Cycloocta-1,5-diene

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1,5-Cyclooctadiene
Skeletal formula of 1,5-cyclooctadiene
Ball-and-stick model of 1,5-cyclooctadiene
Identifiers
InChI InChI=1/C8H12/c1-2-4-6-8-7-5-3-1/h1-2,7-8H,3-6H2/b2-1-,8-7-
InChIKey VYXHVRARDIDEHS-QGTKBVGQBM
Standard InChIKey VYXHVRARDIDEHS-QGTKBVGQSA-N
CAS number [111-78-4]
EC number 203-907-1
ChemSpider 74815
Properties
Chemical formula C8H12
Molar mass 108.18 g/mol
Appearance clear colorless liquid
Density 0.882 g/ml, liquid
Melting point

-69.5 °C

Boiling point

151 °C

Solubility in water -
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

1,5-Cyclooctadiene is the organic compound with the chemical formula C8H12. Generally abbreviated COD, this diene is a useful precursor to other organic compounds and serves as a ligand in organometallic chemistry.[1][2]

Synthesis

1,5-Cyclooctadiene can be prepared by dimerization of butadiene in the presence of a nickel catalyst, a coproduct being vinylcyclohexene. Approximately 10,000 tons were produced in 2005.[3]

Reactions and applications

Organic reactions

COD reacts with borane to give 9-borabicyclo[3.3.1]nonane, commonly known as 9-BBN, a reagent in organic chemistry used in hydroborations. COD adds SCl2 (or similar reagents) to give 2,6-dichloro-9-thiabicyclo[3.3.1]nonane:[4]

2,6-Dichloro-9-thiabicyclo[3.3.1]nonane, synthesis and reactions

The resulting dichloride can be further modified as the di-azide or di-cyano derivative in a nucleophilic substitution aided by anchimeric assistance.

Metal complexes

1,5-COD typically binds to low-valence metals via both alkene groups. The complex Ni(cod)2 is a precursor to several nickel(0) and Ni(II) complexes. Metal-COD complexes are attractive because they are sufficiently stable to be isolated, often being more robust than related ethylene complexes. The stability of COD complexes is attributable to the chelate effect. The COD ligands are easily displaced by other ligands, such as phosphines.

Structure of M(cod)2 for M = Ni, Pd, Pt.

Ni(COD)2 is prepared by reduction of anhydrous nickel acetylacetonate in the presence of the ligand, using triethylaluminium [5]

1/3 [Ni(C5H7O2)2]3 + 2 COD + 2 Al(C2H5)3 → Ni(COD)2 + 2 Al(C2H5)2(C5H7O2) + C2H4 + C2H6

The related Pt(COD)2 is prepared by a more circuitous route involving the dilithium cyclooctatetraene:[6]

Li2C8H8 + PtCl2(COD) + 3 C7H10 → [Pt(C7H10)3] + 2 LiCl + C8H8 + C8H12
Pt(C7H10)3 + 2 COD → Pt(COD)2 + 3 C7H10

Extensive work has been reported on complexes of COD, much of which can has been described in volumes 25, 26, and 28 of Inorganic Syntheses. The platinum complex has been used in many syntheses:

Pt(COD)2 + 3 C2H4 → Pt(C2H4)3 + 2 COD

COD complexes are useful as starting materials, one noteworthy example is the reaction:

Ni(cod)2 + 4 CO(g) ⇌ Ni(CO)4 + 2 COD

The product Ni(CO)4 is highly toxic, thus it is advantageous to generate it in the reaction vessel as opposed to being dispensed directly. Other low-valent metal complexes of COD include Mo(COD)(CO)4, [RuCl2(COD)]n, and Fe(COD)(CO)3. COD is an especially important in the coordination chemistry of rhodium(I) and iridium(I), examples being Crabtree's catalyst and cyclooctadiene rhodium chloride dimer. The square planar complexes [M(COD)2]+ are known (M = Rh, Ir).

References

  1. ↑ Buehler, C; Pearson, D.Survey of Organic Syntheses. Wiley-Intersciene, New York. 1970.
  2. ↑ Shriver, D; Atkins, P.Inorganic Chemistry. W. H. Freeman and Co., New York. 1999.
  3. ↑ Thomas Schiffer, Georg Oenbrink “Cyclododecatriene, Cyclooctadiene, and 4-Vinylcyclohexene” in Ullmann’s Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim.
  4. ↑ Roger Bishop 9-Thiabicyclo[3.3.1]nonane-2,6-dione. Org. Synth., <http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV9P0692>; Coll. Vol., 9, 692Díaz, David Díaz (2006). "2,6-Dichloro-9-thiabicyclo[3.3.1]nonane: Multigram Display of Azide and Cyanide Components on a Versatile Scaffold". Molecules 11: 212–218. doi:10.3390/11040212. 
  5. ↑ Schunn, R; Ittel, S. (1990). "Bis(1,5-Cyclooctadiene) Nickel(0)". Inorg. Synth. 28: 94. doi:10.1002/9780470132593.ch25. 
  6. ↑ Crascall, L; Spencer, J. (1990). "Olefin Complexes of Platinum". Inorg. Synth. 28: 126. doi:10.1002/9780470132593.ch34. 

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