Synthesis and Characterization of Ferrocenyl Chlorins, 1,1′-Ferrocene-Linked Chlorin Dimers, and their BODIPY AnaloguesAnna I. Arkhypchuk, Andreas Orthaber, and K. Eszter Borbas*

Department of Chemistry, Ångstrom Laboratory, Uppsala University, Box 523, 75120 Uppsala, Sweden

*S Supporting Information

ABSTRACT: We present the synthesis and characterization ofmeso-ferrocenyl-substituted hydroporphyrins (chlorins) and1,1′-linked chlorin dimers. The dipyrromethane chlorinprecursors were also transformed into Fc-substituted BODIPYsand 1,1′-ferrocenyl-linked BODIPY dimers. The chlorin dimerswere studied by 1D and 2D NMR experiments and DFTcalculations, which showed that their solution structures weredependent on the central metal. Monomeric and dimericNi(II) chlorins had similar 1H NMR spectra. Monomeric anddimeric free base, Zn(II), and Pd(II) chlorins, on the otherhand, showed significantly more different spectra. The eclipsedconformer of the free base chlorin dimer was calculated to beenergetically more favored than the open form. The chlorin and BODIPY fluorescence emissions were quenched in the Fc-substituted compounds; these could be recovered by oxidation of the Fe(II) center. Cyclic voltammetry showed up to fiveoxidation waves for the free base chlorin dimer, which suggests that the macrocycles were not behaving independently of eachother.

■ INTRODUCTION

Tetrapyrroles are some of the most versatile frameworks for thewell-defined arrangement of functional units. They are at thecore of molecules with applications in sensing and imaging,medical diagnostics, therapeutics, artificial photosynthesis, andcatalysis, as well as in supramolecular architectures. Combiningthe tetrapyrrole with a redox-active unit, such as a metallocene(most often ferrocene, FcH), affords external control over thedesired activity: e.g., fluorescence emission and singlet oxygenproduction.1−4 Ferrocene provides a handle for a redox readoutin sensors5 and for controlling electronic6 and conformationalchanges.7 Thus, Fc incorporation into functional tetrapyrroleshas been a successful strategy to create molecular memorydevices,8 machines,9 and wires,10 has provided increasedselectivity for multielectron oxygen reduction,11 and hasfurnished model systems for electron transfer in artificialphotosynthesis.12 Interestingly, ferrocene can generate reactiveoxygen species in cells upon the recovery of its Fe2+ oxidationstate from its one-electron-oxidized form.13,14 This property isincreasingly being taken advantage of in cancer therapeutics tooverride the defense mechanisms of tumor cells.15

The location of the ferrocene, its distance from theoligopyrrolic core, and the type of linkage between the twodepend on balancing synthetic necessities with exerting thedesired control over the oligopyrrole’s properties.16−19 Thecyclopentadienyl (Cp) ring can be attached to tetrapyrrolesthrough C−C bonds at the macrocycle periphery,20,21 throughC−M22,23 or X/L−M24 bonds to a suitable central metal, or byreplacement of one of the pyrrole rings with a cyclopentadienyl

surrogate25 (see Figure 1 for generalized structures).26 Variouspossibilities exist for BODIPY27,28 functionalizations, whichplace the Fc onto the indacene periphery or onto the boronatom.26 Multiple Fc units in the same molecule can give rise tometal−metal coupling, in some cases even over remarkablylong (>10 Å) distances.29 This has been probed in Fc-substituted single-pyrrole models30 as well as in oligopyrroles.31

Given how prominently artificial photosynthesis featuresamong the potential applications of Fc-functionalized oligo-pyrroles, it is somewhat surprising that little work has beendone on Fc-functionalized hydroporphyrins. Hydroporphyrinsare porphyrinic tetrapyrroles lacking one or more peripheraldouble bonds. The most common hydroporphyrins are thechlorins,33,34 which contain one partially reduced pyrrole ring(Figure 1b). Chlorins constitute the cores of the chlorophyllsand as such are responsible for light harvesting and photosyn-thesis on Earth. To date, there has been a single report oncovalently Fc-modified chlorins (Figure 1b),32 which usednaturally derived pyropheophorbide functionalized though itsisocyclic ring. Most of the products were unstable andunderwent oxidative ring opening upon exposure to air.While a ruthenocene derivative could be isolated and studied,the Fc analogue proved labile upon photoexcitation, whichprecluded its spectroscopic investigation. Here, we presentchlorin monomers carrying one Fc unit and chlorin dimerslinked by a 1,1′-ferrocenyl group. We report the chemical,

Received: December 30, 2016Published: February 10, 2017

Article

pubs.acs.org/IC

© 2017 American Chemical Society 3044 DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

photophysical, and electrochemical characterization of thesespecies and compare them to the analogous BODIPY dyes.These compounds are interesting additions to the availablearsenal of Fc-functionalized oligopyrroles by combining the Fc-redox chemistry with light-harvesting ability in the red region.

■ RESULTS AND DISCUSSIONSynthesis. Monomeric and dimeric chlorins were prepared

following Lindsey’s method35−37 as shown in Schemes 1 and 2.To access the monomeric Fc chlorin, ferrocene wasincorporated in the 10-positions of the tetrapyrroles. Knownferrocenyl dipyrromethane 220 was obtained in 64% yield fromaldehyde 1 following a reported procedure. Monoformylationof 2 was possible under Vilsmeier conditions, although 3 wasobtained in only modest yields. This was due to the lowreactivity of 2 at room temperature, which necessitated theheating of the reaction mixture. However, at high temperatures2 has limited stability; furthermore, diformylation becomesprominent. Bromination of 3 with NBS afforded a so-calledEastern half (a 1-bromodipyrromethane, 4), which wascondensed with a Western half (a tetrahydrodipyrrin, 5;38

Scheme 1) in a two-step procedure without purification of thelinear tetrapyrrolic intermediate. The Zn chelate ZnChlFc wasisolated after column chromatography on silica gel in 11.6%yield. The bottleneck of the synthesis appeared to be thepreparation of 3. Therefore, we tested an alternativecondensation that avoids its use. Monobromination of 2 wasselective and high-yielding. The resulting 6 was condensed withformyl Western half 5CHO 39 under the standard conditions togive the target ZnChlFc in an excellent yield (43%).

The Fc-linked chlorin dimer (ZnChl)2Fc was synthesized

from the ferrocenyl dialdehyde 7 in a procedure analogous tothat described above (Scheme 2). Two alternatives wereexplored, and the protocol avoiding formylation of the Fc-substituted dipyrromethane again proved superior. Briefly,monoformylation of both dipyrromethane units in 840

(available from 7) to 9 proceeded in 22% yield. The massbalance is accounted for by decomposed starting material andsmall amounts of overformylated products. Dibromination of 9,followed by condensation with 5,38 gave (ZnChl)2

Fc in 3.8%yield. Alternatively, dibromination of 8 to 11 was quantitative,and the subsequent macrocyclization proceeded in 15% yield.This is in the range usually observed for meso-substitutedchlorins. The ferrocenylated monomeric BODIPY dyeBODIPYFc and the ferrocene-linked dimer BODIPY2

Fc wereprepared from the appropriate dipyrromethanes by oxidation tothe dipyrrins with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzo-quinone) and complexation with BF3·OEt2 (Scheme 3).The central Zn(II) ion could be removed upon treatment of

ZnChlFc or (ZnChl)2Fc with TFA (trifluoroacetic acid) to

furnish ChlFc or (Chl)2Fc, respectively. We could install Cu(II),

Ni(II), and Pd(II) instead of Zn(II) by treatment of the freebase compounds with Cu(OAc)2 at room temperature or withNi(OAc)2 or Pd(acac)2 under microwave irradiation

41,42 in thepresence of a large excess of pyridine (Schemes 1 and 2).The chlorins and the BODIPYs were characterized by 1H

and 13C NMR spectroscopy and high-resolution ESI-MS. A fullassignment of 1H NMR resonances was possible by acombination of 1D and 2D experiments (see the Figures S1−S25 in the Supporting Information). Additionally, we were ableto obtain single crystals of BODIPYFc suitable for crystallog-raphy by slow solvent evaporation from a saturated solution ina CH2Cl2−isopropyl alcohol mixture (Figure 2). The BODIPYcore shows typical metrical parameters. The (Cp) ring of theferrocenyl substituent is twisted by 35.2(2)° with respect to theBODIPY core about the C5−C10 axis; this value is close to thatfound in a previously reported crystal structure (42°).43 Thesolid-state packing is dominated by short Cp−centroiddistances of 3.72 Å indicative of weak π−π interactions aswell as short F···H interactions (2.48−2.51 Å) well below thesum of their van der Waals radii (2.65 Å).The solution structures of the chlorin dimers were further

analyzed by NOESY NMR and variable-temperature 1H NMR.The chlorins could be divided in two groups depending on thecentral metal ions. The spectra of the monomeric and dimericNi(II) chelates have similar 1H NMR spectra. The minordifferences are due to small upfield shifts of the aromaticsignals. The shifts are largest for H-7, H-13, H-8, and H-12 andsmallest for H-5 and H-15 (Figure 3). This suggests that insolution NiChlFc and (NiChl)2

