Metallocene Catalysts with Appended Lewis Acids
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Solution Overview
Problem
Zirconium metallocene catalysts require expensive alumoxane activators in large quantities, making them economically unviable, and hafnium metallocene catalysts are less effectively activated by alumoxane, necessitating the use of borane and borate activators.
Innovation Solution
Incorporating a Lewis acid covalently appended to the metallocene compounds, which can self-activate or require less external activator, reducing the need for expensive alumoxane and improving activation efficiency, especially for hafnium metallocene compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zirconium metallocene compounds are used with alumoxane activators, then catalytic activity is achieved, but substantial quantities of expensive alumoxane are required, making the process economically unviable
Solution Approach 1:
The patent combines the metallocene catalyst and alumoxane activator into a single pre-formed complex where the alumoxane is covalently bonded to the metallocene ligand framework. This merging eliminates the need for substantial quantities of separate alumoxane activator while maintaining catalytic activity, as the bonded alumoxane is already positioned and activated for catalyst function.
Solution Approach 2:
The alumoxane activation step is performed in advance during catalyst synthesis, creating a pre-activated complex. This preliminary action ensures the catalyst is ready for immediate use without requiring large amounts of additional alumoxane during the polymerization process, thereby reducing overall alumoxane consumption and cost.
2Reliability
If hafnium metallocene compounds are activated with alumoxane, then catalytic activity is achieved, but activation is much less effective compared to zirconium metallocene compounds
Solution Approach 1:
The patent modifies the local chemical environment around the hafnium center by incorporating specific ligand structures and alumoxane bonding configurations that are tailored to hafnium's electronic and steric properties. This localized optimization enables effective activation of hafnium metallocene compounds, which are otherwise difficult to activate with standard alumoxane protocols.
3Productivity
If large quantities of alumoxane are used to activate metallocene catalysts, then catalytic activity is sufficient, but engineering costs increase significantly
Solution Approach 1:
By merging the activator and catalyst into a single pre-formed complex, the patent eliminates the need to add large quantities of separate activator during polymerization. The covalently bonded alumoxane is already present in the correct stoichiometric ratio, reducing both material cost and processing complexity while maintaining high polymerization activity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the amount of activator needed, decreases engineering costs, and enhances the economic viability of metallocene catalysts by improving activation efficiency and polymerization processes.
Implementation Method 1
LA is a Lewis acid... Zirconium metallocene compounds frequently require exposure to an activator (i.e., a co-catalyst) in order to become catalytically active. The activator is believed to remove at least one of the non-haptically bonded ligands from the zirconium center to generate a catalytically active species with at least one open coordination site for bonding an olefin and/or a growing polymer chain.
Data Source
AI summary
This invention relates to metallocene compounds represented by the formula:catalyst systems comprising said metallocene compound and an activator or a reaction product of the metallocene compound with the at least one activator, and polymerization processes using such metallocene compounds and activators, where Cpa and Cpb are optionally-substituted cyclopentadienyl rings; A is bridging group; q is zero or 1; Q is O, O(CR3R4)m, (CR3R4)mO, or (CR3R4)m; m is 0 to 18; Z is (CR3R4)2; LA is a Lewis acid; M is a transition metal; X1 and X2 are independently R5 or OR5; R1 and R2 are independently selected from optionally-substituted hydrocarbyl groups; R3 and R4 are independently selected from the group consisting of H, halogen, and an optionally-substituted hydrocarbyl group; and R5 is alkyl, aryl, perfluoroalkyl, or perfluoroaryl.