A cooperative model for metallocene catalyst activation by methylaluminoxane†

IF 3.5 3区 化学 Q2 CHEMISTRY, INORGANIC & NUCLEAR
Scott Collins and Mikko Linnolahti
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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).

Abstract Image

甲基铝氧烷活化茂金属催化剂的协同模型
用DFT研究了rac-Me2Si(η - 5- ind)2ZrMe2 (SBIZrMe2)的活化和MAO, (MeAlO)6(Me3Al)4 (6,4), (MeAlO)7(Me3Al)5(7,5)和(MeAlO)26(Me3Al)9(26,9)的片状模型。这些活化剂可以由SBIZrMe2可逆地形成外球离子对(OSIP) [SBIZrMe2AlMe2] [(MeAlO)n(Me3Al)mMe] 3 ([n,m]−=[7,4]−和[26,8]−)或接触离子对(CIP) SBIZrMe-μ- me -6,4 (2b)。Me3Al从3解离生成CIP SBIZrMe-μ-Me-n,m(2)通常是不利的,但在甲苯连续体中是可逆的。虽然从me3al结合平衡的角度来看,计算出的势垒确实与mao基阴离子的配位能力相符,但涉及CIP 2的丙烯插入具有均匀的高势垒90-100 kJ mol-1,远高于mao活化催化剂的实验结果。中性薄片6,4与阴离子[7,4]−结合形成杂化阴离子[13,8]−。CIP SBIZrMe-μ- me -13,8 (2e)对丙烯的插入屏障小于60 kJ mol-1。sbizrme2,7,5和6,4生成[SBIZrMe2AlMe2][13,8] (3e)是有利的,但解离成2e和½Al2Me6则不是。催化剂与[Al]在恒定[Zr]下形成的模拟表明,两种MAO组分形成的2e或3e等物质解释了在足够高的Al:Zr比下MAO活化的茂金属配合物的高活性。
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来源期刊
Dalton Transactions
Dalton Transactions 化学-无机化学与核化学
CiteScore
6.60
自引率
7.50%
发文量
1832
审稿时长
1.5 months
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.
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