New Ru(II) complexes with anionic and neutral N-donor ligands as epoxidation catalysts: An evaluation of geometrical and electronic effects

Article abstract of DOI:10.1021/ic100862y

The synthesis of a family of new Ru complexes containing the meridional trpy ligand with general formula [Ru^II(T)(D)(X)]ⁿ⁺ (T = 2,2′:6′,2″-terpyridine (trpy); D = 3,5-dimethyl-2-(2-pyridyl) pyrrolate (pyrpy), and 2-(1-Methyl-3-pyrazolyl)pyridine (pypz-Me); X = Cl, H₂O) have been described. All complexes have been spectroscopically characterized in solution through ¹H NMR and UV-vis techniques, and the chloro complexes have also been characterized in the solid state through monocrystal X-ray diffraction analysis. The pyrpy ligand undergoes an oxidation at the 3-position of the pyrrolate ring during the formation of the corresponding aqua complex thus generating the analogous compound containing the oxidized ligand pyrpy-O. The redox properties of all complexes have also been studied by means of CV and DPV techniques, where both geometrical (trans vs cis) and electronic (neutral vs anionic) effects can be unveiled and rationalized. Finally, the reactivity of the whole set of Ru-OH₂ complexes has been tested with regard to the epoxidation of different alkenes with PhI(OAc) ₂. In all cases good selectivities and conversions were obtained. Furthermore, total retention of the initial cis configuration was achieved when using these catalysts to epoxidize cis-β-methylstyrene.

Full text of DOI:10.1021/ic100862y

7
072 Inorg. Chem. 2010, 49, 7072–7079
DOI: 10.1021/ic100862y
New Ru(II) Complexes with Anionic and Neutral N-Donor Ligands as Epoxidation
Catalysts: An Evaluation of Geometrical and Electronic Effects
†
,||
†
,†
,†
||
Mohamed Dakkach, M. Isabel L ꢀo pez, Isabel Romero,* Montserrat Rodr ´ı guez,* Ahmed Atlamsani,
§
†
‡,§
Teodor Parella, Xavier Fontrodona, and Antoni Llobet
†
Departament de Quı´mica i Serveis T eꢁ cnics de Recerca, Universitat de Girona, Campus de Montilivi, E-17071
‡
Girona, Spain, Institute of Chemical Research of Catalonia (ICIQ), Av. Paı¨sos Catalans 16, E-43007
Tarragona, Spain, Departament de Quı ´m ica i Servei de RMN Universitat Aut oꢁ noma de Barcelona, Cerdanyola
del Vall eꢁ s, E-08193 Barcelona, Spain, and Laboratoire de Physico-Chimie des Interfaces et Environnement,
D eꢀ partement de Chimie, Facult eꢀ des Sciences, Universit eꢀ Abdelmalek Essaadi, B.P.: 2121 93000 T eꢀ touan,
Morocco
§
||
Received May 2, 2010
II
The synthesis of a family of new Ru complexes containing the meridional trpy ligand with general formula [Ru (T)-
nþ
0 0 00
(
lyl)pyridine (pypz-Me); X = Cl, H O) have been described. All complexes have been spectroscopically characterized in
D)(X)] (T = 2,2 :6 ,2 -terpyridine (trpy); D = 3,5-dimethyl-2-(2-pyridyl)pyrrolate (pyrpy), and 2-(1-Methyl-3-pyrazo-
2
1
solution through H NMR and UV-vis techniques, and the chloro complexes have also been characterized in the solid
state through monocrystal X-ray diffraction analysis. The pyrpy ligand undergoes an oxidation at the 3-position of the
pyrrolate ring during the formation of the corresponding aqua complex thus generating the analogous compound
containing the oxidized ligand pyrpy-O. The redox properties of all complexes have also been studied by means of CV and
DPV techniques, where both geometrical (trans vs cis) and electronic (neutral vs anionic) effects can be unveiled and
rationalized. Finally, the reactivity of the whole set of Ru-OH complexes has been tested with regard to the epoxidation of
2
different alkenes with PhI(OAc) . In all cases good selectivities and conversions were obtained. Furthermore, total
2
retention of the initial cis configuration was achieved when using these catalysts to epoxidize cis-β-methylstyrene.
Introduction
In the particular field of redox catalysis, the relationship
between performance and structure of a catalyst is further
complicated by the presence of multiple redox state species
involved in the catalytic cycle. Therefore, the thermodynamic
and kinetic characterization of the reactions that undergo the
different oxidation state species of a particular catalyst is of
paramount importance to understand and optimize catalyst
performance.
Ruthenium polypyridyl complexes have been extensively
studied over the years because they enjoy a combination of
unique chemical, electrochemical, and photochemical pro-
1,2
perties that has allowed the exploration of a wide variety of
3
4
fields including bioinorganic chemistry and catalysis.
*
To whom correspondence should be addressed. E-mail: marisa.romero@
udg.edu (I.R.); montse.rodriguez@udg.edu (M.R.).
1) (a) Lappin, A. G.; Marusak, R. A. Coord. Chem. Rev. 1991, 109, 125–
80. (b) Griffith., W. P. Chem. Soc. Rev. 1992, 21, 179–185. (c) Wing-Sze Hui, J.;
A particularly interesting family of redox catalysts is the
(
so-called Ru-OH type of complexes. These Ru-aquo com-
2
1
plexes can easily lose protons and electrons and reach higher
oxidation states as exemplified below, where L5 represent
polypyridylic type of ligands,
Wong, W.-T. Coord. Chem. Rev. 1998, 172, 389–436. (d) Clarke, M. J. Coord.
Chem. Rev. 2002, 232, 69–93. (e) Meyer, T. J.; Huynh, M. H. V. Inorg. Chem.
2
003, 42, 8140–8169.
(
2) (a) Balzani, V.; Juris, A. Coord. Chem. Rev. 2001, 211, 97–115. (b)
Sauvage, J.-P.; Collins, J.-P.; Chambron, J.-C.; Guillerez, S.; (c) Coudret, C.;
Balzani, V.; Barigelletti, F.; De Cola, L.; Fannigni, L. Chem. Rev. 1994, 94, 993–
þ
- e-
H
- H - e-
þ
-
II
III
IV
1
019. (d) Meyer, T. J. Acc. Chem. Res. 1989, 22, 163.
L Ru -OH s ss ss s L Ru -OH s ss ss s L Ru dO
F F
5 2 5 5
R R
(
3) (a) Kelly, S. O.; Barton, J. K. Science 1999, 238, 375. (b) Hall, D. B.;
þ H þ e
þ
-
þ H þ e
þ
-
Holmlin, R. E.; Barton, J. K. Nature 1996, 384, 731. (c) Burrows, C. J.; Muller,
J. G. Chem. Rev. 1998, 98, 1109. (d) Weatherly, S. C.; Yang, I. V.; Thorp, H. H. J.
Am. Chem. Soc. 2001, 123, 1236.
