [τ is the angular parameter commonly used to describe the geometry around the metal center in pentacoordinate complexes, and defined as τ = (α − β)/60 (α and β are the two largest L−M−L bond angles, with α ≥ β)],25 a short V−N distance of ca. 1.65−1.66 Å with almost linear V−N−C imido linkage typical of such imido complexes, two mutually cis chlorine atoms (with Cl−V−Cl angle of ca. 130° and mean V− Cl bonds of ca. 2.31 Å, and two mutually trans axial phosphine ligands [P−V−P = 164−169°] with V−P distances of ca. 2.50 Å. The phenyl substituent of PMe2Ph phosphines is oriented differently in 1 and 2; this does not seem to be due to steric effects, but most probably results from crystal packing.

1

2

3′

V−N N−C V−Cl

1.654(4) 1.387(6) 2.3070(8)

V−P

2.4879(8)

V−N−C Cl−V−Cl P−V−P τ

180 131.68(6) 169.17(5) 0.62

1.663(6) 1.391(9) 2.318(2) 2.303(2) 2.517(2) 2.489(2) 175.5(5) 129.03(9) 165.50(8) 0.61

1.6510(19) 1.452(3) 2.3038(8) 2.3279(8) 2.4827(8) 2.4921(8) 176.73(16) 131.93(3) 164.38(3) 0.54

Before getting to the catalytic behavior of 1−3, it may be useful to make a rough classification based on the electronic and steric properties of the investigated complexes. Whereas the electron donor ability should increase in the order 1 < 2 < 3 (as anticipated from the electron-donating or withdrawing nature of the substituents on the imido moiety), a tentative C


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Organometallics Table 2. Homo- and Co-Polymerization of Ethylene with Norbornene by 1−3/Et2AlCl/ETAa entry

V-cat

1 2 3 4 5f 6 7 8 9 10 11 12 13

1 2 3 3 3 2 2 2 1 3 3 3 3

NB (mol L−1

0.57 0.57 0.57 0.57 0.57 0.08 0.29 1.16

NB/E

time (min)

yield (mg)

activityb

4 4 4 4 4 0.5 2 8

2 2 2 5 20 0.5 2 15 2 2 2 2 2

172 180 163 317 1280 94 250 980 380 360 285 458 109

2072 2168 1956 1522 1536 4513 3012 1568 4578 4320 3420 5496 1308

NBc (mol %)

Mwd (kg mol−1)

Mw/Mnd 2.4 2.2 2.4 2.2 3.0

35.4 35.7 35.8 36.4 36.8 13.0 30.4 39.3

140 163 198 109 206 g 147 107 137 155 110 108 178

2.1 2.5 2.0 2.1 1.9 1.8 2.1

Tg (Tm)e (°C) (139) (138) (136) g g 81 82 83 85 85 −4 (50) 56 101

Polymerization conditions: ethylene pressure, 1.01 bar; total volume, 25 mL (toluene); V-cat, 2.5 μmol; Al/V = 500; ETA/V = 10; temperature, 20 °C. bActivity in kgpol (molV h)−1. cDetermined by 13C NMR. dDetermined by SEC. eDetermined by DSC. fTotal volume, 50 mL. gNot determined. a

(Mw = 140 000 g mol−1, entry 1) < 2 (Mw = 163 000, entry 2) < 3 (Mw = 198 000, entry 3). The observed trend may be correlated to concomitant effects of steric and electronic ligand perturbations. Considering only the electronic properties of 1− 3, the fact that 3 formed a PE with the highest molecular weight may be because the electron-donating tert-butyl group on the imido moiety strengthens the V−N bond, thus improving the stability of the electron-deficient catalytic intermediate and reducing the chain transfer. In the same way, however, we cannot rule out that the steric bulk of the tert-butyl imido group may also contribute to inhibit the associative chain transfer.30 The obtained PEs are linear polymers, with melting temperatures (Tm) in the range 136−139 °C, crystallinity of about 75% (ΔHm ca. 216 J mol−1, Figure S4), and reasonably narrow, unimodal molecular weight distributions (Mw/Mn ca. 2), suggesting the presence of well-defined active species. Catalyst 3/Et2AlCl/ETA was further examined to study its stability over time (Table 2, entries 4 and 5). The polymer yield increased with increasing polymerization time, but as in case of most vanadium based catalysts,10,28,31 a drop-off in activity was observed. The activity at 5 min was 1522 kgPol molV−1 h−1, about 78% of that in the first 2 min likely due to the catalyst deactivation and mass transport limitations caused by filling of the reactor with the swollen polymer. Indeed, the polymerization occurred so fast that the solution viscosity increased after a few minutes. Likewise, the molecular weight of the polymer obtained with prolonging the reaction time was lower than that obtained at 2 min (Table 2, entry 3 vs 4). This may be due to the embedment of the active vanadium species that limits monomer diffusion and chain propagation, probably for the demand of a more diluted solution. In order to overcome this issue and keep the viscosity of the medium reasonable, we carried out a polymerization test in a more diluted solution (Table 2, entry 5, total volume = 50 mL, time = 20 min). Under these conditions, the overall productivity strongly increased with product obtained on the order of grams, and the polymer molecular weight remained reasonably high (Table 2, entry 5, Mw = 206 000 g mol−1). Also of note, the activity at 20 min was close to that at 5 min (1522 vs 1536 kgpol molV−1 h−1, entries 4 and 5, respectively). This result suggests that 2 is fairly stable over the investigated polymer-

explanation to rationalize the steric properties remains difficult at this stage. On the basis of structural data, 1 and 2 have almost a planar hindrance (Figures 1 and 3, respectively), while the tert-butyl-imido group in 3 is a bulky group in all three dimensions (see the structure of 3′ in Figure 2). Qualitatively, the topographic steric maps of imido ligands in 1−3 generated using the SambVca 2 Web26 showed how the isopropyl ortho substituents in 2 promote a higher steric protection to the vanadium when compared to the chlorine substituents in 1 and the tert-butyl imido moiety in 3 (see Supporting Information files for 1, 2, and 3′). Polymerization of Ethylene. Alkylaluminums (i.e., AlMe3, AliBu3, Et2AlCl) and aluminoxanes (i.e., MAO, MMAO) have a fundamental role in the polymerization of olefins catalyzed by vanadium complexes. The unique performance of each complex strongly depends on the nature of the Al activator.27 Herein, with the aim of selecting the most suitable cocatalyst, 2 was first solely employed to run preliminary tests in combination with MAO and Et2AlCl. Polymerization tests with 2/MAO (from 500 to 1500 equiv to V) under 1 bar of ethylene and at room temperature produced poly(ethylene)s (PEs) in very low yield, while 2/Et2AlCl exhibited at least 1 order of magnitude higher activities. This result is consistent with our previous results by using some V(III) complexes containing phosphine ligands,28 and it is not completely unexpected since many vanadium complexes gave better performance in the presence of simple chloroalkylaluminum reagents rather than with aluminoxanes.29 A possible explanation is the formation of different catalytically active species (isolated or associated cation) from the combination of vanadium complex and Al activator, depending on the nature of the activator.27,29 Hence, Et2AlCl was the activator of choice for the following experiments. Table 2 summarizes relevant data for the polymerization of ethylene using 1−3. The polymerizations were carried out under the same set of conditions using 500 equiv of Et2AlCl and 10 equiv of ETA21 at an ethylene pressure of 1 atm in toluene at room temperature. All the complexes were instantaneously activated, and good activities were obtained. Changes in the imido ligand substitution brought about little effect on the activity for the polymerization of ethylene under the conditions employed. In contrast, the type of imido ligand has a pronounced influence on the PE molecular weight, which increased in the order 1 D


