Electronic Control of RuII Complexes with Proximal Oxophilic Phenylselenium Tethers: Synthesis, Characterization, and Activation of Molecular Oxygen

Article abstract of DOI:10.1002/ejic.201600123

Various ruthenium(II) complexes with proximal oxophilic phenylselenium groups of the general formula [Ru^IIL^AL^B]X₂{L^A= L^B= 6,6′-bis[(4-methoxyphenyl)selanyl]-2,2′-bipyridine; 6,6′-bis[(nitrophenyl)selanyl]-2,2′-bipyridine; 3,6-bis(phenylselanyl)dipyrido[3,2-a:2′,3′-c]phenazine; L^A= 6,6′-bis(phenylselanyl)-2,2′-bipyridine, L^B= terpyridine} were prepared. The substitution patterns of these compounds were designed to have different electron-withdrawing/-donating properties or different binding motifs in comparison to the previously reported compound with L^A= L^B= 6,6′-bis(phenylselanyl)-2,2′-bipyridine. The research objective was to evaluate the potential of these compounds to activate ground-state molecular oxygen to form higher-valent Ru–O–Se bonds by cleavage of the O–O bond of O₂. All of the compounds prepared indeed activated O₂to form Ru–O–Se moieties, as observable by UV/Vis spectroscopy, mass spectrometry, or X-ray crystallography.

Full text of DOI:10.1002/ejic.201600123

DOI: 10.1002/ejic.201600123
Full Paper
Oxygen Activation
II
Electronic Control of Ru Complexes with Proximal Oxophilic
Phenylselenium Tethers: Synthesis, Characterization, and
Activation of Molecular Oxygen
[
a]
[a]
[a]
[b]
[b]
Kaiji Shen, Haviv Ben-David, Alexander Laskavy, Gregory Leitus, Linda J. W. Simon,
and Ronny Neumann*[
a]
Abstract: Various ruthenium(II) complexes with proximal oxo- different binding motifs in comparison to the previously re-
philic phenylselenium groups of the general formula [Ru L- ported compound with LA = L = 6,6′-bis(phenylselanyl)-2,2′-
II
B
A
B
A
B
L ]X {L = L = 6,6′-bis[(4-methoxyphenyl)selanyl]-2,2′-bipyr- bipyridine. The research objective was to evaluate the potential
2
idine; 6,6′-bis[(nitrophenyl)selanyl]-2,2′-bipyridine; 3,6-bis(phen- of these compounds to activate ground-state molecular oxygen
A
ylselanyl)dipyrido[3,2-a:2′,3′-c]phenazine; L = 6,6′-bis(phenyl- to form higher-valent Ru–O–Se bonds by cleavage of the O–O
B
selanyl)-2,2′-bipyridine, L = terpyridine} were prepared. The bond of O . All of the compounds prepared indeed activated
2
substitution patterns of these compounds were designed to O to form Ru–O–Se moieties, as observable by UV/Vis spectro-
2
have different electron-withdrawing/-donating properties or scopy, mass spectrometry, or X-ray crystallography.
Introduction
in these reactions is the use of two electrons and two protons
to reduce one atom of O to water and form a reactive high-
2
The activation of molecular oxygen by a dioxygenase mecha-
nism and its use in selective oxidative transformations of or-
ganic substrates, such as hydrocarbons, alcohols, amines, and
sulfides, is one of the holy grails of green chemistry and of
valent oxido–metal species with the other oxygen atom of O2.
Although very reactive oxido–metal species, typically those of
iron, can be formed in this way, this concept suffers from the
principle problem that the reducing agent becomes the limiting
or sacrificial reagent; thus, the inherent ecological advantage of
[
1]
fundamental importance in the science of oxidation catalysis.
Historically, the one-catalytic-reaction-site paradigm for the ac-
tivation of molecular oxygen together with the target substrate
has largely failed to yield the desired selective catalytic transfor-
mations; therefore, it is desirable to find new catalysts for such
transformations. The use of oxygen from air as the primary
oxidant for catalytic oxidative transformations has clear advan-
tages from an ecological and an economic point of view. How-
using O as the oxidant is negated. A more desirable methodol-
2
ogy is to utilize a dioxygenase pathway in which an oxygen
molecule is cleaved to form two high-valent oxido–metal moie-
ties. This concept has been realized in only a very few cases
with ruthenium complexes. Groves and co-workers showed
such dioxygenase reactivity with sterically hindered porphyrin–
[
3]
ruthenium compounds. Drago and co-workers also claimed
ever, the chemical properties of ground-state molecular oxygen
2
+
molecular oxygen activation with cis-[Ru(L) (H O) ] (L = 2,9-
2
2
2
3
(
triplet O ) limit its usefulness as an oxidant for wide-ranging
2
dimethylphenanthroline) complexes. In this compound, the
higher-valent oxido– and dioxido–ruthenium complexes
synthetic applications. The limiting properties are the radical
nature of molecular oxygen, the strong oxygen–oxygen bond,
and the fact that the one-electron reduction of oxygen is gener-
ally not favored thermodynamically.
