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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Palladium N(CH2CH2P(i)Pr2)2-dialkylamides: synthesis, structural characterization, and reactivity
Alexander N Marziale1, Eberhardt Herdtweck, Jörg Eppinger
1Technische Universität München, Department Chemie, Lichtenbergstrasse 4, D-85747 Garching b München, Germany.
Inorganic Chemistry
|March 14, 2009
Summary
New palladium(II) PNP pincer complexes were synthesized and deprotonated to form stable dialkylamides. These complexes exhibit high N-basicity and unique bonding, explained by DFT calculations.
Area of Science:
- Organometallic Chemistry
- Coordination Chemistry
- Catalysis
Background:
- Palladium PNP pincer complexes are versatile ligands in organometallic chemistry.
- Understanding the electronic and structural properties of palladium-nitrogen bonds is crucial for catalytic applications.
Purpose of the Study:
- To synthesize and characterize novel palladium(II) aminodiphosphine PNP pincer complexes.
- To investigate the stability, reactivity, and electronic properties of the resulting amido complexes.
- To elucidate the nature of the palladium-nitrogen bond through structural and computational methods.
Main Methods:
- Synthesis of palladium(II) PNP pincer complexes.
- Deprotonation reactions to form amido complexes.
- Oxidation and N-methylation reactions.
- Determination of N-H acidities (pKa).
- Single crystal X-ray diffraction for structural characterization.
- Density functional theory (DFT) calculations.
Main Results:
- Successfully prepared palladium(II) aminodiphosphine PNP pincer complexes [PdR(PNP(H))]PF(6).
- Synthesized stable dialkylamides [PdR(PNP)] via deprotonation, resistant to beta-H elimination.
- Obtained cationic amido complexes [PdL(PNP)]PF(6) and N-methylated products [PdCl(PNP(Me))]OTf.
- Determined N-H acidities for amino complexes (pKa = 24.2(1) and 23.2(1)).
- Structural characterization revealed pyramidal nitrogen atoms and provided insights into Pd-N bonding.
- DFT calculations supported the bonding model involving sigma-donation and pi-interactions.
Conclusions:
- The synthesized palladium amido complexes are stable and exhibit high N-basicity.
- The Pd-N(amido) bond is characterized by strong sigma-donation and repulsive pi-interactions.
- These findings provide a deeper understanding of palladium-nitrogen bonding in pincer complexes and their potential reactivity.
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