This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
Article Cite This: Organometallics XXXX, XXX, XXX−XXX
pubs.acs.org/Organometallics
Zinc-Mediated Chain Transfer from Hafnium to Aluminum in the Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1‑Octene Revealed by Job Plot Analysis Eric S. Cueny and Clark R. Landis* Department of Chemistry, University of Wisconsin−Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
Downloaded via 185.89.100.72 on February 11, 2019 at 18:25:13 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: This report applies a Job plot analysis to demonstrate that dialkyl Zn reagents mediate chain transfer between Hf-pyridyl amido polymerization catalysts and AlR3 chain-transfer agents. Polyoctene produced in the presence of both ZnEt2 and AlEt3 is lower in molecular weight and has a narrower distribution than polyoctene produced in the presence of ZnEt2 alone. I2 labeling and NMR analysis of polymer chain ends enable quantification of the amount of Zn- and Al-polymeryls produced during polymerization. A Job plot of the number of Zn and Al polymer chains produced versus the mole fraction of ZnEt2 at constant moles of Zn + Al reveals a nonlinear relationship. The nonlinearity of the Job plot indicates cooperative exchange between Zn and Al. The chain-transfer agent, AlEt3, inhibits initiation, but not propagation, of polymerization as catalyzed by the Hf-pyridyl amido complex. This inhibition can be obviated by a two-step polymerization protocol. AliBu3 does not inhibit initiation or propagation and can be used as a chain-transfer agent without the need for a two-step polymerization protocol. Chain transfer using the ZnEt2/AliBu3 system is not as efficient as ZnEt2/AlEt3, presumably due to the increased steric bulk of the isobutyl groups.
■
(Figure 1).18−20 We found that ∼50% of rac-1 is active in the polymerization of 1-octene when rac-1 is preactivated with
INTRODUCTION In polymerization, chain transfer between the active catalyst and metal alkyls such as Zn or Al allows for the production of more than one polymer chain per catalyst under otherwise living polymerization conditions.1 Sita2,3 and Gibson4−6 demonstrated that reversible chain transfer between Hf- or Fe-based catalysts and ZnEt2 results in polymers with narrow molecular weight distributions (MWDs). The number of polymer chains generated in these polymerizations depends solely on the ZnEt2 concentration. Chain shuttling polymerization is an industrial method used to produce olefin block copolymers with alternating blocks of “hard” and “soft” polyethylene.7 Two different catalysts are used in combination with ZnEt2, the chain-shuttling reagent, that reversibly transfers polymer chains between the two catalyst centers. The hafnium-pyridyl amido precatalyst (rac-1) produces the “soft” polymer chains through the incorporation of 1-octene. This catalyst has been the subject of several studies due to its use in chain shuttling polymerization,7,8 production of isotactic polypropylene,9−12 unique Brønsted acid activation pathway,13 and proposed first insertion of monomer into the Hf−naphthyl bond.14−17 In previous studies, our group has applied chromophore quench-labeling technology to study 1-octene polymerization as catalyzed by rac-1 in the presence of chain-transfer reagents such as ZnEt2 and AlEt3 using 2 as the quench-labeling reagent © XXXX American Chemical Society
Figure 1. Hafnium pyridyl amido precatalyst (rac-1) and pyrenyl isonitrile quench-labeling reagent (2).
