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1,2‐Functionalized Imidazoles as Palladium Ligands: An Efficient and Robust Catalytic System for the Fluorine‐Free Hiyama Reaction
Author(s) -
Martínez Regina,
Pastor Isidro M.,
Yus Miguel
Publication year - 2014
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201301439
Subject(s) - chemistry , catalysis , palladium , imidazole , reagent , aryl , electrophile , ligand (biochemistry) , combinatorial chemistry , coupling reaction , fluorine , organic chemistry , polymer chemistry , biochemistry , alkyl , receptor
A variety of hydroxy‐ and amino‐functionalized imidazoles were prepared from 1‐methyl‐ and 1‐(diethoxymethyl)imidazole by means of isoprene‐mediated lithiation followed by reaction with an electrophile. These compounds in combination with palladium acetate were screened as catalyst systems for the Hiyama reaction under fluorine‐free conditions using microwave irradiation. The systematic study of the catalytic system showed 1‐methyl‐2‐aminoalkylimidazole derivative L1 to be the best ligand, which was employed under solvent‐free conditions with a 1:2 Pd/ligand ratio and TBAB (20 mol‐%) as additive. The study has revealed an interaction between the Pd/ligand ratio and the amount of TBAB. The established catalytic system presented a certain degree of robustness, and it has been successfully employed in the coupling of a range of aryl bromides and chlorides with different aryl siloxanes. Furthermore, both reagents were employed in an equimolecular amount, without an excess of organosilane.