Formation of group 11 metal(I)-arene complexes: Bonding mode and molecule-responsive spectral variations

Article abstract of DOI:10.1021/om020668h

Two N(n-Pr)PPh₂ groups appended to the 9,10-anthracene positions through methylene spacers as a bidentate ligand coordinate with Cu⁺, Ag⁺, and Au⁺ ions efficiently to afford endocyclic metal complexes with metal-η⁶-arene bonding, rarely observed for the group 11 metal ions. The three-center metal-NP and metal-η⁶-arene bonding patterns in the endocyclic complexes were confirmed using ab initio and density functional calculations. The close metal-anthracene centroid distances significantly affected absorption and fluorescence properties of the complexes in solution. Among them the Cu⁺ complex has the shortest metal-anthracene distance and most drastic spectral abnormality. The close distances also controlled the endocyclic-exocyclic metal transition of the complexes, wherein the equilibrium heavily favored the former on account of η⁶ interactions. These complexes reacted with phosphines in solution to give highly fluorescent species that were proposed to possess the exocyclic configuration with the three-coordinated metal center. These exocyclic metal complexes as well as the ligand itself all form respective excimers from their singlet excited states to exhibit an additional broad fluorescence at about 455 nm. The excimers are assumed to arise from an interaction of the excited anthracene moiety with an N-P group of the ground state exocyclic molecule. The observed molecule-responsive light-switchable spectral variations have been discussed in terms of structural changes in the endocyclic-exocyclic metal transitions.

Full text of DOI:10.1021/om020668h

Organometallics 2003, 22, 633-640
633
F or m a tion of Gr ou p 11 Meta l(I)-Ar en e Com p lexes:
Bon d in g Mod e a n d Molecu le-Resp on sive Sp ectr a l
Va r ia tion s
Feng-Bo Xu,† Qing-Shan Li,† Li-Zhu Wu,‡ Xue-Bing Leng,† Zu-Cheng Li,†
Xian-Shun Zeng,† Yuan L. Chow,§,† and Zheng-Zhi Zhang*,†
State Key Laboratory of Elemento-Organic Chemistry, Nankai University,
Tianjin 300071, People’s Republic of China, and Technical Institute of Physics and Chemistry,
the Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
Received August 15, 2002
Two N(n-Pr)PPh2 groups appended to the 9,10-anthracene positions through methylene
spacers as a bidentate ligand coordinate with Cu+, Ag+, and Au+ ions efficiently to afford
endocyclic metal complexes with metal-η6-arene bonding, rarely observed for the group 11
metal ions. The three-center metal-NP and metal-η6-arene bonding patterns in the
endocyclic complexes were confirmed using ab initio and density functional calculations.
The close metal-anthracene centroid distances significantly affected absorption and
fluorescence properties of the complexes in solution. Among them the Cu+ complex has the
shortest metal-anthracene distance and most drastic spectral abnormality. The close
distances also controlled the endocyclic-exocyclic metal transition of the complexes, wherein
the equilibrium heavily favored the former on account of η6 interactions. These complexes
reacted with phosphines in solution to give highly fluorescent species that were proposed to
possess the exocyclic configuration with the three-coordinated metal center. These exocyclic
metal complexes as well as the ligand itself all form respective excimers from their singlet
excited states to exhibit an additional broad fluorescence at about 455 nm. The excimers
are assumed to arise from an interaction of the excited anthracene moiety with an N-P
group of the ground state exocyclic molecule. The observed molecule-responsive light-
switchable spectral variations have been discussed in terms of structural changes in the
endocyclic-exocyclic metal transitions.
In tr od u ction
fluorescence variations as indicators,1a,b which have
distinct advantages in terms of sensitivity, selectivity,
and response time. As binding components, chelators,
podands, coronands, and cryptands1b containing a num-
ber of heteroatoms of group 15 and 16 elements are
commonly used. Characteristically, these ionophore
components are designed with a finite cavity size for
selectivity purposes and are constructed around or
attached to a fluorophore component,1f for which an-
thracene has many advantages (such as its strong
fluorescent behavior and ease of functionalization) and
has been used widely.2,3 Many studies have revealed a
variety of recognition mechanisms on binding and
photophysical events.1e,f
Ligands with the nitrogen-phosphorus bond contrib-
ute to an important group of compounds.4,5 Whereas
both elements are extensively used as coordinating
heteroatoms in ionophore designs, a N-P group as a
composite center for coordination has seldom been
tested, which has prompted us to explore its application
in fluoroionophore chemistry. Our design is that each
N(n-Pr)PPh2 group through one methylene spacer was
attached to the 9,10-positions of anthracene, as shown
Studies of fluoroionophores have attracted much
attention in the past decade1-3 owing to their enormous
potential for application as molecular sensors in many
fields related to life and living. Fluoroionophore sensors
generally consist of an ion-binding component trans-
duced to a signaling unit; the latter generally uses
* Corresponding author. E-mail: zzzhang@public.tpt.tj.cn.
† State Key Laboratory of Elemento-Organic Chemistry, Nankai
University.
‡ Technical Institute of Physics and Chemistry, the Chinese Acad-
emy of Sciences.
§ Emeritus Professor at Simon Fraser University, Burnaby, Canada.
