Electronic and magnetic communication in mixed-valent and homovalent ruthenium complexes containing phenylcyanamide type bridging ligands

Article abstract of DOI:10.1021/ja067255i

Four new phenylcyanamido-bridge dinuclear ruthenium complexes [{Ru(tpy)(thd)}₂(μ-L)] with tpy = 2,2′:6′,2″- terpyridine, thd = 2,2,6,6-tetramethyl-3,5-heptanedione and L = dcbp = 4,4′-dicyanamidobiphenyl; bcpa = bis(4-cyanamidophenyl)acetylene;

Full text of DOI:10.1021/ja067255i

Published on Web 01/17/2007
Electronic and Magnetic Communication in Mixed-Valent and
Homovalent Ruthenium Complexes Containing
Phenylcyanamide Type Bridging Ligands
Muriel Fabre and Jacques Bonvoisin*
Contribution from the CEMES/CNRS, NanoSciences Group, BP 94347, 29 rue Jeanne MarVig,
31055 Toulouse cedex 4, France
Received October 10, 2006; E-mail: jbonvoisin@cemes.fr
Abstract: Four new phenylcyanamido-bridge dinuclear ruthenium complexes [{Ru(tpy)(thd)}2(µ-L)] with
tpy ) 2,2′:6′,2′′-terpyridine, thd ) 2,2,6,6-tetramethyl-3,5-heptanedione and L ) dcbp ) 4,4′-dicyanami-
dobiphenyl; bcpa ) bis(4-cyanamidophenyl)acetylene; bcpda ) bis(4-cyanamidophenyl)diacetylene; bcpea
) 9,10,-bis(4-cyanamidophenylethynyl)anthracene have been prepared and fully characterized. The mixed
valent Ru(II)Ru(III) and homovalent paramagnetic Ru(III)Ru(III) forms of all the complexes were
electrochemically generated and studied by UV-vis-NIR and EPR spectroscopy. Electronic communication
was quantified by the electronic coupling parameter Vab extracted from intervalence measurements in the
near IR area, and magnetic communication was quantified in terms of the exchange coupling constant J,
accessible from the intensity of the EPR signal when varying the temperature. Exponential decays for both
electronic and magnetic coupling versus intermetallic distance were obtained and discussed.
1. Introduction
the electron-transfer process will be probed by the intensity of
the intervalence transition (IT) in the NIR, according to the
relation devised by N. Hush in 1967.8 This yields the electronic
coupling parameter Vab describing the amount of electronic
interaction between remote sites. From this interaction, one can
devise general rules for the design of efficient bridging ligands
allowing long-distance electron transfer. In addition, mixed-
valence compounds can be simple models for the expanding
domain of nanojunctions, in which a single molecule is bridging
two nanoscale metallic conductors.9 However, as the sizes of
the compounds increase, synthetic problems become more acute,
particularly with a decrease in free ligand solubility. In addition,
the electronic coupling decreases and its detection become
problematic. Thus, there is a need for new classes of compounds
and/or new methods that would be more easily accessible and
would exhibit or allow reaching either stronger metal-metal
couplings or longer metal-metal distances than conventional
systems studied so far. Some chemistry alternatives can be found
by using cyclometallated complexes.10 With increasing inter-
metallic distance and/or diminishing transfer abilities of the
spacer, more sensitive detection methods must be applied. If
the terminal groups at each extremity of the bridging ligand
are paramagnetic, determination of the exchange constant J
provides the information. This can be accomplished by magnetic
susceptometry or EPR spectroscopy for J g 1 cm-1 and by EPR
It is almost a truism now that, after the inception of the
Creutz-Taube ion [(H3N)5Ru(pyrazine)Ru(NH3)5]5+ in 1969,1
studies of mixed/intermediate valence complexes and their role
in intramolecular electro- and magnetocommunication have
become vital parts of contemporary research in coordination
chemistry.2-6 Much effort has been invested in the elucidation
of the role that the nature of the spacer between two interacting
units plays in governing the redox splitting between successive
electron-transfer steps (electrocommunication) and the sign and
magnitude of exchange coupling of unpaired spins (magneto-
communication). The ability of the spacer to transmit electronic
effects has commonly been studied by electrochemistry, using
the redox splitting, i.e., the potential difference of consecutive
redox steps as a measure of intramolecular intermetallic com-
munication. One has to remember that even in the unfavorable
case where this potential difference is small, leading to a single
electrochemical wave a comfortable proportion of mixed valence
species (>50%) exists in solution,2 except if inversion of
standard potentials occurs7 which is not the case here. In this
work, once the mixed valence species is obtained, from a
practical point of view, instead of the redox splitting method,
(1) Creutz, C.; Taube, H. J. Am. Chem. Soc. 1969, 91 (14), 3988.
(2) Launay, J.-P. Chem. Soc. ReV. 2001, 30, 386.
(3) Launay, J.-P.; Coudret, C. Wires Based on Metal Complexes. Electron
Transfer in Chemistry; Wiley-VCH: 2001; Vol. 5, p 3.
(4) Kahn, O. Molecular Magnetism; Wiley-VCH: 1993.
(5) Crutchley, R. J. AdV. Inorg. Chem. 1994, 41, 273.
(6) Ward, M. D. Chem. Soc. ReV. 1995, 24 (2), 121. Paul, F.; Lapinte, C. Coord.
Chem. ReV. 1998, 178-180, 431. McCleverty, J. A.; Ward, M. D. Acc.
Chem. Res. 1998, 31 (12), 842. Brunschwig, B. S.; Sutin, N. Coord. Chem.
ReV. 1999, 187, 233. Kaim, W.; Klein, A.; Gloeckle, M. Acc. Chem. Res.
2000, 33 (11), 755. Demadis, K. D.; Hartshorn, C. M.; Meyer, T. J. Chem.
ReV. 2001, 101, 2655. Ward, M. D.; McCleverty, J. A. J. Chem. Soc., Dalton
Trans. 2002, (3), 275.
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Soc. 2001, 123 (27), 6669.
(8) Hush, N. S. Prog. Inorg. Chem. 1967, 8, 391.
(9) Joachim, C.; Gimzewski, J. Europhys. Lett. 1995, 30, 409. Langlais, V. J.;
Schlittler, R. R.; Tang, H.; Gourdon, A.; Joachim, C.; Gimzewski, J. K.
Phys. ReV. Lett. 1999, 83 (14), 2809. Rousset, V.; Joachim, C.; Rousset,
B.; Fabre, N. J. Phys. III 1995, 5, 1983.
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5880.
9
1434
J. AM. CHEM. SOC. 2007, 129, 1434-1444
10.1021/ja067255i CCC: $37.00 © 2007 American Chemical Society

Phenylcyanamido-Bridge Ru Complexes
A R T I C L E S
Scheme 1
spectroscopy for much smaller J values. At this point, an
important question must be addressed which is to know whether
the more important phenomena of intramolecular long-distance
electron transfer and energy transfer are somehow related to
electron-spin exchange coupling, bearing in mind that ET is a
one-electron process, whereas exchange coupling is a two-
electron process. In fact, as Forbes11 has pointed out, both
processes are facets of the more general donor-acceptor
interaction having in common the electron-transfer matrix
element Vab. The possibility of correlating J and Vab has already
been addressed by other authors.5,12-17 Our own contribution
to the field is to find good candidates which will allow obtaining
both J (in the homovalent/isovalent paramagnetic form) and Vab
(in the mixed valent MV form) in order to then correlate them.
The bridging ligand containing cyanamide group seems to be
particularly well suited since strong interactions have been
obtained in homovalent18 or MV ruthenium complexes.19
Following this line, few years ago, we have reported two series
of dinuclear ruthenium complexes containing cyanamide deriva-
tives as bridging ligands.20,21 For both series, Vab and J could
not be obtained because of stability and/or solubility problems.
