Article Cite This: Macromolecules XXXX, XXX, XXX−XXX
Mechanism of Insertion Polymerization of Allyl Ethers Florian P. Wimmer,†,§ Lucia Caporaso,‡ Luigi Cavallo,§ Stefan Mecking,† and Laura Falivene*,§ †
Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany Dipartimento di Chimica e Biologia, Università di Salerno, Via Papa Paolo Giovanni II, I-84084 Fisciano, Italy § Physical Sciences and Engineering Division, Kaust Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia ‡
S Supporting Information *
ABSTRACT: The copolymerization of ethylene (E) with allyl ethyl ether (AEE) by [di(2-dianisyl)phosphine-2yl]benzenesulfonato Pd(II) as a catalyst is investigated by DFT calculations and compared with the copolymerization of E with diallyl ether (DAE). For AEE, both 1,2- and 2,1-monomer insertions lead to a very stable O-Chelate product (a fivemembered and a four-membered ring, respectively) that hinders any further ethylene insertion. As for DAE, a first 2,1-insertion (favored by 1.8 kcal mol−1 vs the 1,2-insertion) leads to the four-membered O-Chelate product that easily evolves to the most stable intermediate with the second DAE CC bond coordinated to the metal promoting the following 1,2-insertion. The 2,1 + 1,2 DAE insertion product, bearing a five-membered cyclic unit, is stabilized by a β-agostic interaction that easily opens in favor of E coordination and insertion. Based on the proposed copolymerization mechanism, the stereochemistry of the E/DAE copolymer is studied and the experimental microstructure explained. Finally, [di(2-anisyl)phosphine-2-yl]benzenesulfon(methyl)amido Pd(II) species showing a greater regioselectivity toward a first DAE 2,1-insertion (ΔΔG of −3.6 kcal mol−1) are suggested to be a promising catalyst.
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INTRODUCTION Vinyl polymers, like poly(meth)acrylates or vinyl acetate homoand copolymers, are employed on a vast scale and the factors influencing the polymerization behavior of the corresponding monomers in insertion polymerization are widely understood.1−4 In contrast, the (co)polymerization of polar allyl monomers (i.e., CH2CHCH2X) remains challenging. Any attempts to polymerize these monomers applying free-radical or cationic polymerization fail, presumably due to the formation of stable π radicals or cations that slow down or terminate the chain growth.5−7 Solely free-radical polymerizations in the presence of additional Lewis or Bronsted acids yielded high molecular mass polymers.8,9 Recently, the coordination− insertion copolymerization of these monomers with ethylene using nickel or palladium catalysts has been reported.10−14 However, both the catalytic activity and the incorporation rate of the polar monomer remain relatively low, mostly because the coordination of the X group to the metal center hinders chain propagation. Furthermore, with allyl ether monomers, the formation of O-chelated species paves the route toward β-OR elimination, leading to chain termination. © XXXX American Chemical Society
We reported on a new approach to overcome some of these limitations. Copolymerization of diallyl ether (DAE) with E by a diaryl phosphinsulfonato Pd(II) catalyst proceeded with significantly higher productivities and much higher incorporation (20 mol % vs 4 mol %) compared to the analogous monoallyl ether (AEE).15 13C NMR analysis showed that differently from the AEE/E copolymer having a linear backbone with the AEE monomer incorporated primarily into the chain, the DAE/E copolymer shows a variety of microstructures due to the presence of the two allylic double bonds. The intramolecular insertion of the second allyl moiety of DAE leads to cyclic repeat units (see Scheme 1) up to 99%. We now further illuminate the particular beneficial polymerization properties of diallyl ether by a DFT approach. Received: April 12, 2018 Revised: May 22, 2018