[Ph3C][B(C6F5)4] at 50 °C. ZnEt2 does not inhibit polymerization and undergoes fast, irreversible chain transfer.18,19 AlEt3 inhibits initiation of polymerization; however, this limitation can be overcome by using a two-step polymerization protocol where AlEt3 is added 10 s after polymerization is initiated.20 AlEt3 does behave as a chain-transfer reagent but undergoes a slower chain transfer than ZnEt2 by ∼1 order of magnitude. For this reason, we sought a chain-transfer method that could Received: December 12, 2018
A
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
polymerizations with only ZnEt2 (Table 1). These differences cannot be attributed to Al exchange with Hf because AlEt3 is a much slower chain-transfer reagent than ZnEt2.20 We propose that these changes to the MWD arise from Zn/Al exchange. Job Plot Analysis Indicates ZnEt2 and AlEt3 Act as Cooperative Chain-Transfer Agents. A Job plot analysis24 of the number of polymer chains per Zn + Al (determined via I2 labeling and NMR analysis of polymer chain ends; see the Supporting Information for details) versus the mole fraction of ZnEt2 in polymerization provides evidence for Zn-mediated exchange between Hf and Al.25 When ZnEt2 is used as the chain-transfer reagent, ∼1 polymer chain per Zn is produced;18,19 but using AlEt3 as the sole chain transfer agent, just ∼0.4 polymer chains per Al result.20 If ZnEt2 and AlEt3 work independently, then a linear relationship between the polymer chains per Zn + Al and mole fraction of ZnEt2 would be seen. In this case, the sum of polymer chains on Zn + Al is expected to increase with ZnEt2 concentration, because ZnEt2 is the faster chain-transfer reagent. However, we observe a nonlinear relationship between the polymer chains per Zn + Al and the mole fraction of ZnEt2 (Figure 3); thus, cooperative exchange occurs with more chains/metal than would be observed for either metal alone. Both the Job plot analysis and increased number of polymer chains per Zn + Al are consistent with ZnEt2-mediated exchange between Hf and Al in 1catalyzed 1-octene polymerization. ZnEt2 Acts as a Mediator for Chain Transfer between Hf and Al at “Catalytic” Concentrations of ZnEt2. Evidence for Zn-mediated chain transfer persists even at low concentrations of ZnEt2 (∼1 equiv relative to added Hf catalyst). To determine this, polymerizations were conducted using the two-step protocol,23 varying the initial ZnEt2 concentration (0.08−0.32 mM) and keeping the AlEt 3 concentration constant (1.6 mM). The number of polymer chains per Zn + Al is plotted versus the initial concentration of ZnEt2 (Figure 4). The dashed red line represents a hypothetical linear increase in the number of polymer chains produced by increasing ZnEt2, i.e., the increase due to ZnEt2 and AlEt3 working independently. However, the number of polymer chains produced per Zn + Al more than doubles (from ∼0.4 to 0.9) when using 0.08 mM ZnEt2 (5 mol % relative to [AlEt3]) compared to a polymerization without any added ZnEt2. That is, 0.08 mM ZnEt2 in the presence of 1.6 mM AlEt3 produces ∼1.5 mM polymer chains, whereas just ∼0.7 mM chains are produced in the absence of ZnEt2. These data clearly indicate that only a small amount of ZnEt2 is required to achieve a significant enhancement in the number of polymer chain produced by chain transfer, i.e., Zn can be used in a “catalytic” amount. Why Is More Than One Polymer Chain per Zn + Al Produced? In previous studies, we observed no more than one polymer chain per Zn or Al in the 1-catalyzed polymerization of 1-octene with ZnEt2 or AlEt3 as chaintransfer agents.18−20 Apparently, the steric interactions during exchange between the Hf-catalyst and Zn(Et)- or Al(Et)2polymeryl preclude a second transalkylation event during the time of reaction. When both Zn and Al are present, more than one polymer chain per Zn + Al can arise from polymeryl exchange between Zn and Al. In order to account for the effect of ZnEt2 on chain transfer between rac-1 and AEt3, we propose that (1) fast chain transfer occurs between rac-1 and ZnEt2 and (2) the resulting Zn(Et)-polymeryl undergoes rapid exchange with AlR2Et to make AlR2-polymeryl and regenerate ZnEt2
use the best features of AlEt3 and ZnEt2 as chain-transfer agents. Sita and co-workers developed the “ternary living coordinative chain-transfer polymerization” (t-LCCTP) where Zn mediates the reversible exchange of polymer chains between the Hf and Al centers.21 Under t-LCCTP conditions, ZnEt2 undergoes fast, reversible chain transfer with Hf, while AlEt3 serves as the primary resting place for polymer chains produced by the Hf catalyst.21,22 In principle, a similar strategy could be applied to the polymerization of 1-octene using precatalyst rac-1: ZnEt2 could undergo fast, irreversible chain transfer with rac-1, then Zn and Al exchange would liberate ZnEt2. The regenerated ZnEt2 will then undergo further exchange with Hf. In this report, we examine the use of Zn- and Al-alkyl chaintransfer agents, together, in the 1-catalyzed polymerization of 1-octene. First, the effect of ZnEt2 and AlEt3 on the MWD is compared with ZnEt2 alone. Using I2 labeling and subsequent NMR analysis of the polymer chain ends, we quantify the number of polymer chains produced per Zn + Al. We compare the number of polymer chains produced per Zn + Al versus the mole fraction of ZnEt2 using a Job-like plot. Varying the initial concentration of 1-octene influences the number of polymer chains per Zn + Al generated. To avoid using a two-step polymerization protocol, we replace AlEt3 with AliBu3 and compare the number of polymer chains per Zn + Al vs the mole fraction of ZnEt2.
