2
M. Diaz-Couce et al. / Inorganica Chimica Acta xxx (2016) xxx–xxx
where L or (L)
2
represent mono- or bidentate nitrogen ligands,
was performed on a Perkin Elmer Optima 4300DV using In as inter-
nal standard.
showed significant activity as catalyst precursors in olefin epoxida-
tion [22]. Their immobilization in porous materials, namely derived
from MCM-41, led to improvement of their catalytic properties, for
several L ligands, as reviewed recently [23].
2.3. Catalytic epoxidation of materials
In this work, we describe the catalytic behavior of an immobi-
The materials were tested in epoxidation of olefins and alcohols,
namely cis-cyclooctene, styrene, R-(+)-limonene, 1-octene and
trans-hex-3-en-1-ol, using tert-butylhydroperoxide (tbhp) as oxi-
dant (5.5 M in n-decane). The catalytic oxidation tests were carried
out at 398 K, using toluene as solvent. The reactions occurred
under air in a reaction vessel equipped with a magnetic stirrer
and a condenser. In a typical experiment, the vessel was loaded
with olefin or alcohol (100 mol%), oxidant (200 mol%) and 3 mL
of solvent. The final volume of the reaction was ca. 6 mL. The addi-
tion of the oxidant determined the initial time of the reaction. Con-
version, product yields and stereochemistry were monitored by
sampling periodically and analyzing the products on a Shimadzu
QP2010-Plus GC/MS system and a capillary column (Teknokroma
TRB-5MS, TRB-1MS or Restek Rt-bDEXsm) operating in the linear
velocity mode. Recycling tests were carried out as described above
using the recycled materials as catalyst; conversion and product
yields were monitored as described above. After each cycle (24 h)
0
lized complex similar to [MoI
2
3
(CO) (bpy)] (bpy = 2,2 -bipyridyl),
where the bpy ligand had to be modified in order to functionalize
the LDH materials. For this purpose, two carboxylate substituents
0
were introduced in the 4,4 positions (H
2
BDC), so that the dianion
might intercalate in an anionic clay, leaving the diamine function-
ality available for coordination to the metal (Scheme 1). Two differ-
3
+
2+
2+
3+
2+
ent clays, with Al and Zn or Mg , as M and M , respectively,
were chosen as supports.
2
. Experimental
2
.1. General
3
All reagents, including the Mg/Al clay (LDHMg/Al-CO ), were
obtained from Aldrich and used as received. Commercial grade
solvents were dried and deoxygenated by standard procedures
2 2
the catalyst was filtered, washed which CH Cl several times and
(
dichloromethane, dimethylformamide (dmf) over calcium
hydride), distilled under nitrogen, and kept over 4 Å molecular
sieves. The Zn/Al clay (LDHZn/Al-CO ) was synthesized by the
methodology previously described [24]. [Mo(CO) (NCMe)
21] and [Mo(CO) (bpy) ] (1) (X = I , Br ) [25] were prepared
by reported procedures.
dried prior to reuse in a new catalytic cycle.
3
2
2
.4. Synthesis of materials and catalysts
3
X
2
2
]
[
X
3 2
2
2
.4.1. Synthesis of LDHM/Al materials-BDC (M = Zn, Mg)
A mixture of H BDC (7.30 mmol) in deionized type II water
20 mL) with KOH (14.6 mmol) was stirred until complete solubi-
lization. This solution was then added to a suspension of the LDH
LDHZn/Al or LDHMg/Al) clay (1.00 g) in freshly distilled dmf
2
(
2
.2. Catalysts characterization
(
FTIR spectra were obtained by Diffuse Reflectance (DRIFT) mea-
(25 mL) at 343 K, and the reaction mixture was stirred at the same
temperature for 48 h.
All the manipulations were carried out under a dry N2 atmo-
sphere to prevent the uptake of carbonate anions. The resulting
materials were then filtered off, washed with deionized type II
water (3 ꢃ 20 mL), and dried in a desiccator under vacuum.
ꢀ
1
surements on a Nicolet 6700 in the 400–4000 cm range with
ꢀ1
13
4
cm resolution. Solid state C NMR measurements were per-
formed at room temperature on a Tecmag Redstone/Bruker 300
WB spectrometer operating at 75.47 MHz. Samples (ꢂ200 mg)
were packed into 7 mm o.d. zirconia rotors, equipped with Kel-F
caps. The standard magic angle spinning (MAS) cross polariza-
tion–dipolar decoupling RF pulse sequence (CP–DD) was used
under about 4 kHz spinning rate. 13C spectra were recorded with
2
.4.1.1. LDHZn/Al-BDC. Elemental analysis (%): found C 18.27, H 3.41,
N 2.27.
DRIFT (KBr
262 (vs), 1024 (vs), 801 (s).
2
ms contact time, 90° RF pulses of around 4
l
s, 4 s recycling delay
ꢀ1
m
/cm ): 3385 (vs), 2963 (vs), 1619 (vs), 1403 (vs),
and a number of scans higher than 900. The Hartmann–Hahn con-
dition was optimized using glycine; it was also the external refer-
ence to set the chemical shift scale (13CO at 176.03 ppm). Powder
XRD measurements were taken on a Philips Analytical PW
1
XRD (2h, planes): 4.85 (003), 8.962 (006), 12.12 (009).
2.4.1.2. LDHMg/Al-BDC. Elemental analysis (%): found C 14.58 H 4.17
3
050/60 X’Pert PRO (theta/2 theta) equipped with X’Celerator
detector and with automatic data acquisition (X’Pert Data Collector
v2.0b) software), using a monochromatized Cu-K radiation as
N 2.71.
DRIFT (KBr
t
/cmꢀ1): 3400 (vs), 1601 (s), 1539 (m), 1389 (s), 776
(
a
(
s).
incident beam, 40 kVꢀ30 mA. TGA studies were performed using
a Netzsch F3 Jupiter system in ISIS, Neutron & Muon Source on
Rutherford Appleton Laboratory. The measurements were done in
the 300–1073 K temperature range using a heating rate of
XRD (2h, planes): 4.71 (003), 9.83 (006), 13.80 (009).
2.4.2. Synthesis of LDH materials-BDC-MoX
[Mo(CO) (NCMe) ] (0.3 g) was added to a suspension of
LDHM/Al-BDC (0.75 g) in dichloromethane (10 mL). The slurry was
2
ꢀ
1
1
0 K min under N
2
atmosphere. Microanalyses for CHN and Mo
X
3 2
2
quantitation were performed at CACTI, University of Vigo. CHN
analyses were performed on a Fisons EA 1108; Mo quantification
stirred under a N
2
atmosphere, at room temperature, for 24 h.
COOH
COO-
HOOC
-OOC
N
N
N
N
BDC
0
N
N
bpy
H
2
BDC
Scheme 1. 2,2 -Bipyridine and derivatives.