Dihydropentalenes from the palladium( II )-induced cyclotetramerisation of acetylenes; X -ray crystal structures of two dihydropentalenes

Phenyl- or p-chlorophenyl-acetylene reacts with [PdL(ButCCHCHCButCl)Cl](L = 2,5-dithiahexane) to give the dihydropentalenes (IIa, R1= Ph) and (IIb, R1= C6H4Cl-p), which are isostructural with the orange tetramer (Ph4C8H4) obtained from the reaction of phenylactylene with PdCl2; the structures of (IIb) and of the purple tetramer (Ph4C8H4) also obtained from the latter reaction have been elucidated by X-ray crystallography.