Air-Stable and Catalytically Active Phosphinous Acid Transition-Metal Complexes

作者：Kurscheid Boris; Belkoura Lhoussaine; Hoge Berthold^*

来源：Organometallics, 2012, 31(4): 1329-1334.

DOI：10.1021/om200697u

Secondary phosphane oxides R2P(O)H are most frequently used as preligands for phosphinous acid R2POH (R = alkyl, aryl) transition-metal complexes, which are very efficient catalysts for cross-coupling reactions. To investigate the influence of electron-deficient substituents on the catalytic activity, the coordination properties of bis(trifluoromethyl)-, bis(pentafluoroethyl)-, and bis[2,4-bis(trifluoromethyl)phenyl]phosphinous acid toward catalytically relevant metals, such as palladium and platinum, are studied. The novel phosphinous acid palladium complexes reveal a high catalytic activity in Heck and Suzuki cross-coupling reactions. Because of the strong dependence of these processes on the reaction conditions, a systematic solvent and base screening with 1-bromo-3-fluorobenzene and phenyl boronic acid as model reactants is performed. The most efficient solvent/base system consists of 2-propanol and potassium phosphate, providing a full conversion and a TON of around 10 000 after 20 h at room temperature with a catalyst loading of 0.01 mol % palladium. A catalyst loading of only 0.004 mol % palladium still leads to a nearly full conversion after 20 h at room temperature. During the catalytic reaction, the formation of the corresponding phosphinic acid R2P(O)OH is observed. Further investigations lead to the conclusion that palladium nanoparticles represent the catalytically active species. We also succeeded in the generation of palladium nanoparticles, which exhibit an extremely high catalytic activity in Suzuki cross-coupling reaction with TONs over 60 000 and TOFs larger than 40000.

• 出版日期2012-2-27