Multiple C-H bond cleavage of the alkyl group in (2,6-Dialkylphenoxo) ruthenium(II) complexes

Article abstract of DOI:10.1021/om5000248

The metathetical reaction between cis-RuCl₂(PMe ₃)₄ and an excess amount of potassium 2,6- dimethylphenoxide rapidly produces an oxaruthenacycle by the sp³ C-H bond cleavage reaction of the o-methyl group. With potassium 2,6-diethyl- and 2,6-diisopropylphenoxides, multiple C-H bond cleavage of o-alkyl groups occurs to give unsaturated oxaruthenacycles. These multiple activations are triggered by the sp³ C-H bond cleavage of the o-alkyl group from bis(2,6-dialkylphenoxo)ruthenium(II) to form a saturated ruthenacycle followed by β-hydride elimination and dehydrogenation from the resulting (2-alkenyl-6-alkylphenoxo)(hydrido)ruthenium(II) intermediate.

Full text of DOI:10.1021/om5000248

Article
pubs.acs.org/Organometallics
Multiple C−H Bond Cleavage of the Alkyl Group in (2,6-
Dialkylphenoxo)ruthenium(II) Complexes
Masafumi Hirano,* Yasuto Yanagisawa, Endin Mulyadi, Nobuyuki Komine, and Sanshiro Komiya†
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16
Nakacho, Koganei, Tokyo 184-8588, Japan
S
* Supporting Information
ABSTRACT: The metathetical reaction between cis-RuCl2(PMe3)4 and an excess
amount of potassium 2,6-dimethylphenoxide rapidly produces an oxaruthenacycle by
the sp3 C−H bond cleavage reaction of the o-methyl group. With potassium 2,6-
diethyl- and 2,6-diisopropylphenoxides, multiple C−H bond cleavage of o-alkyl
groups occurs to give unsaturated oxaruthenacycles. These multiple activations are
triggered by the sp3 C−H bond cleavage of the o-alkyl group from bis(2,6-
dialkylphenoxo)ruthenium(II) to form a saturated ruthenacycle followed by β-
hydride elimination and dehydrogenation from the resulting (2-alkenyl-6-
alkylphenoxo)(hydrido)ruthenium(II) intermediate.
Scheme 1
INTRODUCTION
■
The C−H bond cleavage reaction is one of the most promising
inlets for environmentally benign molecular transformation
promoted by transition-metal compounds. One of the keys to
the C−H bond cleavage reaction is a directing group to bring a
C−H bond in proximity to the transition-metal center.1 An
aryloxo group is one such good directing group. For example,
Bergman and co-workers documented an sp2 C−H bond
cleavage reaction by ortho metalation from a cis-bis(4-
methylphenoxo)ruthenium(II) complex (eq 1).2 Perkin and
co-workers documented competitive sp3 and sp2 C−H bond
cleavage reactions of phenols by WH(PMe3)4(PMe2CH2-
κ1P,η1C), as shown in Scheme 1.3
ments such as cyclohexenyl and isopropenyl by multiple
abstractions of hydrogen atoms from the alkyl groups.
We previsouly documented sp3 C−H bond cleavage
reactions of 2,6-dimethylphenoxo and 2,6-dimethylbenzene-
thiolato complexes of Ru(II)13 and Pt(II).14
As illustrated in Scheme 2, a five-coordinate bis(2,6-
dimethylbenzenethiolato)ruthenium(II) complex gives a thiar-
uthenacycle by a concerted sp3 C−H bond cleavage reaction at
room temperature.13a This reaction goes through the internal
electrophilic substitution (IES) mechanism,15 where one of the
chalcogen atoms acts as a directing group of the 2-methyl group
and the other is a proton acceptor at the Ru(II) center. In this
case either of the o-methyl groups is forced in proximity to the
metal center, which makes the sp3 C−H bond activation
reaction facile.
In this reaction, although 2-methylphenol (o-cresol) leads to
the sp3 C−H bond cleavage reaction of the o-methyl group, the
reactions with 2-ethyl-, 2-isopropyl-, and 2-tert-butylphenols
result in the sp2 C−H bond cleavage reaction, implying
difficulty in the C−H bond cleavage of the higher alkyl
homologues. Nevertheless, some related multiple hydrogen
abstractions from higher alkyl homologues such as cyclohexyl
and isopropyl have been documented for Ru(II) (eqs 2,4 3,5
and 46), Pt(IV),7 Rh(I),8 Ir(I),9,10 Ir(III),11 and Nb(V).12
Interestingly, these reactions generally give unsaturated frag-
Received: January 10, 2014
Published: February 18, 2014
© 2014 American Chemical Society
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metathetical method was better than the process starting from
Ru(η4-1,5-COD)(η6-1,3,5-COT)/PMe3 or fac-Ru(6-η1:1−3-η3-
C8H10)(PMe3)3, we supposed that such a metathetical method
using cis-1 must be much more effective for the formation of 2.
Preparation of cis-RuCl2(PMe3)4 (cis-1). Although trans-1
is widely known to be prepared by the reaction of
RuCl2(PPh3)3 with PMe3,18 its cis analogue cis-1 has not been
reported until quite recently.19 We have independently found
an alternative preparation method of cis-1, by the protonolysis
of cis-RuCl(OAc)(PMe3)4 with dry HCl, in 95% yield.
Metathesis Reaction of cis-1 with Potassium Aryl-
oxides. With Potassium 2,6-Dimethylphenoxide. To our
surprise, the reaction of cis-1 with 3 equiv of potassium 2,6-
dimethylphenoxide in THF at 19 °C produced 2 very quickly
(within 8 min) in 99% yield (Scheme 3). Although the isolation
of 2 had been reported previously,13e,f we now could obtain
Scheme 2
Scheme 3. C−H Bond Cleavage Reactions of o-Alkyl Groups
a
in Aryloxido Ligands
In the line of exploration assessment, we set up a series of
studies for C−H bond activation reactions using bis(2,6-
dimethylphenoxo)-, bis(2-ethyl-6-methylphenoxo)-, bis(2,6-di-
ethylphenoxo)-, and bis(2,6-diisopropylphenoxo)ruthenium(II)
compounds and found multiple C−H bond activation from the
o-alkyl groups. In this report, we describe facile and multiple
C−H bond activation of the o-alkyl groups induced by
ruthenium(II) complexes and discuss the total features of the
reaction mechanisms.
