1447768-82-2Relevant academic research and scientific papers
Phosphines with tethered electron-withdrawing olefins as ligands for efficient Pd-catalyzed aryl-alkyl coupling
Gioria, Estefania,Martinez-Ilarduya, Jesus M.,Garcia-Cuadrado, Domingo,Miguel, Jesus A.,Genov, Miroslav,Espinet, Pablo
, p. 4255 - 4261 (2013/09/02)
A group of phosphine/alkene ligands L = Ph2P(2-RC 6F4) (R = CH=CHMe, CH=CHPh, CH=CHCOPh) or Ph 2P(CH2)2CF=CF2 and their [PdCl 2L] complexes have been prepared. These phosphines are easy to prepare and fairly stable toward oxidation. Their palladium complexes feature chelated L structures with the double bond coordinated as the Z isomer, except for Ph2P(CH2)2CF=CF2, where the double bond is not coordinated and the complex is a dimer with Cl bridges. The ligands have been tested for their activity in the Negishi palladium-catalyzed aryl-alkyl coupling, where there is a competition of coupling and reduction products. Only the ligands forming chelated PdII complexes rise the coupling/reduction ratio to values 42/58 or higher. Of these, it is the ligand bearing the more electron-withdrawing substituent (R = CH=CHCOPh) that is the one producing remarkably high selectivity toward coupling: 90/10 under the usual Negishi conditions, and noticeably higher (97/3) if the proportion of ZnEt 2 in the reaction is lowered. These results fit well with the hypothesis that chelating phosphines with tethered electron-acceptor olefins improve the selectivity toward coupling products mostly because they reduce the activation barrier for C-C coupling, and not because they protect the complex from β-H elimination.