(1) (a) Czarnik, A. W. In Topics in Fluorescence Spectroscopy;
Rakowicz, J ., Ed.; Plenum Press: New York, 1994; Vol. 4, p 49. (b)
Valeur, B. In Topics in Fluorescence Spectroscopy; Rakowicz, J ., Ed.;
Plenum Press: New York, 1994; Vol. 4, p 21. (c) Bissell, R. A.; de Silva,
A. P.; Gunaratne, H. Q. N.; Lynch, P. L. M.; Maguire, G. E. M.; McCoy,
C. P.; Sandanayake, K. R. A. S. Top. Curr. Chem. 1993, 168, 223. (d)
Czarnik, A. W. Acc. Chem. Res. 1994, 27, 302. (e) Fabbrizzi, L.; Poggi,
A. Chem. Soc. Rev. 1995, 197. (f) de Silva, A. P.; Gunaratne, H. Q. N.;
Gunnlangsson, T.; Huxley, A. J . M.; McCoy, C. P.; Rademacher, J . T.;
Rice, T. E. Chem. Rev. 1997, 97, 1515.
(2) (a) Fages, F.; Desvergne, J . P.; Bouas-Laurent, H.; Marsau, P.;
Lehn, J . M.; Kotzyba-Hibert, F.; Albrecht-Gary, A. M.; Al-J oubbeh, M.
J . Am. Chem. Soc. 1989, 111, 8672. (b) Desvergne, J . P.; Fages, F.;
Bouas-Laurent, H.; Marsau, P. Pure Appl. Chem. 1992, 62, 1231. (c)
Ishikawa, J .; Sakamoto, H.; Nakao, S.; Wada, H. J . Org. Chem. 1999,
64, 1913.
(3) (a) Fages, F.; Desvergne, J . P.; Bouas-Laurent, H. J . Am. Chem.
Soc. 1989, 111, 96. (b) We are grateful to Professor J . P. Desvergne
for making the fluorescence excitation and absorption spectra of 9,10-
dipropylanthracene available to us.
(4) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; J ohn
Wiley: New York, 1980; p 460.
(5) (a) Riess, J . G. Phosphorus Sulfur 1986, 27, 93. (b) Shaw, R. A.
Pure Appl. Chem. 1975, 44, 317. (c) Krishnamurthy, S. S. Phosphorus,
Sulfur Silicon 1994, 87, 101.
10.1021/om020668h CCC: $25.00 © 2003 American Chemical Society
Publication on Web 01/11/2003

634 Organometallics, Vol. 22, No. 4, 2003
Xu et al.
Sch em e 1
Sch em e 2
in 9,10-bis{N-n-propyl-N-(diphenylphosphino)amino-
methyl}anthracene (L1), which has been prepared for
the study (Scheme 1). We wish to describe L1 in the
formation of group 11 metal complexes and unusual
chemistry thereof. For comparison, 9,10-bis{(2-diphen-
ylphosphino)ethyl}anthracene (L2) is also prepared and
its reaction with AgClO4 is studied.
to give L1-silver(I) (abbreviated as L1Ag+) perchlorate
in good yield.10a Under similar conditions L1 reacted
with Cu(CH3CN)4ClO4 to afford L1-copper(I) (L1Cu+)
perchlorate. L1 reacted with Au(Me2S)Cl to afford L1-
gold(I) chloride (L1AuCl), which was converted to L1-
gold(I) (L1Au+) perchlorate by treating with silver
perchlorate in dichloromethane. L1Au+ was also ob-
tained by a sequential reaction of L1 with the two
reagents in a one-pot operation. These chelated com-
plexes with η6 bonding8,9 to the central ring of the
anthracene (see Scheme 1) have been confirmed by
X-ray analysis; the cycle coordinated with metal by η6
bonding is referred to as endocyclic metal coordination.
L1AuCl obviously possessed a covalent Au-Cl bond
without η6 bonding with the anthracene ring and has a
structure with a full cycle that is referred to as exocyclic
metal coordination (also see Scheme 2). A brief account
on the preparation and properties of L1Ag+ was pub-
lished previously.10a All these L1-metals were stable in
crystalline states for extended storage and also in
solution for several weeks. The ligand L2 was prepared
from 9,10-bis(2-chloroethyl)anthracene with Ph2PLi and
reacted with AgClO4 under similar conditions to give
L2-silver (L2Ag+) perchlorate (Scheme 1).
Resu lts a n d Discu ssion
Liga n d s a n d Meta l Com p lexes. The ligand L1 was
synthesized from 9,10-bis(N-propylaminomethyl)anthra-
cene (L0)6 and chlorodiphenylphosphine in the presence
of triethylamine to scavenge hydrogen chloride in
anhydrous benzene under a nitrogen atmosphere.10a L0
was readily prepared from 9,10-bis(chloromethyl)an-
thracene and n-propylamine.7 L1 in dichloromethane
under nitrogen was reacted with silver(I) perchlorate
(6) (a) Hong, S. Y.; Czarnik, A. W. J . Am. Chem. Soc, 1993, 115,
3330. (b) Akkaya, E. U.; Huston, M. E.; Czarnik, A. W. J . Am. Chem.
Soc. 1990, 112, 3590.
(7) Badger, G. M.; Cook, J . W. J . Chem. Soc. 1939, 802.
(8) Mascal, M.; Kerdelhue´, J . L.; Blake, A. J .; Cooke, P. A. Angew.
Chem., Int. Ed. 1999, 38, 1968.
(9) Andrianatoandro, H.; Bararns, Y.; Marsau, P.; Desbergne, J . P.;
Fages, F.; Bouas-Laurent, H. Acta Crystallogr. 1995, B51, 293.
(10) (a) Xu, F. B.; Weng, L. H.; Sun, L. J .; Zhang, Z. Z. Organome-
tallics 2000, 19, 2658. (b) Xu, F. B. Ph.D. Dissertation, Institute of
Elemento-Organic Chemistry, Nankai University, J une 2001.