Here we present the successful synthesis of four new dinuclear
ruthenium complexes (see Scheme 1) with terpyridine (tpy) and
bulky “acac” type ancillary ligands named thd, with four
cyanamide derivatives bridging ligands with formula [{Ru(tpy)-
(thd)}2(µ-L)] with tpy ) 2,2′:6′,2′′ terpyridine, thd ) 2,2,6,6-
tetramethyl-3,5-heptanedione, and L ) dcbp ) 4,4′-dicyana-
midobiphenyl; bcpa ) bis(4-cyanamidophenyl)acetylene; bcpda
) bis(4-cyanamidophenyl)diacetylene; bcpea ) 9,10,-bis(4-
cyanamidophenylethynyl)anthracene. In addition, the work
described here provides the first quantitative experimental
comparison of the decay law for both the electronic (in the MV
form) and the magnetic (in the homovalent paramagnetic form)
coupling parameters versus intermetallic distance using the same
family of compounds for both phenomena.
2. Results and Discussion
Synthesis. The synthesis of [Ru(tpy)(thd)(TMSepcyd)] 2 from
[Ru(tpy)(thd)(Ipcyd)] 1 was adapted from literature procedures.22
The Trimethylsilyl-protected alkyne complex [Ru(tpy)(thd)-
(TMSepcyd)] 2 was prepared by a Sonogashira cross-coupling
reaction between the iodoruthenium complex 1 and trimethyl-
silylacetylene under classic conditions ((Pd(PPh3)2Cl2, CuI,
piperidine, DMF). Complex [{Ru(tpy)(thd)}2(µ-dcbp)] 3 was
synthesized using a method adapted from the Suzuki cross-
coupling between a halogenaryl and an arylboronic ester.23 It
is a one-pot synthesis, the arylboronic ester being generated in
situ. Complex 1 was put in solution in DMF with 0.5 equiv of
bis(pinacolato)diboran in the presence of PdCl2dppf catalyst and
K2CO3 as basic agent (Scheme 2). Complex [{Ru(tpy)(thd)}2-
(µ-bcpea)] 6 was synthesized by a Sonogashira cross-coupling
reaction between the iodoruthenium complex 1 and 9,10-
diethynylanthracene, which is formed in situ by deprotection
of 9,10-bis(3-hydroxy-3-methylbutynyl)anthracene with potas-
sium tert-butoxide (Scheme 2). Complex [{Ru(tpy)(thd)}2(µ-
bcpa)] 4 was synthesized by a Sonogashira cross-coupling
reaction between the iodoruthenium complex 1 and the ethyn-
ylated complex [Ru(tpy)(thd)(epcyd)] formed in situ by depro-
tection of the trimethylsilyl-protected alkyne complex 2 with
potassium carbonate, under classic conditions (Pd(PPh3)2Cl2,
CuI, piperidine, and DMF) but in the presence of a strong base
such as DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) given the
weak reactivity of the alkyne function toward deprotonation
(Scheme 3). Complex [{Ru(tpy)(thd)}2(µ-bcpda)] 5 was ob-
tained by a homo coupling reaction using the ethynylated
complex [Ru(tpy)(thd)(epcyd)] formed in situ in the same way
as for complex 4. This reaction was performed with DBU and
copper(I) chloride in dry pyridine with oxygen bubbling.
Electrochemistry. Cyclic voltammograms (CV) of the
complexes were recorded in dichloromethane under an argon
(11) Forbes, M. D. E.; Ball, J. D.; Avdievich, N. J. Am. Chem. Soc. 1996, 118,
4707.
(12) Felthouse, T. R.; Hendrickson, D. N. Inorg. Chem. 1978, 17 (9), 2636.
Bayly, S. R.; Humphrey, E. R.; de Chair, H.; Paredes, C. G.; Bell, Z. R.;
Jeffery, J. C.; McCleverty, J. A.; Ward, M. D.; Totti, F.; Gatteschi, D.;
Courric, S.; Steele, B. R.; Screttas, C. G. J. Chem. Soc., Dalton Trans.
2001, (9), 1401. Shultz, D. A.; Fico, R. M. J.; Bodnar, S. H.; Krishna
Kumar, R.; Vostrikova, K. E.; Kampf, J. W.; Boyle, P. D. J. Am. Chem.
Soc. 2003, (125), 11761. Elschenbroich, C.; Plackmeyer, J.; Nowotny, M.;
Harms, K.; Pebler, J.; Burhgaus, O. Inorg. Chem. 2005, 44, 955.
Elschenbroich, C.; Plackmeyer, J.; Nowotny, M.; Behrendt, A.; Harms,
K.; Pebler, J.; Burghaus, O. Chem. Eur. J. 2005, 11, 7427.
(13) Bertrand, P. Chem. Phys. Lett. 1985, 113, 104.
(14) Nelsen, S. F.; Ismagilov, R. F.; Powell, D. R. J. Am. Chem. Soc. 1998,
120 (8), 1924. de Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J.-F.;
Toupet, L.; C., L. Organometallics 2005, 24, 4558.
(15) Brunold, T. C.; Gamelin, D. R.; Solomon, E. I. J. Am. Chem. Soc. 2000,
122, 8511.
(16) Weiss, E. A.; Ahrens, M. J.; Sinks, L. E.; Gusev, A. V.; Ratner, M. A.;
Wasielewski, M. R. J. Am. Chem. Soc. 2004, 126 (17), 5577.
(17) Weiss, E. A.; Wasielewski, M. R.; Ratner, M. A. Top. Curr. Chem. 2005,
257, 103.
(18) Aquino, M. A. S.; Lee, F. L.; Gabe, E. J.; Bensimon, C.; Greedan, J. E.;
Crutchley, R. J. J. Am. Chem. Soc. 1992, 114 (13), 5130.
(19) Rezvani, A. R.; Evans, C. E. B.; Crutchley, R. J. Inorg. Chem. 1995, 34
(18), 4600. Mosher, P. J.; Yap, G. P. A.; Crutchley, R. J. Inorg. Chem.
2001, 40(6), 1189.
(20) Fabre, M. A.; Jaud, J.; Bonvoisin, J. J. Inorg. Chim. Acta 2005, 358 (7),
2384.
(21) Sondaz, E.; Jaud, J.; Launay, J.-P.; Bonvoisin, J. Eur. J. Inorg. Chem. 2002,
1924.
(22) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 16 (50),
4467.
(23) Nising, C. F.; Schmid, U. K.; Nieger, M.; Bra¨se, S. J. Org. Chem. 2004,
69, 6830.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1435

A R T I C L E S
Fabre and Bonvoisin
Scheme 2. Synthesis of [{Ru(tpy)(thd)}2(µ-dcbp)] 3 and [{Ru(tpy)(thd)]}2(µ-bcpea)] 6
Scheme 3. Synthesis of [{Ru(tpy)(thd)}2(µ-bcpa)] 4 and [{Ru(tpy)(thd)}2(µ-bcpda)] 5
atmosphere with 0.1 M tetrabutylammonium hexafluorophos-
phate (TBAH) (see Figure 1 and Table 1). The E1/2 potentials
were determined from the average of the anodic and cathodic
peak potentials for reversible waves. For irreversible waves, only
the anodic peak potentials are reported.
In reduction, no wave was observed at least down to -1.5
V. In oxidation, several waves were observed. The first
reversible wave around 0.2 V was attributed to the Ru(II/III)
couple. For complexes 4-6, with the longest metal-metal
distance (RMM ) 18.5, 21.0, and 25.1 Å), the redox potentials
of the ruthenium centers are too close to be distinguished, and
a single bielectronic wave is then observed. One can notice that
as the intermetallic distance decreases, the difference ∆E
between anodic and cathodic potentials increases (from 88 mV
for 6 to 108 mV for 4). This can be explained by the increase
of the energy gap between the two individual ruthenium redox
potentials when the metal-metal distance decreases.
