Dendrimers with a Copper(I) Bis(phenanthroline) Core: Synthesis, Electronic Properties, and Kinetics

Article abstract of DOI:10.1021/ic049945y

The copper(I) bis(chelate) complex Cu(L⁰)₂ has been prepared from 2,9-diphenethyl-1,10-phenanthroline and Cu(CH3CN)4BF4. Derivative Cu(L⁰)₂ has been characterized by NMR, UV-vis spectroscopy, and X-ray crystallography. Interestingly, owing to the presence of the ethylene linker, the interligand π-π stacking interactions between the phenyl rings and the phenanthroline subunits in Cu(L⁰) ₂ do not induce significant distortions of the pseudotetrahedral symmetry around the Cu(I) center in the solid state or in solution. Following the synthesis of Cu(L⁰)₂ dendrimers Cu(L ^1-4)₂ with a Cu(I) bis(2,9-diphenethyl-1,10-phenanthroline) core surrounded by Frechet type dendritic branches have been prepared and the kinetics of their cyanide-assisted demetalation studied. Importantly, the surrounding dendritic wedges have no significant influence on the coordination geometry of the Cu(I) center, as deduced from their absorption spectra. Therefore, the variations of the rate constants only reflect changes resulting from the presence of the dendritic branches. The kinetics of the cyanide-mediated demetalation reaction indeed revealed that cyanide diffusion through the dendritic shell is slightly influenced by the size of the branches. Significant effects were observed in the kinetics when going from the third to the fourth generation and have been ascribed to changes in the lipophilicity around the metallic core as a result of dendritic encapsulation.

Full text of DOI:10.1021/ic049945y

Inorg. Chem. 2004, 43, 3200−3209
Dendrimers with a Copper(I) Bis(phenanthroline) Core: Synthesis,
Electronic Properties, and Kinetics
Elzbieta Gumienna-Kontecka,† Yannick Rio,‡,§ Cyril Bourgogne,‡ Mourad Elhabiri,† Re´my Louis,|
,†
,§
Anne-Marie Albrecht-Gary,* and Jean-Franc¸ois Nierengarten*
Laboratoire de Physico-Chimie Bioinorganique, UniVersite´ Louis Pasteur et CNRS (UMR 7509),
Ecole Europe´enne de Chimie, Polyme`res et Mate´riaux (ECPM), 25 rue Becquerel,
67087 Strasbourg Cedex 2, France, Groupe des Mate´riaux Organiques, Institut de Physique et
Chimie des Mate´riaux de Strasbourg, UniVersite´ Louis Pasteur et CNRS (UMR 7504),
23 rue du Loess, B.P. 43, 67034 Strasbourg, France, Groupe de Chimie des Fullere`nes et des
Syste`mes Conjugue´s, UniVersite´ Louis Pasteur et CNRS (UMR 7504), ECPM, 25 rue Becquerel,
67087 Strasbourg Cedex 2, France, and Laboratoire d’Electrochimie et de Chimie Physique du
Corps Solide, UniVersite´ Louis Pasteur et CNRS (UMR 7512), 4 rue Blaise Pascal,
67070 Strasbourg Cedex, France
Received January 13, 2004
The copper(I) bis(chelate) complex Cu(L0)2 has been prepared from 2,9-diphenethyl-1,10-phenanthroline and
Cu(CH CN)4BF . Derivative Cu(L0)2 has been characterized by NMR, UV−vis spectroscopy, and X-ray crystallography.
3
4
Interestingly, owing to the presence of the ethylene linker, the interligand π−π stacking interactions between the
phenyl rings and the phenanthroline subunits in Cu(L0)2 do not induce significant distortions of the pseudotetrahedral
symmetry around the Cu(I) center in the solid state or in solution. Following the synthesis of Cu(L0)2, dendrimers
Cu(L1-4)2 with a Cu(I) bis(2,9-diphenethyl-1,10-phenanthroline) core surrounded by Fre´chet type dendritic branches
have been prepared and the kinetics of their cyanide-assisted demetalation studied. Importantly, the surrounding
dendritic wedges have no significant influence on the coordination geometry of the Cu(I) center, as deduced from
their absorption spectra. Therefore, the variations of the rate constants only reflect changes resulting from the
presence of the dendritic branches. The kinetics of the cyanide-mediated demetalation reaction indeed revealed
that cyanide diffusion through the dendritic shell is slightly influenced by the size of the branches. Significant
effects were observed in the kinetics when going from the third to the fourth generation and have been ascribed
to changes in the lipophilicity around the metallic core as a result of dendritic encapsulation.
Introduction
interdisciplinary branch of science located at the interfaces
between chemistry, physics, and biology. Dendritic macro-
molecules have shown a wide range of physical and chemical
properties that make them attractive for applications in fields
including drug delivery,2 catalysis,3 and optoelectronics.4
Many future developments will rely on our ability to
In recent years, the rapid advances in dendrimer synthetic
chemistry have moved toward the creation of functional
systems with increased attention to potential applications.1
This has given impetus to make dendrimer research a truly
* Authors to whom correspondence should be addressed.
E-mail: amalbre@chimie.u-strasbg.fr (A.-M.A.-G.); jfnierengarten@
chimie.u-strasbg.fr (J.-F.N.).
(2) For examples, see: (a) Kono, K.; Liu, M.; Fre´chet, J. M. J.
Bioconjugate Chem. 1999, 10, 1115. (b) Malik, N.; Wimattanapatapee,
R.; Klopsch, R.; Lorenz, K.; Frey, H.; Weener, J. W.; Meijer, E. W.;
Paulus, W.; Duncan, R. J. Controlled Release 2000, 65, 133. (c)
Grinstaff, M. W. Chem.sEur. J. 2002, 8, 2839.
(3) (a) Oosterom, G. E.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M. Angew. Chem., Int. Ed. 2001, 40, 1828. (b) Twyman, L.
J.; King, A. S. H.; Martin, I. K. Chem. Soc. ReV. 2002, 31, 69. (c)
Che, C.-M.; Huang, J.-S.; Zhang, J.-L. C. R. Chimie 2003, 6, 1105.
(d) van Klink, G. P. M.; Dijkstra, H. P.; van Koten, G. C. R. Chimie
2003, 6, 1079. (e) Ribourdouille, Y.; Engel, G. D.; Gade, L. H. C. R.
Chimie 2003, 6, 1087. (f) Soai, K.; Sato, I. C. R. Chimie 2003, 6,
1097.
† Laboratoire de Physico-Chimie Bioinorganique, Universite´ Louis
Pasteur et CNRS.
‡ Groupe des Mate´riaux Organiques, Institut de Physique et Chimie des
Mate´riaux de Strasbourg, Universite´ Louis Pasteur et CNRS.
§ Groupe de Chimie des Fullere`nes et des Syste`mes Conjugue´s, ECPM.
| Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide,
Universite´ Louis Pasteur et CNRS.
(1) (a) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendrimers and
Dendrons: Concepts, Syntheses, Applications; VCH: Weinheim,
Germany, 2001. (b) Dendrimers and other Dendritic Polymers;
Fre´chet, J. M. J., Tomalia, D. A., Eds.; Wiley: Chichester, U.K., 2001.
3200 Inorganic Chemistry, Vol. 43, No. 10, 2004
10.1021/ic049945y CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/02/2004

Dendrimers with a Copper(I) Bis(phenanthroline) Core
Scheme 1
understand their intimate properties. However, structural
information is quite difficult to obtain for dendritic molecules.
Actually, even if dendrimers have precise compositional and
constitutional aspects, they exhibit many possible conforma-
tions.1 In addition, they generally lack long-range order in
the condensed phase and structural characterization of large
dendrimers by X-ray crystallography is nearly impossible.
Therefore, the best way to characterize dendritic structures
relies on indirect spectroscopic methods.5 As part of this
research, the systematic study of dendrimers with an active
core unit as a function of the generation number is of
particular interest.5,6 Information about the shielding of the
central unit is derived from the effect the dendritic shell has
on some specific properties of the core. For example, kinetic
studies of chemical reactions involving the central core unit
give insight into substrate diffusion through the dendritic shell
and allow for an evaluation of the accessibility of the core.5
On the other hand, specific changes in the microenvironment
of electroactive7 and/or photoactive5,8 cores are conveniently
analyzed by monitoring the redox and/or photophysical
properties as a function of the generation number. In a recent
paper,9 we reported the synthesis and the electrochemical
properties of the dendritic Cu(I) bis(phenanthroline) com-
plexes derived from ligands L0-4 (Scheme 1). When the size
of the dendritic shell is increased, the electron transfer
kinetics are attenuated. This effect has been observed for
several examples of dendrimers with an electroactive core7
and illustrates the dendritic shell effect that leads to a more
hindered approach of the core to the electrode.
a
Scheme 2. Preparation of Cu(L0)2
In this paper, we now report in detail the preparation of
L0-4 and of the corresponding Cu(I) complexes Cu(L0-4)2.
