Half sandwich compound

Early studies on (η6-C6H6)Cr(CO)3 were carried out by Natta, Ercoli and Calderazzo,[4] and Fischer and Ofele,[5][6] and the crystal structure was determined by Corradini and Allegra in 1959.

Subsequent treatment with an acid results in the addition of a nucleophile to the benzene ring at a site ortho ("cine"), meta or para ("tele") to the ipso carbon (see Arene substitution patterns).

The resulting organolithium compound serves as a nucleophile in various reactions, for example, with trimethylsilyl chloride:[citation needed] (η6-C6H6)Cr(CO)3 is a useful catalyst for the hydrogenation of 1,3-dienes.

[17] Typical arene tricarbonyl piano stool complexes of Mn(I) and Re(I) are cationic and thus exhibit enhanced reactivity toward nucleophiles.

[18][19] Half-sandwich compounds employing Ru(II), such as (cymene)ruthenium dichloride dimer, have been mainly investigated as catalysts for transfer hydrogenation.

[20] 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).

[22] (η6-C6H6)RuCl2 readily undergoes ligand exchange via cleavage of the chloride bridges, making this complex a versatile precursor to Ru(II) piano stool derivatives.