Acetylenes and noble metal compounds. Part XI. Reactions of di-methyl acetylenedicarboxylate with dibenzylideneacetone–palladium and –platinum complexes: pallada- and platina-cyclopentadienes

Abstract

Dimethyl acetylenedicarboxylate (RC₂R) reacted with the zerovalent dibenzylideneacetone (dba) palladium complexes to give the palladacyclopentadiene, [Pd(C₄R₄)]_n, characterised as the adducts Pd(C₄R₄)L₂[L = Ph₃P, (PhO)₃P, p-toluidine; L₂= Ph₂PCH₂CH₂PPh₂, bipy and phen]. [Pd(C₄R₄)]_n reacted with bromine to give Br(CR)₄Br, with air and Pd(PhCN)₂Cl₂ to give the furan R₄C₄O, and with acetylenes R′C₂R′to give the benzenes R₄R′₂C₆(R′= COOMe or Ph). The platinum analogue, [Pt(C₄R₄)]_n, has also been detected and was characterised as [Pt(C₄R₄)(Ph₃P)₂]. The mechanism of the formation of the metallacyclopentadienes and benzenes is discussed.