Seven-coordinated chiral uranyl(VI) salen complex as effective catalyst for C–H bond activation of dialkylanilines under visible light

Article abstract of DOI:10.1016/j.poly.2016.12.033

A new chiral uranyl(VI) complex incorporating a tetradentate salen ligand is reported. The synthesized uranyl complex is studied by microanalyses, spectroscopic and X-ray diffraction studies. The structural studies reveal a slightly distorted pentagonal bipyramid coordination environment around uranyl ion. Interestingly, the uranyl complex was found to be potential visible light active catalyst for C–H bond functionalization of dialkylanilines, and afforded moderate to excellent yield of corresponding α-aminonitriles when exposed to visible light for 8?h in the presence of NaCN and acetic acid as cyanide source, and H₂O₂as oxidant.

Full text of DOI:10.1016/j.poly.2016.12.033

Accepted Manuscript
Seven–Coordinated chiral uranyl(VI) salen complex as effective catalyst for C-
H bond activation of dialkylanilines under visible light
Mohammad Azam, Saud I Agata Al-Resayes Trzesowska-Kruszynska, Rafal
Kruszynski, Pawan Kumar, Suman L. Jain
PII:
S0277-5387(16)30684-2
DOI:
http://dx.doi.org/10.1016/j.poly.2016.12.033
POLY 12391
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
1 October 2016
21 December 2016
25 December 2016
Please cite this article as: M. Azam, S.I.A. Al-Resayes Trzesowska-Kruszynska, R. Kruszynski, P. Kumar, S.L.
Jain, Seven–Coordinated chiral uranyl(VI) salen complex as effective catalyst for C-H bond activation of
dialkylanilines under visible light, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.12.033
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Seven–Coordinated chiral uranyl(VI) salen complex as effective catalyst for
C-H bond activation of dialkylanilines under visible light
Mohammad Azam1*, Saud I Al-Resayes1 Agata Trzesowska-Kruszynska2 Rafal Kruszynski2,
,
,
Pawan Kumar3,4, Suman L. Jain3
1Department of Chemistry, College of Science, King Saud University, P. O. Box 2455, Riyadh
11451, KSA
2Institute of General and Ecological Chemistry, Lodz University of Technology, Zeromskiego
116, 90-924, Lodz, Poland
3CSIR Indian Institute of Petroleum, Hardwar road Mohkampur, Dehradun 248005 India.
4Academy of Scientific and Industrial Research (AcSIR), New Delhi 110001, India
For Correspondence:
Email: azam_res@yahoo.com Tel & Fax: +966-1-4675982
1

Abstract
A new chiral uranyl(VI) complex incorporating a tetradenate salen ligand is reported. The
synthesized uranyl complex is studied by microanalyses, spectroscopic and X–ray diffraction
studies. The structural studies reveal a slightly distorted pentagonal bipyramid coordination
environment around uranyl ion. Interestingly, the uranyl complex was found to be potential
visible light active catalyst for C–H bond functionalization of dialkylanilines, and afforded
moderate to excellent yield of corresponding α–aminonitriles when exposed to visible light for 8
hours in the presence of NaCN and acetic acid as cyanide source, and H2O2 as oxidant.
Keywords: Chiral uranyl(VI) salen complex; C-H bond activation; Photocatalysis; Visible light;
Dialkylanilines
2