Fc have similar geometries. Thefree base, Zn(II), and Pd(II) chlorins, on the other hand, hadsignificantly more different monomeric and dimeric spectra(Figure 3). Specifically, the H-8 and H-12 resonances areshifted downfield in the dimers in comparison to themonomers. The other signals are shifted upfield, most notablyH-13 and H-5. Ni(II) chelation by porphyrins and chlorins isknown to result in macrocycle ruffling to accommodate thesmall metal ion; free base, Zn(II), and Pd(II) chlorins, on theother hand, are quite planar. It is possible that the nonplanarityof the Ni(II) chlorins would prevent the two macrocycles in(NiChl)2

Fc from adopting certain geometries that are availableto (Chl)2

Fc, (ZnChl)2Fc, and (PdChl)2

Fc (vide infra).

Figure 1. (a) Possible porphyrin structures carrying directly linked orfused metallocenes. (b) Chlorins (pheophorbides) covalently attachedto Fc units reported to date.32 (c) Access to 10-substituted ferrocenyl-chlorin and meso-Fc-BODIPY from the same Fc-dipyrromethaneprecursor.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3045

The NOESY spectra of (ZnChl)2Fc at room temperature and

at 90 °C were essentially identical (Figures S1−S4 in theSupporting Information). Even at high temperature, very strongNOE cross-peaks were seen between H-8 and H-12 and the Fcprotons. Variable-temperature 1H NMR-spectra were recordedbetween +95 and −75 °C (Figure 4). When the sample wascooled from 95 to 25 °C, all aromatic peaks moved downfield,with the largest changes being observed for H-8 (Δδ 0.3 ppm),H-12 (Δδ 0.3 ppm), and H-20 (Δδ 0.6 ppm). Upon furthercooling, between ca. −40 and −60 °C a coalescence point wasreached. Continued lowering of the temperature to −75 °Cresulted in the emergence of two sets of signals, which weretentatively assigned to the open and eclipsed forms of the dimer(vide infra). A full assignment of the new peaks was notpossible due to the low solubility of (ZnChl)2

Fc at lowtemperatures and the resulting poor spectrum quality.In order to further probe the dimer geometries, we

performed density functional (DFT) calculations on (Chl)2Fc

and (ZnChl)2Fc. The structures were fully optimized using the

M06-2X functional with a 6-311G** triple-ζ basis set, which isknown to perform well also for noncovalent interactions.44,45

Two minimum structures were identified on the PES

corresponding to the open and the eclipsed forms (Figure 5and Figure S26 in the Supporting Information). In the openform of (Chl)2

Fc the dihedral angle between the chlorins aboutthe ferrocene swivel axis is 142.5°, while the chlorin planes twistby 44.3 and 45.0°. Consequently, no interaction between thetwo chlorin fragments is observed. The dihedral angle in theclosed form is 11.2°, and the ferrocene takes a slightly eclipsedconformation. Both angles between the chlorin and the Cpplanes are significantly reduced to 37.5°, which results in shortdistances between the two chlorin fragments: e.g., a centroiddistance of 3.66 Å and short C···N/C (3.20/3.28 Å) distances.Importantly, the closed isomer is more stable by 11 kcal mol−1

(Gibbs free energy, ΔG) according to our gas-phasecalculations. Similarly, the closed form of (ZnChl)2

Fc is morestable by ca. 19 kcal mol−1. The dihedral angle is reduced from141.8 to 12.1° in the closed form,while the angles between theCp and the chlorin planes are only slightly reduced (40.9/42.8°in the closed form vs 45.9/46.0° in the open form).Interestingly, a very short intermetallic distance (3.30 Å) andshort C···N/C···C distances (∼3.2 Å) support stronginteraction between the two chlorin fragments in the closedform.

Scheme 1. Preparation of the Zn(II) Chelate of Mono-Fc-chlorin ZnChlFc and its Transformation into ChlFc and MChlFc (M =Cu, Ni, Pd)a

aTMPi = 2,2,6,6-tetramethylpiperidine.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3046

UV−Vis Absorption and Emission Spectroscopy. Thespectra of the monomeric and dimeric Fc chlorins are shown inFigures 6 and 7 and in Figures S27−S30 in the SupportingInformation, while those for the monomeric and dimeric

BODIPYs are shown in Figure 8 and Figure S31 in theSupporting Information. The data are summarized in Table 1.The room-temperature absorption spectra of MChlFc and(MChl)2

Fc are similar. The most important differences are thehigher Qy band intensities relative to the Soret bands in thedimeric species, in comparison to the corresponding mono-mers. A small blue shift of the Soret bands (5−10 nm) andminor broadening of both the Soret and Qy bands of the dimersare also seen in the dimers. The order of the Qy bands is asexpected on the basis of previous reports and is the same forboth monomers and dimers: the most blue-shifted bands arefor the Pd species and the most red-shifted bands are for thefree base macrocycles. The Ni(II) chlorins had the mostbroadened spectra, which is in line with previous reports onNi(II) porphyrins and chlorins and is caused by macrocycledistortion.46 Additionally, the blue shift of the Soret band of(NiChl)2

Fc in comparison to NiChlFc was negligible (2 nm),again showing that the Ni chelates behaved anomalously.The UV−vis absorption spectrum of (ZnChl)2

Fc wasmodestly temperature dependent (Figure 7). The room-temperature and 85 °C spectra were essentially superimposable,with only small changes observed in the Qy region. However,when the solution was cooled to −85 °C, the Soret band red-shifted by 12 nm and the Qy band blue-shifted by ∼1 nm. Evenmore importantly, the Soret to Qy ratio decreased dramatically,from 4.8 to 2.4. These data support the conclusions of theNMR experiments that at low temperatures the chlorin dimersadopt a conformation different from that of the room-temperature structure. However, the dimers aggregate at lowtemperature, as seen from the NMR spectra, and both theaggregation and the adoption of a cofacial arrangement by thechlorin rings are expected to affect the absorption spectra. TheUV−vis absorption spectra of the monomeric and dimericBODIPYs were similar (Figure 8). The most prominentfeatures were sharp bands at λabs 507 nm and λabs 512 nm forBODIPYFc and BODIPY2

Fc, respectively, assigned to the 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene core. Additionally,broad, low-intensity bands are seen for both chromophores inthe red, stretching all the way to the near-infrared. These areattributed to charge-transfer bands on the basis of similarspectral features observed in other Fc-substituted BODIPYs.12

Free base chlorins and BODIPYs without Fc are usuallystrongly fluorescent (Φ ≈ 20−30%, 32% for chlorophyll a), asare, to a smaller extent, Zn chlorins (Φ ≈ 5%).42,47,48 Thecovalent attachment of an Fc unit resulted in essentiallycomplete quenching of the fluorescence of these chromo-phores, presumably due to photoinduced electron transfer(PeT) from the Fc to the excited state chromophore. Thedriving force (ΔE) for electron transfer was calculated for a freebase chlorin (eq 1). E1/2

ox (D) and E1/2red (A) are the oxidation and

reduction potentials (vs NHE) of the donor (Fc, 0.65 eV, Table2) and the acceptor (chlorin, −1.17 eV), respectively. Eexc(A) isthe excited state energy of the acceptor (chlorin singlet), whichwas approximated with the higher-energy maximum of theemission spectrum (639 nm, 1.94 eV). ΔECoul is the attractionbetween the radical ion pair resulting from PeT. Thecontribution of this term is usually small.49 Its lower limitwas estimated by an established value for complete chargeseparation in acetonitrile (0.06 eV). As we work in CH2Cl2,which has a lower ε, we expect this term to be larger. Theseapproximations give ΔE = −0.18 eV (−0.12 eV without the lastterm), indicating that electron transfer is possible.

