Hydrophilic (ν6-Arene)-Ruthenium(II) Complexes with P-OH ligands as catalysts for the isomerization of allylbenzenes and C-H bond arylation reactions in water

Article abstract of DOI:10.1021/acs.organomet.9b00463

Half-sandwich ruthenium(II) complexes containing ν⁶-coordinated 3-phenylpropanol and phosphinous-acid-type ligands, namely, [RuCl₂(ν⁶-C₆H₅CH₂CH₂CH₂OH){P(OH)R₂}] (R = Me (2a), Ph (2b), 4-C₆H₄CF₃ (2c), 4-C₆H₄OMe (2d), OMe (2e), OEt (2f), and OPh (2g), have been synthesized in 44-88% yield by reacting [RuCl₂{ν⁶:κ¹(O)-C₆H₅CH₂CH₂CH₂OH}] (1) with the appropriate pentavalent phosphorus oxide R₂P(═O)H. The structure of [RuCl₂(ν⁶-C₆H₅CH₂CH₂CH₂OH){P(OH)Me₂}] (2a) was unequivocally confirmed by X-ray diffraction methods. Compounds 2a-g proved to be catalytically active in the isomerization of allylbenzenes into the corresponding (1-propenyl)benzene derivatives employing water as the sole reaction solvent, with [RuCl₂(ν⁶-C₆H₅CH₂CH₂CH₂OH){P(OH)(OPh)₂}] (2g) showing the best performance and a broad substrate scope (73-93% isolated yields with E/Z ratios around 90:10 employing 1 mol % of 2g and 3 mol % of K₂CO₃, and performing the catalytic reactions at 80 °C for 4-24 h). The results herein presented show for the first time the utility of phosphinous acids as auxiliary ligands for metal-catalyzed olefin isomerization processes, reactions in which a cooperative role for the P - OH unit is proposed. On the other hand, the utility of complexes 2a-g as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly discussed.

Full text of DOI:10.1021/acs.organomet.9b00463

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
Hydrophilic (η6‑Arene)−Ruthenium(II) Complexes with P−OH
Ligands as Catalysts for the Isomerization of Allylbenzenes and C−H
Bond Arylation Reactions in Water
́
́
Rebeca Gonzalez-Fernandez, Pascale Crochet,* and Victorio Cadierno*
́
́
́
Laboratorio de Compuestos Organometalicos y Catalisis (Unidad Asociada al CSIC), Centro de Innovacion en Química Avanzada
́
́
́
(ORFEO−CINQA), Departamento de Química Organica e Inorganica, Instituto Universitario de Química Organometalica
́
“Enrique Moles”, Facultad de Química, Universidad de Oviedo, Julian Clavería 8, E-33006 Oviedo, Spain
S
* Supporting Information
ABSTRACT: Half-sandwich ruthenium(II) complexes containing
η6-coordinated 3-phenylpropanol and phosphinous-acid-type ligands,
namely, [RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)R2}] (R = Me
(2a), Ph (2b), 4-C6H4CF3 (2c), 4-C6H4OMe (2d), OMe (2e), OEt
(2f), and OPh (2g), have been synthesized in 44−88% yield by
reacting [RuCl2{η6:κ1(O)-C6H5CH2CH2CH2OH}] (1) with the
appropriate pentavalent phosphorus oxide R2P(O)H. The
structure of [RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)Me2}] (2a)
was unequivocally confirmed by X-ray diffraction methods.
Compounds 2a−g proved to be catalytically active in the isomer-
ization of allylbenzenes into the corresponding (1-propenyl)benzene
derivatives employing water as the sole reaction solvent, with
[RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g) showing
the best performance and a broad substrate scope (73−93% isolated
yields with E/Z ratios around 90:10 employing 1 mol % of 2g and 3 mol % of K2CO3, and performing the catalytic reactions at
80 °C for 4−24 h). The results herein presented show for the first time the utility of phosphinous acids as auxiliary ligands for
metal-catalyzed olefin isomerization processes, reactions in which a cooperative role for the POH unit is proposed. On the
other hand, the utility of complexes 2a−g as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly
discussed.
Scheme 1. Cooperative Effect of Phosphinous Acid Ligands
in Ru-Catalyzed Nitrile Hydration
INTRODUCTION
■
Phosphinous acids PR2OH (R = alkyl or aryl groups) and their
heteroatom-substituted counterparts, i.e., compounds P-
(OR)2OH and P(NR2)2OH, have emerged in recent years as
a useful class of auxiliary ligands in homogeneous catalysis.1 In
particular, ruthenium complexes containing these types of
ligands have led to relevant results in catalytic nitrile hydration
reactions2 and directing-group-assisted C−H bond arylation
processes,3 with mechanistic investigations pointing to a
cooperative effect of the P−OH ligands in both trans-
formations.4 Thus, density functional theory (DFT) calcu-
lations on the ruthenium-catalyzed nitrile hydrations indicated
that the reactions proceed through the initial formation of a
five-membered metallacyclic intermediate by intramolecular
addition of the phosphinous acid to the ruthenium-
coordinated nitrile, the subsequent hydrolysis of the metalla-
cycle leading to the final amide product (Scheme 1).2b,d,5 In
the case of the C−H bond arylation processes, computational
studies performed by Ackermann and co-workers revealed that
the phosphinous acid ligands facilitate the key C−H cleavage
step.3d Thus, as shown in Scheme 2, under the basic conditions
required in these types of reactions, the phosphinous acid is
transformed into the corresponding phosphinito anion PR2O−,
which is responsible for the abstraction of the ortho-aryl
proton.
Received: July 8, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.9b00463
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Article
Scheme 2. Cooperative Effect of PR2OH Ligands in Ru-
Catalyzed C−H Bond Arylation Processes
Scheme 4. Ru-Catalyzed Isomerization/Claisen
Rearrangement of Diallyl Ethers in Water
Concerning their preparation, transition metal complexes
with phosphinous acids and related P−OH ligands are usually
generated by reacting the appropriate metallic precursor with a
pentavalent phosphorus oxide (Scheme 3).1,4,6 In solution,
investigations on the application of phosphinous acids as
ligands in metal-catalyzed olefin isomerization processes,1
prompted us to synthesize analogous arene−ruthenium(II)
complexes with this type of ligand and evaluate their catalytic
potential. The isomerization of allylbenzene derivatives
(Scheme 5) was chosen as the model reaction given their
Scheme 3. Synthesis of Metal Complexes with Phosphinous
Acid Ligands from Secondary Phosphine Oxides
Scheme 5. Metal-Catalyzed Isomerization of Allylbenzenes
these air-stable compounds exist in equilibrium with their
trivalent tautomers, which is driven toward the latter by
coordination to the metal center. Although much less
employed, alternative methods of synthesis involving the
hydrolysis of P−C, P−Cl, P−N, or P−OR bonds in
coordinated phosphines, chlorophosphines, aminophosphines,
and phosphites, respectively, are also known.4,7
Very recently, we reported that hydrophilic arene−
ruthenium(II) complexes containing η6-coordinated 2-phenyl-
ethanol and 3-phenylpropanol ligands [RuCl2{η6-
C6H5CH2(CH2)nCH2OH}(L)] (n = 0, 1; L = phosphine or
phosphite; A) are able to catalyze, in combination with NaOH,
the transformation of diallyl ether derivatives B into syntheti-
cally useful γ,δ-unsaturated aldehydes D in water (Scheme 4).8
The process involves the initial Ru-catalyzed isomerization of
the diallyl ether substrates B into the corresponding allyl vinyl
ethers C, followed by a thermal Claisen rearrangement of C
into the final products D.