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DOI: 10.1021/acs.macromol.8b00783 Macromolecules XXXX, XXX, XXX−XXX
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higher in energy. Starting from 1-Coor-T the two available 1,2and 2,1-insertion transition states (1,2−1-TS-Ins-T and 2,1−1TS-Ins-T, respectively) were evaluated. Transition state 2,1-1TS-Ins-T is only 1.4 kcal mol−1 lower in energy than 1,2−1TS-Ins-T, with an overall free energy barrier starting from 1Coor-C of 20.4 kcal mol−1. Both the 1,2- and 2,1-insertions lead to an O-Chelate species stabilized by coordination of the oxygen atom of the inserted AEE unit to the metal. The fivemembered 1,2-O-Chelate is 8.3 kcal mol−1 lower in energy than the four-membered cyclic product formed after the corresponding 2,1-insertion. In conclusion, calculations suggest a low kinetic selectivity in favor of the 2,1-insertion (ΔΔG‡ = 1.4 kcal mol−1). The lower selectivity compared to that calculated for acrylate monomers (2,1-insertion is favored by approximately 7 kcal mol−1 for methyl acrylate)25 is the result of electronic and steric effects: the rather low polarization of the AEE double bond results in a lower preference for 2,1-insertion; the lower steric hindrance of the allyl ether monomer favors 1,2-insertion. In fact, stoichiometric experimental studies showed a preference for 1,2-insertion of AEE into the (P∧O)Pd Me fragment.15 To further understand the differences between DAE and AEE from a catalyst deactivation point of view, the energy landscape of E insertion after AEE insertion was investigated (see Figure 2). From 1,2-O-Chelate, E coordination requires opening of the O-chelate and overcoming a free energy barrier of 10 kcal mol−1, with the following coordination intermediate laying 8 kcal mol−1 above 1,2-O-Chelate + E. Insertion of the coordinated E into the Pd−C bond occurs via transition state 2-TS-Ins-E-T. The overall free energy barrier from 1,2-OChelate to 2-TS-Ins-E-T sums up to 26.3 kcal mol−1, resulting in a β-agostic product at the same energy level as the O-chelate starting species. Moving to the 2,1-O-Chelate, since this four-membered product is less stable compared to the five-membered 1,2-OChelate, E coordination requires overcoming a lower free energy barrier (of only 5 kcal mol−1). However, the resulting intermediate 2-Coor-E-C is similar in energy to the O-Chelate. The following insertion with a free energy barrier of 19.4 kcal mol−1 from 2,1-O-Chelate leads to a β-agostic product almost 9 kcal mol−1 more stable than the O-Chelate starting species. Overall, calculations clearly show that E insertion after an AAE 1,2-insertion is hindered by both kinetics and thermodynamics, as it starts from a very stable 1,2-O-Chelate intermediate. After the kinetically favored AEE 2,1-insertion, E coordination to the more strained 2,1-O-Chelate can occur more easily. However, the resulting E coordination intermediate is in equilibrium with
Scheme 1. Conceivable Polymer Microstructures Resulting from Copolymerization of E and AEE or DAE, Respectively
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COMPUTATIONAL DETAILS All the DFT geometry optimizations were performed at the GGA BP8616,17 level with the Gaussian09 package.18 The electronic configuration of the systems was described with the 6-31G(d) basis set for H, C, P, S, N, and O while for Pd we adopted the quasi-relativistic LANL2DZ ECP effective core potential.19 All geometries were characterized as minimum or transition state through frequency calculations. The reported free energies were built through single point energy calculations on the BP86/6-31G(d) geometries using the M06 functional and the TZVP basis set on main group atoms.20,21 Solvent effects were included with the PCM model using toluene as the solvent.22,23 To this M06/TZVP electronic energy in solvent, thermal corrections were included from the gas-phase frequency calculations at the BP86/6-31G(d) geometries.