Often the activation of molecular oxygen by metal com-
plexes is performed in a reductive manner by general pathways
that mimic the mechanisms of monooxygenase enzymes that
2
+
2+
[
Ru(L) H O(O)] and [Ru(L) (O) ] are accessible with an oxi-
2 2 2 2
dant such as H O , but it remains very debatable if this is the
2
2
[
4]
case with O2. Our group has also contributed in this area, and
we showed such activity with ruthenium-substituted polyoxo-
[
5]
metalates. More recently, we prepared a bipyridine–ruth-
enium(II) complex with phenylselenium tethers that can acti-
[
2]
have oxido–iron reactive intermediates. The common theme
[
6]
vate O intramolecularly, that is, the O=O bond is split, and
2
Ru–O–Se moieties are formed (Scheme 1).
[
[
a] Department of Organic Chemistry, Weizmann Institute of Science,
Rehovot 76100, Israel
The experimental evidence indicated that the coordination
of two oxygen atoms around the ruthenium atom after O acti-
E-mail: Ronny.Neumann@weizmann.ac.il
2
http://www.weizmann.ac.il/Organic_Chemistry/neumann/
b] Department of Chemical Research Support, Weizmann Institute of Science,
Rehovot 76100, Israel
III
vation and scission of the O–O bond is best formulated as Se –
IV
III
O–Ru –O–Se . Therefore, it was of interest to see if similar com-
pounds with different electronic properties or coordination
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600123.
modes would also activate O in a similar manner, for example,
2
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2
Scheme 1. Activation of O by bipyridine–ruthenium(II) complexes with proximal arylselenium tethers.
if electron-donation/-withdrawing effects around the impend- an electron-donating methoxy substituent on the SePh tether
ing formation of the Ru–O–Se moiety might influence the react- had no discernible effect on the activation of O , the formation
2
2
2+
ivity.
of the dioxido compound [Ru(L ) (O) ] , or the subsequent
2 2
oxygen-transfer reaction.
The subsequent objective was to prepare an analogous li-
Results and Discussion
gand with an electron-withdrawing NO substituent. The 1,2-
2
bis(4-nitrophenyl)diselane compound was prepared by a previ-
ously reported method, but its reaction with 6,6′-dibromo-
The pathway for the synthesis of the ligands L and L and the 2,2′-bipyridine failed, presumably because the in situ formed
formulas of the corresponding Ru complexes are presented in selenide is insufficiently nucleophilic for the substitution reac-
Ligand and Complex Synthesis
[
7]
1
2
II
Scheme 2.
tion to proceed. As an alternative, the nitro substituent was
As previously reported,[6] L1 was prepared by the reaction introduced by the nitration of L to yield L , which was obtained
1
3
3
of 1,2-diphenyldiselane with 6,6′-dibromo-2,2′-bipyridine under as a mixture of various isomeric forms of L and mononitrated
basic conditions with the in situ formation of the selenide anion and trinitrated derivatives. The subsequent preparation of
3
2+
and nucleophilic substitution. The ruthenium complex [Ru(L )
(H O)
2 2
]
2
(3) as an impure mixture was not problematic,
1
2+
1
[
Ru(L ) (H O) ] (1) was prepared by metalation of L with but the low purity of the compound complicated the analysis
2
2
2
RuCl ·xH O under reducing conditions and the subsequent sub- of the reaction of 3 with O .
3
2
2
stitution of the chlorido ligands to yield the diaqua complex.
To test the effect of an electron-withdrawing moiety in a
2
2
2+
4
The ligand L and [Ru(L ) (H O) ] (2) were successfully pre- different way, L with an electron-withdrawing phenazine moi-
2
2
2
pared in a completely analogous manner. Compound 2 was ety was prepared as the desired derivative of the well-known
treated with O2 in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) at (dipyridophenazine) dppz ligand. The formation of the ligand
4
room temperature, and as previously observed for 1, a dioxido L required a more potent nucleophile than the one produced
2
2+
[6]
compound, [Ru(L ) (O) ] , was cleanly formed at similar rates.
in situ by the reaction of 1,2-diphenyldiselane with cesium
2
2
[
8]
The ESI mass spectrum showed the molecular peak at m/z = hydroxide, which led to substitution at the 2- and 9-positions
93.03. The reactions of [Ru(L ) (O) ] with alkenes such a 2,3- by SePh and OH. Therefore, the selenide was prepared by using
2
2+
5
2 2
dimethyl-2-butene showed the same reactivity as that previ- sodium methoxide in the presence of hydrazine to form a so-
1
2+
ously observed for [Ru(L ) (O) ] ; therefore, the substitution of dium selenolate nucleophile. The unstable nucleophile was
2
2
II
Scheme 2. Pathway of ligand synthesis and formulas of the Ru complexes prepared.
