Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

Richards, Philip I, Lawson, Gavin T, Bickley, Jamie F, Robertson, Craig M ORCID: 0000-0002-4789-7607, Iggo, Jonathan A ORCID: 0000-0001-8070-1226 and Steiner, Alexander ORCID: 0000-0002-4315-6123 (2019) Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays INORGANIC CHEMISTRY, 58 (5). pp. 3355-3363. ISSN 0020-1669, 1520-510X

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Abstract

Trimethylaluminum finds widespread applications in chemical and materials synthesis, most prominently in its partially hydrolyzed form of methylalumoxane (MAO), which is used as a cocatalyst in the polymerization of olefins. This work investigates the sequential reactions of trimethylaluminum with hexaprotic phosphazenes (RNH) <inf>6</inf> P <inf>3</inf> N <inf>3</inf> (=XH <inf>6</inf> ) equipped with substituents R of varied steric bulk including tert-butyl (1H <inf>6</inf> ), cyclohexyl (2H <inf>6</inf> ), isopropyl (3H <inf>6</inf> ), isobutyl (4H <inf>6</inf> ), ethyl (5H <inf>6</inf> ), propyl (6H <inf>6</inf> ), methyl (7H <inf>6</inf> ), and benzyl (8H <inf>6</inf> ). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH <inf>n</inf> ] ^n-6 accommodate multinuclear arrays of [AlMe <inf>2</inf> ] ⁺ and [AlMe] ²⁺ . Reactions were monitored by ³¹ P NMR spectroscopy, and structures were determined by single-crystal X-ray diffraction. They included 1H <inf>4</inf> (AlMe <inf>2</inf> ) <inf>2</inf> , 1H <inf>3</inf> (AlMe <inf>2</inf> ) <inf>3</inf> , 2H <inf>3</inf> (AlMe <inf>2</inf> ) <inf>3</inf> , 3(AlMe <inf>2</inf> ) <inf>4</inf> AlMe, 4H(AlMe <inf>2</inf> ) <inf>5</inf> , 4(AlMe <inf>2</inf> ) <inf>6</inf> , {5H(AlMe <inf>2</inf> ) <inf>4</inf> } <inf>2</inf> AlMe, 5(AlMe <inf>2</inf> ) <inf>6</inf> , 6(AlMe <inf>2</inf> ) <inf>6</inf> , {7(AlMe <inf>2</inf> ) <inf>4</inf> AlMe} <inf>2</inf> , and 8(AlMe <inf>2</inf> ) <inf>6</inf> . The study shows that subtle variations of the steric properties of the R groups influence the reaction pathways, levels of aggregation, and fluxional behavior. While [AlMe <inf>2</inf> ] ⁺ is the primary product of the metalation, [AlMe] ²⁺ is utilized to alleviate overcrowding or to aid aggregation. At the later stages of metalation, [AlMe <inf>2</inf> ] ⁺ groups start to scramble around congested sites. The ligands proved to be very robust and extremely flexible, offering a unique platform to study complex multinuclear metal arrangements.

Item Type:	Article
Uncontrolled Keywords:	3402 Inorganic Chemistry, 34 Chemical Sciences
Depositing User:	Symplectic Admin
Date Deposited:	19 Feb 2019 10:24
Last Modified:	16 Jun 2026 05:21
DOI:	10.1021/acs.inorgchem.8b03448
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3033091
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