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RESULTS AND DISCUSSION AEE Reactivity. Starting from 1-Me (referenced as zero point energy structure in Figure 1) formed by release of the DMSO moiety from the precatalyst, AEE coordinates in the available position cis to the O atom of the ligand forming 1Coor-C, nearly 9 kcal mol−1 lower in energy than 1-Me + AEE. This π coordination is only 0.5 kcal mol−1 more stable than the competitive κ-O monomer coordination. As observed in the acrylate polymerization, insertion from 1-Coor-C is higher in energy (by approximately 10 kcal mol−1) than insertion from the less stable 1-Coor-T intermediate with the monomer trans to the oxygen atom of the ligand.24 The cis-to-trans isomerization of 1-Coor-C to 1-Coor-T takes place via a 5-fold coordinated Berry’s pseudorotation transition state involving the coordination of one additional sulfonate oxygen atom2 with a barrier of 7.6 kcal mol−1. Isomerization through the alternative tetrahedral transition state was found to be slightly
Figure 1. Calculated AEE reaction pathways. Free energies (kcal mol−1) in toluene. B
DOI: 10.1021/acs.macromol.8b00783 Macromolecules XXXX, XXX, XXX−XXX
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Figure 2. Calculated ethylene insertion pathways after AEE 1,2-insertion (top) and 2,1-insertion (bottom). Free energies (kcal mol−1) in toluene. The energy reference point is 1-Me + AEE as in Figure 1.
Scheme 2. DAE Insertion Pathways
Figure 3. Favored DAE reaction pathways. Free energies (kcal mol−1) in toluene.
insertion of the second CC double bond, will be denoted as 2,1 + 1,2. The most favored pathways corresponding to 1,2 + 1,2 and 2,1 + 1,2 sequences are reported in Figure 3. This implies that the second CC insertion exclusively occurs in the 1,2regiochemistry, as the transition state for 2,1-insertion is highly strained and therefore energetically disfavored (see Figure S1). All the species reported refer to the most stable stereoisomers (for a more detailed discussion on the stereochemistry of DAE insertion see next section).
the 2,1-O-Chelate. These results account for the experimental finding that the copolymerization of AEE/E is challenging.15 DAE Reactivity. All conceivable insertion sequences are reported in Scheme 2. For both the first and the second CC bond insertion reactions, 1,2- and 2,1-insertion pathways were calculated. Considering that both CC bonds of DAE can react, this gives rise to four possible mechanistic pathways depending on the regioselectivity of the two successive CC insertion steps. As an example, the sequence originated by the initial 2,1insertion of the first CC double bond, followed by 1,2C
DOI: 10.1021/acs.macromol.8b00783 Macromolecules XXXX, XXX, XXX−XXX
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Figure 4. Calculated E insertion pathway after a first DAE 2,1-insertion. Free energies (kcal mol−1) in toluene. The energy reference point is 1-Me + DAE as in Figure 3.
Figure 5. Calculated E insertion pathway after a DAE 2,1 + 1,2-insertion. Free energies (kcal mol−1) in toluene. The zero point energy is 1-Me + DAE as in Figure 3.
