1246472-35-4Relevant academic research and scientific papers
Cavity-shaped ligands: Calix[4]arene-based monophosphanes for fast Suzuki-Miyaura cross-coupling
Monnereau, Laure,Semeril, David,Matt, Dominique,Toupet, Loic
experimental part, p. 9237 - 9247 (2010/09/15)
Five conical calix[4]arenes that have a PPh2 group as the sole functional group anchored at their upper rim were assessed in palladiumcatalysed cross-coupling reactions of phenylboronic acid with aryl halides (dioxane, 100°C, NaH). With arylbromides, remarkably high activities were obtained with the catalytic systems remaining stable for several days. The performance of the ligands is comparable to a Buchwald-type triarylphosphane, namely, (2'-methyl[1,1'-biphenyl]-2-yl)diphenylphosphane, which in contrast to the calixarenyl phosphanes tested may display chelating behaviour in solution. With the fastest ligand, 5-diphenylphosphanyl-25,26,27,28-tetra(p-methoxy)benzyloxy- calix[4]arene (8), the reaction turnover frequency for the arylation of 4-bromotoluene was 321000 versus 214000 mol-(ArBr).mol(Pd)-1.h -1 for the reference ligand. The calixarene ligands were also efficient in Suzuki cross-coupling reactions with aryl chlorides. Thus, by using 1 mol% of [Pd(OAc)2] associated with one of the phosphanes, full conversion of the deactivated arenes 4-chloroanisole and 4-chlorotoluene was observed after 16 h. The high performance of the calixarenyl-phosphanes in Suzuki-Miyaura coupling of aryl bromides possibly relies on their ability to stabilise a monoligand [Pd0L(ArBr)] species through supramolecular binding of the Pd-bound arene inside the calixarene cavity.
