Stoichiometric C-H Bond Cleavage Reaction in a Bis(carboxylato)ruthenium(II) Complex and Its Application to the Catalytic H-D Exchange Reaction of Carboxylic Acids

Article abstract of DOI:10.1002/cctc.201200686

A cationic complex [Ru{OC(O)CMe=CH₂-κ²O,O'}(PMe₃)₄]⁺CH₂=CMeCO₂^- (5a) and its related carboxylato complexes are newly prepared by the reaction of [cis-RuH₂(PMe₃)₄] (4) with carboxylic acids in methanol in 76-100% yield. Complex 5a reversibly transforms to the neutral form [cis-Ru{OC(O)CMe=CH₂-κ¹O}₂(PMe₃)₄] (2a) in nonpolar solvents. Complex 2a reversibly liberates a PMe₃ group to give [Ru{OC(O)CMe=CH₂-κ¹O}{OC(O)CMe=CH₂-κ²O,O'}(PMe₃)₃] (12a) from which a stereoselective C-H bond cleavage reaction occurs to give a ruthenalactone [Ru{OC(O)CMe=CH-κ²O,C}(PMe₃)₄] (1a) from the release of methacrylic acid. Complexes 2a and 5a also give 1a but the prior dissociation of a PMe₃ is indispensable for the C-H bond cleavage reaction. Complex 1a establishes an equilibrium with 2a (or 5a) in solution. In this reaction, one coordinated carboxylato ligand is engaged in the C-H bond cleavage reaction as a proton acceptor, but neither the added carboxylato anion nor typical proton acceptors such as proton sponge assist the reaction. In [D₄]MeOH, a catalytic stereospecific deuteration of carboxylic acids has been achieved by 4, in which the equilibrium between 5a and 1a plays a key role.

Full text of DOI:10.1002/cctc.201200686

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DOI: 10.1002/cctc.201200686
Stoichiometric CÀH Bond Cleavage Reaction in
a Bis(carboxylato)ruthenium(II) Complex and Its
Application to the Catalytic H–D Exchange Reaction of
Carboxylic Acids
Masafumi Hirano,* Ryo Fujimoto, Kohei Hatagami, Nobuyuki Komine, and
Sanshiro Komiya*[a]
A cationic complex [Ru{OC(O)CMe=CH2-k2O,O’}(PMe3)4]+CH2= of methacrylic acid. Complexes 2a and 5a also give 1a but
À
CMeCO2 (5a) and its related carboxylato complexes are newly
prepared by the reaction of [cis-RuH2(PMe3)4] (4) with carboxyl-
ic acids in methanol in 76–100% yield. Complex 5a reversibly
transforms to the neutral form [cis-Ru{OC(O)CMe=CH2-
k1O}2(PMe3)4] (2a) in nonpolar solvents. Complex 2a reversibly
the prior dissociation of a PMe3 is indispensable for the CÀH
bond cleavage reaction. Complex 1a establishes an equilibri-
um with 2a (or 5a) in solution. In this reaction, one coordinat-
ed carboxylato ligand is engaged in the CÀH bond cleavage
reaction as a proton acceptor, but neither the added carboxy-
lato anion nor typical proton acceptors such as proton sponge
assist the reaction. In [D4]MeOH, a catalytic stereospecific deut-
eration of carboxylic acids has been achieved by 4, in which
the equilibrium between 5a and 1a plays a key role.
liberates
a
PMe3 group to give [Ru{OC(O)CMe=CH2-
k1O}{OC(O)CMe=CH2-k2O,O’}(PMe3)3] (12a) from which a stereo-
selective CÀH bond cleavage reaction occurs to give a ruthena-
lactone [Ru{OC(O)CMe=CH-k2O,C}(PMe3)4] (1a) from the release
Introduction
The activation of an inactive CÀH bond by transition metal
complexes is a new frontier in synthetic organic chemistry.[1]
Together, these stoichiometric and catalytic reactions provide
new methodologies in this field. We have previously reported
internal CÀH bond cleavage reactions in RuII[2] and PtII[3] com-
plexes that have a metalÀchalcogen bond. Interestingly, a late-
transition-metal complex that has two metalÀchalcogen
bonds, such as bis(arenethiolato) or bis(aryloxo) complexes,
showed quite high activity toward the internal CÀH (and CÀO)
bond activation reaction.[2b,e,3] We have also documented a stoi-
chiometric reaction of [Ru(h4-1,5-COD)(h6-1,3,5-COT)]/PMe3
(COD=cyclooctadiene, COT=cyclooctatriene) with methacrylic
Scheme 1. Bis(methacrylato)ruthenium(II) intermediate 2a.
cleavage reaction. The carboxylato anion is currently employed
as a good hydrogen acceptor, or more precisely, as a proton
acceptor[5] in some catalytic processes, and this concept is
a breakthrough in catalysis that involves a CÀH bond cleavage
step in inactive compounds.[6] Moreover, the addition of car-
boxylic acids as cocatalysts is known to enhance some catalytic
CÀH bond activation processes promoted by bis(carboxylato)
acid to produce
a
ruthenalactone [Ru{OC(O)CMe=CH-
k2O,C}(PMe3)4] (1a) by the CÀH bond cleavage reaction
(Scheme 1).[4]
During the formation of 1a, an elusive intermediate as-
signed to a new bis(methacrylato) complex, [cis-Ru{OC(O)CMe= complexes of PdII and RuII.[7] Despite such an outstanding po-
CH2-k1O}2(PMe3)4] (2a), was observed as a key compound for
the internal CÀH bond cleavage reaction. We have retained
a strong interest in 2a because one of its carboxylato ligands
is considered to act as a hydrogen acceptor for the CÀH bond
tential for the carboxylato complexes, detailed studies that
focus on their reactivities, particularly on CÀH bond activation,
are largely unknown at the molecular level.
In pioneering work that focused on carboxylato complexes
and CÀH bond activation, Sakaki and co-workers shed light on
Fujiwara’s early finding of catalytic CÀH bond activation pro-
moted by a (carboxylato)palladium(II) complex that used
[PdCl2](styrene)/acetic acid or [Pd(OAc)2]/styrene/acetic acid[8]
and theoretically revealed the role and importance of the car-
boxylato ligand in [Pd(O2CH-k2O,O’)2] in CÀH bond cleavage re-
actions.[9] Afterwards, Davies, Macgregor and a co-worker
documented the role of the acetato ligand in the PdII complex
[a] Prof. M. Hirano, R. Fujimoto, K. Hatagami, N. Komine, Prof. S. Komiya
Department of Applied Chemistry
Tokyo University of Agriculture and Technology
2-24-16 Nakacho, Kongai, Tokyo 184-8588 (Japan)
Fax: (+81)423-887-044 (MH), (+81)423-887-043 (SK)
(MH), (SK)
E-mail: hrc@cc.tuat.ac.jp
komiya@cc.tuat.ac.jp
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As a typical example, the characterization of cat-
ionic methacrylato complex 5a is described. The
31P{1H} NMR spectrum of 5a in [D4]MeOH showed
a typical A2X2 pattern at d=À1.08 and 22.29 ppm,
which suggests a cis configuration in an octahedral
geometry. In the 1H NMR spectrum, a virtual triplet
and a multiplet at d=1.43 (18H) and 1.45 ppm (18H)
are assigned to the mutually trans and cis PMe3 li-
gands, respectively. A set of singlets at d=1.89 (s,
3H), 5.49 (s, 1H), and 5.98 ppm (s, 1H) are assigned
as the coordinating methacrylato resonances. As the
intensity of the resonances at d=1.87 (3H), 5.18
(1H), and 5.70 ppm (1H) increased upon the stepwise
addition of sodium methacrylate without change to
the chemical shift or half-widths, these resonances
are assigned to the liberated methacrylato anion. The
IR spectrum of 5a in KBr involves intense bands at
Scheme 2. Six- and four-membered transition states for CÀH bond activation.
is to abstract the agostic H atom via a six-membered transition
state rather than the alternative four-membered state
(Scheme 2).[10]
However, detailed experimental studies on stoichiometric re-
actions of carboxylato complexes on CÀH bond activation still
remain largely unexplored, although several CÀH bond activa-
tion processes by isolable mono(carboxylato)palladium(II) com-
plexes have been elucidated.[11] Such studies would provide an
intrinsic understanding of the nature of carboxylato complexes
of late transition metals, and the bis(carboxylato) complex 2
would be one of the best examples to achieve this.
In this article, we report the isolation of a series of RuII com-
plexes with mono- and bis(carboxylato) groups, a mechanism
for the CÀH bond cleavage reaction, and an application
toward the catalytic H–D exchange reaction of carboxylic acids
by the CÀH bond cleavage reaction.
1597(vs) and 1429(s) cmÀ1, probably assignable to the asym-
metric and symmetric stretching vibration of the C=O bond in
the methacrylato anion. Nakamoto documented the relation-
ship between the coordination mode of a carboxylato ligand
and the differential frequency between the asymmetric and
symmetric nCO bands (D) for which bidentate, ionic, and mon-
odentate carboxylato ligands have D=42–190, 164–201, and
228–470 cmÀ1, respectively.[12] According to this criterion, the
value observed (D=168 cmÀ1) is an intermediate between the
bidentate and ionic carboxylato ligands.
Results and Discussion
Preparation of (carboxylato)ruthenium(II) complexes
Cationic carboxylato complexes
An independent experiment of the reaction of 4 with meth-
acrylic acid under reduced pressure showed the formation of
H2 in 160% yield by using Tçpler pump and GLC analyses.
These spectroscopic and physical data are consistent with the
formation of 5a.
The recrystallization of 5a–f failed, but the addition of KBPh4
to a methanol solution of 5a immediately resulted in a pale-
yellow precipitate. Recrystallization of this precipitate from
cold acetone gave the analytically pure corresponding borate
salt 6a as pale-yellow columns in 54% yield [Eq. (2)].
The 31P{1H} NMR spectrum of 6a in [D6]acetone shows an
A2X2 pattern at d=À0.47 and 22.73 ppm. The 1H NMR spec-
trum is quite similar to that of 5a, but the resonances from
the noncoordinating methacrylato anion were replaced by
those for BPh4À. The IR spectrum in KBr showed a weak band
at 1579 cmÀ1 and an intense band at 1427 cmÀ1, which sug-
gests asymmetric and symmetric nCO bands for the coordinat-
As briefly described in the introduction, we have previously
unsuccessfully tried to prepare [Ru{OC(O)R}2(PMe3)4] (2) from
[Ru(h4-1,5-COD)(h6-1,3,5-COT)]. Instead, an aqua complex
[cis,fac-Ru{OC(O)CMe=CH2-k1O}2(PMe3)3(H2O)]
(3a)[4]
was
formed by the reaction with a trace amount of contaminated
water. Our next strategy was the metathesis reaction of [RuCl2-
(PMe3)4] with a carboxylate salt, but this method also gave
a complex mixture. Protonolysis of [cis-RuH2(PMe3)4] (4) with
carboxylic acid in benzene produced a certain amount of 2,
but it decomposed during the work-up. However, we finally
succeeded to prepare cationic mono(carboxylato)ruthenium(II)
5, an ionized isomer of 2, by employing methanol as a solvent,
and 5 was obtained in 76–100% yield [Eq. (1)]. The quantita-
tive formation of 5a–f was observed by NMR studies in
[D4]MeOH.
