Mono‐ and dinuclear oxime palladacycles bearing diphosphine ligands: An unusual coordination mode for dppe

Abstract

Three new oxime‐based palladacycles, namely [Pd{C,N‐C6H4{C(Me)NOH}‐2}(dppm)]ClO4 (1), [Pd2{C,N‐C6H4{C(Me)NOH}‐2}2(dppe)2(μ‐dppe)](ClO4)2 (2) and [Pd{C,N‐C6H4{C(Me)NOH}‐2}(dppmS2)]ClO4 (3), were synthesized by the reaction of dinuclear oxime complex [Pd{C,N‐C6H4{C(Me)NOH}‐2}(μ‐Cl)]2 with different diphosphine ligands (dppm, dppe and dppmS2). The synthesized complexes were characterized using Fourier transform infrared, 31P NMR, 1H NMR and 13C NMR spectroscopic methods and elemental analyses, and their molecular structures were elucidated using X‐ray crystallography. The structure of 2 is worthy of note as it is the first oxime palladacycle where there are both bridging (P–) and chelating (P^P) dppe ligands, giving rise to a dinuclear complex. The palladium atom is in a five‐coordinate, square pyramidal P3NC environment, while in 3 the palladium atom is in a distorted square planar environment, coordinated by the oxime ligand and a chelating (S^S) dppmS2 ligand. These complexes were employed as efficient catalysts for the Suzuki–Miyaura cross‐coupling reaction of several aryl bromides with phenylboronic acid. The in vitro cytotoxicity of the compounds was also evaluated against human tumour cell lines (HT29, A549 and HeLa) using the MTT assay method. The results indicate that the dinuclear complex 2 has greater catalytic and anticancer activity in comparison with the mononuclear complexes 1 and 3.