{"title":"A cooperative model for metallocene catalyst activation by methylaluminoxane†","authors":"Scott Collins and Mikko Linnolahti","doi":"10.1039/D4DT03124E","DOIUrl":null,"url":null,"abstract":"<p >Activation of rac-Me<small><sub>2</sub></small>Si(η<small><sup>5</sup></small>-Ind)<small><sub>2</sub></small>ZrMe<small><sub>2</sub></small> (SBIZrMe<small><sub>2</sub></small>) and sheet models for MAO, (MeAlO)<small><sub>6</sub></small>(Me<small><sub>3</sub></small>Al)<small><sub>4</sub></small> (6,4), (MeAlO)<small><sub>7</sub></small>(Me<small><sub>3</sub></small>Al)<small><sub>5</sub></small> (7,5), and (MeAlO)<small><sub>26</sub></small>(Me<small><sub>3</sub></small>Al)<small><sub>9</sub></small> (26,9) was studied <em>via</em> DFT. These activators can reversibly form an outer-sphere ion-pair (OSIP) [SBIZrMe<small><sub>2</sub></small>AlMe<small><sub>2</sub></small>] [(MeAlO)<small><sub><em>n</em></sub></small>(Me<small><sub>3</sub></small>Al)<small><sub><em>m</em></sub></small>Me] <strong>3</strong> ([<em>n</em>,<em>m</em>]<small><sup>−</sup></small> = [7,4]<small><sup>−</sup></small>and [26,8]<small><sup>−</sup></small>) or a contact ion-pair (CIP) SBIZrMe-μ-Me-6,4 (<strong>2b</strong>) from SBIZrMe<small><sub>2</sub></small>. Dissociation of Me<small><sub>3</sub></small>Al from <strong>3</strong> to form CIP SBIZrMe-μ-Me-<em>n</em>,<em>m</em> (<strong>2</strong>) is generally unfavourable but reversible in toluene continuum. Propene insertion involving CIP <strong>2</strong> features uniformly high barriers of 90–100 kJ mol<small><sup>−1</sup></small>, which are much higher than those experimentally observed for MAO-activated catalysts, though the calculated barriers do track with the coordinating ability of the MAO-based anion, as also suggested by the position of the Me<small><sub>3</sub></small>Al-binding equilibria. The binding of the neutral sheet 6,4 to anion [7,4]<small><sup>−</sup></small> leads to a hybrid anion [13,8]<small><sup>−</sup></small>. The barrier to propene insertion involving CIP SBIZrMe-μ-Me-13,8 (<strong>2e</strong>) is lower than 60 kJ mol<small><sup>−1</sup></small>. Formation of [SBIZrMe<small><sub>2</sub></small>AlMe<small><sub>2</sub></small>][13,8] (<strong>3e</strong>) from SBIZrMe<small><sub>2</sub></small>, 7,5 and 6,4 is favorable, though dissociation into <strong>2e</strong> and ½ Al<small><sub>2</sub></small>Me<small><sub>6</sub></small> is not. Simulations of catalyst speciation <em>vs.</em> [Al] at constant [Zr] indicate that the formation of species such as <strong>2e</strong> or <strong>3e</strong> from two components of MAO explains the high activity observed for MAO-activated metallocene complexes at sufficiently high Al : Zr ratios. Dedicated to Walter Kaminsky (1941–2024).</p>","PeriodicalId":71,"journal":{"name":"Dalton Transactions","volume":" 6","pages":" 2331-2339"},"PeriodicalIF":3.5000,"publicationDate":"2024-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://pubs.rsc.org/en/content/articlepdf/2025/dt/d4dt03124e?page=search","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Dalton Transactions","FirstCategoryId":"92","ListUrlMain":"https://pubs.rsc.org/en/content/articlelanding/2025/dt/d4dt03124e","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, INORGANIC & NUCLEAR","Score":null,"Total":0}
引用次数: 0
Abstract
Activation of rac-Me2Si(η5-Ind)2ZrMe2 (SBIZrMe2) and sheet models for MAO, (MeAlO)6(Me3Al)4 (6,4), (MeAlO)7(Me3Al)5 (7,5), and (MeAlO)26(Me3Al)9 (26,9) was studied via DFT. These activators can reversibly form an outer-sphere ion-pair (OSIP) [SBIZrMe2AlMe2] [(MeAlO)n(Me3Al)mMe] 3 ([n,m]− = [7,4]−and [26,8]−) or a contact ion-pair (CIP) SBIZrMe-μ-Me-6,4 (2b) from SBIZrMe2. Dissociation of Me3Al from 3 to form CIP SBIZrMe-μ-Me-n,m (2) is generally unfavourable but reversible in toluene continuum. Propene insertion involving CIP 2 features uniformly high barriers of 90–100 kJ mol−1, which are much higher than those experimentally observed for MAO-activated catalysts, though the calculated barriers do track with the coordinating ability of the MAO-based anion, as also suggested by the position of the Me3Al-binding equilibria. The binding of the neutral sheet 6,4 to anion [7,4]− leads to a hybrid anion [13,8]−. The barrier to propene insertion involving CIP SBIZrMe-μ-Me-13,8 (2e) is lower than 60 kJ mol−1. Formation of [SBIZrMe2AlMe2][13,8] (3e) from SBIZrMe2, 7,5 and 6,4 is favorable, though dissociation into 2e and ½ Al2Me6 is not. Simulations of catalyst speciation vs. [Al] at constant [Zr] indicate that the formation of species such as 2e or 3e from two components of MAO explains the high activity observed for MAO-activated metallocene complexes at sufficiently high Al : Zr ratios. Dedicated to Walter Kaminsky (1941–2024).
期刊介绍:
Dalton Transactions is a journal for all areas of inorganic chemistry, which encompasses the organometallic, bioinorganic and materials chemistry of the elements, with applications including synthesis, catalysis, energy conversion/storage, electrical devices and medicine. Dalton Transactions welcomes high-quality, original submissions in all of these areas and more, where the advancement of knowledge in inorganic chemistry is significant.