Synthesis and comparative characteristic of organophosphorus dendrimers with phenoxy and deuterophenoxy end groups

Article abstract of DOI:10.1134/S1070363208110479

Two series of generation 0 to 6 phosphorus dendrimers (6 to 384 end groups) are synthesized starting from the cyclotriphosphazene core. The series are distinguished by the type of their terminal groups: O-C₆H₅ in first series and O-C₆D₅ in the other. These functions are chemically analogous, but they give different spectroscopic signatures which afford detailed information about the structure of these dendrimers.

Full text of DOI:10.1134/S1070363208110479

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 11, pp. 2257–2264. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © C. Padie, C.-O.Turrin, A.-M. Caminade, J.-P. Majoral, V.L. Furer, I.I. Vandyukova, V.I. Kovalenko, 2008, published in Rossiiskii
Khimicheskii Zhurnal, 2008, Vol. 52, No. 1, pp. 100–106.
Synthesis and Comparative Characteristic
of Organophosphorus Dendrimers with Phenoxy
and Deuterophenoxy End Groups
C. Padiea, C.-O.Turrina, A.-M. Caminadea, J.-P. Majorala,
V. L. Furerb, I. I. Vandyukovab, and V. I. Kovalenkob
a National Scientific Research Center (CNRS), Toulouse, France
b Arbuzov Institute of Organic and Physical Chemistry, Kazan Research Center, Russian Academy of Sciences,
ul. Arbuzova 8, Kazan, 420088 Tatarstan, Russia
e-mail: koval@iopc.knc.ru
Received January 24, 2008
Abstract—Two series of generation 0 to 6 phosphorus dendrimers (6 to 384 end groups) are synthesized
starting from the cyclotriphosphazene core. The series are distinguished by the type of their terminal groups:
O–C6H5 in first series and O–C6D5 in the other. These functions are chemically analogous, but they give
different spectroscopic signatures which afford detailed information about the structure of these dendrimers.
DOI: 10.1134/S1070363208110479
contribute much into the properties of these nano-
molecules.
INTRODUCTION
Dendrimers are nanomolecules synthesized from
monomers that combine with each other to form a tree-
like structure [1]. The growth begins with a core, viz. a
polyfunctional center. The name of these compounds
completely reflects their structure; it was introduced by
Tomalia et al. [2] and originates from two Greek roots:
“dendron” (tree) and “meros” (part). The tree-like
structure is formed by a repetition of one and the same
reaction sequence to give, at the end of each cycle, one
new generation and identically growing number of
branches. After several generations, the dendrimer gets
highly branched, polyfunctional, and, as a rule,
spherically shaped. Due to the presence of a great
number of end groups, many branches form internal
cavities coming down to the core.
Dendrimers are also isomolecular polyfunctional
polymers with quite specific solubilities, viscosities,
and thermal stabilities. Their application field is
extending from year to year and includes molecular
and supramolecular chemistry, catalysis, basic
research, nanotechnologies, sensors, and materials for
photonics, biology, diagnostics, medicine, etc. Such
extensive applications are due to the fact that
dendrimers exhibit properties of polymers: Their
functional groups are readily accessible on the surface
and available for controlled modification; these
molecules feature porosity, flexibility of inner
branches, accessibility of the core, etc. Most industries
make use of this new class of special polymers [3].
A dendrimer consists of three different parts:
Research on dendrimers contributes into the
understanding the behavior of such nanomolecules not
only from the reactivity but also from the
physicochemical standpoints. Studying physicochem-
ical properties of dendrimers is not a trivial task, since
one has to know, along with the chemical composition
and uniformity, molecular morphology and shape. The
dendrimer science is at the interface between
molecular and polymer chemistry. Dendrimers are
obtained by step-by-step controlled synthesis, but they
(1) a core: an atom or a group having at least two
indentical reaction centers;
(2) branches of repetitive units radiating from the
core and having at least one branching point; the units
built up by an exponential law, forming concentric
layers called generations;
(3) various functional end groups which are mostly
localized at the dendrimer periphery (surface) and
2257

2258
PADIE et al.
also pertain to polymers due to their their repetitive
structure made of monomers. A priory they benefit
from analytical techniques applied in organic synthesis
and polymer chemistry.
