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

3 years ago

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

Ferdinand Belaj, Lydia M. Peschel, Christof Holzer, Antoine Dupé, Nadia C. Mösch-Zanetti

The synthesis, spectroscopic characterization, and catalytic activities of a series of PdII 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)(EPh3)] (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 PPh3 > IMes ≈ AsPh3 > SbPh3. 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 G0W0 calculations were performed to rationalize the facile reduction and, hence, excellent activities of the dinuclear complexes. Palladium(II) complexes bearing a mercaptoaryl-oxazoline ligand are synthesized and characterized. These complexes show high activities as catalysts for C–C coupling reactions in water with turnover frequencies (TOFs) of up to 16000 h–1. DFT and G0W0 calculations help to rationalize the catalytic behaviors of these complexes.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/ejic.201700823