ð1Þ
(
4) (a) Murahashi, S. I.; Takaya, H.; Naota, T. Pure Appl. Chem. 2002, 74,
The sequential loss of protons and electrons allows to
easily reach reactive Ru dO species, and as a consequence
they have been widely used as redox catalysts for the oxida-
tion of both organic and inorganic substrates. A large
amount of literature has emerged during the past two decades
IV
1
9–24. (b) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98, 2599–
2
660. (c) Rodríguez, M.; Romero, I.; Llobet, A.; Deronzier, A.; Biner, M.; Parella,
T.; Stoeckli-Evans, H. Inorg. Chem. 2001, 40, 4150–4156. (d) Jauregui-Haza,
U. J.; Dessoudeix, M.; Kalck, Ph.; Wilhelm, A. M.; Delmas, H. Catal. Today
2
001, 66, 297–302.
pubs.acs.org/IC
Published on Web 07/02/2010
r 2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7073
related to this system, mainly because of the rich oxidative
properties of the Ru dO species. In addition, the reaction
Scheme 1. Ligands Used in This Work
IV
mechanisms for the oxidation of several substrates by
IV
Ru dO have been thoroughly described together with the
5
establishment and optimization of catalytic processes.
The redox potentials, and therefore the performance, of
a Ru-OH catalyst can be tuned through the ligands with
2
the addition of electron donating or withdrawing groups.
This is expected to respectively decrease and increase the
Ru(IV)/Ru(III) and Ru(III)/Ru(II) redox potentials, and
thus allows to generate a family of catalysts with a fine-tuned
position of the monodentate ligand (Cl or H O) with
2
regard to the pyrrolate or pyrazole ring of the ligands
pyrpy and pypz-Me, respectively.
6
III
The trichloro Ru complex [Ru Cl (trpy)], 1, is used as
reactivity. In addition to the electronic effects, examples also
3
exist where sterically hindered ligands strongly influence
starting material, followed by reduction with NEt . The
3
the reactivity of a RudO system with regard to substrate
oxidation.
didentate ligand, either pyrpy (previously deprotonated
with NEt ) or pypz-Me, is added to form the correspond-
7
3
While a wide variety of Ru-OH complexes containing
neutral polypyridylic ligands has been described, the number
2
ing monochloro Ru(II) complexes, 2, for the pyrpy case
and a mixture of trans and cis isomers (trans-4 and cis-4)
for the pypz-Me case. The two isomers of complex 4 are
easily separated through column chromatography. The
exclusive formation of the trans isomer in 2 is not simple
to explain though it must be due to electronic factors
arising from the negative charge of the pyrrolate ring,
since structural parameters are almost identical in the two
families of complexes. No evidence for the existence of the
other possible geometrical isomer has been obtained
either in the solid state or in solution.
of such complexes containing anionic ligands is much
8
smaller. Furthermore the number of Ru-OH complexes
2
9
with N-based anionic ligands is even more limited.
In the present work we present the preparation, charac-
terization, and catalytic performance of a new family of
Ru-Cl and Ru-OH complexes containing the meridional
2
0 0 00
2
,2 :6 :2 -terpyridine (trpy) ligand and completing the octa-
hedral coordination with non symmetric didentate ligands.
The didentate ligands used are pyridylpyrrole (Hpyrpy) and
pyrazolylpyridine (pypz-Me) that are depicted in Scheme 1.
Upon deprotonation the Hpyrpy ligand is expected to co-
ordinate in a chelating manner and exert a strong donation
The Ru-OH complexes trans-3, trans-5, and cis-5 are
2
easily obtained from the corresponding Ru-Cl complexes
in the presence of Ag . However, for the case of complex
þ
10
effect over the Ru center because of its anionic character. On
the other hand the non symmetric neutral pypz-Me ligand is
expected to allow evaluation of steric effects depending on its
3
containing the pyrrolate ligand, the isolated Ru-aqua
complex has experienced the oxidation of the carbon
atom C23. This carbon is situated in between of the two
methyl substituents of the pyrpy ligand, leading to the
new anionic ligand pyrpy-O (scheme 1), as confirmed by
NMR spectroscopy (see below).
It is worth mentioning here that whereas the two
isomers of chloro complex 4 are stable to light irradiation
in solution, their corresponding aqua complexes trans-5
and cis-5 are not. They undergo mutual isomerization
under a constant intensity of white light irradiation,
11,12
mode of coordination toward the Ru center.
The catalytic
performance of this new family of complexes has been tested
with regard to the epoxidation of alkenes and is reported
herein.
Results and Discussion
Synthesis and Crystal Structures. The synthetic strategy
followed for the preparation of the complexes described
in the present paper is outlined in Scheme 2. The nomen-
clature trans or cis for complexes refers to the relative
leading always to a trans/cis mixture of approximately
1
1
.25:1. The H NMR spectrum of the resulting mixture
(obtained from cis-5 irradiation) is shown in the Support-
ing Information.
(
5) (a) Bryant, J. R.; Matsuo, T.; Mayer, J. M. Inorg. Chem. 2004, 43,
The crystal structures of chloro complexes trans-2,
trans-4, and cis-4 have been solved by X-ray diffraction
analysis. Figure 1 displays the molecular structures of the
complexes whereas their main crystallographic data are
reported in Table 1 and Supporting Information, Table
S1. Selected bond distances and angles can be found in the
Supporting Information, Tables S2 and S3.
1
587. (b) Sala, X.; Poater, A.; Romero, I.; Rodríguez, M.; Llobet, A.; Solans, X.;
Parella, T.; Santos, T. M. Eur. J. Inorg. Chem. 2004, 612. (c) Yip, W.-P.; Yu,
W.-Y.; Zhu, N.; Che, C.-M. J. Am. Chem. Soc. 2005, 127, 14239. (d) Zong, R.;
Thummel, R. P. J. Am. Chem. Soc. 2005, 127, 12802.
(
6) (a) Llobet, A. Inorg. Chim. Acta 1994, 221, 125. (b) Szczepura, L. F.;
Maricich, S. M.; See, R. F.; Churchill, M. R.; Takeuchi, K. J. Inorg. Chem. 1995,
4, 4198.
7) Huynh, M. H. V.; Witham, L. M.; Lasker; Wetzler, M.; Mort, B.;
Jameson, D. L.; White, P. S.; Takeuchi, K. J. J. Am. Chem. Soc. 2003, 125,
3
(
In all cases, the Ru metal centers adopt an octahedrally
distorted type of coordination where the trpy ligand is
bonded in a meridional manner and the pyrpy and pypz-
Me ligands act in a didentate fashion. The sixth coordina-
tion site is occupied by the chloro ligand. All bond
distances and angles are within the expected values for
3
4
1
08.
(
8) Dovletoglou, A.; Adeyemi, S. A.; Meyer, T. J. Inorg. Chem. 1996, 35,
120.
(
9) Fackler, N. L. P.; Zhang, S.; O’Halloran, T. V. J. Am. Chem. Soc.
996, 118, 481–482.
(
10) (a) Klappa, J. J.; Geers, S. A.; Schmidtke, S. J.; MacManus-Spencer,
L. A.; McNeill, K. Dalton Trans. 2004, 883–891. (b) Emmert; Brandl, F. Ber.
Chem. 1927, 60, 2211. (c) Chiswell Inorg. Chim. Acta 1937, 9, 2024. (d) Pucci,
D.; Aiello, I.; Aorea, A.; Bellusci, A.; Crispini, A.; Ghedini, M. Chem. Commun.