The ORTEP view of L1Cu+ is shown in Figure 1 as a
representative example: L1Au+ in Supporting Informa-

Group 11 Metal(I)-Arene Complexes
Organometallics, Vol. 22, No. 4, 2003 635
Ta ble 1. Selected Bon d Dista n ces, Bon d An gles, a n d Rela ted Da ta of th e Liga n d a n d Com p lexes
compond
L1
L1CuClO4
L1AgClO4
L1AuClO4
L2AgClO4
P(1)-N(1) (Å)
1.664
1.680
1.666
1.657
2.136
2.2140
153.97
169.6
168.5
2.498
2.773-3.021
172.3
5.075
3.5896
1.669
1.671
2.4029
2.4056
169.9
172.4
171.5
2.79
3.053-3.157
175.4
1.672
1.664
2.3208
2.3239
171.6
169.0
171.1
3.00
3.118-3.246
176.1
P(2)-N(2) (Å)
P(1)-M(I) (Å)
P(2)-M(I) (Å)
2.439
2.440
177.9
171.2
168.5
3.148
3.282-3.606
174.7
P(1)-M(I)-P(2) (deg)
C(1)-C(2)-C(9) (deg)
C(2)-C(9)-C(16) (deg)
M(I)-An (Å)a
175.9
175.9
M(I)-Can (Å)b
angle of An (deg)c
An-An (Å)d
180
4.336
3.4162
4.312
3.4076
An+An (Å)e
a
b
The distance of the metal ion to the centroid of anthracene. The distances of the metal ion to the six carbon atoms of the middle ring
in anthracene. c The dihedral angle between the two side rings in anthracene. The distance between the two centroids of the two π-π
d
stacking anthracene rings. e The distance between the two planes of the two π-π stacking anthracene rings.
higher order than sp2); the dihedral angle between the
two side rings in L1Cu+ was the smallest (at 172.3°) in
comparison to that in the other two. Third, the an-
thracene rings were closely packed in parallel at about
3.41 Å distance for L1Ag+ and L1Au+; for L1Cu+ the
π-π stacking was staggered and the corresponding
distance is 3.59 Å. These features are rare phenomena
for group 11 metal ions. There is only one example of
η6-π bonding for Cu+,8 two for Ag+,8,9 and none for Au+.
The metal-arene centroid distance at 2.50 Å for L1Cu+
and 2.79 Å for L1Ag+ are the shortest ever observed
among all known examples; the closest reported values
prior to this report were 2.97 Å8 and 2.92 Å,9 respec-
tively. However, the Ag-anthracene centroid distance
F igu r e 1. ORTEP view of L1Cu+.
is 3.148 Å in the endocyclic coordination L2Ag+ (Scheme
2). L2 reacts with the other reagents Cu(CH3CN)4ClO4
and Au(SMe2)Cl, respectively, to give complexes with
completely different structures.10b
Ligand L1, as a bidentate coordinating unit, can easily
clutch these univalent group 11 metal ions; that capacity
should be credited to its two N-P functions to chelate
the metals over the space above the anthracene π-face.
The bonding features in these endocyclic complexes
(L1Cu+, L1Ag+, and L2Ag+) were also examined using
both ab initio (Hartree-Fock, HF) and density func-
tional (hybrid nonlocal, B3LYP) methods.11a The results
(Table 2) from Bader’s atoms-in-molecule (AIM) analysis
of the electron densities11e are emphasized, although all
relevant molecular orbitals (MOs from HF/LanL2DZ)
and Kohn-Sham orbitals (KSOs from B3LYP/LanL2DZ)
have also been examined carefully. According to Bader’s
AIM theory,11e there is bonding if a bond critical point
F igu r e 2. ORTEP view of L2Ag+.
(BCP) is found around the connecting line between the
two atoms, or among three or more atoms. Furthermore,
for similar bonds, the larger the electron density (F) at
the BCP, the stronger the bond is. Table 2 presents the
values of electron density F, ellipticity (ꢀ ) λ1/λ2 - 1),
tion and L1Ag+ in ref 10a. For comparison, the crystal
structure of L2Ag+ is shown in Figure 2. Some molec-
ular dimensions characteristic of these metal complexes
and pertinent for the discussion are listed in Table 1.
The first significant feature was the bonding of the
metal to six carbon atoms of the anthracene central ring,
indicating a η6 coordination mode; that is, the distance
of the metal to the centroid of the mid-benzene ring was
short, and that in L1Cu+ (at 2.498 Å) was distinctly
shorter than the corresponding distance in the other
two. Second, two anthracene 9,10-carbon atoms were
markedly bent forward out of coplanar configuration.
Also, the two side benzene rings were bent backward
at the anthracene 9,10-carbons probably through rehy-
bridization to a nonplanar configuration (i.e., with a
(11) (a) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; et al. Gaussian
98 (Revision A.7); Gaussian, Inc.: Pittsburgh, PA, 1998. (b) For
example: Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham,
M. A.; Shirley, W. A.; Mantzaris, J . J . Chem. Phys. 1988, 89, 2193. (c)
Curtiss, L. A.; McGrath, M. P.; Blaudeau, J .-P.; Davis, N. E.; Binning,
R. C., J r.; Radom, L. J . Chem. Phys. 1995, 103, 6104. (d) For example:
Kaupp, M.; Schleyer, P. V. R.; Stoll, H.; Preuss, H. J . Chem. Phys.
1991, 94, 1360, and references therein. (e) Bader, R. F. W Atoms in
Molecules: A Quantum Theory; Oxford University Press: Oxford, 1990.
