Organocopper(III) PhenanthriporphyrinâExocyclic Transformations

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Organocopper(III) PhenanthriporphyrinExocyclic Transformations Kamil Kupietz, Michał J. Białek, Agata Białońska, Bartosz Szyszko, and Lechosław Latos-Grażyński* Department of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland

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ABSTRACT: 5,6-Dimethoxyphenanthriporphyrin 1 and 5,6-dioxophenanthriporphyrin 2 act as suitable organometallic ligands for copper(III), adopting trianionic [CCNN] coordination cores. Under oxidizing conditions, in the presence of methanol, copper(III) phenanthriporphyrin 1‑Cu undergoes transformation to copper(III) phenanthriporphodimethene with methoxy substituents attached to two trans meso positions. Addition of acids to 1‑Cu yields two isomeric copper(III) isophenanthriporphyrins protonated on one of the meso carbon atoms. Protonation of copper(III) 5,6-dioxophenanthriporphyrin 2‑Cu yields the aromatic diprotonated complex 2‑Cu‑H22+. In the presence of HBF4 2‑Cu undergoes borylation at the carbonyl oxygen atoms, forming an aromatic exocyclic boron(III) complex.

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INTRODUCTION A reconstruction of regular, contracted, or expanded porphyrin frames realized through the replacement of pyrrolic ring(s) with other carbocycle(s) provides a promising strategy for the exploration of coordination and organometallic chemistry confined in a macrocyclic environment. Molecules comprising structural features of mono- and polycyclic aromatic hydrocarbons and polypyrrolic macrocycles, including aceneporphyrinoids, exemplify this approach.1−5 They are represented by mbenziporphyrin,6,7 p-benziporphyrin,8,9 benzocarbaporphyrin,10 1,4-naphthiporphyrin,11,12 24-thia-1,4-naphthiporphyrin,11 22-hetero-1,5-naphthiporphyrins,13 1,3-naphthiporphyrin,14 1,3-oxynaphthiporphyrin, 12 meso-anthriporphyrin,15 naphtho[2,3-b]carbaporphyrin,16 and pyreniporphyrin.17 These hybrid compounds frequently act as macrocyclic organometallic ligands. They reveal unique electronic and molecular structures, providing a specific macrocyclic environment for coordination leading to atypical intramolecular metal−arene interactions and enforcing nontrivial reactivity such as benzene ring contraction.5,11,18−22 In light of this, the incorporation of phenanthrene into a porphyrinoid frame seems to be a strategy to create the peculiar dicarbaporphyrinoid−phenanthriporphyrin 1 (Scheme 1).23−26 Simple transformations of antiaromatic 1 led to a nonaromatic macrocycle incorporating a phenanthrenequinone unit5,6-dioxophenanthriporphyrin 2.27 It has been demonstrated that phenanthriporphyrin 1 acts as a distinctively antiaromatic ligand, producing the hypervalent organophosphorous(V) derivative 1-P. It opened exciting routes to explore coordination chemistry based on the specific reactivity of the phenanthrene unit.23 Phenanthrene can hardly be considered as a suitable ligand for metal ions,28−36 although its geometry and the position of the inner carbon atoms strikingly resemble the well-established 1,10-phenanthroline, so frequently used as a chelating, aromatic ligand. The incorporation of the biphenyl © XXXX American Chemical Society

Scheme 1. Phenanthriporphyrin 1 and Related Macrocycles: 5,6-Dioxophenanthriporphyrin 2 and adj-Dicarbacorrole 3

unit into the corrole frame afforded 3, a nonaromatic adjdicarbacorrole with the CCNN coordination core, which demonstrated a capability to bind a copper(III) cation to form 3‑Cu.37 Recently, Sessler and co-workers reported on the synthesis of bis-dicarbacorrole with two adj-CCNN subunits.25,26 In fact, a dibenzo[g,p]chrysene moiety has been incorporated into the macrocyclic structure. Formally, this molecule can be treated as a fused pair of phenanthriporphyrins. The bis-dicarbacorrole acts as a macrocyclic ligand that coordinates two copper(III), two palladium(II), or simultaneously copper(III) and palladium(II) cations, forming a heterobimetallic complex which displays an organic π-radical character.25 As a part of our continuing efforts aimed at exploring the organometallic chemistry of diamagnetic and paramagnetic metallocarbaporphyrinoids, here we report on the synthesis and spectroscopic and structural characterization of copper(III) complexes of 5,6-dimethoxyphenanthriporphyrin 1 and 5,6-dioxophenanthriporphyrin 2. In this context, we wish Received: October 23, 2018

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DOI: 10.1021/acs.inorgchem.8b02997 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