■
RESULTS AND DISCUSSION To begin our investigation, we used the same preactivation and two-step polymerization protocol as before (vide supra) to ensure (1) that all of the catalyst activates and (2) that AlEt3 is prevented from inhibiting initiation.18,20 Preactivation is performed by heating rac-1 and [Ph3C][B(C6F5)4] at 50 °C for 3 min prior to polymerization; this process quantitatively generates cationic complex I (Scheme 1).13,18 In the two-step Scheme 1. Generation of the Cationic Complex (I)
protocol,23 polymerization reactions were initiated by addition of a toluene solution of the activated catalyst (I) (0.083 mM) to a toluene solution of 1-octene (503.2 mM) and ZnEt2. After 10 s of polymerization, AlEt3 was added to the reaction (Figure 2). The concentrations of ZnEt2 and AlEt3 were varied, but the total concentration of ZnEt2 + AlEt3 was held constant at 1.6 mM. Polymerizations were quenched using 6 equiv of 2 at various time points. These conditions were used for all experiments herein unless otherwise specified. Comparison of Polyoctene MWDs Produced in the Presence of ZnEt2 and AlEt3. The MWD of polyoctene produced in the presence of both ZnEt2 and AlEt3 is markedly different than polyoctene produced in the presence of ZnEt2 alone. Using both ZnEt2 and AlEt3, the MWDs of polyoctene (Figure 2) are depressed in number-average molecular weight (Mn) and have a narrower dispersity index (Đ) than those of B
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 2. Two-step polymerization of 1-octene catalyzed by I, where I = the product of preactivation of rac-1 with [Ph3C][B(C6F5)4]. (a) MWD of polymerizations where [ZnEt2] = 0.8 mM and [AlEt3] = 0.8 mM. (b) MWD of polymerizations where [ZnEt2] = 0.4 mM and [AlEt3] = 1.2 mM. (c) MWD of polymerizations where [ZnEt2] = 0.2 mM and [AlEt3] = 1.4 mM. (d) MWD of polymerizations where [ZnEt2] = 1.6 mM performed in the absence of any AlEt3 for comparison.
Table 1. Molecular Weight Data for Polyoctene Produced with Different Mole Fractions of ZnEt2 with [ZnEt2 + AlEt3] = 1.6 mMa mole fraction ZnEt2
conversion (%)
Mn (kg mol−1)
Đ
0.125 0.25 0.5 1.0
77 83 81 79
26.3 21.4 20.7 28.3
3.4 3.2 3.0 8.1
a
Conditions: [1-octene] = 503.2 mM, [I] = 0.0829 mM, toluene, 50 °C, [ZnEt2] + [AlEt3] = 1.6 mM, where AlEt3 is added after 10 s of polymerization. Reactions quenched with 2 at 120 s. Conversion of 1octene determined by 1H NMR spectroscopy, Mn determined by GPC relative to polystyrene standards, and Đ = Mw/Mn.
Figure 3. Job plot of polymer chains per Zn + Al vs the mole fraction of ZnEt2. Total concentration of ZnEt2 plus AlEt3 used in the reaction is 1.6 mM. Reactions were run using the two-step polymerization protocol for 120 s and quenched with 2, followed by I2 labeling. Each point represents separate experiments and error bars represent standard deviation between duplicates. Dashed red line represents the hypothetical linear increase in polymer chains per Zn + Al due to ZnEt2 and AlEt3 working independently.
