Catalytic racemization of secondary alcohols with new (arene)Ru(II)-NHC and (arene)Ru(II)-NHC-tertiary phosphine complexes
| Autor: | Natália Marozsán, Antal Udvardy, Éva Kováts, Henrietta Győrváriné Horváth, Ferenc Joó, Anikó Erdei, Mihály Purgel |
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| Rok vydání: | 2018 |
| Předmět: |
Agostic interaction
Reaction mechanism 010405 organic chemistry Process Chemistry and Technology 010402 general chemistry Rate-determining step 01 natural sciences Medicinal chemistry Toluene Catalysis 0104 chemical sciences chemistry.chemical_compound Természettudományok chemistry Physical and Theoretical Chemistry Kémiai tudományok Racemization Phosphine Acetophenone |
| Zdroj: | Molecular Catalysis. 445:248-256 |
| ISSN: | 2468-8231 |
| DOI: | 10.1016/j.mcat.2017.11.040 |
| Popis: | Five new complexes of the type [RuCl2(NHC)(η6-arene)] (4, 5, and 6) and [RuCl(NHC)(η6-arene)(PR3)]Cl (7 and 8) (NHC N-heterocyclic carbene = bmim, emim; arene = benzene, p-cymene; PR3 = PPh3 or pta = 1,3,5-triaza-7-phosphaadamantane) were synthetized and applied as catalysts (together with the known [RuCl2(bmim)(η6-p-cymene)] (3) with and without added PPh3) in racemization of optically active secondary alcohols in toluene. The highest catalytic activity, TOF = 9.3 h−1 (ee as low as 1.3% in 4 h at 95 °C) was observed in racemization of (S)-1-phenylethanol with a catalyst (4 mol%) prepared in situ from 3 and 1 equivalent of PPh3. It is of practical significance that formation of acetophenone byproduct was suppressed to 3.5% by 17% v/v isopropanol in toluene. DFT calculations revealed that the rate determining step in the suggested reaction mechanism was the agostic coordination of hydrogen on the chiral carbon atom of the alcohol substrate. |
| Databáze: | OpenAIRE |
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