Rhodium Complexes of Carbaporphyrins, Carbachlorins, adj

1 day ago - Synopsis. The reactions of [Rh(CO)2Cl]2 with a series of carbaporphyrin, carbachlorin, and dicarbaporphyrinoid structures have been ...
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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Rhodium Complexes of Carbaporphyrins, Carbachlorins, adjDicarbaporphyrins, and an adj-Dicarbachlorin Timothy D. Lash,* William T. Darrow, Alissa N. Latham, Navneet Sahota, and Gregory M. Ferrence Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States

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ABSTRACT: The macrocyclic cavities in carbaporphyrins are well suited for the formation of metalated derivatives. A carbaporphyrin diester and a naphthocarbaporphyrin reacted with [Rh(CO)2Cl]2 to give good-to-excellent yields of rhodium(I) complexes, and these were fully characterized by X-ray crystallography. Both rhodium(I) derivatives were converted into rhodium(III) complexes in refluxing pyridine, albeit in moderate yields. Carbachlorins also formed rhodium(I) complexes, but these could not be further transformed into rhodium(III) products. The rhodium(III) complexes incorporate two axial pyridine ligands, which exhibit strongly shielded resonances in their 1H NMR spectra, and the rhodium(III) carbaporphyrin diester was further characterized by X-ray crystallography. adj-Dicarbaporphyrins also formed rhodium(I) complexes, but these reactions involved the relocation of a proton to generate an internal methylene unit. The environments associated with the two faces of the resulting macrocycles are very different from one another, and this results in the 1H NMR chemical shifts for the two internal methylene protons being separated by well over 3 ppm. Although the diatropicities of rhodium(I) complexes for monocarbaporphyrins and carbachlorins are comparable to those of the parent ligands, the chemical shifts for rhodium(I) dicarbaporphyrins are consistent with a significant reduction in the porphyrinoid aromaticity. A dicarbachlorin also gave a rhodium(I) complex, but this species fully retained the diatropic characteristics of the parent ligand. Nevertheless, the internal CH2 unit still gave two widely separated doublets indicative of radically differing environments for the two faces of the macrocycle. Rhodium(I) dicarbaporphyrin and dicarbachlorin complexes were further characterized by X-ray crystallography.

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complexes have been reported, including in catalysis19 and C−H bond activation.20 However, the rhodium complexes of true carbaporphyrins have received far less attention. Recently, a 23-methylcarbaporphyrin was shown to react with [Rh(CO)2Cl]2 to give the methylene-bridged rhodium(III) complex 9 (Figure 2),21 and related meso-tetraaryl complexes were obtained by the ring contraction of metalated benziporphyrins.22 In addition, the rhodium(III) derivatives 10 of azuliporphyrins have also been reported.23 In this paper, the syntheses of rhodium complexes for a series of closely related carbaporphyrin-type structures are reported. Specifically, metalation of a naphthocarbaporphyrin, a carbaporphyrin diester, carbachlorins, adj-dicarbaporphyrins, and a dicarbachlorin has been investigated. The results demonstrate that mono- and dicarbaporphyrins, as well as related dihydrocarbaporphyrins, are versatile ligands that readily generate rhodium derivatives.

INTRODUCTION Carbaporphyrinoid systems have been widely studied over the last 25 years.1,2 These porphyrin analogues differ from regular porphyrins in that one or more of the internal nitrogen atoms have been replaced by carbon atoms. N-Confused porphyrins 13,4 have received the most attention and have been shown to form diverse metalated derivatives,5,6 but investigations into the coordination chemistry of other classes of carbaporphyrinlike systems7 such as azuliporphyrins 28 and benziporphyrins 39,10 have also received a considerable amount of attention (Figure 1). True carbaporphyrins such as 411 and 512,13 did not initially garner the same level of interest, but these macrocycles have also been shown to facilitate the formation of transitionmetal complexes. The reaction of 5 with silver(I) acetate affords the related silver(III) complexes 6,14,15 and similar gold(III) derivatives have also been reported.15 Benzocarbaporphyrin 5a also reacted with [Rh(CO)2Cl]2 to give excellent yields of the rhodium(I) complex 7 (Scheme 1).16 When 7 was refluxed in pyridine, rhodium(III) complex 8a was formed. In addition, when 5a was heated with [Ir(COD)2Cl]2 and pyridine in p-xylene, the related iridium(III) complex 8b was generated in moderate yield.16 Similar rhodium(I) and rhodium(III) complexes of N-confused porphyrins have also been reported.17 Rhodium complexes of porphyrins have been known for over 50 years,18 and numerous applications for these © XXXX American Chemical Society

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RESULTS AND DISCUSSION Rhodium(I) and Rhodium(III) Complexes of Carbaporphyrins and Carbachlorins. Recently, synthetic routes to modified carbaporphyrin structures 1124 and 1225 have been developed. Carbaporphyrin dimethyl ester 11 was reacted with Received: March 12, 2019

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DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Scheme 2. Synthesis of Rhodium(I) and Rhodium(III) Carbaporphyrins

Figure 1. Selected examples of carbaporphyrinoid systems.

Scheme 1. Synthesis of Rhodium and Iridium Complexes of a Benzocarbaporphyrin

spectrum for 13 showed two strong peaks at 2066 and 2011 cm−1 corresponding to the cis-carbonyl ligands, together with an additional absorption at 1698 cm−1 due to the ester carbonyl groups (Figure 3). The 1H NMR spectrum in CDCl3 indicated that 13 had fully retained the aromatic characteristics of the carbaporphyrin macrocycle. The internal CH and NH gave rise to upfield resonances at −4.94 and −1.09 ppm, respectively, while the external meso-protons appeared as four strongly deshielded 1H singlets at 9.40, 9.44, 10.02, and 10.37 ppm (Figure 4). Although the carbaporphyrin precursor 11 has two planes of symmetry, one that bisects the macrocycle and the other describing the plane of the system, these are lost in the rhodium(I) complex. Hence, there are only two peaks for the meso-protons in the 1H NMR spectrum of 11, but four meso-proton resonances are present in 13. The methyl groups in 13, which are equivalent in 11, afford two 3H singlets at 3.35 and 3.45 ppm due to the lack of symmetry. The significantly deshielded values for these resonances also indicate that the substituents lie close to a powerful macrocyclic ring current. The methylene units of the ethyl

Figure 2. Examples of rhodium(III) carbaporphyrinoid complexes.

[Rh(CO)2Cl]2 in refluxing dichloromethane to give the related rhodium(I) complex 13 in 70−99% yield (Scheme 2). The IR B

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. Partial IR spectra for rhodium(I) complexes: (A) the rhodium(I) carbaporphyrin 13 showing the characteristic CO stretching modes for the carbonyl ligands and ester moieties; (B) 15 showing one of the carbonyl absorptions as a Fermi doublet.

Figure 5. UV−vis spectra of the rhodium(I) complex 13 (red line) and the rhodium(III) carbaporphyrin derivative 14 (blue line) in dichloromethane.

geometry, with the rhodium(I) atom displaced by 1.5623(6) Å from the 24-atom mean macrocyclic plane of the porphyrinoid framework. The previously reported carbaporphyrin complex 716 has its rhodium(I) atom similarly displaced by 1.5958(2) Å from the porphyrinoid framework. Furthermore, the Rh−N and Rh−CCO distances in 13 are indistinguishable from those of 7. In fact, the 60.32(4)° dihedral angle that the Rh−N23− N24−C25−C26 plane makes with the mean macrocyclic plane is similar to the corresponding 61.78(2)° dihedral angle observed for 7. The 0.188 Å root-mean-square (rms) distance that the framework atoms lie from their mean plane indicates that the macrocycle has a reasonably planar motif. However, the 13.8(1)°, 9.3(1)°, 13.0(1)°, and 12.0(1)° dihedral angles between the framework plane and the respective cyclopentadiene and three pyrrolic mean planes indicate that there is some distortion from planarity that is presumably needed to accommodate the two internal hydrogen atoms. The hydrogen atoms attached to the internal carbon atom and uncoordinated pyrrolic nitrogen atom were clearly identifiable in the difference Fourier map of the X-ray structure, making the oxidation assignment clear. Although some variations in the bond lengths are evident, the metrics of the framework bond distances are consistent with a delocalized π-bonding model with the π system for the dimethyl maleate unit decoupled from the [18]annulene core. The bonds directly connected to the meso-carbon atoms, C4−C5, C5−C6, C9− C10, C10−C11, C14−C15, C15−C16, C19−C20, and C20− C1, varied from 1.384(3) to 1.410(3) Å, in reasonable agreement with the expected aromatic bond lengths. When 13 was heated with pyridine for 30 min, the rhodium(III) complex 14 was generated in 28% yield. Two pyridine units were incorporated as axial ligands. The aromatic character of 14 was again evident from the 1H NMR spectrum. The rhodium(III) complex was somewhat insoluble in chloroform, but reasonable quality NMR spectra could be obtained in benzene-d6. The α protons of the pyridine units were shielded by the macrocyclic ring current to give a 4H doublet at 2.33 ppm, and while the β and γ protons were less affected, these were still significantly shifted upfield to 4.10 and 4.70 ppm, respectively. The carbaporphyrin ring regained its symmetry in 14, and for this reason, there are only two 2H singlets for the meso-protons, both of which were strongly deshielded, appearing at 9.46 and 10.59 ppm. The UV−vis

Figure 4. 500 MHz 1H NMR spectrum of rhodium(I) carbaporphyrin dimethyl ester 13 in CDCl3.

substituents are diastereotopic and produce several multiplets between 3.63 and 3.96 ppm. The 13C NMR spectrum for 13 further confirmed the asymmetry of the complex and gave four resonances for the meso-carbon atoms at 92.4, 102.8, 107.5, and 116.7 ppm, while the internal CH (C-21) appeared at 108.9 ppm. Two downfield doublets due to the carbonyl ligands were observed at 177.0 and 178.7 ppm (1JRh−C = 69.9 and 67.7 Hz, respectively), with the coupling resulting from the presence of the NMR-active nucleus rhodium-103 (I = 1/2). The UV−vis spectrum of 13 gave two relatively weak Soretlike bands at 357 and 490 nm, together with small Q bands at 569 and 611 nm (Figure 5). It should be noted that 13 and all of the other rhodium(I) complexes reported in this paper are racemic compounds because of the absence of any symmetry elements. The structural identity of 13 was further demonstrated by single-crystal X-ray diffraction (XRD; Figure 6). The XRD results confirmed the presence of a dicarbonylrhodium(I) moiety that is coordinated to two adjacent pyrrolic nitrogen atoms in a typical square-planar L2Rh(CO)2 coordination C

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms are rendered arbitrarily small for clarity) of the rhodium(I) carbaporphyrin 13.

