Bidentate Ru(ii)-NC complexes as catalysts for the dehydrogenative reaction from primary alcohols to carboxylic acids

Article abstract of DOI:10.1039/c9dt01414d

Four Ru(ii)-NC complexes were synthesized by one-step processes from the corresponding NC ligands with RuHCl(CO)(PPh₃)₃. These complexes were tested as catalysts for alcohol dehydrogenative reactions, and complex {(C₅H₄N)-(C₆H₄)}RuCl(CO)(PPh₃)₂ (1) showed the highest activity. With KOH as the nucleophile and 0.5 mol% catalyst loading, a series of carboxylic acids were synthesized in toluene without any oxidant. Catalyst 1 could be transformed to complex {(C₅H₄N)-(C₆H₄)}RuH(CO)(PPh₃)₂ (6) when treated with KOH and benzyl alcohol. Complex 6 further reacted with PhCHO and H₂O to generate product {(C₅H₄N)-(C₆H₄)}Ru(OCOPh)(CO)(PPh₃)₂ (7). Complexes 6 and 7 exhibited similar efficiency to complex 1, suggesting that they can be regarded as the catalytic intermediates of 1.

Full text of DOI:10.1039/c9dt01414d

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Bidentate Ru(II)-NC complexes as catalysts for the dehydrogenative
DOI: 10.1039/C9DT01414D
reaction from primary alcohols to carboxylic acids
Dawei Gong,† Bowen Hu,† and Dafa Chen*,†
† MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage,
School of Chemical Engineering & Technology, Harbin Institute of Technology, Harbin 150001,
People's Republic of China.
Electronic supplementary information (ESI) available: Crystallographic data for complexes 3 and
7, and IR and NMR spectra of the new compounds. CCDC 1890662 and 1890663. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
Four Ru(II)-NC complexes were synthesized by one-step processes from the corresponding NC
ligands with RuHCl(CO)(PPh3)3. These complexes were tested as catalysts for alcohol
dehydrogenative reactions, and complex {(C5H4N)-(C6H4)}RuCl(CO)(PPh3)2 (1) showed the
highest activity. With KOH as the nucleophile and 0.5 mol% catalyst loading, a series of
carboxylic acids were synthesized in toluene without any oxidant. Catalyst 1 could be transformed
to complex {(C5H4N)-(C6H4)}RuH(CO)(PPh3)2 (6) when treated with KOH and benzyl alcohol.
Complex
6
further reacted with PhCHO and H2O to generate product
{(C5H4N)-(C6H4)}Ru(OCOPh)(CO)(PPh3)2 (7). Complexes 6 and 7 exhibited similar efficiency as
complex 1, suggesting they can be regarded as the catalytic intermediates of 1.
Introduction
Carboxylic acid is an important structure in organic synthesis, especially in total synthesis of
natural products and medicinal chemistry. However, synthesis of carboxylic acids in industrial
production is regularly carried out by aldehydes with stoichiometric amount of oxidants, which
generated waste and environmental problem.1
In 2013, Milstein et al. treated a Ru-NNP pincer complex for acceptorless dehydrogenation of
primary alcohols with OH- to carboxylic acids under oxidant-free condition.2 Since then, a series
of ruthenium complexes featuring tridentate NNP,3 PNP4-7 and NNN,8,9 bidentate NN,10 and NHC
ligands,11,12 have been expanded for such transformation. Besides, several other transition-metal
based homogenous catalysts, including Ir,13-15 Rh,16 Ni17, Mn18 and Zn19 complexes, were also
developed. Most of the systems were carried out in water2-7,10,12-14,16, or alcohols,9,17,18 while some
were efficient in toluene.8,11,15
The first example in toluene was reported in 2016 by the Madsen’s group.11 They used a
Ru-NHC complex (1 mol%) as the catalyst, and in the presence of PCy3HBF4 and KOH, a series
of benzyl alcohols (6 h) and aliphatic alcohols (24 h) were translated into corresponding

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carboxylic acids (Scheme 1). The authors stated that lipophilic alcohols might performDbOeI:t1t0e.r10i3n9/C9DT01414D
toluene than in water, and the generated carboxylic acid salts was easier to be isolated. Szymczak
and coworkers later designed a Ru-NNN complex to catalyze this kind of reactions (18 h), and the
catalyst loading was decreased to 0.2 mol% (Scheme 1).8 More recently, Williams et al. used the
Ir-COD catalysts (0.2 mol%) for this reaction with a broad substrate scope (around 40 h), and
several intermediates were identified (Scheme 1).15 Due to our continuous interest in developing
catalysts for H2-relating reactions,20-23 herein we present a bidentate Ru-NC complex
{(C5H4N)-(C6H4)}RuCl(CO)(PPh3)2 (1) (0.5 mol%) for such dehydrogenative reactions (6 h)
(Scheme 1). The air- and moisture- stable complex 1 is easily synthesized, and two critical
intermediates
{(C5H4N)-(C6H4)}RuH(CO)(PPh3)2
(6)
and
{(C5H4N)-(C6H4)}Ru(OCOPh)(CO)(PPh3)2 (7) were isolated and characterized.
Scheme 1. The oxidant-free dehydrogenative catalysts from primary alcohols to carboxylic acids in toluene
Results and discussion
Synthesis and characterization of the complexes
Reactions of 2-phenylpyridine and 2-(1-naphthalenyl)pyridine with RuHCl(CO)(PPh3)3 in
refluxing toluene gave complexes {(C5H4N)-(C6H4)}RuCl(CO)(PPh3)2 (1) and
{(C5H4N)-(C10H6)}RuCl(CO)(PPh3)2 (2) in high yields (90% for 1; 82% for 2), respectively
(Scheme 2). The aromatic protons of 1 locate at 8.58-6.28 ppm, and those of 2 are exhibited at
8.81-6.25 ppm. Each of their IR spectra shows a strong CO absorption (1919 cm-1 for 1; 1915 cm-1
for 2). In fact, complexes 1 and 2 have been synthesized by Clark et al., while they used a
two-step method and Hg(OAc)2 was needed.24,25

