Selective hydrogenation of C6 dienic compounds using homogeneous Cp*-ruthenium (II) catalyst

Abstract

Selective hydrogenations of C6 dienic compounds bearing two or more conjugated double bonds in trans position using homogeneous ruthenium catalysts were performed. The following compounds of high purity (over 99%) were prepared: benzyl (2E,4E)-hexa-2,4-dienoate, (2E,4E)-hexa-2,4-dien-1-yl benzoate, (2E,4E)-hexa-2,4-dien-1-yl (2E,4E)-hexa-2,4-dienoate, (2E,4E)-di-n-butyl muconate and di((2E,4E)-hexa-2,4-dien-1-yl) (2E,4E)-hexa-2,4-dienedioate. The ruthenium half sandwich complex [Cp*Ru(butyl sorbate)]CF₃SO₃ was prepared and used as catalysts for hydrogenation of above mentioned compounds. Commercially available muconic acid was also chosen to test the catalytic activity and the selectivity of Ru complexes [Cp*Ru (butyl sorbate)] CF₃SO₃. Hydrogenations were carried out in homogeneous arrangement using diethyl ether as a solvent. The reaction conditions were set to 50 °C and 4 MPa. All the above mentioned C6 dienic compounds, except muconic acid and (2E,4E)-di-n-butyl muconate, were hydrogenated to corresponding (Z)-hex-3-enoic compounds with high selectivity (up to 97%). In the case when two conjugated systems were present the hydrogenation in both chains was observed.