S. Figueiredo et al. / Journal of Organometallic Chemistry 723 (2013) 56e64
57
were measured on a Bruker optics Tensor 27 equipped with a Spe-
cac Golden Gate Mk II ATR accessory having a diamond top-plate
and KRS-5 focussing lenses. FT-Raman spectra were recorded on
a RFS-100 Bruker FT-Spectrometer equipped with a Nd:YAG laser
with an excitation wavelength of 1064 nm. 1H NMR spectra were
measured with a Bruker CXP 300 instrument; chemical shifts are
quoted in parts per million and referenced to tetramethylsilane.
All preparations and manipulations were carried out using
standard Schlenk techniques under nitrogen. Where appropriate,
solvents were dried by standard procedures, distilled under
nitrogen, and kept over 4 Å molecular sieves. 1H-Pyrazole (98%,
SigmaeAldrich), KOH (ꢂ99%, SigmaeAldrich), DMSO (ꢂ99%, Lab-
Scan), MgSO4 (José M. Vaz Pereira), chloroform (ꢂ99%, Sigmae
Aldrich), CH2Br2 (99%, SigmaeAldrich), Mo(CO)6 (Fluka), and
diethyl ether (99.5%, SigmaeAldrich) were purchased from
commercial sources and used as received. The ligand bis(pyrazol-1-
yl)methane (BPM) was prepared as described in the literature [7].
Satisfactory elemental analyses were obtained, and the spectro-
scopic data (1H NMR and FT-IR) were in agreement with the pub-
lished data.
982 (w), 950 (vs), 920 (m), 875 (s), 777 (w), 735 (w), 656 (w), 610
(w), 578 (m), 529 (m), 400 (w), 362 (w), 341 (w). 1H NMR (300 MHz,
25 ꢁC, DMSO-d6):
d
¼ 7.95 (d, 2H, 3-H pz), 7.49 (d, 2H, 5-H pz), 6.40
(s, 2H, CH2), 6.29 (t, 2H, 4-H pz). 13C NMR (75 MHz, 25 ꢁC, DMSO-
d6):
¼ 140.1 (3-C pz), 130.6 (5-C pz), 106.3 (4-C pz), 64.2 (CH2).
d
2.4. X-ray crystallography
Single crystals of [MoO(O2)2(BPM)] (2) were manually har-
vested from the crystallization vial, immersed in silicone grease
(Dow Corning) and mounted on a glass fibre with the help of
a Stemi 2000 stereomicroscope equipped with Carl Zeiss lenses.
Data were collected on a Bruker X8 Kappa APEX II CCD area-
detector diffractometer (Mo K
a graphite-monochromated radia-
ꢀ
tion,
l
¼ 0.71073 A) controlled by the APEX2 software package [8]
and equipped with an Oxford Cryosystems Series 700 cryostream
monitored remotely using the software interface Cryopad [9].
Images were processed using SAINTþ [10], and data were cor-
rected for absorption by the multiscan semi-empirical method
implemented in SADABS [11].
The structure was solved using the Patterson synthesis algo-
rithm implemented in SHELXS-97 [12], which allowed the imme-
diate location of the crystallographically independent Mo6þ centre
and most of the heaviest atoms. The remaining non-hydrogen
atoms were located from difference Fourier maps calculated from
successive full-matrix least-squares refinement cycles on F2 using
SHELXL-97 [12a,13]. All non-hydrogen atoms were successfully
refined using anisotropic displacement parameters. Hydrogen
atoms bound to carbon were placed at their idealized positions
using appropriate HFIX instructions in SHELXL: 23 for the eCH2e
methylene group and 43 for the aromatic CH groups of the pyr-
azolyl rings. All these atoms were included in subsequent refine-
ment cycles in riding motion approximation with isotropic thermal
displacements parameters (Uiso) fixed at 1.2 ꢃ Ueq of the parent
carbon atoms.
