Naphtho[2,3âb]carbaporphyrins - ACS Publications - American

Article Cite This: J. Org. Chem. 2018, 83, 11825−11838

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Naphtho[2,3‑b]carbaporphyrins Eric Y. Grabowski, Deyaa I. AbuSalim, and Timothy D. Lash* Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States

J. Org. Chem. 2018.83:11825-11838. Downloaded from pubs.acs.org by UNIV OF NEW ENGLAND on 10/05/18. For personal use only.

S Supporting Information *

ABSTRACT: Acid-catalyzed condensation of a benzo[f ]indane dialdehyde with a tripyrrane, followed by an oxidation step, afforded the first example of a naphtho[2,3-b]-21carbaporphyrin. This π-extended porphyrinoid system is strongly aromatic and gave a porphyrin-like UV−vis spectrum with a Soret band at 432 nm. Protonation with TFA gave a monocation, but under highly acidic conditions a Cprotonated dication was generated. Reaction of the naphthoporphyrin with ferric chloride produced a 21-chloro derivative. Alkylation with methyl iodide and potassium carbonate gave a 22-methyl derivative, and this reacted with palladium(II) acetate to afford a palladium(II) complex in which the internal methyl group had migrated from a nitrogen to a carbon atom. Treatment of the naphthocarbaporphyrin with silver(I) acetate generated the corresponding silver(III) complex. In naphtho[2,3-b]-21-carbaporphyrin and many of its derivatives, the aromatic conjugation pathways appear to bypass the naphthalene unit, and for this reason the UV−vis spectra were little affected. However, the diprotonated dication and the palladium(II) complex have aromatic pathways that pass through the naphthalene moiety, and this leads to large bathochromic shifts for these species. The results provide insights on the influence of fused aromatic units on the reactivity, spectroscopic properties, and aromatic characteristics of carbaporphyrinoid systems.

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INTRODUCTION Porphyrins and related macrocyclic systems represent an important family of heterocyclic aromatic compounds.1−3 The origin of the aromatic properties for the porphyrins has often been ascribed to the presence of diaza[18]annulene substructures within the macrocyclic framework,4,5 although many theoretical studies indicate that these characteristics derive from the 6π electron pyrrolic subunits.6 Nevertheless, global conjugation is responsible for most of the spectroscopic properties, including the large diamagnetic ring currents observed by proton NMR spectroscopy.7 Porphyrins readily form metalated derivatives, and these metalloporphyrins (primarily hemes and chlorophylls) have many important functions in nature.1 In addition, applications for porphyrin derivatives cover a wide spectrum of areas that include photodynamic therapy,8 the development of fluorescence sensors,9 catalysis,10 and molecular information storage.11 Inspired by the versatility of the porphyrins, closely related heterocyclic systems have been intensively investigated.12−14 Carbaporphyrins 1 and 2 (Figure 1) are members of an important group of porphyrin analogues in which one of the core nitrogens has been replaced with a carbon atom.12 True carbaporphyrins of this type have received a considerable amount of attention12 alongside related macrocyclic systems such as N-confused porphyrins 3 (NCPs),15,16 azuliporphyrins 4,17 and benziporphyrins 5.18 In particular, benzocarbaporphyrins such as 219 have been shown to undergo selective oxidations at the core carbon atom20 and generate organometallic complexes under mild conditions (Scheme 1).21,22 Reactions of 2 with ferric chloride in the presence of alcohol solvents afforded carbaporphyrin ketals 620 that exhibit potent © 2018 American Chemical Society

Figure 1. Carbaporphyrinoid systems.

activity in the treatment of leishmaniasis.23 In water, these reactions resulted in the formation of a 21-chlorocarbaporphyrin 7 together with a nonaromatic dione (structure not shown).20 In addition, porphyrin analogue 2 generated stable organometallic derivatives and reacted with silver(I) acetate at room temperature to form silver(III) complex 8.21 Furthermore, alkylation of 2 with methyl or ethyl iodide in the presence of potassium carbonate afforded N-alkylation products 9 together with minor C-alkylated derivatives 10.24 Carbaporphyrins 9 reacted with palladium(II) acetate in Received: July 10, 2018 Published: August 31, 2018 11825

DOI: 10.1021/acs.joc.8b01748 J. Org. Chem. 2018, 83, 11825−11838

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The Journal of Organic Chemistry Scheme 1. Selected Reactions of Benzocarbaporphyrin 2

bands,28 while naphtho[2,3-c]porphyrin 15 showed more significant changes.29 Specifically, the Soret band for 14 appeared at 415 nm and the longest wavelength Q-band at 630 nm,28 while 15 showed these peaks at 420 and 643 nm.29 These effects are substantially magnified when multiple fused rings are present on the porphyrin chromophore.30 How these effects translate to porphyrin analogues such as carbaporphyrins is less well studied. In this work, we targeted the synthesis of a naphtho[2,3-b]carbaporphyrin 16 (Scheme 2) to

refluxing acetonitrile to give palladium(II) organometallic complexes 11 where the alkyl groups had undergone a migration from the nitrogen to the internal carbon atom (Scheme 1).24 Benzocarbaporphyrins have also been shown to give stable rhodium(I), rhodium(III), and iridium(III) derivatives.22 An alternative approach to modifying the porphyrin chromophore involves the introduction of fused aromatic rings. However, the effects due to ring fusion vary considerably.25 For instance, phenanthroporphyrins 12 (Figure 2) only show small bathochromic shifts to the Soret and Q bands compared to regular porphyrins,26 but acenaphthoporphyrins 13 gave rise to far larger effects including the production of triply split Soret bands and strongly red-shifted Q bands.27 Naphtho[1,2-b]porphyrin 14 similarly gave only minor shifts to longer wavelengths for the Soret and Q

Scheme 2. Synthesis of a Naphtho[2,3-b]-21-carbaporphyrin

investigate how the presence of a linearly annealed naphthalene unit affected the properties of the carbaporphyrin system. It was not only of interest to see how the UV−vis absorption spectra would be altered but also to find out what effects this structural modification has on the aromatic

Figure 2. Selected porphyrins with fused aromatic rings. 11826


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The Journal of Organic Chemistry characteristics and reactivity for this π-extended porphyrin analogue.