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DOI: 10.1039/C9DT01414D
Scheme 2. Synthesis of complexes 1-4
1
Complexes 3 and 4 were synthesized using a similar procedure (Scheme 2). Each of the H
NMR spectra exhibits 38 aromatic and 2 alkyl protons, and the 31P{1H} NMR spectra shows a
singlet (29.0 ppm for 3; 32.1 ppm for 4), suggesting each contains two chemically equivalent PPh3
groups. The CO bands in their IR spectra appear at 1925 and 1942 cm-1, respectively. The
structure of 3 was further identified by X-ray single crystal diffraction method (Figure 1). 3 is in
an octahedral geometry, with a bidentate NC ligand, a Cl, a CO and two trans-PPh3 coordinating
with the central ruthenium atom.
Fig 1. Solid-state structure of 3. The thermal ellipsoids are displayed at 30% probability. Hydrogen atoms and
solvents have been omitted for clarity. phenyl rings on PPh3 ligands have been omitted for clarity. Selected bond
distances (Å): Ru(1)-N(1), 2.1648(20); Ru(1)-P(1), 2.4022(7); Ru(1)-P(2), 2.3792(7); Ru(1)-C(1), 2.0063(28);
Ru(1)-Cl(1), 2.5261(8) (Å).
Complex 1 was further treated with AgBF4 in the presence of CO at room temperature, and
complex [{(C5H4N)-(C6H4)}Ru(CO)2(PPh3)2][BF4] (5) was formed (Scheme 3). The IR spectrum
of 5 shows two absorptions at 2040 and 1983 cm-1 for its CO ligands. A singlet at 31.3 ppm is
-
present in its 31P{1H} NMR spectrum. 19F NMR exhibits a singlet at -154.0 ppm for the BF4 anion.
Complexes 1-5 were easily synthesized in high yields and showed good stability both in the solid
state and in solution under air. For example, no decomposition was observed after dissolved in
CDCl3 for one week under air, monitored by 1H NMR spectroscopy.

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DOI: 10.1039/C9DT01414D
Scheme 3. Synthesis of 5
Catalysis
The reaction of benzyl alcohol with KOH (1.5 eq.) was chosen as the model reaction (Table 1).
After refluxing in toluene for 6 h, 1 showed high catalytic performance (91%), 2-4 gave moderate
yields (56 - 74%), and 5 could not catalyze this reaction (Table 1, Entries 1-5). When the reaction
time was extended to 9 h, for catalysts 1, 3 and 4, almost no change was found for the conversions,
suggesting these three complexes nearly reached their maximum conversion in 6 h. While for
catalyst 2, the conversion was 67%, higher than that in 6 h. In shorter times (1 h and 3 h), the
conversions were also recorded (for 1-4: 1 h: 29%, 16%, 24%, 23%, respectively; 3 h: 68%, 36%,
50%, 56%, respectively). These data indicate the catalytic performance of 1-4 is not accordant
with electronics at the metal centers based on 31P{1H} and ν(CO) values, probably because some
other factors, such as steric effect, also influence the reaction. NaOH was not as good as KOH,
probably due to the lower basic strength (Table 1, Entry 6). The amounts of KOH were also
important for this reaction, and the conversions were significantly decreased if its amount was
increased to 2 equivalences or more (Table 1, Entries 7-9). On the other hand, when the
temperature was reduced to 100 oC, the conversion was only 52% (Table 1, Entry 10).
Table 1. Optimization of reaction conditions for dehydrogenative reaction
Entry
1
[Ru]
1
Base
Conversion (%)a
KOH (1.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
NaOH (1.5 eq.)
KOH (1.0 eq.)
KOH (2.0 eq.)
KOH (2.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
KOH (1.5 eq.)
91 (92b)
56 (67b)
70 (73b)
74 (76b)
0
2
2
3
3
4
4
5
5
6
1
37
7
1
86
8
1
71
9
1
64
10
11
12
13
1
52c
6
91
7
90
8
65
a Reaction conditions: benzyl alcohol (2 mmol), base (3 mmol), toluene (6 mL), N2, catalyst (0.5 mol%), 120 oC, 6
h; the conversion was calculate by GC using dodecane (1 mmol) as the internal standard. b The conversion after 9

