Metalation and Selective Oxidation of Diphenyl-23-oxa-, -thia-, and

Sep 5, 2017 - The availability of diphenyl-23-oxa-, -thia-, and -selena-21-carbaporphyrins has enabled the reactivity of these systems to be investiga...
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Metalation and Selective Oxidation of Diphenyl-23-oxa‑, -thia‑, and -selena-21-carbaporphyrins Timothy D. Lash* and Gregory M. Ferrence Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States S Supporting Information *

ABSTRACT: The availability of diphenyl-23-oxa-, -thia-, and -selena-21-carbaporphyrins has enabled the reactivity of these systems to be investigated and contrasted. All three heterocarbaporphyrins reacted with palladium(II) acetate in refluxing chloroform−acetonitrile to give organometallic palladium(II) derivatives in good yields. These structures are stable and give UV−vis spectra that show increasing broadening and bathochromic shifts as the size of the heteroatom increases. Nickel(II) acetate in refluxing N,N-dimethylformamide reacted with the oxa- and thiacarbaporphyrins under nitrogen to give the corresponding nickel(II) complexes, but the selenacarbaporphyrin did not metalate under these conditions. The NMR spectra for all of the metal complexes showed that they possess strong diamagnetic ring currents, although the palladium complexes gave larger downfield shifts that were slightly diminished when larger heteroatoms were present in the porphyrinoid cavity. Reactions of the oxacarbaporphyrin with nickel(II) acetate in the presence of air led to a unique oxidation reaction that afforded a weakly diatropic 21-oxycarbaporphyrin, and low yields of a related product were also obtained from the thiacarbaporphyrin.

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benzo unit has also been reported.17 Related organometallic complexes have also been obtained indirectly by palladium(II)-, gold(III)-, or rhodium(III)-mediated ring contractions of benziporphyrins.21−23 In addition to the rich coordination chemistry reported for carbaporphyrinoids, selective oxidations have also been observed in reactions with transition-metal reagents. For instance, azuliporphyrins react with copper(II), silver(I), or cobalt reagents to give 21-oxyazuliporphyrins such as 9,24−26 while tetraphenylbenziporphyrin 10a reacts with silver(I) acetate to afford the 21-acetoxy derivative 10b.27 Similar reactivity is observed for dimethoxybenziporphyrins.28 Although a considerable amount of work has been reported on the metalation of carbaporphyrinoids,3 very few studies on the reactions of heterocarbaporphyrins with transition-metal reagents have been reported.29,30 22- and 23-oxacarbaporphyrins have been shown to give stable nickel(II) and palladium(II) organometallic complexes, and in one case, a platinum(II) derivative was obtained in low yield.31−33 In addition, 23thiacarbaporphyrins have been reported to give good yields of palladium(II) complexes.34,35 However, there are no detailed reports on the synthesis and properties of metalated heterocarbaporphyrins. Recently, we reported a new route to carbaporphyrins and heterocarbaporphyrins from carbatripyrrin 11.36 The reaction of 11 with furan, thiophene, or selenophene dicarbinols 12 in the presence of boron trifluoride etherate, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded a series of diphenylheterocarbaporphyrins 13

INTRODUCTION Carbaporphyrinioid systems,1,2 porphyrin-like structures that have one or more carbon atoms within the macrocyclic cavity, have been shown to be versatile ligands that can generate stable organometallic derivatives.3 Metalation of N-confused porphyrins 1a has been particularly well documented,4,5 and these porphyrin isomers can act as dianionic or trianionic ligands in the generation of organometallic complexes such as 1b, 1c, and 2 (Chart 1). Azuliporphyrins 3a are generally dianionic ligands and form complexes 3b−3f with nickel(II), palladium(II), platinum(II), rhodium(III), iridium(III), and ruthenium(II),6 and benziporphyrins such as 4a similarly afford a broad range of metalated derivatives such as 4b and 4c.7−9 Tropiporphyrins 5a react with silver(I) acetate to give silver(III) complexes 5b,10 as do N-confused porphyrins11 and carbaporphyrins such as 6.12−14 True carbaporphyrins, which contain cyclopentadiene units that in some cases are fused to aromatic rings (e.g., 6a and 7), have attracted a considerable amount of attention over the last 20 years (Chart 1).15−18 Much of the coordination chemistry for this system has been conducted on benzocarbaporphyrins 6a because of the ease of preparation and stability of these porphyrinoids. In addition to forming silver(III) complexes 6b,12,13 carbaporphyrins 6a react with gold(III) acetate to form gold(III) derivatives (e.g., 6c), although good yields are only obtained using meso-substituted structures.13 More recently, 6a has been shown to form stable rhodium(III) and iridium(III) complexes 6d and 6e, respectively.19 Following N-alkylation with methyl or ethyl iodide, benzocarbaporphyrins react with palladium(II) acetate to give palladium(II) complexes 8,20 and a similar derivative without the fused © 2017 American Chemical Society

Received: July 30, 2017 Published: September 5, 2017 11426

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

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Inorganic Chemistry Chart 1. Selected Carbaporphyrinoid and Metalloporphyrinoid Structures

