η3-Allylpalladium Complexes from Medium-Ring Cycloalkenes

The dimeric η 3 -allylpalladium chloride complexes formed from various cycloalkenes (C 7 −C 13 ) and some methyl- and tert -butyl-substituted cycloalkenes have been characterized by 1 H and 13 C NMR spectroscopy and in selected cases by X-ray crystallography. The formation of syn and anti isomers in the larger ring systems is demonstrated, and complexes with a rearranged ring system are formed from tert -butylcyclodecene and tert -butylcyclododecene. The sesquiterpene, carophyllene, is shown to form an η 3 -allyl exocyclic complex, exclusively from the ( E )-double bond. Cis and trans isomers, with respect to allyl group orientation in these halo-bridged dimers, have been identified by low-temperature (190K) NMR spectroscopy, and their interconversion (Δ G ⧧ ≈ 11 kcal/mol) is considered to involve a “cubic” η 3 -allylpalladium chloride tetramer.