An Easily Prepared Tetraphosphine and Its Use in the Palladium-Catalyzed Suzuki–Miyaura Coupling of Aryl Chlorides

About Solid Phase vs. Liquid Phase in Suzuki-Miyaura Reaction

A critical review of conclusions about the putative heterogeneous mechanism in the Suzuki-Miyaura coupling by supported Pd solids is reported. In the first section, the turnover frequencies (TOF) of 20 well-established homogeneous catalysts are shown to be in the range 200 to 1,000,000,000 h − 1 . The evidences used to prove a heterogeneous mechanism are discussed and another interpretation is proposed, hypothesizing that only the leached species are responsible for the catalytic reaction, even at ppb levels. Considering more than 40 published catalytic systems for which liquid phase Pd content have been reported, activities have been computed based on leached Pd concentrations and are shown to be in the range TOF 150 to 70,000,000 h − 1 . Such values are compatible with those found for the well-established homogeneous catalysts which questions the validity of the conclusions raised by many papers about the heterogeneous (solid) nature of Suzuki-Miyaura catalysis. Last, a tentative methodology is proposed which involves the rational use of well-known tests (hot-filtration test, mercury test…) to help to discriminate between homogeneous and heterogeneous mechanisms.

Pd/Pt metallacyclopropa[60]fullerene complexes bearing versatile phosphorous ylide ligands; a comprehensive multi-spectroscopic, electrochemistry, theoretical and catalytic studies

The synthesis of new Pd/Pt metallacyclopropa[60]fullerene complexes containing unsymmetrical phosphorus ylides [Ph₂P(CH₂)_nPPh₂ = C(H)C(O)C₆H₄-p-OMe] (n = 1, (Y¹); n = 2, (Y²)) has been reported. The synthesized complexes exhibit different structures, including two P,C- chelated [(η²-C₆₀)Pd(κ²-Y¹)] (1) and [(η²-C₆₀)Pt(κ²-Y¹)] (2) complexes and two P-coordinated [(η²-C₆₀)Pd(Y²)₂] (3) and [(η²-C₆₀)Pt(Y²)₂] (4) complexes with chain structures. Characterization of all compounds was performed by multi-neclear NMR spectroscopies (¹H, ¹³C and ³¹P NMR) and other conventional techniques such as IR, UV-Vis, SEM and cyclic voltammetry (CV) analyses. In this regard, the presence of all characteristic chemical shifts in the IR and NMR spectra proposed the formation of desired products. Also, theoretical studies were used to investigate the nature of metal-ligands in all complexes. In addition, a comparison between the catalytic activity of Pd complexes 1 and 3 was evaluated in the Suzuki-Miyaura reaction of various aryl chlorides with phenylboronic acid, which revealed a meaningful difference between the catalytic activity of complexes 1 and 3.