Of the different ruthenium complexes A employed as
catalysts, those containing phosphite ligands P(OR)3 resulted
more effective than their phosphine PR3 counterparts.8 NMR
experiments carried out with aqueous solutions of these
compounds made evident a different behavior upon addition of
NaOH. Thus, while the phosphite-containing complexes
evolved into metallic species containing coordinated P-
(OR)2OH units, due to the base-promoted hydrolysis of the
P(OR)3 ligands, the addition of NaOH to aqueous solutions of
the phosphine ones led mainly to Cl−/OH− metathesis
processes. Accordingly, we assumed that the higher catalytic
activity of the phosphite derivatives was related with the in situ
formation of P(OR)2OH-containing complexes which could
act as the real active species for the initial CC bond
migration step. This fact, along with the lack of previous
ease of access and the high interest of the process from both
academic and industrial points of view, because the resulting
(1-propenyl)benzene products are relevant synthetic inter-
mediates in organic chemistry, and also because they usually
feature biological activity and applicability in the production of
pesticides, fragrances, cosmetics, flavors, and pharmaceuticals.9
The catalytic behavior of the synthesized Ru(II) complexes in
the ortho-arylation of 2-phenylpyridine was also evaluated,
employing for both catalytic transformations environmentally
friendly water as the solvent. The results derived from these
studies are presented herein.
RESULTS AND DISCUSSION
■
In our previous work on the isomerization/Claisen rearrange-
ment of diallyl ethers B using the ruthenium(II) derivatives A
as catalysts (Scheme 4), we found that the nature of the η6-
coordinated arene ligand, i.e., 2-phenylethanol (n = 0) or 3-
phenylpropanol (n = 1), did not exert any effect on the
catalytic activity of the complexes.8 That is why in the present
study we focused exclusively on η6-3-phenylpropanol deriva-
tives given the more convenient and higher-yield access to the
c o r r e s p o n d i n g p r e c u r s o r [ R u C l 2 { η 6 : κ 1 ( O ) -
C6H5CH2CH2CH2OH}] (1).10 Thus, as shown in Scheme 6,
a series of [RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)R2}]
complexes containing symmetrically substituted phosphinous
(2a−d) and phosphorous acid (2e−g) ligands could be
synthesized by treatment of THF solutions of 1 with the
corresponding secondary phosphine oxide or H-phosphonate,
respectively, the reactions involving the previously commented
P(O)H to POH tautomerization process (Scheme 3). As
expected due to the presence of two OH groups in their
B
DOI: 10.1021/acs.organomet.9b00463
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As previously found in the related complexes A (Scheme 4),8
the 1H and 13C{1H} NMR spectra of 2a−g showed the
equivalence of the CHortho and CHmeta protons and carbons of
the η6-coordinated 3-phenylpropanol units, consistent with the
presence of a symmetry plane in the complexes. A broad
resonance at δH 2.90−3.40 ppm, assigned to the OH group of
Scheme 6. Synthesis of the Arene−Ruthenium(II)
Complexes 2a−g
1
the 3-phenylpropanol ligand, was also observed in the H
NMR spectra of all these compounds, not finding on the
contrary those corresponding to the POH units.12 None-
theless, two distinguishable v(OH) absorption bands (in the
range 3207−3421 cm−1) were found in their IR spectra.
A single-crystal X-ray diffraction study on complex
[RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)Me2}] (2a) un-
equivocally confirmed the molecular structures proposed for
compounds 2a−g. ORTEP views are shown in Figure 1 along
with selected structural parameters.
The complex features a typical three-legged piano-stool
geometry, with the ruthenium atom surrounded by the η6-
bonded 3-phenylpropanol molecule, two chlorides, and the
phosphorus atom of the dimethylphosphinous acid ligand. The
Ru−P(1) and P(1)−O(2) bond lengths observed (2.3004(9)
and 1.592(3) Å, respectively) were comparable to those found
in the crystal structure of the related species [RuCl2(η6-p-
cymene){P(OH)Me2}] (Ru−P = 2.3078(1) Å and P−O =
1.613(3) Å).2a It is also worthy of note that, in marked
contrast to what is usually observed in the solid state crystal
structures of ruthenium(II) complexes of type [RuCl2(η6-
arene){P(OH)R2}],2a,3e,13 no intramolecular H-bonding of the
hydroxyl group of the phosphinous acid with the chloride
ligands was present in this case. Instead, the P−OH unit is
involved in an intermolecular hydrogen bond with the
hydroxyl group of the 3-phenylpropanol ligand, thus leading
to the formation of dimeric aggregates in the solid state
(Figure 1). According to the classification of Jeffrey,14 the
distances and angle of the O(2)−H(200)···O(1) contact
[O(2)−H(200) = 0.81(6) Å; O(1)−H(200) = 1.86(6) Å;
O(1)−O(2) = 2.645(4) Å; O(2)−H(200)−O(1) = 165(6)°]
allow it to be classified as “moderate”, basically electrostatic in
structures, compounds 2a−g, which were isolated as air-stable
orange solids in moderate to high yield (44−88%), are
perfectly soluble in water and other polar solvents, such as
alcohols, DMSO, or acetone,11a and completely insoluble in n-
alkanes or diethyl ether.
Complexes 2a−g were characterized by elemental analyses,
IR, and multinuclear NMR spectroscopy (details are given in
the Experimental Section).11b In this regard, the 31P{1H} NMR
spectra made evident the clean formation of a unique
phosphorus-containing product, featuring a singlet resonance
strongly deshielded (Δδ = 84.7−114.6 ppm) with respect to
that of the starting ligand precursor R2P(O)H (see Table 1).
Table 1. 31P{1H} NMR Data for Compounds R2P(O)H
and Complexes 2a−g
a
b
R2P(O)H
Me2P(=O)H
Ph2P(=O)H
(4-C6H4CF3)2P(=O)H
(4-C6H4OMe)2P(=O)H
(MeO)2P(=O)H
(EtO)2P(=O)H
δP
complex 2
δP
23.2 ppm
21.8 ppm
17.9 ppm
21.0 ppm
10.6 ppm
7.4 ppm
2a
2b
2c
2d
2e
2f
118.9 ppm
106.9 ppm
102.6 ppm
106.0 ppm
118.8 ppm
114.7 ppm
115.0 ppm
(PhO)2P(=O)H
0.4 ppm
2g
a
b
Spectra recorded in CDCl3 at 25 °C. Spectra recorded in acetone-d6
at 25 °C.
