Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

Abstract

Carbene transfer reactions are very important transformations in organic synthesis, allowing the generation of structurally challenging products by catalysed cyclopropanation, cyclopropenation, carbene C-H, N-H, O-H, S-H, and Si-H insertion, and olefination of carbonyl compounds. In particular, chiral and achiral metalloporphyrins have been successfully explored as biomimetic catalysts for these carbene transfer reactions under both homogeneous and heterogeneous conditions. In this work the use of synthetic metalloporphyrins (MPorph, M = Fe, Ru, Os, Co, Rh, Ir, Sn) as homogeneous or heterogeneous catalysts for carbene transfer reactions in the last years is reviewed, almost exclusively focused on the literature since the year 2010, except when reference to older publications was deemed to be crucial.

High Magnetic Anisotropy of a Square-Planar Iron-Carbene Complex

“…Transition-metal carbene complexes are a hallmark of organometallic chemistry and have long been studied due to a fundamental interest in their unique metal–carbon multiple bonds , and the resulting reactivity in organometallic transformations and catalysis. , Several important CR 2 group transfer reactions, such as cyclopropanation of olefins, C–H functionalization via carbene insertion, , and olefin metathesis, , rely on metal carbene species as key reactive intermediates that facilitate the construction of complex carbon frameworks in organic synthesis. , The broad range of observed reactivity stems from the diverse electronic structures of the metal-carbene complexes, depending on the carbene substituents and the metal center involved. Aside from N-heterocyclic carbenes, which show relatively sparse reactivity and are often used as strongly σ-donating spectator ligands in catalysis, more reactive carbene ligands are typically assigned to one of three distinct classes: (a) Fischer-type carbenes, which are electrophilic at carbon and prefer low-valent, electron-rich metal centers; , (b) Schrock-type carbenes or alkylidenes, which are nucleophilic at carbon and prefer high-valent, electron-poor metal centers; , and (c) carbene radicals, which have been implicated in several catalytic C–H and C–C bond forming reactions and have attracted significant interest in recent years. − …”

An In-Depth Computational Study of Alkene Cyclopropanation Catalyzed by Fe(porphyrin)(OCH3) Complexes. The Environmental Effects on the Energy Barriers

“… 1 Moreover, bioinspired iron porphyrin systems have been described that are able to transfer a carbene moiety in processes involving the formation of similar iron carbene intermediates, 2 which show the carbene functionality on one of the two axial positions in the coordination sphere of iron, the other one being considered empty 3 or, more often, occupied by neutral ligands such as imidazole derivatives 3b , 4 or anionic ligands such as chloride, methoxy, or methylthiolate. 5 A lot of investigations have been performed to disclose the mechanism of carbene formation as well as of the subsequent carbene transfer reaction to C=C 6 and C–H 7 bonds with the fundamental contribution of theoretical calculations. To describe satisfactorily the electronic features of these systems, very simple computational models of the porphyrin complexes have been usually used, for example, simple porphine, thus neglecting the contribution of the overall environment in which the catalytic active metal is operating, whether it is a protein or the ligand skeleton of a bioinspired system.…”

Tropylium-Catalyzed O–H Insertion Reactions of Diazoalkanes with Carboxylic Acids

“…The O–H insertion reaction of diazoalkanes is a reaction of fundamental interest in organic chemistry as it allows the direct and concise synthesis of α-oxygenated carboxylic acid derivatives. , A classic approach toward O–H functionalization is exemplified in the reaction of diazomethane with carboxylic acids, which proceeds via protonation of diazomethane followed by nucleophilic substitution of the diazonium ion intermediate to form methyl esters. , This method finds numerous applications in organic chemistry ranging from method development to total synthesis . This approach is, however, limited to simple diazoalkane substrates like diazomethane because the crucial proton-transfer step is significantly hampered in the case of structurally more complicated and less Brønsted basic frameworks such as aryldiazoacetates. − Thus, O–H functionalization reactions of this latter type of diazo compounds commonly require a different activation process, with transition-metal catalysis being one of the most advanced approaches in modern organic synthesis (Scheme a). , Despite the advances made in this areain particular with regard to enantioselective O–H functionalization reactions, costs and toxicity of either the metal or its requisite ligand represent limitations of this approach, thus making metal-free approaches toward O–H functionalization very attractive.…”