Synthesis of metallocarbonyl substituted 1,2,3- triazole complexes via copper(I)-catalyzed azide- alkyne cycloaddition

Article abstract of DOI:10.1139/V10-107

(ν₅-C⁵H⁵)M(CO)^x(ν ₁-N-maleimidato) (M = Fe, x = 2; M = W, x = 3) complexes react with propargylamine and propargyl alcohol giving products from the Michael addition to the ν₁-N-maleimidato

Full text of DOI:10.1139/V10-107

991
Synthesis of metallocarbonyl substituted 1,2,3-
triazole complexes via copper(I)-catalyzed azide–
alkyne cycloaddition
Bogna Rudolf
Abstract: (h5-C5H5)M(CO)x(h1-N-maleimidato) (M = Fe, x = 2; M = W, x = 3) complexes react with propargylamine and
propargyl alcohol giving products from the Michael addition to the h1-N-maleimidato ligand. Metallocarbonyl compounds
bearing a terminal alkyne group were reacted with organic azides affording corresponding 1,2,3-triazoles in high yields.
One of these metallocarbonyl 1,2,3-triazoles (M = Fe, x = 2) was characterized by X-ray diffraction.
Key words: copper(I)-catalyzed azide–alkyne cycloaddition, click chemistry, metallocarbonyl complexes, X-ray structure.
5
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Resume : Les complexes (h -C5H5)M(CO)x(h -N-maleimidato) (M = Fe, x = 2; M = W, x = 3) reagissent avec la propar-
1
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gylamine et l’alcool propargylique pour conduire a la formation de produits d’addition de Michael sur le ligand h -N-ma-
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leimidato. La reaction de composes metallocarbonyles portant un groupe alcyne terminal avec des azotures organiques
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conduit a la formation des 1,2,3-triazoles correspondants avec des rendements eleves. Faisant appel a la diffraction des
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rayons-X, on a caracterise le metallocarbonyl-1,2,3-triazole dans lequel M = Fe et x = 2.
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Mots-cles : cycloaddition azoture–alcyne catalysee par le cuivre(I), chimie de cliquage, complexes metallocarbonyles,
structure, diffraction des rayons X.
It appeared of interest to introduce a terminal alkyne
group to compounds 1 or 2 to form metallocarbonyl com-
plexes that would be able to react with organic azides. Such
a process could be an entry to new selective labeling of bio-
molecules, using the CuAAC reaction. In this paper, I report
the synthesis of two new metallocarbonyl complexes bearing
terminal alkyne ligands, 3 and 4, and a preliminary study of
their reactions with organic azide derivatives in the presence
of a Cu(I) catalyst. The structure of the 1,3-cycloaddition
product, 5, has been established by a single crystal X-ray
analysis.
Introduction
The copper(I) catalyzed, regioselective synthesis of 1,4-
disubstitututed-1,2,3-triazoles, from azides and terminal al-
kynes, which was developed by Sharpless et al., has been
shown to be amongst the most popular reactions recently
studied, known as ‘‘click chemistry’’1–3. There have been
numerous applications of this reaction in the fields of bio-
conjugation, materials science, and drug discovery.4–7 Cop-
per(I)-catalyzed azide–alkyne cycloaddition (CuAAC) has
been used to obtain conjugates which possess numerous
functional subunits with fluorescent or electrochemical prop-
erties.8,9 However, this methodology has not yet been ap-
plied to connecting metallocarbonyl complexes with organic
ligands. In view of this situation, I became interested in
exploring the CuAAC reaction as a synthetic method for
preparating 1,4-disubstitututed-1,2,3-triazoles bearing IR-
detectable metallocarbonyl complexes.10 Over the past years
we have explored the chemistry of the metallocarbonyl (h5-
C5H5)M(CO)x(h1-N-maleimidato) complexes of Fe, 1, and
W, 2,11,12 which were applied as labels of peptides and pro-
teins, with potential applications in immunoassay analysis.12–16
Results and discussion
The Huisgen 1,3-cycloaddition of organic azides and al-
kynes has been shown to be the most direct route to obtaining
1,2,3-triazoles. The use of Cu(I) complexes in this process led
to the formation of one regioisomer, a 1,4-disubstituted 1,2,3-
triazole derivative. Cu(I) halide salts can also be used, or,
alternatively, the Cu(I) complex could be generated in situ
by the reduction of Cu(II) salts.1–3 The reaction could be
performed in various solvents or mixtures of organic sol-
vents, or in water. Owing to the high regioselectivity, high
yields, and an exceptional tolerance towards a wide range
of functional groups and reaction conditions, the copper(I)-
catalyzed azide–alkyne cycloaddition has been found to
have numerous applications in biochemistry research, allow-
ing the regioselective incorporation of various labels to bio-
molecules.17–20
Received 21 May 2010. Accepted 29 June 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on 8 September
2010.