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Organometallics

hypothesis, straight calculation of the topographic steric maps for 1, 2, and 3′ over just the stable conformation of the complexes in the crystals, showed that isopropyl-aryl substituents in 2 promote higher steric protection to the metal (see Supporting Information). Similarly to the results found for the homopolymerization of ethylene, 3 formed the copolymer with the highest molecular weight, followed by 2 and 1, respectively. The more electronrich compound 3 is less prone to chain transfer: the presence of the alkyl imido moiety has an advantage in preparing polymers with high molecular weight. Analysis of thermal properties by DSC revealed that all the copolymers did not exhibit melting events, but only a Tg (Figure S5). This suggests the formation of amorphous copolymers with homogeneous composition.32 Copolymerization of Ethylene with Norbornene at Different Comonomers Feedstock Compositions. A series of experiments were carried out at different feed compositions (NB/E from 0.5 to 8) by using 3. The results are shown in Table 2. There is a dependence of the activity on the norbornene feedstock concentration: it increased moving from NB = 0.08 to 0.29 mol L−1 (entries 11 and 12, respectively), but a further increase in the comonomer concentration results in a decrement in activity, likely due to a favored norbornene coordination to the active sites32,34,35 and to the fact that the copolymerization was preferred to the homopolymerization of each of the two comonomers. Increasing the charged norbornene, its content in the copolymer increased, although it did not exceed 39.3 mol % (Figure 4A). However, interestingly, a high norbornene incorporation was already reached at NB/E = 2 (Table 2, entry 12, NB = 30.4 mol %). The higher the norbornene feedstock concentration, the higher the copolymers molecular weight, meaning that the coordination of norbornene slows down the chain termination reactions. The coordination of norbornene mitigates chain transfer for stereoelectronic reasons, since the β-H elimination requires the coplanarity of the V−C(α) bond and the β-H atom, and this disposition is impossible when norbornene is the last inserted unit.36 Narrow and unimodal molecular weight distributions were found at all the NB/E feed ratio investigated (Mw/Mn = 1.8−2.1). As concerns the copolymer thermal properties, except for entry 11, which has a low norbornene content (NB = 13.0 mol %) and hence exhibited also a melting temperature peak, all the other copolymers exhibited only a Tg [56 < Tg (°C) < 101, Figure S6]. In Figure 4B, the evolution of Tg versus norbornene content in the copolymers is plotted. A linear relationship between the norbornene content in the copolymers and Tg is clearly observed, revealing that the differences in Tg values mainly arise from the different amount of incorporated norbornene. Copolymerization of Ethylene with Norbornene at Different ETA/V Ratio. We systematically examined the effect of ETA dosage at norbornene feedstock concentration of 0.57 mol L−1 (NB/E = 4) by using 1 and 3. The copolymerizations were performed over the range of ETA/V mole ratio from 5 to 300. Relevant data are summarized in Table 3. We chose 1 and 3 because these two complexes appear to be electronically and sterically rather different. The plot of activity versus the ETA/V ratio, displayed in Figure 5A, shows that the amount of ETA strongly affects the activity. The trend in activity is strongly dependent on the complex employed. It is interesting to note that the activity of

ization time and that the use of a more dilute solution is beneficial. Copolymerization of Ethylene with Norbornene. The results for the copolymerization of ethylene (E) with norbornene (NB) by 1−3 in the presence of Et2AlCl (500 equiv to V) and ETA (10 equiv to V) at NB/E feed ratio of 4 are summarized in Table 2. Copolymerization lifetime study in the range from 30 s to 15 min was first evaluated with 2 to explore the effect of the reaction time on the activity and norbornene incorporation (Table 2, entry 6−8). The overall productivity increased with the increase of the polymerization time, and grams of product were recovered in 15 min (entry 8). There was, however, a drop-off in activity over time. The activity at 15 min was 1568 kgpol molV−1 h−1, about 52% of that in the first 2 min. Catalyst deactivation, even in the presence of reoxidant, is not the only factor determining the lower activity. It may also be due to the occurrence of mass transport limitations since a large amount of polymer was obtained during the copolymerization. Analysis of thermal properties by DSC revealed that the copolymers did not exhibit melting events, but only a glass transition temperature (Tg) consistent with the norbornene incorporation. This suggests that the copolymers have a homogeneous composition32 and that there is no obvious compositional drift even for a prolonged reaction time and an extremely high norbornene conversion in the first seconds of the copolymerization (Table 2, entry 6). Successively, all the complexes were investigated under the same set of conditions; a copolymerization time of 2 min was chosen intentionally because such time with high and appropriate norbornene conversion allowed for a better differentiation and comparison of catalyst activities. The (imido)V(IV) complexes gave high Mw copolymers with narrow, unimodal Mw/Mn, suggesting that the copolymerization took place with a single catalytically active species. The observed activities were higher than those found in the polymerization of ethylene. The coordination of norbornene speeds up the propagation rate. When both ethylene and norbornene are available for the active species, all the complexes are instantaneously activated and the copolymerization proceeds at significant rates, particularly at the initial stage (Table 2, entry 6). The enhanced activity may be due to the coordination of the nucleophilic and sterically demanding norbornene that, in some cases, is expected to stabilize the active site.33 Complex 2 having isopropyl substituents on the N-aryl ring exhibited lower activity compared to 1 and 3 under the same conditions (Table 2, entries 7, 9, and 10, respectively). This result is, so far, ambiguous regarding clear trends in the effect of electronic or steric ligand properties. The catalytic performance for the copolymerization of ethylene with norbornene deviates from an expected trend moving from the more electron-deficient 1 to the more electron-rich 3 (more tBu-N → V donation). It is likely that steric effects could have a key role and some hypothesis can be extracted. Indeed, we can tentatively ascribe this result to the fact that the steric shielding by the bulkier isopropyl-aryl substituents in 2, which can arrange in the axial position of the vanadium center, leads to an enhanced discrimination of ethylene and norbornene. The increased steric interaction between bulky norbornene and bulky isopropyl-aryl substituents would offer a significant impediment to the coordination and insertion of bulkier comonomer, thus depressing both chain propagation rate and norbornene incorporation. Consistent with this E


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Organometallics

Figure 5. Plot of activity (A) and copolymer molecular weight (B) versus the ETA/V molar ratio.

Figure 4. Plot of NB incorporated in the copolymers versus the NB/E feed molar ratio (A) and plot of the copolymers Tg versus the NB incorporated in the copolymers (B) (Table 2, entry 10−13).

(N-ClAr, 1). This is because 1, bearing a 2,6-Cl-substitution on the aryl moiety, could have a pronounced preference to accept electron density from ETA through the chelation of the carbonyl oxygen to the metal active species as anticipated by Gibson.37 This possible chelation of the carbonyl oxygen may contribute to stabilization of the vanadium active intermediate and may explain the enhanced reactivity of 1. In contrast, in the case of the more electron-rich complex 3, 50:1 equiv of ETA to V seem to be sufficient to poison the active sites and rapidly lower the productivity. In this case, it seems that the

1 increased upon addition of ETA moving from 10 to 150 equiv to V, but then the productivity drops off rapidly (Figure 5A). Conversely, 3 gave a slight increase in activity going from 5 to 10 equiv of ETA to V and then a rapid decrease in the activity was observed. The different behavior exhibited by 1 and 3 with varying the charged ETA may be explained by considering the rough classification of the two imido ligands as rather electron-donating (N-tBu, 3) and electron-withdrawing

Table 3. Copolymerization of Ethylene with Norbornene by 1 and 3 at Different ETA/V Ratioa entry

V-cat

ETA/V

yield (mg)

activityb

NBc(mol %)

Mwd (kg mol−1)

Mw/Mnd

Tge (°C)

9f 14 15 16 17 10f 18 19

1 1 1 1 3 3 3 3

10 50 150 300 5 10 50 150

380 483 598 353 292 360 228 135

4578 5819 7205 4236 3518 4320 2684 1627

36.4 37.5 39.1 34.9 35.7 36.8 34.8 33.6

137 87 42 39 164 155 143 103

2.0 1.9 1.8 2.1 2.6 2.1 1.7 1.7

85 87 87 81 80 85 79 75

a Polymerization conditions: ethylene pressure, 1.01 bar; total volume, 25 mL (toluene); V-cat, 2.5 μmol; Al/V = 500; temperature, 20 °C; time, 2 min; [NB]/[E] feed ratio, 4 mol/mol; NB feedstock concentration, 0.57 mol L−1. bActivity in kgpol (molV h)−1. cDetermined by 13C NMR. d Determined by SEC. eDetermined by DSC. fFirst reported in Table 2.

F


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Organometallics excess of ETA potentially competes with the (co)monomer coordination and insertion and suppresses the polymerization. This may account for inferior performance of 3. The molecular weight of the resulting polymers was also strongly affected by the charged amount of ETA (Figure 5B): the higher the ETA/V ratio, the lower the molecular weight. It seems that ETA behaves as a chain transfer agent; that is, it acts as reagent that both terminates (or contributes to increase chain transfer rate) and facilitates reinitiating of a growing polymer chain, as we previously observed with some V(III) complexes.28 Moreover, interestingly, the dependence of the copolymer molecular weight on ETA/V ratio shown in Figure 5B proves once more a different ETA response exhibited by the two complexes. At ETA/V = 150, 3 gave a copolymer with a molecular weight more than two times greater than the copolymer from 1. Although the structure of the catalytically active species (as well as the vanadium oxidation state and the specific interaction of ETA with the active sites) is still unclear at this moment, some clear trends have been identified experimentally by changing the amount of ETA and using the two electronically and sterically different complexes 1 and 3. In the light of these data, we speculate that the active intermediate is an intimate combination of the three reagents (the V precursor, the Al cocatalyst, and ETA) and shows single-site behavior. Copolymerization of Ethylene with Norbornene at Different Temperature. With the feed of 10 equiv of ETA, a series of copolymerizations were carried out at different temperatures from 0 to 70 °C to evaluate the thermal stability of 1−3. The results are summarized in Table 4.