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then treated quickly with 6,6′-dibromo-2,2′-bipyridine to obtain
4
4
L as a bright yellow solid. [Ru(L ) (Cl ) ] (4a) was prepared by
2
2 2
4
treating L with [Ru(COD)Cl ] (COD = cyclooctadiene) to give a
2
dark blue, almost black, crystalline product.
4
The electronic absorption spectra of [Ru(L ) (Cl ) ] in HFIP
2
2 2
and dichloromethane (DCM) are characterized by intense li-
gand-centered transitions in the UV region and a metal-to-li-
gand charge-transfer (MLCT) transition in the visible region. The
spectrum in HFIP shows a broad absorption in the visible region
with a maximum at λ = 487 nm (ε = 9000; Figure 1). Interest-
ingly, the complex exhibits a bathochromic effect; when dis-
solved in DCM, it is blue, and a new higher maximum appears
at λ = 560 nm (ε = 13010; Figure 1). The peaks at λ = 320 and
Figure 2. Spectra showing the formation of the oxido species from 4 (2.0 μM)
at room temperature in HFIP under 1 bar of O
recorded every 2000 s.
2
. The spectra shown were
3
83 nm in HFIP and DCM, respectively, are characteristic of the
1
as a result of O–O bond cleavage, [RuL tpyO][PF ] , as was veri-
6
2
π–π* transitions of the dppz ligand. The low-energy bands at
λ = 487 and 560 nm are assigned as MLCT Ru(dπ)→dppz(π*)
transitions. On the basis of previous observations that the pro-
tonation of the phenazine moiety, for example, in [Pt(dppz)Cl2],
can lead to blueshifted spectra because of a lower degree of
1
6
fied by mass spectrometry. The reaction of 5 with O gave
2
1
16 2+
[
RuL tpy O] with a peak at m/z = 408.47 (z = 2), whereas the
1
8
1
18 2+
reaction of 5 with O gave [RuL tpy O] (6) with a peak at
2
1
2+
m/z = 409.50 (z = 2). [RuL tpyO] was recrystallized from both
water and chloroform [Equation (1)].
[
9]
4
conjugation in the ligand, we dissolved [Ru(L ) (Cl ) ] in DCM,
2
2 2
and a few drops of AcOH yielded the dark orange colored, blue-
shifted visible spectrum.
(
1)
The structure derived by X-ray diffraction is shown in Fig-
ure 3, and selected bond lengths and angles are listed in
Table 1. The structure shows the presence of one oxygen atom
between the ruthenium and selenium sites, and the Se–O bond
(
1.713 Å) is longer than that observed for SeO, but similar to
–
[10]
the bond length of SeO . The coordination geometry around
the ruthenium center is a distorted octahedron with Ru–N bond
lengths ranging from 1.969 to 2.089 Å and an Ru–O bond
length of 2.086 Å. This structure around the Ru center and the
Ru–O–Se moiety is quite similar to those previously reported
Figure 1. UV/Vis spectrum of 4 in HFIP (orange) and DCM (blue).
1
for [Ru(L ) (O) ]. However, there is an interesting structural
2
2
anomaly. The phenyl ring attached to the Ru–O–Se moiety is
almost exactly parallel to the terpyridine ligand, presumably
to give [Ru(L ) (H O) ] (4). This complex was then exposed to because of π–π bonding interactions. A look at the crystal pack-
4
[
Ru(L ) (Cl ) ] was treated with a mixture of HPF and NH PF
2
2 2
4
6
4
6
2+
2
2
2
a positive pressure of O in HFIP, and the reaction was moni- ing reveals that this structure is further stabilized by a dimeriza-
2
tored by UV/Vis spectroscopy. An isosbestic point in the visible tion interaction of two enantiomers (Figure 4). This pair is also
region (455 nm) and four isosbestic points in the UV region stabilized by the formation of a rhomboid –[Se–O–Se–O]– moi-
(
Figure 2) were observed over a reaction time of 10000 s. This ety with lengths of 1.713 and 2.817 Å and angles of 70.47 and
rate of the formation of the oxido species is the same as that 109.53°. The packing and rhomboid structure are slightly af-
observed from 1 within a 10 % error. As previously demon- fected by the solvent used in crystallization. For example, a crys-
strated, this suggests the activation of O and the formation of tal obtained from water showed Se–O bond lengths of 1.704
2
Se–O–Ru groups. The reactivity of this oxido compound, osten- and 3.057 Å.
4
2+
1
2+
sibly [Ru(L ) (O) ] , was the same as that of the similar dioxido
Interestingly, [RuL tpyO] was clearly diamagnetic, in con-
trast to the previously reported [Ru(L ) (O) ] , which was
2
2
1
2+
1
1
2+ [6]
compound [Ru(L ) (O) ] prepared from L .