Scheme 1. Synthesis of Diphenylheterocarbaporphyrins

information has previously been available. Suitable crystals of 13a and 13b were obtained for X-ray diffraction. The results not only confirmed these structures but also provided insight into the conformations of these macrocyclic ligands. The molecular structure of 13a (Figure 1) shows that the

Figure 1. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms rendered arbitrarily small for clarity) of oxacarbaporphyrin 13a.

porphyrinoid is slightly ruffled, as evidenced by the 8.29° and 7.92° pyrrole, the 8.51° furan, and the 8.32° indene tilts relative to the mean macrocycle plane. We previously suggested that the 15.5° tilt of the indene unit in benzocarbaporphyrins 6a relieves steric crowding in the central cavity due to the presence of three hydrogen atoms.16 The lesser tilt to the indene moiety in 13a is consistent with the less crowded central cavity with only two hydrogen atoms. With the exception of the C1−C2 and C3−C4 bond lengths, a Mogul geometry check validated all bond distances to be within the typical ranges.37 The molecular structure of 13b showed that the thiophenecontaining macrocycle has a similar conformation (Figure 2). Consistent with the placement of the internal pyrrolic hydrogen atom on N22, the corresponding pyrrole subunit is tilted 13.3° relative to the mean macrocyclic plane, whereas the other

(Scheme 1).36 This series represents a valuable matched set of ligands that can be used to explore the coordination chemistry of heterocarbaporphyrins, and we set out to further investigate the formation of nickel(II) and palladium(II) complexes. The results reported below provide valuable insight into how the properties of the metalated porphyrinoids vary as the core heteroatom is altered. In addition, an unexpected oxidation reaction was observed that resulted in the formation of a new class of carbaporphyrinoids.

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RESULTS AND DISCUSSION Although the synthesis and spectroscopic characterization of 13a−13c has been published previously,36 no structural

Figure 2. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms rendered arbitrarily small for clarity) of thiacarbaporphyrin 13b. 11427

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

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Inorganic Chemistry pyrrole unit is only tilted by 1.16°. The thiophene to mean macrocycle plane tilt is 8.45°, and the indene is tilted by 8.32°. Initially, reactions of 13a−13c with palladium(II) acetate in refluxing acetonitrile were investigated. In each case, rapid complexation was observed to produce the related palladium derivatives 14a−14c in 72−98% yield (Scheme 2). The result Scheme 2. Preparation of Palladium(II) Heterocarbaporphyrins

Figure 4. 500 MHz 1 H NMR spectrum of palladium(II) oxacarbaporphyrin 14a in CDCl3.

8.58 and 9.04 ppm. The benzo protons adjacent to the macrocycle, 21,31-H, appeared at 8.49−8.52 ppm. These values are consistent with the arene protons being deshielded due to the proximity of the macrocyclic ring current but not being directly involved in the delocalization pathway. The 1H NMR spectrum for the thia analogue 14b was similar. The mesoprotons gave a 2H singlet at 10.06 ppm, the thiophene protons were present as a 2H singlet at 8.92 ppm, and the pyrrolic protons gave two 2H doublets at 8.72 and 9.03 ppm. The 21,31H’s for the benzo unit were noted as a multiplet at 8.44−8.47 ppm. Most of the results suggest that the diatropicity is slightly reduced, although the resonance for pyrrolic protons at positions 8 and 17 was shifted downfield compared to the equivalent signal for 14a. Far more significant results were observed in the 1H NMR spectrum for the selenium-containing complex 14c (Figure 5). In this case, the ortho and meta

for selenacarbaporphyrin was particularly significant because this is the first example of a metalated derivative for this system. The crude products were purified by column chromatography on grade 2 alumina, followed by recrystallization from chloroform−methanol. The UV−vis spectra for these complexes varied substantially, although clear trends were noted (Figure 3). Solutions of palladium(II) oxacarbaporphyrin 14a

Figure 3. UV−vis spectra of palladium(II) 23-oxa-21-carbaporphyrin 14a (red line), palladium(II) 23-thia-21-carbaporphyrin 14b (green line), and palladium(II) 23-selena-21-carbaporphyrin 14c (purple line) in chloroform.

in chloroform gave a series of strong bands between 370 and 500 nm and minor Q-like bands at 582 and 609 nm. The thia complex 14b produced broadened and less intense bands, showing two Soret-like bands at 437 and 504 nm and a broad absorption between 600 and 700 nm. The selena complex 14c showed further bathochromic shifts with moderately strong absorptions at 409, 457, 524, and 552 nm and a broad peak at 728 nm (Figure 3). Hence, as the heteroatom increases in atomic number, the observed absorptions decrease in intensity and shift to longer wavelengths. The 1H NMR spectrum for palladium(II) oxacarbaporphyrin 14a in CDCl3 clearly indicated that the macrocycle fully retained its aromatic characteristics (Figure 4). The mesoprotons were shifted downfield to give a 2H singlet at 10.10 ppm, while the furan protons appeared as a 2H singlet at 8.92 ppm and the pyrrolic protons gave rise to two 2H doublets at

Figure 5. 500 MHz 1 H NMR spectrum of palladium(II) selenacarbaporphyrin 14c in CDCl3.

