Porphyrin <i>N</i>-Pincer Pd(II)-Complexes in Water: A Base-Free and Nature-Inspired Protocol for the Oxidative Self-Coupling of Potassium Aryltrifluoroborates in Open-Air

• Main Authors: Sana Siva Prasad, Bandameeda Ramesh Naidu, Marlia M. Hanafiah, Jangam Lakshmidevi, Ravi Kumar Marella, Sivarama Krishna Lakkaboyana, Katta Venkateswarlu
• Format: Article
• Language: English
• Published: MDPI AG 2021-09-01
• Series: Molecules
• Subjects: porphyrin <i>N</i>-pincer Pd(II)-complexes; water; nature-inspired conditions; potassium aryltrifluoroborates; self-coupling; symmetrical biaryls
• Online Access: https://www.mdpi.com/1420-3049/26/17/5390

Metalloporphyrins (and porphyrins) are well known as pigments of life in nature, since representatives of this group include chlorophylls (Mg-porphyrins) and heme (Fe-porphyrins). Hence, the construction of chemistry based on these substances can be based on the imitation of biological systems. Inspired by nature, in this article we present the preparation of five different porphyrin, <i>meso</i>-tetraphenylporphyrin (<b>TPP</b>), <i>meso</i>-tetra(<i>p</i>-anisyl)porphyrin (<b>T<i>p</i>AP</b>), tetrasodium <i>meso</i>-tetra(<i>p</i>-sulfonatophenyl)porphyrin (<b>TST<i>p</i>SPP</b>), <i>meso</i>-tetra(<i>m</i>-hydroxyphenyl)porphyrin (<b>T<i>m</i>HPP</b>), and <i>meso</i>-tetra(<i>m</i>-carboxyphenyl)porphyrin (<b>T<i>m</i>CPP</b>) as well as their <i>N</i>-pincer Pd(II)-complexes such as Pd(II)-<i>meso</i>-tetraphenylporphyrin (<b>PdTPP</b>), Pd(II)-<i>meso</i>-tetra(<i>p</i>-anisyl)porphyrin (<b>PdT<i>p</i>AP</b>), Pd(II)-tetrasodium <i>meso</i>-tetra(<i>p</i>-sulfonatophenyl)porphyrin (<b>PdTST<i>p</i>SPP</b>), Pd(II)-<i>meso</i>-tetra(<i>m</i>-hydroxyphenyl)porphyrin (<b>PdT<i>m</i>HPP</b>), and Pd(II)-<i>meso</i>-tetra(<i>m</i>-carboxyphenyl)porphyrin (<b>PdT<i>m</i>CPP</b>). These porphyrin <i>N</i>-pincer Pd(II)-complexes were studied and found to be effective in the base-free self-coupling reactions of potassium aryltrifluoroborates (PATFBs) in water at ambient conditions. The catalysts and the products (symmetrical biaryls) were characterized using their spectral data. The high yields of the biaryls, the bio-mimicking conditions, good substrate feasibility, evading the use of base, easy preparation and handling of catalysts, and the application of aqueous media, all make this protocol very attractive from a sustainability and cost-effective standpoint.