New Ru(ii) N′NN′-type pincer complexes: synthesis, characterization and the catalytic hydrogenation of CO2 or bicarbonates to formate salts

Article abstract of DOI:10.1039/c6nj03855g

[RuCl(L1)(MeCN)₂]Cl (1) and [RuCl(L2)(MeCN)₂]Cl (2) complexes were prepared through the reaction of [RuCl₂(p-cymene)]₂ with 2,6-bis(benzimidazole-2-yl)-4-hydroxy-pyridine (L1) or 2,6-bis(benzimidazole-2-yl) pyridine (L2) in acetonitrile, respectively. The treatment of [Ru(OTf)(L2)(MeCN)₂]OTf (3) with 1 equivalent of PPh₃ in ethanol resulted in the formation of [Ru(L2^-1)(MeCN)(PPh₃)₂]OTf (4), in which one of the N-H moieties of L2 is deprotonated to give an anionic ligand (L2^-1). It was found that complex 1 can catalyze the hydrogenation of CO₂ to formate salts, producing sodium formate in 34.0% yield with a turnover number (TON) of 407 under the optimized conditions. Further investigations revealed that complexes 1-4 can efficiently catalyze the hydrogenation of sodium bicarbonate to sodium formate, and the catalytic activity follows the order 4 > 1 > 2 ≈ 3. In particular, sodium formate was obtained in good yield (77%) with a high TON (1530) when complex 4 was used as the catalyst. The present results illustrate a new example of Ru(ii) complexes bearing a rigid N′NN′ framework for the efficient hydrogenation of CO₂ to formate salts in a homogeneous system.

Full text of DOI:10.1039/c6nj03855g

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
New Ru(II)-N′NN′ Typed Pincer Complexes: Synthesis,
Characterization and the Catalytic Hydrogenation of CO or
Bicarbonates to Formate Salts
2
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Zengjin Dai, Qi Luo, Hengjiang Cong, Jing Zhang,* and Tianyou Peng*
www.rsc.org/
2 2 2 2
Complexes [RuCl(L1)(MeCN) ]Cl (1) and [RuCl(L2)(MeCN) ]Cl (2) were prepared from [RuCl (p-cymene)] with 2,6-
bis(benzimidazole-2-yl)-4-hydroxy-pyridine (L1) and 2,6-bis(benzimidazole-2-yl) pyridine (L2) in acetonitrile, respectively.
-
The treatment of [Ru(OTf)(L2)(MeCN)
2
]OTf (3) with 1 equivalent of PPh
3
in ethanol resulted in the formation of [Ru(L2
1
-1
)
(MeCN)(PPh
3
)
2
]OTf (4), in which one of the N-H moiety of L2 was deprotonated to give an anionic ligand (L2 ). It was
2
found that complex 1 can catalyze the hydrogenation of CO to formate salts, in which the sodium formate was obtained
in 34.0% yield with turnover numbers (TON) of 407 under the optimized condition. Further investigations reveal
complexes 1 ~ 4 can efficiently catalyze the hydrogenation of sodium bicarbonate to sodium formate, and the catalytic
activity follows the order 4 > 1 > 2 ≈ 3. Especilly, sodium formate was obtained in good yield (77%) and high TON (1530)
when complex 4 was loaded. The present results illustrate a new example of Ru(II) complexes bearing rigid N′NN′
framework for efficient hydrogenation of CO
2
to formate salts in a homogeneous system.
Ru(II) complex; hydrogenation
Keyword: N′NN′ pincer ligands;
of
CO
2
;
formate
salts
(
KOH or organic amines) are critical for thus conversion, and
Introduction
the pincer ligands reported are normally constituted by strong
electron-donating phosphine or N-heterocycle carbene
donors. Therefore, it is still challenged to find alternatives to
phosphorus containing ligands since elemental phosphorus
was normally prepared from phosphate rock with high energy
Alkali formates are widely used both in chemical industry and
1
, 2
our daily life.
