A comparative study of the reactivity of the σ(Pd–Csp2, ferrocene) and σ(Pd–Csp2, biphenyl) bonds in cyclopalladated complexes derived from [Fe(η5-C5H5)(η5-C5H4CHNC6H4C6H5-2)]

Abstract

A study has been made of the reactivity of the σ(Pd-C_sp²) bond in the di-μ-chloro-bridged cyclopalladated complexes [Pd{(η⁵-C₅H₃CHNC₆H₄C₆H₅-2)Fe(η⁵-C₅H₅)}(μ-Cl)]₂1a and [Pd{(C₆H₄-2-C₆H₄)NCH(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}(μ-Cl)]₂1b {which differ in the nature of the metallated carbon atom C_{sp², ferrocene} or C_{sp², biphenyl}, respectively} towards the alkynes, R¹CCR² {with R¹ = R² = Et; R¹ = H, Me or Ph, and R² = Ph; or R¹ = R² = CO₂Me}. Thus palladacycles containing seven-, eight-, nine- and ten-membered rings have been isolated and characterized. The crystal structure of [Pd{(EtCCEt)₂(C₆H₄-2-C₆H₄)NCH(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}Cl] has also been determined and confirms the presence of a [6, 6, 10] tricyclic system arising from fusion of the two hexagonal rings of the biphenyl group and a ten-membered palladacycle generated through bis(insertion) of hex-3-yne into the σ(Pd–C_{sp², biphenyl}) bond in 1b.