Bifunctional metallodendrimers based on AB5 derivatives of cyclotriphosphazene as core and P,N ligands as terminal functions Metallodendrimers Special Issue

Article abstract of DOI:10.1016/j.ica.2013.05.021

The specific functionalization of hexachlorocyclotriphosphazene with one function different from the five others was used for the synthesis of bifunctional dendrimers having one protected amine linked to the core and either 5 phosphines or 10 phosphine imines (P,N ligands) as terminal groups. In the latter case, reaction with PdCl₂(COD) affords the corresponding complexes of the P,N ligands. All compounds were characterized by multinuclear NMR, and particularly by ³¹P NMR, which proved to be a very precious tool for the characterization of sophisticated structures such as dendrimers.

Full text of DOI:10.1016/j.ica.2013.05.021

Inorganica Chimica Acta 409 (2014) 121–126
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Bifunctional metallodendrimers based on AB5 derivatives of
cyclotriphosphazene as core and P,N ligands as terminal functions
Mar Tristany a,b, Régis Laurent a,b, Hanna Dib a,b, Luca Gonsalvi c, Maurizio Peruzzini c,
Jean-Pierre Majoral a,b, Anne-Marie Caminade a,b,
⇑
a CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France
b Université de Toulouse, UPS, INPT, F-31077 Toulouse Cedex 4, France
c Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organometallici, (ICCOM-CNR) Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 27 May 2013
The specific functionalization of hexachlorocyclotriphosphazene with one function different from the five
others was used for the synthesis of bifunctional dendrimers having one protected amine linked to the
core and either 5 phosphines or 10 phosphine imines (P,N ligands) as terminal groups. In the latter case,
reaction with PdCl2(COD) affords the corresponding complexes of the P,N ligands. All compounds were
characterized by multinuclear NMR, and particularly by 31P NMR, which proved to be a very precious tool
for the characterization of sophisticated structures such as dendrimers.
Metallodendrimers Special Issue
Keywords:
Dendrimer
Phosphine
Ó 2013 Elsevier B.V. All rights reserved.
Phosphine imine (P,N) ligands
Palladium
31P NMR
1. Introduction
of functions on the other side; they are often synthesized by associ-
ating two dendrons by their core. Other examples of bifunctional
The main structural property of dendrimers is the presence of a
large number of functional groups easily accessible and gathered
in a single chemical entity. Such unique feature has led to many dif-
ferent usesofdendrimersinthefields ofmaterials, biologyandcatal-
ysis, to name as a few [1]. The increasing demand for more
sophisticated dendrimeric compounds, especially those having at
least two types of functional groups, has stimulated the imagination
of researchers. The simplest way consists in a statistical grafting of
two or more types of functions as terminal groups of dendrimers
[2], but such approach is rather contradictory with a perfectly de-
finedstructure, whichis anothermaincharacteristic ofclassicalden-
drimers. However, it has been shown that phosphorus-containing
dendrimers allows the precise grafting of two different functions
on each terminal group, in a 1:1 ratio for the whole structure [3].
Dendrons (dendritic wedges) have a single functional group at the
level of the core, and several functional groups (of another type) as
terminal groups [4]; however their shape generally resembles that
of a cauliflower instead of a bowl for most dendrimers. ‘‘Janus’’ den-
drimers [5] have one type of functions on one side and another type
dendrimersincludenewbranchesgrownfromwithinamaindendri-
mer, creating a bowl having ‘‘patches’’ of two functions on the sur-
face [6]. Finally, ‘‘off-center’’ dendrimers [7] are dendrimers in
which one function of a multivalent core is ‘‘sacrificed’’ for grafting
a function different from those that will allow the growing of the
branches. They are reminiscent to dendrons, but their structure is
more globular. All these different types of dendrimeric structure
are often synthesized for precise purposes, for instance to introduce
a fluorescent group [8].
In this paper we have synthesized several ‘‘off-center’’ metallo-
dendrimers, all based on the hexachlorocyclotriphosphazene core,
in which the reactivity of one chlorine atom among six can be dif-
ferentiated. The internal structure is of type phosphorhydrazone.
The ‘‘off-center’’ function is a protected amine, and the terminal
groups are P,N ligands suitable for the complexation of PdCl2.
These dendrimers were tentatively designed as potentially graf-
table to materials, or to have tunable solubility (through the amino
group located off-center).
2. Experimental
⇑
Corresponding author at: CNRS, LCC (Laboratoire de Chimie de Coordination),
205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France. Tel.: +33 5 61
33 31 25; fax: +33 5 61 55 30 03.