For complex 3, which presents the shortest metal-metal
distance (RMM ) 16 Å), ∆E is much bigger (188 mV) and one
can observe a separation into two waves which corresponds to
the successive oxidation of the two ruthenium centers. Dif-
ferential pulse voltammetry (DPV) (see Supporting Information)
was also performed in the range -0.1 to 0.4 V in order to
measure the comproportionation constants KC for complexes
3-6. The results are shown in Table 2; the KC constants were
(24) Fabre, M.; Jaud, J.; Hliwa, M.; Launay, J.-P.; Bonvoisin, J. Inorg. Chem.
2006, 45 (23), 9332.
(25) Aquino, M. A. S.; White, C. A.; Bensimon, C.; Greedan, J. E.; Crutchley,
R. J. Can. J. Chem. 1996, 74 (11), 2201.
(26) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20 (4), 1278.
9
1436 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Phenylcyanamido-Bridge Ru Complexes
A R T I C L E S
Figure 1. Cyclic voltammetry of 3, 4, 5, and 6 (CH2Cl2, 0.1 M TBAH, 0.1 V‚s-1).
Table 1. Electrochemical Data, vs ECS, in CH2Cl2, 0.1 M TBAH, 0.1 V/sa
/
III
RuII
E1 2, V (
ligand
a (V)
complex
∆E, mV)
E
ref
/
[Ru(tpy)(thd)Cl]
1
0.198 (83)
0.200 (78)
-
24
24
1.064
3
0.137 (180)
-0.215 (100)
0.188 (108)
0.225 (88)
0.725 (78)-0.938 (73)
0.775 (80)-0.945 (85)
0.884-1.030
this work
25
this work
this work
this work
b
[{Ru(NH3)5}2(µ-dcbp)][PF6]4
4
5
6
1.030
0.211 (83)
0.764-0.930
a E1/2 ) (Ea + Ec)/2; ∆E ) |Ea - Ec|. Ea: anodic peak. b In CH3CN.
Table 2. Oxidation Potentials and Comproportionation Constants
from DPV for Complexes 3, 4, 5, and 6 in DCM
Table 3. UV-Vis-NIR Absorption Data of the Investigated
Compounds in DCM
1
1
complex
E
°
1 (V/ECS)
E
°
2 (V/ECS)
KC
complex
λ ‚ )
max in nm (ꢀ × 10-3 in M- cm-
3
4
5
6
0.091
0.184
0.205
0.184
0.219
0.268
0.271
0.234
145 ( 5
26 ( 2
3
4
5
6
278 (73), 318 (69), 357sh (51), 578 (12)
278 (67), 318 (61), 386 (62), 574 (12)
278 (69), 318 (62), 408 (70), 570 (13)
270 (115), 318 (68), 344 (57), 434 (25), 552 (59)
272 (68), 312 (66), 1306 (37)
272 (69), 314 (71), 1160 (23)
272 (69), 314 (68), 1141 (29)
276 (121), 314 (65), 488 (58), 868 (17), 1234 (29)
13 ( 1
7.0 ( 0.5
32+
42+
52+
62+
obtained by the method described by Richardson and Taube.26
The obtained values range from KC ) 7 to KC ) 145 from the
longest compound 6 to the shortest compound 3 and are quite
usual for MV complexes with such metal-metal distances.
Electronic Absorption. The dinuclear compounds have been
characterized by UV-vis-NIR spectroscopy in DCM (see
Table 3). The spectra are comparable to those of the mono-
nuclear and dinuclear compounds already studied with the same
phenylcyanamide type ligands.20,24
The narrow and intense bands around 280 and 320 nm
correspond to terpyridine ligand (π f π*). The larger and less
intense band around 570 nm is attributable to dπ(RuII) f π*-
(tpy) MLCT transition. Its position and intensity are about the
same for 3 to 5, but for 6, an intraligand transition from bcpea2-
appears in this area (344 nm) as it has already been observed
in the analogous complex [{Ru(tpy)(acac)}2(µ-bcpea)].20 Finally,
the transitions at 357 nm for 3, 386 nm for 4, and 408 nm for
5 can be attributed to intraligand transitions from the bridging
ligand according to the fact that they are shifted to lower energy
when the conjugation of the bridge increases. Spectra of
electrogenerated Ru(III)Ru(III) species are shown in Figure 2.
As previously observed for other Ru(III) complexes contain-
ing phenylcyanamide type ligand,24 one can note the disappear-
ance of the transition at 570 nm corresponding to the
dπ(RuII) f π*(tpy) MLCT transitions and the appearance of a
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1437

A R T I C L E S
Fabre and Bonvoisin
Figure 2. (Top) UV-vis-NIR spectra of 3, 4, 5, and 6 in DCM. (Bottom)
UV-vis-NIR spectra of 32+, 42+, 52+, and 62+ in DCM.
Figure 3. Spectroelectrochemical oxidation of 3 in DCM, 0.1 M TBAH
(electrolysis at 0.46 V vs SCE). (Top) 3 f 3+. (Bottom) 3+ f 32+
.
Table 4. Intervalence Transition Parameters and Experimental Vab
Values for 3+, 4+, 5+, and 6+
broader and more intense band in the near infrared area (1000-
1500 nm) which is attributed to π(µ-L) f dπ(RuIII) LMCT type
transition. The intensity and position of these bands vary for
each studied complex, which is consistent with the attribution
proposed above: LMCT transition from the bridge to the metal
should be highly dependent on the structure of the bridging
ligand.
RMM
(Å)
νmax
¯
∆ν1/
¯
ꢀmax
×
‚
103
Vab
2
1
1
1
1
complex
(cm-
)
(cm-
)
(L
‚
mol-
cm-
)
(eV)
3+
4+
5+
6+
16.0 3800 ( 300 4290 ( 300 23.9 ( 2.1 0.099 ( 0.005
18.5 5020 ( 120 3910 ( 290
21.0 5950 ( 150 3760 ( 240
25.1 5830 ( 380 3420 ( 310
7.0 ( 1.0 0.051 ( 0.003
3.6 ( 0.7 0.034 ( 0.002
3.0 ( 1.1 0.024 ( 0.003
Mixed Valent Species: Intervalence Transitions and
Electronic Coupling. Spectroelectrochemical studies of di-
nuclear complexes 3-6 were performed in DCM. Oxidation of
complexes 3-6 by electrolysis at controlled potential with
coulommetry were followed by UV-vis-NIR spectroscopy.
The electrolysis was performed at 0.46 V, which allows the
oxidation of the ruthenium centers only. During the oxidation,
for all four complexes, the dπ(RuII) f π*(tpy) MLCT bands
between 500 and 750 nm decrease in intensity and two new
bands appear: The first one between 1100 and 1300 nm
corresponds to a π(µ-L) f dπ(RuIII) LMCT transition. The
second one in the near infrared area (between 1500 and 2000
nm) corresponds to a Metal to Metal Charge Transfer (MMCT)
or Intervalence Transition (IT). The intensity of this band reaches
a maximum at half oxidation and then decreases when the
oxidation is prolonged. For the shortest complex 3, the IT is
clearly visible (λ ) 2078 nm, see Figure 3). When the metal-
metal distance increases (from 3 to 6), the intensity of this
transition decreases (hypochromic effect) and the IT is shifted
toward shorter wavelengths (hypsochromic effect), where it is
partly masked by the LMCT transition (see Table 4). Conse-
quently, the IT becomes more and more difficult to detect and
is almost undetectable for the longest complex 6 (see Supporting
Information Figures S2-S4).
