Cyclotrimerization of phenylethynes to fulvene: reactivity of cis-dichloro(1,1′-bis(diphenylphosphino)ferrocene)palladium(II)

In the presence of triethylamine (NEt3) and ethanol (EtOH), phenylethyne (or phenylacetylene, PhCCH) underwent cyclotrimerization: cis-dichloro(1,1′-bis(diphenylphosphino)ferrocene)palladium(II), [PdCl2(dppf)] (1), reacted with phenylethyne to give [Pd(dppf)(2,3,5-triphenylfulvene)] (2). Reaction of 2 with dimethyl acetylenedicarboxylate in dichloromethane gave [Pd(dppf)(CH3O2CCCCO2CH3)] (3) and a free 2,3,5-triphenylfulvene. Crystallographic data for 2·H2O: triclinic space group P, a=10.658(2), b=10.896(2), c=21.080(3) Å, α=85.303(9)°, β=76.556(9)°, γ=80.447(10)°, Z=2, R(wR2)=0.0487(0.1083).