The X-ray structure of Cu(L0)2 in the solid state has been
resolved. In solution, NMR and UV-vis characterization and
cyanide-assisted dissociation kinetics of the L0-4 bis(chelate)-
cuprous complexes have been carried out. For the sake of
comparison, the demetalation kinetics of the Cu(I) complexes
of neocuproine (2,9-dimethyl-1,10-phenanthroline ) dmp)
and 2,9-di(p-anisyl)-1,10-phenanthroline (dap) have been also
examined.
a Reagents and conditions: (a) LDA (2 equiv), THF, -78 °C, then benzyl
bromide, -78 °C to room temp (55%); (b) Cu(CH3CN)4BF4, CH2Cl2,
CH3CN, room temp (96%).
Results and Discussion
Synthesis and X-ray Crystal Structure of Cu(L0)2. The
synthesis of the Cu(I) complex Cu(L0)2 is depicted in Scheme
2. Compound L0 was prepared from dmp by deprotonation
of the methyl groups with lithium diisopropylamide (LDA)
to generate the corresponding dicarbanionic species,10 fol-
lowed by reaction with benzyl bromide. The Cu(I) complex
Cu(L0)2 was then obtained in 96% yield by treatment of L0
with Cu(CH3CN)4BF4 in CH2Cl2/CH3CN at room tempera-
ture.
(4) (a) Balzani, V.; Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi,
M. Acc. Chem. Res. 1998, 31, 26. (b) Fisher, M.; Vo¨gtle, F. Angew.
Chem., Int. Ed. 1999, 38, 884. (c) Adronov, A.; Fre´chet, J. M. J. Chem.
Commun. 2000, 1701. (d) Balzani, V.; Ceroni, P.; Juris, A.; Venturi,
M.; Campagna, S.; Puntoriero, F.; Serroni, S. Coord. Chem. ReV. 2001,
219, 545. (e) Newkome, G. R.; He, E.; Moorefield, C. N. Chem. ReV.
1999, 99, 1689. (f) Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Chem.
ReV. 1999, 99, 1747. (g) Zeng, F.; Zimmerman, S. C. Chem. ReV.
1997, 97, 1681. (h) Chow, H.-F.; Mong, T. K.-K.; Nongrum, M. F.;
Wan, C.-W. Tetrahedron 1998, 54, 8543. (i) Smith, D. K.; Diederich,
F. Chem.sEur. J. 1998, 4, 1353. (j) Bosman, A. W.; Janssen, H. M.;
Meijer, E. W. Chem. ReV. 1999, 99, 1665. (k) Adronov, A.; Fre´chet,
J. M. J. Chem. Commun. 2000, 1701. (l) Inoue, K. Prog. Polym. Sci.
2000, 25, 453. (m) Nierengarten, J.-F. Top. Curr. Chem. 2003, 228,
87.
1
The air-stable complex Cu(L0)2 was characterized by H
and 13C NMR spectroscopy, elemental analysis, and X-ray
crystallography. In the structure, two different conformers
(noted A and B) are observed for the Cu+(L0)2 cation. As
shown in Figure 1, the main difference among them is the
orientation of the four terminal phenyl subunits. In the first
one, the two phenyl groups of both ligands are located on
either side of the plane of their phenanthroline core (anti
conformation) and cation A adopts a helical type structure.
In contrast, whereas one ligand of cation B is also in an anti
conformation, the two phenyl moieties belonging to the other
(5) (a) Hecht, S.; Fre´chet, J. M. J. Angew. Chem., Int. Ed. 2001, 40, 74
and references therein. (b) Gorman, C. B.; Smith, J. C. Acc. Chem.
Res. 2001, 34, 60.
(6) Nierengarten, J.-F. C. R. Chimie 2003, 6, 725.
(7) (a) Cameron, C. S.; Gorman, C. B. AdV. Funct. Mater. 2002, 12, 17
and references therein. (b) Gorman, C. B. C. R. Chimie 2003, 6, 911.
(8) Nierengarten, J.-F.; Armaroli, N.; Accorsi, G.; Rio, Y.; Eckert, J.-F.
Chem.sEur. J. 2003, 9, 36.
(9) Rio, Y.; Accorsi, G.; Armaroli, N.; Felder, D.; Levillain, E.; Nieren-
garten, J.-F. Chem. Commun. 2002, 2830.
(10) Nierengarten, J.-F.; Dietrich-Buchecker, C. O.; Sauvage, J.-P. New J.
Chem. 1996, 20, 685.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3201

Gumienna-Kontecka et al.
Figure 1. Representation of the two conformers of Cu+(L0)2 seen in the
X-ray crystal structure and details of the coordination sphere around the
Cu(I) cation for both of them.
Figure 2. Stacking within the Cu(L0)2 lattice. (A) View highlighting
intermolecular π-π stacking interactions between two neighboring cations
(orange, conformer A; green, conformer B). (B) View down the crystal-
lographic axis a revealing alternated layers of the two conformers of the
Cu+(L0)2 cation in the X-ray crystal structure (orange, conformer A; green,
conformer B; red, the BF4- anions). (C) Details of the packing in the layer
containing conformer A (view down the crystallographic axis c). (D) Details
of the packing in the layer containing conformer B (view down the
crystallographic axis c).
Table 1. Bond Distances (Å) and Angles (deg) within the Coordination
Spheres for Both Conformers of Cu(L0)2 (See Figure 1 for the
Numbering)
conformer A
conformer B
Cu(1)-N(1)
2.020(9)
2.023(9)
2.027(8)
2.027(8)
83.4(4)
126.4(3)
124.7(3)
122.6(3)
122.6(4)
82.6(4)
Cu(2)-N(5)
2.029(7)
2.041(8)
2.024(8)
2.047(8)
82.3(3)
128.5(3)
123.4(4)
121.6(3)
124.8(3)
82.2(3)
Cu(1)-N(2)
Cu(2)-N(6)
Cu(1)-N(3)
Cu(1)-N(4)
Cu(2)-N(7)
Cu(2)-N(8)
N(1)-Cu(1)-N(2)
N(1)-Cu(1)-N(3)
N(1)-Cu(1)-N(4)
N(2)-Cu(1)-N(3)
N(2)-Cu(1)-N(4)
N(3)-Cu(1)-N(4)
N(5)-Cu(2)-N(6)
N(5)-Cu(2)-N(7)
N(5)-Cu(2)-N(8)
N(6)-Cu(2)-N(7)
N(6)-Cu(2)-N(8)
N(7)-Cu(2)-N(8)
one ligand and the phenyl subunits of the other one in both
A and B, close inspection of the crystal packing reveals a
network of intermolecular π stacking interactions between
the different aromatic rings of neighboring Cu+(L0)2 cations.
For example, the simultaneous π-π interactions of a phenyl
unit of cation A with two aromatic rings of the neighboring
cation B are highlighted in Figure 2A. Specifically, a
phenanthroline moiety and a phenyl ring belonging to the
second ligand of cation B are both involved in intermolecular
π-π stacking interactions with the same phenyl unit of A.
It can be added that the two aromatic rings of B giving rise
to this intermolecular stacking are themselves in π-π
interactions in a face-to-edge manner. As previously men-
tioned, there is no flattening of the two ligands relative to
one another due to the crystal packing forces. It seems that
the latest forces have only an influence on the dihedral angle
between the phenanthroline core and the terminal phenyl
subunits. In other words, rotation around the CH2CH2 linker
is sufficient to optimize intermolecular contacts within the
crystal lattice and there is no need to further distort the
coordination sphere around the Cu(I) cation.
one are located on the same side relative to the plane of
their phenanthroline unit (syn conformation).
The coordination sphere around the Cu(I) cation is quite
similar for both conformers (Figure 1 and Table 1). In crude
terms, the coordination geometry is pseudotetrahedral, but
there are some significant deviations from the tetrahedral
symmetry. In particular, the chelate-bite angle is only 82.2-
83.4°, a typical value for such phenanthroline complexes.11-14
However, unlike what is typically seen in the solid state
structures of related copper(I) complexes, there is no
flattening of the two ligands relative to one another (toward
a square-planar geometry) as a consequence of the crystal
packing forces.11-14 Effectively, the dihedral angle between
the ligands planes is almost 90° for both A and B. As a
consequence, the four Cu-N distances are almost identical
and the geometry of the copper/nitrogen framework is quite
regular by comparison with the cases of other Cu(I) bis-
(phenanthroline) complexes.