(Scheme 2). As ZnEt2 is regenerated, it continues to undergo chain transfer with Hf. If the Zn/Al exchange can occur when there is at least one Al-bound polymeryl (R and/or R1 = polyoctyl in Scheme 2), then multiple polymer chains per Zn + Al can be generated via this mechanism. The regeneration of ZnEt2 is not a new concept. Gibson, who first discovered ZnEt2 as a chain-transfer reagent,4 used Ni(acac)2 as a catalyst for regenerating ZnEt2 from Zn(Pol)2 and ethylene (Scheme 3).5,26 Cariou developed an Fe catalyst that could regenerate ZnEt2 in situ.27 Published reports have
shown that Zn/Al exchange discussed herein occurs rapidly28−31 and is the basis for Sita’s t-LCCTP.21 However, this is the first report of Zn/Al exchange used in combination with a high performance industrial catalyst like the Hf-pyridyl amido system (rac-1). C
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 4. Number of polymer chains per Zn + Al vs the [ZnEt2]0. Reactions were performed using the two-step protocol for 120 s and quenched with 2, followed by I2 labeling. Conditions: [1-octene] = 503.2 mM, [I] = 0.0829 mM, toluene, 50 °C, [ZnEt2] = 0.08−0.32 mM, and [AlEt3] = 1.6 mM. Each point represents separate experiments and error bars represent standard deviation between duplicates. Dashed red line represents the hypothetical linear increase in polymer chains per Zn + Al due to ZnEt2 and AlEt3 working independently.
Figure 5. Comparison of the MWDs of polyoctene produced at 120 s upon varying the mole fraction of ZnEt2 used in the polymerization: (blue) [ZnEt2] = 0.8 mM and [AlEt3] = 0.8 mM; (green) [ZnEt2] = 0.4 mM and [AlEt3] = 1.2 mM; (orange) [ZnEt2] = 0.2 mM and [AlEt3] = 1.4 mM; (purple) [ZnEt2] = 1.6 mM without any AlEt3.
we hypothesized that increasing the initial concentration of 1octene would lead to an increase in the number of polymer chains per Zn + Al. We tested various initial 1-octene concentrations with the 1:1 ratio of ZnEt2/AlEt3, where the maximum number of polymer chains per Zn + Al was observed in Figure 3. The number of polymer chains produced per Zn + Al increases up to ∼2 polymer chains per Zn + Al going from 0.25−1.5 M 1-octene (Figure 6).
Scheme 2. Exchange Between Zn and Ala
a
Only one of the exchange reactions is shown, Zn(Et)Pol with Al(R)(R1)Et. R = Et or polyoctene, R1 = Et or polyoctene.
Scheme 3. Regeneration of ZnEt2 from Zn-Polymerylsa
Figure 6. Plot of polymer chains per Zn + Al vs the initial concentration of 1-octene in polymerization. Reactions were run using the two-step polymerization protocol for 120 s and quenched with 2, followed by quenching with I2. Conditions: [I] = 0.083 mM, [ZnEt2] = 0.8 mM, [AlEt3] = 0.8 mM, in toluene at 50 °C. The initial concentration of 1-octene was varied from 0.25−1.5 M. Each point represents separate experiments and error bars represent standard deviation between duplicates.
a
[E] = Ni- or Fe-catalyst; Zn-polymeryls are generated via exchange between ZnEt2 and a polymerization catalyst; R = ethyl or polymeryl.
