Title

Transition Metal‐Catalyzed and MAO‐Assisted Olefin Polymerization. Cyclic Isomers of Sinn’s Dimer Are Excellent Ligands in Iron Complexes and Great Methylating Reagents

Abstract

Methylaluminoxane (MAO) is the most commonly used co‐catalyst for transition metalcatalyzed olefin polymerization, but the structures of MAO species and their catalytic functions remain topics of intensive study. We are interested in MAO‐assisted polymerization with catalysts L(R2)FeCl2 (L = tridentate pyridine‐2,6‐diyldimethanimine; imine‐R = Me, Ph). It is our hypothesis that the MAO species is not merely enabling Fe−Me bond formation but functions as an integral part of the active catalyst, a MAO adduct of the Fe‐precatalyst [L(R2)FeCl]+. In this paper, we explored the possible structures of acyclic and cyclic MAO species and their complexation with pre‐catalysts [L(R2)FeCl]+ using quantum chemical approaches (MP2 and DFT). We report absolute and relative oxophilicities associated with the Fe←O(MAO) adduct formation and provide compelling evidence that oxygen of an acyclic MAO species (i.e., O(AlMe2)2, 4) cannot compete with the O‐donor in cyclic MAO species (i.e., (MeAlO)2, 7; MeAl(OAlMe2)2, cyclic 5). Significantly, our work demonstrates that intramolecular O→Al dative bonding results in cyclic isomers of MAO species (i.e., cyclic 5) with high oxophilicities. The stabilities of the [L(R2)FeClax(MAO)eq]+ species demonstrate that 5 provides for the ligating benefits of the cyclic MAO species 4 without the thermodynamically costly elimination of TMA. Mechanistic implications are discussed for the involvement of such Fe−O−Al bridged catalyst in olefin polymerization.

Department(s)

Chemistry

Comments

This work was supported by the Missouri University of Science and Technology, by a grant from the Petroleum Research Fund of the American Chemical Society (#53415-ND4), and, in part, by a grant from the National Science Foundation #1665487.

Keywords and Phrases

Iron Pre‐catalyst; Methylaluminoxane (MAO); Molecular Modeling; Olefin Polymerization; Oxophilicity; Pre‐catalyst MAO Adduct

International Standard Serial Number (ISSN)

2073-4344

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2022 The Authors, All rights reserved.

Creative Commons Licensing

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Publication Date

01 Mar 2022

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