Synthesis, characterization and catalytic activity of dioxidouranium(VI) complexes of ONNO tetradentate Mannich bases

Article abstract of DOI:10.1016/j.ica.2019.04.034

The reaction of dibasic tetradentate ONNO donor Mannich bases, derived from ethylenediamine and 2,4–di–tert–butylphenol (H₂L¹) (I), 2,4–di–methylphenol (H₂L²) (II), 2–tert–butyl–4–methylphenol (H₂L³) (III) and 2,4–di–chlorophenol (H₂L⁴) (IV), with U^VIO₂(MeCOO)₂·2H₂O in a 1:1 M ratio in refluxing MeOH gave the corresponding mononuclear trans-dioxidouranium(VI) complexes of the type trans-[U^VIO₂L(MeOH)] (H₂L = H₂L¹ to H₂L⁴) (1–4). The synthesized complexes are stable in air, reddish-brown in color and soluble in most solvents. These complexes are characterized by elemental analysis, various spectroscopic (FT-IR, UV/Vis, ¹H and ¹³C NMR) techniques and single-crystal X-ray analysis of 3 and 4. The complexes adopt distorted pentagonal bipyramidal geometry around the metal centre. The ligand acts as tetradentate, coordinating through two phenolato oxygen and two imino nitrogen atoms; two oxido groups are trans to each other. These complexes are used as catalysts to study the oxidative bromination of thymol and styrene. The catalytic oxidative bromination of thymol resulted in the formation of three products namely, 2-bromothymol, 4-bromothymol and 2,4-dibromothymol while oxidative bromination of styrene gave two products, 2-bromo-1-phenylethane-1-ol and 1-phenylethane-1,2-diol. In order to find out the optimized reaction conditions for the fixed concentration (10 mmol) of substrate, effects of different amounts of catalyst, KBr, HClO₄, and oxidant (H₂O₂) have been investigated. Under the optimized reaction conditions, all the complexes have shown good catalytic potentials for the oxidative bromination of substrates, establishing the functional similarity to vanadium dependent haloperoxidases. Changes in the UV–visible absorption spectra of dioxidouranium(VI) complexes upon addition of H₂O₂ suggest the formation of the corresponding oxidoperoxidouranium(VI) complexes.

Full text of DOI:10.1016/j.ica.2019.04.034

Accepted Manuscript
Research paper
Synthesis, characterization and catalytic activity of dioxidouranium(VI) com-
plexes of ONNO tetradentate Mannich bases
Mannar R. Maurya, Bekele Mengesha, Shailendra K. Maurya, Fernando
Avecilla
PII:
S0020-1693(18)31774-2
https://doi.org/10.1016/j.ica.2019.04.034
ICA 18879
DOI:
Reference:
Inorganica Chimica Acta
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24 November 2018
11 April 2019
15 April 2019
Please cite this article as: M.R. Maurya, B. Mengesha, S.K. Maurya, F. Avecilla, Synthesis, characterization and
catalytic activity of dioxidouranium(VI) complexes of ONNO tetradentate Mannich bases, Inorganica Chimica
Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.04.034
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Synthesis, characterization and catalytic activity of dioxidouranium(VI)
complexes of ONNO tetradentate Mannich bases
Mannar R. Mauryaa,*, Bekele Mengeshaa, Shailendra K. Mauryaa, Fernando Avecillab
aDepartment of Chemistry, Indian Institute of Technology Roorkee, Roorkee–247667, India. E–mail:
rkmanfcy@iitr.ac.in; Fax: +91 1332 273560; Tel: +91 1332 285327
https://www.iitr.ac.in/CY/rkmanfcy
bGrupo Xenomar, Centro de Investigacións Científicas Avanzadas (CICA), Departamento de
Química, Facultade de Ciencias, Universidade da Coruña, Campus de A Coruña, 15071 A
Coruña, Spain
Keywords: Dioxidouranium(VI) complexes; Mannich bases; Crystal structure; Catalytic
activity; Oxidative bromination; NMR spectroscopy.
Abstract
The reaction of dibasic tetradentate ONNO donor Mannich bases, derived from ethylenediamine
and 2,4–di–tert–butylphenol (H2L1) (I), 2,4–di–methylphenol (H2L2) (II), 2–tert–butyl–4–
methylphenol (H2L3) (III) and 2,4–di–chlorophenol (H2L4) (IV), with UVIO2(MeCOO)2·2H2O in
a 1:1 molar ratio in refluxing MeOH gave the corresponding mononuclear trans-
dioxidouranium(VI) complexes of the type trans-[UVIO2L(MeOH)] (H2L = H2L1 to H2L4) (1–4)
The synthesized complexes are stable in air, reddish-brown in color and soluble in most solvents.
There complexes are characterized by elemental analysis, various spectroscopic (FT-IR, UV/Vis,
1H and 13C NMR) techniques and single-crystal X-ray analysis of 3 and 4. The complexes adopt
distorted pentagonal bipyramidal geometry around the metal centre. The ligand acts as
tetradentate, coordinating through two phenolato oxygen and two imino nitrogen atoms; two
oxido groups are trans to each other. These complexes are used as catalysts to study the
1

oxidative bromination of thymol and styrene. The catalytic oxidative bromination of thymol
resulted in the formation of three products namely, 2-bromothymol, 4-bromothymol and 2,4-
dibromothymol while oxidative bromination of styrene gave two products, 2-bromo-1-
phenylethane-1-ol and 1-phenylethane-1,2-diol. In order to find out the optimized reaction
conditions for the fixed concentration (10 mmol) of substrate, effects of different amounts of
catalyst, KBr, HClO4, and oxidant (H2O2) have been investigated. Under the optimized reaction
conditions, all the complexes have shown good catalytic potentials for the oxidative bromination
of substrates, establishing the functional similarity to vanadium dependent haloperoxidases.
Changes in the UV-visible absorption spectra of dioxidouranium(VI) complexes upon addition
of H2O2 suggest the formation of the corresponding oxidoperoxidouranium(VI) complexes.
1. Introduction
Amongst the actinides, uranium can exist in five oxidation states, +2, +3, +4, +5 and +6
but only the +4 and +6 states are stable enough to be of practical importance. Uranium
complexes are generally dominated by the [UVIO2]2+ moiety in +6 oxidation state and forms
complexes very similar to group 6 transition metal analogues [MVIO2]2+ (M = Cr, Mo and W)
and even similar to [VO2]+. However, the basic difference between [MO2] 2+/[VO2]+ and
[UVIO2]2+ moieties is that former ones generally have cis-MO2 group while dioxido group in
uranyl ion in their complexes is essentially trans; the angle being close to 180o. Further,
depending upon the reaction conditions and ligands used the equatorial plane of uranyl
complexes can further extend the coordination number by four, five or six resulting in the
formation of complexes of varied geometries [1]. During past one decade, a good number of
papers on [UVIO2]2+- complexes of polydentate ligands have appeared [1-15] but the catalytically
potential of these complexes has been narrowly explored [16]. Such complexes are generally
associated with one solvent/neutral donor molecule in equatorial position which is flexible in
nature and may play an important role in catalytic reactions like vanadium, molybdenum and
tungsten complexes [17-24]. Adam in 2015 has reported dioxidouranium(VI) complexes
catalyzed oxidation of various alkenes using H2O2 and TBHP as oxidant [16] and showed that
these complexes can act as potential oxidation catalysts but oxidative halogenation of organic
substrates has only been reported by us very recently [25]. Such catalytic reaction is generally
2

