Abstract
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, meso-tetraphenylporphyrin (TPP), meso-tetra(p-anisyl)porphyrin (TpAP), tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (TSTpSPP), meso-tetra(m-hydroxyphenyl)porphyrin (TmHPP), and meso-tetra(m-carboxyphenyl)porphyrin (TmCPP) as well as their N-pincer Pd(II)-complexes such as Pd(II)-meso-tetraphenylporphyrin (PdTPP), Pd(II)-meso-tetra(p-anisyl)porphyrin (PdTpAP), Pd(II)-tetrasodium meso-tetra(p-sulfonatophenyl)porphyrin (PdTSTpSPP), Pd(II)-meso-tetra(m-hydroxyphenyl)porphyrin (PdTmHPP), and Pd(II)-meso-tetra(m-carboxyphenyl)porphyrin (PdTmCPP). These porphyrin N-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.
Highlights
IntroductionSynthetic and natural metalloporphyrins are well-known examples of nitrogen-bridged polycyclic compounds and are largely distributed in nature
This transformation using PdTPP, PdTpAP, PdTmHPP, and PdTmCPP, each with 0.1 mol% in 4 mL 1:1, vol:vol mixture of water and DMF was observed to provide 2a in 21%, 39%, 58%, and 67% in 4h and indicated that the catalyst, PdTSTpSPP was highly suitable for the self-coupling of 1a
The catalyst loading studies, using 0.07 mol%, 0.05 mol%, and 0.03 mol% showed the formation of 2a in 98%, 98%, and 82% in 15 min, 15 min and 60 min, suggesting the requirement of 0.05 mol% PdTSTpSPP as catalyst for the self-coupling of
Summary
Synthetic and natural metalloporphyrins are well-known examples of nitrogen-bridged polycyclic compounds and are largely distributed in nature. Metalloporphyrins display vital catalytic significance in the basic reactions of life; for example, as heme (a cofactor of hemoglobin) in oxygen transport [1,4] and as chlorophyll (which is able to convert sunlight to energy) in photosynthesis of plants [4,5] (Scheme 1). Despite these efficient biochemical, photochemical, Molecules 2021, 26, 5390 as heme (a cofactor of hemoglobin) in oxygen transport [1,4] and as chlorophyll (which is as heme (a cofactor of hemoglobin) transportof [1,4]
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