The traditional synthesis of industrial scale
alkali formates are performed by the use of toxic CO under
3
high pressure (20 atm) and high temperature (140-150 °C), or
3
8
26
consumption (46,000 kJ/kg). In 2012, Fujita and co-workers
hydrolysis of harmful chloroform which has potential
carcinogenicity. In the past two decades, catalytic
reported an air stable and water soluble di-nuclear Ir(III)
complex with pH-depending 4, 4’, 6, 6’-tetramethoxybi-
pyrimidine ligand, which exhibited high efficiency for the
hydrogenation of CO
2
to formates has attracted much
attention, driven by the seeking for the environmentally
friendly and recyclable energy source. For instance, a number
of homogeneous systems based on noble metal complexes
hydrogenation of bicarbonate salt or CO
2
to potassium
-1
formate in KOH-water solution (TOF, 54000 h ). Himeda and
2
1
4
-13
14-19
20-28
and Ir
co-workers developed the half-sandwich Ru(II) complexes
with 4,4’-dihydroxy-2,2’-bipyridine or 4,7-dihydroxy-1,10-
phenanthroline ligands, which were applied in the
such as Ru,
Rh
have been developed for this
“
“
green” process, in which complexes bearing electron-rich
bulky” pincer ligands displayed high catalytic efficiency with
4
hydrogenation of CO
HCO K was obtained in 51% yield with the turnover numbers
(TON) of 5100. They also found that the Ru(II) complexes with
,2’-bipyridine or 1,10-phenanthroline analogues exhibited
2
in 1 M KOH aqueous solution and the
turnover numbers (TONs) easily exceeding 10 and turnover
4
frequency (TOF) higher than 10 h in some cases as shown in
-1
2
1
3, 22, 24, 27, 43
Scheme 1.
Essentially, the ultimate goal for catalyst
2
design should develop metal complexes containing both little
toxic, cheap metal centers, and ligands prepared with
components consuming little energy. Although several systems
very lower catalytic activity (TON less than 100 after 20h).
These examples indicate metal complexes based on
2
9-33
34-35
Co,
36
37 polydentate ligands with nitrogen donors might also be
based on cheaper metals such as Fe,
Ni and Cu
2
efficient in the catalytic hydrogenation of CO to formates.
have been developed for the hydrogenation of CO or alkali
bicarbonate to formates in recently years, the special additives
2
However, transition metal complexes based on NNN-typed
pincer ligands are not reported to the best of our knowledge.
Herein, we present new Ru(II) complexes bearing 2,6-
College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, P. bis(benzimidazole-2-yl)pyridine (N
R. China.
′
efficiently catalyze the hydrogenation of CO
NN
′
)
ligands, which
or sodium
2
E-mail: jzhang03@whu.edu.cn (J. Zhang); typeng@whu.edu.cn (T. Peng).
Original catalytic data, CIF file of complex
See DOI: 10.1039/x0xx00000x.
bicarbonate to sodium formate under a relatively mild
condition. The sodium formate can be obtained in 77% yield
4 (CCDC 1505525) has been provided.
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(
TON ~ 1530). Although a number of Ru(II) complexes with 2.36 ppm, which is assigned to the CH
rigid N NN
hydrogenation of ketones, dehydrogenation of alcohols to center in the meridional position. In the P{ H} NMR
3
group of acetonitrile
′
′ ligands have been applied in the catalytic transfer ligand, indicating the acetonitrile ligand coordinate to metal
3
9
42
31
1
4
0
corresponding carboxylic acid derivatives, and hydrogenation spectrum, only one singlet signal appears at 30.60 ppm. This
4
of nitriles, none of them has been found the application in observation indicates the two phosphorus atoms of complex
1
4
the homogeneous hydrogenation of CO
2
till now.
are magnetic equivalent and located at the axial positions in an
octahedral coordination geometry around the metal center.
Representative pincer complexes reported before
N
N
X
N
N
Ru
P
Ru
P
N
H
CO
N
-
-
Cl
H
X=Cl , Br
CO
Mes
Mes
or HCOO-
Pidko, 2014, ChemCatChem
Pidko, 2015, ACS. Catal.
