Investigations on synthesis, thermolysis, and coordination chemistry of aminophosphine oxides

Article abstract of DOI:10.1080/00958972.2013.806656

Some aminophosphine oxides (AmPOs), (R₁)(R₂)(R ₃)P=O [R₁=R₂=R₃= HNCH ₂CH=CH₂; R₁= R₂=Ph, R ₃=HNCH₂CH=CH₂; R

Full text of DOI:10.1080/00958972.2013.806656

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Investigations on synthesis,
thermolysis, and coordination
chemistry of aminophosphine oxides
E. Veerashekhar Goud a , B.B. Pavan Kumar a , Yacham Shruthi a
, Arijitha Paul a , Akella Sivaramakrishna a , Kari Vijayakrishna a
C.V.S. Brahmananda Rao b , K.N. Sabharwal b & H.S. Clayton c
,
a Chemistry Division, School of Advanced Sciences, VIT
University , Vellore , India
b Chemistry Group, Indira Gandhi Centre for Atomic Research ,
Kalpakkam , India
c Department of Chemistry , UNISA , Pretoria , South Africa
To cite this article: E. Veerashekhar Goud , B.B. Pavan Kumar , Yacham Shruthi , Arijitha
Paul , Akella Sivaramakrishna , Kari Vijayakrishna , C.V.S. Brahmananda Rao , K.N. Sabharwal
& H.S. Clayton (2013) Investigations on synthesis, thermolysis, and coordination chemistry
of aminophosphine oxides, Journal of Coordination Chemistry, 66:15, 2647-2658, DOI:
10.1080/00958972.2013.806656
To link to this article: http://dx.doi.org/10.1080/00958972.2013.806656
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Journal of Coordination Chemistry, 2013
http://dx.doi.org/10.1080/00958972.2013.806656
Investigations on synthesis, thermolysis, and coordination
chemistry of aminophosphine oxides
E. VEERASHEKHAR GOUD†, B.B. PAVAN KUMAR†, YACHAM SHRUTHI†,
ARIJITHA PAUL†, AKELLA SIVARAMAKRISHNA*†, KARI VIJAYAKRISHNA†,
C.V.S. BRAHMANANDA RAO‡, K.N. SABHARWAL‡ and H.S. CLAYTON§
†Chemistry Division, School of Advanced Sciences, VIT University, Vellore, India
‡Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India
xDepartment of Chemistry, UNISA, Pretoria, South Africa
(Received 25 May 2012; in final form 22 March 2013)
Some aminophosphine oxides (AmPOs), (R1)(R2)(R3)P=O [R1 = R2 = R3 = HNCH2CH=CH2; R1 =
R2 = Ph, R3 = HNCH2CH=CH2; R1 = R2 = R3 = HNNMe2; R1 = R2 = Ph, R3 = HNNMe2; R1 = R2 = R3 =
NC4H8O; R1 = R2=Ph, R3 = NC4H8O], have been synthesized. The coordination chemistry of these
AmPOs is studied with La(III), Th(IV), and U(VI) salts. The products are characterized by various
analytical and spectroscopic techniques, and the thermal properties of the ligands and their complexes
examined. The TGA data for these compounds show different decomposition temperatures, as well as
thermal stability of the metal complexes. Comparisons are made among different ligands on their
selective complexing ability towards some chosen metal salts. Mulliken population analysis shows
that the basicity of P=O of ligand increases with an increase in the number of P-bonded amino
groups.
Keywords: Aminophosphine oxide; Lanthanum(III); Thorium(IV); Uranium(VI) complexes;
Thermogravimetric analysis
1. Introduction
Ligands containing either trivalent or pentavalent phosphorus have interest throughout
inorganic and organic chemistry, due to their wide range of applications as insecticides and
antitumor agents and their involvement in a number of catalytic reactions [1–3]. Among
these ligand systems, phosphines or phosphine oxides containing P–N bonds represent a
major class of molecules as potential precursors to P–N backbone polymeric materials [4],
active ligands [5], and various other applications [6]. This area is likely to continue to grow
as the demand for carefully designed ligands has been increasing in nuclear industries for
treatment and separation of nuclear waste. In this context, understanding the nature of
aminophosphine oxide (AmPO) ligands in coordination spheres of selected f-metals is
important, especially as they possess potentially reactive P–N linkage and extra donor
alkene moiety or –NMe2. Little work has been focused on extraction and coordination
chemistry of AmPO ligands with lanthanides and actinides [3, 7, 8].
*Corresponding author. Email: asrkrishna@vit.ac.in
Ó 2013 Taylor & Francis