EXPERIEMNTAL
The synthesis and all subsequent operations were
performed in vacuum devices under dry argon. All
solvents were preliminarily dried and distilled (THF
and ether on Na/benzophenone, and pentane and
dichloromethane on P2O5).
Since 1994 the French National Center for
Scientific Research has been involved in research on
synthesis, properties, and practical application of
dendrimers containing one phosphorus atom in each
divergence point and –СНО or –Р–(S)Cl2 as end
groups [4]. As judged from the chemical properties of
these two substituents, they can be functionalized,
thereby modifying the properties of the parent
nanomolecules [5]. The dendrimers of our interest are
mainly characterized by multinuclear NMR (especially
31Р NMR), whereas such mass spectral techniques as
MALDI–TOF proved unfeasible here, since laser
irradiation partially destroyed the denrimer molecules
[6]. Fourier-transform IR and Raman spectroscopy
proved to be the most interesting and appropriate
analytical techniques, and they formed the basis for the
long-term and fruitful collaboration between the
research groups from Toulouse and Kazan [7]. In
particular, we have performed an experimental and
theoretical (DFT) research [8] on the effect of the
generation [9] and core of dendrimers {P(S), vinyl
[10], N3P3 [11]} on their structure.
1
13
31
The H, C, and P NMR spectra were measured
in CDCl3 on Bruker ARX250, AV300, AV400, and
AV500 spectrometers against 85% H3PO4 (31P) and
SiMe4 (1H and 13C). The 1H and 13C NMR spectra were
registered using the Jmod and two-dimensional HMBC
and HMQC techniques (when necessary); the 31P
NMR spectra were registered using broad-band proton
decoupling or CW decoupling. Dendrimers 1-Gn
dendrimers were synthesized as described in [13]. In
the assignment of NMR spectra we made use of the
atom numbering shown in Fig. 1.
Synthesis of Compounds 2-G0 and 2-G0
D
Phenol and phenol-d5, 1.0 g, and 4 g of cesium
carbonate were added to a solution of 0.5 g of
hexachlorotriphosphazene in 50 ml of THF. The
resulting mixture was stirred overnight at ambient
temperature and then further centrifuged for 30 min at
10000 rpm. The supernatant was collected, filtered
through Celite, and dried at reduced pressure. Excess
phenol was evaporated at reduced pressure, and the
oily residue was purified by liquid chromatography
Quite recently we initiated studies of surface
functional groups of dendrimers [12]. To this end, we
synthesized two novel families of organophosphorus
dendrimers containing surface phenoxy and
pentadeuterophenoxy groups. The phenoxy group was
chosen, since it was expected to be readily added to the
P(S)Cl2 groups of our dendrimers and also due to the
commercial availability of its fully deuterated analog;
thus we could compare structurally similar substituents
with different spectral signatures. Moreover, the
phenoxy group can be considered as “neutral” with
respect to the structure of dendrimers, i.e. it should
slightly affect their properties. The present paper
described the synthesis of the two novel families, each
containing sixth generation dendrimers.
on silica gel (eluent hexane–ethyl acetate, 3:1). Pure
fractions were collected and dried; as a result,
transparent crystals were obtained.
1
Compound 2-G0 [16]. Yield 70%. H NMR spec-
trum, δ, ppm: 7.26–7.13 m (18H, Cc-H, Cd-H), 7.00 d
(3JHH 8.3 Hz, 12H, Cb). 31P{1H} NMR spectrum, δP,
ppm: 11.5 (P0). 13C{1H} NMR spectrum, δC, ppm:
150.7 d (2JCP 8.3 Hz, Ca), 129.5 (Cc), 124.9 (Cd), 121.1
(Cb).