2
2
2 2
The pentacoordinate compound 5 was prepared by treating clearly paramagnetic. In the 77Se NMR spectrum, peaks were
1
a 1:1 mixture of L /terpyridine (tpy) with RuCl under reducing observed at δ = 496 and 1040 ppm. The latter can be attributed
3
IV
conditions followed by hydrolysis of the chlorido ligand, as de- to an Se species; thus, the coordination around the activated
II
IV
scribed in the Experimental Section. This complex was charac- oxygen atom is best described as an Ru –O–Se moiety.
1
13
77
terized by ESI-MS analysis and H, C, and Se NMR spectro-
As complex 5 has only one labile site that can accommodate
scopy. Despite many attempts, no crystal structure was ob- only one oxygen atom transfer from O , it was worthwhile to
2
1
tained. The dissolution of 5(PF ) and [RuL tpy(H O)][PF ] in investigate the reaction of 5 with O in more detail (Scheme 1),
6
2
2
6 2
2
HFIP and the reaction with 1 bar of O at room temperature for as an intermolecular reaction would be required, unlike the re-
2
24 h or bubbling of oxygen for 2 h yielded the oxido complex actions for 1–4. One immediate observation was that the use
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The evolution of 6 from 5 at 15 °C was monitored kinetically at
λ = 391 nm (Figure 5, right). Interestingly, one can clearly ob-
serve a two-step formation of 6, with two observed pseudo-
–1
first-order rate constants (O is in excess), k = 0.029 s and
k = 0.0068 s .
2
2
1
–1
Figure 5. Left: UV/Vis spectra of 5 (full line) and 6 (dotted line). Right: change
in absorbance at λ = 391 nm as a function of time. The solutions were 46 μ
in 50 % TFE/dichloromethane. The formation of 6 was initiated by the addi-
tion of 1 bar of O
M
2
.
As both steps are first order in a ruthenium species, we hy-
pothesize that the reaction occurs according to the following
1
2+
Figure 3. Structure of the [RuL tpyO] cation with thermal ellipsoids at 50 %
probability. The anions, solvent molecules, and hydrogen atoms are omitted
for clarity. Ru: magenta, Se: green, N: blue, O: red, C: black.
steps (Scheme 3). First, 5 reacts with O to form a hydroperoxo
2
intermediate species, and then the intermediate decomposes
with O–O bond cleavage, which may be assisted by the TFE
[
6,11]
solvent.
1
2+
Table 1. Selected bond lengths [Å] and angles [°] for [RuL tpyO] crystallized
from chloroform.
Bond lengths
Bond angles
Ru1–N1
Ru1–N2
Ru1–N3
Ru1–N4
Ru1–N5
2.076(4)
N2–Ru1–N5
N2–Ru1–N3
N5–Ru1–N3
N2–Ru1–N1
N5–Ru1–N1
N3–Ru1–N1
N2–Ru1–O1
N5–Ru1–O1
170.0(2)
79.5(2)
99.1(2)
79.6(2)
101.8(2)
159.0(2)
83.0(2)
87.2(2)
N3–Ru1–O1
N1–Ru1–O1
N2–Ru1–N4
N5–Ru1–N4
N3–Ru1–N4
N1–Ru1–N4
O1–Ru1–N4
Se1–O1–Ru1
92.3(2)
87.2(2)
110.8(2)
79.1(2)
93.6(2)
91.9(2)
165.7(2)
115.1(2)
Scheme 3. Proposed pathway for the formation of 6 from 5.
1.969(5)
2.053(5)
2.089(5)
2.006(5)
Conclusions
Ru1–O1 2.086(4)
O1–Se1 1.713(4)
Various ruthenium(II) complexes with proximal oxophilic phen-
ylselenium tethers were prepared to test their potential for the
activation of O by cleavage of the O–O bond to yield Ru–O–
2
Se moieties. The variation of the electronic properties and types
of ligands used as well as a comparison of tetracoordinate ver-
sus pentacoordinate complexes revealed that all compounds
reacted to activate O . For the pentacoordinate compound 5,
2
O activation led to the formation of an unusual structure ow-
2
ing to intramolecular π–π stacking interactions and intermolec-
ular stabilization by the formation of additional weak Se–O
bonds. All of the oxido compounds prepared were reactive to-
wards PPh as a substrate to form the corresponding phosphine
3
oxide but were not reactive with weak nucleophiles such as
terminal alkenes.
1
2+
Figure 4. Dimer presentation of the structure of [RuL tpyO] with thermal
ellipsoids at 50 % probability. The anions, solvent molecules, and hydrogen
atoms are omitted for clarity. Ru: magenta, Se: green, N: blue, O: red, C: black.
