Hydro-aza-(C59N)fullerenes: Formation Mechanism and Hydrogen Substitution
Regina Eigler,[a] Frank W. Heinemann,[b] and Andreas Hirsch*[a]

Abstract: Azafullerenes are as yet the only synthetically available heterofullerenes. Herein, we present plausible reac- tion pathways towards pentaaryl azafullerenes, focusing on
the reactivity of hydro-azafullerene intermediates and their regiochemistry. The X-ray structure of a b’-hydro-tetraaryl

adduct is presented for the first time. The reactivity of dihy- dro-azafullerene adducts is demonstrated here through H- abstraction in mass spectrometric experiments. Moreover, hydride abstraction and subsequent hydroxylation is possi- ble, as well as deprotonation followed by alkylation.

Introduction

In heterofullerenes, carbon atoms of the fullerene cage are re- placed by heteroatoms. Most of the heterofullerenes reported to date have only been generated in the gas phase and de- tected by mass spectrometry.[1] As yet, the only heterofuller- enes that can be synthesized in macroscopic quantities are the mono-azafullerenes C59N 1 (Figure 1) and C69N, which are iso-

Figure 1. Structures of the C59N radical 1, the monohydride C59NH 2 (R’ =H), and the azafullerene derivatives 3 with the 6,9,12,15,18-addition pattern in- volving an isolated pyrrole substructure.

lated as stable dimers (C59N)2 and (C69N)2, respectively.[2–4] Azafullerene derivatives have been prepared and character-
ized predominantly as mono adducts C59NR 2.[5–12] However, a few oligo adducts have also been investigated. Two main ad-
dition patterns can be generated, either an octahedral addition

C60 adducts with an isolated cyclopentadiene substructure within the fullerene skeleton.[18] The latter class of azafullerene derivatives has recently been investigated as acceptor com- pounds in the context of organic photovoltaic solar cells, dem- onstrating the application potential of azafullerenes.[19–21]
In contrast to the broad variety of hydro-C60 fullerenes,[22]
the properties of hydro-azafullerenes are unexplored. The sim- plest mono adduct C59NH (2, R’ = H)[5,11] and C59NH(OOtBu)4 (3, R’ = H)[4] are the only examples of hydro-azafullerene adducts
that have been obtained on a preparative scale. A higher degree of hydrogenation was obtained for the pentahydro- azafullerene C59NH5, which was generated by in situ hydroge- nation of (C59N)2 in the gas phase using C60H36 as a hydrogena- tion agent.[23] We have recently reported that hydro-azafuller- enes with one or two hydrogen addends and four or three aryl addends, respectively (Scheme 1 a, for example, 6 and 9), can

Scheme 1. a) Schematic structures of a’,a’-dihydro azafullerene 6 and b’- hydro-azafullerene 9; b) pentaarylation reaction[17] with monoaryl adduct 2

pattern,

[13]

similar to the Th-symmetric hexakis adduct of C60,[14]

as intermediate structure using the C59N precursor 4[24] (reaction conditions: R(R’)-H, air, p-TsOH, o-DCB, 150 8C).

or a pentakis addition pattern C59NR5 3,[4,15–17] comparable to

be formed through an oligoarylation reaction sequence

[a] Dr. R. Eigler, Prof. Dr. A. Hirsch
Department Chemie und Pharmazie
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) Henkestrasse 42, 91054 Erlangen (Germany)
E-mail: [email protected]
[b] Dr. F. W. Heinemann
Department Chemie und Pharmazie
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) Egerlandstrasse 1, 91058 Erlangen (Germany)
Supporting information and ORCID from the author for this article are available on the WWW under http://dx.doi.org/10.1002/chem.201505115.

Chem. Eur. J. 2016, 22, 1 – 8 1

(Scheme 1 b).[17] However, the chemical properties of these hydro adducts, especially with regard to further hydrogen sub- stitution, have not been investigated.
Herein, we present a comprehensive study on: a) the reac- tion mechanism of the formation of dihydro-triaryl, hydro-tet- raaryl, and pentaaryl azafullerenes, b) X-ray crystal structure
analysis of a b’-H isomer of the hydro-tetraaryl adduct 9, and
c) the regiochemistry of substitution reactions of the fullerene H atoms. In particular, we demonstrate the facile hydride ab-

© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim &

straction and subsequent hydroxylation, as well as deprotona- tion followed by alkylation, of a’,a’-dihydro-azafullerene 6.

Results and Discussion
Recently, we reported the formation and isolation of the de- picted dihydro-azafullerenes 5 a–8a and hydro-azafullerenes 9a and 10 a, which are intermediates in the described pentaar- ylation reaction (Scheme 2).[17] The dihydro-triaryl azafullerenes

Scheme 2. Proposed mechanism of the pentaarylation of C59N starting from the mono adduct 2a. The protonation and arylation sequence leads to the dihydro-triaryl adducts 5a–8a through plausible reaction pathways i), ii), and iii). Further arylation under air atmosphere leads to hydro-tetraaryl adducts and finally the pentaaryl adduct 3a.