The addition of trifluoromethanesulfonic or tetrafluoroboric acid to nonaromatic 2‑Cu in CD2Cl2 afforded the aromatic diprotonated species 2‑Cu‑H22+, thus following the route discussed in detail for protonation of dioxophenanthriporphyrin 2.27 Under anhydrous conditions, in the presence of HBF4· Et2O or BF3·Et2O, 2‑Cu‑H22+ undergoes the exocyclic coordination of boron difluoride cation, forming 2‑Cu‑BF2+. Boron trifluoride, tetrafluoroboric acid, and tetrafluoroborates are known to undergo decomposition via dissociation of fluoride(s) to produce a variety of reactive products, including BF2+.27,38−44 1‑Cu and 2‑Cu are stable in solution and can be purified by column chromatography. In the presence of TFA or HCl (gaseous) both compounds undergo gradual demetalation to give 1-H+ or 2-H+, respectively. Originally, the identities of 1‑Cu and 2‑Cu were confirmed by high-resolution mass spectrometry and NMR spectroscopy. The electronic absorption spectra of 1‑Cu, 2‑Cu, and 2‑Cu‑H22+ are presented in Figure 1. These complexes have spectral characteristics resembling those of appropriate antiaromatic (1‑Cu), nonaromatic (2‑Cu), or aromatic (2‑Cu‑H22+) porphyrinoids. 1‑Cu, 2‑Cu, and 2‑Cu‑H22+ preserve an effective Cs symmetry of the free bases. Consequently, the representative 1 H NMR spectra of 1‑Cu, 2‑Cu, and 2‑Cu‑H22+ (Figure 2) contain the AB pattern of pyrrole resonances accompanied by a characteristic set of dimethoxyphenanthrene or phenanthrenequinone signals resembling markedly the 1H NMR spectra of phenanthriporphyrinoids 1 and 2. The disappearance of inner hydrogen resonances H(22) and H(25) accompanied by the simplification of the H(2) pattern, as the H(2)−H(22) scalar coupling is missing after coordination,

to shed some light on the peculiar reactivity of these complexes toward protic and Lewis acids which may constitute a remarkable chemical tool suitable for the reversible modification of the carbaporphyrin frames and their physicochemical properties.

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RESULTS AND DISCUSSION Formation and Characterization of Copper(III) Complexes. Reaction of copper(II) acetate and 5,6-dimethoxyphenanthriporphyrin 1 or 5,6-dioxophenanthriporphyrin 2 afforded eventually an insertion of copper(III) into their coordination cores to produce the four-coordinate complexes 1‑Cu and 2‑Cu (Schemes 2 and 3). 1 and 2 act as macrocyclic trianionic ligands coordinating the metal through two nitrogen atoms and two inner carbon atoms of the phenanthrene moiety. Scheme 2. Synthesis of Copper(III) 5,6Dimethoxyphenanthriporphyrin 1‑Cua

a Reaction conditions: Cu(OAc)2·H2O (1.6 equiv), o-dichlorobenzene, reflux, 2 h, 98%.

Scheme 3. Synthesis and Reactivity of Copper(III) 5,6-Dioxophenanthriporphyrin 2‑Cua

Reaction conditions: (a) Cu(OAc)2·H2O (3 equiv), chloroform, reflux, 2 h, yield 97%; (b) 2‑Cu, HBF4·Et2O, dichloromethane; (c) HBF4·Et2O, benzene, precipitates after 1 h from the reaction mixture. The 18e π-delocalization route of 2‑Cu‑BF2+ is marked in magenta. a

B


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Inorganic Chemistry

Figure 1. UV−vis electronic spectra (298 K, CH2Cl2) of (A) 1‑Cu (black); (B) 2‑Cu (blue), and 2‑Cu‑H22+ (red).

Figure 3. Molecular structure of 1‑Cu. In the side projection the phenyl substituents are omitted for clarity.

Figure 2. 1H NMR spectra of (A) 1‑Cu, (B) 2‑Cu, and (C) 2‑Cu‑H22+ (600 MHz, 300 K, CD2Cl2).

is consistent with the formation of two CuIII−C bonds. Significantly, 1‑Cu conserves the paratropicity of 1, as reflected by the 1H NMR spectrum, demonstrating a characteristic pattern expected for an antiaromatic porphyrinoid (Figure 2). On the other hand, the spectrum of 2‑Cu resembles that of monoprotonated 5,6-dioxophenanthriporphyrin 2-H+, revealing the nonaromatic properties (Figure 2),27 whereas strong aromatic features are visible for 2‑Cu‑H22+. The geometries of 1‑Cu and 1‑Cu‑BF2+, determined by single-crystal X-ray diffraction, are presented in Figures 3 and 4. Multiple attempts to grow crystals of 2‑Cu failed. The molecular structures reflect the predisposition of the

Figure 4. Molecular structure of 2‑Cu‑BF2+. In the side projection the phenyl substituents are omitted for clarity. The tetrafluoroborate counterion and solvent are not shown.

copper(III) center for a nearly square-planar geometry in dicarbaporphyrinoid surroundings with two nitrogen atoms and two carbon atoms occupying the equatorial positions. Actually, the coordination core of 1‑Cu‑BF2+ resembles some fundamental features of copper(III) dicarbacorrole and copper(III) bis-dicarbacorrole.25,37 The Cu−C(22), Cu− C(25), Cu−N(26), and Cu−N(27) bond lengths of C


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Inorganic Chemistry Scheme 4. Synthesis of Copper(III) Phenanthriporphodimethenes 1‑Cu(OCH3)2a

a Reaction conditions: (a) Cu(OAc)2·H2O (7.8 equiv), chloroform/methanol (2/1), 90 °C, 24 h, yield 50% (molar ratio of stereoisomers 1/3); (b) 1‑Cu in chloroform/methanol, reflux in the presence of copper(II), 10 h, yield 59%.

affording phlorin-like structures,7,53−55 including the nucleophilic attack at the meso position of uranyl sapphyrin.56 The formation of two stereoisomers of copper(III) phenanthriporphodimethenes of Cs and C2 symmetry (syn and anti) has been supported by identification of the respective subsets of resonances distinguished by the coherent relative intensities in the 1H NMR of the reaction products (Figure 5).

