From metal salt, reducing agent and ligand

Some examples of the application of this method are listed inTableXIII. 

Metal Salt Reducing Agent Ligand Product 

MnCU eras CrCla FeCla Ph2CO Na+ Zn/Hg A1 (AlQs) RCH2CH2MgX CO/100 atm. 150 C CO Benzene Olefin Mn2(CO)io Cr(CO)6 ( -C6H6)2Cr+ Fe olefin complex 

The reduction of a metal salt by aluminium and aluminium trichloride in the presence of an aromatic hydrocarbon, which is illustrated in Table XIII, provides the most general method known for the preparation of bis-ff-arene complexes. It was first used by Fischer and Hafner for the synthesis of bis-w-arene chromium complexes (Fischer s reducing Friedel-Crafts proceditfe). 

The cation 6.1 may readily be reduced to bis-fl--benzene chromium by aqueous sodium dithionite  

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