Aqueous-Phase Chemistry of η³-Allylpalladium(II) Complexes with SulfonatedN-Heterocyclic Carbene Ligands: Solvent Effects in the Protolysis of Pd–C Bonds and Suzuki–Miyaura Reactions

Abstract

The synthesis of water-soluble η 3 -allyl Pd(II) complexes containing sulfonated N-heterocyclic carbene (NHC) ligands of general formula [Pd(NHC) n (η 3 -allyl)Cl 2−n ] is reported (n = 1 (1) or 2 ( 8)). Monocarbene complexes were obtained with the most sterically hindered NHC ligands, and biscarbenes with the less sterically hindered NHCs. The behavior of the isolated complexes in water under acidic, neutral, or alkaline conditions has been studied. The complexes are rather stable in water under neutral or alkaline conditions, although displacement of the chlorido ligand by water or hydroxide occurs under these conditions. In acidic media, Pd−NHC bonds are protolysed, and it is especially noteworthy that this protolysis occurs preferentially to that of the Pd−allyl bonds in the case of the complexes with the less-sterically hindered NHC ligands. This behavior contrasts with that observed in dimethyl sulfoxide (dmso), where the Pd− allyl bonds are selectively broken upon treatment with Bronsted acids. In addition, Pd−NHC bond breaking was promoted by the addition of a strong σ-donor ligand such as cyanide. Complex 1a is an active catalyst for the Suzuki−Miyaura cross-coupling of water-soluble aryl chlorides in neat water under moderate conditions (typically, 0.5 mol % Pd and 60 °C).

Combining lipid-mimicking-enabled transition metal and enzyme-mediated catalysis at the cell surface of E. coli

“…as anticancer agents. 26,27 They can be readily prepared from the commercially available dimeric allyl–palladium complex and the respective imidazolium salt precursor. Herein, we chose a N -isopropylated CHIM derivative instead of the N -methylated salt as an imidazolium precursor for the synthesis of CHIM–Pd since more bulky N -substituents have been described to be beneficial for complex stability in aqueous medium and to lead preferentially to monocarbene complex formation.…”

“…Herein, we chose a N -isopropylated CHIM derivative instead of the N -methylated salt as an imidazolium precursor for the synthesis of CHIM–Pd since more bulky N -substituents have been described to be beneficial for complex stability in aqueous medium and to lead preferentially to monocarbene complex formation. 27 At the same time, isopropyl substituents were expected to still be small enough to only marginally affect faithful membrane integration. 28 The integration of CHIM–Pd was quantified by single-cell inductively coupled plasma mass spectrometry (scICP-MS).…”

π-Allylpalladium Complexes in Synthesis: An Update

“…In this context, de Jesús and co-workers prepared and studied a series of water-soluble η 3 -allylpalladium(II) complexes with sulfonated N-heterocyclic carbene ligands. 92 In particular, complex 225 is an active precatalyst for the Suzuki-Miyaura coupling of water-soluble aryl chlorides in neat water under moderate conditions (typically, 0.5 mol% Pd, 60 °C) (Figure 3). Remarkably, under such conditions, the activation of the precatalyst is likely to occur by transmetalation with the arylboronic acid followed by reductive elimination of (Ar)allyl.…”

Synthesis and a combined experimental/theoretical structural study of a comprehensive set of Pd/NHC complexes witho-,m-, andp-halogen-substituted aryl groups (X = F, Cl, Br, CF3)

“…In the studies by de Jesús and coworkers, Pd/NHC complexes containing -SO 3 Na groups showed high solubility in water and activity in the Suzuki-Miyaura reaction carried out in the aqueous phase. 30,31 Plenio and coworkers reported an easy method for the preparation of -SO 3 Na substituted Pd/ NHC complexes, which showed high yields in Sonogashira and Suzuki-Miyaura cross-couplings. 32 Tuning biological activity is the key application of functional group effects in the medicinal and pharmaceutical applications of Pd/NHC complexes.…”