Preparation of trinuclear ruthenium clusters based on piconol ligands and their application in Oppenauer-type oxidation of secondary alcohols

Article abstract of DOI:10.1002/aoc.6336

Treatment of Ru₃(CO)₁₂ with one equivalent of 2-indolyl-6-pyridinyl-alcohol ligands 2-(C₈H₆N)-6-(CR¹R²OH)C₅H₃N (R¹ = R² = Me (L1H); R¹ = R² = C₂H₅ (L2H); R¹, R² = ?(CH₂)₄- (L3H);& R¹, R² = ?(CH₂)₅- (L4H)) in refluxing THF afforded the corresponding trinuclear ruthenium clusters L(μ₂-H)Ru₃(CO)₉ (1a–1d), respectively. All the novel Ru complexes were well characterized by NMR, elemental analyses and IR spectra. Structures of complexes 1a, 1c, and 1d were further determined by X-ray crystallographic studies. Complexes 1a–1d were applied to catalytic Oppenauer-type oxidation of secondary alcohols with acetone as oxidant, and complex 1a was found to be the most efficient catalyst.

Full text of DOI:10.1002/aoc.6336

Received: 16 April 2021
DOI: 10.1002/aoc.6336
Revised: 3 June 2021
Accepted: 4 June 2021
R E S E A R C H A R T I C L E
Preparation of trinuclear ruthenium clusters based on
piconol ligands and their application in Oppenauer-type
oxidation of secondary alcohols
Qing Dong1
Jin Lin1
| Zongwen Ma1
| Guo-Liang Lu2
| Zhiqiang Hao1
| Zhangang Han1
|
1National Experimental Chemistry
Teaching Center (Hebei Normal
Abstract
University), Hebei Key Laboratory of
Organic Functional Molecules, College of
Chemistry and Materials Science, Hebei
Normal University, Shijiazhuang, China
2Auckland Cancer Society Research
Centre, Faculty of Medical and Health
Sciences, The University of Auckland,
Auckland, New Zealand
Treatment of Ru3(CO)12 with one equivalent of 2-indolyl-6-pyridinyl-
alcohol ligands 2-(C8H6N)-6-(CR1R2OH)C5H3N (R1 = R2 = Me (L1H);
R1 = R2 = C2H5 (L2H); R1, R2 = À(CH2)4- (L3H);& R1, R2 = À(CH2)5-
(L4H)) in refluxing THF afforded the corresponding trinuclear ruthenium
clusters L(μ2-H)Ru3(CO)9 (1a–1d), respectively. All the novel Ru complexes
were well characterized by NMR, elemental analyses and IR spectra.
Structures of complexes 1a, 1c, and 1d were further determined by X-ray
crystallographic studies. Complexes 1a–1d were applied to catalytic
Oppenauer-type oxidation of secondary alcohols with acetone as oxidant, and
complex 1a was found to be the most efficient catalyst.
Correspondence
Zhiqiang Hao and Jin Lin, National
Experimental Chemistry Teaching Center
(Hebei Normal University), Hebei Key
Laboratory of Organic Functional
Molecules, College of Chemistry and
Materials Science, Hebei Normal
University, Shijiazhuang 050024, China.
Email: zqhao@hebtu.edu.cn;
K E Y W O R D S
Oppenauer-type oxidation, piconol ligands, ruthenium clusters
linjin@hebtu.edu.cn
Funding information
Science Foundation of Hebei Normal
University, Grant/Award Numbers:
L2017Z02, L2018B08; Education
Department Foundation of Hebei
Province, Grant/Award Numbers:
QN2019036, ZD2018005; Hebei Natural
Science Foundation of China, Grant/
Award Numbers: B2017205006,
B2019205087
1 | INTRODUCTION
amounts of chromium-, manganese-based oxide or
sodium periodate (NaIO4) as oxidants, which are hazard-
Aldehydes and ketones are important intermediates that
are widely used in pharmaceutical, polymer, and fine
chemical industries.[1,2] The oxidation of alcohols to the
corresponding carbonyl compounds is a fundamental
reaction in organic synthesis.[3–5] Typical alcohol
oxidation methods usually involve stoichiometric
ous to the environment and require special disposal
procedures.[6,7] In this aspect, the Oppenauer-type
oxidation of alcohols (alcohol transfer oxidation) is a
desirable method, in which acetone is used not only as a
hydrogen acceptor but also as the solvent.[8,9] In the past
two decades, transition metal complexes such as Ir,[10]
Appl Organomet Chem. 2021;e6336.
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© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6336

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DONG ET AL.