T / P (H2, CO2)
solvent / base
TONs / TOF (h-1)
120 °C / 30 atm, 10 atm
DMF / DBU
84 °C / 39 atm, 1 atm
DMF / DBU
~37000 / 1100000
~6000 / 99100
H
O
H
P
t
O
H
H
P Bu2
N
Ir
H
N
N
Ir
H
P
Ir
P
P
PtBu2
H
H
H
H
i
P=P Pr
Hazari, 2011, JACS
185 °C / 28 atm, 28 atm 140 °C / 40 atm, 20 atm
Nozaki, 2009, JACS
T / P (H2, CO2) 200 °C / 25 atm, 25 atm
Zhou, 2015, Chem. Sci.
solvent / base
THF, H2O / KOH
H2O / KOH
THF, H2O / KOH
TONs / TOF (h-1
348000 / 14500
450000 / 22500
)
300000 / 150000
Scheme 2. Synthesis of complexes 1 ~ 4
This Work
OH
+
Cl-
+
OTf-
H
H
H
N
N
N
N
For further determination the structure of
suitable for X-ray diffraction analysis were obtained by slow
diffusion of diethyl ether into the concentrated solution of in
ethanol. As shown in Figure 1, the structure of confirms the
4, single crystals
N
N
Cl
N
Ru
N
N
Ru
N
N
N
Ph3P
N
PPh3
4
4
1
4
Ru(II) center adopts a slightly distorted octahedral geometry
with one coordination plane defined by three N atoms of the
T / P (H2, CO2)
solvent / base
TONs / TOF (h-1
130 °C / 30 atm, 0
130 °C / 30 atm, 0
THF, H2O / NaHCO3
THF, H O / NaHCO
2
3
)
1370 / 57
1530 / 63
N
′
NN
two triphenylphosphine ligands occupy the axial positions (P1-
Ru1-P2, 177.53(3) ), respectively. The bond distance of Ru1-N1
2.090(2)Å) is shorter than that of Ru1-N4 (2.145(2) Å), which
′ ligand and one N atom of the acetonitrile ligand, while
Scheme 1. Typical transition metal-pincer complexes for
hydrogenation of CO to formates.
°
2
(
is consistent with the asymmetric N’NN’ ligand with one
imidazoyl “arm” is deprotonated. This observation is different
Results and discussion
to the reported complex [RuH(NNN
3 2
′)(PPh ) ] (NNN′ = 2-(N-
Synthesis and Characterization of Ru(II) Complexes 1~4:
propyl-benzimidazol-2-yl)-6-(1-H-benzimidazoyl-2-yl)pyridine),
When ligand 2,6-bis(benzimidazole-2-yl)-4-hydroxy-pyridine in which the bond distances of Ru-N(imidazole) are similar
3
9a
(
L1) and 0.5 equivalent of [RuCl
acetonitrile for 12 h,
]Cl (
) was obtained in a good yield (Scheme (2.040(2)Å) and Ru-P (triphenylphosphine) are similar to the
, 90%). The H NMR spectrum of complex
shows two singlet other reported Ru(II) complexes with 2,6-bis(benzimidazole-2-
2
(p-cymene)]
2
were refluxed in (2.079 and 2.085 Å, respectively). Furthermore, the bond
complex distances of Ru-N(pyridyl) (2.000(2) Å), Ru-N(acetonitrile)
mono-cationic
[RuCl(L1)(MeCN)
2
1
1
2
1
3
9
peaks with integration of three protons each at 2.08 and 3.11 yl)pyridine ligands. Chattopadhyay and co-worker reported a
ppm, respectively, which can be assigned to the CH
groups of dicationic complex [Ru(L2)(PPh (MeCN)]·(ClO in which the
two acetonitrile ligands. This observation is consistent with the bond distances of Ru-N(imidazole) are not equivalent (2.137(8)
3
3
)
2
4 2
)
3
9d
two acetonitrile ligands coordinated to the Ru(II) center in and 2.101 Å, respectively) in the crystal structure, although
4
2
axial and meridional position, respectively. With similar the neutral ligand L2 is coordinated to the Ru(II) center with
procedure, [RuCl(L2)(MeCN) ]Cl L2
2,6-bis- the coordination geometry similar to that of complex . It was
benzimidazole-2-yl)pyridine) was prepared by the use of L2 found that three kinds of hydrogen bonds exist in the single
instead of L1 and [Ru(OTf)(L2)(MeCN) ]OTf
was crystal structure of complex : N2⋅⋅⋅H-O2 (N⋅⋅⋅O distance of
synthesized by the extraction of two chlorides from complex
2.721 Å), N5’-H⋅⋅⋅O2 (N⋅⋅⋅O distance of 2.732 Å), O1-H1⋅⋅⋅O4
with two equivalents of AgOTf in methanol. The reaction of (O⋅⋅⋅O distance of 2.875 Å) and O7-H7⋅⋅⋅O4 (O⋅⋅⋅O distance of
complex with one equivalent of PPh
in ethanol resulted in 2.913 Å) (see the supporting information section).