NOE difference proton NMR spectroscopy showed a weak interaction between the OH protons and one of the bridging CH2 protons, confirming that the expected exo-diol had been formed. Reaction of 24 with potassium periodate in a mixed solvent system (THF/water) gave the required dialdehyde 20. The dialdehyde was somewhat unstable but could be stored in the freezer for several weeks. Tripyrrane 2535 was reacted with 20 in the presence of trifluoroacetic acid, and following oxidation with 2 equiv of DDQ, naphthocarbaporphyrin 16 was isolated in 43% yield. The UV−vis spectrum of 16 in 1% triethylamine−chloroform gave a Soret band at 432 nm and a series of Q bands at 517, 554, 607, and 668 nm (Figure 3). These values are only

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RESULTS AND DISCUSSION It was anticipated that the synthesis of naphtho[2,3-b]-21carbaporphyrin 16 could be carried out using the “3 + 1” modification of the MacDonald condensation31 (Scheme 2), and this required the availability of benzo[f ]indene dialdehyde 17b. This dialdehyde was targeted by adapting a procedure previously reported for the synthesis of an analogous indene dialdehyde 17a (Scheme 3).32 Benzo[f ]indene (18b) was Scheme 3. Synthesis of Indene and Benz[f ]indene Dialdehydes

generated by a literature procedure33 and reacted with DMF dimethyl acetal in toluene over a 10 h period while gradually distilling out the methanol that was generated as a byproduct from the reaction. Although indene gives good yields of the corresponding enamine 19a under these conditions, only inferior yields of impure 19b could be obtained, and even then, the results were poorly reproducible. Therefore, an alternative route to the related indane dialdehyde 20 was developed (Scheme 4). Excess norbornadiene was reacted with α,α,α′,α′-

Figure 3. UV−vis spectra of naphthocarbaporphyrin 16:free base in 1% Et3N−CHCl3 (red line); monocation 16H+ in 0.5% TFA−CHCl3 (green line).

bathochromically shifted by 6−10 nm compared to benzocarbaporphyrin 2 (Table 1), indicating that the naphthalene Table 1. UV-vis Spectra (λmax/nm) for Benzo- and Naphthocarbaporphyrins and the Corresponding Monoprotonated Cations and Diprotonated Dicationsa

Scheme 4. Synthesis of Indane Dialdehyde 20

Soret band 16 2 16H+ 2H+ 16H22+ 2H22+

432 424 453 437 455 426

Q bands 517 510 563 473 599

554 544 601 550 614

607 602 613 586 708

668 662 673 611 774 662

a

The UV−vis spectra for 219 and 16 were run in 1% triethylamineCHCl3; 16H+ was run in 0.5% TFA−CHCl3 and 2H+ in 0.01% TFA− CH2Cl2;19 16H22+ was recorded in 1% concd HCl in TFA and the spectrum for 2H22+ was obtained in 50% TFA−CHCl3.19

unit is not strongly interacting with the porphyrin chromophore. The proton NMR spectrum for 16 in CDCl3 demonstrated that the system had retained strongly diatropic characteristics, as the external meso-protons appeared downfield as two 2H singlets at 9.76 and 10.00 ppm, while the internal NH and CH resonances appeared upfield at −3.87 and −6.55 ppm, respectively (Figure 4). The naphthalene protons in 16 gave rise to a 2H singlet (21,31-H) at 9.09 ppm and two 2H multiplets at 8.26 (22,32-H) and 7.62 (23,33-H) ppm. The 21,31-protons are shifted downfield due to their spatial proximity to the macrocyclic ring current, but the remaining values are typical of substituted naphthalenes and the results

tetrabromo-o-xylene and potassium iodide in DMF to give naphthonorbornadiene 21.34 Initially, a quinodimethane intermediate 22 is generated and this undergoes a Diels− Alder cycloaddition with norbornadiene to give adduct 23. Subsequent elimination of 2 equiv of HBr then afforded 21. Treatment of 21 with alkaline solutions of potassium permanganate generated the related diol 24 in 62% yield. 11827


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of 16H22+ was obtained in neat TFA. The internal methylene unit gave rise to a 2H singlet at −2.20 ppm, while the external meso-protons afforded two 2H singlets at 10.90 and 11.03 ppm. Importantly, the naphthalene protons were also strongly deshielded, producing a 2H singlet at 10.41 ppm and two 2H multiplets at 8.64 and 9.28 ppm. These results indicate that the aromatic ring current for 16H22+ extends through the fused naphthalene moiety. When 2 drops of d-TFA were added to a solution of 16 in CDCl3, the proton NMR spectrum showed immediate deuterium exchange with the NH and 21-H protons. Slow exchange of the meso-protons was also noted after 1 day, indicating that meso-protonated species such as 16xH+ and 16yH+, or related dications, are in equilibrium with 16H+ (Scheme 5). Similar observations were previously reported for benzocarbaporphyrin 2.19b

Figure 4. 500 MHz proton NMR spectrum of naphthocarbaporphyrin 16 in CDCl3.

Scheme 5. Protonation of Naphthocarbaporphyrin 16

indicate that the porphyrinoid ring current does not pass through this fused benzenoid unit. The carbon-13 NMR spectrum for 16 in CDCl3 confirmed that the macrocycle has a plane of symmetry. The meso-protons were identified at 95.8 and 97.1 ppm, while the internal CH appeared at 114.6 ppm. Addition of TFA to 16 generated deep green colored solutions of the related monocation 16H+ (Scheme 2). The UV−vis spectrum of 16H+ in 0.5% TFA−chloroform was substantially red-shifted (Table 1) compared to the corresponding benzocarbaporphyrin monocation 2H+ (Scheme 1). The Soret band was observed at 453 nm, compared to 437 nm for 2H+, while the longer wavelength absorptions appeared at 563, 601, 613, and 673 nm. Further addition of TFA to solutions of 2 gave rise to mixtures of protonated species and produced C-protonated dication in 50% TFA (Scheme 1). However, the second protonation of naphthocarbaporphyrin 16 did not occur as easily, and in 1% TFA−chloroform only the monoprotonated species was evident. In 50% TFA− CDCl3, a mixture of 16H+ and dication 16H22+ (Scheme 2) was observed by proton NMR spectroscopy. The UV−vis spectrum in neat TFA gave rise to a new spectrum, although the intensity of the Soret band was enhanced upon addition of concd hydrochloric acid (Figure 5). A strong Soret band was observed at 455 nm together with a series of Q bands at 599, 708, and 774 nm. The absorptions are substantially red-shifted compared to those reported for the analogous benzocarbaporphyrin dication 2H22+ (Table 1). The proton NMR spectrum

As benzocarbaporphyrin 2 was selectively oxidized with ferric chloride (Scheme 6),20 the reactivity of naphthocarbaScheme 6. Reactions of Naphthocarbaporphyrin 16 with Ferric Chloride and Silver(I) Acetate

porphyrin 16 toward this reagent was investigated (Scheme 3). However, reaction of 16 with ferric chloride in chloroform− methanol failed to give the expected carbaporphyrin ketal 26, and only unidentifiable degradation products were observed. It was hypothesized that the naphthalene ring might be prone to oxidation reactions and that this was responsible for the observed results. Although no isolatable carbaporphyrin ketals products were observed under any of the conditions investigated, the 21-chloro derivative 27a could be isolated in 70% yield when a solution of 16 in dichloromethane was reacted with aqueous ferric chloride. In some experiments, a dichlorinated product 27b was observed, but this species could

Figure 5. UV−vis spectrum of diprotonated naphthocarbaporphyrin dication 16H22+ in 1% hydrochloric acid−TFA. 11828