Introduction
The chemistry of uranyl complexes, dominated by uranyl(VI) dication, has received remarkable
attraction over the years, and has found a variety of applications as molecular receptors in the
area of supramolecular chemistry, reactivity, coordination behavior and small molecule
activation [1-3]. Furthermore, Uranyl(VI) dication UO22+ is a chemically robust species owing to
strong covalent character of the axial U=O bond making its coordination chemistry quite
exclusively limited in the equatorial plane. Moreover, uranyl(VI) dication is essentially a linear
O=U=O species due to repulsion from its oxygen atoms forcing the coordinating ligand nearly
into a plane perpendicular to the axis of the ion [4-12].
Uranyl(VI) dication is surrounded by 4-6 donor atoms at equatorial positions and exists in
octahedral, pentagonal bipyramidal or hexagonal bipyramidal coordination environment [13].
Over the last few years, research on complexes featuring uranium is being explored in catalysis
i.e. hydrogenation of alkenes, oligomerization, dimerization, hydrosilation, and hydroamination
of terminal alkynes [14]. Interestingly, the large ionic radii and 5f valence orbitals provide
actinides characteristic properties useful for catalysis [15].
In the recent decades, visible light assisted photochemical transformations have become a
promising and useful tool in green organic synthesis as they use light which is an inexpensive,
nonpolluting and endlessly renewable energy source, and can be carried out at room temperature
under mild conditions [16].
2+
Bakac and his co-workers reported that the uranyl(VI) dication (UO2 ) has strong property to
photocatalytically oxidize organic substrates in air [17-19], and absorbs visible light to produce
2+
a strongly oxidizing excited state, *UO2 (E0 = 2.6 V), quenched by a variety of organic
substrates [20]. The resulting U(V) species can then be oxidized back to UO22+ in the presence of
3

2+
oxygen [18]. Furthermore, studies have shown that *UO2 reacts with alcohol by H-atom
abstraction to give UO2H+ and an organic radical [17]. In addition, low molecular weight alkanes
and alkenes react with *UO22+ by H-atom abstraction, electron transfer and oxygen atom transfer
[18, 21, 22]. Recent work identified a U(V) species as a quenching product in the absence of
oxygen, and suggested H-atom abstraction as the quenching mechanism [17].
We describe here the synthesis and structural study of a new chiral uranyl complex with a salen
ligand, 2, 2'-((1E,1'E)-(cyclohexane-1,2-diylbis(azanyl-ylidene))bis(methanylylidene))diphenol,
H2L [Fig 1], and assessing its application as a photocatalyst for C-H bond activation of
dialkylanilines to afford corresponding α-amino nitriles using NaCN/acetic acid as cyanide
source and hydrogen peroxide as oxidant in the presence of visible light (Scheme 1).
R1= H, -CH3, -OCH3, Cl, Br, R2 = -CH3, R3= H, -CH3
Scheme 1. C-H bond functionalization of dialkylanilines by uranyl(VI) complex in the presence
of visible light
Experimental
Materials and instrumentation
Dialkylanilines, n-tert-butyl amine (n-Bu)3N (90 %), sodium cyanide (99.98%), acetic acid
(≥99.7%), hydrogen peroxide (30 wt%), methanol HPLC grade (≥99.9%) were purchased from
Sigma-Aldrich and used as received without further purification. Ethanol, N,N-dimethyl
4

formamide, acetonitrile were obtained from various commercial sources and dried prior use by
standard methods and stored over 4 Ao molecular sieves. tert.-butyl-hydroperoxide was bought
from Sigma-Aldrich. Uranyl acetate was procured from commercial source, BDH chemical
company, England and used as received. Chiral salen ligand, H2L [Scheme 2] was prepared
following method reported in literature [23]. The microanalyses were performed on Elementar
1
13
Varrio elemental analyzer. H- and C-NMR spectra were collected from Jeol spectrometer at
400 MHz (1H-NMR) and 100 MHz (13C-NMR), respectively in CDCl3. FT-IR spectra were
collected using Perkin Elmer 621 spectrophotometer at 400-4000 cm-1 at pressed KBr discs.
Synthesis of chiral uranyl(VI) complex
To a stirred solution of chiral salen ligand (0.09 g, 28 mmol) in 15 ml ethanol, uranylacetate
dihydrate (0.118 g, 28 mmol) was added in equimolar ratio at room temperature in air. The
obtained resulting solution was left for stirring for 5 h. An orange color solution was obtained,
which was clarified by filtration to remove any turbidity. The orange colored filtrate solution was
kept for few days at room temperature. Good quality crystals were produced within few days
[Scheme 2].
Molecular Formula, C22H26N2O5U, Molecular Weight, 636.48, Color, Orange; Yield: 80 %,
Anal. Cal: C, 41.52; H,4.12; N, 4.40: Found: C, 41.50; H,4.07; N,4.38 % IR (KBr): 1629
ν(C=N), 1344 ν(Carom–O) , 908 asy(UO2), 850 sym(UO2), 1HNMR (CDCl3): δ (ppm) 7.24 (t, 2H,
J = 7.32 Hz, Ph-Hb), 7.13 (d, 2H, J = 7.32 Hz, Ph-Ha), 6.92 (d, 2H, J = 8.04, Ph-Hd), 6.78 (t, 2H,
J = 8.04 Hz, Ph-Hc), 3.18-3.28 (m, 2H, -N-CH-CH-N-), 1.73-1.89 (m, 4H, -CH2-CH2-CH2-CH2-
), 1.31-1.43 (m, 4H, -CH2-CH2-CH2-CH2-), 13CNMR (CDCl3): δ (ppm) 161.1 (-CH=N), 164.7 (-
C-O), 116.8-132.2 (Ar-C), 72.6 (N-CH-CH-N), 33.1 (-CH2-CHN-CHN-CH2-), 29.7 (-CH2-
CH2-CH2-CH2-)
5

