Synthesis of cyclohexadienyl ruthenium arene complexes by replacement of acetonitrile ligands in [(η5-C6H7)Ru(MeCN)3]+

• A general approach to cyclohexadienyl ruthenium arene complexes is presented.
• Cyclohexadienyl ruthenium cation [(η5-C6H7)Ru]+ is less arenophilic than [CpRu]+.
• Cyclohexadienyl ligand occasionally undergoes hydrogen abstraction giving benzene.

Heating of the cyclohexadienyl ruthenium complex [(η5-C6H7)Ru(MeCN)3]+ (1) with arenes results in replacement of acetonitrile ligands giving complexes [(η5-C6H7)Ru(arene)]+ (arene = toluene, o-xylene, hexamethylbenzene, p-toluidine, benzo-15-crown-5, ethyl ester of N-acetylphenylalanine) in 53–93% yields. Similar reaction of 1 with naphthalene produces labile complex [(η5-C6H7)Ru(naphthalene)]+ which readily undergoes solvolysis in acetone. The reaction of 1 with 1,5-cyclooctadiene unexpectedly gives the benzene complex [(η3,η2-C8H11)Ru(C6H6)]+ in 44% yield, as a result of formal abstraction of two hydrogen atoms. Energy decomposition analysis revealed that the cyclohexadienyl ruthenium cation [(η5-C6H7)Ru]+ is less arenophilic then [CpRu]+ due to weaker orbital interaction with arenes. The structure of [(η5-C6H7)Ru(benzo-15-crown-5)]PF6 was established by X-ray diffraction.

Replacement of labile acetonitrile ligands in [(η5-C6H7)Ru(MeCN)3]+ by arenes produces the cyclohexadienyl ruthenium arene complexes [(η5-C6H7)Ru(arene)]+, while similar reaction with 1,5-cyclooctadiene unexpectedly gives the cyclooctadienyl ruthenium benzene complex [(C6H6)Ru(η3,η2-C8H11)]+, as a result of hydrogen abstraction.Figure optionsDownload as PowerPoint slide