1
Compound 2-G0D. Yield 73%. H NMR spectrum,
δ, ppm: 7.28–7.03 (undeuterated phenol residue). 31P
Fig. 1. Atom numbering used in the assignment of NMR signals of generation 3 dendrimers.
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SYNTHESIS AND COMPARATIVE CHARACTERISTIC
2259
31
{1H} NMR spectrum, δP, ppm: 11.5. 13C{1H} NMR
spectrum, δC, ppm: 150.6 (Ca), 128.9 (tD, lJCD 24.4 Hz,
Cc), 124.3 (tD, JCD 23.9 Hz, Cd), 120.7 (tD, JCD
(3JHP 10.1 Hz, 18H, CH3–N–P1). P{1H} NMR spec-
trum, δP, ppm: 66.1 (P2), 65.9 (P1), 11.9 (P0). C{1H}
13
NMR spectrum, δC, ppm: 151.6 (Ca), 150.8 (C11, C01),
139.3 d (3JCP 15.1 Hz, CH=NNP1), 138.8 d (3JCP 14.1
Hz, CH=NNP2), 132.8 (C14), 132.5 (C04), 129.5 (tD, 1JCD
1
1
24.4 Hz, Cb).
23.6 Hz, Cc), 128.7 (C1 , C03), 125.3 (tD, JCD 23.3 Hz,
3
1
Synthesis of Dendrimers 2-Gn and 2-GnD
with Phenol End Froups
Cd), 122.2 (C12), 121.9 (C02), 121.4 (tD, JCD 24.7 Hz,
1
Cb), 33.5 d (2JCP 12.4 Hz, CH3NP).
A dendrimer with P(S)Cl2 end groups, 0.5 g, was
dissolved in 30 ml of distilled THF containing 1.2
equiv (by chlorine) of phenol and 2.4 equiv of cesium
carbonate. The mixture was stirred overnight at
Compound 2-G3. Yield 78%. 1H NMR spectrum, δ,
ppm: 7.85–6.80 m (450H, C6H5, CHAr, CH=N), 3.20 m
(126H, CH3NP). 31P{1H} NMR spectrum, δP, ppm:
66.0 (P3), 65.8 (P1, P2), 11.8 (P0). 13C{1H} NMR
spectrum, δC, ppm: 151.2 (Ca, C11, C01), 150.7 d (2JCP
5.1 Hz, C21), 138.6 d (3JCP 13.4 Hz, CH=N), 132.3 (C24,
C14, C04), 129.5 (Cc), 128.2 (C23, C13, C03), 125.4 (Cd),
121.7 (C22, C12, C02), 121.4 (Cb), 33.2 d (2JCP 12.8 Hz,
CH3NP).
ambient temperature
.
After centrifuging, the
supernatant was filtered on Celite, reduced to 3 ml,
and diluted with 150 ml of pentane. A white
precipitate formed and was filtered off and washed
with pentane (3×150 ml).
Compound 2-G1. Yield 81%. 1H NMR spectrum, δ,
ppm: 7.59 d (3JHH 8.6 Hz, 12H, C03H), 7.53 d (3JHP
1.4 Hz, 6H, CH=N), 7.21 m (60H, C6H5), 6.97 d (3JHH
8.6 Hz, 12H, C02H), 3.21 d (3JHP 10.3 Hz, 18H,
1
Compound 2-G3D. Yield 56%. H NMR spectrum,
δ, ppm: 7.92–6.82 m (210H, CHAr, CH=N), 3.30–3.00
31
m (126H, CH3NP). P{1H} NMR spectrum, δP, ppm:
66.1 (P1), 66.0 (P3), 65.9 (P2), 11.8 (P0). 13C{1H} NMR
spectrum, δC, ppm: 151.5 d (2JCP 6.0 Hz, Ca), 150.9 d
(2JCP 7.0 Hz, C21, C11, C01), 139.5 m (CH=N), 138.9 d
(3JCP1 13.0 Hz, CH=NNP3), 132.7 (C24, C14, C04), 129.5
(tD, JCD 25.1 Hz, Cc), 128.7 (C23, C13, C03), 125.3 (tD,
31
CH3NP). P{1H} NMR spectrum, δP, ppm: 66.0 (P1),
11.9 (P0) . 13C{1H} NMR spectrum, δC, ppm: 151.1
(C10), 150.6 (Ca), 138.4 d (3JCP 14.0 Hz, CH=N), 132.2
2
(C40), 129.5 (Cc), 128.2 (C03), 125.4 (Cd), 121.4 (C0 ),
121.3 (Cb), 33.0 d (2JCP 12.3 Hz, CH3NP).