RESULTS AND DISCUSSION
■
We have documented the formation of Ru[OC6H3(CH2-
2)(Me-6)-κ1O,η1C](PMe3)4 (2) by either the reaction of
Ru(η4-1,5-COD)(η6-1,3,5-COT)/PMe3 with 2,6-dimethylphe-
nol (2,6-xylenol) or the reaction of Ru(η4-1,5-COD)(η6-1,3,5-
COT)/PMe3 with allyl 2,6-dimethylphenyl ether.13e,f A key
compound formed from the Ru(η4-1,5-COD)(η6-1,3,5-COT)/
PMe3 system was fac-Ru(6-η1:1−3-η3-C8H10)(PMe3)3,16 and
treatment of the isolated intermediate with 2,6-dimethylphenol
gave 2 in 91% yield, but these reactions were very sluggish (10
days at 70 °C).13e In the present study, we attempted to
prepare 2 by a metathetical reaction between RuCl2(PMe3)4
(1) and potassium 2,6-dimethylphenoxide. With 1 equiv of
potassium 2,6-dimethylphenoxide, trans-RuCl2(PMe3)4 (trans-
1) gave 2 (38%) and a small amount of cis-RuCl2(PMe3)4 (cis-
1; 11%) in THF at 50 °C for 46 h. Treatment of trans-1 with 2
equiv of potassium 2,6-dimethylphenoxide in THF at 50 °C
produced 2 in high yield (92%) after 45 h, during which time
only trans-1 and 2 were observed by NMR.17 Although this
a
Isolated yields are noted in parentheses.
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single crystals of 2 and the molecular structure was
unambiguously determined as shown in Figure 1.
obtained at room temperature after 13 h. These data suggest
this unknown species A to be cis-RuCl(OC6H3Me2-2,6-
κ1O)(PMe3)4, and it readily reacts with the second potassium
2,6-dimethylphenoxide to give 2 (Scheme 4). In fact, A never
gives 2 in the absence of further addition of potassium 2,6-
dimethylphenoxide, so that a direct formation of 2 from A can
be ruled out.
Scheme 4
Although we have documented the isolation of fac-
Ru(SC6H3Me2-2,6-κ1S)2(PMe3)3 and formation of the thiar-
uthenacycle Ru[SC6H3(CH2-2)(Me-6)-κ2S,C](PMe3)4 by the
internal electrophilic substitution mechanism (Scheme 2),13a
we failed to get any evidence for the putative bis(aryloxo)
analogue B even at low temperature. The formation of 2 from
cis-1 was suppressed in the presence of added PMe3 (9 equiv).
In DMSO/THF (2/1 v/v), 2 formed slowly and it took 1 h at
19 °C to give 2 in 70% yield. Since the consumption of the
dichlorido complex cis-1 was slow, the first metathetical
reaction between cis-1 and potassium 2,6-dimethylphenoxide
seemed to be suppressed in this solvent system.
We also tried the metathetical reaction of cis-RuClMe-
(PMe3)4 with potassium 2,6-dimethylphenoxide, where cis-
RuMe(OC6H3Me2-2,6-κ1O)(PMe3)4 was expected to be
formed in situ, to give 2. Compound 2 was obtained in 98%
yield at 19 °C after 4.3 h with concomitant formation of
methane in 88% yield.
We are delighted with these findings of this efficient pathway
for the sp3 C−H bond cleavage reaction of the o-methyl group
at room temperature. This success led us to attempt a series of
reactions of cis-1 with 2,6-dialkylphenoxides.
Figure 1. Molecular structures of Ru[OC6H3(CH2-2)(Me-6)-
κ1O,η1C](PMe3)4 (2) and Ru[OC6H3(CH2-2)(Et-6)-κ1O,η1C]-
(PMe3)4 (3). All hydrogen atoms and incorporated solvent are
omitted for clarity. Ellipsoids represent 50% probability.
With 2-Ethyl-6-methylphenoxide. When potassium 2-ethyl-
6-methylphenoxide was employed in this reaction, Ru-
[OC6H3(CH2-2)(Et-6)-κ1O,η1C](PMe3)4 (3) was exclusively
obtained in 94% yield (Scheme 3); the molecular structure of 3
is depicted in Figure 1. This fact indicates that the methyl group
is much more susceptible to C−H bond cleavage reaction than
the ethyl group.
With 2,6-Diethylphenoxide. Surprisingly, in the case of the
reaction of cis-1 with potassium 2,6-diethylphenoxide, the six-
membered unsaturated ruthenacycle 4 (47%) was predom-
inantly obtained with concomitant formation of the five-
membered ruthenacycle 5 (7%), although this reaction needed
gentle warming above 50 °C. When this reaction was
performed in the presence of 3 equiv of PMe3, complex 4
was obtained as the sole product, which was isolated by
recrystallization from cold hexane in 33% yield. No significant
The reaction of cis-1 with 2.5 equiv of potassium 2,6-
dimethylphenoxide was monitored by NMR in THF at −80 °C.
At the beginning of the reaction, a mixture of the dichlorido
complex cis-1 (45%), the oxaruthenacycle 2 (35%), and
unknown species A (25%) having an ABX2 pattern was
observed in the 31P{1H} NMR and finally A converted into the
oxaruthenacycle 2 upon warming to room temperature. The
final yield of 2 was 99%. Therefore, this unknown species A
would be an intermediate in this reaction.
1
Although a detailed analysis of A by H NMR was difficult
because of severe overlapping of signals, the ABX2 pattern
suggests an octahedral compound having four PMe3 groups
with two different ligands in the mutually cis positions. When
cis-1 was treated with 1.2 equiv of potassium 2,6-dimethylphen-
oxide, a mixture of A (25%), cis-1 (35%), and 2 (50%) was
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acceleration or suppression effect was observed for the
formation of 4 and 5 by adding a radical scavenger such as
galvinoxyl, using t-BuCHCH2 as a hydrogen acceptor, or
changing the solvent from THF to acetone.
nature of 5 in methanol, while 4 was insoluble. On this basis,
we succeeded in isolating 5 by the following procedure.
Namely, heating the isolated 4 to 50 °C in benzene gave an
equilibrium mixture with 5 (vide infra),20 from which 5 was
isolated as analytically pure pale yellow crystals in 19% yield.
The 31P{1H} NMR of 5 in benzene-d6 shows an AM2X pattern
suggesting an octahedral complex having four phosphorus
atoms with two different groups in mutually cis positions. The
most characteristic features in the 1H NMR are the two
correlated multiplets at δ 6.83 (1H) and δ 5.01 (1H). These
two protons bind to the same carbon appearing at δ 109.0 (s)
on the basis of a HETCOR experiment. Therefore, these two
1H resonances are assignable to the geminal methylene protons.
We therefore characterized this compound to be a five-
membered oxaruthenacycle having an exo methylene group
(Scheme 3).
The reaction profile for cis-1 with potassium 2,6-diethylphen-
oxide showed a pattern much more complex than that with
potassium 2,6-dimethylphenoxide. In the 31P{1H} NMR
spectra, this reaction rapidly gave a new species having an
ABX2 spin system with concomitant formation of AMNX,
AM2X, and AXY resonances within 8 min at room temperature,
though the AMNX resonance broadened at room temperature
and sharpened at −80 °C. Although the detailed analysis of
these species was difficult, we believe the ABX2 species to be cis-
RuCl(OC6H3Et2-2,6-κ1O)(PMe3)4 because of the similarity to
A, and the AMNX and AM2X species may be assignable to E
and F, respectively, because of the C1 and Cs symmetries of the
structures (Chart 1).