5 a–8a were generated by treatment with p-TsOH and a solu- tion of anisole in 1,2-dichlorobenzene (o-DCB) under an argon atmosphere. Under the same conditions, but in the presence of air, the reaction proceeded further to the hydro-tetraaryl azafullerenes 9a and 10 a, finally producing the pentaaryl aza- fullerene 3 a. The intermediates 5 a–10 a were isolated and characterized. The structures of 6 a, 8 a, and 3a could be un- ambiguously verified by X-ray crystallographic analysis.[17,25] The two hydro-azafullerenes 9a and 10 a were characterized by NMR spectroscopy combined with selective synthesis of the
a’-H isomer 10 a starting from the dihydro-azafullerene 6 a.[17]

Herein, we propose a detailed mechanism of the entire reac- tion sequence shown in Scheme 2. This includes the dihydro adducts 5 a–8a exhibiting different addition patterns (Scheme 2 i), ii), and iii)). The proposed reaction starts with a protonation step of the mono adduct 2 a, forming an azaful- lerene that can serve as an electrophile in a subsequent elec- trophilic aromatic substitution reaction with an aromatic com- pound, in this case anisole. This step can take place again, leading to the dihydro adducts 5 a–8a with a 6,9,12,15,18-addi- tion pattern. These intermediates already contain the addition pattern that is present in the pentaaryl adduct 3 a. The subse- quent arylation reaction of the dihydro-triaryl adducts 5 a–8a requires the abstraction of hydrogen atoms to form the hydro- tetraaryl adducts 9a and 10 a and finally the pentaaryl adduct 3a (Scheme 2).
The described dihydro and hydro adducts are intermediates in the formation of the pentaaryl adduct. Mixed pentaaryl ad- ducts can also be obtained using this type of addition chemis- try, which we demonstrate here with the synthesis of the Cs- symmetric mixed pentaaryl adduct 3 b. The corresponding re- action procedure is outlined in Scheme 3. The dihydro and

Scheme 3. Pentaarylation sequence of C59N using 1 as starting material and monoaryl adduct 2b as intermediate to form the mixed pentaaryl adduct
3b (reaction conditions: i) p-TsOH, o-DCB, microwave, 200 8C, yield: 38 %;
ii) air, p-TsOH, o-DCB, 150 8C, 10 h, yield: 19 %).

hydro adducts serve as intermediates during the formation of 3 b. The first step of the reaction is the selective synthesis of monodiphenyl azafullerene adduct 2 b. In the next step, the mixed pentaaryl adduct 3b is obtained after another fourfold arylation reaction of 2b with ethoxybenzene. The product 3b was fully characterized by mass spectrometry and IR, UV/Vis, and NMR spectroscopies.
Moreover, for the first time, we were able to crystallize the
b’-hydro isomer with phenoxyphenyl addends 9c and deter-
mine its structure by X-ray crystallography (Figure 2). Com- pound 9c was prepared from C59N precursor 4 under pentaarylation conditions with diphenyl ether as the aryl com- pound as reported previously[17] (Scheme 1), and single crystals of 9c were grown from a solution in toluene. The structure contains one toluene molecule per formula unit, and both enantiomers are present in the unit cell (Figure 2 b). One of the four phenoxyphenyl addends is disordered and two preferred orientations were refined. Hydro-azafullerene 9c shows colum- nar packing in the crystal (Figure 2 c) and the four aryl addends form a cavity that is occupied by a toluene molecule.

Figure 2. Single-crystal X-ray structure of 9c: a) chemical structure, b) ORTEP representation with ellipsoids at the 50 % probability level (C gray, N blue, O red, H white), and c) space-filling model of the packing motif (C yellow/pink, N blue, O red, H white, toluene gray); hydrogen atoms of the addends are omitted for clarity.

Recently, in the context of another arylation, we reported higher reactivity of the hydro-tetraaryl adduct 10 a with the hy-
drogen addend in the a’-position compared to that of the
hydro-tetraaryl adduct 9 a.[17] To further elucidate the chemical reactivity of dihydro-azafullerenes 5 a–8 a, we carried out fur-
ther studies on the chemical behavior of the hydrogen atoms in the a’-positions.
Under mass spectrometric conditions, the hydrogen atoms in the a’-positions of the dihydro-triaryl adduct 6a can be re-
moved. The loss of hydrogen was found to be general, and APPI-TOF high-resolution mass spectra showed a corresponding ion peak at m/z 1044 for all four dihydro adducts 5 a–8 a. The reactivity can best be demonstrated for the dihydro adduct 6a
with both hydrogen addends in the a’-positions. Thus, an addi-
tional molecular ion peak at m/z 1043 is seen for 6a due to the loss of two hydrogen addends (Figure 3).
Moreover, the reactivity of the hydrogen addend in the a’-
position can be further demonstrated by attempted dehydro- genation using Pd/C in o-DCB at high temperature. Although mass spectrometry of the crude reaction mixture indicated the formation of dehydrogenated species, no defined dehydrogen- ation products could be isolated. Nevertheless, dehydrogena- tion and subsequent hydroxylation of the dihydro-triaryl aza- fullerenes 5 a–8a using 2,3-dichloro-5,6-dicyano-1,4-benzoqui- none (DDQ) was evidently achieved for the first time (Scheme 4). Monohydroxylated and dihydroxylated azafuller- ene adducts 11 a and 12 a could be isolated from the mixture containing all four isomers 5 a–8a under the given conditions (Scheme 4). This finding can be explained in terms of hydride abstraction with DDQ and subsequent reaction with water that is present in the reaction mixture. Monohydroxylated 11 a and dihydroxylated azafullerene derivative 12 a were characterized by mass spectrometry, IR and UV/Vis spectroscopies, and NMR techniques. The dihydroxylated adduct 12 a exhibits Cs symme-

Figure 3. Reaction scheme of dihydro-triaryl azafullerene 6a under APPI-TOF MS conditions: top) high-resolution APPI-TOF mass spectrum of 6a; below) calculated spectra showing the loss of two hydrogen addends resulting in the detection of [M—2H]+ species.

