The Carbon-Metal Delocalized Pi Bond

As indicated above, in a complex such as [C2H4ptCl3], the Pt(II) is assumed to have a 6d configuration. Ethylene and each of the three 

Molecular orbital and resonance structure representation of cyclopentadienyl anion. 

It has become increasingly popular to represent [C5H5]- by the structure shown in Fig. 6d. This representation is a valence bond structure notation it is intended to represent the five equivalent resonance structures (three of these are shown as Figs. 6c, /, and g the other two are similar), in which the negative charge is located at each carbon in turn. Each double bond is thus only a partial double bond and, if the usual notation of writing a partial double bond by a dashed line were applied, the structure would be written as 6h. The solid circle (6d) is a rapid way to write the 66 structure. In a completely analogous 

In writing structures of the transition metal complexes, it is convenient to employ the convention of a dashed (or solid) line to connect the carbon atoms on the ligand which are part of a delocalized tt system and a single 

From the MO point of view, the three carbon prr AO s of the allyl system combine to generate three MO s, all of which will have a node in the plane of the carbon atoms. Because all the carbon atoms are sp, the C—C—C angle should be approximately 120° and the three carbon atoms as well as the five hydrogen atoms all lie in one plane (Fig. 9). The three MO s are shown in Figs. 10a, 6, and c. 

---