Overall, these results are in agreement with the experimental evidence that the microstructure P4 (see Scheme 2) is not detected in the polymer. Although the NMR analysis cannot distinguish P1 and P2, the calculations rule out P1 formation. Finally, the favored formation of P3 agrees with the experimentally observed preference for this microstructure.9 Moving to the copolymerization reactions, E insertion can occur after both the insertion of the first DAE CC bond and the insertion of the second DAE CC bond. To this end, we studied the competition between E and the second DAE CC bond insertion after the first DAE CC bond insertion. As already reported for AEE, insertion of E is easier after a DAE 2,1-insertion. The corresponding energy pathway is reported in Figure 4. Comparing the energy profile in Figure 4 with the blue pathway in Figure 3, it emerges that the thermodynamics of the second DAE CC bond insertion is the driving force for the formation of P3 over the formation of a polymer resulting from the incorporation of the first DAE allyl moiety followed by the insertion of E. In fact, despite similar reaction barriers to the coordination and insertion (4.6 vs 4.0 kcal mol−1 for 2-TSCoor and 18.2 vs 16.5 kcal mol−1 for 2-TS-Ins-T for E and DAE, respectively). Barriers for E insertion were calculated starting from the O-chelated species whereas barriers for secondary DAE insertion were calculated starting from 2,1−2Coor-C intermediate, the second DAE CC bond coordination intermediate 2-Coor-C is lower in energy than the E coordination intermediate 2-Coor-E-C by 10.7 kcal mol−1, and the corresponding β-agostic insertion product 2-β-C is favored by 6.8 kcal mol−1 over 2-β-C-E. In short, the main reaction intermediates turn out to be much more stable along the two consecutive DAE insertions pathway, making insertion of E after insertion of only one DAE CC bond rather unlikely. As a last step, we considered E incorporation after formation of P3 obtained from the most favored DAE 2,1 + 1,2-insertion pathway (see Figure 5). Since P3 is stabilized by a β-agostic interaction with the metal (cf. O-Chelate products in the other cases), the following E coordination (3-Coor-E-C) is favored by 3 kcal mol−1 over P3. The successive E insertion has a free energy barrier of 16.7
Following the dissociation of DMSO, coordination of DAE to the vacant coordination site cis to the oxygen atom of the ligand leads to 1-Coor-C favored by almost 10 kcal mol−1 over 1-Me + DAE. As observed for AEE, the competitive κ-O monomer coordinated complex is almost isoenergetic with the π-complex. From 1-Coor-C the system isomerizes to 1-Coor-T (almost 12 kcal mol−1 higher in energy than 1-Coor-C) with a free energy barrier of 20.2 kcal mol−1. From 1-Coor-T the 2,1insertion (blue profile in Figure 3) is kinetically favored by 1.8 kcal mol−1 over 1,2-insertion (red profile in Figure 3) with an overall insertion barrier of 21 kcal mol−1. As expected on the basis of results already observed for AEE, the five-membered 1,2-O-Chelate is almost 10 kcal mol−1 lower in energy than the four-membered 2,1-O-Chelate. For both O-Chelate structures, coordination of the second CC bond occurs by opening of the O-Chelate interaction through 1-TS-Coor. From 2-Coor-C another cis/trans isomerization to the less stable 2-Coor-T is required in order to undergo the most favorable insertion. From the five-membered 1,2-O-Chelate the free energy barrier for coordination of the second CC bond is almost 13 kcal mol−1, and 2-Coor-C is uphill in energy by 5 kcal mol−1. The following isomerization to 2-Coor-T and insertion require almost 23 kcal mol−1 affording the Pd−alkyl product containing a six-membered cycle and stabilized by a β-agostic interaction, P2. Starting from the less stable 2,1-O-Chelate, an easy opening of the Pd−O interaction (free energy barrier of only 4 kcal mol−1) affords 2-Coor-C, 10 kcal mol−1 downhill in energy. Both the isomerization to 2-Coor-T and the successive insertion are about 7 kcal mol−1 lower than for the 1,2-pathway (in Figure 3, compare the energy values of 2-TS-Isom and 2TS-Ins for the corresponding isomers). The overall insertion energy barrier (of 18.8 kcal mol−1) is almost 4.2 kcal mol−1 lower than the one required to reach P2 even though the latter is 4 kcal mol−1 more stable than P3 bearing a five-membered cyclic unit. In conclusion, calculation results clearly show that despite the thermodynamic preference for P2 formation, the overall kinetics make P3 the most favored product. D
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Figure 6. Conceivable microstructures of DAE/E copolymers with their abundance in the polymers15 and difference in free energy barriers (kcal mol−1, in toluene).