2.2. cis-[Mo(CO)4(BPM)] (1)
A mixture of Mo(CO)6 (2.02 g, 7.65 mmol) and the ligand BPM
(1.13 g, 7.65 mmol) was vacuum-dried for 15 min. Dry toluene
(20 mL) was then added under a continuous flow of nitrogen. The
mixture was heated at 110 ꢁC with stirring for 4 h under a contin-
uous flow of nitrogen. After cooling to room temperature, the
mixture was filtered, and the resultant greenish-yellow precipitate
was washed with diethyl ether (3 ꢃ 20 mL), and finally vacuum-
dried. Yield: 2.45 g (90%). Anal. Calcd for C11H8MoN4O4: C, 37.10;
H, 2.26; N, 15.73. Found: C, 36.73; H, 2.16; N, 15.74%. FT-IR (KBr,
cmꢀ1):
1927 (vs,
n
¼ 3150 (w), 3139 (m), 3035 (w), 2956 (w), 2017 (s,
n(CO)),
n
(CO)), 1871 (vs, (CO)), 1804 (vs, (CO)), 1515 (m), 1459
n
n
(m), 1428 (s), 1401 (s), 1330 (m), 1300 (w), 1283 (s), 1221 (m), 1096
(s), 1066 (m), 1054 (m), 980 (s), 916 (w), 892 (m), 850 (m), 762 (s),
734 (s), 730 (m), 647 (m), 607 (s), 581 (s), 560 (m), 494 (w), 463 (w),
The last difference Fourier map synthesis showed the highest
peak (0.285 e Åꢀ3) located at 0.67 A from Mo1, and the deepest hole
ꢀ
418 (m), 392 (m), 368 (s). FT-Raman (cmꢀ1):
n
¼ 3152 (w), 3138 (w),
(ꢀ0.448 e Åꢀ3) at 0.70 A from C5 close to the medium point of the
ꢀ
3036 (w), 2956 (w), 2017 (vs),1911 (w), 1871 (vs),1803 (s), 1519 (w),
1457 (w), 1427 (w), 1414 (w), 1401 (w), 1330 (w), 1280 (vs), 1240
(w), 1222 (w), 1153 (w), 1097 (w), 1066 (w), 1055 (w), 982 (m), 921
(w), 848 (w), 775 (w), 760 (w), 730 (w), 646 (w), 603 (w), 583 (w),
487 (s), 461 (m), 410 (m), 393 (w). 1H NMR (300 MHz, 25 ꢁC, DMSO-
bond with C6. Information concerning crystallographic data
collection and structure refinement details is summarized inTable 1.
2.5. Catalytic olefin epoxidation
d6):
d
¼ 8.18 (d, 2H, 3-H pz), 7.92 (d, 2H, 5-H pz), 6.49 (t, 2H, 4-H pz),
The liquid-phase catalytic epoxidation of cis-cyclooctene (Cy,
95%, SigmaeAldrich) was carried out with magnetic stirring
(800 rpm), under air, in closed borosilicate micro reactors (5 mL)
equipped with a valve to allow sampling. Typically, the reaction
mixtures consisted of an amount of catalyst equivalent to
43 ꢃ 10ꢀ3 mmol of molybdenum, 4.3 mmol of Cy and 6.6 mmol of
oxidant. The olefin þ oxidant mixture was pre-heated in a ther-
mostated oil bath (55 ꢁC) for 10 min, after which time the catalyst
was added. This point was considered as time zero.
tert-Butylhydroperoxide (TBHP, 5e6 M in decane, Sigmae
Aldrich) and aqueous H2O2 (30% w/w in water, SigmaeAldrich)
were used as oxidants. The reactions were performed without
adding a co-solvent or by using 2 mL of 1,2-dichloroethane (DCE),
nitromethane (MeNO2), acetonitrile (ACN), n-hexane (hex) or
ethanol (EtOH). The other substrates studied (without using co-
6.39 (s, 2H, CH2). 13C NMR (75 MHz, 25 ꢁC, DMSO-d6):
d
¼ 220.4
(CO), 146.2 (3-C pz), 133.9 (5-C pz), 107.3 (4-C pz), 62.6 (CH2).
2.3. [MoO(O2)2(BPM)] (2)
After a catalytic run at 55 ꢁC for 24 h using complex 1
(1.43 mmol) as catalyst precursor, cis-cyclooctene (143 mmol) as
substrate, and TBHP (220 mmol, 5e6 M in decane) as oxidant
(please see Section 2.5 for more details), the reaction mixture was
cooled to ambient temperature, filtered, and kept under nitrogen in
a fridge during one week, whereupon a small crop of yellow crystals
of 2 was obtained. Yield: 0.08 g (17%). Anal. Calcd for C7H8MoN4O5:
C, 25.94; H, 2.49; N, 17.29. Found: C, 25.82; H, 2.37; N, 17.37%. FT-IR
(KBr, cmꢀ1):
n
¼ 3147 (w), 3138 (w), 3118 (m), 3100 (m), 3030 (w),
2987 (w), 1516 (m),1457 (m),1430 (m),1403 (s), 1335 (w),1295 (m),
1277 (s), 1225 (m), 1153 (w), 1110 (w), 1097 (w), 1082 (m), 1065 (m),
1000 (m), 949 (vs,
(m), 776 (m), 730 (m), 655 (m), 634 (w), 603 (m), 582 (m), 535 (m),
400 (m), 366 (w). FT-Raman (cmꢀ1):
solvents) were 1-octene, trans-2-octene, (R)-(þ)-limonene and
a-
pinene. The influence of the temperature on the catalytic activity
was evaluated using Cy without co-solvents.
n(Mo]O)), 925 (w), 914 (w), 866 (s, n(OeO)), 790
The oxidation processes were monitored by gas chromatog-
raphy (GC) using a GC Chrompack CP 9001 with a 25 m OPTIMA
FFAP MachereyeNagel capillary column and a flame ionization
detector (FID), at regular intervals of 15 min during the first hour,
n
¼ 3146 (m), 3119 (w), 3100
(w), 3030 (w), 2986 (w), 1517 (w), 1465 (w), 1431 (w), 1405 (w),
1335 (w), 1275 (w), 1247 (w), 1224 (w), 1152 (w), 1110 (w), 1099 (w),