This feature article provides an overview of the application of organic azides for the intermolecular amination of sp(3) and sp(2) C-H bonds. The catalytic activity of several metal complexes was reviewed underlining both synthetic and mechanistic aspects of the C-H amination. The majority of the aminated compounds reported in literature have been collected in this paper to provide a compendium of published procedures. In addition, the discussion of involved mechanisms has been included to assist the reader to envisage the future potential of organic azides in the synthesis of aza-derivatives.
This paper describes the synthesis of allylic amines by aryl azides (ArN 3 ) catalysed by [Ru(TPP)CO] (TPP = dianion of tetraphenylporphyrin). The employment of aryl azides renders the methodology sustainable as the formation of molecular nitrogen is the only stoichiometric byproduct. The isolation of catalytic intermediates and spectroscopic and kinetic studies revealed interesting information about the reaction mechanism, which could improve its catalytic efficiency in future research. An important result is the X-ray characteri-
A DFT-based theoretical analysis describes the allylic amination of cyclohexene by 3,5(CF 3 ) 2 phenylazide catalyzed by [Ru](CO) ([Ru]= Ru(TPP), TPP = dianion of tetraphenylporphyrin). The activation of an azide molecule (RN 3 ) at the free ruthenium coordination site allows the formation of a monoimido complex [Ru](NR)(CO) with the eco-friendly dismissal of a N 2 molecule. The monoimido complex can undergo a singlet→triplet interconversion to confer a diradical character to the RN ligand. Hence, the activation of the allylic C−H bond of cyclohexene (C 6 H 10 ) occurs through a C−H•••N interaction over the transition state. The formation of the desired allylic amine follows a "rebound" mechanism in which the nitrogen and carbon atom radicals couple to yield the organic product. The release of the allylic amine restores the initial [Ru](CO) complex and allows the catalytic cycle to resume by the activation of another azide molecule. On the singlet PES, the CO ligand may however be eliminated from the monoimido complex [Ru](NR)(CO) S , opening the way to an alternative catalytic cycle which also leads to allylic amine through comparable key steps. A second azide molecule occupies the vacant coordination site of [Ru](NR) S to form the bis-imido complex Ru(TPP)(NR) 2 , which is also prone to the intersystem crossing with the consequent C−H radical activation. The process continues until the azide reactant is present. The interconnected cycles have similarly high exergonic balances. Important electronic aspects are highlighted, also concerning the formation of experimentally observed byproducts.
Keywords: Cyclopropanation / Diazo compounds / Porphyrins / Cobalt / Rhodium / IridiumThe one-pot reaction of diazo compounds with olefins represents a useful strategy to synthesise cyclopropanes, which are important both as starting materials for the synthesis of organic compounds and because of their intrinsic pharmaceutical properties. Herein we describe the catalytic activity of group 9 metal porphyrin complexes to cyclopropanate ole-
The catalytic activity of the iron(III) C2 chiral porphyrin Fe(2)(OMe) in alkene cyclopropanation is herein reported. The catalyst promoted the reaction of differently substituted styrenes with diazo derivatives with trans-diastereoselectivities and enantioselectivities up to 99:1 and 87 %, respectively. In addition, high TON and TOF values (up to 10 000 and 120 000 h(-1) , respectively) were observed indicating good activity and stability of the catalyst in optimized experimental conditions. The study of the cyclopropanation reaction revealed that the porphyrin skeleton is composed of two 'totem' parts which were independently responsible for the observed enantio- and diastereoselectivities. To further our research we also investigated the catalytic role of the methoxy axial ligand coordinated to the iron atom. The molecular structure of Fe(2)(OMe) was optimized by DFT calculations which were also employed to achieve a better understanding of the mechanistic details of the carbene transfer reaction.
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