The 31P{1H} NMR spectrum of 4 in benzene-d6 showed an
AM2X pattern at δ 12.88, 0.26, and −15.59, suggesting an
octahedral complex with two inequivalent substituents at the
mutually cis positions. The resonances at δ 12.88 and −15.59
are assignable to the phosphorus atoms trans to the oxygen and
carbon, respectively, on the basis of the characteristic trans
influence. In the 1H NMR spectrum, a 3H triplet at δ 1.49 and
a 2H quartet at δ 2.93 are assignable to the o-ethyl group and
the resonances at δ 7.30 (d, 1H), 7.28 (d, 1H), and 6.77 (t, 1H)
are assigned as the aromatic protons. The most characteristic
1
features in the H NMR are two multiplets at δ 7.58 (m, 1H)
and 7.51 (m, 1H). A HETCOR experiment suggested the
former and latter signals have spin correlations with different
carbons, whose 13C{1H} NMR resonances were observed at δ
158.5 (dtd, JC−P = 62, 17, 9 Hz) and δ 131.2 (m), respectively.
These protons are therefore assigned as the alkenyl methine
protons at the α and β carbons. The most unambiguous
structural information was obtained by an X-ray analysis
(Figure 2).
Chart 1
The AXY species, a predominant product at the initial stage,
was identified as mer-RuH[OC6H3(CHCH2-2)(Et-6)-
κ1O,η2C,C′](PMe3)3 (8; 62% at 2 h) (vide infra), which
gradually converted into 4 (50%) and 5 (8%) with several
Figure 2. Molecular structure of Ru[OC6H3(C1HC2H-2)(Et-6)-
κ1O,η1C2](PMe3)4 (4). All hydrogen atoms and the incorporated
hexane are omitted for clarity. Ellipsoids represent 50% probability.
21
unidentified species involving cis-RuH2(PMe3)4 (15%) after
48 h. Compound 8 was obtained from the reaction mixture by
recrystallization from cold hexane. The molecular structure is
shown in Figure 3.
The revealed molecular structure indicates an octahedral
complex with a six-membered oxaruthenacycle. The bond
distance C(7)−C(8) is 1.342(7) Å, suggesting CC double-
bond character, while C(9)−C(10) has a typical single-bond
distance (1.531(11) Å). The C(2)−C(7)−C(8) (129.0(5)°)
and Ru(1)−C(8)−C(7) (126.8(4)°) bond angles and the
C(2)−C(7)−C(8)−Ru(1) dihedral angle (3.2(8)°) are con-
sistent with sp2 hybridization for the C(7) and C(8) carbons.
All these features are consistent with the structure estimated by
the NMR analysis.
The 31P{1H} NMR spectrum of 8 shows an AXY pattern at δ
17.5, 6.3, and 3.9, and the coupling constant between the
signals at δ 6.3 and 3.9 is quite large (J = 207 Hz), suggesting
these PMe3 ligands to be mutually trans to each other. A
characteristic upfield resonance in the 1H NMR at δ −6.99 (dt,
1
1H) is assignable to the hydride. In the H NMR spectrum,
three multiplets at δ 4.51 (1H), 2.76 (1H), and 2.41 (1H)
coupled to each other are observed. A 13C NMR and HETCOR
study suggests that the proton resonating at δ 4.51 is
connecting to the carbon resonating at δ 72.5, and both of
the protons at δ 2.76 and 2.41 bind to the same carbon
resonating at δ 52.5. These protons are therefore characterized
as the vinylic methine and methylene protons. These NMR
Isolation of the minor product 5 from the mixture obtained
from the reaction of cis-1 with potassium 2,6-diethylphenoxide
resulted in failure. However, we found the practically soluble
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data are consistent with the molecular structure revealed by the
X-ray analysis.
Heating of 4 in benzene-d6 at 50 °C produced 5, and the
[4]/[5] ratio reached a constant (0.9) after 30 h. For the
backward reaction, heating of 5 in benzene-d6 at 50 °C resulted
in the formation of 4 and the [4]/[5] ratio also reached 0.9.
Unfortunately, because of unavoidable decomposition during
these experiments, we could not determine the accurate
equilibrium constant. However, the reversibility between 4
and 5 was confirmed. No reaction occurred in the presence of
added PMe3 for these forward and backward reactions,
suggesting this transformation to require prior dissociation of
the PMe3 ligand.
With Potassium 2,6-Diisopropylphenoxide. Along similar
lines, we studied the C−H bond activation reaction of the o-
isopropyl group. The reaction of cis-1 with 3 equiv of potassium
2,6-diisopropylphenoxide at 50 °C in THF for 24 h produced a
mixture of Ru[OC6H3(CMeCH-2)(iPr-6)-κ1O,η1C](PMe3)4
(6) and fac-Ru[OC6H3{C(CH2)2-2}(iPr-6)-κ1O,η3C,C′,C″]-
(PMe3)3 (7) in 41% and 11% yields, respectively, from which
compound 7 was obtained as the sole compound in 10% yield.
Compound 7 shows an AX2 pattern in the 31P{1H} NMR
spectrum. This pattern suggests a five-coordinate complex
Figure 3. Molecular structure of mer-RuH[OC6H3(CHCH2-2)(Et-
6)-κ1O,η2C,C′](PMe3)3 (8). All hydrogen atoms, except those in the
vinyl and hydride groups, and the incorporated hexane molecule are
omitted for clarity. Ellipsoids represent 50% probability.
1
having Cs symmetry. The H NMR spectrum in benzene-d6
shows correlated resonances at δ 1.40 (d, 6H) and δ 3.54 (sept,
1H), suggesting an isopropyl group. The resonances at δ 1.78
(dd, 2H) and 3.48 (br, 2H) are assignable to the anti or syn
Scheme 5
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methylene protons in the η3-allylic moiety. In a HETCOR
experiment, these four methylene protons are found to connect
to the same carbon at δ 44.8. This carbon resonance was
observed as a multiplet, probably due to CPAPXPX′ coupling.
From these characteristic features, we can assign this compound
as the η3-allylic compound 7. On the other hand, compound 6
was purely obtained by the treatment of 7 with PMe3 in
benzene-d6 at 70 °C. The 31P{1H} NMR spectrum shows an
external aryloxide anion. Such a mechanism has been proposed
for [Ru(p-cyene)(2-phenylpyridine)(OAc)]+.22 We believe this
process to be less likely because (i) the formation rate on the
basis of the time−yield curves for 4 remained unchanged
regardless of the concentration of potassium 2,6-diethylphen-
oxide, (ii) no solvent effect was also observed on the rate
between THF (ε = 7.32) and acetone (ε = 20.7),23 and (iii) the
treatment of 2 with 1 equiv of 2,6-dimethylbenzenethiol gave a
thiaruthenacycle complex (Scheme 6), which supported a
putative formation of an (aryloxo)(arenethiolato)ruthenium(II)
intermediate followed by proton abstraction by the basic
aryloxo ligand.
