In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands. The arenes have the formula C_nH_n, substituted derivatives (for example C_n(CH₃)_n) and heterocyclic derivatives (for example BC_nH_n+1). Because the metal is usually situated between the two rings, it is said to be "sandwiched." A special class of sandwich complexes are the metallocenes.