Figure 7. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms are rendered arbitrarily small or omitted for clarity) of the rhodium(III) complex 14.

spectrum of 14 gave several Soret-like bands at 356, 393, and 463 nm and Q bands at 531 and 573 nm (Figure 5). Highresolution electrospray ionization mass spectrometry (ESI MS) confirmed the molecular formulas for 13 and 14. The X-ray structure for 14 (Figure 7) demonstrated that the rhodium(III) atom is six-coordinate with the pyrrolic nitrogen atoms and internal cyclopentadienyl carbon atoms occupying the equatorial planes of the nearly idealized octahedral coordination environment. As was the case for 13, the structure displayed framework metrics consistent with a delocalized π-bonding model, with the π system for the dimethyl maleate unit disconnected from the [18]annulene core. The bonds directly connected to the meso-carbon atoms varied from 1.382(3) to 1.404(3) Å, as would be expected for the components of a delocalized aromatic system. The

rhodium(III) atom is displaced by only 0.0810(5) Å from the 24-atom mean macrocyclic plane of the porphyrinoid framework, and the 0.077 Å rms distance that the framework atoms lie from their mean plane indicates that the macrocycle is essentially planar, and this is further supported by the 5.0(1)°, 3.5(1)°, 5.8(1)°, and 2.7(1)° dihedral angles between the framework plane and the respective cyclopentadiene and three pyrrolic mean planes. A search of the Cambridge Structural Database (version 5.40, November 2018 update) returned seven similar bis(pyridine)rhodium(III) porphyrinoids, including the closely related structure 8a16 and a similar bis(pyridine)(N-confused porphyrinato)rhodium(III) complex.17a In 14, the 2.0641(18) and 2.0720(18) Å distances between the rhodium atom and axial pyridine ligands are very similar to the values reported for 8a and the N-confused D

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the case for 14, the rhodium(III) complex was insufficiently soluble in chloroform to obtain NMR spectra in this solvent, but good results were obtained using benzene-d6 (Figure 9).

porphyrin complex. The 2.0454(18) and 2.0485(18) Å Rh− Ncis distances between the rhodium atom and equatorial pyridine ligands cis to the Rh−C linkage are also very similar to the 2.0392(19) and 2.0499(19) Å distances observed in 8a. In addition, the Rh−C bond [1.986(2) Å] and the Rh−Ntrans distance trans to the Rh−C linkage [2.1046(19) Å] are indistinguishable from those observed for 8a. As is typical for related metalated carbaporphyrins, the Rh−Ntrans distance is significantly longer than the Rh−Ncis distances because of the stronger σ-donating character of carbon compared to the nitrogen atoms. Naphtho[2,3-b]carbaporphyrin (12) similarly reacted with [Rh(CO)2Cl]2 to give the related rhodium(I) complex 15 in 72% yield. Interestingly, the IR spectrum for rhodium(I) naphthocarbaporphyrin (15) gave three peaks near 2000 cm−1 for the carbonyl ligand stretching rather than the two that might have been expected (Figure 3). In this case, the lowerfrequency peak appears to be a Fermi doublet that results from interactions with an aromatic overtone. The 1H NMR spectrum for 15 showed that the macrocycle had lost its plane of symmetry and also demonstrated the presence of a strong diamagnetic ring current. The inner CH and NH resonances appeared at −5.19 and −2.48 ppm, while the external meso-protons gave four 1H singlets between 9.78 and 10.34 ppm. These results suggest that the ring current in 15 is slightly larger than that observed for 13, although the shifts are similar to those seen for the rhodium(I) benzocarbaporphyrin complex 7.16 In the 13C NMR spectrum, the meso-carbon resonances were identified at 93.8, 97.5, 103.1, and 105.0 ppm, while the internal CH gave a peak at 123.0 ppm. The carbonyl resonances appeared as two doublets (1JRh−C = 69.0 and 67.1 Hz, respectively) at 177.6 and 178.4 ppm. The UV−vis spectrum for 15 was far more porphyrin-like than had been the case for the previous series, showing a strong Soret band at 481 nm and several Q bands between 566 and 680 nm (Figure 8).

Figure 9. 500 MHz 1H NMR spectrum of the rhodium(III) naphthocarbaporphyrin 16 in benzene-d6 at 60 °C.

The 1H NMR spectrum for 16 indicated that the ring current for the naphthocarbaporphyrin complex was stronger than that seen for its rhodium(III) congener 14. The pyridine resonances were observed at 1.44 ppm (α-H), 3.92 ppm (βH), and 4.58 ppm (γ-H), while the meso-protons appeared downfield at 10.07 and 10.56 ppm. The presence of a plane of symmetry was evident from both the 1H and 13C NMR spectra. In the 13C NMR spectrum, the meso-carbon atoms were identified at 94.7 and 102.8 ppm. High-resolution ESI MS confirmed the molecular formula for 16. The UV−vis spectrum of the complex retained a strong Soret band at 447 nm and gave several Q bands between 530 and 606 nm (Figure 8). A very broad absorption centered on 851 nm was also noted. The UV−vis spectrum for the benzocarbaporphyrin complex 8a was very similar to that obtained for 16, again indicating that the naphthalene unit only weakly interacts with the carbaporphyrin π system. Although suitable crystals could not be obtained to structurally characterize the rhodium(III) complex 16, the Xray structure of 15 was determined (Figure 10). This verified the presence of a dicarbonylrhodium(I) moiety that is coordinated to two adjacent pyrrolic nitrogen atoms in a fashion analogous to that of 7 and 13. Square-planar L2Rh(CO)2 coordination geometry is observed, with the rhodium(I) atom displaced by 1.5544(4) Å from the 24-atom mean macrocyclic plane of the porphyrinoid framework. The Rh−N and Rh−CCO distances in 15 are indistinguishable from those of 7 and 13, and, as expected, the 59.70(5)° dihedral angle that the Rh−N23−N24−C25−C26 plane makes with mean macrocyclic plane is also similar. Although the 0.210 Å rms distance that the framework atoms lie from their mean

Figure 8. UV−vis spectra of the rhodium(I) complex 15 (red line) and the rhodium(III) naphthocarbaporphyrin derivative 16 (blue line) in dichloromethane.

The wavelengths observed for 15 were very similar to those previously reported for 7,16 indicating that the naphthalene unit has little effect on the carbaporphyrin chromophore in 15. High-resolution ESI MS confirmed the identity of 15. When a solution of 15 in pyridine was refluxed for 1 h, the rhodium(III) complex 16 was formed in 21% yield. As was E

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 10. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms are rendered arbitrarily small for clarity) of 15.

Scheme 3. Rhodium(I) Complexes of Carbachlorins

complicated. The reaction of 17 with [Rh(CO)2Cl]2 could potentially afford two different regioisomers, 19a and 19b, both of which would be racemic (Scheme 3). The 1H and 13C NMR spectra for the product derived from 17 were consistent with isolation of a single product, although trace amounts of an isomer were observed during chromatography. Unfortunately, the spectroscopic data could not be used to identify which isomer had been generated, and attempts to obtain crystals suitable for X-ray crystallographic analysis were unsuccessful. The product, hereafter designated as 19, was strongly aromatic, and the 1H NMR spectrum showed the presence of four downfield singlets for the meso-protons between 9.24 and 9.86 ppm. As would be expected, the internal CH appeared as an upfield singlet at −5.88 ppm, while the NH gave a resonance at −3.37 ppm. Because the rhodium must lie on one side of the macrocycle, the carbachlorin methylene unit is diastereotopic and gives rise to two strongly coupled 1H doublets at 5.48 and 5.59 ppm (2JHH = 16.4 Hz). The 13C NMR spectrum showed the meso-carbon resonances at 94.2, 97.9, 103.5, and 106.8 ppm, and the internal CH appeared at 127.8 ppm. As expected, the carbonyl ligands gave rise to two doublets at 178.2 and 178.6 ppm. The IR spectrum also confirmed the presence of the CO units, affording two sharp absorptions at 2066 and 2010 cm−1. The carbachlorin complex gave a porphyrin-like UV−vis spectrum (Figure 11), producing a Soret band at 451 nm, a secondary absorption at 361 nm, and Q bands at 537,

plane indicates that the macrocycle is reasonably planar, the 14.03(3)°, 12.85(7)°, 12.34(7)°, and 13.45(7)° dihedral angles between the framework plane and the respective benz[f ]indene and three pyrrolic mean planes indicate that there is some distortion to accommodate the two internal hydrogen atoms. The hydrogen atoms attached to the internal carbon atom and uncoordinated pyrrolic nitrogen atom were clearly identifiable in the difference Fourier map of the X-ray structure, and like 7 and 13, the metrics of the framework bond distances are consistent with a delocalized π-bonding model, with the π system for the naphthalene-unit decoupled from the [18]annulene core. The bonds connected to the naphthalene unit, C1−C2 and C3−C4, were relatively long [1.475(2) and 1.476(2) Å, respectively], while the bonds directly connected to the meso-carbon atoms fell into a typical aromatic bondlength range of 1.389(2)−1.409(2) Å. The syntheses of the carbachlorins 17 and 18 were recently reported,24 and the formation of rhodium derivatives for these structures was also investigated (Scheme 3). Both carbachlorins reacted with [Rh(CO)2Cl]2 to give rhodium(I) complexes, but attempts to convert these into rhodium(III) derivatives related to 14 and 16 were unsuccessful. The high-resolution ESI MS spectra for these products were consistent with those expected for the rhodium(I) complexes. However, while 11 and 12 can only give one racemic product in each case, the outcomes for reactions with 17 and 18 are potentially more F

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 4. Synthesis and Metalation of adjDicarbaporphyrins

Figure 11. UV−vis spectrum of the rhodium(I) carbachlorin 19 in dichloromethane.