1
3
this type of complexes.
The comparison of cis versus trans geometries reveals
significant differences in some structural parameters. For
2
009, 1550–1552.
11) Fusco, R. Pyrazoles, Pyrazolines, Pyrazolidines, Imidazoles and
(
Condensed Rings. In The Chemistry of Heterocyclic Compounds; Wiley,
R. H., Ed.; Interscience Publishers: New York, 1967; Vol. 22, pp 1-174, .
(13) Sens, C.; Rodrı
´
guez, M.; Romero, I.; Parella, T.; Benet-Buchholz, J.;
Llobet, A. Inorg. Chem. 2003, 42, 8385–8394.
(
12) Thiel W. R.; Eppinger J. Chem.;Eur. J. 1997, 3. No. 5, 696.

7
074 Inorganic Chemistry, Vol. 49, No. 15, 2010
Dakkach et al.
Scheme 2. Synthetic Strategy
a
Table 1. Crystal Data for Compounds trans-4 and cis-4
trans-4
cis-4
empirical formula
C
24 6
H20ClF -
C
51
H46Cl
8 12
F -
N
6
PRu
N
12 2
Ru
P
2
formula weight
crystal system
space group
673.95
triclinic
P1
1602.68
orthorhombic
Pca2(1)
15.863(5)
13.625(4)
28.230(8)
90
90
90
6102(3)
4
ꢀ
˚
a [A]
10.419(16)
12.120(19)
13.14(2)
73.52(2)
67.41(2)
83.96(3)
1469(4)
2
ꢀ
˚
b [A]
ꢀ
˚
c [A]
R [deg]
β [deg]
γ [deg]
ꢀ
˚
3
V [A ]
formula units/cell
temp, K
300(2)
1.524
0.749
100(2)
1.745
0.983
-3
F
calc, [Mg/m ]
1
-
μ [mm
]
final R indices, [I > 2σ(I)]
R indices [all data]
R
1
= 0.0559
R = 0.0578
1
2
2
wR = 0.1370
= 0.0949
wR = 0.1544
wR = 0.1107
1
R = 0.1262
2
R
1
2
wR = 0.1301
P
P
P
P
a
2
2 2
2 2 1/2
) ]
R
1
=
||F
o
| - |F
o
c
||/ |F
o
|; wR
2
= [ w(F
o
- F
c
) / w(F
).
o
,
2
2
2
2
2
c
where w = 1/[σ (F
) þ (0.0042P) ] and P = (F
o
þ2F
to the pyrazole. This effect is even larger in the case of the
anionic pyrrolate ring in the trans complex 2, with a
˚
Ru-Cl bond distance of 2.432 A.
The Cl-Ru-N trans angle in the complexes is also
slightly dependent on the type of isomer. In complexes 2
and trans-4, the trans geometry allows the establishment
of an intramolecular H-bond between the Cl ligand and
the H(16) atom of the pyridyl ring of the didentate ligand
(
either pyrpy or pypz-Me; for trans-4 the H(16)-Cl
˚
˚
distance is 2.652 A, the C(16)-Cl is 3.256 A, and the
angle Cl-H(16)-C(16) is 13.8°; see Figure 1), whereas
this interaction is not present in the isomer cis-4. As a
consequence, the trans bonding angle Cl(1)-Ru(1)-N(5)
in complexes 2 and 4 is significantly smaller than 180°
Figure 1. Ortep plot and labeling schemes for compounds (A) trans-4
and (B) cis-4.
(
172.3° and 170.4° for 2 and trans-4, respectively). Com-
instance, it is interesting to note that the Ru-Cl bond
length in cis-4 complex, where the Cl atom is placed trans
plex cis-4 can only form such H-bonds through intermole-
cular interactions and this is manifested in the zigzag
arrangement of the molecules in the crystal structure (see
the Supporting Information, Figure S2).
˚
to the pyridyl Npy atom of pypz-Me, is larger (2.407 A)
than the analogous distance found in the trans-4 complex
˚
2.340 A). In the latter case the Cl atom is trans to the
(
pyrazole Npz atom of the ligand, thus denoting the
stronger trans influence of the pyridine ring with respect
Spectroscopic Properties. The one-dimensional (1D)
and two-dimensional (2D) NMR spectra of all complexes
were registered in d -acetone or D O and are presented in
6
2

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7075
Figure 3. UV-vis spectra for complexestrans-4, cis-4, trans-5, and cis-5.
1
Figure 2. H NMR spectrum of complex trans-4.
section, were extracted from their Pourbaix diagrams
(vide infra) and are displayed in Table 2 together with
electrochemical information.
Redox Properties. The redox properties of the com-
pounds have been determined by cyclic voltammetry
Figure 2 and in the Supporting Information. The absence
of a resonance for H(23), expected to appear around
1
5
3
-5.5 ppm in the H NMR spectrum of complex trans-
(see the Supporting Information, Figure S5) confirms
(CV) and differential pulse voltammetry (DPV) experi-
the oxidation of the pyrpy ligand during the synthesis, as
described previously. The resonances found for all com-
plexes are consistent with the structures obtained in the
solid state.
The UV-vis spectra for both trans- and cis- isomers of
complexes 4 and 5 are displayed in Figure 3, and those for
ments. Chlorocomplexes trans-4 and cis-4, containing the
neutral pypz-Me ligand, exhibit a reversible monoelec-
tronic Ru(III/II) redox wave at around 0.8 V versus
SSCE. On the other hand complex trans-2, with the
anionic pyrrolate ligand, reaches the Ru(III) oxidation
state at a much lower potential (0.21 V) as expected from
the higher σ-donation arising from the negative charge of
the pyrpy ligand. This sharp decrease of the E1/2(III/II)
value is similar to the one observed for analogous Ru
2
and 3 are gathered in the Supporting Information,
Figure S10 together with a tentative assignment of the
absorptions observed (Supporting Information, Table
S4). The complexes exhibit ligand based π-π* bands
below 350 nm and relatively intense bands above 350 nm
mainly due to dπ-π* MLCT transitions and also d-d
1
5a
complexes bearing neutral or anionic oxazoline ligands
and, in the case of complex trans-2, this also allows the
occurrence of the Ru(IV/III) redox couple within the CV
range (at 0.79 V), which is a quite uncommon pheno-
menon for Ru(II) chlorocomplexes (see Supporting Infor-
1
4
transitions at lower energy. For the Ru-Cl complexes
the MLCT bands are shifted to the red with regard to the
corresponding Ru-OH species because of the relative
2
16
mation for additional electrochemical information).
destabilization of the dπ(Ru) levels provoked by the
anionic chloro ligand (compare for instance trans-4 and
trans-5 spectra in Figure 3). A similar effect is also
observed when comparing complexes containing the neu-
tral pypz-Me or the anionic pyrpy ligand (complexes
trans-4 and 2 respectively, see Supporting Information).
