Question

Question #77174

Answer 1

dπ-pπ bonding is the formation of a π molecular orbital by the overlap of a d orbital on one atom with a `p` or `p"*"` orbital on another atom.

Explanation:

An example is the orbital overlap in a metal carbonyl such as Ni(CO)₄.

Usually, one atom supplies both electrons to the new bond. If the `d` orbital supplies the electrons, the process is called backbonding.

Phosphorus does not form dπ-pπ bonds, because the `d` orbitals on P are too high in energy.

However, the lone-pair electrons in phosphines (R₃P) make good `σ` donors to the d orbitals of transition metals.

Electron withdrawing groups lower the energies of the `σ"*"` orbitals. These antibonding orbitals can then act as backbonding `π` acceptors.

PF₃ is almost as good an acceptor as CO. Phosphites [(RO)₃P] are about half as good as CO.