2648
E.V. Goud et al.
Here, we describe the synthesis, coordination chemistry, and thermolysis of some
selected aminophosphine oxides [(R1)(R2)(R3) P=O, where R1 = R2 = R3 = HNCH2CH=CH2;
R1 = R2 = Ph, R3 = HNCH2CH=CH2; R1 = R2 = R3 = HNNMe2; R1 = R2 = Ph, R3 = HNNMe2;
R1 = R2 = R3 = NC4H8O; R1 = R2 = Ph, R3 = NC4H8O]. In order to gain more insight into the
nature of metal complexes, further studies have been carried out to observe the effect of
substituents on phosphorus. To the best of our knowledge, this contribution represents the
first example of thermolysis of various metal–AmPO complexes.
2. Results and discussion
2.1. Synthesis and characterization of ligands and metal complexes
Condensation between amines and phosphorus(V)oxychlorides was used for the prepara-
tion of aminophosphine oxides and phenyl aminophosphine oxides as given in scheme 1.
The reactions of La(NO3)3, LaCl3, UO2(NO3)2, and Th(NO3)4 with selected AmPOs are
shown in scheme 2. Though the preliminary reactions were performed with 1 : 6 metal to
ligand molar ratio, subsequent studies gave satisfactory yields of metal complexes with
1 : 3 M ratio for U and Th salts and 1 : 3.5 for La salts at room temperature for 10 h.
Complexes of multicoordinate ligands (L1–L6) with salts of lanthanum and uranium in a
solvent mixture of CH2Cl2 and ethanol (5 : 1) were isolated as crystalline solids.
[LaCl3(L1)3], [LaCl3(L2)3], [LaCl3(L3)3], [LaCl3(L4)3], [La(NO3)3(L5)3], [La(NO3)3(L6)3],
[UO2(NO3)2(L1)2], [UO2(NO3)2(L2)2], [UO2(NO3)2(L3)2], [UO2(NO3)2(L4)2], [UO2(NO3)2
(L5)2], [UO2(NO3)2(L6)2], [UO2(NO3)2(dppeO2)], [Th(NO3)4(L5)2], and [Th(NO3)4(L6)2]
were further purified by washing with CHCl3 (2 ꢀ 10 mL) to remove unreacted free ligands
and further characterized by spectroscopic and analytical techniques. Most of these com-
plexes were soluble in polar solvents like CH3CN and DMSO. All analytical and spectro-
scopic data of the metal complexes of L1–L4 are given in table 1. Table 2 reveals
characterization data of metal complexes associated with L5 and L6.
R
Et3N
3 H-R
POCl3 +
R
P
R
O
-3 Et3N.HCl
or
or
HN-N(CH3)2
N
O
R =
HN
R
P
Et3N
- Et3N.HCl
+
Ph2POCl H R
Ph
O
Ph
or HN-N(CH3)2
R = HN
R
P
Et3N
-2 Et3N.HCl
R
O
PhPOCl2
R = N
+
2 H-R
Ph
O
Scheme 1. Synthesis of aminophosphine oxide ligands.