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The Journal of Organic Chemistry not be fully purified. Chloronaphthocarbaporphyrin 27a retains a plane of symmetry and maintains highly diatropic characteristics. The proton NMR spectrum for 27a showed the NH protons upfield at −3.74 ppm, while the meso-protons were strongly deshielded, giving rise to two 2H singlets at 9.74 and 9.92 ppm. The UV−vis spectrum of 27a was bathochromically shifted compared to 16, and the Soret band appeared at 441 nm while the longest wavelength Q-band showed up at 676 nm. Addition of TFA gave a monocation 22aH+ that showed a strong Soret band at 463 nm. As had been the case for benzocarbaporphyrin 2,21 naphthocarbaporphyrin 16 reacted with silver(I) acetate to give the corresponding silver(III) complex 28 (Scheme 6). Unfortunately, the complex had poor solubility in organic solvents, and while a proton NMR spectrum was obtained it was not possible to run a carbon-13 NMR spectrum. At 52 °C, the meso-protons for the complex were observed as two 2H singlets at 9.85 and 9.90 ppm, demonstrating that the complex has a strong diatropic ring current. The 21,31-protons on the naphthalene unit were also strongly deshielded to 9.03 ppm due to their proximity to the porphyrinoid ring. The UV−vis spectrum of 28 (Figure 6) showed a small bathochromic shift

Scheme 7. Methylation and Metalation of Naphthocarbaporphyrins

benzocarbaporphyrin series, the initially formed complex 32 underwent a methyl group migration to give the symmetrical C-methyl structure 31. Although the complex retains strongly aromatic properties, the conjugation pathway has been relocated through the naphthalene ring. In the proton NMR spectrum for 31, the meso-protons appeared as two 2H singlets at 9.13 and 9.85 ppm, while the internal methyl group gave a peak at −2.18 ppm (Figure 7). In addition, the naphthalene

Figure 6. UV−vis spectrum of silver(III) complex 28 in CHCl3.

compared to the benzocarbaporphyrin complex 8, and the Soret band for 28 appeared at 439 nm compared to 437 nm for 8. The results demonstrate that the favored aromatic pathway for the silver(III) complex does not involve the fused naphthalene unit. Some carbon-13 NMR data could be garnered from the HSQC NMR spectrum, and the mesocarbons were identified at 97.6 and 100.6 ppm. Reaction of 16 with methyl iodide and potassium carbonate afforded the asymmetrical N-methyl derivative 29 in 62% yield (Scheme 7), and only trace amounts of a C-methylated product 30 could be detected. This chemistry only differs very slightly from the results obtained for 2,24 where approximately 10% yields of C-alkyl products 10 were formed as byproducts in addition to N-alkyl derivatives 9 (Scheme 1). The UV−vis spectrum for 29 was bathochromically shifted compared to 16 and the N-alkyl analogue 9a. However, the differences are not consistent with any significant changes in the conjugation pathways. The proton NMR spectrum of 29 also confirmed that the structure retained strongly diatropic characteristics, and the internal CH and methyl resonances were observed at −5.85 and −4.06 ppm, respectively. The meso-protons appeared as four 1H singlets at 9.55, 9.70, 9.99, and 10.05 ppm. N-Methylcarbaporphyrin 29 was refluxed with palladium(II) acetate to give a palladium(II) organometallic derivative 31 in 77% yield. As had been the case for the

Figure 7. 500 MHz proton NMR spectrum of palladium(II) naphthocarbaporphyrin 31 in CDCl3.

protons were shifted downfield, particularly the 21,31-protons which appeared at 9.69 ppm. These results strongly support the involvement of the naphthalene unit as part of the aromatic circuit. The carbon-13 NMR spectrum for 31 again confirmed the presence of a plane of symmetry. In porphyrins and their aromatic analogues, the meso-carbons are generally shifted upfield to 95−100 ppm.35b,36 Interestingly, only one of the meso-carbons (5,20-CH) for 31 appears upfield at 106.9 ppm, while the 10,15-CH resonance shows up at 120.6 ppm. However, the naphthalene 21,31-resonance appears at a 11829


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functionals, B3LYP, M06-2X, and B3LYP-D,38,39 and the relative Gibbs free energy was also determined with B3LYP. By all of these measures, NapCP-22,24-H was found to be the most stable, while tautomer NapCP-22,23-H was approximately 5 kcal/mol higher in energy (Table 2). This did not come as a surprise, as the internal hydrogens in NapCP-22,24H are better situated for hydrogen bonding interactions, while minimizing lone pair-lone pair repulsion.40 The remaining two tautomers have an internal methylene group, and while they retain an 18π electron delocalization pathway, these structures are significantly higher in energy. NapCP-21,23-H was calculated to be between 9.93 and 12.68 kcal/mol higher in energy, while NapCP-21,22-H is destabilized by nearly 20 kcal/mol. The latter structure is more sterically crowded and places two lone pairs on nitrogen atoms that are adjacent to one another, explaining the differences between these two forms. Previous calculations for carbaporphyrins and benzocarbaporphyrins have shown that tautomers with internal CH2 units are usually less favored even though the cavity of NapCP21,23-H is not sterically crowded.41,42 Nucleus-independent chemical shift (NICS) calculations43 were also performed, and these confirmed the diatropic character for all four tautomers (Table 2). In these calculations, a large negative value is consistent with an aromatic compound, while a large positive result points toward an antiaromatic species. Values close to zero imply that the system is nonaromatic. Standard NICS calculations consider the effects due to σ and π electrons and may not always reliably assess aromatic characteristics. For this reason, NICSzz calculations were also carried out, as these primarily measure the effects due to the π system. These calculations were performed 1 Å above the ring (NICS(1)zz). The values obtained using NICSzz are much larger than those produced by NICS, and as the same trends were noted using both techniques only the results obtained using standard NICS calculations will be discussed below to avoid confusion. The NICS values for tautomers with an internal methylene group were much smaller than those for NapCP-22,24-H and NapCP-22,23-H, indicating that these structures have reduced diatropicity. NICS calculations were also performed for the individual rings, and these results can be used to deduce the favored delocalization pathways in these systems. In NapCP22,24-H, the results are consistent with a conventional 18π electron delocalization pathway (Figure 9), and the less favored tautomer NapCP-22,23-H gave similar results. In

comparatively upfield value of 108.6 ppm. Overall, the results indicate that the diatropic characteristics of the palladium complex are slightly reduced compared to naphthocarbaporphyrin 16. The UV−vis spectrum of 31 (Figure 8) was

Figure 8. UV−vis spectrum of palladium complex 31 in CHCl3.