Spectrophotometric acid-base titrations of the Ru-
aquo complexes trans-3, trans-5, and cis-5 were carried
The redox properties of Ru-aqua complexes are pH
dependent because of the capacity of the aqua ligand to
lose protons upon oxidation of the complex, which also
makes the upper oxidation states easily accessible:
II
nþ
III
nþ
½Ru ðLÞðtrpyÞðH2OÞꢀ f ½Ru ðOHÞðLÞðtrpyÞꢀ
þ
-
þ H þ e
ð3Þ
out to calculate their pK (eq 2, L = pypz-Me or pyrpy-O)
a
which led to values of 9.75, 10.1, and 10.75, respectively.
Isosbestic points confirming net conversion were found in
all cases (for complex 3 at 340, 419, and 527 nm; for
complex trans-5 at 290, 320, 331, 425, and 486 nm; for
complex cis-5 at 317, 331, 341, 427, and 486 nm; see
Supporting Information, Figure S11 for a detailed pro-
cedure description and spectra registered).
III
nþ
IV
nþ
½
Ru ðOHÞðLÞðtrpyÞꢀ f ½Ru ðOÞðLÞðtrpyÞꢀ
þ
-
þ H þ e
ð4Þ
The complete thermodynamic information regarding
the Ru-aqua type of complex can be extracted from the
Pourbaix diagrams, exhibited in Figure 4 for complex
II
nþ
½
Ru ðLÞðtrpyÞðH2OÞꢀ
f
II
pKalðRu Þ
(15) (a) Serrano, I.; Sala, X.; Plantalech, E.; Rodrıguez, M.; Romero, I.;
´
Jansat, S.; G oꢀ mez, M.; Parella, T.; Stoeckli-Evans, H.; Solans, X.; Font-
Bardia, M.; Vidjayacoumar, B.; Llobet, A. Inorg. Chem. 2007, 46, 5381–
II
ðn - 1Þþ
þ Hþ
The pK values for the Ru(III) oxidation states in all
½
Ru ðLÞðtrpyÞðOHÞꢀ
ð2Þ
5
389. (b) Sala, X.; Santana, N.; Serrano, I.; Plantalech, E.; Romero, I.; Rodríguez,
a
M.; Llobet, A.; Jansat, S.; G ꢀo mez, M.; Fontrodona, X.. Eur. J. Inorg. Chem.
2007, 5207–5214. (c) Nishiyama, H.; Shimanda, T.; Itoh, H.; Sugiyama, H.;
Motoyama, Y. Chem. Commun. 1997, 1863–1864.
Ru-aquo complexes, which are discussed in the following
(16) Wasylenko, D. J.; Ganesamoorthy, C.; Koivisto, B. D.; Henderson,
(
14) Balzani, V.; Juris, A.; Veturi, M. Chem. Rev. 1996, 96, 759.
M. A.; Berlinguette, C. P. Inorg. Chem. 2010, 49, 2202–2209.

7
076 Inorganic Chemistry, Vol. 49, No. 15, 2010
Dakkach et al.
a
Table 2. pK and Electrochemical Data (pH = 7, E1/2 in V vs SSCE) for the Aquocomplexes Described in This Work and Others for Purposes of Comparison
a
complex (trpy)(D)Ru-OH
b
c
entry
2
E
1/2 (III/II)
0.49
0.55
0.39
0.47
0.48
0.20
0.21
0.38
0.19
E
1/2 (IV/III)
0.62
ΔE
E°(IV/II)
pK
a
(II)
pK
a
(III)
ref
1
2
3
4
5
6
7
8
9
(trpy)(bpy)Ru-OH
trans-3
2
130
<0
180
50
0.555
0.55
0.48
0.495
0.54
9.7
1.7
1.21
0.95
1.65
1.8
4.4
2
27a
e
e
d
9.75
10.1
10.75
>10
11.0
10.0
10.0
11.2
trans-5
cis-5
0.57
0.52
0.60
e
(trpy)(box-C)Ru-OH
(trpy)(box-O)Ru-OH
trans-(trpy)(pic)Ru-OH
cis-(trpy)(pic)Ru-OH
(trpy)(acac)Ru-OH
2
120
15a
15a
27b
27b
18b
2
2
0.45
0.56
0.56
240
180
370
0.33
0.47
0.375
2
3.7
5.2
2
a
0
0
0
0
D stands for didentate ligand, according to the following abbreviations: box-C = 4,4 -dibenzyl-4,4 ,5,5 -tetrahydro-2,2 -bioxazole; box-O =
0 0 0
-[((1 S)-1 -hydroxymethyl-2 -phenyl)ethylcarboxamide]-(4S)-4-benzyl-4,5-dihydrooxazole; pic = picolinate; acac = acetylacetonate. ΔE = E1/2(IV/
c d e
III) - E1/2(III/II) in mV. Average value calculated according to: E°(IV/II) = [E1/2(IV/III) þ E1/2(III/II)]/2, in V.
b
2
E1/2(IV/II) in V. This work.
separation of the (IV/III) and (III/II) redox couples (see
Supporting Information, Figure S15).
We also attempted to isolate the oxidized Ru dO
IV
IV
form of trans-3 by adding 2 equiv of Ce to an aqueous
solution of the Ru(II) complex followed by addition of
saturated aqueous NH PF . A yellow precipitate was
4
6
initially obtained that nevertheless turned into a brown
solid after a few minutes thus preventing its characteriza-
tion. The extra stabilization of the Ru(IV) oxidation state
gained thanks to the presence of the anionic pyrpy-O
ligand is thus not sufficient to stabilize the oxo complex in
the solid state, a fact that is in turn in agreement with the
IV
capability of the Ru dO species to react in the presence
of oxidizable substrates (see below the Catalytic Epox-
idation section).
E1/2 values at neutral pH for the three aquocomplexes
described in this work are gathered in Table 2, together
with additional electrochemical and pK data for other
Figure 4. Pourbaix diagram of complex 3. The pH-potential regions of
stability for the various oxidation states and their dominant proton
compositions are indicated.
a
relevant Ru-trpy-aqua complexes previously reported in
the literature for purposes of comparison. In all entries of
Table 2, the notation cis or trans (to the aquo ligand) is
referred to a ligand having higher σ-donor (or lower
π-acceptor) capacity than a pyridyl ring.
trans-3 and in Supporting Information, Figure S14 for
complexes trans-5 and cis-5.