Scheme 2. Preparation of the Fc-Linked Chlorin Dimer(ZnChl)2

Fc and its Transformation into (Chl)2Fc and

(MChl)2Fc (M = Cu, Ni, Pd)

Scheme 3. Preparation of the BODIPYs

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3047

Δ = − − −E E E E E(D) (A) (A)1/2ox

1/2red

exc Coul (1) Further support for fluorescence quenching by PeT wasprovided by the recovery of the chlorin and BODIPY emission

Figure 2. X-ray structure of BODIPYFc: perspective view with ellipsoids at the 50% probability level. Selected distances (Å) and angles (deg): C5−C10 1.460(4), B1−N1 1.540(4), B1−N2 1.532(4), B1−F1 1.389(4), B1−F2 1.391(4), N1−B1−N2 106.3(2).

Figure 3. Aromatic regions of the 1H NMR spectra of the monomeric (top) and dimeric (bottom) Fc chlorins NiChlFc and (NiChl)2Fc (left) and

ZnChlFc and (ZnChl)2Fc (right).

Figure 4. Variable-temperature 1H NMR spectra (aromatic region) of (ZnChl)2Fc in toluene-d8.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3048

Figure 5. Calculated rotamers of (ZnChl)2Fc at the M06-2X/6-311G** level of theory: (a) top view of the open form and (b) top and (c) side views

of the closed form.

Figure 6. UV−vis spectra of (left) MChlFc and (right) (MChl)2Fc in CH2Cl2 at room temperature.

Figure 7. UV−vis spectra of (ZnChl)2Fc at different temperatures in

toluene.Figure 8. UV−vis absorption spectra of monomeric and dimericBODIPYs in CH2Cl2.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3049

upon oxidation of the Fe(II) center. Fe(II) was oxidized toFe(III) in ChlFc and (Chl)2

Fc with Fe(ClO4)3. Fe(III) is astrong enough oxidant to affect the Fe(II) → Fe(III)transformation (0.77 V (in water)) without oxidizing thechromophores. The dark green solutions turned dark red uponthe addition of Fe(ClO4)3. Upon oxidation the Soret bands ofboth the monomeric and the dimeric chlorins red-shifted to asmall extent without broadening significantly. Under the sameconditions, the Qy bands broadened and were bathochromicallyshifted and their short-wavelength satellites intensified (FigureS32 in the Supporting Information). Oxidation has a strongelectronic effect, in addition to modestly decreasing the Cp−Cpdistance; the significance of the latter is expected to be higherfor dimers than for monomers. Dimeric chlorins were in

general less emissive than their monomeric analogues,presumably due to the short chlorin−chlorin distance inthese compounds, which results in self-quenching.

Electrochemistry. Cyclic voltammetry of all compoundswas measured, and the results are summarized in Table 2 and inFigures S33 and S34 in the Supporting Information. Thecompounds show complex behavior and undergo multipleredox processes. Monomeric chlorins have two reductions,assigned to macrocycle-based processes on the basis ofcomparison with simple free base chlorins.50 The first reductionis usually reversible. There are two macrocycle-based oxidationsin addition to the first oxidation around 0 eV, which is Fc-based. Chlorin dimers have more complicated voltammograms,exhibiting stepwise oxidations with up to five well-resolvedpeaks (see e.g. (Chl)2

Fc). This suggests that there is electroniccommunication between the chlorin macrocycles mediated bythe Fc unit. Oxidation of Fe(II) to Fe(III) is observed at 0.02−0.10 eV but can also be at as lower potentials: e.g. −0.02 and−0.04 eV for (CuChl)2

Fc and (ZnChl)2Fc, respectively. The

order of the oxidation and reduction potentials follows theorder expected on the basis of the electron-withdrawingproperties of the central metal ion in the chlorin (Zn < Cu <Pd).51 The Ni chlorins behaved differently from the othermetalated and free base chlorins: e.g., NiChlFc had a reductionpotential at the most negative value (at −1.88 eV), which mightbe due to structural factors. For the monomeric and dimeric Znchelates, a sharp peak is observed for the anodic scan at +0.06V, which is probably a stripping effect: i.e., release of metal fromdeposited material during irreversible oxidative scans.BODIPYFc has fully reversible first oxidation and reduction

peaks at 0.3 and −1.32 eV, respectively. Only the secondoxidation at 1.30 eV is irreversible. BODIPY2

Fc has five peaks inall in the CV (two reductions and three oxidations), all ofwhich are irreversible. Extensive decomposition and materialdeposition onto the electrode were observed in this case. Thespectroelectrochemical investigations of ZnChlFc and(ZnChl)2

Fc were inconclusive. Studies with Bu4NPF6 aselectrolyte were not satisfactory, most probably because ofthe small separation between the oxidation processes. Using thebulkier NaBARF (BARF = tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate) as the electrolyte, the first two oxidationprocesses could be separated. However, UV−vis absorptionspectroscopy showed substantial broadening of the Soret bandand the slow disappearance of the Q band (Figures S45−S48 inthe Supporting Information) for both compounds, suggestingthe decomposition of these species.

■ CONCLUSIONSThe syntheses of free base and metalated ferrocene-substitutedchlorins and the analogous BODIPY dyes are reported. Chlorinmacrocyclizations resulted from condensing a tetrahydrodipyr-rin with ferrocenyl 1-bromo-9-formyldipyrromethanes or aformylated tetrahydrodipyrromethane with ferrocenyl 1-bro-modipyrromethanes. The latter method gave excellent yields ofboth monomeric and dimeric chlorins, highlighting the way thestabilities of dipyrromethane derivatives can affect macro-cyclization yields. The UV−vis absorption spectra of thedimeric species were similar to those of the monomers, withonly small differences noted, mostly in the Soret region. Thefluorescence emissions of all Fc-substituted compounds werequenched. Emission could be partially restored by chemicaloxidation of the Fe(II) center in Fc, thus suggesting thatquenching proceeds through electron transfer to the

Table 1. Photophysical Properties of Fc Chlorins andBODIPYs

compoundλ(Soret),nma λ(Qy), nm

aI(λS)/I(λQ)

bλem,nma,c

ZnChlFc 410 615 4.82ChlFc 407 647 5.39 (637f)NiChlFc 410 611 3.19PdChlFc 404 597 3.42CuChlFc 408 610 3.77(ZnChl)2

Fc 400 615 4.83(Chl)2

Fc 399 647 6.32 (639f)(NiChl)2

Fc 408 612 3.23(PdChl)2

Fc 399 598 3.36(CuChl)2

Fc 401 612 3.79ChlFc+ d 412 537, 616, 768e 639(Chl)2

Fc+ d 394 636 8.1 640BODIPYFc 359, 506BODIPY2

Fc 362, 513BODIPYFc+ d 504 488, 516BODIPY2

Fc+ d 500, 402 488, 519aRecorded in CH2Cl2 at room temperature. bDetermined byintegration of the peak area. cExcitation was carried out at the Soretband. dObtained by addition of Fe(ClO4)3 to the sample. eMultiplebands, not regular chlorin Q bands. fPossibly due to contaminant, as itis at higher energy than the chlorin absorption and is very weak.

Table 2. Cyclic Voltammetry Data for the Fc-SubstitutedChlorins and BODIPYs

compound reduction,a eV oxidation,a eV

ZnChlFc −2.32, −1.79b 0.02,b 0.24,b 0.73c

ChlFc −2.22, −1.80b 0.02,b 0.51, 0.90NiChlFc −1.88 0.07,b 0.39,b 0.77, 1.12PdChlFc −2.31, −1.83b 0.06,b 0.53, 0.98, 1.13, 1.21CuChlFc −2.35, −1.85b 0.04,b 0.37,b 0.85, 1.11, 1.24(ZnChl)2

Fc −2.31, −2.12,d −2.01,d−0.04b

0.18,b 0.33,b 0.74, 0.94

(Chl)2Fc −2.17, −1.74b 0.008, 0.41, 0.61, 0.90, 1.09

(NiChl)2Fc −1.80b 0.09,b 0.26,b 0.43,b 0.82,

1.12(PdChl)2

Fc −2.33, −1.80b 0.10,b 0.30, 0.60(CuChl)2

Fc −1.85,b −0.02b 0.32, 0.57, 0.94,e 1.16BODIPYFc −1.32b 0.30,b 1.30BODIPY2

Fc −1.74, −1.31 0.35, 0.59, 1.16e

aMeasured for 1 mM solutions of the analyte in CH2Cl2 (0.1 MNBu4PF6) with a glassy-carbon electrode and ν = 100 mV/s. Allpotentials are given versus Fc+/0. bPeak is reversible; reported valuecorresponds to E1/2 = (Epa + Epc)/2.

cPeak features large tail. dTwopeaks that are not well-resolved and are very broad. eShoulder.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3050

chromophore from the ferrocene. The presence of the redox-active Fc and one or two hydroporphyrin units resulted in richredox chemistry forMChlFc and (MChl)2

Fc. Taken together, Fcchlorins are interesting as rare red-absorbing, redox-activesystems with potential as models of electron transfer inphotosynthesis. Designs wherein the Fc unit and the chlorin orthe BODIPY are connected by a linker are conceivable andcould be useful in controlling the electron transfer. Applicationsof these or similar compounds as fluorescent sensors for redoxsensing are conceivable, and the multiple well-resolved redoxstates of some of these compounds make them interesting asmolecular memory devices.