In order to get the electronic coupling Vab, it is necessary to
have the spectrum of the pure mixed valence state, i.e., once
corrected from the homovalent species.2 Because the IT appears
sometimes as a shoulder or extra absorption on the longer
wavelength’s side, it is important to perform a deconvolution
of the spectrum in order to have all the parameters (position,
extinction coefficient, width) which are required to calculate
the parameter Vab using the Hush formula.8,27 The deconvolu-
tions for the four complexes are available in the Supporting
Information (Figure S5). The experimental parameters of the
intervalence transition for all the dinuclear complexes are
gathered in Table 4.
The RMM values in Table 4 were calculated taking the average
of the metal-metal distance in the syn and anti conformation
(see Scheme 4). In each of the conformations, the distances were
evaluated using a geometry optimized structure using molecular
mechanics with the Cerius2 software.28
In Figure 4 is illustrated the evolution of Vab with metal-
metal distance. The decay law was obtained using the first three
values, which corresponds to the repetition of an alkyne unit:
[(tpy)(thd)RusNCNsPhs(CtC)nsPhsNCNsRu(tpy)(thd)]
with n ) 0, 1, or 2 for complexes 3, 4, or 5, respectively. One
(27) Hush, N. S. Coord. Chem. ReV. 1985, 64, 135.
(28) Cerius2, 4.2; Accelrys Inc: San Diego, CA, 2000.
9
1438 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Phenylcyanamido-Bridge Ru Complexes
A R T I C L E S
Scheme 4. Syn and Anti Conformations of Dinuclear Compounds
has to notice the distinction between the spacer (repeat of alkyne
units) to the bridge which also includes the phenylcyanamide
entity.2 The decay of Vab follows an exponential law as given
by eq 1, as it has already been observed and reported
elsewhere.2,3
and others.14,36 Complex 6 should not follow the present series
with n ) 3, the spacer being not of the same chemical nature
(anthracene vs acetylene).2 Another alternative for the fact that
compound 6, with the anthracene bridge, does not follow the
decay law would be to claim that, for such a long compound,
the energy gap is comparable to the reorganization energy or
electronic coupling and so superexchange and sequential mech-
anisms can compete. An increase in Vab for 6 could be due to
the dominance of an incoherent channel, namely a hopping
process as it has already been evoked for charge and spin
transport through para-phenylene oligomers.16,17
Homovalent Species: Magnetic Coupling. The RuIII-RuIII
species were electrochemically generated. Total oxidation was
checked by linear voltammetry after oxidation (see Figure S6).
LV allowed us to estimate that the dinuclear compounds were
oxidized up to 98%.
Vab ) Vab° exp(-γ RMM
)
(1)
The decay slope was found to be γ ) 0.21 ( 0.03 Å-1. This
value is twice or three times bigger than the one usually
observed for various series (0.07-0.12 Å-1).2 This could be
explained by the nature of the repeat units of the bridging ligand.
By using a simple tight binding model, it has been shown that
the structure of the bridge plays a crucial role on the electronic
coupling.29-31 For all the compounds in Launay’s review,2 the
bridging ligands show essentially vinylene or phenylene spacers.
The difference could thus be attributed to the alkyne nature of
the spacer which may be less good π-connectors32 than polyene
ones or which presents some bond-length alternation effect.33
A bigger damping factor (γ) for the acetylene bridge compared
to ethylene ones was also predicted by theory.34 This has to be
nuanced due to the recent results of Crutchley et al. who showed
that the decay factor is about the same for ethylene or acetylene
spacers.35 The value of Vab obtained for the longest complex 6
appears to be noticeably higher than the one which would be
extrapolated for the same distance with the above decay law.
The peculiar role of anthracene, inserted in a molecular bridge,
in mediating the electronic effect and more precisely its
amplification effect has already been noticed by our group10
The EPR spectra of the oxidized species were then performed
in frozen DCM solutions at 30 K (Figure 5). The spectra are
quite broad, with a peak to peak separation of about 500 G,
and present an anisotropic shape. The Lande´ factors are gathered
in Table 5.
The g factors are in the range of 2.15 to 2.19, which is very
comparable to the values obtained for 1+.24 These signals are
that of an effective S ) 1 spin state resulting from the mag-
1
netic interaction of two S ) /2 spin states carried by each
ruthenium(III). The spectra keep the characteristics of a mono-
1
nuclear ruthenium(III) S )
/ spin state but with larger
2
bandwidths. They also show a weak signal at half field, which
is typical of a spin triplet and corresponds to a ∆MS ) 2
forbidden transition.
To measure the magnetic coupling for each complex, EPR
measurements at several temperatures can be performed.37 In
Figure 6 are reported the product of the intensity of the EPR
signal times the temperature versus the temperature for the four
complexes 3-6. Equation 2 was used in order to extract the
magnetic interaction J. The first term corresponds to the Bleaney
(29) McConnell, H. M. J. Chem. Phys. 1961, 35, 508.
(30) Joachim, C. Chem. Phys. 1987, 116, 339.
(31) Joachim, C.; Launay, J.-P.; Woitellier, S. Chem. Phys. 1990, 147, 131.
(32) Falgarde, F.; Katz, N. E. Polyhedron 1995, 14 (9), 1213.
(33) Kushmerick, J. G.; Holt, D. B.; Pollack, S. K.; Ratner, M. A.; Yang, J. C.;
Schull, T. L.; Naciri, J.; Moore, M. H.; Shashidhar, R. J. Am. Chem. Soc.
2002, 124, 10654.
(34) Magoga, M.; Joachim, C. Phys. ReV. B 1997, 56 (8), 4722.
(35) Xu, G.-L.; Zou, G.; Ni, Y.-H.; DeRosa, M. C.; Crutchley, R. J.; Ren, T.
J. Am. Chem. Soc. 2003, 125 (33), 10057.
(36) Piet, J. J.; Taylor, P. N.; Anderson, H. L.; Osuka, A.; Warman, J. M.
J. Am. Chem. Soc. 2000, 122, 1749. Taylor, P. N.; Wylie, A. P.; Huuskonen,
J.; Anderson, H. L. Angew. Chem., Int. Ed. 1998, 37 (7), 986. Hoshino,
Y.; Suzuki, T.; Umeda, H. Inorg. Chim. Acta 1996, 245, 87.
(37) Bencini, A.; Gatteschi, D. EPR of Exchange Coupled Systems; Springer-
Verlag: 1990; p 58.
Figure 4. Decay law for the electronic coupling parameter Vab in log scale
vs the metal-metal distance RMM
.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1439

A R T I C L E S
Fabre and Bonvoisin
Figure 5. Experimental and simulated EPR spectrum of 32+, 42+, 52+, and 62+ in frozen DCM solution (30 K).
Table 5. EPR Parameters for 32+, 42+, 52+, and 62+ in Frozen
One has to notice that the magnetic couplings for 3-6 are
quite strong, from J ) -33(4) cm-1 for the shortest to J )
-13(2) cm-1 for the longest complex. No other examples of
such couplings for such metal-metal distances, at least with
ruthenium complexes, are found in the literature. Figure 7 shows
the decay law of the magnetic coupling versus the metal-metal
distance, it follows an exponential law, as given by eq 3.
DCM Solution (30 K)
complex
gx
gy
gz
<g>
32+
42+
52+
62+
2.35
2.38
2.41
2.20
2.11
2.14
2.14
2.14
2.05
2.02
1.93
2.10
2.17
2.19
2.17
2.15
Bowers equation,4 which describes the intramolecular interaction
between two S ) /2 spins, and the second term takes into
|J| ) J° exp(- γ′RMM
)
(3)
1
account the residual paramagnetism due to the presence of traces
of the mixed valent species.