599, and 651 nm. The carbachlorin isomer 18 reacted similarly to afford a rhodium(I) derivative in 75% yield. In this case, two diastereomeric products, 20a and 20b, might be formed (Scheme 3). The 1H NMR spectrum for the isolated product indicated that one isomer predominated and no more than a trace amount of the diastereomer was present. Spectroscopic studies gave no information on the identity of the observed stereoisomer, and crystals suitable for XRD analysis could not be obtained. In every other respect, the rhodium complex 20 closely resembled 19, and for this reason, the results will not be further discussed. Rhodium Complexes of Dicarbaporphyrins and a Related Dicarbachlorin. Dicarbaporphyrins have also been synthesized, but few metalation reactions have been carried out on these systems. Diindenylmethane (21) was shown to react with the dipyrrylmethane dialdehyde 22a in the presence of potassium hydroxide to give the adj-dicarbaporphyrin 23 (Scheme 4).26 This aromatic system was fully characterized and shown to undergo sequential mono- and diprotonation.26 adj-Dibenzodicarbaporphyrins could exist in a number of fully conjugated tautomeric forms (Figure 12), although density functional theory studies showed that the observed tautomer 24a was the most stable.26 Nevertheless, tautomers 24b and 24c were calculated as only 1.52 and 2.06 kcal mol−1, respectively, less stable than tautomer 24a. The fourth form, 24d, with two internal methylene units was calculated to be 28.28 kcal mol−1 higher in energy.26 Hence, tautomers 24b and 24c are likely to be thermodynamically accessible, whereas 24d would not be. The dicarbaporphyrin 23a reacted with palladium(II) acetate to give the remarkable palladium complex 25a (Scheme 4).26 This structure consists of a palladium(IV) ion that is sandwiched between two palladium(II) dicarbaporphyrin dianions.26 Unfortunately, attempts to form similar nickel or platinum complexes have been unsuccessful. However, we can now report the successful synthesis of rhodium(I) complexes for this system. In order to fully assess this system, two related dicarbaporphyrins 23b and 23c were synthesized. Dialdehydes 22a and 22c were prepared using previously described methods,27 but a slightly different approach was used to prepare 22b (Scheme 5). α-Unsubstituted pyrrole ester 2628 was reacted with dimethoxymethane in the presence of ptoluenesulfonic acid to give the dipyrrylmethane diester 27, and this was saponified and decarboxylated with sodium

Figure 12. Aromatic tautomers of adj-dibenzodicarbaporophyrin.

Scheme 5. Synthesis of the Dipyrrylmethane Dialdehyde 22b

G

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry hydroxide in ethylene glycol at 200 °C to afford 28. The Vilsmeier−Haack reaction with benzoyl chloride/N,N-dimethylformamide (DMF) gave an imine salt 29, and subsequent base-catalyzed hydrolysis afforded the required dialdehyde 22b. Dipyrrylmethane dialdehydes 22b and 22c were refluxed with 21 and potassium hydroxide in ethanol for 4 days to give 12−13% yields of the new dicarbaporphyrins 23b and 23c. As would be expected, the UV−vis spectra for 23b and 23c were very similar to the results obtained for 23a. The dicarbaporphyrin 23b gave a Soret band at 454 nm and a series of Q bands between 540 and 656 nm (Figure 13). In 1%

Figure 14. 500 MHz 1H NMR spectrum of the rhodium(I) dicarbaporphyrin 30a in benzene-d6.

attributed to the internal CH2 unit in structure 30a (Scheme 4). The protons are not equivalent because the rhodium ion must lie on one side of the macrocycle, and geminal coupling leads to the observed doublets. Nevertheless, the large difference in the chemical shifts (Δδ 3.42 ppm) attests to the two faces of the macrocycle producing very distinct chemical environments. The inner sp2 CH gave an upfield singlet at 1.09 ppm in CDCl3 and 1.40 ppm in C6D6. The rhodium complex effectively corresponds to the less favorable dicarbaporphyrin tautomers 24b and 24c, but this naturally results from the necessity to relocate one of the hydrogen atoms so that the rhodium(I) complex can be formed. The 1H NMR spectrum for 30a indicates that the global aromatic character is somewhat reduced. The meso-protons appeared between 8.66 and 9.27 ppm in CDCl3 or between 8.71 and 9.20 ppm in benzene-d6. Interestingly, in CDCl3, the mesoproton 20-H showed up as a triplet (4JHH = 1.6 Hz) because of allylic coupling, an interaction that indicates the presence of a significant degree of olefinic character (Figure S84). It is also noteworthy that the methyl substituents gave rise to singlets close to 2.9 ppm in CDCl3 and near 2.7 ppm in C6D6. In strongly aromatic porphyrinoids, the methyl resonances are commonly shifted downfield to 3.6 ppm,29 and even in the parent dicarbaporphyrins, these units appear at 3.0−3.3 ppm.26 Therefore, the observed methyl group resonances also indicate that the macrocyclic diatropicity has been diminished. The reduced macrocyclic ring current appears to be due, at least in part, to the 18π-electron conjugation pathway running through one of the benzo units.26 NICS(0) calculations gave a value of −11.84 ppm for tautomer 24a, but 24b or 24c afforded values of ca. −8 ppm,26 reduced negative values that are in line with the observed decrease in the diatropicity for the rhodium(I) derivative. The 13C NMR spectrum in CDCl3 confirmed the absence of a plane of symmetry and showed the meso-carbon resonances at 108.1, 111.2, 113.6, and 117.7 ppm. The internal CH2 was identified at 44.8 ppm, while the 22-CH gave a peak

Figure 13. UV−vis spectra of the dicarbaporphyrin 23b: (red line) free base in dichloromethane; (green line) monoprotonated cation in 1% TFA/dichloromethane; (purple line) diprotonated dication in 1% hydrochloric acid/TFA.

trifluoroacetic acid (TFA)/dichloromethane, the corresponding monocation only gave broad bands with no clear Sorettype absorptions, but in TFA containing a small amount of hydrochloric acid, a diprotonated species was formed that produced a strong Soret band at 478 nm and a distinctive absorption at 780 nm (Figure 13). Tetramethyldicarbaporphyrin (23b) has very poor solubility in organic solvents, and it was not possible to run a 13C NMR spectrum for this compound. However, a 1H NMR spectrum for 23b could be obtained in CDCl3 at 50 °C. The aromatic properties of the macrocycle were evident because of the presence of three strongly deshielded singlets for the meso-protons at 8.91 ppm (1H), 9.38 ppm (2H), and 9.94 ppm (1H). In addition, the inner CH and NH resonances appeared at high upfield values of −5.44 and −5.01 ppm, respectively. The related dibutyldicarbaporphyrin 23c gave similar results, although its superior solubility characteristics allowed a 13C NMR spectrum to be obtained. The reaction of 23a with [Rh(CO)2Cl]2 in refluxing dichloromethane gave the rhodium(I) complex 30a in 57% yield (Scheme 4). The 1H NMR spectrum of this product in CDCl3 showed the presence of a 1H doublet (J = 22.9 Hz) at −1.65 ppm, but initially no complementary multiplet or doublet could be identified in the spectrum. However, the 1 H−1H COSY NMR spectrum showed that a second doublet was present at 1.5 ppm that was obscured by the CH3 resonances of the ethyl substituents. When the 1H NMR spectrum was rerun in benzene-d6 (Figure 14), two doublets could be observed at −1.67 and +1.75 ppm, and these were H

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Inorganic Chemistry at 127.3 ppm. Two overlapping doublets for the carbonyl units were observed near 182 ppm. The UV−vis spectrum for 30a gave two relatively weak Soret bands at 337 and 410 nm and a prominent absorption at 676 nm (Figure 15). The

coordination geometry, with the rhodium(I) atom displaced by 1.621(2) Å from the 24-atom mean macrocyclic plane of the porphyrinoid framework. The hydrogen atom attached to the internal sp2-hybridized carbon atom was clearly identifiable in the difference Fourier map of the X-ray structure; however, the hydrogen atoms attached to the internal sp3-hybridized methylene could only be inferred from the distended 1.486(10) Å C6−C22 and 1.484(9) Å C9−C22 bond distances and NMR data and were placed according to the standard riding model. The metrics of the framework bond distances are generally consistent with a delocalized π-bonding model, but there is a larger degree of bond-length variation within the macrocycle than had been noted for 13−15. The bond lengths on either side of the meso-carbon atoms fell within the range of 1.363(10)−1.433(9) Å, a difference of 0.07 Å. The bonds directly connected to three of the meso-carbon atoms showed differences of >0.05 Å, demonstrating significant bond-length alternation. The C1−C2 and C3−C4 bonds that are connected to one of the fused benzo units are relatively long [1.479(9) and 1.487(8) Å, respectively], as would be expected if this unit is disconnected from the macrocyclic π system. However, the bonds connected to the second benzo unit, C6−C7 and C8−C9, are also relatively long, giving values of 1.461(9) and 1.434(10) Å, even though these are incorporated into the [18]annulene core. These results are reasonable given the significantly reduced aromatic properties observed for this system. As would be expected, the 2.085(6) and 2.101(5) Å Rh−N distances and 1.857(7) and 1.858(8) Å Rh−CCO distances in 30a are nearly indistinguishable from those for the monocarbaporphyrin congeners 7, 13, and 15. Nevertheless, 30a differs from these structures in that it possesses an internal methylene unit. The single-bond character of C6−C22 and C9−C22 is confirmed by the relatively long bond lengths of 1.486(10) and 1.484(9) Å, respectively, while the more delocalized nature of C1−C21 and C4−C21 is evidenced by the respective 1.444(8) and 1.385(9) Å bond lengths. The 61.9(1)° dihedral angle that the Rh−N23−N24−C25−C26 plane makes with the mean macrocyclic plane is slightly more tilted compared to those of 7, 13, and 15, and while the 0.220 Å rms distance that the framework atoms lie from their mean plane indicates a

