Synthesis and structures of ruthenium-NHC complexes and their catalysis in hydrogen transfer reaction

Article abstract of DOI:10.3762/bjoc.11.194

Ruthenium complexes [Ru(L1)₂(CH₃CN)₂](PF₆)2 (1), [RuL1(CH₃CN)₄](PF₆)₂ (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl- 1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel-NHC complexes with [Ru(p-cymene)₂Cl₂]₂ in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH₃CN)₄](PF₆)₂ with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh₃)(CH₃CN)₃](PF₆)₂ (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones.

Full text of DOI:10.3762/bjoc.11.194

Synthesis and structures of ruthenium–NHC complexes and
their catalysis in hydrogen transfer reaction
Chao Chen1, Chunxin Lu2, Qing Zheng1, Shengliang Ni*1, Min Zhang3
and Wanzhi Chen*3
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2015, 11, 1786–1795.
1College of Life Sciences, Huzhou University, Huzhou 313000, China,
2College of Biological, Chemical Sciences and Engineering, Jiaxing
University, Jiaxing 314001, China and 3Department of Chemistry,
Zhejiang University, Hangzhou 310007, China
doi:10.3762/bjoc.11.194
Received: 04 July 2015
Accepted: 09 September 2015
Published: 30 September 2015
Email:
Shengliang Ni* - shengliangni@163.com;
Wanzhi Chen* - chenwzz@zju.edu.cn
This article is part of the Thematic Series "N-Heterocyclic carbenes".
Guest Editor: S. P. Nolan
* Corresponding author
© 2015 Chen et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
N-heterocyclic carbene; ruthenium; transfer hydrogenation
Abstract
Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-
1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetalla-
tion reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal
structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or
pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of
[RuL1(CH3CN)4](PF6)2 with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated
acetonitrile ligands and afforded [RuL1(PPh3)(CH3CN)3](PF6)2 (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The mole-
cular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven
to be efficient catalysts for transfer hydrogenation of various ketones.
Introduction
N-Heterocyclic carbenes (NHCs) have been recognized as a structural diversities and potential applications in coordination
class of strong donating ligands which can stabilize various chemistry and homogenous catalysis. NHC ligands containing
metal complexes of catalytic importance. Transition metal additional phosphine, nitrogen, oxygen, and sulfur donating
complexes bearing NHCs are more stable to air, moisture, heat, groups [8-16] have been reported.
and tolerant toward oxidation compared to phosphine ligands
[1-7]. Among NHCs, functionalized NHC ligands have been In the family of metal complexes supported by functionalized
extensively studied in recent years because of their intriguing NHCs, ruthenium complexes have long been a research focus
1786

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
on various applications such as catalysis and photochemistry Raney nickel afforded the nickel–NHC complexes which were
[17-26]. However, the majority of such ruthenium complexes not isolated [30]. The subsequent reaction of the generated
often contain coordinated aromatic carbocycles [27-29]. In nickel–NHC complexes with a quarter equivalent of [Ru(p-
contrast, only a few examples Ru(II) complexes of functional- cymene)Cl2]2 in refluxing acetonitrile solution afforded bis-
ized NHCs containing easily dissociating acetonitrile ligands NHC complex [Ru(L1)2(CH3CN)2](PF6)2 (1) in a yield of 76%
have been studied [30-32]. We have reported the synthesis of (Scheme 1). When a half equivalent of [Ru(p-cymene)Cl2]2
some pyridine- and phenanthrolin-functionalized Ru(II)–NHC and an excess of NH4PF6 were employed under the same
complexes containing acetonitrile ligands [33,34]. The most conditions, the reaction afforded the mono-NHC complex
notable example is the acetonitrile-coordinated dinuclear [RuL1(CH3CN)4](PF6)2 (2) in 53% yield. It is worth noting that
Ru(II)–NHC complex derived from 3, 6-bis(N- most of the structurally characterized acetonitrile complexes are
(pyridylmethyl)imidazolylidenyl)pyridazine, which is a very obtained through the reaction of halides with silver complexes
efficient catalyst for the oxidation of alkenes [35]. In continua- (AgPF6 or AgBF4) in acetonitrile solution [20]. The reaction in
tion of our studies on functionalized Ru(II)–NHC complexes refluxing acetonitrile is more convenient than the above
containing acetonitrile ligands, we herein report the synthesis mentioned procedure. The formulations of complexes 1 and 2
and characterization of three pyrimidine- and pyridine-function- were first characterized by NMR measurements and further
alized NHC–ruthenium complexes containing two, four, and confirmed by elemental analysis and X-ray diffraction. In the
three acetonitrile ligands, respectively. These complexes show 1H NMR spectra of complexes 1 and 2, disappearance of the
good catalytic activity in the transfer hydrogenation of ketones. resonances assigned to the imidazolium acidic CH and
The reaction of acetonitrile-coordinated Ru–NHC complex 2 p-cymene protons were observed. The acetonitrile protons of
with other donors such as triphenylphosphine and 1,10-phenan- complex 1 were found at 2.41 ppm as a singlet. However, the
throline was also studied.
protons of acetonitrile ligands of complex 2 were found at 2.52,
2.12, and 1.96 ppm as three singlets. This illustrates that the
three acetonitrile ligands in complex 2 are magnetic unequiva-
lent. The 13C NMR spectra of 1 and 2 exhibit resonance signals
at 193.1 and 193.0 ppm ascribed to the carbenic carbons.