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h. c100 oC.
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DOI: 10.1039/C9DT01414D
With the optimal conditions (Table 1, Entry 1), a series of primary alcohols were subjected to
test the substrate scope and functional group tolerance (Table 2). For benzyl alcohol and its
derivatives, the catalyst 1 showed high conversions, no matter if they were electron-rich or
electron-deficient (Table 2, Entries 1-13). For 4-bromobenzyl alcohol, the product was a mixture
of 4-bromobenzoic acid and benzoic acid (43% benzoyl acid determined by NMR. Table 2, Entry
4). 2-Methybenzyl alcohol showed poor conversion (Table 2, Entry 12), which was similar to the
Williams’ systems.15 For 2-chlorobenzyl alcohol, the product was dehalogenated benzoic acid
(Table 2, Entry 13).26 2-Naphthalenemethanol and 4-phenyl-1-butanol showed 85% and 75%
conversions, comparable to the benzyl alcohols (Table 2, Entries 14-15). For aliphatic alcohols,
the conversions were about 60% (Table 2, Entries 16-17).
Table 2. Substrate scope for dehydrogenative reaction of primary alcohols using precatalyst 1
Entry Alcohol
Product
Conversion (%)a Isolated
(%)b
yield
1
2
91%
89%
90%
85%
90%
90%
75%
89%
84%
88%
80%c
87%
88%
72%
3
4
5
6
7
8
86%
89%
82%
85%
9

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DOI: 10.1039/C9DT01414D
10
11
90%
87%
85%
48%
82%
45%
12
13
86%
75%
85%
83%
68%
80%
14
15
16
17
64%
62%
55%
50%
a Reaction conditions: primary alcohol (2 mmol), KOH (3 mmol), toluene (6 mL), 1 (0.5 mol%), refluxing in 120
oC for 6 h; the conversion was calculated by GC using dodecane (1 mmol) as the internal standard. b The aqueous
phase was acidified with 1 mL of 6 M HCl and ethyl acetate was used to extract the product for three times. c Yield
determined by 1H NMR, and it was a mixture with 43% of benzoic acid.
Intermediates isolation and catalytic cycles
In order to study the mechanism of such transformation, the Hg and PPh3 poisoning tests were
carried out, respectively. Excess of Hg (Hg:Ru = 400:1) or PPh3 (PPh3:Ru = 5:1) did not influence
the conversion obviously, suggesting the catalytic process is homogeneous, and PPh3 dissociation
is not involved in the rate-determining step.
The acceptorless dehydrogenation of primary alcohols with OH- to carboxylic acids might
proceed through two intermediates: aldehyde and/or ester.15,18 Firstly, GC-FID was used to
monitor the reaction of benzyl alcohol with KOH in toluene, however, neither benzaldehyde nor
benzyl benzoate was detected. This is because both are easily converted into benzoic acid and
benzyl alcohol under the catalytic condition. For example, when benzaldehyde (1 mmol) reacted
o
with KOH (1.5 mmol) in toluene (3 mL) for 1 h at 120 C, a Cannizzaro reaction occured and
benzaldehyde was consumed completely (Scheme 4, eqn (1)), which was consistent with Madsen’
results.11 Benzyl benzoate gave a similar result (Scheme 4, eqn (2)). In order to further distinguish
these two pathways, in the presence of catalyst 1 (0.005 mmol), benzyl alcohol (3 mL) was treated
with KOH (1.0 mmol) without extra solvent, and after 6 hours at 120 oC, benzaldehyde (about 0.2
mmol from GC analysis) but not benzyl benzoate was detected (Scheme 4, eqn (3)). The results
suggest ester as a less-likely intermediate.27

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DOI: 10.1039/C9DT01414D
Scheme 4. Control experiments to distinguish between those two pathways
In order to indentify H2 was the side product, some hydrogenation reactions were carried out
(Table 3). The catalytic reactions were tested in a closed system. When 1.0 eq. styrene and 1
mol% Pd/C were added into the catalytic system of benzyl alcohol with KOH, styrene was
transformed to ethylbenzene (32%, Table 3, Entry 1). In the absence of catalyst 1 or Pd/C, poor
conversions were shown (Table 3, Entries 2-3). The use of 5% Pd/C was found to increase the
yield of ethylbenzene dramatically (95%, Table 3, Entry 4). These results proved the release of H2
during the transformation of primary alcohols to carboxylic acids.
Table 3. Hydrogenation of styrene using Pd/C in the catalytic system
Entry
Complex 1
0.5 mol%
0.5 mol%
--
Pd/C
1 mol%
--
Conversion (%)a
1
2
3
4
32
0
1 mol%
5 mol%
4
0.5 mol%
95%
a
Reaction conditions: styrene (1 mmol), primary alcohol (1 mmol), KOH (1.5 mmol), toluene (3 mL), 1 (0.5
mol%), Pd/C, refluxing in a close system at 120 oC for 6 h; the conversion was determined by GC using dodecane
(1 mmol) as the internal standard.
To isolate some catalytic intermediates, complex 1 was then reacted with KOH (2 eq.) and
benzyl alcohol (2 eq.) in refluxing toluene. After 1.5 hours, 1 was completely consumed, and
besides the precipitated PhCOOK, a yellow-green product was isolated in 75% yield (Scheme 5).
1
The H NMR shows one characteristic triplet at -11.25 ppm for the Ru-H, and several peaks at
8.53-6.33 ppm for its aromatic protons. The data are consistent with those of complex
{(C5H4N)-(C6H4)}RuH(CO)(PPh3)2 (6) reported by Kawano et. al.28