Scheme 4. Hydroxylation of azafullerenes at the a’-position by hydride ab- straction using DDQ and subsequent treatment with water.

try, as demonstrated by 1H and 13C NMR spectroscopy, while adduct 11 a has C1 symmetry. NOE NMR measurements corro- borated the structure of the monohydroxylated azafullerene
11 a, with the remaining hydrogen addend in the b’-position.
This leads to the conclusion that hydride abstraction followed by the addition of OH— occurred exclusively at the a’-position.
Not only hydride abstraction but also deprotonation is possi- ble. For this purpose, Bu4NOH was used as a base,[26] and ex-
periments revealed that both a’-positions of dihydro-azafuller-
ene 6a could be deprotonated and subsequently methylated using MeI in 11 % yield (Scheme 5).
Monomethylated products could also be observed by mass spectrometry; however, no defined products could be isolated. The dimethylated azafullerene 13 a was characterized by mass

Scheme 5. Deprotonation and subsequent methylation to afford dimethylat- ed azafullerene 13 a with methyl groups in the a’-positions in 11 % isolated
yield.

spectrometry and IR, UV/Vis, and NMR spectroscopies. The HMBC 2D NMR spectrum depicted in Figure S12 shows a corre- lation peak of the methyl groups with the signal of the a-pyr-
rolic C atom. Accordingly, the methylation occurred at the a’-
position.
A distinct and unprecedented color change from orange-red to dark-green appeared on adding the base Bu4NOH to the starting material 5 a–8 a. In C60 chemistry, a deep-green color is characteristic of RC60— anions.[27,28] In particular, the UV/Vis spectrum of deprotonated 5 a–8a shows absorptions between 600 and 1200 nm (Figure 4). The generated intermediates are

Figure 4. UV/Vis spectra of dihydro adducts 5a–8a before and after addition of Bu4NOH base in degassed o-DCB and UV/Vis spectrum of 13 a, measured in CH2Cl2.

air-sensitive, which could be proven by quenching the solution with aerial oxygen, whereupon the distinct absorptions be- tween 600 nm and 1200 nm disappeared. The addition of MeI to the solution of the deprotonated species led to another color change from dark-green to red, indicating formation of the penta-adduct 13 a.

Conclusions

The reported hydro and dihydro adducts are intermediates in the described pentaarylation reaction. One plausible mecha- nism for the formation of the dihydro adducts has been re-
vealed, and X-ray structure determination of a b’-hydro-tetraar-
yl adduct has been achieved. The chemical reactivity of dihy- dro-azafullerenes has been further investigated. Such struc- tures with a 6,9,12,15,18-addition pattern and hydrogen sub-
stituents in the a’- and b’-positions show pronounced
reactivity at the a’-position. The higher reactivity of the a’-hy-
drogen addend has been demonstrated under mass spectro- metric conditions by the loss of up to two hydrogen addends from dihydro adduct 6 a. Dehydrogenation experiments on di- hydro adducts 5 a–8a with Pd/C did not lead to defined dehy- drogenation products. However, hydride abstraction using DDQ and subsequent reaction with water produced hydroxy- lated azafullerene derivatives 11 a and 12 a. Thus, substitution of the hydrogen addend by OH— occurred exclusively at the
a’-position. Additionally, deprotonation at both a’-positions
was achieved by treatment with Bu4NOH, and subsequent methylation led to the dimethylated azafullerene 13 a. Again,
deprotonation and methylation occurred at the a’-position.
Detailed experimental results demonstrate the preferred reac- tivity of dihydro-azafullerenes in terms of hydride and proton
abstraction at the a’-position.

Experimental Section
General information
Working techniques: All reagents and solvents were purchased from commercial sources (Aldrich, Acros, Fisher Scientific). Solvents were distilled prior to use, except for o-DCB and CS2, which were used as received. Toluene and ethyl acetate were distilled from po- tassium carbonate. Deuterated solvents (CDCl3, CD3OD, and [D4]-o- DCB) were purchased from Deutero or Eurisotop and HPLC grade solvents were purchased from VWR and used as obtained. C60 (99 %) was provided by io li tec nanomaterials. Reactions were monitored by thin-layer chromatography (TLC) on silica 60 F254 TLC aluminum foils (Merck). All other solvents and reagents were com- mercially available and were used as received. Products were iso- lated by column chromatography using silica gel (deactivated, 0.04–0.063 mm/230–400 mesh ASTM, Macherey–Nagel). Yields are given in percentages with respect to the reactant, which was used as one equivalent (equiv) unless otherwise noted.
NMR spectra were acquired on JEOL EX 400, JEOL Alpha 500, Bruker Avance 300, Bruker Avance 400, or Bruker Avance 600 NMR spectrometers. NMR chemical shifts (d) are given in parts per mil- lion (ppm), referenced to the solvent signals of CHCl3/CDCl3 (d=
7.24 ppm for 1H, 77.00 ppm for 13C). 1H NMR coupling constants (J) are reported in hertz (Hz) and the multiplicities of splitting patterns are indicated as follows: s (singlet), d (doublet), t (triplet), q (quar- tet), m (multiplet), br (broad signals) or a combination with the latter. All 13C NMR spectra were measured with pulse delay times of 8 s. COSY, HSQC, HMBC, and NOE experiments were conducted, when needed, to assign the 1H and 13C signals and the respective structures. Calculated 13C NMR spectra (B3LYP/6–31G(d) level) were used for comparison and assignment of the experimental 13C NMR data, especially for assignment of the signals of sp3 carbon atoms

