Palladium catalysis Suzuki/Heck reactions

Under all the conditions studied, addition of bare Si02-SH to Heck or Suzuki coupling reactions using a variety of bases, aryl halides and solvents resulted in complete cessation of the catalytic activity (35). These results suggest that catalysis with this precatalyst is also associated with labile palladium species that... 

Supported ultra small palladium on magnetic nanopartides used as catalysts for Suzuki cross-coupling and Heck reactions. Advanced Synthesis and Catalysis, 349, 1917-1922. 

Stewart and Whiting have reported a useful application of sequential Heck and Suzuki coupling reactions of a vinylborane pinacol ester with palladium catalysis to generate a tetraene (equation 147)260. 

Application of the complexes 63 in the Mizoroki-Heck reaction did not reveal higher activity than the previously examined palladium(II) complexes. However, in the Suzuki-Miyaura reaction, a drastically increased activity was observed with complex 63. Catalysis starts without a measurable induction period at mild temperatures accompanied by an extraordinarily high turnover frequency (TOF) of 552 [mol product x mol Pd x h ] at the start of the reaction for the coupling of p-chlorotoluene and phenyl boronic acid [Eq. (48)]. ... 

The first studies that intentionally used colloidal nanocatalysts were reported independently by Beller et al. [50] and Reetz et al. [51] using chemical reduction and electrochemical techniques, respectively, to synthesize colloidal palladium nanoparticles for the Heck reaction. Both Beller and Reetz concluded that the solution-phase catalysis occurred on the surface of the nanoparticle, without confirming that a homogeneous catalytic pathway was nonexistent. Le Bars et al. [52] demonstrated an inverse relationship between the size of Pd nanoparticles and the TOF (normalized to the total number of surface atoms) for the Heck reaction (Fig. 18.4a). After normalizing the rate to the density of defect sites (for each nanoparticle size) (Fig. 18.4b), the TOF for all particle sizes was identical. Colloidal PVP-capped palladium nanoparticles synthesized by ethanol reduction are effective catalysts for Suzuki cross-coupling reactions in aqueous solution [53]. The El-Sayed group reported that the initial rate of reaction increased linearly with the concentration of Pd nanoparticles [53] and the catalytic activity was inversely proportional to the... 

While there is no catalytic activity for the Suzuki and Heck reactions in filtered solutions (which should only contain dissolved molecular Pd species) [61] recent work by Thathagar et al. [6] indicates that leached Pd species are critical participants in the catalysis. Their experimental setup consisted of a cell divided into two sections by a membrane with a pore size of 10 nm. The insoluble base, NaOAc, which is necessary for the reaction to occur, was positioned on one side of the membrane, while 15 nm colloidal palladium nanoparticles (which were larger than the 10 nm... 

The coupling of terminal alkynes with aryl or vinyl halides under palladium catalysis is known as the Sonogashira reaction and is rather like the Heck reaction. It is a catalytic process, requiring a palladium(O) complex it is performed in the presence of base, and generally uses copper iodide as a co-catalyst. One partner—the aryl or vinyl halide—is the same as in the Stille and Suzuki couplings but the alkyne needs no metal to activate it the reaction works with the alkyne itself. 

The formation of C-C bonds is one of the important fields of synthetic organic chenustry. Modern methods are in the focus of scientists in academia and industry, often being connected to catalysis. Products based on catalysis represent more than 90% of the total amount of new compounds. Presently, palladium-catalysed reactions play a dominant role. For example, Mizoroki-Heck reactions, as well as Stille, Suzuki, Negishi, Kumada and Sonogashira couplings, are in the standard toolbox of organic chemists [1]. 

The field of palladium catalysis is also progressing rapidly. The Tsuji-Trost and Mizoroki-Heck reactions have been mentioned earher, however other C-C coupling reactions (Miyaura-Suzuki, Sonogashira and Stille) are now extensively used in organic chemistry, and the search for non-polluting Sonogashira and Miyaura-Suzuki reactions is being actively pursued. 

Palladium (Pd) is among the most widely used transition metals in industrial applications. Catalysis has been by far the most common use for palladium, with carbon-carbon coupling reactions such as the StiUe reaction, Suzuki reaction, Heck reaction and hydrogenahon reactions being amongst the most prominent More recently, palladium has also been found to play a fundamental role in several processes related to the life sciences. These applications have included its use as a catalyst to manufacture pharmaceuticals and agricultural herbicides [1], in the degradation of harmful environmental pollutants [2, 3], and as a sensor [4] for the detection of various analytes. While the uses of palladium are extensive, there remain several additional applications yet to be uncovered as the metal is reduced to the nanoscale. 

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

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