Iron Catalysis in Organic Synthesis

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Alan Ford,† Hugues Miel, Aoife Ring,† Catherine N. Slattery,† Anita R. Maguire,*,†,‡ and M. Anthony McKervey* †Department of Chemistry and ‡School of Pharmacy, Analytical and Biological Chemistry Research Facility, Synthesis and Solid State Pharmaceutical Centre, University College Cork, Cork, Ireland Almac Discovery Ltd., David Keir Building, Stranmillis Road, Belfast BT9 5AG, United Kingdom Almac Sciences Ltd., Almac House, 20 Seagoe Industrial Estate, Craigavon BT63 5QD, United Kingdom

Modern Organic Synthesis with α-Diazocarbonyl Compounds

Globally increasing energy demands and environmental concerns related to the use of fossil fuels have stimulated extensive research to identify new energy systems and economies that are sustainable, clean, low cost, and environmentally benign. Hydrogen generation from solar-driven water splitting is a promising strategy to store solar energy in chemical bonds. The subsequent combustion of hydrogen in fuel cells produces electric energy, and the only exhaust is water. These two reactions compose an ideal process to provide clean and sustainable energy. In such a process, a hydrogen evolution reaction (HER), an oxygen evolution reaction (OER) during water splitting, and an oxygen reduction reaction (ORR) as a fuel cell cathodic reaction are key steps that affect the efficiency of the overall energy conversion. Catalysts play key roles in this process by improving the kinetics of these reactions. Porphyrin-based and corrole-based systems are versatile and can efficiently catalyze the ORR, OER, and HER. Becau...

Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems

Recent studies on the reactions of α-diazocarbonyl compounds

Corrole-based applications.

A thorough mechanistic investigation has been performed on the reactions of primary and secondary amines with diazoacetates, which proceed uniquely quickly and efficiently when catalyzed by iron(III) corroles and porphyrins. Two major differences in relation to other metal-based catalysts are that the iron complexes are not poisoned by excess amine and that metal-carbene intermediates are apparently not involved in the reaction pathway. The results instead point towards nitrogen ylide intermediates formed by nucleophilic attack of the amines on diazoacetate-coordinated iron complexes. Nitrogen ylides are also formed when allyl- and propargyl-substituted tertiary amines react with diazoacetates, a scenario that smoothly leads to 2,3-rearrangement reaction products with catalytic amounts of the iron(III) complexes. Similar findings regarding the superiority of the iron(III) complexes (in terms of catalyst loading, chemical yields, and reaction conditions) were obtained with thiols (S--H insertion) and sulfides (2,3-rearrangement reactions), which suggest similar mechanisms operate in these cases.

Iron(III) corroles and porphyrins as superior catalysts for the reactions of diazoacetates with nitrogen- or sulfur-containing nucleophilic substrates: synthetic uses and mechanistic insights.

Iron porphyrins catalyze the synthesis of non-protected amino acid esters from ammonia and diazoacetates

Iron corroles and porphyrins catalyze the reactions of amines with ethyl diazoacetate extremely efficiently, leading to complete and rapid conversion into N-substituted glycine ethyl esters by simultaneous addition of the substrates to the catalysts. The selectivity toward activation of the NH bonds is remarkable and quite different from other catalysts.

Iron Corroles and Porphyrins as Very Efficient and Highly Selective Catalysts for the Reactions of α-Diazo Esters with Amines

Despite of the many similarities between corroles and porphyrins, the chemistry of the former remained undeveloped for decades because of severe synthetic obstacles. The recent discoveries of facile methodologies for the synthesis of triarylcorroles and the corresponding metal complexes allowed for their utilization in various fields. This survey reveals many examples where corroles were used as the key components in catalysis, sensing of gaseous molecules and medicine-oriented research. The focus in all these cases was on the special features of corroles: stabilization of high valent transition metal ions, unique photophysical properties, large NH acidity, facile synthetic manipulation and distinct catalytic properties. The latter aspect includes several examples of reactions that are not catalyzed by any non-corrole metal complex, such as the iron-based aziridination by Chloramine-T, the clean disproportionation of peroxynitrite, and the very facile N–H activation of amines.

Iris Aviv

Papers

Corrole-based applications.

Iron(III) corroles and porphyrins as superior catalysts for the reactions of diazoacetates with nitrogen- or sulfur-containing nucleophilic substrates: synthetic uses and mechanistic insights.

Iron porphyrins catalyze the synthesis of non-protected amino acid esters from ammonia and diazoacetates

Iron Corroles and Porphyrins as Very Efficient and Highly Selective Catalysts for the Reactions of α-Diazo Esters with Amines

Corrole-Based Applications