Alkylation of nitrogen heterocycles with 1,3-bis(hydroxymethyl)ferrocene. Generation of the ferrocene dicarbocation [{1,3-(CH2) 2C5H3}Fe(C5H5)] 2+

Article abstract of DOI:10.1007/s11172-010-0361-3

The alkylation of imidazole and 5-benzyloxycarbonyl-3,4-diethylpyrrole with 1,3-bis-(hydroxymethyl)ferrocene (1) afforded bis-imidazole (4) and bis-pyrrole (7) derivatives of ferrocene, respectively. The reaction of diol 1 with trifluoroacetic acid gave t

Full text of DOI:10.1007/s11172-010-0361-3

Russian Chemical Bulletin, International Edition, Vol. 59, No. 11, pp. 2098—2101, November, 2010
2098
Alkylation of nitrogen heterocycles with 1,3ꢀbis(hydroxymethyl)ferrocene.
Generation of the ferrocene dicarbocation [{1,3ꢀ(CH2)2C5H3}Fe(C5H5)]2+
D. M. Panov,a A. V. Polezhaev,a A. V. Polukeev,a P. V. Petrovskii,a and A. A. Koridzea,b
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. Eꢀmail: koridze@ineos.ac.ru
bInstitute of Metalloorganic Chemistry, I. Javakhishvili Tbilisi State University,
3 Chavchavadze Avenue, 0128 Tbilisi, Georgia.
Fax: (995 32) 22 5107
The alkylation of imidazole and 5ꢀbenzyloxycarbonylꢀ3,4ꢀdiethylpyrrole with 1,3ꢀbisꢀ
(hydroxymethyl)ferrocene (1) afforded bisꢀimidazole (4) and bisꢀpyrrole (7) derivatives of
ferrocene, respectively. The reaction of diol 1 with trifluoroacetic acid gave the dicarbocationic
complex [{1,3ꢀ(CH2)2C5H3}Fe(C5H5)]2+ (2) characterized by 1H NMR spectroscopy.
Key words: ferrocene, (ferroceneꢀ1,3ꢀdiyl)dimethylium, imidazole, pyrrole, ferrocenylꢀ
methylation.
Previously,1 we have reported on the phosphorylation
of 1,3ꢀbis(hydroxymethyl)ferrocene (1) giving ferrocene
diphosphines {1,3ꢀ(R2PCH2)2C5H3}Fe(C5H5) (R = Pri,
But). The latter were used as the starting compounds for
the synthesis of P,C,P pincer complexes with the ferrocene
backbone. Rhodium,1 palladium,2,3 iridium,4 and rutheꢀ
nium5 bis(phosphine) pincer complexes with the ferrocene
or ruthenocene backbone are presently known. These comꢀ
plexes have attracted interest due to their ability to actiꢀ
vate small molecules and hydrocarbon substrates and catꢀ
alyze a variety of reactions, among which of great imporꢀ
tance is the homogeneous dehydrogenation. Recently,4 it
has been shown that the iridium complex IrH2[{2,5ꢀ
(But2CH2)2C5H2}Fe(C5H5)] is the most active catalyst for
alkane dehydrogenation among all known homogeneous
systems.
The chemistry of metalloceneꢀbased pincer complexes
is in its infancy. In the future, it is necessary to use in
a greater extent the potential of these systems conditioned
by the sandwich geometry of metallocenes and the ability
to vary the metallocene central atom and its oxidation
state in the case of the iron atom in ferrocene. It would
expect that pincer complexes having the metallocene backꢀ
bone would be used for the creation of new generation
polymetallic catalysts and materials having useful photoꢀ
physical and sensor properties. The progress in this area is
related to the development of convenient methods for
the synthesis of functionalized 1,3ꢀdisubstituted metalꢀ
locenes,3—9 which are nowadays much more difficult to
synthesize compared to 1,1´ꢀ and 1,2ꢀdisubstituted anaꢀ
logs. It is also necessary to design pincer ligands containꢀ
ing donor atoms other than phosphorus, for example, carꢀ
bon atoms of Nꢀheterocyclic carbenes and nitrogen atoms
of Nꢀheterocycles.
In the present study, we describe the first results on the
synthesis of precursors of new types of pincer ligands based
on ferrocene. The alkylation of imidazole and substituted
pyrrole with diol 1 afforded the diimidazole and dipyrrole
derivatives of ferrocene, respectively.
Results and Discussion
The ferrocenylmethylation can be performed with the
use of ferrocenylmethyl halides (rather unstable comꢀ
pounds), ferrocenylcarbinols, or ferrocenylmethylammoꢀ
nium salts.10 These reactions proceed through the formaꢀ
tion of αꢀferrocenyl carbocations, whose enhanced stabilꢀ
ity is well known.11 The ferrocene carbocations were charꢀ
1
acterized by H, 13C, and 57Fe NMR spectroscopy. The
most stable of them, as well as their ruthenium and osmiꢀ
um analogs, were isolated as crystalline salts and were
studied by Xꢀray diffraction.11,12 Unlike ferrocene monoꢀ
carbocations, ferrocene 1,1´ꢀ and 1,2ꢀdicarbocations are
substantially less stable.13,14 The latter ions are generated
from the corresponding carbinols at low temperatures
with the use of superacids, such as FSO3H—SbF5
or CF3SO3H—oleum. It should be noted that ferrocene
1,3ꢀdicarbocations have not been observed previously.
In the present study, diol 1 was used as the alkylating
agent in the reactions with heterocycles and it was of inꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2045—2047, November, 2010.
1066ꢀ5285/10/5911ꢀ2098 © 2010 Springer Science+Business Media, Inc.