Results and Discussion
Synthesis and characterization of
[Ru(L1)2(CH3CN)2](PF6)2 (1),
[RuL1(CH3CN)4](PF6)2 (2) and
[RuL2(CH3CN)3](PF6)2 (3)
The ruthenium–NHC complexes 1 and 2 are stable in air and
under light irradiation. Single crystals suitable for X-ray diffrac-
The ruthenium–NHC complexes 1 and 2 were synthesized by tion could be obtained by slow diffusion of Et2O into CH3CN
using the corresponding nickel–NHC complexes as the carbene solutions and the detailed structure of 1 is depicted in Figure 1.
transfer agent [36]. The reaction of imidazolium salt HL1(PF6) In complex 1, the central ruthenium ion is hexacoordinated by
(L1 = 3-methyl-1-(pyrimidine-2-yl)imidazolylidene) with two bidentate NHC ligands and two acetonitrile ligands in an
Scheme 1: Synthesis of complexes 1 and 2.
1787

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
octahedral geometry. One NHC ligand, one acetonitrile ligand Ru(L1)(CH3CN)2 plane, whereas the other two acetonitrile
and one carbon atom of the other NHC ligand occupy the equa- molecules occupy the axial positions. The bond length of
torial plane in which two carbon atoms of two NHC ligands are Ru–CNHC is 1.989 Å, which is slightly shorter than those found
mutually trans-arranged. The remaining acetonitrile ligand and in Ru–NHC complexes [12-18] and in complex 1. The bond
one nitrogen atom of the NHC ligand lie on the axial positions. distance of Ru–Nacetonitrile (2.113 Å) at the trans-position of the
The angles (N–Ru–N) of adjacent nitrogen atoms and Ru(II) ion carbene ligand is longer than the other three Ru–Nacetonitrile
are in the range of 83.9 to 94.0°. The Ru–C distance (2.066 Å) bonds (2.023–2.033 Å) and the Ru–Npyrimidine (2.064 Å).
is consistent with the reported values in known Ru–NHC
complexes [17-29]. The Ru–Npyrimidine distance (2.081 Å) is
slightly longer than Ru–Nacetonitrile (2.033 Å).
Figure 2: Structural view of 2 showing 30% thermal ellipsoids. All
hydrogen atoms and PF6− were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)–C(2) 1.989(7), Ru(1)–N(5)
2.023(5), Ru(1)–N(8) 2.027(5), Ru(1)–N(7) 2.033(6), Ru(1)–N(4)
2.064(5), Ru(1)–N(6) 2.113(6), C(2)–Ru(1)–N(5) 88.3(2),
C(2)–Ru(1)–N(8) 91.2(2), N(5)–Ru(1)–N(8) 179.3(2), C(2)–Ru(1)–N(7)
99.8(3).
Figure 1: Structural view of 1 showing 30% thermal ellipsoids. All
hydrogen atoms and PF6− were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)–N(5) 2.033(4), Ru(1)–C(2)
2.066(5), Ru(1)–N(4) 2.081(4), N(5)#1–Ru(1)–N(5) 83.9(2),
N(5)–Ru(1)–C(2) 87.87(16), C(2)#1–Ru(1)–C(2) 171.2(3),
N(5)–Ru(1)–N(4) 91.12(16), C(2)#1–Ru(1)–N(4) 95.88(17),
N(5)–Ru(1)–N(4)#1 174.20(14). Symmetry code: #1 −x, y, −z+1/2.
Similarly, the reaction of the in situ generated nickel–NHC
complex from imidazolium salt HL2(PF6) (L2 = 1,3-
bis(pyridin-2-ylmethyl)benzimidazolylidene) with a half
equivalent of [Ru(p-cymene)Cl2]2 and an excess of NH4PF6 in
a refluxing acetonitrile solution afforded the tri-acetonitrile
coordinated Ru(II)–NHC complex [RuL2(CH3CN)3](PF6)2 (3)
in a yield of 61% (Scheme 2). The formation of 3 was also
confirmed by the 1H NMR and 13C NMR spectra. The 1H NMR
spectrum of 3 shows characteristic resonance signals due to the
The cationic structure of 2 is shown in Figure 2. The central
Ru(II) ion is surrounded by one pyrimidine-functionalized NHC
ligand and four acetonitrile ligands also in a typical octahedral
geometry. The Ru ion lies on a twofold axis. The bidentate
NHC ligand and two cis-arranged acetonitrile molecules form a
Scheme 2: Synthesis of 3.
1788

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
pyridyl, methylene, benzimidazolylidene and acetonitrile
groups. The absence of a benzimidazole acidic C2-H proton
illustrates the formation of the Ru–C bond. The acetonitrile
protons appear at 2.35 and 2.08 ppm as two singlets. The
13C NMR spectrum of 3 exhibits a resonance peak at 190 ppm,
which is ascribed to the carbenic carbon atom. Complex 3 has
been further identified by X-ray crystallography and the
cationic structure of molecular 3 is depicted in Figure 3. The
ruthenium ion is coordinated by a tridentate pincer NHC ligand
and three acetonitrile ligands also in an octahedral geometry.
