A. Bafti et al.
Molecular Catalysis 512 (2021) 111764
idealized positions and refined by the use of the riding model with Uiso
= 1.2Ueq of the connected carbon atom or as ideal CH3 groups with Uiso
= 1.5Ueq. Hydrogen atoms attached to oxygen atoms (O2, O6 and O7)
and nitrogen atoms (N3) were located in the difference Fourier maps at
the final stages of the refinement procedure. Their coordinates were
of complex 3∙MeCN at 160 ◦C for two hours.
Complex 3*∙MeCN, [MoO2(L3)]2∙MeCN obtained from the more
concentrated acetonitrile solution, V(MeCN)=10 mL. Dark orange-
brown product. Yield: 0,550 g (92 %). Mass fraction of elements, w /
%, calculated (experimental) for C16H14MoN4O5: C 43.13 (41.98); H
3.02 (2.36); N 11.74 (10.14). Selected IR data (cm‒1): 3341, 3207
–
–
H
refined freely but with restrained N H distances of 0.86(2) Å and O
distances of 0.82(2) Å. All refinements were performed using
SHELXL-2013 [47] The SHELX programs operated within the Olex2
suite. [48] Geometrical calculations and molecular graphics were done
with Mercury. [49]
(NH ), 1551 (C
N
imine), 1232 (C Ophenolate), 902, 925 (MoO22+), 870
–
–
–
2
–
...
–
(Mo O Mo). TG: calcd. for MoO , 34.47 %, found 35.27 %, for MeCN
calcd. 4.91 %, found 4.15 %; com3plex decomposition 301-469 ◦C.
Complex 4, [MoO2(L4)]2. Dark red product. Yield: 0.532 g (89 %).
Mass fraction of elements, w / %, calculated (experimental) for
C28H22Mo2N6O10: C 42,33 (41,18); H 2,79 (1,89); N 10,58 (9,78).
4.3. Theoretical calculations
Selected IR data (cm‒1): 3330, 3267 (NH ), 1603 (C
N
imine), 1230
–
–
2
(C Ophenolate), 947 (Mo N), 919, 872, (MoO22+). TG: calcd. for MoO3,
36.24 %, found 37.17 %.
–
–
The geometries of all species under investigation were optimized
without any symmetry constraint with the Gaussian 09 rev. D01 pro-
gram suite, [50] with the DFT approach using the B3LYP
three-parameter functional [51–53] in conjunction with the 6-31G*
basis set [54–57] for the light atoms (O, N, C, H) and the CEP-31G set for
the Mo atom. [58,59] The geometries of all complexes and intermediates
were optimized from starting geometries determined or inspired by
X-ray diffraction without any symmetry constraint. All coordinates have
been listed in SI (Tables S13). Frequency analysis confirmed that the
optimized geometries of all the stable compounds and intermediates
were local minima. The transition states were optimized using a pre-
liminary scan of a relevant internal coordinate, followed by full opti-
mization of the TS guided by the knowledge of such coordinates. All
optimized geometries were confirmed to be stationary points and local
minima (for stable molecules or reaction intermediates) or first-order
saddle points (for the TSs) by frequency analyses. For all the TSs, anal-
ysis of the imaginary frequency confirmed the expected motion along
the reaction coordinate. Those values and the relative schemes have
been added Table S11-S14) The calculated frequencies were also used to
derive the thermochemical parameters at 298 K according to the stan-
dard approximations (ideal gas, rigid rotor and harmonic oscillator).
Solvent effects were included using PCM single point calculations on the
gas-phase optimized geometries. [60]
Polynuclear complex 4** [MoO2(L4)]nobtained by solvothermal
procedure from methanol. Reaction time: 4 h, reaction temperature:
110 ◦C. Dark red product. Selected IR data (cm‒1): 3333, 3270 (NH2),
1603 (C
N
imine), 1232 (C-Ophenolate), 918, 875, (MoO22+). TG: calcd. for
–
–
MoO3, 36.24 %, found 36.08 %; complex decomposition 322-489 ◦C.
Mononuclear complexes [MoO2(L)(MeOH)] General procedure:
0.083 g (0.306 mmol) of the H2L1-4 ligand was dissolved in 50 mL of
methanol and refluxed for 1 h after which 0.1 g (0.307 mmol) of
[MoO2(acac)2] was added. The yellow reaction mixture was cooled to
room temperature and then stored at -8 ◦C for one month. The obtained
products were filtered off.
Complex 1a, [MoO2(L1)(MeOH)] Orange product. Yield: 0.015 g
(12.8 %). Mass fraction of elements, w / %, calculated (experimental) for
C
15H15MoN3O6, are: C, 41.97 (41.32); H, 3.52 (3.283); N, 9.79 (9.42).
Selected IR data (cm‒1): 3331, 3256 (NH2), 1613 (C
Nimine), 1574
–
–
(C C), 1327 (C O), 1240 (C Ophenolate), 916 (MoO22⁺), 893 (MoO22+).
–
–
–
–
TG: calcd. for MoO3, 33.54 %, found 33.54 %, for MeOH calcd. 7.46 %,
found 7.46 %.