Novel 1,3ꢀdisubstituted ferrocene compounds
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 11, November, 2010 2099
Scheme 2
terest to characterize the corresponding dicarbocationic
complex [{1,3ꢀ(CH2)2C5H3}Fe(C5H5)]2+ (2).
We found that complex 2 is generated in the reaction
of diol 1 with trifluoroacetic acid at room temperature
(Scheme 1).
Scheme 1
Scheme 3
The reaction was carried out directly in an NMR tube
by adding the acid to a solution of the diol in CDCl3. The
1H NMR spectrum, which was recorded immediately after
the addition of the acid, unambiguously indicates that
complex 2 was formed in quantitative yield. The 1H NMR
spectrum shows singlets for the cyclopentadienyl protons
at δ 4.22 (5 H, C5H5), 4.40 (2 H, H(3), H(4)), and
4.47 (1 H, H(2)) and for four methylene protons at δ 5.13
(4 H, CH2). All signals are rather narrow, without
evidence of the broadening, except for the signal for
the methylene protons, which is slightly broadened at
the base of the peak due apparently to the unresolved
spinꢀspin coupling. Dicarbocation 2 appeared to be
not quite stable. At room temperature, it quite rapidly
decomposes in the aboveꢀmentioned solution. It should
be noted that the metallocene dicarbocations observed
previously belong to either tertiary ions13 or polyalkylꢀ
metallocene ions.14 Unlike these ions, primary dicarboꢀ
cation 2 does not contain substituents stabilizing the posiꢀ
tive charge at the carbocationic center or in the cycloꢀ
pentadienyl rings.
The ferrocenylmethylation of the pyrrole moiety with
diol 1 was performed by an example of the reaction of
compound 6. We chose pyrrole 6 because we intended to
use product 7 formed in this reaction (Scheme 4) for the
design of porphyrinoid system containing the ferrocene
unit included in the macrocycle. Under mild conditions,
the benzyl protecting group can be removed from dipyrrole
derivative 7, and the aromatic diacid thus obtained can be
Scheme 4
The alkylation of imidazole 3 with diol 1 was carried
out by refluxing in acetic acid. Diimidazole derivative 4
was obtained in 58% yield (Scheme 2) and was isolated as
yellow needles.
The quaternization of compound 4 with methyl iodide
afforded salt 5 in 89% yield (Scheme 3).
1
Complexes 4 and 5 were characterized by H NMR
spectroscopy and elemental analysis. Salt 5 is the starting
compound for the preparation of the C,C,Cꢀbis(Nꢀheteroꢀ
cyclic) carbene pincer ligand.

