Well-Defined Surface Species [(≡Si—O—)W(═O)Me₃] Prepared by Direct Methylation of [(≡Si—O—)W(═O)Cl₃], a Catalyst for Cycloalkane Metathesis and Transformation of Ethylene to Propylene

Abstract

The silica-supported tungsten oxo-trimethyl complex [(SiO)W(O)Me 3 ] was synthesized using a novel SOMC synthetic approach. By grafting the inexpensive stable compound WOCl 4 on the surface of silica, partially dehydroxylated at 700°C (SiO 2-700 ), a well-defined monopodal surface complex [(SiO)W(O)Cl 3 ] was produced. The supported complex directly methylated with ZnMe 2 and transformed into [(SiO)W(O)Me 3 ], which we fully characterized by microanalysis, IR, mass balance and SS NMR ( 1 H, 13 C, 1 H− 13 C HETCOR, 1 H− 1 H DQ and TQ). [(Si O)W(O)Me 3 ] has two conformational isomers on the surface at room temperature. The conversion of one to the other was observed at 318 K by variable-temperature 13 C CP/MAS and 1 H spin echo MAS solid-state NMR; this was also confirmed by NMR and DFT calculations. [(SiO)W(O)Me 3 ] was found to be active in cyclooctane metathesis and to have a wide distribution range in ring-contracted and ring-expanded products. In addition, [(SiO)W(O)Me 3 ] proved to be highly active for selective transformation of ethylene to propylene compared to other silica-supported organometallic complexes.

Silica‐Grafted SnIV Catalysts in Hydrogen‐Transfer Reactions

“…For instance, the metal may form additional bonds to the surface during a thermal treatment (that is, multipodal anchoring) ,. All these synthetic steps can be monitored by various characterization techniques (FTIR, UV/Vis and solid‐state NMR spectroscopy) and often change the activity of the catalyst ,–…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…WH 3 /Al 2 O 3-500 converts ethylene into propylene at 150 8 8Ci nacontinuous-flow reactor with ar emarkable selectivity of 95 %, reaching aT ON of 1120 after 120 ho n stream. [226] Ther esults obtained in astatic reactor at 150 8 8Csuggest that this catalyst has higher activity and selectivity than other silica-supported organometallic complexes.S imilar to the WH 3 /Al 2 O 3-500 described above,t he proposed mechanism involves the formation of tungsten carbene-hydride active species. [224] Thep roposed reaction mechanism involves ethylene dimerization to form 1-butene,i somerization of 1-butene to form 2-butenes,a nd ethylene/2-butene cross-metathesis (Scheme 14 a).…”

“…Theselectivity for butenes remains below 4.5 %, while higher olefins are present only in trace amounts (< 0.5 %). [226] 6. Thec atalyst deactivates by forming long-chain alkyl intermediates as ar esult of multiple ethylene insertion into the tungsten-alkyl bonds.…”

Eine Brücke zwischen industriellen und wohldefinierten Trägerkatalysatoren

“…Mehrfache Ethyleninsertion in W‐Alkyl‐Bindungen unter Bildung langkettiger Alkylkomplexe deaktiviert den Katalysator. [225 Kürzlich wurde ein weiterer ETP‐Katalysator auf W‐Basis aus ZnMe 2 und WOCl 4 auf Siliciumdioxid hergestellt, was die Katalysatorvorstufe (≡SiO)W(=O)(CH 3 ) 3 liefert (Schema b) . Die Ergebnisse in einem statischen Reaktor bei 150 °C weisen darauf hin, dass dieser Katalysator eine höhere Aktivität und Selektivität als andere metallorganische Komplexe auf Siliciumdioxidträgern aufweist.…”

“…Die Ergebnisse in einem statischen Reaktor bei 150 °C weisen darauf hin, dass dieser Katalysator eine höhere Aktivität und Selektivität als andere metallorganische Komplexe auf Siliciumdioxidträgern aufweist. Ähnlich wie bei WH 3 /Al 2 O 3‐500 umfasst der vorgeschlagene Mechanismus die Entstehung von aktiven W‐Carben‐Hydrid‐Spezies …”