Cooperative chain transfer involving Zn and Al explains the observed polyoctene MWDs (Figure 2). When ZnEt2 alone is used, fast chain transfer between Zn and the Hf-catalyst yields low MW polymer until available Zn sites saturate, i.e., one polymer chain per Zn. Upon saturation, high MW polymer grows from the Hf-catalyst resulting in the bimodal MWD of Figure 2d. When both ZnEt2 and AlEt3 are present, polymeryl exchange between Zn and Al (Scheme 2) regenerates ZnEt2. The regenerated ZnEt2 then undergoes fast chain transfer with the Hf catalyst. Thus, Zn sites do not saturate, fast chain transfer continues, and the MWD remains monomodal. Figure 5 depicts the MWDs obtained at 120 s reaction time for various mole fractions of ZnEt2. These plots (Figures 2 and 5) clearly illustrate the effect of added AlEt3 on the MWD of polyoctene produced by rac-1. Increasing the Initial 1-Octene Concentration Leads to Increased Polymer Chains per Zn + Al. Because the Zn and Al sites do not appear to saturate under these conditions,
Why does the number of polymer chains produced maximize at nearly two polymer chains per Zn + Al? At the stoichiometry of two polymer chains per Zn + Al, there are either two polymer chains on Zn and two on Al or one polymer chain on Zn and three on Al. Under either scenario, the concentration of ZnEt2, the regenerated chain-transfer agent, is minimal. Thus, chain transfer slows significantly upon approaching two polymer chains per Zn + Al. Therefore, we do not observe more than two polymer chain per Zn + Al, even at the highest concentration of 1-octene tested. These results strongly support the cooperative effect of Zn on chain transfer between Hf and Al; however, the two-step polymerization protocol23 required to prevent inhibition of initiation from the AlEt3 is a significant limitation to its implementation. We replaced AlEt3 with AliBu3 because AliBu3 does not inhibit initiation or propagation of rac-1.20 However, D
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
The MWD is lower in overall MW and has a narrower Đ than using ZnEt2 alone. The differences in the MWDs result from Zn/Al polymeryl exchange during the polymerization; Job plot analysis provides strong evidence for this exchange. Job plot analysis indicates that Zn and Al work cooperatively, not as independent chain-transfer agents. The ZnEt2 serves as the fast chain-transfer reagent, undergoing rapid exchange with the Hf-polymeryls. The newly formed Zn(Et)-polymeryl then exchanges with AlEt3 to regenerate ZnEt2 and continue undergoing chain transfer with Hf. In other words, ZnEt2 mediates chain transfer. This process enables more than one polymer chain to be produced per Zn + Al. With ZnEt2 or AlEt3 alone, 1.0 and ∼0.4 polymer chains per chain-transfer agent were produced, respectively.18−20 The MW depression and narrower Đ in the presence of Zn and Al result because ZnEt2 is constantly replenished by exchange with Al; thus, Zn sites do not saturate and fast chain transfer continues resulting in broad, monomodal MWDs. The data strongly support Zn-mediated chain transfer but require use of a two-step protocol23 to prevent inhibition of initiation caused by AlEt3. We can overcome this by switching to AliBu3 because it does not inhibit initiation or propagation. Job plot analysis of polymerizations using ZnEt2 and AliBu3 reveals similar nonlinear behavior as ZnEt2 and AlEt3. Thus, Zn-mediated chain transfer works with either AlEt3 or AliBu3, albeit less efficiently using AliBu3. The polyoctene MWDs resulting from Zn-mediated chaintransfer polymerization in the presence of rac-1 do not resemble those of Sita’s t-LCCTP. The polymers produced by t-LCCTP have a very narrow MWD (Đ ≤ 1.10), and all Zn and Al sites engage in polymeryl exchange reactions.21 These discrepancies are explained by two key distinctions between Zn-mediated chain transfer in the 1-catalyzed polymerization of 1-octene and Sita’s t-LCCTP: (1) In the homopolymerization of 1-octene, chain transfer between rac-1 and Zn is irreversible. (2) Zn(Et)-polymeryl cannot undergo further chain transfer with rac-1. These differences mean that the narrow MWDs and complete conversion of Zn- and Al-alkyls to polymeryls that Sita observed cannot be achieved under the conditions studied herein. The structures of rac-1 and Sita’s catalyst are very different and have significantly different rate constants for propagation, chain transfer, and so on. More specifically, there is an approximately three-orders of magnitude higher propagation rate for rac-1 versus the Sita catalyst. However, Sita’s catalyst has similar rates of forward and reverse chain transfer, whereas rac-1 has a much higher rate of forward chain transfer than reverse chain transfer in the homopolymerization of 1-octene. This work highlights the unconventional use of the Job plot to reveal Zn-mediated chain transfer between Hf and Al in the Hf-pyridyl amido-catalyzed polymerization of 1-octene. The process does not lead to t-LCCTP because chain transfer between Hf and Zn, under these conditions, is irreversible. To our knowledge, this is the first report of using a Zn-mediated chain transfer in conjunction with a high-performance catalyst and the first example of Job plot analysis to provide evidence for Zn-mediated chain transfer.