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bis(methacrylato)ruthenium(II) complex 2a in a nonpolar sol-
vent. Thus, we recrystallized 5a from carefully distilled water-
and oxygen-free THF and hexane to give pale-yellow single
crystals of 2a in 70% yield [Eq. (3)].
ing carboxylato ligand, respectively. This differential (D=
152 cmÀ1) is consistent with k2 coordination of the carboxylato
group.
The molecular structure of 6a is depicted in Figure 1. The
cationic ruthenium fragment has a k2-methacrylato group in
a slightly distorted octahedral geometry. No significant differ-
The 31P{1H} NMR spectrum of 2a in [D6]benzene shows an
1
A2X2 pattern at d=À2.62 and 14.57 ppm. In the H NMR spec-
trum, a multiplet at d=1.07 ppm (18H) and a virtual triplet at
d=1.33 ppm (18H) are assigned to the mutually cis and trans
PMe3 ligands. A set of resonances at d=2.28 (s, 6H), 5.34 (dd,
2H), and 6.29 ppm (d, 2H) are assigned to the methyl and al-
kenyl protons, which suggests that two methacrylato ligands
are equivalent. The IR spectrum of 2a in KBr showed an in-
tense band at 1562 cmÀ1 assigned to the asymmetric nCO
band, but the corresponding symmetric nCO band is obscure.
More unambiguous structural information was obtained from
the XRD structure analysis (Figure 2).
The Ru(1)ÀO(1) and Ru(1)ÀO(3) [2.153(2) and 2.182(2) ꢁ]
bond lengths are typical of RuÀO covalent bonds. However,
those of Ru(1)ÀO(2) and Ru(1)ÀO(4) are beyond covalent
bonds [more than 3.3 ꢁ]. These two methacrylato groups are
thus regarded as k1-carboxylato ligands. The C(2)ÀC(3) and
C(6)ÀC(7) [1.331(4) and 1.341(5) ꢁ] bond lengths indicate their
C=C character. Therefore, these methacrylato groups have
Figure 1. Molecular structure of 6a. All H atoms and the borate anion are
omitted for clarity. Ellipsoids represent 50% probability.
ence was observed in the Ru(1)ÀO(1) and Ru(1) ÀO(2)
[2.2193(12) and 2.2130(13) ꢁ] and C(1)ÀO(1) and C(1)ÀO(2)
[1.275(2) and 1.269(2) ꢁ] bond lengths. However, the Ru(1)À
P(1) and Ru(1)ÀP(4) distances [2.3871(4) and 2.3810(4) ꢁ] are
significantly longer than those of Ru(1)ÀP(2) and Ru(1)ÀP(3)
[2.2489(5) and 2.2619(5) ꢁ], probably because of the strong
trans influence of PMe3.[13] Notably, the torsion angles of O(1)À
C(1)ÀC(2)ÀC(3) and O(2)ÀC(1)ÀC(2)ÀC(3) are 2.0(2) and
À177.99(16)8, respectively, which suggests conjugation of the
p orbitals among these atoms.
Neutral bis(carboxylato) complexes
The NMR spectra of 5a measured in [D6]benzene revealed two
1
methacrylato groups in the H NMR spectrum that were equiv-
alent to an A2X2 pattern in the 31P{1H} NMR spectrum along
with the presence of a small amount of the aqua adduct 3a.
This means that the two methacrylato ligands are completely
equivalent, which suggests the conversion of 5a to the neutral
Figure 2. Molecular structure of 2a. All H atoms are omitted for clarity. Ellip-
soids represent 50% probability.
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cisoid and transoid conformations in the solid state. However,
the cisoid and transoid conformers would change quickly in
solution because these methacrylato groups are observed to
be equivalent in the 1H NMR spectrum.
Other carboxylato complexes
Andersen and Mainz reported the formation of [cis-Ru(OAc-
k1O)2(PMe3)4] from the phosphine exchange reaction of
[Ru(OAc-k2O,O’)2(PPh3)2] with PMe3.[14] This method is also a po-
tential route to 2 and related compounds with PMe3 ligands.
By a modification of this method, we prepared the bis(carboxy-
lato) complex of PPh3 as the first step to 2. The metathesis re-
action of [RuCl2(PPh3)3] with five equivalents of sodium metha-
crylate produced a bis(triphenylphosphine) complex, [trans-
Ru{OC(O)CMe=CH2-k2O,O’}2(PPh3)2] (7a), and the related tris(tri-
phenylphosphine) complexes 8a and 8 f were obtained with
one equivalent of sodium carboxylate (Scheme 3).
Figure 3. Molecular structure of 9a. All H atoms are omitted for clarity. Ellip-
soids represent 50% probability.
structural information that 9a has k1- and k2-methacrylato
groups with a meridional TRIPHOS ligand (Figure 3).
The addition of excess PMe3 to the carboxylato(chlorido)
complexes 8a or 8 f in boiling hexane produced [cis-
Ru{OC(O)R-k1O}Cl(PMe3)4] [R=CMe=CH2 (10a), Ph (10 f)] in 72–
84% yield [Eq. (5)].
Scheme 3. Metathesis reactions that use carboxylato anions.
However, attempts to prepare 2a by the addition of PMe3 to
7a gave a complex mixture that involved 5a. However, the
treatment of 7a with TRIPHOS (Ph2PC2H4PPhC2H4PPh2) pro-
duced analytically pure pale-yellow crystals of 9a in 86% yield
[Eq. (4)].
The treatment of 2a with DMPE (Me2PC2H4PMe2) in benzene
at 708C resulted in a phosphine-exchange reaction that gave
[cis-Ru{OC(O)CMe=CH2-k1O}2(DMPE)2] (11 a) in 45% yield
[Eq. (6)].
The NMR spectrum of 9a showed dynamic behavior in solu-
tion, which was probably a result of the flexibility of the TRI-
PHOS ligand and not because of the fluxionality of the metha-
crylato fragments as these magnetically inequivalent methacry-
lato resonances remained sharp throughout the variable-tem-
perature NMR experiments. XRD analysis provided compelling
Notably, Field and co-workers have recently documented
the direct formation of a similar compound [cis-Ru{OC(O)Me-
k1O}2(DMPE)2] by the reaction of [cis-RuMe2(DMPE)2] with
CO2,[15] and Bergman and co-workers have reported the forma-
tion of [cis-Ru{OC(O)Ph-k1O}2(DMPE)2] by the acidolysis of [cis-
RuMe2(DMPE)2] with benzoic acid.[16]
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Reactions of (carboxylato)ruthenium(II) complexes
water in [D6]benzene gave 3a instantly and quantitatively
[Eq. (9)].
Reversible dissociation of PMe3 and the formation of aqua
adducts
Complex 2a, which has four PMe3 ligands, is prone to the lib-
eration of a PMe3 ligand by heat or even at room temperature
(RT). Heating solid 2a without solvent at 908C under vacuum
produced a k1- and k2-methacrylato complex with three PMe3
ligands 12a [Eq. (7)].
Alternatively, 3a can be prepared by the reaction of 2a with
water. However, this reaction did not reach completion and
gave a mixture of 2a and 3a in 26 and 74%, respectively. The
liberated PMe3 probably suppresses the formation of 3a. In
the case of the benzoato complex 2 f, the aqua complex 3 f
was obtained by the treatment of 2 f with water in 48% yield
(95% by NMR). The molecular structure of 3 f is depicted in
Figure 4.
The 31P{1H} NMR spectrum of 12a in [D8]toluene showed
a slightly broad singlet at d=28.3 ppm at 208C, which broad-
ened on cooling. Although we could not stop the fluxionality
even at the lowest accessible temperature (À908C), we ob-
served two broad signals at around d=34 and 24 ppm in a 2:1
1
ratio. In the H NMR spectra, the three PMe3 and two metha-
crylato resonances were equivalent and appeared at 208C at
d=1.13 (27H), 2.16 (6H), 5.23 (2H), and 6.30 ppm (2H) but
they broadened significantly at À908C. This dynamic behavior
of 12a probably arises from rapid exchange between the k1-
and k2-methacrylato ligands through a five-coordinate inter-
mediate on the NMR time-scale. Although we could not deter-
mine the meridional/facial geometry of 12a because of the
fluxionality, we drew the meridional geometry in Equation (7)
in keeping with its analogue 9a.
If a [D6]benzene solution of 2a was heated, the reversible
formation of 12a and its aqua adduct 3a with the liberation of
a PMe3 ligand was observed. Compound 3a is formed by the
unavoidable contamination of water, and at low temperatures
(below 208C), the resonances of 3a and 12a could be sepa-
rately assigned in the NMR spectrum, however, they overlap at
temperatures near RT. Thus, we treated the total amount of
12a and 3a as a single RuP3 species for descriptive purposes
and evaluated the equilibrium that concerns the reversible lib-
eration of PMe3 by the van ’t Hoff plot [Eq. (8)].
Figure 4. Molecular structure of 3 f. All H atoms are omitted for clarity. Ellip-
soids represent 50% probability.
Although O(2) and O(4) are orientated toward O(5), the
O(5)ÀO(2) and O(5)ÀO(4) [2.600(4) and 2.631(4) ꢁ] distances are
significantly shorter than the sum of the van der Waals radius
of O [2.80 ꢁ].[17] Thus, these O atoms must interact weakly
through H bonding. The H atoms in the aqua ligand were
found from the differential Fourier map and they pointed at
the carbonyl O atoms in the benzoate ligands (not shown in
Figure 4).
This reaction is slightly exothermic, and the positive entropy
value is consistent with the liberation of a PMe3 ligand.
Comparatively, the bis(methacrylato)ruthenium(II) complex
with a bidentate ligand 11 a did not react with water even at
708C. Thus, the liberation of a phosphine ligand promotes the
formation of the aqua complex.
The aqua adduct 3a was also produced by the reaction of
12a with water. The treatment of 12a with one equivalent of
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Complex 3a reproduced 2a by the addition of PMe3 in
[D6]benzene, and the same reaction in [D4]MeOH gave 5a
(Scheme 4).
