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

The mononuclear arene-ruthenium(II) derivatives [RuCl2(η6-arene)(PTA-Me)] (arene = C6H6 (3a), p-cymene (3b), 1,3,5-C6H3Me3 (3c), C6Me6 (3d)), containing the ionic phosphine ligand 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane chloride (PTA-Me), have been synthesized and fully characterized. These complexes were evaluated as potential catalysts for the redox isomerization of allylic alcohols. Among them, best results in terms of activity were obtained with complex [RuCl2(η6-C6H6)(PTA-Me)] (3a) which, in combination with K2CO3 (2.5 equiv. per Ru), was able to selectively isomerize a number of allylic alcohols RCH(OH)CHCH2 (R = H, aryl, alkyl or heteroaryl group) into the corresponding carbonyl compounds RC(O)CH2CH3 in refluxing THF (TOF values up to 800 h−1). Complex [RuCl2(η6-C6H6)(PTA-Me)] (3a) was adsorbed onto the Montmorillonite K-10 clay, and the resulting solid proved also active in the isomerization of the model substrate 1-octen-3-ol. In addition, it could be easily separated from the reaction media by simple filtration and reused several times (up to 11 consecutive runs) with retention of its efficiency.

Graphical abstractArene-ruthenium(II) complexes containing the ionic phosphine ligand 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane chloride (PTA-Me) showed to be efficient catalysts for the redox isomerization of allylic alcohols. The most active one, namely [RuCl2(η6-C6H6)(PTA-Me)], was supported in the smectite-type clay Montmorillonite K-10. The resulting heterogeneous system is also active in the catalytic process, can be easily separated, and reused several times with retention of its efficiency.Figure optionsDownload full-size imageDownload high-quality image (197 K)Download as PowerPoint slideHighlights► [RuCl2(η6-C6H6)(PTA-Me)] is a new catalyst for the isomerization of allylic alcohols. ► This complex was immobilized onto the smectite-type clay Montmorillonite K-10. ► The resulting solid material proved also active in the isomerization process. ► In addition, it could be reused for a large number of runs without loss of activity.