Uranium complexes of cyclic O,O-bidentate ligands with the P-N-P backbone

Article abstract of DOI:10.1016/j.ica.2011.04.007

The formation of uranium complexes of novel ligands belonging to phosphorylated 2-oxo-1,2-azaphospholane series, namely 2-ethoxy-1- diethoxyphosphoryl-2-oxo-1,2λ⁵-azaphospholane (1a) and both individual ^R,^R- and ^R,^S- diastereomers of the related 2-oxo-2-phenyl-1,2λ⁵- azaphospholanes 1b,c with different surrounding at the exocyclic phosphorus atom, has been studied. The structures of the complexes of ML composition obtained in the reaction with uranyl nitrate in 1:1 ratio were found to depend on the difference in donor properties of the oxygen atom of endo- and exocyclic phosphoryl groups. The ligand 1a possessing the greater difference, serves as O-monodentate one with metal-oxygen bonding via the endocyclic PO function while both isomers of 1b,c coordinate to uranyl cation in a O,O-bidentate fashion. In solutions the ML complexes reacted with air oxygen to afford (μ₂-peroxo)-bridged uranium complexes [{UO₂(L)NO ₃}₂(μ₂-O₂)] which structures were confirmed by X-ray crystallography data.

Full text of DOI:10.1016/j.ica.2011.04.007

Inorganica Chimica Acta 373 (2011) 130–136
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Inorganica Chimica Acta
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Uranium complexes of cyclic O,O-bidentate ligands with the P–N–P backbone
Inga M. Aladzheva, Olga V. Bykhovskaya, Yulia V. Nelyubina, Zinaida S. Klemenkova, Pavel V. Petrovskii,
⇑
Irina L. Odinets
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow 119991, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
The formation of uranium complexes of novel ligands belonging to phosphorylated 2-oxo-1,2-azaphos-
pholane series, namely 2-ethoxy-1-diethoxyphosphoryl-2-oxo-1,2k5-azaphospholane (1a) and both indi-
vidual R⁄,R⁄- and R⁄,S⁄-diastereomers of the related 2-oxo-2-phenyl-1,2k5-azaphospholanes 1b,c with
different surrounding at the exocyclic phosphorus atom, has been studied. The structures of the com-
plexes of ML composition obtained in the reaction with uranyl nitrate in 1:1 ratio were found to depend
on the difference in donor properties of the oxygen atom of endo- and exocyclic phosphoryl groups. The
ligand 1a possessing the greater difference, serves as O-monodentate one with metal–oxygen bonding via
the endocyclic P@O function while both isomers of 1b,c coordinate to uranyl cation in a O,O-bidentate
Received 28 December 2010
Received in revised form 14 March 2011
Accepted 4 April 2011
Available online 15 April 2011
Keywords:
Uranium complexes
1-Phosphoryl-2-oxo-1,2k5-azaphospholanes
Diastereomers
fashion. In solutions the ML complexes reacted with air oxygen to afford (l2-peroxo)-bridged uranium
complexes [{UO2(L)NO3}2(
l
2-O2)] which structures were confirmed by X-ray crystallography data.
X-ray crystallography
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
for photonic devices and sensors, NMR shift reagents for carboxylic
acids, phenols and carboxylates or even biologically active
compounds [6]. It is worth noting that all metal complexes formed
by the above mentioned P–N–P ligands were derived from the
linear compounds whereas the cyclic ones are advantageous for
selectivity over the complex formation owing to increased rigidity
and modification in the electronic effects and may provide the
other coordination pattern [7]. Recently, we have developed the
facile and general cascade synthesis of phosphoryl substituted
2-oxo-1,2-azaphospholanes, i.e., the first cyclic ligand systems
with the P–N–P backbone [8]. In order to understand the impact
of adding the cyclic skeleton to the ligand backbone which pro-
vides one endocyclic and one exocyclic phosphorus atoms differing
in electronic and steric properties, it seems reasonable to estimate
and compare the coordination behavior of these cyclic ligands with
that for the known acyclic analogs.
In the present study, we report the complexing features of two
recently developed ligands [8] and a new one belonging to the
above family of the cyclic P–N–P ligands towards uranyl cation,
i.e., UO22+, known to be the most stable form of uranium existing
in the liquid acidic radioactive wastes [9]. Noteworthy, in the case
of the ligands with chiral phosphorus atoms pure diastereomers
were used. The choice of uranium as a metal was dictated by a
few basic motives, namely, a desire to explore the fundamental as-
pects of 5f-elements reactivity and coordination behavior, under-
stand the bonding interactions between the metal center and the
particular ligand as well as the fact that a number of uranium-
containing complexes possess optical [10] and magnetic [11] prop-
erties and have been shown to be useful in such applications as
The rapid development of coordination chemistry of f-elements,
i.e., lanthanides and actinides, is connected with complementary
fundamental and applied investigations and it is difficult to say
in which particular area – coordination chemistry or material sci-
ence – the most impressed results were achieved. The complexes
of f-elements attract considerable attention due to their unique
luminescent and magnetic properties defining their relevance to
luminescent systems with long lifetimes, photostability, and line-
like emission bands [1], diagnostic tools in biological sciences,
e.g., markers for immunofluorescent assays or paramagnetic con-
trast agents in magnetic resonance imaging [1c,f,2], second-order
nonlinear optical (NLO) chromophores [3] as well as practical
reprocessing of nuclear wastes [4].