Figure 15. UV−vis spectra of rhodium(I) dicarbaporphyrinoids: (red line) the rhodium(I) dibenzodicarbaporphyrin 30a; (blue line) the rhodium(I) dicarbachlorin 32.

dicarbaporphyrin 23b also reacted with [Rh(CO)2Cl]2 to give the rhodium(I) complex 30b in 49% yield, and this afforded similar spectroscopic results. It is noteworthy that while 30a gave two absorptions in the IR spectrum at 2064 and 1998 cm−1, the IR spectrum for 30b gave four peaks in this region. This was attributed to both peaks being split into Fermi doublets due to overlap with aromatic overtones. The structures were also confirmed by high-resolution ESI MS. Attempts to react the dibutyldicarbaporphyrin 23c with [Rh(CO)2Cl]2 gave poor results, and this chemistry was not further pursued. An X-ray crystal structure of 30a (Figure 16) confirmed its identity as an adj-dicarbaporphyrin that has been metalated by a dicarbonylrhodium(I) moiety that coordinates to the two pyrrolic nitrogen atoms in a typical square-planar L2Rh(CO)2

Figure 16. Color POV-Ray rendered ORTEP III drawing (50% probability level, hydrogen atoms rendered arbitrarily small for clarity) of rhodium(I) dicarbaporphyrin 30a. I

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry generally planar motif, the distortions from planarity evidenced by the slightly larger 16.4(2)°, 8.8(2)°, 15.4(3)°, and 14.1(3)° dihedral angles between the framework plane and the respective indene, hydroindene, and two pyrrolic mean planes are presumably necessary to accommodate the three internal hydrogen atoms. The palladium complex 25a26 is a highly unusual structure, but its spectroscopic characterization was somewhat hampered because of poor solubility in organic solvents. Because the dibutyldicarbaporphyrin 23c was available, we took the opportunity to further investigate this type of complex with the expectation that the butyl substituents would increase the solubility for this system. The reaction of 23c with palladium(II) acetate in refluxing acetonitrile gave 25c in 75% yield (Scheme 4). The complex showed the anticipated improvement in the solubility, and this allowed higher-quality NMR spectra to be obtained. The porphyrinoid rings in 25c are essentially nonaromatic, and the meso-protons were observed as three singlets at 7.24 ppm (2H), 7.67 ppm (2H), and 7.98 ppm (4H). The methyl groups gave rise to a 12H singlet at 2.56 ppm, again indicating that there was no significant global aromatic ring current. In the 13C NMR spectrum, the mesocarbon atoms appeared at 87.3, 106.4, and 113.2 ppm. The UV−vis spectrum did not resemble a porphyrin-like system, showing only medium-intensity bands at 384 and 434 nm. High-resolution ESI MS confirmed that the molecular formula was C80H72N4Pd3. In an earlier paper, the synthesis of the dicarbachlorin 31 with a coordination core similar to that of the dicarbaporphyrin 23 was reported.30 However, in this case, the free base structure already favored a tautomer with an internal CH2 rather than the more conventional sp2 CH. The dicarbachlorin 31 was reacted with [Rh(CO)2Cl]2 in refluxing dichloromethane, and following purification by column chromatography and recrystallization from chloroform/hexanes, the rhodium(I) complex 32 was isolated in 67% yield (Scheme 6). In the 1H NMR spectrum (Figure 17), the internal CH2

Figure 17. 500 MHz 1H NMR spectrum of the rhodium(I) dicarbachlorin 32 in CDCl3.

13

C NMR spectrum showed the meso-carbon resonances at 106.4, 110.4, 110.5, and 115.2 ppm, the inner CH2 appeared at 38.9 ppm, and the internal methine proton was located at 136.0 ppm. Two doublets were noted for the carbonyl ligands at 180.1 and 180.7 ppm. The IR spectrum also showed the presence of carbonyl ligands, giving two strong peaks at 2062 and 2003 cm−1, and the molecular formula for 32 was confirmed by high-resolution ESI MS. The UV−vis spectrum for 32 was somewhat porphyrin-like, particularly in comparison with 30a and 30b, showing two medium-sized Soret bands at 390 and 453 nm and a series of Q bands between 546 and 683 nm (Figure 15). A single-crystal XRD structure of 32 (Figure 18) was obtained, and this confirmed that the pyrrolic nitrogen atoms of adj-dicarbachlorin coordinate with the dicarbonylrhodium(I) moiety in a typical square-planar L2Rh(CO)2 geometry, with the rhodium(I) atom displaced by 1.706(1) Å from the 24-atom mean macrocyclic plane of the porphyrinoid framework. Unfortunately, the X-ray structure contained substantial, 50:50, disorder between the cyclopentadiene and cyclopentene rings such that it was necessary to utilize the corresponding C−C bond distances from the previously reported structure of 31 to obtain a stable and high-quality model.30 As such, further analysis of the metrics of the framework bond distances has limited value. Nevertheless, the extent of bond-length alternation appears to be reduced compared to 30a, as would be expected for this strongly aromatic system. The atoms of the dipyrrolic moiety and rhodium coordination environment are well ordered. The Rh−N and Rh−CCO distances in 32 are nearly indistinguishable from those in 7, 13, 15, and 30a. As is the case for 30a, complex 32 possesses an internal aromatic CH and a methylene unit. The 66.37(6)° dihedral angle that the Rh−N23−N24−C25−C26 plane makes with the mean macrocyclic plane is the largest tilt so far observed in the series, and while the 0.222 Å rms distance that the framework atoms lie from their mean plane indicates a generally planar motif, the distortions from planarity evidenced by the slightly larger 9.0(1)°, 10.0(1)°, 16.39(4)°, and 17.71(5)° dihedral angles between the framework plane and the respective cyclopentene, cyclopentadiene, and two pyrrolic mean planes quantify this as the least-planar macrocyclic framework in the series.

Scheme 6. Synthesis of a Rhodium(I) Dicarbachlorin

again gave rise to two widely separated geminally coupled doublets (2JHH = 20.9 Hz) because of the markedly different environments for the two faces of the macrocyclic ring. Unlike 30a, complex 32 showed the presence of a very strong diatropic ring current and the two doublets for the 21-CH2 appeared at −5.88 and −3.13 ppm, while the internal methine proton gave an upfield singlet at −3.14 ppm. The meso-protons were similarly deshielded, giving four 1H doublets at 8.86, 9.26, 9.34, and 9.85 ppm, and the external cyclopentadiene protons gave two 1H doublets at 9.31 and 9.50 ppm. Furthermore, the methyl substituents gave rise to two 3H singlets at 3.12 and 3.25 ppm, values that attest to an increased ring-current effect. The diastereotopic CH2CH2 unit in the reduced chlorin ring was also strongly deshielded and afforded a series of complex multiplets between 3.92 and 4.74 ppm. The J

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 18. Color POV-Ray-rendered ORTEP III drawing (50% probability level; hydrogen atoms are rendered arbitrarily small for clarity) of the rhodium(I) dicarbachlorin 32.

Table 1. Crystallographic Data of the Compoundsa CCDC chemical formula M temperature (K) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalc (g cm−3) Rint (sin θ/λ)max (Å−1) F000 μMo Kα (mm−1) measd reflns indep reflns obsd reflns [I > 2σ(I)] R[F2 > 2σ(F2)] wR(F2) goodness of fit no. of reflns no. of param no. of restraints

13·0.5 C5H12

14·CHCl3

15

30a

32

1892084 C39.5H44N3O6Rh 723.61 100(2) monoclinic P21/c 13.4948(19) 15.793(2) 16.844(2) 90 97.519(9) 90 3558.9(9) 4 1.351 0.1147 0.69 1496 0.527 137707 11341 8036 0.0390 0.0916 1.006 11341 458 2

1892085 C46H47Cl3N5O4Rh 943.14 100(2) triclinic P1̅ 10.8459(16) 11.9279(19) 18.027(3) 82.680(10) 74.386(9) 71.549(9) 2128.4(6) 2 1.472 0.0857 0.71 972 0.640 80485 12430 9313 0.0400 0.0875 1.024 12430 551 8

1892083 C41H38N3O2Rh 707.65 100(2) monoclinic P21/c 13.3372(17) 16.006(2) 15.842(2) 90 102.560(7) 90 3301.0(7) 4 1.424 0.0468 0.65 1464 0.558 131217 11808 9649 0.0292 0.0748 1.042 11808 433 2

1554586 C38H31N2O2Rh 650.56 100(2) triclinic P1̅ 10.4870(7) 11.3543(7) 12.5115(9) 78.459(5) 83.215(5) 85.314(5) 1446.85(17) 2 1.493 0.0956 0.80 668 0.629 19927 5746 3836 0.0721 0.1878 1.044 5746 380 0

1892082 C30H29N2O2Rh 552.46 100(2) triclinic P1̅ 10.5354(3) 11.2770(3) 12.3972(3) 69.6120(10) 66.1420(10) 68.896(2) 1220.69(6) 2 1.503 0.0563 0.068 568 0.730 42618 7593 6755 0.0268 0.0714 1.064 7593 332 20