kcal mol−1 and affords the new β-agostic product almost 12 kcal mol−1 lower in energy than P3. Comparing these results (see Figure 5) with those already discussed for the AEE/E copolymerization and reported at the bottom of Figure 2 (i.e., E insertion after AEE 2,1-insertion), it clearly emerges that the overall insertion energy barriers are comparable for the two monomers and that the easier E insertion on P3 is mainly due to a most favored E coordination. In conclusion, calculations show that the success of the DAE/E copolymerization is ascribed to a favorable DAE 2,1 + 1,2-insertion with formation of a product (P3) stabilized by a weaker β-agostic interaction facilitating the following E insertion. Stereochemistry of the DAE/E Copolymerization. As already reported in the Introduction, different microstructure motifs can result from the possible reaction pathways of the DAE/E copolymerization (see Figure 6). Structure I originates from a first incorporation of DAE followed by insertion of E, whereas the complete incorporation of DAE yields cyclic structures defining the regio- and stereochemistry of the repeat units. As reported in the previous section, structures cis-II/trans-II result from a 2,1 + 1,2insertion and structures cis-III/trans-III are yielded by a 1,2 + 1,2-insertion. The cis microstructure results from two consecutive CC insertions leading to two asymmetric carbon atoms with opposite chirality (R,S) or (S,R) in the second insertion product, whereas the trans microstructure is reached after two consecutive CC insertions leading to two asymmetric carbon atoms with the same chirality (R,R) or (S,S). Calculations on microstructures obtained from the 2,1 + 1,2insertion (structure II) show that the trans structure is favored over the cis by 2.2 kcal mol−1. In contrast, no meaningful difference was found in the case of microstructures coming from 1,2 + 1,2-insertion (structure III) (ΔΔG‡ = 0.1 kcal mol−1). Starting from a first CC insertion leading to the formation of e.g. a S asymmetric carbon atom, the transition state geometries of the second CC insertion are reported in Figure 7. All transition states show a syn relative disposition of the C1−C2 and C3−C4 bonds required to close the cycles with the energetically favored conformation. However, in the case of structure II, leading to a five-membered cycle, the asymmetric carbon atom formed in the first 2,1-insertion (C4) is directly involved in the 2-TS-Ins, leading to a preference for the trans structure due to the position of the −CH2CH3 group far from the phosphino sulfonate ligand scaffold (see Figure 7). By comparison, in the case of III, the first asymmetric carbon atom formed in the 1,2-insertion (C4) is not involved in the 2-TSIns and the −CH3 group is distant from the P∧O ligand in
Figure 7. Transition state geometries of the second CC DAE insertion leading to Trans-II and Cis-II structures (top) and to TransIII and Cis-III structures (bottom) and their relative GTol in kcal mol−1. Labels S and R refer to the chirality defined after the two consecutive insertions.
both cis and trans structures. As a consequence, the III-2-TSIns is not stereoselective. Overall, these results agree with the experimental ratios reported (Figure 6). Catalyst Screening. With these insights, we considered suitable catalysts exhibiting a higher kinetic selectivity for the 2,1-insertion of the first DAE CC bond. This higher selectivity would further suppress the formation of the very stable five-membered O-Chelate that retards polymerization. The [di(2-anisyl)phosphine-2-yl]benzenesulfon(methyl)amido Pd(II) catalyst has previously been revealed to be more electron-donating than the analogous sulfonate ligand, with a steric requirement that can be properly tuned via the choice of the group on the N atom.25 We focused here on the complex bearing a −CH3 group on the N atom (designated P∧N in the following); see Scheme 3. A previous study revealed this P∧N catalyst to be slightly more sterically crowed than the benzenesulfonato Pd(II) catalyst (designated P∧O in the following), i.e., %VBur26 of 51.6 and 48.2, respectively. E
DOI: 10.1021/acs.macromol.8b00783 Macromolecules XXXX, XXX, XXX−XXX
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48.3. Nicely, the ΔΔG decreases from 3.6 kcal mol−1 for P∧NMe to 1.5 kcal mol−1 for R = H. The results reported in this last section could aid the rational design of a better catalyst for allyl ether monomer polymerizations. Experiments on the E/DAE polymerization in the presence of di(2-anisyl)phosphine-2-yl]benzenesulfon(methyl)amido Pd(II) complex are in progress.