Due to the highly oxophylic nature of f-elements they interact
strongly with phosphoryl donors forming stable complexes and
various monodentate and bidentate organophosphorus com-
pounds found application for extraction and separation of these
elements [5]. Among the bidentate ligands, imidodiphosphorus
derivatives, bearing flexible (X)P–N–P(Y) skeleton and displaying
a broad diversity of coordination pattern in neutral or deproto-
nated form with a variety of metals, are of undoubted interest
due to potential industrial uses in metal extraction or application
of the complexes as catalytic systems, new luminescent materials
⇑
Corresponding author. Tel.: +7 499 135 9356.
E-mail address: odinets@ineos.ac.ru (I.L. Odinets).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.04.007

I.M. Aladzheva et al. / Inorganica Chimica Acta 373 (2011) 130–136
131
2
catalysis, anion and neutral molecule sensing, and small molecule
activation [12].
CDCl3): d = 1.93 (d, JPH = 18.9 Hz, 3H, CH3), 2.04–2.54 (m, 4H,
PCH2CH2), 3.53–3.68, 3.90–4.05 (2 m, 1H + 1H, NCH2), 7.19–7.66
(m, 10H, 2 ꢂ C6H5). 1H NMR (400 MHz, CD3NO2): d = 2.11 (d,
2JPH = 14.2 Hz, 3H, CH3), 2.50–2.75 (m, 4H, PCH2CH2), 3.65–3.75,
4.00–4.11 (2 m, 1H + 1H, NCH2), 7.60–7.88, 7.89–7.97, 7.98–8.08,
8.14–8.25 (4 m, 10H, 2 ꢂ C6H5). 13C NMR (100 MHz, CDCl3):
2. Experimental
2.1. Materials and methods
1
2
d = 15.6 (d, JPC = 89.5 Hz, CH3), 22.4 (d, JPC = 7.0 Hz, PCH2CH2),
29.4 (dd, JPC = 88.4 Hz, JPC = 3.3 Hz, PCH2), 47.5 (d, JPC = 13.9 Hz,
1
3
2
The NMR spectra were recorded on a Bruker AMX-400 instru-
ment in CDCl3, CD3CN, and CD3NO2 solutions. The chemical shifts
(d) were internally referenced by the residual solvent signals rela-
3
3
NCH2), 127.8 (d, JPC = 13.1 Hz, Cm), 128.1 (d, JPC = 13.1 Hz, Cm),
2
2
129.9 (Ci), 130.9 (d, JPC = 10.6 Hz, Co), 131.2 (d, JPC = 10.6 Hz, Co),
4
4
tive to tetramethylsilane (1H and 13C) or externally to H3PO4 31P).
(
131.7 (d, JPC = 2.9 Hz, Cp), 131.8 (d, JPC = 2.9 Hz, Cp), 132.2 (d,
1JPC = 122.5 Hz, Ci). 31P NMR (162 MHz, CDCl3): d = 30.7 (d,
The 13C NMR spectra were registered using the JMODECHO mode;
the signals for the C atoms bearing odd and even numbers of
protons have opposite polarities. IR spectra were recorded on a
2JPP = 5.8 Hz), 45.9 (d, JPP = 4.4 Hz). 31P NMR (162 MHz, CD3NO2):
2
2
2
d = 31.5 (d, JPP = 3.7 Hz), 47.5 (d, JPP = 3.7 Hz).
Magna-IR 750 FTIR-spectrometer (Nicolet Co., resolution 2 cmꢀ1
,
2.3. Synthesis of complexes
scan number 128, KBr pellets or nujol). Melting points were deter-
mined with an Electrothermal IA9100 Digital Melting Point
Apparatus and were uncorrected. Ph(EtO)PCl was obtained via
the known procedure [13], other reagents were used as purchased
without further purification (Acros).
