Rational design of galactopyranoside-substituted N-heterocyclic carbene palladium(ii) complexes. Stable and efficient catalyst for C–C coupling in aqueous media

Abstract

Three palladium(ii) complexes bearing galactopyranoside-based NHC ligands have been synthesized. Catalytic studies reveal that the complexes are active and reusable.

Structure‐Activity Relationships of Glucose‐based PdII‐Bis(NHC) Complexes in a Model Suzuki‐Miyaura Reaction

“…The structure of the PEPPSI complex 19 was confirmed via NMR, which shows all expected pyridine signals and the palladium-NHC bond at ~152 ppm, as expected for such a PEPPSI complex. [15,30] The PEPPSI complex 19 was then used in our model Suzuki-Miyaura reaction (Table 2, entries [19][20]. Similar to 5 h, the best Pd II -bis(NHC) complex of this work, 19 leads to > 99 % yield at 0.005 mol%, further proving the generally high activity of the mesitylene-and glucopyranoside-substituted imidazoylidene ligand.…”

“…The synthesis of 19 was adapted from a recent work by Fiego and Silbestri et al, who investigated galactopyranoside-based PEPPSI complexes. [30] The synthetic strategy is similar to the one employed by us for Pd IIbis(NHC) complexes in this work, whereas firstly a silver complex is formed, which is then transformed into the PEPPSI complex by addition of palladium chloride and pyridine in equimolar amounts to 3 h. This procedure is, however, less selective than the formation of Pd II -bis(NHC) complexes and leads to bis(pyridine)PdCl 2 as side product, while also some starting material 3 h was not converted. Thus, an lower yield of only 44 % was achieved.…”