The van ’t Hoff plot for K2 (K2 =[2a]/[cation of 5a][methacrylato
anion]) in the range of À30 to 108C gave the following ther-
modynamic
parameters:
DH=À9.0 kJmolÀ1
,
DG298 =
À12 kJmolÀ1, DS=11 J molÀ1 KÀ1. This shows that the thermo-
dynamic energy difference between 5a and 2a is small and
a slightly positive entropy may suggest the slight association
of the solvent molecule for cationic 5a.
Formation of ruthenalactone by CÀH bond activation
Cationic carboxylato complexes
Heating 5a at 708C in the presence of 30 equivalents of 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) in [D6]DMSO produced
a ruthenalactone 1a in 93% yield within 10 h. If this reaction
took place in the presence of 30 equivalents of DBU and 10
equivalents of PMe3, the formation of 1a was significantly sup-
pressed (8% in 20 h and 63% in 457 h) [Eq. (10)].
Scheme 4. Reaction of 3a with PMe3.
Interconversion between cationic and neutral bis(carboxylato)
complexes
The results described above indicate the formation of cationic
mono(carboxylato)ruthenium(II) complex 5 and neutral bis(car-
boxylato)ruthenium(II) complex 2 depending on the solvent.
To clarify this solvent-dependent reaction, the isomerization
between 5a and 2a was observed by NMR spectroscopy
(Table 1).[18]
Similar treatment of the cationic complex 6a with 30 equiva-
lents of DBU at 708C gave 1a in 94% in 20 h. In the presence
of 10 equivalents of PMe3 under the same conditions, 6a gave
1a only in 23% after 291 h. The treatment of 6a with potassi-
um phenoxide also gave 1a in 79% yield. However, the treat-
ment of 6a with sodium methacrylate produced 1a only in
11% yield, and 1a was not formed by treatment with proton
sponge (1,8-bis(dimethylamino)naphthalene), NEt3, TMEDA
(Me2NC2H4NMe2), pyridine, or DMAP (4-N,N-dimethylaminopyri-
dine). These results suggest that i) the CÀH bond cleavage re-
action requires prior dissociation of PMe3, ii) some bases assist
the CÀH bond cleavage reaction but those abilities cannot be
explained by their basicity,[19] iii) the added carboxylato anion
does not promote the CÀH bond cleavage reaction at all, and
iv) this CÀH bond cleavage reaction is not a spontaneous de-
protonation from the carboxylato ligand.
As shown in Table 1, the forward and backward reactions
gave the same results within experimental errors, and the equi-
librium shifts to the 5a and 2a sides in polar and nonpolar sol-
vents, respectively. In acetone, a mixture of cationic and neu-
tral carboxylato complexes was observed. The formation of 3a
and 12a was suppressed at low temperature in [D6]acetone.
Table 1. Reversible isomerization between 5a and 2a.[a]
Single crystals of 1a were obtained from cold toluene/
hexane, and the molecular structure is depicted in Figure 5.
The overall structure of 1a is a ruthenalactone with an octa-
hedral geometry. The Ru(1)ÀC(3) and Ru(1)ÀO(1) bond lengths
are 2.0869(17) and 2.1428(15) ꢁ, respectively. One of the au-
thors previously reported the formation and molecular struc-
ture of [fac-RuH(CH=CMeCO2Bu-k2C,O)(PPh3)3] by the CÀH
bond activation of butyl methacrylate with [cis-RuH2(PPh3)4], in
which RuÀO is a coordinate bond.[20] According to this report,
the RuÀC and RuÀO distances are 2.061(10) and 2.246(7) ꢁ, re-
spectively. The similar length of the RuÀC bond and significant-
ly shorter RuÀO bond in 1a reflect covalent bonding charac-
ters for both. The O(2)ÀC(1) [1.234(3) ꢁ] and C(2)ÀC(3)
Solvent
Starting compound
NMR yield [%]
2a 3a+12a PMe3
5a
1
2
3
4
5
6
7
8
[D6]benzene 5a
[D6]benzene 2a
0
0
73
66
32 37
29 42
24
34
31
24
0
0
7
0
20
23
25
17
0
0
0
0
[D6]acetone
[D6]acetone
[D4]MeOH
[D4]MeOH
[D6]DMSO
[D6]DMSO
5a
2a
5a
2a
5a
2a
100
100
93
0
0
0
0
100
[a] T=208C, starting complex=0.020–0.025 mmol, solvent=550–600 mL.
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Figure 6. Molecular structure of 1 f. All H atoms are omitted for clarity. Ellip-
soids represent 50% probability.
Figure 5. Molecular structure of 1a. All H atoms are omitted for clarity. Ellip-
soids represent 50% probability.
crylic acid by base was key in this reaction. However, in spite
of almost the same basicity of DBU (pKa =12) and proton
sponge (pKa =12.34), the significant difference in their reactivi-
ties suggests that they do not perform just as Brønsted bases.
We believe that they participate in the CÀH bond cleavage
step (vide infra).
[1.340(3) ꢁ] bond lengths suggest double bond characters,
whereas O(1)ÀC(1) [1.295(2) ꢁ], C(1)ÀC(2) [1.494(3) ꢁ], and
C(2)ÀC(4) [1.512(3) ꢁ] are regarded as single bonds. This result
shows that an sp2 CÀH bond in the methacrylato ligand in 5a
or 6a is cleaved to give 1a.
Complex 1a shows an AM2X pattern at d=11.6, 0.22, and
À11.7 ppm in the 31P{1H} NMR spectrum in [D6]benzene, and
two doublets at d=0.88 (9H) and 1.09 ppm (9H) and a virtual
If we employed PMe3 as a base in this reaction, 1a was ob-
tained quantitatively in the presence of 30 equivalents of PMe3
in [D6]benzene at 708C, although the reaction was slow (175 h
at 708C). In this reaction, the formation of phosphabetaine
13a was observed, which was independently characterized by
the reaction of methacrylic acid with PMe3 (Scheme 5).[21]
1
triplet at d=0.96 ppm (18H) are observed in the H NMR spec-
trum. This pattern is consistent with the cis structure of 1a in
an octahedral geometry. The H NMR spectrum shows a singlet
1
at d=2.43 ppm (3H) and broad peak in the alkenyl region at
d=7.86 ppm (1H), which are assigned to the methyl and me-
thine protons, respectively.
Similarly, treatment of the benzoato complex 6 f with DBU
in [D6]DMSO at 1008C produced the corresponding ruthenalac-
tone 1 f in 43% yield (Figure 6).
Neutral carboxylato complexes
The reaction of 2a with a base showed a more complicated
result. For example, the treatment of 2a with five equivalents
of DBU in [D6]benzene at 708C for 3 h produced 1a in 49%
yield with the concomitant formation of a mixture of tris(phos-
phine) species 3a and 12a (41%) and liberated PMe3 (35%).
This reaction reached a steady state, which suggests the pres-
ence of an equilibrium between 1a and 2a. The yield of 1a in-
creased to 64% with an increase of DBU (10 equivalents), and
decreased to 31% with a decrease of DBU (one equivalent)
under similar conditions. The yield of 1a decreased to 6–9% if
proton sponge, pyridine, or 2,6-lutidine was employed in the
reaction. This suggests that the trapping of the evolved metha-
Scheme 5. Reaction of methacrylic acid with PMe3.
As the incorporation of a deuterium atom was observed in
the 2-position of the phosphabetaine if the reaction took place
in [D4]MeOH, the most probable formation mechanism of the
phosphabetaine would be the protonation of PMe3 by metha-
crylic acid to give [HPMe3]+[CH2=CMeCO2]À followed by hydro-
phosphination to the unsaturated counteranion.
Contrary to the PMe3 complex 2a, the reaction of the DMPE
analogue 11 a with PMe3 did not give the ruthenalactone but
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gave a cationic complex [Ru{OC(O)CMe=CH2-k1O}-
(DMPE)2(PMe3)]+[CH2=CMeCO2]À (14a) in 41% yield
[Eq. (11)].
This result suggests the importance of the prior
dissociation of PMe3 for the CÀH bond cleavage reac-
tion. Similar treatment of the TRIPHOS complex 9a
with PMe3 produced a mixture of orthometalated
complexes of the TRIPHOS ligand 15a and 16a
[Eq. (12)].
constant is described as K3 =[cation of 5a][methacrylato
anion]/[1a][methacrylic acid]. The K3 value was
almost independent (K3 =0.055–0.070) of the temper-
ature (50–808C), which suggests that there is little
thermodynamic difference between the compounds.
Heating the neutral bis(benzoato) complex 2 f to
708C yielded the orthometalated product 1 f in 21%
in 10 h in the presence of DBU. However, the similar
treatment of 2 f with PMe3 did not afford 1 f at all,
and 2 f was recovered in 79%. As the liberated ben-
zoic acid cannot form a phosphabetaine such as 13a,
PMe3 may not be an effective base in this reaction. A
similar
orthometalation
from
[cis-Pt{O-
C(O)Ph}2(PiPr2C2H4PiPr2)] at 1608C for 8 d has recently
been documented by Jones and co-workers.[22]
The reaction in [D4]MeOH is notable. In [D4]MeOH,
ruthenalactone 1a was not observed at all on the
treatment of 5a at 508C for 11 h. Instead, regio- and
stereoselective deuteration occurred to give [D2]5a
(Scheme 6).
Although 9a has almost the same structure as the PMe3
complex 12a, the orthometalation of the phenyl group pro-
ceeds for 9a prior to the internal CÀH bond cleavage reaction
of the carboxylato ligand. Thus, we concluded that monoden-
tate alkylphosphines such as PMe3 encourage the CÀH bond
activation of the carboxylato group.
The H–D exchange reaction exclusively occurred at
the cis position to the carbonyl group in both coordinated and
liberated methacrylato anions and no incorporation of D was
observed in other positions. The similar treatment of 1a in the
presence of one equivalent of methacrylic acid in [D4]MeOH at
508C for 45 h gave [D2]5a in quantitative yield with 100 at%
D. These results strongly suggest that this reaction proceeds
by the CÀH bond cleavage reaction via ruthenalactone. How-
ever, no incorporation of D was observed by the similar treat-
ment of 11 a in [D4]MeOH. This suggests the importance of the
prior dissociation of a P atom from the RuII center. Consistently,
the aqua complex 3a, which has three PMe3 ligands, under-
went a cis-selective H–D exchange reaction of the methacryla-
Reversibility of the reaction between the bis(methacrylato)
complex and ruthenalactone
In the absence of base, heating a [D6]DMSO solution of the
cationic methacrylato complex 5a at 708C reached a steady
state of a mixture of 5a (74%) and 1a (22%) along with small
amount of 3a (4%) n 1 h [Eq. (13)].