2.3.1. [UO2(1a)(NO3)2](2)
A solution of UO2(NO3)2ꢁ6H2O (0.260 g, 0.517 mmol) in ethanol
(3 mL) was added dropwise to a solution of the ligand 1a (0.184 g,
0.646 mmol) in the same solvent (2 mL) at 20 °C. In 3 h at 20 °C, the
mixture was concentrated to ca.1 mL in vacuo and then diethyl
ether (2 mL) was added and the mixture was kept overnight at
20 °C. The precipitated yellow solid product was filtered off,
washed with diethyl ether and dried in vacuo. Yield: 0.220 g
(63%). Mp 135.5–142.5 °C (ethanol-diethyl ether). Anal. Calc. for
C9H21N3O13P2U: C, 15.90; H, 3.09; N, 6.18; P, 9.13. Found: C,
2.2. Synthesis of the ligands
The known 2-oxo-2-phenyl-1,2-azaphospholanes 1a,b were ob-
tained via the reported procedure developed by us recently [8].
2.2.1. 1-[Methyl(phenyl)phosphoryl]-2-oxo-2-phenyl-1,2k5-
azaphospholane (1c)
15.94; H, 2.95; N, 5.76; P, 9.17%. IR (nujol):
m = 2998, 2937, 1530,
1480, 1280, 1273 (P@O), 1178 (P@O), 1158, 1041, 1028, 992, 932
(UO2), 811. 1H NMR (400 MHz, CD3CN): d = 1.19 (t, JHH = 7.0 Hz,
A solution of Ph(EtO)PCl (7.6 g, 40 mmol) in benzene–CHCl3
(2:1, 30 mL) mixture was added dropwise to a stirred suspension
of HBrꢁNH2(CH2)3Br (4.6 g, 21 mmol) and Et3N (6.4 g, 63 mmol) in
the same mixed solvent (60 mL) at 0–2 °C. The reaction mixture
was refluxed for 1 h and cooled to ambient conditions. Then MeI
(8.9 g, 63 mmol) was added and the mixture was gently refluxed
for 2 h. On cooling, hexane (60 mL) was added and the mixture
was kept overnight. The precipitate of Et3NꢁHHal was filtered off
and the solvent was removed in vacuo. The residue was purified
by column chromatography (silica gel, CHCl3–MeOH, gradient elu-
tion from 100:1 to 100:10) to give the individual R⁄,S⁄- and R⁄,R⁄-
diastereomers as colorless thick oils. Both isomers crystallized on
treatment with Et2O. Total yield: 2.5 g (50%). Anal. Calc. for
3
3
3
3H, CH3), 1.22 (t, JHH = 7.0 Hz, 3H, CH3), 1.56 (t, JHH = 7.0 Hz, 3H,
CH3), 2.30–2.60 (m, 4H, PCH2CH2), 3.58–3.75 (m, 2H, NCH2),
4.15–4.38 (m, 4H, OCH2), 4.55 (q, JHH = 6.7 Hz, 2H, OCH2). 31P
3
2
NMR (162 MHz, CDCl3): d = 1.80 (d, JPP = 16.1 Hz), 56.0 (br. s).
2.3.2. [{UO2(1a)(NO3)}2(l2-O2)](3)
A solution of UO2(NO3)2ꢁ6H2O (0.200 g, 0.400 mmol) in ethanol
(3.5 mL) was added dropwise to a solution of the ligand 1a
(0.114 g, 0.400 mmol) in the same solvent (3 mL) at 20 °C. In
3 days, the resulting yellow crystals of 3 were filtered off, washed
with ethanol and dried in vacuo. Yield: 0.042 g (17%). Anal. Calc. for
C
18H42N4O22P4U2: C, 17.06; H, 3.32; N, 4.42; P 9.79. Found: C,
17.12; H, 3.30; N, 4.37; P, 9.81%. IR (nujol): = 1495, 1293,
C16H19NO2P2: C, 60.19; H, 5.96; N, 4.39; P, 19.44. Found: C,
m
59.97; H, 5.96; N, 4.45; P, 19.09%.
1272,1218(P@O), 1191, 1174(P@O), 1159, 1033, 995, 918(UO2),
906, 816, 744.1H NMR (400 MHz, CDCl3): d = 1.23–1.36 (m, 3H,
CH3), 1.60–1.72 (m, 7H, 6H 2 ꢂ CH3 + 1H PCH2CH2), 1.80–1.97 (m,
1H, PCH2CH2), 1.97–2.14, 2.16–2.34 (2m, 1H + 1H, PCH2), 3.47–
3.78 (m, 2H, NCH2), 4.61 - 4.90 (m, 6H, 3 ꢂ OCH2). 31P NMR
2.2.1.1. Data for (R⁄,S⁄)-1c. Mp 129.5–131.0 °C (diethyl ether). IR
(KBr):
m = 3055, 2858, 1440, 1219 (P@O), 1198 (P@O), 1120,
1060, 1032, 1023, 1006, 983. 1H NMR (400 MHz, CDCl3): d = 1.54
2
2
(d, JPH = 14.4 Hz, 3H, CH3), 2.00–2.30 (m, 4H, PCH2CH2), 3.22–
(162 MHz, CDCl3): d = 6.30–7.00 (m), 58.6 (d, JPP = 10.0 Hz), 58.9
2
2
3.36, 3.58–3.73 (2 m, 1H + 1H, NCH2), 7.49–7.63, 7.92–8.06 (2 m,
10H, 2 ꢂ C6H5). 1H NMR (400 MHz, CD3NO2): d = 1.92 (d,
2JPH = 14.4 Hz, 3H, CH3), 2.47–2.76 (m, 4H, PCH2CH2), 3.66–3.79,
3.87–4.02 (2 m, 1H + 1H, NCH2), 7.90–8.10, 8.23–8.37 (2 m, 10H,
(d, JPP = 10.0 Hz), 59.0 (d, JPP = 9,8 Hz).
