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PEPPSI‐Effect on Suzuki–Miyaura Reactions Using 4,5‐Dicyano‐1,3‐dimesitylimidazol‐2‐ylidene‐Palladium Complexes: A Comparison between trans ‐Ligands
Author(s) -
Baier Heiko,
Kelling Alexandra,
Holdt HansJürgen
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201500010
Subject(s) - imes , chemistry , palladium , carbene , phenylboronic acid , medicinal chemistry , ligand (biochemistry) , pyridine , aryl , catalysis , stereochemistry , organic chemistry , alkyl , receptor , biochemistry
The PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12 – 15 with the structure [PdCl 2 {(CN) 2 IMes}(3‐R‐py)] ( 12 : R = H; 13 : R = Cl; 14 : R = Br; 15 : R = CN) bearing the maleonitrile‐based N‐heterocyclic carbene (NHC) (CN) 2 IMes ({(CN) 2 IMes}: 4,5‐dicyano‐1,3‐dimesitylimidazol‐2‐ylidene) were prepared. Solid state structures of 14 and 15 were obtained. Complexes 14 and 15 adopt a slightly distorted square‐planar coordination geometry in the solid state with the substituted pyridine ligand trans to the NHC. Catalytic activities of precatalysts 12 – 15 were studied and subsequently compared to complexes [PdCl 2 {(CN) 2 IMes}(PPh 3 )] ( 4 ) and [PdCl(dmba){(CN) 2 IMes}] ( 5 ) recently reported by our group in the Suzuki–Miyaura reaction of various aryl halides and phenylboronic acid. Reactions using previously reported [PdCl 2 (IMes)(py)] (IMes: 1,3‐dimesitylimidazol‐2‐ylidene) ( 1 ) were also carried out and their results contrasted to those involving 12 – 15 , 4 and 5 . Differences in initiation rates and the catalytically active species related to the seven complexes in regards to the “throw away ligand” were investigated. Poisoning experiments with mercury show that palladium nanoparticles are responsible for the catalytic activity.