1
1JCD 23.9 Hz, Cd), 122.2 (C22, C12, C02), 121.4 (tD, JCD
1
24.1 Hz, Cb) 33.4 d (2JCP 13.1 Hz, CH3NP).
Compound 2-G1D. Yield 85%. H NMR spectrum,
3
δ, ppm: 7.60 m (18H, C0 H, CH=N), a signal of
Compound 2-G4. Yield 76%. 1H NMR spectrum, δ,
ppm: 7.92–6.81 m (930H, C6H5, CHAr, CH=N), 3.19 m
(270H, CH3NP). 31P{1H} NMR spectrum, δP, ppm: 66.1
incompletely deuterated phenol, 6.90 d (3JHH 8.4 Hz,
2
12H, C0 H), 3.20 s (3JHP 10.3 Hz, 18H, CH3NP).
31P{1H} NMR spectrum, δP, ppm: 66.1 (P1), 11.8 (P0).
13C{1H} NMR spectrum, δC, ppm: 151.6 m (Ca), 150.9
d (2JCP 5.0 Hz, C01), 138.8 d (3JCP 14.1 Hz, CH=N),
13
(P1, P2, P3, P4), 11.8 (P0). C{1H} NMR spectrum, δC,
ppm: 151.2 d (2JCP 7.1 Hz, Ca, C01–2), 150.5 d (2JCP
1
7.0 Hz, C3 ), 138.7 m (CH=N), 132.3 (C04–3), 129.5
1
132.6 (C04), 129.5 (tD, JCD 24.7 Hz, Cc), 128.7 (C03),
(Cc), 128.2 (C0–33), 125.4 (Cd), 121.8 (C02–3), 121.4 d
125.3 (tD, 1JCD 22.1 Hz, Cd), 121.8 (C02), 121.4 (tD, 1JCD
24.2 Hz, Cb), 33.4 d (2JCP 12.4 Hz, CH3NP).
(3JCP 4.1 Hz, Cb), 33.1 d (2JCP 12.7 Hz, CH3NP).
1
Compound 2-G2. Yield 78%. 1H NMR spectrum, δ,
ppm: 7.56 m (54H, CHAr, CH=N), 7.19 m (120H,
C6H5), 6.78 m (36H, CHAr), 3.24 d (3JHP 10.3 Hz, 36H,
CH3NP2), 3.16 d (3JHP 6.8 Hz, 18H, CH3NP1). 31P{1H}
NMR spectrum, δP, ppm: 66.1 (P2), 65.9 (P1), 12.0
Compound 2-G4D. Yield 75%. H NMR spectrum,
δ, ppm: 7.85–7.00 m (450H, CHAr, CH=N), 3.40–3.00
m (270H, CH3NP). P{1H} NMR spectrum, δP, ppm:
31
65.8 (P1, P2, P3, P4), 11.8 (P0). 13C{1H} NMR spectrum,
δC, ppm: 151.6 d (2JCP 6.0 Hz, Ca), 150.8 d (2JCP
7.0 Hz, C0–31), 139.5 d (3JCP 12.1 Hz, CH=NNP), 139.9
d (3JCP 14.1 Hz, CH=NNP4), 132.7 (C04–3), 129.5 (tD,
1JCD 23.6 Hz, Cc), 128.7 (C03–3), 125.4 (tD, 1JCD 24.1 Hz,
13
(P0). C{1H} NMR spectrum, δC, ppm: 151.1 d (2JCP
6.4 Hz, Ca, C01), 150.5 d (2JCP 7.1 Hz, C11), 138.4 d (3JCP
14.0 Hz, CH=N), 132.3 (C14, C04), 129.5 (Cc), 128.2
(C13, C03), 125.4 (Cd), 121.6 (C12, C02), 121.3 (Cb), 33.0 d
(2JCP 12.7 Hz, CH3NP).
