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Cocatalyst effects in Hf-catalysed olefin polymerization: taking well-defined Al–alkyl borate salts into account

Gaia Urciuoli abc, Francesco Zaccaria *ac, Cristiano Zuccaccia *bc, Roberta Cipullo *ac, Peter H. M. Budzelaar a, Antonio Vittoria a, Christian Ehm ac, Alceo Macchioni bc and Vincenzo Busico ac
aDepartment of Chemical Sciences, Federico II University of Naples, via Cinthia, 80126 Napoli, Italy. E-mail: francesco.zaccaria@unina.it; rcipullo@unina.it
bDepartment of Chemistry, Biology and Biotechnology and CIRCC, University of Perugia, via Elce di Sotto 8, 06123 Perugia, Italy. E-mail: cristiano.zuccaccia@unipg.it
cDPI, P.O. Box 902, 5600 AX Eindhoven, the Netherlands

Received 6th December 2023 , Accepted 22nd December 2023

First published on 2nd January 2024


Abstract

Hafnium catalysts for olefin polymerization are often very sensitive to the nature of cocatalysts, especially if they contain “free” aluminium trialkyls. Herein, cocatalyst effects in Hf-catalysed propene polymerization are examined for four Hf catalysts belonging to the family of CS-symmetric (Hf-CS-Met) and C2-symmetric (Hf-C2-Met) metallocenes, as well as of octahedral (Hf-OOOO) and pentacoordinated (Hf-PyAm) “post-metallocenes”. The performance of the recently developed {[iBu2(PhNMe2)Al]2(μ-H)}+[B(C6F5)4] (AlHAl) cocatalyst is compared with that of established systems like methylalumoxane, phenol-modified methylalumoxane and trityl borate/tri-iso-butylaluminium. The worst catalytic performance is observed with MAO. Conversely, the best cocatalyst varies depending on the Hf catalyst used and the performance indicator of interest, highlighting the complexity and importance of selecting the right precatalyst/cocatalyst combination. AlHAl proved to be a suitable system for all catalysts tested and, in some cases, it provides the best performance in terms of productivity (e.g. with hafnocenes). Furthermore, it generally leads to high molecular weight polymers, also with catalysts enabling easy chain transfer to Al like Hf-PyAm. This suggests that AlHAl has a low tendency to form heterodinuclear adducts with the cationic active species, therefore preventing the formation of dormant sites and/or termination events by chain transfer to Al.


Introduction

Optimization of molecular catalysts typically implies tailoring of ancillary ligands and/or variation of metal centres for property modulation.1 Molecular catalysts for olefin polymerization represent a noticeable example in this respect: over the last few decades, tremendous progress in the development of group 4 metallocene2 and “post-metallocene”3,4 catalysts has resulted in a large variety of high-performance systems, some of them being currently employed in commercial processes.5

The structure of (pre)catalysts, however, is not the only variable determining polymerization performance, since activators or – more generally – cocatalysts are an equally important component of the catalytic pool.6–8 First, productivity is strongly dependent on the nature of the cocatalyst, which determines the effectiveness of precatalyst activation and impurity scavenging, and is often involved in side reactions with the active species.6–12 Furthermore, the cocatalyst usually provides the cationic active species with a counterion, therefore determining ion pairing interactions6,13–15 that potentially influence catalytic activity16–24 and stereoselectivity.25–29

An intriguing example of cocatalyst effects concerns Hf catalysts. Hafnocenes, for instance, have long been found to be poorly active and unable to compete with their Zr-based analogues,30–33 until highly effective cocatalysts other than methylaluminoxane (MAO)34,35 became readily available in research laboratories. The group of Rieger first demonstrated that hafnocenes and zirconocenes actually show comparable productivity when using, instead of MAO, a binary cocatalyst comprising an alkyl abstractor like [Ph3C][B(C6F5)4] (trityl borate, TTB) and an alkylating and impurity scavenging agent like tri-iso-butylaluminium (TIBAL).36 Later studies by the group of Busico revealed that a similar increase in hafnocene productivity can be achieved by using MAO/BHT,37 that is, a modified MAO in which the residual trimethylaluminium (TMA) component is scavenged by reaction with a sterically hindered phenol (i.e. 2,6-di-tert-butyl-4-methylphenol, BHT).38–41 A significant increase of polymer molecular weights and smaller effects on polymer stereoregularity were also observed.37

The cocatalyst sensitivity is therefore attributed to the generally higher tendency of hafnocenes to form Hf/Al heterodinuclear adducts, which represent dormant intermediates and are involved in chain termination events via chain transfer to Al (Scheme 1).12,37,42–45 This is particularly problematic with TMA, while bulkier Al–alkyls like TIBAL are less prone to forming such adducts.6,8,12


image file: d3dt04081j-s1.tif
Scheme 1 Formation of dormant Hf/Al heterodinuclear adducts and chain transfer to aluminium as potential side reactions in olefin polymerization. L = ancillary ligand; R = methyl or polymeryl.

