Efficient Synthesis and Microwave-Assisted Sonogashira Reactions of Triflate-Substituted Porphyrin

Porphyrins that bear halogens at the meso-aryl positions are useful building blocks for the preparation of light-harvesting arrays and materials through cross-coupling procedures. Despite the wide use of such intermediates, their scale-up and purification are usually hampered by tedious chromatographic separations because of the statistical nature of the synthetic protocol and the similar polarity of the different products. Here, we propose the use of porphyrins bearing a triflatophenyl group as alternative starting materials for palladium cross-coupling reactions. In particular, purification of the zinc 5,10,15-triaryl-20-(4-triflatophenyl)porphyrin (ZnP-OTf) model compound by column chromatography proved to be much easier compared to porphyrin analogues that carry halogen substituents. This is the result of the increased polarity of compounds functionalized by highly polar triflate groups if compared to those substituted by halogens. To show the value of the triflatophenylporphyrin model compound in cross-coupling reactions, we developed a microwave-assisted Sonogashira protocol that quantitatively converts the ZnP-OTf to the corresponding alkynylphenylporphyrin, in relatively short reaction times. Finally, we showed that the proposed ZnP-OTf building block can be conveniently converted into an alkynyl-linked molecular wire to bridge the zinc porphyrin donor with the [60]fullerene acceptor in a molecular dyad. The prepared dyad showed efficient photoinduced charge separation from singlet ZnP excited state to [60]fullerene in a polar solvent. A new triflatophenylporphyrin building block for Pd-catalyzed cross-coupling reactions is proposed. Compared to halophenylporphyrins, its purification it is much easier. The triflatophenylporphyrin is also suitable in microwave-assisted Sonogashira cross-coupling and, to further showcase its utility, has been used to prepare a donor-acceptor array.image