Ru,[11] Fe[12]-catalyzed Oppenauer-type reactions have
gained great attention. Among these transition metal
complexes, Ru-based catalysts were widely investigated
and were found to be highly efficient. For example,
Nishibayashi et al have documented the use of chiral
ferrocenyloxazolinylphosphine-ruthenium complex (a in
Chart 1) as the catalyst for oxidative kinetic resolution of
racemic secondary alcohols.[13] In 2014, Wang et al
reported an NNC-pincer Ru (II) complex (b in Chart 1),
which was proven to be an efficient catalyst for the
Oppenauer-type oxidation of secondary alcohols.[11b]
Recently, Kühn and Baratta used a N-heterocyclic
carbene (NHC) ruthenium catalyst (c in Chart 1) for the
Oppenauer-type oxidation of alcohols and transfer hydro-
genation of ketones.[14] However, most of the Ru com-
plexes applied contain phosphine ligands, which require
multistep synthesis and may be sensitive to air. Thus, the
development of highly active phosphine-free ligand-based
Ru complexes for such reaction is still urgent.
Transition-metal carbonyl complexes as a potent cata-
lyst have attracted much attention in organic chemistry
due to their high catalytic activity and good stability.[15,16]
Moore et al reported the pyridyl-based Ru3 clusters as an
efficient catalyst for the acylation of pyridine.[17] Singh
et al introduced the synthesis of secondary amines cata-
lyzed by Ru3(hep)2(CO)8 (hep-H = 2-(2-hydroxyethyl)
pyridine) clusters.[18] We recently reported a series of
pyridine-alcohol and salicylaldiminato-supported tri-
nuclear ruthenium carbonyl complexes as catalysts for
the oxidation of alcohols and synthesis of amides and
nitriles.[19] Herein, we report the synthesis of trinuclear
ruthenium clusters bearing indolyl-pyridinyl-alcohol
ligands for Oppenauer-type oxidation of secondary
alcohols.
2 | RESULTS AND DISCUSSION
2.1 | Synthesis and characterization of
2-indolyl-6-pyridinyl-alcohol ligands
Monolithiation reaction of 2,6-dibromopyridine at À78ꢀC
in diethyl ether gave the corresponding 2-lithiopyridine
salts, which further reacted with diversely substituted
ketones to yield a series of 2-bromopyridine-alcohols
compounds. Next, the Ullmann condensation reaction of
these compounds with benzopyrrole catalyzed by
CuI/K2CO3 system at 110ꢀC in DMSO for 12 h generated
the 2-indolyl-6-pyridinyl-alcohol ligands L1H–L4H in
64%–86% yields (Scheme 1). The 1H NMR spectra of
L1H-L4H show a singlet at 4.43, 4.71, 4.25, and
4.26 ppm, respectively, which is assigned to the charac-
teristic hydroxyl proton. The IR spectra of L1H–L4H all
have a strong broad absorption band at ca. 3300 cmÀ1
owing to the stretching vibration of the O─H bond. The
electrospray ionization mass spectrometry (ESI-MS) ana-
lyses revealed signals at m/z = 253.3 (L1H), 281.1 (L2H)
279.0 (L3H), and 293.1 (L4H) corresponding to the
cation mass fragments [M + H]+.
2.2 | Synthesis and characterization of
ruthenium clusters 1a–1d
Thermal treatment of 2-indolyl-6-pyridinyl-alcohol
ligands L1H–L4H with Ru3(CO)12 in refluxing THF
gave the ruthenium carbonyl complexes [2-(C8H6N)-
6-(CR1R2O)C5H3N] (μ2-H)Ru3(CO)9 (R1 = R2 = Me (1a);
R1 = R2 = C2H5 (1b); R1, R2 = À(CH2)4- (1c); R1,
R2 = À(CH2)5- (1d)), respectively in 70%–85% yields
(Scheme 2). All of these Ru complexes were isolated as air-
stable solids and well characterized by NMR spectroscopy,
IR, and elemental analysis. The absence of hydroxyl pro-
ton in the 1H NMR spectra of 1a–1d indicated the success-
ful generation of the Ru─O bond via deprotonation. The
characteristic singlet around À12 ppm could be ascribed
to Ru─H resonance, which confirmed the presence of
CHART 1 Selected ruthenium complexes for Oppenauer-type
SCHEME 1 Synthesis of indolyl-pyridinyl-alcohol ligands
L1H–L4H
oxidation reactions

DONG ET AL.
