C. Rodrigues et al. / Journal of Molecular Structure 1111 (2016) 84e89
85
temperature were studied in order to identify the optimal condi-
tions for activity of the catalysts.
N, 1.94%. IR (KBr): 695 and 498 cmꢁ1
,
n
(C¼Npy), 512 cmꢁ1
,
n
(RueP),
413 cmꢁ1 (RueN), 335, 313 and 286 cmꢁ1
n , n(RueCl). UVeVis
(CH2Cl2): 528 (1248), 450 (800) and 349 (1125) Mꢁ1 cmꢁ1
.
2. Experimental section
mer-[RuCl3(dppb)(4-tBupy)] 4 Yield: 87 mg (83%). Calc. for
C
37H41NP2Cl3Ru: C, 57.78; H, 5.37; N, 1.82%. Found: C, 57.51; H, 5.43;
2.1. Materials and methods
N, 1.77%. IR (KBr): 694 and 500 cmꢁ1
,
n
(C¼Npy), 514 cmꢁ1
, n(RueP),
416 cmꢁ1 (RueN), 336, 316 and 287 cmꢁ1
, n , n(RueCl). UVeVis
2.1.1. Chemistry
(CH2Cl2): 530 (1860), 441 (1200) and 350 (1750) Mꢁ1 cmꢁ1
.
Solvents were purified by standard methods. All chemicals used
were of reagent grade or comparable purity. RuCl3$3H2O, triphe-
nylphosphine (PPh3), 1,4-bis(diphenylphosphino)butane (dppb),
pyridine (py), 4-methylpyridine (4-Mepy), 4-vinylpyridine (4-Vpy),
4-tert-butylpyridine (4-tBupy) and 4-phenylpyridine (4-Phpy)
were used as received from Aldrich. The precursors [RuCl2(PPh3)3],
[RuCl2(dppb)(PPh3)] and mer-[RuCl3(dppb)(H2O)] were prepared
according to the literature [25,33,34]. The mer-[RuCl3(dppb)(py)] 1,
mer-[RuCl3(dppb)(4-Mepy)] 2, mer-[RuCl3(dppb)(4-Vpy)] 3, mer-
[RuCl3(dppb)(4-tBupy)] 4 and mer-[RuCl3(dppb)(4-Phpy)] 5 com-
plexes were prepared according to the modified procedures [26].
mer-[RuCl3(dppb)(4-Phpy)] 5 Yield: 89 mg (84%). Calc. for
C
39H37NP2Cl3Ru: C, 59.36; H, 4.73; N, 1.78%. Found: C, 59.66; H,
4.63; N, 1.77%. IR (KBr): 695 and 495 cmꢁ1
,
n
(C¼Npy), 513 cmꢁ1
,
n
(RueP), 413 cmꢁ1 (RueN), 336, 313 and 290 cmꢁ1
, n , n(RueCl).
UVeVis (CH2Cl2): 536 (1250), 449 (850) and 353 (1450) Mꢁ1 cmꢁ1
.
2.1.5. Instrumentation
Elemental analyses were performed in a Fison EA 1108 model.
The FTIR spectra of the powder complexes were recorded from
KBr pellets in the 4000e200 cmꢁ1 range, in a BomeneMichelson FT
MB-102 instrument.
The UVeVis spectra of the complexes, in dichloromethane so-
lution, concentration of 1 ꢂ 10ꢁ3 mol Lꢁ1, were recorded with a
Hewlett Packard diode array e 8452 A.
2.1.2. X-ray crystallography
Red crystals of mer-[RuCl3(dppb)(4-Phpy)] were grown by slow
evaporation of a dichloromethane/n-hexane/diethyl ether solution
(2:1:1) at room temperature. The data collection was performed
The Electron Paramagnetic Resonance (EPR) spectra in the solid
state was measured at 77 K using a Varian E-109 instrument
operating at the X band frequency, within a rectangular cavity (E-
248) fitted with a temperature controller. X-band (9.4 GHz) EPR
spectra were recorded at 100 K on an EMX cw-spectrometer
(Bruker) equipped with a liquid N2 cryostat and a temperature
controller with a modulation frequency of 100 kHz, a microwave
power 6.3 mW and modulation amplitude of 5 G.
using Mo-K
a
radiation (
l
¼ 71.073 pm) on a BRUKER APEX II Duo
diffractometer. Data reduction and absorption correction were
carried out with the Bruker SAINT package. The structure was
solved with SHELXS97 using direct methods [35] and all non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters with SHELXL97 [36]. The hydrogen atoms were calculated
at idealized positions using the riding model option of SHELXL97
[36]. See in supporting information Table 1S, the detailed infor-
mation about the structure determination.