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DOI: 10.1039/C9DT01414D
Scheme 5. Synthesis of 6
As PhCHO is regarded as the primary intermediate of PhCH2OH to PhCOOK,2-18 we then
tested the reaction of 6 with PhCHO in the presence of H2O, and a yellow powder
{(C5H4N)-(C6H4)}Ru(OCOPh)(CO)(PPh3)2 (7) was generated (Scheme 5). The IR spectrum of 7
shows one intense absorption at 1933 cm-1 for the carbonyl ligand. The 31P{1H} NMR exhibits a
singlet at 33.6 ppm. Single-crystal X-ray diffraction analysis reveals that complex 7 is a ruthenium
carboxylate, which is formed through the replacement of the hydride in 6 by a benzoyloxy group
(Figure 2). When complex 7 was treated with benzyl alcohol and KOH in refluxing toluene,
complex 6 could be regenerated again (Scheme 5). It should be noted that when 6 reacted with
PhCOOH directly, complex RuH(CO)(η3-OCOPh)(PPh3)2 (8)31 rather than 7 was generated
(Scheme 7). On the other hand, complex 6 could not react with PhCOOK.
Scheme 6. Transformation between 6 and 7
Fig 2. Solid-state structure of 7. The thermal ellipsoids are displayed at 30% probability. Hydrogen atoms and
solvents have been omitted for clarity. phenyl rings on PPh3 ligands have been omitted for clarity. Selected bond
distances (Å): Ru(1)-N(1), 2.1641(44); Ru(1)-P(1), 2.3730(17); Ru(1)-P(2), 2.4107(17); Ru(1)-C1, 2.0462(64);
Ru(1)-C19, 1.8504(65); Ru(1)-O(1), 2.1811(43).

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DOI: 10.1039/C9DT01414D
Scheme 7. Synthesis of 8
Complexes 6-8 were also tested as the catalysts for the dehydrogenative reaction of benzyl
alcohol with KOH, with similar conditions. The conversions were 91%, 90% and 65% (Table 1,
Entries 11-13), respectively. The yields of complexes 6 and 7 were comparable to that of Entry 1
in Table 2, when 1 was chosen as the catalyst, suggesting they can be considered as the catalytic
intermediates of 1. The conversions of complexes 1 and 6-8 in shorter times further verified this
inference (Table S1).
According to the related literatures,10,11,15,18 and based on the above results, a possible
mechanism is proposed in Scheme 8. Firstly, 1 reacts with KOH and PhCH2OH to form a Ru-OR
intermediate A. -Hydride elimination of A generates the intermediate 6 and PhCHO. 6 then
reacts with PhCHO and water to produce B with the release of one molecule of H2. Although
attempts to detect B were unsuccessful, similar intermediates have been proposed in previous
literatures.3,7,10 B then loses another molecule of H2 to form 7. PhCOOK is finally made by the
reaction of 7 with KOH and PhCH2OH, and the catalytic cycle is finished. It should be noted that
even without any catalyst, the Cannizzaro reaction would happen between PhCHO and KOH,
generating a mixture of PhCOOK and PhCH2OH.15,18 So the Cannizzaro reaction can not be
excluded in our system, and probably it simultaneous occur with the main catalytic cycle, similar
to Madsen’s and Williams’ systems.11,15 What should be noted is that although PPh3 dissociation
is not the rate-determining step, the dissociation-association behavior of one of the PPh3 ligands
might happen during the catalytic cycle, because β-hydride elimination needs an open site.

