allyl-metal complex

Coordination compound of a metal and the organic allyl (CH2:CHCH2) group. Allyl-metal complexes are very reactive to oxygen, inflaming in air. The allyl groups are easily replaced by other ligands such as the carbonyl group, CO.

There are two principal types: the sigma complex, in which the allyl group is directly and singly bonded to the metal, as in any of the organometallic compounds, for example in a manganese complex, CH2:CHCH2Mn(CO)5; and the pi-complex, where delocalization of the pi-electrons in the allyl system gives an allyl ligand which replaces two monodentate ligands on the metal (for example CH2CHCH2Mn(CO)4).