2.1. General
E-mail addresses: mar.tristany@gmail.com (M. Tristany), regis.laurent@lcc-
toulouse.fr (R. Laurent), hanna.dib@lcc-toulouse.fr (H. Dib), l.gonsalvi@iccom.cnr.it
(L. Gonsalvi), maurizio.peruzzini@iccom.cnr.it (M. Peruzzini), majoral@lcc-toulou-
se.fr (J.-P. Majoral), caminade@lcc-toulouse.fr (A.-M. Caminade).
All reactions were carried out under argon, using standard
Schlenk techniques. All solvents were distilled (THF and ether over
sodium/benzophenone, pentane over phosphorus pentoxide, and
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.05.021

122
M. Tristany et al. / Inorganica Chimica Acta 409 (2014) 121–126
CH2Cl2 over CaH2), and degassed when phosphines were used. 1H,
13C, 31P NMR spectra were recorded with Bruker AC 200, AC 250,
DPX 300 or AMX 400 spectrometers. References for NMR chemical
shifts are 85% H3PO4 for 31P NMR, SiMe4 for 1H and 13C NMR. The
attribution of 13C NMR signals has been done using Jmod, or two
dimensional HMBC and HMQC experiments when necessary. The
numbering used for NMR assignments is depicted in Scheme 1.
Phosphine 2[9], 4-hydroxytriphenylphosphine [10], and core AB5
[11] were prepared as described.
in a Schlenk tube under argon atmosphere. The mixture was cooled
to 0 °C in an ice-water bath and to this suspension a solution of AB5
core (202 mg, 0.367 mmol) in THF (4 mL) was added. The mixture
was stirred at room temperature overnight (31P NMR monitoring).
The salts were centrifuged off, the solvent was concentrated in vac-
uum and flushed with pentane to afford 4-G00 in 50% yield (322 mg,
0.18 mmol) as a white foam solid. 31P{1H} NMR (121.5 MHz, CDCl3,
d (ppm)): ꢀ6.7 (m, PIII), 8.6 (s, N3P3). 1H NMR (300 MHz, CDCl3, d
(ppm)): 1.53 (s, 9H, tBu), 2.69 (t, JHH = 6.8 Hz, 2H, CH2Ar), 3.35
(br s, 2H, CH2N), 4.61 (br s, 1H, NH), 6.90–7.10 (m, 15H, Harom),
7.22 (m, 11H, Harom), 7.3–7.45 (m, 43H, Harom), 7.45–7.8 (m, 5H,
2.2. Synthesis and characterization of phosphine 1
H
arom). 13C{1H} NMR (75.5 MHz, CDCl3, d (ppm)): 28.57 (s, CH3C),
35.45 (s, CH2Ar), 41.77 (s, CH2N), 79.39 (s, CCH3), 121.18 (br s,
C02, C12), 128.7 (d, JCP = 6.7 Hz, Cm), 128.93 (s, Cp), 129.98 (s, 10C,
C14), 129.9 (s, C03), 133.72 (d, JCP = 19.6 Hz, 20C, Co), 135.1 (s,
C13), 136.0 (s, C04), 137.1 (d, JCP = 10 Hz, Ci), 149.07 (br s, 1C, C01),
151.14 (br s, C11), 155.9 (s, C@O). MS (IS, CHCl3/MeOH/formic acid,
positive) m/z: 1757.9 [M].
A solution of tyramine (239 mg, 1.74 mmol) in hot EtOH (8 mL)
was added dropwise to a solution of 2-(diphenylphosphino)benz-
aldehyde (505 mg, 1.69 mmol) in hot EtOH (8 mL). The mixture
was left stirring at 45 °C for 2 h (31P NMR monitoring). Solvent
was removed in vacuum to afford 1 in 84% yield (603 mg,
1.47 mmol) as a pale yellow powder. 31P{1H} NMR (121.25 MHz,
CDCl3, d (ppm)): ꢀ14.1 (s, PIII). 1H NMR (300 MHz, CDCl3, d
(ppm)): 2.73 (t, JHH = 7.55 Hz, 2H, CH2Cx4), 3.75 (t, JHH = 7.55 Hz,
2H, NCH2), 6.72 (d, JHH = 8.25 Hz, 2H, Cx2H), 6.97 (d, JHH = 8.25 Hz,
2H, Cx2H), 6.9–7.0 (m, 1H, Cy3H), 7.20–7.75 (m, 12H, Harom), 7.97
(br s, 1H, OH), 8.04 (dd, JHH = 6.9 Hz, JHH = 3.9 Hz, 1H, Cy8H), 8.97
(d, JHP = 4.8 Hz, 1H, CH@N). 13C{1H} NMR (75.5 MHz, CDCl3, d
(ppm)): 36.42 (s, CH2Cx4), 62.98 (s, CH2N), 115.61 (s, Cx2), 127.79
(d, JCP = 4.0 Hz, Cy5), 128.79 (d, JCP = 7.2 Hz, Cm), 128.97 (s, Cx4),
129.09 (s, Cp), 129.23 (s, Cy6), 129.84 (s, Cx3), 130.64 (s, Cy4),
133.32 (s, Cy3), 134.13 (d, JCP = 20.4 Hz, Co), 136.19 (d, JCP = 9.2 Hz,
Ci), 137.73 (d, JCP = 18.6 Hz, Cy1), 138.95 (d, JCP = 17.2 Hz, Cy2),
155.02 (s, Cx1), 161.31 (d, JCP = 23 Hz, CH@N). MS (DCI/NH3, CHCl3,
positive) m/z: 410.4 [M+1].