(f) Note: these results are similar to those calculated from B3LYP/3-
21G*. For example, for L1Ag, B3LYP/3-21G* gave BCP electron
3
densities of 0.078, 0.165, 0.016 e/a0 for Ag-P, N-P, and Ag-Cring
bonds, respectively, and other properties are also similar. (g) The plots
were made using: Schaftenaar, G. Molden; CAOS/CAMM Center
Nijmegen: Toernooiveld, Nijmegen, The Netherlands, 1991.

636 Organometallics, Vol. 22, No. 4, 2003
Xu et al.
Ta ble 2. B3LYP /STO-3G* AIM Bon d in g P r op er ties
3
(in a tom ic u n its, i.e., G in e/a 0 a n d 32G in e/a 05) of
Com p lexes L1Cu +, L1Ag+, a n d L2Ag+
molecule
bonda
F
32F
ꢀ
λ1
λ2
λ3
L1Cu+ Cu-P
L1Ag+ Ag-P
L2Ag+ Ag-P
L1Cu+ N-P
L1Ag+ N-P
L2Ag+ C-P
0.098
0.081
0.069
0.158
0.157
0.122 0.040 -0.079 -0.076 0.277
0.187 0.021 -0.080 -0.078 0.344
0.150 0.005 -0.066 -0.065 0.281
0.780 0.227 -0.219 -0.178 1.178
0.742 0.213 -0.214 -0.177 1.130
0.149 -0.079 0.110 -0.169 -0.152 0.242
L1Cu+ Cu-Cring 0.021
L1Ag+ Ag-Cring 0.012
L2Ag+ Ag-Cring 0.007
0.066 5.511 -0.015 -0.002 0.083
0.046 1.126 -0.006 -0.003 0.054
0.023 4.504 -0.004 -0.001 0.028
a
M-Cring denotes the metal atom weakly bonding with a carbon
atom in the central phenyl ring detected in the AIM analysis, and
each M-Cring stands for two slightly different bonds except for
L2Ag+, which has only one such bond found, and so the data for
each bond are an arithmetic average except for L2Ag+.
and other properties at the BCPs of the relevant bonds
in these complexes obtained using B3LYP/STO-3G*11f
As shown in Table 2, the most important feature is
that the bonding in L1Cu+ is overall much stronger than
that in L1Ag+, which is, in turn, much stronger than
L2Ag+. First, the Cu-P bond possesses larger electron
density than the Ag-P bond (0.098 vs 0.081 e/a03),
indicating the different bond strength. Second, the
bonding between the metal and N-P group in L1Cu+
is modestly stronger than that in L1Ag+, as indicated
by its larger ellipticity (ꢀ), implying its slightly greater
orbital overlap in the Cu-NP triangle than in the Ag-
NP one (Figure 3). Third, the electron densities on the
Cu-Cring bonds (Cring denotes a C atom in the central
ring of the anthracene) are much denser than those on
corresponding Ag-Cring bonds in L1Ag+ (0.021 vs 0.012
e/a03), demonstrating that the former are stronger than
the latter. This indicates that Cu-η6-arene bonding in
L1Cu+ must be stronger than Ag-η6-arene in L1Ag+
because a M-Cring bond represents a localized metal-
η6-arene coordination. These results also agree well with
crystal structure features of these complexes.
F igu r e 3. Contour plots of HF/LanL2DZ molecular orbital
159 (upper), which indicates tri-center Ag-CN bonding in
L1Ag+, and 117 (lower) in L2Ag+ (for reference) on the
plane roughly containing the neighboring N-P-Ag-P-N
and C-P-Ag-P-C atoms, respectively. Solid contours are
at 0.005, 0.010, ..., 0.095 e/a03, and negative contours are
dashed.
sentially an anthracene type)2,3 with red-shifts. In
contrast, L1Cu+ showed a broad charge transfer band
visibly different from that of the other two. The broad
absorption spectrum of L1Cu+ is probably a consequence
of the shorter Cu-anthracene centroid distance and the
bending of the two side benzene rings out of coplanarity
(Table 1) and suggests that the original rigid anthracene
configuration is destroyed. The absorption spectrum is
obviously dominated by a ligand-to-metal charge trans-
fer process. L1 in dichloromethane showed a strong
anthracenoid fluorescence spectrum at <10-6 M. As
increasing its concentration a broad emission at 455 nm
emerged and increased (Figure 5), the corresponding
excitation spectra were regular anthracenoid type with-
out such concentration effects. At 10-6 M concentration,
these L1-metals exhibited weak fluorescence spectra
(Figure 4b) that, when enlarged, resembled the pattern
of L1 and essentially an anthracenoid type.2,3 Finally,
L1AuCl under comparable conditions showed an intense
fluorescence spectrum, as in Figure 6, and also a new
broad fluorescence at 456 nm at higher concentrations
(at 10-4 M).
The comparison of the bonding data of L1Ag+ with
respect to those of L2Ag+ provides the important
contribution of the N-P group to the complex formation.
First, the electron density on the Ag-P bond in L1Ag+
is larger than that in L2Ag+. Second, although the
average Ag-N distance is around 3.5 Å, which indicates
no direct bond is formed between them, the far larger
ellipticity of the N-P bond in L1Ag+ than that of the
C-P bond in L2Ag+ (0.213 vs 0.110 e/a03) indicates that
the former would favor the formation of the three-center
Ag-NP bonding much more significantly over the Ag-
CP bonding. In fact, inspection of relevant MOs for these
two complexes reveals that the Ag-NP bonding is
present, whereas the Ag-CP cannot be found (see
Figure 311g). Third, as represented by the Ag-Cring
bonds, the Ag-η6-arene bond in L1Ag+ is also much
stronger than that in L2Ag+. These theoretical results
clearly indicate that there are three-center, triangle
metal-NP bonding and metal-η6-arene coordinating
features shown in the crystal structures for these
endocyclic complexes L1M+.