Figure 6. Plot of activity versus copolymerization temperature.

that 1 decomposed faster at elevated temperature may be due to the lower steric hindrance around the vanadium active species provided by the N-2,6-Cl2-C6H3 ligand (Figure 1). In contrast, 3 gave rather high productivity and activity as high as 1988 kgpol molV−1 h−1 even at 70 °C. The instability over temperature correlates with the dominant chain transfer. The molecular weight of the resultant polymers decreased with increasing polymerization temperature, indicating that higher temperature accelerates chain transfer. This is related to the higher tendency to give β-H elimination at a last enchained ethylene unit, followed by a fast displacement of a vinyl-terminated copolymer. Consistent, in the 1H NMR spectra of copolymers obtained at high temperature there is a prevalence of vinyl chain end groups (at 4.7−4.9 ppm, Figure S7) over those of internal vinylene end groups due to chain isomerization and allylic activation after ethylene insertion (a multiplet centered at 5.13 ppm) and unsaturated norbornenyl chain start by C−H bond activation of a norbornene unit and further isomerization (a multiplet centered at 5.31 ppm).39 The molecular weight distributions remained quite narrow and unimodal, indicating that the polymerization took place with uniform catalytically active species even at 70 °C. In addition, however, a copolymer with a molecular weight as high as 516 000 g mol−1 and a norbornene content of 34.1 mol % was obtained at subambient temperature (Table 4, entry 22). Copolymer Microstructure. The microstructure of E/NB copolymers was investigated by 13C NMR. As an example, the 13 C NMR spectrum of entry 7 is shown in Figure 7. The signals of each chemical shift region were assigned according to the literature,40 as follows: 42.0−54.0 ppm, C2/ C3; 34.5−42.0 ppm, C1/C4; 31.0−34.5 ppm, C7; 26.0−31.0 ppm, C5/C6 and ethylene CH2. The spectrum shows the typical pattern of an alternating copolymer from an additiontype norbornene copolymerization with cis exo−exo enchainment. The dominant signals are those of alternating and isolated norbornene units, with traces of norbornene diads. The relative intensities of peaks at 45.7 and 45.2 ppm, assigned to C2/C3 of norbornene in the alternating isotactic and syndiotactic NB−E−NB−E−NB sequences, respectively, also revealed that the copolymers have a random tacticity (Table S1). No significant differences in the microstructure of the copolymers obtained by 1−3 were observed. All the

Table 4. Copolymerization of Ethylene with Norbornene at Different Temperaturea entry

Vcat

T (°C)

yield (mg)

activityb

NBc (mol %)

Mwd (kg mol−1)

Mw/ Mnd

9e 20 21 22 7e 23 24 10e 25 26

1 1 1 2 2 2 2 3 3 3

20 50 70 0 20 50 70 20 50 70

380 259 30 168 250 210 60 360 312 165

4578 3108 360 2016 3012 2520 720 4320 3759 1988

36.4 35.1 f 34.1 35.7 35.0 f 36.8 37.2 37.6

137 44 f 516 147 55 18 155 39 23

2.0 1.8 1.8 2.1 2.1 1.9 2.1 1.8 1.7

a

Polymerization conditions: ethylene pressure, 1.01 bar; total volume, 25 mL (toluene); V-cat, 2.5 μmol; Al/V = 500; ETA/V = 10; time, 2 min; [NB]/[E] feed ratio, 4 mol/mol; NB feed concentration, 0.57 mol L−1. bActivity in kgpol (molV h)−1. cDetermined by 13C NMR. d Determined by SEC. eFirst reported in Table 2. fNot determined.

Generally, the activity decreased with increasing the polymerization temperature, as commonly observed for other vanadium catalysts.38 This may be due to a thermal deactivation likely associated with a faster reduction to lowvalent less active or inactive V(II) species even in the presence of ETA. Changes in the ligand pattern had a strong influence on the catalysts stability over temperature (Figure 6). A more pronounced reduction in activity was observed for 1 and 2 bearing a ligand with an aryl moiety, the highest one being for the most electron-poor ortho-Cl-substituted complex 1. It is likely that steric effects may also play a role. Indeed, the fact G


Article

Organometallics

Figure 7. 13C NMR spectrum of E/NB copolymer obtained with 2/Et2AlCl/ETA (Table 2, entry 7, NB = 35.7 mol %, isolated NB units = 44 mol %, alternated NB units = 54 mol % (isotactic/syndiotactic = 25:19), NB diads = 2 mol %; D refers to a NB diad).

Table 5. Copolymerization of Ethylene with Dicylopentadiene, 5-Ethylidene-2-Norbornene, and 5-Vinyl-2-norbornene by 1− 3/Et2AlCl/ETAa entry

V-cat

comonomer (Y)

yield (mg)

activityb

Yc (mol %)

Mwd (kg mol−1)

Mw/Mnd

Tge (°C)

27 28 29 30 31 32 33

1 2 3 1 2 3 2

DCPD DCPD DCPD ENB ENB ENB VyNBf

252 141 62 292 279 162

3036 1692 747 3518 3361 1952

20.9 19.1 22.1 33.7 35.3 31.4

51 64 67 166 230 239

2.0 2.3 2.2 3.2 2.0 1.7

62 54 57 76 78 74

a Polymerization conditions: ethylene pressure, 1.01 bar; total volume, 25 mL (toluene); V-cat, 2.5 μmol; Al/V = 500; ETA/V = 10; temperature, 20 °C; time, 2 min; [Y]/[E] feed ratio, 4 mol/mol; comonomer feedstock concentration, 0.57 mol L−1. Comonomer (Y) abbreviations: DCPD = dicyclopentadiene; ENB = 5-ethylidene-2-norbornene; VyNB = 5-vinyl-2-norbornene. bActivity in kgpol (molV h)−1. cDetermined by 1H NMR. d Determined by SEC. eDetermined by DSC. fNot active.

derivatives was investigated by using dicyclopentadiene (DCPD), 5-ethylidene-2-norbornene (ENB), and 5-vinyl-2norbornene (VyNB) (Table 5). All the complexes proved to be highly active in the copolymerization of ethylene with DCPD and ENB, while they seem to be poisoned by the extra vinyl double bond of VyNB. At the moment, we do not have an exhaustive explanation, but it can likely be due to the vinylic C−H bond activation for VyNB, which determines facile β-H elimination and subsequent chain transfer. Both the two DCPD and ENB cyclic dienes insert into the macromolecular chain via the enchainment of the double bond of the norbornene ring, while the second CC bond is

copolymers show weak resonances at 27.5 and 29.3 ppm assigned to C5/C6 rac-connected norbornene diblocks,40a while resonances that identify meso-connected ones were not detected.41 Unexpectedly, no resonances were detected in the regions that would clearly identify longer comonomer blocks (53.7−49.3, 44.7−40.7, and 27.3−25.7 ppm) even for the copolymer with a norbornene content as high as 39.3 mol % (Table 2, entry 13). This means that after two consecutive insertions of norbornene, a further insertion of ethylene is the only one possible. Copolymerization of Ethylene with Norbornene Derivatives. The ability of 1−3 to incorporate norbornene H


Article

Organometallics retained without cross-linking. Steric influences emerge clearly in the copolymerization of ethylene with DCPD and ENB. The activities for the copolymerization of ethylene with DCPD and ENB were lower than those obtained for the copolymerization of ethylene with norbornene (Table 2). This can be due to the increased steric interaction with bulky DCPD and ENB but also, and in particular for DCPD, to a possible coordination of the extra CC donor double bond (the one that is not involved in the copolymerization reaction) to the metal center, thus inhibiting the propagation rate, as already observed by Li et al. in the case of some V(V) and zirconium based catalysts.42 Nonetheless, for the rather unconstrained 1, with the less electron-donating imido ligand, a rather high activity was observed (Table 5, entries 27 and 29). It is likely that electronic ligand effects may also play a role. Indeed, in an analogous manner for both DCPD and ENB comonomers, but differently from what has been observed in the case of norbornene (Table 2), the activity increased as the electronwithdrawing character of the complexes increased, thus moving from 3 to 1. The presence of chlorine atoms on the 2,6position of the aryl-imido moiety (1) has a positive effect on the activity,11c and this beneficial effect was more evident in the case of DCPD. This may likely be due to the greater “accessibility” of the extra CC double bond of DCPD compared with that of ENB (Table 5, entry 27 vs 28 and 30 vs 31) that increases the chance of the more electron-deficient 1 to be active, at least more than 2 and 3. Conversely, in the case of the more electron-rich 3, the interaction between the metal center and the cyclopentene ring of DCPD may account for the inferior performance of 3. On the other hand, electronic ligand influences on the comonomer incorporation are ambiguous, while the influence of the steric bulk is more explicit. Indeed, steric effects strongly limit incorporation of bulkier DCPD, as concluded from the lower content of DCPD in the copolymers compared to ENB. Similarly to the results found for the homopolymerization of ethylene and copolymerization of ethylene with norbornene, 3 formed copolymers with the highest molecular weight, followed by 2 and 1. This confirms that 3 with the more electron-donating N-tBu imido ligand is less prone to chain transfer, preferentially undergoing chain propagation rather than chain transfer. Remarkably, the copolymerization with ENB formed copolymers with the highest molecular weights, followed by those obtained with norbornene and DCPD, respectively. This indicates that the coordination of ENB slows down the chain termination reactions although, so far, the exact mechanism remains unclear. Experimentally, this behavior cannot be fully explained by taking into account the electronic and steric features of the vanadium complexes alone: additional factors such the different steric properties of the investigated cyclic olefins and the different deactivation (or stability) paths of the investigated complexes should also be considered. The copolymer microstructure was established by 13C NMR.43 In the case of E/DCPD copolymers, the peaks at 130.6 and 128.8 ppm in 13C NMR spectrum (Figure 8) and those at about 5.5 and 5.4 ppm in the 1H NMR spectra (Figure S8) were assigned to sp2 C and H atoms, respectively, revealing that the copolymers contain unreacted cyclopentene units.44 This suggests that the reaction took place selectively at the norbornene unit and that no cross-linking occurred. The dominant signals in the 13C NMR spectra are those at 51.6 (C9), 44.4 (C6), 42.8 (C7), 40.8 (C4), 38.9 (C8), 35.9 (C5),

Figure 8. 13C NMR spectrum of E/DCPD copolymer obtained with 2/Et2AlCl/ETA (Table 5, entry 28, DCPD = 19.1 mol %). DCPD diad and blocks longer than the diads are marked with a cross.