Pourbaix diagram for complex trans-3 shows a unique
pH-dependent redox process throughout the whole pH
range with a change in the slope value (from approxi-
mately 60 to 30 mV/pH unit) at pH around 9.7, a behavior
that is generally indicative of the occurrence of a two-
electron (IV/II) redox process. To confirm this point we
have performed a redox spectrophotometric titration of
the complex, both chemically (with Ce(IV) as oxidant)
and electrochemically (through a controlled-potential
electrolysis of a neutral aqueous solution of the complex
at an applied potential of E = 0.57 V). In any case we
obtained identical sets of spectra which are displayed in
Supporting Information, Figure S12 for the electroche-
mical oxidation experiment. The presence of isosbestic
points at 446, 362, and 337 nm indicates a net conversion
from the initial to the final species that in both chemical
and electrochemical experiments is obtained upon the
transfer of 2 electrons. In contrast, pyrazole complexes
trans-5 and cis-5 show two monoelectronic processes as
indicated in eqs 2 and 3. For the trans-5 isomer these
two redox processes are clearly differentiated as displayed
in the Pourbaix diagram (Supporting Information, Fig-
ure S14) whereas for complex cis-5 an apparent single
wave enclosing the two monoelectronic transfers is ob-
served in CV experiments. Thus, we carried out a DPV
experiment on cis-5 and performed a mathematical de-
convolution of the wave obtained, resulting in a 50 mV
A first look at Table 2 shows that complex trans-3 is a
particular case since it is the only one presenting a
bielectronic wave. This characteristic seems to arise from
a specific balance between σ-donor and π-acceptor prop-
erties of the ancillary ligands (as expressed by the
1
7
Meyer-Lever plot ) and, in this case, the anionic pyr-
py-O ligand looks appropriate to lead the Ru(III) state to
disproportion. However, the ΔE value is not only gov-
erned by the ligands but also by the geometry of the
complex. Thus, when comparing for instance entries 3
and 4, or 7 and 8 in Table 2 one can see that coordination
of a relatively good σ-donor (or less π-acceptor) ligand in
a trans fashion with respect to the aquo ligand lowers
E1/2(III/II) with respect to the analogous cis isomer hence
1
8
stabilizing the Ru(III) species. The Ru(IV/III) redox
potential is also affected when comparing isomeric pico-
linate complexes but to a much lesser extent in the case of
trans-5 and cis-5. This could be a consequence of the steric
encumbrance of the methyl group of the pypz-Me ligand.
These data illustrate how the electron density is more
effectively transmitted to the metal center in a trans
(17) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271.
(18) (a) Leising, R. A.; Takeuchi, K. J. Inorg. Chem. 1987, 26, 4391–4393.
(b) Bessel, C. A.; Leising, R. A.; Takeuchi, K. J. J. Chem. Soc; Chem. Commun.
1991, 883–835.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7077
a
2
Table 3. Catalytic Epoxidation Performance of trans-3, trans-5, and cis-5 for the Epoxidation of a Variety of Alkenes Using PhI(OAc) as Oxidant
complex
trans-3
trans-5
cis-5
conversion (%) selectivity (%)
b
c
i
entry
alkene
styrene
trans-stilbene
cis-β-methylstyrene
cyclooctene
conversion (%) selectivity (%)
ν
conversion (%) selectivity (%)
ν
i
ν
i
1
2
3
4
5
6
80
>99
55
>99
30
55
62
86
69
>99
>99
87
6.3
10.8
3.7
43
96
90
>99
53
84
96.5
84
99
>99
97
74
3.4
6.0
7.9
72
47
>99
>99
10
84
79
86
>99
90
96
5.3
2.9
7.9
e
d
1-octene
4-vinylcyclohexene
1.6
4.2
2.7
7.6
f
85
8.3
a
Conditions: alkene (50 mM), complex (0.5 mM), oxidant PhI(OAc)
2
2 2
(100 mM), CH Cl (2.5 mL), 25 °C, 24 h, biphenyl (15 mM) as internal standard.
-6 -1 d
b
c
Selectivity for epoxide, (Yield/Conversion) ꢁ 100. v
i
is defined as initial rate for substrate consumption (expressed in 10 mol h ). % of cis-epoxide:
3
e f
complex 3, 100%; complex trans-5, 98%; complex cis-5, 97%. Analysis performed after 15 h. Epoxidation on the cyclohexene ring.
fashion with regard to the aqua group than in cis, and
it is also interesting to note that this is a particular fea-
ture of aquocomplexes since the corresponding trans-4 and
cis-4 chlorocomplexes display almost identical E1/2(III/II)
values.
Also, for a given trans or cis geometry, anionic ligands
(
i.e., entries 6, 7, and 9) in general decrease the redox
potentials with regard to neutral ligands (entries 1, 3, and
). Complex 3 appears as an exception to this trend but
5
this might be due to the oxidation of the initial pyrpy
ligand which would make it a worse σ-donor as the
corresponding chlorocomplex 2 displays clearly lower
E1/2(III/II) redox potential than both isomer complexes 4.
Catalytic Epoxidations. The catalytic activity of the
ruthenium aquocomplexes trans-3, trans-5, and cis-5 was
investigated in the epoxidation of a diversity of alkenes
using different oxidants, given the interest of the epoxi-
dation reaction in both bulk and fine chemicals, that use
Figure 5. Drawing showing the steric interactions for the cis/trans 5
scenarios with the approaching substrate (trpy ligand is situated perpen-
dicular to the pypz-Me ligand and has been omitted for clarity purposes).
trans-3 and trans-5 complexes contain a pyridine C-H
bond nearly parallel to the Ru-O bond whereas in sharp
contrast for cis-5 this position is occupied by a C-Me
group and thus will exert a much stronger steric effect (see
Figure 5).
1
9
them as starting materials for a variety of reactions.
Initial essays were performed with styrene and trans-
stilbene as test substrates using complex trans-3 as cata-
lyst and varying solvents and oxidants and the results are
reported in the Supporting Information. Optimal reacti-
vity was achieved with the following conditions: CH Cl
as solvent; PhI(OAc)2 as oxidant; catalyst/substrate/
oxidant molar ratio of 1:100:200. These conditions were
then used to test all substrates with the three aquocom-
plexes, trans-3, trans-5, and cis-5, and their performance
is gathered in Table 3. No epoxidation occurred in the
absence of catalyst in any case.
For the case of styrene (entry 1, Table 3), where in our
particular set of complexes steric effects will not play
major role, electronic effects are expected to strongly
dominate the reactivity. Indeed we observe a strong
correlation with redox potentials; thus the higher the
E°(IV/II) the higher the efficiencies obtained (trans-3 >
cis-5 > trans-5). Steric effects are expected to play an
important role for the case of trans-stilbene, and this is
exactly what we observed as reflected in the entry 2 of
Table 3. Complexes trans-3 and trans-5 are very active
toward the epoxidation of trans-stilbene with high initial
2
2
Complexes trans-3, trans-5, and cis-5 constitute an
excellent ground to study the influence of electronic and
steric effects on the Ru(IV)dO group with regard to the
epoxidation of olefins. It is interesting to realize here that
complex trans-3 containing the anionic pyrpy ligand has
the highest E°(IV/II) redox potential 0.55 V, compared to
consumption rates v , and practically complete conver-
i
sion whereas the v and conversion for the sterically
i
hindered cis-5 drops substantially manifesting the com-
bination of electronic and steric effects. The activity of
catalysts trans-3, trans-5, and cis-5 was also tested with
regard to their capacity to epoxidize cis-β-methyl-styrene
0
.48 and 0.495 V for the complexes containing the neutral
(entry 3, Table 3). Complexes containing the pypz-Me
pypz-Me ligand trans-5 and cis-5, respectively (see
Table 3). On the other hand it is also interesting to bear
in mind the spatial arrangement of the ligands close to the
RudO active group where the olefin will approach. The
ligand perform much better than the one containing the
pyrpy ligand, and it is striking to see that in all cases the
isomerization to the trans-epoxide is practically non-
existent. This is in agreement with a potential O-atom
transfer concerted mechanism, which is in turn consistent
with the low stability of Ru(III) that favors 2e- versus
(
19) (a) Smith, J. G. Synthesis 1984, 629–656. (b) Schneider, C. Synthesis-
Stuttgart 2006, 3919–3944. (c) Weissermel, K. Industrial Organic Chemistry,
rd ed.; VCH: Weinheim, 1997. (d) Xia, Q.-H.; Ge, H.-Q.; Ye, C.-P.; Liu, Z.-M.;
3
Su, K.-X. Chem. Rev. 2005, 105, 1603. (e) Che, C.-M.; Huang, J.-S. Chem.