2.3.3. [UO2(L)(NO3)2](4,5) (general procedure)
A solution of UO2(NO3)2ꢁ6H2O (0.32 mmol) in ethanol (3 mL)
was added dropwise to a solution of a single diastereomer of the
corresponding ligand (1b,c, 0.32 mmol) in ethanol (2 mL) at
20 °C. In one day (1b) or 1 h (1c), the resulting precipitate was col-
lected by filtration, washed with diethyl ether, and dried in vacuo.
1
2 ꢂ C6H5). 13C NMR (100 MHz, CDCl3): d = 16.3 (d, JPC = 87.0 Hz,
2
1
CH3), 21.9 (d, JPC = 7.3 Hz, PCH2CH2), 29.4 (dd, JPC = 80.0 Hz,
3JPC = 3.7 Hz, PCH2), 47.5 (dd, JPC = 13.9 Hz, JPC = 2.2 Hz, NCH2),
2
2
3
3
128.5 (d, JPC = 13.2 Hz, Cm), 128.8 (d, JPC = 13.2 Hz, Cm), 131.3 (d,
2JPC = 10.6 Hz, Co), 131.5 (d, JPC = 10.5 Hz, Co), 131.6 (d,
2
1JPC = 124.0 Hz, Ci), 131.8 (d, JPC = 2.9 Hz, Cp), 132.4 (d,
4
2.3.3.1. Data for [UO2{(R⁄,S⁄)-1b}(NO3)2] ((R⁄,S⁄)-4). Yellow solid;
yield: 0.174 g (73%). Anal. Calc. for C17H21N3 O11P2U: C, 27.46; H,
2.83; N, 5.65; P, 8.34. Found: C, 27.39; H, 2.81; N, 5.59; P, 8.27%.
4JPC = 2.9 Hz, Cp), 132.8 (d, JPC = 121.0 Hz, Ci). 31P NMR (162 MHz,
1
CDCl3): d = 30.9 (s), 48.0 (s). 31P NMR (162 MHz, CD3NO2):
2
2
d = 30.6 (d, JPP = 5.2 Hz), 48.2 (d, JPP = 5.1 Hz).
IR (nujol):
m = 3065, 2995, 1524, 1440, 1284, 1165 (P@O), 1145
(P@O), 1117, 1037, 1025, 1007, 935 (UO2). 1H NMR (400 MHz,
3
2.2.1.2. Data for (R⁄,R⁄)-1c. Mp 125.5–127.5 °C (diethyl ether). IR
CD3CN): d = 1.25 (t, JHH = 6.9 Hz, 3H, CH3), 2.40–2.62 (m, 2H,
(KBr):
m
= 3057, 2970, 1589, 1444, 1437, 1215 (P@O), 1200
PCH2CH2), 2.64–2.82, 2.87–3.08 (2 m, 1H + 1H, PCH2), 3.70–3.90,
4.00–4.16 (2 m, 1H + 1H, NCH2), 4.27 (q, JHH = 7.6 Hz, 2H, OCH2),
3
(P@O), 1117, 1071, 1020, 1005, 990, 906. 1H NMR (400 MHz,

132
I.M. Aladzheva et al. / Inorganica Chimica Acta 373 (2011) 130–136
7.28–7.40, 7.53–7.64, 7.68–7.85 (3 m, 10H, 2 ꢂ C6H5). 31P NMR
(162 MHz, CD3CN): d = 23.4 (s), 66.8 (s).
Table 1
Crystal data and structure refinement parameters for (R⁄,S⁄)-1c, 3, and 6.