2‑Cu‑BF2+ equal to 1.955(7), 1.952(9), 1.910(5), and 1.924(6) Å are similar to the respective bond lengths of other copper(III) carbaporphyrinoids, in which the trigonal carbon atom of an incorporated carbocycle or a heterocarbocycle is σ-coordinated.25,37,45−47 Examination of the structural data of 1‑Cu demonstrated that the effect of copper(III) coordination on the macrocyclic conjugation is negligible. The marked increase of diatropicity in comparison to 2-H+ and 2‑Cu, as revealed previously for 2‑Cu‑H22+ by 1H NMR, is corroborated by the bond length modifications imposed by the perimeter borylation encountered in 2‑Cu‑BF2+.27 The bond length pattern of 2‑Cu‑BF2+ and that previously reported for 2BF2-H2+ reveal striking similarities, but in comparison with 2H+ characteristic modifications have been noted. Evidently, the C(4)−C(5) and C(5)−C(6) bonds of 2‑Cu‑BF2+ demonstrate equalization of bond lengths, reflecting some aromatic character in contrast to their single-bond nature and isolation from the macrocyclic π conjugation encountered in 2-H+. Significantly, the C(5)−O (1.208(3) Å) and C(6)−O (1.211(3) Å) distances of 2-H+ are markedly shorter than the C(5)−O (1.300(8) Å) and C(6)−O (1.315(9) Å) bond lengths of 2‑Cu‑BF2+. These values are in the low range limit of bond length values detected for catecholborates, which vary from 1.310 to 1.389 Å.48−51 Thus, the boron(III) coordination converts the double CO bonds into essentially single bonds via an intramolecular rearrangement. Porphodimethene Formation. In search of the specific conditions for copper(III) insertion into phenanthriporphyrin 1, several routes were probed to elaborate an efficient procedure, yielding diamagnetic 1‑Cu (Scheme 4). An attempt to insert copper(III) under milder conditions using a mixture of chloroform and methanol as the solvent yielded directly copper(III) phenanthriporphodimethene 1‑Cu(OCH3)2. Subsequently, it was established that under oxidizing conditions (copper(II) in excess acts as an oxidizing agent) 1‑Cu is also readily transformed to 1‑Cu(OCH3)2 (Scheme 4). The reaction of 1‑Cu(OCH3)2 with hydrochloric acid recovers 1‑Cu with 50% yield. Previously it has been reported that activation of the pbenziporphyrin unit toward nucleophilic addition via gold(III) coordination afforded eventually 5,20-dialkoxy-p-benziporphodimethene.52 In fact the nucleophilic attachment of methoxide or hydroxide at the meso position of porphyrinoids or metalloporphyrinoids has been identified on several occasions,

Figure 5. 1H NMR (600 MHz, CD2Cl2, 300 K) spectrum of copper(III) phenanthriporphodimethenes 1‑Cu(OCH3)2-anti and 1‑Cu(OCH3)2-syn.

The number of resonances in each particular subset is consistent with their Cs and C2 molecular symmetries, respectively, but the specific assignment to a given stereoisomer was not feasible. In particular, the 5,6- and 11,21methoxy signals allowed identification of the nature of the additional meso substituents. At the same time the 13C chemical shift of C(11) and C(21) of 1‑Cu(OCH3)2 (86.6 ppm) is consistent with the tetrahedral hybridization of the meso carbon substituted by the oxygen atom of the methoxy group and three sp2 carbon atoms.52,57 The anti stereoisomer of 1‑Cu(OCH3)2 has been identified by X-ray crystallography (Figure 6). Two RR and SS enantiomers of 1‑Cu(OCH3)2-anti contain two tetrahedral meso carbon atoms. The enantiomers occupy the same crystallographic position with ordered localization of the tetrahedral meso carbon atoms and their methoxy and phenyl substituents. Complementary to this, the macrocyclic frames reveal the 1/1 disorder being rotated in-plane by 180° with respect to each other. The complex exhibits square-planar geometry of the copper(III), resembling the structures of 1‑Cu and 2‑Cu‑BF2+. In spite of the sp3-hybridized meso carbon D


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Inorganic Chemistry

course of this procedure 1 was completely consumed. The excess of copper(II) salt was removed by chromatography on the short (4 cm) silica gel column saturated with HCl vapors and/or by recrystallization from benzene. Heating of 1‑CuSA in boiling o-dichlorobenzene yielded coper(III) phenanthriporphyrin 1‑Cu, clearly identifying 1‑CuSA as the intermediate product of copper(III) insertion. The insertion was systematically followed by using two specific 1H NMR windows. In the case of feasible diamagnetic species, the spectroscopic analysis was focused on the analytically effective −10 to +20 ppm range typical for phenanthriporphyrinoids. Consequently, diamagnetic 1‑Cu and the mixture of diamagnetic degradation products have been identified. The exploration in the second window (−200 to 200 ppm) assumed that a form of interest might be paramagnetic. The remarkable response, consistent with the formation of the paramagnetic copper(II) phenanthriporphyrin 1‑CuSA, has been detected in the 1H NMR spectrum collected in the paramagnetic 1H NMR range of 0−70 ppm (Figure 7).