Recently, we identified an unusual Al–alkyl borate salt (AlHAl, Fig. 1), behaving as a single component cocatalyst like MAO but exhibiting a well-defined structure like typical organic borate salts (e.g. TTB).46 Among the desirable properties of this species is the stability of its dinuclear Al–alkyl cation, which features coordinatively saturated aluminium centres possessing “latent” Lewis acidity.47AlHAl has been tested in combination with representative zirconocene catalysts in propene polymerization in toluene46 and, upon suitable structural modification, in ethylene/1-hexene copolymerization in hydrocarbon solvents at high temperatures.48 In both cases, it proved to be competitive with established cocatalysts, offering the advantage of requiring only ∼50 equivalents (or even less) for efficient precatalyst activation and impurity scavenging. It therefore requires orders of magnitude lower Al/Zr ratios compared to MAO (typically on the order of 103–104).34


image file: d3dt04081j-f1.tif
Fig. 1 Structure of the AlHAl cocatalyst.46

Owing to the stabilized nature of the Al centres and the low Al/M ratio required (M = group 4 metal), AlHAl is expected to exhibit a low tendency to form heteronuclear adducts with transition metal active species, potentially making it suitable for applications with Hf catalysts. Herein, the performance of AlHAl is compared with that of established systems such as MAO, MAO/BHT and TTB/TIBAL for representative examples of four classes of Hf-based metallocene and “post-metallocene” catalysts.

Results and discussion

The four Hf catalysts studied are shown in Fig. 2. They were selected as representative examples of the widely studied classes of CS- and C2-symmetric metallocenes, as well as of the less explored families of hexa- and penta-coordinated “post-metallocenes”. They include:

(1) A CS-symmetric metallocene (Hf-CS-Met), the same that was studied in one of the aforementioned literature papers on cocatalyst effects;37

(2) A 2,4-substituted silyl-bis(indenyl) C2-symmetric metallocene (Hf-C2-Met);49

(3) A “post-metallocene” catalyst featuring a tetradentate OOOO–ligand of the type patented by DOW chemicals (Hf-OOOO);50–53

(4) A pentacoordinated Hf-pyridylamido catalyst of the type used industrially for the production of olefin block copolymers via chain shuttling copolymerization (Hf-PyAm).54–56


image file: d3dt04081j-f2.tif
Fig. 2 Hafnium-based precatalysts studied.

These systems were tested in propene polymerization under reaction conditions analogous to those of literature reports,37 that is, in toluene at moderate pressure (2 bar) and temperature (60 °C). For screening purposes, the concentration of each cocatalyst was fixed at typical values that guarantee efficient impurity scavenging and activating ability, that is, [Al] = 10 mM for MAO and MAO/BHT,57 1 mM for TIBAL57 and 0.1 mM for AlHAl.46,48 Hafnium concentration (4–30 × 10−6 M) and reaction time (10–120 min) were varied depending on the productivity of each catalytic system to obtain reasonable polymer yields. Along with productivity, polymer molecular weight and stereoregularity have been selected as performance indicators. The results are summarized in Table 1; variations of performance indicators with respect to MAO are graphically summarized in Fig. 3.


image file: d3dt04081j-f3.tif
Fig. 3 Variation of productivity (Rp), polymer molecular weight (Mn) and stereoselectivity (σ) with respect to MAO: for each catalyst, variation of each performance parameter is reported as a ratio with respect to polymerization carried out with MAO (see also Table 1).
Table 1 Summary of propene polymerization resultsa
Entry Catalyst [Hf] (10−6 M) Cocatalyst [Al]/[Hf] R p (kgPP mmolCat−1 h−1) M n[thin space (1/6-em)]b (kDa) M w[thin space (1/6-em)]b (kDa) PDI σ P sk[thin space (1/6-em)]d
a In toluene (5 mL), 60 °C, ppropene = 2 bar (30 psi); [Al] = 10 mM for MAO and MAO/BHT, 1 mM for TIBAL or 0.1 mM for AlHAl; [B]/[Hf] = 5 for dichloride precatalysts Hf-CS-Met and Hf-C2-Met,37,49 1 for Hf-OOOO[thin space (1/6-em)]52 or 2 for Hf-PyAm,59,60 according to previously optimized procedures. b As determined by GPC. c Probability of inserting propene with the favoured enantioface at each of the two enantiotopic sites. d Conditional probability of “skipped insertion”. e [Al] = 3 mM, see the main text. See also Table S1.†
1 Hf-CS-Met  20 MAO  500 0.11  54  110 2.0 0.96 0.13
2 20 MAO/BHT 500 1.3 399 877 2.2 0.95 0.20
3 20 TTB/TIBAL 50 1.6 411 970 2.4 0.96 0.21
4 20 AlHAl 10 5.5 340 759 2.3 0.95 0.22
5 Hf-C2-Met 30 MAO 333 0.05 91 269 2.9 0.999
6 30 MAO/BHT 333 0.12 136 397 2.9 0.997
7 12 TTB/TIBAL 100 3.3 74 168 2.3 0.995
8 12 AlHAl 20 3.2 52 117 2.2 0.993
9 Hf-OOOO 10 MAO 1000 3.6 5.6 22 3.8 0.87
10 10 MAO/BHT 1000 8.4 299 702 2.3 0.87
11 10 TTB/TIBAL 100 4.0 31 67 2.2 0.89
12 10 AlHAl 20 3.1 55 125 2.3 0.88
13 Hf-PyAm 4 MAO 750e 4.0 11 66 6.1 0.994
14 4 MAO/BHT 750e 27 801 1944 2.4 0.994
15 4 MAO/BHT 2500 24 678 1586 2.4 0.994
16 4 TTB/TIBAL 250 24 60 176 2.9 0.994
17 4 AlHAl 50 5.9 296 947 3.2 0.995


