Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron Porphyrinoid Dimer

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3 ⁵⁺, which is connected through a fourfold rotaxane, was prepared. Heterodimer 3 ⁵⁺ catalyzed ethane oxidation in the presence of H₂O₂ at a relatively low temperature. The site-selective complexation of 3 ⁵⁺ with an additional anionic porphyrin (TPPS⁴⁻) through π–π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3 ⁵⁺ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS⁴⁻ to 3 ⁵⁺ enhanced the catalytic activity.     

Homohelicity induction of propylene-linked zinc bilinone dimers by complexation with chiral amine and α-amino esters. Preorganization of structurally coupled homohelical subunits

Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters.     

Novel ring transformation of thiazolidine to oxazolidine: acyl halide-promoted intramolecular rearrangement of 4(R)-hydroxymethyl-3-methyl-1,3-thiazolidine

An interesting transformation occurs during acylation of 4(R)-hydroxymethyl-3-methyl-1,3-thiazolidine when 4(R)-acylthiomethyl-3-methyl-1,3-oxazolidines are yielded: the reaction competing with O-acylation is controlled by the bulkiness of the acyl group.