UO2(OAc)2.2H2O
(0.118 g, 28 mmol)
N
N
N
O
N
O
a
c
UO2
OH
OH HO
alcohol
b
d
(a)
(b)
Scheme 2. Preparation of chiral uranyl(VI) complex; (a) Chiral salen ligand; (b) Chiral salen
uranyl(VI) complex
Crystal structure determination
The crystallographic data for the orange prsim crystal of chiral uranyl(V) complex were
collected using KM-4-CCD automatic diffractometer with graphite-monochromated CuKα (λ =
1.54178 Å) radiation with ω scan mode. Crystallographic details and refinement are given in
Table 1. Lorentz, polarization and numerical absorption [24] corrections were applied during the
data reduction [24]. All the non-hydrogen atoms were refined anisotropically on F2 using full-
matrix, least-squares methods. The SHELXS, SHELXL and SHELXTL [25] programs were
applied for all calculations. Selected bond lengths and angles are given in Table 2 and
intermolecular interactions are listed in Table 3.
Photocatalytic C–H bond activation of dialkylanilines
The reaction mixture of dialkylaniline (1 mmol), sodium cyanide (1.0 mmol, 49.0 mg), acetic
acid (1 mL), hydrogen peroxide (30 wt %; 1.5 mL) and uranyl(VI) complex (2 mol%, 12.7 mg)
were stirred continuously together in methanol (5 mL) in round bottom flask under the
irradiation visible light (20 Watt LED) having intensity at vessel 75 W m–2 at room temperature.
The progress of the reaction was monitored by running TLC on silica gel plate. After completion
6

of the reaction, the mixture was diluted with sodium bicarbonate (NaHCO3) solution and
extracted with ethyl acetate. The organic layer, so formed, was washed with brine water followed
by drying over anhydrous Na2SO4 under reduced pressure. The crude product so obtained was
purified with column chromatography over silica gel using ethyl acetate and hexane as eluent to
afford corresponding α–aminonitriles. The identification and quantitative determination of
product was done with GC–MS and obtained spectral data was matched with authentic samples
in GCMS library.
Results and Discussions
A perspective view of uranyl complex structure is shown in Fig 1. The asymmetric part of the
unit cell contains the two complex molecules and all atoms, except these ones belonging to
bridging part of the cyclohexane moiety are related by non-crystallographic pseudosymmetry
centre. Two pairs of carbon atoms (C8:C58, C13:C63) and neighbouring hydrogen atoms are not
interrelated by symmetry centre, due to chiral centres located at these C atoms. The other parts of
the complex molecules are mutually symmetry deepened. This affects the reflections statistics,
which show rather the centrosymmetric behaviour than the non-centrosymmetric one. This
situation is similar to those observed in crystal structure of triethylammonium bis(µ-2,2'-
(cyclohexane-1,2-diylbis(nitrilomethylylidene)) diphenolato )-trichloro-di-zinc [23], in which
two pairs of complex cations are related by pseudosymmetry. The all chiral centres (located at
C8, C13, C58 and C63 atoms) of the dominant crystal phase have the S configuration. The
symmetry independent complex molecules possess almost identical conformations
(Supplementary Information S1), and the root mean squares deviation of superimposed
molecules is 0.146(17) Å, respectively (the most distant equivalent atoms C17:C67 are separated
at 0.282(8) Å, respectively).
7

