Question 77174

Jan 4, 2015

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 $p \text{*}$ 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.