bearing the aryl addends and for differentiation between the a- and b-pyrrolic carbon atoms. UV/Vis spectroscopy was carried out with a Varian Cary 5000 UV-Vis-NIR spectrophotometer. IR spectros- copy was conducted on a Bruker Tensor 27 or a Varian 660 FTIR spectrometer. The IR spectra were measured from samples on a ZnSe window. The signals are labeled with the following abbrevi- ations: vs (very strong), s (strong), m (medium), w (weak), vw (very weak), and br (broad). Mass spectrometry (MS) was performed on a Shimadzu AXIMA Confidence spectrometer. MALDI-TOF mass spectra were recorded using tert-2-(3-(4-tert-butyl-phenyl)-2- methyl-2-propenylidene)malononitrile (DCTB) as matrix. High-reso- lution mass spectra (HRMS) were measured on a UHR-TOF Bruker maXis 4G spectrometer using atmospheric pressure photoioniza- tion (APPI) or electrospray ionization (ESI). Mass spectra were mea- sured in positive mode unless otherwise noted. High-resolution ESI spectra of azafullerene derivatives 11 a and 12 a were acquired by the Drewello group (Universität Erlangen-Nürnberg) on a micrO- TOF-Q II from Bruker Daltonics (Bremen), a quadrupole time-of- flight (QTOF) instrument with MS/MS capability.
CCDC 1442280 (9 c) contains the supplementary crystallo- graphic data for this paper. These data are provided free of charge by The Cambridge Crystallographic Data Centre. Inten- sity data were measured from a single crystal of compound 9c

(250 mL). The brown suspension was centrifuged and the solid was washed with pentane (50 mL). The crude mixture was dissolved in the minimum volume of CS2 and purified by column chromatogra- phy on silica gel (100 g, toluene/cyclohexane, 1:3). Mono adduct 2b eluted at the solvent front as a green fraction. After evapora- tion of the solvent, reprecipitation from CS2/pentane, and drying in vacuum, 2b (35.3 mg, 40.3 mmol, 38 %) was obtained as a black solid. 1H NMR (400 MHz, CS2/CDCl3, RT): d= 8.91 (m, 2 H), 8.08 (m, 2 H), 7.78 (m, 2 H), 7.53 (m, 2 H), 7.43 ppm (m, 1 H); 13C NMR
(100 MHz, CS2/CDCl3, RT): d= 154.39 (2 C), 148.65 (2 C), 147.78 (1 C),
147.58 (4 C), 147.29 (2 C), 147.16 (2 C), 146.60 (2 C), 146.41 (2 C),
146.23 (2 C), 145.85 (3 C), 145.66 (2 C), 145.04 (2 C), 145.02 (2 C),
144.60 (2 C), 144.31 (2 C), 143.98 (2 C), 143.15 (2 C), 142.76 (2 C),
142.64 (1 C), 142.09 (2 C), 141.80 (2 C), 141.49 (2 C), 141.45 (2 C),
141.02 (2 C), 140.88 (2 C), 140.13 (1 C), 139.97 (1 C), 139.83 (2 C),
137.52 (2 C), 132.98 (2 C), 128.94 (2 C), 128.57 (2 C), 127.82 (1 C),
127.65 (2 C), 127.20 (2 C), 124.06 (2 C), 82.70 ppm (1 C); FTIR (ZnSe):
n˜ = 3058 (vw), 3006 (vw), 2957 (vw), 2851 (vw), 1581 (w), 1549 (m),
1510 (s), 1486 (m), 1422 (s), 1407 (m), 1317 (w), 1196 (w), 1183 (m),
1092 (w), 966 (w), 899 (w), 846 (m), 825 (w), 750 (vs), 719 (w),
693 cm—1 (s); UV/Vis (CH2Cl2): lmax (log e) = 259 (5.11), 322 (4.58),
443 (3.82), 551 (3.27), 590 (3.25, sh), 721 (2.97), 804 nm (3.01 L mol—1 cm—1); MS (MALDI-TOF, matrix: DCTB, CH2Cl2, neg.):
m/z: 875 [M]C—, 722 [C N]—; HRMS (APPI, toluene/MeCN): m/z calcd

with a Bruker Kappa APEX 2 ImS Duo diffractometer using MoKa
radiation (QUAZAR focusing Montel optics, l= 0.71073 Å).

for C71H9NC+

[M]C+

59
: 875.0729; found: 875.0731.

Data were corrected for Lorentz and polarization effects; semi- empirical absorption corrections were performed on the basis of multiple scans (SADABS 2008/1).[29] The structure was solved by direct methods and refined by full-matrix least-squares pro- cedures on F2 using SHELXTL NT 6.12.[30] All non-hydrogen atoms were refined anisotropically. The compound crystallized with one molecule of toluene per formula unit. One of the Ph- O-Ph units was found to be disordered. Two preferred orienta- tions were refined and resulted in site occupancies of 64.5(5) and 35.5(5) % for the atoms C90–C95 and C90 A–C95 A, respec- tively. The NC4 ring of the C59N moiety was found to be disor- dered. Atoms N1 and C1 change their positions, and the re- fined site occupancies were 56(4) and 44(4) % for N1/C1 and N1 A/C1 A, respectively. Similarity and pseudo-isotropic re- straints were applied to the anisotropic displacement ellipsoids of the disordered atoms. All hydrogen atoms were placed in positions of optimized geometry, and their isotropic displace- ment parameters were tied to those of their corresponding carrier atoms by a factor of 1.2 or 1.5.

