Structure and Bonding in Metal Alkene Complexes

Probably the first metal alkene complex was Zeise s salt, K[Pt(C2H4)Cl3] or the bridged compound [PtCl2(C2H4)]2. These compounds were first prepared by Zeise in about 1825. The palladium analogs of these compounds are also now known. A large number of metal alkene complexes are known, and some of the chemistry of these materials will be described here. 

In this case, the bond between the carbon atoms is about the same as it is for a C-C single bond. Moreover, unlike the anion of Zeise s salt, the carbon atoms are in the plane formed by platinum and the other ligands. Clearly, this represents a significant difference from the usual alkene complexes. In essence, a three-membered C-P-C ring is formed. It appears in this case that the ability of the 

CHAPTER 21 Complexes Containing Metal-Carbon and Metal-Metal Bonds 

Other organic ligands can be bound in more than one way also. For example, the allyl group can be bound by a cr-bond between the metal and one carbon atom (rf) or as a 7r donor encompassing all three carbon atoms (ry3)  

Butadiene can function as a donor of four electrons in which the bonding is delocalized. A complex of this type is Fe(CO)3(774-C4H8)( which has the structure 

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