Commun. 2009, 3996–4015. (f) Chatterjee, D. Coord. Chem. Rev. 2008, 252,
(20) (a) Masllorens, E.; Rodrıguez, M.; Romero, I.; Roglans, A.; Parella,
´
T.; Benet-Buchholz, J.; Poyatos, M.; Llobet, A. J. Am. Chem. Soc. 2006, 128,
5306–5307. (b) Yu, X.-Q.; Huang, J.-S.; Che, C.-M. J. Am. Chem. Soc. 2000,
122, 5337–5342.
1
76–198. (g) Gupta, K. C.; Sutar, A. K.; Linb, C.-C. Coord. Chem. Rev. 2009,
2
53, 1926–1946.

7
078 Inorganic Chemistry, Vol. 49, No. 15, 2010
e- transfer process (see ΔE values in Table 2). This is an
interesting and relevant phenomenon to be controlled
Dakkach et al.
2
0
III
the complexes [Ru Cl (trpy)], 1 (trpy is 2,2 :6 ,2 -terpyridine),
26
0 0 00
1
3
were prepared as described in the literature. All synthetic manipula-
tions were routinely performed under nitrogen atmosphere using
Schlenk tubes and vacuum line techniques. Electrochemical experi-
since Mn-salen complexes generally yield a mixture of
21
cis/trans isomerization epoxides. It is also very interesting
to compare the activity of our catalysts with regard to
styrene (entry 1, Table 3) and cis-β-methylstyrene (entry 3,
ments were performed under either N
degassed solvents.
2
or Ar atmosphere with
II
trans-[Ru Cl(pyrpy)(trpy)] 0.3CHCl
3
3
, trans-2 0.3CHCl . A
3
3
Table 3). For complexes cis-5 and trans-5 the v significantly
i
sample of 1 (0.2 g, 0.45 mmol) was added to a 250 mL round
bottomed flask containing a solution of LiCl (0.057 g, 1.36 mmol)
dissolved in 85 mL of EtOH (96%), under magnetic stirring. Then
increases when comparing the oxidation of styrene versus
cis-β-methylstyrene whereas the opposite effect takes place
in the case of trans-3. This clearly suggests that for cis-5 and
trans-5 the RudO has strong electrophilic character
whereas for trans-3 the RudO group displays the opposite
effect. This result is in agreement with the relative value of
the Ru(IV)/Ru(II) redox potentials obtained for these
complexes and puts forward the strong ligand influence
into the nature and reactivity of the RudO active group. It
is pertinent to mention here that in general related Mn
NEt
was stirred at room temperature for 30 min. Next pyrpy (0.077 g,
.45 mmol) together with NEt (0.1 mL, 0.7 mmol) dissolved in
3
(0.25 mL, 1.73 mmol) was added, and the reaction mixture
0
3
EtOH was added, andthe mixture was heatedat reflux for 3 h. The
solution was then cooled and filtered off in a frit. A dark solid was
obtained that was recrystallized from CHCl /diethyl ether obtain-
3
ing the violet chlorocomplex 2. Yield: 0.1 g (41.1%). Anal. found
(
22 5 3
calcd) for C26H N ClRu 0.3CHCl : C, 54.74 (54.76); N, 11.73
3
1
(12.14); H, 4.34 (3.90). H NMR (600 MHz, acetone-d ) δ (ppm):
6
complexes such as Mn(phen) (x = 1 or 2; phen is phen-
x
9.91 (d, H16), 8.52 (d, H7, H9), 8.44(d, H1, H15), 7.90 (d, H4,
H12), 7.82 (m, H8), 7.81(m, H2, H14), 7.77 (t, H18), 7.66 (d, H19),
22
athroline) present mainly an electrophilic character. It is
also interesting to see here that catalysts cis- and trans-5
containing the more σ-donating pyrazole ligand display
much better performances than their homologues contain-
7
(
.34 (t, H3, H13), 7.06 (t, H17), 5.11 (s, H23), 2.3(s, H25, Me), 0.96
s, H26, Me). For the NMR assignment we have used the same
numbering scheme as for the X-ray displayed in Figure 1. IR
-1
(
(
νmax, cm ): 1594 (m), 1481 (m),1355 (m), 1276 (m), 971 (s), 632
m). E1/2(III/II) = 0.21 V, E1/2(IV/III) = 0.79 V versus SSCE.
23
ing pyridylic or imidazole type of ligands only.
The ability of the catalysts was also tested with aliphatic
substrates. With cyclooctene we obtain complete conver-
sion with our catalysts (entry 4, Table 3) and with
-1
-1
UV-vis (CH Cl ):- λmax, nm (ε, M cm ) 240 (13670), 278
2
2
þ
(
11490), 320 (19390), 540(3050).ESI-MS (m/z): 541.1 [M þ H ].
II
trans-[Ru (pyrpy-O)(trpy)]OH ](PF ), trans-3. A sample of
2
6
1
-octene we have modest to low performances with all
AgNO3 (0.031 g, 0.184 mmol) was added to a solution of
acetone/H O (1:2) (30 mL) containing 2 (0.050 g, 0.092 mmol)
and heated at reflux for 2 h. After cooling the precipitated AgCl
was filtered off through a frit containing Celite. Afterward
three catalysts in agreement with their lower reactivity
toward unactivated monosubstituted alkenes. Finally the
catalysts show activity toward the ring epoxidation of
2
4 6
NH PF (1 mL) was added to the filtrate, and the volume
4
-vinylciclohexene with again better performances for the
reduced in a rotary evaporator. A precipitate appeared that
trans-5 and cis-5 that have lower redox potentials than
trans-3 which again is in agreement with the electrophilic
character of the former.
1
was washed with cold water (3 ꢁ 5 mL). Yield: 0.045 g (71%). H
2
NMR (600 MHz, D O) δ (ppm): 9.49 (d, H16), 8.56 (d, H19),
8
.41(d, H7), 8.36 (d, H9), 8.32 (d, H12), 8.24 (d, H4), 8.19 (t,
In conclusion, we have synthesized and characterized a
new family of Ru-OH complexes where the ligand design
H18), 8.05 (t, H8), 7.95 (t, H17), 7.93 (t, H13), 7.87 (t, H3), 7.51
(d, H15), 7.38 (d, H1) 7.29 (t, H14), 7.22 (t, H2), 1.89 (s, H25),
0.23 (s, H26). IR (νmax, cm ): 3654 (m), 1606 (m), 1450 (m),
1288 (w), 836 (s), 554 (m). E1/2 (IV/II), phosphate buffer pH = 7:
2
-
1
strongly influences sterics and electronics as evidenced by
their spectroscopic and redox properties. This is in turn
manifested by the reactivity of these complexes toward
the epoxidation of a series of aromatic and aliphatic
alkenes.
