Catalytic Behaviour of Calixarenylphosphanes in Nickel-Catalysed Suzuki-Miyaura Cross-Coupling

Two upper-rim-functionalised calix[4] arenes, 5-diphenylphosphino- 25,26,27,28-tetra-benzyloxycalix[4] arene and 5-diphenylphosphino-25,26,27,28-tetra-(p-anisyl) methyloxy calix[4] arene, were investigated in the nickel-catalysed crosscoupling of phenylboronic acid with aryl bromides. The catalytic activities are higher than those observed for other triarylphosphanes, notably PPh3 and P(o-tolyl)(3) as well as the Buchwald-type ligand o-biph-PPh2 [TOFs up to 2600 mol(ArPh) mol(Ni)(-1) h(-1)], but the production of large amounts of dehalogenation product could not be avoided, thus strongly contrasting with the classical Pd-catalysed reaction. Good activities were also obtained with aryl chlorides, even at room temperature. The higher efficiency of 1 and 2 relative to that of the Buchwald ligand 3 probably arises from the ease with which these two calix-phosphanes may form appropriate monophosphine complexes before the oxidative addition step.