Fig 1. X-ray structure of uranyl complex plotted with 50% probability of displacement ellipsoids.
The hydrogen atoms were omitted for clarity.
8

Fig 2. The coordination polyhedral of uranyl complex
Uranium atom is seven-coordinated and form a pentagonal plane with two imine nitrogen atoms,
two alkoxide oxygen atoms and one hydroxyl oxygen atom from coordinated ethanol lying in the
equatorial plane, whereas two oxide oxygen atoms are located at axial position resulting a
slightly distorted pentagonal bipyramid coordination sphere [26] with the oxide oxygen atoms
positioned at the polyhedron apexes [Fig 2]
The 2-hydroxidebenzylideneamino moieties of both molecules of uranyl complex are slightly
distorted from planarity (the largest deviations from the respect weighted least squares planes are
0.147(78), 0.185(7), 0.155(7) and 0.146(6) Å, respectively for N1, N2, C57 and N 52 atoms).
The cyclohexane rings show slightly distorted chair conformation, with the Cs asymmetry
parameters [27] (placed on opposite ring atoms) in range 0.44-6.00, and C2 asymmetry
parameters [27] (placed on opposite ring bonds) in range 1.35-8.08. The asymmetric unit
9

molecules are assembled to the dimer via O—H•••O intermolecular hydrogen bonds [Table 3,
Fig. 3]. Additionally the dimer is internally linked by C—H•••O interaction, which can be
classified as weak hydrogen bond [28] [Table 3]. The neighbouring dimers are well separated
and they are not connected by any classical or non-classical interactions. The stacking
interactions are not observed within the crystal structure of uranyl complex (the aromatic rings
are surrounded by aliphatic moieties).
The U(1)-O(3) = 1.773 (8) A° and U(1)-O(4) = 1.816 (9) A° bond distances in the studied uranyl
complex are typical values reported for such type of uranyl complexes [29-31]. Furthermore,
O=U=O angle (177.6(4)o) indicate that uranyl moiety is slightly bent [1]. The U-Ophen [U(1)-O(1)
= 2.231(7)A° and U(1)-O(2): mean 2.315(6) A°] and U-Nimi U(1)-N(1) = 2.528(9) A° and
U(1)-N(2) = 2.564(9) A° bond distances are in close agreement reported for such type of uranyl
complexes [29-34]. Furthermore, the U–Ophen distance, [(U(1)–O(1) and U(1)–O(2)], is relatively
greater than the axial oxygens [(U(1) –O(3) and U(1)–O(4)] due to overlap between the 6d and
5f orbitals of the uranium atom and the three p orbitals (or two p and one hybrid sp orbitals) of
each axial oxygen giving the linear structure [29]. U-Oalc bond length [U(1)-O(5) = 2.429 (9) A°]
is comparable to U-Osolvent distances reported for mononuclear uranyl(VI) salen complexes [1].
Interestingly, U-Oalc bond distance is significantly lengthier than that of U-Ophe distances due to
the formation of centrosymmetric dimeric species, and steric overcrowding of equatorial
coordination spheres with solvent in the uranyl complex [29].
10

Fig 3. The part of molecular packing showing the hydrogen bonded dimer. The atoms are drawn
as spheres of arbitrary radii. The O—H•••O hydrogen bonds are indicated by dashed lines
IR spectra of uranyl complex (Supplementary Information S2) show various vibrations at 500–
4000 cm-1 consistent with the geometry revealed from X-ray analyses. A strong band due to
ν(C=N) vibrations is observed at 1629 cm-1 in uranyl complex [29]. The vibration due to
coordinated phenolic hydroxyl group at 1344 cm-1 is ascribed to ν(Carom–O) vibrations [31].
Bands at 908 cm-1 and 850 cm-1, attributed to the asymmetric and symmetric stretching vibration
of (O=U=O) group, respectively, indicate that the uranyl moiety is linear in the studied complex,
and these values assigned for the vibrations are in close agreement with the values already
reported in literature [1, 35]. Furthermore, there is no significant effect of coordinated ethanol on
asymmetric vibrations of uranyl moiety. However, low intensity vibrations of uranyl moiety due
11