Synthetic procedures and characterization data
Dihydro-triaryl azafullerenes 5 a–8a were synthesized according to
a literature procedure.[17] The synthetic procedure and characteriza- tion data for b’-hydro-tetraaryl azafullerene 9c can also be found
in the literature.[17]
4’-Biphenylhydroazafullerene (2 b): [60]Ketolactam 4 (90 mg,
105.2 mmol, 1 equiv) was dissolved in o-DCB (15 mL). Biphenyl (1.6 g, 10.5 mmol, 100 equiv) and p-TsOH (133 mg, 0.70 mmol, 20 equiv) were added and the mixture was heated in a microwave
oven at 200 8C for 16 h. The reaction mixture was then passed
through a column of silica gel (150 g, cyclohexane) to remove p- TsOH and biphenyl. The fraction containing mono adduct 2b (Rf = 0.88, toluene/cyclohexane, 1:3) was concentrated to dryness and residual biphenyl was removed by dissolution in methanol

9-(4’-Biphenyl)-6,12,15,18-tetrakis(4’-ethoxyphenyl)azafullerene
(3 b) and rac-b’-hydro-6-(4’-biphenyl)-9,12,15-tris(4’-ethoxyphe- nyl)azafullerene (9 b): 4’-Biphenylhydroazafullerene 2b (22 mg,
25.0 mmol, 1 equiv) was dissolved in o-DCB (10 mL). Ethoxybenzene (2 mL) and p-TsOH (95 mg, 0.5 mmol, 20 equiv) were added. The
mixture was stirred in a preheated oil bath at 150 8C, passing
a slow steady stream of air over the solution. The reaction was monitored by TLC. After 10 h, the mixture was cooled to RT and separated by column chromatography on silica gel (100 g, tolu- ene). Further purification was achieved by automated flash column chromatography on a Puri-Flash silica gel column (15 mm, 40 g,
gradient from 100 % cyclohexane to 100 % toluene). After separa- tion of residual mono adduct 2b (green band), b’-H tetraaryl
adduct 9b (Rf = 0.67, toluene) eluted as a red band and a trace of
a’-H-tetraaryl adduct 10 b (Rf = 0.67, toluene) eluted thereafter.
Pentaaryl adduct 3b (red band, Rf = 0.49, toluene) was subsequent- ly eluted using 100 % toluene. The hydro-tetraaryl adduct fractions and pentaaryl adduct fraction were concentrated to dryness and
the products were reprecipitated from CS2/pentane. After drying in vacuum, b’-H tetraaryl adduct 9b (1.1 mg, 0.9 mmol, 4 %) and
mixed pentaaryl adduct 3b (6.5 mg, 4.8 mmol, 19 %) were obtained as red solids.
9-(4’-Biphenyl)-6,12,15,18-tetrakis(4’-ethoxyphenyl)azafullerene (3 b): 1H NMR (400 MHz, CDCl3, RT): d= 7.74 (m, 2 H), 7.62 (m, 4 H),
7.54 (m, 6 H), 7.44 (m, 4 H), 7.35 (m, 1 H), 6.74 (m, 4 H), 6.70 (m, 4 H),
3.99 (q, 3J = 7.0 Hz, 4 H), 3.96 (q, 3J = 7.0 Hz, 4 H), 1.40 (t, 3J = 7.0 Hz,
6 H), 1.37 ppm (t, 3J = 7.0 Hz, 6 H); 13C NMR (100 MHz, CDCl3, RT):
d= 158.39 (2 C), 158.18 (2 C), 154.64 (2 C), 154.28 (2 C), 152.58 (2 C),
149.30 (2 C), 148.88 (2 C), 148.77 (1 C), 148.67 (2 C), 148.48 (2 C),
147.81 (2 C), 147.75 (2 C), 147.71 (2 C), 147.68 (2 C), 147.41 (2 C),
146.71 (1 C), 146.62 (2 C), 146.51 (4 C), 146.36 (2 C), 146.31 (2 C),
146.11 (2 C), 145.80 (2 C), 144.46 (2 C), 144.28 (2 C), 143.89 (2 C),
143.65 (2 C), 143.27 (2 C), 141.30 (1 C), 140.32 (1 C), 137.33 (1 C),
136.69 (2 C), 132.34 (2 C), 131.50 (2 C), 129.33 (4 C), 129.09 (4 C),
128.85 (2 C), 128.45 (2 C), 127.72 (2 C), 127.63 (1 C), 127.40 (2 C),
127.12 (2 C), 114.58 (4 C), 114.50 (4 C), 74.16 (1 C), 63.54 (4 C), 59.67
(2 C), 58.42 (2 C), 14.83 (2 C), 14.76 ppm (2 C); FTIR (ZnSe): n˜ = 3060
(vw), 3033 (w), 2978 (m), 2926 (w), 2901 (w), 2878 (w), 1609 (m),

