Dewar–Chatt–Duncanson model

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Orbital interactions in a metal-ethylene complex. On the left, a filled pi-orbital on C2H4 overlaps with an empty d-orbital on the metal. On the right, an empty pi-antibonding orbital on C2H4 overlaps with a filled d-orbital on the metal

The Dewar–Chatt–Duncanson model is a model in organometallic chemistry that explains the chemical bonding in transition metal alkene complexes. The model is named after Michael J. S. Dewar,[1] Joseph Chatt and L. A. Duncanson.[2][3]

The

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

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. ^ Dewar, M. Bulletin de la Société Chimique de France 1951, 1 8, C79
  2. doi:10.1039/JR9530002939
  3. doi:10.1039/JR9550004456
  4. ISBN 0-13-035471-6
    ..
  5. ^ Herrmann/Brauer: Synthetic Methods of Organometallic and Inorganic Chemistry Georg Thieme, Stuttgart, 1996
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