The decay slope was found to be γ′ ) 0.10 ( 0.01 Å-1. It
has to be noted that this decay slope is the lowest one obtained
so far. In addition, one has to notice that the point corresponding
to complex 6 with the anthracene unit is aligned with the three
other points contrary to what was observed above for the
electronic coupling. Anthracene does not seem to play a
particular role for magnetic coupling or at least not as particular
as for the electronic coupling!
C1
T
C2
T
1
Itotal
)
×
+
(2)
1
3
J
kBT
1 + exp -
(
)
All the curves shown in Figure 6 present a drop at low
temperature which is characteristic of an antiferromagnetic
interaction. Magnetic parameters are reported in Table 6.
9
1440 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Phenylcyanamido-Bridge Ru Complexes
A R T I C L E S
Figure 6. Double integrated EPR signal intensity times temperature (Itotal × T) of 32+, 42+, 52+, and 62+ versus temperature: experimental (dots) and
simulated (lines).
Table 6. Magnetic Parameters for 32+, 42+, 52+, and 62+
a
a
1
complex
RMM (Å)
C1
C2
J (cm-
)
Rb
32+
42+
52+
62+
16.0
18.5
21.0
25.1
1.2 × 1011
5.8 × 109
1.1 × 1011
2.2 × 1010
3.3 × 1010
4.2 × 108
9.9 × 109
3.4 × 109
-33 ( 4
-25 ( 3
-20 ( 2
-13 ( 2
0.0004
0.0043
0.0003
0.0010
2
2
a Arbitrary units. b R ) ∑ |Itotal - Ifit| /∑ Itotal
.
Very few studies have been reported concerning the depen-
dency of the magnetic interaction with intermetallic distances,38
probably due to the difficulties of finding good objects to study.
Wasielewski et al. found a slope of -0.37 Å-1 in a study of
magnetic interactions through p-phenylene bridges in a series
of radical pairs.16 The nearly same value was found by Journaux
et al. on dinuclear copper(II) metallacyclophanes with extended
π-conjugated aromatic bridges.39
Figure 7. Decay law of the magnetic coupling versus the metal-metal
distance RMM
.
Comparison of the Electronic and Magnetic Coupling
Parameters. We obtained two decay laws versus the interme-
tallic distance for the electronic coupling Vab and the magnetic
coupling J for the same complex series. The slopes γ and γ′
are, respectively, 0.21 and 0.1 Å-1. The question is to know
how one can compare these two values?
developed by Kramers in 193440 and largely developed by
Anderson in considering the magnetic properties of solid
insulators.41 Considering antiferromagnetic exchange interactions
in π-stacked crystals, Soos pointed out an approximate relation-
ship using the transition energy of charge transfer (CT) band
42
(hνCT): J ≈ V2/hνCT
.
For an intramolecular ET system, the
A relationship between the magnetic superexchange coupling
J and the electron-transfer superexchange coupling V was first
stabilization of the adiabatic minima relative to parabolic
diabatic (V ) 0) surfaces that interact by an electronic coupling
matrix element V is -V2/(λ + ∆G°), where λ is the vertical
(38) Julve, M.; Verdaguer, M.; Faus, J.; Tinti, F.; Moratal, J.; Monge, A.;
Gutierrez-Puebla, E. J. Am. Chem. Soc. 1987, 26, 3520. Bu¨rger, K.;
Chaudhuri, P.; Wieghardt, K.; Nuber, B. Chem. Eur. J. 1995, 1 (9), 583.
Cano, J.; De Munno, G.; Sanz, J.-L.; Ruiz, R.; Faus, J.; Lloret, F.; Julve,
M.; Caneschi, A. J. Chem. Soc., Dalton Trans. 1997, 1915.
(39) Pardo, E.; Faus, J.; Julve, M.; Lloret, F.; Munoz, M. C.; Cano, J.;
Ottenwaelder, X.; Journaux, Y.; Carrasco, R.; Blay, G.; Fernandez, I.; Ruiz-
Garcia, R. J. Am. Chem. Soc. 2003, 125 (36), 10770.
(40) Kramers, H. A. Physica 1934, 1, 182.
(41) Anderson, P. W. Phys. ReV. 1950, 79 (2), 350. Anderson, P. W. Phys.
ReV. 1959, 115 (1), 2. Anderson, P. W. In Magnetism; Rado, G. T., Suhl,
H., Eds. Academic Press: New York, 1965; Vol. 1, p 25.
(42) Soos, G. T. Ann. ReV. Phys. Chem. 1974, 25, 121.
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1441

A R T I C L E S
Fabre and Bonvoisin
reorganization energy and ∆G° is the free energy change for
the reaction and hνCT ) λ + ∆G°.43 Okamura et al.44 gave eq
4 which describes the stabilization of a diradical pair where the
singlet state is stabilized by ET and the triplet is not.
a general decrease in metal orbital energies, and thus the energy
difference between dπ(RuIII) orbitals and the HOMO of the
bridging ligand is decreasing, since cyanamido type bridging
ligands are known to mediate electronic and magnetic interac-
tions through hole-transfer mechanism.18 Thus, strictly speaking,
there should be two different Vab values to consider: Vab for
electron transfer (Ru(II)-Ru(III) situation) and V′ab for magnetic
interaction (Ru(III)-Ru(III) situation), of which the second one
would have a lower rate of decay. This concept of two different
Vab values has already been introduced by Solomon et al. The
authors found that Vab for the MV system should be half of the
iso-valent one, based on approximate calculations.15 Nelsen et
al. gave a different ratio, based on experimental measurements
(1.15 instead of 2).45 But these studies were performed on just
one compound. In our case, according to the above argument
on orbital energies, we should have two different Vab values
with different decay laws (and incidentally the Vab/V′ab ratio
cannot stay constant with distance). With a V′ab decaying more
slowly with distance than Vab, it is possible to explain the
particularly slow decay of JAF (eq 6).
V2
|E(S ) 0) - E(S ) 1)| )
(4)
(λ + ∆G°)
Making the same assumption as Okamura that only the singlet
is stabilized, and extending the formula toward three state
system, Nelsen obtained the following eq 5:45
2V2
(λ + ∆G°)
|E(S ) 0) - E(S ) 1)| )
(5)
Nelsen by using this equation provided the first quantitative
experimental test of the relationship between J, V, and (λ +
∆G°) based upon the properties of the +1 and +2 oxidation
states of a symmetrical bis-hydrazine compound. The nearly
same expression, eq 6, was given by Bertrand in studying
biological molecules coupled by an exchange interaction13,46
This result is very encouraging since it makes the cyanamide
bridging ligand a very good candidate for mediating magnetic
interaction over a very long distance, since the attenuation factor
is about four times lower than predicted! At this stage, quantum
chemical calculations would be helpful to get insight into this
interesting question. Chemical work is in progress to consolidate
these results by synthesizing an even larger bridge.
V2ab
|JAF| ) 2
(6)
U
where U represents the charge-transfer energy difference
between the initial and final state at the same nuclear config-
uration.
In any case, one can see that J and V should follow the
expression J ≈ V2, and then according to eqs 1 and 3, the
relationship between γ and γ′should at first approximation be
γ′) 2γ, which is almost exactly the opposite of what we
observed, i.e., γ′ ≈ γ/2!
3. Experimental Section
Materials. All chemicals and solvents were reagent grade or better.
[Ru(tpy)Cl3],48 [Ru(tpy)(thd)Cl],24 and [Ru(tpy)(thd)Ipcyd] 124 were
prepared according to literature procedures. Weakly acidic Brockmann
I type alumina (Aldrich) was used.
One possible explanation would be related to the specific
nature of the cyanamide bridge. We have recently shown that
the dicyanamidobenzene ligand, because of the close proximity
in energy of its HOMO with the metal orbitals, can be a
noninnocent bridging ligand.24 Because of its ability to expand
the frontier wave functions on the bridge,47 one could think that
the U term should vary with the intermetallic distance and
decrease for longer bridges. Since U (eq 6) is involved in the
denominator, this would explain the surprising behavior of the
magnetic exchange dependence.
