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Catalytic Transfer Hydrogenation with a Methandiide‐Based Carbene Complex: An Experimental and Computational Study
Author(s) -
Weismann Julia,
Gessner Viktoria H.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201502116
Subject(s) - carbene , dehydrogenation , transfer hydrogenation , catalysis , phosphine , triphenylphosphine , chemistry , catalytic cycle , ruthenium , ligand (biochemistry) , combinatorial chemistry , reaction mechanism , photochemistry , organic chemistry , biochemistry , receptor
The transfer hydrogenation (TH) reaction of ketones with catalytic systems based on a methandiide‐derived ruthenium carbene complex was investigated and optimised. The complex itself makes use of the noninnocent behaviour of the carbene ligand (MCR 2 →MHC(H)R 2 ), but showed only moderate activity, thus requiring long reaction times to achieve sufficient conversion. DFT studies on the reaction mechanism revealed high reaction barriers for both the dehydrogenation of i PrOH and the hydrogen transfer. A considerable improvement of the catalytic activity could be achieved by employing triphenylphosphine as additive. Mechanistic studies on the role of PPh 3 in the catalytic cycle revealed the formation of a cyclometalated complex upon phosphine coordination. This ruthenacycle was revealed to be the active species under the reaction conditions. The use of the isolated complex resulted in high catalytic activities in the TH of aromatic as well as aliphatic ketones. The complex was also found to be active under base‐free conditions, suggesting that the cyclometalation is crucial for the enhanced activity.