Alkyne insertions into the σ-Pd–C(sp2, ferrocene) bond of cyclopalladated complexes containing Schiff bases derived from ferrocene. Crystal structures of [Pd{[(EtCCEt)2(η5-C5H3CRNCH2Ph)]Fe(η5-C5H5)}Cl](R = H or Me)

Abstract

Reactions of di-µ-chloro-bridged cyclopalladated compounds [{[graphic omitted]R′)Fe(η⁵-C₅H₅)](µ-Cl)}₂](R = H, Ph or Me, R′= CH₂Ph; R = H, R′= CH₂CH₂Ph) with alkynes R″CCR″(R″= Et or Ph) have been studied. In all cases these reactions produce nine-membered metallocycles [[graphic omitted]R′)]Fe(η⁵-C₅H₅)}Cl](R″= Et or Ph), which arise from a double insertion of the alkyne. Compounds [[graphic omitted]CH₂Ph)]Fe(η⁵-C₅H₅)}Cl](R = H 4a or Me 4d) have been characterized structurally. Complex 4a is monoclinic, space group C2/c, with a= 30.783(4), b= 11.320(2), c= 20.181(3)Å and β= 127.23(3)°; compound 4d is also monoclinic space group P2₁/a, with a= 20.308(4), b= 11.075(2), c= 12.565(2)Å and β= 92.01(3)°. These structural studies confirm the existence of a bicyclic system arising from the fusion of a nine-membered ring and the C₅H₃ moiety of the ferrocenyl moiety. The differences observed in the reactivity of the σ(Pd–C_{sp², ferrocene}) bond in the cyclopalladated compounds [{[graphic omitted]R′)Fe(η⁵-C₅H₅)](µ-Cl)}₂](R = H, Ph or Me) and in [{[graphic omitted]Me₂}Fe(η⁵-C₅H₅)](µ-Cl)}₂] can be explained in terms of the electron donor ability of the chelated ligand. This property is reflected mainly in the redox potential of the iron centre.