■ EXPERIMENTAL SECTIONAll reactions were performed under Ar using Schlenk techniques if notstated otherwise. Diethyl ether and THF were freshly distilled fromNa/benzophenone prior to use, CH2Cl2 was distilled from CaH2.

1Hand 13C NMR spectra were recorded on a 400 MHz spectrometer(Agilent and JEOL) unless noted otherwise. Chemical shifts (ppm) arereferenced to the internal signal of residual solvent protons. High-resolution mass spectral analyses (HRMS) were performed at theOrganisch Chemisches Institut WWU Munster. Compounds 2,20 5,38

5CHO,39 and 840 were prepared according to literature procedures. TheX-ray crystal structure was solved using direct methods in themonoclinic space group P21/n (No. 14) with four molecules in theunit cell.General Procedure for Vilsmeier Formylation. A sample of 2

or 8 (1 equiv) was dissolved in dry DMF (10 mL), and the solutionwas cooled in an ice−water bath. In a separate vial, POCl3 (1 or 2equiv, respectively) was added to dry DMF (5 mL), and this mixturewas stirred for 10 min, after which it was transferred to thedipyrromethane solution. The reaction mixture was warmed to roomtemperature and was then heated for 2−3 h until no more startingmaterial could be detected by TLC analysis. The reaction wasquenched by the addition of aqueous Na2CO3 (1 M), and the solutionwas diluted with diethyl ether. The phases were separated, and theaqueous layer was extracted three times with diethyl ether. Thecombined organic phase was washed three times with brine, dried(MgSO4), and concentrated. Column chromatography on silica gelusing CH2Cl2/hexane (1/1) as eluent gave the products as pale yellowsolids.3. The compound was prepared starting from 0.320 g (1.22 mmol)

of 2 and 187 mg (1.22 mmol) of POCl3. Rf (EtOAc/pentane, 1/4) =0.1. Yield: 25%, 90 mg. 1H NMR (400 MHz, CDCl3): δ 9.42 (s, 1H,COH), 9.35 (bs, 1H, NH), 8.02 (bs, 1H, NH), 6.96−6.84 (m, 1H,pyrrole), 6.70−6.67 (m, 1H, pyrrole), 6.13 (d, 3JH,H = 6.1 Hz, 1H,pyrrole), 6.00−5.98 (m, 1H, pyrrole), 5.23 (s, 1H, CH), 4.21−4.19(m, 2H, Fc), 4.13 (s, 5H, Fc), 4.05 (m, 2H, Fc). 13C NMR (101 MHz,CDCl3): δ 178.70, 142.56, 132.03, 131.33, 121.56, 117.37, 110.27,108.57, 107.08, 69.13, 68.31, 68.20, 68.11, 67.82, 38.33. HRMS: calcdfor C20H18FeN2ONa [M + Na]+ 381.06609, found 381.06604.9. The compound was prepared starting from 0.10 g (0.21 mmol)

of 8 and 65 mg (0.042 mmol) of POCl3. Rf (5% MeOH in Et2O) =0.63. Yield: 22%, 24 mg. The product was obtained as a mixture ofdiastereomers. 1H NMR (400 MHz, CDCl3): δ 10.00 (bs, 2H, NHisomer 1), 9.87 (bs, 2H, NH isomer 2), 9.30 (s, 4H, CHO isomers 1 +2), 8.44 (bs, 2H, NH isomer 1), 8.41 (bs, 2H, NH isomer 2), 6.87 (t,3JH,H = 4.1,4JH,H = 2.2 Hz, 2H, pyrrole isomer 1), 6.86 (t, 3JH,H =4.1,3JH,H = 2.2 Hz, 2H, pyrrole isomer 2), 6.67 (dd, 3JH,H = 4.1,4JH,H =2.6 Hz, 2H, pyrrole isomer 1), 6.63 (dd, 3JH,H = 4.1,4JH,H = 2.6 Hz, 2H,pyrrole isomer 2), 6.11 (dd, 3JH,H = 3 Hz, 2H, pyrrole isomer 1), 6.10(dd, 3JH,H = 3 Hz, 2H, pyrrole isomer 2), 6.05 (dd, 3JH,H = 3 Hz, 2H,pyrrole isomer 1), 6.05 (dd, 3JH,H = 3 Hz, 2H, pyrrole isomer 2), 5.99−5.93 (m, 4H, pyrrole isomers 1 + 2), 5.03 (s, 2H, CH isomer 1), 4.99(s, 2H, CH isomer 2), 4.03−3.98 (m, 5H, Fc isomers 1 + 2), 3.97−3.95 (m, 1H, Fc isomers 1 + 2), 3.94−3.90 (m, 2H, Fc isomers 1 + 2).13C NMR (101 MHz, CDCl3): δ 178.80, 144.05, 143.81, 131.74,131.66, 131.63, 131.49, 122.79, 117.39, 117.18, 110.19, 110.14, 108.33,

108.32, 106.75, 106.69, 89.39, 69.60, 69.23, 68.87, 68.86, 68.74, 68.72,68.69, 68.43, 38.31, 38.26. HRMS: calcd for C30H26FeN4O2Na [M +Na]+ 553.12978, found 553.12958.

General Procedure for Macrocyclization. Step 1: Bromination.A sample of dipyrromethane or formyl dipyrromethane (1 equiv) indry THF (∼10 mmol/mL) was cooled to −78 °C. To this solutionwas added 1 equiv (for 2 or 3) or 2 equiv (for 8 or 9) of NBSdissolved in THF dropwise. The reaction mixture was stirred for 30min, during which time it was slowly warmed to ca. 0 °C. Stirring wascontinued at this temperature for an additional 15 min. The reactionwas quenched by adding 30 mL of brine, and the mixture was towarmed to room temperature. The phases were separated, and theaqueous layer was extracted twice with diethyl ether. The combinedorganic layers were washed with brine and dried over MgSO4. Thesolvent was removed under reduced pressure (Caution! The water bathtemperature should not exceed 25 °C.) to give the crude product, whichwas directly used in the next step without additional purification.

Step 2: Macrocyclization. Caution! All manipulations should beperformed with the exclusion of light. To a solution of bromodipyrro-methane or 1-bromo-9-formyldipyrromethane (1 equiv for monomericor 0.5 equiv for dimeric species) and 5 (1 equiv) or 5CHO (1 equiv) indry CH2Cl2 (∼10 mM) was added a solution of 5 equiv of p-toluenesulfonic acid monohydrate in MeOH. The solution was stirredfor 30 min, and the reaction was quenched by the addition of 10 equivof TMPi (2,2,6,6-tetramethylpiperidine). The volatile componentswere removed under reduced pressure (Caution! The water bathtemperature should not exceed 25 °C.), and the solid residue wasredissolved in dry CH3CN (∼0.5 mmol/mL). Then, 25 equiv ofTMPi, 15 equiv of Zn(OAc)2, and 3 equiv of AgOTf were added inthat order. After this, the reaction mixture was refluxed for 16−24 h inthe dark open to the air. During this time a dark gray to blacksuspension was formed. The reaction mixture was cooled to roomtemperature. The mixture was filtered through a silica pad which wasthoroughly washed with CH2Cl2. The removal of the solvents gave adark green to black solid, which was purified by columnchromatography on silica gel using a 1/1 mixture of CH2Cl2 andhexane as the eluent. Dark green solids were obtained.

ZnChlFc: Synthesis A, Starting from 3. Bromination was performedon 90 mg (0.31 mmol) of 3 with 55 mg (0.31 mmol) of NBS. Duringmacrocyclization 58 mg (0.31 mmol) of 5, 295 mg (1.55 mmol) of p-toluenesulfonic acid monohydrate, 0.44 g (3.10 mmol) and 1.09 g(7.75 mmol) of TMPi, 0.85 g (4.65 mmol) of Zn(OAc)2, and 240 mg(0.93 mmol) of AgOTf were used. Rf (CH2Cl2/hexane, 1/1) = 0.52.Yield: 12%, 21 mg.