For the backward reaction, the
treatment of 1a with one equiv-
alent of methacrylic acid gave
a
mixture of 5a (75%), 1a
(22%), and 3a (4%) under the
same conditions. Therefore, this
system constitutes the equilibri-
um between 5a and 1a in
[D6]DMSO. As the [5a]:[1a] ratio
was
almost
independent
([5a]:[1a]=3.9–3.0) of the initial
concentration of 5a (0.014–
0.0533m), the ionic pairwise in-
teraction is weak in [D6]DMSO
solution. Thus, the equilibrium Scheme 6. Stoichiometric regio- and stereoselective deuteration.
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to ligands to give [D2]3a in 96 at% D in 6.8 h at 508C in
[D4]MeOH.
To understand the general feature of this stoichiometric
deuteration of carboxylato anions, we screened several carbox-
ylato complexes (Table 2). No H–D exchange reaction took
place for the crotonato, tiglato, or 2-methylpropanoato anions.
The ortho deuteration in benzoato and related compounds
proceeded, but these reactions were sluggish.
Table 3. Catalytic deuteration of the b-hydrogen atom in carboxylic
acids.[a]
Carboxylic acid
t [h]
36
Yield [%]
D content [atom%]
Table 2. Stoichiometric deuteration of the b-position in the carboxylato
anion in [D4]MeOH.[a]
82
63
94
85
Carboxylato anion
t [h]
D content [atom%]
91
24
11
48
86
93
[b]
n.a.
–
77
46
0
0
56
46
–
–
0
0
145
315
0
[a] Conditions: Catalyst=4 (0.02 mmol), carboxylic acid (0.2 mmol),
[D4]MeOH, T=608C.
28
The catalytic H–D exchange reaction of benzoic acid by 4 as
a catalyst precursor failed, although the stoichiometric reaction
proceeded. If the trisphosphine complex 3 f was employed,
the catalysis slowly proceeded to give the ortho deuterated
benzoic acid with 28 at% D in 315 h in [D4]MeOH at 508C.
315
74
313
104
34
0
Plausible catalytic cycle
Considering all the experimental results described above, this
catalysis can be explained as summarized in Scheme 7.
[a] Conditions: starting complex=0.022–0.024 mmol, [D4]MeOH=600 mL,
T=508C. [b] Complex mixture.
Both [cis-RuH2(PMe3)4] and neutral bis(carboxylato) complex
cis-Ru(OC(O)CMe=CH2)2(PMe3)4 (2a) are easily converted into
5a by reaction with methacrylic acid in methanol. Complex 5a
reversibly liberates a PMe3 ligand to give A. As bidentate phos-
phine complex 10a is inactive for the CÀH bond cleavage reac-
tion of the carboxylato ligand, the active catalyst is considered
to be a tris(phosphine) species. Then, a ruthenalactone B forms
with the liberation of methacrylic acid. The equilibrium be-
Catalytic H–D exchange reaction
Catalytic regio- and stereoselective H–D exchange reaction
The CÀH bond cleavage reaction of carboxylic acid itself is
largely unexplored and only pioneering catalytic ortho halo-
genation, alkylation, alkenylation, arylation, and carboxylation
processes have been documented by Yu, Satoh, and Miura’s
groups.[23] The stoichiometric reaction described above prom-
ises regio- and stereoselective catalytic H–D exchange reac-
tions of carboxylic acids. Complex 4a (10 mol%) catalyzed the
H–D exchange reaction of methacrylic acid in [D4]MeOH at
508C to give [D2]methacrylic acid in 97% yield with 94 at% D
[Eq. (14)].
tween
a ruthenalactone and 5a has been established
[Eq. (14)]. The liberated methacrylic acid immediately exchang-
es the proton with D+ in a large excess of [D4]MeOH. The acid-
olysis of B with CH2=CMeCO2D gives C in which the D atom is
exclusively incorporated in the cis position to the carbonyl
group. Finally, the exchange between the carboxylato and car-
boxylic acid releases [D2]methacrylic acid.
In the present CÀH bond cleavage process (A to B in
Scheme 7), prior coordination of the C=C bond to the RuII
center may be an indispensable process because a pseudo-iso-
morphous complex with a saturated ligand, the isobutylato
group (complex D), did not react in either the stoichiometric
or catalytic reactions.
The reaction proceeded regio- and stereoselectively and the
H atom cis to the carbonyl group was exclusively deuterated
along with the acidic proton. Similarly, the catalytic deuteration
of aliphatic carboxylic acids was performed by 4 as a catalyst
precursor (Table 3).
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deprotonation (CMD),[25] and am-
biphilic metal–ligand activation
(AMLA)[26] have been used. The
six-membered transition state E
requires a vacant site, which is
consistent with the prior dissoci-
ation of PMe3 as shown above.
Probably, intermediate D gives
the transition state E. However,
DBU is a good base in this reac-
tion and initiates the CÀH bond
cleavage reaction from 6a. This
cannot be explained by the ba-
sicity of DBU, and it must have
a similar nature to the coordinat-
ing carboxylato group. Although
it is not clear how DBU behaves
in the CÀH bond activation pro-
cess, one of the hypotheses is
the prior coordination of DBU to
RuII though the amidine frame-
work (depicted as F).[27]
Conclusions
We have documented a facile
and general method to prepare
bis(carboxylato)ruthenium(II)
complexes 2. Interestingly, this
compound reversibly transforms
to the cationic form 5 in polar
solvents. The CÀH bond cleav-
Scheme 7. Possible mechanism for the catalytic regio- and stereoselective deuteration of methacrylic acid.
age reaction of the carboxylato ligand in 2 occurs to give
a ruthenalactone 1, which requires prior dissociation of a PMe3
ligand from 2. The thermodynamic stability between 2 and 1 is
almost comparable and they form an equilibrium in a solution.
These results show that the coordinating carboxylato ligand
abstracts the proton from another carboxylato ligand at the
coordinatively unsaturated RuII center. However, an added car-
boxylato anion has almost of no effect on the CÀH bond acti-
vation. Thus, the coordinating carboxylato ligand must play
a role as an internal base in this reaction. This finding sheds
light on the CÀH bond activation process in which a carboxyla-
to ligand becomes engaged as a proton acceptor.
Experimental Section
All manipulations and reactions were performed under dry N2 by
using standard Schlenk and vacuum-line techniques. Benzene, tolu-
ene, hexane, pentane, THF, and Et2O were distilled from sodium
benzophenone ketyl, and acetone was distilled from Drierite.
DMSO was distilled from activated molecular sieves. Methanol and
ethanol were distilled from the corresponding Mg alkoxide. PMe3
was prepared by the reaction of P(OPh)3 with a methyl Grignard re-
agent and purified by distillation followed by repeated drying over
MgSO4 by using a vacuum-distillation technique. [Ru2(O2CMe)4Cl]
was prepared according to a slightly modified literature method
by using O2 gas.[28] [RuCl2(PPh3)3] was prepared according to a litera-
These results clearly show that the carboxylato group does
not act as a simple Brønsted base. This probably suggests the
high ability of the coordinating carboxylato group for proton
abstraction.[5,9,10] An internal base, such as a bound carboxylato
group rather than an external one, plays a key role in the CÀH
bond cleavage step. This mechanism is nowadays widely ac-
cepted as an internal electrophilic substitution (IES) mecha-
nism,[24] although other names such as concerted metalation–
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ture method.[29] Compound 4 was prepared by the reduction of
[Ru2(O2CMe)4Cl] with sodium amalgam in the presence of PMe3
under a H2 atmosphere.[30] For reactions in an NMR tube, internal
CHPh3 or a [D6]benzene solution of PPh3 in a flame-sealed capillary
was used as the internal standard for quantitative analysis. The
NMR spectra were measured by using JEOL LA300 (1H at 300 MHz,
31P at 122 MHz) and JEOL ECX400P (1H at 399.8 MHz, 31P at
(3.8 mL, 0.025 mmol) in [D6]DMSO at 1008C for 20 h to produce 1 f
in 43% yield.
1H NMR (400 MHz, [D6]acetone): d=1.02 (t, J=3.0 Hz, 18H, PMe3),
1.49 (d, J=7.1 Hz, 9H, PMe3), 1.49 (d, J=7.8 Hz, 9H, PMe3), 6.79 (t,
J=7.3 Hz, 1H, C6H4), 6.96 (t, J=7.1 Hz, 1H, C6H4), 7.42 (d, J=7.3 Hz,
1H, C6H4), 7.63 ppm (t, J=6.2 Hz, 1H, C6H4); 31P{1H} NMR (162 MHz,
[D6]acetone): d=À13.7 (td, J=26, 17 Hz, 1P, PMe3), À0.22 (dd, J=
34, 26 Hz, 2P, PMe3), 9.1 ppm (td, J=34, 17 Hz, 1P, PMe3). IR (KBr):
n˜ =3049 (m), 3036 (m), 2974 (m), 2905 (m), 1689 (w), 1644 (w),
1599 (vs), 1571 (s), 1432 (s), 1416 (s), 1334 (vs), 1300 (s), 1278 (s),
1142 (s), 943 (vs), 857 (s), 836 (s), 736 (s), 715 (s), 663 (s), 547 (w),
434 cmÀ1 (m); elemental analysis calcd (%) for C19H40O2P4Ru
(525.48): C 43.43, H 7.67; found: C 44.08, H 7.66.
1
162 MHz) spectrometers. The H and 13C chemical shifts were refer-
1
enced to tetramethylsilane. The H–1H coupling constants for the
complexes refer to the observed peak separations; non-first-order
analysis of the spectra was not attempted. The accuracy of the
coupling constants was estimated from the raw data by taking
into account the experimental error based on the line shape of
each resonance. IR spectra were recorded by using a JASCO
FTIR4100 spectrometer. Elemental analyses were performed by
using a Perkin–Elmer 2400 series II CHN analyzer. The volume of
evolved H2 gas was measured by using a Tçpler pump and ana-
lyzed by GLC by using a Shimadzu GC-8A instrument with a molec-
ular sieve column equipped with a thermal conductivity detector
(TCD, 5 mmꢂ2 m). GC–MS analysis was performed by using a Shi-
madzu QP2100 instrument.
