Influence of substituents on the electrochemical properties of nine-membered palladacycles of general formula [Pd{[(R1CCR2)2(η5-C5H3C(R3)NR4)]Fe(η5-C5H5)}Cl]

Abstract

The reactions of the di-μ-chloro-bridged cyclopalladated complex [Pd{[η⁵-C₅H₃C(H)NCH₂Ph]Fe(η⁵-C₅H₅)}(μ-Cl)]₂ with several alkynes, R¹CCR², in a 1: 4 molar ratio are described. They led to novel nine-membered palladacycles of general formula [Pd{[(R¹CCR²)₂(η⁵-C₅H₃C(H)NCH₂Ph)]Fe(η⁵-C₅H₅)}Cl], and to the di-μ-chloro-bridged derivative [Pd{[(EtO₂CCCPh)(η⁵-C₅H₃C(H)NCH₂Ph)]Fe(η⁵-C₅H₅)}(μ-Cl)]₂, which contains a seven-membered palladacycle. A comparative study of the electrochemical properties of a wide variety of nine-membered palladacycles containing ferrocenyl units of general formula [Pd{[(R¹CCR²)₂(η⁵-C₅H₃C(R³)NR⁴)]Fe(η⁵-C₅H₅)}Cl] {with R³  = H or Me and R⁴  = Ph, CH₂Ph, CH(Me)Ph, CH₂CH₂OH or C₆H₄C₆H₅-2} is also reported. Molecular orbital calculations at a DFT level have also been carried out to rationalize the influence of the nature of the substituents R¹, R², R³ and R⁴ in the nine-membered rings on the electrochemical properties of these two types of palladacycles.