Figure 1. ORTEP-type views of the structure of complex 2a showing the crystallographic labeling scheme (left) and the intermolecular H-bonding
interactions (right). Hydrogen atoms, except those on O(1) and O(2), have been omitted for clarity. Thermal ellipsoids are drawn at the 40%
probability level. Selected bond distances (Å) and angles (deg): Ru−C* = 1.6943(3); Ru−Cl(1) = 2.4013(9); Ru−Cl(2) = 2.4270(9); Ru−P(1) =
2.3004(9); P(1)−C(10) = 1.811(4); P(1)−C(11) = 1.797(4); P(1)−O(2) = 1.592(3); C(1)−O(1) = 1.423(5); C*−Ru−P(1) = 128.61(3); C*−
Ru−Cl(1) = 126.54(3); C*−Ru−Cl(2) = 125.98(3); Cl(1)−Ru−Cl(2) = 87.16(3); Cl(1)−Ru−P(1) = 84.69(3); Cl(2)−Ru−P(1) = 90.34(3);
Ru−P(1)−O(2) = 116.4(1); Ru−P(1)−C(10) = 114.0(1); Ru−P(1)−C(11) = 116.6(2); C(10)−P(1)−C(11) = 103.7(2); C(10)−P(1)−O(2) =
98.8(2); C(11)−P(1)−O(2) = 105.1(2); C* denotes the centroid of the arene unit [C(4), C(5), C(6), C(7), C(8), and C(9)].
C
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nature, among the H-bonds considered most common in
chemical systems.
species in the catalytic cycle (see Figure 2). On the basis of our
previous work,8 we assume that this induction period is
With compounds 2a−g in hand, we next studied their
catalytic potential for the isomerization of allylbenzene
derivatives employing estragole 3a as the model substrate
(Table 2). A first series of experiments, performed in water at
Table 2. Catalytic Estragole (3a) to Anethole (4a)
Isomerization in Water Using Complexes [RuCl2(η6-
a
C6H5CH2CH2CH2OH)(L)] as Catalysts
time
(h)
yield of
b
b
entry
1
catalyst
4a (%) E/Z ratio
2a (L = P(OH)Me2)
2a (L = P(OH)Me2)
2a (L = P(OH)Me2)
2b (L = P(OH)Ph2)
2b (L = P(OH)Ph2)
2b (L = P(OH)Ph2)
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
29
56
83
59
82
94
43
78
94
50
81
93
27
53
87
28
54
83
55
83
>99
4
89:11
90:10
92:8
85:15
88:12
89:11
91:9
Figure 2. Isomerization of estragole (3a) into anethole (4a) in water
catalyzed by complexes 2g and 5 as a function of time.
2
3
4
5
6
7
8
2c (L = P(OH)(4-C6H4CF3)2)
2c (L = P(OH)(4-C6H4CF3)2)
2c (L = P(OH)(4-C6H4CF3)2)
2d (L = P(OH)(4-C6H4OMe)2)
2d (L = P(OH)(4-C6H4OMe)2)
2d (L = P(OH)(4-C6H4OMe)2)
2e (L = P(OH)(OMe)2)
2e (L = P(OH)(OMe)2)
2e (L = P(OH)(OMe)2)
2f (L = P(OH)(OEt)2)
2f (L = P(OH)(OEt)2)
2f (L = P(OH)(OEt)2)
2g (L = P(OH)(OPh)2)
2g (L = P(OH)(OPh)2)
2g (L = P(OH)(OPh)2)
5 (L = P(OPh)3)
associated with the hydrolysis of the coordinated phosphite
ligand P(OPh)3 into P(OH)(OPh)2,17 a slow process at
neutral pH that can be accelerated in basic media. In full
agreement with this last point, when the aqueous solution
containing 5 was pretreated with NaOH (3 equiv) prior to the
addition of the estragole substrate, the profile of the catalytic
reaction drastically changed, and the conversion of 3a into 4a
was faster (see Figure 2).
91:9
93:7
86:14
88:12
89:11
90:10
91:9
92:8
89:11
91:9
93:7
91:9
93:7
93:7
The effect of different additives on the catalytic behavior of
the most active complex [RuCl2(η6-C6H5CH2CH2CH2OH)-
{P(OH)(OPh)2}] (2g) was next explored, employing again
estragole 3a as the model substrate (Table 3). Thus, as shown
in entries 1 and 2, we found that the effectiveness of 2g is not
affected by the addition of the chloride abstractor AgPF6 (1−2
mol %). These observations, along with fact that the
isomerization of 3a into 4a employing a saturated NaCl(aq)
solution as the solvent proceeds with the same efficiency as in
pure water (entry 3), seem to indicate that dissociation of the
chloride ligands is not required for the binding of the substrate
to the metal center.18 On the other hand, while the addition of
HCl to the reaction medium did not lead to significant changes
in the activity of 2g (entries 4 and 5), faster conversions were
observed in the presence of NaOH (entries 6−9). In particular,
employing 3 mol % of NaOH, quantitative conversion of 3a
into 4a was reached in only 5 h (entry 8), with a further
increase in the NaOH:Ru ratio leading to the same results
(entry 9). In additional experiments, the effect of other bases
(3 mol %) on the reaction was investigated (see Table S1 in
the Supporting Information), and we found that the use of
K2CO3 makes it possible to shorten in 1 h the time needed to
completely transform 3a into 4a (entry 10).19 At this point it
should also be noted that, in all the reactions listed in Table 3
and Table S1, the trans-selectivity at the maximum conversion
was almost identical regardless of the additive employed (93−
94%).
80:20
83:17
87:13
5 (L = P(OPh)3)
5 (L = P(OPh)3)
12
50
a
Reactions performed under an argon atmosphere using 2 mmol of
3a, 0.02 mmol of the corresponding ruthenium complex, and 1 mL of
water. Determined by GC (uncorrected GC areas).
b
80 °C with 1 mol % of 2a−g and in the absence of any
additive, indicated that all of them are catalytically active,
providing anethole 4a as the unique reaction product in ≥83%
yield after 8 h (entries 1−7).15 In particular, the best results
were obtained with [RuCl2(η6-C6H5CH2CH2CH2OH){P-
(OH)(OPh)2}] (2g), which generated 4a in almost
quantitative yield and with a very high trans selectivity (93%;
entry 7).16 In order to determine to what extent the presence
of an OH group in the P-donor ligand is beneficial for the
process, the catalytic behavior of the triphenylphosphite
complex [RuCl2(η6-C6H5CH2CH2CH2OH){P(OPh)3}] (5)
was explored under identical reaction conditions. As shown
in entry 8, although it also turned out to be an active catalyst,
its effectiveness was much lower than that of [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g). Thus, after 8
h of heating, only 50% conversion of 3a into 4a was reached.
