Syntheses and NMR and XRD studies of carbohydrate-ferrocene conjugates

Article abstract of DOI:10.1039/c9nj01563a

Carbohydrate-ferrocene conjugates were synthesized and showed that the ferrocene entity appeared to be confined to a low volume so that proton NMR spectroscopy revealed 3 to 4 signals for substituted cyclopentadienyl instead of two usually.

Full text of DOI:10.1039/c9nj01563a

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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DOI: 10.1039/C9NJ01563A
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Syntheses, NMR and XRD studies of carbohydrate-ferrocene
conjugates
Received 00th January 20xx,
Accepted 00th January 20xx
Fanny Peigneguy,[a] Magali Allain,[a,b] Charles Cougnon, [a] Pierre Frère, [a] Benjamin Siegler, [b]
Christine Bressy, [c] and Frédéric Gohier[a]*
DOI: 10.1039/x0xx00000x
Carbohydrate-ferrocene conjugates were synthesized and showed can lead to conformations in which the hydrogen in alpha
that the ferrocene entity appeared to be confined to a low volume position of the substitution becomes magnetically
so that proton NMR spectroscopy revealed 3 to 4 signals for different.[14]
substituted cyclopentadienyl instead of two usually.
N
N
N
N
Fe
Fe
N
Introduction
N
O
O
O
HO
HO
O
HO
HO
CH3
OH
Ferrocenes are entities that have attracted a lot of interest
since their appearance in the middle of the 20th century. They
are present in a wide range of applications integrated in
miscellaneous structures involving an important investment in
the design and the synthesis [1]. Ferrocene has been
associated with carbohydrates to target biological activities,
[2-4] molecular recognition [5] or as a redox detector. [6] They
can be synthesized via side chains containing triazole, amide,
carboxylate, boronate [7], thioether moieties [8].
Transacetalisation is another way to link ferrocene and
carbohydrate [9]. The structures obtained can be complex and
the NMR tool can be very valuable in elucidating certain
conformations. [10-11] Studies on the free rotation of
cyclopentadienyl rings around the Cp-Fe-cp axis have attracted
attention and depending on substitution, eclipsed and
staggered conformations are stable. [1] NMR spectroscopic
studies usually show that alpha and beta hydrogens are
equivalent to two to two and that their chemical shifts depend
on the substituent as shown on chalcones linked to ferrocenes.
[12] Longitudinal relaxation times on the carbons of
substituted cyclopentadienyl have also been measured.
Relaxation time is depending on the degree of mobility of the
cyclopentadienyl ring, ie faster with bulky substituent. [13] The
association of ferrocene with groups such as carbohydrates
OH
R
R = H, F, NO2, NH2
Figure 1. Substituted carbohydrate-ferrocene conjugates.
In the context of our research work on active antifouling
compounds, we have synthesized a series of compounds in
which ferrocene was bound to glucose via a triazole link. The
substitution on anomeric position was varied to study the
influence of substituents on NMR spectroscopic properties and
on the solid state organization.
Experimental
Tosyl chloride, sodium azide, ethynylferrocene, sodium
ascorbate and CuSO4.5H2O were purchased from Aldrich and 1
from Combi-Blocks. 2 was prepared from glucose. [15] 3 and 5
were prepared from 2 using BF3.Et2O in DCM under Ar
atmosphere. [16] 4 was prepared from 1 using Ag2CO3 as
catalyst [17] and 6, 7, 8 and 9 were obtained using MeONa in
methanol. [18] All the compounds obtained have the same
spectroscopic characteristics as those obtained in literature.
Characterizations of the isolated products were carried out in
CDCl3 or (CD3)2SO at 25°C. Chemical shifts are reported in ppm
relative to the solvent residual value: δ=7.26 (CDCl3), 2.50
1
((CD3)2SO) for H NMR and δ= 77.16 (CDCl3), 39.52 ((CD3)2SO)
for 13C NMR. NMR spectra were recorded on a Bruker Avance
300 (1H: 300.1 MHz, 13C: 75.7 MHz, T = 300 K). Spectra were
referenced against the internal NMR-solvent standard.
