Electrophilic Fluoroalkylation of Ni(II) N-Confused Porphyrins with Fluoroalkylarylsulfonium Salts

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Ruthenium N-Confused Porphyrins: Selective Reactivity for Ambident 2-Heteroatom-Substituted Pyridines Serving as Axial Ligands

Three types of ruthenium(II) N-confused porphyrin (NCP) complexes bearing an axial 2-thiopyridine, 2-pyridone, and 2-iminopyridine moiety at the inner carbon atom, respectively, were synthesized. The unique reactivity of the 2-substituted pyridine derivatives (2-X-pyridine; X=SH, OH, NH₂ ) toward the inner carbon atom of the NCP allows the formation of two types of coordinated products (i. e., pyridine donor versus 2-heteroatom donors), as inferred from single-crystal X-ray structures. The selective reactivity was investigated by using density functional theory (DFT) calculations. Finally, the catalytic activity of these ruthenium complexes was demonstrated through the styrene oxidation reactions. As a result, the ruthenium(II) NCP complex bearing a 2-thiopyridine moiety, together with aqueous H₂ O₂ as an oxidant showed the highest selectivity for benzaldehyde (benzaldehyde/styrene oxide=20 : 1).

Synthesis and Properties of Carbaporphyrin and Carbachlorin Dimethyl Esters Derived from Cyclopentanedialdehydes

Norbornenes with two ester substituents were prepared by Diels-Alder cycloadditions of cyclopentadiene with dimethyl fumarate and dimethyl 1,1-ethylenedicarboxylate. Oxidation with potassium permanganate gave good yields of related diols that were oxidatively ring-opened to afford cyclopentane dialdehydes. MacDonald-type "3 + 1" condensations with a tripyrrane, followed by oxidation with DDQ in refluxing toluene, gave carbaporphyrin or carbachlorin products in good yields. The macrocyclic products were highly diatropic and produced porphyrin-like UV-vis spectra. The carbaporphyrin was converted into silver(III) and gold(III) organometallic derivatives. Reaction with methyl iodide in the presence of potassium carbonate gave mono- and dialkylation products, and treatment of the former with Ni(OAc)₂ or Pd(OAc)₂ afforded nickel(II) and palladium(II) complexes. The free base carbaporphyrin and carbachlorin, and the nickel and palladium complexes, were characterized by X-ray crystallography. The carbachlorin also reacted with silver(I) acetate to give a silver(III) derivative. Carbaporphyrins and carbachlorins underwent deuterium exchange at the meso-positions with deuteriated TFA, and this observation indicates that protonation is occurring at the bridging carbons. The new route to carbaporphyrins and carbachlorins has enabled detailed studies on the properties of these systems and provides the foundations for future investigations.