Single-Walled Carbon Nanotube–Polyamidoamine Dendrimer Hybrids for Heterogeneous Catalysis

Abstract

We report the synthesis and catalytic properties of single-walled carbon nanotube-polyamidoamine dendrimers hybrids (SWCNT-PAMAM), prepared via a convergent strategy. The direct reaction of cystamine-based PAMAM dendrimers (generations 2.5 and 3.0) with pristine SWCNTs in refluxing toluene, followed by immobilization and reduction of [PdCl4](2-), led to the formation of highly dispersed small palladium nanoparticles homogeneously confined throughout the nanotube length. One of these functional materials proved to be an efficient catalyst in Suzuki and Heck reactions, able to promote the above processes down to 0.002 mol % showing a turnover number (TON) of 48 000 and a turnover frequency (TOF) of 566 000 h(-1). In addition, the hybrid material could be recovered and recycled for up to 6 times. No leaching of the metal has been detected during the Suzuki coupling. Additional experiments carried out on the spent catalyst permitted to suggest that a "release and catch" mechanism is operative in both reactions, although during Heck reaction small catalytically active soluble Pd species are also present.

Halloysite nanotubes as support for metal-based catalysts

“…9 The chemical functionalization of the tubular nanomaterial plays an important role in improving the dispersibility of the tubes and consequently their catalytic performance.…”

Immobilized Palladium Nanoparticles on Zirconium Carboxy-Aminophosphonates Nanosheets as an Efficient Recoverable Heterogeneous Catalyst for Suzuki–Miyaura and Heck Coupling

“…Solid NMR analyses also confirm the absence of free amine. Compounds 3a-n [22,43,46,54] and 6a-l [15] are known.…”

“…However, the stability and durable catalytic efficiency of nanoparticles, which are very much related to the avoidance of their aggregation and/or their minimal metal leaching in the reaction products, are still a challenge [10,11]. A large number of supports have been used to stabilize the PdNPs, such as carbon materials [12][13][14], inorganic materials [15,16], MOFs [17,18], hybrid materials [19][20][21][22][23][24] and organic polymers [25][26][27].…”

“…Functionalization of the support surface with appropriate functional groups represents a key approach to obtain a better control of the dimensions, dispersion and stability of NPs [20,[22][23][24][25].…”

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

“…In the case of Heck coupling, catalyst 147 again exhibited very high activity and selectivity, converting aryl iodides and bromides with high yields (97%-99%). In all reactions, Recently, polyamidoamine dendrimers (PAMAM) were also immobilized onto single-walled carbon nanotubes (SWCNTs) to obtain suitable supports for palladium nanoparticles [87]. In detail, hybrid supports SWCNT-PAMAM 144a and 144b were prepared by direct reaction between pristine SWCNTs and cystamin-based PAMAM dendrimers 2.5 G 143a and 3.0 G 143b, respectively (Scheme 54).…”