Synthesis and Self‐Organization of Zinc β‐(Dialkoxyphosphoryl)porphyrins in the Solid State and in Solution

Abstract

The first synthesis and self-organization of zinc β-phosphorylporphyrins in the solid state and in solution are reported. β-Dialkoxyphosphoryl-5,10,15,20-tetraphenylporphyrins and their Zn(II) complexes have been synthesized in good yields by using Pd- and Cu-mediated carbon-phosphorous bond-forming reactions. The Cu-mediated reaction allowed to prepare the mono-β-(dialkoxyphosphoryl)porphyrins 1 Zn-3 Zn starting from the β-bromo-substituted zinc porphyrinate ZnTPPBr (TPP = tetraphenylporphyrin) and dialkyl phosphites HP(O)(OR)(2) (R = Et, iPr, nBu). The derivatives 1 Zn-3 Zn were obtained in good yields by using one to three equivalents of CuI. When the reaction was carried out in the presence of catalytic amounts of palladium complexes in toluene, the desired zinc derivative 1 Zn was obtained in up to 72% yield. The use of a Pd-catalyzed C-P bond-forming reaction was further extended to the synthesis of β-poly(dialkoxyphosphoryl)porphyrins. An unprecedented one-pot sequence involving consecutive reduction and phosphorylation of H(2)TPPBr(4) led to the formation of a mixture of the 2,12- and 2,13-bis(dialkoxy)phosphorylporphyrins 5 H(2) and 6 H(2) in 81% total yield. According to the X-ray diffraction studies, 1 Zn and 3 Zn are partially overlapped cofacial dimers formed through the coordination of two Zn centers by two phosphoryl groups belonging to the adjacent molecules. The equilibrium between the monomeric and the dimeric species exists in solutions of 1 Zn and 3 Zn in weakly polar solvents according to spectroscopic data (UV/Vis absorption and NMR spectroscopy). The ratio of each form is dependent on the concentration, temperature, and traces of water or methanol. These features demonstrated that zinc β-phosphorylporphyrins can be regarded as new model compounds for the weakly coupled chlorophyll pair in the photosynthesis process.

Survey of Synthetic Routes towards Phosphorus Substituted Porphyrins

“…The product 50a was isolated in 87 % yield, H 2 TPP being the only side product (Scheme 21). [34] Surprisingly the reactivity of H 2 TPPBr is similar to that of ZnTPPBr and full conversion of the starting bromide using the optimal conditions is obtained.…”

“…It was already shown that the self assembling of these phosphoryl Zn(II) and Cu(II) porphyrins should be observed in solid state and in solution. [30][31][32]34,35] This self assembling leads to 1D and 2D networks. At last but not least, the new A 3 B type phosphorylated porphyrins should be very good precursors in order to construct efficient DSSCs and to develop photocatalysts.…”

“…[33] The A 2 B 2 type phosphorylated porphyrin 46 was obtained using the same conditions by phosphorylation of the tetrabrominated 45 precursor where two bromine atoms are directly linked to the macrocycle ring and another two bromine atoms through an aryl spacer (Scheme 19). [31] The first synthesis of zinc β-phosphorylporphyrins was reported by Vinogradova et al [34] β-Dialkoxyphosphoryl tetraphenylporphyrins and their Zn complexes were synthesized using Cu and Pd catalysts.…”

“…[34] The target products 48 were only obtained in high yield (> 85 %) when the precursor was reacted with phosphites using an excess of copper iodide (3 equiv.) and diamine (21 equiv.).…”

Quantum-Сhemical Insight into the Reactivity of 5-Bromo-10,20-diaryl-porphyrins towards Nucleophiles

“…[3][4][5][6] Transition metalassisted cross-coupling reactions are widely used for porphyrin functionalization. [5,[7][8][9][10][11][12][13][14][15][16] Notwithstanding their versatility, the palladium-mediated cross-coupling reactions require expensive catalysts and ligands that is a limiting factor for their industrial use, in particular in the medical pharmacology.…”