Interestingly, the kinetic profile of this reaction is characterized
by the presence of an induction period, absent in the case of
complex 2g, indicating the slow formation of the real active
On the basis of these results and the previous findings on the
cooperative effect of phosphinous-acid-type ligands in the Ru-
catalyzed CH bond arylation processes shown in Scheme 2,
the reaction pathway depicted in Scheme 7 could be tentatively
proposed for the present CC bond isomerization reaction.
We assume that initial coordination of the estragole substrate
D
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Table 3. Catalytic Estragole (3a) to Anethole (4a)
Isomerization in Water Using Complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g) as a Catalyst:
Scheme 7. Proposed Mechanism for the Estragole to
Anethole Isomerization Catalyzed by 2a−g
a
Effect of Additives
b
b
entry
1
additive
time (h) yield of 4a (%) E/Z ratio
AgPF6 (1 mol %)
AgPF6 (1 mol %)
AgPF6 (1 mol %)
AgPF6 (2 mol %)
AgPF6 (2 mol %)
AgPF6 (2 mol %)
NaCl
2
4
8
2
4
8
2
4
8
2
4
8
2
4
8
2
4
7
2
4
6
2
4
5
2
4
5
2
4
53
83
96
45
77
94
58
87
99
47
79
95
49
81
94
69
92
>99
79
96
>99
86
98
<99
87
98
<99
90
>99
91:9
92:8
93:7
91:9
92:8
93:7
91:9
92:8
93:7
92:8
92:8
93:7
92:8
92:8
93:7
91:9
92:8
93:7
92:8
93:7
93:7
92:8
93:7
93:7
91:9
93:7
93:7
93:7
94:6
2
c
3
NaCl
NaCl
4
HCl (1 mol %)
HCl (1 mol %)
HCl (1 mol %)
HCl (2 mol %)
HCl (2 mol %)
HCl (2 mol %)
NaOH (1 mol %)
NaOH (1 mol %)
NaOH (1 mol %)
NaOH (2 mol %)
NaOH (2 mol %)
NaOH (2 mol %)
NaOH (3 mol %)
NaOH (3 mol %)
NaOH (3 mol %)
NaOH (4 mol %)
NaOH (4 mol %)
NaOH (4 mol %)
K2CO3 (3 mol %)
K2CO3 (3 mol %)
5
6
7
8
9
be converted into the corresponding (1-propenyl)benzenes
4b−k in almost quantitative GC yield and with a high trans-
selectivity (E/Z ratios from 88:12 to 97:3). As a general trend,
those allylbenzenes containing exclusively electron-donor
substituents, i.e., hydroxy or alkoxy groups, in the aromatic
ring required of short times (4−6 h) to be completely
isomerized (compounds 3a,c−f,h; entries 1, 3−6, and 8). A
fast reaction was also observed when the parent allylbenzene
3b (entry 2) was employed as the substrate. Conversely, when
electron-withdrawing substituents, i.e., acetoxy or formyl
groups, were introduced, longer reaction times were needed
to attain full conversion (compounds 3i−k; entries 9−11).
The only exception found was that of 4-allyl-2,6-dimethox-
yphenol 3g, for which a slow isomerization was observed
(entry 7). The higher steric hindrance associated with the
trisubstitution of the aromatic ring could be behind this
anomalous behavior. Also of note is the fact that the (1-
propenyl)benzene products 4a−k can be easily isolated from
the aqueous reaction medium by a simple extraction with
dichloromethane (see details in the Experimental Section),
with complex 2g remaining dissolved in the aqueous phase.21
On the other hand, as previously commented in the
Introduction, Ru(II) complexes with phosphinous-acid-type
ligands, both preformed or generated in situ by mixing the
appropriate ruthenium precursor with a pentavalent phospho-
rus oxide, have proven to be useful catalysts for C−C coupling
reactions through directing-group-assisted C(sp2)−H activa-
tion processes (see Scheme 2).3 However, despite the growing
interest in developing these C−H bond functionalization
10
a
Reactions performed under an argon atmosphere using 2 mmol of
b
3a, 0.02 mmol of complex 2g, and 1 mL of water. Determined by
GC (uncorrected GC areas). A saturated NaCl(aq) solution was
employed as solvent.
c
to the ruthenium center proceeds through a change in the
hapticity of the arene ligand (from η6 to η4), leading to
intermediate π-olefin complex E, which evolves into the
phosphinito derivative F by elimination of HCl. This step is
obviously favored in basic medium and explains the rate
acceleration observed when a base is added to the reaction
mixture.20 Then, the π-allyl intermediate H could be generated
from F by abstraction of one of the methylenic protons by the
phosphinito anion PR2O− (transition state G). Final
protonation of H would lead to I from which the anethole
molecule is displaced by another molecule of the substrate.
The ability of complex [RuCl2(η6-C6H5CH2CH2CH2OH)-
{P(OH)(OPh)2}] (2g) to promote the isomerization of other
commercially available allylbenzene derivatives 3b−k was
subsequently evaluated under the optimized reaction con-
ditions described above, i.e., in water at 80 °C employing 1 mol
% of 2g in combination with 3 mol % of K2CO3 (see Table 4).
To our delight, the process proved to be general, and as was
the case with estragole 3a (entry 1), all tested substrates could
E
DOI: 10.1021/acs.organomet.9b00463
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 4. Isomerization of the Allylbenzene Derivatives 3a−k by Complex [RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)(OPh)2}]
a
(2g) in Water
a
Reactions performed under an argon atmosphere using 2 mmol of the corresponding allylbenzene 3, 0.02 mmol of the Ru(II) complex 2g, 0.06
b
c
mmol of K2CO3, and 1 mL of water. Yields determined by GC (uncorrected GC areas). Isolated yields after workup are given in brackets. E/Z
ratios were determined by GC or by H NMR spectroscopy.