The fluorescence decay dynamics of L1 and L1-metal
perchlorates were investigated with a single photon
counting device to provide lifetimes of their singlet
excited state. While L0 and L2 decayed with a clean
single exponential to give the lifetimes τ ) 3.9 and 2.8
ns, respectively, all L1 and L1-metals did so with double
In studies of absorption, fluorescence and excitation
spectra of L1 and L1M 9,10-diisopropylanthracene3 and
anthracene itself were used as the reference. The
absorption spectra (Figure 4a) showed that L1Ag+ and
L1Au+ possessed the L1 type absorption pattern (es-

Group 11 Metal(I)-Arene Complexes
Organometallics, Vol. 22, No. 4, 2003 637
F igu r e 4. (a) Absorption spectra 1-4 in the order L1, L1Ag+, L1Au+, and L1Cu+ at 1 × 10-6 M in dichloromethane. (b,
c) Excitation (λmonitor ) 433 nm) and fluorescence (λex ) 360 nm) spectra 1-4 in the order L1, L1Cu+, L1Ag+, and L1Au+
at 5 × 10-6 M in dichloromethane [2′-4′ curves are the amplified spectra of 2-4 in (b and c).
new broad emission centered at 455 nm caused by
higher concentrations (see Figure 5). The major com-
ponent with τ2 ) 9-12 ns must come from the decay of
singlet excited state L1. Therefore, the former minor
component was an excimer, formed from dynamic self-
quenching of the latter major component (i.e., singlet
excited state L1). Though L1-metals have weak fluo-
rescence, both L1Ag+ and L1Cu+ also gave double
exponential decay patterns. The quantum yield of
fluorescence (Table 3) was determined by using an-
thracene as the secondary actinometer with Φ ) 0.27.
The low quantum yields of L1-metals agreed with
Figure 4c. It should be mentioned that fluorescence
quantum yields were the sum of the two emitting
species and must be concentration dependent.
The endocyclic structure of L1-metals as defined by
X-ray analysis (see Figure 1) is the basis for the
discussion of observed spectra in relation to the reaction
pattern in Schemes 1 and 2. First of all, weak metal
complex fluorescence in Figure 4c is assumed to arise
from a lack of L1M+ emission due to the metal-arene
interaction, which can be attributed to donation of the
anthracene π-electron cloud to the unoccupied 5s orbital
of the group 11 metal ion.12 As L1AuCl shows strong
fluorescence spectra in contrast to L1Au+, it must have
an exocyclic structure similar to that of L1AuP+, as
shown in Scheme 1.
F igu r e 5. Fluorescence (λex ) 360 nm) spectra 1-7 of L1
in order of increasing concentrations at 6 × 10-6, 8 × 10-6
,
1 × 10-5, 2 × 10-5, 4 × 10-5, 6 × 10-5, and 1 × 10-4 M in
dichloromethane.
The disparity leads us to propose that endocyclic
L1M+ and exocyclic L1M′+ are in equilibrium heavily
in favor of the former (Scheme 2), which is nonfluores-
cent, whereas the latter, L1M′+, causes fluorescence in
analogy with L1AuCl. It follows that the observed weak
emission of the M+ complex solution in Figure 4c arises
solely from a low equilibrium concentration of L1M′+.
In ter action of L1-Metal an d P h osph in es. Whereas
the reaction product L1AuP+ of L1-metal perchlorates
with diphenylphosphine could not be isolated and only
the robust L1-metal perchlorates can be recovered, the
solution of L1Au+/PPh2H (1:5) in CDCl3 revealed four
31P signals at -60 °C (Figure 7). The 31P NMR signals
appear at 35.12 and 0.12 ppm for the ring P and
F igu r e 6. Fluorescence spectra 1-4 of L1AuCl (λex ) 360
nm) in order of increasing concentration at 5 × 10-6, 1 ×
10-5, 5 × 10-5, and 1 × 10-4 M in dichloromethane.
exponentials to give two lifetimes as shown in Table 3.
As the minor component τ1 ()2-3 ns) increased with
the [L1] concentration increase of 10-5 to 10-4 M and
also with the monitoring wavelength 425 nm shifting
to 460 nm, this component must be originated from the
(12) (a) Beberwijk, C. D. M.; van der Kerk, G. J . M.; Leusink, A. J .;
Noltas, J . G. Organomet. Chem. Rev. 1970, 45, 215. (b) Ogimachi, N.;
Andrews, L. J .; Keefer, R. M. J . Am. Chem. Soc. 1956, 18, 2210.

638 Organometallics, Vol. 22, No. 4, 2003
Xu et al.
Ta ble 3. F lu or escen ce Lifetim e a n d Qu a n tu m Yield of th e Liga n d a n d Com p lexes in Dega ssed CH2Cl2
lifetime at 425 nm lifetime at 460 nm
compound
τ1/ns (%)
τ2/ns (%)
τ1/ns (%)
τ2/ns (%)
Φ
L0 (10-5M)
3.9
0.1824
0.1160
L1(10-5 M)
2.7 (7.0)
1.9 (11.5)
2.3 (19.5)
2.4 (22.3)
10.5 (93.0)
8.9 (88.5)
11.2 (80.5)
10.8 (77.4)
3.7 (10.1)
2.2 (15.1)
0.4 (18.3)
0.8 (21.2)
11.8 (89.9)
10.2 (84.9)
11.6 (81.7)
11.1 (78.8)
L1 (10-4 M)
L1CuClO4 (10-4 M)
L1AgClO4 (10-4 M)
L1AuClO4 (10-4 M)
L2 (10-4M)
0.0078
0.0047
0.0024
2.8
external P, respectively, of the complex L1AuP+, in
addition to that at 89.13 ppm for L1Au+ and at 25.50
ppm for unreacted PPh2H. At the L1Au+/PPh2H ratio
of 1:20 in CDCl3 and at -60 °C, the 31P signal of L1Au+
disappeared all together, indicating the complete coor-
dination; at the same time, a signal at -20.17 ppm could
be assigned to the external P of the complex L1AuP+,
and those at 33.50 and 24.75 ppm to the ring P of
L1AuP+ and to bulk PPh2H, respectively. This solution,
on warming up to -20 °C, registered two averaged
signals, one at 34.64 ppm for L1AuP+ and the other at
24.14 ppm for Ph2PH due to a rapid thermal equilibra-
tion of coordination between L1M+ and L1MP+. The fact
that 31P chemical shift variations depend on both PPh2H
concentration and temperature indicates a dynamic
equilibrium of the endo-exo cyclic changes as shown in
Scheme 2.