Scheme 3. Structure of the [Di(2-anisyl)phosphine-2yl]benzenesulfon(methyl)amido Pd(II) Complex Investigated
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CONCLUSIONS A full DFT investigation of the Pd(II)-catalyzed copolymerization of ethylene and allyl ether monomers sheds light on the mechanistic features of this polymerization, allowing to rationalize the peculiar behavior of diallyl ether monomer (DAE) when compared to the monoallyl ether analogue (AEE) as a monomer. For both allyl monomers the kinetic selectivity is slightly in favor of the 2,1-insertion. The strong stabilization of the 1,2insertion product by formation of the five-membered cycle with O-chelate formation is the main obstacle to chain growth. Therefore, the copolymerization process mainly proceeds through the 2,1-incorporation of the allyl monomer. The main difference between AEE/E and DAE/E copolymerization is in the next step: in both cases the following ethylene coordination is energetically not favored being only in equilibrium with the four-membered chelate starting species; however, for the diallyl monomer, after the first CC bond 2,1-insertion, a facile coordination and insertion of the second DAE CC bond is possible. This insertion leads to a Pd-alkyl cyclic unit stabilized by a β-agostic interaction, easy to be overcome by E coordination−insertion. The picture emerging from the calculations agrees with the experimental results confirming and rationalizing the unique behavior of the DAE monomer. The results show that the crucial step is the competition between 1,2 and 2,1-insertion in the first CC bond insertion step. To this end, we computed the energy profiles for DAE/E copolymerization by di(2-anisyl)phosphine-2-yl]benzenesulfon(methyl)amido Pd (II) catalyst species. The suitable greater steric hindrance of the sulfon(methyl)amido moiety disfavors
The most favored pathways (i.e., 1,2 + 1,2-insertion and 2,1 + 1,2-insertion) are reported in Figure 8 and compared to the respective pathways for the P∧O complex. Albeit coordination of DAE to the P∧N complex is almost 2 kcal mol−1 less favored than for the P∧O complex, the insertion barriers are comparable. The favored 2,1-insertion is 3.6 kcal mol−1 lower in energy than the 1,2-insertion, making the first DAE CC bond insertion approximately 2 kcal mol−1 more regioselective compared to the corresponding P∧O complex. Moving to the following steps, 2-Coor-C is 2.4 kcal mol−1 uphill in energy with respect to the O-Chelate after the 1,2insertion (red profile in Figure 8) and 5.3 kcal mol−1 downhill after the 2,1-insertion (blue profile in Figure 8), allowing an easier propagation along the latter pathway, as observed for the P∧O complex. The following CC bond insertion and formation of the β-agostic product are again slightly more favored for the P∧N system. Overall, these results suggest the P∧N catalyst to be a considerably good candidate for the title reaction. In detail, the methyl group bound to the N atom causes unfavorable interactions between the chain on the Pd and the DAE C C substituent (−CH2−O−CH2−CHCH2) to a larger extent in the 1,2-insertion, increasing the selectivity in favor of the first DAE CC bond 2,1-insertion. To further support the hypothesis that the steric demand of the −SO2N−R group is the main cause for the theoretically predicted improved performance of this catalyst, we calculated the ΔΔG(2,1-1TS-Ins − 1,2-1-TS-Ins) in the case of P∧NH, i.e., %VBur of
Figure 8. Calculated DAE 1,2 and 2,1-insertion pathways for the P∧N complex. Free energies (kcal mol−1) in toluene. Numbers in parentheses refer to the P∧O complex (2-Coor-T and 2-TS-Isom are not reported since not involved in the rate-determining step). F
