Coordinative flexibility of a thiophenolate oxazoline ligand in nickel(II), palladium(II), and platinum(II) complexes

Abstract

The synthesis, full characterization, and molecular structures of seven new coordination compounds that feature the 2-(4,4-dimethyloxazolin-2-yl)thiophenolate ligand (S-Phoz) with group 10 metals Ni, Pd, and Pt in the +II oxidation state are presented. The ML2 complexes [Pt(S-Phoz)2] (1a), [Pd(S-Phoz)2] (1b), and [Ni(S-Phoz)2] (2) were prepared starting from MCl2. Compound 1a was obtained isomerically pure in a trans arrangement, whereas its Pd analogue 1b exhibits a dynamic, solvent-dependent cis/trans equilibrium, and 2 adopts a tetrahedral arrangement. The reaction of LiS-Phoz with [cis-MCl2(PPh3)2] precursors resulted in full replacement of the PPh3 for M = Ni and in partial substitution for M = Pt, Pd to yield [Ni(S-Phoz)2] (2), [Pt(κ2-S-Phoz)(κ1-S-Phoz)(PPh3)] (3a), and [Pd(κ2-S-Phoz)(κ1-S-Phoz)(PPh3)] (3b). The Pd compound 3b exhibits an interesting solvent-dependent equilibrium with 1b and PPh3 as demonstrated by 1H and 31P NMR spectroscopy. Compounds [{PdCl(S-Phoz)}2] (4) and [PdCl(S-Phoz)(PPh3)] (5) were synthesized from [PdCl2(NCMe)2]. Molecular structures of compounds trans-1a, trans-1b, 2, 3a, 3b, 4, and 5 were determined by single-crystal X-ray diffraction studies. With the exception of the Ni complex 2, all compounds exhibit distorted square-planar geometries. A series of nickel, palladium, and platinum complexes that contain a thiophenolate oxazoline ligand were prepared. The ligand coordinates preferably in a bidentate manner but shows high coordinative flexibility depending on the metal center.