Air-Stable Pd(II) Precatalysts for Cross-Coupling
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Solution Overview
Problem
There is a need for novel transition metal precatalysts that can be efficiently converted to active catalytic species, as existing methods often require expensive ligands and result in inefficient use of Pd(0) sources, and there is a lack of air- and moisture-stable precatalysts suitable for cross-coupling reactions.
Innovation Solution
Development of novel transition-metal precatalysts, specifically dimeric and monomeric precatalysts of formulas (I) and (II), which are air- and moisture-stable, and can be efficiently converted to active Pd(0) species using a method involving a mixed alkaline/transition metal salt and a specific ligand in an organic solvent, facilitating cross-coupling reactions without forming significant amounts of inactive Pd(I) dimers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If specialized ligands are used in cross-coupling reactions, then catalytic activity is improved, but cost increases significantly
Solution Approach 1:
The patent uses inexpensive, readily available ligands such as PPh3 (triphenylphosphine) and PCy3 (tricyclohexylphosphine) instead of expensive specialized ligands. These common phosphine ligands enable the precatalysts to achieve good catalytic activity at low cost, making the cross-coupling reactions economically feasible.
Solution Approach 2:
The patent changes the oxidation state parameter of the precatalyst from Pd(0) to Pd(II), creating air-stable precatalysts that can be handled and stored more easily. This parameter change allows the use of common ligands while maintaining catalytic effectiveness through the activation mechanism.
2Productivity
If excess ligand is added to generate active Pd(0) species, then catalytic activity is improved, but economic feasibility deteriorates
Solution Approach 1:
The patent prepares Pd(II) precatalysts in advance with stoichiometric amounts of ligand (1:1 Pd:ligand ratio). These precatalysts are air-stable and can be stored before use. During the reaction, they activate in situ to generate the active Pd(0) species, eliminating the need to add excess ligand during the reaction and reducing overall ligand consumption.
Solution Approach 2:
The Pd(II) precatalysts self-activate during the cross-coupling reaction conditions to generate the active Pd(0) catalytic species. The precatalyst contains all necessary components (Pd and ligand) in the correct ratio, and the activation process occurs automatically under reaction conditions without requiring additional ligand addition.
3Productivity
If Pd(0) source is used directly, then catalytic activity is achieved, but air-stability is lost
Solution Approach 1:
The patent changes the oxidation state parameter of the palladium complex from Pd(0) to Pd(II). This parameter change confers air-stability to the precatalyst, allowing it to be handled, stored, and manipulated in air without degradation. The Pd(II) precatalyst activates to Pd(0) in situ under the reducing conditions of the cross-coupling reaction, maintaining catalytic activity while improving stability.
4Productivity
If conventional precatalysts are used, then cross-coupling reactions can proceed, but formation of inactive Pd(I) dimers increases
Solution Approach 1:
The patent changes the initial oxidation state parameter to Pd(II) with a 1:1 Pd:ligand ratio. This parameter change prevents the formation of inactive Pd(I) dimers because the Pd(II) precatalyst activates directly to Pd(0) under the reaction conditions. The stoichiometric ligand coordination in the precatalyst also prevents premature dimerization, ensuring maximum catalytic 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
The new precatalysts demonstrate improved efficiency and stability, allowing for faster conversion to active Pd(0) species, reducing the formation of inactive Pd(I) dimers, and enhancing the performance in cross-coupling reactions such as Suzuki-Miyaura, Buchwald-Hartwig, and other bond-forming processes, with increased activity and compatibility with various substrates.
Implementation Method 1
The active species in catalysis, commonly monoligated Pd(0), is often generated through the addition of excess ligand to a Pd(0) source
Data Source
AI summary
The present invention provides novel transition-metal precatalysts that are useful in preparing active coupling catalysts. In certain embodiments, the precatalysts of the invention are air-stable and moisture-stable. The present invention further provides methods of making and using the precatalysts of the invention.