The phenanthrene complex of ruthenium(II), [Ru(η 6-phenanthrene)(1,5-η 5-cyclooctadienyl)]PF 6 ( 2c), is prepared by the reaction of Ru(η 4-1,5-COD)(η 6-1,3,5-COT) ( 1) with phenanthrene and HPF 6 in 65% yield. Similar treatments with di- tri-, tetra- and pentacyclic arenes give corresponding polycyclic arene complexes, [Ru(η 6-polycyclic arene)(1-5-η 5-cyclooctadienyl)]PF 6 [polycyclic arene = naphthalene ( 2b), anthracene ( 2d), triphenylene ( 2e), pyrene ( 2f) and perylene ( 2g)] in 46–90% yields. The molecular structure of the perylene complex 2g is characterized by X-ray crystallography. Reaction of 2c with NaBH 4 gives a mixture of the 1,5- and 1,4-COD complexes of ruthenium(0), Ru(η 6-phenanthrene)(η 4-1,5-COD) ( 3c) and Ru(η 6-phenanthrene)(η 4-1,4-COD) ( 4c) in 76% in 1:8 molar ratio. The arene exchange reactions among cationic complexes [Ru(η 6-arene)(1-5-η 5-cyclooctadienyl)]PF 6 ( 2) showed the coordination ability of arenes in the following order: benzene ∼ triphenylene > phenanthrene > naphthalene > perylene ∼ pyrene > anthracene, suggesting the benzo fused rings, particularly those of acenes, decreasing thermal stability of the arene complex.