Hf-CS-Met is the only catalyst of the test set producing syndiotactic polypropylene (sPP), with the other three forming isotactic polypropylene (iPP). The performance of Hf-CS-Met in combination with “classical” cocatalysts (Table 1, entries 1–3) is in reasonably good agreement with literature reports.37 MAO provides approximately one order of magnitude lower productivity than TTB/TIBAL (0.11 vs. 1.6 kgPP mmolCat−1 h−1); only a minor difference is instead observed when comparing MAO/BHT and TTB/TIBAL. Polymer molecular weights follow the same trend, with Mn (kDa) varying as 54 (MAO) < 399 (MAO/BHT) ≈ 411 (TTB/TIBAL): the main chain termination route via transfer to aluminium is blocked when using TMA-depleted MAO/BHT or bulky Al–alkyls like TIBAL. Statistical analysis of PP stereosequence distribution by 13C NMR spectroscopy58 shows that the enantioselectivity of the active sites (σ) remains constant, while the conditional probability of “skipped” monomer insertions (Psk) increases going from MAO to MAO/BHT and TTB/TIBAL, leading to slightly less stereoregular polymers. This can be rationalized considering that the formation of heterodinuclear adducts retards site epimerization (i.e. chain relocation without insertion), which is therefore less likely with the TMA-rich MAO cocatalyst.37

The new AlHAl cocatalyst in comparison provides even better productivity than that observed with TTB/TIBAL (5.5 vs. 1.6 kgPP mmolCat−1 h−1, respectively; Table 1, entries 3 and 4). Notably, at the same hafnium concentration used with the other cocatalysts, only 5 equivalents of AlHAl (i.e. [Al]/[Hf] = 10) suffice for efficient scavenging and catalyst activation. The polymer microstructure is nearly unaffected with respect to the TTB/TIBAL case both in terms of molecular weight and stereoregularity.

Also for the isotactic-selective metallocene catalyst screened, Hf-C2-Met, AlHAl and TTB/TIBAL are the best performing cocatalysts, providing similar productivity and polymer molecular weights (Table 1, entries 5 and 6; Fig. 3). MAO and MAO/BHT show significantly worse performance: broad polymer molecular weight distributions and very low iPP yields were obtained, even at nearly three times higher catalyst concentration (Table 1, entries 5 and 6). Interestingly, the stereoselectivity of the Hf-C2-Met/MAO system exceeds that previously reported at much higher propene pressure for the same catalyst49 and even approaches the performance of its Zr analogue61 in combination with TTB/TIBAL: this further exemplifies the complexity of factors determining the performance of hafnocenes, and especially the differences between Hf- and Zr-based catalysts (the so-called “hafnium effect”49,62–64).

For the octahedral “post-metallocene” Hf-OOOO (Table 1, entries 9–12), the cocatalyst effect on productivity is significantly smaller than that with the above-discussed metallocenes: maximum variations by a factor of only ∼3, rather than by one to two orders of magnitude, are observed (Fig. 3). MAO/BHT is the best performing cocatalyst in this case (8.4 kgPP mmolCat−1 h−1), while AlHAl (3.1 kgPP mmolCat−1 h−1) performs similar to MAO and TTB/TIBAL. It is however interesting to analyse the kinetic profiles obtained with this catalyst (Fig. 4a). The difference in productivity between MAO and MAO/BHT appears to be solely due to a rather long induction delay observed in the former case (approximately 15 min), after which the slope of the uptake vs. time profile becomes nearly identical to that of MAO/BHT. The use of AlHAl also leads to an induction delay of approximately 3 min, which is significantly shorter than that with MAO. Polymerization with TTB/TIBAL instead starts very fast and then slows down slightly, up to the point where the slope of the uptake vs. time profile tends to become similar to that of AlHAl. The long induction delay observed with MAO might be due to the formation of heterodinuclear adducts with TMA retarding chain initiation, and can be prevented by trapping this Al–alkyl with BHT, as previously observed for other catalysts.9 Also in the case of AlHAl, the induction delay has been previously observed in zirconocene-catalysed propene polymerization at higher temperatures and pressures.46 Although its origin remains to be fully clarified, it is likely due to a milder precatalyst activation reaction by the N-donor stabilized [AliBu2(PhNMe2)]+ cation46 compared to that of the “naked” transient [AliBu2]+ cation generated by the binary system TTB/TIBAL.65 Consistently, similar induction delays can be observed also when replacing TTB with [PhMe2NH][B(C6F5)4] (anilinium borate, AB), containing the same aniline ligand present in AlHAl.57 While one would normally prefer fast initiation, these short initial delays can actually be exploited to obtain highly controlled polymerization kinetics also with exceedingly active catalysts, since the reactor conditions can equilibrate after catalyst injection and before polymerization fully begins.46,57


image file: d3dt04081j-f4.tif
Fig. 4 Selected monomer uptake vs. reaction time profiles obtained with (a) Hf-OOOO and (b) Hf-PyAm in combination with various cocatalysts (see also Fig. S1).

