New anionic rhodium complexes as catalysts for the reduction of acetophenone and its derivatives

• Published in: RSC advances 2019-01, Vol.9 (2), p.711-72
• Main Authors: Bartlewicz, Olga, Jankowska-Wajda, Magdalena, Maciejewski, Hieronim
• Format: Article
• Language: English
• Subjects: Acetophenone; Catalysis; Catalysts; Catalytic activity; Chemistry; Derivatives; Hydrosilylation; Imidazole; Infrared radiation; Isomers; Low concentrations; Reducing agents; Reduction; Rhodium
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c8ra08954j

New anionic rhodium( iii ) complexes, obtained by a simple reaction of RhCl 3 with organic chlorides (derivatives of imidazole and pyridine), have been employed as catalysts for hydrosilylation (reduction) of acetophenone derivatives. The reactions, in which 1,1,1,3,5,5,5-heptamethyltrisiloxane was a reducing agent, proceeded in a biphasic system because the above complexes are insoluble in the reaction medium. Thereby easy isolation of the complexes from post-reaction mixtures was possible after reaction completion. This is the first example of the application of rhodium complexes of this type as catalysts for ketone reduction. The complexes have shown high activity and enabled obtaining the hydrosilylation product in a very short time and in the range of low concentrations (0.1 mol%). By using FT-IR in situ analysis that enables measuring product concentrations in real time, a comparison has been made of the catalytic activity for hydrosilylation of acetophenone and methoxyacetophenone isomers shown by four rhodium complexes ([C + ][RhCl 4 − ]) differing in cations and the most effective catalyst for this process has been distinguished. Stable rhodium complexes were obtained in a simple way and applied as highly active catalysts for reduction of acetophenone derivatives.