The Carbon-Metal Sigma Bond

In molecular orbital (MO) terminology, the MO formed by overlap between the carbon hybrid orbital and the metal hybrid orbital is called a sigma orbital. An atomic 3 orbital is perfectly spherical and hence has the highest possible symmetry. It has the same sign everywhere, by 

Although the first olefin-transition metal complex, potassium ethylene trichloroplatinite, K[C2H PtCl3], was discovered in 1827, it was not until 1953 that its correct structure was elaborated. Extension by Chatt and 

Duncanson (i) of the molecular orbital bonding concepts of Dewar (2), which he developed to explain the structure of Ag+-olefin complexes, led to the suggestion that ethylene is symmetrically coordinated to the metal. Platinum, atomic number 78, has the electronic configuration of the xenon core (Is 2s 2p 35 3p 3d Z = 54), then 

The ethylene-platinum bonding (a), the common representation emphasizing w electron donation (6), the e-bonding molecular orbital (c), the 7r-bonding molecular orbital. 

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