Cd), 122.2 (C02–3), 121.4 (tD, JCD 22.5 Hz, Cb), 33.4 d
1
(2JCP 12.5 Hz, CH3NP).
1
Compound 2-G5. Yield 79%. 1H NMR spectrum, δ,
ppm: 7.90–7.10 m (1890H, C6H5, CHAr, CH=N), 3.19 s
(558H, CH3NP). 31P{1H} NMR spectrum, δP, ppm:
Compound 2-G2D. Yield 88%. H NMR spectrum,
δ, ppm: 7.60 m (54H, CHAr, CH=N), 7.22 m (36H,
CHAr), 3.25 d (3JHP 10.2 Hz, 36H, CH3–N–P2), 3.20 d
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 11 2008

2260
PADIE et al.
65.9 (P5), 65.7 (P1, P2, P3, P4). 13C{1H} NMR spectrum,
δC, ppm: 150.8 m (Ca, C01–4), 138.8 (CH=N), 132.2 (C04–4),
129.5 (Cc), 128.2 (C03–4), 125.4 (Cd), 122.1 (C02–4),
121.3 (Cb), 33.0 m (CH3NP).
RESULTS AND DISCUSSION
NMR Control During Synthesis of Dendrimers
The synthesis was started with N3P3Cl6 which was
used as a core, by repeating two simple and
quantitative reactions: nucleophilic substitution via 4-
hydroxybenzaldehyde in a basic medium and con-
densation between aldehydes and the phosphorus-
containing hydrazide H2NNMeP(S)Cl2. Dendrimers
with either aldehyde or P(S)Cl2 end groups were
previously synthesized to the eighth generation [13].
1
Compound 2-G5D. Yield 84%. H NMR spectrum,
δ, ppm: 7.95–6.8 m (930H, CHAr, CH=N), 3.35–3.00
31
m (558H, CH3NP). P{1H} NMR spectrum, δP, ppm:
65.9 (P5), 65.7 (P4, P3, P2, P1). 13C{1H} NMR spectrum,
δC, ppm: 151.7 m (Ca), 150.8 m (C01–4), 139.6 m
(CH=N), 138.9 d (3JCP 12.0 Hz, CH=NNP5), 132.7
(C04–4), 129.5 (tD, 1JCD 24.1 Hz, Cc), 128.7 (C03–4), 125.3
m (Cd), 122.2 (C02–4), 121.5 (tD, 1JCD 22.2 Hz, Cb), 33.5
d (2JCP 13.1 Hz, CH3NP).
The substitution reaction was initially performed
directly on the N3P3Cl6 core (1-G0) of the zero-
generation dendrimer, using 6 equiv of phenol or
phenol-d5 in the presence of cesium carbonate as an
inotganic base (Scheme 1).
Reaction progress was followed by 31Р NMR;
initially, the spectrum contained many signals from
different АА'B systems, associated with consecutive
substitution of Cl by phenolic residues. Upon
completion of all substitution reactions, the 31Р NMR
spectra contained a single singlet ay 11.5 ppm in both
cases (2-G0 and 2-G0D).
Compound 2-G6. Yield 87%. 1H NMR spectrum, δ,
ppm: 7.90–6.85 (sl, 3810H, C6H5, CHAr, CH=N), 3.19
(sl, 1134H, CH3NP). 31P{1H} NMR spectrum, δP, ppm:
13
65.7 (P1, P2, P3, P4, P5). C{1H} NMR spectrum, δC,
ppm: 150.8 m (Ca, C01–5), 138.8 m (CH=N), 132.2 (C04–5),
129.5 (Cc), 128.2 (C03–5), 125.4 (Cd), 122.1 (C02–5),
121.3 (Cb), 33.2 m (CH3NP).