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(12) Carrow, B. P.; Nozaki, K. Synthesis of Functional Polyolefins Using Cationic Bisphosphine Monoxide-Palladium Complexes. J. Am. Chem. Soc. 2012, 134 (21), 8802−8805. (13) Ito, S.; Ota, Y.; Nozaki, K. Ethylene/allyl monomer cooligomerization by nickel/phosphine-sulfonate catalysts. Dalton Trans. 2012, 41 (45), 13807−13809. (14) Guironnet, D.; Roesle, P.; Runzi, T.; Gottker-Schnetmann, I.; Mecking, S. Insertion polymerization of acrylate. J. Am. Chem. Soc. 2009, 131 (2), 422−3. (15) Jian, Z.; Mecking, S. Insertion Homo- and Copolymerization of Diallyl Ether. Angew. Chem., Int. Ed. 2015, 54 (52), 15845−15849. (16) Becke, A. D. Density-Functional Exchange-Energy Approximation with Correct Asymptotic-Behavior. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38 (6), 3098−3100. (17) Perdew, J. P. Density-Functional Approximation for the Correlation-Energy of the Inhomogeneous Electron-Gas. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33 (12), 8822−8824. (18) Frische, M. J.; et al. Gaussian 09, Revision A. 1; Gaussian Inc.: Wallingford, CT, 2009. (19) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297−3305. (20) Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.; Schwerdtfeger, P.; Pitzer, R. M. Accuracy of Energy-Adjusted QuasiRelativistic Abinitio Pseudopotentials - All-Electron and Pseudopotential Benchmark Calculations for Hg, Hgh and Their Cations. Mol. Phys. 1993, 78 (5), 1211−1224. (21) Leininger, T.; Nicklass, A.; Stoll, H.; Dolg, M.; Schwerdtfeger, P. The accuracy of the pseudopotential approximation 0.2. A comparison of various core sizes for indium pseudopotentials in calculations for spectroscopic constants of InH, InF, and InCl. J. Chem. Phys. 1996, 105 (3), 1052−1059. (22) Barone, V.; Cossi, M. Quantum calculation of molecular energies and energy gradients in solution by a conductor solvent model. J. Phys. Chem. A 1998, 102 (11), 1995−2001. (23) Tomasi, J.; Persico, M. Molecular-Interactions in Solution - an Overview of Methods Based on Continuous Distributions of the Solvent. Chem. Rev. 1994, 94 (7), 2027−2094. (24) Haras, A.; Anderson, G. D. W.; Michalak, A.; Rieger, B.; Ziegler, T. Computational Insight into Catalytic Control of Poly(ethylene− methyl acrylate) Topology. Organometallics 2006, 25 (19), 4491− 4497. (25) Jian, Z. B.; Falivene, L.; Wucher, P.; Roesle, P.; Caporaso, L.; Cavallo, L.; Gottker-Schnetmann, I.; Mecking, S. Insights into Functional-Group-Tolerant Polymerization Catalysis with PhosphineSulfonamide Palladium(II) Complexes. Chem. - Eur. J. 2015, 21 (5), 2062−2075. (26) 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 (13), 2286−2293.
the DAE 1,2-insertion, increasing the kinetic preference for the 2,1-insertion toward the formation of the more reactive fourmembered O-Chelate. In conclusion, catalysts with appropriate steric bulk could prevent the formation of accumulating fivemembered O-Chelates, promoting desirable chain growth.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00783. Calculated structures as well as Figure S1 (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (L.F.). ORCID
Florian P. Wimmer: 0000-0002-8479-0390 Luigi Cavallo: 0000-0002-1398-338X Stefan Mecking: 0000-0002-6618-6659 Laura Falivene: 0000-0003-1509-6191 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS F.P.W. thanks the KAUST visiting student research program for funding of his internship at KAUST. Support by the DFG (Me 1388/10-2) is gratefully acknowledged.
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REFERENCES
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