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.

Dinuclear MoV Complexes with Thiophenolate‐oxazoline Ligands: Synthesis, Characterization, and Exceptional Activity in Catalytic Olefin Epoxidation

“…The lack of reactivity with added Lewis bases, as observed for pyridine and acetonitrile, further supports this conclusion. Furthermore, coordinative flexibility and hemilability of ligand L1 has previously been observed in W and Pd complexes , . This flexibility is also demonstrated by the observed trans orientation of L1 in 1 and its cis configuration in 3 , as well as by the dynamic behavior in solution (VT 1 H NMR; Figure ).…”

“…In contrast, in complex 3 the ligands adopt a cis configuration in the solid state, with the oxazoline and thiophenolate rings on the same side of the Mo 2 O 3 S core. These two different stereoisomers point to a certain flexibility and potential hemilability in the coordination mode of ligand L1 , which has been previously observed in palladium(II) complexes . Otherwise, the coordination around the two Mo atoms of 3 is quite similar to that of 1 .…”

“…We observed broad resonances of 1 and 2 in the 1 H NMR spectra in [D 6 ]DMF indicating potential dynamic behavior in solution. This is most likely caused by the hemilability of the thiophenolate‐oxazoline ligand, which we previously observed in its behavior towards Pd II centers, and results in cis/trans isomerization of the complexes. This hemilability is potentially also an important factor for the high catalytic activities of complexes 1 and 2 in olefin epoxidation (vide infra).…”

“…Both, [MoO 2 (pyz) 2 ] complexes and their phenolate‐oxazoline counterparts [MoO 2 (oz) 2 ], showed high activities in the epoxidation of cyclooctene, reaching turnover frequencies (TOF) of 5000 and 4800 h –1 , respectively, which rank both of them among the most active homogeneous Mo epoxidation catalysts according to a review published in 2013 . Recently, we have begun to explore the chemistry of the thiophenolate analogue of the oz ligand, that is, the ligand S‐Phoz ( 1 ; Figure and Scheme ) . Herein, we report on the synthesis, characterization, and catalytic activity in olefin epoxidation of molybdenum complexes that contain the bidentate S,N ligands L1 and L2 .…”

Mercaptoaryl‐Oxazoline Complexes of Palladium and Their High Activities as Catalysts for Suzuki–Miyaura Coupling Reactions in Water

“…Having established our expertise in the coordination of the 2‐(2‐thiophenyl)‐4,4‐dimethyloxazoline (S‐Phoz) ligand with group 6 and 10 metals,, we recognized the potential of our previously reported Pd–(S‐Phoz) system for Suzuki–Miyaura couplings in water. In agreement with the hard and soft acids and bases (HSAB) principle, Pd–S bonds are strong, as this interaction is seen as a soft‐acid, soft‐base bond, which is believed to be beneficial under the usually harsh conditions applied during SMC in water.…”