Palladium migration along linear carbon chains: The detection of eta(1)-eta(2)-enyl intermediates and the study of their rearrangement

The reactions of [PdPfBr(NCMe)(2)] (Pf = C6F5) with stoichiometric amounts of 1,5-hexadiene, 1,6-heptadiene, or 1,7-actadiene aa,law temperature result in the formation of several (eta(1)-eta(2)-enyl.)palladium complexes that isomerize sequentially at different temperatures depending on the ring size of the palladacycles (T-isom: 7.5- < 6.5- < 5.5-membered). These (eta(1)-eta(2)-enyl)palladium derivatives are intermediates in the Pd-migration process, arrested by coordination of the unattacked double bond. The final products of their isomerization are several isomeric Pf-(eta(3)-allyl) palladium complexes (Pf = C6F5). The major allylic derivative in each case arises from Pd migration to the terminal double bond. Minor amounts of (eta(3)-allyl)palladium complexes formed by double bond switches in the process of Pd migration are also seen, but this occurs only on putative 1,5-or 1,6-diene-hydrido-palladium intermediates. A small amount of cyclic organic derivatives coming from the cyclization of (eta(1)-eta(2)-enyl)palladium intermediates is detected in each case. The use of excess diolefin gives rise to additional (eta(3)-allyl)palladium complexes without the Pf group and to the corresponding Pf-suustituted linear dienes. These arise via displacement of the Pf dienes by the starting diolefin in a hydrido-palladium intermediate during the Pd-migration process.