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B. Rudolf. Department of Organic Chemistry, University of Łodz, Tamka 12, Łodz 91-403, Poland.
(e-mail: brudolf@chemia.uni.lodz.pl).
Can. J. Chem. 88: 991–995 (2010)
doi:10.1139/V10-107
Published by NRC Research Press

992
Can. J. Chem. Vol. 88, 2010
There has been no reported research concerning the Huis-
gen 1,3-cycloaddition of metallocarbonyl complexes in the
literature, to my knowledge; however, there were several
published examples of ferrocene compounds bearing azide
or alkyne groups, which underwent the CuAAC reactions
leading to the expected triazole products.21–25 To investigate
the CuAAC reaction of metallocarbonyl complexes with
azides, it was first necessary to synthesize such complexes,
bearing an alkyne group.
Because complex 1 reacted with primary amines at pH 9–10
providing aza-Michael addition products,13 the reaction with
propargylamine seemed a straightforward synthetic approach
for the introduction of the terminal alkyne function to this
complex (eq. [1])
½3ꢀ
The yellow products, 5 and 6, were isolated by flash chro-
matography and crystallized from CH2Cl2–heptane. The
identity and purity of these compounds were confirmed by
spectroscopic methods and elemental analyses. The singlets
1
in the H NMR spectra of 5 and 6 (d 8.06 and 7.51 ppm,
respectively) were attributed to the triazole ring protons,
and provided evidence of the formation of this heterocyclic
ring. The structure of 1,2,3-triazole 5 was also confirmed by
single crystal X-ray diffraction (vide infra).
The 1,2,3-triazole, 7, was synthesized in the same manner
from alkyne complex 4 and p-nitrophenyl azide in the pres-
ence of the CuCl–Cu catalyst (eq. [4]). The expected prod-
uct was isolated in 81% yield, as an orange oil. The lack of
an alkyne proton signal and the appearance of a singlet at d
8.19 ppm in its H NMR spectrum provided evidence of the
formation of a 1,2,3-triazole derivative.
½1ꢀ
1
The reaction was carried out at room temperature in
MeOH–H2O, and afforded a yellow crystalline product. The
1H NMR spectrum confirmed the structure of 3, with the
signal at 6.68 ppm, characteristic of the ethylenic protons in
1, being absent, while the complex signals attributed to the
succinimide ring and the propargyl protons were observed
at 2.42, 3.33, and 3.83, including the acetylene proton sig-
nal, which appeared at 2.09 ppm, as a triplet.
Since it was reported that maleimide derivatives undergo
an oxa-Michael addition reaction with alcohols in the pres-
ence of K2CO3 under mild reaction conditions,26 I decided
to react 2 with propargyl alcohol, to give 4 (eq. [2]). This
reaction resulted in the isolation of a yellow crystalline com-
½4ꢀ
The X-ray crystal structure of 5
Crystals of 5 suitable for X-ray structure determination
were grown from CH2Cl2–heptane. Compound 5 crystallized
in the triclinic P1 space group (see Fig. 1 for the graphical
representation). The selected crystal data and structure re-
finement details are shown in Table 1. The triazole p-nitro-
phenyl substituent was shown to be attached to the
succinimide ring in a position opposite to the Fp moiety.
The best plane of the succimidato ring forms an angle of
44.02(19)8 with the best plane of the Cp ring. The succini-
midato ring was nearly coplanar with the triazole and p-ni-
trophenyl rings. This was shown by the relatively small
values of the dihedral angles, being 9.00(19)8 and
15.87(18)8 for the triazole and phenyl rings, respectively.
The triazole and phenyl rings were found to be coplanar,
with the dihedral angle being 8.61(12)8. No classical hydro-
gen bonds were found for this compound; however, the crys-
1
plex, whose H NMR spectrum confirmed the structure as 4
(Yield 42%)
½2ꢀ
The 1H NMR spectrum showed a triplet at 2.48 ppm,
which was expected for the alkyne proton, with an absence
of the singlet at ~6.7 ppm, characteristic for the olefinic pro-
tons in the substrate, 2. Further evidence of the oxa-Michael
addition to the maleimide double bond were the signals of
the succinimide protons at 2.66, 3.03, and 4.48 ppm.