significantly shifted to longer wavelengths, particularly in the case of the longest wavelength absorption which appeared at 772 nm for 31 compared to 697 nm for 9a. These results further demonstrate that there is much stronger electronic communication between the naphthalene moiety and the carbaporphyrin core in 31 than is the case for free base naphthocarbaporphyrins 16 and 29. To gain further insights into the influence of a fused naphthalene ring on the carbaporphyrin system, density functional theory (DFT) calculations were carried out on unsubstituted naphtho[2,3-b]-21-carbaporphyrin, including four different tautomers, three monoprotonated species, and a diprotonated dication (Tables 2−5). Initially, the structures were optimized using B3LYP with the triple-ζ basis set 6-311+ +G(d,p).37 All four free base structures were shown to be near planar. The four naphthoporphyrin tautomers considered for the free base all have aromatic delocalization pathways and differ only in the arrangement of the core hydrogen atoms. As two hydrogens are being relocated in the tautomeric forms, these structures have been designated to show the positions of those hydrogens, specifically as NapCP-22,24-H, NapCP22,23-H, NapCP-21,23-H, and NapCP-21,22-H. The relative stability of these tautomers was assessed using three different

Table 2. Relative Energies and NICS Values for Four Tautomers of Naphtho[2,3-b]carbaporphyrin

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17-atom 18π electron delocalization pathway that encompasses three of the four subunits. Four diprotonated dicarbaporphyrin tautomers were considered, although only one form (CP21,22,23,24-H22+) is fully conjugated. CP-2,22,23,24H22+ is cross-conjugated and 13.46−14.40 kcal/mol higher in energy. Nevertheless, NICS calculations indicated that this form possesses a moderate diatropic ring current, indicating that contributions from species such as 33 (Figure 11) are involved. Two tautomers with bridging methylene units were considered, and unsurprisingly these species were 19.66−24.30 kcal/mol higher in energy than CPH22+. Nine tautomers of the benzocarbaporphyrin monocation were investigated (Table 4), six of which were protonated on a meso-carbon. The nonaromatic forms were 13.68−24.23 kcal/ mol higher in energy (ΔG 13.85−22.20 kcal/mol) than the most stable tautomer. Three fully conjugated forms were possible: BCP-21,22,24-H+, BCP-22,23,24-H+, and BCP21,22,23-H+. Proton NMR spectroscopy had shown that Nprotonated cations BCP-22,23,24-H+ are formed, but the calculations indicate that the C-protonated structure BCP21,22,24-H+ has the lowest energy. However, the differences are very small, and the experimental results may be due to solvent interactions. Tautomer BCP-21,22,23-H+ is less favored than BCP-21,22,24-H+ due to increased steric crowding and decreased opportunities for intramolecular hydrogen bonding interactions. NICS calculations showed that all three of the fully conjugated forms have strong aromatic ring currents. The results indicate that structures with an internal methylene unit strongly interact with the fused benzene unit. For instance, BCP-21,22,24-H+ gave large negative NICS values for rings a, b, d, and e, and a low negative result for ring c, indicating that the favored ring current runs through the periphery of a, b, c, and e but takes an inside path through ring c. For BCP-21,22,24-H+, the favored conjugation pathway takes an inside track relative to the indene unit and follows the periphery of rings b, c, and d, and this is best described as a 17-atom 18π electron pathway as illustrated for structure 34 (Figure 11). The benzene ring gives a relatively small negative shift and does not appear to be involved to any significant extent in global aromatic delocalization. Three versions of the benzocarbaporphyrin dication were investigated: BCPH 2 2+ , BCP-5,22,23,24-H 2 2+ , and BCP10,22,23,24-H22+ (Table 4). Only BCPH22+ is fully conjugated, and the other two forms were calculated as being 12.86−19.10 kcal/mol higher in energy. NICS calculations for BCPH22+ show that this species has a strong aromatic ring current in agreement with experimental results. All five cyclic subunits have strongly negative NICS values, indicating that the preferred conjugation pathway runs through the periphery of the macrocycle. The aromatic properties can be ascribed to the presence of a 20-atom 18π electron pathway in structure 35A or a 24-atom 22π electron pathway in structure 35B (Figure 11). Three fully conjugated monoprotonated forms for naphthocarbaporphyin, NapCP-22,23,24-H+, NapCP-21,22,23-H+, and NapCP-21,22,24-H+ , were considered (Table 5). Although the structure with three protons on the nitrogen atoms (NapCP-22,23,24-H+) was favored, in agreement with the spectroscopic results, a tautomer with an internal methylene unit, NapCP-21,22,24-H+, was calculated to be only 2.29−2.63 kcal/mol higher in energy. The NICS calculations indicated that NapCP-22,23,24-H+ favors a 17atom 18π electron delocalization pathway that does not

Figure 9. Favored macrocyclic conjugation pathways in naphthocarbaporphyrin tautomers.

NapCP-21,23-H, 18π, 22π, and 26π electron delocalization pathways can be considered (structures A−C, Figure 9), but the NICS data suggest that structure C predominates as the NICS values for rings e and f give large negative values. A similar interpretation can be applied to NapCP-21,22-H. The favored pathway for a ring current within an applied magnetic field can also be demonstrated using anisotropy of induced current density (AICD).44 The AICD plots for NapCP-22,24H and NapCP-21,23-H are shown in Figure 10, and these

Figure 10. AICD plots (isovalues 0.05) of naphthoporphyrin tautomers: NapCP-22,24-H (left) and NapCP-21,23-H (right).

confirm the presence of the proposed delocalization pathways. These results are consistent with calculations previously reported for carbaporphyrins and benzocarbaporphyrins.41,42 DFT calculations had not previously been conducted on protonated carbaporphyrins, and it was therefore necessary to consider the properties of carbaporphyrin and benzocarbaporphyrin cations in addition to naphthocarbaporphyrin cations. For the carbaporphyrin series, nine monoprotonated species were considered (Table 3). Six of these structures were protonated on a meso-carbon, and this interrupts macrocyclic conjugation. All six of these nonaromatic forms are much less stable than the aromatic versions, ranging from 18.64 to 30.35 kcal/mol higher in energy (ΔG 20.14−28.20 kcal/mol) than the most favored tautomer CP-21,22,24-H+. Monocations CP21,22,24-H+ and CP-21,22,23-H+ with internal methylene units are favored over the N-protonated version CP-22,23,24H+. NICS calculations for all three of the fully conjugated forms gave strongly negative values consistent with highly diatropic species. Each of these structures appears to favor a 11831


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The Journal of Organic Chemistry Table 3. Relative Energies and NICS Values for Tautomers of Mono- and Diprotonated Carbaporphyrin

(Figure 13). However, the large negative NICS values for rings e and f of NapCP-21,22,23-H+ and NapCP-21,22,24-H+ indicate that these species favor 27-atom 26π electron delocalization pathways that pass through the naphthalene moiety (Figures 12 and 13). Nevertheless, the NICS(0) results for the species with internal methylene units gave smaller negative values than that for NapCP-22,23,24-H+, indicating that they have reduced macrocyclic aromatic properties. Dication NapCPH22+, which would be formed upon further protonation, has of necessity an interior methylene group but retains significant, albeit reduced, diatropic character, giving a NICS(0) value of −7.67 ppm (Table 5). The NICS values for the individual rings indicate that a 28-atom 26π electron delocalization pathway is favored for this structure (Figure 12), although 24-atom 22π and 20-atom 18π electron delocalization pathways may also play a significant role. This interpretation is again supported by the AICD plot shown in Figure 13.

