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The Dewar–Chatt–Duncanson model is a model in PtCl3(C2H4)">platinum.html" ;"title="/nowiki>platinum">PtCl3(C2H4)sup>.H2O the C−C bond length has increased to 134 picometres from 133 pm for ethylene. In the nickel compound Ni(C2H4)(PPh3)2 the value is 143 pm.
The interaction also causes carbon atoms to "rehybridise" from sp2 towards sp3, which is indicated by the bending of the hydrogen atoms on the ethylene back away from the metal.
The Dewar–Chatt–Duncanson model is a model in organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
that explains the chemical bond
A chemical bond is the association of atoms or ions to form molecules, crystals, and other structures. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons a ...
ing in transition metal alkene complexes. The model is named after Michael J. S. Dewar, Joseph Chatt and L. A. Duncanson.
The alkene
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins.
The Internationa ...
donates electron density
Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typical ...
into a π-acid metal d-orbital
In quantum mechanics, an atomic orbital () is a function describing the location and wave-like behavior of an electron in an atom. This function describes an electron's charge distribution around the atom's nucleus, and can be used to calc ...
from a σ-symmetry bonding orbital between the carbon atoms. The metal donates electrons back from a (different) filled d-orbital into the empty π* antibonding orbital. Both of these effects tend to reduce the carbon-carbon bond order, leading to an elongated C−C distance and a lowering of its vibrational frequency.
In Zeise's salt
Zeise's salt, potassium trichloro(ethylene)platinate(II) hydrate, is the chemical compound with the formula K platinum.html" ;"title="/nowiki>platinum">PtCl3(C2H4)·H2O. The anion of this air-stable, yellow, coordination complex contains an hapt ...
K
The interaction also causes carbon atoms to "rehybridise" from sp2 towards sp3, which is indicated by the bending of the hydrogen atoms on the ethylene back away from the metal. In silico
In biology and other experimental sciences, an ''in silico'' experiment is one performed on a computer or via computer simulation software. The phrase is pseudo-Latin for 'in silicon' (correct ), referring to silicon in computer chips. It was c ...
calculations show that 75% of the binding energy is derived from the forward donation and 25% from backdonation. This model is a specific manifestation of the more general π backbonding
In chemistry, pi backbonding or π backbonding is a π-bonding interaction between a filled (or half filled) orbital of a transition metal atom and a vacant orbital on an adjacent ion or molecule. In this type of interaction, electrons from the ...
model.
Similar to alkenes, alkynes adopt a similar bonding interaction, as shown in the image on the right. Not all alkyne-metal complexes utilize all four of these interactions for bonding (due to reasons like unviable d orbitals).
Main group elements can also form π-complexes with alkenes and alkynes. The β-diketiminato aluminum(I) complex Al (Ar = 2,6-diisopropylphenyl), which bears an Al-based sp''x'' lone pair, reacts with alkenes and alkynes to give alumina(III)cyclopropanes and alumina(III)cyclopropenes in a process analogous to the formation of π-complexes by transition metals. However, in most cases, the backbonding interaction is absent in these complexes due to the lack of energetically accessible filled orbitals for backdonation, resulting in π-complexes that dissociate readily and are therefore more challenging to observe or isolate.
References
{{DEFAULTSORT:Dewar-Chatt-Duncanson Model Organometallic chemistry Chemical bonding