Aminophosphine oxides
2649
[LaCl3(L)3]; L = L1 - L4
R1
P
[La(NO3)3(L)3]; L = L5 and L6
R2
O
[Th(NO3)4(L)2]; L = L5 and L6
[UO2(NO3)2(L)2]; L = L1 - L6
R3
[L1] = R1 = R2 = R3 = HNCH2CH=CH2
[L2] = R1 = R2 = Ph; R3 = HNCH2CH=CH2
[L3] = R1 = R2 = R3 = HNNMe2
[L4] = R1 = R2 = Ph; R3 = HNNMe2
[L5] = R1 = R2 = R3 = NC4H8O
[L6] = R1 = R2 = Ph; R3 = NC4H8O
Scheme 2. Preparation of metal complexes with AmPOs.
The reaction mixtures always posed the problem of separating the desired compounds
from amine hydrochloride salts, which are byproducts of the reaction. The fractional
crystallization method was sufficient to obtain the target AmPOs in a pure form from the
reaction mixtures. The AmPOs were subsequently recrystallized from chloroform and
n-hexane to obtain them as colorless crystalline solids.
Formation of neutral AmPO–metal complexes from pure ligands was observed at room
temperature in chloroform, dichloromethane, and methanol. 1H NMR spectra of all the
complexes with L1 and L2 did not indicate coordination of 1-alkene to the metal center,
i.e. the position of chemical shifts for –CH=CH2 protons in ligands (at δ 5.82 and 5.06,
respectively) was not altered in complexes. Also, the 1H NMR of [UO2(NO3)2(L3)2]
(where L3 = OP(NHNMe2)3) revealed a significant difference in the chemical shifts of the
methyl protons of NNMe2 in the hydrazine, depending on the solvent used. For example,
the position of methyl protons of NNMe2 of free hydrazine (L3) and [UO2(NO3)2(L3)2]
appears at δ 2.57 and 2.85, respectively, in CDCl3 whereas in C6D6 the same compound
showed peaks at δ 2.59 and 2.76.
1
The H NMR spectrum of [UO2(NO3)2(L6)2] showed signals pertaining to N–CH2 and
O–CH2 at δ 3.05 and 3.65, respectively, which slightly differs from signals of free ligand
(δ 3.10 and 3.71, respectively). A similar trend was observed with L5 and these results are
in agreement with the literature [9].
The purity of all the samples has been established by spectral and analytical data,
especially by observing one sharp singlet in their 31P NMR spectra (tables 1 and 2). By
comparing 31P NMR results of the free ligand (for example L6 shows δ 23.5), as well as
the corresponding metal complexes (ranging from δ 19.2–20.4), it is evident that the metal
complexes showed a signal shift with relation to the free ligand, showing evidence of
bonding through the phosphoryl. The solubility of these AmPO–metal complexes in organic
solvents increases with increasing number of allylamino substituents on phosphorus.
Attempts have been made to compare the coordination and thermolysis behavior of
AmPO–metal complexes with [UO2(NO3)2(dppeO2)] (dppe = 1,2-bis(diphenylphosphino)
ethane), as various diphosphine dioxides are well-known ligands in lanthanide and actinide
metal chemistry [10]. The reaction of [UO2(NO3)2·6H2O] with dppeO2 in ethanol yielded
[UO2(NO3)2(dppeO2)]. The IR spectrum shows the ligand coordinated through both

2650
E.V. Goud et al.

Aminophosphine oxides
2651

2652
E.V. Goud et al.
O
N
O
O
O
2 OPPh3
Δ
O PPh3
+
2 L3
U
Ph3P O
O
O
O
N
O
CDCl3
UO2(NO3)2( L3)2
Ph
Ph
P
O
P
N
dppeO2
O
O
O
O
+ 2 L3
O
O
U
O
O
Ph
Ph
N
O
Scheme 3. Ligand exchange reactions.
phosphine oxide oxygens to uranium by replacing all the waters. 31P NMR of this com-
plex showed a singlet at δ 44.3 and no signal at δ 35.8 for free dppeO2, indicating bonding
from both the phosphoryl oxygens with the metal.
IR spectra of the metal complexes derived from L1–L6 for v(P=O) range from 1063 to
1070 cmꢁ1 as strong bands, depending on the nature of substituents on phosphorus (free
ligand ranging from 1120 to 1174 cmꢁ1 as strong bands), indicating coordination through
phosphoryl oxygen. All the bands of nitrates at 1524 (s), 1308 (s) and 1276 (m) cmꢁ1 indi-
cate coordinated bidentate nitrates in 3, 4, 7 and 10–12 [8c]. Broad and weak bands for
La–Cl are assigned at 220–240 cmꢁ1. A band at 930 cmꢁ1 is assigned to O=U=O as
reported earlier [10f].
In order to expand the relatively unexplored ligand addition chemistry of these AmPO–
metal complexes, investigations into their reactivities with various types of ligands were
carried out. The reactivity of [UO2(NO3)2(L3)2], where L3 = OP(NHNMe2)3, was studied
with OPPh3 and 1,10-phenanthroline, and there was no reaction observed at room tempera-
ture even after several days.
The reaction of [UO2(NO3)2(L3)2] with OPPh3 yielded a mixture of products in refluxing
CDCl3. The formation of a known complex showing δ 37.2 for [UO2(NO3)2(OPPh3)2] [11]
by exchanging L3 was observed by 31P NMR spectrum. On the contrary, the 31P NMR
spectrum of [UO2(NO3)2(L3)2] did not show any dissociation on refluxing with a large
excess of 1,10-phenanthroline. 31P NMR spectral analysis shows that dppeO2 can smoothly
exchange with L3 in [UO2(NO3)2(L3)2]. This could be due to the chelating nature of
diphosphine dioxide as shown in scheme 3.
2.2. Theoretical calculations
The electron distributions in aminophosphine oxides (R2N)nR(3–n)P=O were analyzed
through an electrostatic charge analysis. Although atomic charges are not an observable in
quantum mechanics, they are appropriate to get an idea on the electron distribution. In this
study, the Mulliken population analysis was employed. In table 3, Mulliken atomic charges
are reported for the six ligands.