1
AM2X pattern. In the H NMR spectrum the spin-correlated
resonances at δ 1.49 (d, 6H) and δ 3.82 (sept, 1H) show the
presence of an isopropyl group. An olefinic resonance at δ 7.37
(m, 1H) and a slightly broad singlet at δ 2.68 (br s, 3H) suggest
the α-methine and β-methyl groups in 6. The 13C{1H} NMR
spectrum and a HETCOR experiment showed the olefinic α-
methine carbon to be observed at δ 157.1 as doublet of triplets
of doublets by coupling with the PMe3 ligands. The quaternary
olefinic β-carbon and the β-methyl carbon were observed at δ
129.1 (m) and δ 30.1 (d), respectively. These data support the
structure of 6.
Scheme 6
The reaction profile for the treatment of cis-1 with potassium
2,6-diisopropylphenoxide monitored by NMR showed a very
complex pattern, but the time−yield curves suggested the initial
formation of 6 and then 7. Similar to the case for the 2,6-
diethylphenoxo system, no significant acceleration or suppres-
sion effect was observed by the addition of a radical scavenger
such as galvinoxyl or of t-BuCHCH2 as a hydrogen acceptor.
In the presence of 21 equiv of PMe3, the reaction of cis-1 with
2,6-diisopropylphenoxide gave neither 6 nor 7, suggesting the
importance of coordinative unsaturation for the C−H bond
cleavage reaction.
The heating of 6 under vacuum at 150 °C without solvent for
2 h gave a mixture containing 7 in 10% yield. On the other
hand, addition of PMe3 to 7 in benzene-d6 at 70 °C for 12 h
gave 6 in 99% yield. These data suggest reversibility between 6
and 7, although detailed thermodynamic parameters were
difficult to determine.
With 2,6-Di-tert-butylphenoxide. Treatments of the di-
chlorido complex cis-1 with potassium 2,6-di-tert-butylphen-
oxide gave a complex mixture. Similarly, a complex mixture was
also formed by the reaction in the presence of silver nitrate.
Unlike the reaction of cis-RuMe2(PMe3)4 with 2,6-dimethyl-
benzenethiol,3 the treatment of cis-RuMe2(PMe3)4 with 2,6-di-
tert-butylphenol gave a complex mixture.
Possible Pathway and Mechanism for Formation of
the Multiple C−H Bond Cleavage Reactions. As a typical
example of multiple C−H bond cleavage reactions, the reaction
of 2,6-diethylphenoxo complex is discussed in this section.
The formulation of 4 causes three hydrogen atoms to be lost
during this process, which is in sharp contrast with the C−H
bond cleavage of the o-methyl groups in 2 and 3. Although we
observed the formation of neither bis(aryloxo) complex C nor
D even at low temperature, they would be key intermediates in
this reaction (Scheme 5). Note again that we documented the
formation of cis-Ru(SC6H3Me2-2,6-κ1S)2(PMe3)4 and fac-Ru-
(SC6H3Me2-2,6-κ1S)2(PMe3)3, the thiolate analogues of C and
D, by the treatment of trans-1 with KSC6H3Me2-2,6.13a Like the
case for the thiolato analogue, the sp3 C−H bond cleavage
reaction from D would produce E′ or F′, probably by a
concerted internal electrophilic substitution mechanism. Since
oxygen normally has a higher basicity than sulfur, this concerted
abstraction of a proton from the o-alkyl group would be much
faster than that for the arenethiolato system. The alternative
mechanism is deprotonation from the o-methyl group by the
This reaction shows the reversible interconversion via the
putative (aryloxo)(arenethiolato)ruthenium(II) under acidic
conditions, which may exclude abstraction of a methyl proton
by an external base.24
Neither E′ nor F′ is observed at all during the reaction, but
intermediates assignable to E and F are observed by the NMR
analysis. The subsequent β-hydride elimination form the
methyl group in E′ or the methylene group in F′ gives the
hydrido complex G. Compound 8 is considered to be the stable
stereoisomer of G. Then, dehydrogenation from G and rapid
addition of PMe3 would produce the unsaturated 6-membered
ruthenacycle 4. Note that we have reported rapid dehydrogen-
ation from cis-RuH(SC6H3Me2-2,6)(PMe3)3 to form a
thiaruthenacycle Ru[SC6H3(CH2-2)(Me-6)-κ2S,C](PMe3)4.13d
Such a dehydrogenation process is considered to be a σ−bond
metathesis. On the other hand, direct formation of 5 from G is
a less likely process because we observed prior formation of 4.
Although the isomerization mechanism between 4 and 5 is not
clear to date, a direct 1,2-hydrogen shift reaction or further β-
hydride elimination from the ruthenacycle giving a (2-
alkynylaryl)(hydrido)ruthenium(II) intermediate is the possi-
ble pathway.
Reaction of Unsaturated Oxaruthenacycles with
DMAD. In order to understand the difference in reactivities
of 4 and 5, we have tried some reactions using them. A striking
contrast is the reaction using DMAD. The treatment of 4 with
DMAD at room temperature gave the eight-membered
unsaturated ruthenacycle 9 in 54% yield (eq 5). Complex 9
shows an ABX pattern in the 31P{1H} NMR and two 3H
singlets at δ 3.55 and 3.56 assignable to the methoxy groups
and two resonances at δ 4.37 (ddt, J = 9.2, 5.2, 1.2 Hz, 1H) and
5.96 (ddd, J = 9.2, 7.4, 2.3 Hz, 1H) assignable to the alkenyl
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of these solvents were stored under vacuum. The NMR spectra were
recorded on a 399.8 MHz (13C at 100.5 MHz and 31P at 161.8 MHz)
1
spectrometer. Tetramethylsilane was used as the reference for H and
13C spectra and external 85% H3PO4 for 31P spectra. GLC analyses
were performed by a instrument with a FID detector equipped with a
packed PolarPacks Q column.
Reaction of trans-RuCl2(PMe3)4 (trans-1) with Potassium 2,6-
Dimethylaryloxide. trans-RuCl2(PMe3)4 (trans-1; 5.7 mg, 0.012
mmol) and potassium 2,6-dimethylphenoxide (1.7 mg, 0.011 mmol)
were placed in an NMR tube into which THF was introduced. As an
external standard, a capillary containing P(OMe)3/C6D6 was inserted
into the NMR tube. The time course of the reaction was monitored by
NMR. After 46 h at 50 °C, cis-Ru[OC6H3(2-CH2)(6-Me)-κ1O,η1C]-
(PMe3)4 (2) was formed in 38% yield with concomitant formation of
cis-RuCl2(PMe3)4 (cis-1) in 11% yield. Similar treatment with 2 equiv
of potassium 2,6-dimethylphenoxide produced 2 in 92% yield after 45
h at 50 °C. Yields of 2 at 50 °C: 20% (2.5 h), 45% (7.5 h), 79% (21 h),
85% (32 h), and 92% (45 h).
1
methine protons in the H NMR. These data support the
formation of 9 by the insertion of DMAD into the Ru−C bond.