2.5. Synthesis and characterization of dendrimer 5-G00
AB5 core (1.00 g, 1.83 mmol), 4-hydroxybenzaldehyde (1.2 g,
10.0 mmol) and 50 mL of THF were cooled to 0 °C in an ice-water
bath and cesium carbonate (6.5 g, 20.0 mmol) was added. The mix-
ture was stirred at room temperature overnight (31P NMR monitor-
ing). The salts were centrifuged off, the filtrate was concentrated
and flushed with pentane to afford dendrimer 5-G00 in 80% yield
(1.43 g, 1.46 mmol) as a white powder. 31P{1H} NMR (81 MHz,
CDCl3, d (ppm)): 8.6 (s, N3P3). 1H NMR (200 MHz, CDCl3, d
(ppm)): 1.42 (s, 9H, tBu), 2.75 (t, JHH = 6.8 Hz, 2H, CH2Carom), 3.32
(q, JHH = 6.8 Hz, 2H, CH2N), 4.60 (br s, 1H, NH), 6.80–7.20 (m,
14H, Harom), 7.73 (d, JHH = 8.5 Hz, 10H, C13H), 9.93 (s, 5H, CHO).
13C{1H} NMR (75 MHz, CDCl3, d (ppm)): 28.7 (s, CH3C), 35.5 (s, CH2-
Ar), 41.9 (s, CH2N), 79.5 (s, CCH3), 120.7 (s, C02), 121.2 (s, C12), 127.7
(s, C03), 131.4 (s, C13), 131.8 (s, C04), 133.7 (s, C14), 153.4 (s, C01),
154.5 (s, C11), 165.8 (s, C@O), 190.6 (s, CHO) ppm.
2.3. Synthesis and characterization of phosphine 3
A solution of 2-(diphenylphosphino)benzaldehyde (208 mg,
0.72 mmol) in THF (6 mL) was added dropwise to a solution of
Boc-protected ethylenediamine (136.7 mg, 0.85 mmol) in THF
(4 mL) at 0 °C. The mixture was left stirring for 2 days. Solvent
was evaporated to afford phosphine 3 in 80% yield (270 mg,
0.624 mmol) as a white powder. 31P{1H} NMR (101.25 MHz, CDCl3,
d (ppm)): ꢀ11.3 (s). 1H NMR (250 MHz, CDCl3, d (ppm)): 1.46 (s,
9H, tBu), 3.26 (t, JHH = 5.15 Hz, 2H, CH2NH), 3.57 (t, JHH = 5.15 Hz,
2H, CH2N@C), 4.7 (br s, 1H, NH), 6.8–6.9 (m, 1H, Cy3H), 7.2–7.5
(m, 12H, Harom), 7.8–7.9 (m, 1H, Cy8H), 8.75 (d, JHP = 3.0 Hz, 1H,
CH@N). 13C{1H} NMR (75.5 MHz, CDCl3, d (ppm)): 28.7 (s, CH3),
45.4 (s, CH2NH), 54.9 (s, CH2N@C), 70.6 (s, CCH3), 128.5 (d, JCP = 7 -
Hz, Cm), 128.7 (d, JCP = 4 Hz, Cy5), 128.9 (s, Cp), 129.1 (s, Cy6), 130.8
(s, Cy3), 133.3 (s, Cy4), 134.0 (d, JCP = 20 Hz, Co), 135.2 (d, JCP = 9.2 -
Hz, Ci), 137.3 (d, JCP = 18 Hz, Cy1), 138.5 (d, JCP = 17.2 Hz, Cy2), 157.5
(s, C@O), 163.3 (d, JCP = 23 Hz, CH@N).