1
reactions employing environmentally friendly water as the
solvent,22 to date all works involving phosphinous acids have
been carried out in organic media [in most of them, toxic N-
methyl-2-pyrrolidinone (NMP) was used as solvent].3 This
fact prompted us to evaluate the catalytic potential of the
hydrophilic complexes 2a−g for C−H bond arylations in
water. Thus, in a first series of experiments, we investigated the
ortho-phenylation of 2-phenylpyridine 6 with an excess of
chlorobenzene (2.2 equiv) employing complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)Ph2}] (2b) as the model
catalyst (5 mol %). As shown in Table 5, when the mixture
was heated in water at 80 °C for 24 h, the monoarylated
product 7a was generated in very low yield (entry 1). As
expected, the addition of 1 equiv of base to the reaction
medium allowed an improvement of the performance of
complex 2b (entries 2−10). In particular, the best results were
obtained with Cs2CO3 (entry 5), the reaction leading to the
formation of the mono- and diarylated derivatives 7a and 7a′
F
DOI: 10.1021/acs.organomet.9b00463
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 5. Catalytic Arylation of 2-Phenylpyridine (6) in
Water Using Chlorobenzene and Complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)Ph2}] (2b) as a Catalyst:
Table 6. Catalytic Arylation of 2-Phenylpyridine (6) in
Water Using Chlorobenzene: Comparative Performances of
a
Complexes [RuCl2(η6-C6H5CH2CH2CH2OH)(L)]
a
Screening of Different Bases
b
b
entry
catalyst
yield (%)
7a:7a′ ratio
b
b
entry
base
yield (%)
7a:7a′ ratio
1
2
3
4
5
6
7
2a (L = P(OH)Me2)
2b (L = P(OH)Ph2)
73
76
70
74
81
84
80
92:8
92:8
89:11
92:8
91:9
1
2
3
4
5
6
7
8
9
10
22
70
69
61
79
50
52
47
51
31
96
>99
40
76
100:0
83:17
80:20
80:20
91:9
91:9
89:11
91:9
Li2CO3
Na2CO3
K2CO3
Cs2CO3
LiOH
2c (L = P(OH)(4-C6H4CF3)2)
2d (L = P(OH)(4-C6H4OMe)2)
2e (L = P(OH)(OMe)2)
2f (L = P(OH)(OEt)2)
2g (L = P(OH)(OPh)2)
88:12
88:12
a
NaOH
KOH
Reactions performed under an argon atmosphere using 1 mmol of 6,
1 mmol of chlorobenzene, 0.05 mmol of the corresponding ruthenium
b
CsOH·H2O
NaCO2H
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
92:8
complex, 1 mmol of Cs2CO3, and 2 mL of water. Determined by 1H
NMR spectroscopy.
100:0
70:30
67:33
90:10
92:8
c
11
d
C6H5CH2CH2CH2OH){P(OH)(OMe)2}] (2e) which led to a
91:9 mixture of 7a/7a′ in 81% overall yield (entry 5).
Finally, the ability of [RuCl2(η6-C6H5CH2CH2CH2OH){P-
(OH)(OMe)2}] (2e) to catalyze the arylation of 6 with other
aryl halides was briefly explored (see Table 7). In this regard,
12
e
13
f
14
a
Reactions performed under an argon atmosphere using 1 mmol of 6,
2.2 mmol of chlorobenzene, 0.05 mmol of complex 2b, 1 mmol of the
b
1
corresponding base, and 2 mL of water. Determined by H NMR
c
spectroscopy. Reaction performed with 2 equiv of Cs2CO3.
Reaction performed with 3 equiv of Cs2CO3. Reaction performed
with 0.5 equiv of Cs2CO3. Reaction performed with 1 equiv of
Cs2CO3 and 1 equiv of chlorobenzene.
Table 7. Different Arylation Reactions of 2-Phenylpyridine
(6) in Water Using Complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)(OMe)2}] (2e) as a
d
e
f
a
Catalyst
in 79% overall yield, with excellent selectivity toward the
monoarylated one (7a:7a′ ratio of 91:9). The 1H NMR
spectrum of the crude indicated that no side-products are
generated in the process. A further increase in the yield
(>96%) was achieved when 2 and 3 equiv of Cs2CO3 were
employed, but the selectivity toward the monoarylated product
7a was in these cases lower (entries 11 and 12). Conversely,
the use of a substoichiometric amount of Cs2CO3 (0.5 equiv)
significantly decreased the efficiency of the arylation process
(entry 13), confirming that at least 1 equiv of base is needed to
attain a high conversion. On the other hand, as shown in entry
14, a reduction of the amount of chlorobenzene to only 1 equiv
did not lead to significant losses of activity or selectivity. At this
point we would like also to emphasize that the results obtained
with [RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)Ph2}] (2b) in
water compare favorably with those described by Clavier and
co-workers for the same reaction when employing the closely
related diphenylphosphinous acid complex [RuCl2(η6-p-
cymene){P(OH)Ph2}] as the catalyst in NMP.3e Thus, using
5 mol % of this complex, in combination with K2CO3 (3 mol
%), an almost equimolar mixture of 7a and 7a′ was obtained in
49% yield after 24 h of heating at 80 °C.
b
b
entry
Ar
X
yield (%)
7:7′ ratio
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Cl
Br
I
81
86
76
77
78
15
77
57
77
71
75
91:9 (7a/7a′)
81:19 (7a/7a′)
87:13 (7a/7a′)
100:0 (7b/7b′)
91:9 (7c/7c′)
100:0 (7d/7d′)
91:9 (7e/7e′)
82:18 (7f/7f′)
89:11 (7g/7g′)
89:11 (7h/7h′)
92:8 (7i/7i′)
4-C6H4OMe
3-C6H4OMe
2-C6H4OMe
4-C6H4Me
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
2-C6H4Me
9
10
11
4-C6H4C(O)Me
3-C6H4C(O)Me
4-C6H4CF3
a
Reactions performed under an argon atmosphere using 1 mmol of 6,
1 mmol of the corresponding aryl halide, 0.05 mmol of complex 2e, 1
mmol of Cs2CO3, and 2 mL of water. Determined by H NMR
spectroscopy.
b
1
the process was found to be equally effective when bromo- and
iodobenzene were employed as the electrophilic coupling
partners, with only minor differences in reactivity and
selectivity when compared to the reaction carried out with
chlorobenzene (entries 2 and 3 versus entry 1). On the other
hand, as shown in entries 4−11, different aryl chlorides could
also be satisfactorily employed. In general, high yields (>70%)
and a remarkable selectivity toward the monoarylated products
were observed, regardless of the electronic nature or
The catalytic performance of the other synthesized
complexes in the ortho-phenylation of 6 was next explored
using 1 equiv of both PhCl and Cs2CO3. As shown in Table 6,
all of them proved to be catalytically active delivering
predominantly the monoarylated product 7a (7a:7a′ ratios
from 88:12 to 92:8) in high yield. The best compromise in
yield and selectivity was achieved with complex [RuCl2(η6-
G
DOI: 10.1021/acs.organomet.9b00463
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
s, 1H, CH2OH), 2.56 (t, 2H, 3JHH2 = 7.5 Hz, CH2Ph), 1.92−1.83 (m,
2H, CH2CH2Ph), 1.87 (d, 6H, JPH = 10.5 Hz, Me) ppm; P−OH
signal not observed. 13C{1H} NMR (acetone-d6): δ = 111.2 (s, Cipso),
substitution pattern of the aromatic ring. Nonetheless, we
should note that ortho-substituted aryl chlorides led to poorer
results in comparison to their meta- or para-substituted
counterparts (entry 6 versus entries 4 and 5, and entry 8
versus 7), a not surprising fact on the basis of steric grounds.