ZnChlFc: Synthesis B, Starting from 2. Bromination was performedon 40 mg (0.15 mmol) of 2 with 27 mg (0.15 mmol) of NBS. Duringmacrocyclization 33 mg (0.15 mmol) of 5CHO, 144 mg (0.76 mmol) ofp-toluenesulfonic acid monohydrate, 0.21 g (1.52 mmol) and 0.54 g(3.8 mmol) of TMPi, 0.42 g (2.3 mmol) of Zn(OAc)2, and 117 mg(0.45 mmol) of AgOTf were used. Rf (CH2Cl2/hexane, 1/1) = 0.52.Yield: 43%, 28 mg. 1H NMR (400 MHz, CDCl3): δ 9.87 (d, 3JH,H =4.5 Hz, 1H, β-pyrrole), 9.80 (d, 3JH,H = 4.2 Hz, 1H, β-pyrrole), 9.45 (s,1H, meso-H), 8.97 (d, 3JH,H = 4.3 Hz, 1H, β-pyrrole), 8.79 (d, 3JH,H =4.3 Hz, 1H, β-pyrrole), 8.68 (d, 3JH,H = 4.2 Hz, 1H, β-pyrrole), 8.53 (d,3JH,H = 4.5 Hz, 1H, β-pyrrole), 8.50 (s, 1H, meso-H), 8.50 (s, 1H,meso-H), 5.46−5.39 (m, 2H, Fc), 4.79−4.71 (m, 2H, Fc), 4.39 (s, 2H,CH2), 4.23 (s, 5H, Fc), 1.99 (s, 6H, CH3).

13C NMR (101 MHz,CDCl3): δ 170.58, 158.65, 153.89, 152.22, 148.10, 146.59, 145.46,145.35, 133.70, 132.55, 129.52, 127.30, 126.97, 125.74, 121.20, 109.64,96.84, 94.04, 90.04, 70.54, 68.23, 50.10, 45.22, 30.78. HRMS: calcd forC32H26ZnFeN4 ([M]+) 586.0794, found 586.0788.

(ZnChl)2Fc: Synthesis A, Starting from 9. Bromination was

performed starting from 24 mg (0.045 mmol) of 9 with 16 mg(0.090 mmol) of NBS. During macrocyclization 17 mg (0.091 mmol)of 5, 86 mg (0.45 mmol) of p-toluenesulfonic acid monohydrate, 0.127g (0.67 mmol) and 0.32 g (2.25 mmol) of TMPi, 0.247 g (1.35 mmol)of Zn(OAc)2, and 69 mg (0.27 mmol) of AgOTf were used. Rf(CH2Cl2/hexane, 1/1) = 0.41. Yield: 3.8%, 2 mg.

(ZnChl)2Fc: Synthesis B, Starting from 8. Bromination was

performed on 145 mg (0.31 mmol) of 8 with 109 mg (0.61 mmol)

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3051

of NBS. During macrocyclization 66 mg (0.31 mmol) of 5CHO, 291 mg(1.5 mmol) of p-toluenesulfonic acid monohydrate, 0.43 g (3.06mmol) and 1.08 g (7.61 mmol) of TMPi, 0.84 g (4.6 mmol) ofZn(OAc)2, and 235 mg (0.92 mmol) of AgOTf were used. Rf(CH2Cl2/hexane, 1/1) = 0.41. Yield: 15%, 19 mg. 1H NMR (500MHz, toluene-d8): δ 10.06 (bs, 2H, β-pyrrole), 10.00 (bs, 2H, β-pyrrole), 9.06 (s, 2H, meso-H), 8.73 (d, 3JH,H = 4.2 Hz, 2H, β-pyrrole),8.56 (d, 3JH,H = 4.2 Hz, 2H, β-pyrrole), 8.36 (d, 3JH,H = 4.2 Hz, 2H, β-pyrrole), 8.34 (s, 2H, meso-H), 8.16 (d, 3JH,H = 4.2 Hz, 2H, β-pyrrole),8.14 (s, 2H, meso-H), 5.51 (dd, J = 1.8 Hz, 4H, Fc), 4.65 (dd, J = 1.7Hz, 4H, Fc), 3.98 (s, 4H, CH2), 1.79 (s, 12H, CH3).

13C NMR (101MHz, toluene-d8): δ 169.04, 157.23, 153.37, 151.41, 148.03, 147.05,144.64, 144.19, 136.89, 133.19, 131.66, 126.52, 126.29, 125.28, 119.77,108.57, 96.10, 93.78, 92.68, 79.32, 70.07, 49.65, 44.53, 30.43. HRMS:calcd for C54H42Zn2FeN8 ([M]+) 990.1418, found 990.1411.General Procedure for BODIPY Preparation. To a solution of 2

or 8 in CH2Cl2 (25 mL) was added 1 or 2 equiv of DDQ in CH2Cl2 (5mL) as a single portion. The reaction mixture immediately changedcolor to dark brown. Stirring was continued for 5 min at roomtemperature. Then DIPEA (3 mL) was added and stirring wascontinued for another 5 min, after which BF3·OEt2 (3 mL) was added.The reaction was monitored by TLC. Typically, no further changeswere observed after 15 min, and at this point the reaction wasquenched by the addition of brine. The mixture was diluted with Et2Oand was washed three times with water and twice with brine. Theorganic layer was dried over MgSO4. The solid residue after theremoval of the solvent was chromatographed on silica gel.BODIPYFc. The reaction was performed using 25 mg (0.12 mmol)

2. Rf (Et2O) = 0.8. Yield: 62%, 18 mg. 1H NMR (400 MHz, CDCl3): δ7.85 (s, 2H, pyrrole), 7.65 (d, 3JH,H = 4.1 Hz, 2H, pyrrole), 6.58−6.47(m, 2H, pyrrole), 4.97 (t, J = 1.9 Hz, 2H, Fc), 4.75 (t, J = 1.9 Hz, 2H,Fc), 4.21 (s, 5H, Fc). 19F NMR (376 MHz, CDCl3): δ −145.84 (m).13C NMR (101 MHz, CDCl3): δ 146.51, 140.95, 134.86, 129.94,117.49, 79.34, 74.00, 72.18, 71.69. HRMS: calcd for C19H16BF2FeN2([M + H]+) 377.0722, found 377.0747.BODIPY2

Fc. The reaction was performed using 78 mg (0.16 mmol)of 8. Rf (Et2O) = 0.54. Yield: 3%, 3 mg. 1H NMR (400 MHz, CDCl3):δ 7.86 (s, 4H, pyrrole), 7.54 (d, 3JHH = 3.3 Hz, 4H, pyrrole), 6.48 (m,4H, pyrrole), 4.87 (s, 4H, Fc), 4.75 (s, 4H, Fc). 19F NMR (376 MHz,CDCl3): δ −145.79 (m). 13C NMR (101 MHz, CDCl3): δ 148.18,142.38, 134.79, 130.22, 118.11, 81.54, 76.70, 74.85. Repeated attemptsat HRMS analysis were unsuccessful due to sample decomposition.General Procedure for the Preparation of Free Base

Chlorins. To a solution of the Zn chlorin in dry CH2Cl2 (∼0.3 M)was added TFA (∼0.25 mL) as a single portion. The reaction mixturewas stirred at room temperature for 20 min, after which the reactionwas quenched by the addition of Et3N (1 mL), yielding a dark green toblack solution. This was directly loaded onto a silica gel column. Theproduct was eluted with a mixture of CH2Cl2 and hexane (1/1).Removal of the solvent under reduced pressure gave spectroscopicallyclean products as dark green solids.ChlFc. The reaction was performed using 10 mg (0.017 mmol) of

