Alumina palladium-doped

Scheme 4.4 Sonogashira coupling on palladium-doped alumina.

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo- and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [174]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [175]. A solventless Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as a base [176], This approach has been extended to Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 6.52) [177]. 

Lately, a number of papers have dealt with microwave-assisted reactions on palladium-doped A1203. Villemin reported on Stifle, Suzuki, Heck and Trost—Tsuji reactions where potassium fluoride on alumina was used as the base26. The reactions were carried out without solvent or stabilising phosphine ligands in single-mode reactors. The Stifle reactions were noteworthy as the toxic organotin residue remained adsorbed on the solid support, thus allowing a simplified work-up procedure for the otherwise unpleasant, and toxic, stannous by-products. Both the Stifle and the Suzuki reactions could be performed under air. Furthermore, it was noted that with experiments where the... 

Kabalka, G.W., Wang, L., Pagni, R.M., Hair, C.M. and Namboodiri, V., Solventless Suzuki coupling reactions on palladium-doped potassium fluoride alumina, Synthesis, 2003, 217-222. 

In the thermal studies, the reactants were mixed (in the absence of a solvent) with palladium doped, potassium fluoride treated alumina and the mixture heated for four or more hours at temperatures approaching 100 In this portion of the study, we examined the effectiveness of microwave irradiation for enhancing the rate of the reactions. The feasibility of using microwave irradiation to induce organic reactions on solid surfaces in the absence of solvents has been demonstrated previously. As a probe, we investigated the reaction of tolylboronic acid with iodobenzene for various time periods. Table V. 2-Methylbiphenyl was formed readily under a variety of reaction conditions. For convenience, we found it most efficient to simply heat the mixtures for 2 minutes at 100% power. Under these conditions, a small amount of organic material could be observed condensing on the cooler portions of the reaction vessel. 

Some early examples involving microwave-assisted solvent-free Sonogashira couplings using palladium powder doped on alumina/potassium fluoride as catalyst were described by Kabalka and coworkers (Scheme 4.4) [150], In addition, this novel catalytic system has been used in microwave-assisted solvent-free Sonogashira coupling-cyclization of ortho-iodophenol with terminal alkynes, and similarly of ortho-ethynylphenols with aromatic iodides, to generate 2-substituted benzo[b]furans... 

Several methods (wetness-impregnation, electroless plating and sol-gel) can be used to dope ceramic alumina membranes with Pd. Ahmad et al. performed a sol-gel synthesis of palladium-alumina dried gel at 700 °C. They used Autosorb, FTIR and XRD analysis to demonstrate the stability of a palladium-alumina membrane structure with a pore size of 10 nm. However, although this research suggests an application in the H2-separation process, results concerning selectivity and permeability are not provided. Using a... 

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