Functionalized Bis(triazolyl)phenylmethanol–palladium(II) Catalysts for Cross Coupling Reactions in Water

Abstract

PdII‐bis(triazolyl)phenylmethanol complexes bearing different groups (i. e., H, OMe, OH, COOH) directly attached to the benzyl rings were explored as precatalysts for copper‐free Sonogashira and Suzuki–Miyaura coupling reactions in water. Crystal structures reveal a bidentate N,N binding mode of the bis(triazolyl) ligands affording a distorted square planar PdII complexes. With the exception of the phenol‐substituted bis(triazolyl) ligands, the other three Pd complexes exhibited high activities toward Suzuki–Miyaura coupling reactions. Transmission electron microscopy (TEM) study and PPh3 poisoning experiments confirm that bis(triazoly)‐stabilized Pd nanoparticles (Pd NPs) were generated in situ during the catalytic reactions and involved as one of the active catalytic species in the Suzuki–Miyaura cross coupling.

Triazole‐based ligands functionalized silica: Effects of ligand denticity and donors on catalytic oxidation activity of Pd nanoparticles

“…[22] Treatment of 1.2 equiv NaH with Htbtm, Hbtm, and Hpytm in DMF followed by nucleophilic addition of 3-chloropropyl-functionalized silica gel (2.5% Cl or 0.7 mmol Cl g −1 ) under N 2 afforded the corresponding functionalized silica supports (Scheme 1). [21] Similarly, a reaction between the related pyridine-triazole ligand Hpytm and Pd(cod)Cl 2 in CH 2 Cl 2 at room temperature yielded the corresponding (Hpytm)PdCl 2 product in 56% yield. Despite using a slight excess of triazole-based ligands (1.4 equiv) during the immobilization process, only 4-6% of the chloropropyl groups on the surface were functionalized, possibly due to steric hindrance at the deprotonated alkoxide group and the biphasic reaction between the ligand in solution and the solid silica support.…”

“…[21] In a dried Schlenk flask, to a suspension of 60% NaH (5.7 mg, 0.14 mmol) dispersed in paraffin liquid in anhydrous DMF (1 ml) was added a 2 ml DMF solution of triazolyl ligands HL 1 -HL 3 (0.12 mmol) at 0°C under N 2 . [21] In a dried Schlenk flask, to a suspension of 60% NaH (5.7 mg, 0.14 mmol) dispersed in paraffin liquid in anhydrous DMF (1 ml) was added a 2 ml DMF solution of triazolyl ligands HL 1 -HL 3 (0.12 mmol) at 0°C under N 2 .…”

“…[20,21] Meanwhile, the pyridine-triazolyl ligand Hpytm was synthesized via an addition of trimethylsilylacetylide to 1.0 equiv of 2benzoylpyridine in THF to give the 1-(2-pyridyl)-1-phenyl-3-trimethylsilylpropagylalcohol intermediate. Both Htbtm and Hbtm were prepared according to the literatures (Scheme 1).…”

“…The preparation followed that previously reported in the literatures. [21] In a dried Schlenk flask, to a suspension of 60% NaH (5.7 mg, 0.14 mmol) dispersed in paraffin liquid in anhydrous DMF (1 ml) was added a 2 ml DMF solution of triazolyl ligands HL 1 -HL 3 (0.12 mmol) at 0°C under N 2 . After stirring for 30 min at room temperature, the solution was cooled to 0°C upon which 3chloropropyl-functionalized silica (0.12 g, 0.084 mmol Cl) was added.…”

“…Both Htbtm and Hbtm were prepared according to the literatures (Scheme 1). [20,21] Meanwhile, the pyridine-triazolyl ligand Hpytm was synthesized via an addition of trimethylsilylacetylide to 1.0 equiv of 2benzoylpyridine in THF to give the 1-(2-pyridyl)-1-phenyl-3-trimethylsilylpropagylalcohol intermediate. Subsequent reactions with excess K 2 CO 3 followed by addition of 1.2 equiv of PhCH 2 N 3 in the presence of 15 mol% CuSO 4 ·5H 2 O and 45 mol% ascorbic acid in MeOH at room temperature afforded the product HL 3 in 50% yield (Scheme 1).…”