Single Site Supported Cationic Rhodium(I) Complexes for the Selective Redox Isomerization of Allylic Alcohols

Abstract

The isomerization of allylic alcohols to carbonyl compounds by a heterogeneous rhodium complex is reported. Different silica material supports and catalyst/ligand systems were evaluated. The most efficient catalyst in terms of catalytic activity and stability was found to be a cationic rhodium(I) complex with sulfonated phosphine ligands anchored on a mesoporous aluminosilica AlSBA‐15. The heterogeneous complex catalyzed the isomerization of a variety of allylic alcohols in excellent yields with very low catalyst loadings (0.5 mol %). The catalyst could be recycled without significant loss of activity or selectivity. The optimized catalyst was characterized by N2 sorption, powder X‐ray diffraction, transmission electron microscopy, as well as solution and solid‐state nuclear magnetic resonance, and Fourier Transform infrared spectroscopies.

Catalytic isomerization of allylic alcohols promoted by complexes [RuCl2(η6-arene)(PTA-Me)] under homogeneous conditions and supported on Montmorillonite K-10

“…Remarkably, although the activity of the heterogeneous system was comparatively lower than that of the unsupported complex [RuCl 2 (Á 6 -C 6 H 6 )(PTA-Me)] (3a), it could be reused for a large number of runs, with negligible loss of the catalytic activity. Overall, our results, along with those previously reported by Martín-Matute and co-workers [17], clearly demonstrate the great potential of inorganic solids supports for the development of robust heterogeneous catalysts able to promote the synthetically useful isomerization reaction of allylic alcohols.…”

“…Thus, under heterogeneous conditions, the best results were found with MK10-3a-2.5, which was able to generate quantitatively the desired octan-3-one (5a) after 3 h of heating (entry 4). Remarkably, the TOF value attained with this system (67 h −1 ) was slightly higher than that reported by Martín-Matute and co-workers for the isomerization of 4a with a cationic Rh(I) complex anchored onto the mesoporous aluminosilicate AISBA-15 in THF at 80 • C (48 h −1 ) [17]. We must also note that, as a general trend, an increase of the catalytic activity of the solids MK10-3a-x with the weight percentage of ruthenium present in the sample was observed (see entries [1][2][3][4].…”

“…28 ppm. The excellent recyclability of MK10-3a-2.5, superior to that shown by the related heterogeneous system Rh(I)/AISBA-15 described by Martín-Matute and co-workers (up to 5 consecutive cycles) [17], along with the low metal leaching observed attest for the high stability and lifetime of our Ru-based supported catalyst.…”

“…However, the preparation of the support was rather tedious and simpler alternatives are desirable. This fact, along with a recent study by Martín-Matute and co-workers demonstrating the utility of cationic Rh(I) complexes supported onto the mesoporous aluminosilicate AISBA-15 for this catalytic transformation (TOF up to 48 h −1 ; up to five consecutive runs after simple separation of the catalyst by filtration) [17], prompted us to explore more readily available inorganic solids as supports [18]. In particular, we directed our attention to the smectite-type laminar clay Montmorillonite, whose combination of cation exchange, intercalation and swelling properties has been largely exploited for the immobilization of metal catalysts in the last decades [19].…”

Base free transfer hydrogenation using a covalent triazine framework based catalyst

“…Various metals from groups 8, 9, and 10 (including Ir) are known to catalyse this reaction, mostly in the form of homogeneous catalysts. 70 However, a few examples exist for transition metal complexes immobilised on suitable supports, such as RuIJOH) x supported on alumina, 71 a cationic rhodium complex supported on mesoporous silica 72 and, very recently, an iridium N-heterocyclic carbene (NHC) introduced into a metal-organic framework. 73 Isomerisation of allylic alcohols is usually carried out in the presence of additives, such as bases or hydrogen acceptors, to promote the reaction.…”