ZnChlFc. Rf (CH2Cl2/hexane, 1/1) = 0.44. Yield: 70%, 6.3 mg. 1HNMR (400 MHz, CDCl3): δ 10.07 (d, 3JH,H = 4.7 Hz, 1H, β-pyrrole),9.78 (s, 1H, meso-H), 9.70 (d,3JH,H = 4.3 Hz, 1H, β-pyrrole), 9.17 (d,3JH,H = 4.5 Hz, 1H, β-pyrrole), 8.94 (d, 3JH,H = 4.3 Hz, 1H, β-pyrrole),8.94 (s, 1H, meso-H), 8.87 (d, 3JH,H = 4.5 Hz, 1H, β-pyrrole), 8.83 (d,3JH,H = 4.7 Hz, 1H, β-pyrrole), 8.80 (s, 1H, meso-H), 5.53 (m, 2H,Fc), 4.80 (m, 2H, Fc), 4.58 (s, 2H, CH2), 4.23 (s, 5H, Fc), 2.04 (s, 6H,CH3), − 1.28 (bs, 1H, NH), − 1.89 (bs, 1H, NH). 13C NMR (101MHz, CDCl3): δ 175.19, 162.11, 153.67, 149.40, 141.24, 138.42,136.09, 133.41, 131.98, 131.68, 128.48, 128.24, 123.23, 122.49, 119.48,107.60, 96.79, 93.86, 76.50, 70.64, 68.76, 52.00, 31.03. HRMS: calcdfor C32H29FeN4 ([M + H]+) 525.1737, found 525.1739.(Chl)2

Fc. The reaction was performed using 8 mg (0.0081 mmol) of(ZnChl)2

Fc. Rf (CH2Cl2) = 0.7. Yield: 70%, 5 mg. 1H NMR (400MHz, CD2Cl2): δ 9.99 (d,

3JH,H = 4.6 Hz, 2H, β-pyrrole), 9.63 (d, 3JH,H= 4.3 Hz, 2H, β-pyrrole), 9.50 (s, 2H, meso-H), 9.07 (dd, 3JH,H = 4.5,4JH,H = 1.6 Hz, 2H, β-pyrrole), 8.87 (dd, 3JH,H = 4.5, 4JH,H = 1.3 Hz,2H, β-pyrrole), 8.83 (s, 2H, β-pyrrole), 8.70 (s, 2H, meso-H), 8.49 (d,

3JH,H = 4.3 Hz, 2H, β-pyrrole), 8.20 (d, 3JH,H = 4.6 Hz, 2H, β-pyrrole),5.54 (d, 3JH,H = 1.6 Hz, 4H, Fc), 4.91 (d, 3JH,H = 1.6 Hz, 4H, Fc), 4.48(s, 4H, CH2), 2.02 (s, 12H, CH3), − 1.51 (bs, 2H, NH), − 2.20 (bs,2H, NH). 13C NMR (101 MHz, CD2Cl2): δ 175.34, 162.39, 153.67,149.16, 141.09, 138.18, 136.08, 133.15, 131.70, 131.55, 128.32, 128.03,123.09, 122.38, 118.40, 107.19, 96.63, 93.97, 90.35, 79.00, 71.72,51.75, 46.03, 30.73. HRMS: calcd for C54H47FeN8 ([M + H]+)863.3269, found 863.3249.

General Procedure for Preparation of Cu Chlorins. To asolution containing 1 equiv of the free base chlorin in CH2Cl2 (15 mL)was added 5 equiv (ChlFc) or 10 equiv of Cu(OAc)2 ((Chl)2

Fc). Thereaction mixture was stirred at room temperature for 12 h, after whichthe reaction mixture was directly poured onto a silica chromatographycolumn. Elution with a mixture of CH2Cl2 and hexane (1/1) gave theproducts as bright turquoise solids after the removal of the solvents.

CuChlFc. The reaction was performed using 13 mg (0.025 mmol) ofChlFc. Rf (CH2Cl2/hexane, 1/1) = 0.61. Yield: 97%, 14 mg. HRMS:calcd for C32H26FeCuN4 ([M]+) 585.0799, found 585.0799.

(CuChl)2Fc. The reaction was performed using 10 mg (0.012 mmol)

of (Chl)2Fc. Rf (CH2Cl2/hexane, 1/1) = 0.58. Yield: 50%, 6 mg.

HRMS: calcd for C54H42FeCu2N8 ([M]+) 986.1454, found 986.1419.General Procedure for the Preparation of Pd- and Ni-

chlorins. To a solution of 1 equiv of free base chlorin in pyridine (5mL) was added 5 equiv (ChlFc) or 10 equiv ((Chl)2

Fc) of Pd(acac)2 orNi(OAc)2·4H2O. The reaction mixture was irradiated in a microwavereactor for 30 min at 180 °C. After this time the solvent was removedunder reduced pressure and the residue was extracted with CH2Cl2.Column chromatography on silica gel using a mixture of CH2Cl2 andhexane (1/1) as eluent gave bright pink (Pd) or green (Ni) solids aftersolvent removal.

PdChlFc. The reaction was performed using 13 mg (0.025 mmol) ofChlFc. Rf (CH2Cl2/hexane, 1/1) = 0.67. Yield: 30%, 4.8 mg. 1H NMR(400 MHz, CD2Cl2): δ 9.86 (d,

3JH,H = 4.7 Hz, 1H, β-pyrrole), 9.79 (d,3JH,H = 4.8 Hz, 1H, β-pyrrole), 9.62 (s, 1H, meso-H), 8.93 (d, 3JH,H =4.5 Hz, 1H, β-pyrrole), 8.88 (d, 3JH,H = 4.5 Hz, 1H), 8.70 (d, 3JH,H =4.8 Hz, 1H, β-pyrrole), 8.69 (s, 1H, meso-H), 8.65 (s, 1H, meso-H),8.59 (d, 3JH,H = 4.8 Hz, 1H, β-pyrrole), 5.37 (dd, 3JH,H = 1.8 Hz, 2H,Fc), 4.78 (dd, 3JH,H = 1.8 Hz, 2H, Fc), 4.54 (s, 2H, CH2), 4.22 (s, 5H,Fc), 2.00 (s, 6H, CH3).

13C NMR (101 MHz, CD2Cl2): δ 161.50,149.86, 145.34, 143.86, 139.30, 137.78, 137.46, 137.09, 132.63, 131.50,128.27, 126.76, 126.59, 125.66, 121.56, 109.96, 97.62, 95.23, 88.71,76.44, 70.51, 68.50, 49.80, 45.43, 30.34. HRMS: calcd forC32H26FePdN4 ([M]+) 628.0550, found 628.0555.

(PdChl)2Fc. The reaction was performed using 6 mg (0.007 mmol)

of (Chl)2Fc. Rf (CH2Cl2/hexane, 1/1) = 0.73. Yield: 20%, 1.7 mg. 1H

NMR (400 MHz, CDCl3): δ 9.70−9.62 (m, 4H, β-pyrrole), 9.10 (s,2H, meso-H), 8.66 (d, 3JH,H = 4.3 Hz, 2H, β-pyrrole), 8.57 (d, 3JH,H =4.5 Hz, 2H, β-pyrrole), 8.54 (s, 2H, meso-H), 8.35 (s, 2H, meso-H),8.10 (d, 3JH,H = 4.6 Hz, 2H, β-pyrrole), 8.03 (d, 3JH,H = 4.6 Hz, 2H, β-pyrrole), 5.40 (t, J = 1.7 Hz, 4H, Fc), 4.79 (d, J = 1.7 Hz, 4H, Fc), 4.38(s, 4H, CH2), 1.98 (s, 12H, CH3).

13C NMR (101 MHz, CDCl3): δ154.09, 149.23, 145.14, 143.74, 137.93, 137.21, 136.84, 132.51, 131.33,129.07, 127.88, 126.50, 126.39, 125.64, 125.52, 110.08, 97.58, 95.18,90.68, 79.03, 71.00, 49.94, 45.46, 29.62. HRMS: calcd forC54H42FePd2N8 ([M]+) 1070.09755, found 1070.09990.

NiChlFc. The reaction was performed using 7 mg (0.013 mmol) ofChlFc. Rf (CH2Cl2/hexane, 1/1) = 0.54. Yield: 80%, 6.2 mg. 1H NMR(400 MHz, CDCl3): δ 9.34 (d,

3JH,H = 4.7 Hz, 1H, β-pyrrole), 9.30 (d,3JH,H = 4.6 Hz, 1H, β-pyrrole), 9.08 (s, 1H, meso-H), 8.70 (d, 3JH,H =4.5 Hz, 1H, β-pyrrole), 8.56 (d, 3JH,H = 4.5 Hz, 1H, β-pyrrole), 8.39 (d,3JH,H = 4.6 Hz, 1H, β-pyrrole), 8.29 (d, 3JH,H = 4.7 Hz, 1H, β-pyrrole),8.06 (s, 1H, meso-H), 8.01 (s, 1H, meso-H), 5.08 (dd, J = 1.9 Hz, 2H,Fc), 4.64 (dd, J = 1.8 Hz, 2H, Fc), 4.05−4.03 (m, 7H, Fc+CH2), 1.79(s, 6H, CH3).