Note that we have reported a similar reaction of 2 with DMAD
to give 10 and 11 (Chart 2).13b In contrast to 4, 5 did not react
with DMAD under the same conditions, probably due to the
strong Ru−C bond (eq 6).
cis-RuCl2(PMe3)4 (cis-1). To a THF solution (100 mL) of cis-
RuCl(OAc)(PMe3)4 (6.1478 g, 12.3 mmol) was added dry HCl/Et2O
(0.4 M, 30 mL). The solution became a white suspension. Filtration of
the suspension through a Celite pad gave a yellow solution, which was
evaporated to dryness to give a pale yellow solid of cis-1 in 95% yield
(5.269 g, 11.1 mmol). This solid was pure enough to use in further
reactions but could be recrystallized from cold THF as pale yellow
Chart 2
1
crystals (44%). H NMR (400 MHz, DMSO-d6): δ 1.39 (m, 18H,
equatorial PMe3), 1.43 (vt, J = 2.75 Hz, 18H, axial PMe3). 31P{1H}
NMR (162 MHz, DMSO-d6): δ −8.30 (t, J = 33 Hz, 2P), 12.8 (t, J =
33 Hz, 2P).
CONCLUDING REMARKS
Reactions of cis-RuCl2(PMe3)4 (cis-1) with Potassium 2,6-
Dialkylphenoxides. With Potassium 2,6-Dimethylphenoxide. The
treatment of cis-1 with potassium 2,6-dimethylphenoxides gave cis-
Ru[OC6H3(CH2-2)(Me-6)-κ1O,η1C](PMe3)4 (2)13b,d,e in 99% yield
within 8 min. Compound 2 was also obtained by the reaction of cis-
RuCl(OAc)(PMe3)4 with 3 equiv of potassium 2,6-dimethylphenoxide
in 54% yield.
■
From the present studies, the C−H bond activation of o-alkyl
groups has been established. As reported previously,12 the ethyl
group is much less reactive than the methyl group toward the
C−H bond cleavage reaction. However, once the C−H bond
cleavage reaction occurs to give a saturated metallacycle from
bis(aryloxo) species, successive β-hydride elimination followed
by dehydrogenation proceeds rapidly. This is the reason we
obtain unsaturated metallacycles in the case of the C−H bond
cleavage reaction from the higher alkyl groups.
With Potassium 2-Ethyl-6-methylphenoxide. cis-1 (253.9 mg,
0.5331 mmol) was treated with potassium 2-ethyl-6-methylphenoxide
(273.3 mg, 1.568 mmol) in refluxing THF (20 mL) for 20 h. After
removal of all volatile materials, the resulting solid was extracted with
hexane. Recrystallization of the solid from cold hexane gave pale
yellow crystals of Ru[OC6H3(CH2-2)(Me-6)-κ1O,η1C](PMe3)4 (3) in
EXPERIMENTAL SECTION
■
General Procedures. All manipulations and reactions were
performed under dry nitrogen or argon with the use of standard
Schlenk and vacuum line techniques. Benzene, toluene, hexane,
tetrahydrofuran (THF), and Et2O were distilled over sodium
benzophenone ketyl, pentane was distilled over potassium benzophe-
none ketyl, and dichloromethane and acetonitrile were distilled from
Drierite; methanol was distilled under nitrogen from magnesium
methoxide. These solvents were stored under a nitrogen atmosphere.
PMe3 was prepared by the reaction of P(OPh)3 with MeMgI in 67%
yield.25 cis-RuCl(OAc)(PMe3)4 and cis-RuClMe(PMe3)4 were pre-
pared according to the literature methods.26,27 2-Ethyl-6-methylphenol
and 2,6-diethylphenol were prepared from commercially available 2-
ethyl-6-methylaniline and 2,6-diethylaniline according to the literature
methods.28 Potassium aryloxides were prepared by the reaction of
phenol derivatives with 0.9 equiv of KOH in methanol followed by
removal of volatile materials under high vacuum at 100 °C. The yields
of potassium 2,6-dimethylphenoxide, 2-ethyl-6-methylphenoxide, 2,6-
diethylphenoxide, and 2,6-diisopropylphenoxide were 62, 76, 68 and
32%, respectively. Dry HCl gas was generated by the reaction of flame-
dried sodium chloride with H2SO4, and the evolved dry HCl gas was
absorbed into dry Et2O. All other reagents were obtained from
commercial suppliers and were used as received. Benzene-d6 and
toluene-d8 were dried over sodium wire, DMSO-d6 was dried over
molecular sieves 4A, and dichloromethane-d2 was dried over P4O10; all
1
66% yield (191.0 mg, 0.3540 mmol). H NMR (400 MHz, benzene-
d6): δ 0.91 (d, J = 7.3 Hz, 9H, PMe3), 1.02 (vt, J = 2.8 Hz, 18H, PMe3),
1.19 (d, J = 5.5 Hz, 9H, PMe3), 1.53 (t, J = 7.5 Hz, 3H, CH2Me), 2.68
(tt, J = 3.2, 14.2 Hz, 2H, RuCH2), 2.99 (q, J = 7.5 Hz, 2H, CH2Me),
6.82 (t, J = 7.3 Hz, 1H, aromatic), 7.14 (d, J = 6.9 Hz, 1H, overlapped
with C6D5H, aromatic), 7.47 (d, J = 7.3 Hz, 1H, aromatic). 31P{1H}
NMR (162 MHz, benzene-d6): δ −13.9 (dt, J = 14, 25 Hz, 1P,
equatorial PMe3), 0.60 (dd, J = 25, 32 Hz, 2P, axial PMe3), 10.54 (dt, J
= 14, 32 Hz, 1P, equatorial PMe3).
With Potassium 2,6-Diethylphenoxide. cis-1 (283.6 mg, 0.596
mmol) was reacted with 3 equiv of potassium 2,6-diethylphenoxide
(241.2 mg, 1.28 mmol) in the presence of PMe3 (180 μL, 1.80 mmol)
in dry THF (ca. 20 mL) at 50 °C for 24 h, during which time the
yellow solution turned dark brown with deposition of a white solid.
The brown solution was filtered, and all volatile materials were
removed. The resulting residue was extracted with hexane (20 mL ×
4), and the brown hexane solution was evaporated to dryness to give a
solid which was recrystallized from cold hexane to give pale yellow
crystals of Ru[OC6H3(C1HC2H-2)(Et-6)-κ1O,η1C2](PMe3)4 (4) in
33% yield (107.2 mg, 0.20 mmol).
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1H NMR (400 MHz, benzene-d6, spin correlations confirmed
by COSY, HETCOR): δ 0.92 (d, J = 5.87 Hz, 9H, H10), 0.98
(vt, J = 2.93 Hz, 18H, H8), 1.19 (d, J = 5.87 Hz, 9H, H9), 1.49
(t, J = 7.34 Hz, 3H, H5), 2.93 (q, J = 7.34 Hz, 2H, H4), 6.77 (t,
J = 7.34 Hz, 1H, H2), 7.28 (d, J = 7.34 Hz, 1H, H1), 7.30 (d,
1H, H3, overlapped with H1), 7.51 (m, 1H, H7), 7.58 (m, 1H,
H6). 31P{1H} NMR (162 MHz, benzene-d6): δ −15.59 (dt, J =
13, 23 Hz, 1P, equatorial PMe3), 0.26 (dd, J = 23, 35 Hz, 2P,
axial PMe3), 12.88 (dt, J = 13, 35 Hz, 1P, equatorial PMe3).