to either asymmetric transition or symmetric vibrations which are in centosymetric structure are
IR inactive [36].
1H-NMR spectrum of uranyl complex shows (Supplementary Information S3) two sets of signals
corresponding to aliphatic and aromatic protons. A singlet for azomethine proton appears at 8.21
ppm. The cyclohexane bridge protons appear as multiplets at 3.18-3.28 (m, 2H, -N-CH-CH-N-)
in the complex due to the diastereotopic coupling, while the chemical shifts for cyclohexane ring
1
protons were observed at 1.39-1.87 ppm (m, 8H, cyclohexane). Further support for H-NMR
13
spectrum comes from C-NMR spectral findings showing a sharp signal due to azomethine
carbon at 161. 1 ppm, whereas the rest of signals were found at their positions expected.
(Supplementary Information S4).
C–H Bond Activation
The synthesized uranyl complex was tested for C–H bond activation of dialkylanilines using in
situ generated HCN from NaCN/AcOH as cyanide source and hydrogen peroxide as oxidant
under visible light irradiation in methanol. The pKa values for AcOH/ACO- and for HCN/CN- is
4.75 and 9.21 respectively; hence the reaction between NaCN and AcOH will provide HCN in
situ during the reaction. The source of visible light was 20 Watt LED light which has most of the
emission in visible region (λ >400 nm). At first, N,N–dimethylaniline was chosen as
representative substrate for optimization studies by changing the reaction parameters. The
reaction did not occur in the absence of uranyl complex photocatalyst even after prolonged
irradiation time under identical conditions (Table 4, entry 1). However, in the presence of uranyl
photocatalyst under similar conditions, the reaction was completed in 8h and afforded 97%
isolated yield of the corresponding α–aminonitrile (Table 4, entry 2). In order to confirm the
superiority of the uranyl complex, the reaction was carried out using uranium acetate as
12

photocatalyst under otherwise identical conditions (Table 4, entry 3). The reaction was found to
be very slow and yielded only trace amount of the desired product. To confirm the effect of
visible light, the reaction was performed using uranyl complex as photocatalyst in dark, after 24
h, only trace of α-aminonitrile could be isolated which confirmed that visible light irradiation is
essential to provide activation energy for the reaction (Table 4, entry 4). Similarly, the presence
of acetic acid was found to be essential and in its absence, no reaction occurred (Table 4, entry
5). Furthermore, among the various solvents such as ethanol, water, dimethylformamide,
acetonitrile and methanol studied, methanol was found to be promising and afforded highest
product yield under described reaction conditions (Table 4, entry 2, 6–8). Similarly, no reaction
was occurred in the absence of hydrogen peroxide (Table 4, entry 9), however the use of other
oxidants such as molecular oxygen and tert-butyl hydroperoxide (TBHP) afforded poor product
yield (Table 4, entry 10–11). Further, we generalized the reaction to a number of substituted
dialkylanilines under described optimized reaction conditions [Table 5]. In all cases, the reaction
products were identified by comparing their GC–MS with authentic ones. The dialkylanilines
bearing electron donating groups were found to be more active in comparison to those having
electrons withdrawing groups. For example, –CH3, –OCH3 groups substituted dialkylanilines
afforded higher product yield in the range of 94-98% (Table 5, entry 2–4), whereas substrates
having –Cl, –Br groups afforded only 82, 84% yield, respectively (Table 5, entry 5-8). Similarly,
the substrates containing electron donating groups at p–position of aromatic ring were found to
be more reactive (Table 5, entry 2,4) than m–substituted substrates (Table 5, entry 3). Aliphatic
tertiary amines such as n-tert-butyl amine (n–Bu)3N did not give any product under the described
reaction conditions (Table 5, entry 9).
13