AliBu3 alone does not undergo significant chain transfer in the homopolymerization of 1-octene as catalyzed by rac-1.20 Cooperative Zn/Al Exchange Also Occurs with AliBu3. Polymerizations were conducted by addition of the activated catalyst solution (0.083 mM) to a toluene solution of 1-octene (503.2 mM), ZnEt2, and AliBu3 at 50 °C. The concentrations of ZnEt2 and AliBu3 were varied, but the total concentration of Zn + Al was held constant at 1.6 mM. Analysis of the data with a Job plot24 reveals a nonlinear relationship between number of polymer chains per Zn + Al and the mole fraction of ZnEt2 (Figure 7).25 Thus, successful Zn-mediated chain transfer
Figure 7. Job plot of polymer chains per Zn + Al vs the mole fraction of ZnEt2. Total concentration of ZnEt2 plus AliBu3 used in the reaction is 1.6 mM. Reactions were run for 120 s and quenched with 2, followed by I2 labeling. Each point represents separate experiments and error bars represent standard deviation between duplicates. The dashed red line represents the hypothetical linear increase in polymer chains per Zn + Al due to ZnEt2 and AliBu3 working independently.
occurs in the presence of AliBu3. Unlike AlEt3 (vide supra), however, the number of polymer chains per Zn + Al did not exceed 1. This discrepancy is likely a result of slower exchange between AliBu3 and ZnEt(pol) due to increased steric repulsions involving the isobutyl group from AliBu3. Effectively, isobutyl partly mimics the steric effects that cause slow exchange of β-branched polymers resulting from 1,2-insertion of monomer. Although not as efficient as AlEt3, Zn-mediated chain transfer between Hf and Al is successfully achieved using AliBu3 without using the two-step protocol.23 Closer inspection of Figure 7 reveals that more transalkylation between Hf and Zn/Al occurs than there are ethyl groups available to undergo exchange. For example, the ZnEt2 mole fraction of 0.25 (Figure 7) has 0.4 mM ZnEt2 (0.8 mM ethyl groups) and I2 labeling reveals ∼1.1 mM polymer chains bound to Zn + Al. These results suggest that both ZnEt(iBu) and ZniBu2 can undergo transalkylation with Hf, albeit more slowly than ZnEt2. In contrast, ZnEt(Pol) does not undergo any exchange with Hf under the same conditions.18,19 These results demonstrate that subtle steric differences between isobutyl and polyoctene groups on Zn influence exchange with Hf.
■
■
ASSOCIATED CONTENT
S Supporting Information *
CONCLUSIONS We have investigated the effect of using Zn- and Al-alkyls, in combination, on the MWD of polyoctene produced by rac-1.
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00900. E
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
■
(10) Alfano, F.; Boone, H. W.; Busico, V.; Cipullo, R.; Stevens, J. C. Polypropylene “Chain Shuttling” at Enantiomorphous and Enantiopure Catalytic Species: Direct and Quantitative Evidence from Polymer Microstructure. Macromolecules 2007, 40, 7736−7738. (11) Matsumoto, K.; Takayanagi, M.; Sankaran, S. K.; Koga, N.; Nagaoka, M. Role of the Counteranion in the Reaction Mechanism of Propylene Polymerization Catalyzed by a (Pyridylamido)hafnium(IV) Complex. Organometallics 2018, 37, 343−349. (12) Gao, Y.; Chen, X.; Zhang, J.; Chen, J.; Lohr, T. L.; Marks, T. J. Catalyst Nuclearity Effects on Stereo- and Regioinduction in Pyridylamidohafnium-Catalyzed Propylene and 1-Octene Polymerizations. Macromolecules 2018, 51, 2401−2410. (13) Zuccaccia, C.; Macchioni, A.; Busico, V.; Cipullo, R.; Talarico, G.; Alfano, F.; Boone, H. W.; Frazier, K. A.; Hustad, P. D.; Stevens, J. C.; Vosejpka, P. C.; Abboud, K. A. Intra- and Intermolecular NMR Studies on the Activation of Arylcyclometallated Hafnium PyridylAmido Olefin Polymerization Precatalysts. J. Am. Chem. Soc. 2008, 130, 10354−10368. (14) Froese, R. D. J.