Metallocarbonyl complexes, 3 and 4, displayed the char-
acteristic strong absorption bands in their IR spectra, the
nC:O appearing in the 1950–2060 cm–1 spectral region,
which is usually free of any absorption of biomolecules or
biological matrices.
With the successful synthesis of complexes 3 and 4, their
reactivity towards organic azides in the presence of a CuCl–
Cu catalyst were investigated. Both compounds were al-
lowed to react with p-nitrophenyl azide, and complex 3 was
also reacted with (phenylthio)methyl azide. In all cases, the
cycloaddition reaction took place, and the expected triazoles,
5–7, were isolated in 81%–88% yields (eqs. [3] and [4]).
tal structure of
5 was stabilized by several weak
intermolecular, non-covalent interactions of the C–HꢁꢁꢁO
type.
˚
Selected bond lengths (A) and angles (8) are gathered in
Table 2.
Conclusions
The metallocarbonyl complexes 3 and 4, with terminal al-
kyne bonds, have been synthesized, and found to be effec-
tive CuAAC reaction substrates. Under the Sharpless
conditions, the alkynes 3 and 4 effectively reacted with
selected organic azides, affording the corresponding 1,2,3-
triazoles in high yields. We plan to use this technique to de-
velop new bioprobes for Carbonyl Metallo Immuno Assay
(CMIA).
Published by NRC Research Press

Rudolf
993
Fig. 1. ORTEP drawing of compound 5 with the atom-labelling scheme. Displacements ellipsoids are drawn at the 50% probability level.
H atoms are omitted for clarity.
˚
Table 1. Crystallographic data and structure refine-
ment of 5.
Table 2. Bond lengths (A) and angles (8)
for 5.
Chemical formula
C20 H16FeN6O6
293 K
0.71073
˚
Bond lengths (A)
Measurement temperature
Fe(1)—C(6)
Fe(1)—C(7)
Fe(1)—N(1)
Fe(1)—C(1)
C(8)—O(3)
C(10)—N(2)
C(10a)—N(2a)
C(11)—O(4)
C(12A—N(2A)
C(12A)—(C13)
N(1)—C(8)
1.781(2)
1.783 (2)
1.9773(15)
2.083(2)
1.212(3)
1.450(12)
1.451(9)
1.209(2)
1.450(9)
1.523(5)
1.363(2)
1.302(3)
1.349(2)
1.417(2)
1.134(3)
˚
Beam length l (A)
Space group
P1
˚
a (A)
6.6833(3)
11.9347(7)
12.4586(6)
79.417(3)
84.442(3)
85.386(3)
970.25(9)
2
˚
b (A)
˚
c (A)
˚
a (A)
˚
b (A)
˚
g (A)
3
˚
V (A )
Z
Absorption coefficient (mm–1)
Independent reflections
0.83
N(3)—N(4)
N(4)—N(5)
N(5)—C(15)
O(2)—C(7)
5794, 4644
0.6914, 0.7461
0.70
0.0000, 0.0362
0.0426, 0.0568
0.1122
Tmin, Tmax
(sin q/l)max (A )
–1
˚
R(int), R(sigma)
R1 [I > 2s (I)], R1 all
wR2 all
Bond angles (8)
C(7)–Fe(1)–C(1)
C(7)–Fe(1)–N(1)
C(11)–N(1)–Fe(1)
C(20)–C(15)–N(5)
N(2)–C(12)–C(13)
N(2A)–C(10A)–C(11)
N(4)–N(5)–C(15)
O(2)–C(7)–Fe(1)
O(4)–C(11)–C(10)
O(5)–N(6)–C(18)
O(5)–N(6)–O(6)
88.96(9)
95.55(8)
120.72(13)
118.31(17)
112.5(6)
Goodness-of-fit
1.060
Experimental section
113.3(5)
General remarks
118.88(16)
174.19(18)
123.6(2)
118.28(17)
123.84(17)
1
The H NMR spectra were recorded in CDCl3 on a Varian
1
Gemini 200BB (200 MHz for H) spectrometer and refer-
enced to internal tetramethylsilane. The IR spectra were re-
corded in CHCl3 on a FTIR NEXUS (Thermo Nicolet)
spectrometer. Elemental analyses were performed by the
Analytical Services of the Center of Molecular and Macro-
molecular Studies of the Polish Academy of the Sciences
Materials
´ ´
(Łodz). All solvents were purified according to standard pro-
Complexes 1 and 2 were synthesized as previously de-
scribed.11,12 Propargylamine, propargyl alcohol, and (phenyl-
thio)methyl azide were purchased from Sigma-Aldrich.