A marked cocatalyst effect is observed on the molecular weight of polymers produced with Hf-OOOO, which follows the trend MAO (Mn = 5.6 kDa) < TTB/TIBAL (31 kDA) < AlHAl (55 kDa) ≪ MAO/BHT (299 kDa). Saturated polymer chain ends are observed by NMR spectroscopy, suggesting that this trend can be explained based on the same arguments related to the probability of chain transfer to Al, discussed above for Hf-CS-Met. However, it is important to note here that, with respect to MAO, the molecular weight increases by one order of magnitude when using borate systems, and by almost two orders with MAO/BHT, suggesting that Hf-OOOO can have residual interactions even with TIBAL and AlHAl-derived Al–alkyls. The stereoselectivity of this catalyst is relatively low: a similar σ of ∼0.87 is observed with the two aluminoxane cocatalysts, which is slightly lower than that with the borate salt-based systems (∼0.89). With such flexible “post-metallocene” catalyst,50–53 this small difference in stereoselectivity might be ascribed to ion pairing effects on chain epimerization and conformational rearrangements of the cationic active species.52,66–69

The last catalyst studied, namely Hf-PyAm (Table 1, entries 13–17), is generally quite sensitive to the nature of the cocatalyst, since its rather open active pocket and reactive Hf–aryl bond make it particularly prone to interact/react with all other components of the catalytic pool.70–73 Chain transfer reactions via the formation of heterodinuclear adducts are known to be particularly easy with this catalyst, and represent the main chain termination route even in combination with bulky TIBAL.54,56,72–76 Since TMA is known to be particularly detrimental to catalytic performance, polymerization in the presence of MAO was here conducted at a lower [Al] of 3 mM (i.e. Al/Hf = 750); the performance of the MAO/BHT system is nearly the same at [Al] = 3 or 10 mM (Table 1, entries 13–15).

In terms of productivity, MAO/BHT and TTB/TIBAL are the best performing systems for Hf-PyAm, with a similar Rp of ∼24 kgPP mmolCat−1 h−1, which is approximately six times higher than that with MAO (Fig. 3); also in this case, a very long induction delay of ∼25 min contributes towards making the MAO-activated system less productive (Fig. 4b). AlHAl exhibits only a slightly better performance than MAO in terms of averaged productivity (5.9 vs. 4.0 kgPP mmolCat−1 h−1).

The relatively low productivity observed with MAO can be explained based on the ease of formation of dormant heterodinuclear adducts and of side reactions involving the Hf–aryl bond with residual TMA.72,73 This might explain also the low Mn and broad molecular weight distributions observed with this cocatalyst (PDI = 6.1).

Although no conclusive explanation can be drawn, it is instructive to analyse also the possible origins of the somewhat poor performance of AlHAl. The same explanation proposed for MAO hardly applies here: as discussed above, the Al-compounds derived from AlHAl are expected to be less interactive with the active species than TMA. In fact, the polymer molecular weight observed with this cocatalyst (Mn ≈ 300 kDa) is significantly higher than that with MAO and even TTB/TIBAL (11 and 60 kDa, respectively), and it is on the same order of magnitude of the highest one obtained with MAO/BHT (∼700–800 kDa; Fig. 3): this indicates a very low tendency of AlHAl to trigger chain termination by chain transfer to Al even with Hf-PyAm. Ineffective precatalyst activation is also an unlikely explanation since simple methyl abstraction is required with a dimethyl precatalyst like Hf-PyAm. The difference in productivity is therefore likely related to other types of side reactions. For instance, it has been previously shown that the easily accessible Hf-active sites of Hf-PyAm might be poisoned by the dimethylaniline ligand of AB,71,77 which is the same as that present in AlHAl. Double methyl abstraction in the presence of a relatively large excess of cationic and highly Lewis acidic Al–alkyl species might be another possibility.78,79

No cocatalyst effect is observed on the stereoselectivity of Hf-PyAm, which provides highly isotactic PP, as expected.55,80,81

Conclusions

The performance in propene polymerization of four representative metallocene and “post-metallocene” Hf catalysts has been explored in combination with various cocatalysts, namely MAO, MAO/BHT, TTB/TIBAL and the recently developed AlHAl. Cocatalyst effects of variable intensity have been observed (Fig. 3). The productivity of the metallocene catalysts Hf-CS-Met and Hf-C2-Met depends strongly on the cocatalyst nature, while variations are more moderate for Hf-PyAm and Hf-OOOO. The polymer molecular weight exhibits a large variability for all catalysts except Hf-C2-Met, while cocatalyst effects on stereoselectivity are smaller.

MAO is generally the worst performing system, likely due to the side reactions involving its TMA component. Conversely, identifying the best cocatalyst for the whole set of Hf catalysts is not straightforward. MAO/BHT generally provides the highest polymer molecular weight; furthermore, it leads to the highest productivity with the “post-metallocene” catalysts Hf-OOOO and Hf-PyAm, while being rather ineffective in activating the metallocene Hf-C2-Met. Similarly, TTB/TIBAL provides quite high productivities in all cases, but it leads to easy chain transfer to Al with the two “post-metallocenes”.

