Half-sandwich compounds employing Ru(II), such as (cymene)ruthenium dichloride dimer, have been mainly investigated as catalysts for transfer hydrogenation.  These complexes feature three coordination sites that are susceptible to substitution, while the arene ligand is tightly bonded and protects the metal against oxidation to Ru(III).  They are prepared by reaction of RuCl·x(HO) with 1,3-cyclohexadienes. Work is also conducted on their potential as anticancer drugs.
(η-CH)RuCl readily undergoes ligand exchange via cleavage of the chloride bridges, making this complex a versatile precursor to Ru(II) piano stool derivatives.