Narrow Results

The $N$-methylated 25-oxasmaragdyrins were synthesized by reacting 25-oxasmaragdyrins with CH₃I in presence of KOH in THF at reflux temperature. Although the reactions were carried out in presence of excess CH₃I, we obtained only dimethyl-25-oxasma ragdyrins, where $N$-methylations occurred at 24 and 26 “N”s of pyrrole rings of tripyrrane moiety of smaragdyrin core as confirmed by X-ray crystallography. The $N$-methylated-25-oxasmaragdyrins were characterized in detail by 1D and 2D NMR spectroscopy, absorption, fluorescence and electrochemical techniques. The effect of distortion induced by methylation, clearly reflected in structural and electronic properties of the macrocycle. All the pyrrole and furan protons experienced upfield shifts in the ¹H NMR and maximum upfield shifts were noted for the $N$-methylated pyrrole ring protons. The absorption spectra showed broad Soret band and four ill-defined Q-bands with significant reduction in extinction coefficients. The $N$-methylated 25-oxasmaragdyrins were comparatively less fluorescent. The redox studies indicated that they are difficult to oxidize and easier to reduce.

Phosphorus complexes of porphyrinoids such as porphyrins, corroles, $N$-fused porphyrins, $N$-fused expanded porphyrins and expanded porphyrins can be prepared readily by treating the porphyrinoid with phosphorylating agents such as PX₃, PX₅ and POX₃ (X $=$ Cl or Br) under standard reaction conditions. In phosphorus porphyrinoids, the phosphorus is generally high valent $+$5 oxidation state and the coordination number is varied from four to six. The insertion of P(V) into porphyrinoids alters the structure and electronic properties of the macrocycle significantly. Specially, the phosphorus binding mode is different from one porphyrinoid to another. The oxophilicity nature of P(V) in P(V) porphyrinoids is very useful to change variety of axial ligands and also helps to synthesize multi-porphyrin arrays by axial bonding approach. This review summarizes the phosphorus complexes of five different porphyrinoids and discusses their structure and electronic properties as well as their applications in the synthesis of more elaborate P(V) porphyrinoid based architectures.