The symmetrical pincer-type NCN ligand and an acetonitrile
ligand occupy the equatorial plane and the remaining two aceto-
nitrile ligands are located at the axial positions. The N–Ru–N
angles of the three acetonitrile ligands and the Ru(II) ion are
86.03, 89.12 and 174.99°, respectively. Similar to complex 2,
the bond distance of Ru–Nacetonitrile (2.130 Å) at the trans-posi-
tion of the carbene ligand is slightly longer than the other bond
distances of Ru–Nacetonitrile (2.030 and 2.028 Å) and the Ru–C
(1.947 Å) is shorter than that of many known Ru–Ccarbene
distances [17-29].
Figure 3: Structural view of 3 showing 50% thermal ellipsoids. All
hydrogen atoms and PF6− were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)–C(7) 1.947(3), Ru(1)–N(7)
2.028(2), Ru(1)–N(5) 2.030(2), Ru(1)–N(4) 2.104(2), Ru(1)–N(1)
2.105(2), Ru(1)–N(6) 2.130(2), C(7)–Ru(1)–N(7) 94.33(10),
C(7)–Ru(1)–N(5) 90.55(10), N(7)–Ru(1)–N(5) 174.99(9),
C(7)–Ru(1)–N(4) 87.72(10).
their catalytic activities for transfer hydrogenation of ketones.
Firstly, acetophenone was selected as the model substrate to
Catalytic transfer hydrogenation reaction
Ruthenium–NHC complexes are known to be efficient catalysts evaluate the catalytic activities of complexes 1–3. The standard
for transfer hydrogenation reactions [23,37-39]. The experiment was carried out at 80 °C with varied Ru loadings
ruthenium–NHC complexes presented above are stabilized by from 1 to 0.01 mol % and the results are summarized in
strong Ru–carbene bonds and contain 2–4 easily dissociating Table 1. The reaction profiles show that acetophenone could be
acetonitrile molecules, and are thus ideal catalysts. We tested reduced to 1-phenylethanol in 89–99% yield within 0.5 h using
Table 1: Catalytic activities of 1–3 in transfer hydrogenation of acetophenone.a
Entry
Catalyst
Catalyst (mol %)
Time (h)
Yield (%)b
TON/TOF (h−1)
1
2
3
4
1
0.5
0.5
1
89
79
92
90
89/172
790/1580
920/920
0.1
0.1
0.01
1
3
9000/3000
5
6
7
8
1
0.5
0.5
1
99
86
99
97
99/198
860/1720
990/990
0.1
0.1
0.01
2
3
3
9700/3233
9
1
0.5
0.5
1
99
89
99
96
99/198
890/1780
990/990
10
11
12
0.1
0.1
0.01
3
9600/3200
aConditions: acetophenone (1.00 mmol), KOH (20 mol %), and catalyst (1–0.01 mol %) in 3 mL of iPrOH at 80 °C. bThe yields of products were
detected by GC.
1789

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
1 mol % of the Ru catalysts (Table 1, entries 1, 5 and 9). When
the amount of catalysts is decreased to 0.1 mol %, the corres-
ponding conversion still reached 79–89% (Table 1, entries 2, 6
and 10). 1-Phenylethanol could also be obtained in excellent
yields using 0.1 mol % and 0.01 mol % Ru catalysts when the
reaction time was extended to 1 and 3 h, respectively (Table 1,
entries 3, 7, 11 and 4, 8, 12). At catalyst loadings of
0.01 mol %, TOF of 1–3 are 3000, 3233, and 3200 h−1 for
transfer hydrogenation of acetophenone which are nearly iden-
tical to that of [Ru(MeCCmeth)2(CH3CN)2](BF4)2 (MeCCmeth =
1,1'-dimethyl-3,3'-methylene-diimidazol-2,2'-diylidene) [40].
Ruthenium picolyl–NHC complex [(η5 -C5 Me5 )-
Ru(L)(CH3CN)][PF6] (L = 3-methyl-1-(2-picolyl)imidazol-2-
ylidene) is so far one of the most efficient catalyst for transfer
hydrogenation of acetophenone which gave 1-phenylethanol in
a conversion of 93% with a catalyst loading of 0.1 mol %
[20,41]. When the same amount of complexes 1–3 was used,
the reaction gave 1-phenylethanol in 89%, 99% and 99% yields,
respectively. These data illustrate that complexes 1–3 are all
quite active catalysts for transfer hydrogenation reactions. It
seems that complexes 2 and 3 are a bit better than 1 for this
transformation. The trans-effect of carbene ligand may promote
the substitution of trans-positioned acetonitrile ligand by other
substrates in the catalytic reaction.