2
87.8 (s, CHortho or CHmeta), 87.4 (d, JPC = 6.4 Hz, CHortho or
CHmeta), 78.9 (s, CHpara), 60.6 (s, CH2OH), 32.2 and 29.4 (s,
1
CH2CH2Ph), 20.7 (d, JPC = 36.9 Hz, Me) ppm. Elemental Anal.
Calcd (%) for C11H19Cl2O2PRu: C, 34.21; H, 4.96. Found: C, 34.33;
CONCLUSION
■
H, 4.94. (2b) Yield: 0.388 g (76%). IR (KBr): ν = 3381 and 3285 (br,
1
O−H) cm−1. 31P{1H} NMR (acetone-d6): δ = 106.9 (s) ppm. H
In summary, different half-sandwich ruthenium(II) complexes
containing hydrophilic 3-phenylpropanol and phosphinous-
acid-type ligands, i.e., compounds [RuCl2 (η6 -
C6H5CH2CH2CH2OH){P(OH)R2}] (2a−g), have been syn-
thesized, and their effectiveness as catalysts for the isomer-
ization of allylbenzene derivatives, as well as for the ortho-C−H
bond arylation of 2-phenylpyridine, in environmentally friendly
aqueous media has been demonstrated. In general, high
activities and selectivities toward the formation of the
corresponding (E)-(1-propenyl)benzene and monoarylated
products, respectively, were observed. The results herein
presented show for the first time (i) the utility of P(OH)R2
compounds as auxiliary ligands in metal-catalyzed olefin
isomerization processes and (ii) the ability of ruthenium-
(II)−P(OH)R2 complexes to promote the C−H activation
process in water. Overall, this work gives new evidence for the
enormous potential of phosphinous-acid-type ligands in
homogeneous catalysis.
NMR (acetone-d6): δ = 7.80−7.73 (m, 4H, PPh), 7.52−7.49 (m, 6H,
PPh), 5.57−5.49 (m, 4H, CHmeta and CHortho), 4.96 (t, 1H, 3JHH = 5.1
3
Hz, CHpara), 3.62 (t, 2H, JHH = 6.0 Hz, CH2OH), 2.94 (br s, 1H,
3
OH), 2.58 (t, 2H, JHH = 7.5 Hz, CH2Ph), 1.88−1.79 (m, 2H,
CH2CH2Ph) ppm; P−OH signal not observed. 13C{1H} NMR
(CDCl3): δ = 137.5 (d, 1JPC = 60.3 Hz, Cipso of PPh), 131.5 (d, JPC
=
11.3 Hz, CHortho or CHmeta of PPh), 131.3 (s, CHpara of PPh), 128.4
(d, JPC = 10.5 Hz, CHortho or CHmeta of PPh), 113.2 (s, Cipso), 88.2
and 87.9 (s, CHortho and CHmeta), 80.3 (s, CHpara), 61.4 (s, CH2OH),
31.0 and 29.0 (s, CH2CH2Ph) ppm. Elemental Anal. Calcd (%) for
C21H23Cl2O2PRu: C, 49.42; H, 4.54. Found: C, 49.29; H, 4.50. (2c)
Yield: 0.569 g (88%). IR (KBr): ν = 3420 and 3284 (br, O−H) cm−1.
31P{1H} NMR (acetone-d6): δ = 102.6 (s) ppm. 19F{1H} NMR
1
(acetone-d6): δ = −63.5 (s) ppm. H NMR (acetone-d6): δ = 8.09
(dd, 4H, 3JPH = 7.2 Hz, 3JHH = 7.2 Hz, CHortho of C6H4CF3), 7.80 (d,
4H, 3JHH = 7.2 Hz, CHmeta of C6H4CF3), 5.69−5.66 (m, 2H, CHmeta),
3
3
5.59 (d, 2H, JHH = 6.0 Hz, CHortho), 5.18 (t, 1H, JHH = 4.5 Hz,
3
CHpara), 3.64 (t, 2H, JHH = 6.3 Hz, CH2OH), 2.97 (br s, 1H, OH),
2.61 (t, 2H, 3JHH = 7.5 Hz, CH2Ph), 1.90−1.81 (m, 2H, CH2CH2Ph)
ppm; P−OH signal not observed. 13C{1H} NMR (acetone d6): δ =
142.9 (d, 1JPC = 53.5 Hz, Cipso of C6H4CF3), 132.3 (d, 2JPC = 11.9 Hz,
EXPERIMENTAL SECTION
■
2
Synthetic procedures were performed under an atmosphere of dry
argon using vacuum-line and standard Schlenk or sealed-tube
techniques. Organic solvents were dried by standard methods and
distilled under argon before use.23 All reagents were obtained from
commercial suppliers and used without further purification with the
exception of the ruthenium complexes [RuCl2{η6:κ1(O)-
C 6 H 5 C H 2 C H 2 C H 2 O H } ] ( 1 ) 1 0 a n d [ R u C l 2 ( η 6 -
C6H5CH2CH2CH2OH){P(OPh)3}] (5),24 and the secondary phos-
phine oxides R2P(O)H (R = Me,25 Ph,26 4-C6H4CF3,26 4-
C6H4OMe26), which were prepared by following the methods
reported in the literature. Infrared spectra were recorded on a
PerkinElmer 1720-XFT spectrometer. NMR spectra were recorded at
CHortho of C6H4CF3), 131.6 (q, JFC = 34.3 Hz, Cpara of C6H4CF3),
124.6 (m, CHmeta of C6H4CF3), 124.0 (q, JFC = 271.8 Hz, CF3),
1
2
113.9 (d, JPC = 5.9 Hz, Cipso), 89.2 (s, CHortho or CHmeta), 88.7 (d,
2JPC = 6.4 Hz, CHortho or CHmeta), 81.0 (s, CHpara), 60.6 (s, CH2OH),
31.9 and 29.5 (s, CH2CH2Ph) ppm. Elemental Anal. Calcd (%) for
C23H21F6Cl2O2PRu: C, 42.74; H, 3.27. Found: C, 42.81; H, 3.45.
