New Pd(ii) complexes of sulfur ylides; synthesis, X-ray characterization, a theoretical study and catalytic activity toward the Mizoroki–Heck reaction

Abstract

The reaction of sulfur ylides (L) SMe₂C(H)C(O)R (R = 4-nitrophenyl, phenyl, and 3-nitrophenyl) with the dichloro(1,5-cyclooctadiene)palladium(II) complex, [PdCl₂(cod)], in a 2 : 1 ratio gives the new Pd(II) complexes of type cis- and trans-[PdCl₂(SMe₂C(H)C(O)R)₂] (R = phenyl (1), 3-nitrophenyl (2), and 4-nitrophenyl (3)). Characterization of the obtained complexes was performed by elemental analysis, IR, ¹H, ¹³C NMR and mass spectroscopies. Also, the structure of complex trans-[PdCl₂(SMe₂C(H)C(O)C₆H₄-p-NO₂)₂] (3) was characterized by single crystal X-ray analysis. The X-ray crystallography results reveal that the structure of complex 3 contains two Cα-coordinated sulfur ylide ligands in trans geometry. These air/moisture stable complexes were also employed as efficient catalysts for the Mizoroki–Heck cross-coupling reaction of several aryl halides with olefins. The coupled products of these reactions were obtained in good to excellent yields and purity, short reaction times and low catalyst loading. Also a theoretical study on the structure of the complexes 1–3 have been investigated at the BP86/def2-SVP level of theory. The bonding situation between the [PdCl₂] and L₂ fragments [(Ylide)₂] in the [L₂PdCL₂] complexes, were carried out by NBO and energy-decomposition analysis (EDA), as well as their natural orbitals for chemical valence variation (EDA-NOCV). The results confirmed that the contribution of the electrostatic interactions in the Pd–C bond in the complexes is about 50%.