Chemical shifts were expressed in parts per million (ppm) and
were reported as s (singlet), d (doublet), t (triplet), m
(multiplet) and coupling constants J were given in Hz. Mass
a. MOLTECH-Anjou, UMR 6200, CNRS, UNIV Angers,2 bd Lavoisier, 49045 ANGERS
Cedex, France.
b. SFR MATRIX, UFR Sciences, UNIV Angers, 2 bd Lavoisier, 49045 ANGERS Cedex,
France.
c. Laboratoire Matériaux Polymères-Interfaces-Environnement Marin (MAPIEM EA
4323), Université de Toulon, CS 60584, 83041 Toulon cedex 9, France.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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spectra were recorded under EI mode on a VG-Autospec mass 6-Deoxy-6-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)-1-phenyl--D-
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DOI: 10.1039/C9NJ01563A
spectrometer. The main peaks are described according to m/z. glucopyranose 14 Yield: 17 %. Mp: 166-167°C. H NMR
The peak corresponding to molecular mass is expressed as (300MHz, DMSO-d6): δ = 7.95 (s, 1H, triazole-H), 7.12 (dd, J =
(M+•). Analytical grade solvents were used.
7.4 and J = 8.4 Hz, 2H, Ar-H), 6.91 (t, J = 7.4 Hz, 1H, Ar-H), 6.76
6
Formation of azide derivatives (10 and 12) (general (dd, J = 1.0 and J = 8.4 Hz, 2H, Ar-H), 5.53 (d, J = 5.4 Hz, 1H,
procedure): Azide derivative was prepared from alcohol in two OH), 5.41 (d, J = 5.0Hz, 1H, OH), 5.27 (d, J = 4.9 Hz, 1H, OH),
steps. To a solution of glucose derivative (10.4 mmol, 1equiv) 4.82 (d, J = 7.6 Hz, 1H, H-1), 4.76 (d, J = 2.1 and J = 14.3 Hz,
in pyridine (26 ml), was added tosyl chloride (13.6 mmol, 1.3 1H,), 4.68 (m, 1H, Cp-H), 4.55 (m, 1H, Cp-H), 4.41 (dd, J = 9.0
equiv) in portions at 0°C. Once the addition is finished, the and J = 14.3 Hz, 1H, CH2), 4.29 (m, 2H, Cp-H), 3.99 (s, 5H, Cp-H),
reaction mixture was stirred at room temperature overnight. 3.86 (m, 1H, CH), 3.30 (m, 2H, CH), 3.15 (m, 1H). 13C NMR (76
Then, the residue was extracted with ethyl acetate and MHz, DMSO): δ = 157.1, 145.0, 129.2, 121.9, 121.5, 116.2,
washed with water and brine. The organic solution was dried 100.3, 76.1, 74.3, 73.1, 71.3, 69.2, 69.2, 68.1, 66.4, 66.3, 50.9.
over MgSO4 and evaporated at reduced pressure. The crude IR (cm-1): 3292, 1232, 1108 and 1026. HRMS (EI) calculated for
product was purified by flash column chromatography to give C24H25FeN3O5 m/z 491.1144; found 491.1137.
the desired product as a brown solid. The tosylated derivative 6-Deoxy-6-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)-1-(4-
(1.96 mmol, 1equiv) was then directly engaged. It is dissolved nitrophenyl)--D-glucopyranose 15 Yield: 69%. Mp 187.2°C-
in anhydrous DMF (7mL), sodium azide (7.86 mmol, 4equiv) 201°C. 1H NMR (300MHz, DMSO-d6): δ = 7.99 (d, J = 9.3Hz, 2H,
was then added. The solution becomes yellow. The mixture Ar-H), 7.90 (s, 1H, Ar-H), 6.92 (d, J=9.3Hz, 2H, Ar-H), 5.61 (d, J =
was stirred overnight at 70°C. Once the mixture was cooled to 5.4Hz, 1H, OH), 5.57 (d, J = 4.9Hz, 1H, OH), 5.37 (d, J = 4.9Hz,
room temperature, the residue was diluted with ethyl acetate 1H, OH), 5.10 (d, J = 7.5Hz, 1H, H-1), 4.78 (dd, J= 2.1 Hz, J =
and washed several times with brine and dried over MgSO4. 14.3Hz, 1H, H-6), 4.68-4.66 (m, 1H, Cp-H), 4.47-4.46 (m, 1H,
The organic phase was filtered and concentrated in vacuo. Cp-H), 4.38 (m, 1H, H-6), 4.28 (m, 1H, Cp-H), 4.23 (m, 1H, Cp-
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Purification by column chromatography gave
compound.