(2d) Yield: 0.399 g (70%). IR (KBr): ν = 3411 and 3254 (br, O−H)
cm−1. 31P{1H} NMR (acetone-d6): δ = 106.0 (s) ppm. H NMR
1
(acetone-d6): δ = 7.68 (dd, 4H, 3JPH = 10.5 Hz, 3JHH = 8.7 Hz, CHortho
of C6H4OMe), 7.04 (dd, 4H, 3JHH = 8.7 Hz, 4JPH = 1.8 Hz, CHmeta of
C6H4OMe), 5.51−5.46 (m, 4H, CHmeta and CHortho), 4.93 (t, 1H,
3JHH = 5.1 Hz, CHpara), 3.88 (s, 6H, OMe), 3.62 (t, 2H, 3JHH = 6.0 Hz,
25 °C on a Bruker DPX-300 or AV400 instrument. 13C{1H} and H
3
1
CH2OH), 3.06 (br s, 1H, OH), 2.58 (t, 2H, JHH = 7.5 Hz, CH2Ph),
chemical shifts were referenced to the residual signal of deuterated
solvent. All data are reported in ppm downfield from (CH3)4Si. For
19F{1H} NMR spectra, the chemical shifts were referenced to the
CFCl3 standard. DEPT experiments have been carried out for all the
compounds reported in this paper. GC measurements were made on a
Hewlett−Packard HP6890 apparatus (Supelco Beta-Dex 120 column,
30 m length, 250 μm diameter). Elemental analyses were provided by
the Analytical Service of the Instituto de Investigaciones Quimicas
(IIQ-CSIC) of Seville. For column chromatography, Merck silica gel
60 (230−400 mesh) was employed.
1.85−1.80 (m, 2H, CH2CH2Ph) ppm; P−OH signal not observed.
13C{1H} NMR (CDCl3): δ = 161.9 (s, Cpara of C6H4OMe), 133.5 (d,
J
PC = 12.9 Hz, CHortho or CHmeta of C6H4OMe), 129.1 (d, 1JPC = 65.6
Hz, Cipso of C6H4OMe), 113.9 (d, JPC = 11.8 Hz, CHortho or CHmeta of
C6H4OMe), 113.1 (s, Cipso), 88.1 (d, JPC = 5.8 Hz, CHortho or
2
CHmeta), 87.9 (s, CHortho or CHmeta), 80.3 (s, CHpara), 61.4 (s,
CH2OH), 55.5 (s, OMe), 31.2 and 29.1 (s, CH2CH2Ph) ppm.
Elemental Anal. Calcd (%) for C23H27O4Cl2PRu: C, 48.43; H, 4.77.
Found: C, 48.51; H, 4.81. (2e) Yield: 0.276 g (66%). IR (KBr): ν =
3417 and 3212 (br, O−H) cm−1. 31P{1H} NMR (acetone-d6): δ =
́
General Procedure for the Preparation of Complexes
[RuCl2(η6-C6H5CH2CH2CH2OH){P(OH)R2}] (R = Me (2a), Ph
(2b), 4-C6H4CF3 (2c), 4-C6H4OMe (2d), OMe (2e), OEt (2f),
and OPh (2g)). A suspension of complex [RuCl2{η6:κ1(O)-
C6H5CH2CH2CH2OH}] (1) (0.308 g, 1 mmol) and the correspond-
ing R2P(O)H derivative (1.1 mmol) in THF (50 mL) was stirred
for 24 h at room temperature. The reaction mixture was then
evaporated to dryness, the oily residue formed dissolved in the
minimum amount of CH2Cl2 (ca. 5 mL), and the product precipitated
by adding 30 mL of a diethyl ether/hexane mixture (1:1 v/v). The
same precipitation procedure was repeated twice more, and the
reddish orange solid was finally washed with diethyl ether (5 mL) and
dried in vacuo. (2a) Yield: 0.266 g (69%). IR (KBr): ν = 3416 and
3349 (br, O−H) cm−1. 31P{1H} NMR (acetone-d6): δ = 118.9 (s)
1
3
118.8 (s) ppm. H NMR (acetone-d6): δ = 5.76 (td, 2H, JHH = 5.9
Hz, 3JPH = 1.8 Hz, CHmeta), 5.63 (d, 2H, 3JHH = 5.9 Hz, CHortho), 5.47
(t, 1H, JHH = 5.9 Hz, CHpara), 3.77 (d, 6H, JPH = 11.1 Hz, OCH3),
3.64 (t, 2H, JHH = 6.6 Hz, CH2OH), 3.20 (br s, 1H, OH), 2.60 (t,
3
3
3
3
2H, JHH = 7.5 Hz, CH2Ph), 1.93−1.84 (m, 2H, CH2CH2Ph) ppm;
P−OH signal not observed. 13C{1H} NMR (acetone-d6): δ = 113.0
2
2
(d, JPC = 6.7 Hz, Cipso), 89.0 (d, JPC = 7.5 Hz, CHmeta or CHortho),
88.8 (s, CHmeta or CHortho), 80.1 (s, CHpara), 60.5 (s, CH2OH), 52.6
2
(d, JPC = 7.0 Hz, OCH3), 32.0 and 29.3 (s, CH2CH2Ph) ppm.
Elemental Anal. Calcd (%) for C11H19O4Cl2PRu: C, 31.59; H, 4.58.
Found: C, 31.65; H, 4.51. (2f) Yield: 0.196 g (44%). IR (KBr): ν =
3421 and 3224 (br, O−H) cm−1. 31P{1H} NMR (acetone-d6): δ =
114.7 (s) ppm. 1H NMR (acetone-d6): δ = 5.73 (t, 2H, 3JHH = 4.8 Hz,
CHmeta), 5.61 (d, 2H, 3JHH = 5.1 Hz, CHortho), 5.44 (t, 1H, 3JHH = 4.5
ppm. 1H NMR (acetone-d6): δ = 5.70 (td, 2H, 3JHH = 5.6 Hz, 3JPH
=
3
3
1.8 Hz, CHmeta), 5.52 (d, 2H, JHH = 5.6 Hz, CHortho), 5.32 (t, 1H,
Hz, CHpara), 4.21−4.12 (m, 4H, OCH2CH3), 3.64 (t, 2H, JHH = 5.7
3
3JHH = 5.6 Hz, CHpara), 3.65 (t, 2H, 3JHH = 6.3 Hz, CH2OH), 2.90 (br
Hz, CH2OH), 3.46 (br s, 1H, OH), 2.59 (t, 2H, JHH = 7.5 Hz,
H
DOI: 10.1021/acs.organomet.9b00463
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CH2Ph), 1.91−1.85 (m, 2H, CH2CH2Ph), 1.31 (t, 6H, 3JHH = 6.9 Hz,
CrysAlisPro RED.27 An empirical absorption correction was applied
using the SCALE3 ABSPACK algorithm as implemented in the
program CrysAlisPro RED.27 The software package WINGX was used
for space group determination, structure solution, and refinement.28
The structure was solved by Patterson interpretation and phase
expansion using SIR2014.29 Isotropic least-squares refinement on F2
using SHELXL97 was performed.30 During the final stages of the
refinements, all the positional parameters and the anisotropic
temperature factors of all non-H atoms were refined. All H atoms
OCH2CH3) ppm; P−OH signal not observed. 13C{1H} NMR
2
(acetone-d6): δ = 112.5 (s, Cipso), 88.9 (d, JPC = 7.1 Hz, CHmeta or
CHortho), 88.8 (s, CHmeta or CHortho), 81.3 (s, CHpara), 68.4 (s,
OCH2CH3), 60.5 (s, CH2OH), 32.1 and 28.6 (s, CH2CH2Ph), 15.8
(s, OCH2CH3) ppm. Elemental Anal. Calcd (%) for
C13H23O4Cl2PRu: C, 34.99; H, 5.20. Found: C, 35.06; H, 5.19.