34.2 (C10), and 30.5 (C3) assigned to isolated DCPD units, while a number of weak signals at 45.0 (C6), 43.3 (C7), 39.6 (C8) and 36.6 (C5) ppm are characteristic of alternating sequences. Very small signals due to traces of diads and longer DCPD blocks were also detected, their large number being dependent on the different comonomer stereosequences and length.40a In the copolymerization with ENB, the side double bond of the cyclic monomer did not participate in the copolymerization, and each link of ENB in the copolymer contains an ethylidene group. The 1H NMR spectrum shows signals at 5.1 and 5.3 ppm that were assigned to the ethylidene groups; the absence of signals at about 6.0 ppm indicates that the polymerization occurs only via the intracyclic norbornene double bond (Figure S9). The 13C NMR spectrum of entry 31 is shown in Figure 9. The dominant signals are those in the regions at 144−145 and 108−109 ppm assigned to the double bond C5 and C8, respectively, 48.0−50.0 ppm (C4), 42.0−46.0 ppm (C1/C3, with the signals ascribed to C3 located at the higher field), 34.0−38.0 ppm (C6), 31.0−33.0 ppm (C7), 27.0−30.0 ppm (C10/C11 and ethylene CH2), and 11.5−12.5 ppm (C9).45 From the spectrum, it can be seen that both the E and Z configurational ENB isomers reacted (signed with the subscript e and z, respectively, in Figure 9), the ratio between them being 3:1, close to that in the neat monomer. Similar to the DCPD copolymers, the microstructure of ENB copolymers mainly consists of isolated and alternated ENB units, while no longer ENB sequences were detected even for sample 31 with a content of ENB of 35.3 mol %.

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CONCLUSIONS This study reports the synthesis and the characterization of new (imido)V(IV) complexes of the type V(NR)Cl2(PMe2Ph)2 [(R = 2,6-Cl2-C6H3 (1), 2,6-iPr2-C6H3 (2), t Bu (3)] and V(NtBu)Cl2(PMe3)2 (3′), and the application of 1−3 as catalyst precursors for the polymerization of ethylene and copolymerization with various cyclic olefins. The I


Article

Organometallics

Changes in the imido ligand have a strong influence on the catalyst stability with increasing temperature. A more pronounced decomposition was observed for aryl−imido complexes, while the alkyl−imido one exhibited a rather high activity even at 70 °C. Electronic effects from imido substituents play a key role in modulating the molecular weight of the resulting (co)polymers: more electron-donating ligand strengthens the V−N bond and mitigates β-H elimination and subsequent chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. We demonstrated that ETA behaves like a chain transfer agent and to a different extent strongly depending on the type of imido ligand. In conclusion, the results reported herein may provide useful information about the appropriate choice of the N-alkyl (or aryl) moiety, the role of ETA and future catalyst design. We are now exploring the (co)polymerization of ethylene with various olefins by analogous (imido)V(IV) complexes, including 3′, having different coligands. These would be introduced in the future.

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Figure 9. 13C NMR spectrum of the E/ENB copolymer obtained with 2/Et2AlCl/ETA (Table 5, entry 31, ENB = 35.3 mol %).

EXPERIMENTAL SECTION

General Procedures and Materials. Manipulations of air- and moisture-sensitive materials were carried out under an inert atmosphere using a dual vacuum/nitrogen line and standard Schlenk-line techniques or in a glovebox filled with argon. Ethylene and nitrogen were purified by passage over columns of CaCl2 and molecular sieves. Oxygen was removed by fluxing the gases through BTS catalysts. Toluene (Aldrich, ≥99.7%) was refluxed over Na for 8 h and then distilled and stored over molecular sieves. ETA (Aldrich, 97%) was stirred over CaH2 for about 4 h and then distilled under reduced pressure. MAO (Aldrich, 10 wt % solution in toluene) and diethylaluminum chloride (Et2AlCl, Aldrich) were used as received. Norbornene (NB) (Aldrich, 99%) was stirred over molten potassium at 80 °C under nitrogen for 4 h and then distilled. A stock solution was prepared by dissolving 50 g of freshly distilled norbornene in 86.2 mL of toluene. 5-Vinyl-2-norbornene (VyNB) (Aldrich, 95%), 5ethylidene-2-norbornene (ENB) (Aldrich, 99%), and dicyclopentadiene (DCPD) (Aldrich, 95%) were dried over CaH2 at 60 °C under nitrogen for 4 h and distilled under reduced pressure. VyNB, ENB, and DCPD were of commercial grade (mixtures of endo and exo isomers). Deuterated solvent for NMR measurements (C2D2Cl4) (Aldrich, >99.5% atom D) was used as received. V(NMe2)4 was prepared by a modification of a literature procedure.46 Amines 2,6-iPr2-C6H3NH2 and tBuNH2 were dried over KOH, refluxed over CaH2, distilled, and stored over 4 Å molecular sieves under argon before use. Trimethylchlorosilane was distilled and stored over 4 Å molecular sieves under argon before use. Compounds [V( NAr)Cl2]n (Ar = 2,6-iPr2-C6H3 or 2,6-Cl2-C6H3) were prepared according to a known procedure.14 Compound [V(N-2,6-iPr2C6H3)Cl2(PMe2Ph)2] (2) was obtained by reacting [V(N-2,6-iPr2− C6H3)Cl2]n with PMe2Ph according to our published procedure.16 PMe2Ph and PMe3 were purchased from Strem. Synthesis of Vanadium Complexes. Synthesis of [V(N-2,6Cl2-C6H3)Cl2(PMe2Ph)2] (1). To a dichloromethane solution (5 mL) of 150 mg of [V(N-2,6-Cl2-C6H3)Cl2]n (0.532 mM) was added 300 mg of PMe2Ph (2.172 mM) at room temperature. After 2 days of stirring at room temperature, the resulting solution was evaporated to dryness under vacuum. The solid was extracted with toluene, and the solution was filtered on Celite before being evaporated to dryness. The solid was washed with 2 × 5 mL of pentane and then recrystallized by diffusion of pentane into a 1 mL toluene solution, affording red crystals of 1 (yield after drying under vacuum 105 mg, 35%). EPR (CH2Cl2, 20 °C) g = 1.976, Aiso(51V) = 81 G, Aiso(31P) = 30 G. μeff (C6D6, Evans) = 1.7 μB (300 K). Anal. Calcd for C22H25Cl4NP2V (MW 558.14): C, 47.34; H, 4.51; N, 2.51. Found: C, 47.28; H, 4.45; N, 2.62.

target compounds are obtained in a three step reaction from V(NMe2)4 and the corresponding primary amine RNH2, followed by subsequent treatment with trimethylchlorosilane, and addition of phosphine. The complexes present a geometry around the metal center between a distorted trigonalbipyramid and a square pyramid, with an almost linear N− V−C bond, indicating a metal−imido triple bond formulation. In the presence of a low excess of Et2AlCl (500 equiv to V) and ETA (10 equiv to V), 1−3 exhibit high activity in the polymerization of ethylene, affording strictly linear, semicrystalline PEs (Tm > 135 °C) and good stability over time. Introduction of norbornene in the reaction mixture accelerates the propagation rate. Mainly alternating copolymers with efficient norbornene incorporation (up to 39.3 mol %) and uniform composition are obtained already within the first instants of the copolymerization, with no obvious compositional drift even for a prolonged reaction time. While no unfavorable effect is observed in the ethylene homopolymerization, an increase in the imido steric bulk (particularly for 2) leads to decreased activity in the copolymerization of ethylene with norbornene. The increased steric interaction between bulky norbornene and bulky isopropyl-aryl substituents in 2, which can arrange in the axial position, is probably responsible also for the lower comonomer incorporation with this system. The investigated complexes proved to be versatile and active also in the copolymerization of ethylene with DCPD and ENB. Remarkably, the introduction of ENB in the reaction mixture restrains the chain transfer to some extent, affording very high molecular weight copolymers with CC double bonds in the side chains. The introduction of unsaturated reactive groups is of particular interest for the production of functionalized polyolefins and vulcanizable materials. A marked dependence of activity on the imido substituents was found in the copolymerization of ethylene with DCPD and ENB: the activity strongly increases in the order 3 < 2 < 1 with decreasing the ligand electron-donor ability. Steric effect is probably the factor responsible for the poor incorporation of bulkier DCPD compared to norbornene and ENB. J


Article

Organometallics

standards with molar weights ranging from 162 to 5.6 × 106 g mol−1. For SEC analysis, about 12 mg of polymer was dissolved in 5 mL of DCB with 0.05% of BHT as antioxidant. Single Crystal X-ray Diffraction Determination. Crystals suitable for X-ray structure determination were obtained for compounds 1 (by diffusion of pentane into a toluene solution of 1) and 3′ (from cold pentane solutions). The crystals were kept in the mother liquor until they were dipped into perfluoropolyether oil, and their structure was determined. Crystal data collection and processing parameters are given in Table 6.