a
white H), 3.96 (m, 1H, H-5), 3.95 (s, 5H, Cp-H), 3.33 (m, 2H, H-2 and
H-3), 3.22-3.18 (m, 1H, H-4). 13C NMR (300MHz, DMSO-d6): δ =
Phenyl 6-azido-6-deoxy--D-glucopyranose 10. Yield 68 % 161.9, 145, 141.6, 125.5, 121.8, 116.4, 99.3, 76, 75.9, 74.4,
(from tosylate derivative). Mp 98-99 °C. H NMR (300 MHz, 72.9, 71.3, 69.1, 68.2, 68.1, 66.3, 50.9. IR (cm-1): 3533, 3117,
1
DMSO-d6) δ 7.30 (m, 2H, H-arom), 7.02 (m, 3H, H-arom), 5.42 2881, 1657, 1591, 1513, 1493, 1342, 1244, 1062. HRMS (FAB+)
(d, J = 4.8 Hz, 1H, OH), 5.31 (d, J = 5.4 Hz, 1H, OH), 5.21 (d, J = calculated for C24H24FeN4O7 m/z 536.0994; found 536.0993.
6-Deoxy-6-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)-1-(4-fluorophenyl)--D-
4.6 Hz, 1H, OH), 4.95 (d, J = 7.4 Hz, 1H, H-1), 3.59 (m, 1H, H-5),
1
glucopyranose 16 Yield: 55%. Mp 209-211°C. H NMR (300 MHz,
DMSO-d6) δ 7.95 (s, 1H, triazole-H), 6.90 (m, 2H, H-arom), 6.78
(m, 2H, H-arom), 5.53 (d, J = 5.4 Hz, 1H, OH), 5.42 (d, J = 5.0 Hz,
1H, OH), 5.28 (d, J = 4.9 Hz, 1H, OH), 4.76 (m, 2H, H-1 and H-6),
4.68 (m, 1H; Cp-H), 4.57 (m, 1H, Cp-H), 4.41 (m, 1H, H-6 ), 4.30
(m, 2H, Cp-H), 3.98 (s, 5H, Cp-H), 3.83 (m, 1H, H-5), 3.25 (m,
1H, H-3), 3.16 (m, 2H, H-2 and H-4). 13C NMR (76 MHz, DMSO)
δ = 157.2 (d, J = 237 Hz), 153.3 (d, J = 2 Hz), 153.3, 145.0,
121.7, 117.9, 117.8, 115.8, 115.5, 100.8, 76.1, 76.1, 74.3, 73.1,
71.3, 69.2, 68.2, 68.2, 66.3, 66.3, 50.9. IR (cm-1): 3297, 1506,
1169, 1106 and 1033. HRMS (FAB+) calculated for
C24H24FFeN3O5 m/z 509.1049; found 509.1046.
3.45 (m, 2H, H-6 and H-7), 3.28 (m, 2H, H-2 and H-3), 3.15 (s,
1H, H-4). 13C NMR (76 MHz, DMSO) δ = 157.2, 129.4, 122.0,
116.3, 100.2, 76.1, 75.1, 73.2, 70.6, 51.4. IR (cm-1): 2092, 1590,
1491, 1220 and 1064 cm-1.HRMS (FAB neg): calculated for
C12H15N3O5 m/z 280.0933, found 280.0930.
4-fluorophenyl 6-azido-6-deoxy--D-glucopyranose 12. Yield
1
98 % (from tosylate derivative). Mp °C. H NMR (499 MHz,
DMSO-d6) : δ = 7.12 (m, 2H, H-arom), 7.06 (m, 2H, H-arom),
5.42 (d, J = 4.7 Hz, 1H, OH), 5.30 (d, J = 5.5 Hz, 1H, OH), 5.19 (d,
J = 4.6 Hz, 1H, OH), 4.91 (d, J = 7.2 Hz, 1H, H-1), 3.58 (m, 1H, H-
5), 3.44 (m, 2H, H-6 and H-7), 3.27 (m, 2H, H-2 and H-3), 3.13
(m, 1H, H-4). 13C NMR (76 MHz, DMSO-d6) δ = 157.4 (d, J = 237
Hz), 153.5 (d, J = 2 Hz), 118.0 (d, J = 8 Hz), 115.8 (d, J = 23 Hz),
100.8 , 76.0 , 75.1 , 73.1 , 70.6 , 51.4. IR (cm-1): cm-1.HRMS
(FAB neg): calculated for C12H13FN3O5 m/z 298.0839, found
298.0837.