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Figure 11. Favored conjugation pathways in selected mono- and diprotonated carbaporphyrins.

CONCLUSIONS The “3 + 1” variant on the MacDonald condensation has been used to prepare the first examples of naphthocarbaporphyrins 16. Although the aromatic characteristics and UV−vis spectra

involve the fused naphthalene unit (Figure 12). An AICD plot for this species also highlights this conjugation pathway 11832


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The Journal of Organic Chemistry Table 4. Relative Energies and NICS Values for Tautomers of Mono- and Diprotonated Benzocarbaporphyrin

Table 5. Relative Energies and NICS Values for Three Tautomers of Monoprotonated Naphtho[2,3-b]porphyrin and the Related Dication NapCPH22+

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DEPT-135, and NOE difference proton NMR spectroscopy. 2D experiments were performed by using standard software. Highresolution mass spectra (HRMS) were carried out by using a double focusing magnetic sector instrument. 1H and 13C NMR spectra for all new compounds are reported in Supporting Information. 1,4-Methano-1,4-dihydroanthracene (21). Potassium iodide (27.9 g, 0.168 mol) was added to a stirred solution of α,α,α′,α′tetrabromo-o-xylene (10.55 g, 25 mmol) and norbornadiene (23.0 g, 250 mmol) in DMF (100 mL), and the resulting mixture was stirred at this temperature for 16 h. The mixture was poured into water (400 mL) and extracted with ether. The organic phase was dried over sodium sulfate, and the solvent was removed under reduced pressure, initially using a water aspirator and then a vacuum pump. The residue was purified on grade 1 alumina eluting with hexanes and then 2−5% ethyl acetate−hexanes. Further purification on a silica column, eluting with hexanes, afforded the title compound (2.03 g, 10.6 mmol, 42%) as a white solid, mp 77−78 °C (lit. mp33 80−81 °C). 1H NMR (500 MHz, CDCl3): δ 2.24−2.26 (1H, m), 2.38 (1H, dt, J = 1.6, 7.5 Hz) (bridge CH2), 3.98 (2H, pentet, J = 1.7 Hz, 2 × bridgehead CH), 6.75 (2H, t, J = 1.8 Hz, CH = CH), 7.37−7.40 (2H, m), 7.58 (2H, s), 7.68−7.72 (2H, m). 13C NMR (125 MHz, CDCl3): δ 49.8 (2 × bridgehead CH), 66.7 (bridging CH2), 119.5, 125.3, 127.8, 132.3, 142.2, 148.7. exo-1,4-Methano-1,2,3,4-tetrahydro-2,3-dihydroxyanthracene (24). A solution of potassium permanganate (1.212 g, 7.67 mmol) and sodium hydroxide (0.264 g, 6.60 mmol) in water (25 mL) was added to a mixture of 1,4-methano-1,4-dihydroanthracene (1.00 g, 5.21 mmol) in tert-butyl alcohol (25 mL) and water (6 mL) while maintaining the temperature at 0 °C. The resulting mixture was stirred for 20 min at 0 °C, and the reaction was then quenched by the addition of a saturated solution of sodium metabisulfate. The mixture was extracted with ethyl acetate (×4), and the organic solutions were dried over magnesium sulfate. Evaporation of the solvent gave the dialcohol (0.730 g, 3.23 mmol, 62%) as an off-white solid, mp 199− 201 °C. 1H NMR (500 MHz, DMSO-d6): δ 1.72−1.76 (1H, m), 2.24 (1H, dt, J = 1.3, 9.3 Hz) (bridging CH2), 3.21 (2H, t, J = 1.2 Hz, 2 × bridgehead CH), 3.62−3.64 (2H, m, 2 × CHOH), 5.00−5.02 (2H, m, 2 × OH), 7.38−7.41 (2H, m), 7.63 (2H, s), 7.76−7.79 (2H, m). 13 C NMR (125 MHz, DMSO-d6): δ 41.7 (bridging CH2), 50.2 (2 × bridgehead CH), 71.0 (2 × CHOH), 119.7, 125.2, 127.7, 132.7, 144.0. HRMS (EI) m/z: Calcd for C15H14O2 226.09938; found 226.09977. cis-Benzo[f ]indane-1,3-dicarbaldehyde (20). Potassium periodate (245 mg, 1.06 mmol) was added to a the foregoing diol (200.0 mg, 0.884 mmol) in THF (10 mL) and water (4 mL), and the mixture was vigorously stirred at room temperature for 1 h. The mixture was extracted with ether (×3), and the organic solutions were dried over sodium sulfate. Evaporation of the solvent gave the dialdehyde (192.4, 0.86 mmol, 97%) as a light brown oil that solidified on standing. The product is fairly unstable but can be stored in the freezer for several weeks. 1H NMR (500 MHz, CDCl3): δ 2.60−2.66 (1H, m), 2.91−2.96 (1H, m) (2-CH2), 4.16−4.19 (2H, m, 2 × CHCHO), 7.48−7.51 (2H, m, 6,7-CH), 7.82 (2H, s, 4,9-CH), 7.82−7.85 (2H, m, 5,8-CH), 9.76 (2H, d, J = 2.3 Hz, 2 × CHO). 13C NMR (125 MHz, CDCl3): δ 26.0 (CH2), 56.4 (1,3-CH), 124.9 (4,9CH), 126.7 (6,7-CH), 128.1 (5,8-CH), 133.7 (4a,8a-C), 137.2 (3a,9a-C), 199.5 (2 × CHO). HRMS (EI) m/z: Calcd for C15H12O2 224.08373; found 224.08329. 7,18-Diethyl-8,12,13,17-tetramethylnaphtho[2,3-b]carbaporphyrin (16). Tripyrranedicarboxylic acid 2535 (118 mg, 0.260 mmol) was stirred with trifluoroacetic acid (2 mL) under nitrogen for 1 min. The mixture was diluted with dichloromethane (100 mL), dialdehyde 20 (60 mg, 0.27 mmol) was immediately added, and the mixture stirred for 16 h under nitrogen. The resulting solution was neutralized with triethylamine and oxidized by stirring with DDQ (121 mg, 98%, 0.52 mmol) for 3 h. The mixture was washed with water and then with saturated sodium bicarbonate. The solvent was removed under reduced pressure and the residue chromatographed on grade 3 alumina, eluting with dichloromethane, to give a dark red brown band. The solvent was removed under reduced pressure and

Figure 12. Favored conjugation pathways in protonated naphthocarbaporphyrin species.