Observation of the crystal lattice down the crystallographic
axis a reveals alternated layers of cations A and B (Figure
2B). Within the layer formed by conformer A, the Cu+(L0)2
cations are organized in columnar arrays parallel to the
crystallographic axis b (Figure 2C). As already mentioned,
cation A adopts a helical type structure, and it can be noted
that the columns alternate right- and left-handed helical
conformers. As shown in Figure 2D, a similar organization
is observed within the layer containing the Cu+(L0)2 cation
B.
In addition to several intramolecular face-to-edge π
stacking interactions between the phenanthroline moiety of
(11) Eggleston, M. K.; Fanwick, P. E.; Pallenberg, A. J.; McMillin, D. R.
Inorg. Chem. 1997, 36, 4007.
(12) Klemens, F. K.; Palmer, C. E. A.; Rolland, S. M.; Fanwick, P. E.;
McMillin, D. R.; Sauvage, J.-P. New J. Chem. 1990, 14, 129.
(13) Dobson, J. F.; Green, B. E.; Healy, P. C.; Kennard, C. H. L.;
Pakawatchai, C.; White, A. H. Aust. J. Chem. 1984, 37, 649.
(14) Klemens, F. K.; Fanwick, P. E.; Bibler, P. E.; McMillin, D. R. Inorg.
Chem. 1989, 28, 3076.
3202 Inorganic Chemistry, Vol. 43, No. 10, 2004

Dendrimers with a Copper(I) Bis(phenanthroline) Core
a
Scheme 3. Preparation of Cu(L1-4)2
Figure 3. 1H NMR spectra (200 MHz, CD2Cl2, 25 °C) of (A) L3 and (B)
Cu(L3)2.
a Reagents and conditions: (a) LDA (2 equiv), THF, -78 °C, then
p-[(tert-butyldimethylsilyl)oxy]benzyl bromide, -78 °C to room temp
(38%); (b) TBAF, THF, 0 °C (97%); (c) GnBr, K2CO3, 18-C-6, acetone,
∆ (n ) 1, 76%; n ) 2, 95%; n ) 3, 96%; n ) 4, 99%); (d) Cu(CH3CN)4BF4,
CH2Cl2, CH3CN, room temp (n ) 1, 95%; n ) 2, 72%; n ) 3, 92%; n )
4, 85%).
dendrimers being observed. In all the cases, a singly charged
ion peak assigned to the Cu(I) complex after loss of the
tetrafluoroborate counteranion ([M - BF4]+) was observed.
The 1H NMR spectra of Cu(L1-4)2 provided good evidence
for their formation. Effectively, as a result of the ring current
effect of one phenanthroline subunit on the 2,9-substituents
of the second one in the complex, the signals of the protons
belonging to the groups directly attached to the phenanthro-
line core are shielded by about 1.0 ppm in Cu(L1-4)2 when
Synthesis and Characterization of the Dendritic Cu(I)
Complexes Cu(L1-4)2. The synthesis of the dendritic ligands
L1-4 and the corresponding Cu(I) complexes is shown in
Scheme 3. Treatment of dmp with LDA at -78 °C followed
by reaction of the resulting dicarbanion with p-[(tert-
butyldimethylsilyl)oxy]benzyl bromide gave 1 in a moderate
yield (38%). Actually, products of monoalkylation were also
formed in the reaction, making the purification of 1
particularly difficult. However, since sufficient quantities of
compound 1 were thus obtained, no particular efforts were
made to optimize this step. Cleavage of the phenolic TBDMS
ethers in 1 was then achieved by reaction with an excess of
tetrabutylammonium fluoride (TBAF) in THF at 0 °C.
Diphenol 2 thus obtained was treated with benzyl bromide
G1Br in the presence of K2CO3 and 18-crown-6 (18-C-6) in
refluxing acetone to give the first generation ligand L1. The
next generation compounds L2-4 were prepared by reaction
of 2 with the corresponding Fre´chet type dendritic benzylic
bromides15 G2-4Br under similar conditions. The dendritic
Cu(I) complexes Cu(L1-4)2 were finally obtained in good
yields by treatment of the corresponding ligands L1-4 with
Cu(CH3CN)4BF4 in CH2Cl2/CH3CN at room temperature.
The coordination of the phenanthroline ligand to the Cu(I)
cation was easily observed by an instantaneous color change
of the solution upon addition of the Cu(I) salt. Actually, the
colorless ligand solution became orange-red due to the
apparition of the metal-to-ligand charge transfer (MLCT)
band characteristic of the Cu(I) bis(2,9-disubstituted-1,10-
compared to the signals in the corresponding ligands L1-4
.
This particular behavior is specific of such copper(I)
complexes.16 As a typical example, the 1H NMR spectra of
L3 and Cu(L3)2 recorded in CD2Cl2 are shown in Figure 3.
In addition to the signals corresponding to the dendritic
1
branches, the H NMR spectrum of L3 is characterized by
two sets of AB quartets and a singlet in a typical pattern for
a 2,9-disubstituted-1,10-phenanthroline: an AA′XX′ system
for the p-disubstituted phenyl ring and an A2X2 system for
the CH2CH2 linker. Upon complexation to the Cu(I) cation,
dramatic changes are observed for the chemical shifts of Ha,
Hb, Hc, Hd, and He, showing that the CH2CH2-phenyl-
OCH2 moieties attached to one phenanthroline ligand are
located on either side of the other one in Cu(L3)2. In addition,
the particularly important shielding observed for the signals
of protons Hc and Hd also suggests strong interligand π-π
stacking interactions in the Cu(I) complex between the
p-disubstituted phenyl rings and the phenanthroline subunits.
This appears quite reasonable on the basis of the X-ray
crystal structure of the corresponding model compound
Cu(L0)2. It can also be noted that there are no complexation-
induced changes in the chemical shifts for the signals
corresponding to the poly(benzyl ether) dendritic wedges.
The latter observation suggests that there are no particular
π stacking interactions between the phenanthroline moieties
and the dendritic benzylic units in CH2Cl2 solutions.
phenanthroline) derivatives (see below). Compounds Cu(L1-4
)
2
1
were characterized by H and 13C NMR spectroscopy and
elemental analysis. In addition, the structures of dendrimers
Cu(L2-4
)
were also confirmed by MALDI-TOF mass
Electronic Absorption Spectra. The electronic spectra
of Cu(dmp)2, Cu(dap)2, and Cu(Ln)2 were recorded under
2
spectrometry, with no peaks corresponding to defected
(15) (a) Hawker, C.; Fre´chet, J. M. J. Chem. Commun. 1990, 1010. (b)
Hawker, C.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990, 112, 7638.
(16) Dietrich-Buchecker, C. O.; Marnot, P. A.; Sauvage, J.-P.; Kintzinger,
J.-P. NouV. J. Chim. 1984, 8, 573.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3203

Gumienna-Kontecka et al.
Table 2. Absorption Maxima and Extinction Coefficients of
a
Cu(dmp)2, Cu(dap)2, and Cu(Ln)2
λ
max (nm) (ꢀmax (M-1 cm-1))
CH2Cl2/CH3CN/H2O )
CH2Cl2/CH3CN/H2O )
compound
50/48/2 (v/v/v)a
15/80/5 (v/v/v)b
Cu(dmp)2
Cu(dap)2
Cu(L0)2
Cu(L1)2
Cu(L2)2
Cu(L3)2
Cu(L4)2
456 (8360)
430 (2610)
455 (6050)
455 (5300)
456 (6100)
456 (6100)
456 (6150)
455 (8300)
430 (2800)
a I ) 0.05 M (Bu4NBF4); T ) 25.0 ( 0.2 °C. b I ) 0.1 M
(n-C4H9)4NCF3SO3; T ) 25.0 ( 0.1 °C; ref 17. The errors were estimated
to be within 1 nm for the wavelengths and 5% for the extinction coeffi-
cients.