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SCHEME 2 Synthesis of trinuclear ruthenium clusters
TABLE 1 Summary of the crystal
Complex
1a
1c
1d
data for compound 1a, 1c, and 1d
Formula
C25H16N2O10Ru3
807.61
C27H18N2O10Ru3
833.64
C28H20N2O10Ru3
847.67
Formula weight
Crystal system
Space group
a (Å)
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
9.8933 (8)
15.1293 (13)
18.9675 (15)
90
9.6057 (5)
15.3825 (8)
19.0049 (9)
90
9.297 (2)
9.8564 (18)
31.950 (7)
90
b (Å)
c (Å)
α (ꢀ)
β (ꢀ)
92.828 (3)
90
92.724 (5)
90
90.02 (2)
90
γ (ꢀ)
V (Å3)
2835.6 (4)
4
2805.0 (2)
4
2927.8 (11)
4
Z
Dcalc (mg/m3)
1.892
1.974
1.923
μ (mmÀ1
)
1.634
1.655
1.587
F (000)
1568
1624
1656
θ
max (ꢀ)
25.02
24.998
24.999
Collected reflns
13,846
12,021
12,883
Uniq reflns
4999
4942
5136
Rint
0.0291
0.0346
0.1022
GOF
1.083
1.057
1.051
R1
0.0523
0.0422
0.1282
wR2
0.0657
0.0700
0.2672
Largest diff peak, hole (e ÅÀ3
)
0.96 and À0.436
0.68 and À0.800
2.512 and À1.453
hydride in the structure and explained their diamagnetic
crystallographic data, collection parameters, and refine-
ment parameters are listed in Table 1. Their molecular
structures are depicted in Figures 1–3 together with
1
nature in the H NMR spectra. The 13C chemical shifts
located in the range of 186–204 ppm confirmed the
existence of several carbonyl groups. Every IR spectrum of
1a–1d displays five strong absorption bands corresponding
to the terminal carbonyls. The disappearance of the broad
peaks around 3300 cmÀ1 of the free ligands L1H–L4H
also indicated the binding of the hydroxyl oxygen atom to
the ruthenium center.
1
selected bond distances and angles, respectively. The H
NMR spectra clearly indicated the presence of Ru─H
bond in the complexes. Thus, the hydride was added
during the crystal refinement as a μ2-H atom, which is
similar to the compound {μ3-η2:η4:η5-(C5H4N)(C9H5)
(C═CPhCH═CPh)}(μ2-H)Ru3(CO)6 reported in the
literature.[20] As shown, all the three complexes consist
of a trinuclear cluster coordinated by an indolyl-
pyridinyl-alcohol ligand, and the three Ru atoms form an
isosceles triangle. The Ru-Ru distances of 1a, 1c, and 1d
are in the range of 2.74–2.81 Å, which are similar to those
in our previously reported Ru complexes[21] (2.74–2.82 Å)
2.3 | Crystal structures of 1a, 1c, and 1d
The solid-state structures of 1a, 1c, and 1d were
further determined by single-crystal crystallography. The

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DONG ET AL.
FIGURE 1 Perspective view of 1a (CCDC: 1939064) with
thermal ellipsoids drawn at 50% probability level. Hydrogens
are omitted for clarity. The selected bond lengths (Å) and
angles (ꢀ): Ru(1)-N(1) 2.235(3), Ru(1)-O(1) 2.085(3), Ru(2)-O(1)
2.120(3), Ru(1)-Ru(2) 2.7620(5), Ru(2)-Ru(3) 2.8127(5), Ru(1)-Ru(3)
2.7538(5). Ru(1)-Ru(3)-Ru(2) 59.485(13), Ru(1)-O(1)-Ru(2)
82.12(10), O(1)-Ru(1)-Ru(2) 49.49(7), O(1)-Ru(2)-Ru(1) 48.40(8)
FIGURE 3 Perspective view of 1d (CCDC: 2040871) with
thermal ellipsoids drawn at 50% probability level. Hydrogens are
omitted for clarity. The selected bond lengths (Å) and angles (ꢀ):
Ru(2)-N(2) 2.200(13), Ru(2)-O(1) 2.090(9), Ru(1)-O(1) 2.147(9),
Ru(2)-Ru(1) 2.7454(16), Ru(1)-Ru(3) 2.8012(17), Ru(2)-Ru(3)
2.7459(17). Ru(2)-Ru(3)-Ru(1) 59.32(4), Ru(2)-O(1)-Ru(1) 80.8(3),
O(1)-Ru(2)-Ru(1) 50.5(2), O(1)-Ru(1)-Ru(2) 48.7(2)
1c, and 2.200(13) Å for 1d, respectively) are in the normal
range and are also close to the pyridine-based Ru
clusters.[18,23]
2.4 | Catalytic activities of new
trinuclear ruthenium complexes
We chose 1-phenylethanol as the model substrate and
ruthenium complex 1a as the catalyst in Oppenauer-type
oxidation to screen the reaction conditions. The results are
summarized in Table 2. Initially, various bases were
screened and employment of different bases indicated
Na2CO3 was the best one to give the acetophenone in max-
imum yield of 91% (Table 2, entries 1–8). Next, the catalyst
loading effect on the reaction was examined. Reducing the
loading of 1a from 1.0 to 0.5 mol% resulted in the decrease
of the yield of acetophenone from 91% to 72% (entry 9). A
substantial drop in yield was also observed when the
amount of Na2CO3 was reduced from 1.0 to 0.5 mmol
(entry 10). Extension of reaction duration from 8 to 10 h
did not improve the yield efficiently, whereas shortening
the time to 6 h lowered the yield to 82% (entries 11–12).