Experimental Section
General: The H, 13C, and 77Se NMR spectra were recorded at 400
1
of 2,2,2-trifluoroethanol (TFE) as a solvent was much more ef-
or 500 MHz with Bruker Avance spectrometers. Mass spectra in the
fective than the use of HFIP for O activation with 5, and the electrospray ionization mode were measured with either a Waters
2
reaction was completed in less than 30 s. In a mixture of 50 % Xevo-G2-QTOF high-resolution accurate mass spectrometer or a
TFE in dichloromethane, the evolution of the oxido complex 6 Waters SQD (single quadropole) mass spectrometer. Elemental anal-
ysis was carried out with a Thermo CHN analyzer.
from the aqua complex 5 can be observed readily at a conve-
nient time period of 30 min by UV/Vis spectroscopy, and Materials: Reagents that were available from commercial sources
isosbestic points occur at λ = 413 and 518 nm (Figure 5, left). such as 2,9-dibromo-1,10-phenanthroline and 6,6′-dibromo-2,2′-bi-
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1
pyridine were used without further purification. L and 1 were syn- at 80 °C. 2,9-Dibromo-1,10-phenanthroline-5,6-dione (618 mg,
thesized as described previously.[
6]
1.68 mmol) was likewise dissolved in a minimal amount of absolute
EtOH at 80 °C. The fully dissolved dione was poured directly into
the stirred solution of o-phenylenediamine. Within seconds, a fluffy
light green precipitate began to form. The mixture was further
heated to reflux for 15 min and then stirred for another 15 min.
After cooling to room temperature, the solid was separated by cen-
trifugation and was washed with EtOH until the wash turned from
light orange to light green. The solid was further washed twice with
diethyl ether and dried under high vacuum to give a light green
2
Ligand L : First, 1,2-bis(4-methoxyphenyl)diselane was prepared by
dissolving 4-bromoanisole (5.0 mL, 40.0 mmol) in dry tetrahydro-
furan (THF; 800 mL) cooled to –65 °C. 1.5
was added slowly with stirring. The temperature of the reaction
mixture was increased to 0 °C, and the stirring was continued for
.5 h. Se powder (3.54 g, 44.8 mmol) was added in a single portion.
After 20 min, the temperature was increased to room temperature,
and the reaction mixture was stirred for an additional 100 min. A
saturated aqueous NH Cl solution (40 mL) was added slowly until
no gas was released. The reaction mixture changed to orange, and
M tBuLi in pentane (55 mL)
1
powder. Yield 83 %. 1H NMR (300 MHz, CDCl ): δ = 7.96 (d, J =
3
4
8
3
.40 Hz, 2 H), 7.97 (dd, J = 6.50, 3.40 Hz, 2 H), 8.35 (dd, J = 6.50,
.40 Hz, 2 H), 9.45 (d, J = 8.44 Hz, 2 H) ppm. ESI-MS: m/z = 440.09
a yellow precipitate formed. The product was extracted with Et O
and isolated by silica gel chromatography (eluent: 65 % CH Cl +
5 % n-hexane). ESI-MS: m/z = 374.12. H NMR (300 MHz, CDCl ):
2
+
+
+
4
[M + H] , 462.80 [M + Na] , 902.62 [2 M + Na] . L was synthesized
2
2
1
under Schlenk-line conditions according to a modified literature
3
3
[
14]
3
3
procedure.
Three separate 20 mL vials were equipped with stir-
δ = 3.79 (s, 6 H), 6.81 (d, 4 H, J = 6.00 Hz), 7.52 (d, 4 H, J = 9.00 Hz)
ppm. 1 C{ H} NMR (75.47 MHz, CDCl ): δ = 55.16, 110.19, 114.59,
3
1
ring magnets. diBr-dppz (100 mg, 0.226 mmol) was weighed into
vial A, which was then capped with a rubber septum, purged three
times, and left under an Ar flow; a minimum amount of dry DMSO
was then added to dissolve the diBr-dppz. Similarly, 1,2-diphenyldi-
selane (141 mg, 0.452 mmol) was weighed into vial B, deaerated,
and then dissolved in a minimum amount of dry DMSO. Hydrazine
monohydrate (12.669 μL, 0.260 mmol) was then added to vial B.
Sodium methoxide (48.84 mg, 0.904 mmol) was weighed into vial C,
deaerated, and dissolved in a minimal amount of dry DMSO with
gentle heating. The contents of vial C were then transferred into
vial B with a syringe; vial C was rinsed with a small amount of dry
DMSO, which was also added to vial B. The mixture in vial B was
stirred for 5–10 min and then transferred into vial A, which was
then placed in an oil bath preheated to 110 °C. Within minutes, the
yellow mixture turned deep red, was then left under positive argon
pressure for 8 h, and subsequently cooled to room temperature.
