(Ethynylferrocenyl)phosphine ruthenium complexes in catalytic β-oxopropyl benzoate formation

The synthesis of a series of (ethynylferrocenyl)phosphino ruthenium compounds of type (FcCC)R2P(RuCl2(η6-p-cymene)) (3a, R = C6H5; 3b, R = 2-CH3C6H4; 3c, R = cC4H3O; 3d, R = t-Bu; 3e, R = cC6H11; p-cymene = 1-iC3H7-4-CH3-C6H4; Fc = Fe(η5-C5H4)(η5-C5H5)) and (RuCl2(η6-p-cymene))(FcCC)P(CCPPh2(RuCl2(η6-p-cymene)))2 (10) resulting from the addition of ferrocenylphosphines P(CCFc)R2 (1a–1e) or P(CCFc)(CCPPh2)2 (9) to [RuCl2(η6-p-cymene)]2 (2) is described. The structures of 3b, 3c and 10 in the solid state are reported confirming the expected tetrahedral coordination sphere about the phosphorus atom as well as the “piano-stool” arrangement about the ruthenium atom(s). Ruthenium complexes 3 and 10 are catalytically active under mild conditions in the alkyne-to-carboxylic acid coupling as it was shown for the reaction of propargyl alcohol with benzoic acid. A comparison with literature known [RuCl2(PR3)(η6-p-cymene)] catalysts is presented.

Graphical abstractThe synthesis of (FcCC)R2P(RuCl2(η6-p-cymene)) and P(RuCl2(η6-p-cymene))(FcCC)(CCPPh2(RuCl2(η6-p-cymene))2 (R = C6H5, 2-CH3C6H4, cC4H3O, tBu, cC6H11; p-cymene = 1-iC3H7-4-CH3-C6H4) is described. The structures of three samples in the solid state are reported. The use of these molecules in the synthesis of β-oxopropyl benzoate is discussed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Monodentate (ethynylferrocenyl)phosphine ruthenium complexes were prepared. ► They are efficient catalysts in the formation of β-oxopropyl benzoate. ► The activity is dependent on steric and electronic effects. ► Electron-poor or moderate electron-rich/bulky phosphine ligands are best suited.