observed by model vanadium complexes in the presence of oxidant, halide ion and acid, and
considered as a functional mimic of enzymes haloperoxidases [17-20]; a critical review on
sustainable bromination of organic compounds has been recently reported by Conte et. al. [26].
Herein we have now prepared and characterized dioxidouranium(VI) {trans-[UO2]2+} complexes
of ligands derived from Mannich bases of ethylenediamine and 2,4–substituted phenols (H2L1-4,
Scheme 1), and report our findings on the oxidative bromination of thymol and styrene in the
line of functional models of vanadium dependent haloperoxidases. Very recently, we reported
dioxidomolybdenum(VI) complexes of these ligands where they act as dibasic tetradentate,
coordinating through the two Ophenolate and two Namine atoms. These complexes catalyze oxygen
atom transfer (OAT) between benzoin and dimethyl sulfoxide (DMSO) in acetonitrile at 80 °C
and result in almost 99 % conversion in only 18 h of reaction time [27].
2. Experimental section
2.1. Materials and general methods
UVIO2(MeCOO)2·2H2O (Loba chemie, India), thymol, KBr (S.D. fine chemicals, India),
methanol (SRL, India), n-hexane, perchloric acid, 30% H2O2, and DMSO (Rankem, India) were
used as obtained. Other chemicals and solvents were of analytical reagent grade. Ligands I to IV
were prepared as reported in our previous paper [27].
Elemental (C, H and N) analysis of the complexes was carried out on an Elementar model
Vario–EI–III after drying the samples at 100 °C. IR spectra were recorded as KBr pellets on a
Nicolet 1100 FT–IR spectrometer. Electronic spectra of the complexes were recorded in MeCN
1
13
on a Shimadzu 2600 UV–Vis spectrophotometer. H and C NMR spectra were recorded in
CDCl3/DMSO-d6 on a JEOL ECX 400 MHz spectrometer. The catalytic activity of the metal
complexes were studied using Shimadzu 2010 gas chromatogram with an Rtx-1 capillary column
(30 m × 0.25 mm × 0.25 μm), and their % conversion and product selectivity were calculated
using peak area of substrate and respective products.
2.2. Preparation of complexes [UVIO2L1-4(MeOH)] (1 – 4)
A representative method for [UVIO2L1(MeOH)] (1) is given here. A solution of
UVIO2(MeCOO)2·2H2O (0.424 g, 1 mmol) in 20 mL MeOH was added to a stirred suspension of
ligand H2L1 (0.496 g, 1 mmol) ) in MeOH (100 mL) (1:1 molar ratio) and the resulting reaction
mixture was heated under reflux on a water bath for 10 h. During this period ligands slowly
3

dissolved and red-brown colored complex precipitated instead. After reducing the solvent
volume to ca. 40 mL and cooling to room temperature, the precipitated solid was collected by
filtration, washed with MeOH (2 × 5 mL) and dried under vacuum.
Complexes 2, 3, and 4 were prepared similarly using UVIO2(MeCOO)2·2H2O (0.424 g, 1.0
mmol) in 20 mL MeOH and respective ligands (1 mmol) in 100 mL MeOH. Slow evaporation of
methanolic solution of 3 produced single crystals suitable for X-ray study. Crystals of
[UVIO2L4(EtOH)] (now numbered 4a) were grown in EtOH by slow evaporation. All
analytical measurements were made after drying the metal complexes at 110 ˚C for 5 h.
Data for [UVIO2L1(MeOH)] (1). Yield: 0.605 g (76%). Anal. Calcd for C33H54N2O5U
(796.83 g mol−1): C, 49.74; H, 6.83; N 3.52. Found: C, 49.3; H, 7.0; N, 3.6%. λ[nm] (ɛ, litre
1
mole–1 cm–1): 242 (5.63 × 103), 281 (4.45 × 103 ), 394 (3.62 × 103), 474 (3.41 × 103). H NMR
(400 MHz, CDCl3): δ (ppm) = 7.33 (s, 2H), 6.86 (s, 2H) (aromatic), 2.51 (s, 2H, -NH), 3.87 (s,
13
2H), 2.93 (s, 2H) (-CH2-), 1.63 (s, 4H) (-CH2CH2-), 1.34 (s, 18H), 1.19 (s, 18H) (-CH3). C
NMR (400 MHz, DMSO-d6): δ (ppm) = 166.65, 138.16, 136.31, 128.97, 125.88, 124.24, 22.57,
122.33, 57.54, 52.84, 35.57, 33.88, 32.57, 31.04.
Data for [UVIO2L2(MeOH)] (2). Yield: 0.515 g (82.0%). Anal. Calcd for C21H30N2O5U
(628.51 g mol−1): C, 40.13; H, 4.81; N, 4.46. Found: C, 40.47; H, 4.65; N 4.55%. λ[nm] (ɛ, litre
1
mole–1 cm–1): 242 (6.76 × 103), 290 (4.31 × 103), 402 (3.5 × 103 ), 490 (3.82 × 103). H NMR
(400 MHz, CDCl3): δ (ppm) = 6.99 (s, 1H), 6.92 (s, 3H) (aromatic), 5.40 (s, 2H, -NH), 4.71-4.69
(dd, 2H), 4.18-4.15 (dd, 2H) (-CH2-), 3.90 (t, 2H), 3.70 (t, 2H) (-CH2CH2-), 3.25 (s, 3H) (CH3 of
13
MeOH), 2.32 (s, 3H), 2.12 (s, 3H) (CH3). C NMR (400 MHz, DMSO-d6): δ (ppm) = 165.88,
130.50, 127.78, 127.29, 126.55, 123.27, 56.30, 52.82, 20.47, 17.24.
Data for [UVIO2L3(MeOH)] (3). Yield: 565 g (79%). Anal. Calcd for C27H42N2O5U
(712.67 g mol−1): C, 45.50; H, 5.94; N, 3.93. Found: C, 45.2; H, 5.8; N, 4.0%. λ[nm] (ɛ, litre
1
mole–1 cm–1): 242 (broad) (5.4 × 103), 272 (5.95 × 103), 391 (3.08 × 103), 474 (2.3 × 103). H
NMR (400 MHz, CDCl3): δ (ppm) = 6.85 (s, 2H), 6.64 (s, 2H) (aromatic), 3.81 (s, 2H), 2.94 (s,
2H) (-CH2-), 3.25 (s, 3H)(CH3 of MeOH), 2.51 (s, -NH), 2.12 (s, 4H) (-CH2CH2-), 1.61s, 9H)
1.32 (s, 9H) (CH3). 13C NMR (400 MHz, DMSO-d6): δ (ppm) = 153.69, 135.49, 127.31, 126.84,
126.54, 122.33, 57.58, 56.82, 34.65, 34.36, 30.86, 29.59, 20.69.
4