Figure 6. Molecular structure of copper(III) phenanthriporphodimethene 1‑Cu(OCH3)2-anti. In the side projection the central mesophenyl substituent is omitted for clarity.

atoms the phenanthriporphodimethene is almost planar with the tetrahedral carbon atoms C(11) and C(21) located in the equatorial plane. Such a structural feature resembles that detected for several complexes of metalloporphodimethenes.58−60 However, it has been also noted that the tetrapyrrolic skeletons of porphodimethenes and metalloporphodimethenes frequently adopt a rooflike conformation with a dihedral angle between two dipyrromethene moieties markedly smaller than 180°.44,58−61 Sitting-Atop Paramagnetic Intermediate Complex. The modest modification of the procedure applied for copper(III) porphodimethenes 1‑Cu(OCH3)2, namely lowering of the reaction temperature, afforded the readily transforming species 1‑CuSA with a small admixture of 1‑Cu (Scheme 5). The reaction mixture also contained the acyclic products of the phenanthriporphyrin degradation. In the

Figure 7. 1H NMR spectrum of 1‑CuSA (600 MHz, CD2Cl2, 300 K). The inset presents the comparison of the derivative with deuterated 14,18- and 16-Ph positions.

A Curie plot for the 1H NMR resonances of 1‑CuSA is given in the Figure 8. The experimental data are consistent with linear behavior over the whole temperature range (300−190 K). Thus, it should be noted that 1‑CuSA yielded a wellresolved 1H NMR spectrum demonstrating the resonances characterized by relatively small line widths (60.2 ppm, 567 Hz; 53.9 ppm, 545 Hz; 24.8 ppm, 1165 Hz; 300 K) (Figure 7). It remains in contrast with monomeric copper(II) com-

Scheme 5. Formation of Paramagnetic Complexa

Three plausible structures are presented. Reaction conditions: chloroform/methanol (2/1), Cu(OAc)2·H2O (4.1 equiv), room temperature, 20 h.

a

E


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1‑Cu‑2 (molar ratio 3.2/1 at 300 K) followed by demetalation to 1-H22+, as shown in Scheme 6 and Figure 8. An addition of base (collidine or ammonia) recovers 1‑Cu accompanied, however, by 1. Thus, in contrast to the protonation of 1, the two isomers of isophenanthriporphyrin 1-1 and 1-2 have been stabilized by the coordination of copper(III) in 1‑Cu‑1 and 1‑Cu‑2.27 For completeness, the copper(III) isophenanthriporphyrin 1‑Cu‑3, presumably involved in the initial step of demetalation, has been also included in the Scheme 6. The relevant, reversible protonation of the coordinated inner carbon atoms of carbaporphyrinoids were previously reported in the case of nickel(II) m-benziporphyrin,80 gold(III) 21carbaporphyrin,52 nickel(II), copper(II), and iron(III) Nconfused porphyrin,67,81,82 and iron(III) 2-methyl-N-confused porphyrin.83 The 1H NMR spectrum of 1‑Cu‑1 resembles that of 1H22+.27 1‑Cu‑2 demonstrates the resonances in the same spectroscopic region, but their number is doubled due to the intrinsic asymmetry of the molecule. The tetrahedral geometry of meso C(16) (1‑Cu‑1) or C(11) (1‑Cu‑2) breaks the πconjugation path and has been confirmed by the 13C NMR chemical shift of C(16) (50.4 ppm) in 1‑Cu‑1 and respective H(16) (6.10 ppm) as well as H(11) (6.18 ppm) resonances. Theoretically, three principal isomers of copper(III) isophenanthriporphyrin 1‑Cu‑n can be visualized. The structures of these species, including the hypothetical 1‑Cu‑3, were subjected to DFT optimization (Scheme 6 and Tables S7− S11). The analysis demonstrated a very small energy difference among 1‑Cu‑1 and 1‑Cu‑2 and, quite unexpectedly, 1‑Cu‑3. This is in contrast with the previously reported relative stability of isophenanthriporphyrins and their cationic derivatives.27 Evidently, the copper(III) coordination stabilizes the least favorable structure of isophenanthriporphyrin. In fact, the observed demetalation of 1‑Cu due to the acid addition is expected to involve 1‑Cu‑3 and related species. Thus, in thermodynamic terms, the inner-core protonation route, leading eventually to demetalation, was found to be energetically comparable to the directly identified meso carbon protonation. Remarkably, the response to the initial steps of titration is quite atypical, as illustrated in Figure 9. First, the stepwise addition of HBF4 resulted in gradual broadening of all resonances to such an extent that they eventually became beyond detection (Figure 9B). The increase in line width evidently varied depending on the hydrogen position in the molecular structure. The mildest broadening was detected for

Figure 8. Curie plot for resonances of 1‑CuSA.