Subsequently, the control experiments showed that with-
out catalyst or base, the oxidation reaction either did not
occur or gave very low yield (entries 13–14). Furthermore,
lowering the reaction temperature to 50ꢀC led to 73% yield
of acetophenone (entry 15). Finally, the other three Ru
complexes 1b–1d were also examined under the optimized
conditions mentioned above. As shown, 1b–1d displayed
FIGURE 2 Perspective view of 1c (CCDC: 2040935) with
thermal ellipsoids drawn at 30% probability level. Hydrogens
are omitted for clarity. The selected bond lengths (Å) and
angles (ꢀ): Ru(1)-N(1) 2.222(3), Ru(1)-O(1) 2.071(3), Ru(2)-O(1)
2.112(2), Ru(1)-Ru(2) 2.7621(5), Ru(2)-Ru(3) 2.8128(5), Ru(1)-Ru(3)
2.7491(5). Ru(1)-Ru(3)-Ru(2) 59.539(12), Ru(1)-O(1)-Ru(2)
82.65(10), O(1)-Ru(1)-Ru(2) 49.31(7), O(1)-Ru(2)-Ru(1) 48.04(8)
and slightly longer than that of ꢁ2.73 Å in the
Ru3(CO)8(μ-OC6H4OMe-2)2 complex.[22] The Ru─O bond
lengths in 1a, 1c, and 1d (2.085(3) Å, 2.071(3) Å, and
2.090(9) Å, respectively) are consistent with that of
2.076(3) Å in (PyCMe2O)Ru3(CO)8 complex.[19a] The
Ru─N bond distances (2.235(3) Å for 1a, 2.222(3) Å for

DONG ET AL.
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TABLE 2 Screening of condition
for the Oppenauer-type oxidation of
1-phenylethanol
Entry
1
Cat. (mol%)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (1.0)
1a (0.5)
1a (1.0)
1a (1.0)
1a (1.0)
—
Base
Time (h)
Yield (%)[a]
Et3N
8
8
8
8
8
8
8
8
8
8
10
6
8
8
8
8
8
8
8
47
53
60
43
65
83
80
91
72
78
92
82
—
12
73
87
80
75
41
2
t-BuONa
t-BuOK
DABCO
Cs2CO3
K2CO3
NaHCO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
—
3
4
5
6
7
8
9
10[b]
11
12
13
14
15[c]
16
17
18
19
1a (1.0)
1a (1.0)
1b (1.0)
1c (1.0)
1d (1.0)
Ru3(CO)12 (1.0)
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Note: Reaction conditions: 1-phenylethanol (1.0 mmol), acetone (5.0 ml), and base (1.0 mmol).
aDetermined by GC analysis (average of two trials).
bNa2CO3 (0.5 mmol).
cTemperature = 50ꢀC.
good catalytic activities achieving decent yields of
75%–87% (entries 16–18). But the complex 1a with methyl
substituents showed the best catalytic activity. This may be
due to the small steric hindrance of the methyl groups,
which is beneficial to the coordination of the substrate to
the metal ruthenium atom. For comparison, Ru3(CO)12
was also tested as a catalyst under the same conditions,
but only gave 41% yield (entry 19), indicating the ligands
play an important role in the homogeneous catalytic sys-
tem. Thus, the optimized conditions for the Oppenauer-
type oxidation of 1-phenylethanol are as follows: 1a
(1.0 mol%) as the catalyst, acetone as the oxidant and
solvent, and Na2CO3 (1 equivalent) as the base, at a tem-
perature of 60ꢀC and reaction for 8 h.