A more convincing explanation about the lower attenuation
of J with distance could be given using the McConnell model,29
revisited by Joachim et al.30,31 This model cannot give quantita-
tive values for the electronic and magnetic coupling through a
given ligand, but it can give the trends when some structural
parameters are varied and help in the design of efficient bridging
ligands. In this model, it has been shown that when the energy
difference between the metal localized states and ligand localized
states is decreasing, then the damping factor (γ) is also
decreasing.31 Now, when one goes from the mixed-valent Ru-
(II)-Ru(III) to the iso-valent Ru(III)-Ru(III) species, there is
Physical Measurements. UV-visible spectra were recorded on a
Shimadzu UV-3100 spectrophotometer. 1H and 13C NMR spectra were
recorded on a Bruker AMX-500 in CD2Cl2. IR spectra of samples in
KBr pellets were taken on a Perkin-Elmer 1725 FT-IR spectropho-
tometer. Mass spectra were recorded by the “Service de Spectroscopie
de Masse” of Paul Sabatier University using ES (Perkin-Elmer Sciex
System API 365). Cyclic voltammograms were obtained with an
Autolab system (PGSTAT 100) in dry dichloromethane (DCM) (0.1
M tetrabutylammonium hexafluorophosphate, TBAH) at 25 °C with a
three-electrode system consisting of platinum-disk working (1 mm
diameter), platinum-wire counter, and saturated calomel reference
electrodes. Electrochemical oxidations were performed by electrolysis
with coulometry in dry dichloromethane (0.1 M TBAH) at 25 °C at
fixed potential with a three-electrode system consisting of platinum-
net working, platinum-wire counter, and saturated calomel reference
electrodes. Frozen solution EPR experiments were performed in DCM
with a typical concentration of 5 × 10-4 M on a Bruker Elexys 500 E
X-band spectrometer (equipped with a Bruker NMR Teslameter).
Synthesis of Complexes. Synthesis of [Ru(tpy)(thd)(TMSepcyd)]
2. In a Schlenk tube, [Ru(tpy)(thd)(Ipcyd)] 1 (612 mg, 0.805 mmol),
CuI (26 mg, 0.14 mmol, 17 mol %), and Pd(PPh3)2Cl2 (28 mg, 0.040
mmol, 5.0 mol %) were placed in solution in the solvent mixture DMF/
piperidine (4 :1, 12 mL) previously degassed with argon. Trimethyl-
silylacetylene was added under argon. The reaction mixture was stirred
at room temperature for 3.5 h and then evaporated to dryness. The
crude was purified by column chromatography (weakly acidic alumina;
solvent, dichloromethane; eluent, dichloromethane/ethanol 99.5:0.5) to
give a dark blue powder of 2 (530 mg, 0.725 mmol, 90%). ES mass
(43) Sutin, N. Prog. Inorg. Chem. 1983, 30, 441.
(44) Okamura, M. Y.; Isaacson, R. A.; Feher, G. Biochim. Biophys. Acta 1979,
546, 394.
(45) Nelsen, S. F.; Ismagilov, R. F.; Teki, Y. J. Am. Chem. Soc. 1998, 120 (9),
2200.
(46) Bertrand, P., Application of Electron Transfer Theories to Biological
Systems. In Structure and Bonding; Spring-Verlag: Berlin Heidelberg,
1991; Vol. 75, p 1.
(47) Ruiz, E.; Rodriguez-Fortea, A.; Alvarez, S. Inorg. Chem. 2003, 42 (16),
4881.
(48) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg. Chem. 1980, 19 (5),
1404.
9
1442 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007

Phenylcyanamido-Bridge Ru Complexes
A R T I C L E S
spectrum (CH3CN) m/z: 732.6 [M + H]+ (calcd 732.2); 546.2 [Ru-
(tpy)(thd)(HCN) + H]+ (calcd 546.2); 518.3 [Ru(tpy)(thd)]+ (calcd
518.1). 1H NMR (CD2Cl2 δ ) 5.35) δ: 8.65 (2H, ddd, J1 ) 5.5 Hz, J2
) 1.6 Hz, J3 ) 0.8 Hz, H6); 8.17 (2H, ddd, J1 ) 8.1 Hz, J2 ) 1.3 Hz,
J3 ) 0.8 Hz, H3); 8.09 (2H, d, J ) 8.0 Hz, H3′); 7.88 (2H, ddd, J1 )
8.1 Hz, J2 ) 7.6 Hz, J3 ) 1.6 Hz, H4); 7.55 (1H, t, J ) 8.0 Hz, H4′);
7.52 (2H, ddd, J1 ) 7.6 Hz, J2 ) 5.5 Hz, J3 ) 1.3 Hz, H5); 7.00 (2H,
d, J ) 8.6 Hz, Hm); 6.21 (2H, d, J ) 8.6 Hz, Ho); 5.66 (1H, s, Hc);
1.59 (9H, s, He′); 0.52 (9H, s, Ha′) ; 0.24 (9H, s, Hi). 13C NMR (CD2-
Cl2 δ ) 53.48) δ: 196.9 (Cb); 196.8 (Cd); 160.9 (C2′); 159.6 (C2); 154.8
(Cf); 150.7 (C6); 135.1 (C4); 132.3 (Cm); 126.7 (C4′); 126.0 (C5); 125.5
(CNCN); 121.3 (C3); 120.2 (C3′); 118.9 (Co); 109.7 (Cp); 107.3 (Cg); 90.3
(Ch); 88.9 (Cc); 41.6 (Ce); 40.2 (Ca); 28.7 (Ce’); 27.6 (Ca’); -0.1 (Ci).
Anal. Calcd for RuC38H43N5O2Si: C, 62.4; H, 5.9; N, 9.6. Found: C,
62.6; H, 5.7; N, 9.5. IR ν/cm-1 2179s (NCN); 2146s (CtC).
[Ru(tpy)(thd)(epcyd)] was used without further purification. It was
dissolved in the solvent mixture DMF/piperidine (4:1, 25 mL) and added
under argon to a Schlenk tube charged with [Ru(tpy)(thd)(Ipcyd)] (220
mg, 0.289 mmol), CuI (12 mg, 0.063 mmol, 22 mol %), and Pd(PPh3) -
2
Cl2 (11 mg, 0.016 mmol, 5.4 mol %). DBU (91 µL, 0.608 mmol, 2.1
equiv) was added under argon to the mixture, which was stirred at
room temperature for 1.5 h and then evaporated to dryness under a
vacuum. The crude reaction residue was adsorbed on alumina and
purified by column chromatography (weakly acidic alumina; solvent,
dichloromethane; eluent, dichloromethane/ethanol 99.2:0.8 then 98.5:
1.5). The compound was dissolved in the solvent mixture dichlo-
romethane/ethanol (4:1, 50 mL), and addition of 150 mL of cyclohexane
precipitated a dark green powder of 4 (213 mg, 0.165 mmol, 57%).
