Cyclic Biarylphosphine Ligands for Faster Low-Temperature Coupling
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Solution Overview
Problem
Existing palladium-catalyzed cross-coupling reactions, particularly Buchwald-Hartwig couplings, require long reaction times and high temperatures when using N-heterocyclic aryl halides, leading to undesired side reactions and reduced yields.
Innovation Solution
The use of cyclic biarylphosphines containing a phosphorus atom and a silicon atom in the heterocyclic ring as ligands in palladium complexes, enabling efficient carbon-heteroatom bond formation at lower temperatures and shorter reaction times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional phosphine ligands are used in palladium-catalyzed Buchwald-Hartwig couplings with N-heterocyclic aryl halides, then the carbon-heteroatom bond formation can proceed, but the reaction requires long reaction times and high temperatures, leading to undesired side reactions and reduced yields
Solution Approach 1:
The patent modifies the ligand structure by incorporating a silicon atom into the heterocyclic ring of the biarylphosphine ligand. This structural parameter change creates a cyclic biarylphosphine with enhanced electronic and steric properties that accelerate the catalytic cycle, enabling high-yield couplings at lower temperatures and shorter times without compromising product formation efficiency
2Speed
If high temperature is applied to accelerate the coupling reaction, then the reaction rate increases, but undesired side reactions occur and yields are reduced
Solution Approach 1:
By changing the ligand's structural parameters to include a silicon-containing heterocyclic ring, the catalyst achieves high activity at lower temperatures. The silicon atom's electropositive character and specific bonding geometry modify the palladium center's reactivity, allowing efficient coupling at 60-80°C rather than requiring 100-120°C, thus preventing side reactions while maintaining fast reaction rates
3Quantity of substance
If long reaction times are used to achieve complete conversion, then more starting material is converted, but productivity decreases and side reactions increase
Solution Approach 1:
The ligand is pre-designed with optimal electronic and steric properties through the incorporation of the silicon-containing heterocyclic ring structure. This preliminary structural optimization ensures that the palladium catalyst enters the catalytic cycle with high activity from the start, achieving rapid initial rates that drive complete conversion within short times without requiring prolonged reaction conditions that would reduce productivity
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 cyclic biarylphosphines facilitate high-yield carbon-heteroatom bond formation in palladium-catalyzed couplings, such as Buchwald-Hartwig couplings, even with N-heterocyclic aryl halides, by reducing reaction times and temperatures.
Implementation Method 1
The use of cyclic biarylphosphines containing a phosphorus atom and a silicon atom in the heterocyclic ring as ligands in palladium complexes, enabling efficient carbon-heteroatom bond formation at lower temperatures and shorter reaction times
Data Source
AI summary
The present invention relates to a phosphine of formula (1) wherein: - Q is SiR3R4, GeR3R4, SnR3R4, AsR3 or Se; - m is 0, 1, 2 or 3; - n is 0, 1, 2 or 3, provided that m + n ≥ 1; - the R groups are independently of one another a hydrogen atom or a C1-4 alkyl; or two R groups bonded to the same carbon atom form a 4- to 7-membered ring together with that carbon atom; or, provided that m + n ≥ 2, two R groups bonded to different carbon atoms form a 4- to 7-membered ring together with those carbon atoms; - Ar1 is an aryl; - Ar2 is an aryl; - R3 and R4 are independently of one another a C1-4 alkyl, a C5-7 cycloalkyl or an aryl; or R3 and R4 together with the Si, Ge or Sn atom form a 4- to 7-membered ring.