Multidentate Ligand Blocking for Alkyne Metathesis
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Solution Overview
Problem
Current catalysts for alkyne metathesis face challenges with undesired alkyne polymerization and lack of tunability, limiting their selectivity and activity, particularly due to interference from small molecules like 2-butyne, and existing ligands like silsesquioxane lack structural flexibility for studying structure-activity relationships.
Innovation Solution
Development of multidentate organic ligands that block one substrate-binding site of the metal center, incorporating customizable electron-withdrawing substituents to enhance metathesis activity and functional group tolerance, and using N-quaternized multidentate ligands to bind to metals, such as tris(arylmethyl)ammonium-coordinated Mo(VI) propylidyne catalysts, which show robustness and high catalytic activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional alkoxide/phenoxide/siloxide/amide ligands are used in metal-alkylidyne catalysts, then the catalysts can perform alkyne metathesis, but coordination of small molecules like 2-butyne leads to undesired alkyne polymerization and nonproductive reaction pathways
Solution Approach 1:
The patent extracts the problematic coordination sites from the catalyst by using a multidentate ligand that occupies specific positions on the metal center, thereby removing the ability of small molecules like 2-butyne to coordinate and cause polymerization, while preserving the metathesis activity through the retained open site
Solution Approach 2:
The multidentate ligand performs multiple functions simultaneously: it provides structural support to the catalyst, blocks coordination sites to prevent polymerization, and maintains the metal-alkylidyne bond necessary for metathesis activity, thereby achieving both productivity and selectivity
2Object-generated harmful factors
If siloxane-based ligands like POSS and silica are used to prevent alkyne polymerization, then polymerization is overcome, but the catalyst structure lacks tunability making it difficult to study structure-activity relationships
Solution Approach 1:
The ligand is segmented into multiple coordination sites that can be independently modified with different substituents (R1, R2, R3, R4, R5, R6), allowing systematic variation of steric and electronic properties to study structure-activity relationships while maintaining the polymerization-blocking function
Solution Approach 2:
Different regions of the ligand molecule have different functions: the core multidentate structure blocks polymerization sites, while the peripheral substituents (R groups) provide tunable electronic and steric properties that can be optimized for specific metathesis reactions without affecting the anti-polymerization function
3Reliability
If catalysts are designed to block substrate-binding sites to prevent polymerization, then selectivity improves, but catalytic activity may be reduced due to fewer available sites
Solution Approach 1:
The multidentate ligand partially occupies the metal center coordination sphere by blocking only the sites susceptible to polymerization, while leaving one open site available for productive metathesis substrate binding, achieving selectivity without sacrificing activity
Solution Approach 2:
The multidentate ligand acts as an intermediary that mediates between the metal center and substrates: it blocks harmful small molecule coordination while facilitating productive alkyne metathesis through the remaining open site, thereby reconciling selectivity and activity requirements
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 new catalysts exhibit strong resistance to small alkyne polymerization, significantly enhanced catalytic activity, and improved functional group tolerance, enabling efficient metathesis of challenging substrates with high stability and selectivity.
Implementation Method 1
Coordination of small molecules, in particular 2-butyne (a common metathesis byproduct), to the hexavalent Mo-alkylidyne complex
Implementation Method 2
N-quaternized multidentate ligands, capable of binding to metals, such as tris(arylmethyl)ammonium-coordinated Mo(VI) propylidyne catalysts
Implementation Method 3
incorporating customizable electron-withdrawing substituents to enhance metathesis activity and functional group tolerance
Data Source
AI summary
The invention relates to highly active and selective catalysts for alkyne metathesis. In one aspect, the invention includes a multidentate organic ligand wherein one substrate-binding site of the metal center is blocked. In another aspect, the invention includes N-quaternized or silane-based multidentate organic ligands, capable of binding to metals. In yet another aspect, the invention includes N-quaternized or silane-based multidentate catalysts. The catalysts of the invention show high robustness, strong resistance to small alkyne polymerization and significantly enhanced catalytic activity compared to their corresponding non-quaternized or non-silane-based multidentate catalyst analogs.