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DOI: 10.1039/C9DT01414D
Scheme 8. proposed reaction mechanism
Conclusions
In summary, a series of bidentate Ru(II)-NC complexes (1-5) have been synthesized and
applied to the conversion of primary alcohols to the corresponding carboxylic acids in the absence
of oxidant. Among these five complexes, 1 showed the highest activity. Some contrast
experiments were used to study the mechanism and two critical intermediates 6 and 7 were
isolated and characterized. Complex 7, which was produced by the reaction of complex 6 with
PhCHO and water, could convert back to complex 6 in the presence of benzyl alcohol and KOH.
Based on this interconversion, a possible catalytic mechanism was proposed. The results in this
manuscript provide a new type of easily synthesized air- and moisture- stable complexes for
acceptorless dehydrogenation of primary alcohols to carboxylic acids under oxidant-free
condition.
Experimental
General considerations
All manipulations were carried out under an inert nitrogen atmosphere using a Schlenk line.
Solvents were distilled from appropriate drying agents under N2 before use. All reagents were
purchased from commercial sources. Liquid compounds were degassed by standard
freeze-pump-thaw procedures prior to use. RuHCl(PPh3)3(CO),29 3-(2-pyridyl)indene30 and
1
2-(2-pyridyl)indene30 were prepared as previously described, respectively. The H and 31P{1H}
NMR spectra were recorded on a Bruker Avance 400 spectrometer. The 1H NMR chemical shifts

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were referenced to residual solvent as determined relative to Me4Si (δ = 0 ppm). The 31P{1H}View Article Online
DOI: 10.1039/C9DT01414D
chemical shifts were reported in ppm relative to external 85% H3PO4. The 19F NMR chemical
shifts were referenced to residual solvent as determined relative to CFCl3 (δ = -95.0 ppm).
Elemental analyses were performed on a Perkin-Elmer 240C analyzer. X-ray diffraction studies
were carried out in a SuperNova X-ray single crystal diffractometer. Data collections were
performed using four-circle kappa diffractometers equipped with CCD detectors. Data were
reduced and then corrected for absorption. Solution, refinement and geometrical calculations for
all crystal structures were performed by SHELXTL.
Synthesis of 1:24 2-Phenylpyridine (0.23 g, 1.5 mmol) and RuHCl(PPh3)3(CO) (0.95 g, 1 mmol)
were dissolved in toluene (10 mL) and the solution was refluxed for 12 h. The mixture was
allowed to cool to room temperature and filtered. The product was washed by n-hexane and
filtered in vacuo to give 1 as a yellow powder (0.76 g, 90%). Anal. Calcd for C48H38ClNOP2Ru: C,
68.36; H, 4.54; N, 1.66. Found: C, 68.72; H, 4.79; N, 1.57. 1H NMR (400 MHz, CDCl3, ppm):
8.58 (d, J = 5.6 Hz, 1H), 7.45 (d, J = 8 Hz, 1H), 7.38-7.30 (m, 14H), 7.20-7.08 (m, 18H) , 6.81 (d,
J = 7.6 Hz, 1H), 6.65 (t, J = 6.4 Hz, 1H), 6.28 (t, J = 8 Hz, 2H). 31P{1H} NMR (162 MHz, CDCl3,
ppm): 33.7. IR (νCO, cm-1): 1919 (s).
Synthesis of 2:25 2-(1-Naphthalenyl)pyridine (0.25 g, 1.2 mmol) and RuHCl(PPh3)3(CO) (0.95 g,
1 mmol) were dissolved in toluene (10 mL) and the solution was refluxed for 12 h. The mixture
was allowed to cool to room temperature and the organic phase was evaporated under vacuum.
Residue was purified by column chromatography on silica gel (ethyl acetate/petroleum ether, v:v
= 20:1) to give 2 as a yellow powder (0.73 g, 82%). Anal. Calcd for C52H40ClNOP2Ru: C, 69.91;
H, 4.51; N, 1.57. Found: C, 70.04; H, 4.85; N, 1.48. 1H NMR (400 MHz, CDCl3, ppm): 8.81-8.80
(m, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.96 (d, J = 8.0 Hz, 1H), 7.56 (d, J = 8.0 Hz, 1H), 7.39-7.04 (m,
33H), 6.90 (d, J = 8.0 Hz, 1H), 6.58 (d, J = 8.0 Hz, 1H), 6.25-6.24 (m, 1H). 31P{1H} NMR (162
MHz, CDCl3, ppm): 32.3. IR (νCO, cm-1): 1915 (s).
Synthesis of 3: 3-(2-Pyridyl)indene (0.23 g, 1.2 mmol) and RuHCl(PPh3)3(CO) (0.95 g, 1 mmol)
were dissolved in toluene (10 mL) and the solution was refluxed for 12 h. The mixture was
allowed to cool to room temperature and the organic phase was evaporated under vacuum.
Residue was purified by column chromatography on silica gel (ethyl acetate/petroleum ether, v:v
= 20:1) to give 3 as a yellow powder (0.47 g, 53%). A yellow blocky crystal was recrystallized by
o
vapor diffusion of n-hexane into a CH2Cl2 solution of 3 at room temperature. Mp: 235 C (dec).
Anal. Calcd for C51H40ClNOP2Ru: C, 69.50; H, 4.57; N, 1.59. Found: C, 69.70; H, 4.75; N, 1.50.
1H NMR (400 MHz, CDCl3, ppm): 8.77 (d, J = 5.2 Hz, 1H), 7.72-7.68 (m, 1H), 7.57-7.55 (m,
12H), 7.36-7.17 (m, 6H), 6.13-6.06 (m, 15H), 6.90-6.84 (m, 2H), 6.21 (t, J = 6.4 Hz, 1H), 1.68 (s,
2H). 31P{1H} NMR (162 MHz, CDCl3, ppm): 29.0. IR (νCO, cm-1): 1925 (s). A satisfactory 13C
NMR spectrum was not obtained because of its low solubility.
Synthesis of 4: 2-(2-Pyridyl)indene (0.23 g, 1.2 mmol) and RuHCl(PPh3)3(CO) (0.95 g, 1 mmol)
were dissolved in toluene (10 mL) and the solution was refluxed for 12 h. The mixture was