With the optimized reaction conditions in hand, we
sought to explore the generality and limitation of the
present catalytic system. The results for the oxidation of
secondary alcohols are summarized in Table 3. As shown,
acetophenones bearing electron-donating methyl and
methoxy substituents gave rise to the desired products in
yields between 88% and 92% (Table 3, entries 1–4) regard-
less of whether the group was at an ortho, meta, or para
position, showing no obvious steric effect. The electron-
withdrawing groups such as chloro and bromo on the
acetophenone formed the corresponding ketones in rela-
tively low yields of 70%–80% (entries 5–8), indicating that
the electronic nature of substituents had some effects on
product yields. We were pleased to observe that the
catalytic system worked well for sterically hindered
alcohols (e.g., 1-(2-naphthyl)ethanol, diphenylmethanol,
9H-fluoren-9-ol, and benzoin) (entries 9–12). Fused benzyl
alcohols such as 1-tetralol and 1-indanol, under these con-
ditions, also afforded the corresponding ketones in high
yield (94% and 92%, respectively, entries 13 and 14). Fur-
thermore, Ru cluster 1a could chemoselectively oxidized
the secondary alcohol moiety in 1-phenyl-1,2-ethanediol
to produce the hydroxyacetophenone in 80% yield
(entry 15), displaying good chemoselectivity of the present
catalytic system. Non-benzyl alcohols including cyclic
alcohols and linear aliphatic alcohols were also efficiently

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DONG ET AL.
TABLE 3 Oppenauer-type oxidations of alcohols catalyzed by complex 1a
Entry
Substrate
Time (h)
Yield (%)[a]
1
92
2
3
90
91
4
5
88
80
6
7
77
75
8
70
9
90
92
88
10
11
12
83

DONG ET AL.
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TABLE 3 (Continued)
Entry
Substrate
Time (h)
Yield (%)[a]
13
94
14
15
92
80
16
17
83
85
18
81
Note: Reaction conditions: secondary alcohol (1.0 mmol) and acetone (5.0 ml).
aDetermined by GC analysis (average of two trials).
SCHEME 3 Proposed mechanism for Ru-catalyzed
Oppenauer-type oxidation of secondary alcohols

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DONG ET AL.
oxidized to the corresponding ketones in >80% yields
under the same conditions without using a higher loading
of catalyst or extending the reaction time (entries 16–18).
Taken previous reports into account,[11,17] a plausible
mechanism was proposed in Scheme 3 based on
trinuclear pathway. Initially, 1a reacted with sodium alk-
oxide (from substrate alcohol and NaOH) to give the
Ru-alkoxide species I, which underwent β-elimination to
form Ru─H intermediate II and ketone product. Then,
coordination of acetone to the in-situ generated Ru─H
species gave species III, which upon insertion of the
ketone into the Ru─H bond, gave the Ru-alkoxide species
IV. Finally, base-promoted alcohol metathesis with IV
regenerated species I and finished the catalytic cycle. It
should be pointed out that the possibility of non-
trinuclear Ru carbonyl species being involved in the cata-
lytic reaction cannot be ruled out.
alcohol compounds were synthesized according to the
literature.[25]
4.2 | Synthesis of 2-(C8H6N)-6-(CMe2OH)
C5H3N (L1H)
Under a N2 atmosphere, a mixture of 2-(6-bromopyridin-
2-yl)propan-2-ol (1.21 g, 5.5 mmol), indole (0.43 g,
3.7 mmol), CuI (0.07 g, 0.36 mmol), and K2CO3 (1.01 g,
7.3 mmol) in 30 ml of DMSO was stirred at 110ꢀC for
12 h. After cooled to room temperature, 10 ml of brine
was added to the mixture, and the solution was extracted
with dichloromethane (3 Â 15 ml). The combined
organic phase was dried with Na2SO4, and then, the sol-
vent was removed under reduced pressure. The obtained
product was purified by column chromatography (Al2O3,
ethyl acetate: petroleum ether = 1:10) to give L1H as a
1
red oil (0.80 g, 86% yield). H NMR (CDCl3, 400 MHz,
3 | CONCLUSION
298 K): δ 8.11 (d, J = 8.3 Hz, 1H, Py-H), 7.81
(t, J = 7.9 Hz, 1H, Py-H), 7.67 (d, J = 7.8 Hz, 2H, Ar-H,
Py-H), 7.35 (d, J = 8.0 Hz, 1H, Ar-H), 7.29 (d, J = 8.0 Hz,
1H, Ar-H), 7.23 (d, J = 5.6 Hz, 1H, Ar-H), 7.21
(s, 1H, Ar-H), 6.72 (s, 1H, Ar-H), 4.43 (s, 1H, OH), 1.62 (s,
6H, CH3) ppm. 13C NMR (CDCl3, 101 MHz, 298 K): δ
166.2, 150.8, 139.6, 134.9, 130.4, 126.1, 121.2, 112.8, 105.5,
72.4, 40.8, 30.6 ppm. MS (ESI, m/z): 253.3 [M + H]+.