In view of the reversible interaction, the reaction
dynamics between L1-metals and various phosphines
were studied by fluorescence monitors. Dichloromethane
solutions of L1Cu+, L1Ag+, and L1Au+ (at 5 × 10-6 M)
became strongly fluorescent on addition of tributylphos-
phine, diphenylphosphine, or triphenylphosphine (g10-5
M).10a When the solution of L1M+ (5 × 10-6 M) was
titrated with a solution of Ph2PH (2.5 × 10-6 to 5 × 10-5
M), a significant enhancement of fluorescence was
observed. As shown in Figure 8a, it reached the maxi-
mum at the ratio of 10 for L1Ag+ and L1Au+ and at
that of 32 for L1Cu+. The ratio demonstrated the
dynamics of the coordinating interaction of PPh2H, the
equilibrium of which was in favor of L1-metals, par-
ticularly in the case of L1Cu+. The exocyclic metal
coordination of L1MP+, as shown in Scheme 2, is
proposed to visualize the reaction. The relative intensi-
ties compared with L1 (5 × 10-6 M) increase 3-5-fold,
while compared with L1M+ (5 × 10-6 M) they increase
F igu r e 8. (a) Plots of recorded relative fluorescence
intensities at 456 nm as in (b) against the ratio of HPPh2/
L1M+; [L1M+] ) 5 × 10-6 M in dichloromethane (L1Cu+,
9; L1Ag+, b; L1Au+, 2). (b) Fluorescence emission differ-
ence spectrum (λmonitor ) 433 nm) between L1Ag+ (5 × 10-6
M) in the presence of HPPh2 (2 × 10-5 M) (s) and using
410 nm as the reference point and the emission curve of
Figure 4c as a substitute for the L1AgP+ fluorescence curve
(- - -). (‚‚‚‚) represents the fluorescence excimer spectrum.
F igu r e 7. 31P NMR spectra of the mixture of L1AuClO4
and Ph2PH in CDCl3: (a) L1AuClO4/Ph2PH (1:5, molar
ratio), -60 °C; (b) L1AuClO4/Ph2PH (1:20, molar ratio), -60
°C; (c) L1AuClO4/Ph2PH (1:20, molar ratio), -20 °C;

Group 11 Metal(I)-Arene Complexes
Organometallics, Vol. 22, No. 4, 2003 639
excimer which is derived from a modification of, rather
than stabilization of, the parent excited state. It is a
great challenge to delineate the conformation of such
transient complexes in the future.
Fluorescence intensities of both L1 and L1AuCl were
not affected by the presence of PR3. Finally it should
be added that the L1-metal fluorescence pattern was
not affected at all in the presence of nitrogen ligands,
such as acetonitrile, pyridine, and aniline. Therefore,
the equilibrium pattern shown in Scheme 2 is a good
reaction potentially adaptable for the off-on molecular
switch design for phosphine in terms of selectivity and
sensitivity.
F igu r e 9. Fluorescence emission spectra of L2Ag+ (1 ×
2 × 10-4, and 3 × 10-4 M in dichloromethane.
10-5 M) in order of increasing PPh2H at 5 × 10-5, 1 × 10-4
,
Con clu sion s
Using a new fluoroionophore, two N-P coordinating
groups containing L1, we have prepared novel non-
emissive endocyclic group 11 metal aromatic η6-com-
plexes L1M+. The three-center metal-NP and metal-
η6-arene bonding features in these complexes have been
confirmed using ab initio and density functional calcula-
tions. Owing to the formation of the charge transfer
complexes compound L1 functions as an on-off switch
for these ions. The reversible interaction of L1M+ with
PR3 maintains the exocyclic metal configuration, which
affords strong fluorescence. Therefore, L1M+ complexes
function as off-on switches for the neutral molecule
PR3. The series of L1 compounds including L1, L1MP+,
and L1AuCl exhibits a new concentration-dependent
emission at about 455 nm due to an excimer formation.
We propose that the excited anthracene moiety of these
substrates is modified by interaction with the N-P
function of another substrate to give the new excimer.
80-150-fold. Figure 8b shows the resolved curve of the
fluorescence at [L1Ag+] ) 5 × 10-6 M in the presence
of HPPh2 at 2 × 10-5 M using 410 nm as the reference
point and the emission curve of Figure 4c as a substitute
for the L1AgP+ fluorescence curve. This demonstrated
that the new structureless band was broad and centered
at about 456 nm.
Similarly, titration of Ph2PH to a L2Ag+ solution in
CH2Cl2 (1 × 10-5 M) exhibits the sequential fluorescence
enhancement, but the pattern demonstrated that the
spectra were the anthracenoid type and no new peak
appeared (Figure 9).