Figure 4. Electronic spectra of the Cu(dmp)2 (dot), Cu(dap)2 (dash dot),
Cu(L0)2 (solid), and Cu(L4)2 (dash) complexes. Solvent: CH2Cl2/CH3CN/
H2O ) 50/48/2 (v/v/v); I ) 0.05 M (Bu4NBF4); T ) 25.0 ( 0.2 °C.
the experimental conditions used for the kinetic studies (see
below) and are depicted in Figure 4 and Supporting Informa-
tion Figure S1. By comparison with the cases of previous
studies,17 the visible absorption of Cu(dmp)2 and Cu(dap)2
appears not to be significantly sensitive to changes of ionic
strength and solvent (Table 2).
The absorption spectra of Cu(Ln)2 (350-600 nm) display
the characteristic features of Cu(I) bis(phenanthroline)
complexes. Their MLCT bands are constituted by a main
absorption (band II) centered at 455 nm with two satellite
shoulders (bands III and I) at 380 and 510 nm, respectively
(Figure 4 and Supporting Information Figure S1). Band II
corresponds to the b2(xz) f b3(ψ) transition polarized along
the z axis which joins the metal and ligand centers. The
shoulders at lower (band I) and higher (band III) energies
have been attributed to the b3(yz) f b2(ψ) transition polarized
along the z axis and to the b3(yz) f a(ø) and b3(yz) f b1(ø)
transitions polarized along the x and y axes, respec-
tively.11,18-21
the interligand π-π stacking interactions between the phenyl
groups and the phenanthroline moieties evidenced by NMR
(Figure 3) do not induce significant distortions of the
pseudotetrahedral symmetry around the Cu(I) center in
solution. The latter observation is in good agreement with
the coordination geometry observed for Cu(L0)2 in the solid
state. Since the spectroscopic properties are not changing
within the series of Cu(Ln)2 complexes (Table 2, Figure 4,
and Supporting Information Figure S1), it may be also
concluded that increased size of the surrounding dendritic
wedges does not affect the electronic structure of the central
Cu(I) bis(phenanthroline) core. In other words, the dendrons
have no influence on the coordination geometry of the Cu(I)
center. This is expected, since the bulky substituents are not
directly attached to the phenanthroline ligand.18
Kinetics. The cyanide-assisted demetalation of the den-
dritic Cu(I) complexes Cu(Ln)2 was studied in an analogous
way to that adopted for the Cu(I) catenates.25 All the
experiments were carried out in a freshly prepared homo-
geneous ternary solvent, CH2Cl2/CH3CN/H2O ) 50/48/2
(v/v/v), which was chosen in order to solubilize both the
reactants and the products of the decomplexation reaction.
For comparison purposes, the demetalation kinetics of
Cu(dmp)2 and Cu(dap)2 were also studied under the same
experimental conditions. Previous studies on their decom-
plexation by cyanide were carried out in homogeneous mixed
solvents, either CH3CN/H2O ) 90/10 (by weight)25 or CH2-
Cl2/CH3CN/H2O ) 15/80/5 (v/v/v).26,27 The latter is a suitable
solvent for all the Cu(Ln)2 complexes studied in this work
except for the largest one (Cu(L4)2), which demands a higher
quantity of CH2Cl2. Hence, solvents with an increasing
amount of CH2Cl2 were tested and the optimal solubility was
achieved with a ternary solvent, CH2Cl2/CH3CN/H2O ) 50/
48/2 (v/v/v).
Interestingly, the shapes of the MLCT absorption spectra
of the dendritic Cu(Ln)2 complexes are rather similar to that
of Cu(dmp)2, for which spectral characteristics were assigned
assuming a slightly distorted tetrahedral coordination
geometry.18,22-23 In contrast, for Cu(dap)2, the tetrahedral
symmetry around the copper(I) center is strongly distorted
due to the interligand π-π stacking interactions.24 This is
reflected by a hypochromic blue-shift of the MLCT absorp-
tion maximum, bandwidth broadening, and a considerable
increase of the absorption of band I relative to that of band
II (Figure 4 and Table 2).11,19 The MLCT absorption features
of the Cu(Ln)2 complexes (Table 2) suggest therefore that
(17) Meyer, M.; Albrecht-Gary, A.-M.; Dietrich-Buchecker, C. O.; Sauvage,
J.-P. Inorg. Chem. 1999, 38, 2279.
(18) For a review on the photophysical properties of Cu(I) bis(phenan-
throline) derivatives, see: Armaroli, N. Chem. Soc. ReV. 2001, 30,
113.
(19) Phifer, C. C.; McMillin, D. R. Inorg. Chem. 1986, 25, 1329.
(20) Parker, W. L.; Crosby, G. A. J. Phys. Chem. 1989, 93, 5692.
(21) Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli,
N. J. Am. Chem. Soc. 2001, 123, 6291.
(25) Albrecht-Gary, A.-M.; Saad, Z.; Dietrich-Buchecker, C. O.; Sauvage,
J.-P. J. Am. Chem. Soc. 1985, 107, 3205.
(22) Ichinaga, A. K.; Kirchhoff, J. R.; McMillin, D. R.; Dietrich-Buchecker,
C. O.; Marnot, P. A.; Sauvage, J.-P. Inorg. Chem. 1987, 26, 4290.
(23) Everly, R. M.; McMillin, D. R. J. Phys. Chem. 1991, 95, 9071.
(24) Geoffroy, M.; Wermeille, M.; Dietrich-Buchecker, C. O.; Sauvage,
J.-P.; Bernardinelli, J.-P. Inorg. Chim. Acta 1990, 167, 157.
(26) Chambron, J. C.; Dietrich-Buchecker, C.; Nierengarten, J. F.; Sauvage,
J.-P.; Solladie´, N.; Albrecht-Gary, A.-M.; Meyer, M. New J. Chem.
1995, 19, 409.
(27) Meyer, M.; Albrecht-Gary, A.-M.; Dietrich-Buchecker, C. O.; Sauvage,
J.-P. J. Am. Chem. Soc. 1997, 119, 4599.
3204 Inorganic Chemistry, Vol. 43, No. 10, 2004

Dendrimers with a Copper(I) Bis(phenanthroline) Core
Table 3. Experimental Pseudo-First-Order Decomplexation Rate Constants of Bis(chelate) Copper(I) Complexes by Cyanidea
Cu(dmp)2
Cu(dap)2
Cu(L0)2
Cu(L1)2
Cu(L2)2
Cu(L3)2
Cu(L4)2
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
[CN-]0
(mM)
kobs
(s-1
)
(s-1
)
(s-1
)
(s-1
)
(s-1
)
(s-1
)
(s-1
)
0.60
0.75
0.91
1.05
1.21
1.37
1.51
1.81
2.12
2.42
2.44(1)
3.12(2)
3.58(4)
4.24(4)
4.68(2)
5.22(6)
5.84(2)
6.88(2)
7.7(1)
1.88
2.82
3.27
3.76
4.25
4.7
0.3348(8)
0.355(4)
0.3635(6)
0.3714(5)
0.377(1)
0.383(1)
0.3972(8)
0.419(4)
0.61
0.76
0.92
1.06
1.22
1.36
1.52
1.83
2.44
0.084(1)
0.114(2)
0.136(1)
0.159(1)
0.183(2)
0.194(1)
0.216(1)
0.255(1)
0.344(2)
0.60
0.90
1.04
1.19
1.35
1.49
1.79
2.39
0.0672(8)
0.1172(4)
0.1366(9)
0.1540(7)
0.184(1)
0.204(1)
0.244(2)
0.3526(5)
0.59
0.89
1.03
1.19
1.34
1.49
1.78
2.38
0.067(2)
0.1154(9)
0.1390(7)
0.1606(5)
0.1806(5)
0.2068(8)
0.247(1)
0.346(1)
0.60
0.74
0.90
1.04
1.20
1.35
1.49
1.79
2.09
2.39
0.0658(8)
0.0900(7)
0.1130(7)
0.1346(9)
0.1524(5)
0.1734(5)
0.195(1)
0.235(2)
0.277(2)
0.321(2)
0.76
0.92
1.06
1.22
1.36
1.52
1.83
2.44
0.068(4)
0.0907(6)
0.108(1)
0.128(1)
0.142(1)
0.1603(1)
0.1843(6)
0.2523(6)
5.64
7.53
8.71(6)
a Solvent: CH2Cl2/CH3CN/H2O ) 50/48/2 (v/v/v); I ) 0.05 M (Bu4NBF4); T ) 25.0 ( 0.2 °C. Values in parentheses are errors on the last significant
digit estimated as standard deviation, 1σ.