Notably, AlHAl appears to be comparable with the established cocatalysts. In terms of productivity, it provides the best performance with the two metallocene catalysts and, although it performs worse with Hf-OOOO and Hf-PyAm, productivity is at most 5-fold lower than that with MAO/BHT. Polymer molecular weights are always similar (e.g. with Hf-C2-Met and Hf-OOOO) or even higher (e.g. with Hf-PyAm) than those obtained with TTB/TIBAL, and sometimes comparable to those obtained with MAO/BHT (Hf-CS-Met); this indicates that AlHAl exhibits a very low tendency to induce chain termination via chain transfer to aluminium.

These results therefore provide some more insight into the complexity of cocatalyst effects in Hf-catalysed olefin polymerization. Furthermore, they show that AlHAl represents a promising addition to the toolbox of currently available cocatalysts: it is broadly applicable with metallocene and “post-metallocene” catalysts, and it can be successfully employed in cases where chain transfer to aluminium is undesirable, including with catalysts enabling very easy transalkylation like Hf-PyAm.

Experimental part

Materials and methods

All manipulations of air-sensitive compounds were conducted under argon or nitrogen using Schlenk techniques and/or MBraun LabMaster 130 glove boxes. Hf-CS-Met (MCAT), MAO (Lanxess), BHT (Merck), TIBAL (Lanxess), and TTB (Acros) were purchased and used as received. Toluene (Romil) was purchased and purified by passing it through a mixed-bed activated Cu/4 Å molecular-sieve column in an MBraun SPS-5 unit (final concentration of O2 and H2O < 1 ppm). Propene (Linde) was purchased and purified by passing it through a mixed-bed activated-Cu/4 Å molecular-sieve column. Hf-C2-Met,49Hf-OOOO,52,53Hf-PyAm[thin space (1/6-em)]80 and AlHAl[thin space (1/6-em)]46 were synthesized according to literature procedures.

Polymerization experiments

Propene polymerization experiments were performed in a Freeslate (formerly Symyx) parallel pressure reactor setup with 48 reaction cells (PPR48), fully contained in a triple MBraun glovebox operating under nitrogen. The cells, each with a liquid working volume of 5.0 mL, feature an 800 rpm magnetically coupled stirring, and individual online reading/control of the temperature, pressure, monomer uptake, and monomer uptake rate. Experiments were carried out according to established experimental protocols57,82–84 under reaction conditions used in previous literature reports on Hf catalysts,37 but without pre-contacting precatalysts and cocatalysts prior to injection into the reactors. All experiments were performed at least in duplicate. A detailed experimental procedure is reported in the ESI.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This research forms a part of the research program of DPI (project 857). A part of this work has been funded by the European Union – NextGenerationEU under the Italian Ministry of University and Research (MUR) National Innovation Ecosystem grant ECS00000041 – VITALITY; we acknowledge Università degli Studi di Perugia and MUR for support within the project Vitality. The authors wish to thank the group of Prof. A. Z. Voskoboynikov (Moskow State University, Russian Federation) for the synthesis of Hf-C2-Met and Dr Eric Cuthbert for the synthesis of Hf-OOOO. F. Z. thanks the Federico II University of Naples and PON – Ricerca e Innovazione (DM 1062) for a research fellowship.