1580 (w), 1508 (vs), 1487 (w), 1476 (m), 1458 (vw), 1418 (vw), 1391
(w), 1299 (m), 1250 (vs), 1179 (s), 1117 (m), 1088 (vw), 1047 (s),
1010 (vw), 963 (w), 923 (w), 901 (w), 839 (w), 820 (m), 803 (vw), 755
(w), 697 (vw), 658 cm—1 (w); UV/Vis (CH2Cl2): lmax (log e): 240 (5.12),
262 (5.05, sh), 276 (5.04, sh), 357 (4.42), 398 (3.97, sh), 444 (3.60,
sh), 480 (3.47), 533 nm (3.17 Lmol—1 cm—1, sh); MS (MALDI-TOF,
matrix: DCTB, CH2Cl2): m/z: 1359 [M]C+; HRMS (APPI, toluene/ MeCN): m/z calcd for C103H46NO4+ [MH]+: 1360.3421; found: 1360.3421.
rac-b’-Hydro-6-(4’-biphenyl)-9,12,15-tris(4’-ethoxyphenyl)azaful- lerene (9 b): 1H NMR (400 MHz, CDCl3, RT): d= 7.81 (m, 2 H), 7.74
(m, 2 H), 7.71 (m, 2 H), 7.53 (m, 2 H), 7.50 (m, 2 H), 7.43 (m, 2 H), 7.42
(m, 2 H), 7.34 (m, 1 H), 6.91 (m, 2 H), 6.88 (m, 2 H), 6.68 (m, 2 H), 5.71
(s, 1 H), 4.05 (q, 3J = 7.0 Hz, 2 H), 4.02 (q, 3J = 7.0 Hz, 2 H), 3.94 (q,
3J = 7.0 Hz, 2 H), 1.42 (t, 3J = 7.0 Hz, 3 H), 1.40 (t, 3J = 7.0 Hz, 3 H),
1.36 ppm (t, 3J = 7.0 Hz, 3 H). Due to a low signal-to-noise ratio, only the resolved 13C NMR signals are listed below. 13C NMR (100 MHz, CDCl3, RT): d= 158.56 (1 C), 158.33 (2 C), 128.92 (2 C), 128.83 (2 C), 128.73 (2 C), 128.46 (2 C), 127.55 (2 C), 127.38 (2 C), 127.10 (2 C), 114.90 (2 C), 114.83 (2 C), 114.53 (2 C), 74.03 (1 C), 63.54 (2 C), 63.54 (1 C), 58.68 (1 C), 58.47 (1 C), 58.32 (1 C), 45.54 (1 C), 14.86 (1 C), 14.80 (1 C), 14.75 ppm (1 C); FTIR (ZnSe): n˜ = 3361 (vw), 3059 (vw), 3031 (w), 2977 (m), 2923 (w), 2853 (w), 1659 (vw), 1633 (vw), 1609 (m), 1580 (w), 1508 (vs), 1487 (w), 1476 (w), 1458 (w), 1418 (vw), 1391 (w), 1298 (m), 1249 (s), 1178 (s), 1117 (w), 1088 (vw), 1046 (m), 1009 (vw), 957 (w), 923 (w), 903 (w), 834 (w), 820 (w), 803 (w), 756 (w), 697 (w), 658 cm—1 (w); UV/Vis (CH2Cl2): lmax (log e): 240 (5.06), 260 (5.01), 275 (4.99), 356 (4.37), 399 (3.95), 444
(3.58, sh), 480 (3.42, sh), 533 nm (3.12 Lmol—1 cm—1, sh); MS (MALDI-
TOF, matrix: DCTB, CH2Cl2): m/z: 1239 [M]C+; HRMS (APPI, toluene/ MeCN): m/z calcd for C95H38NO3+ [MH]+: 1240.2846; found: 1240.2837.
rac-b’-Hydro-6-hydroxy-9,12,18-tris(4’-methoxyphenyl)azafuller- ene (11 a) and 6,12-dihydroxy-9,12,15-tris(4’-methoxyphenyl)- azafullerene (12 a): A mixture of the four isomers of dihydrotris(4’-
methoxyphenyl)azafullerene 5 a–8a (30 mg, 28.7 mmol, 1 equiv) was dissolved in anhydrous o-DCB (10 mL) in a small heat-dried Schlenk tube. DDQ (13 mg, 57.4 mmol, 2 equiv) was dissolved in o- DCB (1 mL) and then added to the Schlenk tube. The solution was then thoroughly degassed by four cycles of vacuum treatment and
argon saturation. The reaction mixture was stirred at 608C under
argon for 7 days and then purified by column chromatography on silica gel (80 g, toluene). A trace of residual unconverted dihydro- triaryl adduct 7a eluted at the solvent front, followed by undefined adducts. Monohydroxylated product 11 a (Rf = 0.45, toluene/ethyl acetate, 9:1) was subsequently eluted with toluene/ethyl acetate (95:5) and dihydroxylated product 12 a (Rf = 0.26, toluene/ethyl acetate, 9:1) was isolated by flash column chromatography using the same eluent. The fractions were concentrated to dryness. Dihy- dro-triaryl adduct 7a (0.1 mg, 0.1 mmol, 0.4 %), monohydroxylated azafullerene 11 a (10.5 mg, 9.9 mmol, 35 %), and dihydroxylated aza-
fullerene 12 a (5.7 mg, 5.3 mmol, 19 %) were obtained as orange solids after precipitation from CS2/pentane and drying in vacuum. rac-b’-Hydro-6-hydroxy-9,12,18-tris(4’-methoxyphenyl)azafuller- ene (11 a): 1H NMR (400 MHz, CDCl3, RT): d= 8.01 (m, 2 H), 7.89 (m, 2 H), 7.60 (m, 2 H), 7.00 (m, 2 H), 6.88 (m, 2 H), 6.83 (m, 2 H), 5.53 (s,
1 H), 3.85 (s, 3 H), 3.83 (s, 3 H), 3.81 (s, 3 H), 3.31 ppm (s, 1 H);
13C NMR (100 MHz, CS2/CDCl3, RT): d= 159.61 (1 C), 158.90 (1 C),
158.86 (1 C), 157.90 (1 C), 154.82 (1 C), 152.16 (1 C), 151.00 (1 C),
150.34 (1 C), 149.56 (1 C), 148.84 (1 C), 148.65 (2 C), 148.64 (1 C),
148.51 (1 C), 148.45 (1 C), 148.43 (1 C), 148.06 (1 C), 147.77 (1 C),
147.70 (1 C), 147.45 (1 C), 147.44 (1 C), 147.37 (1 C), 147.35 (1 C),
147.33 (1 C), 147.29 (1 C), 147.05 (1 C), 146.92 (1 C), 146.90 (1 C),