13C{1H} NMR (100.5 MHz, benzene-d6, spin correlations
confirmed by HETCOR): δ 15.51 (s, C8), 18.40 (dt, J = 3, 11
Hz, C11), 15.34 (d, J = 22 Hz, C12), 23.04 (d, J = 25 Hz, C13),
25.74 (s, C7), 111.51 (s, C2), 126.54 (s, C1), 129.88 (s, C6),
130.09 (s, C3), 131.15 (m, C9), 132.53 (d, J = 5 Hz, C4),
158.50 (ddt, J = 9, 17, 62 Hz, C10), 160.23 (m, C5). Anal.
Calcd for C22H46OP4Ru·0.5C6H14: C, 50.49, H, 8.98. Found: C,
49.60, H, 8.73.
A yellow solution of the isolated 4 (80.0 mg, 0.145 mmol) in
benzene (10 mL) was stirred at 50 °C for 24 h and was evaporated to
give a dark brown oil, which was extracted with cold methanol to give
a yellow solution. The solution was evaporated to give a brown oil,
which was extracted with hexane and crystallized at −30 °C to give
pale yellow crystals of Ru[OC6H3(C1C2H2-2)(Et-6)-κ1O,η1C1]-
(PMe3)4 (5) in 19% yield (15 mg, 0.027 mmol).
1H NMR (400 MHz, benzene-d6, spin correlations confirmed
by COSY, HETCOR): δ −6.99 (dt, J = 20.5, 33.0 Hz, 1H, H9),
0.64 (d, J = 7.3 Hz, 9H, H10, H11, or H12), 1.17 (d, J = 5.9 Hz,
9H, H10, H11, or H12), 1.34 (d, J = 8.8 Hz, 9H, H10, H11, or
H12), 1.41 (t, J = 7.3 Hz, 3H, H5), 2.41 (m, 1H, H7 or H8),
2.73 (q, J = 7.3 Hz, 1H, H4), 2.76 (m, 1H, H7 or H8), 2.89 (q,
J = 7.3 Hz, 1H, H4), 4.51 (m, 1H, H6), 6.65 (t, J = 7.3 Hz, 1H,
H2), 7.06 (d, J = 7.3 Hz, 1H, H1), 7.26 (d, J = 7.3 Hz, 1H, H3).
31P{1H} NMR (162 MHz, benzene-d6): δ 3.91 (dd, J = 30, 207
Hz, 1P), 6.29 (dd, J = 31, 207 Hz, 1P), 17.46 (dd, J = 30, 31
Hz, 1P). 13C{1H} NMR (100.5 MHz, benzene-d6, spin
correlations between the carbons and hydrogens confirmed
by HETCOR): δ 52.25 (s, C10), 72.45 (s, C10), 110.99 (s,
C2), 123.80 (s, C1), 125.96 (s, C3).
The reaction of cis-1 with potassium 2,6-diethylphenoxide in THF
was monitored by 31P{1H} NMR. The reaction mixture initially gave
an ABX2 resonance which was tentatively assigned as cis-RuCl-
(OC6H3Et2-2,6-κ1O)(PMe3)4 (A). 31P{1H} NMR (THF, 162 MHz,
21.5 °C): δ −4.50 (t, J = 33 Hz, 2P), 13.65 (q, J = 33 Hz, 1P), 15.45
(q, J = 33 Hz, 1P). Then, we also observed formation of an AM2X
species, which may be assignable to the six-membered saturated
oxaruthenacycle Ru[OC6H3(CH2CH2-2)(Et-6)-κ1O,η1C](PMe3)4
(F′). 31P{1H} NMR (THF, 162 MHz, −20 °C): δ −17.44 (td, J =
23, 12 Hz, 1P), −0.48 (dd, 34, 23 Hz, 2P), 13.94 (td, J = 34, 12 Hz,
1P). In the meantime, broadened resonances were also observed,
which sharpened at −60 °C as an AMNX system. This AMNX species
is consistent with the five-membered saturated oxaruthenacycle
Ru[OC6H3(CHMe-2)(Et-6)-κ1O,η1C](PMe3)4 (E′). 31P{1H} NMR
(THF, 162 MHz, −60 °C): δ −13.30 (td, J = 24, 12 Hz, 1P), −4.69
(ddd, J = 327, 33, 24 Hz, 1P), 3.20 (ddd, J = 327, 33, 24 Hz, 1P), 11.40
(td, J = 33, 12 Hz, 1P). As a major intermediate, complex 8 was also
observed during the reaction. The time course for the reaction of cis-1
with potassium 2,6-diethylphenoxide (2 equiv) was as follows at 50 °C
in THF: 10 min, 1 (0%), A (0%), 8 (18%), 4 (28%), 5 (7%); 22 h, 1
(0%), A (0%), 8 (10%), 4 (48%), 5 (9%); 35 h, 1 (0%), A (0%), 8
(2%), 4 (50%), 5 (9%); 48 h, 1 (0%), A (0%), 8 (0%), 4 (50%), 5
(8%).
1H NMR (400 MHz, benzene-d6, spin correlations confirmed
by COSY, HETCOR): δ 1.01 (vt, J = 2.9 Hz, 18H, H8), 1.06
(d, J = 7.3 Hz, 9H, H9 or H10), 1.16 (d, J = 5.9 Hz, 9H, H9 or
H10), 1.50 (t, J = 7.3 Hz, 3H, H5), 2.95 (q, J = 7.3 Hz, 2H,
H4), 5.01 (m, 1H, H6 or H7), 6.78 (t, J = 7.3 Hz, 1H, H2),
6.83 (m, 1H, H6 or H7), 7.16 (d, J = 7.3 Hz, 1H, H1,
overlapped with CD5H), 7.97 (d, J = 7.3 Hz, 1H, H3). 31P{1H}
NMR (162 MHz, benzene-d6): δ −14.79 (td, J = 24, 13 Hz, 1P,
equatorial PMe3), −5.4 (dd, J = 24, 33 Hz, 2P, axial PMe3),
7.28 (td, J = 33, 13 Hz, 1P, equatorial PMe3). 13C{1H} NMR
(100.5 MHz, benzene-d6, spin correalations confirmed by
HETCOR): δ 15.03 (s, C8), 109.00 (s, C10), 112.57 (s, C2),
118.64 (s, C1), 126.35 (s, C3), 180.21 (dtd, J = 65, 16, 9 Hz,
C9). Anal. Calcd for C22H46OP4Ru: C, 47.91, H, 8.41. Found:
C, 47.89, H, 8.57.