References

  1. L. Falivene, Z. Cao, A. Petta, L. Serra, A. Poater, R. Oliva, V. Scarano and L. Cavallo, Nat. Chem., 2019, 11, 872–879 CrossRef CAS PubMed.
  2. W. Kaminsky, Macromol. Symp., 2016, 360, 10–22 CrossRef CAS.
  3. J. Klosin, P. P. Fontaine and R. Figueroa, Acc. Chem. Res., 2015, 48, 2004–2016 CrossRef CAS PubMed.
  4. M. C. Baier, M. A. Zuideveld and S. Mecking, Angew. Chem., Int. Ed., 2014, 53, 9722–9744 CrossRef CAS PubMed.
  5. M. Stürzel, S. Mihan and R. Mülhaupt, Chem. Rev., 2016, 116, 1398–1433 CrossRef PubMed.
  6. F. Zaccaria, L. Sian, C. Zuccaccia and A. Macchioni, in Advances in Organometallic Chemistry, ed. P. J. Perez, Elsevier, Amsterdam, The Netherlands, 2020, vol. 73, pp. 1–78 Search PubMed.
  7. E. Y. X. Chen and T. J. Marks, Chem. Rev., 2000, 100, 1391–1434 CrossRef CAS PubMed.
  8. M. Bochmann, Organometallics, 2010, 29, 4711–4740 CrossRef CAS.
  9. R. Cipullo, P. Melone, Y. Yu, D. Iannone and V. Busico, Dalton Trans., 2015, 44, 12304–12311 RSC.
  10. X. Desert, J. F. Carpentier and E. Kirillov, Coord. Chem. Rev., 2019, 386, 50–68 CrossRef CAS.
  11. X. Desert, F. Proutiere, A. Welle, K. Den Dauw, A. Vantomme, O. Miserque, J. M. Brusson, J. F. Carpentier and E. Kirillov, Organometallics, 2019, 38, 2664–2673 CrossRef CAS.
  12. L. Tensi, R. D. J. Froese, R. L. Kuhlman, A. Macchioni and C. Zuccaccia, Chem. – Eur. J., 2020, 26, 3758–3766 CrossRef CAS PubMed.
  13. R. Tanaka, O. A. Ajala, Y. Nakayama and T. Shiono, Prog. Polym. Sci., 2023, 142, 101690 CrossRef CAS.
  14. A. Macchioni, Chem. Rev., 2005, 105, 2039–2073 CrossRef CAS PubMed.
  15. W. E. Piers, in Advances in Organometallic Chemistry, Academic Press, 2004, vol. 52, pp. 1–76 Search PubMed.
  16. L. Sian, A. Macchioni and C. Zuccaccia, ACS Catal., 2020, 10, 1591–1606 CrossRef CAS.
  17. F. Song, R. D. Cannon and M. Bochmann, J. Am. Chem. Soc., 2003, 125, 7641–7653 CrossRef CAS PubMed.
  18. C. N. Rowley and T. K. Woo, Organometallics, 2011, 30, 2071–2074 CrossRef CAS.
  19. G. Lanza, I. L. Fragala and T. J. Marks, J. Am. Chem. Soc., 1998, 120, 8257–8258 CrossRef CAS.
  20. Y. Gao, J. Chen, Y. Wang, D. B. Pickens, A. Motta, Q. J. Wang, Y. W. Chung, T. L. Lohr and T. J. Marks, Nat. Catal., 2019, 2, 236–242 CrossRef CAS.
  21. A. Laine, B. B. Coussens, J. T. Hirvi, A. Berthoud, N. Friederichs, J. R. Severn and M. Linnolahti, Organometallics, 2015, 34, 2415–2421 CrossRef CAS.
  22. L. Rocchigiani, G. Ciancaleoni, C. Zuccaccia and A. Macchioni, Angew. Chem., Int. Ed., 2011, 50, 11752–11755 CrossRef CAS PubMed.
  23. F. Song, R. D. Cannon, S. J. Lancaster and M. Bochmann, J. Mol. Catal. A: Chem., 2004, 218, 21–28 CrossRef CAS.
  24. C. Alonso-Moreno, S. J. Lancaster, J. A. Wright, D. L. Hughes, C. Zuccaccia, A. Correa, A. Macchioni, L. Cavallo and M. Bochmann, Organometallics, 2008, 27, 5474–5487 CrossRef CAS.
  25. S. A. Miller and J. E. Bercaw, Organometallics, 2006, 25, 3576–3592 CrossRef CAS.
  26. M. Mohammed, M. Nele, A. Al-Humydi, S. Xin, R. A. Stapleton and S. Collins, J. Am. Chem. Soc., 2003, 125, 7930–7941 CrossRef CAS PubMed.
  27. M. A. Giardello, M. S. Eisen, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1995, 117, 12114–12129 CrossRef CAS.
  28. M. C. Chen and T. J. Marks, J. Am. Chem. Soc., 2001, 123, 11803–11804 CrossRef CAS PubMed.
  29. V. Busico, R. Cipullo, F. Cutillo, M. Vacatello and V. Van Axel Castelli, Macromolecules, 2003, 36, 4258–4261 CrossRef CAS.
  30. J. A. Ewen, R. L. Jones, A. Razavi and J. D. Ferrara, J. Am. Chem. Soc., 1988, 110, 6255–6256 CrossRef CAS PubMed.
  31. J. A. Ewen, L. Haspeslach, J. L. Atwood and H. Zhang, J. Am. Chem. Soc., 1987, 109, 6544–6545 CrossRef CAS.
  32. W. J. Gauthier, J. F. Corrigan, N. J. Taylor and S. Collins, Macromolecules, 1995, 28, 3771–3778 CrossRef CAS.