0
.55 V versus SSCE. UV-vis (phosphate buffer pH = 7): λmax,
-1 -1
nm (ε, M cm ) 271 (11960), 311 (11580), 511 (4000). ESI-MS
-
(
m/z): 540.1 [M - PF
6
].
trans and cis-[Ru Cl(pypz-Me)(trpy)](PF
0.8CH Cl . A sample of 1 (0.150 g, 0.22 mmol) was added to a
00 mL round bottomed flask containing a solution of LiCl
O (3:1),
(0.06 mL, 0.42 mmol) was
II
6
), trans-4 and cis-
4
1
2
2
3
Experimental Section
Materials. All reagents used in the present work were ob-
tained from Aldrich Chemical Co and were used without further
purification. Reagent grade organic solvents were obtained
from SDS and high purity deionized water was obtained by
passing distilled water through a nanopure Mili-Q water pur-
(0.018 g, 0.44 mmol) dissolved in 40 mL of EtOH/H
under magnetic stirring. Then, NEt
2
3
added, and the reaction mixture was stirred at room tempera-
ture for 30 min. Afterward pypz-Me (0.052 g, 0.218 mmol) was
added and heated at reflux for 3 h. The hot solution was then
ification system. RuCl
3
2H
2
O, was supplied by Johnson and
Matthey Ltd. and was used as received.
Preparations. Ligandspyrpy(3,5-dimethyl-2-(2-pyridyl)pyrrole)
4 6
filtered off in a frit, and a saturated aqueous solution of NH PF
3
(1.5 mL) was added. After reduction of the volume in a rotary
evaporator a precipitate formed that was filtered off and washed
several times with water. The solid obtained in this manner was a
mixture of complexes trans-4 and cis-4 that can be separated by
24
25
and pypz-Me (2-(1-Methyl-3-pyrazolyl)pyridine) (Scheme 1) and
column chromatography (silica; CH Cl /acetone 90:10). Both
2
chlorocomplexes were recrystallized from CH Cl /ether, and
2 2
(
21) (a) Jacobsen, E. N.; Zhang, W.; G u€ ler, M. L. J. Am. Chem. Soc. 1991,
13, 6703–6704. (b) Cavallo, L.; Jacobsen, H. J. Org. Chem. 2003, 68, 6202–
2
1
6
207.
the resulting precipitates were filtered on a frit, washed with a
small amount of ether and pentane, and dried under vacuum.
For trans-4: yield, 0.042 g (28.5%). Anal. Found (Calcd) for
(
(
22) Terry, T. J.; Stack, T. D. J. Am. Chem. Soc. 2008, 130, 4945–4953.
23) (a) Hamelin, O.; Menage, S.; Charnay, F.; Chavarot, M.; Pierre,
J. L.; P ꢀe caut, J.; Fontecave, F. Inorg. Chem. 2008, 47, 6413–6420. (b) Murali,
M.; Mayilmurugan, R.; Palaniandavar, M. Eur. J. Inorg. Chem. 2009, 3238–
3
C
24
H
20
N
6
ClRuPF
6
: C, 42.62 (42.77); N, 12.15 (12.47); H, 2.85
1
(2.99). H NMR (600 MHz, acetone-d ) δ (ppm): 10.20 (dt,
H16), 8.73 (d, H7, H9), 8.61 (dt, H4, H12), 8.50 (dt, H19), 8.32
6
249.
(
24) Bolm, C.; Weickhardt, K.; Zehnder, M.; Glasmacher, D. Chem. Ber.
1
991, 124, 1173–1180.
(
(
25) Huckel, W.; Bretschneider, H. Chem. Ber. 1937, 9, 2024.
26) Sullivan, B. P.; Calvert, J. M.; Meyer, T. J. Inorg. Chem. 1980, 19,
(27) (a) Binstead, R. A.; Meyer, T. J. J. Am. Chem. Soc. 1987, 109, 3287–
3297. (b) Llobet, A.; Doppelt, P.; Meyer, T. J. Inorg. Chem. 1988, 27, 514–520.
1
404–1407.

Article
Inorganic Chemistry, Vol. 49, No. 15, 2010 7079
(
(
3
td, H18), 8.17 (t, H8), 8.00 (td, H3, H13), 7.88 (td, H17), 7.84
ddd, H1, H15), 7.59 (d, H22), 7.45 (td, H2, H14), 7.21 (d, H23),
.05 (s, H24). IR (νmax, cm ): 1619 (w), 1450 (m), 1251 (w), 833
and reductive peak potentials (Epa þ Epc)/2 at a scan rate of 100
mV/s whereas they were directly taken from the maximum of the
peak in DPV experiments. Unless explicitly mentioned the con-
centration of the complexes were approximately 1 mM. In aqu-
eous solutions the pH was adjusted from 0 to 2 with 5 M HCl.
Potassium chloride was added to keep a minimum ionic strength
of 0.1 M. From pH 2-10, 0.1 M phosphate buffers were used, and
-
1
(
s), 761 (m), 555 (m). E1/2(CH Cl ) = 0.79 V versus SSCE. UV-
2
2
-1 -1
2 2
vis (CH Cl ): λmax, nm (ε, M cm ) 239 (15960), 274 (15650),
3
21 (13660), 400(3300), 501 (3550).
For cis-4, yield: 0.038 g (26%). Anal. Found (Calcd) for
C H N ClRuPF 0.8CH Cl : C, 40.10 (40.15); N, 11.56
from pH 10-12 diluted, CO free, NaOH. Bulk electrolyses were
2
4
20
6
6
3
2
2
2
1
(
(
(
11.32); H, 3.03 (2.93). H NMR (600 MHz, acetone-d
6
) δ
ppm): 8.69 (d, H7,H9), 8.59 (dt, H4, H12), 8.43 (d, H22), 8.18
carried out in a three-compartment cell using carbon felt from
SOFACEL as the working electrode.
The H NMR spectroscopy was carried out on a a Bruker
1
ddd, H19), 8.17 (t, H8), 8.09 (ddd, H1, H15), 8.00 (td, H3, H13),
7
6
1
.72 (td, H18), 7.59 (d, H23), 7.47 (td, H2,H14), 7.37(ddd, H16),
DPX 200 MHz or a Bruker 600 MHz. Samples were run in
acetone-d or CDCl , with internal references (residual protons
6 3
and/or tetramethylsilane). Elemental analyses were performed
using a CHNS-O Elemental Analyzer EA-1108 from Fisons.
ESI-MS experiments were performed on a Navigator LC/MS
chromatograph from Thermo Quest Finnigan, using acetonitrile
-
1
.96 (td, H17), 4.76 (s, H24). IR (νmax, cm ): 1627 (w), 1448 (m),
253 (w), 833 (s), 763 (m), 555 (w). E1/2(CH Cl ) = 0.80 V versus
2
2
-
1
-1
SSCE. UV-vis (CH Cl ): λmax, nm (ε, M cm ) 241 (17260),
2
2
280 (14130), 318 (14640), 409 (3440), 499 (3180). For the NMR
assignment we have used the same numbering scheme as for the
X-ray displayed in Figure 1.
as a mobile phase.