1
Compound 2-G6D. Yield 85%. H NMR spectrum,
δ, ppm: 7.90–6.85 (sl, 1890H, CHAr, CH=N), 3.19 sl
(1134H, CH3NP). 31P{1H} NMR spectrum, δP, ppm:
13
65.8 (P1, P2, P3, P4, P5). C{1H} NMR spectrum, δC,
The same substitution reactions were performed in
generation 1–6 phosphorus-containing dendrimers 1-
Gn (n 1–6) in the presence of cesium carbonate, using
phenol or phenol-d5 (Scheme 2).
ppm: 151.6 m (Ca), 150.9 m (C01–5), 139.6 m (CH=N),
139.0 (CH=NNP6), 132.7 (C04–5), 129.5 (tD, 1JCD 24.1 Hz,
Cc), 128.7 (C03–5), 125.4 m (Cd), 122.2 (C02–5), 121.4 (tD,
1JCD 22.6 Hz, Cb), 33.5 m (CH3NP).
In all cases, the signal of end P(S)Cl2 groups (δP
64 ppm) gradually converted into a signal at δP
71 ppm, corresponding to the P(S)ClOAr group.
Finally, a signal at δP 66 ppm appeared, which
evidenced the reaction completion and the formation
of P(S)(ОAr)2. 31Р NMR spectroscopy allows direct
monitoring substitution progress at all terminal groups
of the dendrimer with an accuracy of up to 0.5%.
Moreover, signals related to different generations are
readily distinguishable up to the third generation
(Fig. 2).
Scheme 1. Synthesis of generation 0 dendrimers
H
H
H
H
H
H
O
O
H
H
H
P
H
O
H
H
H
N
N
H
H
O
H
P
P
N
H H
H
H
H
H
O
H
H
O
H
H
H
H
H
H
Structural Characterization of Dendrimers
D
D
D
D
D
D
All the dendrimers obtained were characterized by
1
means of Н and 13С NMR. The proton NMR tech-
O
O
D
D
D
D
P
D
D
D
D
D
N
P
N
P
nique is poorly informative, since the aromatic and
hydrazone groups, on the one hand, and methyl group,
on the other, are impossible to distinguish. By contrast,
13С NMR shows interesting results. First of all, both
the dendrimer families give signals in the same
regions. However, the signals of dendrimers with
D
O
O
N
D D
D
D
D
D
O
D
D
O
D
D
D
D
D
D
2-G0D
2-G0D
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SYNTHESIS AND COMPARATIVE CHARACTERISTIC
2261
Scheme 2. Synthesis of generations 1 to 6 dendrimers
S
Me
12HO-C6H5
Cs2CO3
H
C=N−N−P−(OC6H5)2
[N3P3]−Ο
[N3P3]−Ο
S
Me
2-G1
Cl
Cl
H
6
6
−
C=N−N−P
[N3P3]−Ο
S
Me
H
12HO-C6D5
Cs2CO3
1-G1
C=N−N−P−(OC6D5)2
6
2-G1D
S
Me
S
Me
H
H
24HO-C6H5
Cs2CO3
C=N−N−P−Ο
[N3P3]−Ο
[N3P3]−Ο
C=N−N−P−(OC6H5)2
S
Me
S
Me
2-G2
2
6
H
H
C=N−N−P
[N3P3]−Ο
C=N−N−P−(PCl2 2
−
6
S
Me
S
Me
24HO-C6D5
Cs2CO3
H
H
C=N−N−P−(OC6D5)2
C=N−N−P−Ο
2-G2D
2
6
S
S
Me
Me
S
Me
48HO-C6H5
H
H
H
C=N−N−P−(OC6H5)2
C=N−N−P−Ο
C=N−N−P−Ο
Cs2CO3
2-G3
2
2
6
1-G3
−
S
S
Me
Me
S
Me
H
H
H
48HO-C6D5
Cs2CO3
C=N−N−P−(OC6D5)2
C=N−N−P−Ο
C=N−N−P−Ο
2-G3D
2
2
6
S
Me
S
Me
S
Me
S
Me
H
H
96HO-C6H5
H
H
C=N−N−P−(OC6H5)2
C=N−N−P−Ο
C=N−N−P−Ο
C=N−N−P−Ο
Cs2CO3
2-G4
2
2
2
6
1-G4
−
S
Me
S
Me
S
Me
S
Me
96HO-C6D5
Cs2CO3
H
H
H
H
C=N−N−P−(OC6D5)2
C=N−N−P−Ο
C=N−N−P−Ο
C=N−N−P−Ο
2-G4D
2
2
2
6
...
