Well‐Defined Silica‐Supported Zirconium–Benzyl Cationic Species: Improved Heterogenization of Single‐Site Polymerization Catalysts

Abstract

Zr(CH2Ph)4 (1) was grafted onto a recently disclosed hybrid material based on amorphous silica that features unique phenol grafting sites {[(≡SiO)2(AlOC6H4OH)(Et2O)] (H)}. A monopodal tribenzyl surface species, structurally similar to the silica‐supported species previously disclosed [≡SiOZr(CH2Ph)3] (2), was obtained and fully characterized as [(≡SiO)2(AlOC6H4OZr(CH2Ph)3)(Et2O)] (3). The activation of both these species by B(C6F5)3 proceeded by benzyl abstraction to yield the inner‐sphere ion pairs [≡SiOZr(CH2Ph)2]+[(PhCH2)B(C6F5)3]– (4) and [(≡SiO)2(AlOC6H4OZr(CH2Ph)2)(Et2O)]+[(PhCH2)B(C6F5)3]– (5), respectively. These surface species were fully characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analyses, and 1H, 13C, 11B, and 19F solid‐state NMR spectroscopy. These isolated cationic catalysts displayed increased ethylene polymerization activity compared to the neutral species. Most importantly, the heterogenization of the cationic complex with the phenol spacer (5) led to a fourfold increase in productivity compared to that of the silica counterpart 4, in agreement with reduced surface interactions and improved electrophilicity.

Synthesis of Phenanthridines through Palladium‐Catalyzed Cascade Reaction of 2‐Halo‐N‐Ms‐arylamines with Benzyl Halides/Sulfonates

“…Benzyl bromide derivatives 2a – 2h were readily available from either inexpensive arenecarbaldehydes, toluene derivatives, or a commercial source (Scheme b and c) . By starting from phenylmethanol under different reaction conditions, benzyl chloride ( 2i ), benzyl mesylate ( 2j ), benzyl tosylate ( 2k ), and benzyl acetate ( 2l ) were obtained in 78, 73, 85, and 89 % yield, respectively (Scheme d) …”

“…The chemical shifts ( δ ) of the 13 C NMR (100 MHz) signals are reported in ppm relative tetramethylsilane (TMS) and by employing the solvent resonance as the internal standard. N ‐Ms‐arylamines 1a – 1o , benzyl chloride ( 2i ), benzyl mesylate ( 2j ), benzyl tosylate ( 2k ), and benzyl acetate ( 2l ) were prepared according to reported procedures , . Unless otherwise stated, other substrates (i.e., 2a – 2h ) were purchased from commercial suppliers.…”

Single‐Site Heterogeneous Catalysts: From Synthesis to NMR Signal Enhancement

“…Various complexes, such as halide complexes, complexes with silanol, olefinic, cyclopentadienyl, amide, silane, and other ligands, can be used as precursors for synthesis of heterogeneous catalysts . The nature of the metal is also varied, and mono‐ and polynuclear complexes of Ti, Zr, Hf, Zn, V, Cr, W, Fe, Ni, Ag, Au, Ru, Rh, Pd, Pt, Ir, and even calixarene complexes of Ti and Ta can be used. Coordination of the metal complex to the SiO 2 surface occurs by substitution of one or more ligands to form the Me−O−Si bond, in which Me is one of the abovementioned metals.…”

“…Moreover, active centers must be independent of each other and the interaction energies with reagents for all active centers should be the same . In the last decade, interest in such systems has been increasing steadily . The synthesis of single‐site catalysts allows one to control and optimize activity and selectivity of heterogeneous catalysts.…”

“…[19] In the last decade, interest in such systems has been increasing steadily. [19][20][21][22][23][24][25][26] The synthesis of single-site catalysts allows one to control and optimize activity and selectivity of heterogeneous catalysts.…”