With Potassium 2,6-Diisopropylphenoxide. The treatment of
Ru[OC6H3{C(CH2-2)(iPr-6)-κ1O, η3C1,C2,C3}(PMe3)4 (7) (7.0 mg,
0.014 mmol) with 10 equiv of PMe3 at 70 °C for 12 h in benzene-d6
gave 6 in 99% yield.
1H NMR (400 MHz, benzene-d6, spin correlations confirmed
by COSY, HETCOR): δ 0.92 (d, 9H, H10, overlapped with
H8), 0.95 (vt, J = 3.2 Hz, 18H, H8), 1.18 (d, J = 5.5 Hz, 9H,
H9), 1.49 (d, J = 6.9 Hz, 6H, H5), 2.68 (s, 3H, H6), 3.82 (sep,
J = 6.9 Hz, 1H, H4), 6.83 (t, J = 7.3 Hz, 1H, H2), 7.33 (d, J =
From the mother liquor for the recrystallization of 4, further
recrystallization from cold hexane deposited a small amount of crystals
containing RuH[OC6H3(CHCH2-2)(Et-6)-η2C,C′](PMe3)3 (8)
and 5. A crystal of 8 was picked from the mixture, and its molecular
structure was revealed by an X-ray analysis.
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37% (12 h), 43% (22 h), and 48% (35 h). (b) Reaction of cis-1 (9.6
mg, 0.020 mmol) with potassium 2,6-diethylphenoxide (18.9 mg,
0.100 mmol, 10 equiv/Ru) in THF (0.60 mL) at 50 °C: yield of 3,
13% (2 h), 26% (5 h), 40% (12 h), 48% (22 h), and 49% (35 h).
Effect of Solvent on the Rate of Formation of 4. (a) Reaction
of cis-1 (9.8 mg, 0.021 mmol) with potassium 2,6-diethylphenoxide
(9.5 mg, 0.051 mmol, 2.5 equiv/Ru) in THF (0.60 mL) at 50 °C: yield
of 4, 23% (3 h), 31% (5 h), 39% (11 h), and 40% (21 h). (b) Reaction
of cis-1 (9.8 mg, 0.021 mmol) with potassium 2,6-diethylphenoxide
(9.1 mg, 0.048 mmol, 2.4 equiv/Ru) in acetone (0.60 mL) at 50 °C,
21% (3 h), 26% (5 h), 37% (11 h), and 43% (21 h).
Reaction of Ru[OC6H3(CH2-2)(Me-6)](PMe3)4 (2) with 2,6-
Dimethylbenzenethiol. In an NMR tube, complex 2 (14.5 mg,
0.0276 mmol) was dissolved in benzene-d6 (0.6 mL), and then 2,6-
dimethylbenzenethiol (3.6 μL, 0.027 mmol) was added with a
hypodermic syringe. After 37 h at room temperature, Ru[SC6H3(CH2-
2)(Me-6)](PMe3)4 (100%) and 2,6-dimethylphenol (104%) were
formed.
7.3 Hz, 1H, H1), 7.37 (m, 1H, H7), 7.57 (d, J = 7.3 Hz, 1H,
H3). 31P{1H} NMR (162 MHz, benzene-d6): δ 16.4 (dt, J = 12,
23 Hz, 1P, equatorial PMe3), 0.60 (dd, J = 23, 35 Hz, 2P, axial
PMe3), 11.56 (dt, J = 12, 35 Hz, 1P, equatorial PMe3). 13C{1H}
NMR (100.5 MHz, benzene-d6, spin correlations confirmed by
HETCOR): δ 18.56 (vt, J = 2.9, 12.5 Hz, C12), 21.81 (d, J =
15.3 Hz, C13), 22.98 (d, J = 24.9 Hz, C14), 24.70 (s, C8),
26.46 (s, C7), 30.05 (d, J = 8.6, C10), 111.53 (s, C2), 123.02 (s,
C1), 124.59 (s, C3), 129.06 (br, C9), 129.46 (s, C6), 137.37
(d, J = 3.8 Hz, C4), 157.51 (dtd, J = 8.6, 17.3, 62.8 Hz, C11),
160.06 (s, C5).
cis-1 (1.0282 g, 2.159 mmol) and 2.4 equiv of potassium 2,6-
diisopropylphenoxide (1.1363 g, 5.2519 mmol) were placed in a 150
mL Schlenk tube, into which THF was transferred by valve-to-valve
distillation. The reaction in refluxing THF for 2 h gave an ocher
solution with a white precipitate. The filtered solution was evaporated
to dryness, and the resulting solid was extracted with hexane (20 mL ×
3). Removal of all volatile materials under vacuum at 150 °C gave
Ru[OC6H3{C(CH2)2-2)(iPr-6)-κ1O,η3C1,C2,C3}(PMe3)4 (7) as a pale
yellow solid in 11% yield (119.2 mg, 0.2367 mmol).
Reaction of Ru[OC6H3(C1HC2H-2)(Et-6)-κ1O,η1C2](PMe3)4
(4) with DMAD. A benzene (2 mL) solution of 4 (22 mg, 0.040
mmol) and DMAD (15 μL, 0.12 mmol) was stirred for 5 h at room
temperature to give a yellow precipitate. After removal of the solution,
the precipitate was washed with hexane to give a yellow powder of
Ru[OC6H3{CHCHC(CO2Me)C(CO2Me)-2}(Et-6)](PMe3)3
(9) in 54% yield (15 mg, 0.022 mmol). 1H NMR (400 MHz, CD2Cl2):
δ 1.08 (t, J = 7.4 Hz, 3H, CH2Me), 1.26 (d, J = 6.9 Hz, 9H, PMe3),
1.31 (d, J = 8.0 Hz, 9H, PMe3), 1.53 (d, J = 9.2 Hz, 9H, PMe3), 2.37
(dq, J = 13.7, 7.4 Hz, 1H, CH2Me), 2.43 (dq, J = 13.7, 7.4 Hz, 1H,
CH2Me), 3.55 (s, 3H, CO2Me), 3.56 (s, 3H, CO2Me), 4.37 (ddt, J =
9.2, 5.2, 1.2 Hz, 1H, CH), 5.96 (ddd, J = 9.2, 7.4, 2.3 Hz, 1H, 
CH), 6.14 (t, J = 7.4 Hz, 1H, aromatic), 6.69 (d, J = 7.4 Hz, 1H,
aromatic), 6.70 (d, J = 7.4 Hz, aromatic). 31P{1H} NMR (162 MHz,
CD2Cl2): δ −6.42 (t, J = 27 Hz, 1P), 9.03 (dd, J = 38, 27 Hz, 1P), 11.2
(dd, J = 28, 27 Hz, 1P).
