Английская Википедия:1,5-Cyclooctadiene

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Cycloocta-1,5-diene is a cyclic hydrocarbon with the chemical formula Шаблон:Chem2, specifically Шаблон:Chem2.

There are three configurational isomers with this structure, that differ by the arrangement of the four C–C single bonds adjacent to the double bonds. Each pair of single bonds can be on the same side (Шаблон:Chem name) or on opposite sides (Шаблон:Chem name) of the double bond's plane; the three possibilities are denoted Шаблон:Chem name, Шаблон:Chem name, and Шаблон:Chem name; or (Шаблон:Chem name), (Шаблон:Chem name), and (Шаблон:Chem name). (Because of overall symmetry, Шаблон:Chem name is the same configuration as Шаблон:Chem name.)

Generally abbreviated COD, the Шаблон:Chem name isomer of this diene is a useful precursor to other organic compounds and serves as a ligand in organometallic chemistry. It is a colorless liquid with a strong odor. 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.

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:

Файл:Synthesis of 9-BBN dimer.png

COD adds Шаблон:Chem2 (or similar reagents) to give 2,6-dichloro-9-thiabicyclo[3.3.1]nonane:

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

The resulting dichloride can be further modified as the diazide or dicyano derivative in a nucleophilic substitution aided by anchimeric assistance.

Metal complexes

• Selected metal 1,5-COD complexes.
• Bis(cyclooctadiene)nickel(0).

  Bis(cyclooctadiene)nickel(0).

• Crabtree's catalyst.

  Crabtree's catalyst.

• Шаблон:Chem2]].

  Шаблон:Chem2]].

• Co(1,5-cyclooctadiene)(cyclooctenyl).

  Co(1,5-cyclooctadiene)(cyclooctenyl).

• Dichloro(1,5‐cyclooctadiene)palladium

  Dichloro(1,5‐cyclooctadiene)palladium

• cyclooctadiene iridium chloride dimer

  cyclooctadiene iridium chloride dimer

• Dichloro(1,5‐cyclooctadiene)platinum

  Dichloro(1,5‐cyclooctadiene)platinum

1,5-COD binds to low-valent metals via both alkene groups. 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.

Шаблон:Chem2 is prepared by reduction of anhydrous nickel acetylacetonate in the presence of the ligand, using triethylaluminium

Шаблон:1/3Шаблон:Chem2

The related Шаблон:Chem2 is prepared by a more circuitous route involving the dilithium cyclooctatetraene:

Шаблон:Chem2

Шаблон:Chem2

Extensive work has been reported on complexes of COD, much of which has been described in volumes 25, 26, and 28 of Inorganic Syntheses. The platinum complex is a precursor to a 16-electron complex of ethylene:

Шаблон:Chem2

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

Шаблон:Chem2

The product Шаблон:Chem2 is highly toxic, thus it is advantageous to generate it in the reaction vessel upon demand. Other low-valent metal complexes of COD include cyclooctadiene rhodium chloride dimer, cyclooctadiene iridium chloride dimer, and Шаблон:Chem2, and Crabtree's catalyst.

The Шаблон:Chem2 complexes with nickel, palladium, and platinum have tetrahedral geometry, whereas Шаблон:Chem2 complexes of rhodium and iridium are square planar.

(E,E)-COD

Файл:EE-COD synthesis.svg

E,E-COD synthesis (Stöckmann et al. 2011)

The highly strained trans,trans isomer of 1,5-cyclooctadiene is a known compound. (E,E)-COD was first synthesized by George M. Whitesides and Arthur C. Cope in 1969 by photoisomerization of the cis,cis compound. Another synthesis (double elimination reaction from a cyclooctane ring) was reported by Rolf Huisgen in 1987. The molecular conformation of (E,E)-COD is twisted rather than chair-like. The compound has been investigated as a click chemistry mediator.