Design of silica-tethered metal complexes for polymerization catalysis

Abstract

Metal complex catalysts that are covalently tethered to oxide supports have been utilized for many years as hybrid molecular/ heterogeneous catalysts. In this work, recent results from our laboratory in the area of silica-tethered metal complex polymerization catalysts are reviewed. The critical parameters for catalyst design when catalyst recovery and recycle are important are discussed in the context of silica-immobilized CuBr complexes for atom transfer radical polymerization (ATRP) as well as silica-tethered Zn-bdiiminate (BDI) complexes for lactide or epoxide/CO 2 polymerization. Additionally, a new strategy for the preparation of siteisolated metal complex catalysts on a silica surface is illustrated through the design of tethered constrained geometry catalysts (CGCs) for ethylene polymerization. The novel synthetic protocol is demonstrated to result in catalysts that appear to be more welldefined and that have improved catalytic properties. Major challenges and future directions in the field of oxide-tethered metal complex catalysis are discussed.

Urea and Thiourea-Functionalized Mesoporous Silica Nanoparticle Catalysts with Enhanced Catalytic Activity for Diels–Alder Reaction

“…Toward this goal, several design prerequisites, such as tuning the degree of surface functionalization [5][6][7], controlling the spatial distribution of functional groups [8,9], and improving the hydrothermal stability of the catalytic materials [10][11][12][13][14], have been recently demonstrated.…”

Ethylene polymerization using metallocenes supported on MgCl2/SiCl4−n (n-C6H13O)n

“…Consequently, polymers may have been formed from both the activated mono-site catalyst in solution, probably affording the fraction with the narrower MWD value, and from the heterogeneous supported catalyst generating the fraction with the broader MWD. In addition, other factors for 2 Experimental conditions: catalysts = 5 µmol; T = 25 • C; p = 1.0 bar. ; t = 1 h; χ = crystallinity degree.…”

“…Currently there is an increasing interest, of both industry and academy, in supporting single-site catalysts for olefin polymerization [1,2]. Despite the fact that catalysts derived from metallocenes afford high activity, special polymer properties and narrow molecular weight distributions, their application is restricted because of technical problems like reactor fouling and the high concentration of co-catalyst required for the activation of these complexes.…”

Asymmetric Hydrogenation and Transfer Hydrogenation of Ketones

“…The above-mentioned properties of the inorganic supports will facilitate the applications of the materials in reactions carried at higher temperatures and their use in continuous-flow reactions. In the past decade a lot of research effort has been devoted to the development of adequate procedures to attach homogenous catalysts onto inorganic supports (Merckle & Blümel, 2005;Crosman et al, 2005;Corma et al, 2005;Jones et al, 2005;Melero et al, 2007). Immobilization via covalent bonds is undoubtedly the most convenient, but on the other hand, it is the most challenging method for immobilization to perform on such supports (Jones et al, 2005;Steiner et al, 2004;Pugin et al, 2002;Sandree et al, 2001).…”

“…In the past decade a lot of research effort has been devoted to the development of adequate procedures to attach homogenous catalysts onto inorganic supports (Merckle & Blümel, 2005;Crosman et al, 2005;Corma et al, 2005;Jones et al, 2005;Melero et al, 2007). Immobilization via covalent bonds is undoubtedly the most convenient, but on the other hand, it is the most challenging method for immobilization to perform on such supports (Jones et al, 2005;Steiner et al, 2004;Pugin et al, 2002;Sandree et al, 2001). For example, micelle templated silicas (MTS) featuring a unique porous distribution and high thermal and mechanical stabilities can be easily functionalized by the direct grafting of the functional organo-silane groups on their surfaces (McMorn & Hutchings, 2004;Heckel & Seebach, 2002;Bigi et al, 2002, Clark & Macquarrie, 1998Tada & Iwasawa, 2006).…”