Data for [UVIO2L4(MeOH)] (4). Yield: 0596 g (84%). Anal. Calcd for C17H18Cl4N2O5U
(710.17 g mol−1): C, 28.75; H, 2.55; N 3.94. (Found: C, 28.6; H, 2.4; N, 4.1%. λ[nm] (ɛ, litre
mole–1 cm–1): 241 (5.53 × 103 ), 273 (4.22 × 103), 374 (3.4 × 103), 466 (2.6 × 103). 1H NMR (400
MHz, CDCl3): δ (ppm) = 7.49 (s, 2H), 7.33 (s, 2H) (aromatic), 6.10 (s, 2H, -NH), 4.65 (dd, 2H)
(-CH2-), 4.36 (dd, 2H) (-CH2CH2-), 3.30 (s, 3H) (CH3 of MeOH). 13C NMR (400 MHz, DMSO-
d6): δ (ppm) = 163.14, 130.61, 127.58, 123.55, 117.60, 55.21, 52.55.
2.3. X-Ray crystal structure determination
Three-dimensional X-ray data were collected on a Bruker Kappa Apex CCD diffractometer at
room temperature for 3 and at 100(2) K for 4a, by the - scan method. Reflections were
measured from a hemisphere of data collected from frames, each of them covering 0.3º in . A
total of, 81578 for 3 and 87961 for 4a, reflections measured were corrected for Lorentz and
polarization effects and for absorption by multi-scan methods based on symmetry-equivalent and
repeated reflections. Of the total, 6254 for 3 and 8678 for 4a, independent reflections exceeded
the significance level (F/F) > 4.0. After data collection an empirical absorption correction
(SADABS) [28] was applied, and the structures were solved by direct methods and refined by
full matrix least-squares on F2 data using SHELX suite of programs [29] Refinements were done
with allowance for thermal anisotropy of all non-hydrogen atoms. In 3, hydrogen atoms were
included in calculated position and refined in the riding mode, except for O(1M), O(2M) and
N(1), which were located in difference Fourier map and fixed to the atoms. In 4a, hydrogen
atoms were included in calculated position and refined in the riding mode, except for O(1M),
O(2M), N(1), N(2) and N(4) which were located in difference Fourier map and fixed to the
atoms. Due to disorder around EtOH molecule bonded to U(2) atom in compound 4a, two
positions for carbon atoms of EtOH molecule were refined with anisotropic atomic displacement
parameters. The site occupancy factor was 0.66286 for C(3MA) and C(4MA). A final difference
Fourier map showed a high residual density outside: 3.250 and –1.428 e.Å–3 for 3 and 1.440 and
2
–2.417 e.Å–3 for 4a, next to the uranium atoms. A weighting scheme w = 1/[σ2(Fo ) + (0.036900
2
P)2 + 61.142097 P] for 3, and w = 1/[σ2(Fo ) + (0.000000 P)2 + 34.178295 P] for 4a, where P =
(|Fo|2 + 2|Fc|2)/3, were used in the latter stages of refinement. Further details of the crystal
structures determination are given in Table 1. CCDC 1876854 (for 3) and 1876855 (for 4a)
5

contain the supplementary crystallographic data for the structures reported in this paper. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at doi: $$$$$.
<<Table 1>>
2.4. Catalytic activity study
Note: HClO4 is explosive in nature, though we did not face any problem in handling it at lower
scale. However, a due precaution must be taken in its handling.
2.4.1. Oxidative bromination of thymol
Thymol (1.50 g, 10 mmol), 30% aqueous H2O2 (2.27 g, 20 mmol) and KBr (2.38 g, 20
mmol), were mixed in a flask containing 20 mL water and stirred at room temperature. The
catalyst (0.001 g, 1.6 × 10-3 mmol) and 70% HClO4 (10 mmol, 1.43 g) was then added to it and
the reaction mixture was stirred at room temperature for 2 h. A small aliquot at every 30 min was
withdrawn, extracted with n-hexane, dried over anhydrous Na2SO4 and analyzed quantitatively
by gas chromatograph on the basis of their relative peak area of the respective product. The
confirmation of products was carried out by GC-MS after their separations.
2.4.2. Oxidative bromination of styrene
Styrene (1.04 g, 10 mmol), 30% aqueous H2O2 (2.27 g, 20 mmol) and KBr (2.38 g, 20
mmol), were mixed in a flask containing 20 mL water and stirred at room temperature. The
catalyst (0.001 g, 1.6 × 10-3 mmol) and 70% HClO4 (20 mmol, 2.86 g in 2 equal portions, one at t
= 0 min and other at t = 30 min) was then added to it and the reaction mixture was stirred at
room temperature for 2 h. A small aliquot at every 30 min was withdrawn, extracted with n-
hexane, dried over anhydrous Na2SO4 and analyzed quantitatively by gas chromatograph as
mentioned above. The confirmation of products was carried out by GC-MS after their
separations.
3. Results and Discussion
Ligands I – IV (H2L1−4) were prepared by the condensation of ethylenediamine,
formaldehyde and 2,4–substituted phenols (1 : 2 : 2 molar ratio) in MeOH (Scheme 1, above)
6