protons attached to the phenyl substituents gave rise to two separate multiplets at 7.08 and 8.98 ppm for the former and 7.5 and 7.93 ppm for the latter. These results indicate that rotation of the phenyl units is sterically restrained and that the macrocycle is folded so that the two sides of the aryl substituent fall into very different chemical environments. This implies that the large selenium atom in 14c has introduced a considerable degree of macrocyclic distortion compared to 14a or 14b. The aromatic ring current for 14c is also somewhat reduced. The meso-protons appeared as a 2H singlet at 9.99 ppm, the selenophene protons at 8.91 ppm, and the pyrrolic 11428

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Inorganic Chemistry protons at 8.57 and 8.96 ppm. In addition, the 21,31-H’s for the benzo unit gave rise to a multiplet at 8.38−8.42 ppm, approximately 0.1 ppm upfield compared to the equivalent resonance in 14a. Nevertheless, the data strongly indicate that 14c retains most of its aromatic characteristics. Overall, the data from the UV−vis and 1H NMR spectra are consistent with reduced planarity in these porphyrinoids upon going from X = O to S to Se. The 13C NMR spectra for 14a−14c all indicated that the macrocycles have a plane of symmetry, although the results also show that the two sides of the phenyl groups have been differentiated in 14c. The unsubstituted meso-carbons gave resonances at 113.9, 117.2, and 119.4 ppm for 14a−14c, respectively. The identities of these complexes were further confirmed by high-resolution electrospray ionization mass spectrometry [HR-MS (ESI)]. Crystals suitable for structural analysis were obtained for palladium(II) oxacarbaporphyrin 14a and selenacarbaporphyrin 14c (Figures 6 and 7). The palladium(II) center in 14a resides

lengths, and the 1.479(8) Å C1−C2 and 1.480(7) Å C3−C4 bond lengths are, like the aforementioned structures, distended. The presence of a large selenium atom forces the selenophene ring to cant substantially, 36.0°, relative to the rest of the macrocycle’s framework atoms, leaving the remainder of the core to be rather flat. The pyrrole to mean macrocycle plane tilts are 2.86° and 2.25°, and the indene is tilted by 3.13°. The C21−Pd−Se bond angle is 164.01(7)°, with the selenium atom forced out of the Pd−C21−N22−N24 plane to accommodate the steric constraints imposed by the porphyinoid macrocycle. This is the first X-ray structural characterization of a palladated selenophene. The 166 examples (100 structures) in the Cambridge Structural Database (version 5.38, May 2017 update) containing an R2Se−PdL3 fragment indicate that the typical palladium(II)-to-selenium bonding distance is 2.41(4) Å, so while the Pd−Se distance in 14c is short, it appears to be within the normal range. Reactions of 13a−13c with nickel(II) acetate gave mixed results (Scheme 3). The best results were obtained when the Scheme 3. Metalation and Oxidation of Heterocarbaporphyrins with Nickel(II) Acetate

Figure 6. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms rendered arbitrarily small for clarity) of palladium(II) oxacarbaporphyrin 14a.

Figure 7. Color POV-Ray rendered ORTEP III drawing (50% probability level; hydrogen atoms rendered arbitrarily small for clarity) of palladium(II) selenacarbaporphyrin 14c.

in a typical square-planar coordination environment with 1.959(3) Å Pd−C21, 2.023(2) Å Pd−N22, 2.176(2) Å Pd− O, and 2.022(2) Å Pd−N24 bond lengths, and the distended 1.480(4) Å C1−C2 and 1.480(4) Å C3−C4 bond lengths suggest that the fused benzo unit is isolated from the main macrocyclic π system (Figure 6). The Pd−C and Pd−O bond distances in 14a are similar to (within 0.02 Å) a closely related meso-unsubstituted palladium(II) 21-carba-22-oxabenzo[b]porphyrin.33 The porphyrinoid is, however, less planar with 8.45° and 8.73° pyrrole to mean macrocycle plane tilts and 9.96° furan and 6.37° indene to mean macrocycle plane tilts. As had been anticipated, the structure of 14c is relatively distorted due to the presence of a selenium atom within the porphyrinoid core, and the coordination environment around the palladium(II) center is distorted from square-planar (Figure 7). The core distances are reasonable, with 1.967(2) Å Pd−C21, 2.072(4) Å Pd−N22, 2.3487(3) Å Pd−Se, and 2.063(4) Å Pd−N24 bond

heterocarbaporphyrin was refluxed with nickel(II) acetate in N,N-dimethylformamide (DMF). The selenacarbaporphyrin failed to give any metalated product under any of the conditions examined. Oxa- and thiacarbaporphyrins 13a and 13b both reacted, but the organometallic products were contaminated by a second species that was difficult to remove by column chromatography. A similar byproduct was observed when 13a was reacted with nickel(II) acetate in refluxing acetonitrile. These reactions were carried out open to the air, and it was plausible that an oxidation reaction was taking place. When the reactions were repeated under nitrogen, 13a and 13b both gave excellent yields of nickel(II) derivatives 15a and 15b (Scheme 3). These organometallic complexes were again purified on grade 3 alumina and recrystallized from chloroform−methanol. The compounds were stable at room temperature in both the solid state and in solution. When 11429