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allowed to cool to room temperature and the organic phase was evaporated underDvOaI:c1u0.u10m39./C9DT01414D
Residue was purified by column chromatography on silica gel (ethyl acetate/petroleum ether, v:v
o
= 20:1) to give 4 as a yellow powder (0.65 g, 74%). Mp: 224 C (dec). Anal. Calcd for
C51H40ClNOP2Ru: C, 69.50; H, 4.57; N, 1.59. Found: C, 69.60; H, 4.79; N, 1.48. 1H NMR (400
MHz, CDCl3, ppm): 8.35 (d, J = 5.6 Hz, 1H), 7.52-7.29 (m, 15H), 7.12-6.87 (m, 21H), 6.17 (t, J =
6.4 Hz, 1H) , 3.10 (s, 2H). 31P{1H} NMR (162 MHz, CDCl3, ppm): 32.1. IR (νCO, cm-1): 1942 (s).
A satisfactory 13C NMR spectrum was not obtained because of its low solubility.
Synthesis of 5: Complex 1 (0.10 g, 0.12 mmol) was dissolved in CH2Cl2 (10 mL) and AgBF4
(0.05 g, 0.25 mmol) dissolved in 5 mL water was added. Then ethanol (5 mL) was added, and CO
gas was slowly passed for 1.5 h until the mixture became colorless. After filtered, the solution was
washed with water, and the organic phase was separated. Ethanol (20 mL) was added to the
organic phase. The volume was reduced in vacuo until crystals appeared. The mixture was filtered
o
in vacuo to give 5 as a colorless powder (0.06 g, 55%). Mp: 242 C (dec) Anal. Calcd for
C49H38NO2P2BF4Ru: C, 63.79; H, 4.15; N, 1.17. Found: C, 63.90; H, 4.30; N, 1.07. 1H NMR (400
MHz, CDCl3, ppm): 8.04-8.03 (m, 1H), 7.60 (t, J = 8 Hz, 1H), 7.49 (d, J = 8.0 Hz, 1H), 7.38-7.36
(m, 7H), 7.28-7.26 (m, 13H), 7.09-7.00 (m, 12H), 6.96 (d, J = 5.6 Hz, 1H), 6.87-6.85 (m, 1H) ,
6.76 (t, J = 6.4 Hz, 1H). 31P{1H} NMR (162 MHz, CDCl3, ppm): 30.3. 19F NMR (376 MHz,
CDCl3, ppm): -154.0. IR (νCO, cm-1): 1983 (s), 2040 (s). A satisfactory 13C NMR spectrum was not
obtained because of its low solubility.
Synthesis of 6:26 Complex 1 (0.14 g, 0.16 mmol), KOH (0.02 g, 0.32 mmol) and benzyl alcohol
(0.04 g, 0.32 mmol) were dissolved in toluene (3 mL) and the solution was refluxed for 1.5 h. The
mixture was allowed to cool to room temperature and filtered through a Celite. After reduced in
vacuo, the product was washed by EtOH and recrystallized from CH2Cl2 and petroleum ether to
give 6 as a yellow powder (0.10 g, 74%). Anal. Calcd for C48H39NOP2Ru: C, 71.28; H, 4.86; N,
1.73. Found: C, 71.60; H, 4.99; N, 1.56. 1H NMR (400 MHz, CDCl3, ppm): 8.53 (d, J = 4.2 Hz,
1H), 7.37-7.36 (m, 12H), 7.17-7.02 (m, 22H), 6.65 (t, J = 6.8 Hz, 1H), 6.50 (t, J = 6.0 Hz, 1H),
6.33 (t, J = 7.2 Hz, 1H), -11.25 (t, J = 18.4 Hz, 1H). 31P{1H} NMR (162 MHz, CDCl3, ppm): 54.4.
IR (νCO, cm-1): 1892 (s).
Synthesis of 7: Complex 6 (0.13 g, 0.16 mmol), H2O (0.03 g, 1.60 mmol) and benzaldehyde (0.17
g, 1.60 mmol) were dissolved in toluene (10 mL) and the solution was refluxed for 6 h until IR (in
toluene) showed no 6 was remaining in this mixture. The mixture was allowed to cool to room
temperature and reduced in vacuo. The product was washed by n-hexane and filtered in vacuo to
give 7 as a yellow powder (0.13 g, 85%). A yellow blocky crystal was recrystallized by gas
o
diffusion of n-hexane into a toluene solution of 7 at room temperature. Mp: 218 C (dec). Anal.
Calcd for C55H43NO3P2Ru: C, 71.11; H, 4.67; N, 1.51. Found: C, 71.30; H, 4.82; N, 1.44. 1H NMR
(400 MHz, CDCl3, ppm): 8.89 (d, J = 5.2 Hz, 1H), 7.68 (d, J = 6.8 Hz, 1H), 7.28-7.09 (m, 27H),
7.00-6.96 (m, 10H), 7.74-7.72 (m, 2H), 6.60-6.57 (m, 2H). 31P{1H} NMR (162 MHz, CDCl3,