Table 2: Transfer hydrogenation using complexes 2 and 3.a
Entry
1
Substrate
Catalyst Time (h) Yield (%)b
2
3
2
0.5
0.5
1
99
99
99
2
3
4
5
6
7
3
2
3
2
1
1
1
1
98
99
97
96
8
9
3
2
3
1
1
1
90
93
92
Since complexes 2 and 3 are found to be the efficient catalysts
for transfer hydrogenation of acetophenone, we further explored
their catalytic potential in the reduction of other aromatic and
aliphatic ketones. The reaction conditions are similar as those
described in the transfer hydrogenation of acetophenone and
0.1 mol % of Ru catalyst is utilized. The obtained results are
given in Table 2. Complexes 2 and 3 are found to be very active
in transfer hydrogenation of cyclohexanone, and cyclohexanol
are almost quantitatively yielded within 0.5 h (Table 2, entries 1
and 2). The catalyst systems are also found to be good for the
reduction of aromatic ketones bearing electron-withdrawing
substituents (Table 2, entries 3–8) and electron-donating groups
(Table 2, entries 9 and 10), and the target product could be
obtained in excellent yields (90–99%). Bulkier aromatic ketone
benzophenone is also tested in this reaction with 92% and 94%
conversion after 3 h (Table 2, entries 11 and 12). In addition, it
10
11
12
2
3
3
3
92
94
13
14
2
3
3
3
83
80
aConditions: substrate (1.00 mmol), KOH (20 mol %), catalyst
(0.1 mol %) in 3 mL of iPrOH at 80 °C. bThe yields of products were
detected by GC.
is worth mentioning that the two ruthenium complexes exhib- coordinated Ru–NHC complexes with other ligands were
ited a high tolerance towards sulfur species, 2-acetylthiophene studied. The reaction of complex 2 with an excess of triphenyl-
is efficiently hydrogenated (Table 2, entries 13 and 14) with an phosphine and 1,10-phenanthroline in heat acetonitrile solution
increased reaction time of 3 h.
afforded 4 and 5, respectively. Even excess triphenylphosphine
and 1,10-phenanthroline were used, only one and two coordin-
ated acetonitrile ligands were substituted in complexes 4 and 5.
Crystallization by slow diffusion of diethyl ether into their ace-
tonitrile solutions gave 4 as a yellow solid in 40% yield and 5 as
an orange yellow solid in 63% yield (Scheme 3). The yields of
complexes 4 and 5 are relatively lower than complexes 1–3, but
Reactions of tetra-acetonitrile Ru(II)–NHC
complex 2 with triphenylphosphine and
1,10-phenanthroline
The coordinated acetonitrile ligands could be easily replaced by
various N- and P-donors [22]. The reactions of the acetonitrile-
1790

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
Scheme 3: Synthesis of complexes 4 and 5.
still in the normal range as compared with the similar reaction
[33]. In the 1H NMR of 4, singlets at 2.14 and 2.07 ppm are
ascribed to three CH3CN ligands, and the rest peaks are
belonged to NHC and triphenylphosphine ligand. 1H NMR
investigation of 5 suggests that complex 5 contains one NHC
ligand, one phenanthroline ligand and two acetonitrile ligands.
The CH3CN protons of 5 are founded at 2.53 and 2.28 ppm. In
the 13C NMR, the carbene carbons of complexes 4 and 5 are
found at 190 and 200 ppm, respectively.
The structures of 4 and 5 determined by X-ray diffraction
analysis are shown in Figure 4 and Figure 5. In the cationic
structure of 4, the acetonitrile ligand at the trans-position of the
NHC is substituted by a triphenylphosphine ligand. The CNPN
atoms form the equatorial plane. The other two acetonitrile
ligands are still trans-arranged at the axial positions. The
P–Ru–N angles of three acetonitrile ligands and pyrimidine are
92.91, 92.06, 88.91, and 98.34°. The Ru–C bond distances
being 2.039 Å is slightly longer than those of 2 and 3, but
similar to complex 1. The Ru–P bond distance is 2.4080 Å,
which are no difference from those of reported Ru(II)
complexes [3,4]. In complex 5, the central Ru ion is coordin-
ated by one NHC ligand, one 1,10-phenanthroline ligand and
two acetonitrile molecules. The NHC ligand, one acetonitrile
ligand and one nitrogen atom of phenanthroline occupy the
equatorial plane in which the carbon atom of NHC ligand is
trans to the nitrogen atom of phenanthroline with the
C(2)–Ru(1)–N(6) angle of 169.08°, the acetonitrile molecule is
trans to the pyrimidine group with the N(8)–Ru(1)–N(1) angle
of 176.42°. The rest coordination nitrogen atoms of acetonitrile
and phenanthroline lie on the axial positions with the
N(7)–Ru(1)–N(5) angle of 173.74°.
Figure 4: Structural view of 4 showing 30% thermal ellipsoids. All
hydrogen atoms and PF6− were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)–N(5) 2.012(4), Ru(1)–N(7)
2.020(4), Ru(1)–N(6) 2.025(4), Ru(1)–C(7) 2.039(4), Ru(1)–N(1)
2.120(4), Ru(1)–P(1) 2.4080(11), N(5)–Ru(1)–N(7) 173.83(16),
N(5)–Ru(1)–N(6) 87.01(16), N(7)–Ru(1)–N(6) 89.42(15),
N(5)–Ru(1)–C(7) 92.27(17), N(5)–Ru(1)–P(1) 92.91(11),
C(7)–Ru(1)–P(1) 173.12(16).
Conclusion
In summary, Ru–NHC complexes bearing pyrimidine- and pyri-
dine-functionalized NHC ligands have been prepared through a
carbene transfer reaction using nickel–NHC as the carbene
source. Their structures have been definitely determined by
X-ray crystallography. The catalytic behavior of di-, tetra- and
1791

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
concentrated and poured into Et2O (30 mL) to precipitate the
product. Compound 1 was obtained as a yellow solid.