  33. A. Razavi and J. L. Atwood, J. Organomet. Chem., 1993, 459, 117–123 CrossRef CAS.
  34. H. S. Zijlstra and S. Harder, Eur. J. Inorg. Chem., 2015, 2015, 19–43 CrossRef CAS.
  35. W. Kaminsky, Macromolecules, 2012, 45, 3289–3297 CrossRef CAS.
  36. B. Rieger, C. Troll and J. Preuschen, Macromolecules, 2002, 35, 5742–5743 CrossRef CAS.
  37. V. Busico, R. Cipullo, R. Pellecchia, G. Talarico and A. Razavi, Macromolecules, 2009, 42, 1789–1791 CrossRef CAS.
  38. V. Busico, R. Cipullo, F. Cutillo, N. Friederichs, S. Ronca and B. Wangt, J. Am. Chem. Soc., 2003, 125, 12402–12403 CrossRef CAS PubMed.
  39. F. Zaccaria, C. Zuccaccia, R. Cipullo, P. H. M. Budzelaar, A. Macchioni, V. Busico and C. Ehm, Eur. J. Inorg. Chem., 2020, 2020, 1088–1095 CrossRef CAS.
  40. F. Zaccaria, C. Zuccaccia, R. Cipullo, P. H. M. Budzelaar, A. Macchioni, V. Busico and C. Ehm, ACS Catal., 2019, 9, 2996–3010 CrossRef CAS.
  41. R. A. Stapleton, B. R. Galan, S. Collins, R. S. Simons, J. C. Garrison and W. J. Youngs, J. Am. Chem. Soc., 2003, 125, 9246–9247 CrossRef CAS PubMed.
  42. C. Ehm, R. Cipullo, P. H. M. Budzelaar and V. Busico, Dalton Trans., 2016, 45, 6847–6855 RSC.
  43. E. Zurek and T. Ziegler, Organometallics, 2002, 21, 83–92 CrossRef CAS.
  44. G. Theurkauff, A. Bondon, V. Dorcet, J. F. Carpentier and E. Kirillov, Angew. Chem., Int. Ed., 2015, 54, 6343–6346 CrossRef CAS PubMed.
  45. D. E. Babushkin, N. V. Semikolenova, V. A. Zakharov and E. P. Talsi, Macromol. Chem. Phys., 2000, 201, 558–567 CrossRef CAS.
  46. F. Zaccaria, C. Zuccaccia, R. Cipullo, P. H. M. Budzelaar, A. Vittoria, A. Macchioni, V. Busico and C. Ehm, ACS Catal., 2021, 11, 4464–4475 CrossRef CAS.
  47. C. J. Harlan, A. R. Barron and S. G. Bott, J. Am. Chem. Soc., 1995, 117, 6465–6474 CrossRef CAS.
  48. G. Urciuoli, F. Zaccaria, C. Zuccaccia, R. Cipullo, P. H. M. Budzelaar, A. Vittoria, C. Ehm, A. Macchioni and V. Busico, Polymers, 2023, 15, 1378 CrossRef CAS PubMed.
  49. A. Vittoria, G. P. Goryunov, V. V. Izmer, D. S. Kononovich, O. V. Samsonov, F. Zaccaria, G. Urciuoli, P. H. M. Budzelaar, V. Busico, A. Z. Voskoboynikov, D. V. Uborsky, C. Ehm and R. Cipullo, Polymers, 2021, 13, 2621 CrossRef CAS PubMed.
  50. T. R. Boussie, O. Brummer, G. M. Diamond, A. M. LaPointe, M. K. Leclerc, C. Micklatcher, P. Sun and X. Bei, Int. Pat. ApplUS7241714B2, 2007 Search PubMed.
  51. E. T. Kiesewetter, S. Randoll, M. Radlauer and R. M. Waymouth, J. Am. Chem. Soc., 2010, 132, 5566–5567 CrossRef CAS PubMed.
  52. E. N. T. Cuthbert, A. Vittoria, R. Cipullo, V. Busico and P. H. M. Budzelaar, Eur. J. Inorg. Chem., 2020, 2020, 541–550 CrossRef CAS.
  53. E. N. T. Cuthbert, V. Busico, D. E. Herbert and P. H. M. Budzelaar, Eur. J. Inorg. Chem., 2019, 2019, 3396–3410 CrossRef CAS.
  54. D. J. Arriola, E. M. Carnahan, P. D. Hustad, R. L. Kuhlman and T. T. Wenzel, Science, 2006, 312, 714–719 CrossRef CAS PubMed.
  55. T. R. Boussie, G. M. Diamond, C. Goh, K. A. Hall, A. M. LaPointe, M. K. Leclerc, V. Murphy, J. A. W. Shoemaker, H. Turner, R. K. Rosen, J. C. Stevens, F. Alfano, V. Busico, R. Cipullo and G. Talarico, Angew. Chem., Int. Ed., 2006, 45, 3278–3283 CrossRef CAS.
  56. A. Vittoria, V. Busico, F. D. Cannavacciuolo and R. Cipullo, ACS Catal., 2018, 8, 5051–5061 CrossRef CAS.
  57. C. Ehm, A. Mingione, A. Vittoria, F. Zaccaria, R. Cipullo and V. Busico, Ind. Eng. Chem. Res., 2020, 59, 13940–13947 CrossRef CAS.
  58. V. Busico and R. Cipullo, Prog. Polym. Sci., 2001, 26, 443–533 CrossRef CAS.
  59. G. Antinucci, A. Vittoria, R. Cipullo and V. Busico, Macromolecules, 2020, 53, 3789–3795 CrossRef CAS.
  60. R. Shang, H. Gao, F. Luo, Y. Li, B. Wang, Z. Ma, L. Pan and Y. Li, Macromolecules, 2019, 52, 9280–9290 CrossRef CAS.