Cyclic voltammetry (CV) experiments of the complexes, in so-
lution, were conducted in an electrochemical analyzer BAS model
100B Instrument. These experiments were carried out at room
temperature in CH2Cl2 containing 0.10 mol Lꢁ1 Bu4NClO4 (TBAP)
(Fluka Purum) as a support electrolyte using a one-compartment
cell, where the working and auxiliary electrodes were stationary
Pt foils, and the reference electrode was Ag/AgCl, 0.10 mol Lꢁ1 TBAP
in CH2Cl2. Under these conditions ferrocene was oxidized at 0.43 V
(Fcþ/Fc).
2.1.3. Catalytic studies
Hydrogenation reactions were performed in 25 and 75 mL
stainless steel autoclaves equipped with an overhead magnetic
stirrer, a pressure indicator and a thermocouple for temperature
registration. The autoclaves were equipped with an electrical
heating/cooling system to control the temperature inside the
vessel. The hydrogenation active catalyst substrate/Ru-complex
was prepared in situ, once the Ru-complexes used were pre-
catalysts. The autoclave was charged with Ru-complex (0.013,
0.015 or 0.026 mmol), substrate (1.5 or 6.9 mmol), MeOH (20 or
6 mL). The system was flushed three times with H2. Then, the
autoclave was pressurized with H2 (15, 50 or 100 bar) and heated to
a temperature of 80 or 160 ꢀC, for 15 or 24 h. After the reaction, the
homogeneous reaction mixture was cooled down in an ice bath to
room temperature, and the upper organic layer was analyzed by
GC-FID and GC-MS.
All the NMR experiments were recorded on BRUKER
DRX400 MHz equipment; in a BBO 5 mm probe at 298 K, using
CDCl3 (1H) and CH2Cl2
(
31P{1H}) as solvents, TMS for internal
reference for 1H.
GC analysis was run on a Shimadzu CLASS-VPTM instrument
(50 m capillary column, carrier gas: 3 atm N2 and FID detector).
3. Results and discussion
3.1. Characterization of complexes containing Ru(III)
IR spectra for all complexes show the typical band of coordi-
2.1.4. Preparation of ruthenium (III) complexes
nated phosphine 512e514 cmꢁ1
413e421 cmꢁ1
n
(RueP) and pyridine ligands
mer-[RuCl3(dppb)(N)], N ¼ 4-vinylpyridine (4-Vpy), 4-tert-butyl-
pyridine (4-tBupy) and 4-phenylpyridine (4-Phpy): Ruthenium (III)
complexes 3, 4 and 5 were synthesized similar to described in the
literature for the synthesis of the 1 and 2 [26], reacting an equi-
molar amount of N-heterocyclic ligands (0.153 mmol) with the mer-
[RuCl3(dppb)(H2O)] precursor (0.100 g, 0.153 mmol). The reaction
mixture was refluxed and stirred for 6 h, under Ar atmosphere, in a
Schlenk flask. The final pink solutions were concentrated to ca.
2 mL and 10 mL of n-hexane, previously degassed, were added in
order to obtain pink precipitates. The solids were filtered off, well
rinsed with n-hexane and diethyl ether and dried in vacuum.
n(RueN). Three bands were observed, from 336 to
286 cmꢁ1 n(RueCl), suggesting a meridional (mer) arrangement of
the chlorine ligands [37]. The electronic spectra of the complexes in
CH2Cl2 solutions in the UVeVis region, showed three characteristic
bands. The bands near 530, 450, and 350 nm can be tentatively
attributed to Cl/Ru, N/Ru and P/Ru, ligand-metal charge
transfer (LMCT), respectively [25,26].
The presence of ruthenium(III) species was confirmed by mag-
netic susceptibility experiments and EPR measurements (see Fig.1).
The EPR spectra of 1e3 complexes measured in frozen dichloro-
methane solution are shown in Fig. 1. All these complexes show
rhombic signals, typical for isolated Ru(III) ions in a rhombic
environment [38,39]. The positions of the signals were reproduced
mer-[RuCl3(dppb)(4-Vpy)]
3 Yield: 90 mg (85%). Calc. for
C
35H35NP2Cl3Ru: C, 56.88; H, 4.77; N,1.90%. Found: C, 57.10; H, 5.03;