Activation of CH bonds of N-donor ligands by palladium compounds

Abstract

Some cyclometallated palladium(II) compounds have been synthesized from the ortho- and para-chloro isomers of the imine [ClC6H4CHNCH2C6H5]. The C-H bond aryl activation was performed by the metallation agent Pd(AcO)2 and the expected acetate-bridged cyclometallated compounds [Pd{μ-AcO}{ClC6H3CHNCH2C6H5}]2 have been obtained. Some reactions of [Pd{μ-AcO}{ClC6H3CHNCH2C6H5}]2 were performed and three type of compounds have been obtained; the bridged dinuclear, the neutral mononuclear and the ionic mononuclear. The respective halogen-bridged analogues [Pd{μ-X}{ClC6H3CHNCH2C6H5}]2 were formed after reacting acetate-bridged compounds with LiBr or LiCl. Splitting reaction took place, when acetate-bridged compounds react with phosphines, but depending of the nature of the phosphine different products could be formed. Neutral mononuclear cyclometallated compounds were obtained by reacting with PPh3, whereas ionic mononuclear cyclometallated compounds were obtained by reaction with diphosphine dppe (Ph2PCH2CH2Ph). The products were characterized by 1H and 31P NMR, IR and MS-ESI+. It has been found some tendencies through the products: i) the ortho-chloro atoms show an interaction with the imine proton in all the compounds obtained; ii) monodentated phosphines or pyridines adopt a trans arrangement with the imine nitrogen that tend to shield the nearest proton of the metallated aryl ring; iii) dinueclear compounds are more rigid than mononueclear compounds.