Table 4. Kinetic Parameters Relative to the Dissociation of
Bis(chelate) Copper(I) Complexes by Cyanidea
compound
kD ( σ (s-1
)
kCN ( σ (M-1 s-1
)
Cu(dmp)2
Cu(dap)2
Cu(L0)2
Cu(L1)2
Cu(L2)2
Cu(L3)2
Cu(L4)2
0.53 ( 0.09
3423 ( 63
14.5 ( 0.8
143 ( 2
139 ( 3
139 ( 3
131 ( 2
103 ( 1
0.314 ( 0.003
b
b
b
b
b
a Solvent: CH2Cl2/CH3CN/H2O ) 50/48/2 (v/v/v); I ) 0.05 M (Bu4NBF4);
T ) 25.0 ( 0.2 °C. b The value of kD was constrained to zero.
the only cuprous product would be CuI(CN)43-, the overall
reaction could be written:
CuI(L)2+ + 4CN- f 2L + CuI(CN)4
(1)
3-
A monoexponential absorbance decay observed in the
seconds time range indicates a single rate-limiting decom-
plexation step. The excellent agreement between the initial
absorbance and the spectrophotometric data measured for
the Cu(I) complexes corresponds to the absence of faster
steps prior to the recorded one. As an example, Figure 5A
displays the recording of absorption versus time at 465 nm
for Cu(L4)2. The variations of the pseudo-first-order rate
constants, kobs (Table 3), with the analytical cyanide con-
centrations show a linear dependence. The corresponding
data are given in Figure 5B for the Cu(L4)2 complex, while
they are presented in Supporting Information Figure S2 for
Cu(dmp)2, Cu(dap)2, and Cu(L0-3)2.
Figure 5. (A) Kinetic trace recorded for the dissociation of complex
Cu(L4)2 and (B) plot of its pseudo-first-order rate constant, kobs, as a function
of cyanide concentration. [Cu(L4)2]0 ) 1.47 × 10-5 M; [CN-]0 ) 1.22 ×
10-3 M. Solvent: CH2Cl2/CH3CN/H2O ) 50/48/2 (v/v/v); I ) 0.05 M
(Bu4NBF4); T ) 25.0 ( 0.2 °C; wavelength of detection, λ ) 456 nm.
The second-order rate constants were calculated by non-
weighted linear regression and are given together with their
corresponding standard deviations31 in Table 4.
The corresponding rate law is expressed by eq 2, where
kD and kCN (Table 4) stand for the monomolecular dissocia-
tion and cyanide-assisted bimolecular rate constants, respec-
tively.
Cyanide anion is a strong nucleophile known to form very
stable Cu(I) complexes.28-30 The cyanide-assisted demeta-
lation kinetics of the bis(chelate) complexes Cu(dmp)2,
Cu(dap)2, and Cu(Ln)2 have been examined in excess of
CN-. If we suppose that under our experimental conditions
d[CuI(L)2 ]
+
+
ν ) -
0 ) kobs[CuI(L)2 ]0 )
dt
+
{kD + kCN[CN-]0}[CuI(L)2 ]0 (2)
(28) Kunschert, F. Z. Z. Anorg. Allg. Chem. 1904, 41, 359.
(29) Bjerrum, J. Metal Ammine Formation in Aqueous Solution; P. Haase
and Son: Copenhagen, Denmark, 1957.
(30) Hefter, G.; May, P.; Sipos, P. J. Chem. Soc., Chem. Commun. 1993,
1704.
(31) Microcal Origin; Microcal Software, Inc.: Northampton, MA, 1991-
1997.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3205

Gumienna-Kontecka et al.
Figure 6. Schematic representation of the cyanide-assisted dissociation of the cuprous core of all the Cu(I) complexes examined in this work.
Table 5. Kinetic Parameters for the Decomplexation of Cu(dmp)2 and Cu(dap)2 by Cyanide
Cu(dmp)2
Cu(dap)2
k
D (s-1
)
kCN (M-1 s-1
)
kD (s-1
)
kCN (M-1 s-1
)
CH3CN/H2O ) 90/10a
4.8 ( 0.6
2.9 ( 0.3
0.53 ( 0.09
820 ( 43
1920 ( 20
3421 ( 60
0.48 ( 0.01
0.50 ( 0.01
0.311 ( 0.003
6.5 ( 0.7
8.8 ( 0.4
14.9 ( 0.8
CH3CN/CH2Cl2/H2O ) 80/15/5 (v/v/v)b
CH3CN/CH2Cl2/H2O ) 48/50/2 (v/v/v)c
a I ) 0.1 M (Bu4NClO4); T ) 25.0 ( 0.1 °C; ref 25. b I ) 0.1 M (Bu4NCF3SO3); T ) 25.0 ( 0.1 °C; ref 29. c I ) 0.05 M (Bu4NBF4); T ) 25.0 (
0.2 °C; uncertainties are estimated as 1σ.
For Cu(Ln)2, the Student32 test indicated that kD was not
statistically significant at the 95% probability level, and thus,
the experimental data were adjusted to a line passing through
the origin by linear regression.
rounding solvent than it is in Cu(dmp)2. As it was already
discussed,17 the smaller kD values for Cu(dap)2 reflect its
higher thermodynamic stability when compared to the case
of Cu(dmp)2. The entwined structure of Cu(dap)2 is also
more resistant to changes in solvent permittivity and viscosity
(Table 5). For Cu(Ln)2, the pathway related to the solvent-
induced dissociation is disfavored and becomes insignificant
with respect to the cyanide-assisted path. This suggests that
the thermodynamic stability of the Cu(Ln)2 complexes is
even higher than that of Cu(dap)2. This may be related to
the combination of a poorly distorted coordination geometry
of the metallic core with effective interligand π-π stacking
interactions providing very good protection of the metal
center from external contacts with the solvents. In the case
of Cu(dap)2, even if the π-π interactions stabilize the
complex, they are also responsible for the flattening distortion
of the pseudotetrahedral geometry, facilitating contacts of
the Cu(I) core with the solvents and thus allowing the
solvent-induced dissociation.
In the presence of cyanide, the studied phenanthroline-
based Cu(I) complexes dissociate according to a single rate-
determining step mechanism. The experimental rate law (eq
2) supports a process which involves a dissociation path
related to the intrinsic properties of the complex in the
absence of cyanide, kD, and a bimolecular cyanide-mediated
pathway, kCN. The first-order rate constant, kD, then primarily
reflects the thermodynamic stability of the complexes,
whereas the bimolecular rate constant, kCN, expresses the
accessibility of the copper(I) center, giving information about
the topography and the compactness around the metal
ion.17,25-27 Our data could agree very well with the following
mechanism (Figure 6), which was already proposed for
25-27
Cu(dmp)2 and Cu(dap)2
and remains valid for the
analogous complex Cu(L0)2, as well as for the four higher
generations of dendrimers.
Very interestingly, the bimolecular rate constant, kCN
,
For the sake of comparison with the Cu(Ln)2 complexes,
we have reexamined the bis(chelate) copper(I) complexes
Cu(dmp)2 and Cu(dap)217,25 under the experimental condi-
tions of this work. Both have been studied previously under
slightly different experimental conditions, and our results are
consistent with former data. The corresponding kD and kCN
values are collected in Table 5.
Due to intramolecular π-π stacking interactions between
the anisyl substituents and the phenanthroline core, Cu(dap)2
shows an entwined and stabilized structure24 in which the
Cu(I) center is noticeably more protected against the sur-
mainly reflects the shielding effect of the cuprous cation
resulting from the bulkiness of the substituents directly
connected to the 2,9-positions of the phenanthroline moieties.
kCN is indeed about 2 orders of magnitude lower for Cu(dap)2
than for Cu(dmp)2 and only 1 order of magnitude lower for
Cu(L0)2 than for Cu(dmp)2 (Tables 4 and 5). These data
are in line with the degree of stacking shown by the
respective X-ray structures (Figure 2) of these three bis-
(chelate) Cu(I) complexes.23,33
The influence of the increased size of the polybenzyloxy
substituents on the protection of the central Cu(I) bis-
(33) The Cambridge Structural Database reference codes for the crystal
structures of Cu(dmp)2 are CABKEV, DAWKOB, DMPNCU, DMP-
NCU01, DMPRCU, MPHCUN, and MPHCUN01.
(32) Commissariat a` l’Energie Atomique. Statistique Applique´e a` l’Ex-
ploitation des Mesures; Masson: Paris, 1979.