(Yields: 1, 76%; II, 74%; III, 50% and IV, 62%) [27]. Reaction of these ligands with
UVIO2(MeCOO)2·2H2O in 1:1 molar ratio in MeOH (Scheme 1, bottom), results in the formation
of the corresponding dioxidouranium(VI) complexes, [UVIO2(L1−4)(MeOH)] (1–4) in good
yields. All complexes are air stable red-brown solids and soluble in common organic solvents
such as MeOH, CHCl3, MeCN, DMSO, DMF etc.
<<Scheme 1>>
3.1. Solid state characterization
ORTEP diagram for the complexes [UO2L3(MeOH)] (3) and [UO2L4(EtOH)] (4a) are
shown in Figs. 1 and 2, respectively and their crystal packing are presented in Figs. 3 and 4,
respectively. Selected bond distances and angles are given in Table 2. Both compounds are
mononuclear complexes, which crystallize in a monoclinic space group P21/n and present two
complexes in the asymmetric unit. The structures adopt a distorted pentagonal bipyramidal
geometry around of metal centre. The ligands act as tetradentate, coordinating through two
phenoxido oxygen and two amine nitrogen atoms. The amine nitrogen atoms present a distorted
sp3 hybridized bonding network. U centres complete the coordination sphere by bonding to two
Ooxido terminal oxygen atoms and one oxygen atom from solvent molecules (MeOH or EtOH).
The UVI=O bond lengths [1.769(8)-1.766(4) Å in compound 3 and 1.766(4)-1.796(4) in
compound 4a] are similar to other in the literature [15, 30] The two distances UVI–Ophenoxido
[2.215(8)-2.235(9) Å in compound 3 and 2.304(4)-2.205(4) Å in compound 4a] are shorter than
the UVI–Osolvent [2.585(8) Å in compound 3 and 2.455(4) Å in compound 4a]. The equatorial
plane is occupied by the Ophenoxido atoms, O(3) and O(4), by the Namine atoms, N(1) and N(2) and
by the oxygen atom (O1M) of MeOH or ETOH molecules. They are distorted respect to the
planarity, [mean deviation from the plane 0.0856(60) Å in compound 3 and 0.0956(29) Å in
compound 4a]. In an ideal pentagonal bipyramidal polyhedron the angle between adjacent atoms
of equatorial plane is 72º. The angles between adjacent atoms are in the range 68.9(4)º-77.1(3)º
in compound 3 and between 67.32(15)º-78.58(14)º in compound 4a (see Table 2). The terminal
oxido atoms occupy the axial sites. The angle between the plane containing the two terminal
oxido atoms and U(1) atoms with the equatorial planes are 89.97(31)º in 3 and 89.49(1.02)º in
4a. The crystal packing present hydrogen bonds between the electronegative atoms (see Table S1
7

of SI and Figs 3 and 4), which determine dimeric aggregates in antiparallel form. - Interactions
are not present in the structures.
<<Figures 1-4>> <<Table 2>>
3.2. Spectral studies
IR spectroscopic analyses of all the ligands and the uranium complexes were carried to
confirm the coordination modes of ligands. The IR spectra of all complexes exhibit one sharp
band around 850-868 cm–1 (Table S2 of SI), due to the asymmetric (ν3) stretching of trans-[UO2]
core [13, 31]. Coordination of phenolate oxygen and nitrogen functionalities could not be
ascertained unequivocally by IR spectral study because the spectra of the ligands as well as
complexes both exhibit ν(OH) and ν(NH) bands around 3400 and 3100 cm-1, respectively. The
former band may be only due to the coordinated MeOH. However, coordination of these
functionalities are well supported by single crystal X-ray study (vide supra). The characteristic
band due to methylene group appears in the spectra of the ligands as well as the complexes
around 2800–3000 cm–1.
Experimental section collects UV/Vis spectral data of trans–[UO2]2+ complexes recorded
in MeCN and Figs. S1 and S2 of SI) give detail of the spectral profiles of ligands and complexes,
respectively. The detail interpretation of spectral data of ligands is reported earlier [27]. UV-Vis
region of the spectra of complexes essentially show two bands which seem like split bands of
* transition. A medium intensity band at ca. 390 nm is assigned due to n* transition
while a low intensity band at ca. 470 nm is assigned due to the ligand to metal charge transfer
transition[14, 32].
1H NMR spectra of ligands and complexes recorded in CDCl3, presented in the
experimental section also supplement the coordinating modes of ligand to the metal complex.
Thus, the absence of the signal in complexes, that appears at δ = 10.25–10.73 ppm due to two
equivalent nature of phenolic –OH protons in ligands, indicates the coordination of the phenolic
oxygen after its deprotonation [27]. Signals due to methylene groups (connecting to –N and
aromatic ring) and –NH protons have no systematic trend but are observed in ligands as well as
in complexes. Protons of methyl group of MeOH appear at ca. 3.3 ppm. Aromatic protons of all
ligands and complexes and methyl protons of ligands I, II and III and their corresponding
complexes appear in the expected region with slight variations.
8

13
13
The C NMR data recorded in DMSO-d6 are listed in the experimental section; a C
NMR spectrum of complex 4 is presented here as a representative (Fig. S3 of SI). The
13
coordination–induced C NMR chemical shifts due to coordination of phenolic oxygens and
imino nitrogens further supplement the binding mode of the ligands. A significant shifts, Δ =
[(complex) – (ligand)] was observed for the signals of the carbon atoms in the vicinity of the
coordinating atoms (Table 3). Thus, the carbons bearing the phenolic oxygens (C1/C1′) with a Δ
value of –0.52 to 15.82 ppm, ethylene carbons (connecting to –NH and aromatic, C7/C7′) with a
Δ value of –2.06 to 6.19 ppm and ethylene carbons (-CH2CH2-, C8/C8′) with a Δ value of 1.05
to 6.83 ppm confirm the coordination of the corresponding accompanying functionalities to
uranium. Other signals in the spectra of complexes appear well within the expected region.
<<Table 3>>
3.3. Catalytic activity study
3.3.1. Oxidative bromination of thymol
The synthesized complexes 1, 2, 3 and 4 have been used as catalyst to study catalytic
oxidative bromination of thymol (a monoterpene) in the presence of KBr, 70% aqueous HClO4
and 30% H2O2 in aqueous solution under appropriate reaction conditions. All reactions were run
in triplicate and carried out in a 100 mL reaction flask in aqueous medium at room temperature.
The bromination reaction takes place on the most activated site as a result of electrophilic
aromatic substitution in the phenolic ring. Thus, the oxidative bromination of thymol led to the
formation of 2-bromothymol and 4- bromothymol while further bromination of these also gave
2,4- dibromothymol (Scheme 2). In fact, these products are usual and reported in the literature
[24, 33]. As observed in cis-[MO2]- complexes (M = V, Mo and W) [23,24,32,33], the reaction
of complexes with KBr in the presence of H2O2 and HClO4, catalytically generate HOBr and/or
Br+, Br2, Br3– which brominate thymol. A similar reaction may also be presumed by trans-
[UO2]2+- complexes.
<<Scheme 2>>
In order to obtain the best suited reaction conditions for the maximum oxidative
brominated products, reaction conditions were optimized considering 2 as a representative
9