146.87 (1 C), 146.72 (1 C), 146.35 (1 C), 146.19 (1 C), 146.08 (1 C),
146.02 (1 C), 146.00 (1 C), 145.98 (1 C), 145.91 (1 C), 145.39 (1 C),
145.09 (1 C), 145.06 (1 C), 145.01 (1 C), 144.84 (1 C), 144.33 (1 C),
144.18 (1 C), 144.09 (2 C), 143.74 (1 C), 143.64 (1 C), 143.27 (1 C),
143.16 (1 C), 143.05 (1 C), 142.86 (1 C), 142.81 (1 C), 135.52 (1 C),
133.84 (1 C), 132.43 (1 C), 132.36 (1 C), 131.27 (1 C), 129.61 (1 C),
128.68 (2 C), 128.54 (2 C), 128.21 (2 C), 123.70 (1 C), 114.33 (2 C),
114.16 (2 C), 114.14 (2 C), 73.50 (1 C), 72.95 (1 C), 58.87 (1 C), 58.22
(1 C), 54.92 (1 C), 54.89 (1 C), 54.86 (1 C), 45.37 ppm (1 C); FTIR
(ZnSe): n˜ = 3418 (w, br), 2952 (w), 2926 (m), 2853 (vw), 2833 (vw),
1606 (w), 1581 (vw), 1509 (vs), 1459 (m), 1439 (vw), 1418 (vw),
1299 (w), 1251 (s), 1178 (s), 1110 (vw), 1032 (m), 960 (vw), 906 (vw),
839 (m), 815 (w), 754 (vw), 650 cm—1 (w); UV/Vis (CH2Cl2): lmax =
237, 261 (sh), 277, 356, 400 (sh), 443 (sh), 480, 533 nm (sh); MS (MALDI-TOF, matrix: DCTB, CH2Cl2): m/z: 1061 [M]C+, 1044
[M OH]+; HRMS (ESI-TOF, CH2Cl2/MeOH, 2:3, NaCl): m/z calcd for C80H23NO4NaC+ [M+Na]+: 1084.1519; found: 1084.1487; MS/MS: m/z calcd for C80H22NO3+ [M—OH]+: 1044.1594; found: 1044.1482.
6,12-Dihydroxy-9,12,15-tris(4’-methoxyphenyl)azafullerene
(12 a): 1H NMR (400 MHz, CDCl3, RT): d= 8.25 (m, 2 H), 7.83 (m, 4 H),
7.09 (m, 2 H), 6.88 (m, 4 H), 3.87 (s, 3 H), 3.80 (s, 6 H), 3.44 ppm (s,
2 H); 13C NMR (100 MHz, CDCl3, RT): d= 160.23 (1 C), 159.06 (2 C),
157.70 (2 C), 150.50 (2 C), 150.23 (2 C), 149.23 (1 C), 149.01 (2 C),
148.78 (2 C), 148.33 (2 C), 147.84 (2 C), 147.42 (4 C), 147.37 (2 C),
147.17 (2 C), 146.94 (2 C), 146.45 (2 C), 146.34 (1 C), 146.19 (2 C),
146.01 (2 C), 145.80 (2 C), 145.14 (2 C), 145.09 (2 C), 144.46 (2 C),
143.73 (2 C), 143.49 (2 C), 143.42 (2 C), 143.19 (2 C), 143.17 (2 C),
134.13 (2 C), 132.33 (2 C), 132.12 (2 C), 130.25 (1 C), 129.09 (2 C),
128.89 (4 C), 114.79 (2 C), 114.36 (4 C), 73.85 (3 C), 59.10 (2 C), 55.50
(1 C), 55.41 ppm (2 C); FTIR (ZnSe): n˜ = 3386 (w, br), 2995 (vw), 2926
(w), 2852 (w), 2832 (w), 1605 (w), 1580 (vw), 1509 (vs), 1459 (m),
1439 (w), 1419 (w), 1298 (w), 1251 (s), 1179 (s), 1103 (w), 1028 (m),
972 (vw), 958 (vw), 906 (w), 839 (w), 814 (w), 794 (vw), 770 (vw),
757 (vw), 650 cm—1 (w); UV/Vis (CH2Cl2): lmax (log e): 237 (4.98), 260
(4.85, sh), 278 (4.84), 352 (4.24), 400 (3.90, sh), 444 (3.51, sh), 480 (3.35), 533 nm (3.06 Lmol—1 cm—1, sh); MS (MALDI-TOF, matrix:
DCTB, CH2Cl2): m/z: 1077 [M]C+, 1060 [M—OH]+, 1044 [M—2 OH+H]+; HRMS (ESI-TOF, CH2Cl2/MeOH, 2:3, NaCl): m/z calcd for C80H23NO5Na+ [M+Na]+: 1100.1468; found: 1100.1416; MS/MS:
m/z calcd for C80H22NO4+ [M—OH]+: 1060.1543; found: 1060.1356.
9,12,15-Tris(4’-methoxyphenyl)-6,12-dimethylazafullerene (13 a): A mixture of the four isomers of dihydrotris(4’-methoxyphenyl)aza-
fullerene 5 a–8a (20 mg, 19.1 mmol, 1 equiv) was dissolved in anhy- drous o-DCB (5 mL) in a heat-dried Schlenk tube. The solution was then thoroughly degassed by four pump-freeze-thaw cycles. A
0.1 M solution of Bu4NOH in methanol (40 mL, 40.1 mmol, 2.1 equiv)
was added to the solution under argon, resulting in a color change from orange to dark-green. Methyl iodide (27 mg, 11.9 mL, 191 mmol, 10 equiv) was added to the stirred reaction mixture after 10 min, whereupon a color change from dark-green to red oc- curred. The reaction mixture was then purified by column chroma- tography on silica gel (20 g, toluene). Dimethylated azafullerene derivative 13 a (Rf = 0.79, toluene/ethyl acetate, 9:1) was obtained as a first fraction. Subsequent fractions contained monomethylated
dihydro-triaryl adducts that could only be characterized by MS (MALDI-TOF, matrix: DCTB, CH2Cl2): m/z: 1059 [M]C+. The dimethyl- triaryl adduct fraction was concentrated to dryness and azafuller- ene 13 a (2.3 mg, 2.1 mmol, 11 %) was obtained as a red solid after drying in vacuum. 1H NMR (400 MHz, CDCl3, RT): d= 7.94 (m, 2 H), 7.84 (m, 4 H), 7.09 (m, 2 H), 6.91 (m, 4 H), 3.89 (s, 3 H), 3.83 (s, 6 H),
2.17 ppm (s, 6 H); 13C NMR (100 MHz, CDCl3, RT): d= 159.76 (1 C),
158.90 (2 C), 155.36 (2 C), 154.75 (2 C), 152.86 (2 C), 150.29 (2 C),
149.59 (2 C), 148.79 (2 C), 148.75 (1 C), 148.54 (2 C), 147.76 (2 C),

