The role of Pd colloids as catalysts in the phosphane-free methoxycarbonylation of iodobenzene
作者:Anna M. Trzeciak、Wojciech Wojtków、Józef J. Ziółkowski、Józef Wrzyszcz、Mirosław Zawadzki
DOI:10.1039/b401912a
日期:——
The catalytic activity of PdCl2(cod) (1) in the methoxycarbonylation of iodobenzene (at 40–70 °C, 1–5 atm of CO, in methanol solution) increased remarkably when tetra-n-butylammonium salts [nBu4N]X (X = Br, Cl, I, BF4, PF6) were added to the system. XRD analyses confirmed that under methoxycarbonylation reaction conditions palladium was reduced to a Pd colloid of nanometer size, 2.0–5.6 nm, which was responsible for the catalytic activity. In the absence of ammonium salts fast deactivation of the colloid was observed, even when PVP (polyvinylpyrrolidone) was added as a stabilizer. Catalytic tests performed with isolated Pd colloid demonstrated its high catalytic activity in methoxycarbonylation when used together with [nBu4N]X salts. A mechanism of palladium reduction to Pd nanoparticles is proposed.
PdCl2(cod) (1)在碘苯的甲氧基羰基化反应中(在40–70°C,1–5 atm CO,甲醇溶液中)的催化活性在加入四正丁铵盐[nBu4N]X(X = Br, Cl, I, BF4, PF6)后显著提高。XRD分析确认在甲氧基羰基化反应条件下,钯被还原为纳米级的Pd胶体,尺寸为2.0–5.6 nm,这一胶体是催化活性的来源。在没有铵盐的情况下,即使加入了聚乙烯吡咯烷酮(PVP)作为稳定剂,胶体也迅速失活。使用分离的Pd胶体进行催化测试证明其在与[nBu4N]X盐一起使用时具有较高的甲氧基羰基化催化活性。提出了一种钯还原为Pd纳米粒子的机制。