Synthesis of Cyclopentadienyl-Based Trioxo-rhenium Complexes and Their Use as Deoxydehydration Catalysts

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• 作者：Suresh Raju ; Christian A. M. R. van Slagmaat ; Jing Li ; Martin Lutz ; Johann T. B. H. Jastrzebski ; Marc-Etienne Moret ; Robertus J. M. Klein Gebbink
• 刊名：Organometallics
• 出版年：2016
• 出版时间：July 11, 2016
• 年：2016
• 卷：35
• 期：13
• 页码：2178-2187
• 全文大小：481K
• 年卷期：0
• ISSN：1520-6041

文摘

The cyclopentadienyl-based trioxo-rhenium complexes Cp^tttReO₃ (Cp^ttt = 1,2,4-tritert-butylcyclopentadienyl) 1b and Cp*ReO₃ (Cp* = pentamethylcyclopentadienyl) 4b) are known to be active catalysts for the deoxydehydration (DODH) of vicinal diols to olefins. Here, we report on the preparation of a series of complexes of the general formula Cp′ReO₃ (Cp′ = 1,3-di-tert-butylcyclopentadienyl (Cp^tt, 2b, 18%), 1,2,3-triisopropylcyclopentadienyl (3b, 4%), 1,2,3-trimethyl-4,5,6,7-tetrahydroindenyl (6b, 36%), and tetramethylcyclopentadienyl (7b, 33%)) in which the electronic and steric properties of the Cp′ ligand are varied. These complexes were synthesized via oxidative decarbonylation from the corresponding Cp′Re(CO)₃ complexes with either H₂O₂ or tBuOOH. An in situ NMR investigation revealed that complexes 2b, 3b, and 6b are unstable under the oxidizing reaction conditions. This information was used to determine the optimal reaction time to isolate the complexes 2b, 3b, and 6b. These “piano-stool” configurated Cp′ReO₃ complexes were characterized spectroscopically and by single crystal X-ray diffraction. The new complexes 2b, 3b, 6b, and 7b were found to be generally less thermally stable than Cp^tttReO₃ (1b) or Cp*ReO₃ (4b). It appeared that 2b and 6b were better catalysts for the DODH of 1,2-octanediol to octene with PPh₃ as an oxygen-atom acceptor. Remarkably, the less substituted Cp′ReO₃ complexes (1b, 2b, and 3b) afforded significantly less 2-octene (presumably from isomerization of the primary 1-octene product) in comparison to those containing per-alkylated Cp-moieties (4b and 6b).