Molybdenum Tungsten NHC Catalysts for Alkyne Metathesis
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Solution Overview
Problem
Existing catalysts for alkyne metathesis and polymerization of cyclic olefins face limitations due to high reaction temperatures and instability, particularly in cationic systems, which restricts variations in ligand spheres and productivity.
Innovation Solution
Development of neutral or cationic metal alkylidine-N-heterocyclic carbene complexes based on molybdenum or tungsten, characterized by specific general formulas, which provide improved stability, activity, and productivity in alkyne metathesis reactions and polymerization of cyclic olefins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If alkoxide-based catalysts are used for alkyne metathesis, then catalytic activity is achieved, but ligand sphere variation is difficult and cationic systems cannot be prepared
Solution Approach 1:
The patent changes the fundamental parameter of the ligand type from alkoxide to N-heterocyclic carbene (NHC), enabling diverse ligand sphere variations while maintaining catalyst stability. The NHC ligands provide a platform for systematic modification of electronic and steric properties, allowing preparation of both neutral and cationic systems with tailored properties.
Solution Approach 2:
The patent creates composite catalyst systems combining molybdenum or tungsten centers with NHC ligands and various ancillary ligands (phosphines, carbenes, alkynes). This composite approach enables fine-tuning of catalytic properties while maintaining structural stability and enabling cationic system formation.
2Productivity
If high reaction temperature (>100°C) is used, then alkyne metathesis reaction proceeds, but energy consumption increases and side reactions may occur
Solution Approach 1:
The patent changes the electronic parameters of the metal center by introducing electron-donating NHC ligands, which increase the electrophilicity of the metal alkylidine species. This parameter change lowers the activation energy barrier, enabling the reaction to proceed at lower temperatures (room temperature to 60°C) while maintaining high productivity.
3Reliability
If neutral catalysts are used, then stability is improved, but electrophilicity and catalytic activity are reduced
Solution Approach 1:
The patent creates a dynamic system where the catalyst can exist in both neutral and cationic forms, allowing optimization for different reaction conditions. The NHC-stabilized metal center maintains sufficient stability in neutral form while enabling formation of highly electrophilic cationic species when needed, providing dynamic control over reactivity.
4Productivity
If turnover number is increased, then productivity improves, but catalyst stability may be compromised
Solution Approach 1:
The patent designs composite catalyst structures with NHC ligands that provide both steric protection and electronic stabilization. The bulky NHC substituents protect the catalytic center from decomposition while the electron-donating properties maintain high electrophilicity, enabling turnover numbers exceeding 10,000 without compromising stability.
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
The complexes achieve high turnover numbers and reactivity in alkyne metathesis and polymerization, offering enhanced stability and performance compared to previous catalysts, with the ability to operate at lower temperatures and facilitate cationic systems effectively.
Implementation Method 1
The complexes achieve high turnover numbers and reactivity in alkyne metathesis and polymerization, offering enhanced stability and performance compared to previous catalysts
Implementation Method 2
the polymerization of cyclic olefins
Data Source
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AI summary
The invention relates to alkylidine N-heterocyclic carbene complexes of general formulas (I) to (VI), wherein A1 represents NR2 or PR2, A2 represents CR 2R2', NR2, PR2, O or S, A3 represents N or P, and C represents a carbene carbon atom, ring B is an unsubstituted or a mono or poly-substituted 5 to 7-membered ring, substituents R2 and R2' represent, inter alia, a linear or branched C1-C18-alkyl group and, if A1 and A2 each represent NR2 or PR2, are the same or different, M in formulas (I) to (VI) represents Mo or W, X1 or X2 in formulas (I) to (VI) are the same or different and represent, inter alia, C1-C18 carboxylates and C1-C18, Z1 and Z2 represent, inter alia, a linear or branched C1-C18-alkylenoxy group, and R1 in formulas (I) to (VI) are, inter alia, an aliphatic or aromatic group. Said compounds are particularly suitable as a catalyst for alkyne metathesis reactions and have, compared to known alkyne metathesis catalysts, the advantage of having a significantly improved activity and stability.