13C NMR (101 MHz, CDCl3): δ 161.06, 149.92, 146.80,145.29, 141.47, 139.14, 138.80, 138.09, 133.77, 132.72, 128.65, 127.64,127.20, 126.40, 119.72, 108.75, 95.78, 93.31, 87.36, 75.54, 70.34,68.69, 50.11, 45.98, 28.41. HRMS: calcd for C32H26FeN4Ni ([M]+)580.08549, found 580.08545.

(NiChl)2Fc. The reaction was performed using 10 mg (0.012 mmol)

of (Chl)2Fc. Rf (CH2Cl2) = 0.71. Yield: 30%, 3 mg. 1H NMR (400

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3052

MHz, CDCl3): δ 9.20 (d,3JH,H = 4.8 Hz, 2H, β-pyrrole), 9.18 (d, 3JH,H

= 4.7 Hz, 2H, β-pyrrole), 8.97 (s, 2H, meso-H), 8.65 (d, 3JH,H = 4.8Hz, 2H, β-pyrrole), 8.37 (d, 3JH,H = 4.5 Hz, 2H, β-pyrrole), 8.33 (d,3JH,H = 4.5 Hz, 2H, β-pyrrole), 8.10 (d, 3JH,H = 4.7 Hz, 2H, β-pyrrole),8.01 (s, 2H, meso-H), 7.98 (s, 2H, meso-H), 5.02 (s, 4H, Fc), 4.38 (s,4H, Fc), 4.04 (s, 4H, CH2), 1.81 (s, 12H, CH3).

13C NMR (101 MHz,CDCl3): δ 161.05, 149.98, 146.80, 145.28, 141.37, 139.11, 138.09,133.66, 132.70, 128.44, 127.72, 127.18, 126.52, 118.96, 108.77, 95.79,93.39, 88.11, 72.48, 50.13, 45.96, 28.45. HRMS: calcd forC54H42FeN8Ni2, ([M

+]) 974.15846, found 974.15920.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/acs.inorg-chem.6b03158.

Additional characterization and 1H and 13C NMR spectraof all new compounds (PDF)X-ray crystallographic data for BODIPYFc (CIF)

■ AUTHOR INFORMATIONCorresponding Author*E-mail for K.E.B.: eszter.borbas@kemi.uu.se.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was funded by the Swedish Research Council(project grant 2013-4655 to K.E.B.) and by Stiftelsen OlleEngkvist Byggmastare (postdoctoral fellowship to A.I.A.).

■ REFERENCES(1) Vecchi, A.; Erickson, N. R.; Sabin, J. R.; Floris, B.; Conte, V.;Venanzi, M.; Galloni, P.; Nemykin, V. N. Electronic properties ofmono-substituted tetraferrocenyl porphyrins in solution and on a goldsurface: Assessment of the influencing factors for photoelectrochem-ical applications. Chem. - Eur. J. 2015, 21, 269−279.(2) Lau, J. T. F.; Jiang, X.-J.; Ng, D. K. P.; Lo, P.-C. A disulfide-linkedconjugate of ferrocenyl chalcone and silicon(IV) phthalocyanine as anactivatable photosensitiser. Chem. Commun. 2013, 49, 4274−4276.(3) Tropiano, M.; Kilah, N. L.; Morten, M.; Rahman, H.; Davis, J. J.;Beer, P. D.; Faulkner, S. Reversible luminescence switching of a redox-active ferrocene-europium dyad. J. Am. Chem. Soc. 2011, 133, 11847−11849.(4) Lehr, J.; Tropiano, M.; Beer, P. D.; Faulkner, S.; Davis, J. J.Reversible redox modulation of a lanthanide emissive molecular film.Chem. Commun. 2015, 51, 6515−6517.(5) Langton, M. J.; Beer, P. D. Rotaxane and catenane host structuresfor sensing charged guest species. Acc. Chem. Res. 2014, 47, 1935−1949.(6) Nijhuis, C. A.; Ravoo, B. J.; Huskens, J.; Reinhoudt, D. N.Electrochemically controlled supramolecular systems. Coord. Chem.Rev. 2007, 251, 1761−1780.(7) Muraoka, T.; Kinbara, K.; Aida, T. Mechanical twisting of a guestby a photoresponsive host. Nature 2006, 440, 512−515.(8) Pomarico, G.; Vecchi, A.; Mandoj, F.; Bortolini, O.; Cicero, D.O.; Galloni, P.; Paolesse, R. The corrole and ferrocene marriage:5,10,15-triferrocenylcorrolato Cu. Chem. Commun. 2014, 50, 4076−4078.(9) Scottwell, S. O.; Crowley, J. D. Ferrocene-containing non-interlocked molecular machines. Chem. Commun. 2016, 52, 2451−2464.(10) Nemykin, V. N.; Purchel, A. A.; Spaeth, A. D.; Barybin, M. V.Probing the electronic properties of a trinuclear molecular wireinvolving isocyanoferrocene and iron(II) phthalocyanine motifs. Inorg.Chem. 2013, 52, 11004−11012.

(11) Samanta, S.; Mittra, K.; Sengupta, K.; Chatterjee, S.; Dey, A.Second sphere control of redox catalysis: Selective reduction of O2 toO2

− or H2O by an iron porphyrin catalyst. Inorg. Chem. 2013, 52,1443−1453.(12) Zatsikha, Y. V.; Maligaspe, E.; Purchel, A. A.; Didukh, N. O.;Wang, Y.; Kovtun, Y. P.; Blank, D. A.; Nemykin, V. N. Tuningelectronic structure, redox, and photophysical properties in asym-metric NIR-absorbing organometallic BODIPYs. Inorg. Chem. 2015,54, 7915−7928.(13) Gasser, G.; Ott, I.; Metzler-Nolte, N. Organometallic anticancercompounds. J. Med. Chem. 2011, 54, 3−25.(14) Mooney, A.; Tiedt, R.; Maghoub, T.; O’Donovan, N.; Crown, J.;White, B.; Kenny, P. T. M. Structure-activity relationship and mode ofaction of N-(6-ferrocenyl-2-naphthoyl) dipeptide ethyl esters: Novelorganometallic anticancer compounds. J. Med. Chem. 2012, 55, 5455−5466.(15) Arambula, J. F.; McCall, R.; Sidoran, K. J.; Magda, D.; Mitchell,N. A.; Bielawski, C. W.; Lynch, V. M.; Sessler, J. L.; Arumugam, K.Targeting antioxidant pathways with ferrocenylated N-heterocycliccarbene supported gold(I) complexes in A549 lung cancer cells. Chem.Sci. 2016, 7, 1245−1256.(16) Sharma, R.; Gautam, P.; Mobin, S. M.; Misra, R. β-substitutedferrocenyl porphyrins: Synthesis, structure, and properties. DaltonTrans. 2013, 42, 5539−5545.(17) Misra, R.; Dhokale, B.; Jadhav, T.; Mobin, S. M. Donor-acceptormeso-alkynylated ferrocenyl BODIPYs: Synthesis, structure, andproperties. Dalton Trans. 2013, 42, 13658−13666.(18) Omeroglu, I.; Arslan, T.; Biyiklioglu, Z.; Tosun, G. Novelphthalocyanines bearing 4-ferrocenylphenoxy substituents and theirelectrochemistry. J. Organomet. Chem. 2014, 749, 261−265.(19) Misra, R.; Dhokale, B.; Jadhav, T.; Mobin, S. M. Heteroatom-connected ferrocenyl BODIPYs: Synthesis, structure, and properties.Organometallics 2014, 33, 1867−1877.(20) Nemykin, V. N.; Galloni, P.; Floris, B.; Barrett, C. D.; Hadt, R.G.; Subbotin, R. I.; Marrani, A. G.; Zanoni, R.; Loim, N. M. Metal-freeand transition-metal tetraferrocenylporphyrins part 1: Synthesis,characterization, electronic structure, and conformational flexibility ofneutral compounds. Dalton Trans. 2008, 4233−4246.(21) Nemykin, V. N.; Rohde, G. T.; Barrett, C. D.; Hadt, R. G.;Sabin, J. R.; Reina, G.; Galloni, P.; Floris, B. Long-range electroniccommunication in free-base meso-poly(ferrocenyl)-containing por-phyrins. Inorg. Chem. 2010, 49, 7497−7509.(22) Solntsev, P. V.; Sabin, J. R.; Dammer, S. J.; Gerasimchuk, N. N.;Nemykin, V. N. Unexpected fluorescence properties in an axially σ-bonded ferrocenyl-containing porphyrin. Chem. Commun. 2010, 46,6581−6583.(23) Dammer, S. J.; Solntsev, P. V.; Sabin, J. R.; Nemykin, V. N.Synthesis, characterization, and electron-transfer processes in indiumferrocenyl-containing porphyrins and their fullerene adducts. Inorg.Chem. 2013, 52, 9496−9510.(24) Nemykin, V. N.; Dudkin, S. V.; Fathi-Rasekh, M.; Spaeth, A. D.;Rhoda, H. M.; Belosludov, R. V.; Barybin, M. V. Probing electroniccommunications in heterotrinuclear Fe-Ru-Fe molecular wires formedby ruthenium(II) tetraphenylporphyrin and isocyanoferrocene or 1,1′-diisocyanoferrocene ligands. Inorg. Chem. 2015, 54, 10711−10724.(25) Wang, H. J. H.; Jaquinod, L.; Olmstead, M. M.; Vicente, M. G.H.; Kadish, K. M.; Ou, Z.; Smith, K. M. Synthesis, characterization,and electrochemical studies of β,β′-fused metallocenoporphyrins.Inorg. Chem. 2007, 46, 2898−2913.(26) Vecchi, A.; Galloni, P.; Floris, B.; Dudkin, S. V.; Nemykin, V. N.Metallocenes meet porphyrinoids: Consequences of a ″fusion″. Coord.Chem. Rev. 2015, 291, 95−171.(27) Treibs, A.; Kreuzer, F. H. Difluoroboryl complexes of di- andtripyrrylmethenes. Justus Liebigs Ann. Chem. 1968, 718, 208−223.(28) Wagner, R. W.; Lindsey, J. S. Boron-dipyrromethene dyes forincorporation in synthetic multi-pigment light-harvesting arrays. PureAppl. Chem. 1996, 68, 1373−1380.(29) Maligaspe, E.; Pundsack, T. J.; Albert, L. M.; Zatsikha, Y. V.;Solntsev, P. V.; Blank, D. A.; Nemykin, V. N. Synthesis and charge-