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

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Inorganic Chemistry

for palladium complexes 14a−14c, where the meso-carbon moved downfield upon going from oxygen to sulfur to selenium. The identities of the nickel complexes were further supported by HR-MS (ESI). The structure of nickel complex 15b was also confirmed by X-ray crystallography (Figure 9). The nickel(II) center resides

15c was refluxed with nickel(II) acetate in DMF under nitrogen, unreacted starting material was recovered. However, when the reaction was conducted open to the air, the porphyrinoid underwent extensive decomposition. The UV−vis spectra for the nickel complexes 15a and 15b not only differed considerably from one another (Figure 8) but

Figure 9. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms rendered arbitrarily small for clarity) of nickel(II) thiacarbaporphyrin 15b.

in a distorted square-planar coordination environment with 1.891(5) Å Ni−C21, 2.020(5) Å Ni−N22, 2.1147(14) Å Ni− S23, and 2.023(5) Å Ni−N24 bond lengths. The 203 structures in the Cambridge Structural Database (version 5.38, May 2017 update) containing an R2S−NiL3 fragment indicate that the typical nickel(II)-to-sulfur bonding distance is 2.19(5) Å, so while the Ni−S distance in 15b is short, it appears to be within the normal range. Similar to 14c, the macrocyclic steric constraints coupled with the size of the chalcogen atom force the sulfur atom out of the Ni−C21−N22−N24 plane, resulting in a 168.89(15)° C21−Ni−S bond angle. The thiophene ring cants substantially, 21.4°, relative to the rest of the macrocycle’s framework atoms, leaving the remainder of the core to be virtually planar. The pyrrole to mean macrocycle plane tilts are 1.99° and 3.04°, while the indene is tilted by 1.46°. When 13a was reacted with nickel(II) acetate in refluxing DMF open to atmospheric oxygen for 3 h, the anomalous product 16a was obtained as the only isolatable product (Scheme 3). Longer reaction times gave variable results and sometimes resulted in decomposition. HR-MS showed that nickel was not present in this structure, and the molecular formula was determined to be C37H24N2O2. The UV−vis spectrum of 16a gave rise to three moderately strong bands at 359, 399, and 465 nm and a broad absorption centered on 696 nm (Figure 10). The 1H NMR spectrum of 16a (Figure 11) indicated that the system had greatly reduced aromatic character, showing the meso-protons as a 2H singlet at 8.08 ppm. A broad resonance at 9.93 ppm consistent with the presence of two NH protons was observed, while the pyrrole units gave two 2H doublet of doublets at 6.93 and 7.61 ppm and the furan protons appeared as a 2H singlet at 7.46 ppm. The coupling observed for the pyrrolic units showed that transannular coupling to the NH protons was occurring in addition to coupling between the inequivalent 7,18- and 8,17H’s. These results indicate that the unique oxycarbaporphyrin 16a had been generated. The 13C NMR spectrum showed a downfield resonance at 188.2 ppm that was consistent with a ketone-type carbonyl unit. These data also showed that the structure has a plane of symmetry and the meso-carbons could be identified at 117.8 ppm. Oxyoxacarbaporphyrin 16a is the keto tautomer of 21-hydroxyoxacarbaporphyrin. The structure possesses a 20π electron conjugation pathway around the

Figure 8. UV−vis spectra of nickel(II) 23-oxa-21-carbaporphyrin 15a (red line) and nickel(II) 23-thia-21-carbaporphyrin 15b (purple line) in chloroform.

also did not show any significant resemblance to the spectra obtained for palladium(II) complexes 14a−14c. Nickel(II) oxacarbaporphyrin 15a gave a Soret band at 400 nm and weaker broad absorptions between 450 and 650 nm, while the thia complex 15b gave a broader weakened Soret-like band at 418 nm and broad absorptions between 500 and 800 nm. The differences are at least consistent with the trends noted for 14a−14c and suggest that 15b has reduced planarity compared to 15a. The 1H NMR spectrum of 15a indicates that this structure has reduced diatropicity compared to the corresponding palladium complex 14a. The meso-proton showed up as a 2H singlet at 9.88 ppm, while the furan protons gave a 2H singlet at 8.84 ppm and the pyrrole moieties gave two 2H doublets at 8.57 and 8.99 ppm. These values are shifted between 0.01 and 0.22 ppm upfield compared to the corresponding palladium complex. In addition, the 21,31-H’s on the benzo unit were shifted upfield by 0.06 ppm, indicating that the proximal diamagnetic ring current was reduced. Nickel(II) cations are slightly too small to fit into a porphyrin-type cavity, and this commonly results in the macrocycle becoming slightly distorted. Nevertheless, the system can still be considered to be strongly aromatic. The 1 H NMR spectrum of nickel thiacarbaporphyrin 15b gave rise to small downfield shifts compared to 15a, indicating improved diatropicity. The meso-proton resonance appeared at 10.03 ppm, the thiophene protons at 9.20 ppm, and the pyrrole protons at 8.75 and 9.02 ppm. The larger sulfur atom may be beneficial in this case by reducing the size of the macrocyclic cavity. However, other factors may be involved such as the reduced electronegativity of sulfur compared to oxygen that may be beneficial in macrocyclic π-electron delocalization. Given the UV−vis data, the results are not really consistent with increased planarity for 14b. The 13C NMR spectra for 15a and 15b further confirmed the presence of a plane of symmetry in these structures. The unsubstituted meso-carbons were identified at 111.7 and 115.6 ppm for 15a and 15b, respectively. The downfield shift noted for 15b is consistent with the results 11430