  61. C. Ehm, A. Vittoria, G. P. Goryunov, P. S. Kulyabin, P. H. M. Budzelaar, A. Z. Voskoboynikov, V. Busico, D. V. Uborsky and R. Cipullo, Macromolecules, 2018, 51, 8073–8083 CrossRef CAS.
  62. M. R. Machat, A. Fischer, D. Schmitz, M. Vöst, M. Drees, C. Jandl, A. Pöthig, N. P. M. Casati, W. Scherer and B. Rieger, Organometallics, 2018, 37, 2690–2705 CrossRef CAS.
  63. A. Schöbel, E. Herdtweck, M. Parkinson and B. Rieger, Chem. – Eur. J., 2012, 18, 4174–4178 CrossRef PubMed.
  64. A. Razavi, L. Peters and L. Nafpliotis, J. Mol. Catal. A: Chem., 1997, 115, 129–154 CrossRef CAS.
  65. M. Bochmann and M. J. Sarsfield, Organometallics, 1998, 17, 5908–5912 CrossRef CAS.
  66. G. Ciancaleoni, N. Fraldi, R. Cipullo, V. Busico, A. Macchioni and P. H. M. Budzelaar, Macromolecules, 2012, 45, 4046–4053 CrossRef CAS.
  67. E. Romano, P. H. M. Budzelaar, C. De Rosa and G. Talarico, J. Phys. Chem. A, 2022, 126, 6203–6209 CrossRef CAS PubMed.
  68. A. Dall'Anese, P. S. Kulyabin, D. V. Uborsky, A. Vittoria, C. Ehm, R. Cipullo, P. H. M. Budzelaar, A. Z. Voskoboynikov, V. Busico, L. Tensi, A. Macchioni and C. Zuccaccia, Inorg. Chem., 2023, 62, 16021–16037 CrossRef.
  69. A. Vittoria, P. S. Kulyabin, G. Antinucci, A. N. Iashin, D. V. Uborsky, E. N. T. Cuthbert, P. H. M. Budzelaar, A. Z. Voskoboynikov, R. Cipullo, C. Ehm and V. Busico, ACS Catal., 2023, 13, 13151–13155 CrossRef CAS.
  70. K. Matsumoto, M. Takayanagi, S. K. Sankaran, N. Koga and M. Nagaoka, Organometallics, 2018, 37, 343–349 CrossRef CAS.
  71. C. Zuccaccia, A. Macchioni, V. Busico, R. Cipullo, G. Talarico, F. Alfano, H. W. Boone, K. A. Frazier, P. D. Hustad, J. C. Stevens, P. C. Vosejpka and K. A. Abboud, J. Am. Chem. Soc., 2008, 130, 10354–10368 CrossRef CAS PubMed.
  72. L. Rocchigiani, V. Busico, A. Pastore, G. Talarico and A. Macchioni, Angew. Chem., Int. Ed., 2014, 53, 2157–2161 CrossRef CAS PubMed.
  73. L. Rocchigiani, V. Busico, A. Pastore and A. Macchioni, Organometallics, 2016, 35, 1241–1250 CrossRef CAS.
  74. E. S. Cueny and C. R. Landis, Organometallics, 2019, 38, 926–932 CrossRef CAS.
  75. P. D. Hustad, R. E. Kuhlman, E. M. Carnahan, T. T. Wenzel and D. J. Arriola, Macromolecules, 2008, 41, 4081–4089 CrossRef CAS.
  76. E. S. Cueny, H. C. Johnson, B. J. Anding and C. R. Landis, J. Am. Chem. Soc., 2017, 139, 11903–11912 CrossRef CAS PubMed.
  77. E. S. Cueny, M. R. Nieszala, R. D. J. Froese and C. R. Landis, ACS Catal., 2021, 11, 4301–4309 CrossRef CAS.
  78. E. Y. X. Chen, W. J. Kruper, G. Roof and D. R. Wilson, J. Am. Chem. Soc., 2001, 123, 745–746 CrossRef CAS PubMed.
  79. A. Al-Humydi, J. C. Garrison, W. J. Youngs and S. Collins, Organometallics, 2005, 24, 193–196 CrossRef CAS.
  80. K. A. Frazier, H. Boone, P. C. Vosejpka and J. C. Stevens, Int. Pat. ApplUS2004/0220050A12004, 2004 Search PubMed.
  81. C. De Rosa, R. Di Girolamo and G. Talarico, ACS Catal., 2016, 6, 3767–3770 CrossRef CAS.
  82. C. Ehm, A. Vittoria, G. P. Goryunov, V. V. Izmer, D. S. Kononovich, P. S. Kulyabin, R. Di Girolamo, P. H. M. Budzelaar, A. Z. Voskoboynikov, V. Busico, D. V. Uborsky and R. Cipullo, Macromolecules, 2020, 53, 9325–9336 CrossRef CAS.
  83. P. S. Kulyabin, G. P. Goryunov, M. I. Sharikov, V. V. Izmer, A. Vittoria, P. H. M. Budzelaar, V. Busico, A. Z. Voskoboynikov, C. Ehm, R. Cipullo and D. V. Uborsky, J. Am. Chem. Soc., 2021, 143, 7641–7647 CrossRef CAS PubMed.
  84. C. Ehm, A. Vittoria, G. P. Goryunov, V. V. Izmer, D. S. Kononovich, O. V. Samsonov, R. Di Girolamo, P. H. M. Budzelaar, A. Z. Voskoboynikov, V. Busico, D. V. Uborsky and R. Cipullo, Polymers, 2020, 12, 1005 CrossRef CAS PubMed.

Footnote

Electronic supplementary information (ESI) available: Full polymerization results, polymerization procedure and kinetic profiles. See DOI: https://doi.org/10.1039/d3dt04081j

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