plexes,62−65 including copper(II) porphyrinoids.63,66,67 However, it was reported that moderately strong coupled binuclear copper(II) systems display sharp ligand 1H NMR signals68−74 due to rapid electron relaxations T1e.68,70,71,75 Accordingly, in order to account for the detected hyperfine shift pattern, we have decided to explore the simplest hypothetical structures 1‑CuSA-B shown in Scheme 5. An implied bridging moiety is expected to warrant weak to moderate ferro- or antiferromagnetic interactions, as firmly established in the representative variety of chloride (fluoride)bridged copper(II) dimers.38,76−79 The detected downfield positions of the β-H pyrrole resonances of copper(II) porphyrinoids were found to be consistent with the considerable dx2−y2 metal orbital contribution to the SOMO and the σ-delocalization of the spin density.63,66,67 In classical terms the pattern of the hyperfine shift detected for 1‑CuSA seems to be consistent with the (dxy)2(dxzdyz)4(dz2)2(dx2−y2)1 metal electronic ground state with a singly occupied dx2−y2 orbital interacting with a ligand σ orbital. This provides a route to a σ-delocalization of the dx2−y2 unpaired electron, affording a positive contact shift contribution. The downfieldshifted resonances at 60.0 and 54.0 ppm assigned tentatively to H(13,19) and H(14,18) reflect the positive spin density at β-H pyrrolic positions. Protonation Studies of 1‑Cu. The 1H NMR titration studies, wherein aliquots of HBF4·Et2O in dry CD2Cl2 were added to the initial sample of 1‑Cu in CD2Cl2, yielded copper(III) isophenanthriporphyrin complexes 1‑Cu‑1 and Scheme 6. Protonation of 1‑Cua

a

Calculated energies of copper(III) isophenanthriporphyrins 1‑Cu‑n were obtained from DFT optimized models. F


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documented by 1H NMR that formation of 1‑Cu‑1 and 1‑Cu‑2 was accompanied by formation of 1-H22+ and, by default, demetalation.27 Thus, the removal of, formally, copper(III) cation from the coordination sphere of 1 provides a strong oxidizing reagent capable of accomplishing oneelectron oxidation of 1‑Cu to (1‑Cu)+•. The electron paramagnetic resonance (EPR) spectrum of (1‑Cu)+• (g = 2.002, dichloromethane, 77 K) displays a pattern that suggests an electronic structure with a dominating cation radical contribution (Figure S32).89 The effect of addition of (1‑Cu)+• to a solution of 1‑Cu has been probed in an independent experiment. Namely, a solution of the strong oxidizing reagent tris(4-bromophenyl)ammoniumyl hexachloroantimonate (Magic Blue) was added to a solution of 1‑Cu, reproducing the previously detected selective broadening of all resonances in the presence of acids (Figure S8) with the smallest effect displayed, as expected for the proposed mechanism, for the H(3,8) signal. The addition of zinc powder readily recovered the starting species 1‑Cu. DFT Analysis of (1‑Cu)+•. Formally, the electronic structure of (1‑Cu)+• corresponds to the classical description expected for a copper(III) π-cation porphyrinoid radical in a square-planar (CCNN) surrounding reflecting the (dxy)2(dxzdyz)4(dz2)2-P+• electronic configuration. To assess the electronic structure of (1‑Cu)+•, population analysis was performed. In fact, the SOMO of the (1‑Cu)+• shows a significant resemblance to the features of total spin density distribution shown in Figure 10. The experimentally

Figure 9. 1H NMR spectrum (600 MHz, CD2Cl2, 300 K) (A) of 1‑Cu, (B) after addition of 0.5 μL of HBF4·Et2O (1/15 CD2Cl2), (C) after addition of 25 μL of HBF4·Et2O (1/15 CD2Cl2). The subsets of resonances corresponding to the respective species are as follows: 1‑Cu‑1 (green), 1‑Cu‑2 (blue), and 1-H22+ (red).

the H(3,8) resonance of phenanthrene. At this stage, the intensity ratio between the broadened H(3,8) resonance and the visible already formed counterparts 1‑Cu‑1 (Figure 9B) equals ca. 50/1. Eventually, the H(3,8) peak disappeared once a sufficient excess of HBF4 had been added. The UV spectroscopic changes are rather minor at the initial titration stages (Figures S27 and S28). An attempt to apply trifluoroacetic or hydrochloric acid under conditions similar to those for the tetrafluoroboric acid, for the perimeter-centered protonation of 1‑Cu, failed to produce copper(III) isophenanthriporphyrins 1‑Cu‑1 and 1‑Cu‑2. Still, the selective broadening of resonances encountered in the case of HBF4 titration has been reproduced. The similarity in the response to initial HBF4 addition in comparison to the addition of TFA/HCl excluded the perimeter reactivity as a reason for the detected broadening behavior (Figure S7). The simultaneous observation of 1‑Cu‑1 and 1‑Cu‑2 resonances together with the broadened H(3,8) of 1‑Cu points out that these forms are in the very slow exchange limits. The 1H NMR behavior of 1‑Cu can be understood in terms of the effect of electron transfer reactions between the diamagnetic molecule and its reduced/oxidized paramagnetic counterpart.62,84−88 In case of the relatively long T1e relaxation, which is typical for copper(II) complexes or organic radicals,62 one can presume that the small amount of paramagnetic species in the equilibrium will produce the marked broadening of all resonances. Thus, a linear relationship between the observed half line width and the contact shift (δci) in square is expected.62,84−88 Thus, to account for the observed spectroscopic changes (Figure 9B and Figure S7) the simplest feasible electron exchange process is considered (eq 1). This model

Figure 10. Plot of the (1‑Cu)+• total spin density surface with isovalue 0.0004 e/Å3 and the positive spin density marked in blue.

