Open-chain acyclic pentadienyl complexes

4-pentadiene is deprotonated by n-butyllithium in the presence of tetrahydro-furan to yield an orange solution of pentadienyllithium. The potassium derivative can be prepared from either 1, 3- or 1,4-pentadiene in THF using LiBu /KOBu or potassium metal in the presence of triethylamine. While the pentadienyl group adopts a W configuration in the lithium derivative, it is U shaped in the potassium salt. 

Reaction of pentadienyl anions with anhydrous dihalides of the First Transition Series in THF yields a series of acyclic pentadienyl complexes (Fig. 9.15). The 2,4-dimethylpentadienyl derivatives are generally more robust than the unsubstituted compounds and most work has been done on them. 

The 14-electron titanium complex is monomeric and thermally robust, unlike titanocene itself (p. 290). It adds only one molecule of CO or PF, to yield 16-electron adducts Tilj/ -Me CjHJjL in which the two pentadienyl ligands are parallel and eclipsed. 

It is to be expected that a wide range of pentadienyl complexes, analogous to cyclopentadienyls, remain to be discovered. Pentadienyltricarbonylmanganese, analogous to cymantrene, CpMn(CO)j has been prepared from MejSnCjH, and Mn(CO)5Br. It adds basic ligands such as PMe under mild conditions to give // derivatives. This easy interconversion seems to be a feature of pentadienyl 

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