2.6. Synthesis and characterization of dendrimer 5-G1
Dendrimer 5-G00 (1.43 g, 1.46 mmol) was dissolved into 25 mL
of CHCl3. A 0.259 M solution of H2NNMeP(S)Cl2 in CHCl3 (31 mL,
8.0 mmol) was added to this solution cooled to 0 °C in a ice-water
bath. The solution was stirred overnight while allowing the tem-
perature to rise slowly to room temperature. After complete reac-
tion (1H NMR monitoring) the solvent was removed in vacuum and
the product was purified by repeated precipitation with pentane
from a chloroform solution to afford 5-G1 in 91% yield (2.38 g,
1.33 mmol) as a pale yellowish solid. 31P{1H} NMR (121.5 MHz,
CDCl3, d (ppm)): 8.2 (s, N3P3), 62.4 (s, P@S). 1H NMR (300 MHz,
CDCl3, d (ppm)): 1.44 (s, 9H, tBu), 2.75 (t, JHH = 7.6 Hz, 2H, CH2C),
3.26 (m, JHH = 7.6 Hz, 2H, CH2N), 3.47 (d, JHP = 14.0 Hz, 15H, Me),
6.8–7.1 (m, 14H, Harom), 7.5–7.7 (m, 15H, Harom, CH@N). 13C{1H}
NMR (75.5 MHz, CDCl3, d (ppm)): 28.44 (s, CH3C), 31.99 (d,
JCP = 12.8 Hz, CH3N), 35.66 (s, CH2Ar), 41.87 (s, CH2N), 79.46 (s,
CCH3), 121.01 (s, C02), 121.36 (s, C12), 128.64 (s, C03), 129.80 (s,
2.4. Synthesis and characterization of phosphinodendrimer 4-G00
4-hydroxytriphenylphosphine (550 mg, 1.97 mmol), cesium
carbonate (1.29 g, 3.95 mmol) and 6 mL of THF were introduced
Scheme 1. Numbering used the assignment of NMR signals.

M. Tristany et al. / Inorganica Chimica Acta 409 (2014) 121–126
123
C13), 131.27 (s, C14), 136.02 (s, C04), 140.73 (d, JCP = 15.6 Hz, CH@N),
151.7 (br s, C01, C11), 155.6 (s, C@O).
7.6–7.7 (m, 3H, Harom) 7.7–7.8 (m, 2H, Harom), 8.01 (br s, 1H,
CH@N). 13C{1H} NMR (100.62 MHz, CD2Cl2, d (ppm)): 28.1 (s,
CH3), 41.1 (s, CH2NH), 65.8 (s, CH2N@C), 79.3 (s, CCH3), 121.1 (d,
JCP = 49.4 Hz, Cy2), 125.6 (d, JCP = 60.1 Hz, Ci), 129.1 (d, JCP = 12 Hz,
Cm), 132.5 (d, JCP = 3 Hz, Cp), 133.1 (d, JCP = 2 Hz, Cy6), 134.0 (d,
JCP = 11 Hz, Co), 134.1 (d, JCP = 4 Hz, Cy5), 134.2 (d, JCP = 3 Hz, Cy4),
136.2 (d, JCP = 8 Hz, Cy3), 136.7 (d, JCP = 16 Hz, Cy1), 155.3 (s,
C@O), 164.8 (d, JCP = 9 Hz, CH@N).
2.7. Synthesis and characterization of dendrimer 6-G1
Dendrimer 5-G1 (104.5 mg, 0.059 mmol), cesium carbonate
(438 mg, 1.34 mmol) and 10 mL of THF were cooled to 0 °C in an
ice-water bath. To this suspension was added a solution of phos-
phine 1 (314.7 g, 0.769 mmol) in THF (7 mL). The mixture was stir-
red at room temperature overnight (31P NMR monitoring). The
salts were filtered off, the filtrate was concentrated and flushed
with pentane to afford dendrimer 6-G1 in 73% yield (236.7 mg,
0.043 mmol) as a white powder. 31P{1H} NMR (121.5 MHz, CDCl3,
d (ppm)): ꢀ13.49 (s, PIII), 8.49 (s, N3P3), 63.12 (s, P@S). 1H NMR
(300 MHz, CDCl3, d (ppm)): 1.38 (s, 9H, tBu), 2.5–2.7 (br m, 22H,
CH2Carom), 3.1–3.3 (m, 17H, CH2Carom, MeN), 3.5–3.7 (br m, 20H,
CH2Carom), 4.5 (br s, 1H, NH), 6.80–7.1 (m, 64H, CHarom), 7.2–7.8
(m, 135H, CHarom, CH@N–N), 7.8–8.0 (br s, 10H, CHarom), 8.78 (br
s, 10H, CH@N–C). 13C{1H} NMR (75.5 MHz, CDCl3, d (ppm)): 28.42
(s, CH3C), 33.09 (m, CH3N), 35.50 (br s, CH2C04), 36.66 (s, CH2Cx4),
41.50 (br s, CH2NH), 62.67 (s, CH2N@C), 79.5 (s, CCH3), 121.21 (br
s, C02, C12, Cx2), 127.76 (br s, Cy5), 128.25 (br s, C03), 128.61 (d,
JCP = 7.02 Hz, Cm), 128.84 (s, Cp, Cy6), 129.87 (s, C13, Cx3), 130.19
(s, Cy4), 132.12 (br s, C14), 133.33 (s, Cy3), 134.0 (d, JCP = 20 Hz,
Co), 136.59 (d, JCP = 9.3 Hz, Ci and C04), 137.12 (s, Cx4), 137.40 (d,
JCP = 19.8 Hz, Cy1), 138.5 (br m, CH@NN), 139.34 (d, JCP = 17 Hz,
Cy2), 148.08 (d, JCP = 7.0 Hz, Cx1), 151.28 (br s, C01, C11), not ob-
served (C@O), 160.13 (d, JCP@20.5 Hz, CH@N–C).