observed broadening effect was related to the paramagnetic line width at the given positions, assuming domination of the scalar contribution by the contact shift (the amount of spin density) generated in the radical structure. The paramagnetic species, even existing in a relatively small relative concentration, can be instrumental in the specific line broadening due to the fast exchange. As previously described, the densities determined in the course of DFT calculations have been converted into the contact shifts of the attached protons (Tables S7 and S8).90−92 The linear relation between half line width and the contact shift (δci) in square has been applied to evaluate the relative line broadening in relation to the arbitrary assumed Δδν1/2 = 1 of H(3,8). Thus, the following broadening pattern can be expected for the perimeter resonances: Δδν1/2(H(14))/

requires one-electron oxidation of 1‑Cu to form a copper(III) π-cation radical of phenanthriporphyrin (1‑Cu)+•. It has been G


Article

Inorganic Chemistry Δδν1/2(H(13))/Δδν1/2(H(2))/Δδν1/2(H(3))/ Δδν1/2(Methoxy(5)) = 54/36/7/1/1. The analysis leads to the fundamental conclusion that the calculated spin distribution of (1‑Cu)+• accounted reasonably well, at least qualitatively, for the detected line broadening. In terms of the fast electron exchange analyzed in detail above, the process leaves the H(3,8) line deceptively deserted in the whole spectrum (Figure 9B and Figures S7 and S8).

1‑Cu(OCH3)2 (syn and anti, ratio 1/3) with an overall yield of 6.0 mg (50%). Similar reactivity was observed for direct conversion of 1‑Cu to 1‑Cu(OCH3)2, by refluxing 1‑Cu in the same mixture of solvents in the presence of copper(II) salt for 10 h with a 7.0 mg (59%) yield. Stereoisomer A. Not all of the signals were identified due to overlapping. 1H NMR (600 MHz, CD2Cl2, 300 K): δ 7.91 (d, 2H, 3J = 8.4 Hz, 3,8-H), 7.63−7.60 (m, 4H, 11,21-o-Ph), 7.52−7.50 (m, 2H 16-o-Ph), 7.42 (d, 2H, 3J = 8.4 Hz, 2,9-H), 7.25 (m, 4H, 11,21-m-Ph), 7.14 (tt, 2H, 11,21-p-Ph), 6.66 (d, 2H, 3J = 4.3 Hz, 14,18-H), 6.64 (d, 2H, 3J = 4.3 Hz, 13,19-H), 4.06 (s, 6H, 5,6-OCH3), 3.24 (s, 6H, 11,21-OCH3). 13C NMR (151 MHz, CD2Cl2, 300 K, by HSQC): δ 134.5 (14,18), 130.7 (16-o-Ph), 128.6 (11,21-m-Ph), 127.8 (2,9), 127.2 (11,21-p-Ph), 126.2 (11,21-o-Ph), 122.6 (3,8), 118.5 (13,19), 61.5 (5,6-OCH3), 52.5 (11,21-OCH3). HRMS (ESI): m/z 723.1707 [M − OCH3]+, calcd for C46H32CuN2O3+ 723.1703. 1H NMR (600 MHz, C6D6, 285 K): δ 8.03 (d, 2H, 3J = 8.3 Hz, 3,8-H), 7.94−7.91 (m, 4H, 11,21-o-Ph), 7.67 (d, 2H, 3J = 8.3 Hz, 2,9-H), 7.38−7.35 (m, 1H, 16-p-Ph), 7.10−7.06 (m, 6H, {7.10, 11,21-m-Ph}, {7.06, 16-mPh}), 6.97−6.89 (m, 4H, {6.94, 2H, 16-o-Ph}, {6.92, 2H, 11,21-pPh}), 6.77 (d, 2H, 3J = 4.3 Hz, 13,19-H), 6.65 (d, 2H, 3J = 4.3 Hz, 14,18-H), 3.76 (s, 6H, 5,6-OCH3), 3.26 (s, 6H, 11,21-OCH3). 