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Scheme 4. Oxidation of Benzocarbaporphyrins with Ferric Chloride

Figure 10. UV−vis spectra of 21-oxy-23-oxa-21-carbaporphyrin 16a (red line) and 21-oxy-23-thia-21-carbaporphyrin 16b (blue line) in chloroform.

was performed in a mixture of dichloromethane and water for 1 h, an oxidative chlorination took place to give 21chlorocarbaporphyrin 18. However, when the reaction time was extended to 16 h, a second nonaromatic derivative 19 was generated in 22% yield (Scheme 4).40 Here, oxidation has occurred at both the internal carbon and a meso bridge to afford a diketo product. Although these reactions may be related, the formation of oxycarbaporphyrin 16a is unique. It is worth noting that the 10 and 15 positions are protected by phenyl substituents in the present case, and this may prevent oxidation at this position to give structures like 19. The formation of an oxidation product was also noted in reactions of thiacarbaporphyrin 13b with nickel(II) acetate in refluxing DMF when exposed to air (Scheme 3). However, this transformation was associated with a significant amount of degradation. When the reaction was carried out for 16 h, oxycarbaporphyrin 16b could be isolated in up to 10% yield. The UV−vis spectrum for 16b was similar to 16a (Figure 10), although two of the stronger bands had coalesced to give a strong absorption at 414 nm, followed by a slightly smaller one at 467 nm. In common with 16a, the UV−vis spectrum of 16b also gave a broad band at 687 nm. The 1H NMR spectrum showed that 16b had diatropic character comparable to that of 16a. The meso-protons appeared at 8.04 ppm, while the pyrrolic protons produced two 2H doublet of doublets at 7.20 and 7.58 ppm (the latter is obscured by overlap with some of the phenyl protons) and the thiophene protons were observed at 7.69 ppm. The internal NH protons appeared as a broad 2H singlet at 9.32 ppm. The 13C NMR spectrum gave a peak at 184.4 ppm for the carbonyl moiety and the unsubstituted meso-carbons afford a resonance at 117.1 ppm. Both the 1H and 13C NMR spectra confirmed that the structure has a plane of symmetry. The identity of 16b was further confirmed by HR-MS (ESI).

Figure 11. 500 MHz 1H NMR spectrum of 21-oxy-23-oxacarbaporphyrin 16a in CDCl3.

periphery of the macrocycle but does not appear to be antiaromatic. In fact, the NMR data suggest that 16a is weakly diatropic and the external protons are shifted significantly downfield from the equivalent resonances for nonaromatic porphyrinoids such as benziporphyrins7 and heterobenziporphyrins.38 This can be explained if dipolar resonance structures such as 16a′ or delocalized structures such as 16a″ contribute to the overall properties of the macrocycle because these possess 18π electron delocalization pathways (Scheme 3). The IR spectrum showed no strong absorptions above 1600 cm−1, and the carbonyl stretch was tentatively assigned to a peak at 1546 cm−1. This result is consistent with a structure that has dipolar resonance structures of the type described above. Intramolecular hydrogen bonding may further decrease the observed frequency. Although the results show that molecular oxygen is involved, the mechanism for this reaction is not known. When nickel complex 15a was refluxed in DMF under nitrogen, no reaction took place, but when the experiment was conducted in the presence of air, the complex was gradually converted to 16a. Molecular oxygen is also involved in the transition-metalmediated conversion of azuliporphyrins into oxyazuliporphyrins such as 9.24−26 meso-Unsubstituted benzocarbaporphyrins 6a have previously been shown to react with a large excess of ferric chloride in the presence of alcohol solvents to give aromatic carbaporphyrin ketals 21,39,40 where oxidation has occurred at the same internal carbon atom (Scheme 4). When the reaction

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CONCLUSIONS Diphenyloxa-, -thia-, and -selenacarbaporphyrins reacted with palladium(II) acetate in acetonitrile to give stable palladium(II) complexes. These derivatives were characterized by spectroscopic methods, and the structures of the oxa and selena complexes were confirmed by X-ray crystallography. The results suggest that the macrocycles become increasing distorted as the size of the heteroatom increases. The palladium(II) selenacarbaporphyrin is particularly notable because this is the first 11431