Synthesis of [V(N-tBu)Cl2(PMe2Ph)2] (3). Step 1. A toluene solution (5 mL) of 400 mg of V(NMe2)4 (1.760 mM) and 283.2 mg of tBuNH2 (3.872 mM) was heated overnight at 100 °C giving a dark brown-red solution. Removal of the volatiles under vacuum gave a sticky solid that was triturated several times with 2 mL of pentane and dried under vacuum for a prolonged period of time to afford a red solid (composed of [V(μ-N-tBu)(NMe2)2]2 and a minor amount of [(tBuNH)(Me2N)V(μ-N-tBu)2V(NMe2)2] as already discussed in analogous titanium systems.23a Step 2. To this solid was added toluene (2 mL) and excess Me3SiCl (2.0 g), and the red-purple solution was stirred overnight at 100 °C. Removal of the volatiles under vacuum and washing with cold pentane afforded a dark pink solid (150 mg) that is attributed to a complex of composition close to [V(μ-N-tBu)Cl2]n by analogy to related titanium systems.23b Step 3. To this pink solid (150 mg of [V(μ-N-tBu)Cl2]n) were added 3 mL of toluene and then 322.2 mg of PMe2Ph (2.332 mM). The brown-red solution was stirred at room temperature for 3 days. The volatiles were removed under vacuum for a prolonged period of time to get rid of excess PMe2Ph (which renders 3 more soluble in pentane). The solid was extracted with toluene (3 × 1 mL), the solution was filtered through a bed of Celite, and the filtrate was evaporated to dryness. The resulting brown-red solid was briefly washed with 2 mL of cold pentane and dried under vacuum to afford 345 mg of 3 (yield 42% based on V(NMe2)4). EPR (pentane, 20 °C) g = 1.978, Aiso(51V) = 85 G, Aiso(31P) = 29 G. μeff (Evans) = 1.8 μB (300 K). Anal. Calcd for C20H31Cl2NP2V (MW 469.26): C, 51.19; H, 6.66; N, 2.98. Found: C, 50.88; H, 6.89; N, 3.02. Synthesis of [V(N-tBu)Cl2(PMe3)2] (3′). The complex was prepared by the method described above for 3. Crystals were obtained by cooling a pentane solution of 3′ to −20 °C. EPR (CH2Cl2, 20 °C) g = 1.994, Aiso(51V) = 85 G, Aiso(31P) = 29 G. μeff (Evans) = 1.7 μB (300 K). Anal. Calcd for C10H27Cl2NP2V (MW 345.12): C, 34.80; H, 7.89; N, 4.06. Found: C, 35.20; H, 7.88; N, 4.07. General (co)Polymerization Procedure. Polymerizations were carried out in a 25 mL round-bottomed Schlenk flask. Prior to starting polymerization, the reactor was heated to 110 °C under vacuum for 1 h and backfilled with nitrogen. The reactor was charged at room temperature with toluene, the comonomer, ETA, and Et2AlCl in that order. The solution was degassed, and ethylene was added until saturation. Polymerization was started by adding a toluene solution (2 mg mL−1) of vanadium complex via syringe under continuous flow of ethylene. Polymerizations were stopped with methanol containing a small amount of hydrochloric acid; the precipitated polymers were collected by filtration, repeatedly washed with fresh methanol, and finally dried in vacuum at room temperature to constant weight. Characterization. EPR spectra were recorded on a Bruker Elexsys E580 spectrometer. Elemental analyses were performed at the Laboratoire de Chimie de Coordination (Toulouse, France) (C,H,N) or by the Service Central de Microanalyses du CNRS at Lyon (France) (C,H,N). Magnetic susceptibility data were measured in solution by 1H NMR (Evans method).47 NMR spectra were recorded on a Bruker NMR Advance 400 spectrometer operating at 400 MHz (1H) and 100.58 MHz (13C) working in the PFT mode at 103 °C. 13C NMR experiments were performed with 10 mm probe in C2D2Cl4 and referred to hexamethyldisiloxane (HMDS) as internal standard. The relaxation delay was 16 s. Differential scanning calorimetry (DSC) scans were carried out on a PerkinElmer Pyris 1 instrument equipped with a liquid subambient device under helium atmosphere. The sample, typically 5 mg, was placed in a sealed aluminum pan, and the measurement was carried out from −80 to 150 °C using heating and cooling rate of 20 °C min−1. Tg and Tm values were recorded during the second heating. Mw and Mw/Mn were obtained by a high temperature Waters GPCV2000 size exclusion chromatography (SEC) system equipped with a refractometer detector. The experimental conditions consisted of three PL Gel Olexis columns, ortho-dichlorobenzene (DCB) as the mobile phase, 0.8 mL/min flow rate, and 145 °C temperature. The calibration of the SEC system was constructed using 18 narrow Mw/Mn poly(styrene)

Table 6. Crystallographic Data, Data Collection, and Refinement Parameters for 1 and 3′ chemical formula formula wt cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z Dcalc, g cm−3 μ(Mo Kα), mm−1 F(000) θ range (deg) measured reflns unique reflns/Rint params/restraints final R indices, all data goodness of fit Δρmax, Δρmin CCDC number

1

3′

C22H25Cl4NP2V 558.11 monoclinic P2/c 8.2193(6) 9.7378(7) 16.9126(11) 90 103.578(3) 90 1315.82(16) 2 1.409 0.545 570 2.4−26.4 39104 2687/0.035 140/0 R = 0.049 wR = 0.123 1.15 0.67, −0.51 1843200

C10H27Cl2NP2V 345.1 orthorhombic Pbca 15.436 (3) 9.012 (2) 26.306 (5) 90 90 90 3659.4 (13) 8 1.253 0.99 1448 2.0−22.5 16660 2336/0.116 154/0 R = 0.032 wR = 0.088 1.07 0.30, −0.28 1843201

The chosen crystals were mounted on a Mitegen micromount and quickly cooled down to 180 K. The selected crystals of 1 (orange, 0.17 × 0.10 × 0.03 mm3) and 3′ (colorless, 0.35 × 0.25 × 0.15 mm3) were mounted, respectively, on a Xcalibur or a Bruker Kappa APEX II using molybdenum (λ = 0.71073 Å) and equipped with an Oxford Cryosystems cooler device or an Oxford Cryosystems Cryostream Cooler Device. The unit cell determination and data integration were carried out using CrysAlis RED package or APEX II.48−50 The structures have been solved by Direct Methods using SIR9251 and refined by least-squares procedures with SHELXS-201652 included in the software packages WinGX version 1.63.53 Atomic Scattering Factors were taken from the International tables for X-ray Crystallography.54 All hydrogen atoms were refined by using a riding model. All non-hydrogen atoms were anisotropically refined. Drawings of molecules have been performed with the program Ortep-3 for Windows.55 Details of the structure solution and refinements are given in the Supporting Information, together with a full listing of atomic coordinates, bond lengths and angles, and displacement parameters for all structures. These data have also been deposited at the Cambridge Crystallographic Data Centre. CCDC 1843200 and 1843201 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. K