(R⁄,S⁄)-1c
3
6
2.3.3.2. Data for [UO2{(R⁄,R⁄)-1b}(NO3)2] ((R⁄,R⁄)-4). Bright yellow
crystalline solid; yield: 0.173 g (73%). Anal. Calc. for C17H21N3
O11P2U: C, 27.46; H, 2.83; N, 5.65; P, 8.34. Found: C, 27.61; H,
Empirical formula
Formula weight
Crystal system
Space group
Z
a (Å)
b (Å)
c (Å)
C
19H22NO2P2 C20H44Cl6N4O22P4U2 C36H44N6O16P4U2
358.32
triclinic
P1
1505.23
monoclinic
P21/n
1416.71
monoclinic
P21/n
ꢀ
2.93; N, 5.46; P, 8.32%. IR (nujol):
m = 3064, 2685, 1593, 1522,
2
2
2
1493, 1442, 1288, 1264, 1161 (P@O), 1146 (P@O), 1129, 1114,
8.9423(10)
10.2986(12) 13.6464(13)
11.5088(13) 17.5531(17)
91.806(2)
108.893(3)
111.072(2)
922.49(18)
1.290
9.5495(9)
11.9708(14)
10.5641(12)
18.365(2)
–
1031, 1019, 998, 987, 938 (UO2). 1H NMR (400 MHz, CD3NO2):
3
d = 1.71 (t, JHH = 6.8 Hz, 3H, CH3), 2.63–2.82 (m, 2H, PCH2CH2),
a
(°)
–
3.02–3.18, 3.16–3.35 (2 m, 1H + 1H, PCH2), 3.76–3.88, 4.11–4.25
(2 m, 1H + 1H, NCH2), 4.60–4.75 (m, 2H, OCH2), 7.68–7.84, 7.85–
8.00, 8.15–8.26, 8.35–8.45 (4 m, 10H, 2 ꢂ C6H5). 31P NMR
(162 MHz, CD3NO2): d = 25.7 (s), 68.3 (s).
b (°)
99.598(2)
–
103.647(2)
–
c
(°)
V (Å3)
2255.4(4)
2.216
77.47
2256.9(5)
2.085
73.83
Dcalc (g cmꢀ1
)
Linear absorption,
2.46
l
(cmꢀ1
)
2.3.3.3. Data for [UO2{(R⁄,S⁄)-1c}(NO3)2] ((R⁄,S⁄)-5). Bright yellow
crystalline solid; yield: 0.180 g (81%). Anal. Calc. for C16H19N3
O10P2U: C, 26.93; H, 2.66; N, 5.89; P, 8.70. Found: C, 26.84; H,
F(0 0 0)
2hmax (°)
Reflections measured 8559
Independent
reflections
Observed
378
54
1428
58
1348
54
21 672
5992
18 355
4895
3995
2.85; N, 5.97; P, 8.62%. IR (nujol):
m = 3063, 2918, 1592, 1521,
1439, 1281, 1143 (P@O), 1111 (P@O), 1050, 1035, 1026, 989, 933
(UO2), 892. 1H NMR (400 MHz, CD3NO2): d = 2.58 (d, 2JPH = 13.2 Hz,
3H, CH3), 2.68–3.40 (m, 4H, PCH2CH2), 4.10–4.28, 4.29–4.44 (2m,
1H + 1H, NCH2), 7.48–7.65, 7.66–7.86, 7.87–7.97, 7.98–8.20 (4 m,
10H, 2 ꢂ C6H5). 31P NMR (162 MHz, CD3CN): d = 53.2, (s), 66.0 (s).
3221
4558
3922
reflections
[with I > 2
Parameters
R1
r(I)]
218
298
291
0.0468
0.1168
1.006
0.0349
0.0916
1.009
0.0587
0.1611
1.145
wR2
Goodness-of-fit
2.3.3.4. Data for [UO2{(R⁄,R⁄)-1c}(NO3)2] ((R⁄,R⁄)-5). Yellow solid;
yield: 0.150 g (66%). Anal. Calc. for C16H19N3 O10P2U: C, 26.93; H,
2.66; N, 5.89; P, 8.70. Found: C, 26.93; H, 2.65; N, 5.65; P, 8.66%.
D
q
/
max Dqmin
0.518/ꢀ0.378 1.825/ꢀ1.107
4.446/ꢀ2.016
(e Åꢀ3
)
IR (nujol):
m = 3061, 2919, 1592, 1522, 1490, 1440, 1289, 1265,
1147 (P@O), 1109 (P@O), 1053, 1031, 1024, 986, 937 (UO2). 1H
NMR (400 MHz, CD3NO2): d = 2.60–2.86 (m, 2H, PCH2CH2), 2.73
intermediate cyclic P(III)-species. The related ligand 1c was first
obtained in the present study by modification of the above-men-
tioned one-pot procedure where the intermolecular Arbuzov reac-
tion under the action of methyl iodide was used at the last
synthetic step (Scheme 1).
2
(d, JPH = 14.3 Hz, 3H, CH3), 3.00–3.13, 3.14–3.31 (2m, 1H + 1H,
PCH2), 3.68–3.83, 3.99–4.15 (2m, 1H + 1H, NCH2), 7.70–7.86,
7.87–8.02, 8.13–8.27, 8.30–8.46 (4m, 10H, 2 ꢂ C6H5). 31P NMR
(162 MHz, CD3NO2): d = 54.1 (s), 67.3 (s).