In conclusion, we have synthesized
a series of
indolyl-pyridinyl-alcohol ligand-coordinated trinuclear
ruthenium clusters by reactions of Ru3(CO)12 with
2-indolyl-6-pyridinyl-alcohol compounds, which were
well characterized by NMR, IR, and so on. These Ru
complexes exhibit excellent catalytic activity in the
Oppenauer-type oxidation of secondary alcohols in
the presence of Na2CO3, of which complex 1a is the most
active. These catalysts are easy to synthesize and stable to
air and moisture. The present catalytic system features
broad substrate scope, high catalytic activity, low catalyst
loading and good chemoselectivity.
4.3 | Synthesis of 2-(C8H6N)-6-[C
(C2H5)2OH]C5H3N (L2H)
Following
the
procedure
for
L1H,
from
3-(6-bromopyridin-2-yl)pentan-3-ol, L2H was obtained
as a red oil (0.66 g, 64% yield). 1H NMR (CDCl3,
400 MHz, 298 K): δ 8.10 (d, J = 8.3 Hz, 1H, Py-H), 7.81
(d, J = 10.4 Hz, 1H, Py-H), 7.72–7.62 (m, 2H,
Ar-H, Py-H), 7.35–7.28 (m, 2H, Ar-H), 7.22
(d, J = 9.3, 1H, Ar-H), 7.18–7.10 (m, 2H, Ar-H),
6.72 (d, J = 3.4 Hz, 1H, Ar-H), 4.71 (s, 1H, OH), 2.03–1.79
(m, 4H, CH2), 0.94–0.62 (m, 6H, CH3). ppm.13C NMR
(CDCl3, 101 MHz, 298 K): δ 163.7, 150.6, 139.4, 135.0,
130.5, 126.2, 121.4, 112.5, 105.7, 34.7, 7.9 ppm. MS
(ESI, m/z): 281.1 [M + H]+.
4 | EXPERIMENTAL
4.1 | General considerations
All manipulations were carried out under an argon atmo-
sphere using a Schlenk line. The solvents were dried and
distilled prior to use by the literature methods. All
reagents purchased commercially were used directly
1
without further purification. H NMR and 13C{1H} NMR
spectra were recorded on a Zhongke-Niujin Quantum-I
400 spectrometer. Elemental analyses were performed
using a Vario EL III analyzer. IR spectra were recorded
as KBr disks on a Thermo Fisher iS50 spectrometer. Mass
spectroscopy was performed with an AB SCIEX 3200
Q-TRAP mass spectrometer. GC measurements were per-
formed on Agilent GC7890B equipment using an Agilent
DB-FFAP (30 m  320 μm) column. Ru3(CO)12 was syn-
thesized according to the literature.[24] 2-Bromopyridyl
4.4 | Synthesis of 2-(C8H6N)-
6-[C (CH2)4OH]C5H3N (L3H)
Following the procedure for L1H, from 1-(6-bromopyridin-
2-yl)cyclopentan-1-ol, L3H was obtained as a red oil
1
(0.73 g, 71% yield). H NMR (CDCl3, 400 MHz, 298 K): δ
8.11 (d, J = 8.3 Hz, 1H, Py-H), 7.80 (t, J = 7.9 Hz, 1H,

DONG ET AL.
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Py-H), 7.72–7.61 (m, 2H, Ar-H, Py-H), 7.36–7.28 (m, 2H,
Ar-H), 7.22 (d, J = 9.9 Hz, 2H, Ar-H), 6.70 (s, 1H, Ar-H),
4.25 (s, 1H, OH), 1.83 (d, J = 25.1, 8H, cyclopentyl-H)
ppm.13C NMR (CDCl3, 101 MHz, 298 K): δ 166.3, 150.7,
139.5, 134.9, 130.4, 126.1, 121.2, 114.1, 110.7, 105.6, 73.4,
38.4, 22.1 ppm. MS (ESI, m/z): 279.0 [M + H]+.
