Copper β-trinitrocorrolates

Abstract

The β-nitration reaction carried out on the corrole macrocycle has been shown to be extremely regioselective, although the reduced symmetry of the macrocycle could potentially lead to a huge number of possible regioisomers. We recently reported that the careful use of AgNO2/NaNO2 as a nitrating system enabled the achievement in good yields of mono- and dinitro-derivatives on both corrole free base and its copper complex, proving to be an efficient and cost-effective method. In this work, we present a detailed study of the scope of this method using TtBuCorrH3 as a model corrole. A further increase of the oxidant pushes the nitration up to the functionalization of three β-pyrrolic positions, although concomitant decomposition of the macrocycle is also observed. The application of the proven nitration method with a five-fold excess of both silver and sodium nitrites with respect to corrole, afforded the 2,3,17-(NO2)3-TtBuPCorrCu as the main product, in 25% yield, together with traces of another compound identified by X-ray crystallographic analysis as the 3,8,17-(NO2)3-TtBuPCorrCu isomer. In light of these recent results, we also reinvestigated the characterization of the nitration products obtained from bis-substitution reactions, allowing among others the identification of the copper 3,8-(NO2)2 corrolate.

Corrole and nucleophilic aromatic substitution are not incompatible: a novel route to 2,3-difunctionalized copper corrolates

“…The monitoring of such a variation by UV-vis spectroscopy evidenced the rapid formation, upon base addition, of the singly reduced form of copper 3-nitrocorrolate (Figure 1, dashed line), whose facile generation in the presence of DBU has been recently observed by us during the electrochemical characterization of the (NO 2 ) x -TtBuPCorrCu compounds (x= 0,1,2). 16b …”

“…28 In these reactions, the compounds are able to lose the X − with a simultaneous 1,2-hydride shift, to give products of hydrogen substitution with the nucleophile moiety after the elimination of HX from the intermediate σ-adduct. In fact, the introduction of one or two amino groups on Cu and Ge nitrocorrolates by using 4-amino-4H-1,2,4-triazole as nucleophile 16b is just such an example of VNS reaction on the corrole macrocycle.…”

“…Our attempts in most cases led to the target transformations, such as the peripheral insertion of varied functionalities 11 (halogens, formyl, nitro and sulphonic groups) or β-fused aromatic rings, 12 but they also serendipitously led to corrole metamorphosis into new intriguing macrocycles such as isocorroles, 13 hemiporphycenes 14 and aza-hemiporphycenes, 15 evidencing the unique reactivity of this contracted porphyrinoid. In particular the nitration reaction on β-pyrrolic positions was thoroughly studied by our group and to date several mono-, bis- and tris-functionalized 16 corrole derivatives have been achieved by using different reaction protocols. The reasons for our interest in such functionalizations have to be clearly found in the intrinsic synthetic value of the nitro group, which makes nitrocorroles excellent starting platforms for further elaboration.…”

“…To the best of our knowledge, the β-amination reaction on nitrocorrolates is to date the only example in the literature dealing with this kind of research in corrole chemistry. 16b With the aim to expand these investigations in corrole macrocycle, we used the Cu corrole complex 3-(NO 2 )TtBuCorrCu in reactions at the C2 pyrrolic position with carbon-centered nucleophiles, as outlined in Scheme 1. The 2,3-difunctionalized corrolates ( 1 ) and ( 2 ) were obtained in acceptable yields, introducing nucleophilic aromatic substitution reactions as a synthetic tool for peripheral functionalization of the electron-rich corrole ring.…”

3-NO2-5,10,15-triarylcorrolato-Cu as a versatile platform for synthesis of novel 3-functionalized corrole derivatives

“…In this field, we investigated modification of the corrole macrocycle by using the β-nitration reaction of corroles because the nitro group is particularly versatile for introduction of further modifications of the macrocycle 11 . In the last few years, we have focused our efforts on the definition of several synthetic protocols for the convenient preparation of β-nitrocorrole derivatives bearing from one to four nitro groups, both on corrole free base and metal complexes 3,12 . Beyond the development of synthetic protocols, these studies also highlighted additional aspects of these nitrated species, such as the electrochemical and spectroscopic features with relation to the number of nitro groups inserted.…”