13C NMR (151 MHz, C6D6, 285 K): δ 171.1 (4,7) - from HMBC, 162.6 (12,20 or 15,17), 150.1 (22,23), 147.1 (11,20-ipso-Ph), 146.2 (16 or16-ipso-Ph), 146.0 (5,6), 138.9 (16 or 16-ipso-Ph), 138.1 (1,10), 135.9 (12,20/15,17), 135.0 (14,18), 131.2 (16-o-Ph), 130.8 (16-pPh), 129.0 (16-m-Ph), 128.5 (22,25), 127.8 (11,21-m-Ph), 127.4 (11,21-p-Ph), 126.8 (2,9), 126.7 (11,21-o-Ph), 123.2 (3,8), 119.3 (13,19), 86.6 (11,21), 61.2 (5,6-OCH3), 52.7 (11,21-OCH3). Stereoisomer B. 1H NMR (600 MHz, CD2Cl2, 300 K): δ 7.87 (d, 2H, 3J = 8.4 Hz, 3,8-H), 7.54 (m, 4H, 11,21-o-Ph), 7.45 (m, 2H, 16-oPh), 7.28 (d, 2H, 3J = 8.4 Hz, 2,9-H), 6.61 (d, 2H, 3J = 4.4 Hz, 14,18H), 6.50 (d, 2H, 3J = 4.4 Hz, 13,19-H), 4.05 (s, 6H, 5,6-OCH3), 3.25 (s, 6H, 11,21-OCH3). 13C NMR (151 MHz, CD2Cl2, 300 K, from HSQC): δ 134.4 (14,18), 127.8 (16-o-Ph), 127.0 (2,9-H), 126.1 (11,21-o-Ph), 122.4 (3,8), 119.3 (13,19), 61.5 (5,6-OCH3), 52.6 (11,21-OCH3). HRMS (ESI): m/z 723.1707 [M − OCH3]+, calcd for C46H32CuN2O3+ 723.1703. Paramagnetic Copper(II) Complex of 11,16,21-Triphenyl5,6-dimethoxyphenanthriporphyrin (1‑CuSA). 5,6-Dimethoxyphenanthriporphyrin 1 (20 mg, 0.032 mmol) was dissolved in CH2Cl2 (20 mL), and then a methanol (10 mL) solution of Cu(OAc)2·H2O (25 mg, 0.13 mmol) was added. The solution was stirred at room temperature for 20 h. The solvent was evaporated under reduced pressure, and the brownish residue was dissolved in chloroform and the solution filtered through a piece of cotton. The solvent was removed with a rotary evaporator, and the crude product was purified by column chromatography on silica gel in a gradient from dichloromethane to 1% methanol/dichloromethane. The product was eluted as the last, brownish fraction. After evaporation, the product was dissolved in benzene and filtered through a cotton wool. Yield: ca. 8.0 mg. 1 H NMR (600 MHz, CD2Cl2, 300 K): δ 60.2, 53.9, 24.6, 14.2, 8.2, 7.8, 7.3, 5.1, 4.2, 4.1, 3.1, 1.4, 1.3, 1.1. Copper(III) 11,16,21-Triphenyl-5,6-dioxophenanthriporphyrin (2‑Cu). In a 60 mL high-preasure vessel equipped with a magnetic stirrer bar, 5,6-dioxophenanthriporphyrin 2 (10 mg, 0.017 mmol) was dissolved in chloroform (30 mL). The solution was degassed by bubbling N2; after 15 min Cu(OAc)2·H2O (10 mg, 0.05 mmol) was added and the solution was refluxed for 2 h. The solvent was removed under reduced pressure, and the bluish residue was dissolved in dichloromethane and the solution filtered through a short (2 cm) silica gel pad. Yield: 10.7 mg (97%). 1 H NMR (600 MHz, CDCl3, 305 K): δ 8.61 (d, 2H, 3J = 8.3 Hz, 3,8-H), 7.94 (d, 2H, 3J = 8.3 Hz, 2,9-H), 7.77−7.62 (m, 12H, o-mPh), 7.59−7.56 (m, 7H, pyrr + p-Ph {7.59 (d, 2H, 3J = 5.2 Hz, 13,19/ 14,18), 7.56 (d, 2H, 3J = 5.2 Hz, 13,19/14,18)}. The solubility of the compound in CDCl3 is very low; after a few minutes from dissolution 2‑Cu precipitates. HRMS (ESI): m/z 663.1129 [M + H]+, calcd for C43H24CuN2O2+ 663.1128. UV−vis (CH2Cl2, 298 K): λmax (nm) (log ε) 370 (3.5), 385 (3.6), 451 (3.4), 478 (3.3), 614 (3.4), 671 (3.6).

