Synthesis and Application of Novel Modified Amido-Phosphinite Ligands and Their Palladium (II) and Platinum (II) Complexes as a New Green Homogeneous Catalyst for Mizoroki-Heck and Suzuki–Miyaura Couplings

Abstract

The novel mandelamide N-[2-(phenylthio)phenyl]mandelamide (1) was prepared by reacting 2-(phenylthio)aniline with DL-mandelic acid under solvent-free conditions employing a microwave-assisted synthesis protocol. Subsequently, this mandelamide, 1, was converted into amidophosphinite ligands 2–4, which include Ph, Cy, or ⁱPr moieties. Treatment of ligands 2–4 with MCl₂(cod) (M = Pd, Pt; cod = 1,5-cyclooctadiene) give complexes cis-[Pd(C₂₀H₁₆NOS{OPR₂})₂Cl₂] (R = Ph (2a); Cy (3a); ⁱPr (4a)), and cis-[Pt(C₂₀H₁₆NOS{OPPh₂})₂Cl₂] 2b, respectively. The obtained compounds were characterized by NMR and FT-IR spectroscopy, LC–MS/MS, and microanalysis. Palladium complexes 2a–4a were applied as catalysts in the aqueous Suzuki–Miyaura coupling of aryl halides (I, Br, Cl) with arylboronic acids under mild reaction conditions and low palladium loadings. Complex 2a demonstrated the highest catalytic efficiency. Evaluation of a range of para-substituted aryl halides under optimized conditions (100°C, 4 min, 0.5 mol% catalyst, H₂O/K₂CO₃) resulted in yields of up to 97% and maximum TOF values of 2910 h⁻¹. In addition, complexes 2a–4a demonstrated appreciable catalytic performance in Mizoroki–Heck cross-coupling reactions between styrene and aryl bromide derivatives, yielding trans-stilbene products. High yields were obtained for activated substrates within notably short reaction times. The amido-phosphinite ligand-based metal complexes were electrochemically characterized, and their HOMO and LUMO energy levels were determined.