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Collins S, Joshi A, Linnolahti M. Formation and Structure of Hydrolytic Methylaluminoxane Activators. Chemistry 2021; 27:15460-15471. [PMID: 34436806 PMCID: PMC8596698 DOI: 10.1002/chem.202102463] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Indexed: 01/14/2023]
Abstract
Methylaluminoxane (MAO) activators have sheet structures which form ion-pairs on reaction of neutral donors such as octamethyltrisiloxane (OMTS). The ion-pairs can be detected by electrospray ionization mass spectrometry (ESI-MS) in polar media. The growth of these reactive precursors during hydrolysis of Me3 Al can be monitored using ESI-MS. Density functional theory, combined with numerical simulation of growth, indicates that this process involves rapid formation of low MW oligomers, followed by assembly of these species into low MW sheets. These can grow through further addition of low MW oligomers or by fusion into larger sheets. The mechanism of these growth processes leads to the prediction that even-numbered sheets should be favored, and this surprising result is confirmed by ESI-MS monitoring experiments of both activator growth and MAO aging.
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Affiliation(s)
- Scott Collins
- Former affiliation: Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada)
| | - Anuj Joshi
- UVic Genome BC Proteomics Research Centre sup, 4464 Markham St #3101, Victoria, BC V8Z 5N3, Canada
| | - Mikko Linnolahti
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, Yliopistokatu 7, 80100, Joensuu, Finland
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Collins S, Hasan G, Joshi A, McIndoe JS, Linnolahti M. Are Methylaluminoxane Activators Sheets? Chemphyschem 2021; 22:1326-1335. [PMID: 33971081 PMCID: PMC8362195 DOI: 10.1002/cphc.202100268] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 05/07/2021] [Indexed: 11/14/2022]
Abstract
Density functional theory calculations on neutral sheet models for methylaluminoxane (MAO) indicate that these structures, containing 5‐coordinate and 4‐coordinate Al, are likely precursors to ion‐pairs seen during the hydrolysis of trimethylaluminum (Me3Al) in the presence of donors such as octamethyltrisiloxane (OMTS). Ionization by both methide ([Me]−) and [Me2Al]+ abstraction, involving this donor, were studied by polarizable continuum model calculations in fluorobenzene (PhF) and o‐difluorobenzene (DFB) media. These studies suggest that low MW, 5‐coordinate sheets ionize by [Me2Al]+ abstraction, while [Me]− abstraction from Me3Al‐OMTS is the likely process for higher MW 4‐coordinate sheets. Further, comparison of anion stabilities per mole of aluminoxane repeat unit (MeAlO)n, suggest that anions such as [(MeAlO)7(Me3Al)4Me]−=[7,4]− are especially stable compared to higher homologues, even though their neutral precursors are unstable.
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Affiliation(s)
- Scott Collins
- Department of Chemistry, University of Victoria, 3800, Finnerty Road, Victoria, BC, V8P 5 C2, Canada
| | - Galib Hasan
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, Yliopistokatu 7, 80100, Joensuu, Finland.,Institute for Atmospheric and Earth System Research (INAR) c/o Department of Chemistry, University of Helsinki, A.I Virtasen Aukio 1, 00014, Helsinki, Finland
| | - Anuj Joshi
- Department of Chemistry, University of Victoria, 3800, Finnerty Road, Victoria, BC, V8P 5 C2, Canada.,UVic Genome BC Proteomics Research Centre, 4464, Markham St #3101, Victoria, BC V8Z 5N3, Canada
| | - J Scott McIndoe
- Department of Chemistry, University of Victoria, 3800, Finnerty Road, Victoria, BC, V8P 5 C2, Canada
| | - Mikko Linnolahti
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, Yliopistokatu 7, 80100, Joensuu, Finland
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Joshi A, Collins S, Linnolahti M, Zijlstra HS, Liles E, McIndoe JS. Spectroscopic Studies of Synthetic Methylaluminoxane: Structure of Methylaluminoxane Activators. Chemistry 2021; 27:8753-8763. [PMID: 33780574 DOI: 10.1002/chem.202100271] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Indexed: 11/06/2022]
Abstract
Hydrolysis of trimethylaluminum (Me3 Al) in polar solvents can be monitored by electrospray ionization mass spectrometry (ESI-MS) using the donor additive octamethyltrisiloxane [(Me3 SiO)2 SiMe2 , OMTS]. Using hydrated salts, hydrolytic methylaluminoxane (h-MAO) features different anion distributions, depending on the conditions of synthesis, and different activator contents as measured by NMR spectroscopy. Non-hydrolytic MAO was prepared using trimethylboroxine. The properties of this material, which contains incorporated boron, differ significantly from h-MAO. In the case of MAO prepared by direct hydrolysis, oligomeric anions are observed to rapidly form, and then more slowly evolve into a mixture dominated by an anion with m/z 1375 with formula [(MeAlO)16 (Me3 Al)6 Me]- . Theoretical calculations predict that sheet structures with composition (MeAlO)n (Me3 Al)m are favoured over other motifs for MAO in the size range suggested by the ESI-MS experiments. A possible precursor to the m/z 1375 anion is a local minimum based on the free energy released upon hydrolysis of Me3 Al.