2.10. Synthesis and characterization of dendrimer complex 6-G1-Pd10
A solution of palladium dichloride (1,5-cyclooctadiene) (60 mg,
0.21 mmol) in CH2Cl2 (3 mL) was added to a suspension of dendri-
mer 6-G1 (116 mg, 0.021 mmol) in CH2Cl2 (3 mL). The mixture was
left stirring for 3 h. The solvent was evaporated under vacuum to
afford 6-G1-Pd10 in 92% yield (147 mg, 0.0193 mmol) as a yellow
powder. 31P{1H} NMR (121.5 MHz, DMSO-d6, d (ppm)): 8.5 (s,
N3P3), 30.8 (s, P–Pd), 62.4 (s, P@S). 1H NMR (300 MHz, DMSO-d6,
4
d (ppm)): 1.30 (s, 9H, tBu), (2H, CH2C0 under DMSO), 2.9–3.0 (br
s, 20H, CH2Cx4), 3.2–3.5 (br m, 17H, CH2Carom, MeN), 4.4–4.7 (m,
20H, CH2N@C), 6.9–7.3 (m, 45H, Harom), 7.3–8.0 (m, 155H, Harom
,
CH@N–N), 8.0–8.2 (m, 10H, Harom
,
CH@N–C). 13C{1H} NMR
(75.5 MHz, DMSO-d6, d (ppm)): 28.5 (s, CH3C), 33.3 (m, CH3N),
36.3 (s, CH2C04), 41.7 (s, CH2NH), 36.5 (s, CH2Cx4), 68.3 (s, CH2-
2
N@CH), 79.0 (s, CCH3), 121.2 (d, JCP = 49 Hz, Cy2), 121.4 (Cx2, C0
,
C12), 125.5 (s, Cx3), 125.6 (d, JCP = 61 Hz, Ci), 128.1 (s, C03, C13),
129.0 (d, JCP = 12 Hz, Cm), 130.1 (s, Cp), 131.7 (d, JCP = 10 Hz, Cm),
132.4 (br s, C14), 133.0 (br s, Cy4, Cy5, Cy6), 134.1 (d, JCP = 10 Hz,
Co), 134.6 (br s, Cy3), 136.6 (s, C04), 136.8 (s, Cx4),137.9 (d, JCP = 19 -
Hz, Cy1), 138.9 (br d, JCP = 12 Hz, CH@NN), 149.0 (s, Cx1), 151.5 (br s,
C01, C11), 155.9 (s, C@O), 162.1 (br s, CH@N–C).
2.8. Synthesis and characterization of dendrimer 7-G1
Dendrimer 5-G1 (201.3 mg, 0.113 mmol), cesium carbonate
(1.07 g, 3.29 mmol) and 6 mL of THF were cooled to 0 °C in an
ice-water bath. A solution of phosphine 2 (422.9 g, 1.11 mmol) in
THF (4 mL) was added to this suspension. The mixture was stirred
at room temperature overnight (31P NMR monitoring). The salts
were filtered off, the filtrate was concentrated and flushed with
pentane to afford dendrimer 7-G1 in 66% yield (389.8 mg,
0.074 mmol) as a yellow powder. 31P{1H} NMR (121.5 MHz, CDCl3,
d (ppm)): ꢀ13.13 (s, PIII), 8.44 (s, N3P3), 62.98 (s, P@S). 1H NMR
(300 MHz, CDCl3, d (ppm)): 1.40 (s, 9H, tBu), 2.65 (m, 2H, CH2-
Carom), 3.2–3.4 (m, 17H, CH2Carom, MeN), 4.6 (br s, 1H, NH), 6.9–
7.7 (m, 199H, CHarom, CH@N–N), 8.13 (m, 10H, CHarom), 8.99 (t,
2.11. Synthesis and characterization of dendrimer complex 7-G1-Pd10
A solution of palladium dichloride (1,5-cyclooctadiene) (60 mg,
0.21 mmol) in CH2Cl2 (3 mL) was added to a suspension of dendri-
mer 7-G1 (109.1 mg, 0.0208 mmol) in CH2Cl2 (4 mL). The mixture
was left stirring for 2 h. The solvent was evaporated under vacuum
to afford 7-G1-Pd10 in 90% yield (132.4 mg, 0.019 mmol) as a yel-
low powder. 31P{1H} NMR (121.5 MHz, DMSO-d6, d (ppm)): 8.1
(s, N3P3), 31.3 (s, P–Pd), 62.2 (s, P@S). 1H NMR (300 MHz, DMSO-
d6, d (ppm)): 1.26 (s, 9H, tBu), (2H, CH2Carom under DMSO signal),
3.2–3.5 (br m, 17H, CH2Carom, MeN), 6.9–7.3 (m, 45H, Harom), 7.3–
8.0 (m, 155H, Harom, CH@N–N), 8.0–8.2 (br s, 10H, Harom), 8.5–8.7
J = 4.8 Hz, 10H, CH@N–C). 13C{1H} NMR (75.5 MHz, CDCl3,
d
(ppm): 28.46 (s, CH3C), 33.04 (d, JCP = 12.15 Hz, CH3N), 35.7 (br s,
CH2C04), 41.70 (br s, CH2NH), 79.4 (s, CCH3), 121.02 (br s, C02),
121.34 (br s, C12,), 121.96 (br s, Cx2), 122.08 (s, Cx3), 128.30 (br s,
Cy5), 128.44 (s, 10C, Cy6, C03), 128.97 (s, Cp), 129.09 (d, JCP = 7.17 Hz,
Cm and C03), 129.83 (s, C13), 130.95 (s, Cy4), 132.0 (m, C14), 133.63
