Metallocenes electron donor-acceptor complexes

Similar hydrogen exchange reactions take place over the electron donor-acceptor complexes of the metallocenes with various organic electron acceptors such as quinones, and nitro- and cyano-substituted compounds (7). The hydrogen exchange reaction between acetylene or molecular hydrogen, and various EDA complexes of metallocenes proceeded at room temperature via bonded hydrogen (HZ) in the complexes, but did not take place over either metallocenes or quinones alone under the same reaction conditions. 

Stmctures 2.43 and 2.41 are examples of metallocene complexes. As shown by 2.43, metallocenes of the M elements without any other additional ligands have a common structure. Because of the presence of double bonds, the ligand Cp, like benzene, butadiene, COT, and 1,5-COD, acts both as an acceptor and as a donor. Electron density is donated from its filled r-orbitals. Electron density from the metal d orbitals is accepted in its antibonding r-orbitals. 

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