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Affiliation(s)
- Anuj Joshi
- Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
| | - Scott Collins
- C/o Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
| | - Mikko Linnolahti
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, Yliopistokatu 7, 80100, Joensuu, Finland
| | - Harmen S Zijlstra
- Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
| | - Elena Liles
- Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
| | - J Scott McIndoe
- Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada
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Zaccaria F, Budzelaar PHM, Cipullo R, Zuccaccia C, Macchioni A, Busico V, Ehm C. Reactivity Trends of Lewis Acidic Sites in Methylaluminoxane and Some of Its Modifications. Inorg Chem 2020; 59:5751-5759. [PMID: 32271565 PMCID: PMC7997381 DOI: 10.1021/acs.inorgchem.0c00533] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Indexed: 11/28/2022]
Abstract
The established model cluster (AlOMe)16(AlMe3)6 for methylaluminoxane (MAO) cocatalyst has been studied by density functional theory, aiming to rationalize the different behaviors of unmodified MAO and TMA-depleted MAO/BHT (TMA = trimethylaluminum; BHT = 2,6-di-tert-butyl-4-methylphenol), highlighted in previous experimental studies. The tendency of the three model Lewis acidic sites A-C to release neutral Al fragments (i.e., AlMe2R; R = Me or bht) or transient aluminum cations (i.e., [AlMeR]+) has been investigated both in the absence and in the presence of neutral N-donors. Sites C are most likely responsible for the activation capabilities of TMA-rich MAO, but TMA depletion destabilizes them, possibly inducing structural rearrangements. The remaining sites A and B, albeit of lower Lewis acidity, should be still able to release cationic Al fragments when TMA-depleted modified MAOs are treated with N-donors (e.g. [AlMe(bht)]+ from MAO/BHT). These findings provide tentative interpretations for earlier observations of donor-dependent ionization tendencies of MAO and MAO/BHT and how TMA depleted MAOs can still be potent activators.