deuterated end groups differ from those form the
undeuterated analog and appear as characteristic
triplets (1JCD ≈ 23 Hz) for the Сb, Cc, and Cd atoms
(Fig. 1). These features allow identification of signals
of end group. Detailed examination of these three
signals shows that one of them is especially sensitive
to generation. Actually, the signal of the Cd carbon
(which is para with respect to oxygen) gets broader in
the fourth generation, which makes difficult
determination of the coupling constant. This phenol-
menon is even more expressed in the fifth and sixth
generations. Broadening of NMR signals is normally
associated with a loss of mobility. Our observation
provides clear evidence for enhancing steric
hindrances in dendrimers, beginning with the fourth
generation. Two hypotheses can be suggested to
explain this phenomenon: (1) some real steric
hindrance on the surface or (2) certain functional
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PADIE et al.
ppm
Fig. 2. 31Р NMR spectrum of generation 3 dendrimer 2-G3D
.
groups turn inward the structure, which is facilitated
with increasing generation, on account of increasing
flexibility of branches with their elongation.
Actually, the number of functional groups increases
by two for each further generation, and the
corresponding bands should follow this simple
arithmetic progression, unless other factors are
considered (such as medium, conformation, and intra-
and intermolecular interactions). Of these factors, the
flexibility of the fragments in question will be affected
by those that affect the lifetime of vibration levels,
and, as a result, the shape and width of the
corresponding IR bands. Such analysis, especially
detailed for dendrimers 2-GnD, revealed only slight
changes in the IR spectra of the internal part of
dendrimers of any generation (probably, the zero
generation is an exception). This finding means that
To obtain evidence for the suggested steric
hindrance, we made use of IR spectroscopy. This
method provides solid-state data, whereas 13С NMR
gives information about the state in solution. The IR
spectra of the zero-generation 2-G0 and 2-G0D were
assigned using DFT calculations [11]. The resulting
data were also used to assign the IR spectra of further
generation dendrimers. Such approach gave us
evidence to show that the IR bands of surface
functional groups are the most informative.
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SYNTHESIS AND COMPARATIVE CHARACTERISTIC
2263
Blanchard-Desce, M., Angew, Chem. Int. Ed., 2006,
vol. 45, p. 4645; (d) Griffe, L., Poupot, M., Marchand, P.,
Maraval, A., Turrin, C.O., Rolland, O., Métivier, P.,
Bacquet, G., Fournié, J.J., Caminade, A.M., Poupot, R.,
and Majoral, J.P., Ibid., 2007, vol. 46, p. 2523.
the shape and conformation of internal branches
scarcely change with changing molecular size or
generation number. By contrast, the width of the IR
bands of surface groups varies with generation. In
higher generations, beginning with the fourth, the
conformation of end groups is violated due to steric
hindrances [12].
4. Launay, N., Caminade, A.M., Lahana, R., and Majoral, J.P.,
Angew, Chem. Int. Ed., 1994, vol. 33, p. 1589.
5. (a) Caminade, A.M. and Majoral, J.P., Prog. Polym.
Sci., 2005, vol. 30, p. 491; (b) Caminade, A.M. and
Majoral, J.P., J. Mater, Chem., 2005, vol. 15, p. 3643;
(c) Caminade, A.M. and Majoral, J.P., Coord. Chem.