Found (%): C, 38.67; H, 2.17; N, 3.11. 1H NMR
(CDCl3, 400 MHz, 298 K): δ 7.74 (t, J = 7.8 Hz, 1H,
Py-H), 7.67 (d, J = 7.8 Hz, 1H, Py-H), 7.58 (d, J = 7.9 Hz,
1H, Py-H), 7.32 (d, J = 8.1 Hz, 1H, Ar-H), 7.24–7.17
(m, 2H,
Ar-H),
7.15–7.11
(m,
2H,
Ar-H),
6.82 (d, J = 3.2 Hz, 1H, Ar-H), 1.13 (d, J = 13.5 Hz, 10H,
ethyl-H), À12.04 (s, 1H, Ru-H) ppm. 13C NMR
(CDCl3, 101 MHz, 298 K) δ203.5, 197.0, 193.6, 186.1,
139.0, 135.8, 129.9, 127.8, 124.1, 122.0, 121.8, 121.6,
120.7, 119.8, 111.0, 102.7, 93.7, 29.7, 6.7 ppm. IR
(υCO, KBr, cmÀ1): 2092(s), 2045(s), 2016(s), 1985(s),
1935(s).
4.5 | Synthesis of 2-(C8H6N)-
6-[C (CH2)5OH]C5H3N (L4H)
Following the procedure for L1H, from 1-(6-bromopyridin-
2-yl)cyclohexan-1-ol, L4H was obtained as a red oil (0.79 g,
1
73% yield). H NMR (CDCl3, 400 MHz, 298 K): δ 8.12 (d,
J = 8.1 Hz, 1H, Py-H), 7.84 (t, J = 7.9 Hz, 1H, Py-H), 7.69
(d, J = 5.6 Hz, 2H, Ar-H, Py-H), 7.37 (d, J = 8.0 Hz, 1H,
Ar-H), 7.33–7.27 (m, 2H, Ar-H), 7.21 (t, J = 7.2 Hz, 1H,
Ar-H), 6.72 (d, J = 3.3 Hz, 1H, Ar-H), 4.26 (s, 1H, OH),
2.00–1.63 (m, 10H, cyclohexyl-H) ppm.13C NMR (CDCl3,
101 MHz, 298 K): δ 166.3, 150.8, 139.5, 134.9, 130.4, 123.2,
121.2, 115.2, 112.7, 105.5, 73.3, 38.4, 25.6, 22.1 ppm. MS
(ESI, m/z): 293.1 [M + H]+.
4.8 | Synthesis of 1c
The preparation of 1c was carried out using a proce-
dure and molar ratios similar to those described for
the synthesis of 1a but with L3H as the ligand.
Complex 1c was obtained as a yellow solid (0.09 g,
34% yield). Anal. Calc. for C27H18N2O10Ru3: C,
38.90; H, 2.18; N, 3.36. Found (%): C, 39.14; H,
1.92; N, 3.15. 1H NMR (CDCl3, 400 MHz, 298 K): δ
7.84 (t, J = 7.8 Hz, 1H, Py-H), 7.75 (d, J = 7.7 Hz, 1H,
Py-H), 7.40–7.22 (m, 6H, Ar-H, Py-H), 6.90
(d, J = 3.3 Hz, 1H, Ar-H), 2.50–2.33 (m, 2H
cyclopentyl-H), 2.21–2.09 (m, 2H, cyclopentyl-H), 1.96
(d, J = 14.9 Hz, 2H, cyclopentyl-H), 1.75 (s, 2H,
cyclopentyl-H), À11.84 (s, 1H, Ru-H) ppm. 13C NMR
(CDCl3, 101 MHz, 298 K): δ 203.8, 199.5, 197.5, 193.4,
190.3, 185.7, 167.9, 139.7, 136.1, 132.4, 130.9, 128.9,
127.5, 123.3, 121.6, 118.8, 101.3, 65.6, 45.7, 42.8, 30.6,
29.7, 24.5, 24.0, 19.2, 13.7 ppm. IR (υCO, KBr, cmÀ1):
2094(s), 2052(s), 2017(s), 1969(s), 1932(s).
4.6 | Synthesis of 1a
Under a N2 atmosphere, a mixture of L1H (0.08 g,
0.32 mmol), Ru3(CO)12 (0.21 g, 0.32 mmol), in 20 ml of
THF was refluxed for 12 h. After cooling to room temper-
ature, the solvent was removed under reduced pressure.
The residue was purified by column chromatography on
Al2O3 (ethyl acetate: petroleum ether = 1: 20) to give 1a
as a yellow solid (0.11 g, 43% yield). Anal. Calc. for
C25H16N2O10Ru3: C, 37.18; H, 2.00; N, 3.47. Found (%): C,
37.43; H, 1.77; N, 3.65. 1H NMR (CDCl3, 400 MHz,
298 K):
δ 8.11 (d, J = 8.3 Hz, 1H, Py-H), 7.81
(t, J = 7.9 Hz, 1H, Py-H), 7.68 (d, J = 5.6 Hz, 2H, Ar-H,
Py-H), 7.37–7.20 (m, 4H, Ar-H), 6.71 (d, J = 3.4 Hz, 1H,
Ar-H), 1.62 (s, 6H, CH3), À11.98 (s, 1H, Ru-H) ppm. 13C
NMR (CDCl3, 101 MHz, 298 K): δ 203.8, 199.4, 199.0,
197.3, 197.2, 193.3, 190.3, 185.9, 168.2, 139.7, 136.0, 129.8,
127.4, 123.3, 121.7, 119.2, 111.0, 106.7, 102.7, 89.1, 34.1,
31.3 ppm. IR (υCO, KBr, cmÀ1): 2095(s), 2051(s), 2001(s),
1970(s), 1931(s).