Yield: 307 mg, 76%. Anal. calcd for C20H22F12N10P2Ru: C,
30.27; H, 2.79; N, 17.65; found: C, 30.19; H, 2.82; N, 17.55;
1H NMR (400 MHz, DMSO-d6) δ 8.77 (d, J = 4.8 Hz, C4H3N2,
2H), 8.31 (d, J = 2.0 Hz, C3H2N2, 2H), 8.09 (d, J = 4.8 Hz,
C4H3N2, 2H), 7.90 (d, J = 2.0 Hz, C4H3N2, 2H), 7.27 (t, J =
4.8 Hz, C4H3N2, 2H), 4.17 (s, CH3, 3H), 2.41 (s, CH3CN, 6H);
13C NMR (100 MHz, DMSO-d6) δ 193.1 (Ru-C), 166.2, 159.8,
158.7, 128.6, 127.0, 120.0, 117.9, 37.7, 4.17.
Synthesis of [RuL1(CH3CN)4](PF6)2 (2). A mixture of
HL1(PF6) (153 mg, 0.5 mmol), excess Raney nickel (300 mg)
in 10 mL MeCN was stirred at 80 °C for 24 h. After it was
cooled to room temperature, the solution was filtered through
Celite. Then [Ru(p-cymene)Cl2]2 (153 mg, 0.25 mmol) and
NH4PF6 (163 mg, 1.0 mmol) was added to the filtrate and
stirred at reflux for 12 h. The mixture was filtered through
Celite to remove precipitated NiCl2 and all volatiles were
evaporated under reduced pressure. The residue was washed
with water and dried in vacuo. The yellow residue was
dissolved in MeCN and concentrated to about 2 mL. The addi-
tion of Et2O induced precipitation of the product as a yellow
solid. Yield: 190 mg, 53%. Anal. calcd for C16H20F12N8P2Ru:
C, 26.86; H, 2.82; N, 15.66; found: C, 26.70; H, 2.90; N, 15.58;
1H NMR (400 MHz, DMSO-d6) δ 9.12 (d, J = 4.8 Hz, C4H3N2,
1H), 8.85 (d, J = 4.8 Hz, C4H3N2, 1H), 8.00 (d, J = 2.4 Hz,
C3H2N2, 1H), 7.48 (t, J = 2.4 Hz, C4H3N2, 1H), 7.36 (d, J =
2.4 Hz, C3H2N2, 1H), 4.04 (s, CH3, 3H), 2.52, (s, CH3CN, 3H),
2.12, (s, CH3CN, 6H), 1.96, (s, CH3CN, 3H); 13C NMR
(100 MHz, DMSO-d6) δ 193.0 (Ru-C), 180.9, 166.6, 158.4,
158.3, 157.4, 128.7, 125.7, 125.6, 117.7, 116.2, 35.8, 2.64, 2.20,
1.77.
Figure 5: Structural view of 5 showing 30% thermal ellipsoids. All
hydrogen atoms and PF6− were omitted for clarity. Selected bond
lengths (Å) and angles (deg): Ru(1)–C(2) 2.007(5), Ru(1)–N(8)
2.022(4) Ru(1)–N(7) 2.049(4), Ru(1)–N(5) 2.063(4), Ru(1)–N(1)
2.077(4), Ru(1)–N(6) 2.126(4), C(2)–Ru(1)–N(8) 99.06(18),
C(2)–Ru(1)–N(7) 91.10(17), N(8)–Ru(1)–N(7) 87.76(16),
C(2)–Ru(1)–N(5) 95.03(17), N(8)–Ru(1)–N(5) 90.05(16),
N(7)–Ru(1)–N(5) 173.74(16). Symmetry code: #1 x, −y+3/2, z.
tri-acetonitrile-coordinated ruthenium complexes in transfer
hydrogenation reactions was studied. These ruthenium
complexes were found to be highly efficient catalysts for
transfer hydrogenation of ketones. The catalytic properties of
the ruthenium complexes in other organic transformation will
be further studied.
Experimental
All chemicals were obtained from commercial suppliers in Synthesis of [RuL2(CH3CN)3](PF6)2 (3). According to the
reagent grade quality and were used as received. HL1PF6 and same procedure as described for 2, complex 3 was obtained
HL2PF6 were synthesized according to the reported method as a yellow soild. Yield: 249 mg, 61%. Anal. calcd for
[42,43]. 1H and 13C NMR spectra were recorded on a Bruker C29H31F12N9P2Ru ([RuL2(CH3CN)3](PF6)2)·2CH3CN: C,
Avance-400 (400 MHz) spectrometer operating at 400 MHz for 38.85; H, 3.48; N, 14.06; found: C, 38.70; H, 3.60; N, 14.08;
1H and at 100 MHz for 13C. Chemical shifts (δ) were expressed 1H NMR (400 MHz, DMSO-d6) δ 8.90 (d, J = 4.4 Hz, C5H4N,
in ppm downfield to TMS at δ = 0 ppm and coupling constants 2H), 8.11 (t, J = 6.4 Hz, C5H4N, 2H), 7.95–7.92 (m, C6H4, 4H),
(J) were expressed in Hz. Elemental analyses were performed 7.64 (t, J = 5.2 Hz, C5H4N, 2H), 7.41–7.40 (m, C5H4N, 2H),
by a Flash EA 1112 ThermoFinnigan analyzer.