2100
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 11, November, 2010
Panov et al.
(t, 1 H, subst. Cp, J = 1.5 Hz); 7.68—7.69 (m, 2 H, imidazole);
7.77—7.78 (m, 2 H, imidazole); 9.14 (s, 2 H, imidazole).
Found (%): C, 36.99; H, 4.15; N, 8.11. C20H24FeI2N4•H2O.
Calculated (%): C, 37.06; H, 4.04; N, 8.64.
1,3ꢀBis[5ꢀ(benzyloxycarbonyl)ꢀ3,4ꢀdiethylpyrrolꢀ2ꢀyl)methyl]ꢀ
ferrocene (7). A. A solution of diol 1 (0.125 g, 0.51 mmol), pyrꢀ
role 6 (0.250 g, 0.97 mmol), and TsOH (0.050 g) in anhydrous
ethanol was refluxed under argon for 3 h. The reaction mixture
was evaporated to dryness. The residue was chromatographed
on an aluminum oxide column with the use of dichloromethane
as the eluent. After the recrystallization, dipyrrole 3 was obꢀ
tained as a yellow powder in a yield of 0.19 g (51%).
B. Bentonite Kꢀ10 (1.33 g) was added to a solution of diol 1
(0.125 g, 0.51 mmol) and pyrrole 6 (0.250 g, 0.97 mmol) in
dichloromethane (30 mL). The suspension was stirred under
argon at ~20 °C for 3 h. The reaction mixture was filtered, the
filtrate was evaporated to dryness, and dipyrrole 7 was obtained
in a yield of 0.296 g (81%), m.p. 125—127 °C. 1H NMR (CDCl3),
δ: 1.07 (t, 6 H, CH3CH2, J = 7.4 Hz); 1.14 (t, 6 H, CH2CH3,
J = 7.4 Hz); 2.40 (q, 4 H, CH2CH3, J = 7.4 Hz); 2.73 (q, 4 H,
CH2CH3, J = 7.4 Hz); 3.55 (s, 4 H, pyrroleꢀCH2); 4.10 (s, 3 H,
subst. Cp); 4.17 (s, 5 H, Cp); 5.28 (s, 4 H, PhCH2); 7.29—7.41
(br.m, 10 H, H arom.); 8.88 (br.s, 2 H, NH). 13C NMR (CDCl3),
δ: 15.8, 16.1 (CH3CH2); 16.9, 18.2 (CH3CH2); 25.7 (pyrroleꢀ
CH2); 65.4 (PhCH2); 68.1, 68.9, 69.7, 85.1 (Cp, subst.
Cp); 115.9, 122.8, 131.9, 133.7 (pyrrole); 127.8, 128.0, 128.4,
136.4 (Ph); 160.9 (CO2). Found (%): C, 72.68; H, 6.33;
N, 3.83. C44H48FeN2O4. Calculated (%): C, 72.93; H, 6.08;
N, 3.87.
decarboxylated and involved in the "3+1" condensaꢀ
tion with dicarbonyl derivatives of various aromatic
or heterocyclic systems. Previously,15 it has been noted
that pyrrole derivatives related to compound 7 offer wide
possibilities for the synthesis of various carbaporphyꢀ
rinoid systems according to the 3+1 condensation, which
is a versatile approach providing high yields of carbaporꢀ
phyrins.
pꢀToluenesulfonic acid and Bentonite Kꢀ10 were used
as catalysts in the synthesis of compound 7. The product
was obtained in a yield of the 51 and 81%, respectively, as
a yellow crystalline compound. Compound 7 was characꢀ
1
terized by H and 13C NMR spectroscopy and elemental
analysis.
In summary, we characterized for the first time the
ferrocene dicarbocation generated from 1,3ꢀbis(hydrꢀ
oxymethyl)ferrocene 1. The reactions of diol 1 with imidꢀ
azole 3 and pyrrole 6 in an acidic medium afforded
diimidazole derivative 4 and dipyrrole derivative 7, resꢀ
pectively.
Experimental
All starting compounds and solvents were dried and purified
before use according to standard procedures. Diol 1 (see Ref. 1)
and substituted pyrrole 6 (see Ref. 16) were synthesized accordꢀ
1
ing to known procedures. The H and 13C NMR spectra were
recorded on a Bruker Avanceꢀ400 spectrometer (400.13 MHz
for 1H and 100.25 MHz for 13C). Elemental analysis was carried
out in the Laboratory of Microanalysis of the A. N. Nesmeyanov
Institute of Organoelement Compounds of the Russian Acadeꢀ
my of Sciences.
References
1. A. A. Koridze, A. M. Sheloumov, S. A. Kuklin, V. Yu. Laꢀ
gunova, I. I. Petukhova, F. M. Dolgushin, M. E. Ezerꢀ
nitskaya, P. V. Petrovskii, A. A. Macharashvili, R. V. Chedia,
Izv. Akad. Nauk, Ser. Khim., 2002, 988 [Russ. Chem. Bull.,
Int. Ed., 2002, 51, 1077].
2. A. A. Koridze, S. A. Kuklin, A. M. Sheloumov, F. M. Dolꢀ
gushin, V. Yu. Lagunova, I. I. Petukhova, M. G. Ezerꢀ
nitskaya, A. S. Peregudov, P. V. Petrovskii, E. V. Vorontsov,
M. Baya, R. Poli, Organometallics, 2004, 23, 4585.
3. S. A. Kuklin, F. M. Dolgushin, P. V. Petrovskii, A. A. Koꢀ
ridze, Izv. Akad. Nauk, Ser. Khim., 2006, 1879 [Russ. Chem.
Bull., Int. Ed., 2006, 55, 1950].
4. S. A. Kuklin, A. M. Sheloumov, F. M. Dolgushin, M. G.
Ezernitskaya, A. S. Peregudov, P. V. Petrovskii, A. A. Koꢀ
ridze, Organometallics, 2006, 25, 5466.
5. A. M. Sheloumov, F. M. Dolgushin, M. V. Kondrashev,
P. V. Petrovskii, Kh. A. Barbakadze, O. I. Lekashvili, A. A.
Koridze, Izv. Akad. Nauk, Ser. Khim., 2007, 1695 [Russ.
Chem. Bull., Int. Ed., 2007, 56, 1757].
1,3ꢀBis[(1Hꢀimidazolꢀ1ꢀyl)methyl]ferrocene (4). A solution
of diol 1 (0.23 g, 0.94 mmol) and imidazole 3 (0.38 g, 5.56 mmol)
in glacial AcOH (5 mL) was refluxed under argon for 4 h. The
reaction mixture was evaporated to dryness, and the residue was
dissolved in methanol (5 mL). Then potassium carbonate (0.5 g)
was added. The reaction mixture was stirred for ~14 h,
poured into water (20 mL), and extracted with dichloromethane
(2×50 mL). The combined extracts were dried over MgSO4, the
solution was concentrated to ~10 mL, and diethyl ether (~50 mL)
was added. The precipitate that formed was filtered off and
washed with hexane. Compound 4 was obtained as small yellow
needleꢀlike crystals in a yield of 0.19 g (58%), m.p. 145—148 °C.
1H NMR (CDCl3), δ: 4.09 (s, 5 H, Cp); 4.17 (m, 3 H, subst. Cp);
4.77 (s, 4 H, CH2); 6.85 (s, 2 H, imidazole); 6.99 (s, 2 H, imidꢀ
azole); 7.43 (s, 2 H, imidazole). Found (%): C, 60.96; H, 4.93;
N, 15.03. C18H18FeN4•CH3OH. Calculated (%): C, 60.33;
H, 5.86; N, 14.81.
1,1´ꢀ[Ferroceneꢀ1,3ꢀdiylbis(methylene)]bis(3ꢀmethylꢀ1Hꢀ
imidazolium) diiodide (5). Methyl iodide (1 mL) was added to
a solution of compound 4 (0.19 g, 0.55 mmol) in MeCN (10 mL).
The reaction mixture was stirred at ~20 °C in the dark under
argon for 3 days. The solution was evaporated to dryness. The
residue was recrystallized from a methanol—diethyl ether mixꢀ
ture. Salt 5 was obtained as a yellow powder in a yield of 0.31 g
6. R. Butler, B. Woldt, M.ꢀZ. Oh, D. J. Williams, Inorg. Chem.
Commun., 2006, 9, 1255.
7. M. Steurer, Y. Wang, K. Mereiter, W. Weissensteiner,
Organometallics, 2007, 26, 3850.
8. C. Pichon, B. Odell, J. M. Brown, Chem. Commun.,
2004, 598.
9. S. V. Safronov, A. M. Sheloumov, A. Z. Kreindlin, A. A.
Kamyshova, F. M. Dolgushin, A. F. Smol´yakov, P. V. Petroꢀ
vskii, M. E. Ezernitskaya, A. A. Koridze, Izv. Akad. Nauk,
1
(89%), m.p. 160 °C. H NMR (DMSOꢀd6), δ: 3.84 (s, 6 H,
CH3); 4.31 (s, 5 H, Cp); 4.54 (d, 2 H, subst. Cp, J = 1.5 Hz); 4.70