The interaction of L1-metals with Ph2PH is repre-
sented by the coordination of metal to stabilize the
exocyclic configuration in L1M′ +, which is present in
low concentrations as in Figure 4c. Two consecutive
unfavorable equilibria in Scheme 2 demand a high
concentration of PPh2H (e.g., >1.5 × 10-4 M for L1Cu+)
to complete the L1MP+ formation. The first endo-exo
equilibrium consists of the rupture of η6 bonding to give
unstable bis-coordinate L1M′+. Thus, L1M′+ is vastly
unfavorable until coordinated by PR3 (or chloride).
The presence of concentration-dependent new fluo-
rescence at about 455 nm is ubiquitous in this series
that includes L1, L1MP+, and L1AuCl, but absent in
L2AgP+. The broad new emission must come from an
excimer in each case, and the excimer interaction must
involve a component of the L1 framework since L2AgP+
does not show the excimer peak. Further, the excimer
must have different geometry from that of the an-
thracene excimer having the π-orbital overlap since this
and allied systems13 fluoresce in the 570-580 nm
region. Subject to future studies, we propose that the
excited anthracene moiety of these substrates is modi-
fied by interaction with the N-P function of another
substrate to give the new 456 nm fluorescence. The new
456 nm fluorescence has a broad shape typical for an
excimer type, but a shorter lifetime (τ1 ) 2-3 ns) than
the parent anthracenoid fluorescence (τ2 ) 9-12 ns).
To our knowledge, an excimer from aromatic π-orbital
interaction generally results in fluorescence at longer
wavelengths and with longer lifetimes14 that logically
arise from stabilized complexes with a lower potential
energy.14d The present excimer shows neither of these
characteristics and may represent a transient type
Exp er im en ta l Section
Gen er a l Com m en ts. All reactions were carried out under
a nitrogen atmosphere using standard Schlenk or vacuum line
techniques. All solvents were thoroughly dried and deoxygen-
ated by standard methods and distilled immediately before
use. Column chromatography was carried out using silica gel
of 300-400 mesh. 9,10-Bis(N-propylaminomethyl)anthra-
cene, L1, and L1Ag+ were prepared according to literature
methods.7,10a IR spectra were recorded on a Bruker FT-IR
Equinox-55 infrared spectrophotometer in the range 4000-
400 cm-1 using KBr disks. 1H NMR and 31P NMR spectra were
recorded on a Bruker AC-200 NMR spectrometer. Elemental
analyses were performed by a Yanaco MT-3 analyzer. The
luminescent spectra and UV-absorption spectra were con-
ducted on a Perkin-Elmer LS-50B luminescence spectrometer
and a Shimadzu UV-1601PC UV-visible spectrophotometer,
respectively. Melting points were determined on a Yanaco
micromelting point apparatus MP-500. Luminescence decay
measurements of the ligand and complexes were performed
with a Horiba NAES-1100 single photon counting nanosecond
fluorescence spectrometer.
P r ep a r a tion of L1Cu P er ch lor a te. To a solution of
anthracenodiphosphine L1 (0.344 g, 0.50 mmol) in CH2Cl2 (20
mL) was added solid Cu(CH3CN)4ClO4 (0.164 g, 0.5 mmol)
under dinitrogen, and the resulting solution was stirred for 2
h at room temperature. The filtrate, after filtering off some
(14) (a) Forster, T.; Kasper, K. Z. Physik. Chem. N. F. 1954, 1, 275.
(b) Yoshihara, K.; Kasuya, T.; Inoue, A.; Nagakura, S. Chem. Phys.
Lett. 1971, 9, 469. (c) Chow, Y. L.; Cheng, X. E.; J ohansson, C. I. J .
Photochem. Photobiol. A: Chem. 1991, 57, 247. (d) Chow, Y. L.;
J ohansson, C. I. Chem. Phys. Lett. 1994, 231, 541. (e) Chow, Y. L.;
J ohansson, C. I. J . Phys. Chem. 1995, 99, 17558.
(13) (a) Sclafani, J . A.; Maranto, M. T.; Sisku, T. M.; Arman, S. A.
V. Tetrahedron Lett. 1996, 37, 2193. (b) Tahara, R.; Hasebe, K.;
Nakamura, H. Chem. Lett. 1995, 953.

640 Organometallics, Vol. 22, No. 4, 2003
Xu et al.
insoluble materials, was diluted with diethyl ether to afford
air-stable yellow crystals of L1Cu perchlorate (0.240 g, 75.3%),
mp 220-222 °C. Anal. Calcd for C46H46ClCuN2O4P2: C, 64.98;
room temperature. The filtrate of the mixture was evaporated
to a small volume. The residue was diluted with ether to give
yellow crystals of L2Ag perchlorate (0.24 g, 74.1%), mp 210-
212 °C. Anal. Calcd for C42H36AgClO4P2: C, 62.28; H, 4.48.
1
H, 5.70; N, 3.06. Found: C, 64.83; H, 5.40; N, 3.06. H NMR
(CDCl3): 0.67-0.83 (t, J ) 7 Hz, 6H, 2CH3), 1.40-1.75 (m,
4H, 2CH2), 3.06-3.20 (t, J ) 7 Hz, 4H, 2CH2), 5.20-5.30 (s,
4H, 2CH2), 6.64-6.84 (m, 8H, C6H5), 7.10-7.24 (m, 8H, C6H5),
7.46-7.60 (m, 4H, C6H5), 7.70-7.81 (m, 4H, 4CH), 8.32-8.45
(m, 4H, 4CH) ppm. 31P NMR (CDCl3): 34.56 (s) ppm.
