Synthesis of di-, tri-, tetra- and pentacyclic arene complexes of ruthenium(II):[Ru(η6-polycyclic arene)-(1-5-η5-cyclooctadienyl)]PF6 and their reactions with NaBH4

The phenanthrene complex of ruthenium(II), [Ru(η6-phenanthrene)(1,5-η5-cyclooctadienyl)]PF6 (2c), is prepared by the reaction of Ru(η4-1,5-COD)(η6-1,3,5-COT) (1) with phenanthrene and HPF6 in 65% yield. Similar treatments with di- tri-, tetra- and pentacyclic arenes give corresponding polycyclic arene complexes, [Ru(η6-polycyclic arene)(1-5-η5-cyclooctadienyl)]PF6 [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 NaBH4 gives a mixture of the 1,5- and 1,4-COD complexes of ruthenium(0), Ru(η6-phenanthrene)(η4-1,5-COD) (3c) and Ru(η6-phenanthrene)(η4-1,4-COD) (4c) in 76% in 1:8 molar ratio. The arene exchange reactions among cationic complexes [Ru(η6-arene)(1-5-η5-cyclooctadienyl)]PF6 (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.