ES mass spectrum (CH3CN) m/z: 1293.6 [M + H]+ (calcd 1293.4);
776.6 [Ru(tpy)(thd)(bcpaH) + H]+ (calcd 776.2); 647.6 [M + 2H]2+
(calcd 647.2); 546.5 [Ru(tpy)(thd)(HCN) + H]+ (calcd 546.2). 1H NMR
(CD2Cl2/CD3OD, 4:1) δ: 8.62 (4H, d, J ) 5.4 Hz, H6); 8.20 (4H, d,
J ) 8.0 Hz, H3); 8.12 (4H, d, J ) 8.0 Hz, H3′); 7.89 (4H, ddd, J1 ) 8.0
Hz, J2 ) 7.7 Hz, J3 ) 1.5 Hz, H4); 7.58 (2H, t, J ) 8.0 Hz, H4′); 7.52
(4H, ddd, J1 ) 7.7 Hz, J2 ) 5.4 Hz, J3 ) 1.5 Hz, H5); 7.01 (4H, d, J
) 8.3 Hz, Hm); 6.28 (4H, d, J ) 8.3 Hz, Ho); 5.65 (2H, s, Hc); 1.55
(18H, s, He′); 0.49 (18H, s, Ha′). 13C NMR (CD2Cl2/CD3OD, 4:1) δ:
197.1 (Cb); 197.0 (Cd); 161.0 (C2′); 159.8 (C2); 152.0 (Cf); 150.8 (C6);
135.5 (C4); 131.7 (Cm); 127.5 (C4′); 126.2 (C5); 125.2 (CNCN); 121.6
(C3); 120.4 (C3′); 118.5 (Co); 112.2 (Cp); 89.0 (Cc); 88.2 (Cg); 41.6
(Ce); 40.3 (Ca); 28.7 (Ce′); 27.6 (Ca′). Anal. Calcd for Ru2C68H68N10O4-
(H2O) : C, 62.4; H, 5.4; N, 10.7. Found: C, 62.4; H, 5.1; N, 10.9. IR
ν/cm-1 2152s (NCN). UV-vis-NIR CH2Cl2, λ in nm (ꢀ × 10-3 in
L‚mol-1‚cm-1): 278 (67), 318 (61), 386 (62), 574 (12). Cyclic
voltammetry (CH2Cl2, 0.1 M TBAH, 0.1 V‚s-1, vs SCE): E1/2(RuII/
RuIII) ) 0.188 V.
Synthesis of [{Ru(tpy)(thd)}2(µ-dcbp)] 3. A Schlenk tube was
charged with [Ru(tpy)(thd)(Ipcyd)] (200 mg, 0.263 mmol), potassium
carbonate (109 mg, 0.789 mmol, 3.0 equiv), PdCl2dppf (8.9 mg, 0.011
mmol, 4.1 mol %), and bis(pinacolato)diboron (33.4 mg, 0.132 mmol,
0.50 equiv). It was evacuated and backfilled with argon. DMF (10 mL)
was added under argon, and the reaction mixture was stirred at 75 °C
for 15 h. The solvent was removed under a vacuum. The crude was
adsorbed on alumina and purified by column chromatography (weakly
acidic alumina; solvent, dichloromethane; eluent, dichloromethane/
ethanol 99:1 then 98.5:1.5). The third band (blue-green) was collected,
evaporated to dryness, and dissolved in the solvent mixture dichlo-
romethane/ethanol (4:1, 5 mL). Cyclohexane (20 mL) was added to
precipitate a dark blue-green powder of 3 (22.4 mg, 0.018 mmol, 13%).
ES mass spectrum (CH3CN) m/z: 1269.3 [M + H]+ (calcd 1269.4);
752.4 [Ru(tpy)(thd)(dcbpH) + H]+ (calcd 752.2); 635.3 [M + 2H]2+
(calcd 635.2); 546.2 [Ru(tpy)(thd)(HCN) + H]+ (calcd 546.2); 518.3
[Ru(tpy)(thd)]+ (calcd 518.1). 1H NMR (CD2Cl2/CD3OD, 4:1) δ: 8.63
(4H, d, J ) 5.4 Hz, H6); 8.20 (4H, d, J ) 8.0 Hz, H3); 8.11 (4H, d,
J ) 8.0 Hz, H3′); 7.88 (4H, ddd, J1 ) 8.0 Hz, J2 ) 7.7 Hz, J3 ) 1.2
Hz, H4); 7.56 (2H, t, J ) 8.0 Hz, H4′); 7.52 (4H, ddd, J1 ) 7.7 Hz,
J2 ) 5.4 Hz, J3 ) 1.2 Hz, H5); 7.04 (4H, d, J ) 8.3 Hz, Hm); 6.33 (4H,
d, J ) 8.3 Hz, Ho); 5.65 (2H, s, Hc); 1.55 (18H, s, He′); 0.48 (18H, s,
Ha′). 13C NMR (CD2Cl2/CD3OD, 4:1) δ: 197.1 (Cb); 197.0 (Cd); 161.1
(C2′); 159.8 (C2); 150.8 (C6); 149.6 (Cf); 135.4 (C4); 131.1 (Cp); 127.3
(C4′); 126.3 (Cm); 126.2 (C5); 124.6 (CNCN); 121.5 (C3); 120.4 (C3′);
118.7 (Co); 89.0 (Cc); 41.7 (Ce); 40.3 (Ca); 28.7 (Ce′); 27.6 (Ca′). Anal.
Calcd for Ru2C66H68N10O4(H2O): C, 61.7; H, 5.5; N, 10.9. Found: C,
61.5; H, 5.1; N, 11.2. IR ν/cm-1 2163s (NCN). UV-vis-NIR CH2-
Cl2, λ in nm (ꢀ × 10-3 in L‚mol-1‚cm-1): 278 (73), 318 (69), 357sh
Synthesis of [{Ru(tpy)(thd)}2(µ-bcpda)] 5. To a solution of [Ru-
(tpy)(thd)(TMSepcyd)] (299 mg, 0.409 mmol) in 35 mL of methanol
previously degassed with argon was added potassium carbonate (125
mg, 0.904 mmol, 2.2 equiv). The mixture was stirred under argon at
40 °C for 2.5 h and then evaporated to dryness to yield a blue residue
of [Ru(tpy)(thd)(epcyd)], which was kept under argon and used without
further purification. A three-necked round-bottom flask equipped with
an adaptor connected to an oxygen source was charged with CuCl (18
mg, 0.18 mmol, 44 mol %). Pyridine (10 mL) and DBU (123 µL, 0.82
mmol, 2.0 equiv) were added, and the mixture was warmed to 40 °C
and vigorously stirred while bubbling oxygen. The initially yellow
solution turned green after several minutes, and the blue residue of
[Ru(tpy)(thd)(epcyd)], previously prepared and dissolved in 15 mL
pyridine, was added. The reaction mixture was stirred at 40 °C with
oxygen bubbling. Additional reactants were added after 2 h (42 mol %
of CuCl and 1.0 equiv of DBU) and after 3 h (17 mol % of CuCl and
1.0 equiv of DBU). After 4 h of stirring, the mixture was evaporated
to dryness under a vacuum. The green residue was adsorbed on alumina
and purified by column chromatography (weakly acidic alumina;
solvent, dichloromethane; eluent, dichloromethane/ethanol 99.5:0.5 then
99:1). The second band (dark green) was collected, evaporated to
dryness, and redissolved in the solvent mixture dichloromethane/ethanol
(4:1, 50 mL). Addition of 150 mL of cyclohexane precipitated a dark
green powder of 5 (180 mg, 0.137 mmol, 67%). ES mass spectrum
(CH3CN) m/z: 1317.7 [M + H]+ (calcd 1317.4); 800.5 [Ru(tpy)(thd)-
(bcpdaH) + H]+ (calcd 800.2); 659.2 [M + 2H]2+ (calcd 659.2); 546.5
1
[Ru(tpy)(thd)(HCN) + H]+ (calcd 546.2). H NMR (CD2Cl2/CD3OD,
4:1) δ: 8.61 (4H, d, J ) 5.4 Hz, H6); 8.21 (4H, d, J ) 8.1 Hz, H3);
8.13 (4H, d, J ) 8.0 Hz, H3′); 7.89 (4H, ddd, J1 ) 8.1 Hz, J2 ) 7.5 Hz,
J3 ) 1.5 Hz, H4); 7.59 (2H, t, J ) 8.0 Hz, H4′); 7.52 (4H, ddd, J1 )
7.5 Hz, J2 ) 5.4 Hz, J3 ) 1.2 Hz, H5); 7.05 (4H, d, J ) 8.4 Hz, Hm);
6.29 (4H, d, J ) 8.4 Hz, Ho); 5.65 (2H, s, Hc); 1.54 (18H, s, He′); 0.48
(18H, s, Ha′). 13C NMR (CD2Cl2/CD3OD, 4:1) δ: 197.1 (Cb); 197.0
(Cd); 161.0 (C2′); 159.8 (C2); 153.9 (Cf); 150.8 (C6); 135.5 (C4); 133.1
(Cm); 127.6 (C4′); 126.2 (C5); 124.6 (CNCN); 121.6 (C3); 120.4 (C3′);
(51), 578 (12). Cyclic voltammetry (CH2Cl2, 0.1 M TBAH, 0.1 V‚s-1
vs SCE): E1/2(RuII/RuIII) ) 0.137 V.