Although the exact mechanism of the reaction is known at this stage, however the mechanism for
ruthenium catalyzed oxidative cyanation of tertiary amines is very well explained by Murahashi
et al in the literature [37]. In analogy to the Murahashi mechanism and existing photocatalytic
oxidation with uranyl complexes report [38], a plausible mechanism for the photocatalytic C–H
activation of dialkylanilines with uranyl complex is shown in Scheme 3. After absorption of
visible light, uranyl complex gets excited and reacts with dialkylaniline to abstract H–atom from
α–carbon of dialkylanilines to give a radical intermediate coordinated with complex [17]. This
radical undergoes one electron transfer from amine to uranium complex to form UO2(V)+1 cation
intermediate, which subsequently reacts with hydrogen peroxide to give an intermediate having
UO2(VI)+2 cation. Finally, hydrogen cyanide (HCN) generated in situ from the reaction of
NaCN/acetic acid interacts with uranyl peroxo intermediate and provide cyanide ion which
undergoes nucleophilic attack on the iminium ion intermediate gives the corresponding α–
aminonitrile, water, and the uranyl complex completing the catalytic cycle (Scheme 3).
14

C R3
H
+
O U O H
R1R2N-CH R3
C R3
H
O U O H +
H
2+
*
O U
O
H2O2
2+
H2O
O
O U
R3
C
H
R1R2N-CH R3
CN
2+
OOH
O U
R3
C
H
C R3
H
H+
H2O
HCN
2+
AcOH + NaCN
CN
O OH
H+
O U
CN
Scheme 2: Plausible mechanism of visible light driven C–H bond functionalization of
dialkylanilines by chiral uranyl complex.
Supplementary Data: Tables of crystal data and structure refinement, anisotropic displacement
coefficients, atomic coordinates and equivalent isotropic displacement parameters for non–
hydrogen atoms, H–atom coordinates and isotropic displacement parameters, bond lengths and
interbond angles have been deposited with the Cambridge Crystallographic Data Centre under
No. CCDC1442015.
Acknowledgements:
The authors would like to extend their sincere appreciation to the Deanship of Scientific
Research at king Saud University for funding this work through Research Group number (RG –
1436–003). PK and SLJ are thankful to Director IIP for providing permission to publish these
finding.
15

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18

Table 1. Crystal and structure refinement data of uranyl complex
Compound
Uranyl complex
C22H26N2O5U
Empirical formula
Formula weight
636.48
Crystal system, space group
Unit cell dimensions [Å, °]
monoclinic, P21 (No. 4)
a = 10.373(2)
b = 9.6822(19)
c = 22.267(5)
β
= 96.73(3)
Volume [Å3]
2221.0(8)
4, 1.903
20.866
1216
Z, Calculated density [Mg/m3]
Absorption coefficient [mm-1]
F(000)
Crystal size [mm]
0.108, 0.106, 0.101
4.00 to 72.42
θ
range for data collection [°]
Index ranges
-12≤h≤12, -11≤k≤11, -27≤1≤27
Reflections collected / unique
Completeness [%]
22348 / 7956 [R(int) = 0.0460]
99.6 (to
θ = 67°)
Min. and max. transmission
Data / restraints / parameters
Goodness-of-fit on F2
0.116, 0.172
7956 / 1$ / 544
1.066
R1 = 0.0498, wR2 = 0.1304
R1 = 0.0499, wR2 = 0.1306
5.095, -5.060
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff. peak and hole [e•Å-3]
19