(s, Cy3), 134.08 (d, JCP = 20 Hz, Co), 136.0 (br s, C04), 136.53 (d,
JCP = 9.6 Hz, Ci), 138.7 (d, JCP = 20 Hz, Cy1), 139.35 (d, JCP = 16.5 Hz,
Cy2), 139.5 (br m, CH@NN), 148.79 (d, JCP = 7.1 Hz, Cx1), 148.8 (s,
Cx4), 151.35 (br s, C01, C11), 155.8 (br s, C@O), 158.77 (d, JCP = 20.9 -
Hz, CH@N–C).
(br s, 10H, CH@N–C). 13C{1H} NMR (75.5 MHz, DMSO-d6,
d
(ppm)): 28.7 (s, CH3C), 33.5 (m, CH3N), 36.5 (s, CH2C04), 41.8 (s,
CH2NH), 78.8 (s, CCH3), 121.4 (Cx2, C02, C12), 121.8 (d, JCP = 49 Hz,
Cy2), 125.4 (s, Cx3), 125.5 (d, JCP = 62 Hz, Ci), 129.4 (s, C03, C13),
129.7 (d, JCP = 10 Hz, Cm), 132.5 (br s, C14), 133.0 (d, JCP = 2 Hz,
Cp), 133.7 (br s, Cy4, Cy5, Cy6), 134.3 (d, JCP = 11 Hz, Co), 135.3 (br
s, Cy3), 136.8 (d, JCP = 15 Hz, Cy1), 136.9 (s, C04), 138.4 (br s,
CH@NN), 149.2 (br s, Cx1), 149.5 (s, Cx4), 151.3 (m, C01, C11),
168.3 (br s, CH@N–C).
2.9. Synthesis and characterization of complex 3-Pd
3. Results and discussion
A
solution of palladium dichloride (1,5-cyclooctadiene)
Before starting the synthesis of the dendrimeric structure, we
have designed 3 types of P,N ligands potentially usable for grafting
onto the P(S)Cl2 terminal functions of the dendrimers. As the most
suitable functions for such purpose are phenols and amines, we
tried to functionalize the P,N ligands with such functions. All the
P,N ligands in this paper are obtained by condensation reactions
between 2-(diphenylphosphino)benzaldehyde and functionalized
primary amines. The reaction with tyramine in hot ethanol affords
the phosphine 1, in the same conditions than those already
(119 mg, 0.417 mmol) in CH2Cl2 (2 mL) was added to a solution
of phosphine 3 (180 mg, 0.417 mmol) in CH2Cl2 (2 mL) and the
mixture was left stirring one hour at room temperature. Solvent
was evaporated under vacuum to afford the complex 3-Pd in 87%
yield (220 mg, 0.328 mmol). 31P{1H} NMR (162 MHz, CD2Cl2, d
(ppm)): 31.0 (s). 1H NMR (400 MHz, CD2Cl2, d (ppm)): 1.34 (s,
9H, tBu), 3.44 (q, JHH = 5.8 Hz, 2H, CH2NH), 4.59 (t, JHH = 5.8 Hz,
2H, CH2N@C), 7.0–7.1 (m, 1H, Cy3H), 7.3–7.5 (m, 8H, Harom),

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M. Tristany et al. / Inorganica Chimica Acta 409 (2014) 121–126
The function that we intended to place ‘‘off-center’’ is an amine,
since it can react easily with aldehydes, for instance to be linked to
other dendrimers or to materials, and it can also be alkylated or
protonated, to afford an ammonium that may modify the solubil-
ity. However the presence of a primary amine is not compatible
with the presence of P–Cl functions, thus the amine has to be pro-
tected. We used the Boc-protected tyramine for the reaction with
N3P3Cl6. The AB5 core was obtained in this way, as described pre-
viously [11]. This compound has a very characteristic 31P NMR
spectrum, consisting of a ‘‘triplet’’ at d = 15.6 ppm and a doublet
at d = 25.9 ppm with a coupling constant JPP = 61.0 Hz. The reaction
of the AB5 core with 5 equivalents of phenol should induce the dis-
appearance of this system to give a pseudo singlet in 31P NMR. We
first tried the reaction of phosphine 1 directly onto the AB5 core,
but the reaction never went to completion, even after several days,
and the phosphine became partially oxidized. In order to verify if
the steric hindrance was responsible for the poor reactivity, we
tested the reaction of 4-hydroxytriphenylphosphine (Scheme 3).
