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

The synthesis, spectroscopic characterization, and catalytic activities of a series of Pd II complexes bearing the monoanionic, bidentate ligand 2‐(2‐thiophenyl)‐4,4‐dimethyloxazoline (S‐Phoz) are reported. These complexes were used as precatalysts for Suzuki–Miyaura coupling reactions under aqueous conditions. The dimers [{PdX(S‐Phoz)} 2 ] (X = Cl, Br, I; 1 – 3 ) were treated with the N‐heterocyclic carbene (NHC) ligand 1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene (IMes) to afford the mononuclear complexes [PdX(S‐Phoz)(IMes)] (X = Cl, Br, I; 4 – 6 ). The σ‐donor/π‐acceptor complexes [PdCl(S‐Phoz)(EPh 3 )] (E = P, As, Sb; 7 – 9 ) were synthesized to evaluate the influence of a second donor ligand on the catalytic activity. Within the [PdCl(S‐Phoz)L] series, the activity trend for L follows the trend PPh 3 > IMes ≈ AsPh 3 > SbPh 3 . The sulfur‐bridged dinuclear complexes 1 – 3 are highly active for the benchmark coupling of p ‐bromoacetophenone with phenylboronic acid and exhibit turnover frequencies (TOFs) of up to 16000 h –1 . DFT and G 0 W 0 calculations were performed to rationalize the facile reduction and, hence, excellent activities of the dinuclear complexes.