Novel 1,3ꢀdisubstituted ferrocene compounds
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 11, November, 2010 2101
Ser. Khim., 2010, 1694 [Russ. Chem. Bull., Int. Ed., 2010,
59, No. 9].
10. Ferrocenes. Homogeneous Catalysis. Organic Synthesis. Mateꢀ
rials Science, Eds A. Togni, T. Hayashi, WileyꢀVCH, Weinꢀ
heim, 1995.
14. M. I. Rybinskaya, A. Z. Kreindlin, P. V. Petrovskii, R. M.
Minyaev, R. Hoffmann, Organometallics, 1994, 13, 3903.
15. T. D. Lash, Eur. J. Org. Chem., 2007, 5461.
16. T. D. Lash, J. R. Belletini, J. A. Bandian, K. B. Couch,
Synthesis, 1994, 2, 170.
11. A. A. Koridze, Usp. Khim., 1986, 55, 277 [Russ. Chem. Rev.
(Engl. Transl.), 1986, 55, 113].
12. S. Barlow, A. Cowley, J.ꢀC. Green, T.ꢀJ. Brunker, T. Hasꢀ
call, Organometallics, 2001, 20, 5351.
Received June 7, 2010;
13. C. U. Pittman, Tetrahedron Lett., 1967, 3619.
in revised form September 6, 2010