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3053

transfer dynamics in a ferrocene-containing organoboryl aza-BODIPYdonor-acceptor triad with boron as the hub. Inorg. Chem. 2015, 54,4167−4174.(30) Goetsch, W. R.; Solntsev, P. V.; Van Stappen, C.; Purchel, A. A.;Dudkin, S. V.; Nemykin, V. N. Electron-transfer processes in 3,4-diferrocenylpyrroles: Insight into a missing piece of the polyferrocenyl-containing pyrroles family. Organometallics 2014, 33, 145−157.(31) Ziegler, C. J.; Chanawanno, K.; Hasheminsasab, A.; Zatsikha, Y.V.; Maligaspe, E.; Nemykin, V. N. Synthesis, redox properties, andelectronic coupling in the diferrocene aza-dipyrromethene andazaBODIPY donor-acceptor dyad with direct ferrocene-α-pyrrolebond. Inorg. Chem. 2014, 53, 4751−4755.(32) Nikkonen, T.; Moreno Oliva, M.; Taubert, S.; Melchionna, M.;Kahnt, A.; Helaja, J. Synthesis, aromaticity and photophysicalbehaviour of ferrocene- and ruthenocene-appended semisyntheticchlorin derivatives. Chem. - Eur. J. 2015, 21, 12755−12768.(33) Lindsey, J. S. De novo synthesis of gem-dialkyl chlorophyllanalogues for probing and emulating our green world. Chem. Rev.2015, 115, 6534−6620.(34) Borbas, K. E. Chlorins. In Handbook of Porphyrin Science; WorldScientific: Singapore, 2016; pp 1−149.(35) Strachan, J.-P.; O’Shea, D. F.; Balasubramanian, T.; Lindsey, J. S.Rational synthesis of meso-substituted chlorin building blocks. J. Org.Chem. 2000, 65, 3160−3172.(36) Taniguchi, M.; Ra, D.; Mo, G.; Balasubramanian, T.; Lindsey, J.S. Synthesis of meso-substituted chlorins via tetrahydrobilene-aintermediates. J. Org. Chem. 2001, 66, 7342−7354.(37) Ptaszek, M.; McDowell, B. E.; Taniguchi, M.; Kim, H.-J.;Lindsey, J. S. Sparsely substituted chlorins as core constructs inchlorophyll analogue chemistry. Part 1: Synthesis. Tetrahedron 2007,63, 3826−3839.(38) Ptaszek, M.; Bhaumik, J.; Kim, H.-J.; Taniguchi, M.; Lindsey, J.S. Refined synthesis of 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin, adeceptively simple precursor to hydroporphyrins. Org. Process Res. Dev.2005, 9, 651−659.(39) Kim, H.-J.; Dogutan, D. K.; Ptaszek, M.; Lindsey, J. S. Synthesisof hydrodipyrrins tailored for reactivity at the 1- and 9-positions.Tetrahedron 2007, 63, 37−55.(40) Benniston, A. C.; Sirbu, D.; Turta, C.; Probert, M. R.; Clegg, W.Synthesis, molecular structure and properties of a ferrocene-baseddifluoropyrrolo-oxaborole derivative. Eur. J. Inorg. Chem. 2014, 2014,6212−6219.(41) Dean, M. L.; Schmink, J. R.; Leadbeater, N. E.; Bruckner, C.Microwave-promoted insertion of group 10 metals into free baseporphyrins and chlorins: Scope and limitations. Dalton Trans. 2008,1341−1345.(42) Xiong, R.; Andres, J.; Scheffler, K.; Borbas, K. E. Synthesis andcharacterisation of lanthanide-hydroporphyrin dyads. Dalton Trans.2015, 44, 2541−2553.(43) Rao, M. R.; Kumar, K. V. P.; Ravikanth, M. Synthesis of boron-dipyrromethene-ferrocene conjugates. J. Organomet. Chem. 2010, 695,863−869.(44) Andersson, L. A.; Loehr, T. M.; Stershic, M. T.; Stolzenberg, A.M. Spectral properties of cis- and trans-metallooctaethylchlorins:Effects of pyrroline ring stereochemistry and macrocyclic conforma-tion. Inorg. Chem. 1990, 29, 2278−85.(45) Zhao, Y.; Truhlar, D. G. The M06 suite of density functionalsfor main group thermochemistry, thermochemical kinetics, non-covalent interactions, excited states, and transition elements: two newfunctionals and systematic testing of four M06-class functionals and 12other functionals. Theor. Chem. Acc. 2008, 120, 215−241.(46) Feng, L.; Slanina, Z.; Sato, S.; Yoza, K.; Tsuchiya, T.; Mizorogi,N.; Akasaka, T.; Nagase, S.; Martin, N.; Guldi, D. M. Covalently linkedporphyrin-La@C82 hybrids: Structural elucidation and investigation ofintramolecular interactions. Angew. Chem., Int. Ed. 2011, 50, 5909−5912.(47) Taniguchi, M.; Ptaszek, M.; McDowell, B. E.; Boyle, P. D.;Lindsey, J. S. Sparsely substituted chlorins as core constructs in

chlorophyll analogue chemistry. Part 3: Spectral and structuralproperties. Tetrahedron 2007, 63, 3850−3863.(48) Kee, H. L.; Kirmaier, C.; Tang, Q.; Diers, J. R.; Muthiah, C.;Taniguchi, M.; Laha, J. K.; Ptaszek, M.; Lindsey, J. S.; Bocian, D. F.;Holten, D. Effects of substituents on synthetic analogs of chlorophylls.Part 1: Synthesis, vibrational properties and excited-state decaycharacteristics. Photochem. Photobiol. 2007, 83, 1110−1124.(49) Mechanisms and dynamics of fluorescence quenching. InPrinciples of Fluorescence Spectroscopy; Lakowicz, J. R., Ed.; Springer:Boston, MA, 2006; pp 331−351.(50) Xiong, R.; Arkhypchuk, A. I.; Kovacs, D.; Orthaber, A.; Borbas,K. E. Directly linked hydroporphyrin dimers. Chem. Commun. 2016,52, 9056−9058.(51) Fuhrhop, J. H.; Kadish, K. M.; Davis, D. G. Redox behavior ofmetallo octaethylporhyrins. J. Am. Chem. Soc. 1973, 95, 5140−5147.

Inorganic Chemistry Article

DOI: 10.1021/acs.inorgchem.6b03158Inorg. Chem. 2017, 56, 3044−3054

3054