Figure 13. AICD plots (isosurface values 0.05) of naphthocarbaporphyrin monocation NapCP-22,23,24-H+ (left) and C-protonated dication NapCPH22+ (right).

were similar to benzocarbaporphyrins, the reactivity of 16 toward FeCl3 was greatly altered. Reaction with silver(I) acetate afforded a silver(III) derivative, while protonation sequentially afforded aromatic mono- and dications. Alkylation with methyl iodide and potassium carbonate afforded a 22methyl derivative, and this reacted with palladium(II) acetate to give a palladium(II) organometallic complex where the methyl group had migrated onto the internal carbon atom. The UV−vis spectra of the palladium(II) complex and the naphthocarbaporphyrin dication show large bathochromic shifts due to π-electron delocalization through the fused naphthalene moiety, while free base 16, N-methyl derivative 24, and silver complex 23 were little affected by the presence of the 10π electron arene unit. The results provide valuable insights into the effects caused by formally extending the πsystems of carbaporphyrinoid systems.

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EXPERIMENTAL SECTION

Melting points are uncorrected. NMR spectra were recorded using a 400 or 500 MHz NMR spectrometer and were run at 302 K unless otherwise indicated. 1H NMR values are reported as chemical shifts δ, relative integral, multiplicity (s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad peak) and coupling constant (J). Chemical shifts are reported in parts per million (ppm) relative to CDCl3 (1H residual CHCl3 δ 7.26, 13C CDCl3 triplet δ 77.23) or DMSO-d6 (1H residual DMSO-d5 pentet δ 2.49, 13C d6-DMSO heptet δ 39.7), and coupling constants were taken directly from the spectra. NMR assignments were made with the aid of 1H−1H COSY, HSQC, 11834


Article


CH), 124.8, 126.5 (23,33-CH), 129.0 (22,32-CH), 133.2, 133.7, 133.8, 136.72, 136.79, 139.9, 140.1, 140.3, 141.1. HRMS (ESI) m/z: [M + H]+ Calcd for C39H39ClN3 584.2836; found 584.2869. 7,18-Diethyl-8,12,13,17,22-pentamethylnaphtho[2,3-b]carbaporphyrin (29). Naphthocarbaporphyrin 16 (66.1 mg, 0.120 mmol) was stirred with potassium carbonate (601 mg, 4.35 mmol) and methyl iodide (30 drops) in acetone (60 mL) under reflux for 16 h. The mixture was washed with water and evaporated under reduced pressure. The residue was run through a silica column, eluting with chloroform, and two colored fractions were observed. The latter major fraction was evaporated under reduced pressure and the residue recrystallized from chloroform−methanol to yield the N-methylcarbaporphyrin 29 (42.2 mg, 0.075 mmol, 62%), as purple crystals, mp >300 °C. UV−vis (7.145 μM in 1% Et3N−CHCl3): λmax (log ε): 441 (5.33), 523 (4.16), 558 (4.30), 623 (3.78), 685 (3.53). UV−vis (7.145 μM in 0.5% TFA−CHCl3): λmax (log ε): 372 (4.46), 403 (4.59), 462 (5.11), 573 (4.01), 611 (4.25), 623 (4.30), 685 (3.75). UV−vis (7.145 μM in 50% TFA−CHCl3): λmax (log ε): 330 (4.49), 371 (4.48), 402 (4.60), 439 (sh, 4.71) 463 (5.09), 567 (3.99), 610 (4.24), 623 (4.28), 685 (3.80). 1H NMR (500 MHz, CDCl3): δ −5.85 (1H, s, 21-H), −4.06 (3H, s, 22-CH3), −2.45 (1H, br s, NH), 1.44 (3H, t, J = 7.7 Hz), 1.84 (3H, t, J = 7.7 Hz), 1.87−1.91 (6H, m) (4 × CH2CH3), 3.22 (3H, s, 7-CH3), 3.58 (3H, s, 18-CH3), 3.66− 3.76 (2H, m), 3.89−4.07 (6H, m) (4 × CH2CH3), 7.60−7.65 (2H, m, 23,33-H), 8.24−8.30 (2H, m, 22,32-H), 9.09 (1H, s, 31-H), 9.16 (1H, s, 21-H), 9.55 (1H, s, 15-H), 9.70 (1H, s, 10-H), 9.99 (1H, s, 5-H), 10.05 (1H, s, 20-H); 1H NMR (500 MHz, 10 μL TFA−CDCl3): δ −6.47 (1H, s, 21-H), −5.13 (1H, s), −5.10 (1H, s) (2 × NH), −4.29 (3H, s, N−CH3), 1.42 (3H, t, J = 7.7 Hz), 1.74 (3H, t, J = 7.7 Hz), 1.82 (3H, t, J = 7.7 Hz), 1.86 (3H, t, J = 7.7 Hz) (4 × CH2CH3), 3.26 (3H, s, 7-CH3), 3.62 (3H, s, 18-CH3), 3.70−3.76 (2H, m), 4.03−4.18 (6H, m) (4 × CH2CH3), 7.65−7.68 (2H, m, 23,33-H), 8.20−8.24 (2H, m, 22,32-H), 9.03 (1H, s, 21-H), 9.07 (1H, s, 31-H), 10.00 (1H, s), 10.03 (1H, s) (10,15-H), 10.25 (1H, s, 5-H), 10.33 (1H, s, 20-H); 13 C NMR (125 MHz, CDCl3): δ 11.7 (18-CH3), 11.8 (7-CH3), 16.3 (CH2CH3), 17.6 (CH2CH3), 18.47 (CH2CH3), 18.49 (CH2CH3), 19.8 (CH2CH3), 19.9 (CH2CH3), 20.0 (CH2CH3), 20.1 (CH2CH3), 31.7 (N−CH3), 95.1 (15-CH), 97.9 (10-CH), 99.8 (20-CH), 102.1 (5-CH), 118.5 (21-CH), 119.1 (31-CH), 122.1 (21-CH), 125.6 (23or 33-CH), 125.7 (23- or 33-CH), 127.0, 129.03 (22- or 32-CH), 129.05 (22- or 32-CH), 132.7, 133.7, 133.9, 134.2, 134.5, 134.7, 139.8, 141.3, 141.5, 142.3, 142.8, 142.92, 142.96, 145.0, 147.2, 149.0, 150.3; 13 C NMR (125 MHz, trace TFA−CDCl3): δ 11.7 (CH3), 12.0 (CH3), 15.8 (CH2CH3), 16.8 (CH2CH3), 17.69 (CH2CH3), 17.73 (CH2CH3), 19.94 (CH2), 19.96 (CH2), 20.13 (CH2), 20.18 (CH2), 31.5 (N−CH3), 94.5 (10- or 15-CH), 96.4 (10- or 15-CH), 103.0 (20-CH), 105.5 (5-CH), 120.5 (21-CH), 121.2 (31-CH), 124.3 (21CH), 126.8 (23- or 33-CH), 126.9 (23- or 33-CH), 129.24 (22- or 32CH), 129.29 (22- or 32-CH), 131.8, 134.1, 134.2, 136.0, 137.3, 137.4, 137.6, 138.0, 138.4, 139.5, 140.0, 141.16, 141.22, 141.9, 142.0, 142.2, 150.0, 154.5. HRMS (ESI) m/z: [M + H]+ Calcd for C40H42N3 564.3379; found 564.3364. [7,18-Diethyl-8,12,13,17,21-pentamethylnaphtho[2,3-b]carbaporphyrinato]palladium(II) (31). Palladium(II) acetate (15 mg, 0.067 mmol) was added to a solution of N-methylnaphthocarbaporphyrin 29 (16.0 mg, 0.029 mmol) in acetonitrile (14.6 mL), and the solution was stirred under reflux for 4 h. The solution was cooled, diluted with chloroform, and washed with water, and the organic layer was separated and then evaporated to dryness. The residue was chromatographed on silica, eluting with 30% dichloromethane− hexanes, and the product was collected as a reddish/brown band. The solvent was evaporated to dryness and the residue recrystallized from chloroform−methanol to yield the palladium(II) complex (15.3 mg, 0.023 mmol, 77%) as dark purple crystals, mp >300 °C. UV−vis (13.32 μM in CHCl3): λmax (log ε): 353 (4.51), 435 (4.67), 772 (4.21). 1H NMR (500 MHz, CDCl3): δ −2.18 (3H, s, 21-CH3) 1.65−1.69 (12H, m, 4 × CH2CH3), 3.16 (6H, s, 7,18-CH3), 3.54− 3.60 (8H, m, 4 × CH2CH3), 7.81−7.84 (2H, m, 23,33-H), 8.50−8.54 (2H, m, 22,32-H), 9.13 (2H, s, 10,15-H), 9.69 (2H, s, 21,31-H), 9.85 (2H, s, 5,20-CH). 13C NMR (125 MHz, CDCl3): δ 11.5 (7,18-CH3),