the formation of [Ru(L2 )(MeCN)(PPh ]OTf ( ) in a modest
yield (Scheme 2, 42%). The H NMR spectrum of complex
exhibits one singlet peak with integration of three protons at
2
(
2)
(
=
4
(
,
2
(
3)
4
2
3
3
-1
3
)
2
4
1
4
2
| J. Name., 2012, 00, 1-3
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In preliminary studies, complex
1
was chosen as the catalyst
precursor for the hydrogenation of CO
2
. A model reaction was
carried out by using complex
1
(0.05 mmol), alkali hydroxide
(
60 mmol) in solvent (20 mL) and heated at 130 °C under H
2
(initial pressure: 15 atm) and CO
2
(initial pressure: 15 atm) for
2
4 h. The results are listed in Table 1. When NaOH and a
O (1/1, v/v) were used, sodium
formate was obtained in 18.7% yield (based on the base) with
TON ~ 225, which is better than that in pure H O or ethanol
Table 1, entries 1 ~ 3). Using KOH as the base resulted in the
mixture solvent of THF/H
2
2
(
formation of formate in a relatively lower yield (5.8%) under
the same condition (Table 1, entry 4). As expected, increasing
the initial pressure of H
2
to 30 atm afforded a higher yield
(
34.0%), which is almost two times than that under lower
2
pressure of H (15 atm) (Table 1, entry 5). After optimizing the
NaOH concentration, it was found the best initial NaOH
concentration is 6.0 M in water (Table 1, entries 5 ~ 7). With
Figure 1
at the 30% probability level. All hydrogen atoms and solvents are
omitted for clarity. Selected bond lengths (Å): Ru1-N1, 2.090(2); 280) was observed, indicating the higher pressure of H
.
The structure of complex 4 with thermal ellipsoids drawn total pressure of CO
/CO from 2:1 to 1:2, a relatively lower TON (from 407 to
is favor
2 2
and H at 45 atm, changing the ratio of
H
2
2
2
to the formation of formate. As expected, no product was
Ru1-N4, 2.145(2); Ru1-N3, 2.000(2); Ru1-P1, 2.3967(6); Ru1-P2,
detected without the catalyst under the same condition (Table
2
1
7
.3897(6); Ru1-N
56.50(7); N3-Ru1-N
8.69(7); N4-Ru1-N3, 77.82(7)
a
, 2.040(2); Selected bond angles(
°): N1-Ru1-N4,
1, entry 10). The control experiment with the addition of
a
, 174.70(7); P1-Ru1-P2, 177.53(3), N1-Ru1-N3,
mercury (excess relative to the complex 1) gave almost the
.
same yield (18.0%), indicating the catalytic reaction is
homogenous (Table 1, entries 1 and 12).
Catalytic Hydrogenation of CO
2
:
Table. 1 Screening of reaction conditions for hydrogenation of CO
2
using complex 1 as catalyst precursor
a, b
P (H
(
2
)
atm)
P (CO
2
)
n(MOH)
(mmol)
Solvent
(v/v)
THF/H O 1:1
Yield
Entry
TON
(atm)
15
15
15
15
15
15
15
15
30
15
15
15
(%)
18.7
3.3
16.3
5.8
34.0
8.7
32.1
19.2
23.3
0
1
2
3
4
5
6
7
8
15
15
15
15
30
30
30
30
15
15
15
15
NaOH, 60
NaOH, 60
NaOH, 60
KOH, 60
NaOH, 60
NaOH, 90
NaOH, 30
NaOH, 60
NaOH, 60
NaOH, 60
none
2
225
40
196
70
407
156
385c
231
280
–
EtOH
O
H
2
THF/H
THF/H
THF/H
THF/H
THF/H
THF/H
THF/H
THF/H
THF/H
2
O 1:1
O 1:1
O 1:1
O 1:1
O 1:1
O 1:1
O 1:1
O 1:1
O 1:1
2
2
2
2
2
2
2
2
9
d
1
0
1
1
0
18.0
–
217
e
1
2
NaOH, 60
a
Reaction condition: base (entries1-5, 60 mmol; entry 6, 90 mmol; entry 7, 30 mmol), catalyst
1 (0.05 mmol, 29.0 mg) and
d
b
solvent (20 mL), 130 °C, 24 h. The yield based on the base. The reaction temperature is 100 °C. TON=n(HCOOM)/n(catalyst
e
The control experiment was carried out without the complex 1. 3.20g Hg (16.0 mmol, 320 equivalents to complex 1) was added.