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Mechanism of Activation of a Hafnium Pyridyl−Amide Olefin Polymerization Catalyst: Ligand Modification by Monomer. J. Am. Chem. Soc. 2007, 129, 7831−7840. (15) Zuccaccia, C.; Busico, V.; Cipullo, R.; Talarico, G.; Froese, R. D. J.; Vosejpka, P. C.; Hustad, P. D.; Macchioni, A. On the First Insertion of α-Olefins in Hafnium Pyridyl-Amido Polymerization Catalysts. Organometallics 2009, 28, 5445−5458. (16) Busico, V.; Cipullo, R.; Pellecchia, R.; Rongo, L.; Talarico, G.; Macchioni, A.; Zuccaccia, C.; Froese, R. D. J.; Hustad, P. D. Uni et Trini”: In Situ Diversification of (Pyridylamide)hafnium(IV) Catalysts. Macromolecules 2009, 42, 4369−4373. (17) Zhang, J.; Motta, A.; Gao, Y.; Stalzer, M. M.; Delferro, M.; Liu, B.; Lohr, T. L.; Marks, T. J. Cationic Pyridylamido Adsorbate on Brønsted Acidic Sulfated Zirconia: A Molecular Supported Organohafnium Catalyst for Olefin Homo- and Co-Polymerization. ACS Catal. 2018, 8, 4893−4901. (18) Cueny, E. S.; Johnson, H. C.; Anding, B. J.; Landis, C. R. Mechanistic Studies of Hafnium-Pyridyl Amido-Catalyzed 1-Octene Polymerization and Chain Transfer Using Quench-Labeling Methods. J. Am. Chem. Soc. 2017, 139, 11903−11912. (19) Johnson, H. C.; Cueny, E. S.; Landis, C. R. Chain Transfer with Dialkyl Zinc During Hafnium−Pyridyl Amido-Catalyzed Polymerization of 1-Octene: Relative Rates, Reversibility, and Kinetic Models. ACS Catal. 2018, 8, 4178−4188. (20) Cueny, E. S.; Johnson, H. C.; Landis, C. R. Selective QuenchLabeling of the Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene in the Presence of Trialkyl-Aluminum Chain-Transfer Reagents. ACS Catal. 2018, 8, 11605−11614. (21) Wei, J.; Zhang, W.; Sita, L. R. Aufbaureaktion Redux: Scalable Production of Precision Hydrocarbons from AlR3 (R = Et or iBu) by Dialkyl Zinc Mediated Ternary Living Coordinative Chain-Transfer Polymerization. Angew. Chem., Int. Ed. 2010, 49, 1768−1772. (22) Knap, J. E.; Leech, R. E.; Reid, A. J.; Tamplin, W. S. Safe Handling of Alkylaluminum Compounds. Ind. Eng. Chem. 1957, 49, 874−879. (23) Herein, we define the two-step protocol as a polymerization where I is added to effect polymerization. Then, 10 s after the addition of I, AlEt3 is added to the reaction. This procedure is conducted to overcome inhibition of initiation caused by AlEt3 see ref 20. (24) Renny, J. S.; Tomasevich, L. L.; Tallmadge, E. H.; Collum, D. B. Method of Continuous Variations: Applications of Job Plots to the Study of Molecular Associations in Organometallic Chemistry. Angew. Chem., Int. Ed. 2013, 52, 11998−12013. (25) We refer to plots of observable property versus mole fraction as a Job plot analysis. We recognize that the Job plot method commonly refers to a determination of the stoichiometry of aggregations by plotting a property (e.g., absorbance) versus mole fraction. We use Job plot due to the similarity of plotting an observable vs mole
Experimental details, polymerization procedure, molecular weight data, estimation of number of and concentration of polymer chains, I2 labeling of Zn- and Al-polymeryls (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Clark R. Landis: 0000-0002-1499-4697 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This research was supported by The Dow Chemical Company. We thank Dr. Matthew Christianson, Dr. Heather Spinney, and Dr. Daniel Arriola for helpful discussions. We thank Dr. Anna Kiyanova (UW-Madison Soft Materials Characterization Laboratory) for help with the GPC. We acknowledge the NSF through the University of Wisconsin Nanoscale Science and Engineering Center (DMR-0832760 and 0425880) for funding the GPC and the Soft Materials Laboratory. We acknowledge the NSF (CHE-1048642), NIH (S10 OD012245), and the Paul and Margaret Bender Fund for support of the NMR facility.