Article

Organometallics

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(3) (a) Baier, M. C.; Zuideveld, M. A.; Mecking, S. Postmetallocenes in the industrial production of polyolefins. Angew. Chem., Int. Ed. 2014, 53, 9722−9744. (b) Guo, L.; Liu, W.; Chen, C. Late transition metal catalyzed α-olefin polymerization and copolymerization with polar monomers. Mater. Chem. Front. 2017, 1, 2487−2494. (c) Eagan, J. M.; Xu, J.; Di Girolamo, R.; Thurber, C. M.; Macosko, C. W.; LaPointe, A. M.; Bates, F. S.; Coates, G. W. Combining polyethylene and polypropylene: Enhanced performance with PE/iPP multiblock polymers. Science 2017, 355, 814−816. (d) Peng, D.; Yan, X.; Yu, C.; Zhang, S.; Li, X. Transition metal complexes bearing tridentate ligands for precise olefin polymerization. Polym. Chem. 2016, 7, 2601−2634. (e) McInnis, J. P.; Delferro, M.; Marks, T. J. Multinuclear Group 4 Catalysis: Olefin Polymerization Pathways Modified by Strong Metal−Metal Cooperative Effects. Acc. Chem. Res. 2014, 47, 2545−2557. (4) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Late-Metal Catalysts for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100, 1169−1203. (b) van Doremaele, G.; van Duin, M.; Valla, M.; Berthoud, A. On the Development of Titanium κ1-Amidinate Complexes, Commercialized as Keltan ACE Technology, Enabling the Production of an Unprecedented Large Variety of EPDM Polymer Structures. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2877−2891. (c) Flisak, Z.; Sun, W. H. Progression of Diiminopyridines: From Single Application to Catalytic Versatility. ACS Catal. 2015, 5, 4713− 4724. (5) (a) Cundari, T. R. Transition metal imido complexes. J. Am. Chem. Soc. 1992, 114, 7879−7888. (b) Coles, M. P.; Gibson, V. C. New homogeneous ethylene polymerization catalysts derived from transition metal imido precursors. Polym. Bull. 1994, 33, 529−533. (c) Coles, M. P.; Dalby, C.; Gibson, V. C.; Little, I. R.; Marshall, E. L.; Ribeiro da Costa, M. H.; Mastroianni, S. Transition metal imido catalysts for ethylene polymerisation. J. Organomet. Chem. 1999, 591, 78−87. (6) Bolton, P. D.; Mountford, P. Transition Metal Imido Compounds as Ziegler−Natta Olefin Polymerisation Catalysts. Adv. Synth. Catal. 2005, 347, 355−366. (7) (a) Khalimon, A. Y.; Peterson, E.; Lorber, C.; Kuzmina, L. G.; Howard, J. A. K.; van der Est, A.; Nikonov, G. I. Imido-Supported Borohydrides of Titanium, Vanadium and Molybdenum. Eur. J. Inorg. Chem. 2013, 2013, 2205−2211. (b) Nguyen, V. H.; Vendier, L.; Etienne, M.; Despagnet-Ayoub, E.; Breuil, P.-A. R.; Magna, L.; Proriol, D.; Olivier-Bourbigou, H.; Lorber, C. Titanium−Imido Complexes with Pendant Groups − Synthesis, Characterization, and Evaluation of Their Role as Precatalysts for Ethylene Polymerization. Eur. J. Inorg. Chem. 2012, 2012, 97−111. (c) Lorber, C.; Vendier, L. Routes to New N-Heterocyclic Carbene Titanium(IV) Imido Complexes. Organometallics 2008, 27, 2774−2783. (d) Lorber, C.; Choukroun, R.; Vendier, L. Reaction of p-Toluenesulfonylamide and M(NMe2)4 (M = Ti, V): Generation of Electron-Deficient Imido Complexes of Early Transition Metals. Inorg. Chem. 2007, 46, 3192− 3202. (e) Lorber, C.; Choukroun, R.; Vendier, L. A General and Facile One-Step Synthesis of Imido−Titanium(IV) Complexes: Application to the Synthesis of Compounds Containing Functionalized or Chiral Imido Ligands and Bimetallic Diimido Architectures. Eur. J. Inorg. Chem. 2006, 2006, 4503−4518. (f) Lorber, C.; Vendier, L. Synthesis and structure of early transition metal NHC complexes. Dalton Trans. 2009, 6972−6984. (g) Lorber, C.; Vendier, L. Imido− Titanium/Molybdenum Heterobimetallic Systems. Switching from η6Arene to Fischer-Type Aminocarbene Complexes by Tuning Reactivity Conditions. Organometallics 2010, 29, 1127−1136. (8) Theopold, K. H. Homogeneous Chromium Catalysts for Olefin Polymerization. Eur. J. Inorg. Chem. 1998, 1998, 15−24. (9) Lorber, C., Vanadium organometallics. In Chemistry, Molecular Sciences and Chemical Engineering (Major Reference Works); Reedijk, J., Ed.; Elsevier: Waltham, MA. 2015; pp 1−78. (10) Nomura, K.; Zhang, S. Design of Vanadium Complex Catalysts for Precise Olefin Polymerization. Chem. Rev. 2011, 111, 2342−2362. (11) For selected paper on (imido)vanadium(V) complexes, see: (a) Nomura, K.; Oshima, M.; Mitsudome, T.; Harakawa, H.; Hao, P.;

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00502. EPR spectra, (co)polymer sample data, including microstructural analysis, DSC, and 1H NMR spectra (PDF) Three-dimensional structure of compound 1 (XYZ) Three-dimensional structure of compound 2 (XYZ) Three-dimensional structure of compound 3′ (XYZ) Topographic steric maps generated using SambVca 2 Web26 of imido ligands in compound 1 (PDF) Topographic steric maps generated using SambVca 2 Web26 of imido ligands in 2 (PDF) Topographic steric maps generated using SambVca 2 Web26 of imido ligands in 3′ (PDF) Accession Codes

CCDC 1843200−1843201 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail address: [email protected] (C. Lorber). *E-mail address: [email protected] (G. Leone). ORCID

Giorgia Zanchin: 0000-0003-0161-4963 Ivana Pierro: 0000-0002-1296-198X Giovanni Ricci: 0000-0001-8586-9829 Christian Lorber: 0000-0003-1361-5373 Giuseppe Leone: 0000-0001-6977-2920 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca), project PON-DIATEME 2007-2013. The CNRS is thanked for its support. The authors thank Fulvia Greco and Daniele Piovani for skilled technical assistance. Giuseppe Leone acknowledges Arnaldo Rapallo for fruitful discussions.

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REFERENCES

(1) (a) Chen, C. Designing catalysts for olefin polymerization and copolymerization: beyond electronic and steric tuning. Nat. Chem. Rev. 2018, 2, 6−14. (b) Stürzel, M.; Mihan, S.; Mülhaupt, R. From Multisite Polymerization Catalysis to Sustainable Materials and AllPolyolefin Composites. Chem. Rev. 2016, 116, 1398−1433. (c) Klosin, J.; Fontaine, P. P.; Figueroa, R. Development of Group IV Molecular Catalysts for High Temperature Ethylene-α-Olefin Copolymerization Reactions. Acc. Chem. Res. 2015, 48, 2004−2016. (2) (a) Brintzinger, H. H.; Fischer, D.; Mülhaupt, R.; Rieger, B.; Waymouth, R. M. Stereospecific Olefin Polymerization with Chiral Metallocene Catalysts. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143− 1170. (b) Kaminsky, W. New polymers by metallocene catalysis. Macromol. Chem. Phys. 1996, 197, 3907−3945. (c) Sinn, H.; Kaminsky, W. Ziegler-Natta Catalysis. Adv. Organomet. Chem. 1980, 18, 99−149. L


Article

Organometallics Tsutsumi, K.; Nagai, G.; Ina, T.; Takaya, H.; Sun, W.-H.; Yamazoe, S. ACS Omega 2017, 2, 8660−8673. (b) Nagai, G.; Mitsudome, T.; Tsutsumi, K.; Sueki, S.; Ina, T.; Tamm, M.; Nomura, K. Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic N-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety. J. Jpn. Pet. Inst. 2017, 60, 256−262. (c) Diteepeng, N.; Tang, X.; Hou, X.; Li, Y. S.; Phomphrai, K.; Nomura, K. Ethylene polymerisation and ethylene/norbornene copolymerisation by using aryloxo-modified vanadium(V) complexes containing 2,6-difluoro-, dichloro-phenylimido complexes. Dalton Trans. 2015, 44, 12273− 12281. (d) Nomura, K.; Bahuleyan, B. K.; Zhang, S.; Veeresha Sharma, P. M.; Katao, S.; Igarashi, A.; Inagaki, A.; Tamm, M. Synthesis and Structural Analysis of (Imido)vanadium(V) Dichloride Complexes Containing Imidazolin-2-iminato- and Imidazolidin-2iminato Ligands, and their Use as Catalyst Precursors for Ethylene (Co)polymerization. Inorg. Chem. 2014, 53, 607−623. (e) Igarashi, A.; Zhang, S.; Nomura, K. Ethylene Dimerization/Polymerization Catalyzed by (Adamantylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands: Factors Affecting the Ethylene Reactivity. Organometallics 2012, 31, 3575−3581. (12) (a) Zhang, S.; Nomura, K. Highly Efficient Dimerization of Ethylene by (Imido)vanadium Complexes Containing (2Anilidomethyl)pyridine Ligands: Notable Ligand Effect toward Activity and Selectivity. J. Am. Chem. Soc. 2010, 132, 4960−4965. (b) Nomura, K.; Igarashi, A.; Katao, S.; Zhang, W.; Sun, W.-H. Synthesis and Structural Analysis of (Imido)Vanadium(V) Complexes Containing Chelate (Anilido)Methyl-imine Ligands: Ligand Effect in Ethylene Dimerization. Inorg. Chem. 2013, 52, 2607−2614. (13) For selected papers on (imido)vanadium(IV) complexes, see: (a) Hagen, H.; Bezemer, C.; Boersma, J.; Kooijman, H.; Lutz, M.; Spek, A. L.; van Koten, G. Vanadium(IV) and -(V) Complexes with O,N-Chelating Aminophenolate and Pyridylalkoxide Ligands. Inorg. Chem. 2000, 39, 3970−3977. (b) Preuss, F.; Tabellion, F.; Overhoff, G.; Reiss, G. Z. tBuN = VCl2 · 1,2-Dimethoxoethan, eine Schlüsselverbindung zur Darstellung von zweikernigen, diamagnetischen tert-Butylimidovanadium(IV)-Verbindungen. Z. Anorg. Allg. Chem. 2000, 626, 1665−1675. (c) Preuss, F.; Perner, J.; Frank, W.; Reiss, G. Z. Indenylvanadium(V)-Verbindungen. Darstellung, Struktur und NMR-spektroskopische Untersuchungen. Z. Anorg. Allg. Chem. 1999, 625, 901−909. (d) Davis, J. A.; Davie, C. P.; Sable, D. B. Directed reactivity at a vanadium(II) thiolate center: synthesis and structure of a novel vanadium thiolate complex and its reaction product with azobenzene. Chem. Commun. 1998, 1649−1650. (e) Preuss, F.; Hornung, G.; Frank, W.; Reiss, G.; Muller-Becker, S. Z. Komplexbildung des tert-Butyliminovanadium(V)-trichlorids mit O-Donor-Liganden. Z. Anorg. Allg. Chem. 1995, 621, 1663−1671. (14) Lorber, C.; Donnadieu, B.; Choukroun, R. Synthesis and X-ray characterization of a monomeric Cp-free d1-imido−vanadium(IV) complex. Dalton Trans. 2000, 4497−4498. (15) Lorber, C.; Choukroun, R.; Donnadieu, B. Synthesis and Structure of a Series of New d 1-Aryl Imido−Vanadium(IV) Complexes Stabilized by N-Donor Ligands. Inorg. Chem. 2002, 41, 4217−4226. (16) Lorber, C.; Choukroun, R.; Donnadieu, B. Synthesis and Crystal Structure of Unprecedented Phosphine Adducts of d1-Aryl Imido−Vanadium(IV) Complexes. Inorg. Chem. 2003, 42, 673−675. (17) For selected papers and reviews on COCs, see: (a) Cheng, H. L.; Cai, Z. G. (Anilino)anthraquinone Nickel-Catalyzed Random Copolymerization of Norbornene and Ethylene. ChemCatChem 2018, 10, 497−500. (b) Song, X. Y.; Yu, L. J.; Shiono, T.; Hasan, T.; Cai, Z. G. Synthesis of Hydroxy-Functionalized Cyclic Olefin Copolymer and Its Block Copolymers with Semicrystalline Polyolefin Segments. Macromol. Rapid Commun. 2017, 38, 1600815. (c) Na, Y.; Zhang, D.; Chen, C. Modulating polyolefin properties through the incorporation of nitrogen-containing polar monomers. Polym. Chem. 2017, 8, 2405− 2409. (d) Pei, L.; Tang, L.; Gao, H. Homo- and Copolymerization of Ethylene and Norbornene with Anilido−Imine Chromium Catalysts. Polymers 2016, 8, 69−79. (e) Hong, M.; Yang, G.-F.; Long, Y. Y.; Yu,

