Designing ‘Totem’ C₂‐Symmetrical Iron Porphyrin Catalysts for Stereoselective Cyclopropanations

Abstract

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.

Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

“…The iron centre of the tetrapyrrolic macrocycle activates the diazo compound; its C 2 -symmetrical feature induces high trans -diastereoisomeric ratios, whereas the chiral hat controls the enantiocontrol leading to a diastereoselectivity enhancement ( Figure 1 ) [ 49 , 50 ]. The aforementioned results led the authors to prepare other C 2 -symmetrical chiral iron(III) porphyrins, where the chiral binaphthyl unit was replaced by an aminoacid moiety.…”

Computational Investigations of Heme Carbenes and Heme Carbene Transfer Reactions

“…These studies are inspired by the excellent catalytic performance of native cytochrome P450s for numerous biochemicalr eactions, [12] which has also stimulated the development of biomimetic iron porphyrin complexes for av arietyo f catalytic carbene transfer reactions. [13] Thisn ovel class of biocatalysts can achieve high yields and high chem-, regio-, and stereoselectivity resultsf or carbene transfer reactions. For example,aMb-basedm utant was found to catalyze cyclopropanation of styrene with up to 99 %y ield, 99.9 %d iastereomeric excess (de), and 99.9 %e nantiomeric excess (ee).…”

“…[14i] However,t he NMRs pectroscopy properties were found to be sensitivet oe lectronic structure differences. [14a] For electronic structure I,abroad range of experimental 13 CNMR chemical shifts of the carbon atoms of the carbene in IPCs, including five-and six-coordination, as wella sd onor-donor, donor-acceptor, and acceptor-acceptor carbenes, were computationally reproduced, with al inear theory versus experimentc orrelation coefficient of R 2 = 0.982 and am ean absolute deviation (MAD) of 6.7 ppm or 2.34 %o ft he experimental shift range (Figure 1A). [14a] However,r esultsf or S = 1o rS = 2s tates for electronic structure II,a so bserved in Fe IV specieso fh eme/nonheme proteins and model systems, [12,23] yieldede rrors of about 9000 and 30 000 ppm, respectively.C omputationalr esultso btained for electronic structure III also cannot give good predic- tions, [14d] with R 2 % 0.1.…”

Iron catalysts with N-ligands for carbene transfer of diazo reagents

“…These chiral ligands were first used as cobalt(II) derivatives 77,78 and more recently as iron(III) complexes by E. Gallo, B. Boitrel and co-authors. 79,80 The parent compound of this class of ligands is -tetra-(2-aminophenyl)porphyrin (TAPPH 2 ) (78) (Scheme 27) whose functionalization of the four amino groups permitted the building of different C 2 -symmetrical frames onto the N 4 porphyrin core. The 'bis-strapped' porphyrin, which shows the chiral environment surrounding both faces of the tetrapyrrolic core, was used to synthesize Fe(III)(79)OMe, which promoted the reaction of several alkenes with acceptor-only diazo derivatives.…”