Details in the crystallographic information file submitted to the Cambridge Crystallographic Data Centre.

a

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CONCLUSIONS

the macrocycle itself, and the structures are therefore chiral in nature. All of the rhodium(I) complexes described in this paper were isolated in racemic form, but otherwise these reactions are stereo- and regioselective. The rhodium(I) complexes mostly retain the aromaticity of the porphyrinoid precursors, although these properties are somewhat diminished in rhodium(I) complexes of adj-dicarbaporphyrins. In refluxing

Mono- and dicarbaporphyrins have been shown to readily form rhodium(I) complexes, and this chemistry has been extended to reactions with related carbachlorins. The metalated derivatives lose any elements of symmetry found in the carbaporphyrinoid precursors, including the plane describing K

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

silica gel column, eluting with 20:80 dichloromethane/hexanes, and a green band was collected. The solvent was evaporated and the residue recrystallized from chloroform/hexanes to yield the naphthocarbaporphyrin complex (18.5 mg, 0.0261 mmol, 72%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2065, 2017, 1993. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 378 (4.69), 481 (5.03), 566 (4.11), 603 (4.06), 624 (sh, 3.94), 680 (2.73). 1H NMR (500 MHz, CDCl3): δ −5.19 (1H, s, 21-H), −2.48 (1H, s, NH), 1.68 (3H, t, J = 7.7 Hz), 1.78−1.85 (9H, three overlapping triplets; 4CH2CH3), 3.54 (3H, s), 3.65 (3H, s, 7,18-CH3), 3.78−3.92 (2H, m), 3.94−4.02 (2H, m), 4.04−4.12 (4H, m, 4CH2CH3), 7.58−7.63 (2H, m, 23,33-H), 8.23−8.28 (2H, m, 22,32-H), 9.10 (1H, s), 9.15 (1H, s, 21,31-H), 9.78 (1H, s), 9.83 (1H, s, 10,15-H), 10.09 (1H, s), 10.34 (1H, s, 5,20-H). 13 C NMR (125 MHz, CDCl3): δ 11.6, 12.3, 17.4, 17.5, 18.2, 18.3, 19.9, 19.96, 19.98, 20.6, 93.8, 97.5, 103.1, 105.0, 119.0, 119.2, 123.0 (21-CH), 125.6, 125.7, 128.9, 129.1, 132.0, 132.61, 132.63, 133.8, 133.9, 135.0. 136.3, 139.0, 139.2, 139.7, 140.1, 142.3, 143.4, 146.3, 147.5, 153.69, 153.71, 155.2, 177.6 (d, 1JRh−C = 69.0 Hz, CO), 178.4 (d, 1JRh−C = 67.1 Hz, CO). HRMS (ESI). Calcd for C41H39N3O2Rh ([M + H]+): m/z 708.2097. Found: m/z 708.2089. [8,12,13,17-Tetraethyl-2,3-dihydro-2,3-dimethoxycarbonyl7,18-dimethyl-21-carbaporphyrinato](dicarbonyl)rhodium(I) (20). The carbachlorin 1824 (24.7 mg, 0.0435 mmol) was reacted with [Rh(CO)2Cl]2 (17.0 mg, 0.044 mmol) and sodium acetate (35.8 mg) in dichloromethane (50 mL) under the previously described conditions. The crude product was run through a silica column, eluting with 20:80 dichloromethane/hexanes, and a green band was collected. Recrystallization from chloroform/hexanes gave the carbachlorin complex (23.6 mg, 0.0325 mmol, 75%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2061, 1995, 1734 (ester). UV− vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 362 (4.51), 451 (4.86), 538 (3.64), 553 (sh, 3.57), 599 (3.69), 651 (3.96). 1H NMR (500 MHz, CDCl3): δ −5.19 (1H, s, 21-H), −2.48 (1H, s, NH), 1.68 (3H, t, J = 7.7 Hz), 1.78−1.85 (9H, three overlapping triplets, 4CH2CH3), 3.54 (3H, s), 3.65 (3H, s, 7,18-Me), 3.78−3.92 (2H, m), 3.94−4.02 (2H, m), 4.04−4.12 (4H, m, 4CH2CH3), 7.58−7.63 (2H, m, 23,33H), 8.23−8.28 (2H, m, 22,32-H), 9.10 (1H, s), 9.15 (1H, s; 21,31-H), 9.78 (1H, s), 9.83 (1H, s, 10,15-H), 10.09 (1H, s), 10.34 (1H, s, 5,20H). 13C NMR (125 MHz, CDCl3): δ 11.6, 12.3, 17.4, 17.5, 18.2, 18.3, 19.9, 19.96, 19.98, 20.6, 93.8, 97.5, 103.1, 105.0, 119.0, 119.2, 123.0 (21-CH), 125.6, 125.7, 128.9, 129.1, 132.0, 132.61, 132.63, 133.8, 133.9, 135.0, 136.3, 139.0, 139.2, 139.7, 140.1, 142.3, 143.4, 146.3, 147.5, 153.69, 153.71, 155.2, 177.6 (d, 1JRh−C = 69.0 Hz, CO), 178.4 (d, 1JRh−C = 67.1 Hz, CO). HRMS (ESI). Calcd for C37H41N3O6Rh ([M + H]+): m/z 726.2050. Found: m/z 726.2083. [8,12,13,17-Tetraethyl-2,3-dihydro-2,2-dimethoxycarbonyl7,18-dimethyl-21-carbaporphyrin](dicarbonyl)rhodium(I) (19). The carbachlorin 1724 (20.0 mg, 0.0352 mmol), [Rh(CO)2Cl]2 (14.0 mg, 0.036 mmol), and sodium acetate (29.5 mg) in dichloromethane (40 mL) were reacted under the previous conditions. Recrystallization from chloroform/hexanes gave the rhodium complex (16.5 mg, 0.0227 mmol, 65%) as a dark solid. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2066, 2010, 1739 (ester). UV− vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 361 (4.61), 451 (4.96), 537 (3.83), 552 (sh, 3.75), 578 (sh, 3.65), 599 (3.82), 651 (4.05). 1H NMR (500 MHz, CDCl3): δ −5.88 (1H, s, 21-CH), −3.37 (1H, s, NH), 1.62 (3H, t, J = 7.7 Hz), 1.74−1.80 (9H, three overlapping triplets, 4CH2CH3), 3.41 (3H, s, 18-Me), 3.50 (3H, s, 7-Me), 3.59 (3H, s), 4.16 (3H, s, 2OMe), 3.73−3.89 (2H, m), 3.91−4.02 (2H, m), 4.03−4.13 (4H, m, 8H, m, 4CH2CH3), 5.48 (1H, d, J = 16.4 Hz), 5.59 (1H, d, J = 16.4 Hz, 3-CH2), 9.24 (1H, s, 5-H), 9.77 (1H, s, 10or 15-H), 9.78 (1H, s, 20-H), 9.86 (1H, s, 10- or 15-H). 13C NMR (125 MHz, CDCl3): δ 11.4 (7-Me), 12.3 (18-Me), 17.5, 18.32, 18.40, 19.9, 20.6, 45.7 (3-CH2), 53.0 (OMe), 53.6 (OMe), 67.1 (2-C), 94.2 (10- or 15-CH), 97.9 (5-CH), 103.5 (10- or 15-CH), 106.8 (20-CH), 127.8, 129.6, 130.1, 133.6, 136.3, 138.4, 138.6, 139.1, 139.2, 140.9, 142.4, 144.0, 146.0, 151.6, 155.9, 171.7, 172.4, 178.2 (d, 1JRhC = 68.2 Hz), 178.6 (d, 1JRhC = 67.2 Hz). HRMS (ESI). Calcd for C37H41N3O6Rh ([M + H]+): m/z 726.2050. Found: m/z 726.2065.

pyridine, the rhodium(I) carbaporphyrin and naphthocarbaporphyrin complexes were converted into aromatic rhodium(III) complexes, albeit in modest yields. The results significantly extend the coordination chemistry of carbaporphyrins and dicarbaporphyrins, and the rhodium complex 32 represents the first example of a metal complex for the dicarbachlorin system. The structural diversity and chiral characteristics of these compounds provide foundations for further investigations in this area.