In that case, the reaction went to completion after only one night,
and the compound 4-G00 was characterized by 31P NMR showing a
singlet corresponding to the core at d = 8.6 ppm, and another signal
corresponding to the phosphines at d = ꢀ6.7 ppm. Thus the steric
hindrance is not responsible for the poor reactivity of 1, and elec-
tronic influence of the substituent in para position of the OH has
certainly to be taken into account. As there is no imine function
in this compound (4-G00), we tried to deprotect the Boc-protected
amine with TFA, but the protonation of the phosphine
(d31P = 0 ppm) was observed instead of the deprotection of the
amine.
Scheme 2. Synthesis of functionalized diphenylphosphino ligands.
reported for obtaining the phosphine 2[9] (Scheme 2). The reaction
with the Boc-protected ethylenediamine was carried out in THF to
afford the phosphine 3. It was not possible to use directly the
unprotected ethylenediamine, as the condensation occurred on
both sides, whatever the conditions used. The phenol group of
the phosphines 1 and 2 is directly suitable for the reaction with
the P(S)Cl2 groups, whereas the Boc-protection has first to be re-
moved from the phosphine 3. For this purpose, we have tried the
reaction with trifluoroacetic acid (TFA), a classical method of
deprotection, which was already used in the case of Janus dendri-
mers containing hydrazone linkages [12]. However, in the case of 3,
the imine linkage is not stable under these conditions, and it was
cleaved as shown by the disappearance of the imine function and
the reappearance of aldehyde signals in 1H NMR. Thus only phos-
phines 1 and 2 were used later on for the reaction with the PCl2
functions of the dendrimers.
As we have previously observed that the reactivity of the P(S)Cl2
functions is higher than that of N3P3Cl6, we decided to grow the
dendrimer from the AB5 core. The first reaction is the substitution
with 4-hydroxybenzaldehyde, to afford the dendrimer 5-G00, char-
acterized in 31P NMR by a pseudo singlet at d = 8.6 ppm. Starting
from the aldehydes, the next step for the classical growing of
the phosphorus dendrimers is the condensation with the
Scheme 3. Synthesis of ‘‘off-center’’ dendrimers functionalized by one Boc-protected tyramine and several diphenylphosphino groups.

M. Tristany et al. / Inorganica Chimica Acta 409 (2014) 121–126
125
Fig. 1. Chemical structure of the ‘‘off-center’’ dendrimer 7-G1, and its 31P NMR spectrum. A): enlargement of the signal corresponding to the P=S groups; B) enlargement of the
signal corresponding to the Ar-PPh2 groups
phosphorhydrazide H2NNMeP(S)Cl2[13], which affords the dendri-
mer 5-G1 (Scheme 3). The completion of the reaction is character-
ized by the disappearance of the signal corresponding to the
aldehydes in 1H NMR at d = 9.93 ppm. Dendrimer 5-G1 is the start-
ing compound for the grafting of the phenol phosphines 1 and 2. In
both cases, an intermediate signal corresponding to the reaction of
only one Cl per P(S)Cl2 is first observed at ca. 70 ppm in 31P NMR,
which totally disappears when the reaction has gone to comple-
tion. The reaction of 10 equivalents of the phosphine 1 with 5-G1
affords the dendrimer 6-G1, whereas the reaction of 10 equivalents
of phosphine 2 with 5-G1 affords the dendrimer 7-G1 (Scheme 3).
