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Dewar–Chatt–Duncanson model

Dewar–Chatt–Duncanson model

The Dewar–Chatt–Duncanson model is a model in organometallic chemistry that explains the type of chemical bonding between an alkene and a metal (π-complex) in certain organometallic compounds. The model is named after Michael J. S. Dewar,[1] Joseph Chatt and L. A. Duncanson.[2][3]

The π-acid alkene donates electron density into a metal d-orbital from a π-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 K[PtCl3(C2H4)].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.[4] In silico calculations show that 75% of the binding energy is derived from the forward donation and 25% from backdonation.[5] This model is a specific manifestation of the more general π backbonding model.

References

[1]
Citation Linkopenlibrary.orgDewar, M. Bulletin de la Société Chimique de France 1951, 1 8, C79
Sep 26, 2019, 2:01 AM
[2]
Citation Linkdoi.org"Olefin co-ordination compounds. Part III. Infra-red spectra and structure: attempted preparation of acetylene complexes" J. Chatt and L. A. Duncanson, Journal of the Chemical Society, 1953, 2939 doi:10.1039/JR9530002939
Sep 26, 2019, 2:01 AM
[3]
Citation Linkdoi.orgDirecting effects in inorganic substitution reactions. Part I. A hypothesis to explain the trans-effect J. Chatt, L. A. Duncanson, L. M. Venanzi, Journal of the Chemical Society, 1955, 4456-4460 doi:10.1039/JR9550004456
Sep 26, 2019, 2:01 AM
[4]
Citation Linkopenlibrary.orgMiessler, Gary L.; Donald A. Tarr (2004). Inorganic Chemistry. Upper Saddle River, New Jersey: Pearson Education, Inc. Pearson Prentice Hall. ISBN 0-13-035471-6..
Sep 26, 2019, 2:01 AM
[5]
Citation Linkopenlibrary.orgHerrmann/Brauer: Synthetic Methods of Organometallic and Inorganic Chemistry Georg Thieme, Stuttgart, 1996
Sep 26, 2019, 2:01 AM
[6]
Citation Linkdoi.org10.1039/JR9530002939
Sep 26, 2019, 2:01 AM
[7]
Citation Linkdoi.org10.1039/JR9550004456
Sep 26, 2019, 2:01 AM
[8]
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Sep 26, 2019, 2:01 AM