Similar to the ligand 1b [8], two diastereomers of 1c were sep-
arated by column chromatography and characterized by IR and
multinuclear NMR spectroscopy. The structure of one of the diaste-
reomers of 1c that demonstrated the upfield chemical shift for the
exocyclic phosphorus atom and low-field signal for the endocyclic
one was determined by a single crystal X-ray diffraction study.
According to these data, the isomer crystallizing as a crystallosol-
vate with benzene molecule possesses the opposite configuration
2.4. X-ray crystallography
Single crystals of the compounds (R⁄,S⁄)-1c and 6 were grown
by crystallization from benzene and acetonitrile, respectively.
The suitable for X-ray study crystal of 3 (head-to-tail form) was ob-
tained by sublimation from chloroform solution. All diffraction
data for 3 and 6 were collected on a Bruker SMART APEX II CCD dif-
⁄
of the chiral centers, i.e., (R ,S⁄)-1c (Fig. 1). In a crystal, the mole-
fractometer [k(Mo K
(R⁄,S⁄)-1c on a Bruker SMART 1000 CCD diffractometer [k(Mo
) = 0.71072 Å, -scans] at 120 K. The substantial redundancy
a) = 0.71072 Å, x-scans] at 100 K, those for
cules of this ligand, which lack any convenient proton donor, are
hold together by a number of weak C–Hꢁ ꢁ ꢁO, C–Hꢁ ꢁ ꢁ , and Hꢁ ꢁ ꢁH
p
Ka
x
contacts; the smallest Cꢁ ꢁ ꢁO and Cꢁ ꢁ ꢁC distances being 3.374(3),
3.748(3), and 4.201(3) Å, respectively. The formation of the 3D
framework is completed by C–Hꢁ ꢁ ꢁO (Cꢁ ꢁ ꢁO 3.273(3)–3.288(3) Å)
in data allows the empirical absorption correction to be made with
the SADABS program [14] using multiple measurements of equiv-
alent reflections. The structures were solved by direct methods
and refined by the full-matrix least-squares technique against F2
in the anisotropic-isotropic approximation. All calculations were
performed with the SHELXTL software package [15]. Crystal data
and structure refinement parameters are listed in Table 1.
and C–Hꢁ ꢁ ꢁ
p (C. . .C 3.611(3) Å) interactions with the solvate ben-
zene species.
Noteworthy, the comparison of X-ray data and the 31P NMP
spectra for individual diastereomers of 1b,c allowed to conclude
that the isomer of 1-phosphoryl-2-oxo-1,2k5-azaphospholane with
the opposite configuration of chiral phosphorus atoms (R⁄,S⁄) dem-
onstrates a downfield chemical shift of the endocyclic phosphorus
atom in the 31P NMR spectra in CDCl3 solution and a smaller JPP
coupling constant as compared to that with the identical configu-
ration of the P⁄-atoms (see Supplementary data, Table S1).
3. Results and discussion
3.1. Synthesis of the cyclic ligands with the P–N–P backbone 1a–c
The cyclic O,O-bidentate ligands with the P–N–P backbone used
in this investigation represent 1-phosphorylated 2-oxo-1,2-
azaphospholanes. The recently developed synthetic approach to
the first representatives of this family of compounds, i.e., 1a,b
[8], was based on the intramolecular Arbuzov reaction of the
N,N-bis-P(III)-substituted 3-bromopropylamines generated in situ
from phosphorus(III) acid chlorides, followed by oxidation of the
3.2. Complexes of cyclic O,O-bidentate ligands 1a–c with uranylnitrate
Organophosphorus O,O-ligands such as methylene bisphos-
phine oxides [16], carbamoylmethylphosphine oxides [17], phos-
phorylated ureas [18], and acyclic ligands with the P–N–P

I.M. Aladzheva et al. / Inorganica Chimica Acta 373 (2011) 130–136
133
, 1-2 h
-EtBr
Et3N (3 equiv)
0-5 oC
.
[R(EtO)P]2N(CH2)3Br
2 R(EtO)PCl + HBr NH2(CH2)3Br
H2O2, tert-BuOH, 0 oC
R1
R
OEt
N
R
P
P
N
R
P
P
R
MeI, , 2h
O
Δ
O
O
1
-EtI
a: R=R1=OEt
b: R=Ph, R1=OEt
c: R=Ph, R1=Me
Scheme 1. One-pot synthesis of N-phosphoryl-2-oxo-1,2-azaphospholanes 1a–c.
Therefore, the ligand 1a bearing ethoxy groups at both phos-
phorus atoms, was found to form two different uranium complexes
depending on the reaction time. In other words, if reaction mixture
(EtOH) was worked-up in less than 3 h (see Section 2), only light
yellow crystalline complex of ML composition [UO2(1a)(NO3)2]
(2) was isolated in 63% yield (Scheme 2). At the same time, if the
reaction mixture was kept for 3 d under ambient conditions and
on exposure to air before the work-up, the other uranium complex
3, [{UO2(1a)NO3}2(l2-O2)], was obtained (17% yield).