5.85 (s, CH2, 4H), 2.35, (s, CH3CN, 6H), 2.08 (s, CH3CN, 3H);
13C NMR (100 MHz, DMSO-d6) δ 192.0 (Ru-C), 154.1, 148.2,
Synthesis of [Ru(L1)2(CH3CN)2](PF6)2 (1). A mixture of 140.5, 134.7, 125.5, 125.3, 125.0, 117.2, 116.6, 111.4, 50.5,
HL1(PF6) (306 mg, 1.0 mmol), excess Raney nickel (500 mg) 2.80, 2.15.
in 10 mL MeCN was stirred at 80 °C for 24 h. After it was
cooled to room temperature, the solution was filtered through Synthesis of [RuL1(PPh3)(CH3CN)3](PF6)2 (4). A mixture of
Celite. Then [Ru(p-cymene)Cl2]2 (153 mg, 0.25 mmol) 2 (142 mg, 0.2 mmol) and triphenylphosphine (262 mg,
was added to the solution and stirred at reflux for 12 h. 1.0 mmol) in 5 mL CH3CN was stirred at 80 °C for 6 h. Then
After filtration through a plug of Celite, the mixture was the mixture was filtered through Celite and all volatiles were
1792

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
evaporated under reduced pressure. The residue was washed 128.3, 128.2, 127.4, 127.2, 127.1, 126.4, 119.5, 118.5, 37.1,
with ethyl acetate and dried in vacuo. The yellow residue was 4.56, 3.83, 1.62.
dissolved in CH3CN and crystallization by slow diffusion
Typical procedure for catalytic transfer
of Et2O into the CH3CN solution gave 4 as yellow solid.
Yield: 75 mg, 40%. Anal. calcd for C32H32F12N7P3Ru: C, hydrogenation reaction
41.04; H, 3.44; N, 10.47; found: C, 41.10; H, 3.40; N, 10.58; The ketone (1.0 mmol), KOH (0.2 mmol) and 2 mL of iPrOH
1H NMR (DMSO-d6) δ 8.99 (s, 1H), 8.46 (s, 1H), 8.38 (s, 1H), were placed in a Schlenk tube. Anisole (0.25 mmol) was added
7.87 (s, 1H), 7.57(s, 13H), 7.42 (s, 2H), 7.25 (s, 1H), 4.11 (s, as an internal GC standard. The mixture was heated at 80 °C
3H), 2.14 (s, 6H), 2.07 (s, 3H); 13C NMR (DMSO-d6) δ 192.2 and then catalyst solution (0.01 mmol, 0.001 mmol, or
(Ru-C), 183.8, 182.8, 163.4, 158.6, 157.9, 132.0, 131.9, 131.7, 0.0001 mol of ruthenium complexes in iPrOH (1 mL) was
131.5, 129.0, 128.7, 127.9, 127.6, 127.5, 127.4, 127.2, 127.1, injected. Aliquots (0.2 mL) were taken at fixed time intervals,
126.3, 125.5, 117.9, 116.4, 116.3, 35.8, 2.15, 1.72.
quenched with 1 mL of H2O and extracted with 3 mL of Et2O.
The product yields were determined by GC analysis.
Synthesis of [RuL1(Phen)(CH3CN)2](PF6)2 (5). A mixture of
2 (142 mg, 0.2 mmol) and 1,10-phenanthroline·1H2O (198 mg, X-ray diffraction analysis
1.0 mmol) in 5 mL CH3CN was stirred at 80 °C for 6 h. Then Single-crystal X-ray diffraction data were collected at 298(2) K
the mixture was filtered through Celite to afford a yellow solu- on a Siemens Smart-CCD area-detector diffractometer with a
tion. Crystallization by slow diffusion of Et2O into the CH3CN MoKα radiation (λ = 0.71073 Å) by using a ω-2θ scan mode.
solution gave 5 as an orange yellow solid. Yield: 103 mg, 63%. Unit-cell dimensions were obtained with least-squares refine-
Anal. calcd for C24H22F12N8P2Ru: C, 35.43; H, 2.73; N, 13.77; ment. Data collection and reduction were performed using the
found: C, 35.50; H, 2.90; N, 13.80; 1H NMR (DMSO-d6) δ 9.77 Oxford Diffraction CrysAlisPro software [44]. All structures
(dd, J = 1.2 and 4.0 Hz, 1H), 9.08 (dd, J = 0.8 and 6.4 Hz, 1H), were solved by direct methods, and the non-hydrogen atoms
8.75 (dd, J = 1.6 and 4.0 Hz, 1H), 8.44–8.38 (m, 3H), 8.32–8.29 were subjected to anisotropic refinement by full-matrix least
(m, 2H), 7.94 (d, J = 1.6 Hz, 1H), 7.73 (dd, J = 4.4 and 6.4 Hz, squares on F2 using the SHELXTXL package [45]. Hydrogen
1H), 7.68 (dd, J = 1.6 and 6.4 Hz, 1H), 7.11 (dd, J = 4.0 and atom positions for all of the structures were calculated and
4.4 Hz, 1H), 4.23 (s, 3H), 4.22 (s, 3H), 2.53, 2.28 (s, CH3CN, allowed to ride on their respective C atoms with C–H distances
each 3H); 13C NMR (DMSO-d6) δ 192.3 (Ru-C), 161.9, 159.9, of 0.93–0.97 Å and Uiso(H) = −1.2–1.5Ueq(C). Details of the
159.0, 157.5, 152.5, 148.0, 146.6, 138.8, 137.4, 130.9, 130.6, X-ray experiments and crystals data are summarized in Table 3.