3206 Inorganic Chemistry, Vol. 43, No. 10, 2004

Dendrimers with a Copper(I) Bis(phenanthroline) Core
of polyether branches with a p-nitroaniline solvatochromic
probe attached to their focal point showed a pronounced
batochromic shift of the absorption maxima in nonpolar
solvents such as CCl4 as well as in dichloromethane. The
most dramatic change occurred between the third and the
fourth generations. The same pattern of discontinuities was
also evidenced in an earlier study on the same polyether
dendrimers dealing with variation of the intrinsic viscosity
with the generation number.36 These changes are in line with
computational studies, which led to the conclusion that higher
generation dendrimers with flexible units had the highest
density distribution at the center of the molecule.37-40
Conclusion
Figure 7. kCN vs generation number (n) of the Cu(Ln)2 dendrimers.
Solvent: CH2Cl2/CH3CN/H2O ) 50/48/2 (v/v/v); I ) 0.05 M (Bu4NBF4);
T ) 25.0 ( 0.2 °C.
The copper(I) bis(chelate) complex Cu(L0)2 has been
prepared from 2,9-diphenethyl-1,10-phenanthroline and
Cu(CH3CN)4BF4. Interestingly, owing to the presence of the
ethylene linker, the interligand π-π stacking interactions
between the phenyl rings and the phenanthroline subunits
in Cu(L0)2 do not induce significant distortions of the
pseudotetrahedral symmetry around the Cu(I) center in the
solid state or in solution. The latter observations are in sharp
contrast with the strong distortion of the Cu(I) complexes
of phenanthroline ligands with phenyl substituents directly
attached on their 2,9-positions. Importantly, the combination
of a poorly distorted coordination geometry of the metallic
core with effective interligand π-π stacking interactions
provides very good protection of the metal center and the
thermodynamic stability of Cu(L0)2 is higher than that of
the Cu(I) complexes of 2,9-diphenyl-1,10-phenanthroline
ligands. Following the synthesis of Cu(L0)2, dendrimers
Cu(L1-4)2 with a Cu(I) bis(2,9-diphenethyl-1,10-phenan-
throline) core surrounded by Fre´chet type dendritic branches
have been prepared. It is important to stress that the increased
size of the surrounding dendritic wedges has no significant
influence on the coordination geometry of the Cu(I) center.
Therefore, the variations observed in the kinetics of the
cyanide-assisted demetalation of dendrimers Cu(Ln)2 (n )
0-4) only reflect changes resulting from the presence of the
dendritic branches. Actually, the discontinuity which has
been observed between the third and the fourth generation
could be explained by changes in the lipophilicity around
the metallic core as a result of dendritic encapsulation. The
cyanide-mediated dissociation of Cu(I) bis(phenanthroline)
complexes is effectively sensitive to polarity. In conclusion,
kinetic studies have provided interesting information not only
on the accessibility of the central Cu(I) cation but also on
other dendritic effects such as changes in micropolarity
around the Cu(I) bis(phenanthroline) core.
(phenanthroline) core was evaluated by comparing the results
obtained within the series of Cu(Ln)2 complexes, with n )
0-4 (Scheme 1). It may be expected that, as the molecular
size of the dendritic branches increases, their ability to
encapsulate functional cores becomes more efficient and
specific-site-isolated microenvironments may be created.5,34
Both the dendritic shell and the microenvironment formed
inside could then affect CN- in its approach to the central
core. When the size and bulkiness of the substituents attached
to the Cu(I) bis(phenantroline) core are increased, a decrease
of the bimolecular rate constants, kCN, is observed (Table
4). Although the rate of the reaction of cyanide with the
dendritic complexes slightly decreases from Cu(L0)2 to
Cu(L3)2, a plot of kCN versus generation number (n) (Figure
7) shows a noticeable discontinuity upon going from the third
to the fourth generation, Cu(L3)2 w Cu(L4)2. Since the
cyanide anion is small (bond length ∼1.2 Å) and possesses
a linear structure, the increasing bulkiness of the branches
along the series of dendrimers up to Cu(L3)2 does not
comprise a big steric hindrance for it. The corresponding
bimolecular rate constants indeed do not decrease drastically
(Figure 7). A key problem seems to be the spatial structure
and the location of the end groups. Flexible benzyloxy
dendrons probably extend to the periphery of the molecule,
and the central core remains open and accessible to CN- to
the same extent. The discontinuity in kCN observed in the
transition from the third to the fourth generation presumably
corresponds to the process in which the branches fold back
into the interior of the molecule. The conformation of the
extended structure to the globular one in consequence gives
rise to geometric encapsulation of the central Cu(I) bis-
(phenanthroline) complex and to the formation of a “lipo-
philic sphere” with a specific isolated interior. While
approaching the central copper(I) core, CN- experiences a
more lipophilic environment which would affect its solvation.
(35) Hawker, C. J.; Karen, L. W.; Fre´chet, J. M. J. J. Am. Chem. Soc.
1993, 115, 4375.
(36) Mourey, T. H.; Turner, S. R.; Rubenstein, M.; Fre´chet, J. M. J.;
Hawker, C. J.; Karen, L. W. Macromolecules 1992, 25, 2401.
(37) Karatasos, K.; Adolf, D. B.; Davies, G. R. J. Chem. Phys. 2001, 115,
5310.
(38) Murat, M.; Grest, G. S. Macromolecules 1996, 29, 1278.
(39) Boris, D.; Rubinstein, M. Macromolecules 1996, 29, 7251.
(40) Lescanec, R. L.; Muthukumar, M. Macromolecules 1990, 23, 2280.
Our data correlate well with previous studies reporting on
the microenvironment created within Fre´chet type dendritic
branches35 in which analysis of UV-vis absorption spectra
(34) Dykes, G. M. J. Chem. Technol. Biotechnol. 2001, 76, 903.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3207

Gumienna-Kontecka et al.
THF (20 mL) at 0 °C. The resulting solution was stirred for 1 h at
0 °C. A few drops of water were then added, and the mixture was
evaporated to dryness. Column chromatography (SiO2, acetone/
Experimental Section
General Methods. Reagents and solvents were purchased as
reagent grade and used without further purification. All reactions
were performed in standard glassware under an inert Ar atmosphere.
Evaporation and concentration were done at water aspirator
pressure, and drying was done in Vacuo at 10-2 Torr. Column
chromatography: silica gel 60 (230-400 mesh, 0.040-0.063 mm)
was purchased from E. Merck. Thin-layer chromatography (TLC)
was performed on glass sheets coated with silica gel 60 F254
purchased from E. Merck; visualization was achieved by UV light.
NMR spectra were recorded on a Bruker AC 200 spectrometer (200
MHz) with solvent peaks as reference. Mass measurements were
carried out on a Bruker BIFLEX matrix-assisted laser desorption
time-of-flight mass spectrometer (MALDI-TOF) equipped with
SCOUT high resolution optics, an X-Y multisample probe, and a
gridless reflector. Ionization was accomplished with the 337 nm
beam from a nitrogen laser with a repetition rate of 3 Hz. All data
were acquired at a maximum accelerating potential of 20 kV in
the linear positive ion mode. The output signal from the detector
was digitized at a sampling rate of 1 GHz. A saturated solution of
1,8,9-trihydroxyanthracene (dithranol Aldrich EC: 214-538-0) in
CH2Cl2 was used as a matrix. Typically, a 1/1 mixture of the sample
solution in CH2Cl2 was mixed with the matrix solution and 0.5 µL
of the resulting mixture was deposited on the probe tip. Calibration
was performed in the external mode with insulin (5734.6 Da) and
ACTH (2465.2 Da). Elemental analyses were performed by the
analytical service at the Institut Charles Sadron (Strasbourg, France).
1
CH2Cl2 ) 3/2) yielded 2 (0.41 g, 97%, colorless solid). H NMR
(acetone-d6, 200 MHz): 3.04 (m, 4H), 3.31 (m, 4H), 6.75 (d, J )
8 Hz, 4H), 7.03 (d, J ) 8 Hz, 4H), 7.55 (d, J ) 8 Hz, 2H), 7.84
(s, 2H), 8.27 (d, J ) 8 Hz, 2H), 8.67 (s, 2H).
General Procedure for the Preparation of Ligands L1-4. A
mixture of 2 (1 equiv), the appropriate benzylic bromide (2 equiv),
K2CO3 (5 equiv), and 18-crown-6 (0.5 equiv) in acetone was
refluxed for 48 h. The resulting mixture was diluted with CH2Cl2,
filtered, and evaporated. The crude product was then purified, as
outlined in the following text.
