The reaction of [Ru(η 5-C 7H 11) 2H]BF 4 ( 1; (η 5-C 7H 11) = η 5-2,4-dimethylpentadienyl (DMP)) with 2-electron or cyclic 6-electron ligands gives the salts [Ru(η 5-C 7H 11)L 3]BF 4 (L CO, PMe 3, P(OMe) 3, CH 3CN; L 3 = 1,1,1-tris(diphenylphosphinomethyl)ethane) and [Ru(η 5-C 7H 11)(η n -ring)]BF 4 ((η n -ring) = η 6-cyclohepta-1,3,5-triene, η-cycloocta-1,3,5,7-tetraene, η 6-arene, η 5-thiophene). In the presence of a halide salt, 1 reacts with 4-electron diene ligands to give neutral [Ru(η 5-C 7H 11)(diene)X] complexes (X I, Cl, and (diene) = η 4-buta-1,3-diene; η 4-2,3-dimethylbuta-1,3-diene, η 2:η 2- cycloocta-1,5-diene) and with 2-electron ligands to give neutral [Ru(η 2-C 7H 11)L 2X] complexes (X I, Br, Cl and L CO, P(OMe) 3, PMe 3; X I and L 2 = bis(diphenylphosphino)ethane; X Cl and L 2 = N,N,N′,N′-tetramethylethylenediamine). [Ru(η 5-C 6H 7)(η 4-C 6H 8)I] is the product of the reaction of 1 with cyclohexa-1,3-diene and KI. The complexes [Ru(η 5-C 7H 11)(P(OMe) 3) 3]BF 4 and [Ru(η 5-C 7H 11)L 2I] (LCO, P(OMe) 3) have been crystallographically characterized. Complexes of the type [Ru(η 5-C 7H 11)L 3] + and [Ru(η 5-C 7H 11)L 2X] exhibit dynamic behaviour in solution due to rotation of the DMP ligand with respect to the RuL 3 or RuL 2X groups, and activation energies for twelve of the complexes have been evaluated. Exchange of free and coordinated acetonitrile in solutions of [Ru(η 5-C 7H 11)(NCCH 3) 3]BF 4 is non-stereospecific and associative in character.