Rev., 2005, vol. 249, p. 1917; (d) Majoral, J.P.,
Caminade, A.M., and Laurent, R., ACS Symp. Ser.
no. 928. Metal-containing and Metallosupramolecular
Polymers and Materials, Schubert, USA, Newkome,
and Manners, I., Eds., 2006, ch. 17, p. 230; (e) Cami-
nade, A.M., Maraval, A., and Majoral, J.P., Eur. J.
Inorg, Chem., 2006, p. 887; (f) Caminade, A.M., Tur-
rin, C.O., Laurent, R., Rebout, C., and Majoral, J.P.,
Polym. Int., 2006, vol. 55, p. 155; (g) Caminade, A.M.,
Turrin, C.O., Laurent, R., Maraval, A., and Majo-
ral, J.P., Curr. Org, Chem., 2006, vol. 10, p. 2333.
6. Blais, J.C., Turrin, C.O., Caminade, A.M., and Majo-
ral, J.P., Anal, Chem., 2000, vol. 72, p. 5097.
7. Vandukov, A.E., Shagidullin, R.R., Kovalenko, V.I.,
Caminade, A.M., and Majoral, J.P., Structure and
Dynamics of Molecular Systems, Kazan: Mar. Gos.
Tekh. Univ., 1998, vol. 3, p. 64.
CONCLUSIONS
Two novel families of opganophosphorus den-
drimers of generations 0 to 6, with similar surface
functional groups (phenoxy and deuterophenoxy) were
synthesized, aimed at gaining further insight into the
structure of such nanomolecules. Solution 13С NMR
and solid-state IR studies led us to two converging
conclusions: steric hindrances associated with surface
functional groups begin to reveal themselves in the
fourth generation (96 end functional groups), are well
defined in the fifth and sixth generation (192 and 384
end functional groups, respectively). This phenomenon
has been studied for years to obtain contradictory
results for dendrimers of different types [14]. It should
be noted that steric hindrances in these generatyions of
phosphorus-containing dendrimers are still not strong
enough to prevent further synthesis involving surface
functional groups (31Р NMR data), block the surface,
and prevent penetration of solvent molecules into the
structure. We previously showed that this phenomenon
is associated with quasitotal disappearance of spectral
signals from the internal structure [15], but this is not
observed in our present case.
8. (a) Furer, V.L., Vandyukov, A.E., Majoral, J.P.,
Caminade, A.M., and Kovalenko, V.I., Vibr. Spectrosc.,
2006, vol. 40, p. 155; (b) Furer, V.L., Vandyukov, A.E.,
Majoral, J.P., Caminade, A.M., and Kovalenko, V.I.,
J. Mol. Struct., 2006, vol. 785, p. 133; (c) Furer, V.L.,
Vandyukov, A., Majoral, J.P., Caminade, A.M., and
Kovalenko, V., Chem. Phys., 2006, vol. 326, p. 417.
9. (a) Kovalenko, V.I., Furer, V.L., Vandyukov, A.E.,
Shagidullin, R.R., Majoral, J.P., and Caminade, A.M.,
J. Mol. Struct., 2002, vol. 604. p. 45; (b) Furer, V.L.,
Kovalenko, V.I., Vandyukov, A.E., Majoral, J.P., and
Caminade, A.M., Spectrochim. Acta A, 2002, vol. 58,
p. 2905; (c) Furer, V.L., Kovalenko, V.I., Vandyu-
kov, A.E., Majoral, J.P., and Caminade, A.M., Vibr.
Specrosc., 2003, vol. 31, p. 71; (d) Furer, V.L., Van-
dyukov, A.E., Majoral, J.P., Caminade, A.M., and
Kovalenko, V.I., Spectrochim. Acta A, 2004. vol. 60,
p. 1649; (e) Furer, V.L., Majoral, J.P., Caminade, A.M.,
and Kovalenko, V.I., Polymer, 2004. vol. 45, p. 5889;
(f) Furer, V.L., Vandukova, I.I., Majoral, J.P.,
Caminade, A.M., and Kovalenko, V.I., Vibr. Spectrosc.,
2007, vol. 43, p. 351.
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