c
1).
Further investigations were performed by using alkali yield of sodium formate dramatically decreased to 18% (TON
carbonates or alkali bicarbonates instead of gaseous CO under 720) (table 2, entry 3). It is noted that using sodium carbonate
the H pressure (30 atm) in 1:1 ratio of THF/H O (v/v). To our (1 M) as the CO source resulted in the formation of the
delight, when 0.05 mol% of complex and sodium bicarbonate formate salt in very poor yield (2.2%) under the same
10 mmol) were loaded, sodium formate was obtained in 69% condition (Table 2, entry 4). A control experiment was carried
2
2
2
2
1
(
yield (based on NaHCO
3
, TON 1370) after heating at 130° C for out by adding mercury drop to the catalytic system in which
was loaded, which resulted in the formation of
44.5%, TON 890) (Table 2, entries 1, 2). Upon increasing the the formate salt in 48% yield (Table 2, entry 8 and supporting
initial NaHCO concentration from 1 M to 2 M (in water), the
24 h, which is higher than that of potassium bicarbonate used the complex 3
(
3
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information), indicating the homogeneous catalysis is
dominating in the system.
Experimental Section
All experiments with metal complexes were carried out under
a high purity nitrogen or argon atmosphere using the standard
Schlenk techniques. THF was purified according to standard
procedures under an argon atmosphere and kept in the
Table. 2 Hydrogenation of bicarbonate/ carbonate to formate
salts catalyzed by complexes 1 ~ 4
spherical reservoir bottle with
4 Å molecular sieve.
1
Commercially available reagents were used as received. The H
1
and C spectra were recorded at 300 MHz, 75 MHz Varian
3
a
Yield
%)
1
Gemini 300 spectrometer. The H NMR chemical shifts are
Entry catalyst
base
concentration
TON
(
referenced to the residual hydrogen signals of the deuterated
1
2
3
4
5
6
7
1
1
1
1
2
3
4
NaHCO
KHCO
3
3
1 M
1 M
2 M
1 M
1 M
1 M
1 M
1 M
1 M
69
45
18
2.2
57
59
77
48
0
1370
890
720
44
1140
1180
1530
960
–
1
solvent or TMS, and the C NMR chemical shifts are
3
1
referenced to the C signals of the deuterated solvent.
3
NaHCO
3
4
4
45
L2 and [RuCl (p-cymene)]
46
Na
2
CO
3
Compounds of L1
,
were
2
2
NaHCO
NaHCO
NaHCO
NaHCO
NaHCO
3
3
3
3
3
synthesized according to the published procedures.
Synthesis and Characterization of Complexes 1-4
b
8
9
3
Synthesis and Characterization of Complex 1. To a solution of
[RuCl (p-cymene)] (1 mmol, 0.61 g) in acetonitrile (60 mL) was
none
a
2
2
Reaction condition: MHCO
5 μmol), H O (10 mL), and THF (10 mL) in a 100 mL autoclave under
(30 atm), 130 °C, 24 h. Yield=n(HCOOM)/n(MHCO ).