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EXPERIMENTAL SECTION

Samples of X-ray-quality crystals were suspended in mineral oil at ambient temperature, and a suitable crystal was selected, mounted on a MiTeGen Micromount, and transferred to a Bruker AXS SMART APEX II CCD X-ray diffractometer. The XRD data were collected at 100(2) K using Mo Kα (λ = 0.71073 Å) radiation. Table 1 summarizes the data collection and refinement parameters for the five X-ray structures reported in this manuscript. Additional X-raystructure-specific experimental details are provided in the Supporting Information and affiliated crystallographic information files. Melting points are uncorrected. NMR spectra were recorded using a 400 or 500 MHz NMR spectrometer and 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), dimethyl sulfoxide (DMSO)-d6 (1H residual DMSO-d5 pentet δ 2.49; 13C septet δ 39.7), and benzene-d6 (1H residual benzene-d5 resonance δ 7.15; 13C C6D6 triplet δ 128.0), and coupling constants were taken directly from the spectra. NMR assignments were made with the aid of 1H−1H COSY, HSQC, DEPT-135, and NOE difference 1H NMR spectroscopy. 2D experiments were performed using standard software. High-resolution mass spectrometry (HRMS) was carried out using a double-focusing magnetic sector instrument. 1H and 13C NMR spectra for all new compounds are reported in the Supporting Information. [8,12,13,17-Tetraethyl-2,3-dimethoxycarbonyl-7,18-dimethyl-21-carbaporphyrinato](dicarbonyl)rhodium(I) (13). The carbaporphyrin diester 1124 (60.2 mg, 0.106 mmol) was dissolved in dichloromethane (111 mL) under nitrogen. Anhydrous sodium acetate (84.7 mg) was then added, followed by tetracarbonyldi-μ-chlorodirhodium(I) (40.4 mg, 0.10 mmol), and the mixture refluxed overnight under nitrogen. The solvent was removed under reduced pressure and the residue chromatographed on grade 3 alumina, eluting with chloroform. A dark-green band was collected and recrystallized with chloroform/hexanes to afford the rhodium(I) carbaporphyrin (76.2 mg, 0.105 mmol, 99%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2066, 2011, 1698 (ester). UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 357 (4.66), 490 (4.61), 569 (4.00), 611 (3.74), 723 (3.27). 1H NMR (500 MHz, CDCl3): δ −4.94 (1H, s, 21-H), −1.09 (1H, s, NH), 1.60 (3H, t, J = 7.7 Hz), 1.72−1.76 (9H, m, 4CH2CH3), 3.35 (3H, s, 7-Me), 3.45 (3H, s, 18-Me), 3.63−3.71 (1H, m), 3.72−3.86 (3H, m), 3.87−3.96 (4H, m, 4CH2CH3), 4.21 (3H, s, 3-CO2Me), 4.26 (3H, s, 2-CO2Me), 9.40 (1H, s), 9.44 (1H, s, 10,15-H), 10.02 (1H, s, 20-H), 10.37 (1H, s, 5-H). 13C NMR (125 MHz, CDCl3): δ 11.4 (18-Me), 12.1 (7-Me), 17.1, 17.3, 17.8, 18.0, 19.6, 19.7, 19.8, 20.4, 52.4 (3-CO2CH3), 52.5 (2-CO2CH3), 92.4 (10- or 15-CH), 102.8 (10- or 15-CH), 107.5 (20CH), 108.9 (21-CH), 116.7 (5-CH), 128.3, 128.4, 132.2, 133.6, 135.8, 135.9, 137.9, 138.4, 138.55, 138.63, 141.9, 144.8, 150.5, 150.6, 158.8, 158.1, 167.2 (ester CO), 167.8 (ester CO), 177.0 (d, 1 JRh−C = 69.9 Hz, CO), 178.7 (d, 1JRh−C = 67.7 Hz, CO). HRMS (ESI). Calcd for C37H39N3O6Rh ([M + H]+): m/z 724.1894. Found: m/z 724.1887. [8,12,13,17-Tetraethyl-7,18-dimethyl-21-carbanaphtho[2,3b]porphyrinato](dicarbonyl)rhodium(I) (15). The naphthocarbaporphyrin 1225 (20.1 mg, 0.0365 mmol) was reacted with [Rh(CO)2Cl]2 (15.2 mg, 0.039 mmol) and sodium acetate (29.8 mg) under the foregoing conditions. The product was purified on a L

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry [8,12,13,17-Tetraethyl-2,3-dimethoxycarbonyl-7,18-dimethyl-21-carbaporphyrinato](dipyridine)rhodium(III) (14). The rhodium(I) complex 13 (10.0 mg, 0.0138 mmol) was dissolved in pyridine (10 mL) and refluxed under nitrogen in a preheated oil bath for 30 min. The solvent was removed under reduced pressure and the residue chromatographed on grade 3 alumina, eluting with toluene. A dark band was collected and recrystallized with chloroform/hexanes to yield the rhodium(III) carbaporphyrin 14 (3.2 mg, 0.0039 mmol, 28%) as dark crystals. Mp: >300 °C. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 356 (4.44), 393 (4.43), 427 (sh, 4.50), 450 (sh, 4.59), 463 (4.63), 531 (3.92), 573 (4.14). 1H NMR (500 MHz, C6D6): δ 1.74 (6H, t, J = 7.5 Hz), 1.82 (6H, t, J = 7.5 Hz), 2.33 (4H, d, J = 5.9 Hz, 4 × α-pyridine-H), 3.25 (6H, s, 17,18-Me), 3.73−3.80 (8H, m, 4CH2CH3), 4.02 (6H, s, 2OMe), 4.09−4.12 (4H, m, 4 × β-pyridine-H), 4.70 (2H, dt, J = 1.6 and 7.6 Hz, 2 × γ-pyridine-H), 9.46 (2H, s, 10,15-H), 10.59 (2H, s, 5,20-H). 13 C NMR (125 MHz, C D6): δ 11.3 (7,18-Me), 17.6, 18.3, 19.9, 20.2, 51.4 (2OMe), 94.2 (10,15-CH), 113.1 (5,20-CH), 121.2 (4 × βpyridine-CH), 129.5, 133.6 (2 × γ-pyridine-CH), 136.2, 138.4, 139.1, 139.2, 141.8, 142.2, 142.5, 148.5 (4 × α-pyridine-CH), 167.7 (2C O). HRMS (ESI). Calcd for C45H46N5O4Rh: m/z: 823.2605. Found: m/z 823.2638. [8,12,13,17-Tetraethyl-7,18-dimethyl-21-carbanaphtho[2,3b]porphyrinato](dipyridine)rhodium(III) (16). 15 (18.5 mg, 0.0261 mmol) was dissolved in pyridine (17 mL) and refluxed under nitrogen for 1 h. The solvent was removed under reduced pressure and the residue purified on a grade 3 alumina column, eluting with 50:50 toluene/hexanes. A light-brown band was collected and recrystallized with chloroform/hexanes to yield the rhodium(III) complex (4.5 mg, 0.0056 mmol, 21%) as dark crystals. Mp: >300 °C. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 348 (4.40), 422 (sh, 4.56), 434 (sh, 4.68), 447 (5.04), 458 (sh, 4.68), 530 (3.99), 569 (4.24), 606 (3.47), 851 (3.65). 1H NMR (500 MHz, C6D6, 60 °C): δ 1.44 (4H, d, J = 6.2 Hz, 4 × α-pyridine-H), 1.94 (6H, t, J = 7.6 Hz), 1.99 (6H, t, J = 7.6 Hz, 4CH2CH3), 3.59 (6H, s, 7,18-Me), 3.92 (4H, t, J = 7.1 Hz, 4 × β-pyridine-H), 4.06−4.14 (8H, m, 4CH2CH3), 4.58 (2H, t, J = 7.1 Hz, 2 × γ-pyridine-H), 7.45−7.48 (2H, m, 23,33-H), 8.15−8.18 (2H, m, 22,32-H), 9.18 (2H, s, 21,31-H), 10.07 (2H, s, 10,15-H), 10.56 (2H, s, 5,20-H). 13C NMR (125 MHz, C6D6, 60 °C): δ 11.8, 18.1, 18.6, 20.3, 20.7, 94.7, 102.8, 115.6, 120.6 (4 × βpyridine-CH), 14.9, 129.0, 132.1, 133.1 (2 × γ-pyridine-CH), 133.2, 134.5, 138.2, 139.2, 139.6, 140.3, 140.4, 146.9, 148.1 (4 × α-pyridineCH). HRMS (ESI). Calcd for C49H46N5Rh ([M + H]+): m/z 807.2808. Found: m/z 807.2798. Diethyl 3,3′,4,4′-Tetramethyl-2,2′-dipyrrylmethane-5,5′-dicarboxylate (27). A solution of ethyl 3,4-dimethylpyrrole-2carboxylate28 (1.95 g), dimethoxymethane (0.650 g), and ptoluenesulfonic acid monohydrate (300 mg) in glacial acetic acid (300 mL) was stirred under nitrogen for 1.5 days at 35 °C. The solution was poured into ice/water and then extracted several times with ether. The combined ether layers were washed with water, a 5% aqueous sodium bicarbonate solution, and water again and dried over sodium sulfate, and the solvent was removed under reduced pressure. The residue was recrystallized from ethanol to give dipyrrylmethane (1.28 g, 63%) as a white solid. Mp: 196−197 °C (lit. mp 200−202.5 °C,31a 196−198 °C,31b 196−197 °C31c). 1H NMR (500 MHz, CDCl3): δ 1.31 (6H, t, J = 7.1 Hz, 2CH2CH3), 1.96 (6H, s, 3.3′-Me), 2.25 (6H, s, 4,4′-Me), 3.85 (2H, s, bridge-CH2), 4.26 (4H, q, J = 7.1 Hz, 2OCH2), 9.01 (2H, br, 2NH). 13C NMR (125 MHz, CDCl3): δ 9.0 (3,3′-Me), 10.8 (4,4′-Me), 14.7 (2CH2CH3), 23.4 (bridge-CH2), 60.1 (2OCH2), 117.6, 118.0, 127.7, 129.6, 162.2 (2CO). 3,3′,4,4′-Tetramethyl-2,2′-dipyrrylmethane-5,5′-dicarbaldehyde (22b). A mixture of the dipyrrylmethane 27 (660 mg, 1.91 mmol), sodium hydroxide (1.0 g), and ethylene glycol (10 mL) was stirred under reflux for 1 h. The mixture was cooled, diluted with water, and extracted with hexanes (three times). The combined organic solutions were dried over sodium sulfate and evaporated under reduced pressure to give a pale-brown solid (347 mg, 1.72 mmol, 90%) corresponding to the dipyrrylmethane 28. 1H NMR (500 MHz, CDCl3): δ 2.11 (6H, s, 3.3′-Me), 2.16 (6H, d, J = 1.0 Hz, 4,4′-

