Design, Behavior, and Recycling of Silica-Supported CuBr−Bipyridine ATRP Catalysts

Abstract

A new strategy for immobilizing CuBr/bipyridine (bpy) complexes on silica surfaces is described. An immobilizable, organosilane-containing bpy ligand (SdMBpyTMS) is synthesized and complexed with CuBr followed by addition to four different silica supports, mesoporous SBA-15 with 50 and 100 Å pores, controlled pore glass (CPG) with 240 Å pores, and nonporous Cab-O-Sil EH5. The resulting solids are characterized by a battery of techniques including thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), FT-Raman spectroscopy, 13C and 29Si magic angle spinning (MAS) and cross-polarization magic angle spinning (CP-MAS) spectroscopy, low-temperature nitrogen physisorption, and elemental analysis. Characterization of these solids revealed that a mixture of covalently immobilized mono- and bis-copper coordinated complexes, uncoordinated ligand, and in some cases physisorbed copper exists on the silica surface. The resulting solids are utilized for ATRP of methyl methacrylate (MMA). Whereas catalysts supported on mesoporous SBA-15 are ineffective at controlling the polymerization, CuBr/SdMBpy complexes immobilized on CPG(240) and Cab-O-Sil are effective at mediating the controlled polymerization of methyl methacrylate. Polymerizations with these catalysts achieved >70% conversion, narrow molecular weight distributions (1.29 < PDI < 1.52), and low (undetectable) residual copper content in the final polymer. Application of the “immobilized/soluble hybrid” methodology with these silica supported catalysts did not result in well-controlled polymerizations due to strong partitioning of the soluble catalyst onto the silica support under the conditions employed here, perhaps elucidating a limitation of this methodology with silica-supported catalysts. A new methodology for catalyst regeneration is described utilizing a simple treatment of the used catalyst with AIBN. The AIBN regenerated catalysts can be recycled with moderate conversions and narrow molecular weight distributions comparable to the first catalyst use.

A Recoverable, Metal-Free Catalyst for the Green Polymerization of ε-Caprolactone

“…In contrast, other recoverable polymerization catalysts that we have studied such as CuBr-bipyridine complexes that are tethered to silica supports for atom transfer radical polymerization (ATRP) gave different trends. 64,65 In these cases, moieties supported on SBA-15 gave the poorest control over the polymerization, indicating that transport issues may exist on the time scale of the reaction. In contrast, because the reaction rates in -caprolactone polymerization are much slower, the potential transport issues associated with SBA-15 seem to be inconsequential, and good polymer control is observed with high reaction rates (relative to the other catalysts in this study).…”

Adsorption Essays of Palladium in Modified Silica Gel With Thiouronium Groups: Experimental and Theorical Studies

“…The 29 Si-NMR spectra of the group 3-thiouroniumpropyl modified silica gel showed a peak in -105.14 ppm assigned to Q 3 and a new peak at -68.7 ppm assigned to T 3 [30][31][32].…”

“…The characterization of the modified surface is performed with techniques like S BET (Brunauer-Emmett-Teller isotherm) [26], which estimates the surface of a solid, elemental analysis and combined FTIR [27][28][29] and RMN solid state techniques [30][31], which provide a good characterization of the product.…”

“…In the silica gel, a peak associated to the geminal silanols groups is assigned as Q 2 and appears near -90.0 ppm. The simple silanols groups are assigned as Q 3 at -100.0 ppm, and the siloxans Si-O-Si group is assigned as Q 4 at -110.0 ppm [30][31], being the main group in the structure ( Figure 3). The substitution of the silanols groups can also be observed in the Si-C union, whose nomenclature is assigned as T n .…”

Mesoporous organosilica nanotubes containing a chelating ligand in their walls

“…Conventionally, 2,2 ′ -bipyridine has been grafted on porous solids such as silica gel or mesoporous silica, serving as an organic linker for the fixation of metal complexes. 14,15 However, in many cases, the activity of the metal complexes catalysts grafted on porous solids is greatly decreased due to unfavorable interactions between the metal complex and the solid surface and/or limited diffusion of molecules in the narrowed pores. Recently, however, ordered mesoporous organosilicas 16,17 and metal-organic-frameworks (MOFs) [18][19][20][21] Herein, we report the synthesis of organosilica nanotubes containing bipyridine ligands in their walls (denoted as BPy-NT) and the direct formation of an iridium complex on the tube walls (denoted as Ir-BPy-NT).…”