Aminophosphine oxides
2653
Table 3. Selected Mulliken atomic charges for (R2N)nR(3–n)P=O.a
Ligand
P=O
P=O
P–N
P–C
(H2N)3P= O
ꢁ0.654
ꢁ0.680
ꢁ0.661
ꢁ0.645
ꢁ0.686
ꢁ0.681
+1.262
+1.444
+1.297
+1.146
+1.457
+1.456
ꢁ0.637; ꢁ0.637; ꢁ0.641
ꢁ0.649; ꢁ0.649; ꢁ0.648
ꢁ0.626; ꢁ0.639
(Me2N)3P= O
(Me2N)2MeP= O
(Me2N)Me2P= O
(Et2N)3P= O
ꢁ0.566
ꢁ0.605
ꢁ0.547; ꢁ0.548
ꢁ0.641; ꢁ0.650; ꢁ0.652
ꢁ0.639; ꢁ0.640; ꢁ0.659
(nPr2N)3P= O
aElectron units (charge of electron is equal to ꢁ1).
From our results, it is clear that the alkyl chain length of the amino moiety has a negli-
gible effect on the atomic charge at oxygen. However, as the number of amino groups
attached to phosphorus increase, the atomic charge at the oxygen increases significantly
from ꢁ0.645 in (Me2N)Me2P=O to ꢁ0.680 in (Me2N)3P=O. The Mulliken population
analysis is useful for qualitative purposes and provides an effective indicator of the basi-
city of the O-donor of the incoming ligand. We can interpret these data to show that as the
number of P-bonded amino groups increase, the σ-basicity of the P=O group of the ligand
increases.
2.3. Thermogravimetric analysis
Different examples of AmPOs and their metal complexes were subjected to thermogravi-
metric analysis and decomposition of these compounds begins at different temperatures.
The differences in thermal stability are a reflection of the influence that substituents on
phosphorus have on the thermal behavior. However, a feature common to most of them is
that they decompose essentially in a single step. The decomposition temperatures of these
compounds are given in table 4.
TGA curves of metal–AmPO complexes were obtained from 25 to 700 °C. Weight loss
below 100 °C for two of the complexes, i.e. [UO2(NO3)2(L3)2] and [LaCl3(L3)3], where
L3 = OP(NHNMe2)3, was ascribed to the evaporation of solvent from the crystal lattice, as
reported earlier [12]. Weight loss at lower temperatures also indicates the thermal instabil-
ity of the complexes. Weight loss temperatures for the other complexes were in the range
of 150–350 °C, indicating more thermal stability (i.e. no involvement of water or any sol-
vent in thermal stability of these compounds). The TGA of some of the ligands were car-
ried out in order to compare the thermal stability with their corresponding metal
complexes (table 4). Stability of ligands in the presence of metal salts was relatively high
in most cases. Thermal stability of various metal complexes derived from the ligands is
dppeO2 > L6 > L5 > L1 > L3. The shapes of the TG curves obtained for [UO2(NO3)2L2]
(L= AmPO) are nearly the same except for [UO2(NO3)2(dppeO2)]. Mass loss percentages
(TGA and calculated) and temperature ranges of some selected ligands and complexes
obtained in the studies are summarized in table 4. The TGA curves of ligands as well as
complexes are given in figure 1 and Supplementary material. [(UO2(NO3)2(L5)2)] under-
goes decomposition at 260–303 °C, producing a stable residue. Mass losses and IR spectra
suggest (UO2)2P2O7 as the final product. Residues from other metal complexes were their
corresponding metal phosphates and pyrophosphates, which is in agreement with earlier
work [13].