Me), 3.83 (2H, s, bridge-CH2), 6.36 (2H, m, 5,5′-H), 7.21 (2H, br, 2NH). 13C NMR (125 MHz, CDCl3): δ 8.9, 10.5, 22.9 (bridge-CH2), 113.5 (5,5′-CH), 114.4, 118.6, 125.2. The crude dipyrrylmethane was taken up in DMF (3.0 mL) and cooled to 0 °C in a salt/ice bath. Benzoyl chloride (1.0 g, 7.1 mmol) was added dropwise while maintaining the temperature at 0 °C. The salt/ice bath was removed and the mixture stirred for 15 min. Toluene (10 mL) was then added, and the resulting mixture was stirred for a further 1 h while cooling the reaction flask in a salt/ice bath. The precipitate, which corresponds to the imine salt 29, was collected by suction filtration and then dissolved with sodium carbonate (1.0 g) in a 1:1 mixture of ethanol and water (16 mL). The solution was heated in a boiling water bath for 15 min, water (20 mL) was added, and the mixture was allowed to stand at room temperature for 1 h. The resulting precipitate was suction-filtered, recrystallized from ethanol, and dried in vacuo overnight to give the dialdehyde (376 mg, 1.46 mmol, 85%) as a pale-saffron-yellow powder. Mp: 280−285 °C dec (lit.32 mp 295−298 °C dec). 1H NMR (500 MHz, DMSO-d6): δ 1.85 (6H, s, 3,3′-Me), 2.16 (4,4′-Me), 3.84 (2H, s, bridge-CH2), 9.48 (2H, s, 2CHO), 11.17 (2H, br s, 2NH). 13C NMR (125 MHz, DMSO-d6, 70 °C): δ 7.9 (3,3′-Me), 8.4 (4,4′-Me), 22.3 (bridge-CH2), 116.8, 127.9, 129.9, 134.2, 176.2 (2CHO). 12,13,17,18-Tetramethyl-21,22-dicarbadibenzo[b,g]porphyrin (23b). Bis(3-indenyl)methane (21;33 302 mg, 1.24 mmol) was added to a 1% potassium hydroxide solution in ethanol (140 mL) and the mixture purged with nitrogen for 5 min. The dipyrrylmethane dialdehyde 22b (323 mg, 1.25 mmol) was added, and the resulting mixture was refluxed in the dark under nitrogen for 4 days. The solution was cooled to room temperature, diluted with dichloromethane, and washed with brine and water. The organic layer was dried over sodium sulfate, filtered, and evaporated under reduced pressure. The residue was purified by column chromatography on grade 3 alumina, eluting with dichloromethane. The product fractions were further purified on a silica gel column, eluting with dichloromethane. Recrystallization from chloroform/hexanes gave the dicarbaporphyrin (73 mg, 0.16 mmol, 13%) as purple crystals. Mp: >300 °C. UV−vis [1% Et3N/CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 320 (4.42), 368 (4.39), 395 (4.41), 454 (4.84), 480 (sh, 4.52), 540 (4.11), 580 (3.94), 656 (3.79). UV−vis [1% TFA/CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 326 (4.46), 405 (4.58), 453 (sh, 4.47), 625 (sh, 4.02), 678 (4.25), 733 (3.91). UV−vis [1% conc HCl/TFA; λmax/nm (log ε/M−1 cm−1)]: 359 (4.58), 410 (4.44), 452 (4.69), 478 (5.02), 680 (sh, 3.76), 712 (3.84), 780 (4.11). UV−vis (10% DBU/CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 384 (4.43), 450 (sh, 4.69), 465 (4.95), 475 (4.90), 500 (4.14), 515 (sh, 4.02), 578 (4.01), 617 (4.06). 1H NMR (500 MHz, CDCl3, 50 °C): δ −5.44 (2H, 21,22-H), −5.01 (2 × NH), 3.26 (6H, s), 3.31 (6H, s, 12,13,17,18-Me), 7.60−7.65 (4H, m, 22,32,72,82-H), 8.48 (2H, d, J = 6.7 Hz), 8.58 (2H, d, J = 6.7 Hz, 21,31,71,81-H), 8.91 (1H, s, 15-H), 9.38 (2H, s, 10,20-H), 9.94 (1H, s, 5-H). 1H NMR (500 MHz, C6D6, 60 °C): δ −5.38 (2H, 21,22-H), −5.15 (2NH), 2.99 (6H, s), 3.02 (6H, s, 12,13,17,18-Me), 7.62−7.66 (4H, m, 22,32,72,82-H), 8.48−8.50 (2H, m), 8.58−8.60 (2H, m, 21,31,71,81-H), 8.71 (1H, s, 15-H), 9.33 (2H, s, 10,20-H), 10.06 (1H, s, 5-H). 1H NMR (500 MHz, TFA/CDCl3, 50 °C): δ −3.73 (2H, 21CH2), −2.23 (1H, s, 22-H), −0.25 (1H, br s, NH), 0.03 (1H, br s, NH), 3.15 (3H, s), 3.24 (6H, s), 3.28 (3H, s, 12,13,17,18-Me), 7.49− 7.52 (1H, m), 7.55−7.58 (1H, m, 72,82-H), 8.15 (1H, d, J = 6.5 Hz), 8.21 (1H, d, J = 6.8 Hz, 71,81-H), 8.34−8.40 (2H, m, 22,32-H), 9.16 (1H, s, 15-H), 9.31 (1H, d, J = 7.1 Hz), 9.41 (1H, d, J = 7.4 Hz, 21,31H), 9.47 (1H, d), 9.65 (1H, s, 10,20-H), 9.81 (1H, s, 5-H). HRMS (ESI). Calcd for C34H28N2: m/z 464.2252. Found: m/z 464.2245. 13,17-Dibutyl-12,18-dimethyl-21,22-dicarbadibenzo[b,g]porphyrin (23c). 2133 (302 mg, 1.24 mmol) and the dialdehyde 22c27 (428 mg, 1.25 mmol) were reacted under the foregoing conditions. Following purification by column chromatography as described above and recrystallization from chloroform/hexanes, the dibutyldicarbaporphyrin (85.0 mg, 0.155 mmol, 12.5%) was isolated as purple crystals. Mp: >300 °C. UV−vis [CH2Cl2; λmax/nm (log ε/ M−1 cm−1)]: 321 (4.52), 368 (4.44), 394 (sh, 4.45), 455 (5.00), 479 (sh, 4.66), 542 (4.20), 580 (4.06), 655 (3.80). UV−vis [1% TFA/ M

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 327 (4.48), 419 (4.65), 451 (sh, 4.55), 625 (sh, 4.10), 661 (sh, 4.34), 676 (4.37), 733 (3.90). UV−vis [1% conc HCl/TFA; λmax/nm (log ε/M−1 cm−1)]: 360 (4.63), 412 (4.53), 453 (4.79), 479 (5.16), 680 (sh, 3.76), 715 (3.93), 782 (4.29). 1H NMR (500 MHz, CDCl3): δ −6.26 (2H, 21,22-H), −5.82 (2NH), 1.11 (6H, t, J = 7.4 Hz, 2CH2CH3), 1.67 (4H, sextet, J = 7.4 Hz, 2CH2CH3), 2.03 (4H, quintet, J = 7.5 Hz, 2CH2CH2CH2), 3.17 (6H, s, 12,18-Me), 3.56 (4H, t, J = 7.6 Hz, 13,17-CH2), 7.41− 7.47 (4H, m, 22,32,72,82-H), 8.17 (2H, d, J = 6.7 Hz, 21,81-H), 8.26 (2H, d, J = 6.8 Hz, 31,71-H), 8.75 (1H, s, 15-H), 9.02 (2H, s, 10,20H), 9.45 (1H, s, 5-H). 13C NMR (125 MHz, CDCl3): δ 11.5 (12,18Me), 14.3 (2CH2CH3), 23.3 (2CH2CH3), 26.0 (2CH2CH2CH2), 34.5 (13,17-CH2), 87.4 (15-CH), 98.6 (10,20-CH), 109.3 (5-CH), 115.9 (21,22-CH), 120.0 (21,81-CH), 120.3 (31,71-CH), 125.7, 125.9, 130.5, 132.1, 133.8, 135.1, 135.8, 135.9, 140.6, 140.8. HRMS (ESI). Calcd for C40H40N2: m/z 548.3191. Found: m/z 548.3184. [13,17-Diethyl-12,118-dimethyl-21,22-dicarbadibenzo[b,g]porphyrinato](dicarbonyl)rhodium(I) (30a). A mixture of the dicarbaporphyrin 23a26 (100.0 mg, 0.203 mmol), tetracarbonyldi-μchlorodirhodium(I) (80 mg, 0.20 mmol), and sodium acetate (110 mg) in dichloromethane (100 mL) was refluxed with stirring under nitrogen for 1 h. The solution was washed with water and the solvent evaporated under reduced pressure. The residue was purified on a silica gel column, eluting with dichloromethane. Recrystallization from chloroform/methanol gave the rhodium(I) complex (75.6 mg, 0.116 mmol, 57%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/ cm−1 2064, 1998. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 337 (4.57), 410 (4.57), 507 (sh, 4.06), 626 (sh, 4.12), 676 (4.47). 1H NMR (500 MHz, CDCl3): δ −1.65 (1H, d, J = 22.9 Hz, 21-H), 1.09 (1H, s, 22-H), 1.46−1.51 (7H, m, 2CH2CH3 and 21-H), 2.909 (3H, s, 12-Me), 2.914 (3H, s, 18-Me), 3.25−3.46 (4H, m, 13,17-CH2), 7.47 (1H, t, J = 7.3 Hz), 7.56 (1H, t, J = 7.4 Hz, 72,82-H), 8.02 (1H, t, J = 7.4 Hz, 22-H), 8.07 (1H, t, J = 7.4 Hz, 32-H), 8.27 (2H, d, J = 7.4 Hz, 71,81-H), 8.66 (1H, s, 15-H), 9.015 (1H, s, 10-H), 9.022 (1H, d, J = 7.7 Hz, 21-H), 9.05 (1H, d, J = 7.7 Hz, 31-H), 9.22 (1H, t, J = 1.6 Hz, 20-H), 9.27 (1H, s, 5-H). 1H NMR (500 MHz, C6D6, 50 °C): δ −1.67 (1H, d, J = 23.1 Hz, 21-H), 1.32−1.39 (6H, two overlapping triplets, 2CH2CH3), 1.40 (1H, 22-H), 1.75 (1H, d, J = 23.1 Hz, 21H), 2.69 (3H, s), 2.71 (3H, s, 12,18-Me), 3.07−3.28 (4H, m, 13,17CH2), 7.41 (1H, t, J = 7.3 Hz), 7.49 (1H, t, J = 7.2 Hz, 72,82-H), 7.69−7.76 (2H, m, 22,32-H), 8.15 (1H, t, J = 7.4 Hz), 8.21 (1H, d, J = 7.3 Hz, 71,81-H), 8.71 (1H, s, 15-H), 8.74 (2H, d, J = 7.6 Hz, 21,31H), 9.10 (1H, s), 9.20 (2H, s, 10,15,20-H). 13C NMR (125 MHz, CDCl3): δ 11.5 (12,18-Me), 17.1 (2CH2CH3), 19.3 (13,17-CH2), 44.8 (21-CH2), 108.1 (20-CH), 111.2 (5-CH), 113.6 (10-CH), 117.7 (15-CH), 119.9, 120.6, 122.3, 122.4, 125.8, 127.3 (22-CH), 127.6, 128.1, 129.1, 131.8, 132.0, 137.5, 138.1, 140.5, 141.4, 141.9, 142.3, 143.0, 143.4, 144.0, 157.2, 161.7, 181.36 (1JRhC = 69.2 Hz), 181.42 (1JRhC = 68.2 Hz). HRMS (ESI). Calcd for C38H32N2O2Rh ([M + H]+): m/z 651.1510. Found: m/z 651.1510. [12,13,17,18-Tetramethyl-21,22-dicarbadibenzo[b,g]porphyrinato](dicarbonyl)rhodium(I) (30b). 23b (20.0 mg, 0.0430 mmol), [Rh(CO)2Cl]2 (16 mg, 0.041 mmol), and sodium acetate (11 mg) in dichloromethane (20 mL) were reacted under the foregoing conditions. Recrystallization from chloroform/methanol gave the rhodium complex (13.2 mg, 0.021 mmol, 49%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2068, 2057, 2002, 1987. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 338 (4.61), 410 (4.60), 508 (sh, 4.07), 625 (sh, 4.15), 677 (4.49). 1H NMR (500 MHz, CDCl3): δ −1.73 (1H, d, J = 22.9 Hz, 21-H), 1.02 (1H, s, 22H), 1.38 (1H, d, J = 22.9 Hz, 21-H), 2.86 (3H, s), 2.888 (3H, s), 2.893 (3H, s), 2.91 (3H, s, 4 × pyrrole-Me), 7.47 (1H, t, J = 7.3 Hz), 7.56 (1H, t, J = 7.4 Hz, 72,82-H), 8.01 (1H, t, J = 7.4 Hz), 8.06 (1H, t, J = 7.4 Hz, 22,32-H), 8.25−8.27 (2H, m, 71,81-H), 8.66 (1H, s, 15-H), 9.00 (1H, s, 10-H), 9.01−9.05 (2H, m, 21,31-H), 9.21 (1H, d, J = 1.6 Hz, 20-H), 9.26 (1H, s, 5-H). 13C NMR (125 MHz, CDCl3): δ 11.06, 11.10, 11.7, 44.8 (21-CH2), 108.1 (20-CH), 111.2 (5-CH), 113.5, 117.9, 120.0, 120.6, 122.32, 122.38, 125.8, 127.3, 127.6, 128.1, 129.1, 132.6, 132.9, 134.9, 136.7, 137.4, 138.1, 140.5, 141.9, 142.3, 142.7, 143.4, 143.95, 144.00, 157.2, 161.8, 181.3 (1JRhC = 69.8 Hz), 181.4

