Titanium-catalyzed olefin metathesis

Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

“…The formation of this complex, which proceeds with a half-life of % 15 h, is reminiscent of similar reactions that involve related titanocene complexes and, under certain conditions, also zirconocene systems. [31][32][33] In addition to the interconversion between different type III species, by exchange of terminal methyl groups against isobutyl groups, a significant reduction of their total concentrations at elevated [AliBu 3 ] add /[Zr] ratios is apparent from Figure 2. The appearance of new ligand signals (denoted as I H 2 in Figure 2) and of the signals of isobutylene at d = 1.59 and 4.73 ppm, as well as previous observations on related reaction systems, [17,34,35] suggest that the isobutylated adducts III iBuMe and III iBu 2 are partly converted to some hydride species.…”

CH3ReO3 on γ‐Al2O3: Understanding Its Structure, Initiation, and Reactivity in Olefin Metathesis

“…Therefore, Al Oh CH 2 ReO 3 is the stable form of the active site of the catalyst, which probably generates the necessary carbene in situ during metathesis, and thus this system corresponds to a Re-based heterogeneous equivalent of the Tebbe reagent (Scheme 2). [22,23] In conclusion, for CH 3 ReO 3 on g-Al 2 O 3-(500) , a highly efficient olefin metathesis catalyst, the major surface species (85-86 %) correspond to interaction of the oxo ligand of CH 3 ReO 3 with surface Lewis acid sites of alumina, but these are inactive for olefin metathesis. The active site, Al Oh CH 2 ReO 3 , is in fact a minor species (14-15 %), and results from CÀH activation of the methyl ligand of CH 3 ReO 3 on g-alumina.…”

Eine Seltenerdmetallvariante des Tebbe‐Reagens

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Das Tebbe-Reagens [Cp 2 Ti{(m-CH 2 )(m-Cl)Al(CH 3 ) 2 }] (A; Cp = Cyclopentadienyl) gehört zu den schillerndsten metallorganischen Verbindungen.[ [3] und Wolfram-Methylen-Verbindungen (vorgeschlagen als Olefinmetathese-Katalysatoren) [4] röntgenographisch charakterisiert.[3] Obgleich katalytisch aktiv in der Olefinmetathese, [5] wird das Tebbe-Reagens derzeit als effizientes Carbonyl-Methylenierungsreagens eingesetzt. [9, 10] Vorangegangene Untersuchungen unserer Arbeitsgruppe befassten sich mit Seltenerdmetall(III)-TetramethylaluminatKomplexen [L x Ln{Al(CH 3 ) 4 } y ] (y = 1, 2, 3; x + y = 3, L = einzähniger Hilfsligand, Ln = Seltenerdmetall und Sc, Y, La) als Polymerisationskatalysatoren [11,12] und führten zur Isolation von Ln III -Clustern mit Methylen-, [13,14] Methin- [15] und Carbidfunktionalitäten.

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