The solution was added to chloroform (ca. 50 mL), which was then
extracted twice with deionized water and twice with a saturated
NH Cl solution. The organic phase was then dried with Na SO and
3
2
1
21.79, 135.27 ppm. To prepare L , 6,6′-dibromo-2,2′-bipyridine
4.8 mmol) was treated with 1,2-bis(4-methoxyphenyl)diselane
7.2 mmol) and CsOH·H O (13.1 mmol) in dry dimethyl sulfoxide
DMSO; 14.4 mL) under argon at 110 °C for 6 h. After the reaction,
the DMSO was evaporated with a Kugelrohr apparatus. The remain-
ing solid was cooled to room temperature and washed five times
with H O. The ligand was purified by silica gel column chromatogra-
phy (eluent: 65 % CH Cl , 35 % n-hexane; air pressure 0.4 bar). Yield
1 % (white microcrystalline product). ESI-MS: m/z = 529.06. H NMR
500.13 MHz, CDCl ): δ = 6.94 (m, 6 H), 7.51 (dd, 2 H J = 6.00 Hz),
.66 (d, 4 H, J = 5.00 Hz), 8.18 (d, 2 H, J = 5.00 Hz) ppm. C{ H}
NMR (DEPT, 125.76 MHz, CDCl ): δ = 55.37, 115.48, 117.51, 118.50,
24.05, 137.94, 138.51, 153.96, 159.26, 160.63 ppm. Se NMR
95.38 MHz, CDCl ): δ = 453.7 ppm. C H N O Se (526.34): calcd.
C 54.77, H 3.83, N 5.32; found C 54.96, H 3.70, N 5.51.
(
(
(
2
2
2
2
1
6
(
7
3
3
13
1
3
7
7
1
(
3
24 20
2
2
2
[
6]
Complex 2: Complex 2 was prepared in the same manner as 1
2
by first treating L with RuCl ·nH O in ethylene glycol (solvent and
3
2
4
2
4
II
2
reducing agent) in the presence of LiCl to obtain [Ru (L ) Cl ] and
then replacing the Cl ligands with H O to yield 2 with PF countera-
nions. Yield 74 %. ESI-MS: m/z = 577.18. H NMR (400 MHz, CDCl ):
δ = 6.71 (d, 1 H, J = 6.5 Hz), 6.84 (d, 1 H, J = 7.9 Hz), 6.88, (d, 1 H,
J = 7.83 Hz), 7.23 (d, 1 H, J = 8.32 Hz), 7.25–7.50 (m, 18 H), 7.58 (dt,
H, J = 7.83 Hz), 7.61 (d, 2 H, J = 6.35 Hz), 7.66 (t, 1 H, J = 7.83 Hz),
.73 (d, 2 H, J = 6.35 Hz), 7.85 (d, 1 H, J = 7.82 Hz), 7.90 (d, 1 H, J =
.83 Hz), 8.20 (d, 1 H, J = 7.34 Hz), 8.35 (d, 1 H, J = 7.34 Hz) ppm.
2
2
filtered, the solvents were evaporated to dryness from DMSO, and
the product was left under high vacuum at 70 °C overnight. The
solid crude product was then purified by column chromatography
2
6
1
3
(silica; 100 % chloroform); the slowest-moving products were col-
lected first (retention factor of 0.23 on a TLC plate). A second col-
2
7
7
umn (silica; 100 % DCM) was used for the final purification to give
1
a bright yellow product. Yield 66 %. H NMR (500 MHz, CDCl ), δ =
3
7.41 (d, J = 8.55 Hz, 2 H), 7.46–7.54 (m, 6 H), 7.86 (dd, J = 6.71,
C H N O Se Ru(H O) (663.44): calcd. C 31.01, H 2.81, N 2.89;
24
20
2
2
2
2
2
3.05 Hz, 2 H), 7.90 (dd, J = 7.63, 2.14 Hz, 4 H), 8.27 (dd, J = 6.71,
found C 30.54, H 2.78, N 3.02.
13
3
.66 Hz, 2 H), 9.27 (d, J = 8.55 Hz, 2 H) ppm. C NMR: δ = 127.53,
3
1
124.90, 127.91, 129.27, 129, 43, 129.90, 130.36, 133.57, 136.60,
Ligand L and Complex 3: L (0.022 mmol, 10.2 mg) was treated
with fuming HNO (1.0 mL) and 98 % H SO (1.0 mL), which were
added dropwise with the reaction mixture cooled to ca. 0 °C. The
reaction mixture was stirred for an additional 2 d and then neutral-
ized to pH 10 with a saturated aqueous solution of Na CO . The
+
1
6
40.90. 142.36, 147.64, 164.72 ppm. ESI-MS: m/z = 594.8 [M + H] ,
3
2
4
+
+
16.98 [M + Na] , 1210.92 [2 M + Na] . C H N Se (592.41): calcd.
30 18
4
2
C 60.82, H 3.06, N 9.46; found C 60.20, H 3.00, N 9.23.
2
3
Complexes 4a and 4: Compound 4a was prepared by treating L4
product was extracted with CH Cl and EtOAc, dried, and separated
2
2
(
433.5 mg, 730 μmol) and [Ru(COD)Cl ] (85 mg, 303 μmol) in puri-
2
by preparative TLC (eluent: 100 % CH Cl ). The product was charac-
terized by ESI-MS, which showed mostly the desired L with ca.
