Dendrimers, Sonogashira reaction

The dendrimers 23a-c were used in a copper-free Sonogashira-type coupling reaction between phenylacetylene and iodobenzene or bromobenzene. The catalyst amount was 1 mol % per catalytic group (i.e., 1/4, 1/8 and 1/16 mol% depending on the dendrimer generation generations 1, 2 and 3), and the temperature range was 25-120 °C. 

The authors reported the catalytic performance of this dendrimer-stabilized nanoparticle in C-C CTOsscoupUng reactions, including the Suzuki-Miyaura, Sonogashira and Heck, and reduction of 4-nitrophenol. 

Suzuki-Miyaura reactions of iodoarene and bromoarene derivatives were remarkably catalyzed by this dendrimer-stabilized Pd nanoparticle, with the resulting TONs equal to or larger than 10 . The catalytic activity for Sonogashira coupling was also impressive, and only 0.01% mol Pd was required. 

Using related synthetic tools as above, Bunz et al. also performed the synthesis of polyphenylene dendrimers containing a cyclobutadiene CoCP at the core of the dendrimers. The necessary ethynyl phenyl starting materials 292 were prepared using a Pd-catalyzed Sonogashira-type coupling reaction in good yields. The Co-initiated [2-1-21-cycloaddition of the ethynyl units with CpCo(CO)2 proceeded exclusively between the desired internal alkynes to afford 293 (Scheme 50). ... 

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