Formation of triazole ring (14, 15, 16 and 17) (general
procedure): To a solution of azide glucose (3.8 mmol, 1 equiv)
in mixture DMF:H2O (20 mL, 3:1), ethynylferrocene (4.18
mmol, 1.1eq), sodium ascorbate (3 mmol, 0.8 equiv,) and
CuSO4.5H2O (1.52 mmol, 0.4eq,) were added at room
temperature. The reaction mixture was stirred at room
temperature overnight. The mixture was poured into
saturated NH4Cl solution, and then extracted with EtOAc and
washed with NaCl. The organic phase was concentrated under
reduced pressure. The crude product was purified by flash
column chromatography (AcOEt/EtOH, 100:0 to 95:5) to give
the desired product.
6-Deoxy-6-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)-1methyl--D-
1
glucopyranose 17 Yield: . Mp. 219-220°C. H NMR (300MHz,
DMSO-d6): δ = 8.12 (s, 1H, H-triazole), 5.38 (d, 1H, J = 5.8 Hz,
OH), 4.94 (d, 1H, J = 5.0 Hz, OH), 4.83 (d, 1H, J = 6.4 Hz, OH),
4.73 (m, 2H, H-Cp), 4.71 (dd, 1H, J = 2.1 Hz and J = 14.1 Hz, H-
6’), 4.54 (d, 1H, J = 3.6 Hz, H-1), 4.38 (dd, 1H, J = 8.7 Hz and J =
14.1 Hz, H-6), 4.29 (m, 2H, Cp-H), 4.00 (s, 5H, Cp-H), 3.72 (m,
1H, H-5), 3.41 (m, 1H, H-3), 3.22 (m, 1H, H-2), 3.02 (m, 4H; CH3
and H-4). 13C NMR (76 MHz, DMSO-d6) δ = 145.1, 121.3, 99.7,
76.1, 73.1, 71.8, 71.7, 70.6, 69.2, 68.3, 66.5, 54.1, 21.0. IR (cm-
1) : 3329.3, 2898.6-2864.1, 1629.13, 1509.5, 1221.8, 1064.6.
HRMS calculated for C19H23FeN3O5 m/z 429.0987 ; found
429.0988.
6-Deoxy-6-(4-ferrocenyl-1H-1,2,3-triazol-1-yl)-1-(4-
aminoophenyl)--D-glucopyranose 18 To a solution of 15 (900
2 | J. Name., 2012, 00, 1-3
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mg, 1.67 mmol) in ethyl acetate (40 ml) was added SnCl2.2H2O
COMMUNICATION
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OAc
OAc
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DOI: 10.1039/C9NJ01563A
R'
R'OH
O
O
(1.89 g, 5eq, 8.39 mmol) at room temperature. The reaction
mixture was stirred overnight at reflux (80°C). Once the
reaction was completed, the mixture was cooled to room
temperature. The mixture was poured into saturated aqueous
NaHCO3. A white precipitate was formed and filtered. Then,
the reaction mixture was extracted with ethyl acetate, washed
with water and NaCl. Then, the organic phase was dried over
anhydrous MgSO4 and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (AcOEt/EtOH,
100:0 to 90:10) to afford the final compound as an orange-
O
R
AcO
AcO
AcO
BF3.Et2O
AcO
OAc
OAc
3
4
5
2
R' = Ph from
1
R = Br
2 R = O-C(NH)CCl3
1
MeOH
Na
R' = Ph-NO2 from
2
R' = Ph-F from
OH
N3
O
1-TsCl,
pyridine
9
O
O
O
HO
HO
HO
HO
R'
R'
10
11
12
13
14
15
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2-NaN3
DMF
OH
OH
R' = Ph
R' = Ph-NO2
R' = Ph-F
R' = CH3
10
11
12
13
6
R' = Ph
7
8
9
R' = Ph-NO2
R' = Ph-F
R' = CH3
1
yellow solid. Yield: 40 %. Mp: 203-204°C. H NMR (300MHz,
DMSO-d6): δ = 7.95 (s,1H, Ar-H), 6.56 (d, J = 8.7Hz, 2H, Ar-H),
6.38 (d, J = 8.8Hz, 2H, Ar-H), 5.47 (d, J = 5.5 Hz, 1H, OH), 5.33 (
d, J = 5.0 Hz, 1H, OH), 5.21 (d, J = 5 Hz, 1H, OH), 4.76 (dd, J =
2.4Hz, J = 14.5 Hz, 1H, H-6), 4.71 (s, 2H, NH2), 4.67 (m, 1H, Cp-
H), 4.62 (m, 1H, Cp-H), 4.55 (d, J = 7.7 Hz, 1H, H-1), 4.40 (dd, J =
8.8 Hz , J = 14.3 Hz , 1H, H-6), 4.29 (m, 2H, Cp-H), 4.00 (s, 5H,
Cp-H), 3.71 (dt, J = 1.9 Hz, J = 9.2 Hz, 1H, H-5), 3.28 (m, 1H, H-
3), 3.14 (m, 2H, H-2 and H-4). 13C NMR (300MHz, DMSO-d6): δ
= 148.4, 145.1, 143.8, 121.5, 117.9, 114.4, 102.3, 76.1, 76.0,
74.3, 73.2, 71.3, 69.3, 68.2, 68.1, 66.5, 66.4, 50.9. IR (cm-1):
3329, 2898, 1629, 1509, 1221, 1064. HRMS (EI) calculated for
C24H26FeN4O5 m/z 506.1253; Found 506.1258.
