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

Abstract

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.

Synthesis of Nanosheets Containing Uniformly Dispersed PdII Ions at an Aqueous/Aqueous Interface: Development of a Highly Active Nanosheet Catalyst for Mizoroki–Heck Reaction

“…HPMC was synthesized by the reaction of poly(vinyl alcohol) and methyl isothiocyanate according to our previously reported procedure. 32 The synthesis of nanosheets was attempted by generation of the interface with aqueous solutions of different specific gravities and fast cross-linking between thiocarbonyl groups in HPMC and Pd II ions (i.e., dropwise addition of an aqueous solution of Pd II ions with a low specific gravity (1.03 g/cm 3 ) to a dispersed aqueous solution of HPMC with a high specific gravity (1.50 g/cm 3 )). When the aqueous solutions with different concentrations of Pd II ions (4 mL, 8–18 mM, pH 1) were carefully added to the dispersed aqueous solutions of HPMC (0.8 mL, 30 wt %, pH 1), instant cross-linking occurred, resulting in the formation of 12–18 mM film-shaped gels at the interface ( Figure 2 a).…”

“…These are the greatest TON and TOF values reported in heterogeneous polymeric catalysts for the Mizoroki–Heck reaction. 32 , 40 − 49 The reactions in the presence and absence of the polymer without Pd II were tested, and the reaction did not proceed. This high catalytic activity was attributed to the uniform dispersion of Pd II ions in the Pd II nanosheets and the high area of the exposed catalytically active surface.…”

“…HPMC was synthesized by the reaction of poly(vinyl alcohol) and methyl isothiocyanate according to our previously reported procedure. 32 The synthesis of nanosheets was attempted by generation of the interface with aqueous solutions of different specific gravities and fast cross-linking between thiocarbonyl groups in HPMC and Pd II ions (i.e., dropwise addition of an aqueous solution of Pd II ions with a low specific gravity (1.03 g/cm 3 ) to a dispersed aqueous solution of HPMC with a high specific gravity (1.50 g/cm 3 )).…”

“…Recently, the self-assembled gelation behavior of a hydrophilic polymer bearing a metal coordination unit (denoted as HPMC) and Pd II ions has been reported. 32 The HPMC consisted of thiocarbonyl groups for metal coordination and hydroxyl groups for hydrophilicity ( Figure 1 a). Self-assembled gelation occurred through coordination between the thiocarbonyl sulfurs and Pd II ions, providing cross-linked gels.…”

An Imidazole‐Rich Pd(II)‐Polymer Pre‐catalyst for the Suzuki‐Miyaura Coupling: Stability Influenced by Dissolved Oxygen and Reactants Concentration

“…[27] Compared to traditional supports, such as metal oxides or carbon, the support can be more easily tuned by inserting coordinating groups using simple chemical steps. [28][29][30][31][32][33][34] Among the myriad of heterogeneous supports for Pd immobilization, many contain the imidazole group as a key component. For example, Yamada and co-workers [35,36] synthesized a poly(imidazole)-based polymer that was used to encapsulate Pd(II).…”