[cis-Ru{OC(O)CMe=CH2-k1O}2(PMe3)4] (2a): Complex 5a (286.6 mg,
0.4980 mmol) was dissolved in dry THF (1 mL) and hexane (2 mL)
was added. The solution was filtered and stored in a freezer to
give pale-yellow cubes of 2a in 70% yield (212.5 mg,
0.3692 mmol). The other neutral bis(carboxylato) complexes were
1
prepared in a similar way. H NMR (300 MHz, [D6]benzene): d=1.07
(m, 18H, PMe3), 1.33 (vt, J=3.3 Hz, 18H, PMe3), 2.28 (s, 6H, Me),
5.34 (dd, J=3.3, 1.5 Hz, 2H, CH2=CMeCO2 trans to carbonyl),
6.29 ppm (d, J=3.6 Hz, 2H, CH2=CMeCO2 cis to carbonyl);
31P{1H} NMR (121 MHz, [D6]benzene): d=À2.62 (t, J=31.6 Hz, 2P,
PMe3), 14.57 ppm (t, J=31.6 Hz, 2P, PMe3); IR (KBr): n˜ =2975 (m),
2912 (m), 1641 (w), 1562 (vs), 1454 (s), 1402 (vs), 1380 (vs), 1299 (s),
1282 (s), 1238 (s), 941 (vs), 833 (s), 721 (s), 667 (s), 619 cmÀ1 (s); ele-
mental analysis calcd (%) for C20H46O4P4Ru (575.54): C 41.74, H 8.06;
found: C 41.38, H 7.83.
Syntheses
[Ru{OC(O)CMe=CH-k2O,C}(PMe3)4] (1a): Method A: Complex 2a
(79.9 mg, 0.139 mmol) was treated with PMe3 (706 mL, 6.91 mmol)
in benzene at 708C for 120 h. After removal of all volatile materials,
the resulting solid was extracted with THF. After evaporation of the
solution, the solid was recrystallized from the vapor diffusion of
hexane into a toluene solution to give colorless cubes of 1a in
16% yield (10.9 mg, 0.0223 mmol).
[cis-Ru{OC(O)CH=CH2-k1O}2(PMe3)4] (2b): 52%; 1H NMR (400 MHz,
[D6]benzene): d=1.06 (m, 18H, PMe3), 1.31 (vt, J=3.2 Hz, 18H,
PMe3), 2.28 (s, 6H, Me), 5.40 (d, J=6.6 Hz, 2H, CH2=CHCO2),
6.49 ppm (d, J=6.6 Hz, 4H, CH2=CHCO2); 31P{1H} NMR (162 MHz,
[D6]benzene): d=À2.74 (t, J=31.8 Hz, 2P, PMe3), 14.70 ppm (t, J=
31.8 Hz, 2P, PMe3).
Method B: Complex 10a (816.3 mg, 1.552 mmol) was treated with
KOPh (206.6 mg, 1.563 mmol) in tBuOH (20 mL) at 708C for 22 h.
After the removal of volatile materials, the resulting white solid
was extracted with benzene. The benzene solution was washed
with aqueous NaOH repeatedly, then evaporated to dryness and
dried under reduced pressure to yield almost pure 1a as a white
powder in 49% yield (374.8 mg, 0.7658 mmol). After recrystalliza-
tion of the powder from cold toluene, pure 1a was obtained as
colorless crystals in 44% yield (337.0 mg, 0.6855 mmol).
[cis-Ru{OC(O)CMe=CHMe-k1O}2(PMe3)4]
(2c):
65%;
1H NMR
(400 MHz, [D6]benzene): d=1.11 (m, 18H, PMe3), 1.36 (vt, J=3.2 Hz,
18H, PMe3), 1.72 (d, J=6.9 Hz, 6H, b-Me), 2.21 (s, 6H, a-Me),
7.06 ppm (qd, J=7.3, 1.4 Hz, 2H, CHMe=CMeCO2); 31P{1H} NMR
(162 MHz, [D6]benzene): d=À3.09 (t, J=30.6 Hz, 2P, PMe3),
14.0 ppm (t, J=30.6 Hz, 2P, PMe3).
1H NMR (300 MHz, [D6]benzene): d=0.88 (d, J=7.5 Hz, 9H, PMe3),
0.96 (t, J=2.7 Hz, 18 Hz, PMe3), 1.09 (d, J=5.7 Hz, 9H, PMe3), 2.43
(s, 3H, CH=CMeCO2), 7.86 ppm (br, 1H, CH=CMeCO2); 31P{1H} NMR
(122 MHz, [D6]benzene): d=À11.7 (td, J=26, 16 Hz, 1P, PMe3), 0.22
(dd, J=35, 26 Hz, 2P, PMe3), 11.6 ppm (td, J=35, 16 Hz, 1P, PMe3):
IR (KBr): n˜ =2971 (m), 2911 (s), 2871 (w), 1655 (w), 1586 (vs), 1549
(s), 1427 (m), 1340 (s), 1279 (s), 942 (vs), 856 (s), 711 (s), 664 cmÀ1
(s); elemental analysis calcd (%) for C16H40O2P4Ru (490.45): C 39.26,
H 8.24; found: C 39.43, H 7.89.
[cis-Ru{OC(O)Et}2(PMe3)4]
(2d):
53%;
1H NMR
(400 MHz,
[D6]benzene): d=1.05 (m, 18H, PMe3), 1.35 (vt, J=3.2 Hz, 18H,
PMe3), 1.40 (t, J=7.6 Hz, 6H, CH2Me), 2.44 ppm (q, J=7.6 Hz, 4H,
CH2Me). 31P{1H} NMR (162 MHz, [D6]benzene): d=À3.48 (t, J=
31.8 Hz, 2P, PMe3), 14.0 ppm (t, J=31.8 Hz, 2P, PMe3); elemental
analysis calcd (%) for C18H46O4P4Ru (551.52): C 39.20, H 8.41; found:
C 38.79, H 7.96.
[cis-Ru{OC(O)CH2CHMe2}2(PMe3)4] (2e): 70%; 1H NMR (400 MHz,
[D6]benzene): d=1.0–1.2 (m, 4H, CH2), 1.10 (m, 18H, PMe3), 1.30
(vt, J=3.2 Hz, 18H, PMe3), 1.43 (d, J=6.9 Hz, 12H, CHMe2),
2.68 ppm (sept, J=6.9 Hz, 2H, CHMe2); 31P{1H} NMR (162 MHz,
[D6]benzene): d=À4.35 (t, J=31.6 Hz, 2P, PMe3), 13.84 ppm (t, J=
31.6 Hz, 2P, PMe3); elemental analysis calcd (%) for C20H50O4P4Ru
(579.57): C 41.45, H 8.70; found: C 41.43, H 8.63.
[Ru{OC(O)C6H4-k2O,C}(PMe3)4] (1 f): Method A: A similar treatment
of 10 f (844.0 mg, 1.502 mmol) with KOPh (198.4 mg, 1.501 mmol)
as described above for 1a produced 1 f as colorless crystals in
27% yield (211.6 mg, 0.4027 mmol).
Method B: Complex 2 f (3.2 mg, 0.0049 mmol) in an NMR tube in
[D6]benzene was heated at 708C for 10 h in the presence of DBU
(22.0 mL, 0.147 mmol) to give 1 f in 21% yield. (Method C): Com-
plex 2 f (10 mg, 0.015 mmol) in [D6]benzene at 708C for 165 h in
the presence of PMe3 (18.0 mL, 0.177 mmol) produced a small
amount of unknown compound with 79% recovery of 1 f. (Method
D): Complex 6 f (3.4 mg, 0.0051 mmol) was treated with DBU
[cis-Ru{OC(O)Ph}2(PMe3)4]
(2 f):
54%;
1H NMR
(400 MHz,
[D6]benzene): d=1.06 (m, 18H, PMe3), 1.36 (vt, J=3.2 Hz, 18H,
PMe3), 7.22 (t, J=7.3 Hz, 2H, para-Ph), 7.36 (t, J=7.3 Hz, 4H, meta-
Ph), 8.72 ppm (dd, J=6.9, 1.4 Hz, 4H, ortho-Ph); 31P{1H} NMR
(162 MHz, [D6]benzene): d=À2.61 (t, J=31.6 Hz, 2P, PMe3),
14.71 ppm (t, J=31.6 Hz, 2P, PMe3); IR (KBr): n˜ =3036 (w), 3016 (w),
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2975 (m), 2913 (s), 1604 (vs), 1569 (vs), 1425 (m), 1366 (vs), 1337
(vs), 1300 (m), 1275 (m), 1167 (w), 1062 (w), 1024 (w), 975 (sh), 943
(vs), 855 (m), 832 (w), 714 (vs), 668 cmÀ1 (s).
1597 (vs), 1429 (s), 1336 (vs), 1298 (s), 1279 (s), 943 (vs), 856 (s),
831 (s), 714 (vs), 665 (s), 620 (s), 600 (s), 521 cmÀ1 (w). The evolved
gas was measured as follows: compound 4 (9.8 mg, 0.024 mmol)
was placed in a Schlenk tube into which methanol (ca. 1.5 mL) was
introduced by vacuum distillation. Onto the frozen solution was
added methacrylic acid (12.0 mL, 0.142 mmol) under a N2 atmos-
phere and then all materials were frozen by using liquid N2. After
evacuation of all gases at 77 K, the solid was dissolved under re-
duced pressure and stirred for 5 min. Afterwards, the solution was
frozen again to measure the evolved gas by using a Tçpler pump:
H2 (160% yield).
[fac-Ru{OC(O)CMe=CH2-k1O}2(PMe3)3(H2O)] (3a): (Method A): Ru(h4--
1,5-COD)(h6--1,3,5-COT) (572.3 mg, 1.814 mmol) was treated with
PMe3 (740 mL, 7.28 mmol) and then methacrylic acid (306 mL,
3.62 mmol) and distilled water (33 mL, 1.8 mmol) at 508C for 48 h.
The resulting white precipitate was washed with hexane (3ꢂ
20 mL), and the crude product was dried under reduced pressure
to give 3a as an almost pure white powder in 84% yield
(789.1 mg, 1.525 mmol). The powder was recrystallized from THF/
hexane to produce pale-yellow microcrystals of 3a in 58% yield
(544.8 mg, 1.053 mmol).
1
With acrylic acid: 5b: 98% yield. H NMR (400 MHz, [D4]MeOH): d=
1.44 (vt, J=3.4 Hz, 18H, mutually trans-PMe3), 1.50 (m, 18H, PMe3),
5.48 (dd, J=10.1, 2.3 Hz, 1H, CH2=CHCO2 trans to carbonyl in coor-
dinated carboxylato), 5.80 (dd, J=10.6, 1.6 Hz, 1H, CH2=CHCO2
trans to carbonyl in carboxylato anion), 5.97 (dd, J=17.4, 10.6 Hz,
1H, CH2=CHCO2 in carboxylato anion), 6.01 (dd, J=17.4, 2.3 Hz,
1H, CH2=CHCO2 cis to carbonyl in coordinated carboxylato), 6.13
(dd, J=17.4, 10.1 Hz, 1H, CH2=CHCO2 cis to carbonyl in coordinat-
ed carboxylato), 6.23 ppm (dd, J=17.4, 1.6 Hz, 1H, CH2=CHCO2 cis
to carbonyl in carboxylato anion); 31P{1H} (162 MHz, [D4]MeOH): d=
À1.47 (t, J=31.3 Hz, 2P, PMe3), 22.5 ppm (t, J=31.3 Hz, 2P, PMe3).
