Highly Dispersed Pd-SBA15 Materials from Tris(tert-butoxy)siloxy Complexes of Pd(II)

Abstract

Two novel tris(tert-butoxy)siloxy palladium(II) complexes of the form (4,4′-di-tert-butyl-2,2′-bipyridyl)Pd[OSi(OtBu)3](R) were synthesized (1, R = OSi(OtBu)3 and 2, R = CH3). The structures of these compounds were determined by multinuclear NMR spectroscopy and single crystal X-ray diffraction. The solid-state thermolytic chemistry of 1 and 2 was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). These compounds were covalently grafted onto the surface of mesoporous silica (SBA15) under mild, nonaqueous conditions to generate supported Pd(II) centers. Reactions of 1 and 2 with the surface Si–OH groups occurs selectively through the -OSi(OtBu)3 ligand with elimination of HOSi(OtBu)3. The new materials, designated Pd(1)SBA15 and Pd(2)SBA15, were characterized using N2 porosimetry, TGA, powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). The coordination environments of the supported Pd centers were investigated using Fourier-transform infrared (FTIR) spectroscopy, diffuse reflectance UV–vis (DRUV–vis) spectroscopy, and XAS. Comparison with the molecular precursors 1 and 2 revealed that the supported Pd centers share many of the same structural and spectroscopic characteristics. The supported Pd centers were robust in inert atmosphere up to the decomposition temperatures of 1 and 2 (150–200 °C). The catalytic behavior of the PdSBA15 materials in the semihydrogenation of 1-phenyl-1-propyne was studied and compared to that of 1 and 2 in solution; the supported materials exhibited marked enhancements in stability and selectivity to (Z)-1-phenyl-1-propene.

Catalytic hydrogenation of liquid alkenes with a silica-grafted hydride pincer iridium(iii) complex: support for a heterogeneous mechanism

“…25,26 Different from the early TMs, the late ones have been investigated to a lesser extent in the preparation and characterisation of well-defined species featuring a metal-OSi bond. [27][28][29][30][31][32][33] A specific difference from the early TMs is that oxide-grafted hydrides of the late TMs are unstable and tend to aggregate into metal(0) nanoparticles. 3,34,35 We have recently reported that the dihydride pincer complex ijIrH 2 IJPOCOP)] (1) reacts with SBA-15 to give the silica-grafted iridiumIJIII) hydride ijIrHIJO-SBA-15)IJPOCOP)] (2) (POCOP is the pincer ligand 1,3-bisIJdi-tert-butylphosphino)oxy)benzene (Scheme 1).…”

From well-defined Pt(ii) surface species to the controlled growth of silica supported Pt nanoparticles

“…1). 8,9 This approach has been recently used by several groups working on the mechanism and the kinetics of formation of Ir nanoparticles supported on γ-Al 2 O 3 10 or the controlled formation of silica-supported Pd 11 and Pt 12 nanoparticles. Our group has shown that controlling the size and the interface of gold nanoparticles on the silica support via SOMC requires the use of specific molecular precursors with the right ligands.…”

Copper‐Incorporated Porous Polydivinylbenzene as Efficient and Recyclable Heterogeneous Catalyst in Ullmann Biaryl Ether Coupling

“…[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] By providing the "open" space inside the solid support, the porous materials enabled the catalyst-reactant interactions with much higher efficiency. Two good examples of these porous materials reported in the literature that have been used in catalysis are zeolite- [15][16][17][18] and mesoporous silica- [20][21][22][23][24][25][26][27][28][29] based porous materials. The porous organic polymers have attracted much attention because they are very easy to prepare on a large scale under mild conditions compared with other types of porous materials reported in the literature, which were usually synthesized with expensive organic surfactants or templates, and calcination at high temperature is usually required to obtain opening channels.…”