Arene-ruthenium complexes with phosphanylferrocenecarboxamides bearing polar hydroxyalkyl groups-synthesis, molecular structure, and catalytic use in redox isomerizations of allylic alcohols to carbonyl compounds

Article abstract of DOI:10.1002/ejic.201200733

Phosphanylferrocenecarboxamide Ph₂P-fc-CONHCH₂CH ₂OH (1, fc = ferrocene-1,1′-diyl) and its newly synthesized congeners, Ph₂P-fc-CONHCH(CH₂OH)₂ (2) and Ph₂P-fc-CONHC(CH₂OH)₃ (3), were converted to a series of (η⁶-arene)ruthenium complexes [(η⁶- arene)RuCl₂(L-κP)] 5-7, where arene is benzene, p-cymene, and hexamethylbenzene and L = 1-3. All compounds were characterized by multinuclear NMR and IR spectroscopy, by mass spectrometry, and by elemental analysis. The molecular structures of 2, 3, 3O (a phosphane oxide resulting from the oxidation of 3), 5c·CH₂Cl₂, and 6c·Et₂O were determined by single-crystal X-ray diffraction analysis. The ruthenium complexes were further evaluated as catalysts in the redox isomerization of allyl alcohols to carbonyl compounds. Complex [(η⁶-p-cymene) RuCl₂(1-κP)] (5b) proved to be a particularly attractive catalyst, being both readily available and catalytically active. Substrates with unsubstituted double bonds were cleanly isomerized with this catalyst in 1,2-dichloroethane (0.5 mol-% Ru, 80 °C), whereas for those bearing substituents at the double bond (particularly in the position closer to the OH group) lower conversions and selectivities were achieved. A similar trend was noted when pure water was used as the solvent, except that the best results (complete conversion with 2 mol-% Ru) were seen for 1,3-diphenylallyl alcohol, the most hydrophobic substrate.