catalyst. Thus, for 10 mmol of thymol (1.50 g), four different amounts of catalyst (0.0005, 0.001,
0.002, 0.003 g), three different amounts of 30% aqueous H2O2 (10, 20 and 30 mmol), three
different amounts of KBr (10, 20 and 30 mmol) and three different amounts of 70% aqueous
HClO4 (10, 20 and 30 mmol, added in three equal portions to the reaction mixture, first portion at
t = 0 and other two portions after every 30 min intervals) were taken in 20 mL water and the
reaction was carried out at room temperature for 2h. The pH noted just before adding HClO4 was
ca. 5.9 while after addition of first portion i.e. 10 mmol of HClO4, it was ca. 1.0. The pH slowly
increases to ca. 1.5 during the course of reaction but again it comes down to ca. 1.0 after addition
of next 10 mmol of HClO4. Thus, the slow decomposition of complex is very likely during the
course of reaction at such a low pH.
Details of all reaction conditions and the corresponding conversions of thymol are
summarized in Figs. S4-S7 and Table S3 (See SI). It may be concluded from the data presented
in Table S3 that the optimized reaction conditions (entry no. 10) for the best conversion of 10
mmol (1.50 g) of thymol with the catalyst 2 are those using 0.002 g catalyst, 30 mmol 30%
H2O2, 30 mmol KBr, and 30 mmol 70% HClO4. Under these conditions the obtained conversion
is 99% where the selectivity of different major products follows the order: 4-bromothymol (91%)
> 2,4-dibromothymol (5%) > 2-bromothymol (4%). However, reducing the amount of HClO4 to
10 mmol under above reaction conditions results in the reduction of conversion of thymol to
82% but the selectivity of the 2,4-dibromothymol improves to 31% and that of 4-bromothymol
shrinks to 60%. Thus, depends upon the requirement of the desired product(s), reaction
conditions may be tuned. Leaving the reaction for ca. 10h under the conditions of entry 10 of
Table S3, a quantitative conversion of thymol was observed with not much change in the
selectivity of products.
Other three catalysts i.e. 1, 3 and 4 were also tested under the above optimized reaction
conditions and the results are presented in Table 4. All the four complexes show comparable
catalytic activity between 97-99% (also see Fig. 5) along with high turnover frequency. Again 4-
bromothymol is highest in selectivity (ca. 90%). Blank reaction under above reaction conditions
gave only 32 % conversion (Table 4).
<<Table 4>> <<Figure 5>>
10

We have also studied the catalytic potential of complex 2 towards the oxidative
bromination of thymol in different biphasic solvent systems and their effect on the selectivity of
different products. The catalytic potential of 2 is almost the same in most mixed solvent systems
studied here (Table 5) but the selectivity of products slightly varies. The selectivity of 4-
bromothymol is as highest (95%) in CHCl3-H2O followed by 93% in hexane-H2O and 91% in
water. Thus, it seems that 4-bromothymol is the preferred product over 2,4-dibromothymol
possibly due to steric hindrance which does not favour further bromination of monobromothymol
in aprotic solvents (Table 4). The biphasic (H2O-CH3OH) blank reaction under above reaction
conditions gave almost similar conversion as obtained in single phasic system.
<<Table 5>>
These complexes show almost similar conversion as reported for [VVO(acac)(L)] [Hacac
= acetyl acetone, H2L = 6,6'-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-
butylphenol)] (ca. 99%) [20], Cs(H2O)[VVO2{3,5-bis(2-hydroxyphenyl)-1-phenyl-1,2,4-
triazole}] (99%) [5b], [K(H2O)2][VO2L] (H2L = ligands derived from 4,6-diacetyl resorcinol and
isonicotinoyl hydrazide, nicotinoyl hydrazide, benzoyl hydrazide or 2-furoyl hydrazide (90-98%)
[5c] and [MoVIO2L]2+ (H2L = Schiff base ligands derived from 8-formyl-7-hydroxy-4-
methylcoumarin and hydrazides (94-99%) [23], and little better than reported for [WVIO2]2+
complexes (91-96%) [24]. However, the selectivity of 4-bromothymol is relatively high (more
than 90%) for uranium complexes over other catalysts. In case of [UVIO2]2+ complexes, under
optimized reaction conditions higher amounts of KBr, H2O2 and HClO4 (3 equivalent each for 10
mmol of substrate) versus lower amounts of these reagents for vanadium, molybdenum and
tungsten complexes used and this might be responsible for higher amount of 4-bromothymol.
3.3.2. Oxidative bromination of Styrene
The synthesized complexes 1, 2, 3 and 4 have also been used as catalysts to study the
oxidative bromination of styrene. We have considered complex 2 again as a representative
catalyst and the oxidative bromination of styrene was carried out at room temperature in the
presence of KBr, 70% aqueous HClO4 and 30% aqueous H2O2 in water. This led to the formation
of (a) 2-bromo-1-phenylethane-1-ol and (b) 1-phenylethane-1,2-diol along with some minor
11

oxidized products (totaling ca. 1%), though literature reports the formation of one more product
i.e. 1,2-dibromo-1-phenylethane (Scheme 3) [21,33,34].
<<Scheme 3>>
Consequently, the reaction was investigated by changing different parameters that may
affect the rate of styrene bromination and the selectivity of different products. Thus, for 10 mmol
of styrene (1.04 g, 10 mmol), four different amounts of catalyst (0.0005, 0.001, 0.002, 0.003 g),
three different amounts of 30% aqueous H2O2 (10, 20 and 30 mmol), three different amounts of
KBr (10, 20 and 30 mmol) and three different amounts of 70% aqueous HClO4 (10, 20 and 30
mmol, added in three equal portions to the reaction mixture as mentioned above). Details of all
reaction conditions and the corresponding conversion of styrene are summarized in Table S4 and
Figs. S8-S11 of SI. From the data presented in table, it is clear that the optimized reaction
conditions (entry no. 9) for the maximum conversion of 10 mmol (1.04 g) of styrene are those
using 0.001 g (1.6 × 10–3 mmol) of catalyst, 2.26 g (20 mmol) of 30% H2O2, 3.57 g (30 mmol) of
KBr, and 2.86 g (20 mmol) of 70% HClO4. Under these conditions the obtained conversion is
99% where the selectivity of the two products follows the order: 1-phenylethane-1,2-diol (69%)
> 2-bromo-1-phenylethane-1-ol (31%). While the selectivity of products varies with the change
of reaction conditions, their order is maintained for all reaction conditions (Table S4). Again,
leaving the reaction for ca. 10h under the conditions of entry 9 of Table S4, a quantitative
conversion of styrene was observed.
Other three catalysts, i.e. 1, 3 and 4 were also tested under the above optimized reaction
conditions for the maximum conversion of styrene. The results are accessible in Fig. 6 and Table
6. It is clear from the data that all the four complexes show comparable catalytic activity (99%)
along with high turnover frequency showing no effect of the substituents on the benzene ring on
the catalytic activity and within the two products, the selectivity of 1-phenylethane-1,2-diol is
always higher (62-69%) than that of 2-bromo-1-phenylethane-1-ol (31-38%). Blank reaction
gave only 38% conversion
<<Figure 6>> <<Table 6>>
We have also studied the catalytic potential of complex 2 towards the oxidative
bromination of styrene in different biphasic solvent systems and their effect on the selectivity of
12