X-ray Diffraction Studies. X-ray data were collected with a
Rigaku AFC-7R-Mercury II diffractometer with graphite-monochro-
mated Mo Kα radiation at −73.1 °C, with the CrystalClear
programs.29 Data were processed and corrected for Lorentz and
polarization effects and for absorption corrections with numerical
absoprtion correction. Structural solutions and refinements were
carried out with the SIR92 programs.30 The structures were solved by
direct methods using SHELXL31 to locate the heavy atoms, followed
by difference maps for the light non-hydrogen atoms. All hydrogen
atoms, except for a hydrido ligand in 8, were placed at calculated
positions. Alll non-hydrogen atoms were generally given anisotopic
displacement parameters in the final model. In the unit cell of 8 half of
a molecule of disordered hexane was observed as an incorporated
solvent but the atomic coordinates for the hexane molecule were less
accurately determined. The structures were depicted by ORTEP-III32
and POV-RAY33 for Windows.
1H NMR (400 MHz, benzene-d6, spin correlations confirmed
by COSY, HETCOR): δ 0.61 (d, J = 7.3 Hz, 9H, H9), 1.19 (d,
J = 7.3 Hz, 18H, H8), 1.40 (d, J = 6.9 Hz, 6H, H5), 1.78 (m,
2H, H6 or H7), 2.95 (sep, J = 6.9 Hz, 1H, H4), 3.48 (br, 2H,
H6 or H7), 6.69 (t, J = 7.3 Hz, 1H, H2), 7.14 (d, J = 5.9 Hz,
1H, H1, overlapped with C6D5H), 7.45 (d, J = 6.9 Hz, 1H, H3).
31P{1H} NMR (162 MHz, benzene-d6): δ 3.23 (d, J = 33 Hz,
2P, equatorial PMe3), 13.32 (t, J = 33 Hz, 1P, axial PMe3).
13C{1H} NMR (100.5 MHz, benzene-d6, spin correlations
confirmed by HETCOR): δ 20.1 (d, J = 26 Hz, C11), 21.2 (m,
C12), 24.2 (s, C8), 26.0 (s, C7), 44.8 (m, C10), 111.5 (s, C2),
123.8 (s, C1), 125.3 (s, C3), 130.6 (s, C4, C6 or C9), 134.8 (s,
C4, C6 or C9), 136.0 (d, J = 4.8 Hz, C4, C6 or C9), 171.12 (s,
C5).
Reaction of trans-RuCl2(PMe3)4 with AgNO3 and Then with
Potassium 2,6-Dimethylphenoxide. trans-1 (52.1 mg, 0.109
mmol) and AgNO3 (42.9 mg, 0.253 mol) were placed in a Schlenk
tube. After addition of THF, the mixture was stirred at 30 °C for a
night in the dark. A yellow-green solution with a white precipitate was
obtained. A part of the solution was introduced into an NMR tube
with a flame-sealed capillary ampule containing P(OMe)3 in C6D6 as a
standard. Then, potassium 2,6-dimethylphenoxide (35.4 mg, 0.221
mmol) was added to the solution at room temperature. See ref 17.
Reaction of cis-RuClMe(PMe3)4 with Potassium 2,6-Dime-
thylphenoxide. In an NMR tube, with a flame-sealed capillary
ampule containing P(OMe)3 in C6D6 as a standard, cis-RuClMe-
(PMe3)4 (4.4 mg, 0.0097 mmol) with potassium 2,6-dimethylphen-
oxide (1.9 mg, 0.012 mmol) were dissolved in THF (0.6 mL). The
reaction profile was monitored by 31P{1H} NMR, and the reaction
almost reached completion (98%) in 4.3 h at 19 °C. The GLC analysis
with pure ethane as a standard indicates the formation of methane in
88% yield.
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data for 2−4 and 8. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*M.H.: e-mail, hrc@cc.tuat.ac.jp, tel and fax, +81 423 877 044.
Present Address
†Gakushuin University.
Effect of Concentration of Potassium 2,6-Diethylphenoxide
on the Formation of 4. (a) Reaction of cis-1 (9.6 mg, 0.020 mmol)
with potassium 2,6-diethylphenoxide (9.6 mg, 0.049 mmol, 2.5 equiv/
Ru) in THF (0.60 mL) at 50 °C: yield of 4, 13% (2 h), 26% (5 h),
Notes
The authors declare no competing financial interest.
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(18) Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B.; Malik, K. M. A. J. Chem. Soc., Dalton Trans. 1980,
511.
(19) This method is based on the trans to cis isomerization in non-
polar solvent: Fu, C.; Wen, T. B. Acta Crystallogr. 2011, E67, m14.
(20) The rates for the forward and backward reactions in this
equilibrium were very slow at room temperature.
(21) Jones, R. A.; Wilkinson, G.; Colquohourn, I. J.; McFarlane, W.;
Glass, A. M. R.; Hurshouse, M. B. J. Chem. Soc., Dalton Trans. 1980,
2480.
ACKNOWLEDGMENTS
■
We thank Prof. K. Osakada (Tokyo Institute of Technology)
for useful tips on the preparation of Ru(OAc)Cl(PPh3)3. We
also thank Ms. S. Kiyota for elemental analysis. This work was
financially supported by a Grant-in-Aid for Scientific Research
on Innovative Areas “Molecular Activation Directed toward
Straightforward Synthesis” from the Ministry of Education,
Culture, Science and Technology of Japan.
(22) (a) Flegeau, E. F.; Bruneau, C.; Dixneuf, P. H.; Jutand, A. J. Am.
Chem. Soc. 2011, 133, 10161. (b) Fabre, I.; von Wolff, N.; Duc, G. L.;
Flegeau, E. F.; Bruneau, C.; Dixneuf, P. H.; Jutand, A. Chem. Eur. J.
2013, 19, 7595.
(23) Gordon, A. J.; Ford, R. A. The Chemist’s Companion, A Hand
Book of Practical Data, Techniques, and References; Wiley: New York,
1972; p 6.
(24) One of the reviewers asked about protonolysis of the
oxaruthenacycle in relation to the reversibility, and we added the
reaction shown in Scheme 6 during the revision process, which also
supports the IES mechanism. We thank this reviewer for this
suggestion.
(25) Kosolapoff, G. M.; Maier, L. In Organic Phosphorus Compounds;
Wiley: New York, 1972. The procedure referred to the following
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ABBREVIATIONS
■
COD = cyclooctadiene (C8H12); COT = cyclooctatriene
(C8H10); DMAD = dimethyl acetylenedicarboxylate (C6H6O4)
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(17) The prior treatment of trans-1 with AgNO3 dominantly
produced a new AX2 pattern at δ 39.0 (t, J = 34 Hz, 1P) and δ 3.8
(d, J = 34 Hz, 2P) and a singlet at δ −35.1 assignable to [Ag(PMe3)]+
in THF at 20 °C. Immediately after addition of potassium 2,6-
dimethylphenoxide into the solution, complex signals involving
singlets at δ 26.6 and 37.0 and an AX2 pattern at δ 35.0 (t, J = 38
Hz, 1P) and d 1.47 (d, J = 38 Hz, 2P) were observed with a small
formation of 2. Although a detailed analysis was difficult due to the
complexity, no dramatic enhancement effect seems to occur by the
addition of AgNO3 to this system.
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dx.doi.org/10.1021/om5000248 | Organometallics 2014, 33, 1235−1244