According to the IR and NMR spectroscopy data, in the complex
2 the ligand serves as the O-monodentate one with the phos-
phoryl-metal bonding via the endocyclic P@O group. Thus, the IR
spectrum of the complex 2 demonstrated two strong absorption
bands of P@O valence vibrations at 1273 and 1174 cmꢀ1, respec-
tively. Compared with the corresponding data for the free ligand
1a (m
(PO) 1273 and 1234 cmꢀ1), the first band remained un-
Fig. 1. General view of the (R⁄,S⁄)-1cꢁC6H6 in representation of atoms via thermal
changed upon complexation, while the second one is significantly
shifted to a lower frequency. These data are consistent with the
participation of only one phosphoryl moiety in the complex forma-
tion. Two broad intense bands at 1530 and 1280 cmꢀ1 point to the
presence of bidentate chelated nitrate groups [20]; in addition, the
asymmetric uranyl stretching frequency appears at 932 cmꢀ1. In
the 31P-{1H} spectrum of the complex 2, which has revealed two
signals at 1.80 ppm (d, JPP = 16.1 Hz) and 56.0 ppm (br, s) assigned
to the exo- and endocyclic phosphorus atoms, respectively, the sig-
nal of the latter one is downfield shifted (for ca. 10 ppm) relative to
that in the free ligand. Moreover, in 1H NMR spectrum of 2 the sig-
nals of cyclic CH2 protons along with those of the ethoxy group at
the endocyclic phosphorus atom also were downfield shifted com-
pared to the corresponding signals in the free 1a. It should be noted
that 31P NMR monitoring of the reaction of 1a and uranyl nitrate in
1:1 ratio has revealed the formation of complex 2 in a few minutes
after mixing of the reactants. The participation in coordination of
ellipsoids at 50% probability level.
backbone [19] are known to form uranium complexes via O,O-
bidentate chelating fashion. It should be noted that according to
the spectroscopic and structural studies, uranium coordinates the
linear prototypes of 1-phosphoryl-2-oxo-1,2-azaphopholanes 1a–
c to afford chelate complexes of 1:1 composition independent from
the bulkiness of the additional substituent at the nitrogen atom
(methyl or isopropyl), counteranion in the starting uranium salt
(perchlorate or nitrate), nature of the substituents at the phospho-
rus atoms in the ligand, and reaction conditions. The cyclic ligands
1a–c also readily form complexes reacting with uranyl nitrate in
1:1 ratio in neutral solutions. In this case the coordination mode
of the ligand and structure of the complexes were found to depend
upon the ligand nature and the experimental conditions.
OEt
OEt
N
EtO
P
P
O
O
.
O
O
UO2(NO3)2 6H2O
OEt
OEt
(O3N)O2U
UO2(NO3)
O
N
P
P
R=R1=OEt
EtO
O
O
O
R1
R
EtO
P
UO2(NO3)2
N
P
OEt
R
P
P
N
EtO
2
O
O
1a-c
3
.
UO2(NO3)2 6H2O
Ph
N
P
Ph
P
R=Ph, R1=OEt, Me
R=OEt: (R*,S*)-4; (R*,R*)- 4
R=Me: (R*,S*)- 5, (R*,R*)- 5
R
O
O
UO2(NO3)2
4,5
Scheme 2. Different uranium complexes formed by N-phosphoryl-2-oxo-1,2-azaphospholanes 1a–c.

134
I.M. Aladzheva et al. / Inorganica Chimica Acta 373 (2011) 130–136
the endocyclic phosphoryl oxygen only can be explained by its
higher donor properties compared with that of the related exocy-
clic functionality due to the presence of cyclic methylene group
as a substituent at the endo-P atom.
complexes ((R⁄,R⁄)-4, (R⁄,S⁄)-4, (R⁄,R⁄)-5, and (R⁄,S⁄)-5) of ML com-
position [UO2(L)(NO3)2] which precipitated from ethanol solution
as yellow solids in a day (L = (R⁄,R⁄)-1b, (R⁄,S⁄)-1b) or 0.5–1 h
(L = (R⁄,R⁄)-1c, (R⁄,S⁄)-1c) (Scheme 2). Based on the significant coor-
Vice verse, the complex 3 possesses the (
l
2-peroxo)-bridged
dination shift of P@O absorption bands (Dm(PO) = 68–79 and 55–
structure [{UO2(1a)NO3}2 ( 2-O2)] with two fused eight-membered
l
91 cmꢀ1 for the exo- and endo-phosphorus atoms, respectively)
and typical asymmetric stretching frequency of the uranyl cation
(933–938 cmꢀ1) in the IR spectra, downfield shifting both of the
corresponding phosphorus resonances in the 31P-{1H} NMR spectra
and signals of all hydrogen atoms in the ligand structure in the 1H
NMR spectra of isomeric complexes 4 and 5, the bidentate chelat-
ing coordination mode of the ligands 1b,c to uranium has been
suggested in these cases (IR and 31P NMR data for complexes are
summarized in Tables S2 and S3, see Supplementary). Such differ-
ence in complexing behavior between the ligands 1a and 1b,c may
be explained by increased donor properties of both oxygen atoms
in the ligands 1b,c as well as comparability of such properties for
both coordinating P@O functions.