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

Article

Inorganic Chemistry

119.9 (21,31-CH), 127.2 (22,32-CH), 128.2 (m-Ph), 128.7 (p-Ph), 129.9, 131.0 (8,17-CH), 131.9 (7,18-CH), 133.9 (12,13-CH), 134.6 (o-Ph), 134.7, 139.5, 142.0, 143.5, 145.1, 145.5, 148.7. HR-MS (ESI). Calcd for C37H22N2SPd + H: m/z 633.0617. Found: m/z 633.0624. (10,15-Diphenyl-23-Selena-21-carbabenzo[b]porphyrinato)palladium(II) (14c). Selenacarbaporphyrin 13c (20.0 mg, 0.0347 mmol) in 50/50 acetonitrile−chloroform (30 mL) was reacted with palladium(II) acetate (16 mg) for 10 min under the same conditions. Recrystallization from chloroform−methanol gave the metalated selenacarbaporphyrin (17.1 mg, 0.0251 mmol, 72%) as a dark solid. Mp: >300 °C. UV−vis [CHCl3; λmax, nm (log ε, M−1 cm−1)]: 409 (4.37), 457 (4.41), 524 (4.58), 552 (4.45), 671 (sh, 3.77), 728 (3.92). 1 H NMR (500 MHz, CDCl3): δ 7.08 (2H, br d, J = 7.5 Hz, o-Ph), 7.48−7.51 (2H, m, 22,32-H), 7.51−7.56 (2H, m, m-H), 7.69 (2H, tt, J = 1.2 and 7.5 Hz, p-H), 7.93 (2H, br t, J = 7.5 Hz, m-Ph), 8.38−8.42 (2H, m, 21,31-H), 8.57 (2H, d, J = 4.5 Hz, 8,17-H), 8.91 (2H, s, 12,13H), 8.96 (2H, d, J = 4.5 Hz, 7,18-H), 8.98 (2H, br d, J = 7.5 Hz, o-Ph), 9.99 (2H, s, 5,20-H). 13C NMR (125 MHz, CDCl3): δ 119.4 (5,20CH), 119.7 (21,31-CH), 127.0 (22,32-CH), 128.3 (m-Ph), 128.7 (pPh), 130.9 (8,17-CH), 132.67 (7,18-CH), 132.75 (o-Ph), 134.2, 135.7, 136.1 (o-Ph), 140.8 (12,13-CH), 142.1, 142.5, 143.6, 144.8. 150.2, 152.8. HR-MS (ESI). Calcd for C37H22N2SePd + H: m/z 681.0061. Found: m/z 681.0071. (10,15-Diphenyl-23-oxa-21-carbabenzo[b]porphyrinato)nickel(II) (15a). A solution of oxacarbaporphyrin 13a (24.0 mg, 0.0468 mmol) in DMF (25 mL) was refluxed with nickel(II) acetate tetrahydrate (20 mg) under nitrogen for 1 h. The solution was cooled, diluted with chloroform, washed with water, and evaporated under reduced pressure. The residue was purified by column chromatography on grade 2 alumina, eluting with 70% dichloromethane− hexanes, and the product was collected as a greenish fraction. Recrystallization from chloroform−methanol gave the nickel complex (23.7 mg, 0.0416 mmol, 89%) as a dark solid. Mp: 258−260 °C. UV− vis [CHCl3; λmax, nm (log ε, M−1 cm−1)]: 305 (4.44), 400 (4.92), 477 (4.26), 607 (3.76), 641 (3.77). 1H NMR (500 MHz, CDCl3): δ 7.45− 7.49 (2H, m, 22,32-H), 7.72−7.79 (6H, m, m,p-H), 8.05 (4H, d, J = 7.1 Hz, o-H), 8.43−8.46 (2H, m, 21,31-H), 8.57 (2H, d, J = 4.6 Hz, 8,17H), 8.84 (2H, s, 12,13-H), 8.99 (2H, d, J = 4.6 Hz, 7,18-H), 9.88 (2H, s, 5,20-H). 13C NMR (125 MHz, CDCl3): δ 111.7 (5,20-CH), 111.9, 119.0 (21,31-CH), 122.4 (12,13-CH), 126.5 (22,32-CH), 127.9 (m-Ph), 128.7 (p-Ph), 131.6 (8,17-CH), 131.9 (7,18-CH), 133.6 (o-Ph), 140.8, 144.0, 144.8, 145.8, 148.0. HR-MS (ESI). Calcd for C37H22N2ONi + H: m/z 568.1086. Found: m/z 568.1088. (10,15-Diphenyl-23-thia-21-carbabenzo[b]porphyrinato)nickel(II) (15b). Thiacarbaporphyrin 13b (33.5 mg, 0.0634 mmol) in DMF (30 mL) was reacted with nickel(II) acetate (30 mg) under the foregoing conditions. Recrystallization from chloroform−methanol gave 15b (31.4 mg, 0.0536 mmol, 85%) as a dark solid. Mp: >300 °C (dec). UV−vis [CHCl3; λmax, nm (log ε, M−1 cm−1)]: 418 (4.45), 438 (sh, 4.41), 512 (4.03), 652 (3.49). 1H NMR (500 MHz, CDCl3): δ 7.50−7.53 (2H, m, 22,32-H), 7.75−7.80 (6H, m, m,p-H), 8.07−8.10 (4H, m, o-H), 8.44−8.47 (2H, m, 21,31-H), 8.75 (2H, d, J = 4.6 Hz, 8,17-H), 9.02 (2H, d, J = 4.6 Hz, 7,18-H), 9.20 (2H, s, 12,13-H), 10.03 (2H, s, 5,20-H). 13C NMR (125 MHz, CDCl3): δ 115.6 (5,20-CH), 119.5 (21,31-CH), 127.1 (22,32-CH), 127.8, 128.3 (m-Ph), 128.7 (pPh), 131.9 (8,17-CH), 132.4 (12,13-CH), 132.5 (7,18-CH), 132.9, 133.8 (o-Ph), 138.2, 141.3, 145.0, 146.0, 149.4. HR-MS (ESI). Calcd for C37H22N2SNi + H: m/z 585.0935. Found: m/z 585.0933. 10 ,15 -D iphenyl-21-oxo-2 1,2 4-dihy dr o-2 3-oxa -2 1carbabenzo[b]porphyrin (16a). A solution of oxacarbaporphyrin 13a (24.0 mg, 0.0468 mmol) in DMF (25 mL) was refluxed with nickel(II) acetate tetrahydrate (20 mg) open to the air for 3 h. The solution was cooled, diluted with chloroform, washed with water, and evaporated under reduced pressure. The residue was purified by column chromatography on grade 2 alumina, eluting with 70% dichloromethane−hexanes, and the product was collected as a redbrown fraction. Recrystallization from chloroform−methanol gave the oxycarbaporphyrin (20.6 mg, 0.0390 mmol, 83%) as a dark solid. Mp: 209−210 °C. UV−vis [CH2Cl2; λmax, nm (log ε, M−1 cm−1)]: 322 (4.44), 359 (4.61), 399 (4.51), 466 (4.52), 492 (sh, 4.37), 633 (sh,