147.67 (2 C), 147.66 (2 C), 147.60 (2 C), 147.41 (2 C), 146.47 (1 C),
146.36 (2 C), 146.32 (2 C), 146.30 (2 C), 146.14 (2 C), 145.84 (2 C),
145.78 (2 C), 144.44 (2 C), 144.29 (2 C), 143.81 (2 C), 143.51 (2 C),
143.29 (2 C), 141.97 (2 C), 138.22 (2 C), 132.95 (2 C), 131.16 (1 C),
128.93 (4 C), 127.11 (2 C), 127.11 (2 C), 114.67 (2 C), 114.23 (4 C),
76.12 (1 C), 59.45 (2 C), 55.47 (1 C), 55.42 (2 C), 51.23 (2 C),
26.10 ppm (2 C); FTIR (ZnSe): n˜ = 3062 (vw), 3033 (vw), 2995 (w),
2925 (m), 2855 (vw), 2833 (vw), 1607 (w), 1581 (vw), 1509 (vs),
1459 (m), 1418 (w), 1299 (w), 1252 (s), 1178 (s), 1114 (vw), 1036 (m),
907 (vw), 835 (m), 819 (w), 801 (w), 650 cm—1 (vw); UV/Vis (CH2Cl2):
lmax (log e): 238 (4.97), 260 (4.86, sh), 276 (4.83), 357 (4.29), 398
(3.91), 444 (3.55, sh), 478 (3.40), 533 nm (3.08 Lmol—1 cm—1, sh); MS (MALDI-TOF, matrix: DCTB, CH2Cl2): m/z: 1073 [M]C+, 1058
[M CH3]C+; HRMS (APPI, CH2Cl2/toluene/MeCN): m/z calcd for
C+ C+

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Acknowledgements

This work was supported by the SFB 953 and the Graduate School of Molecular Science of the Friedrich-Alexander-Univer- sität Erlangen-Nürnberg (FAU).

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Received: December 21, 2015
Revised: May 12, 2016
Published online on && &&, 0000

FULL PAPER
& Azafullerene Derivatization
R. Eigler, F. W. Heinemann, A. Hirsch*
&& – &&
Hydro-aza-(C59N)fullerenes: Formation Mechanism and Hydrogen Substitution

Regioselectivity in hydro-azafullerene reactions: The reactivity of hydro-aza- fullerene intermediates en route to pen- taaryl derivatives has been explored. Ex- perimental results have shown that both hydride and proton abstraction
occur preferentially at the a’-positions
of dihydro-azafullerenes.