Both dendrimers are characterized by 1H, 13C and 31P NMR. The
case of the 31P NMR spectrum of dendrimer 7-G1 is particularly
cyclotriphosphazene core, three arms are ‘‘up’’ and two arms are
‘‘down’’, and that they interact differently with the sixth function
(the Boc-protected tyramine). This spectrum illustrated the
impressive sensitivity of 31P NMR [14] to account for subtle differ-
ences in the environment of the phosphorus atoms. Indeed, the
P@S groups are at 9 bonds from the N3P3 core (and thus at 18
bonds from the P@S on the other side), and the PIII are at 19 bonds
from the N3P3 core (and thus at 38 bonds from the PIII on the other
side); only through space interactions can account for the differ-
ences observed here.
Thus, we have obtained several ‘‘off-center’’ dendrimers having
two types of functions in a 1:5 or 1:10 ratio. In order to illustrate
the potential of these compounds in organometallic chemistry,
we have attempted to complex PdCl2(COD) (COD = cyclooctadiene)
with the P,N ligands. In order to assign easily the signals to the
functions, it is generally better to perform first the reactions with
model (small) compounds. The presence of the phenol in phos-
phines 1 and 2 is not well compatible with the Cl of PdCl2(COD),
thus we first attempted the complexation with the phosphine 3.
interesting. This compound displays
3 groups of signals at
d = 8.4 ppm for the N3P3 core, d = 63 ppm for the P@S groups and
d = ꢀ13.2 ppm for the phosphines, as expected. However, these
last two signals are not simple, but are each composed of two sing-
lets in a 2/3 (or 3/2) ratio, as shown in Fig. 1. The only way to
account for such phenomenon is that, starting from the flat
Scheme 4. PdCl2 complexes of a monomer and of ‘‘off-center’’ dendrimers.

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M. Tristany et al. / Inorganica Chimica Acta 409 (2014) 121–126
The complexation on phosphorus affording the compound 3-Pd is
easily detected by 31P NMR, which displays the deshielding of the
signal corresponding to the phosphine from d = ꢀ11.3 ppm for 3 to
d = 31.0 ppm for 3-Pd. The complexation on phosphorus is con-
firmed by 13C NMR, on the carbon atoms linked to the phosphorus
atom, which display dramatic changes in both the chemical shifts
and the coupling constants (d Ci = 135.2 ppm (J = 9.2 Hz) for 3; d
Ci = 125.6 ppm (J = 60.1 Hz) for 3-Pd). The complexation has a min-
or influence on the chemical shifts of the CH of the imine functions
(8.75 and 8.01 ppm in 1H NMR, 163.3 and 164.8 ppm in 13C NMR,
for 3 and 3-Pd, respectively). However, the implication of the imine
function in the complexation is ascertained by the changes in the
chemical shifts of the CH2 group linked to the imine (3.57 and
4.59 ppm in 1H NMR, 45.4 and 65.8 ppm in 13C NMR, for 3 and 3-
Pd, respectively).
here, and particularly the possibility to selectively react one Cl of
hexachlorocyclotriphosphazene, is potentially useful for the elabo-
ration of many different types of bifunctional dendrimers. Further-
more, this work affords a new illustration of the usefulness of 31P
NMR to characterize and ascertain sophisticated dendrimeric
structures [14].
Acknowledgements
Thanks are due to the European Community through the con-
tract MRTN-CT-2003-503864 (AQUACHEM) for financial support
(grant to M. Tristany) and the COST program CM0802 (PhoSciNet).
This work was also supported by the CNRS and by the ANR DEND-
SWITCH (grant to H. Dib).
The complexation was then carried out with 10 equivalents of
PdCl2(COD) and 1 equivalent of dendrimer 6-G1 or 7-G1, affording
dendrimer 6-G1-Pd10 or 7-G1-Pd10, respectively (Scheme 4). In
both cases, the behavior observed by NMR is identical to what
was observed for 3-Pd, in particular the large deshielding of the
signal of the phosphines in 31P NMR, from ca. ꢀ13 ppm for 6-G1
and 7-G1 to ca. 31 ppm for 6-G1-Pd10 and 7-G1-Pd10. As the depro-
tection of the Boc-protected amine is not compatible with the pres-
ence of free imine and free phosphines, in a last attempt we have
tried to deprotect the dendrimer 6-G1-Pd10, in which both func-
tions are complexed, and might be stabilized. However, the cleav-
age of the imine function was again observed when adding TFA.
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4. Conclusion
We have synthesized several new dendrimeric compounds pos-
sessing two different types of functions at precise places in their
structure: one Boc-protected amine linked to the core (off-center)
and either 5 phosphines, or 10 phosphine imine (P,N) ligands as
terminal groups. In the latter case, the complexation of PdCl2 with
both the phosphine and the imine was observed as expected. At-
tempted deprotection of the amine failed, due to the high sensitiv-
ity of the imine functions to protonation inducing their cleavage,
even when they are complexed. However, the methodology used