Page 13 of 16
Dalton Transactions
ppm): 33.6. IR (νCO, cm-1): 1933 (s). A satisfactory 13C NMR spectrum was not obtained becausVeiew Article Online
DOI: 10.1039/C9DT01414D
of its low solubility.
Synthesis of 6 from 7: Complex 7 (0.10 g, 0.11 mmol), KOH (0.02 g, 0.32 mmol) and benzyl
alcohol (0.04 g, 0.32 mmol) were dissolved in toluene (10 mL) and the solution was refluxed for
1.5 h. The mixture was allowed to cool to room temperature and filtered through a Celite. After
reduced in vacuo, the residue was washed by n-hexane and filtered in vacuo to give 6 as a yellow
powder (0.04 g, 45%).
Synthesis of 8:31 Complex 6 (0.13 g, 0.16 mmol) and PhCOOH (0.04 g, 0.32 mmol) were
dissolved in CH2Cl2 (10 mL) and the solution was stirred at room temperature for 6 h. The
solution was reduced in vacuo, and the residue was washed by EtOH and recrystallized from
CH2Cl2 and petroleum ether to give 8 as a yellow powder (0.04 g, 35%). Anal. Calcd for
C44H36O3P2Ru: C, 68.12; H, 4.68. Found: C, 68.39; H, 4.84. 1H NMR (400 MHz, CDCl3, ppm):
7.57-7.55 (m, 10H), 7.31-7.30 (m, 15H), 7.29-7.23 (m, 8H), 7.03-6.98 (m, 2H), -16.4 (t, J = 20.0
Hz, 1H). 31P{1H} NMR (162 MHz, CDCl3, ppm): 46.6. IR (νCO, cm-1): 1924 (s).
General procedure for the dehydrogenative oxidation reaction
Ruthenium catalyst (0.01 mmol), base (3 mmol), internal standard (dodecane, 1.0 mmol) and
alcohol (2 mmol) were dissolved in toluene (6 mL) and the solution was refluxed for 6 h under an
o
N2 atmosphere at 120 C. The mixture was allowed to cool to room temperature and 3 mL H2O
was added. After stiring for 5 min and extracted with ethyl acetate for three times, the organic
phase was sampled for GC. 1 mL of 6 M HCl solution was added to the aqueous phase, and then
extracted with ethyl acetate (5 mL) for three times. The organic phase was combined and dried by
Na2SO4. The mixture was reduced in vacuo and yielded the product.
Benzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.16 (d, J = 9.6 Hz, 2H), 7.65 (t, J = 7.6 Hz,
1H), 7.51 (t, J = 7.6 Hz, 2H).
4-Fluorobenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.18-8.15 (m, 2H), 7.18 (t, J = 8.4 Hz,
2H).
4-Chlorobenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.07 (d, J = 8.4 Hz, 2H), 7.49 (d, J =
8.4 Hz, 2H).
4-Bromobenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 7.98 (d, J = 8.4 Hz, 2H), 7.64 (d, J =
8.4 Hz, 2H).
4-Methylbenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.03 (d, J = 8.8 Hz, 2H), 7.30 (d, J =
8.8 Hz, 2H), 2.46 (s, 3H).
4-Methoxybenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.09 (d, J = 8.8 Hz, 2H), 6.98 (d, J =
8.8 Hz, 2H), 3.90 (s, 3H).
3,4-Dimethoxybenzoic acid:12 1H NMR (400 MHz, CDCl3, ppm): 7.82-7.75 (m, 1H), 7.63 (s, 1H),
7.01-6.94 (m, 1H), 4.00 (s, 3H), 3.98 (s, 3H).
3-Fluorobenzoic acid:32 1H NMR (400 MHz, CDCl3, ppm): 7.92 (d, J = 7.6 Hz, 1H), 7.79 (t, J =
9.2 Hz, 1H), 7.49-7.44 (m, 1H), 7.34-7.30 (m, 1H).