3
(10 mmol; entry 3, 20 mmol), catalyst
added L1 (2 mmol, 0.65 g), and the mixture was refluxed for 12
(
2
h under an argon atmosphere. The precipitate was filtered,
H
2
3
b
washed with diethyl ether (3× 10 mL), and then dried under
1
(1.04 g, 90%). H
TON=n(HCOOM)/n(catalyst). 0.58 g Hg (2.9 mmol, 580 equivalents
to the catalyst) was added.
vacuum overnight to yield pure complex
NMR (300 MHz, DMSO-d
1
6
) δ (ppm): 15.14 (s, 2H), 12.42 (s, 1H),
.12 (s, 2H), 7.97 (d, 2H), 7.77 (d, 2H), 7.51 (m, 4H), 3.11 (s, 3H),
8
2
1
1
C
In comparison with complex
tested for the hydrogenation of NaHCO
condition. When NaHCO (10 mmol) was put in 20 mL 1:1 ratio
of THF/H O (v/v) with 0.05 mol% of complex under H (30
1
, complexes
2, 3, 4 were also
1
3
6
.08 (s, 3H); C NMR (75 MHz, DMSO-d ) δ (ppm): 3.54, 4.32,
3
under the optimized
09.92, 113.67, 118.40, 122.23, 124.49, 125.63, 128.09, 134.25,
43.35, 152.33, 152.99, 165.30. Elemental Anal. Calcd. for
3
2
2
2
23 19 7 2
H N Cl ORu(%): C, 47.51; H, 3.29; N, 16.86. Found: C, 47.90;
atm) and heated at 130 °C for 24 h, 57% yield of sodium
formate was achieved with TON ~ 1140 (Table 2, entry, 5).
H, 3.43; N, 16.64.
Synthesis and Characterization of Complex 2. To a solution of
Complex
and less than complex
pyridyl moiety of complex
catalytic cycle. It is noted that sodium formate was obtained in
7% yield (TON 1530) with 0.05 mol% of complex , which is
better than that of complex used. This observation is
consistent with the phenomenon that electron-rich metal
3
displayed almost the same catalytic efficiency with
, indicating the hydroxyl group of
play an important role in the
2 2
[RuCl (p-cymene)] (1 mmol, 0.61 g) in acetonitrile (60 mL) was
2
1
added L2 (2 mmol, 0.62 g), and the mixture was refluxed for 12
1
h under an argon atmosphere. The precipitate was filtered,
washed with diethyl ether (3×10 mL), and then dried under
7
4
1
vacuum overnight to yield pure complex
NMR (300 MHz, DMSO-d
7.49-7.58 (m, 4H); 7.80 (d, J=8.0 Hz, 2H); 8.01 (d, J=7.3 Hz, 2H);
2
(1.00 g, 88%). H
1
6
) δ (ppm): 2.06 (s, 3H); 3.17 (s, 3H);
4
3
center is favor to the hydrogenation of CO
2
,
since the
1
3
8
.22 (t, J=8.0 Hz, 1H); 8.57 (d, J=8.0 Hz, 2H). C NMR (75 MHz,
DMSO-d ) δ (ppm): 3.86, 4.71, 114.07, 118.64, 121.62, 122.44,
25.04, 126.11, 129.95, 134.57, 136.09, 143.29, 152.61, 153.45.
Elemental Anal. Calcd. for C23 Cl Ru(%): C, 48.85; H, 3.39;
triphenylphsophine is a stronger
acetonitrile or the chloride ligand.
σ-donating ligand than the
6
1
H
19
N
7
2
Conclusions
N, 17.34. Found: C, 48.90; H, 3.60; N, 17.12.
Synthesis and Characterization of Complex 3. To a solution of
We have demonstrated four Ru(II) complexes based on rigid
NN typed pincer ligands, which efficiently catalyze the
hydrogenation of CO or sodium bicarbonate to sodium
formate. The higher yields and TONs were achieved when
sodium bicarbonate was used as the CO source than the
gaseous CO . The catalytic reactivity follows the order
, which indicates multiple Lewis base sites of N
framework and electron-rich metal center are favor to the
hydrogenation of CO . The present work may open a new
complex
2 (0.4 mmol, 0.226 g) was added silver trifluoro-
N
′
′
methanesulfonate (0.8 mmol, 0.206 g) in methanol (20 mL) in
the dark, and the mixture solution was stirred at room
temperature for 4 h in the dark. After the white precipitates of
AgCl were filtered off though a celite pad, the red solution was
evaporated to dryness under vacuum. The yellow residue was
then dissolved in ethanol (6 mL) and diethyl ether (30 mL) was
added slowly to precipitate the brown micro-crystals, which
was filtered, washed with diethyl ether (3 × 5 mL), and then
2
2
2
4 > 1 > 2
≈
3
′NN′
2
route to design transition metal complexes as efficient
hydrogenation catalyst bearing poly-dentate ligands with
alternatives to phosphorus or N-heterocycle carbene donors.
dried under vacuum for 12 h to yield complex
3
(0.275 g, 82%).