different products. Thus, catalytic potential of 2 is almost the same in all solvent systems (Table
S5 of SI), except in DCM-H2O where it is slightly lower. However, the selectivity of products
varies. The selectivity 1-phenylethane-1,2-diol follows the order: CH3CN-H2O ≈ Hexane-H2O
(80 %) > CHCl3-H2O (79%) > DCM-H2O (78%) > MeOH-H2O ≈ H2O (67%). Thus, it seems
that the expected product, 1,2-dibromo-1-phenylethane completely hydrolyses with water to 2-
bromo-1-phenylethane-1-ol which in turn further hydrolyses to some extent to 1-phenylethane-
1,2-diol.
Catalytic activity of these complexes towards oxidative bromination of styrene also
compares well with [VVO(OEt)(EtOH)(L)] (H2L = Schiff bases derived from 2-hydroxy-1-
acetonaphthone or 2-hydroxy-1-napthaldehyde and salicylhydrazide, benzoylhydrazide and
anthranylhydrazide) (96-97% conversion with 63-69% selectivity towards diol) and [MoVIO2(X-
Hsal-dahp)(H2O)] [(X-sal = salicylaldehyde and its derivatives, dahp = 1,3-diamino-2-
hydroxypropane) (97-99% conversion with 61% selectivity towards diol) [21, 34]. Their
catalytic activities are even better than recently reported for [UVIO2(pip-2,4-dmp)(MeOH)]
(92%) [25].
3.4. Reactivity
51
It was observed recently by V NMR study by some of us that the [VO(O2)(L)]-type
species is an active intermediate during catalytic study of oxidative bromination of thymol in the
presence of oxidant H2O2 [20]. Conte et al. have written in their review articles that an
oxidomonoperoxidovanadium(V) complex oxidizes the Br− ion to HOBr/Br2 in the presence of
acid [27,35,36]. The formations of similar monoperoxido species have also been suggested as an
active intermediate by molybdenum and tungsten complexes [23, 24]. In order to generate
information for such an intermediate in trans-[UO2]-complexes, we have also treated these
complexes with H2O2 and monitored the changes by UV–Vis spectroscopy. Thus, the sequential
addition of a 30% H2O2 solution (0.108 g, 0.95 mmol) dissolved in 5 mL of MeCN to a 25 mL of
9.97 × 10–2 M solution of [UVIO2L2(MeOH)] (2) in MeCN resulted in the spectral changes as
presented in Fig. 7. The band at 490 nm slowly disappears with a decrease in intensity while 402
nm band slowly becomes shoulder along with marginal increasing in intensity and shifting to 350
13

nm. The UV-band appearing at 290 nm shifts to 286 nm along with only marginally decrease in
intensity. These changes also generate two isosbestic points at 305 and 379 nm which suggest the
transformation of dioxidouranium(VI) complex to its oxidoperoxido form, based on the
knowledge gathered from vanadium, molybdenum and tungsten complexes treated with H2O2
under similar conditions [23, 24, 35]. Other complexes show almost similar spectral changes
upon treatment with H2O2 (Figs. S12-S14 of SI). These spectral changes are similar to
oxidoperoxido- vanadium, molybdenum- and tungsten complexes. However, the mechanism
responsible for the catalytic conversion of Br− ion to HOBr/Br2 may differ as proposed for
haloperoxidases [36, 37]. To gather information, we have recorded MALDI–TOF mass spectrum
of an in-situ generated intermediate after performing catalytic reaction for thymol under the
optimized reaction, as concluded in entry no. 10 of Table S3 i.e. complex 2 (0.002 g), thymol (10
mmol), 30% H2O2 (30 mmol), KBr (30 mmol) and 70% HClO4 (30 mmol), and extracting
reaction mixture in chloroform. An intense peak observed at m/z 954.38 corresponding to the
formula [UVIO(O2)2(L)(diBrth)] (cal. Mass = 954.5) (Fig. S15) possibly suggests the formation
of peroxido species along with the interaction of brominated thymol to uranium. However,
considering the overall coordination number and oxidation 6 of uranium in the above
intermediate, it is likely that tetradentate ligand is coordinated to uranium only though nitrogens
of the four coordinating atoms.
<<Figure 7>>
4. Conclusions
Four trans-dioxidouraniumnum(VI) complexes, trans-[UVIO2L1-4(MeOH)] (1–4) have been
prepared from potential dibasic tetradentate ONNO type Manisch base ligands derived from
ethylenediamine and 2,4–di–tert–butylphenol(H2L1) (I) and 2,4–di–methylphenol (H2L2) (II), ,
2–tert–butyl–4–methylphenol (H2L3) (III), and 2,4–di–chlorophenol (H2L4) (IV). These
complexes have been characterized by various spectroscopic techniques. Single crystal X-ray
study of complexes 3 and 4 confirms a distorted pentagonal bipyramidal geometry around
uranium where ligands act as tetradentate, coordinating through two phenoxido oxygen and two
amine nitrogen atoms. Oxidative bromination of thymol and styrene has successfully been
carried out using these complexes as catalyst, signifying them useful functional model of
14

vanadium dependent haloperoxidases. Under the optimized reaction conditions, all complexes
show comparable catalytic activity (97-99%) towards the oxidative bromination of thymol where
4-bromothymol has highest (89-91%) selectivity among the three products, 2-bromothymol, 4-
bromothymol and 2,4-dibromothymol formed. Similarly, a comparable catalytic conversion
(99%) of styrene with two products, 1-phenylethane-1,2-diol and 2-bromo-1-phenylethane-1-ol
were obtained using these complexes as catalyst where the selectivity of former one is always
higher (62-69%) than that of later one. In the presence of H2O2, the formation of corresponding
oxidoperoxidouranium(VI) complexes, similar to oxidoperoxido- vanadium, molybdenum- and
tungsten complexes, have also been demonstrated in solution but the mechanism possibly
follows the different pathway(s) for the catalytic conversion of Br− ion to HOBr/Br2 than that
proposed for haloperoxidases.
Acknowledgement
B. M. is thankful to the E.F.D.R. Ministry of Education, Addis Ababa, for granting scholarship.
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17

Schemes
R
R
R
OH
+ 2HCHO +
OH
O
HO
MeOH, reflux
H
H
2
H2N
R
NH2
N
N
R'
R'
R'
R
R
R
OH
OH
HO
H
O
O
UO2(MeCOO)2
MeOH, reflux
U
O
H
N
N
NH
NH
R'
R'
R'
R'
R
R′
Ligands
H2L1
Complexes
tert-butyl
Me
tert-butyl
Me
[UVIO2L1(MeOH)] (1)
[UVIO2L2(MeOH)] (2)
[UVIO2L3(MeOH)] (3)
[UVIO2L4(MeOH)] (4)
H2L2
tert-butyl
Cl
Me
H2L3
Cl
H2L4
Scheme 1. Synthetic routes for the preparations of ligands and corresponding
dioxidouranium(VI) complexes along with their structures.
Br
Br
Br
Br
Catalyst
+
+
H2O2, KBr, HClO4
OH
OH
Thymol
OH
OH
2,4-diBrth
2-Brth
4-Brth
Scheme 2. Products of the oxidative bromination of thymol. 2-Brth = 2-bromothymol, 4-Brth =
4-bromothymol and 2,4-dibrth = 2,4-dibromothymol.
18

