Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX
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28-Hetero-2,7-Naphthiporphyrins: Horizontal Expansion of the m‑Benziporphyrin Macrocycle Bartosz Szyszko,* Maksym Matviyishyn, Serhii Hirka, Ewa Pacholska-Dudziak, Agata Białonś ka, and Lechosław Latos-Grażynś ki* Department of Chemistry, University of Wrocław, 14 F. Joliot-Curie St., 50-383 Wrocław, Poland
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S Supporting Information *
ABSTRACT: Replacement of the m-phenylene moiety of mbenziporphyrins with the 2,7-naphthalenyl subunit yielded 28hetero-2,7-naphthiporphyrinsmacrocycles that can be considered as expanded carbaporphyrinoids. This group retains some features of parent m-benziporphyrins, but due to larger size and different shape of the macrocyclic cavity, their coordination properties are different. Upon reduction and conformational rearrangement the 28-thia- and 28-selena-2,7naphthiporphyrin form organophosphorus(V) complexes.
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arbaporphyrinoids might be considered an unorthodox group of macrocyclic ligands providing nontrivial environments for metals and metalloids. These fascinating systems demonstrate Hückel/Möbius aromaticity and antiaromaticity, topology switching, conformational rearrangements, and anions sensing.1 By contributing a porphyrin-like set of donor atoms confined within the cavity of precisely designed size and shape, they are particularly attractive for exploration of organometallic, or in more general terms, organoelement chemistry.2,3 Propinquity of the metal center inside the cavity to the carbocyclic component of the macrocycle furnishes systems with uncommon intramolecular interactions that, on several occasions, led to the activation of both C−H and C−C bonds.3 In this respect, carbaporphyrinoids incorporating phenylene rings,4,5 namely, m-benziporphyrins 1-X,6−9 oxy-m-benziporphyrins,10,11 and p-benziporphyrins 2-X,12,13 were found particularly alluring, giving an access to complexes with metal···arene π, and σ bonds (Figure 1). Benziporphyrins demonstrated formation of coordination compounds with variety of metals, metalloids, and nonmetals.14−23 Moreover, in cases of palladium(II),17 rhodium(III),24 and gold(III)25,26 complexes of 1-NH and 2-NH the metal···π interactions were envisaged to be stimuli of unusual reactivity resulting in the contraction of benzene unit to cyclopentadiene, leading eventually to complexes of 21-carbaporphyrins. Intriguing coordination features of 1-X and 2-X provided an incentive for development of their benzologues, namely naphthiporphyrinoids 3−7 (Figure 1). Hitherto this group consists of 1,3-naphthiporphyrin 3,15 2oxy-1,3-naphthiporphyrin 4,15,27 1,4-naphthiporphyrins 5X,15,28 helical 22-hetero-1,5-naphthiporphyrins 6-X,29 and 1,7-naphthithiacorrole 7.30 Even though the coordination chemistry of 1,3- and 1,4naphthiporphyrins is still in its infancy, it can be anticipated © XXXX American Chemical Society
Figure 1. Benziporphyrins and naphthiporphyrins.
that their metal-binding modes will follow those observed for parent benziporphyrins. In search for nontrivial coordination modes accessible for naphthalene-containing porphyrinoids, the coordination cavity of naphthiporphyrins must be redesigned. Received: July 24, 2019
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DOI: 10.1021/acs.orglett.9b02587 Org. Lett. XXXX, XXX, XXX−XXX
Letter
Organic Letters
structure of the effective C2v symmetry (Figure 2A, S3, S4, S8, Supporting Information). The naphthalene H(24,26) protons
Herein, we report the synthesis and properties of a new constitutional isomer of heteronaphthiporphyrins, namely 28hetero-2,7-naphthiporphyrins. In fact these macrocycles belong to a growing group of dicarbaporphyrinoids.31−39 Initial studies on their coordination behavior proved their ability to act as macrocyclic ligands forming organophosphorus(V) complexes upon reduction. Actually, the modification of 1-X framework by horizontal benzologation of carbocyclic moiety provided systems with the smallest macrocyclic circuit containing 18 atoms,40 therefore being considered expanded carbaporphyrinoids.41−44 Synthesis of 28-hetero-2,7-naphthiporphyrins required preparation of the appropriate naphthalene-containing building blocks (Scheme 1). The crucial starting material for their Scheme 1. Synthesis of 13-X
Figure 2. 1H NMR spectra of (A) 13-Se (CDCl3, 300 K, 600 MHz), and (B) [13-Se-H2]2+ (CDCl3, 220 K, 600 MHz). Methyl peaks were omitted for clarity.
inside the cavity gave rise to a signal at a peculiar position of 9.82 (13-S), 9.93 (13-Se), and 9.91 ppm (13-Te) (chloroform-d, 300 K). More than 2 ppm downfield shift of these resonances, in comparison to the spectra of 8 (7.86 ppm) and 9 (7.51 ppm), reflects the involvement of the protons in hydrogen bonding with N(27) and N(29) atoms of neighboring pyrroles. The remaining naphthalene protons resonate at 7.66−7.63 (H(3,5)), and 7.35−7.25 ppm (H(2,6)) ranges, similarly to 8 and 9. The β-protons of heteroles gave resonances at 6.3−7.1 ppm range, typical for nonaromatic porphyrinoids, implying lack of π-electron macrocyclic conjugation within the molecules of 13-X.29 Analysis of the NOESY map revealed a typical for porphyrinoids, convex (noninverted) conformation of the 13-X molecules in the solution, even though the dimensions of the macrocyclic cavity are large enough for certain degree of subunit(s) rotation, as observed for several expanded porphyrins.47 Upon lowering the temperature from 300 to 220 K (chloroform-d) only very slight shift (
