1,5-Cyclooctadiene

Cycloocta-1,5-diene is a cyclic hydrocarbon with the chemical formula , specifically . 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 () or on opposite sides () of the double bond's plane; the three possibilities are denoted , , and chem name|cis,trans; or (), (), and (). (Because of overall symmetry, is the same configuration as .) Generally abbreviated COD, the 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. 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 (or similar reagents) to give 2,6-dichloro-9-thiabicyclo[3.3.1]nonane: The resulting dichloride can be further modified as the diazide or dicyano derivative in a nucleophilic substitution aided by anchimeric assistance. File:Ni(cod)2.png|[[Bis(cyclooctadiene)nickel(0)]]. File: Crabtree.svg|[[Crabtree's catalyst]]. File: Cyclooctadiene-rhodium-chloride-dimer-2D-skeletal.png|The complex [[Cyclooctadiene rhodium chloride dimer|{{chem2|Rh2(COD)2Cl2}}]]. File:Co(C8H12)(C8H13).png|Co(1,5-cyclooctadiene)(cyclooctenyl). File:PdCl2(cod).png|[[Dichloro(1,5‐cyclooctadiene)palladium]] File:Ir2Cl2 cod 2improved.svg|[[cyclooctadiene iridium chloride dimer]] File:Cl2Ptcod.png|[[Dichloro(1,5-cyclooctadiene)platinum(II)|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.