Dalton Transactions
Page 14 of 16
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3-Chlorobenzoic acid:13 1H NMR (400 MHz, CDCl3, ppm): 8.13 (s, 1H), 8.03 (d, J = 8.0DHOIz: ,101.1H03)9,/C9DT01414D
7.62 (d, J = 8.8 Hz, 1H), 7.62 (d, J = 8.8 Hz, 1H), 7.46 (t, J = 8.0 Hz, 1H).
3-Methoxybenzoic acid:13 1H NMR (400 MHz, CDCl3, ppm): 7.76 (d, J = 7.6 Hz, 1H), 7.67-7.66
(m, 1H), 7.41 (t, J = 8.0 Hz, 1H), 7.20-7.18 (m, 1H), 3.90 (s, 3H).
3-Methylbenzoic acid:13 1H NMR (400 MHz, CDCl3, ppm): 12.33 (br, 1H), 7.92 (d, J = 7.6 Hz,
2H), 7.41 (d, J = 7.6 Hz, 1H), 7.35 (t, J = 7.6 Hz, 1H), 2.41 (s, 3H).
2-Methylbenzoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.08 (d, J = 8.4 Hz, 2H), 7.41 (t, J =
7.6 Hz, 1H), 7.31-7.25 (m, 2H), 2.67 (s, 3H).
4-Phenylbutyric acid:18 1H NMR (400 MHz, CDCl3, ppm): 11.87 (br, 1H), 7.37 (t, J = 8.0 Hz, 2H),
7.28 (t, J = 7.2 Hz, 3H), 2.75 (t, J = 7.2 Hz, 2H), 7.37 (t, J = 7.2 Hz, 2H), 2.89-2.01 (m, 2H).
Naphthalene-2-carboxylic acid:18 1H NMR (400 MHz, CDCl3, ppm): 8.76 (s, 1H), 8.16 (d, J = 8.4
Hz, 1H), 8.02 (d, J = 8.0 Hz, 1H), 7.95 (t, J = 8.4 Hz, 2H), 7.68-7.58 (m, 2H).
n-Hexanoic acid:18 1H NMR (400 MHz, CDCl3, ppm): 2.35 (t, J = 7.6 Hz, 2H), 1.68-1.60 (m, 2H),
1.35-1.32 (m, 4H), 0.92-0.89 (m, 3H).
n-Hepanoic acid:33 1H NMR (400 MHz, CDCl3, ppm): 2.35 (t, J = 7.2 Hz, 2H), 1.67-1.60 (m, 2H),
1.42-1.25 (m, 6H), 0.90-0.87(m, 3H).
PPh3 and Hg poisoning tests
Hg (Hg:Ru = 400:1) or PPh3 (PPh3:Ru = 5:1) was added into the optimum conditions used 1 as the
catalyst. The conversion was unaffected.
Control experiments
Reaction of benzaldehyde with KOH: Benzaldehyde (1 mmol), internal standard (dodecane, 0.5
mmol) and KOH (1.5 mmol) were dissolved in toluene (3 mL) and the solution was refluxed for 1
h under an N2 atmosphere at 120 oC. The mixture was allowed to cool to room temperature and 3
mL H2O was added. After stirring for 5 min and extracted with ethyl acetate for three times, the
organic phase was sampled for GC. The conversion was calculated by GC using dodecane as the
1
internal standard. The ratio of benzoic acid and benzyl alcohol was calculated according to H
NMR.
Reaction of benzyl benzoate with KOH: Benzyl benzoate (1 mmol), internal standard (dodecane,
0.5 mmol) and KOH (1.5 mmol) were dissolved in toluene (3 mL) and the solution was refluxed
o
for 1 h under an N2 atmosphere at 120 C. The mixture was allowed to cool to room temperature
and 3 mL H2O was added. After stirring for 5 min and extracted with ethyl acetate for three times,
the organic phase was sampled for GC. The conversion was calculated by GC using dodecane as
the internal standard. The ratio of benzoic acid and benzyl alcohol was calculated according to 1H
NMR.
Reaction of benzyl alcohol with KOH: Complex 1 (0.005 mmol), base (1.0 mmol), internal
standard (dodecane, 1.0 mmol) and benzyl alcohol (3 mL) were refluxed for 6 h under an N2
o
atmosphere at 120 C. The mixture was allowed to cool to room temperature and 3 mL H2O was
added. After stirring for 5 min and extracted with ethyl acetate for three times, the organic phase

Page 15 of 16
Dalton Transactions
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DOI: 10.1039/C9DT01414D
was sampled for GC. The conversion was calculated by GC using dodecane as the internal
standard.
Hydrogenation
In a schlenk tube, complex 1 (0.005 mmol), base (1.5 mmol), styrene (1 mmol), Pd/C, internal
standard (dodecane, 0.5 mmol) and PhCH2OH (1 mmol) were dissolved in toluene (3 mL). The
solution was refluxed for 6 h under an N2 atmosphere at 120 oC. The mixture was allowed to cool
to room temperature and 3 mL H2O was added. After stirring for 5 min and extracted with ethyl
acetate for three times, the organic phase was sampled for GC. The conversion was calculate by
GC using dodecane as the internal standard.
Conflicts of interest
The authors declare no competing financial interest.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Nos. 21672045
and 21871068), the National Science and Technology Pillar Program during the Twelfth
Five-Year Plan Period (2015BAD15B0502), the China Postdoctoral Science Foundation
(2016M591519), the Heilongjiang Postdoctoral Foundation (LBH-Z16069), and the National
Natural Science Foundation of Heilongjiang (Nos. B2018005 and LC2018005).
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