Preparation of a nonleaching, recoverable and recyclable palladium-complex catalyst for Heck coupling reactions by immobilization on Au nanoparticles

摘要

The loading of a palladium complex immobilized on the surface of Au nanoparticles (NPs) was controlled through coordination to a supported spacer ligand (SL = S(CH_2)_(11)NHP(O)(2-py)_2) to yield catalyst particles of the composition (RS)_xAu(SL)_y(SL- PdCl_2)_z (SR = S(CH_2)_7CH_3; x:y:z = (0.31-2.3):1:(0.45-3.3)) with diameters of 3.1-4.9 nm. A fraction of the supported spacer ligands (23-69%) was left uncapped to capture any soluble Pd species resulting from leaching. These surface-bound Pd(II)-complex catalysts were highly effective for Heck reactions of iodobenzene and alkylacrylates, yielding a maximum turnover frequency (TOF) of 4.87 × 10~4 h~1. Their catalytic activity was three- to tenfold higher than that of their unbound counterparts. These hybrid catalysts could be dissolved and precipitated. They could be quantitatively recovered and effectively recycled 15 times without significant loss of reactivity. The recovered Au NP-supported palladium could be also dissolved, precipitated and isolated. Various spectroscopic analyses were performed to determine a surface-structure composition of (RS)_xAu(SL)_1(SL-Pd~0) _(0.53).