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CONCLUSIONS The present work provides firm evidence that phenanthriporphyrin 1 and dioxophenanthriporphyrin 2 act as flexible molecular frames which are in a position to accommodate a variety of metal ions, exemplified here by copper(III) and to some extent by boron(III) chemistry. It is worth remembering that a phenanthrene unit acting like a ligand has been hardly encountered,28,29 as the extremely rare binding patterns engaging simultaneously C(4) and C(5) carbon atoms of phenanthrene have been recognized in silylated phenanthrenes,30,31 metalated triphenylene derivatives,31−34 and quite recently iridium(III) complexes of phenanthrene.35,36 Potentially, as a result of structural constraints imposed by macrocyclic environments of phenanthriporphyrinoids, one can explore the coordination modes of the phenanthrene moiety. Thus, these dicarbaporphyrinoids enable one to investigate and eventually to control the subtle interplay between their structural flexibility and properties of formed organometallic complexes. In principle they provide a playground for rich organometallic chemistry centered around phenanthrene for a large variety of metal ions.

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EXPERIMENTAL SECTION

Copper(III) 11,16,21-Triphenyl-5,6-dimethoxyphenanthriporphyrin (1‑Cu). In a 60 mL high-pressure vessel with a magnetic stirrer, 11,16,21-triphenyl-5,6-dimethoxyphenanthriporphyrin 1 (20 mg, 0.032 mmol) was dissolved in dry 1,2-dichlorobenzene (20 mL). The solution was degassed by bubbling N2 for 15 min, and Cu(OAc)2·H2O (10 mg, 0.050 mmol) was added. The solution was refluxed for 2 h. The solvent was evaporated under reduced pressure, the greenish residue was dissolved in dichloromethane, and this solution was filtered through a short (3 cm) silica gel column. Yield: 21.3 mg (98%). 1 H NMR (600 MHz, CD2Cl2, 300 K): δ 7.37 (m (tt), 4H, 11,21-mPh), 7.33 (m, 2H, 11,21-p-Ph), 7.30 (m (tt), 2H, 16-m-Ph), 7.25 (m (tt), 1H, 16-p-Ph), 7.13 (m, 4H, 11,21-o-Ph), 7.07 (m, 2H, 16-o-Ph), 6.62 (d, 2H, 3J = 8.6 Hz, 3,8-H), 5.90 (d, 2H, 3J = 8.6 Hz, 2,9-H), 5.59 (d, 2H, 3J = 5.3 Hz, 13,19-H), 5.48 (d, 2H, 3J = 5.3 Hz, 14,18H), 3.68 (s, 6H, 5,6-OCH3). 13C NMR (151 MHz, CD2Cl2, 300 K): δ 175.0 (4,7), 160.6 (12,20/15,17), 156.2 (23,24), 150.8 (12,20/ 15,17), 147.1 (5,6), 138.3 (16-ipso-Ph), 137.9 (11,21-ipso-Ph), 136.2 (11,21), 135.6 (1,10), 134.7 (13,19), 131.4 (16-o-Ph), 130.7 (11,21o-Ph), 130.2 (22,25), 129.9 (14,18), 128.9 (16-m-Ph), 128.7 (11,21m-Ph), 128.1 (11,21-p-Ph), 127.7 (16-p-Ph), 126.7 (2,9), 120.3 (3,8), 111.9 (16), 60.4 (OCH3). HRMS (ESI): m/z 692.1527 [M]+, calcd for C45H29CuN2O2+ 692.1520. UV−vis (CH2Cl2, 298 K): λmax (nm) (log ε) 301 (4.1), 312 (4.1), 379 (4.5), 389 (4.5), 414 (3.9), 445 (3.7), 474 (3.8), 780 (3.2), 864 (3.4), 977 (3.3). Copper(III) 11,16,21-Triphenyl-5,6,11,21-tetramethoxyphenanthriporphyrin (1‑Cu(OCH3)2-syn/anti). Cu(OAc)2·H2O (25.0 mg, 0.13 mmol) was dissolved in a 30 mL mixture of CHCl3 and MeOH (2/1) in a high-pressure vessel. The solvent was degassed by bubbling N2 for 15 min, and then 1 (10 mg, 0.016 mmol) was added and the mixture was heated at 90 °C for 24 h. After that, the solution was cooled, filtered through a piece of cotton, and evaporated under reduced pressure. The crude product was subjected to chromatography (silica gel, CH2Cl2), affording eventually two stereoisomers of H


Article

Inorganic Chemistry Dicationic Form of Copper(III) 11,16,21-Triphenyl-5,6dioxophenanthriporphyrin (2‑Cu‑H22+). 2‑Cu was dissolved in CD2Cl2 in an NMR tube. The solution was titrated with HBF4·Et2O at low temperature (195 K) to give 2‑Cu‑H22+ (the solution changed from bluish to reddish). Addition of a base (TEA, collidine, NH3(g)) reversed the reaction. 1 H NMR (600 MHz, CD2Cl2, 195 K): δ 9.85 (d, 2H, 3J = 8.4 Hz, 3,8-H), 9.55 (d, 2H, 3J = 8.4 Hz, 2,9-H), 9.00 (d, 2H, 3J = 4.9 Hz, 14,18/13,19-H), 8.92 (d, 2H, 3J = 4.9 Hz, 14,18/13,19-H), 8.13 (m(d), 6H, 11,16,21-o-Ph), 7.97 (m (tt), 2H, 11,21-p-Ph), 7.95−7.90 (m (2 x tt), 5H, {7.93, 11,21-m-Ph; 7.92, 16-p-Ph}), 7.89−7.85 (m(tt), 2H, 16-m-Ph). 13C NMR (based on 2D correlation, 151 MHz, CD2Cl2, 195 K): δ 173.8 (4,7), 168.0 (5,6), 153.4 (12,15/17,20), 152.1 (23,24), 150.9 (12,15/17,20), 149.7 (11,21), 139.2 (14,18/ 13,19), 139.0 (14,18/13,19), 136.7 (11,21-ipso-Ph), 136.4 (16-ipsoPh), 136.1 (1,10), 135.4 (16-o-Ph), 134.8 (16), 133.2 (2,9), 133.0 (11,21-o-Ph), 130.1 (11,21-p-Ph), 130.0 (16-p-Ph), 127.9 (11,21-mPh), 127.7 (16-m-Ph), 127.0 (3,8), 117.8 (22,25). Copper(III) 11,16,21-Triphenyl-5,6-dioxaboranephenanthriporphyrin (2‑Cu‑BF2+). The titration (as above) but in C6D6 led to precipitation, affording monocrystals suitable for X-ray crystallography.

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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.8b02997. Additional 1H and 13C NMR, EPR, and HRMS spectra, crystallographic data, structural analysis, DFT-optimized models with relative energies, calculated 1H NMR correlations, and DFT coordinates for all models (PDF) Accession Codes

CCDC 1870397−1870399 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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AUTHOR INFORMATION

Corresponding Author

*L.L.-G.: e-mail, [email protected]; home page, http://llg.chem.uni.wroc.pl/. ORCID

Lechosław Latos-Grażyński: 0000-0003-1230-9075 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Science Centre (Grants 2012/04/A/ST5/00593 and 2016/23/B/ST5/00161) is kindly acknowledged. DFT calculations have been carried out using resources provided by the Wrocław Centre for Networking and Supercomputing (http://wcss.pl).

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REFERENCES

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