cycles and bridging O,O-bidentate coordination mode of the li-
gands to uranium (Scheme 2). The presence of two absorption
bands due to coordinated P@O groups (at 1218 and 1174 cmꢀ1
)
in the IR spectrum of 3 explicitly confirm O,O-bidentate coordina-
tion mode for the ligand. The broad intense absorption bands at
1469 and 1293 cmꢀ1 correspond to the vibrations of coordinated
nitrate groups and antisymmetric uranyl vibration at 918 cmꢀ1 is
shifted to a lower frequency compared with the complex 2. A
medium-weak absorption band at 816 cmꢀ1 may be assigned to
the m(O–O) peroxo vibration [21]. Furthermore, downfield chemi-
cal shifts in the 31P-{1H} NMR spectrum of 3 (unresolved multiplet
in the range 6.30–7.00 ppm for the exo-P atom and three doublets
in the range from 58 to 59 ppm for the endo one) indicate the coor-
dination of the uranium with oxygen atoms of both P@O functions.
Additionally, in the 1H NMR spectrum of 3 the signals of the PCH2,
NCH2, and all OCH2 hydrogen atoms are downfield shifted com-
pared to those in the free ligand due to coordination. Apparently,
bonding of the ligand 1a in complex 3 is realized via head-to-tail
manner. In such a way, the three doublets for the endo-phosphorus
atom in the 31P NMR spectrum may be explained by the presence
of two different conformers of the compound in solutions, i.e., two
closely located doublets with spin coupling constants of ca.10 Hz
are assigned to the conformer having non-equivalent endo-P atoms
Finally, when the reaction of (R⁄,S⁄)-1c and uranyl nitrate was
performed in acetonitrile, in which the above complex (R⁄,S⁄)-5
was more soluble than in EtOH, in a few days the (
l2-peroxo)-
bridged uranium complex [{UO2(R⁄,S⁄)-1c)NO3}2(
l
2-O2)] (6) was
isolated in trace quantities along with the major desired product.
The structure of this peroxo uranium complex was elucidated by
the X-ray diffraction analysis (Fig. 3).
Although the severe disorder of the peroxo and NO3 groups in 3
does not allow analyzing its molecular geometry in detail, the mu-
tual disposition of the constituting moieties can still be assessed.
Thus, the UO2U and NO3 planes are not parallel, and the corre-
sponding dihedral angle is ca. 40° (36.4(5)–38.4(5)°); the latter
deviation from planarity, although being a rare case, was previ-
ously reported for several peroxo complexes of uranium [22]. In
contrast, the O@U@O moiety in 3 is nearly perpendicular to the
NO3 plane (the angle they form is 83.7(5)–87.7(5)°) that is charac-
teristic of such systems. The disposition of the envelope-shaped
heterocycles (the C(2) atom deviates by 0.56(1) Å) of the two che-
lating ligands is a transoid one relative to the mean UO2U plane. In
a crystal, these complexes together with the solvate chloroform
molecules are assembled into the 3D framework by a number of
weak C–Hꢁ ꢁ ꢁO, C–Hꢁ ꢁ ꢁCl, C–Clꢁ ꢁ ꢁO, and Hꢁ ꢁ ꢁH contacts.
3
while the doublet with JPP 9.8 Hz – to the conformer possessing
two equivalent ones. Finally, the proposed structure of head-to-tail
form of 3 (being a crystallosolvate with chloroform, Fig. 2) was
unambiguously confirmed by a single crystal X-ray diffraction
analysis.
At the same time, the ligand nature also influenced on the result
of the complexation. Thus, reaction of any diastereomer of 1b or 1c
with uranyl nitrate in 1:1 ratio in EtOH solution resulted in the
Fig. 2. General view of the complex 3. Hydrogen atoms, atoms of the minor
component of the disordered moieties, and solvate chloroform molecules are not
shown. The atoms labeled with A are obtained from the basic ones by the symmetry
operation ꢀx + 1, ꢀy + 1, ꢀz.
Fig. 3. General view of the complex 6 in representation of atoms via thermal
ellipsoids at 50% probability level. Hydrogen atoms and solvate acetonitrile
molecules are not shown. The atoms labeled with A are obtained from the basic
ones by the symmetry operation ꢀx, ꢀy, ꢀz + 1.

I.M. Aladzheva et al. / Inorganica Chimica Acta 373 (2011) 130–136
135
The structure of complex 6 is somewhat similar to that of the
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