Ligand L1. L1 was prepared from benzyl bromide G1Br and
purified by column chromatography (SiO2, CH2Cl2) (76%, colorless
glassy product). 1H NMR (CDCl3, 200 MHz): 3.25 (m, 4H), 3.50
(m, 4H), 5.04 (s, 4H), 6.92 (d, J ) 8 Hz, 4H), 7.25 (d, J ) 8 Hz,
4H), 7.26-7.45 (m, 10H), 7.47 (d, J ) 8 Hz, 2H), 7.72 (s, 2H),
8.13 (d, J ) 8 Hz, 2H). 13C NMR (CDCl3, 50 MHz): 34.7, 41.2,
70.0, 114.7, 122.7, 125.6, 127.2, 127.4, 127.8, 128.5, 129.5, 134.2,
136.2, 137.2, 145.4, 157.0, 162.0. Anal. Calcd for C42H36N2O2‚
H2O: C, 81.52; H, 6.19; N, 4.53. Found: C, 81.57; H, 6.38; N,
4.23.
Ligand L2. L2 was prepared from G2Br and purified by column
chromatography (SiO2, CH2Cl2) (96%, colorless glassy product).
1H NMR (CDCl3, 200 MHz): 3.27 (m, 4H), 3.53 (m, 4H), 4.98 (s,
4H), 5.04 (s, 8 H), 6.56 (t, J ) 2 Hz, 2H), 6.64 (d, J ) 2 Hz, 4H),
6.91 (d, J ) 8 Hz, 4H), 7.26 (d, J ) 8 Hz, 4H), 7.41 (m, 20H),
7.47 (d, J ) 8 Hz, 2H), 7.72 (s, 2H), 8.13 (d, J ) 8 Hz, 2H). Anal.
Calcd for C70H60O6N2: C, 82.00; H, 5.90; N, 2.73. Found: C, 81.88;
H, 5.96; N, 2.70.
Ligand L3. L3 was prepared from G3Br and purified by column
chromatography (SiO2, CH2Cl2) (91%, colorless glassy product).
1H NMR (CD2Cl2, 200 MHz): 3.25 (m, 4H), 3.49 (m, 4H), 4.97
(s, 12H), 5.02 (s, 16H), 6.55 (m, 6H), 6.68 (m, 12H), 6.91 (d, J )
8 Hz, 4H), 7.25 (d, J ) 8 Hz, 4H), 7.27-7.43 (m, 40H), 7.45 (d,
J ) 8 Hz, 2H), 7.71 (s, 2H), 8.13 (d, J ) 8 Hz, 2H). Anal. Calcd
for C126H108N2O14‚H2O: C, 79.97; H, 5.86; N, 1.48; O, 12.69.
Found: C, 79.95; H, 5.93; N, 1.39; O, 12.37.
Ligand L0. A 2 M solution of LDA in THF (9.6 mL, 19.2 mmol)
was added slowly to a solution of neocuproine (2.00 g, 9.6 mmol)
in anhydrous THF (80 mL) at -78 °C under Ar. After 3 h, a
solution of benzyl bromide (2.3 mL, 19.2 mmol) in THF (10 mL)
was added dropwise. The resulting mixture was stirred for 2 h at
-78 °C and then for 15 h at room temperature. The solution was
then poured into ice water (150 mL). The mixture was extracted
with CH2Cl2 (3 × 100 mL), and the combined organic layers were
dried (MgSO4), filtered, and evaporated. Column chromatography
(SiO2, CH2Cl2/2% MeOH) yielded L0 (2.05 g, 55%, colorless glassy
1
product). H NMR (CDCl3, 200 MHz): 3.35 (m, 4H), 3.60 (m,
4H), 7.35 (m, 10H), 7.50 (d, J ) 8 Hz, 2H), 7.73 (s, 2H), 8.15 (d,
J ) 8 Hz, 2H). 13C NMR (CDCl3, 50 MHz): 35.5, 40.9, 122.6,
125.5, 125.8, 127.2, 128.3, 128.5, 136.2, 141.8, 145.5, 161.9. Anal.
Calcd for C28H24N2: C, 86.56; H, 6.23; N, 7.21. Found: C, 86.47;
H, 6.51; N, 7.11.
Ligand L4. L4 was prepared from G4Br and purified by column
chromatography (SiO2, CH2Cl2) (99%, colorless glassy product).
1H NMR (CD2Cl2, 200 MHz): 3.22 (m, 4H), 3.50 (m, 4H), 4.97
(m, 60H), 6.56 (m, 14H), 6.67 (m, 28H), 6.88 (d, J ) 8 Hz, 4H),
7.22 (d, J ) 8 Hz, 4H), 7.27-7.38 (m, 82H), 7.68 (s, 2H), 8.08 (d,
J ) 8 Hz, 2H). 13C NMR (CDCl3, 50 MHz): 29.6, 34.7, 41.1,
70.0, 101.5, 106.3, 114.7, 122.7, 125.6, 127.2, 127.5, 127.9, 128.5,
129.5, 134.2, 136.1, 136.7, 139.1, 139.7, 156.9, 160.0, 162.0. Anal.
Calcd for C238H204O30N2‚H2O: C, 79.61; H, 5.79; O, 13.82; N, 0.81.
Found: C, 79.37; H, 5.88; O, 13.55; N, 0.81.
General Procedure for the Preparation of the Cu(I) Com-
plexes Cu(L0-4)2. A solution of Cu(CH3CN)4‚BF4 (1 equiv) in
CH3CN was added under an argon atmosphere at room temperature
to a stirred, degassed solution of the appropriate ligand (2 equiv)
in CH2Cl2. The solution turned orange-red instantaneously, indicat-
ing the formation of the complex. After 1 h, the solvents were
evaporated and the crude product purified, as outlined in the
following text.
Compound 1. A 2 M solution of LDA in THF (9.2 mL, 18.4
mmol) was added slowly to a solution of neocuproine (1.90 g, 9
mmol) in anhydrous THF (60 mL) at -78 °C under Ar. After 3 h,
a solution of p-[(tert-butyldimethylsilyl)oxy]benzyl bromide (6.10
g, 20 mmol) in THF (10 mL) was added dropwise. The resulting
mixture was stirred for 2 h at -78 °C and then for 15 h at room
temperature. The solution was then poured into ice water (150 mL).
The mixture was extracted with CH2Cl2 (3 × 100 mL), and the
combined organic layers were dried (MgSO4), filtered, and evapo-
rated. Column chromatography (SiO2, CH2Cl2/2% MeOH) yielded
1
1 (2.30 g, 38%, colorless glassy product). H NMR (CDCl3, 200
MHz): 0.20 (s, 12H), 0.99 (s, 18H), 3.25 (m, 4H), 3.52 (m, 4H),
6.78 (d, J ) 8 Hz, 4H), 7.19 (d, J ) 8 Hz, 4H), 7.45 (d, J ) 8 Hz,
2H), 7.72 (s, 2H), 8.13 (d, J ) 8 Hz, 2H). 13C NMR (CDCl3, 50
MHz): 17.9, 25.5, 34.6, 41.0, 119.7, 122.5, 125.3, 126.9, 129.2,
134.3, 135.9, 145.3, 153.5, 161.7. Anal. Calcd for C40H52O2Si2N2:
C, 74.03; H, 8.08; N, 4.32. Found: C, 73.76; H, 8.17; N, 4.20.
Complex Cu(L0)2. Cu(L0)2 was prepared from L0 and purified
by column chromatography (SiO2, CH2Cl2/2% MeOH) (96%, red-
orange crystals). 1H NMR (CDCl3, 200 MHz): 2.67 (m, 8H), 3.05
(m, 8H), 6.20 (d, J ) 8 Hz, 8H), 6.93 (m, 12H), 7.80 (d, J ) 8 Hz,
4H), 8.12 (s, 4H), 8.60 (d, J ) 8 Hz, 4H). 13C NMR (CDCl3, 50
MHz): 35.3, 42.0, 125.2, 126.2, 126.5, 127.2, 127.9, 128.2, 139.2,
Compound 2. A 1 M solution of TBAF in THF (2.6 mL, 2.6
mmol) was added slowly to a solution of 1 (0.60 g, 1 mmol) in
3208 Inorganic Chemistry, Vol. 43, No. 10, 2004

Dendrimers with a Copper(I) Bis(phenanthroline) Core
143.1, 160.4. Anal. Calcd for C56H48N4CuBF4: C, 72.53; H, 5.22;
N, 6.04. Found: C, 72.72; H, 5.34; N, 6.05.