) δ (ppm): 0.5 (t, J=7.0Hz, 3H),
3
.09 (s, 3H, CH -CN), 2.86 (p, 2H), 3.20 (s, 3H), 6.04 (t, J=4.8 Hz,
1
H NMR (300 MHz, DMSO-d
6
2
1
H), 7.60-7.65 (m, J=7.7 Hz, 4H,), 7.89 (d, J=6.7 Hz, 2H), 8.06
4
| J. Name., 2012, 00, 1-3
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(
dd, J=6.0, 2.5 Hz, 2H), 8.44 (dd, J=22.7, 6.9 Hz, 3H), 14.95 (s, A Bruker KAPPA APEX DUO diffractormeter with graphite-
1
3
2
H, -NH). C NMR (75 MHz, DMSO-d
7.21, 19.23, 59.73, 62.93, 114.58, 118.05, 118.76, 122.24, collect the intensity data for the single crystal of complex
23.48, 126.28, 131.77, 134.68, 138.56, 143.15, 157.07, 153.58. The data was collected at about 100 K using ω-scan techniques.
6
) δ (ppm): 4.10, 4.78, monochromated Mo-Kα (λ= 0.71073 Å) was employed to
1
4.
1
4
7
25 7 7 6 2
Elemental Anal. Calcd for C27H O N F S Ru (Contain one The structure was solved by direct methods using SHELXL-97.
molecule of ethanol) (%): C, 38.66; H, 3.00; N, 11.69 Found: C, Multi-scan empirical absorption corrections were applied to
4
the data set using the program SADABS. The structure was
8
3
8.26; H, 2.89; N, 11.42.
4
Synthesis and Characterization of Complex 4. To a solution of refined with SHELXL-97. Hydrogen atoms bound to carbon
7
complex
3
(0.2 mmol, 0.156 g) in hot ethanol (20 mL) was were placed at calculated positions and refined using a riding
(0.2 mmol, 0.053 g) in ethanol (5 mL). The solution mode. All non-hydrogen atoms were refined by full-matrix
added PPh
3
2
49
was then refluxed for 6h under an argon atmosphere. After least squares on F using the SHELXTL grogram package. Cell
cooling to room temperature, the orange solution was refinement, data collection, and reduction were done by
5
0
evaporated under vacuum to dryness and washed with diethyl Bruker SAINT. The crystallographic data is available in the SI
ether (3× 10 mL). The crude complex of was further purified as CIF file.
4
by column chromatography using silica gel (elute: ethanol) and
recrystallized in ethanol/diethyl ether to afford large red cubes
1
. Yield: 95.0mg (42%). H NMR (300MHz, CD
Acknowledgements
of complex
4
2
Cl
2
) δ
(
ppm): 2.36 (s, 3H); 6.77 (m, 10H); 6.92 (m, 10H); 7.17 (m, 5H);
This work was supported by the Natural Science Foundation of
China (21171134, 21573166), the Natural Science Fund of
Hubei Province (2011CDB441), and the Funds for Creative
Research Groups of Hubei Province (2014CFA007), China. We
also thank Prof. Xiaojun Wu for NMR supporting and analysis.
7
2
1
1
.26 (m, 5H); 7.47 (m, 4H); 7.53 (m, 4H); 7.62 (t, 1H); 7.67 (d,
1
3
H). C NMR (75 MHz, CD
2 2
Cl ) δ (ppm): 4.80, 117.65, 120.80,
22.83, 123.35, 128.37, 129.44, 129.63, 129.85, 130.22, 133.17,
3
33.22, 133.27, 135.69, 141.90, 144.07, 151.89. P{ H} NMR
1
1
(
300 MHz, CD
2
2
Cl
2
) δ (ppm): 30.60. Elemental Anal. Calcd. for
C
58
H
45
O
3
N
7
F
3
P
SRu(%): C, 61.86; H, 4.03; N, 7.46. Found: C,
61.62; H, 4.00; N, 7.56.
Notes
The authors declare no competing financial interests.
General Procedure of Catalytic Hydrogenation
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