example of a metalated derivative with selenium-containing carbaporphyrinoids. Under anaerobic conditions, nickel(II) acetate reacted with the oxa- and thiacarbaporphyrins to give organometallic nickel(II) complexes. The aromatic character for the nickel(II) complex was slightly reduced, possibly because of the macrocycle becoming distorted to accommodate the small nickel(II) cation. Nickel(II) thiacarbaporphyrin was also characterized by X-ray crystallography. When the nickel(II) acetate reactions were carried out in the presence of air, a selective oxidation occurred at the internal carbon to give structurally unique oxycarbaporphyrins. High yields were obtained from the oxacarbaporphyrins, but substantial decomposition took place in the case of the thiophene-containing porphyrinoid. The selenacarbaporphyrin failed to metalate when the reaction was performed under nitrogen and decomposed under aerobic conditions. These results demonstrate that heterocarbaporphyrins have hitherto unexpected reactivity and that these systems are worthy of further investigations.

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EXPERIMENTAL SECTION

Heterocarbaporphyrins 13a−13c were prepared by a previously reported procedure.36 Melting points are uncorrected. NMR spectra were recorded using a 400 or 500 MHz NMR spectrometer and run at 300 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 and 13C CDCl3 triplet δ 77.23), and coupling constants were taken directly from the spectra. NMR assignments were made with the aid of 1H−1H COSY, HSQC, DEPT135 and NOE difference 1H NMR spectroscopy. 2D experiments were performed by using standard software. HR-MS were carried out by using a double-focusing magnetic sector instrument. 1H and 13C NMR spectra for all new compounds are reported in the Supporting Information. (10,15-Diphenyl-23-oxa-21-carbabenzo[b]porphyrinato)palladium(II) (14a). A solution of oxacarbaporphyrin 13a (20.0 mg, 0.0390 mmol) in 50/50 chloroform−acetonitrile (25 mL) was refluxed with palladium(II) acetate (14 mg) for 1 h. The solvent was evaporated under reduced pressure and the residue purified by column chromatography on grade 2 alumina, eluting with dichloromethane. The product eluted as a green fraction. Recrystallization from chloroform−methanol gave the palladium complex (19.6 mg, 0.0317 mmol, 81%) as dark crystals. Mp: >300 °C. UV−vis [CHCl3; λmax, nm (log ε, M−1 cm−1)]: 378 (4.77), 391 (sh, 4.68), 408 (sh, 4.64), 448 (4.53), 473 (4.77), 497 (4.46), 582 (4.08), 609 (4.11). 1H NMR (500 MHz, CDCl3): δ 7.50−7.53 (2H, m, 22,32-H), 7.75−7.83 (6H, m, m,pH), 8.12−8.14 (4H, m, o-H), 8.49−8.52 (2H, m, 21,31-H), 8.58 (2H, d, J = 4.6 Hz, 8,17-H), 8.92 (2H, s, 12,13-H), 9.04 (2H, d, J = 4.6 Hz, 7,18-H), 10.10 (2H, s, 5,20-H). 13C NMR (125 MHz, CDCl3): δ 112.8, 113.9 (5,20-CH), 119.5 (21,31-CH), 123.1 (12,13-CH), 126.9 (22,32-CH), 127.8 (m-Ph), 128.8 (p-Ph), 130.6 (8,17-CH), 130.8 (7,18-CH), 133.9 (o-Ph), 134.4, 141.3, 142.7, 143.0, 144.8, 146.9. HRMS (ESI). Calcd for C37H22N2OPd + H: m/z 617.0845. Found: m/z 617.0859. (10,15-Diphenyl-23-thia-21-carbabenzo[b]porphyrinato)palladium(II) (14b). Thiacarbaporphyrin 13b (20.0 mg, 0.0378 mmol) in 50/50 chloroform−acetonitrile (25 mL) was reacted with palladium(II) acetate (15 mg) for 30 min under the foregoing conditions. Recrystallization from chloroform−methanol gave 14b (23.4 mg, 0.0369 mmol, 98%) as a dark solid. Mp: 291−293 °C. UV− vis [CHCl3; λmax, nm (log ε, M−1 cm−1)]: 401 (sh, 4.44), 437 (4.57), 504 (4.68), 529 (sh, 4.48), 646 (3.93). 1H NMR (500 MHz, CDCl3): δ 7.51−7.54 (2H, m, 22,32-H), 7.75−7.81 (6H, m, m,p-H), 8.12−8.15 (4H, m, o-H), 8.44−8.47 (2H, m, 21,31-H), 8.72 (2H, d, J = 4.6 Hz, 8,17-H), 8.92 (2H, s, 12,13-H), 9.03 (2H, d, J = 4.6 Hz, 7,18-H), 10.06 (2H, s, 5,20-H). 13C NMR (125 MHz, CDCl3): δ 117.2 (5,20-CH), 11432

