Benzaldoxime to benzamide rearrangement catalysed by rhodium(III) hydroxocomplexes: The influence of polynuclear species

• Published in: Applied catalysis. A, General General, 2019-10, Vol.587, p.117242, Article 117242
• Main Authors: Berdyugin, Semen, Volchek, Victoria, Asanova, Tatyana, Kolesov, Boris, Gerasimov, Evgeny, Filatov, Evgeny, Vasilchenko, Danila, Korenev, Sergey
• Format: Article
• Language: English
• Subjects: Heterogeneous catalysts; Primary amides; rhodium(III) hydroxocomplexes
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2019.117242

[Display omitted] •The method for deposition of rhodium(III) hydroxocomplexes with variable nuclearity onto the alumina support was developed.•The catalytic activity of prepared materials was evaluated in the benzaldoxime to benzamide rearrangement under eco-friendly conditions.•The higher catalytic activity of catalysts containing polynuclear hydroxocomplexes in comparison with mononuclear species was demonstrated.•Rhodium subnanoclusters formed in the reaction conditions were proposed as the active sites of the catalysts.•The superiority of polinuclear species was attributed to the pre-organized structure and higher dispersity. Rhodium(III) hydroxide was shown previously to possess the catalytic activity in the rearrangement reaction of primary oximes to amides. Alkaline solutions of rhodium(III) chlorocomplexes are routinely used for Rh(OH)3 preparation and allow for a diversity of rhodium hydroxocomplexes that hold a wide range of catalytic properties. In this study, two Al2O3 supported catalysts containing 1) exclusively [Rh(OH)6]3− species and 2) a mixture of rhodium hydroxocomplexes with one to four rhodium atoms ([Rh(OH)6]3–, [Rh2(μ−OH)2(OH)8]4–, [Rh3(μ−OH)3(OH)12]6–, [Rh4(μ−OH)6(OH)12]6) were prepared, characterised (XRD, Raman, EXAFS) and tested in the benzaldoxime to benzamide rearrangement. The catalyst containing polynuclear complexes possessed at least three times higher turnover frequency (TOF) and better selectivity than the [Rh(OH)6]3– based catalyst. According to the EXAFS data, the reduction of rhodium(III) took place under reaction conditions yielding small rhodium clusters (CNRh-Rh = 4), which were proposed to be the active sites of catalysts.