Table 2. Selected structural data of uranyl complex [Å, °].
U1—O3
U1—O4
U1—O1
U1—O2
U1—O5
U1—N1
U1—N2
1.773(8)
1.816(9)
2.231(7)
2.315(6)
2.429(9)
2.528(9)
2.564(9)
U51—O54
U51—O53
U51—O52
U51—O51
U51—O55
U51—N51
U51—N52
1.770(8)
1.799(7)
2.238(6)
2.299(6)
2.464(8)
2.536(8)
2.571(8)
O3—U1—O4 177.6(4)
O3—U1—O1 86.4(3)
O4—U1—O1 94.9(3)
O3—U1—O2 88.6(3)
O4—U1—O2 91.0(3)
O1—U1—O2 157.1(3)
O3—U1—O5 96.2(3)
O4—U1—O5 86.0(3)
O1—U1—O5 80.5(3)
O2—U1—O5 77.8(3)
O3—U1—N1 92.7(3)
O4—U1—N1 85.8(3)
O1—U1—N1 70.2(3)
O2—U1—N1 132.5(3)
O5—U1—N1 148.7(3)
O3—U1—N2 85.0(3)
O4—U1—N2 92.6(3)
O1—U1—N2 132.7(3)
O2—U1—N2 69.0(3)
O5—U1—N2 146.8(3)
N1—U1—N2 63.9(3)
O54—U51—O53
O54—U51—O52
O53—U51—O52
O54—U51—O51
O53—U51—O51
O52—U51—O51
O54—U51—O55
O53—U51—O55
O52—U51—O55
O51—U51—O55
O54—U51—N51
O53—U51—N51
O52—U51—N51
O51—U51—N51
O55—U51—N51
O54—U51—N52
O53—U51—N52
O52—U51—N52
O51—U51—N52
O55—U51—N52
N51—U51—N52
177.4(4)
92.5(3)
88.6(3)
92.2(3)
87.8(3)
154.7(3)
86.0(3)
96.5(3)
79.0(2)
76.5(2)
87.4(3)
90.1(3)
135.3(2)
69.8(2)
145.3(2)
91.4(3)
86.7(3)
71.7(3)
133.0(2)
150.5(2)
63.7(3)
Table 3. Hydrogen bonds geometry of uranyl complex [Å, °].
____________________________________________________________________________
D—H•••A
d(D-H)
d(H•••A) d(D•••A)
<(DHA)
____________________________________________________________________________
O5—H5O•••O51
O55—H55O•••O2
C21—H21A•••O54
0.99
0.84
0.99
1.59
1.81
2.33
2.577(10)
2.594(10)
3.261(17)
172.3
155.6
155.7
____________________________________________________________________________
20

Table 4. Results of optimization experiments.a
Entry
Solvent
Oxidant
Time (h)
Yield
(%)b
TOF
(h-1)
1c
2
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
C2H5OH
H2O
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
-
24
8
-
97
trace
-
-
12.1
-
3
8
4d
5e
6
24
8
-
-
-
8
92
65
55
72
12
48
84
11.5
8.1
6.8
9
7
8
8
CH3CN
DMF
8
9
8
10
11f
12
CH3OH
CH3OH
CH3OH
18
12
12
0.6
4.0
7.0
O2
TBHPg
aReaction conditions: N,N-dimethylaniline (1 mmol, 121.19 mg), photocatalyst (2 mol%,
12.7 mg), NaCN (1.0 mmol, 49.0 mg), acetic acid (1.0 mL), oxidant (1.5 mL), solvent (5
b
c
d
e
mL); Isolated yield; without Uranium catalyst, In dark, In the absence of acetic acid;
fusing oxygen balloon; gTBHP: tert-Butyl hydroperoxide.
21

Table 5. Uranyl complex catalyzed photochemical C-H activation of tertiary amines.a
Time
(h)
Yield
(%)b
TOF
(h-1)
Entry
Reactant
Product
N
N
N
1
2
3
8.0
7.5
7.0
97
98
93
12.1
13.0
13.3
CN
N
N
CN
CN
N
O
O
O
N
O
N
4
5
6
7
7.0
8.0
8.0
8.0
94
82
85
84
13.4
10.2
10.6
10.5
CN
N
N
CN
Cl
Cl
Cl
Cl
N
N
CN
N
N
CN
Br
Br
Br
Br
N
N
8
9
8.0
88
-
11.0
-
CN
-
24.0
(n-Bu)3N
aReaction conditions: Dialkylaniline substarte (1 mmol), uranyl complex (2 mol%, 12.7
mg), NaCN (1.0 mmol, 49.0 mg), acetic acid (1.0 mL), H2O2 (1.5 mL), methanol (5 mL),
bIsolated yield.
22

A new chiral uranyl(VI) salen complex reported. The complex is seven-coordinated with slightly
distorted pentagonal bipyramid coordination environment. The uranyl complex proved to be
potential visible light active catalyst for C-H bond functionalization of tertiary amines.
23