■
REFERENCES
(1) Valente, A.; Mortreux, A.; Visseaux, M.; Zinck, P. Coordinative Chain Transfer Polymerization. Chem. Rev. 2013, 113, 3836−3857. (2) Zhang, W.; Sita, L. R. Highly Efficient, Living Coordinative Chain-Transfer Polymerization of Propene with ZnEt2: Practical Production of Ultrahigh to Very Low Molecular Weight Amorphous Atactic Polypropenes of Extremely Narrow Polydispersity. J. Am. Chem. Soc. 2008, 130, 442−443. (3) Zhang, W.; Wei, J.; Sita, L. R. Living Coordinative ChainTransfer Polymerization and Copolymerization of Ethene, α-Olefins, and α,ω-Nonconjugated Dienes using Dialkylzinc as “Surrogate” Chain-Growth Sites. Macromolecules 2008, 41, 7829−7833. (4) Britovsek, G. J. P.; Cohen, S. A.; Gibson, V. C.; Maddox, P. J.; van Meurs, M. Iron-Catalyzed Polyethylene Chain Growth on Zinc: Linear α-Olefins with a Poisson Distribution. Angew. Chem., Int. Ed. 2002, 41, 489−491. (5) Britovsek, G. J. P.; Cohen, S. A.; Gibson, V. C.; van Meurs, M. Iron Catalyzed Polyethylene Chain Growth on Zinc: A Study of the Factors Delineating Chain Transfer versus Catalyzed Chain Growth in Zinc and Related Metal Alkyl Systems. J. Am. Chem. Soc. 2004, 126, 10701−10712. (6) van Meurs, M.; Britovsek, G. J. P.; Gibson, V. C.; Cohen, S. A. Polyethylene Chain Growth on Zinc Catalyzed by Olefin Polymerization Catalysts: A Comparative Investigation of Highly Active Catalyst Systems across the Transition Series. J. Am. Chem. Soc. 2005, 127, 9913−9923. (7) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.; Wenzel, T. T. Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization. Science 2006, 312, 714−719. (8) Vittoria, A.; Busico, V.; Cannavacciuolo, F. D.; Cipullo, R. Molecular Kinetic Study of “Chain Shuttling” Olefin Copolymerization. ACS Catal. 2018, 8, 5051−5061. (9) Boussie, T. R.; Diamond, G. M.; Goh, C.; Hall, K. A.; LaPointe, A. M.; Leclerc, M. K.; Murphy, V.; Shoemaker, J. A. W.; Turner, H.; Rosen, R. K.; Stevens, J. C.; Alfano, F.; Busico, V.; Cipullo, R.; Talarico, G. Nonconventional Catalysts for Isotactic Propene Polymerization in Solution Developed by Using High-ThroughputScreening Technologies. Angew. Chem., Int. Ed. 2006, 45, 3278−3283. F
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics fraction (in our case, I2-labeled polymers versus mole fraction of ZnEt2). (26) Vettel, S.; Vaupel, A.; Knochel, P. Nickel-Catalyzed Preparations of Functionalized Organozincs. J. Org. Chem. 1996, 61, 7473−7481. (27) Cariou, R.; Shabaker, J. W. Iron-Catalyzed Chain Growth of Ethylene: In Situ Regeneration of ZnEt2 by Tandem Catalysis. ACS Catal. 2015, 5, 4363−4367. (28) Brown, T. L.; Murrell, L. L. Methyl group exchanges in Lewis acid-base adducts of Group III trimethyl compounds. J. Am. Chem. Soc. 1972, 94, 378−384. (29) Rocchigiani, L.; Busico, V.; Pastore, A.; Macchioni, A. Comparative NMR Study on the Reactions of Hf(IV) Organometallic Complexes with Al/Zn Alkyls. Organometallics 2016, 35, 1241−1250. (30) Jeffery, E. A.; Mole, T. Methyl group exchange reactions of trimethylaluminium dimer. Aust. J. Chem. 1973, 26, 739−748. (31) Fabicon, R. M.; Richey, H. G. Formation of Coordinated RZn(macrocycle)+ Cations and Organozincate Anions from Reactions of Organozinc Compounds and Macrocycles. Organometallics 2001, 20, 4018−4023.
G
DOI: 10.1021/acs.organomet.8b00900 Organometallics XXXX, XXX, XXX−XXX