0 % mononitrated and trinitrated derivatives. Yield 55 %. Com-
pound 3 was prepared in the same way as 1. Yield 83 %. The ESI
mass spectrum showed more than 95 % of the molecular cation at
2
2
fied THF (10 mL) in a pressure tube equipped with a stirring magnet
at 90 °C for 24 h. The dark blue crude solid obtained was washed
several times with THF until the wash was faint blue. Then, the solid
was washed with n-hexane until the filtrate was colorless. The dark
black-blue solid was then dissolved in DCM, the solution was fil-
tered, and the solvents were evaporated to dryness. The product
was purified by column chromatography, first with 100 % DCM to
3
1
II
3
2+
m/z = 1213.80 for [Ru (L ) ]
.
2
4
Ligand L : First, 2,9-dibromo-1,10-phenanthroline-5,6-dione was
prepared according to a known procedure and used without further
remove L4 and then with EtOH/DCM (3:7) to give the black-deep
purification.[
12]
Then, 2,9-dibromodipyrido[3,2-a:2′,3′-e]phenazine
blue crystalline product (82 % yield). H NMR (500 MHz, CDCl ): δ =
1
3
(
diBr-dppz) was prepared by modification of a known procedure
Thus, o-phenylenediamine (185 mg,
.71 mmol) was dissolved in a minimal amount of absolute EtOH
7.17 (d, J = 8.54 Hz, 2 H), 7.28–7.55 (m, 16 H), 7.68 (d, J = 8.70 Hz,
2 H), 7.86–7.96 (m, 8 H), 8.28 (dd, J = 1.00 Hz, 2 H), 8.33 (dd, J =
1.00 Hz, 2 H), 8.99 (d, J = 8.54 Hz, 2 H), 9.17 (d, J = 8.70 Hz, 2 H)
[13]
for the synthesis of dppz.
1
Eur. J. Inorg. Chem. 2016, 2757–2763
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1
Table 2. Crystallographic data for [RuL tpyO].
1
1
[
RuL tpyO]/CHCl
3
[RuL tpyO]/H
2
O
Empirical formula
Formula mass [g mol–1
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
C
37
H
27
N
5
ORuSe
2
·2(NO
3
)·2.6(CHCl
3
)
C
37
H
27
N
5
ORuSe ·2(F P)·2(C H O)
2 6 3 6
]
1251.21
monoclinic
P2 /m
13.004(3)
27.218(5)
13.961(3)
90
109.51(3)
90
4657.8(18)
2
1222.72
triclinic
P1¯
1
13.208(2)
14.253 (2)
14.974 (2)
106.954(5)
104.553(5)
111.569(6)
2295.0(5)
2
ꢀ
[°]
γ [°]
3
V [Å ]
Z
D
calcd. [g cm–3]
1.784
2.404
1.769
2.093
μ [mm–1
]
Collected reflections
Unique reflections
89700
9701
32686
10249
R
int
0.039
0.055
R(F)[ [I > 2σ(I)]
a]
0.0630
0.1623
1.075
0.0440
0.1029
1.013
2
[a]
wR(F ) (all data)
GOF
o c o o c o
a] R = Σ||F – F ||/Σ|F |; wR(F ) = {Σ[w(F – F
2)2]/Σ[w(F ) ]}1/2.
2
2
2 2
[
–
2–
ppm. ESI-MS: m/z = 1321 [M – Cl] , 643.17 [M – 2 Cl] . This com-
1 H), 8.31 (t, 1 H), 8.57 (m, 2 H), 8.70 (d, 1 H), 8.79 (d, 1 H), 8.83 (d,
pound was then treated as reported with NH PF and HPF in water
to yield 4. H NMR (300 MHz, [D ]DMSO): δ = 7.24–7.63 (m, 18 H),
.71 (d, J = 8.80 Hz, 1 H), 7.86–7.96 (m, 4 H), 8.03–8.17 (m, 5 H),
.32–8.47 (m, 4 H), 9.07 (d, J = 8.62 Hz, 1 H), 9.14 (d, J = 8.53 Hz, 1
H), 9.28 (d, J = 8.62 Hz, 1 H), 9.36 (d, J = 8.71 Hz, 1 H) ppm.
NMR (121 MHz, CDCl ): δ = –143.45 (sept, J = 714 Hz, 1 P) ppm.
NMR (282 MHz, CDCl ): δ = –73.33 (d, J = 714 Hz, 6 F) ppm. ESI-MS:
m/z = 1321 [M – H O] , 643.49 [M – H O – Cl] , 1330.49 [2 M –
1 H), 8.91 (dd, 2 H), 9.2 (d, 1 H) ppm. 13C NMR (400 MHz, [D ]DMSO):
4
6
6
6
1
δ = 122.80, 123.64, 123.80, 123.93,124.23, 124.28, 127.29, 127.31,
127.45, 127.51, 127.66, 127.73, 128.16, 129.52, 129.76, 130.92,
131.19, 131.73, 136.29, 136.39, 136.44, 136.50, 136.53, 137.59,
137.83, 138.86, 142.41, 152.75, 152.83, 155.30, 157.87, 158.01,
6
7
8
31
P
F
19
77
159.09, 159.29, 162.09, 168.10, 168.29 ppm. Se NMR (95.38 MHz,
3
2+
CDCl ): δ = 496, 1040 ppm. ESI-MS: m/z =408.59 [M/2] . Crystals
3
3
–
2–
suitable for structural determination by X-ray diffraction were ob-
2
2
–
1
H O] /2. C H N Se Ru(H O) (729.51): calcd. C 48.55, H 2.58, N
tained as follows: From chloroform: [RuL tpyO][PF ] was first puri-
2
30 18
4
2
2
2
6 2
7
.55; found C 47.37, H 2.58, N 7.57.