Propargyl alcohol and propargylamine were distilled before
cedures. Chromatographic separations were performed on
Silica gel Merck 60 (230–400 mesh ASTM). All reactions
were carried out under argon.
Published by NRC Research Press

994
Can. J. Chem. Vol. 88, 2010
from CH2Cl2–heptane (2:1) gave an analytically pure sam-
ple.
use. p-Nitrophenyl azide was synthesized according to
Meudtner and al.27
5 Yield: 45 mg (84%). IR n (cm–1): 2045, 1999 (C:O),
1
1636 (CO imide), 1525, 1343 (NO2). H NMR (200 MHz,
Synthesis of 3
CDCl3) d (ppm): 2.45 (dd, J = 5 Hz, J = 16 Hz, H, succini-
mide), 2.85 (dd, J = 8.2 Hz, J = 16 Hz, H, succinimide),
3.72 (dd, J = 5 Hz, J = 8 Hz, H, succinimide), 4.06 (s, 2H,
CH2), 5.04 (s, 5H, Cp), 7.97 (d, J = 9.1 Hz, 2H), 8.06 (s,
triazole H), 8.41 (d, J = 9.1 Hz, 2H). Anal. calcd. for
C20H16FeN6O6: C 48.80, H 3.28, N 17.07; found: C 48.69,
H 3.41, N 16.89.
Propargylamine (20 ml, 0.37 mmol) and aqueous solution
of K2CO3 pH 9–10 (2 mL) were added to an argon-saturated
solution of complex 1 (100 mg, 0.37 mmol) in MeOH
(3 mL) and the reaction mixture was stirred overnight at rt.
After this time the mixture was diluted with water (15 mL)
and extracted with CH2Cl2 (3 ꢂ 15 mL). The organic phases
were combined, dried over MgSO4, and concentrated under
reduced pressure. The residue was subjected to column chro-
matography; a yellow band containing the starting material 1
was eluted with dichloromethane, followed by a yellow band
containing product 3 eluted with chloroform–MeOH (9:1).
Crystallization from CH2Cl2–heptane (3:1) gave an analyti-
cally pure sample;.yield: 57 mg (47%). IR n (cm–1): 3290
(CH alkyne), 2103 (C:C), 2056, 2009 (C:O), 1639 (CO
6 Yield: 47 mg (88%).IR n (cm–1): 2044, 1993 (C:O),
1636 (CO imide). 1H NMR (200 MHz, CDCl3) d (ppm):
2.38 (dd, J = 5 Hz, J = 18 Hz, H, succinimide), 2.79 (dd, J =
8 Hz, J = 16 Hz, H, succinimide), 3.60 (dd, J = 5 Hz, J =
8 Hz, H, succinimide), 3.91 (s, 2H, CH2), 5.03 (s, 5H, Cp),
5.61 (s, CH2, H), 7.31 (s, 5H), 7.51 (s, triazole H). Anal.
calcd. for C21H19FeN5O4: C 51.13, H 3.88, N14.20; found C
50.98, H 4.17, N 14.23.
1
imide). H NMR (200 MHz, CDCl3) d (ppm): 2.09 (t, J =
7 Yield: 58 mg 81%.IR n (cm–1): 2037, 1932 (C:O),
1636 (CO imide). 1H NMR (200 MHz, CDCl3) d (ppm):
2.66 (dd, J = 4.8 Hz, J = 18 Hz, H, succinimide), 3.04 (dd,
J = 8.3 Hz, J = 20 Hz, H, succinimide), 4.44 (dd, J =
4.8 Hz, J = 8 Hz, H, succinimide), 5.07 (dd, J = 12.5 Hz,
2H, CH2), 5.64 (s, 5H, Cp), 7.98 (d, J = 9 Hz, 2H), 8.19 (s,
H, =CH), 8.43 (d, J = 9 Hz, 2H), 8.06 (s, triazole H). ESI–
MS (M+Na) m/z = 672. Anal. calcd. for C21H15N5O8W: C
38.85, H 2.33, N 10.79; found C39.05, H 2.28 .
