Palladium nanoparticles immobilized on a nano-silica triazine dendritic polymer: a recyclable and sustainable nanoreactor for C–S cross-coupling

Abstract

Efficient synthesis of diaryl sulfides via C–S cross-coupling of aryl halides with disulfides catalyzed by Pdnp-nSTDP is reported.

Heterogeneous Dendrimer-Based Catalysts

“…Mohammadpoor-Baltork and Mirkhani developed Pd nanoparticles, immobilized on nano-silica (10–40 nm), coated with triazine dendritic polymer ( n STDP) [ 342 , 345 ]. The latter was propagated by the repeated alternating stages of triazine trichloride (cyanuric chloride) and bis(3-aminopropyl)amine addition according to the Csp 2 S N 2 mechanism, until G3 dendrons were obtained ( Scheme 18 ).…”

“…The latter was propagated by the repeated alternating stages of triazine trichloride (cyanuric chloride) and bis(3-aminopropyl)amine addition according to the Csp 2 S N 2 mechanism, until G3 dendrons were obtained ( Scheme 18 ). The mean particle size of the further deposited Pd nanoparticles was found to be 3.1 nm [ 342 , 345 ].…”

“…Thus, the synthesized hybrid Pd- n STDP catalyst was studied in Heck and Suzuki C–C cross-coupling reactions ( Scheme 19 ) [ 342 ], as well as in C–S cross-coupling reactions between various arylhalides and diaryldisulfides under both microwave (MW) and conventional thermal conditions ( Scheme 20 ) [ 345 ]. Suzuki coupling proceeded with near quantitative yields (93–96%) within 2–3 h or 6–10 h at room temperature for iodoarenes or bromoarenes, respectively (K 2 CO 3 as a base, DMF/H 2 O (1:3) as a reaction medium) ( Scheme 19 ) [ 342 ]; the use of MW irradiation (200 W, 70 °C) allowed the achievement of the same yields after 2–5 min, both for iodoarenes and bromoarenes.…”

“…In C–S coupling ( Scheme 20 ), yields of 90–95% were achieved within 5 h under conventional thermal conditions (80 °C, Bu 4 NOH, DMF/H 2 O (1:1)) or within 10–15 min under microwave (MW) conditions ( Scheme 20 ) with the TOF values, reaching, in the last case, up to 5700 h −1 , enormously exceeding those for conventional homogeneous and heterogeneous catalytic systems, such as PdCl 2 (dppf)/Zn, CuFe 2 O 4 or Cu 2 S/Fe [ 345 ]. It was found that electron withdrawing para -substituents favored the better reaction yields; nonetheless, it was noticeable only for chloroarenes, converted to the corresponding diarylsulfides with yields of 90–90% after 10 h. Moreover, double C–S coupling was successfully conducted with the various para -and meta -dibromoarenes (including 2,6-dibromopyridine) and diaryldisulfides (including 2,2′-dithiobis(benzothiazole)) under said conditions.…”

Dendrimeric Structures in the Synthesis of Fine Chemicals

“…Dendritic heterogeneous catalyst based on palladium nanoparticles have also been reported to effectively catalyze C-S cross-coupling reactions. In this context, palladium nanoparticles immobilized on nano-silica triazine dendritic polymer (Pdnp-nSTDP) are effective catalysts for the synthesis of diaryl and aryl-heteroaryl sulfides under microwave (MW) irradiation (230 W, 80 °C), in the presence of tetra-butylammonium hydroxide (TBAH) in 1 H 2 O-DMF mixture ( Scheme 6 ) [ 54 ]. Pdnp-nSTDP were prepared starting from a nano-silica 3-amino-propyl-trimethoxysilane platform, followed by the in situ generation and entrapment of Na 2 Pd 2 Cl 6 .…”