2654
E.V. Goud et al.
Table 4. Thermogravimetric analysis data of some AmPOs and their metal complexes.
Temperature
range (°C)
% Weight
loss obtained
Calculated weight loss (%) for
loss of fragment
Compound
L1
25–410; 410–700
100–320; 320–700
60–340; 340–700
50–160; 160–220
21.3;
77.3
26.4;
73.3
27.3;
26.8
32.5;
22.5
36.4
98.5
28.3;
22.6
84.1
82.2
62.5
69.1
68.4
21.8 (NHCH2CH=CH2);
78.2 (Ph2PO)
24.2 (NHNMe2);
L3
76.1 (Ph2PO)
[UO2(NO3)2(L1)2]
[UO2(NO3)2(L3)2]
28.3 (NHCH2CH=CH2);
28.3 (NHCH2CH=CH2)
56.7 (NHNMe2);
23.3 (NO2)
34.2 (NHNMe2)
Decomposes completely
35.3 (dppeO2);
23.3 (NO2)
81.1 (OC4H8N– & C6H5–)
80.7 (OC4H8N– & C6H5–)
61.2 (OC4H8N– & NO2)
65.6 (OC4H8N– & NO2)
62.4 (OC4H8N– & NO2)
[LaCl3(L3)3]
Dppe(O)2
[UO2(NO3)2(DppeO2)]
25–290
170–700
50–360; 380–700
L5
L6
150–238
150–266
266–303
245–294
235–340
[UO2(NO3)2(L5)2]
[Th(NO3)4(L5)2]
[Th(NO3)2(L6)2]
Figure 1. TGA curves of L1 and L3 ligands and their complexes [UO2(NO3)2(L3)2] and [LaCl3(L3)2].
3. Experimental
3.1. Instrumentation
1H, 13C, and 31P NMR spectra were recorded on a Bruker DMX-400 spectrometer and all
1H chemical shifts are reported relative to the residual proton resonance in deuterated
solvents (all at 298 K, CDCl3). Microanalyses (C, H, N) were conducted with a Thermo