Kinetic Studies. All the experiments were carried out in a freshly
prepared homogeneous ternary solvent, CH2Cl2/CH3CN/H2O ) 50/
48/2 (v/v/v). The ionic strength was adjusted to 0.05 M with
tetrabutylammonium tetrafluoroborate (Aldrich, 99%). The scav-
enger reagent tetraethylammonium cyanide (Fluka, purum) was
always used in large excess with respect to the concentrations of
the Cu(I) complexes (∼1.5 × 10-5 M) in order to obtain pseudo-
first-order conditions. The cyanide concentrations were varied in a
range from ∼6 × 10-4 to ∼2.4 × 10-3 M.
Complex Cu(L1)2. Cu(L1)2 was prepared from L1 and purified
by column chromatography (SiO2, CH2Cl2/2% MeOH) (95%,
1
orange glassy product). H NMR (CDCl3, 200 MHz): 2.58 (m,
8H), 2.99 (m, 8H), 4.91 (s, 8H), 6.09 (d, J ) 8 Hz, 8H), 6.44 (d,
J ) 8 Hz, 8H), 7.39 (m, 20H), 7.75 (d, J ) 8 Hz, 4H), 8.02 (s,
4H), 8.52 (d, J ) 8 Hz, 4H). 13C NMR (CDCl3, 50 MHz): 34.5,
42.3, 69.8, 114.5, 125.5, 126.4, 127.4, 129.9, 128.1, 128.24, 128.5,
131.5, 136.9, 137.8, 143.1, 157.0, 160.5. Anal. Calcd for C84H72-
O4N4CuBF4: C, 74.64; H, 5.37; N, 4.15. Found: C, 74.36; H, 5.56;
N, 3.62.
CAUTION! Tetraethylammonium cyanide is highly toxic, and
since hydrogen cyanide is being generated in the presence of acid,
gloVes and a fume hood should be used when handling this
compound.41 Sodium hypochlorite was used in order to oxidize and
destroy cyanide anions in solution.42
Complex Cu(L2)2. Cu(L2)2 was prepared from L2 and purified
by column chromatography (SiO2, CH2Cl2/2% MeOH) (72%,
1
orange glassy product). H NMR (CDCl3, 200 MHz): 2.57 (m,
The kinetic studies were performed at a fixed wavelength
corresponding to the absorption maximum of the MLCT band of
the bis(phenanthroline) Cu(I) complex under study using a stopped-
flow spectrophotometer (Applied Photophysics SX-18MV). The
reactants were mixed in a 1 cm optical cell, and the temperature
was maintained constant at 25.0 ( 0.2 °C. The data sets, averaged
out of at least three replicates, were recorded and analyzed with
the commercial software Biokine.43 This program fits up to three
exponential functions to the experimental curves with the Simplex
algorithm44 after initialization with the Pade´-Laplace method.45,46
8H), 2.98 (m, 8H), 4.85 (s, 8H), 5.05 (s, 16H), 6.08 (d, J ) 8 Hz,
8H), 6.42 (d, J ) 8 Hz, 8H), 6.59 (t, J ) 2 Hz, 4H), 6.65 (d, J )
2 Hz, 8H), 7.41 (m, 40H), 7.73 (d, J ) 8 Hz, 4H), 8.00 (s, 4H),
8.49 (d, J ) 8 Hz, 4H). 13C NMR (CDCl3, 50 MHz): 34.4, 42.2,
69.6, 70.0, 101.2, 105.6, 106.2, 114.5, 139.4, 143.1, 156.9, 160.1,
160.4. MALDI-TOF MS: 2112.2 ([M - BF4]+ calcd for
C140H120O12N4: 2111.8). Anal. Calcd for C140H120O12N4CuBF4: C,
76.40; H, 5.50; N, 2.55. Found: C, 76.54; H, 5.54; N, 2.49.
Complex Cu(L3)2. Cu(L3)2 was prepared from L3 and purified
by column chromatography (SiO2, CH2Cl2/2% MeOH) (92%,
Acknowledgment. This research was supported by the
CNRS and the French Ministry of Research (ACI Jeunes
Chercheurs to J.-F.N.). E.G.-K. thanks the CNRS and Y.R.
the Direction de la Recherche of the French Ministry of
Research for their fellowships. We further thank Dr. D.
Felder for the initial preparation of Cu(L0)2, L. Oswald for
technical help, M. Schmitt for high field NMR spectra, and
J.-M. Strub for MS measurements. The authors are grateful
to Dr. C. O. Dietrich-Buchecker for samples of Cu(dmp)2
and Cu(dap)2.
1
orange glassy product). H NMR (CD2Cl2, 200 MHz): 2.54 (m,
8H), 2.93 (m, 8H), 4.86 (s, 8H), 4.94 (s, 16H), 5.00 (s, 32H), 6.04
(d, J ) 8 Hz, 8H), 6.40 (d, J ) 8 Hz, 8H), 6.56 (m, 12H), 6.67 (m,
24H), 7.29 (m, 80H), 7.68 (d, J ) 8 Hz, 4H), 7.97 (s, 4H), 8.46 (d,
J ) 8 Hz, 4H). MALDI-TOF MS: 3809.7 ([M - BF4]+ calcd for
C252H216N4O28Cu: 3808.5). Anal. Calcd for C252H216N4O28CuBF4‚
H2O: C, 77.27; H, 5.61; N, 1.43. Found: C, 77.09; H, 5.46; N,
1.25.
Complex Cu(L4)2. Cu(L4)2 was prepared from L4 and purified
by column chromatography (SiO2, CH2Cl2/2% MeOH) (85%,
1
orange glassy product). H NMR (CDCl3, 200 MHz): 2.49 (m,
8H), 2.89 (m, 8H), 4.77 (s, 8H), 4.93 (m, 48H), 4.97 (m, 64H),
5.99 (d, J ) 8 Hz, 8H), 6.37 (d, J ) 8 Hz, 8H), 6.53 (m, 84H),
7.29 (m, 160H), 7.59 (d, J ) 8 Hz, 4H), 7.90 (s, 4H), 8.37 (d, J )
8 Hz, 4H). MALDI-TOF MS: 7203.6 ([M - BF4]+ calcd for
Note Added after ASAP: Some errors appeared in the
identification of the contributing institutions in the version
of this paper posted ASAP on April 2, 2004. The institutions
are correctly identified in the version posted on April 16,
2004.
C476H408N4O60: 7201.8). Anal. Calcd for C476H408N4O60CuBF4‚CH2-
Cl2: C, 77.63; H, 5.60; N, 0.76. Found: C, 77.72; H, 5.64; N,
Supporting Information Available: Six figures showing
electronic spectra of Cu(L1)2, Cu(L2)2, and Cu(L3)2; plots of the
pseudo-first-order rate constant, kobs, as a function of cyanide
concentration for Cu(dmp)2, Cu(dap)2, Cu(L0)2, Cu(L1)2, Cu(L2)2,
and Cu(L3)2; an ORTEP drawing of Cu(L0)2; and 1H NMR spectra
of Cu(L1)2, Cu(L2)2, and Cu(L4)2 and CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
0.57.
X-ray Crystal Structure of Cu(L0)2. The red-orange crystal used
for the diffraction study was produced by slow diffusion of MeOH
into a CH2Cl2 solution of Cu(L0)2 (C112H96N8Cu2B2F8, Mr )
1854.76): Triclinic space group P1h, Z ) 2, a ) 13.9285(3) Å,
b ) 17.4020(4) Å, c ) 19.2839(5) Å, R ) 83.339(5)°, â ) 87.924-
(5)°, γ ) 87.230(5)°, V ) 4634.9(2) Å3. The parameters for the
data collection and refinement of diffraction data as well as the
atomic coordinates and the thermal parameters are contained in the
Supporting Information.
IC049945Y
(41) Chemical Safety Data Sheet SD-67. Hydrocyanic acid; Manufacturing
Chemists’ Association: Washington, DC, 1961.
(42) Gerritsen, C. M.; Margerum, D. W. Inorg. Chem. 1990, 29, 2757.
(43) Biokine; Bio-Logic Company: Echirolles, France, 1991.
(44) Nelder, J. A.; Mead, R. Comput. J. 1965, 7, 308.
(45) Enzfitter; Leatherbarrow, J., Ed. Biosoft: Cambridge, U.K., 1987.
(46) Yeramian, E.; Claverie, P. Nature 1987, 326, 169.
UV-Visible Spectrophotometry. The spectrophotometric stud-
ies were carried out on a Kontron Uvikon 941 spectrophotometer
equipped with 1 cm quartz cells (Hellma) thermostated at 25.0 (
0.2 °C. Absorbance data were recorded in a range of wavelengths
from 250 to 650 nm.
Inorganic Chemistry, Vol. 43, No. 10, 2004 3209