Complex 2a, [MoO2(L2)(MeOH)]∙MeOH, Orange product. Yield:
0.075 g (61.5 %). Mass fraction of elements, w / %, calculated (exper-
imental) for C16H21MoN3O7, are: C, 41.48 (40.89); H, 4.57 (3.78); N,
9.07 (8.15). Selected IR data (cm‒1): 3326 (NH2), 1602 (C
Nimine),
–
–
1568 (C C), 1347 (C O), 1261 (C Ophenolate), 938, 919 (MoO22⁺), 891
–
–
–
–
4.4. Preparative part
(MoO22+). TG: calcd. for MoO3, 30.95 %, found 31.33 %, for MeOH calcd.
13.76 %, found 12.97 %.
Dinuclear complexes [MoO2(L)]2 General procedure: 0.083 g
(0.306 mmol) of the H2L1-4 ligand was dissolved in 50 mL of acetonitrile
and 0.1 g (0.307 mmol) of [MoO2(acac)2] was added. The orange re-
action mixture was refluxed for 3 h. The obtained product was filtered
off.
Complex 3a, [MoO2(L3)(MeOH)], Orange product. Yield: 0.043 g
(52 %). Mass fraction of elements, w / %, calculated (experimental) for
C
15H15MoN3O6 are: C 41,97 (41,13); H 3,52 (3,11); N 9,79 (9,01).
Selected IR data (cm‒1): 1595 (C
–
–
–
Nimine), 1227 (C Ophenolate), 1125
(MeOH), 930, 904 (MoO22+), TG: calcd. for MoO3, 33.54 %, found 34.16
%, for MeOH calcd. 7.46 %, found 7.12 %.
Complex 1, [MoO2(L1)]2. Yellow product. Yield: 0.104 g (86.1 %).
Mass fraction of elements, w / %, calculated (experimental), for
Complex 4a, [MoO2(L4)(MeOH)], Orange product. Yield: 0.025 g
(19 %). Mass fraction of elements, w / %, calculated (experimental) for
C
28H22Mo2N6O10, are: C, 42.33 (42.13); H, 2.79 (2.58); N, 10.58
(11.02). Selected IR data (cm‒1): 3251, 3214 (NH ), 1614 (C
N
imine),
–
–
2
1591 (C C), 1341 (C O), 1263 (C Ophenolate), 921, 906 (MoO22⁺), 895
–
–
–
–
C
15H15MoN3O6 are: 3365, 3465 (NH2), C 41,97 (41,02); H 3,52 (2,87);
–
–
N 9,79 (8,31). Selected IR data (cm‒1): 1598 (C
Nimine), 1232
–
(Mo N). TG: calcd. for MoO3, 36.24 %, found 37.41 %.
(C Ophenolate), 1129 (MeOH), 928, 897 (MoO22+), TG: calcd. for MoO3,
33.54 %, found 34.26 %, for MeOH calcd. 7.46 %, found 7.66 %.
Complex 2∙MeCN, [MoO2(L2)]2∙MeCN, Yellow-orange product.
Yield: 0.1064 g (87.8 %). Mass fraction of elements, w / %, calculated
(experimental) for C30H25Mo2N7O10, are: C, 42.33 (41.89); H, 2.79
(1.84); N, 10.58 (9.85). Selected IR data (cm‒1): 3331 (NH2), 1602
–
4.5. Catalysis: general procedure for the epoxidation of olefins
–
–
–
–
– –
), 1568 (C C), 1326 (C O), 1255 (C Ophenolate), 919, 910
(C
N
imine
2⁺
–
(MoO2 ), 879 (Mo N). TG: calcd. for MoO3, 34.47 %, found 35.25 %, for
MeCN calcd. 4.91 %, found 4.98 %.
20 mmol of olefin (2.204 g of cis-cyclooctene or 2.244 g of oct-1-ene)
and 0.1 g of acetophenone were stirred together. 0.25 mol % of Mo(VI)
(pre)catalyst was added in the mixture i.e. 0.05 mmol of the dinuclear
and mononuclear complex. The mixture was stirred and heated up to 80
◦C before adding 40 mmol of oxidant (protocols A-C). Protocol A: 5.48
mL of aqueous TBHP, protocol B: 3.48 mL of H2O2 and protocol C: 7.27
mL of TBHP in decane. All reactions were monitored for 5 h. At defined
times 0, 20, 50, 90, 150, 300 min, aliquots (≈0.1 mL) of the organic
phase were taken from the reaction mixture and diluted with Et2O.
Catalytic reactions were followed along the time through GC measure-
ments. In the reaction in which TBHP in decane was used as the oxidant,
Complex 2, [MoO2(L2)]2. Complex 2 was obtained after the heating
of complex 2∙MeCN at 120 ◦C for two hours.
Complex 3∙MeCN, [MoO2(L3)]2∙MeCN. Dark red product. Yield:
0,494 g (83 %). Mass fraction of elements, w / %, calculated (experi-
mental) for C30H25Mo2N7O10: C 43.13 (42.18); H 3.02 (2.06); N 11.74
(11.01). Selected IR data (cm‒1): 3311, 3196 (NH ), 1585 (C
N
imine),
–
–
2
1199 (C Ophenolate), 922, 890 (MoO22+), 949 (Mo-N). TG: calcd. for
MoO3, 34.47 %, found 35.87 %, for MeCN calcd. 4.91 %, found 4.35 %.
Complex 3, [MoO2(L3)]2. Complex 3 was obtained after the heating
–
10