S.; Li, Y. S. Preparation of novel cyclic olefin copolymer with high glass transition temperature. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3144−3152. (f) Hong, M.; Cui, L.; Liu, S.; Li, Y. S. Synthesis of Novel Cyclic Olefin Copolymer (COC) with High Performance via Effective Copolymerization of Ethylene with Bulky Cyclic Olefin. Macromolecules 2012, 45, 5397−5402. (g) Hong, M.; Wang, Y. X.; Mu, H. L.; Li, Y. S. Efficient Synthesis of Hydroxylated Polyethylene via Copolymerization of Ethylene with 5-Norbornene-2-methanol using Bis(β-enaminoketonato)titanium Catalysts. Organometallics 2011, 30, 4678−4686. (h) Chen, Y.; Mandal, S.; Sen, A. Synthesis of (N−O)-Ligated Palladium(II) Complexes and Their Use in Ethene Homopolymerization and Norbornene Copolymerizations. Organometallics 2010, 29, 3160−3168. (i) Li, X.; Hou, Z. Organometallic catalysts for copolymerization of cyclic olefins. Coord. Chem. Rev. 2008, 252, 1842−1869. (18) (a) Lamonte, R. R.; Mc Nally, D. Cyclic olefin copolymers. Adv. Mater. Processes 2001, 3, 33−36. (b) Losio, S.; Tritto, I.; Boggioni, L.; Mancini, G.; Luciano, G.; Tofani, L.; Viglianisi, C.; Menichetti, S.; Sacchi, M. C.; Stagnaro, P. Fully consistent terpolymeric non-releasing antioxidant additives for long lasting polyolefin packaging materials. Polym. Degrad. Stab. 2017, 144, 167− 175. (c) Bernard, M.; Jubeli, E.; Bakar, J.; Tortolano, L.; Saunier, J.; Yagoubi, N. Biocompatibility assessment of cyclic olefin copolymers: Impact of two additives on cytotoxicity, oxidative stress, inflammatory reactions, and hemocompatibility. J. Biomed. Mater. Res., Part A 2017, 105, 3333−3349. (d) Diaz-Albarran, L. M.; Lugo-Hernandez, E.; Ramirez-Garcia, E.; Enciso-Aguilar, M. A.; Valdez-Perez, D.; Cereceda-Company, P.; Granados, D.; Costa-Kramer, J. L. Development and characterization of cyclic olefin copolymer thin films and their dielectric characteristics as CPW substrate by means of Terahertz Time Domain Spectroscopy. Microelectron. Eng. 2018, 191, 84−90. (e) Denz, M.; Brehm, G.; Hémonnot, C. Y. J.; Spears, H.; Wittmeier, A.; Cassini, C.; Saldanha, O.; Perego, E.; Diaz, A.; Burghammer, M.; Köster, S. Cyclic olefin copolymer as an X-ray compatible material for microfluidic devices. Lab Chip 2018, 18, 171−178. (f) Wouters, B.; Dapic, I.; Valkenburg, T. S. E.; Wouters, S.; Niezen, L.; Eeltink, S.; Corthals, G. L.; Schoenmakers, P. J. A cyclicolefin-copolymer microfluidic immobilized-enzyme reactor for rapid digestion of proteins from dried blood spots. J. Chromatogr. A 2017, 1491, 36−42. (19) Kajiura, H.; Oda, H.; Minami, S. European Patent EP0156464B1, 1985. http://www.mitsuichemicals.com/apel.htm. (20) Brekner, M. J.; Osan, F.; Rohrmann, J.; Antberg, J. US Patent 5,324,801, 1994. https://topas.com/products/topas-coc-polymers. (21) Generally, low activities were registered in the absence of ETA likely due to the rapid formation of inactive V(II). ETA plays a fundamental role in restoring the original oxidation state of vanadium, and restarting the catalytic cycle. See also: Adisson, E.; Deffieux, A.; Fontanille, M.; Bujadoux, K. Polymerization of ethylene at high temperature by vanadium-based heterogeneous Ziegler−Natta catalysts. II. Study of the activation by halocarbons. J. Polym. Sci., Part A: Polym. Chem. 1994, 32, 1033−1041. (22) Lorber, C. Titanium and vanadium imido-bridged complexes. Coord. Chem. Rev. 2016, 308, 76−96. (23) For related titanium systems, see: (a) Lorber, C.; Vendier, L. Novel aspects of the transamination reaction between Ti(NMe2)4 and primary amines. Dalton Trans. 2013, 42, 12203−12219. (b) Lorber, C.; Vendier, L. Tight Encapsulation of a “Naked” Chloride in an Imidotitanium Hexanuclear Host. Inorg. Chem. 2013, 52, 4756−4758. (c) Lorber, C.; Vendier, L. Imido-Bridged Homo- and Heterobimetallic Complexes. Inorg. Chem. 2011, 50, 9927−9929. (24) Khalimon, A. Y.; Peterson, E.; Lorber, C.; Kuzmina, L. G.; Howard, J. A. K.; van der Est, A.; Nikonov, G. I. Imido-Supported Borohydrides of Titanium, Vanadium and Molybdenum. Eur. J. Inorg. Chem. 2013, 2013, 2205−2211. (25) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J. V.; Verschoor, G. C. Synthesis, structure, and spectroscopic properties of copper(II) compounds containing nitrogen−sulphur donor ligands; the crystal and molecular structure of aqua[1,7-bis(N-methylbenziM