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Affiliation(s)
- Francesco Zaccaria
- Dipartimento
di Scienze Chimiche, Università di
Napoli Federico II, Via Cintia, 80126 Napoli, Italy
- Dipartimento
di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Peter H. M. Budzelaar
- Dipartimento
di Scienze Chimiche, Università di
Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Roberta Cipullo
- Dipartimento
di Scienze Chimiche, Università di
Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Cristiano Zuccaccia
- Dipartimento
di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Alceo Macchioni
- Dipartimento
di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Vincenzo Busico
- Dipartimento
di Scienze Chimiche, Università di
Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Christian Ehm
- Dipartimento
di Scienze Chimiche, Università di
Napoli Federico II, Via Cintia, 80126 Napoli, Italy
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Zaccaria F, Sian L, Zuccaccia C, Macchioni A. Ion pairing in transition metal catalyzed olefin polymerization. ADVANCES IN ORGANOMETALLIC CHEMISTRY 2020. [DOI: 10.1016/bs.adomc.2019.08.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Zaccaria F, Zuccaccia C, Cipullo R, Budzelaar PHM, Macchioni A, Busico V, Ehm C. On the Nature of the Lewis Acidic Sites in “TMA‐Free” Phenol‐Modified Methylaluminoxane. Eur J Inorg Chem 2019. [DOI: 10.1002/ejic.201901035] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Francesco Zaccaria
- Dipartimento di Scienze Chimiche Università di Napoli Federico II Via Cintia 80126 Napoli Italy
- Dipartimento di Chimica Biologia e Biotecnologie and CIRCC Università di Perugia Via Elce di Sotto 8 06123 Perugia Italy
| | - Cristiano Zuccaccia
- Dipartimento di Chimica Biologia e Biotecnologie and CIRCC Università di Perugia Via Elce di Sotto 8 06123 Perugia Italy
| | - Roberta Cipullo
- Dipartimento di Scienze Chimiche Università di Napoli Federico II Via Cintia 80126 Napoli Italy
| | - Peter H. M. Budzelaar
- Dipartimento di Scienze Chimiche Università di Napoli Federico II Via Cintia 80126 Napoli Italy
| | - Alceo Macchioni
- Dipartimento di Chimica Biologia e Biotecnologie and CIRCC Università di Perugia Via Elce di Sotto 8 06123 Perugia Italy
| | - Vincenzo Busico
- Dipartimento di Scienze Chimiche Università di Napoli Federico II Via Cintia 80126 Napoli Italy
| | - Christian Ehm
- Dipartimento di Scienze Chimiche Università di Napoli Federico II Via Cintia 80126 Napoli Italy
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Zaccaria F, Zuccaccia C, Cipullo R, Budzelaar PHM, Macchioni A, Busico V, Ehm C. BHT-Modified MAO: Cage Size Estimation, Chemical Counting of Strongly Acidic Al Sites, and Activation of a Ti-Phosphinimide Precatalyst. ACS Catal 2019. [DOI: 10.1021/acscatal.9b00076] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Francesco Zaccaria
- Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Via Cintia, 80126 Napoli, Italy
- Dipartimento di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Cristiano Zuccaccia
- Dipartimento di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Roberta Cipullo
- Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Peter H. M. Budzelaar
- Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Alceo Macchioni
- Dipartimento di Chimica, Biologia e Biotecnologie and CIRCC, Università di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | - Vincenzo Busico
- Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Via Cintia, 80126 Napoli, Italy
| | - Christian Ehm
- Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Via Cintia, 80126 Napoli, Italy
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Linnolahti M, Collins S. Formation, Structure, and Composition of Methylaluminoxane. Chemphyschem 2017; 18:3369-3374. [PMID: 28857416 DOI: 10.1002/cphc.201700827] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 08/31/2017] [Indexed: 11/12/2022]
Abstract
The structurally ill-characterized methylaluminoxane (MAO) is the activator of choice in olefin polymerization catalysis. We have carried out large scale and systematic quantum chemical calculations to simulate the thermodynamics of its formation by controlled hydrolysis of trimethylaluminum (TMA), extending the studies up to 25 Al atoms, and thus, to the real size domain of MAO. In agreement with previous postulates on its structure, MAO is shown to favor cage-like structures, which commonly contain associated TMA, regardless of size or shape. The sites containing associated TMA are reactive, and explain the function of MAO as a catalyst activator. The compositions of MAOs show overall agreement with experiments, and exhibit structural transitions from chains to rings to sheets to eventually cages as a function of size. The most stable cage structure is obtained for a composition of (MeAlO)16 (Me3 Al)6 , which is in precise agreement with mass spectrometric studies of corresponding anions, and adapts a tubular molecular structure with a molecular weight of 1360 g mol-1 . Our mass spectrometric measurements enable detection of both major and minor anion species.