the residue recrystallized from chloroform−methanol to yield the naphthocarbaporphyrin (61.2 mg, 0.111 mmol, 43%) as a fluffy brown solid, mp >300 °C. UV−vis (6.978 μM in 1% Et3N−CHCl3): λmax (log ε): 432 (5.32), 517 (4.04), 554 (4.40), 607 (3.78), 668 (3.72). UV−vis (6.978 μM in 0.5% TFA−CHCl3): λmax (log ε): 387 (4.48), 453 (5.07), 563 (3.99), 601 (4.18), 613 (4.20), 673 (3.68). UV−vis (6.978 μM in 50% TFA−CHCl3): λmax (log ε): 399 (4.54), 459 (4.94), 622 (4.12). 1H NMR (500 MHz, CDCl3): δ −6.55 (1H, s, 21H), −3.87 (2H, br s, 2 × NH), 1.86 (6H, t, J = 7.6 Hz, 8,17CH2CH3), 1.88 (6H, t, J = 7.6 Hz, 12,13- CH2CH3), 3.61 (6H, s, 7,18-CH3), 3.96 (4H, q, J = 7.6 Hz, 12,13-CH2), 4.05 (4H, q, J = 7.6 Hz, 8,17-CH2), 7.61−7.64 (2H, m, 23,33-H), 8.24−8.28 (2H, m, 22,32-H), 9.09 (2H, s, 21,31-H), 9.76 (2H, s, 10,15-H), 10.00 (2H, s, 5,20-H). 1H NMR (500 MHz, trace TFA−CDCl3, monocation 16H+): δ −6.47 (1H, s, 21-CH), −5.02 (1H, s, 23-NH), −3.76 (2H, s, 22,24-H), 1.71 (6H, t, J = 7.7 Hz), 1.85 (6H, t, J = 7.7 Hz) (4 × CH2CH3), 3.60 (6H, s, 7,18-CH3), 4.05−4.13 (8H, m, 4 × CH2CH3), 7.58−7.61 (2H, m, 23,33-H), 8.13−8.16 (2H, m, 22,32-H), 8.98 (2H, s, 21,31-H), 10.07 (2H, s, 10,15-H), 10.33 (2H, s, 5,20-H). 1H NMR (500 MHz, TFA with C6D6 standard, dication 16H22+): −2.20 (2H, s, 21-CH2), 2.11−2.18 (12H, 2 overlapping triplets, 4 × CH2CH3), 3.86 (6H, s, 7,18-CH3), 4.26−4.33 (8H, m, 4 × CH2CH3), 8.63−8.66 (2H, m, 23,33-H), 9.27−9.30 (2H, m, 22,32-H), 10.41 (2H, s), 10.90 (2H, s), 11.03 (2H, s). 13C NMR (125 MHz, CDCl3): δ 11.5 (7,18CH3), 17.4 (8,17-CH2CH3), 18.6 (12,13-CH2CH3), 19.7 (8,17-CH2), 20.2 (12,13-CH2), 95.8 (10,15-CH), 97.1 (5,20-CH), 114.6 (21-CH), 118.8 (21,31-CH), 125.6 (23,33-CH), 129.1 (22,32-CH), 131.9, 133.6, 134.1, 135.2, 135.7, 137.8, 141.0, 144.2, 152.4. 13C NMR (125 MHz, trace TFA−CDCl3, monocation 16H+): δ 11.8 (7,18-CH3), 16.9 (2 × CH2CH3), 17.8 (2 × CH2CH3), 19.95 (2 × CH2), 20.06 (2 × CH2), 94.3 (10,15-CH), 102.9 (5,20-CH), 112.0, 120.5 (21,31-CH), 124.4 (21-CH), 126.5 (23,33-CH), 129.2 (22,32-CH), 134.1, 134.1, 134.5, 136.3, 137.2, 138.0, 140.8, 141.1, 141.9. 13C NMR (125 MHz, TFA = 1 drop concd HCl with C6D6 standard, dication 16H22+): 9.8, 15.2, 16.2, 19.3, 19.6, 37.6 (21-CH2), 107.0, 109.4, 124.9, 128.3, 129.8, 130.2, 135.7, 137.0, 138.9, 140.3, 140.8, 146.5, 151.6, 153.5, 154.2. HRMS (ESI) m/z: [M + H]+ Calcd for C39H40N3 550.3222; found 550.3250. 21-Chloro-7,18-diethyl-8,12,13,17-tetramethylnaphtho[2,3b]carbaporphyrin (27a). A solution of naphthocarbaporphyrin 16 (22 mg, 0.040 mmol) in dichloromethane (10 mL) was vigorously stirred with a solution of ferric chloride (1.62 g, 10 mmol) in water (10 mL) at room temperature overnight. The solution was diluted with dichloromethane and washed with water, and the solvent was removed under reduced pressure. The residue was chromatographed on grade 3 alumina, eluting with chloroform. A deep blue fraction was collected. Recrystallization from chloroform−hexanes afforded chlorocarbaporphyrin 27a (16.5 mg, 0.028 mmol, 70%) as deep green crystals, mp >300 °C. UV−vis (9.127 μM in CHCl3): λmax (log ε): 441 (5.22), 573 (4.35), 614 (3.81), 676 (3.52); UV−vis (9.127 μM in 0.5% TFA−CHCl3): λmax (log ε): 463 (5.06), 570 (3.89), 621 (4.31), 679 (3.57); UV−vis (9.127 μM in 50% TFA−CHCl3): λmax (log ε): 462 (4.89), 570 (3.82), 622 (4.04), 681 (3.78); 1H NMR (500 MHz, CDCl3): δ −3.76 (2H, v br), 1.84−1.88 (12H, 2 overlapping triplets, 4 × CH2CH3), 3.63 (6H, s, 7,18-H), 3.92 (4H, t, J = 7.7 Hz), 4.03 (4H, t, J = 7.7 Hz) (4 × CH2CH3), 7.46−7.49 (2H, m, 23,33-H), 8.03−8.06 (2H, m, 22,32-H), 8.54 (2H, s, 21,31-H), 9.74 (2H, s, 10,15-H), 9.92 (2H, s, 5,20-H); 1H NMR (500 MHz, trace TFA−CDCl3): δ −4.82 (1H, s, 23-NH), −2.44 (2H, s, 22,24-NH), 1.71 (6H, t, J = 7.5 Hz), 1.87 (6H, t, J = 7.5 Hz) (4 × CH2CH3), 3.47 (6H, s, 7,18-CH3), 3.87−4.11 (8H, m, 4 × CH2CH3), 7.49−7.52 (2H, m, 23,33-H), 8.02−8.05 (2H, m, 22,32-H), 8.43 (2H, s, 21,31-H), 9.85 (2H, s, 10,15-H), 10.00 (2H, s, 5,20-H); 13C NMR (125 MHz, CDCl3): δ 11.7 (7,18-CH3), 17.5 (2 × CH2CH3), 18.6 (2 × CH2CH3), 19.7 (2 × CH2CH3), 20.0 (2 × CH2CH3), 96.5 (10,15CH), 98.5 (5,20-CH), 115.1, 118.7 (21,31-H), 125.5 (23,33-CH), 128.6 (22,32-CH), 132.1, 132.8, 133.1, 134.8, 135.5, 138.4, 144.6, 153.5; 13C NMR (125 MHz, trace TFA−CDCl3): δ 11.8 (7,18-CH3), 16.9 (2 × CH2CH3), 17.8 (2 × CH2CH3), 19.9 (2 × CH2CH3), 20.0 (2 × CH2CH3), 93.9 (10,15-CH), 101.2 (5,20-CH), 120.9 (21,3111835