(2g) Yield: 0.325 g (60%). IR (KBr): ν = 3408 and 3207 (br, O−H)
1
cm−1. 31P{1H} NMR (acetone-d6): δ = 115.0 (s) ppm. H NMR
were geometrically located, and their coordinates were refined riding
(acetone-d6): δ = 7.43−7.24 (m, 10H, OPh), 5.59−5.55 (m, 2H,
2
CHmeta), 5.44 (d, 2H, 3JHH = 5.7 Hz, CHortho), 5.00 (t, 1H, 3JHH = 5.1
on their parent atoms. The function minimized was {∑[ω(F0
−
Fc2)2]/∑[ω(F0 )2]}1/2 where ω = 1/[σ2(F0 ) + (0.0499P)2] with
2
2
3
Hz, CHpara), 3.60 (t, 2H, JHH = 6.0 Hz, CH2OH), 3.40 (br s, 1H,
σ(F0 ) from counting statistics, and P = [max(F0 , 0) + 2Fc2]/3.
Atomic scattering factors were taken from International Tables for X-
ray Crystallography, Volume C.31 Geometrical calculations related to
the centroid C* were made with PARST.32 The crystallographic plots
were made with DIAMOND.33
2
2
3
OH), 2.51 (t, 2H, JHH = 7.8 Hz, CH2Ph), 1.86−1.76 (m, 2H,
CH2CH2Ph) ppm; P−OH signal not observed. 13C{1H} NMR
2
(CDCl3): δ = 151.2 (d, JPC = 11.0 Hz, Cipso of OPh), 129.8 (s,
3
CHmeta of OPh), 125.2 (s, CHpara of OPh), 121.5 (d, JPC = 3.5 Hz,
2
2
CHortho of OPh), 114.3 (d, JPC = 6.9 Hz, Cipso), 89.3 (d, JPC = 7.6
Hz, CHmeta or CHortho), 88.8 (s, CHmeta or CHortho), 80.3 (s, CHpara),
61.4 (s, CH2OH), 30.9 and 29.2 (s, CH2CH2Ph) ppm. Elemental
Anal. Calcd (%) for C21H23O4Cl2PRu: C, 46.51; H, 4.27. Found: C,
46.63; H, 4.30.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.9b00463.
General Procedure for the Isomerization of the Allylben-
zene Derivatives 3a−h Catalyzed by Complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)(OPh)2}] (2g). Under an argon atmos-
phere, the corresponding allylbenzene 3a−k (2 mmol), water (1 mL),
the ruthenium(II) complex 2g (0.011 g, 0.02 mmol; 1 mol %), and
K2CO3 (0.008 g, 0.06 mmol; 3 mol %) were introduced into a Teflon-
capped sealed tube, and the reaction mixture was stirred at 80 °C for
the indicated time (see Table 4). The course of the reaction was
monitored by regularly taking samples of ca. 10 μL which, after
extraction with CH2Cl2 (3 mL), were analyzed by GC. Once the
maximum conversion of the starting substrate was reached, the
resulting aqueous solution was allowed to reach room temperature
and extracted with dichloromethane (3 × 5 mL). The combined
organic extracts were dried over anhydrous MgSO4, filtered, and
evaporated to dryness, yielding the corresponding (1-propenyl)-
benzene products 4a−k as oily materials. The identity of compounds
Tables with the screening of different bases in the
estragole-to-anethole isomerization catalyzed by com-
plex 2g, crystallographic information on compound 2a,
NMR spectra of the ruthenium complexes 2a−g and the
1
isolated (1-propenyl)benzene derivatives 4a−k, and H
NMR spectra of the arylation reactions collected in
Table 7 (PDF)
Accession Codes
CCDC 1937935 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
4a−k was confirmed by H and 13C{1H} NMR spectroscopy (copies
of the NMR spectra have been included in the Supporting
Information).
General Procedure for the ortho-Arylation Reactions of 2-
Phenylpyridine Catalyzed by Complex [RuCl2(η6-
C6H5CH2CH2CH2OH){P(OH)(OMe)2}] (2e). Under an argon atmos-
phere, 2-phenylpyridine 6 (143 μL, 1 mmol), the corresponding aryl
halide (1 mmol), water (2 mL), the ruthenium(II) complex 2e (0.021
g, 0.05 mmol; 5 mol %), and Cs2CO3 (0.327 g, 1 mmol) were
introduced into a Teflon-capped sealed tube, and the reaction mixture
was stirred at 80 °C for 24 h. After this time, the aqueous reaction
mixture was cooled to room temperature and extracted with diethyl
ether (4 × 5 mL). The combined organic extracts were dried over
anhydrous MgSO4, filtered, and evaporated to dryness. The oily
residue was dissolved in CDCl3, and the reaction yield and ratio
AUTHOR INFORMATION
Corresponding Authors
*E-mail: crochetpascale@uniovi.es.
*E-mail: vcm@uniovi.es.
ORCID
Pascale Crochet: 0000-0002-4637-8231
Victorio Cadierno: 0000-0001-6334-2815
Notes
■
The authors declare no competing financial interest.
1
between the mono- and diarylated products were determined by H
NMR spectroscopy, through the integration of the signals of the
ACKNOWLEDGMENTS
■
C(5)−H pyridinic protons for the starting material 6 and the products
́
Financial support from the Spanish Ministry of Economy,
Industry and Competitiveness (MINECO project CTQ2016-
75986-P), and the University of Oviedo (project PAPI-18-GR-
2011-0032) is gratefully acknowledged. R.G.-F. thanks MECD
of Spain for the award of a FPU fellowship. Prakash Chemicals
(Budaun, India) is also acknowledged for the generous gift of
the estragole employed in this work. This article is dedicated to
7a−i and 7a′−i. Copies of the NMR spectra of the experiments
collected in Table 7 have been included in the Supporting
Information.
X-ray Crystal Structure Determination of Compound 2a.
Crystals of 2a suitable for X-ray diffraction analysis were obtained by
slow diffusion of n-hexane into a saturated solution of the complex in
dichloromethane. The most relevant crystal and refinement data are
collected in Table S2 (see the Supporting Information). Data
collection was performed with a Rigaku−Oxford diffraction Xcalibur
Onyx Nova single-crystal diffractometer using Cu Kα radiation (λ =
1.5418 Å). Images were collected at a fixed crystal-to-detector
distance of 62 mm using the oscillation method, with 1.30° oscillation
and 2.5−6.0 s variable exposure time per image. The data collection
strategy was calculated with the program CrysAlisPro CCD.27 Data
reduction and cell refinement were performed with the program
́
Professor Ferenc Joo on the occasion of his 70th birthday.
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