Organostannoxane-supported palladium nanoparticles. Highly efficient catalysts for Suzuki-coupling reactions

Abstract

A phosphine-rich hexameric organostannoxanne, [n-BuSn(O)COOL]₆ (PDrum; L = p-PPh₂-C₆H₄-), has been synthesized by a 6:6 reaction between [n-BuSn(O)OH]_n and p-Ph₂PC₆H₄COOH. ¹¹⁹Sn{¹H} NMR of PDrum revealed a single resonance at -481.0 ppm, indicating that it possesses the characteristic drum structure that is well-known among organostannoxanes. Reduction of PdCl₂ with NaBH₄ in the presence of PDrum afforded a palladium nanocomposite, NP-1. HRTEM of NP-1 indicates that the average nanoparticle size is about 3 nm. The latter has been shown to be very effective in mediating Suzuki-coupling reactions involving a number of different substrates. NP-1 can be recycled, and HRTEM analysis of the used catalyst reveals some agglomeration. Treatment of NP-1 with n-hexane and cooling to -25 ° C afforded another palladium nanocomposite, NP-2. The latter also is very effective in catalyzing the Suzuki-coupling reaction. HRTEM of NP-2 shows an average nanoparticle size of about 4.3 nm, which remains nearly unchanged even after catalysis. NP-2 is a composite also containing some amounts of SnO₂.