Synthesis, Structures, and Properties of meso‐Phosphorylporphyrins: Self‐Organization through P–Oxo–Zinc Coordination

Abstract

The synthesis, structures, and optical and electrochemical properties of meso-phosphorylporphyrins are described. The copper-catalyzed carbon-phosphorus cross-coupling reaction of a meso-iodoporphyrin with di-n-butyl phosphite and diphenylphosphane oxide has proved to be an efficient and general method for the synthesis of meso-phosphorylporphyrins. Zinc phosphorylporphyrins thus obtained readily undergo self-organization through P-oxo-Zn coordination to form noncovalently linked, cofacial porphyrin dimers or linear oligomers, which have been characterized by spectroscopic methods and X-ray crystallographic analyses. In toluene, CH(2)Cl(2), and CHCl(3), the zinc phosphorylporphyrins exist mostly as dimers or monomers, depending on their concentrations, the temperature, and the presence of additives. The self-association constants for dimerization in toluene have been determined by UV/Vis absorption titration measurements. The meso-diphenylphosphorylporphyrin dimer displays excitonic coupling of the Soret band with a splitting energy of 940 cm(-1). Fluorescence lifetimes of the zinc phosphorylporphyrins have been found to be affected only slightly by the concentration of the solution, and by the addition of triphenylphosphane oxide, suggesting that the effect of dimerization on their photodynamics in the S(1) state is negligible. On the other hand, the effect of dimerization is clearly reflected in their electrochemical oxidation processes, as the initially produced radical cations are efficiently delocalized over the two porphyrin rings. These findings demonstrate the potential utility of meso-phosphorylporphyrins as new models for the special pair in photosynthesis and as new building blocks for porphyrin-based supramolecular materials.

Insights into the Synthesis and the Solution Behavior of meso‐Aryloxy‐ and Alkoxy‐Substituted Porphyrins

“…Moreover, these data indicate that co-facial dimer II is not a major species present in the studied solutions of Zn-2f, because a strong upfield shift of resonances of β-pyrrol and meso-aryl substituent protons should be observed for dimer II due to ring current effects of the tetrapyrrolic macrocycles. [24,45] The above conclusion is also supported by a comparison of structural parameters obtained for Zn-2f using DFT calculations with those of zinc(II) complexes bearing coordinated anisol fragment and deposited at the Cambridge Crystallographic Data Centre. Indeed, according to the geometry optimization of dimer II performed with the application of SPARTAN'14 software at the B3LYP/6-31G* level, the distance between macrocycles should be approximately 3.16 Å.…”

“…[10] However, nucleophilic aromatic substitution (S N Ar) reactions usually require drastic conditions to proceed. [13][14][15][16][17][18][19][20][21] Therefore, transition-metalcatalyzed reactions were developed as an alternative route to carry out the reactions of haloporphyrins with nucleophiles [11,12,[22][23][24][25][26][27][28] but these reactions also suffer serious drawbacks such as a limited substrate tolerance, the need for specific and expensive ligands, high catalyst loading and time-consuming optimization of experimental conditions; furthermore, difficulties are encountered in reproduction and upscale experiments, and because of contamination of products by toxic metals. For these reasons, it is perhaps not surprising that S N Ar reactions as a tool for the preparation of C-, O-, S-and N-substituted porphyrins have recently been revisited.…”

Multiporphyrin coordination arrays based on complexation of magnesium(ii) porphyrins with porphyrinylphosphine oxides

“…In comparison the self-association constant of the Zn(II) dimer reported by the Japanese group is two orders of magnitude lower (5.9 × 10 −6 M −1 ). 20 The presence of Ni(II) in the phosphine oxide ligands leads to intramolecular fluorescence quenching of the complexes. Although no X-ray quality single crystal for any of the complexes has been obtained so far, the comparison with zinc(II) porphyrinylphosphine oxide polymers 19b,20 leads us to expect very interesting porphyrinporphyrin interactions in the solid state.…”

“…A Japanese group prepared similar phosphine oxides and quantified the self-coordination of the Zn(II) species. 20 Both reports 19b, 20 show only a weak reciprocal interaction between the phosphine oxide ligand and the neighbouring zinc(II) porphyrin, which is not surprising due to the low binding strength of oxo ligands towards zinc(II). In earlier reports it has been well established that zinc(II) porphyrins show a larger affinity towards N-donor ligands than hydroxy or carbonyl ligands.…”

Survey of Synthetic Routes towards Phosphorus Substituted Porphyrins

“…[27] In 2007 Matano and coworkers reported the synthesis of two kinds of meso-phosphorylporphyrins by copper-catalyzed C-P coupling of meso-iodoporphyrinatozinc 27 with di-n-butylphosphite under Buchwald's conditions (Scheme 14). [28] meso-(Di-n-butoxyphosphoryl) porphyrinatozinc 28 Scheme 11.…”