II
trans-[Ru (pypz-Me)(trpy)OH
-5
](PF
A sample of AgNO (0.017 g, 0.102 mmol) was added to a
solution of H O (15 mL) containing trans-4 (0.035 g, 0.051
2
mmol) and heated at reflux for 3 h in absence of light. AgCl was
filtered off through a frit containing Celite. Afterward NH PF
saturated aqueous soluton (1 mL) was added, and the product
was precipitated upon reduction of volume in a rotary evapora-
tor. The green solid obtained was then filtered and washed with
ether and pentane and dried under vacuum. Yield: 0.030 mg
6
)
2
H
2
O, trans-5 H
2
O.
For acid-base spectrophotometric titration, 3-4 ꢁ 10
M
2
3
3
buffered aqueous solutions of the complexes were used. The pH
of the different solutions was adjusted by adding small volumes
(approximately 5 μL) of 7 M NaOH to produce a negligible
3
overall volume change. Redox spectrophotometric titrations
4
6
IV
were performed by sequential addition of a (NH
(NO ] 0.1 M solution in HCl to the complex.
X-ray Structure Determination. Measurement of the crystals
4 2
) [Ce -
3 6
)
were performed on a Bruker Smart Apex CCD diffractometer
˚
(
73.4%). Anal. Found (Calcd) for C24
C, 34.82 (35.10); N, 10.05 (10.23); H, 2.62 (2.97). H NMR (600
MHz, acetone-d /10% D O) δ (ppm): 9.58 (d, H16), 8.84 (d, H7,
H9), 8.68 (d, H4, H12), 8.54 (d, H19), 8.37 (t, H18), 8.33 (t, H8),
H
22
N
6
ORuP
2
F
12
H
2
O:
using graphite-monochromated Mo KR radiation (λ = 0.71073 A)
3
1
from an X-ray tube. Data collection, Smart V. 5.631 (BrukerAXS
1997-02); data reduction, Saintþ Version 6.36A (Bruker AXS
2001); absorption correction, SADABS version 2.10 (Bruker AXS
2001) and structure solution and refinement, SHELXTL Version
6.14 (Bruker AXS 2000-2003). The crystallographic data as well
as details of the structure solution and refinement procedures are
reported in Table 1 and Supporting Information, Table S1.
CCDC 781563 (trans-2), 781564 (trans-4), and 781565 (cis-4)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.uk/data_
request/cif.
6
2
8
7
.10 (t, H3, H13), 7.97 (t, H17), 7.92 (d, H1, H15), 7.58 (d, H22),
.52 (t, H2, H14), 7.22 (d, H23), 3.05 (s, H24). E1/2 (III/II),
-
1
phosphate buffer pH = 7: 0.39 V; IR (νmax, cm ): 3478 (w),
342 (m), 1623 (m), 1448 (m), 1251 (w), 827 (s), 763 (s), 555 (s).
1/2 (IV/III): 0.57 V versus SSCE. UV-vis (phosphate buffer
3
E
pH = 7): λmax, nm (ε, M- cm ) 229 (16460), 271 (17620), 313
1
-1
(
18520), 381 (3100), 459 (3810).
II
cis-[Ru (pypz-Me)(trpy)OH ](PF ) H O, cis-5 H O.
A
sample of AgNO (0.021 g, 0.12 mmol) was added to a solution
2
6 2
3
2
3
2
3
of H O (15 mL) containing cis-4 (0.040 mg, 0.06 mmol) and
heated at reflux for 3 h in absence of light. AgCl was filtered off
through a frit containing Celite. Afterward NH PF saturated
2
Catalytic Studies. Experiments have been performed in anhy-
drous dichloromethane at room temperature. In a typical run,
Ru catalyst (0.5 mM), alkene (50 mM), and PhI(OAc) (100 mM)
4
6
2
aqueous solution (1 mL) was added, and the product was
precipitated from the resulting solution after reduction of volume
in a rotary evaporator. The brown solid obtained was then filtered
and washed with ether and pentane and dried under vacuum.
were stirred at room temperature in dichloromethane (2.5 mL)
for 24 h. The end of the reaction was indicated by the disappear-
ance of solid co-oxidant. After the addition of an internal stan-
dard, an aliquot was taken for gas chromatographic (GC)
analysis. The oxidized products were analyzed in a Shimadzu
GC-17A gas chromatography apparatus with a TRA-5 column
(30 m ꢁ 0.25 mm diameter) incorporating a flame ionization
detector. GC conditions: initial temperature, 80 °C for 10 min;
Yield: 0.025 mg (52%). Anal. Found (Calcd) for C24
uP 12 1.3CH Cl : C, 34.94 (33.32); N, 9.62 (9.21); H, 2.67 (2.71).
H NMR (600 MHz, acetone-d /10% OD ) δ (ppm): 8.78 (d, H7,
22 6
H N OR-
2
F
2
2
3
1
6
2
H9), 8.65 (d, H4, H12), 8.46 (d, H23), 8.31 (t, H8), 8.16 (d, H1,
H15), 8.14 (d, H19), 8.09 (td, H3, H13), 7.71 (td, H17), 7.58 (d,
H23), 7.53 (td, H2,H14), 7.32(d, H16), 6.94 (td, H17), 4.56 (s,
-
1
ramp rate, 10 °C min ; final temperature, 220 °C; injection
temperature, 220 °C; detector temperature, 250 °C; carrier gas,
He at 25 mL min . All catalyticoxidations werecarried out under
-
1
-1
H24). IR (νmax, cm ): 3494 (m), 1630 (w), 1450 (m), 1247 (w), 831
s), 765 (s), 555 (s). E1/2 (III/II), phosphate buffer pH = 7: 0.47 V;
1/2 (IV/III): 0.52 V versus SSCE. UV-vis (phosphate buffer
(
2
a N atmosphere.
E
pH = 7): λmax, nm (ε, M- cm ) 231 (24380), 269 (23330), 311
1
-1
Acknowledgment. This research has been financed by MI-
CINN of Spain (CTQ2007-60476/PPQ, CTQ2007-67918) and
Consolider Ingenio 2010 (CSD2006-0003)). Johnson & Matthey
LTD are acknowledged for a RuCl3 nH O loan. M.D. thanks
(28520), 387 (4390), 455 (4940).
Instrumentation and Measurements. UV/vis spectroscopy was
performed on a Cary 50 Scan (Varian) UV/vis spectrophotometer
with 1 cm quartz cells. CV and DPV experiments were performed
in a IJ-Cambria IH-660 potentiostat using a three electrode cell.
Glassy carbon electrodes (3 mm diameter) from BAS were used as
working electrode, platinum wire as auxiliary, and SSCE as the
reference electrode. All cyclic voltammograms presented in this
work were recorded under nitrogen atmosphere. All E1/2 values
estimated from CV were calculated as the average of the oxidative
3
2
AECID (MAEC) of Spain for the allocation of a MAEC-
AECID grant.
Supporting Information Available: Additional information in
the form of Tables S1-S5 and Figures S1-S16 and crystallo-
graphic data in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.