Heck, Suzuki and Kumada–Corriu cross-coupling reactions mediated by complexes based on the upper rim of diphosphinated calix[4]arenes

Abstract

Two bis-triarylphosphines [5,17-dibromo-11,23-bis(diphenylphosphino)-25,26,27,28-tetrapropoxycalix[4]arene ( 1) and 5,17-bis(diphenylphosphino)-25,26,27,28-tetrapropoxy-calix[4]arene ( 2)] were assessed in metal-catalysed cross-coupling reactions. Effective Heck couplings between aryl bromides and styrene were achieved when operating in DMF at 110 °C with 2 mol% of Pd(OAc) 2 in the presence of Cs 2CO 3; the highest TOF values (ca. 50) being observed with activated aryl bromides. The coupling reaction could be extended to aryl chlorides (conversions of ca. 20% within 24 h) with both ligands, provided the reaction was carried out with NaOAc in a DMF/water mixture. The two phosphines were also found to be efficient in Suzuki cross-coupling of aryl halides with phenyl boronic acid, the turnovers being somewhat lower than those observed in Heck couplings. In Kumada–Corriu cross-coupling of aryl halides with phenylmagnesium bromide, remarkable activities were reached in the presence of palladium or nickel. TONs up to 800 mol(converted PhCl)·mol(Ni) −1 were observed for the conversion of chlorobenzene into biphenyl. Unlike the mono-triaryl phosphine PPh 3, ligands 1 and 2 both promote palladium-catalysed Suzuki and Kumada–Corriu couplings involving chlorobenzene.