HO
HO
Br
OH
Br
Br
Catalyst
+
+
H2O2, KBr, HClO4
(c)
(a)
(b)
Scheme 3. Expected products upon oxidative bromination of styrene: (a) 1,2–dibromo-1-
phenylethane, (b) 2-bromo-1-phenylethane-1-ol and (c) 1-phenylethane-1,2-diol. Only two
products (b and c) were obtained here under optimized reaction conditions.
19

Tables
Table 1
Crystal Data and Structure Refinement for [UO2L3(MeOH)] (3) and [UO2L4(EtOH)] (4a).
3
C27 H42 N2 O5 U
712.66
4a
C18 H20 Cl4 N2 O5 U
724.19
Formula
Formula weight
T, K
296(2)
100(2)
Wavelength, Å
Crystal system
Space group
a/Å
0.71073
Monoclinic
P21/n
0.71073
Monoclinic
P21/n
14.3077(12)
16.2307(13)
24.925(2)
92.714(4)
5781.7(8)
8
10.6553(6)
24.9128(15)
16.9982(10)
97.998(2)
4468.3(5)
8
b/Å
c/Å
β/º
V/Å3
Z
F000
2800
2736
Dcalc/g cm–3
/mm–1
1.637
2.153
5.651
7.776
1.50 to 28.62
0.1152
1.46 to 27.86
0.0715
/ (º)
Rint
Crystal size/ mm3
Goodness-of-fit on F2
R1[I>2(I)] a
wR2 (all data) b
0.21 × 0.16 × 0.05
1.062
0.38 × 0.28 × 0.23
1.119
0.0674
0.0374
0.1721
0.0805
Largest differences peak and hole (eÅ–3) 3.250 and –1.428
1.440 and –2.417
2 2
aR1 = Fo - Fc/Fo. bwR2 = [w(Fo2 -Fc2)2]/[w(Fo ) ]1/2
20

Table 2
Bond lengths [Å] and angles [o] for the compounds for [UO2L3(MeOH)] (3) and [UO2L4(EtOH)]
(4a).
Bond lengths
U(1)-O(1)
3
4a
1.769(8)
1.765(9)
2.215(8)
2.235(9)
2.585(8)
2.526(12)
2.579(10)
3
1.766(4)
1.796(4)
2.304(4)
2.205(4)
2.455(4)
2.623(5)
2.605(5)
4a
U(1)-O(2)
U(1)-O(3)
U(1)-O(4)
U(1)-O(1M)
U(1)-N(1)
U(1)-N(2)
Angles
O(2)-U(1)-O(1)
O(2)-U(1)-O(3)
O(1)-U(1)-O(3)
O(2)-U(1)-O(4)
O(1)-U(1)-O(4)
O(3)-U(1)-O(4)
O(2)-U(1)-O(1M)
O(1)-U(1)-O(1M)
O(3)-U(1)-O(1M)
O(4)-U(1)-O(1M)
O(2)-U(1)-N(2)
O(1)-U(1)-N(2)
O(3)-U(1)-N(2)
O(4)-U(1)-N(2)
O(1M)-U(1)-N(2)
O(2)-U(1)-N(1)
O(1)-U(1)-N(1)
O(3)-U(1)-N(1)
173.8(4)
94.2(3)
87.1(3)
89.7(4)
92.0(4)
151.8(3)
92.8(3)
93.4(4)
77.1(3)
74.8(3)
88.2(3)
86.7(3)
137.3(4)
70.7(4)
145.4(4)
89.7(4)
90.6(4)
69.0(3)
173.48(19)
89.41(17)
90.12(17)
89.82(17)
93.50(17)
153.53(14)
95.29(16)
90.88(16)
75.15(14)
78.58(14)
91.51(16)
84.42(16)
137.21(14)
69.26(15)
147.09(15)
84.46(17)
89.26(17)
70.21(14)
21

O(4)-U(1)-N(1)
O(1M)-U(1)-N(1)
N(2)-U(1)-N(1)
139.2(3)
145.6(3)
68.9(4)
135.99(15)
145.36(14)
67.32(15)
Table 3
13C NMR spectral data (δ in ppm) of ligands and complexes.
Cl
O
U
O
Cl
2'
OH
2
1
6
O
O
1'
3
4
3'
4'
Cl
HN
NH
Cl
6'
5
7
5'
7'
8
8'
Compound a
C1/C1′
C7/C7′
51.35
57.54
(6.19)
58.36
56.30,
(-2.06)
58.05
57.58
(-0.47)
52.31
55.21
(2.90)
C8/C8′
H2L1 (I)
150.83
166.65
(15.82)
153.13
165.88
(12.75)
154.21
153.69
(-0.52)
154.43
163.14
(9.11)
49.69
52.84
(3.15)
51.77
52.82
(1.05)
50.89
56.82
(5.93)
45.72
52.55
(6.83)
[UVIO2L1(MeOH)] (1)
(Δδ)
H2L2 (II)
[UVIO2L2(MeOH)] (2)
(Δδ)
H2L3 (III)
[UVIO2L3(MeOH)] (3)
(Δδ)
H2L4 (IV)
[UVIO2L4(MeOH)] (4)
(Δδ)
a Δδ = [δ (complex) - δ (free ligand)].
22

Table 4
Conversion, turn over frequency and selectivity parameters for various catalysts for the oxidative
bromination of thymol.
Catalyst
TOF [h-1]a Conv. [%] Selectivity [%]
2- Brth
5
4-Brth
2,4-diBrth
5
[UVIO2L1(MeOH)] (1)
[UVIO2L2(MeOH)] (2)
[UVIO2L3(MeOH)] (3)
[UVIO2L4(MeOH)] (4)
Without catalyst
1515
1547
1515
1531
97
99
97
98
32
90
91
90
4
4
6
4
5
6
5
6
89
90
aTOF values calculated at 2 h reaction time.
Table 5
Solvent effect on the oxidative bromination of thymol and selectivity of products catalysed by
complex 2.
Entry
Solvents
Conv. (%)
Selectivity (%)
2- Brth
4
4-Brth
91
2,4-diBrth
5
1
2
3
4
5
6
H2O
99
95
99
99
93
98
MeOH-H2O
DCM-H2O
MeCN-H2O
CHCl3-H2O
C6H14-H2O
3
5
5
2
3
90
88
90
95
93
7
7
5
3
4
23