Method B: Complex 5a (12.2 mg, 0.0244 mmol) was treated with
water (0.5 mL, 0.03 mmol) in [D6]benzene at RT. Complex 3a was
immediately formed in quantitative yield.
1H NMR (300 MHz, [D6]benzene): d=1.05 (brs, 27H, PMe3), 2.09
(brs, 6H, CH2=CMeCO2), 5.25 (t, J=1.8 Hz, 2H, CH2=CMeCO2), 6.22
(d, J=2.7 Hz, 2H, CH2=CMeCO2), 10.3 ppm (brs, 2H, H2O);
31P{1H} NMR (122 MHz, [D6]benzene): d=25.9 (brd, J=38 Hz, 2P,
PMe3), 28.0 ppm (brt, J=38 Hz, 1P, PMe3); IR (KBr): n˜ =3000–2700
(br), 1565 cmÀ1
.
With tiglic acid: 5c: 98%. 1H NMR (300 MHz, [D4]MeOH): d=1.41
(vt, J=3.2 Hz, 18H, PMe3), 1.49 (m, 18H, PMe3), 1.69 (dq, J=7.2,
1.1 Hz, 3H, b-Me in carboxylato anion), 1.78 (m, 9H, a-Me in coordi-
nated carboxylato and carboxylato anion, and b-Me in coordinated
carboxylato), 6.49 (qq, J=6.9, 1.5 Hz, 1H, CHMe=CMeCO2 in car-
boxylato anion), 6.77 ppm (m, 1H, CHMe=CMeCO2 in coordinated
anion); 31P{1H} NMR (121 MHz, [D4]MeOH): d=À0.98 (t, J=30 Hz,
2P, PMe3), 21.92 ppm (t, J=30 Hz, 2P, PMe3); IR (KBr): n˜ =2976 (m),
2910 (s), 2856 (w), 1658 (s), 1577 (vs), 1562 (vs), 1429 (s), 1377 (vs),
1360 (vs), 1340 (vs), 1300 (vs), 1165 (s), 1078 (m), 1007 (w), 943 (vs),
854 (m), 810 (m), 752 (m), 721 (s), 663 (s), 561 (w), 453 cmÀ1 (m).
[fac-Ru{OC(O)Ph-k1O}2(PMe3)3(H2O)] (3 f): Compound 4 (399.7 mg,
0.9812 mmol) was treated with benzoic acid (239.4 mg,
1.960 mmol) in methanol (4 mL) to give 5 f. Afterwards, 5 f was dis-
solved in benzene (15 mL) and water (78.0 mL, 4.33 mmol), and the
mixture was heated at 608C for 42 h followed by removal of all
volatile matter and then recrystallization of the residue from cold
THF to produce pale-yellow microcrystals of 3 f in 48% yield
1
(258.8 mg, 0.4389 mmol). H NMR (400 MHz, [D6]benzene): d=1.03
(brs, 18H, PMe3), 1.20 (brs, 9H, PMe3), 7.11 (t, J=7.3 Hz, 2H, para-
Ph), 7.17 (t, J=7.1 Hz, 4H, meta-Ph), 8.37 (d, J=6.9 Hz, 4H, ortho-
Ph), 10.59 ppm (brs, 2H, H2O); 31P{1H} NMR (162 MHz, [D6]benzene):
d=25.8 (brd, J=40.0 Hz, 2P, PMe3), 28.0 ppm (br, t, J=40.0 Hz, 1P,
PMe3). IR (KBr): n˜ =3426 (br), 3200–2500 (br), 3061 (w), 2977 (w),
2911 (w), 1598 (vs), 1557 (vs), 1535 (s), 1415 (m), 1381 (vs), 1299
(m), 1280 (m), 1170 (w), 1065 (m), 1020 (w), 967 (m), 931 (vs), 851
(m), 826 (m), 724 (vs), 675 (m), 433 cmÀ1 (m).
1
With propionic acid: 5d: 87%. H NMR (400 MHz, [D4]MeOH): d=
1.08 (t, J=7.6 Hz, 6H, Me in carboxylato anion and coordinated
carboxylato), 1.46 (vt, J=3.2 Hz, 18H, PMe3), 1.48 (m, 18H, PMe3),
2.15 (q, J=7.8 Hz, 2H, CH2Me in carboxylato anion), 2.26 ppm (q,
J=7.8 Hz, 2H, CH2Me in coordinated carboxylato). 31P{1H} NMR
(162 MHz, [D4]MeOH): d=À1.85 (t, J=30.4 Hz, 2P, PMe3), 22.1 ppm
(t, J=30.4 Hz, 2P, PMe3).
Reactions of 4 with carboxylic acid in methanol
With isobutylic acid: 5e: 86%; 1H NMR (400 MHz, [D4]MeOH): d=
1.08 (d, J=6.9 Hz, 6H, Me in carboxylato anion), 1.15 (d, J=6.9 Hz,
6H, Me in coordinated carboxylato), 1.46 (vt, J=3.2 Hz, 18H, PMe3),
1.48 (m, 18H, PMe3), 2.35 (sept, J=6.9 Hz, 1H, CHMe2 in carboxyla-
to anion), 2.41 ppm (sept, J=6.9 Hz, 1H, CHMe2 in coordinated car-
boxylato); 31P{1H} NMR (162 MHz, [D4]MeOH): d=À2.24 (t, J=
30.6 Hz, 2P, PMe3), 21.74 ppm (t, J=30.6 Hz, 2P, PMe3).
All reactions of 4 with carboxylic acids in methanol were carried
out in a similar way. The details are described for the reaction with
methacrylic acid as a typical example.
With methacrylic acid: Compound 4 (445.7 mg, 1.094 mmol) was
placed in a Schlenk tube, and methanol (5 mL) was added by sy-
ringe. Methacrylic acid (185 mL, 2.19 mmol) was added by syringe,
and the evolution of gas was observed. The mixture was stirred
under reduced pressure for 5 min at RT, and then all volatiles were
removed under reduced pressure to give of [Ru{OC(O)CMe=CH2-
k2O,O’}(PMe3)4]+[CH2=CMeCO2]À (5a) as a pale-yellow solid in 100%
yield (627.9 mg, 1.091 mmol). 1H NMR (300 MHz, [D4]MeOH): d=
1.43 (vt, J=3.3 Hz, 18H, mutually trans-PMe3), 1.50 (m, 18H, PMe3),
1.87 (s, 3H, Me in carboxylato anion), 1.89 (s, 3H, Me in coordinated
carboxylato), 5.18 (d, J=1.8 Hz, 1H, CH2=CMeCO2 trans to carbonyl
in carboxylato anion), 5.49 (s, 1H, CH2=CMeCO2 trans to carbonyl
in coordinated carboxylato), 5.70 (s, 1H, CH2=CMeCO2 cis to car-
bonyl in carboxylato anion), 5.98 (s, 1H, CH2=CMeCO2 cis to car-
bonyl in coordinated carboxylato); 31P{1H} NMR (122 MHz,
[D4]MeOH): d=À1.08 (t, J=30.4 Hz, 2P), 22.29 ppm (t, J=30.4 Hz,
2P); IR (KBr): n˜ =3093 (w), 2974 (m), 2914 (m), 1695 (w), 1643 (m),
1
With benzoic acid: 5 f: 98%; H NMR (400 MHz, [D4]MeOH): d=1.43
(vt, J=3.2 Hz, 18H, PMe3), 1.55 (m, 18H, PMe3), 7.47 (t, J=7.1 Hz,
5H, meta- and para-Ph in carboxylato anion and meta-Ph in coordi-
nated carboxylato), 7.57 (t, J=7.1 Hz, 1H, para-Ph in coordinated
carboxylato), 7.92 ppm (d, J=7.1 Hz, 4H, ortho-Ph in carboxylato
anion and coordinate carboxylato); 31P{1H} NMR (162 MHz,
[D4]MeOH): d=À1.15 (t, J=30.3 Hz, 2P, PMe3), 22.41 ppm (t, J=
30.3 Hz, 2P, PMe3).
[Ru{OC(O)CMe=CH2-k2O,O’)(PMe3)4]+BPh4
(6a): Compound
4
À
(469.5 mg, 1.144 mmol) was dissolved in methanol (5 mL) in
a Schlenk tube. Methacrylic acid (195.0 mL, 2.308 mmol) was added
by syringe, and the mixture was stirred for 5 min at RT. KBPh4
(391.8 mg, 1.145 mmol) was added to the solution to give a suspen-
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sion. Methanol (3 mL) was added to the suspension to give a solu-
tion, which was stirred for 10 min at RT. After removal of all volatile
materials, the residual solid was extracted by acetone (total:
15 mL). The solution was concentrated to 3 mL under reduced
pressure and filtered. The solution was stored in a freezer to give
yellow columns of 6a in 54% yield (617.7 mg, 0.6125 mmol).
1H NMR (300 MHz, [D6]acetone): d=1.44 (vt, J=3.3 Hz, 18H, PMe3),
1.55 (m, 18H, PMe3), 1.87 (s, 3H, Me), 5.50 (d, J=1.8 Hz, 1H, CH2=
CMeCO2 trans to carboxylato), 5.99 (s, 1H, CH2=CMeCO2 cis to car-
boxylato), 6.77 (t, J=7.1 Hz, 4H, para-Ph), 6.92 (t, J=7.4 Hz, 8H,
meta-Ph), 7.32 ppm (m, 8H, ortho-Ph); 31P{1H} NMR (162 MHz,
[D6]acetone): d=À0.47 (t, J=29.6 Hz, 2P, PMe3), 22.73 ppm (t, J=
29.6 Hz, 2P, PMe3); IR (KBr): n˜ =3053 (m), 3035 (m), 2999 (m), 2981
(m), 2916 (w), 1639 (w), 1579 (m), 1504 (m), 1479 (m), 1427 (vs),
1371 (m), 1305 (s), 1286 (s), 1238 (w), 1132 (w), 1032 (m), 941 (vs),
864 (s), 730 (vs), 706 (vs), 671 (m), 611 cmÀ1 (vs); elemental analysis
calcd (%) for C40H61BO2P4Ru (809.69): C 59.34, H 7.59; found: C
58.89, H 8.08. The other cationic monocarboxylato complexes were
prepared in a similar way.
[fac-Ru{OC(O)Ph-k1O}Cl(PPh3)3] (8 f): This compound was prepared
1
in a similar way to 8a. 80%; H NMR (400 MHz, [D]chloroform): d=
6.8–7.4 ppm (m, OC(O)Ph and PPh3); 31P{1H} NMR (162 MHz,
[D]chloroform): d=29.29 (d, J=26.9 Hz, 2P, PPh3), 50.75 ppm (d,
J=26.9 Hz, 1P, PPh3).
