Pd- and Au-Induced Circular and Fibrous Polymer Gelation via Thiocarbonyl Groups and High Pd Catalyst Activity

Self-assembled gelation behavior of a hydrophilic polymer bearing a metal-coordination unit with metal ions (PdII or AuIII) was investigated upon addition of a dispersed aqueous solution of the polymer to an aqueous solution of metal ions. Self-assembled gels with different morphologies were formed depending on the metal ions used. Spherical and fibrous gels were formed by gelation with PdII and AuIII ions, respectively. The mechanism for formation of the different gel morphology was examined by measuring cross-linking rates, examining coordination sites, and determining mechanical properties. The PdII self-assembled gels efficiently catalyzed the Mizoroki-Heck cross-coupling reaction of a variety of aryl halides and olefins with a turnover number (TON) and turnover frequency (TOF) of greater than 2,762,000 and 138,100 h–1, respectively. These are the greatest TON and TOF values for heterogeneous polymeric catalysts of the Mizoroki-Heck reaction. The AuIII self-assembled fibrous gels, which had nano-order diameter, contained uniformly dispersed gold nanoparticles and could be synthesized by a facile method, i.e., the dropwise addition of a dispersed aqueous solution of the polymer to an aqueous solution of AuIII ion.