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Affiliation(s)
- Mikko Linnolahti
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, FI-80101, Joensuu, Finland
| | - Scott Collins
- Department of Chemistry, University of Victoria, 3800 Finnerty Rd., Victoria, BC, Canada
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Trefz TK, Henderson MA, Linnolahti M, Collins S, McIndoe JS. Mass spectrometric characterization of methylaluminoxane-activated metallocene complexes. Chemistry 2014; 21:2980-91. [PMID: 25556910 DOI: 10.1002/chem.201405319] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Indexed: 11/11/2022]
Abstract
Electrospray-ionization mass spectrometric studies of poly(methylaluminoxane) (MAO) in the presence of [Cp2 ZrMe2 ], [Cp2 ZrMe(Cl)], and [Cp2 ZrCl2 ] in fluorobenzene (PhF) solution are reported. The results demonstrate that alkylation and ionization are separate events that occur at competitive rates in a polar solvent. Furthermore, there are significant differences in ion-pair speciation that result from the use of metallocene dichloride complexes in comparison to alkylated precursors at otherwise identical Al/Zr ratios. Finally, the counter anions that form are dependent on the choice of precursor and Al/Zr ratio; halogenated aluminoxane anions [(MeAlO)x (Me3 Al)y-z (Me2 AlCl)z Me](-) (z=1, 2, 3…︁) are observed using metal chloride complexes and under some conditions may predominate over their non-halogenated precursors [(MeAlO)x (Me3 Al)y Me](-) . Specifically, this halogenation process appears selective for the anions that form in comparison to the neutral components of MAO. Only at very high Al/Zr ratios is the same "native" anion distribution observed when using [Cp2 ZrCl2 ] when compared with [Cp2 ZrMe2 ]. Together, the results suggest that the need for a large excess of MAO when using metallocene dichloride complexes is a reflection of competitive alkylation vs. ionization, the persistence of unreactive, homodinuclear ion pairs in the case of [Cp2 ZrCl2 ], as well as a change in ion pairing resulting from modification of the anions formed at lower Al/Zr ratios. Models for neutral precursors and anions are examined computationally.
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Affiliation(s)
- Tyler K Trefz
- Department of Chemistry, University of Victoria, P.O. Box 3065 Victoria, BC V8W3V6 (Canada)
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Hirvi JT, Bochmann M, Severn JR, Linnolahti M. Formation of octameric methylaluminoxanes by hydrolysis of trimethylaluminum and the mechanisms of catalyst activation in single-site α-olefin polymerization catalysis. Chemphyschem 2014; 15:2732-42. [PMID: 24930450 DOI: 10.1002/cphc.201402298] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Indexed: 11/10/2022]
Abstract
Hydrolysis of trimethylaluminum (TMA) leads to the formation of methylaluminoxanes (MAO) of general formula (MeAlO)n (AlMe3)m. The thermodynamically favored pathway of MAO formation is followed up to n=8, showing the major impact of associated TMA on the structural characteristics of the MAOs. The MAOs bind up to five TMA molecules, thereby inducing transition from cages into rings and sheets. Zirconocene catalyst activation studies using model MAO co-catalysts show the decisive role of the associated TMA in forming the catalytically active sites. Catalyst activation can take place either by Lewis-acidic abstraction of an alkyl or halide ligand from the precatalyst or by reaction of the precatalyst with an MAO-derived AlMe2(+) cation. Thermodynamics suggest that activation through AlMe2(+) transfer is the dominant mechanism because sites that are able to release AlMe2(+) are more abundant than Lewis-acidic sites. The model catalyst system is demonstrated to polymerize ethene.
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Affiliation(s)
- Janne T Hirvi
- Department of Chemistry, University of Eastern Finland, Joensuu Campus, 80101 Joensuu (Finland)
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Linnolahti M, Laine A, Pakkanen TA. Screening the thermodynamics of trimethylaluminum-hydrolysis products and their co-catalytic performance in olefin-polymerization catalysis. Chemistry 2013; 19:7133-42. [PMID: 23576459 DOI: 10.1002/chem.201204450] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Indexed: 11/10/2022]
Abstract
Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)n(AlMe3 )m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe3 molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co-catalytic activity in olefin-polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.
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Affiliation(s)
- Mikko Linnolahti
- Department of Chemistry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland.
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