Table 3: Crystallographic data for complexes 1–5.
1
2
3·2CH3CN
4·CH3CN
5
CCDC number
Formula
1407422
1407423
1407424
1407425
1407426
C20H22F12N10P2
Ru
C16H20F12N8P2
Ru
C29H31F12N9P2
Ru
C34H35F12N8P3
Ru
C24H22F12N8P2
Ru
Fw
793.49
Monoclinic
C2/c
715.41
Monoclinic
P2/n
896.64
Triclinic
977.68
Triclinic
P−1
813.51
Monoclinic,
P21/m
crystal system
space group
P−1
a, Å
23.240(3)
10.3410(5)
16.060(4)
90
11.2914(5)
12.7244(6)
21.4357(11)
90
11.4695(12)
13.1322(14)
13.7721(14)
97.7010
9.9130(16)
12.665(2)
2 18.222(3)
90
10.9570(8)
22.2567(16)
16.8706(11)
90
b, Å
c, Å
α, deg
β, deg
130.19(3)
90
102.469(4)
90
103.2130
94.0570
90
97.384(6)
90
γ, deg
66.96
V, Å3
2948.4(8)
4
3007.2(2)
4
1990.1(4)
2
2105.2(6)
2
4080.1(5)
4
Z
Dcalcd, Mg/m3
Reflections collected
Reflections independent (Rint)
Goodness-of-fit on F2
R (I > 2σI)
1.788
1.580
1.496
1.542
1.324
5571
10931
15882
7390
15951
2597 (0.0289)
1.059
5299 (0.0492)
1.064
7002 (0.0129)
1.053
7390 (0.0000)
1.050
7385 (0.0278)
1.083
0.0539, 0.1465
0.0617, 0.1558
0.0712, 0.2121
0.0913, 0.2322
0.0373, 0.0973
0.0389, 0.0984
0.0418, 0.1020
0.0455, 0.1049
0.0604, 0.1788
0.0794, 0.1904
R (all data)
1793

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
19.Chung, L.-H.; Cho, K.-S.; England, J.; Chan, S.-C.; Wieghardt, K.;
Wong, C.-Y. Inorg. Chem. 2013, 52, 9885–9896.
Supporting Information
doi:10.1021/ic4010196
Supporting Information File:
20.Fernández, F. E.; Puerta, M. C.; Valerga, P. Organometallics 2011, 30,
5793–5802. doi:10.1021/om200665f
Supporting Information File 1
21.Corberán, R.; Mas-Marzá, E.; Peris, E. Eur. J. Inorg. Chem. 2009,
1700–1716. doi:10.1002/ejic.200801095
X-ray crystallographic data CCDC 1407422–1407426.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-11-194-S1.cif]
22.Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2781–2800.
doi:10.1002/ejic.200800323
23.Horn, S.; Gandolfi, C.; Albrecht, M. Eur. J. Inorg. Chem. 2011,
2863–2868. doi:10.1002/ejic.201100143
24.DePasquale, J.; Kumar, M.; Zeller, M.; Papish, E. T. Organometallics
2013, 32, 966–979. doi:10.1021/om300547f
Acknowledgements
25.Yang, D.; Tang, Y.; Song, H.; Wang, B. Organometallics 2015, 34,
2012–2017. doi:10.1021/acs.organomet.5b00256
26.Chen, C.; Zhang, Y.; Hong, S. H. J. Org. Chem. 2011, 76,
10005–10010. doi:10.1021/jo201756z
This work was financially supported by the National Natural
Science Foundation of Zhejiang Province (LQ14B020003).
References
1. Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109, 3677–3707.
27.Semwal, S.; Ghorai, D.; Choudhury, J. Organometallics 2014, 33,
7118–7124. doi:10.1021/om500876k
doi:10.1021/cr800501s
28.Su, G.; Huo, X.-K.; Jin, G.-X. J. Organomet. Chem. 2012, 696,
533–538. doi:10.1016/j.jorganchem.2010.09.018
2. Díez-González, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109,
3612–3676. doi:10.1021/cr900074m
29.Wylie, W. N. O.; Lough, A. J.; Morris, R. H. Organometallics 2012, 31,
2137–2151. doi:10.1021/om300108p
3. Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47,
3122–3172. doi:10.1002/anie.200703883
30.Naziruddin, A. R.; Huang, Z.-J.; Lai, W.-C.; Lin, W.-J.; Hwang, W.-S.
Dalton Trans. 2013, 42, 13161–13171. doi:10.1039/C3DT51161H
31.Naziruddin, A. R.; Zhuang, C.-S.; Lin, W.-J.; Hwang, W.-S.
Dalton Trans. 2014, 43, 5335–5342. doi:10.1039/C3DT53125B
32.Bernet, L.; Lalrempuia, R.; Ghattas, W.; Mueller-Bunz, H.; Vigara, L.;
Llobet, A.; Albrecht, M. Chem. Commun. 2011, 47, 8058–8060.
doi:10.1039/C1CC12615F
4. Edwards, P. G.; Hahn, F. E. Dalton Trans. 2011, 40, 10278–10288.
doi:10.1039/c1dt10864f
5. Hock, S. J.; Schaper, L.-A.; Herrmann, W. A.; Kühn, F. E.
Chem. Soc. Rev. 2013, 42, 5073–5089. doi:10.1039/c3cs60019j
6. Schaper, L.-A.; Hock, S. J.; Herrmann, W. A.; Kühn, F. E.
Angew. Chem., Int. Ed. 2013, 52, 270–289.
doi:10.1002/anie.201205119
33.Liu, X.; Chen, W. Dalton Trans. 2012, 41, 599–608.
doi:10.1039/C1DT11356A
7. Hopkinson, M. N.; Richter, C.; Schedler, M.; Glorius, F. Nature 2014,
510, 485–496. doi:10.1038/nature13384
34.Gu, S.; Liu, B.; Chen, J.; Wu, H.; Chen, W. Dalton Trans. 2012, 41,
962–970. doi:10.1039/C1DT11269D
8. Gradert, C.; Krahmer, J.; Sönnichsen, F. D.; Näther, C.; Tuczek, F.
J. Organomet. Chem. 2014, 770, 61–68.
35.Liu, X.; Chen, W. Organometallics 2012, 31, 6614–6622.
doi:10.1021/om300644h
doi:10.1016/j.jorganchem.2014.08.010
9. Galan, B. R.; Wiedner, E. S.; Helm, M. L.; Linehan, J. C.; Appel, A. M.
Organometallics 2014, 33, 2287–2294. doi:10.1021/om500206e
10.Liu, B.; Pan, S.; Liu, B.; Chen, W. Inorg. Chem. 2014, 53,
10485–10497. doi:10.1021/ic501544d
36.Liu, B.; Liu, X.; Chen, C.; Chen, C.; Chen, W. Organometallics 2012,
31, 282–288. doi:10.1021/om200881s
37.Wang, D.; Astruc, D. Chem. Rev. 2015, 115, 6621–6686.
doi:10.1021/acs.chemrev.5b00203
11.Liu, B.; Liu, B.; Zhou, Y.; Chen, W. Organometallics 2010, 29,
1457–1464. doi:10.1021/om100009u
38.Enthaler, S.; Jackstell, R.; Hagemann, B.; Junge, K.; Erre, G.;
Beller, M. J. Organomet. Chem. 2006, 691, 4652–4659.
doi:10.1016/j.jorganchem.2006.07.013
12.Chen, C.; Qiu, H.; Chen, W. Inorg. Chem. 2011, 50, 8671–8678.
doi:10.1021/ic2012233
39.Danopoulos, A. A.; Winston, S.; Motherwell, W. B. Chem. Commun.
2002, 1376–1377. doi:10.1039/B202814J
13.Zhang, M.; Ni, X.; Shen, Z. Organometallics 2014, 33, 6861–6867.
doi:10.1021/om500930m
40.Lai, Y.-B.; Lee, C.-S.; Lin, W.-J.; Naziruddin, A. R.; Hwang, W.-S.
Polyhedron 2013, 53, 243–248. doi:10.1016/j.poly.2013.01.042
41.Fernández, F. E.; Puerta, M. C.; Valerga, P. Organometallics 2012, 31,
6868–6879. doi:10.1021/om300692a
14.Dang, L.; Guo, J.; Song, H.; Liu, B.; Wang, B. Dalton Trans. 2014, 43,
17177–17183. doi:10.1039/C4DT02198C
15.Borré, E.; Dahm, G.; Aliprandi, A.; Mauro, M.; Dagorne, S.;
Bellemin-Laponnaz, S. Organometallics 2014, 33, 4374–4384.
doi:10.1021/om5003446
42.Zhang, X.; Liu, B.; Liu, A.; Xie, W.; Chen, W. Organometallics 2009, 28,
1336–1349. doi:10.1021/om800982r
16.Bierenstiel, M.; Cross, E. D. Coord. Chem. Rev. 2011, 255, 574–590.
doi:10.1016/j.ccr.2010.10.040
43.Chen, C.; Qiu, H.; Chen, W. J. Organomet. Chem. 2012, 696,
4166–4172. doi:10.1016/j.jorganchem.2011.09.008
44.CrysAlisPro; Oxford Diffraction Ltd: Oxford, UK, 2008.
45.Sheldrick, G. M. SHELXS-97 and SHELXL-97, Program for X-ray
crystal structure refinement, University of Göttingen: Göttingen,
Germany, 1997.
17.Saha, B.; Sengupta, G.; Sarbajna, A.; Dutta, I.; Bera, J. K.
J. Organomet. Chem. 2014, 771, 124–130.
doi:10.1016/j.jorganchem.2013.12.051
18.Dakkach, M.; Fontrodona, X.; Parella, T.; Atlamsani, A.; Romero, I.;
Rodríguez, M. Dalton Trans. 2014, 43, 9916–9923.
doi:10.1039/C4DT00698D
1794

Beilstein J. Org. Chem. 2015, 11, 1786–1795.
License and Terms
This is an Open Access article under the terms of the
Creative Commons Attribution License
(http://creativecommons.org/licenses/by/2.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
(http://www.beilstein-journals.org/bjoc)
The definitive version of this article is the electronic one
which can be found at:
doi:10.3762/bjoc.11.194
1795