Table 6
Conversion, turn over frequency and selectivity parameters for various catalysts for the oxidative
bromination of styrene.
Entry Catalyst
Conv. TOF
Selectivity (%)
–
1 a
(%)
(h )
2-bromo-1-
1-phenylethane-1,2-diol
phenylethane-1-ol
1
2
3
4
5
[UVIO2L1(MeOH)] (1) 99
[UVIO2L2(MeOH)] (2) 99
3094
3094
3094
3094
33
31
37
38
20
67
69
63
62
80
[UVIO2L3(MeOH)] (3) 99
[UVIO2L4(MeOH)] (4) 99
Without catalyst
38
a TOF values calculated at 2 h of reaction time.
Figures
Fig. 1. ORTEP for the compound [UO(L3(MeOH)] (3). All the non-hydrogen atoms are
presented by their 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
24

Fig. 2. ORTEP for the compound [UO2(L4)(EtOH)] (4a). All the non-hydrogen atoms are
presented by their 50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Fig. 3. Crystal packing in the compound [UO2L3(MeOH)] (3). Drawing was done in ball and
sticks with mercury 3.7 program.
25

Fig. 4. Crystal packing in the compound [UO2L4(EtOH)] (4a). Drawing was done in ball and
sticks with mercury 3.7 program.
100
[UVIO2L1(MeOH)] (1)
[UVIO2L2(MeOH)] (2)
[UVIO2L3(MeOH)] (3)
80
60
40
20
0
[UVIO2L4(MeOH)] (4)
Blank
0
20
40
60
80 100 120
Time/min
Fig. 5. Plot presenting conversion of thymol in the presence of different [UO2]2+ complexes and
without catalyst.
26

100
80
60
40
20
0
[UVIO2L1(MeOH)] (1)
[UVIO2L2(MeOH)] (2)
[UVIO2L3(MeOH)] (3)
[UVIO2L4(MeOH)] (4)
Blank
0
20
40
60
80 100 120
Time/min
Fig.6. Plot presenting conversion of styrene in the presence of different [UO2]2+ complexes.
3.5
290
3.0
2.5
[UVIO2(L2)(MeOH)] (2)
2.0
1.5
379
402
1.0
490
0.5
0.0
300
400
500
600
Wavelength nm
Fig. 7. Plots presenting the spectral changes during titration of [UVIO2L2(MeOH)] (2) with
H2O2. Spectra were obtained after successive addition of one drop portions of 30% H2O2 (0.108
g, 0.95 mmol) dissolved in 5 mL of MeCN to 25 mL of 9.97 × 10–2 M solution of 2 in MeCN.
27

Supporting Information
Synthesis, characterization and catalytic activity of dioxidouranium(VI)
complexes of ONNO tetradentate Mannich bases
M. R. Maurya, B. Mengesha, S. K. Maurya, F. Avecilla
Table S1
Hydrogen bonds in the compounds [UO2(L3)(MeOH)] (3) and [UO2(L4)(EtOH)] (4a).
D-H...A
compound
d(D-H) Ǻ d(H...A) Ǻ
d(D...A) Ǻ <(DHA) º
_____________________________________________________________________________
N(2)-H(2)...O(9)
O(1M)-H(1M)...O(3) (3)
N(2)-H(2)...O(9) (3)
(3)
0.91
0.85
0.91
0.85
2.49
2.16
2.49
2.10
3.290(13)
3.006(13)
3.290(13)
2.950(12)
2.760(6)
3.049(6)
2.645(6)
2.935(6)
147.4
179.5
147.4
179.6
148.8
151.0
152.7
140.1
O(2M)-H(2M)...O(6) (3)
O(1M)-H(1M)...O(8) (4a)
N(2)-H(2N)...O(5)#1 (4a)
O(2M)-H(2M)...O(3) (4a)
N(3)-H(3N)...O(2)#2 (4a)
0.85
2.00
0.93
0.91
1.11
2.21
1.80
1.99
______________________________________________________________________
Symmetry transformations used to generate equivalent atoms:
#1 x-1,y,z #2 x+1,y,z
28

Table S2
Selected IR data (in cm–1) for the ligands and complexes with tentative assignments.
Entry Compounds
ν(OH)
ν(N-H)
νasym(O=U=O)
1
2
3
4
5
6
7
8
H2L1 (I)
3440 (b)
3450 (b)
3270 (b)
3430 (b)
3425 (b)
3450 (b)
3440 (b)
3470 (b)
3130
[UVIO2L1(MeOH)] (1)
H2L2 (II)
2834, 3099
3000
850
-
[UVIO2L2(MeOH)] (2)
H2L3 (III)
2960, 3015
3050
868
-
[UVIO2L3(MeOH)] (3)
H2L4 (IV)
2865, 2953
2990, 3128
2899, 3066
868
[UVIO2L4(MeOH)] (4)
863
Table S3
Conversion of thymol (1.5 g, 0.010 mol) using [UVIO2(eda-2,4-dmp)(MeOH)] (2) as a catalyst,
turn over frequency, and selectivity of different products for 2 h of reaction time under different
reaction conditions.
Entry KBr
H2O2
HClO4
Catalyst
Conv. TOF Selectivity [%]
[%]
[h-1]
0.5 (8.0 × 10-4) 46
[g (mmol)] [g (mmol)] [g (mmol)] [mg (mmol)]
2-Brth 4-Brth 2,4-diBrth
1
1.19 (10)
1.19 (10)
1.19 (10)
1.19 (10)
1.19 (10)
1.19 (10)
2.38 (20)
3.57 (30)
3.57 (30)
3.57 (30)
3.57 (30)
1.13 (10)
1.13 (10)
1.13 (10)
1.13 (10)
2.26 (20)
3.39 (30)
3.39 (30)
3.39 (30)
3.39 (30)
3.39 (30)
3.39 (30)
1.43 (10)
1.43 (10)
1.43 (10)
1.43 (10)
1.43 (10)
1.43 (10)
1.43 (10)
1.43 (10)
2.86 (20)
4.29 (30)
4.29 (30)
2875 11
1875 13
1000 12
68
78
76
81
70
67
66
60
85
91
90
21
9
2
1 (1.6 × 10-3)
2 (3.2 × 10-3)
3 (4.8 × 10-3)
2 (3.2 × 10-3)
2 (3.2 × 10-3)
2 (3.2 × 10-3)
2 (3.2 ×10-3)
2 (3.2 × 10-3)
2 (3.2 × 10-3)
blank
60
64
43
66
67
75
82
91
99
32
3
12
7
4
448
12
5
1031 13
1046 12
1172 12
17
21
22
31
12
5
6
7
8
1281
1422
1547
9
3
4
4
9
10a
11
a
6
The optimized conditions mentioned here are the best among the different sets of reactions
carried out.
29