4.9 | Synthesis of 1d
The preparation of 1d was carried out using a proce-
dure and molar ratios similar to those described for
the synthesis of 1a but with L4H as the ligand. Com-
plex 1d was obtained as a yellow solid (0.10 g, 37%
yield). Anal. Calc. for C28H20N2O10Ru3: C, 39.67; H,
1
2.38; N, 3.31. Found (%): C, 39.87; H, 2.27; N, 3.05. H
NMR (CDCl3, 400 MHz, 298 K) δ 7.85–7.77 (m, 1H,
Py-H), 7.72 (t, J = 8.2 Hz, 1H, Py-H), 7.55–7.27 (m,
6H, Ar-H), 6.89 (d, J = 3.1 Hz, 1H, Ar-H), 2.32–2.10
(m, 2H, cyclohexyl-H), 2.09–1.91 (m, 4H, cyclohexyl-
H), 1.86–1.76 (m, 2H, cyclohexyl-H), 1.56 (s, 2H
cyclohexyl-H), À12.20 (s, 1H, Ru-H) ppm. 13C NMR
(CDCl3, 101 MHz, 298 K): δ 204.3, 199.4, 197.7193.4,
189.9, 186.3, 169.2, 139.6, 135.6, 130.9, 130.1, 127.2,
126.9, 123.3, 121.7, 118.9, 107.0, 43.7, 38.1, 25.6,
4.7 | Synthesis of 1b
The preparation of 1b was carried out using a procedure
and molar ratios similar to those described for the
synthesis of 1a but with L2H as the ligand. Complex 1b
was obtained as a yellow solid (0.09 g, 34% yield). Anal.
Calc. for C27H20N2O10Ru3: C, 38.81; H, 2.41; N, 3.35.

10 of 11
DONG ET AL.
21.7 ppm. IR (υCO, KBr, cmÀ1): 2091(s), 2046(s), 2027
(s), 1982(s), 1931(s).
Formal analysis; methodology. jin lin: Project adminis-
tration; supervision; validation. Guo-Liang Lu: Formal
analysis; methodology.
4.10 | General procedure for the
Oppenauer-type oxidation of secondary
alcohols
CONFLICT OF INTEREST
There are no conflicts to declare.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able from the corresponding author upon reasonable
request.
Under a N2 atmosphere, a mixture of 1-phenylethanol
(0.122 g, 1.0 mmol), complex 1a (0.008 g, 0.01 mmol) and
Na2CO3 (0.10 g, 1.0 mmol) in 5 ml of acetone was stirred
at 60ꢀC for 8 h. After it cooled to ambient temperature,
0.1 ml of the reaction mixture was sampled for GC
analysis. The resultant solution was condensed under
reduced pressure and subjected to purification by column
chromatography on Al2O3 (ethyl acetate: petroleum
ether = 1: 15) to give the corresponding acetophenone as
a yellow oily liquid (0.10 g, 85% yield), which was further
identified by comparison with the authentic sample
through NMR.
ORCID
Qing Dong https://orcid.org/0000-0002-5901-8921
Zongwen Ma https://orcid.org/0000-0003-2601-8324
Zhiqiang Hao https://orcid.org/0000-0002-6554-803X
Zhangang Han https://orcid.org/0000-0002-9758-6735
Jin Lin https://orcid.org/0000-0002-0310-6463
Guo-Liang Lu https://orcid.org/0000-0002-2094-0820
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ACKNOWLEDGMENTS
This work was supported by the Hebei Natural Science
Foundation of China (B2017205006 and B2019205087),
the Education Department Foundation of Hebei Province
(ZD2018005 and QN2019036), and the Science
Foundation of Hebei Normal University (L2017Z02 and
L2018B08).
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Qing Dong: Data curation; investigation; methodology.
Zongwen Ma: Investigation; methodology. Zhiqiang
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How to cite this article: Q. Dong, Z. Ma, Z. Hao,
Z. Han, J. Lin, G.-L. Lu, Appl Organomet Chem
2021, e6336. https://doi.org/10.1002/aoc.6336