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.

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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)<sub>6</sub>P<sub>3</sub>N<sub>3</sub> (=XH<sub>6</sub>) equipped with substituents R of varied steric bulk including tert-butyl (1H<sub>6</sub>), cyclohexyl (2H<sub>6</sub>), isopropyl (3H<sub>6</sub>), isobutyl (4H<sub>6</sub>), ethyl (5H<sub>6</sub>), propyl (6H<sub>6</sub>), methyl (7H<sub>6</sub>), and benzyl (8H<sub>6</sub>). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH <sub>n</sub>] <sup>n-6</sup> accommodate multinuclear arrays of [AlMe<sub>2</sub>]<sup>+</sup> and [AlMe]<sup>2+</sup>. Reactions were monitored by <sup>31</sup>P NMR spectroscopy, and structures were determined by single-crystal X-ray diffraction. They included 1H<sub>4</sub>(AlMe<sub>2</sub>)<sub>2</sub>, 1H<sub>3</sub>(AlMe<sub>2</sub>)<sub>3</sub>, 2H<sub>3</sub>(AlMe<sub>2</sub>)<sub>3</sub>, 3(AlMe<sub>2</sub>)<sub>4</sub>AlMe, 4H(AlMe<sub>2</sub>)<sub>5</sub>, 4(AlMe<sub>2</sub>)<sub>6</sub>, {5H(AlMe<sub>2</sub>)<sub>4</sub>}<sub>2</sub>AlMe, 5(AlMe<sub>2</sub>)<sub>6</sub>, 6(AlMe<sub>2</sub>)<sub>6</sub>, {7(AlMe<sub>2</sub>)<sub>4</sub>AlMe}<sub>2</sub>, and 8(AlMe<sub>2</sub>)<sub>6</sub>. 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<sub>2</sub>]<sup>+</sup> is the primary product of the metalation, [AlMe]<sup>2+</sup> is utilized to alleviate overcrowding or to aid aggregation. At the later stages of metalation, [AlMe<sub>2</sub>]<sup>+</sup> 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
Depositing User: Symplectic Admin
Date Deposited: 19 Feb 2019 10:24
Last Modified: 19 Jan 2023 01:02
DOI: 10.1021/acs.inorgchem.8b03448
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3033091