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

Inorganic Chemistry

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3.65), 697 (4.07). IR: νCO 1546 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.83−6.86 (2H, m, 22,32-H), 6.93 (2H, dd, J = 2.2 and 4.1 Hz), 7.20−7.23 (2H, m, 21,31-H), 7.46 (2H, s, 12,13-H), 7.56−7.59 (6H, m, m,p-H), 7.61 (2H, dd, J = 1.7 and 4.1 Hz, 7,18-H), 7.72−7.76 (4H, m, o-H), 8.08 (2H, s, 5,20-H), 8.93 (2H, br s, 2NH). 13C NMR (125 MHz, CDCl3): δ 110.2, 117.8 (5,20-CH), 118.7 (21,31-CH), 121.1 (8,17-CH), 123.4 (7,18-CH), 127.8 (12,13-CH), 128.2 (m-CH), 128.3 (p-CH), 128.4 (22,32-CH), 131.0, 133.1 (o-Ph), 134.2, 134.7, 140.1, 141.4, 155.6, 188.2 (CO). HR-MS (ESI). Calcd for C37H24N2O2: m/z 528.1838. Found: m/z 528.1835. 10,15-Diphenyl-21-oxo-21,24-dihydro-23-thia-21carbabenzo[b]porphyrin (16b). Thiacarbaporphyrin 13b (30.0 mg, 0.0567 mmol) in DMF (30 mL) was reacted with nickel(II) acetate (30 mg) for 16 h under the previous conditions. Recrystallization from chloroform−methanol gave 16b (3.2 mg, 0.0059 mmol, 10%) as a dark solid. Mp: 225−226 °C. UV−vis [CH2Cl2; λmax, nm (log ε, M−1 cm−1)]: 382 (sh, 4.56), 414 (4.65), 467 (4.52), 627 (sh, 3.72), 687 (4.10). IR: νCO 1541 cm−1. 1H NMR (500 MHz, CDCl3): δ 6.87− 6.91 (2H, m, 22,32-H), 7.20 (2H, dd, J = 2.2 and 4.1 Hz), 7.26−7.29 (2H, m, 21,31-H), 7.53−7.57 (2H, m, p-H), 7.58−7.62 (6H, m, m-Ph and 7,18-H), 7.69 (2H, s, 12,13-H), 7.83−7.85 (4H, m, o-H), 8.04 (2H, s, 5,20-H), 9.32 (2H, br s, 2NH). 13C NMR (125 MHz, CDCl3): δ 117.1 (5,20-CH), 119.0 (21,31-CH), 121.6 (8,17-CH), 122.6 (7,18CH), 123.8, 128.4 (m-CH), 128.5 (p-CH), 128.7 (22,32-CH), 131.4, 133.3 (o-Ph), 134.6 (12,13-CH), 135.4, 137.2, 140.0, 142.2, 142.3, 184.4 (CO). HR-MS (ESI). Calcd for C37H24N2S: m/z 544.1609. Found: m/z 544.1609.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01946. Experimental crystallographic details, summary of framework bond distances and angles, structures, and selected UV−vis, MS, 1H, 1H−1H COSY, HSQC, DEPT-135, and 13C NMR spectra (PDF) Accession Codes

CCDC 1564634−1564638 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

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

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Science Foundation under Grant CHE-1465049 and the Petroleum Research Fund, administered by the American Chemical Society. The X-ray diffractometer was funded by NSF Grant CHE-1039689. The authors also thank Purdue University and Dr. M. Zeller for collection and reduction of the X-ray data for compound 14a, supported, in part, by NSF Grant CHE-1625543. 11433

DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434

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DOI: 10.1021/acs.inorgchem.7b01946 Inorg. Chem. 2017, 56, 11426−11434