In chemistry, decomplexation refers to the removal of a ligand from a coordination complex. Decomplexation is of particular interest when the ligand has been synthesized within the coordination sphere of the metal, as is often the case in organometallic chemistry.

Decomplexation by ligand displacement

Ligands can be decomplexed by displacement with another ligand, e.g., a highly basic ligand or the use of high pressures of carbon monoxide. Arenes are liberated from (arene)Cr(CO)3 with pyridine:[1]

(arene)Cr(CO)3 + 3 C5H5N → Cr(CO)3(NC5H5)3 + arene

In this case Cr(CO)3(pyridine)3 can be recycled. Illustrative of this approach is the synthesis of (–)-steganone via a chromium haloarene complex. The synthesis is completed by decomplexation, liberating the natural product.[2]

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1,4,7-Trithiacyclononane can be prepared within the coordination sphere of a metal, and then isolated by decomplexation.[3]

Oxidative decomplexation

Another popular method for decomplexation involves oxidation of a low valent complex. Oxidants include air,[4] dioxirane,[5] ceric ammonium nitrate (CAN), and halogens. Oxidants are selected to avoid reaction with the released organic ligand. Illustrative is the use of ferric chloride to release alkynes from Co2(C2R2)(CO)6. One drawback to this method is that the organometallic center is usually destroyed.[6] One example of oxidative decomplexation involves the CAN-induced release and trapping of cyclobutadiene from cyclobutadieneiron tricarbonyl.[7]

References

  1. ^ E. Peter Kündig (2004). "Synthesis of Transition Metal h6-Arene Complexes". Topics in Organometallic Chemistry. 7: 3–20. doi:10.1007/b94489. ISBN 978-3-540-01604-5.
  2. ^ Monovich, L. G.; Le Huérou, Y.; Ronn, M.; Molander, G. A. (2000). "Total Synthesis of (−)-Steganone Utilizing a Samarium(II) Iodide Promoted 8-Endo Ketyl−Olefin Cyclization". J. Am. Chem. Soc. 122: 52. doi:10.1021/ja9930059.
  3. ^ Sellmann, D.; Zapf, L. (1984). "Simple Route to 1,4,7-Trithiacyclononane". Angewandte Chemie. 96 (10): 799–800(2). doi:10.1002/ange.19840961019.
  4. ^ James H. Rigby; Kevin R. Fales (2000). "7α-Acetoxy-(1Hβ, 6Hβ)-Bicyclo[4.4.1]undeca-2,4,8-triene via Chromium-Mediated Higher Order Cycloaddition". Org. Synth. 77: 121. doi:10.15227/orgsyn.077.0121.
  5. ^ Luch, A.-M.; Jordi, L.; Sánchez-Baeza, F.; Ricart, S.; Camps, F.; Messeguer, A.; Moretó, J. M. (1992). "Dimethyldioxirane in Organometallic Chemistry. II. An Improved Procedure for the Oxidative Decomplexation of Fischer Carbene Complexes". Tetrahedron Letters. 33 (21): 3021–3022. doi:10.1016/S0040-4039(00)79588-8.
  6. ^ Nicholas, K. M. (1987). "Chemistry and Synthetic Utility of Cobalt-Complexed Propargyl Cations". Accounts of Chemical Research. 20 (6): 207–214. doi:10.1021/ar00138a001.
  7. ^ L. Brener; J. S. Mckennis; R. Pettit (1976). "Cyclobutadiene In Synthesis: endo-Tricyclo[4.4.0.02,5]deca-3,8-diene-7,10-dione". Org. Synth. 55: 43. doi:10.15227/orgsyn.055.0043.
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