(1JRhC = 67.5 Hz). HRMS (ESI). Calcd for C36H28N2O2Rh ([M + H]+): m/z 623.1206. Found: m/z 623.1199. [ 3 , 1 7 - D i e t h y l - 1 2 , 1 8 - d i m e t h y l - 7 , 8 - d i h y dr o - 2 1 , 2 2 dicarbaporphyrinato](dicarbonyl)rhodium(I) (32). The dicarbachlorin 3130 (20.0 mg, 0.0510 mmol), [Rh(CO)2Cl]2 (19.5 mg, 0.05 mmol), and sodium acetate (41 mg) in dichloromethane (50 mL) were reacted under the same conditions. Recrystallization from chloroform/hexanes gave the rhodium(I) dicarbachlorin complex (18.9 mg, 0.0342 mmol, 67%) as dark crystals. Mp: >300 °C. IR (ZnSe): νCO/cm−1 2062, 2003. UV−vis [CH2Cl2; λmax/nm (log ε/ M−1 cm−1)]: 357 (sh, 4.48), 390 (4.55), 453 (4.66), 546 (3.83), 588 (4.20), 621 (3.81), 683 (3.60). 1H NMR (500 MHz, CDCl3): δ −5.88 (1H, d, J = 20.9 Hz, 21-H), −3.14 (1H, s, 22-H), −3.13 (1H, d, J = 20.9 Hz, 21-H), 1.56 (3H, t, J = 7.7 Hz), 1.60 (3H, t, J = 7.7 Hz, 2CH2CH3), 3.12 (3H, s, 12-Me), 3.25 (3H, s, 18-Me), 3.53−3.81 (4H, m, 2CH2CH3), 3.92−3.98 (1H, m, 8-H), 4.26−4.31 (1H, m, 7H), 4.61−4.74 (2H, m, 7,8-H), 8.86 (1H, s, 10-H), 9.26 (1H, s, 5-H), 9.31 (1H, d, J = 4.1 Hz, 3-H), 9.34 (1H, s, 15-H), 9.50 (1H, d, J = 4.1 Hz, 2-H), 9.85 (1H, s, 20-H). 13C NMR (125 MHz, CDCl3): δ 12.0 (12,18-Me), 17.3 (CH2CH3), 17.5 (CH2CH3), 19.7 (13,17-CH2), 34.2 (8-CH2), 36.5 (7-CH2), 38.9 (21-CH2), 106.4 (10-CH), 110.4 (15-CH), 110.5 (20-CH), 115.2 (5-CH), 131.4, 133.4, 136.0 (22CH), 136.4 (3-CH), 139.2, 139.6, 139.9 (2-CH), 140.5, 141.9, 143.8, 148.1, 150.5, 153.5, 156.1, 159.1, 180.1 (1JRhC = 67.7 Hz), 180.7 (1JRhC = 69.1 Hz). HRMS (ESI). Calcd for C30H30N2O2Rh ([M + H]+) m/z 553.1362. Found: m/z 553.1340. Bis(μ2-η5-13,17-Dibutyl-12,18-dimethyldibenzo[b,g]-21,22dicarbaporphyrinato)dipalladium(II)palladium(IV) (25c). Palladium(II) acetate (16.4 mg, 0.073 mmol) and the dicarbaporphyrin 23c (18.0 mg, 0.0328 mmol) in acetonitrile (20 mL) were refluxed under nitrogen for 40 min. The solution was diluted with chloroform, washed with water, and dried over sodium sulfate. The solvent was removed under reduced pressure and the product purified on a silica column, eluting with dichloromethane. Recrystallization from chloroform/hexanes gave the tripalladium complex (15.0 mg, 0.0106 mmol, 65%) as a dark solid. Mp: >300 °C. UV−vis [CH2Cl2; λmax/nm (log ε/M−1 cm−1)]: 249 (4.82), 283 (4.80), 318 (sh, 4.72), 384 (4.71), 434 (4.70), 570 (sh, 4.18). 1H NMR (500 MHz, CDCl3): δ 1.00 (12H, t, J = 7.4 Hz, 4CH2CH3), 1.52 (8H, sextet, J = 7.4 Hz, 4CH2CH3), 1.76−1.83 (8H, m, 4CH2CH2CH2), 2.56 (12H, s, 4 × pyrrole-CH3), 2.89−3.04 (8H, m, 4 × pyrrole-CH2), 6.79 (4H, t, J = 7.3 Hz, 2 × 32,72-CH), 7.19 (4H, t, J = 7.3 Hz, 2 × 22,82-CH), 7.24 (2H, s, 2 × 15-H), 7.28 (4H, d, J = 7.3 Hz, 2 × 21,81-H), 7.37 (4H, d, J = 7.3 Hz, 2 × 31,71-CH), 7.67 (2H, s, 2 × 5-H), 7.98 (4H, s, 2 × 10,20-H). 13C NMR (125 MHz, CDCl3): δ 10.8 (4 × pyrrole-Me), 14.3 (4CH2CH3), 22.1 (4CH2CH3), 25.6 (4CH2CH2CH2), 35.1 (4 × pyrrole-CH2), 87.3 (2 × 5-CH), 106.4 (2 × 15-CH), 112.4, 113.2 (2 × 10,20-CH), 118.2 (2 × 21,81-CH), 120.0 (2 × 31,71-CH), 126.2 (2 × 32,72-CH), 129.0 (2 × 22,82-CH), 130.0, 131.8, 136.4, 139.7, 140.8, 144.6, 147.1, 148.2. HRMS (ESI). Calcd for C80H73N4Pd3 ([M + H]+): m/z 1407.2939. Found: m/z 1407.2910.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00721. Experimental details for the X-ray crystallography and selected UV−vis, IR, 1H, 1H−1H COSY, HSQC, DEPT135, and 13C NMR, and MS spectra (PDF) Accession Codes

CCDC 1554586 and 1892082−1892085 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. N

DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Timothy D. Lash: 0000-0002-0050-0385 Gregory M. Ferrence: 0000-0001-7549-3856 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

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 authors also thank NSF-CHE (Grant 1039689) for funding the X-ray diffractometer.

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DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.9b00721 Inorg. Chem. XXXX, XXX, XXX−XXX