,
Synthesis of [{Ru(tpy)(thd)}2(µ-bcpa)] 4. Potassium carbonate (84
mg, 0.61 mmol, 2.1 equiv) was added to a solution of [Ru(tpy)(thd)-
(TMSepcyd)] (211 mg, 0.289 mmol) in 35 mL of methanol previously
degassed with argon. The mixture was stirred under argon at 40 °C for
2.5 h and then evaporated to dryness. The obtained blue residue of
9
J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007 1443

A R T I C L E S
Fabre and Bonvoisin
118.6 (Co); 109.6 (Cp); 89.0 (Cc); 82.7 (Cg); 72.2 (Ch); 41.6 (Ce); 40.3
8.4 Hz, Ho); 5.67 (2H, s, Hc); 1.57 (18H, s, He′); 0.50 (18H, s, Ha′). 13
C
(Ca); 28.7 (Ce′); 27.6 (Ca′). Anal. Calcd for Ru2C70H68N10O4(H2O)0.7
:
NMR (CD2Cl2/CD3OD, 4:1) δ: 197.2 (Cb); 197.0 (Cd); 161.1 (C2′);
159.8 (C2); 153.7 (Cf); 150.8 (C6); 135.6 (C4); 132.4 (Cm); 131.7 (Cj);
127.6 (C4′); 127.3 (Ck); 126.5 (Cl); 126.3 (C5); 124.7 (CNCN); 121.6
(C3); 120.4 (C3′); 118.8 (Co); 118.3 (Ci); 111.2 (Cp); 104.6 (Cg); 89.1
(Cc); 84.6 (Ch); 41.8 (Ce); 40.3 (Ca); 28.7 (Ce′); 27.6 (Ca′). Anal. Calcd
for Ru2C84H76N10O4(H2O): C, 66.8; H, 5.2; N, 9.3. Found: C, 66.9;
H, 5.1; N, 9.3. IR ν/cm-1 2161s (NCN). UV-vis-NIR CH2Cl2, λ in
nm (ꢀ × 10-3 in L‚mol-1‚cm-1): 270 (115), 318 (68), 344 (57), 552
(59). Cyclic voltammetry (CH2Cl2, 0.1 M TBAH, 0.1 V‚s-1, vs SCE):
C, 63.3; H, 5.3; N, 10.5. Found: C, 63.3; H, 5.3; N, 10.5. IR ν/cm-1
2164s (NCN); 2135s (CtC). UV-vis-NIR CH2Cl2, λ in nm (ꢀ ×
10-3 in L‚mol-1‚cm-1): 278 (69), 318 (62), 408 (70), 570 (13). Cyclic
voltammetry (CH2Cl2, 0.1 M TBAH, 0.1 V‚s-1, vs SCE): E1/2(RuII/
RuIII) ) 0.225 V.
Synthesis of [{Ru(tpy)(thd)}2(µ-bcpea)] 6. A Schlenk tube was
charged with [Ru(tpy)(thd)(Ipcyd)] (275 mg, 0.362 mmol), 9,10-bis-
(3-hydroxy-3-methylbutynyl)anthracene (50.8 mg, 0.148 mmol, 0.41
equiv), CuI (17 mg, 0.089 mmol, 24 mol %), and Pd(PPh3)4 (29 mg,
0.025 mmol, 6.9 mol %). It was evacuated and backfilled with argon.
The solvent mixture DMF/piperidine (5:1, 12 mL) and potassium tert-
butoxide (81 mg, 0.72 mmol, 2.0 equiv) were added under argon. The
reaction mixture was stirred under argon at 60 °C for 1.5 h, during
which the color of the mixture changed from blue-green to brown-red
and then to purple. The solvents were removed under a vacuum, and
the crude was purified by column chromatography (weakly acidic
alumina, solvent: dichloromethane, eluent: dichloromethane/ethanol
99.5:0.5 then 99:1). The obtained powder was dissolved in the solvent
mixture dichloromethane/ethanol (4:1, 50 mL) and addition of cyclo-
hexane (100 mL) gave a precipitate, which was filtered, washed with
cyclohexane and diethylether, and dried under a vacuum to yield a
purple powder of 6 (93.1 mg, 0.062 mmol, 35%). ES mass spectrum
(CH3CN) m/z: 1493.4 [M + H]+ (calcd 1493.4); 976.3 [Ru(tpy)(thd)-
(bcpeaH) + H]+ (calcd 976.3); 747.3 [M + 2H]2+ (calcd 747.2); 546.4
[Ru(tpy)(thd)(HCN) + H]+ (calcd 546.2); 518.3 [Ru(tpy)(thd)]+ (calcd
518.1). 1H NMR (CD2Cl2/CD3OD, 4:1) δ: 8.67 (4H, dd, J1 ) 6.6 Hz,
J2 ) 3.3 Hz, Hk); 8.65 (4H, d, J ) 5.4 Hz, H6); 8.24 (4H, d, J ) 8.1
Hz, H3); 8.17 (4H, d, J ) 8.1 Hz, H3′); 7.92 (4H, ddd, J1 ) 8.1 Hz, J2
) 7.5 Hz, J3 ) 1.5 Hz, H4); 7.64 (4H, dd, J1 ) 6.6 Hz, J2 ) 3.3 Hz,
Hl); 7.62 (2H, t, J ) 8.1 Hz, H4′); 7.56 (4H, ddd, J1 ) 7.5 Hz, J2 ) 5.4
Hz, J3 ) 1.5 Hz, H5); 7.36 (4H, d, J ) 8.4 Hz, Hm); 6.44 (4H, d, J )
E
1/2(RuII/RuIII) ) 0.211 V.
Acknowledgment. The authors thank CNRS and MENRS
(M.F.) for financial support, Alain Mari (LCC, Toulouse) for
EPR measurements, Christophe Coudret (CEMES) for helpful
discussions about synthesis, and Jean-Pierre Launay and Chris-
tian Joachim (CEMES) for fruitful advice.
Supporting Information Available: S1, differential pulse
voltammetry for complex 3, 4, 5, and 6 (CH2Cl2, 0.1 M TBAH,
on rotating platinum electrode); S2, spectroelectrochemical
oxidation of 4 in DCM, 0.1 M TBAH (electrolysis at 0.46 V vs
SCE); S3, spectroelectrochemical oxidation of 5 in DCM, 0.1
M TBAH (electrolysis at 0.5 V vs SCE); S4, spectroelectro-
chemical oxidation of 6 in DCM, 0.1 M TBAH (electrolysis at
0.46 V vs SCE); S5, deconvolution of the IV transitions in the
NIR area for 3+, 4+, 5+, and 6+ in DCM; S6, linear voltammetry
for complex 32+, 42+, 52+, and 62+ electrochemically generated.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JA067255I
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1444 J. AM. CHEM. SOC. VOL. 129, NO. 5, 2007