Article

Organometallics midazol-2′-yl)-2,6-dithiaheptane]copper(II) perchlorate. J. Chem. Soc., Dalton Trans. 1984, 1349−1356. (26) (a) Falivene, L.; Credendino, R.; Poater, A.; Petta, A.; Serra, L.; Oliva, R.; Scarano, V.; Cavallo, L. SambVca 2. A Web Tool for Analyzing Catalytic Pockets with Topographic Steric Maps. Organometallics 2016, 35, 2286−2293. (b) SambVca 2.0: a web application for analyzing catalytic pockets, https://www.molnac.unisa.it/ OMtools/sambvca2.0/. (27) Macchioni, A. Ion Pairing in Transition-Metal Organometallic Chemistry. Chem. Rev. 2005, 105, 2039−2074. (28) (a) Zanchin, G.; Pierro, I.; Parisini, E.; Martí-Rujas, J.; Ricci, G.; Leone, G. Synthesis, structure and behavior of vanadium(III) diphosphine complexes in the homo- and co-polymerization of ethylene with norbornene: the ligand donor strength and bite angle make the difference. J. Organomet. Chem. 2018, 861, 142−150. (b) Leone, G.; Pierro, I.; Zanchin, G.; Forni, A.; Bertini, F.; Rapallo, A.; Ricci, G. Vanadium(III)−catalyzed copolymerization of ethylene with norbornene: Microstructure at tetrad level and reactivity ratios. J. Mol. Catal. A: Chem. 2016, 424, 220−231. (29) (a) Phuphuak, Y.; Bonnet, F.; Vendier, L.; Lorber, C.; Zinck, P. Isoprene polymerization mediated by vanadium-[ONNO] complexes. Dalton Trans. 2016, 45, 12069−12077. (b) Lorber, C.; Wolff, F.; Choukroun, R.; Vendier, L. Ethylene Homo- and Copolymerization Activity of a Series of [ONNO]-Type Amine Bis(phenolate) Based Vanadium(II−V) Catalysts. Eur. J. Inorg. Chem. 2005, 2005, 2850− 2859. (c) Gambarotta, S. Vanadium-based Ziegler−Natta: challenges, promises, problems. Coord. Chem. Rev. 2003, 237, 229−243. (d) Hagen, H.; Boersma, J.; van Koten, G. Homogeneous vanadium-based catalysts for the Ziegler−Natta polymerization of α-olefins. Chem. Soc. Rev. 2002, 31, 357−364. (e) Lorber, C.; Donnadieu, B.; Choukroun, R. Synthesis and structure of group 4 and 5 metal complexes with an ancillary sterically demanding diamido ligand. Organometallics 2000, 19, 1963−1966. (30) Wang, J. B.; Lu, L. P.; Liu, J. Y.; Li, Y. S. [ONN]-type amine pyridine (s) phenolate-based oxovanadium (v) catalysts for ethylene homo-and copolymerization. Dalton Trans. 2014, 43, 12926−12934. (31) Wu, J. Q.; Li, Y. S. Well-defined vanadium complexes as the catalysts for olefin polymerization. Coord. Chem. Rev. 2011, 255, 2303−2314. (32) Ravasio, A.; Boggioni, L.; Tritto, I. Copolymerization of ethylene with norbornene by neutral aryl phosphine sulfonate palladium catalyst. Macromolecules 2011, 44, 4180−4186. (33) Yoshida, Y.; Mohri, J.; Ishii, S.; Mitani, M.; Saito, J.; Matsui, S.; Makio, H.; Nakano, T.; Tanaka, H.; Onda, M.; Yamamoto, Y.; Mizuno, A.; Fujita, T. Living copolymerization of ethylene with norbornene catalyzed by bis(pyrrolide−imine) titanium complexes with MAO. J. Am. Chem. Soc. 2004, 126, 12023−12032. (34) Wang, W.; Tanaka, T.; Tsubota, M.; Fujiki, M.; Yamanaka, S.; Nomura, K. Effect of Cyclopentadienyl Fragment in Copolymerization of Ethylene with Cyclic Olefins Catalyzed by Non-Bridged (Aryloxo)(cyclopentadienyl)titanium(IV) Complexes. Adv. Synth. Catal. 2005, 347, 433−446. (35) Nomura, K.; Sagara, A.; Imanishi, Y. Olefin Polymerization and Ring-Opening Metathesis Polymerization of Norbornene by (Arylimido)(aryloxo)vanadium(V) Complexes of the Type VX2(NAr)(OAr‘). Remarkable Effect of Aluminum Cocatalyst for the Coordination and Insertion and Ring-Opening Metathesis Polymerization. Macromolecules 2002, 35, 1583−1590. (36) Ruchatz, D.; Fink, G. Ethene−Norbornene Copolymerization with Homogeneous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 4. Development of Molecular Weights. Macromolecules 1998, 31, 4684−4686. (37) Shaver, M. P.; Allan, L. E. N.; Gibson, V. C. Ethylene Polymerization under Mild Conditions Using Simple Aluminum Alkyls and Chloro Activators. Organometallics 2007, 26, 2252−2257. (38) Hao, X.; Zhang, C.; Li, L.; Zhang, H.; Hu, Y.; Hao, D.; Zhang, X. Use of Vanadium Complexes Bearing Naphthalene-Bridged

Nitrogen-Sulfonate Ligands as Catalysts for Copolymerization of Ethylene and Propylene. Polymers 2017, 9, 325−336. (39) Marconi, R.; Boggioni, L.; Ravasio, A.; Di Colo, F.; Tritto, I.; Stehling, U. M. Terpolymerization of Linear and Alicyclic α-Olefins with Norbornene and Ethylene by ansa-Metallocene Catalysts. Macromolecules 2011, 44, 795−804. (40) (a) Leone, G.; Mauri, M.; Losio, S.; Bertini, F.; Ricci, G.; Porri, L. Copolymerization of ethylene with α-olefins and cyclic olefins catalyzed by a Ti(IV) diisopropoxy complex bearing a tridentate [O−,S,O−]-type bis(phenolato) ligand. Polym. Chem. 2014, 5, 3412− 3423. (b) Ricci, G.; Leone, G.; Rapallo, A.; Biagini, P.; Guglielmetti, G.; Porri, L. Syndiospecific oligomerization and polymerization of norbornene with titanium catalysts. Polymer 2011, 52, 5708−5715. (41) Wendt, R. F.; Mynott, R.; Hauschild, K.; Ruchatz, D.; Fink, G. 13 C NMR studies of ethene-norbornene copolymers: assignment of sequence distributions using 13C-enriched monomers and determination of the copolymerization parameters. Macromol. Chem. Phys. 1999, 200, 1340−1350. (42) (a) Wang, K.; Wang, J.; Li, Y.; Pan, L.; Li, Y. S. Facile Efficient Copolymerization of Ethylene with Norbornene-Containing Dienes Promoted by Single Site Non-Metallocene Oxovanadium(V) Catalytic System. Polymers 2017, 9, 353−364. (b) Li, Y.; Yang, J.; Wang, B.; Li, Y. S. Efficient copolymerization of ethylene with norbornene or its derivatives using half-metallocene zirconium(IV) catalysts. RSC Adv. 2016, 6, 59590−59599. (43) (a) Li, X.; Hou, Z. Scandium-Catalyzed Copolymerization of Ethylene with Dicyclopentadiene and Terpolymerization of Ethylene, Dicyclopentadiene, and Styrene. Macromolecules 2005, 38, 6767− 6769. (b) Hasan, T.; Ikeda, T.; Shiono, T. Homo- and copolymerization of norbornene derivatives with ethene by ansafluorenylamidodimethyltitanium activated with methylaluminoxane. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 4581−4587. (44) Zanchin, G.; Leone, G.; Pierro, I.; Rapallo, A.; Porzio, W.; Bertini, F.; Ricci, G. Addition Oligomerization of Dicyclopentadiene: Reactivity of Endo and Exo Isomers and Postmodification. Macromol. Chem. Phys. 2017, 218, 1600602. (45) (a) Liu, J. Y.; Liu, S. R.; Pan, L.; Li, Y. S. Facile, Efficient Copolymerization of Ethylene with Bicyclic, Non-Conjugated Dienes by Titanium Complexes Bearing Bis(β-Enaminoketonato) Ligands. Adv. Synth. Catal. 2009, 351, 1505−1511. (b) Li, H.; Li, J.; Zhang, Y.; Mu, Y. Homo- and copolymerization of 5-ethylidene-2-norbornene with ethylene by [2-C5Me4-4,6-tBu2C6H2O]TiCl2/AliBu3/Ph3CB(C6F5)4 catalyst system and epoxidation of the resulting copolymer. Polymer 2008, 49, 2839−2844. (46) Bradley, D. C.; Gitlitz, M. H. Metallo-organic compounds containing metal−nitrogen bonds. Part VI. Infrared and nuclear magnetic resonance of dialkylamidoderivatives of titanium, vanadium, zirconium, niobium, hafnium, tantalum, and thorium. J. Chem. Soc. A 1969, 0, 980−984. (47) Loliger, J.; Scheffold, R. Paramagnetic moment measurements by nmr. A micro technique. J. Chem. Educ. 1972, 49, 646−647. (48) Agilent Technologies Xcalibur CCD system, CrysAlisPro Software system, version 1.171.35.19, Agilent Technologies UK Ltd., Oxford, UK, 2011. (49) Oxford Diffraction CrysAlis CCD, CrysAlis RED and associated programs, Oxford Diffraction Ltd, Abingdon, England, 2006. (50) SAINT Bruker; Bruker AXS Inc., Madison, Wisconsin, USA, 2007. (51) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Completion and refinement of crystal structures with SIR92. J. Appl. Crystallogr. 1993, 26, 343−350. (52) Sheldrick, G. M. SHELX97 [Includes SHELXS97, SHELXL97, CIFTAB] - Programs for Crystal Structure Analysis (release 97-2), Institüt für Anorganische Chemie der Universität, Tammanstrasse 4, D-3400 Göttingen, Germany, 1998. (53) Farrugia, L. J. WinGX suite for small-molecule single-crystal crystallography. J. Appl. Crystallogr. 1999, 32, 837−838. N


Article

Organometallics (54) International tables for X-Ray crystallography; Kynoch press: Birmingham, England, 1974; Vol. IV. (55) Farrugia, L. J. ORTEP-3 for Windows - a version of ORTEP-III with a Graphical User Interface (GUI). J. Appl. Crystallogr. 1997, 30, 565−569.

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