P r ep a r a tion of L1Au Cl. To a solution of anthraceno-
diphosphine L1 (0.171 g, 0.25 mmol) in CH2Cl2 (15 mL) was
added solid Au(SMe2)Cl (0.074, 0.25 mmol), and the resulting
solution was stirred for 3 h at room temperature. The filtrate,
after filtering off some insoluble materials, was diluted with
diethyl ether to afford air-stable yellow crystals of L1AuCl
(0.211 g, 91.6%), mp 220-222 °C. Anal. Calcd for C46H46ClN2P2-
Au‚1.5CH2Cl2: C, 54.41; H, 4.71; N, 2.67. Found: C, 55.09;
H, 4.20; N, 2.54. 31P NMR (CDCl3): 75.53 (s) ppm.
P r ep a r a tion of L1Au P er ch lor a te. To a solution of
anthracenodiphosphine L1 (0.172 g, 0.25 mmol) in CH2Cl2 (15
mL) was added solid Au(SMe2)Cl (0.074, 0.25 mmol), and the
resulting solution was stirred for 3 h at room temperature.
Then solid AgClO4 (0.054 g, 0.25 mmol) was added, the
resulting mixture was stirred for 0.5 h at room temperature,
and the mixture was centrifugally separated to remove gener-
ated AgCl. Diethyl ether was diffused into the concentrated
solution to give L1Au perchlorate (0.212 g, 86.2%) as a yellow
crystal, mp 256-258 °C. Anal. Calcd for C46H46AuClN2O4P2:
C, 56.08; H, 4.71; N, 2.84. Found: C, 55.92; H, 4.61; N, 3.10.
31P NMR (CDCl3): 70.60 (s) ppm.
P r ep a r a tion of L2. A solution of n-BuLi in hexane (2.18
M, 21.1 mL) was added dropwise to a solution of Ph2PH (7.6
mL, 44 mmol) in 200 mL of tetrahydrofuran at 0 °C. The
resulting mixture was added dropwise to a solution of 9,10-
bis(2-chloroethyl)anthracene (6.06 g, 20 mmol) in 50 mL of
tetrahydrofuran at 0 °C, after which the mixture was stirred
for 4 h at room temperature. The solvent was removed in a
vacuum, and water (200 mL) was added. The aqueous phase
was extracted with CH2Cl2 (3 × 300 mL) and the organic phase
dried with anhydrous MgSO4 overnight. Most of the CH2Cl2
was removed in a vacuum, and diethyl ether was added to
deposit a colorless solid, which upon recrystallization from
CH2Cl2/diethyl ether afforded an analytically pure product, L2,
4.9 g (40.8%), mp 236-238 °C. Anal. Calcd for C42H36P2‚CH2-
Cl2: C, 75.11; H, 5.57. Found: C, 74.73; H, 5.61. 1H NMR (d6-
DMSO): 3.94-3.97 (t, 4H, 2CH2); 4.07-4.10 (t, 4H, 2CH2),
7.54-7.63 (m, 20H, 4C6H5), 7.90-8.10 (m, 4H, 4CH), 8.35-
8.41 (m, 4H, 4CH). 31P NMR: -12.9 ppm.
Found: C, 62.16; H, 4.50. 31P NMR (CDCl3): 0.08 (J P-107Ag
508.9 Hz; J P-109Ag ) 581.3 Hz) ppm.
)
X-r a y Diffr a ction s of Sin gle-Cr ysta l Str u ctu r a l Deter -
m in a tion . Diffraction experiments were performed on
a
Bruker Smart 1000 CCD diffractometer employing graphite-
monochromatized Mo KR radiation (λ ) 0.71073 Å) and
collecting a hemisphere of data in 1329 frames with 10 s
exposure times. The atom positions were determined using
direct methods employing SHELXTL-97 and successive dif-
ference Fourier map calculations. The full-matrix least-squares
refinement was carried out on F2. All non-hydrogen atoms were
assigned anisotropic temperature factors. Empirical absorption
corrections were applied to the data sets employing SADABS.
Most hydrogen atom positions were calculated and allowed to
ride on the carbon to which they are bonded assuming a C-H
bond length of 0.95 Å. Hydrogen atom temperature factors
were fixed at 1.20 times the isotropic temperature factor of
the carbon atom to which they are bonded. The hydrogen atom
contributions were calculated, but not refined.
X-r a y Cr ysta llogr a p h y. Crystallography data (excluding
structure factors) for the structures reported in this paper have
been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-188735
(L1AgClO4), CCDC-188736 (L1CuClO4), CCDC-188737
(L1AuClO4), and CCDC-188738 (L2AgClO4‚0.5CH2Cl2). Copies
of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ (UK) (fax: (+44)
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Th eor etica l Ca lcu la tion s. All theoretical calculations
were performed on a PC using Gaussian 98.11a All electron
basis sets STO-3G* and 3-21G*11b,c for Cu and Ag complexes
and the ECP set LanL2DZ11d for all including L1Au+ were
used. The geometries were taken from their X-ray crystal-
lographic data.
Ack n ow led gm en t. We gratefully acknowledge the
financial assistance provided by the National Natural
Science Foundation of China (Project No. 20102003).
Su p p or tin g In for m a tion Ava ila ble: Full tables of atomic
coordinates, thermal parameters, and a full list of bond lengths
and bond angles for complexes L1Cu+, L1Au+, and L2Ag+. This
material is available free of charge via the Internet at
http://pubs.acs.org.
P r ep a r a tion of L2Ag P er ch lor a te. To a solution of L2
(0.24 g, 0.40 mmol) in CH2Cl2 (20 mL) was added solid AgClO4
(0.083 g, 0.40 mmol), and the mixture was stirred for 4 h at
OM020668H