[mer-Ru{OC(O)CMe=CH2-k1O}{OC(O)CMe=CH2-k2O,O’)(TRIPHS)] (9a):
Complex 7a (175.8 mg, 0.2209 mmol) was treated with TRIPHOS
(145.8 mg, 0.2727 mmol) in THF at RT for 3 h. Then all volatile ma-
terials were removed, and the resulting yellow powder was recrys-
tallized from THF/hexane to give yellow microcrystals of 9a in 22%
yield (31.0 mg, 0.0478 mmol). 1H NMR (400 MHz, [D8]toluene,
À808C): d=1.53 (s, 3H, CH2=CMeCO2), 1.72 (s, 3H, CH2=CMeCO2),
1.8–2.5 (m, 8H, PC2H4P), 4.98 (s, 1H, CH2=CMeCO2), 5.0 (s, 1H, CH2=
CMeCO2), 5.3 (s, CH2=CMeCO2), 6.81 (m, 6H, Ph), 7.3–7.5 (m, 15H,
Ph), 7.68 (m, 2H, Ph), 7.86 ppm (m, 2H, Ph); 31P{1H} NMR (162 MHz,
[D8]toluene, À808C): d=49.90 (br, 2P, PPh2), 113.64 (br, 1P, PPh);
1H NMR (400 MHz, [D8]toluene, 958C): d=1.27 (s, 3H, CH2=
CMeCO2), 1.53 (s, 3H, CH2=CMeCO2), 2.34 (m, 2H, PC2H4P), 2.48 (m,
2H, PC2H4P), 2.78 (m, 2H, PC2H4P), 3.20 (m, 1H, PC2H4P), 4.61 (s, 1H,
CH2=CMeCO2), 4.90 (s, 1H, CH2=CMeCO2), 5.19 (s, 1H, CH2=
CMeCO2), 5.84 (s, 1H, CH2=CMeCO2), 6.89 (m, 6H, Ph), 6.96 (m, 4H,
Ph), 7.11 (m, 3H, Ph), 7.16 (m, 5H, Ph), 7.37 (m, 3H, Ph), 7.98 ppm
(m, 4H, Ph); 31P{1H} NMR (162 MHz, [D8]toluene, 958C): d=57.11
(br, 2P, PPh2), 133.56 ppm (br, 1P, PPh); elemental analysis calcd
(%) for C42H43O4P3Ru (805.78): C 62.60, H 5.38; found: C 62.52; H
5.89.
[Ru{OC(O)Me=CHMe-k2O,O’}(PMe3)4]+BPh4 (6c): Yellow columns;
À
1
27%; H NMR (300 MHz, [D6]acetone): d=1.46 (vt, J=3.2 Hz, 18H,
PMe3), 1.54 (m, 18H, PMe3), 1.77 (br, 6H, a- and b-Me), 6.77 (t, J=
6.9 Hz, 5H, para-Ph and CHMe=CMeCO2), 6.91 (t, J=7.4 Hz, 8H,
meta-Ph), 7.33 ppm (m, 8H, ortho-Ph); 31P{1H} NMR (121 MHz,
[D6]acetone): d=À0.34 (t, J=30.4 Hz, 2P, PMe3), 22.38 ppm (t, J=
30.4 Hz, 2P, PMe3). IR (KBr): n˜ =3053 (m), 3032 (m), 3000 (m), 2981
(m), 2913 (w), 1654 (m), 1579 (m), 1497 (m), 1429 (vs), 1380 (m),
1327 (w), 1306 (s), 1285 (s), 1174 (w), 1132 (m), 1032 (m), 943 (vs),
856 (m), 837 (m), 732 (s), 705 (s), 669 (s), 611 cmÀ1 (s); elemental
analysis calcd (%) for C41H63BO2P4Ru (823.71): C 59.78, H 7.71;
found: C 59.34, H 7.75.
[cis-Ru{OC(O)CMe=CH2-k1O}Cl(PMe3)4] (10a): Complex 8a (5.3230 g,
5.2783 mmol) was dissolved in hexane (40 mL), and PMe3 (2.60 mL,
25.6 mmol) was added into the solution. After the solution was
heated to reflux for 1 h, it was stored at RT to give pale-yellow
crystals. The resulting crystals were separated, washed with
hexane, and dried under vacuum to give 10a in 72% yield
(2.0125 g, 3.8267 mmol). 1H NMR (400 MHz, [D6]benzene): d=1.01
(d, J=7.8 Hz, 9H, PMe3), 1.20 (d, J=8.7 Hz, 9H, PMe3), 1.39 (vt, J=
3.2 Hz, 18H, PMe3), 2.29 (s, 3H, CH2=CMeCO2), 5.35 (s, 1H, CH2=
CMeCO2), 6.34 ppm (s, 1H, CH2=CMeCO2); 31P{1H} NMR (162 MHz,
[D6]benzene): d=À4.70 (dd, J=33.6, 29.5 Hz, 2P, PMe3), 11.0 (dt,
J=37.7, 29.5 Hz, 1P, PMe3), 15.6 ppm (dt, J=37.7, 33.6 Hz, 1P,
PMe3); IR (KBr): n˜ =3162 (w), 3083 (w), 2975 (s), 2908 (s), 1638 (m),
1588 (vs), 1439 (sh), 1421 (s), 1392 (m), 1359 (vs), 1297 (s), 1278 (s),
1233 (s), 998 (sh), 941 (vs), 857 (s), 828 (s), 718 (s), 666 (s), 616 cmÀ1
(m).
[Ru{OC(O)Ph-k2O,O’}(PMe3)4]+PF6 (6 f): Recrystallized from THF/
À
1
hexane. Pale-yellow columns; 82%; H NMR (400 MHz, [D4]MeOH):
d=1.43 (vt, J=3.2 Hz, 18H, PMe3), 1.55 (m, 18H, PMe3), 7.47 (t, J=
7.1 Hz, 2H, meta-Ph), 7.57 (t, J=7.1 Hz, 1H, para-Ph), 7.94 ppm (t,
J=7.1 Hz, 2H, ortho-Ph); 31P{1H} NMR (162 MHz, [D4]MeOH): d=
À1.15 (t, J=30.3 Hz, 2P, PMe3), 22.41 ppm (t, J=30.3 Hz, 2P, PMe3);
elemental analysis calcd (%) for C19H41F6O2P5Ru (671.46): C 33.99, H
6.15; found: C 34.40, H 6.42.
[trans-Ru{OC(O)CMe=CH2-k2O,O’}2(PPh3)2]
(7a):
RuCl2(PPh3)3
(1.2910 g, 1.35 mmol) and sodium methacrylate (711.6 mg,
6.58 mmol) were dissolved in THF (10 mL) and heated to reflux for
2.5 h. After the reaction, the solution was filtered and all volatile
materials were removed under reduced pressure. The resulting
solid was washed with hexane and dried under reduced pressure
to give 7a as yellow powder in 50% yield (0.7129 g, 0.6737 mmol).
1H NMR (400 MHz, [D6]benzene): d=1.63 (s, 6H, CH2=CMeCO2),
4.86 (s, 2H, CH2=CMeCO2), 5.94 (s, 2H, CH2=CMeCO2), 6.9 (m, 18H,
para- and meta-Ph), 7.50 ppm (m, 12H, ortho-Ph); 31P{1H} NMR
(162 MHz, [D6]benzene): d=67.42 ppm (s); IR (KBr): n˜ =1480,
[cis-Ru{OC(O)Ph-k1O}Cl(PMe3)4] (10 f): This compound was prepared
1
in the same way as 10a. 84%; H NMR (400 MHz, [D6]benzene): d=
1.03 (d, J=7.8 Hz, 9H, PMe3), 1.23 (d, J=8.7 Hz, 9H, PMe3), 1.38 (vt,
J=3.2 Hz, 18H, PMe3), 7.20 (t, J=7.3 Hz, 1H, para-Ph), 7.30 (t, J=
7.3 Hz, 2H, meta-Ph), 8.63 ppm (d, J=7.3 Hz, 2H, ortho-Ph);
31P{1H} NMR (162 MHz, [D6]benzene): d=À4.70 (dd, J=33.3,
29.5 Hz, 2P, PMe3), 10.9 (dt, J=37.2, 29.5 Hz, 1P, PMe3), 15.4 ppm
(dt, J=37.2, 33.2 Hz, 1P, PMe3); IR (KBr): n˜ =3047 (w), 3016 (sh),
2973 (s), 2910 (s), 1607 (vs), 1567 (vs), 1438 (sh), 1419 (m), 1364
(vs), 1298 (s), 1271 (m), 1170 (w), 1062 (w), 1026 (m), 951 (vs), 860
(m), 834 (m), 724 (s), 665 cmÀ1 (s).
1432 cmÀ1
.
[fac-Ru{OC(O)CMe=CH2-k1O}Cl(PPh3)3] (8a): RuCl2(PPh3)3 (5.3954 g,
0.5631 mmol) and sodium methacrylate (608.3 mg, 5.629 mmol)
were heated to reflux in tert-butyl alcohol (47 mL) for 1 h. The re-
sulting brown solid was separated and washed with Et2O, water,
methanol, and then Et2O. The brown solid was dried under re-
duced pressure to give 8a in 94% yield (5.3230 g, 5.2783 mmol).
1H NMR (400 MHz, [D]chloroform): d=1.31 (s, 3H, CH2=CMeCO2),
4.75 (s, 1H, CH2=CMeCO2), 5.33 (s, 1H, CH2=CMeCO2), 6.8–7.4 ppm
(m, 45H, PPh3); 31P{1H} NMR (162 MHz, [D]chloroform): d=7.33 (d,
J=27.7 Hz, 2P, PPh3), 28.25 ppm (t, J=27.7 Hz, 1P, PPh3).
[cis-Ru{OC(O)CMe=CH2-k1O}2(DMPE)2] (11 a): Complex 5a (169.5 mg,
0.2966 mmol) was dissolved in benzene (3 mL), and DMPE (92.0 mL,
0.551 mmol) was added. The reaction mixture was heated at 708C
for 12 h, and then all volatile materials were removed under re-
duced pressure. The residue was extracted with benzene, and the
volatile materials were removed again under reduced pressure to
give 11 a as a white solid in 45% yield (70.2 mg, 0.123 mmol).