fied by column chromatography with acetonitrile/H O (9:1) satu-
2
1
rated with KNO
3
; after the removal of the acetonitrile, crystals of
Complex 5: [Ru(tpy)Cl ] (0.44 g, 1 mmol) and L (0.47 g, 1 mmol)
3
1
[
[
RuL tpyO][NO ] were grown from CHCl /CH Cl . From water:
3
2
3
2
2
were heated to reflux for 4 h in EtOH/H O (75:25; 60 mL) containing
2
1
RuL tpyO][PF ] was dissolved and infused with acetone.
6
2
LiCl (0.1 g, 12 mmol) and triethylamine (0.2 mL) as a reductant. The
hot mixture was filtered, and the ethanol was removed with a rotary
evaporator. The resulting solid was collected by filtration, washed
with water, and dried under vacuum. The crude product was dis-
solved in acetonitrile (2.0 mL) and water (17 mL). HPF6 (65 % in
water; five drops) and NH PF (702 mg) in H O (8.8 mL) were added.
1
X-ray Structure Determination: The crystal data of [RuL tpyO]-
PF6]2 were collected at 100 K with a Bruker Kappa ApexII CCD
[
diffractometer with Mo-Kα (λ = 0.71073 Å) radiation and Miracol
optics. The data were processed with the Bruker Apex2 suite, and
the structure was solved by direct methods in SHELXT-2013. Full-
matrix least-squares refinement was based on F with SHELX-2013.
Selected crystallographic data are presented in Table 2. CCDC
4
6
2
The precipitate was collected and extracted, washed four times with
2
0
.1
M
HPF (100 mL), and dried under vacuum overnight to yield a
6
1
purple solid. Yield: 37.3 %. H NMR (300 MHz, [D ]DMSO): δ = 6.47
1
1
6
1451440 (for [RuL tpyO]/CHCl ) and 1451441 (for [RuL tpyO]/H O)
3
2
(
7
d, 1 H, 9 Hz), 7.08 (dt, 2 H, 9 Hz), 7.28 (t, 2 H, 9 Hz), 7.36–7.50 (m,
H), 7.56 (d, 1 H, 9 Hz), 7.68–7.75 (m, 3 H), 8.01 (t, 2 H, 9 Hz), 8.14
t, 1 H, 9 Hz), 8.21 (d, 2 H, 6 Hz), 8.36 (d, 1 H, 9 Hz), 8.63 (t, 3 H,
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre.
(
1
3
9
1
1
1
1
5
Hz), 8.70 (d, 2 H, 9 Hz) ppm. C NMR (75 MHz, [D ]DMSO): δ =
6
21.62, 121.75, 122.92, 123.89, 127.12, 127.90, 127.99, 129.41,
30.50, 130.59, 131.01, 132.11, 135.50, 135.57, 135.74, 136.22,
36.61, 136.74, 137.33, 138.06, 153.97, 158.26, 160.14, 160.22,
Acknowledgments
7
7
60.77, 167.97, 169.17 ppm. Se NMR (95.38 MHz, CDCl ): δ = 489, This research was supported by the Helen and Martin Kimmel
3
04 ppm.
Center for Molecular Design and the Peter and Bernice Cohn
Catalysis Fund. R. N. is the Rebecca and Israel Sieff Professor of
dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (5 mL), and the solu- Chemistry. Dr. Alexander Khenkin is thanked for his help with
Activation of O : The monoaqua compound 5 (0.1 mmol) was then
2
tion was stirred under 1 bar of O for 24 h. The solvent was removed the analysis of the kinetic experiments.
2
by evaporation, and then the solid was washed with chloroform
and dried in vacuo to obtain the black oxido compound
1
1
[
6
RuL tpyO][PF ]. H NMR (400 MHz, [D ]DMSO): δ = 6.41 (dd, 1 H), Keywords: Oxygen · Ruthenium · Selenium · O–O
6
6
.81 (dt, 1 H), 7.04 (td, 2 H), 7.12 (m, 5 H), 7.30 (m, 3 H), 7.41 (tt, 1
H), 7.53 (dt, 1 H), 7.63 (d, 1 H), 7.67 (t, 1 H), 7.91 (dt, 1 H), 8.17 (dt,
activation · N ligands
Eur. J. Inorg. Chem. 2016, 2757–2763
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Published Online: April 24, 2016
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim