Inorganic Chemistry
Article
129.64, 128.32, 128.23, 123.02, 120.32, 75.09, 53.54. 31P NMR
(161.97 MHz, DMSO-d6): δ (ppm) 55.33 (s, PPh3), −144.19 (sep, PF6).
MS (ESI): m/z calculated for [(η5-C5H5)Ru(κ2-L1)PPh3]+ (L1 =
2-(aminomethyl) pyridine) 537.1 [M]+, found 537.1 [M]+. UV−vis
(dichloromethane, λmax, nm (ε, M−1 cm−1)): 365 (3.7 × 103), 327
(6.8 × 103), 274 (8.0 × 103), 267 (7.1 × 103). The CCDC deposition
number of the complex [Ru]-1 is 1564514.
a higher temperature.29,30 Moreover, the high aqueous and
thermal stability of the studied η5-Cp−Ru(II)−pyridylamine
complexes is also reflected in their two-fold higher catalytic
activity (84% yield of LA, 6 h, 120 °C, 12 mmol of HCOOH)
over the analogous η6-arene−Ru(II) (42% yield of LA, 8 h, 100 °C,
12 mmol of HCOOH).27 Notably, previously explored catalysts
based on a η5-Cp*−Ir complex or other metal nanoparticle
catalysts (Pd/Al2O3 or Au/Nb2O5) required high H2 gas pres-
sure (5−80 bar) and higher temperature (120−170 °C) for
analogous catalytic transformations (Table S9 in the Support-
ing Information).19−26 Therefore, the studied η5-Cp−Ru(II)−
pyridylamine complexes represent a class of highly active cata-
lysts with high thermal and aqueous stability, showing catalytic
activity higher than or on par with that of previously reported
catalytic systems.
Synthesis of [(η5-C5H5)RuPPh3(κ2-(N,N)-N-(pyridin-2-ylmethyl)-
propan-1-amine]PF6 ([Ru]-2). Complex [Ru]-2 was synthesized
following the above general procedure, by using N-(pyridin-2-
ylmethyl)propan-1-amine (L2) (0.165 g, 1.1 mmol) and [(η5-
C5H5)Ru(PPh3)2Cl] (0.363 g, 0.5 mmol). Pale yellow solid, yield
0.225 g (62%). FTIR (ν, cm−1): 3277 ν(N−H stretching), 1605
ν(N−H bending), 1091 ν(C−N), 833 ν(PF6 stretching), 557 ν(PF6
bending). 1H NMR (400 MHz, DMSO-d6): δ (ppm) 8.39 (d, 1H, J =
5.24 Hz), 7.70 (t, 1H, J1 = 7.76 Hz, J2 = 7.52 Hz), 7.46 (t, 3H, J1 =
6.28 Hz, J2 = 8.28 Hz), 7.42 (d, 1H, J = 7.76 Hz), 7.39 (t, 6H, J = 7.56 Hz,
J2 = 7.00 Hz), 7.00 (t, 6H, J1 = 9.28 Hz, J2 = 8.28 Hz), 6.90 (t, 1H,
J1 = 6.52 Hz, J2 = 6.52 Hz), 4.51 (s, 5H), 4.39 (dd, 1H, J1 = 15.56 Hz,
J2 = 15.56 Hz), 4.09−4.02 (m, 1H), 3.29−3.25 (m, 1H), 3.19−3.14
(m, 1H), 2.90−2.88 (m, 1H), 1.40−1.36 (m, 1H), 1.18−1.15 (m, 1H),
0.54 (t, 3H, J1 = 7.28 Hz, J2 = 7.52 Hz). 13C NMR (100 MHz, DMSO-
d6): δ (ppm) 161.23, 155.37, 136.74, 132.99, 132.77, 132.65, 132.61,
130.07, 128.76, 128.67, 123.55, 120.92, 75.68, 61.13, 60.71, 21.49,
10.29. 31P NMR (161.97 MHz, DMSO-d6): δ (ppm) 54.98 (s, PPh3),
−144.19 (sep, PF6). MS (ESI): m/z calculated for [(η5-C5H5)Ru(κ2-
L2)PPh3]+ (L2 = N-(pyridin-2-ylmethyl)propan-1-amine) 579.1
[M]+, found 579.1 [M]+. UV−vis (dichloromethane, λmax, nm
(ε, M−1 cm−1)): 369 (3.7 × 103), 329 (6.7 × 103), 274 (7.5 × 103),
266 (6.6 × 103). The CCDC deposition number of the complex
CONCLUSIONS
■
In summary, we synthesized and characterized (by 1H, 13C, 31P,
NMR, and mass) a series of cationic η5-Cp−Ru(II)−pyridyl-
amine ([Ru]-1−[Ru]-6) and η5-Cp−Ru−pyridylimine ([Ru]-7)
complexes and authenticated the molecular structures of
all the complexes by X-ray crystallography. The synthesized
η5-Cp−Ru−pyridylamine complexes displayed high catalytic
activity for the transformation of the biomass-derived furans,
furfural (1a), 5-HMF (2a), and 5-MF (3a) to the value-added
open-ring products, LA (1b) and diketones (1-HHD (2b),
3-HHD (3b) and 2,5-HD (3c)) with high conversion (>99%)
and selectivity at 120 °C in the presence of formic acid.
Experimental findings demonstrated that the η5-Cp−Ru−
pyridylamine complexes exhibited higher catalytic performance
in comparison to the analogous η5-Cp−Ru−pyridylimine com-
plex, which can be attributed to the hemilabile nature of the
Synthesis of [(η5-C5H5)RuPPh3(κ2-(N,N)-N-(pyridin-2-ylmethyl)-
propan-2-amine]PF6 ([Ru]-3). Complex [Ru]-3 was synthesized
following the above general procedure, by using N-(pyridin-2-ylmethyl)-
propan-2-amine (L3) (0.165 g, 1.1 mmol) and [(η5-C5H5)Ru-
(PPh3)2Cl] (0.363 g, 0.5 mmol). Pale yellow solid, yield 0.240 g
(66%). FTIR (ν, cm−1): 3274 ν(N−H stretching), 1604 ν(N−H
bending), 1093 ν(C−N), 828 ν(PF6 stretching), 556 ν(PF6 bending).
1H NMR (400 MHz, DMSO-d6): δ (ppm) 8.16 (d, 1H, J = 5.24 Hz),
7.76 (t, 1H, J1 = 7.60 Hz, J2 = 7.76 Hz), 7.50 (t, 3H, J1 = 7.56 Hz, J2 =
7.00 Hz), 7.48 (d, 1H, J = 7.75 Hz), 7.44 (t, 6H, J1 = 6.28 Hz, J2 =
8.52 Hz), 7.00 (t, 6H, J1 = 8.80 Hz, J2 = 8.28 Hz), 6.94 (t, 1H,
J1 = 6.28 Hz, J2 = 7.04 Hz), 4.64 (s, 5H), 4.14−4.11 (m, 1H), 3.26−
3.21 (m, 1H), 1.94−1.88 (m, 1H), 0.93 (dd, 6H, J1 = 6.04 Hz, J2 =
6.52 Hz). 13C NMR (100 MHz, DMSO-d6): δ (ppm) 161.55, 154.93,
137.10, 132.82, 132.73, 132.63, 132.44, 130.27, 128.99, 128.90, 123.42,
121.08, 75.33, 58.35, 56.63, 24.72, 20.48. 31P NMR (161.97 MHz,
DMSO-d6): δ (ppm) 54.44 (s, PPh3), −144.17 (sep, PF6). MS (ESI)
m/z calculated for [(η5-C5H5)Ru(κ2-L3)PPh3]+ (L3 = N-(pyridin-2-
ylmethyl)propan-2-amine) 579.2 [M]+, 579.2 found [M]+. UV−vis
(dichloromethane, λmax, nm (ε, M−1 cm−1)): 369 (3.7 × 103), 329
(6.9 × 103), 275 (7.7 × 103), 266 (6.7 × 103). The CCDC deposition
number of the complex [Ru]-3 is 1564515.
pyridylamine ligands and the basicity and bulkiness at Namine
.
Moreover, the studied catalytic system has also been applied to
the transformation of fructose and the gram-scale transforma-
tion of furfural to open-ring products for practical applications.
Therefore, the high catalytic activity along with the aqueous and
thermal stability demonstrated by the studied η5-Cp−Ru(II)
complexes may also find applications in various other high-
temperature catalytic reactions.
EXPERIMENTAL SECTION
■
Procedure for the Synthesis of Cyclopentadienyl-Ruthenium-
(II) Complexes [Ru]-1−[Ru]-7. Complexes [Ru]-1−[Ru]-7 were
synthesized by treating N-substituted pyridylamine (L1−L6) and
pyridylimine (L7) ligands with the cyclopentadienyl−ruthenium
precursor [(η5-C5H5)RuCl(PPh3)2] in methanol (25 mL) under reflux
conditions for 20 h. Later, the volume was reduced to 10 mL, and then
NH4PF6 was added (0.489 g, 3.0 mmol). The resulting solution was
stirred for 12 h at room temperature to obtain the desired complexes
as precipitates, which were washed with diethyl ether (3 × 10 mL) and
dried in air.
Synthesis of [(η5-C5H5)RuPPh3(κ2-(N,N)-N-(pyridin-2-ylmethyl)-
butan-1-amine]PF6 ([Ru]-4). Complex [Ru]-4 was synthesized
following the above general procedure, by using N-(pyridin-2-ylmethyl)-
butan-1-amine (L4) (0.180 g, 1.1 mmol) and [(η5-C5H5)Ru(PPh3)2Cl]
(0.363 g, 0.5 mmol). Pale yellow solid, yield 0.250 g (67%). FTIR
(ν, cm−1): 3127 ν(N−H stretching), 1601 ν(N−H bending), 1092
ν(C−N), 830 ν(PF6 stretching), 557 ν(PF6 bending). 1H NMR
(400 MHz, DMSO-d6): δ (ppm) 8.38 (d, 1H, J = 5.28 Hz), 7.70
(t, 1H, J1 = 7.52 Hz, J2 = 7.52 Hz), 7.45 (t, 3H, J1 = 6.00 Hz, J2 =
6.80 Hz), 7.39 (t, 6H, J1 = 6.52 Hz, J2 = 8.04 Hz), 7.19 (t, 1H, J1 =
9.04 Hz, J2 = 7.28 Hz), 7.00 (t, 6H, J1 = 9.28 Hz, J2 = 8.28 Hz), 6.89
(t, 1H, J1 = 6.52 Hz, J2 = 6.52 Hz), 4.51 (s, 5H), 4.42−4.37 (m, 1H),
4.11−4.03 (m, 1H), 3.24−3.22 (m, 1H), 2.91−2.85 (m, 1H), 1.36−
1.31 (m, 1H), 1.18−1.10 (m, 1H), 0.96−0.91 (m, 1H), 0.77 (t, 3H,
J1 = 7.04 Hz, J2 = 7.24 Hz). 13C NMR (100 MHz, DMSO-d6):
δ (ppm) 161.23, 155.36, 136.75, 133.02, 132.77, 132.65, 130.06,
128.75, 128.65, 123.55, 120.92, 75.70, 60.88, 59.17, 30.53, 18.78,
Synthesis of [(η5-C5H5)RuPPh3(κ2-(N,N)-2-(aminomethyl)-
pyridine]PF6 ([Ru]-1). Complex [Ru]-1 iswas synthesized following
the above general procedure, by using 2-(aminomethyl)pyridine (L1)
(1.180 g, 1.1 mmol) and [(η5-C5H5)Ru(PPh3)2Cl] (0.363 g, 0.5 mmol).
Pale yellow solid, yield 0.210 g (61%). FTIR (ν, cm−1): 3357, 3313
ν(N−H stretching), 1606 ν(N−H bending), 1090 ν(C−N), 832
ν(PF6 stretching), 556 ν(PF6 bending). 1H NMR (400 MHz, DMSO-
d6): δ (ppm) 8.61 (d, 1H, J = 5.20 Hz), 7.56 (t, 1H, J1 = 7.80 Hz, J2 =
7.52 Hz), 7.39 (t, 6H, J1 = 9.28 Hz, J2 = 6.24 Hz), 7.32 (t, 6H, J1 =
8.80 Hz, J2 = 6.28 Hz), 7.28 (d, 1H, J = 8.28 Hz), 7.12 (t, 6H, J1 =
9.28 Hz, J2 = 8.04 Hz), 6.79 (t, 1H, J1 = 6.52 Hz, J2 = 6.28 Hz), 4.36
(s, 5H), 4.03−3.99 (m, 1H). 13C NMR (100 MHz, DMSO-d6):
δ (ppm) 162.28, 155.77, 136.18, 134.35, 133.97, 132.97, 132.86,
H
Inorg. Chem. XXXX, XXX, XXX−XXX