Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

Abstract

Single-site organometallic catalysts supported on solid inorganic or organic substrates are making an important contribution to heterogeneous catalysis. Early and late transition metal single-site catalysts have changed the polyolefin manufacturing industry and research with their ability to produce polymers with unique properties. Moreover, several of these catalysts have been commercialized on a large scale. Their heterogenization for slurry or gas phase olefin polymerization is important to produce polyolefin as beads and to avoid reactor fouling. The large majority of supports currently used in industry are inorganic materials (SiO 2 , Al 2 O 3 , MgCl 2 ), with silica being the most important. Single-site supported catalysts are most commonly prepared by molecular-level anchoring/chemisorption, in which a molecular precursor undergoes reaction with the surface while maintaining most of the ligand sphere of the parent molecule. Chemisorption of discrete organometallic complexes on solid supports yields catalysts with well-defined active sites, greater thermal stability than the homogeneous analogues, and decreased reactor fouling versus the homogeneous analogues. This review presents a detailed account of the synthesis, characterization and polymerization properties of single-site catalysts supported on metal oxides and metal sulfated oxides, primarily carried out at Northwestern University.

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy

“…The photon excitation leads to electron transfer from the apical oxygen O3 to the center Ti atom, reducing the Ti 4+ to the Ti 3+ cation. Then the resulting Ti 3+ ions react with the ambient CO 2 and H 2 O, leading to their reduction and the formation of final products such as CH 4 and CH 3 OH (40). The products noted in Fig.…”

“…ultrafast electron microscopy | single-site photocatalysis | titanium based photocatalyst | ulatrafast phenomena | time-resolved microscopy S ingle-site catalysts of both the thermally and photoactivated kind now occupy a prominent place in industrial-and laboratory-scale heterogeneous catalysis (1)(2)(3)(4)(5)(6)(7)(8). Among the most versatile of these are the ones consisting of coordinatively unsaturated transition metal ions (Ti, Cr, Fe, Mn.…”

Gas-Phase Dimerization of Ethylene under Mild Conditions Catalyzed by MOF Materials Containing (bpy)NiII Complexes

“…Hence, the heterogenization of homogeneous molecular catalysts to improve their stability and reaction scope while preserving, or even enhancing, their tunability and activity-selectivity profile has emerged as one of the frontiers in modern catalysis. [3][4][5][6][7] Concurrently, with well-defined solid-state structures that include both discrete organic linkers and metal-ion/cluster nodes, metal-organic frameworks (MOFs) have recently emerged as a highly promising heterogeneous support for incorporating transition metal catalysts, [8][9] either at the linker sites, [10][11] directly on the nodes, [12][13] or at ligand-modified nodes. 14 These well-defined ligated sites offer homogeneous-like coordination environment for metal species while the hybrid organic-inorganic nature of MOF allows one to extend their reaction scope to temperature 3 ranges at least as high as 350 ºC, 12 much higher than the stability of many organic ligands, and to include gas-phase reactions.…”

Single‐Face/All‐cis Arene Hydrogenation by a Supported Single‐Site d0 Organozirconium Catalyst

“…Owing to the versatility of alcohols and ketones as synthetic intermediates,t hese products can then be modified in many ways to afford avariety of valuable substances. [11] Our group recently reported the kinetics and reaction pathways by which benzene and toluene hydrogenation are catalyzed by Cp*ZrR 3 complexes (Cp* = h 5 -C 5 (CH 3 ) 5 ;R= Me, [12] CH 2 Ph; [13] Figure 1A)chemisorbed on Brønsted acidic sulfated oxides (Cp*ZrR 2 /MS, M = Zr,Al). [10] In particular, electrophilic d 0 catalysts supported on "super" Brønsted acids with large percentages of catalytically significant sites (70 % À98 %) exhibit high activity in technologically relevant olefin polymerization and hydrogenation processes.…”