1H NMR (300 MHz, [D6]benzene): d=0.66 (d, J=7.2 Hz, 6H, PMe2),
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1.03 (d, J=9.3 Hz, 6H, PMe2), 1.1–1.4 (br, 8H, PC2H4P), 1.63 (vt, J=
2.9 Hz, 6H, PMe2), 1.89 (vt, J=4.1 Hz, 6H, PMe2), 2.19 (m, 6H, CH2=
CMeCO2), 5.27 (q, J=1.6 Hz, 2H, CH2=CMeCO2 trans to carbonyl),
6.21 ppm (m, 2H, CH2=CMeCO2); 31P{1H} NMR (121 MHz,
[D6]benzene): d=38.10 (t, J=25 Hz, 2P, PMe2), 54.15 ppm (t, J=
25 Hz, 2P, PMe2); IR (KBr): n˜ =3083 (w), 2964 (m), 2943 (m), 2908
(s), 1641 (sh), 1589 (vs), 1450 (sh), 1414 (s), 1392 (s), 1354 (vs), 1296
(m), 1278 (m), 1265 (m), 1228 (s), 1074 (m), 1022 (w), 931 (vs), 893
(sh), 835 (s), 796 (sh), 735 (s), 702 (s), 648 (m), 609 (m), 455 cmÀ1
(m).
Equilibria
Equilibrium between 2a and 12a: Complex 2a (10.8 mg,
0.0188 mmol) was placed in an NMR tube, and [D6]benzene
(600 mL) was introduced by syringe. The probe temperature of the
NMR was increased from 20 to 708C. In these spectra, signals that
arose from newly formed 12a and 3a overlapped and were calcu-
lated as a RuP3 species. K1(M)=[RuP3][PMe3]/[2a]=0.050 (293 K),
0.0073 (303 K), 0.017 (313 K), 0.021 (323 K), 0.035 (333 K), 0.058
(343 K).
Equilibrium between 5a and 1a in DMSO: Complex 5a (4.7 mg,
0.0082 mmol; 9.6 mg, 0.017 mmol; 18.4 mg, 0.0320 mmol) was dis-
solved in [D6]DMSO (600 mL) and heated at 708C to reach equilibri-
um. A flame-sealed capillary that contained P(OPh)3 in [D6]benzene
was employed. K3 =[1a][methacrylic acid]/[cation of 5a][methacry-
lato anion]=0.066 (0.014m), 0.088 (0.028m), 0.108 (0.0533m).
Reactions with PMe3
Phosphabetaine 13a: PMe3 (460.0 mL, 4.523 mmol) was treated
with methacrylic acid (250.0 mL, 2.959 mmol) in methanol (5 mL) at
508C for 4 h. The removal of all volatile materials at 1008C under
H–D exchange reactions
reduced pressure produced pure Me3P+CH2CHMeCO2 (13a) in
À
Stoichiometric H–D exchange reaction of 5a: Complex 5a
(13.8 mg, 0.0236 mmol) was dissolved in [D4]MeOH and heated at
508C for 11 h. The peak of the methylene proton cis to the carbon-
94% yield (453.0 mg, 2.793 mmol). 1H NMR (400 MHz, [D4]MeOH):
d=1.27 (dd, J=7.0, 1.9 Hz, 3H, CHMe), 1.84 (d, J=14.6 Hz, 9H,
PMe3), 2.13 (ddd, J=15.0, 13.5, 3.4 Hz, 1H, CH2), 2.44 (ddd, J=15.0,
13.5, 11.0 Hz, 1H, CH2), 2.58 ppm (ddq, J=11.0, 7.0, 3.4 Hz, 1H,
CHMe); 31P{1H} NMR (162 MHz, [D4]MeOH): d=26.6 ppm (s, PMe3);
IR (KBr): n˜ =3423 (br), 2970 (m), 2930 (m), 2909 (m), 2871 (w), 1592
(vs), 1460 (w), 1403 (m), 1386 (m), 1358 (m), 1290 (m), 1178 (m),
1119 (m), 1077 (w), 1033 (w), 998 (s), 970 (s), 903 (m), 887 (m), 849
(m), 808 (w), 778 (m), 754 (w), 658 (w), 571 (m), 541 cmÀ1 (w).
1
yl group decreased in the H NMR spectrum in 91 at% D.
Stoichiometric H–D exchange reaction of carboxylato ligands: The
stoichiometric H–D exchange reaction was carried out as follows.
Compound 4 (ca. 10 mg) was placed in an NMR tube into which
[D4]MeOH was introduced. Then, a carboxylic acid was added by
syringe and the reaction system was heated at 508C.
Stoichiometric H–D exchange reaction of 3a: Complex 3a (9.6 mg,
0.019 mmol) was placed in an NMR tube into which [D4]MeOH
(550 mL) was added. The mixture was heated at 508C for 6.8 h,
which resulted in the decrease of the methylene resonance cis to
the carbonyl group in 96 at% D.
Reaction of 9a with PMe3: Complex 9a (14.1 mg, 0.0175 mmol)
was reacted with PMe3 (9.2 mL, 0.088 mmol) in benzene at 708C for
57 h to give a mixture of 15a (48%) and 16a (22%). 15a: H NMR
1
(400 MHz, [D6]benzene): d=0.74 (d, J=8.7 Hz, 9H, PMe3), 0.8–2.8
(m, 8H, PC2H4P), 1.87 (s, 3H, CH2=CMeCO2), 5.06 (s, 1H, CH2=
CMeCO2), 6.01 (s, 1H, CH2=CMeCO2), 6.64 (m, 1H, C6H4), 6.8–7.5 (m,
20H, aromatic), 7.75 (m, 1H, C6H4), 8.00 (m, 1H, C6H4), 8.27 ppm (m,
1H, C6H4); 31P{1H} NMR (162 MHz, [D6]benzene): d=À1.26 (dt, J=
321.3, 31.8 Hz, 1P, PMe3), 39.60 (ddd, J=321.7, 21.7, 14.0 Hz, 1P,
PPhC6H4), 67.03 (ddd, J=32.1, 22.5, 16.3 Hz, 1P, PPh2), 96.21 ppm
(dt, J=32, 15 Hz, 1P, PPh). 16a: 1H NMR (400 MHz, [D6]benzene):
d=1.19 (d, J=7.3 Hz, 9H, PMe3), 1.96 (s, 3H, CH2=CMeCO2), 5.11 (s,
1H, CH2=CMeCO2), 6.15 ppm (s, 1H, CH2=CMeCO2), other signals
were overlapped with major resonances; 31P{1H} NMR (162 MHz,
[D6]benzene): d=À5.08 (dt, J=299.2, 25.6 Hz, 1P, PMe3), 46.10 (dd,
J=25.2, 4.7 Hz, 1P, PPhC6H4), 80.95 (dd, J=23.6, 13.2 Hz, 1P, PPh2),
95.89 ppm (ddd, J=299.8 Hz, 13.2, 4.7 Hz, 1P, PPh).
Catalytic H–D exchange reaction of methacrylic acid: Complex 5a
(11.4 mg, 0.0198 mmol) was placed in an NMR tube into which
[D4]MeOH (600 mL) and methacrylic acid (16.7 mL, 0.198 mmol)
were added. The solution was heated at 508C for 23 h, which re-
sulted in the complete disappearance of the methylene resonance
cis to the carbonyl group. 13C{1H} NMR (100 MHz, [D4]MeOH): d=
18.51 (s, CHD=CMeCO2D), 125.29 (t, J=10.1 Hz, CHD=CMeCO2D),
138.55 (s, CHD=CMeCO2D), 171.23 ppm (s, CHD=CMeCO2D). After
2
the removal of [D4]MeOH, the H NMR spectrum was measured in
methanol. 2H{1H} NMR (61.4 MHz, methanol): d=6.06 ppm (s,
CHD=CO2D).
Catalytic H–D exchange reaction of carboxylic acids: [cis-RuH2-
(PMe3)4] (ca. 10 mg) was dissolved in [D4]MeOH into which carbox-
ylic acid (10 equiv) were added. The solution was heated to at
508C for 24–56 h.
Reaction of 11 a with PMe3: Complex 11 a (10.4 mg, 0.0182 mmol)
and a flame-sealed capillary that contained a [D6]benzene solution
of PPh3 were placed in an NMR tube into which [D6]benzene
(485.0 mL) and PMe3 (19.0 mL, 0.187 mmol) were added. The solu-
tion was heated at 708C for 3.8 h to produce [Ru{OC(O)CMe=CH2-
k1O}(DMPE)2(PMe3)]+[CH2=CMeCO2]À (14a) in 41% yield (conver-
sion of 11 a: 41%). This compound was characterized by 31P NMR
spectroscopy. 31P{1H} NMR (164 MHz, [D6]benzene): d=À8.2 (dtd,
J=256.4, 35.6, 29.8 Hz, 1P, PMe3), 28.8 (dtd, J=269.3, 35.6, 13.5 Hz,
1P, P atom in DMPE trans to a DMPE P atom), 36–39 (m, 2P,
DMPE), 45.4 ppm (tdd, J=29.8, 23.2, 13.5 Hz, 1P, P atom in DMPE
cis to carboxylato).
Crystallographic analysis
A Rigaku AFC7R-Mercury II diffractometer with graphite-monochro-
mated MoKa radiation (l=0.71075 ꢁ) was used for data collection
at 200.0 K. A selected crystal was mounted on a glass capillary and
protected with Paraton N oil. The structures were solved by direct
methods (SIR 92)[31] and refined by a full-matrix least-squares pro-
cedure by using SHELXL-97 programs[32] with CrystalStructure ver-
sion 4.1.[31] The structures were depicted by ORTEP-III[33] and POV-
Ray[34] for Windows. Crystallographic data [CCDC 900814 for cis-
Ru(OC(O)CMe=CH-k2O,C)(PMe3)4 (1a), CCDC 900816 for cis-Ru(O-
C(O)C6H4-k2O,C)(PMe3)4 (1 f), CCDC 900815 for cis-Ru(OC(O)CMe=
Reaction of 3a with PMe3: Complex 3a (7.1 mg, 0.014 mmol) was
treated with PMe3 (70.0 mL, 0.0688 mmol) in [D6]benzene to give
1a immediately in 40% yield. Further treatment at 708C for an
hour produced 1a quantitatively.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 1101 – 1115 1114

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
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Acknowledgements
We thank Ms. S. Kiyota for elemental analysis. We also thank
Prof. K. Osakada (Tokyo Institute of Technology) for useful tips on
the preparation of [Ru2(O2CMe)4Cl]. This work was financially
supported by the Grant-in-Aid for Scientific Research on Innova-
tive Areas “Molecular Activation Directed toward Straightforward
Synthesis” from the Ministry of Education, Culture, Science and
Technology of Japan.
Keywords: deuterium · CÀH activation · metallacycles · P
ligands · ruthenium
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Received: September 27, 2012
Revised: November 30, 2012
Published online on March 6, 2013
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ChemCatChem 2013, 5, 1101 – 1115 1115

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