1.4 Hz, H,CH, alkyne), 2.42 (dd, J = 5.1 Hz, J = 16 Hz, H,
succinimide), 2.83 (dd, J = 7.9 Hz, J = 16 Hz, H, succini-
mide), 3.33 (d, J = 17 Hz, H, CH2), 3.58 (d, J = 17 Hz, H,
CH2), 3.83 (dd, J = 5.1 Hz, J= 16 Hz, H, succinimide), 5.04
(s, 5H, Cp). Anal. calcd. for C14H12FeN2O4:C 54.24, H 3.66,
N 8.54; found C 51.42, H 3.61, N 8.49.
Synthesis of 4
Tungsten complex 2 (120 mg, 0.29 mmol) was dissolved
in propargyl alcohol (3 mL) and a saturated aqueous solu-
tion of K2CO3 (2 mL) was added. Then the reaction mixture
was stirred overnight at rt. After this time, the mixture was
diluted with water (15 mL) and extracted with CH2Cl2 (3 ꢂ
15 mL). The organic phases were combined, dried over
MgSO4, and concentrated at reduced pressure. The residue
was subjected to column chromatography; an orange band
containing the starting material 2 was eluted with hexane–
dichloromethane (1:4), followed by a yellow band containing
product 4 eluted by the mixture of dichloromethane–MeOH
19:1. Crystallization from CH2Cl2–heptane (3:1) gave in an-
alytically pure sample; yield: 59 mg (42%). IR n (cm–1):
3307 (CH alkyne), 2100 (C:C), 2056, 2046, 1959 (C:O),
1655 (CO imide). 1H NMR (200 MHz, CDCl3) d (ppm):
2.48 (t, J = 2.4 Hz, H, CH alkyne), 2.66 (dd, J = 4.6 Hz, J =
20 Hz, H, succinimide), 3.03 (dd, J = 9.2 Hz, J = 16 Hz, H,
succinimide), 4.48 (dd, J = 4.6 Hz, J = 20 Hz, H, succini-
mide), 4.53 (t, 2H, CH2, J = 4 Hz, H, CH2), 5.64 (s, 5H,
Cp). Anal. calcd. for C15H11NO6W:C 37.14, H 2.29, N
2.89; found C 37.25,H 2.47, N 2.89.
X-ray structure determination of 5
Single-crystal X-ray measurement of 5 was performed on
a BRUKER APEX II ULTRAk-axis diffractometer with a
TXS rotating anode using MoKa radiation at 293 K. The
data were collected using the omega scan measurement
method, with 0.5 degrees scan width and 30s maximal
counting time. The q angle for data collection was varied in
the range of 5.00–20.008. The data were corrected with re-
spect to Lorentz and polarization effects. An analytical ab-
sorption correction was applied using SADABS.28 Indexing,
integration, and scaling were performed with original Bruker
Apex II software.29 The structure was solved using direct
methods and refined using SHELXL.30 The refinement was
based on F2 for all reflections. Weighted R factors wR and
all goodness-of-fit S values were based on F2. All non-hy-
drogen atoms were refined anisotropically. Hydrogen atoms
were refined on idealized positions using a riding model.
Supplementary data
Supplementary data for this article are available on the
journal Web site (canjchem.nrc.ca). CCDC 763118 contains
the X-ray data in CIF format for this manuscript. These data
can be obtained, free of charge, via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
Synthesis of metallocarbonyl 1,2,3 -triazoles 5–7
A typical procedure for the 1,3-dipolar cycloaddition of
organic azides to metallocarbonyl alkynes was as follows:
azide (0.11 mmol), CuCl (2 mg), and Cu (50 mg as thin
wire) were added to a solution of 3 or 4 (0.11 mmol) in the
mixture of H2O–tert-butanol (1:1). Then the reaction mix-
ture was stirred overnight. The resulting solution was fil-
tered and concentrated under reduced pressure. The residue
was diluted in CH2Cl2 and crude product was chromato-
graphed on silica gel, using the mixture of MeOH–CH2Cl2
(1:19) as eluent to obtain compounds 5–7. Crystallization
Acknowledgements
Dr. Damian Plaz
˙uk is gratefully acknowledged for the
synthesis of p-nitrophenylazide. The Polish Ministry of Sci-
Published by NRC Research Press

Rudolf
995
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(15) Fischer-Durand, N.; Salmain, M.; Rudolf, B.; Juge, L.; Guer-
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support (Grant PBZ-KBN 118/T09/12).
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