Wanling Mo

Palladium‐Catalyzed Carbonylation of Chloroacetates to Afford Malonates: Controlling the Selectivity of the Product in a Buffer

We report an efficient process for the synthesis of diethyl malonate (DEM) and other malonates through the palladium‐catalyzed carbonylation of chloroacetates. Excellent selectivity (96 %) and yield (94 %) were obtained without the formation of Pd black. For the first time, a weakly alkaline buffer was used to control the selectivity for DEM in the reaction and we discuss the relationship between the buffer medium and selectivity in the reaction. The combination of anisole as the solvent and a Na2HPO4/NaH2PO4 buffer was beneficial for completely restraining the phase‐transfer‐catalyzed substitution of DEM with ethyl chloroacetate, as well as accommodating the proposed [(PPh3)2PdI]−[Bu4N]+ intermediate, by providing a suitable environment for its stable existence. We achieved the highest efficiency in the catalytic cycle by fine‐tuning the balance between the rates of oxidative addition and reductive elimination; moreover, we synthesized a recoverable heterogeneous polymer‐bound Pd catalyst in 85 % yield that could be reused without an appreciable loss in activity over four cycles.

A General Strategy for Open Flask Alkene Isomerization by Ruthenium Hydride Complexes with Non-Redox Metal Salts

A homogenous metal hydride (M−H) catalyst for isomerization normally requires rigorous air‐free techniques. Here, we demonstrate a highly efficient protocol in which simple non‐redox metal ions as Lewis acids can promote olefin isomerization dramatically with a commercially available RuH2(CO)(PPh3)3 complex in an open‐flask system. Isomerization can be accomplished within a short time, and a satisfactory selectivity for different types of unsaturated compounds can be obtained. Meanwhile, an excellent turnover number up to 17208 was achieved under air, and open‐flask gram‐scale experiments further demonstrated the efficiency of the RuH2(CO)(PPh3)3/non‐redox‐metals system. We used FTIR spectroscopy, GC–MS, NMR spectroscopy and kinetics studies to evidence that in the sluggish RuH2(CO)(PPh3)3 catalyst, bloated PPh3 ligands cause steric hindrance for the coordination of the free alkene. Alternatively, the addition of non‐redox metal ions could induce the dissociation of the PPh3 ligand to offer unoccupied coordination sites for the alkene and to form the Mg‐bridged adduct OC−Ru−H2−Mg2+ as the highly active species, which benefited the isomerization significantly through the metal hydride addition–elimination pathway. Finally, this strategy was demonstrated as an impactful approach for hydride catalysts of other transition metals such as Os.