THF/ H2O,
RT, 1 day
Fc
Na Ascorbate
CuSO4,
N
N
N
Fc
N
N
Fc
N
SnCl2
AcOEt
O
O
O
HO
HO
O
HO
HO
R'
OH
OH
NH2
14
15
16
17
R' = Ph ()
18
R' = Ph-NO2 ()
R' = Ph-F ()
R' = CH3 ()
Scheme 1 Syntheses of the different ferrocene-carbohydrate conjugates
Results and Discussion
Different carbohydrates substituted ferrocene have been
synthesized in 5 or 6 steps using classical pathways for these
kinds of syntheses (Figure 1). 3 and 5 were obtained by
glycosylation using Schmidt acceptor 2, and 4 was obtained
from the bromoglucose 1. After deprotection, primary alcohol
(6-9) was transformed in two steps in azide group (10-13) to
introduce ferrocene by cycloaddition (14-17). 15-17 were
obtained in modest yields. Nitro group was then reduced using
tin chloride to afford the amino group (18) (Scheme 1).
Complete NMR study was done on each compound and all the
signals have been attributed. Usually on
a monosubstituted
ferrocene, proton NMR shows three different chemical shifts, one
for proton of the free cyclopentadienyl and two other ones for 
and  protons of the substituted cyclopentadienyl. In the series of
molecules we have synthesized, we can observe up to 5 different
signals for the monosubstituted ferrocene. In the literature, this
behaviour is not mentioned, however we have pointed out in at
least one paper that clicked ferrocenes on acetylated glucose or
mannose showed that the two alpha protons of ferrocene were
magnetically different [14]. No supplementary studies can explain
this behaviour. By comparing compound 17 with the other
derivatives, only three signals correspond to ferrocene, indicating
that the alpha (H8 and H11) and beta (H9 and H10) protons of
substituted ferrocene are equivalent to two to two, and the third
signal (H12) corresponds to the five protons of the free
cyclopentadienyl (Table 1). A simple methoxy in anomeric position
does not influence the NMR shift of ferrocene protons. When the
carbohydrate is functionalized by different aryls, it seems that the
environment of ferrocene changes. It results in a splitting of the
alpha signals and even a splitting of the beta signals for compound
15 (Figure 2).
Fig. 2 Zoom on ferrocene 1H NMR signals of 15.
As it can be seen on figure 2, shift of the proton NMR of the free
cyclopentadienyl is not really influenced by the rest of the
molecule, whereas, for the substituted cyclopentadienyl,  protons
are separated from 0.1 to 0.2 ppm. H assignments were confirmed
by 2D NMR experiments. For compounds 14, 16, 17 and 18, four 1H
NMR signals are present in the spectra and correspond to H-8, H-11,
H-12 and H-9 with H-10 under the same signal. Since, the
environment around the ferrocene seems to influence the chemical
shift of the protons, other NMR experiments were performed on
the different carbohydrates. First, a test with a temperature
increase on compound 15 in DMSO d6 was realized to see if the
alpha and beta hydrogens could become equivalent. When the
temperature is increased, a decrease of the difference in chemical
displacement between the two alpha protons and the two beta
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protons was observed passing from 0.2 to 0.13 ppm difference for
alpha protons
View Article Online
DOI: 10.1039/C9NJ01563A
Table 2. Longitudinal relaxation times of ferrocene protons for compounds 14 to
18.