The Journal of Organic Chemistry 17.5 (2 × CH2CH3), 18.4 (2 × CH2CH3), 19.3 (2 × CH2CH3), 19.7 (2 × CH2CH3), 25.5 (21-CH3), 50.5 (21-C), 106.9 (5,20-CH), 108.6 (21,31-CH), 120.6 (10,15-CH), 126.2 (23,33-CH), 129.2 (22,32-CH), 132.4, 133.0, 137.8, 140.1, 140.5, 141.2, 146.4, 152.3, 164.2. HRMS (ESI) m/z: Calcd for C40H39N3Pd 667.2194; found 667.2183. [7,18-Diethyl-8,12,13,17-tetramethylnaphtho[2,3-b]carbaporphyrinato]silver(III) (28). A solution of naphthocarbaporphyrin 16 (12.1 mg, 220.0 mmol) in dichloromethane (12 mL) was added to silver(I) acetate (12 mg) dissolved in methanol (2.5 mL), and the mixture was stirred at room temperature overnight. The mixture was washed with water and the solvent removed under reduced pressure. The residue was chromatographed on grade 3 alumina, eluting with dichloromethane. A deep red-orange fraction was collected and recrystallized from chloroform−methanol to give the silver(III) complex (8.8 mg, 13.4 mmol, 61%) as purple crystals, mp >300 °C. UV−vis (5.499 μM in CHCl3): λmax (log ε): 439 (5.22), 530 (3.89), 555 (sh, 4.41) 564 (4.63), 602 (4.02). 1H NMR (500 MHz, CDCl3, 52 °C): δ 1.85 (6H, t, J = 7.7 Hz), 1.91 (6H, t, J = 7.7 Hz) (4 × CH2CH3), 3.51 (6H, s, 7,18-CH3), 3.97−4.04 (8H, m (4 × CH2CH3), 7.64−7.67 (2H, m, 23,33-H), 8.27−8.30 (2H, m (22,32H), 9.04 (2H, s, 21,31-H), 9.85 (2H, s, 10,15-CH), 9.90 (2H, s, 5,20CH). 13C NMR (data derived from HSQC spectrum, CDCl3): δ 11.4 (7,18-CH3), 17.4 (2 × CH2CH3), 18.1(2 × CH2CH3), 19.9 (4 × CH2), 97.6 (10,15-CH), 100.6 (5,20-CH), 118.1 (21,31-CH), 125.3 (23,33-CH), 128.8 (22,3 2-H). HRMS (ESI) m/z: Calcd for C39H36AgN3 653.1960; found 653.1971. Computational Studies. All calculations were performed using Gaussian 0945 Rev D.01 running on a Linux-based computer. Energy minimization and frequency calculations of the porphyrinoid systems were performed at the density functional theory (DFT) level of theory with the B3LYP functional and the 6-311++G(d,p) triple-ζ basis set.46−49 Single-point energy calculations were performed on the minimized structures using both the B3LYP-D350 and M062-X51 functionals with a 6-311++G(d,p) triple-ζ basis set. The resulting Cartesian coordinates of the molecules can be found in Supporting Information. Two types of NMR calculations were performed: the GIAO method was used to obtain NICS values,52 and CGST to obtain ACID plots.44,53 NICS(0) was calculated at the mean position of all four heavy atoms in the middle of the macrocycle. NICS(a), NICS(b), NICS(c), NICS(d), NICS(e), and NICS(f) values were obtained by applying the same method to the mean position of the heavy atoms that comprise the individual rings of each macrocycle. In addition, NICS(1)zz, NICS(1a)zz, NICS(1b)zz, NICS(1c)zz, NICS(1d)zz, NICS(1e)zz, and NICS(1f)zz were obtained by applying the same method to ghost atoms placed 1 Å above each of the corresponding NICS(0) points and extracting the zz contribution of the magnetic tensor. ACID for all the compounds were plotted, and these plots can also be found in Supporting Information.

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ACKNOWLEDGMENTS

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REFERENCES

This work was supported by the National Science Foundation under grants CHE-1212691 and CHE-1465049, and the Petroleum Research Fund, administered by the American Chemical Society.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.8b01748.

■

Article

Tables giving Cartesian coordinates, calculated energies, selected bond lengths and AICD plots, and selected 1H NMR, 1H−1H COSY, HSQC, DEPT-135, 13C NMR, MS, and UV−vis spectra (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Timothy D. Lash: 0000-0002-0050-0385 Notes

The authors declare no competing financial interest. 11836


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