攻克棘手的合成目標:八氟置換之紫質
Landmark Synthesis of OctafluoroporphyrinAngew. Chem. Int. Ed. 2016, 55, 5035
Kashi, C.; Wu, C.-C.; Mai, C.-L.; Yeh, C.-Y.; Chang, C. K
金屬卟啉(紫質)扮演着殊多關鍵角色，如自然界之電子轉移，呼吸及光合作用，科技業之氧化催化，光電材料，生醫圈中之光動力療效，螢光技術等等，其重要性及多元性可謂無出其右者。特別是帶有多個氟置換之金屬卟啉，穩定性及化學活性 自成一格。自本人1981年＊成功表現在P450模式的氧化及環氧化反應後，被廣泛應用，其影响頗為世重。推原其故因拉電子基(如氟) 一則將大環氧化電位提高，使之不易遭破壞，二則使產生之[M=O]活性加強，進而使OAT (Ｏ-atom transfer)速度更快，無怪乎大量研究都投注於此。迄今多氟卟啉例子不少，但最経典的八氟卟啉(OFP)仍付闕如，理由並非缺少努力，過去有成串失敗的歷史。余致力此物之催生凡十餘年，歷經三所院校，現今圓滿合成出來。後續及開發仍待努力。
Fluorinated porphyrinoids by virtue of their unique chemical robustness and reactivity are ideal systems for biomimetic applications. In fact, we demonstrated in 1981* a high-yielding catalytic model of cytochrome P450 using Fe(F20-tetraphenylporphyrin), which has spurred widespread interest in polyhalogenated porphyrins as oxidation catalysts. Yet, the most fundamental 2,3,7,8,12,13,17,18-octafluoroporphyrin (OFP) has not been synthesized despite numerous attempts. It is now achieved by self-condensation of tetrafluoro-dipyrrylmethane-2-carboxaldehyde in the presence of MgBr2. MgOFP in solid state revealed an essentially flat structure. The fluoro-groups impart as much as 0.5 V anodic shifts for porphyrin ring oxidation/reduction, as well as hypsochromic shifts in the Uv-vis spectra. The synthetic approach paves the way to exploring the family of octahaloporphyrins (X=F, Cl, Br & I) that have been out of reach thus far.
*C. K. Chang & F. Ebina, NIH SHIFT IN HAEMIN-IODOSYLBENZENE-MEDIATED HYDROXYLATIONS,Chem. Commun. 1981, 778-779.