5
6
7
8
Table 1. 1H NMR chemical shifts of ferrocene in compounds 15-18
T1(s)
H8
2.6
2.5
2.2
2.3
2.0
T1(s)
H9
2.3
2.25
2.0
2.2
T1(s)
H10
2.3
2.25
2.0
2.2
T1(s)
H11
2.4
2.4
2.2
2.3
2.1
Compound
11
10
N
N
9 Fe
14(R =Ph)
15(R = PhNO2)
16(R = PhF)
17(R = CH3)
8
N
O
12
O
HO
HO
R
9
OH
10
11
12
13
14
15
16
17
18
19
20
21
22
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24
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18(R =PhNH2)
2.0
2.0
Compound
14(R =Ph)
H8
H9
H10
4.29
4.22
4.29
4.30
4.29
H11
4.57
4.47
4.57
4.75
4.62
H12
3.98
3.95
3.98
4.00
4.00
In order to understand these differences, crystals were obtained for
each compound to see the organization of the molecules. Although
the results obtained by X-ray diffraction correspond to a solid
phase, these informations are very instructive about the folding of
molecules in solution and is a valuable tool for the proton NMR
interpretation.
4.68
4.67
4.68
4.75
4.67
4.29
4.28
4.30
4.30
4.29
15(R = PhNO2)
16(R = PhF)
17(R = CH3)
18(R =PhNH2)
In the solid state, the compound 17, having the simplest NMR
system, has a very simple stack governed by a network of hydrogen
bonds between OH of carbohydrates. Consequently, ferrocenes are
organized in columns (see SI). Thus, methoxy has little influence on
stacking whereas the other compounds have complicated X-ray
structures due to the anomeric position substitution. The molecules
form a U due to the substitutions of carbohydrates in positions 1
and 6. The spatial arrangement will depend on the substitution of
phenyl. Indeed, when an amine (compound 18) is present in para
position of the anomeric part, it will participate in hydrogen
bonding networks. The amine nitrogen is bound to an adjacent
carbohydrate via a N-H bond while the two amine hydrogens are
engaged in weak bonds with the oxygen of two other adjacent
carbohydrates. The ferrocene is oriented outside of the U shape of
the molecule, therefore far from the amine. The behaviour of
compounds 14, 15 and 16 is different. The ferrocene will be
positioned inside the U. The nitro group points towards the
ferrocene forming a U rather flat, while with the amino group the U
is rather helical (Figure 4).
and 0.06 to 0.03 ppm for beta protons (Figure 3). However, at
120 °C, no coalescence was obtained. A similar experiment has
been realized with compound 18.  protons are magnetically
equivalent at room temperature whereas  protons show different
chemical shifts. When the temperature is raised during the NMR
experience, the chemical shifts of the two alpha protons remain
identical, indicating that the adopted configuration seems blocked.
Thus, another experiment was performed lowering the
temperature to -40°C. We would like to see if the  signals (H-9 and
H10) were able to separate, however we just pointed out an NMR
shift without any separation of the signals. These experiments were
realized in deuterated methanol, DMSO being solid at this
temperature.
Fig. 4. Molecular representations of a) 15 and b) 18.
Fig. 3 Temperature effect on 1H NMR signals of ferrocene in 15
Measurement of longitudinal relaxation times for 15 demonstrates
that T1 H8 and T1 H11 are slightly different whereas T1 H9 and T1 H10
are identical (Table 2). In comparison with 17, the T1 of the
different protons are closer. Thus, even if the gap between the
relaxation time of the protons is not so significant, it means that the
environment around the protons is not exactly the same. Results
for the other compounds (14, 16 and 18) show a similar behavior
than 15.
Conclusions
We have synthesized a series of carbohydrate ferrocene conjugates
varying the nature of the group in anomeric position. We pointed
out that 1H NMR of carbohydrate derivatives could lead to a
splitting of signals of the ferrocene protons. Molecules presenting
aryl in anomeric position are folded in U shape with the ferrocene
that could be positioned inside the U or outside the U if H-bond
exists. The molecular representation shows an environment around
ferrocene protons that is different if the rotation between
ferrocene and triazole is prevented, this would explain the different
chemical shifts of ferrocene protons.
4 | J. Name., 2012, 00, 1-3
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COMMUNICATION
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Conflicts of interest
There are no conflicts to declare.
View Article Online
DOI: 10.1039/C9NJ01563A
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Acknowledgements
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We thank the Direction Générale de l’Armement (DGA) and the
Région Pays de la Loire for the thesis of Fanny Peigneguy.
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1
Carbohydrate-ferrocene conjugates shNoeww Jouarnalsopf Clhietmtiisntryg of all the H NMR signals of the
substituted cyclopentadienyl. XRD of crystals seems to indicate that R group could be
responsible of the splitting of the NMR signals.
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H11
H10
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Fe
H9
H8