Aminophosphine oxides
2655
Flash 1112 Series CHNS-O Elemental Analyzer instrument and Heraeus CHN rapid micro-
analyzer. Infrared spectra were recorded on a Perkin-Elmer Spectrum One FT-IR Spectrom-
eter, Perkin Elmer 1430, Shimadzu UV-240 (and/or Shimadzu NIR 3100), and JEOL JNM
JGX-400 instruments, respectively. Thermogravimetric analyses were carried out on a Per-
kin Elmer TGA-7 and Mettler Toledo SDTA851e from ambient to about 800 °C under air
(50 mL minꢁ1) and at a heating rate of 10.0 °C minꢁ1. Approximately 5 mg of the samples
was used in the TG experiments.
3.2. Materials and methods
All manipulations were carried out under nitrogen using Schlenk line techniques, unless
otherwise stated. Commercially available solvents were distilled from Na metal/benzophe-
none ketyl before use. The phosphorus reagents (Merck and Sigma–Aldrich) including
POCl3, Ph2POCl, and PhPOCl2 were used as received and other reagents (Merck) like
morpholine, n-allylamine, and N,N-dimethylhydrazine were purified by distillation over
KOH [14]. Hydrated metal salts (Loba and Aldrich), [(MEx·yH2O)] where M=La, U, Th;
E=NO3 (x = 2 and y = 6 for U; x = 4 and y = 5 for Th; x = 3 and y = 7 for La), and E=Cl
(x = 3 and y = 7 for La) were used as received. The compounds PO(NHCH2CH=CH2)3
(L1) [15], Ph2PO(NHCH2CH=CH2) (L2) [16], PO(NHNMe2)3 (L3) [17], and Ph2PO
(NHNMe2) [18] (L4) were prepared according to previous literature procedures. Bis
(diphenylphosphino)ethane dioxide [Ph2P(O)CH2CH2P(O)Ph2, dppeO2] was prepared as
described earlier [19]. The proton decoupled 31P NMR chemical shifts of L1 (δ 24.9), L2
(δ 24.4), L3 (δ 26.5), L4 (δ 22.5), and L5 (δ 25.2) were comparable with the literature.
3.2.1. Preparation of dimorpholino–phenylphosphine oxide (L6). To a stirred solution
of morpholine (2.95 g, 33.8 mM) and triethylamine (3.6 g, 35 mM) in toluene–hexane (1 : 1,
25 mL) at ice cold temperature, PhPOCl2 (5.08 g, 26.05 mM) of the same solvent mixture
(20 mL) was added dropwise through a dropping funnel and allowed to stir for 15 h. The
reaction mixture was filtered to separate Et3N·HCl salt and the volume of filtrate was
reduced to ≈ 10 mL under reduced pressure and kept in a refrigerator for 24 h. The
obtained colorless crystalline product was separated and dried under vacuum for 4 h to
1
remove all volatiles. The yield was 6.56 g (85%). m.p.: 98–100 °C. H NMR (CDCl3): δ
3.10 (s, 8H, N–CH2), 3.72 (s, 8H, O–CH2), 7.78–7.32 (m, 5H, Ph); 13C NMR: δ 44.1 (N–
CH2), 66.9 (O–CH2), 128.4–131.2 (Ph); 31P NMR: δ 23.5; Anal. Calcd for C14H21N2O3P:
C, 56.75; H, 7.09; N, 9.46. Found: C, 56.63; H, 7.31; N, 9.52. In a similar manner, trimor-
pholino–phosphine oxide (L5) [20] was also prepared. The spectroscopic data obtained for
L5 were identical to those previously reported.
3.2.2. Synthesis of the metal complexes: general procedure for the preparation of
metal complexes. The following general procedure was used for the preparation
of [UO2(NO3)2(L6)2] and the same procedure was followed for the other metal complexes.
A finely powdered solid of UO2(NO3)2·6H2O (0.28 g, 0.65 mM) was added all at once to a
stirred solution of L6 (1.156 g, 3.9 mM) in CH2Cl2 and ethanol (5 : 1) and the mixture was
stirred for 24 h to get yellow precipitate. The precipitate was washed (3 ꢀ 5 mL) with
dichloromethane to obtain pure UO2(NO3)2(L6)2. In a similar way, LaCl3(L1)3 [LaCl3·7H2O
(0.121 g, 0.326 mM) and L1 (0.245 g, 1.1 mM)], LaCl3(L2)3 [LaCl3·7H2O (0.142 g,

2656
E.V. Goud et al.
0.38 mM) and L2 (0.342 g, 1.33 mM)], LaCl3(L3)3 [LaCl3·7H2O (0.132 g, 0.355 mM) and L3
(0.278 g, 1.24 mM)], LaCl3(L4)3 [LaCl3·7H2O (0.115 g, 0.31 mM) and L4 (0.282 g,
1.08 mM)], La(NO3)3(L5)3 [La(NO3)3·7H2O (0.225 g, 0.499 mM) and L5 (0.533 g,
1.75 mM)], La(NO3)3(L6)3 [La(NO3)3·7H2O (0.176 g, 0.39 mM) and L6 (0.392 g, 1.36 mM)],
Th(NO3)4(L5)2 [Th(NO3)4·5H2O (0.154 g, 0.27 mM) and L5 (0.247 g, 0.81 mM)], Th(NO3)4
(L6)2 [Th(NO3)4·5H2O (0.177 g, 0.31 mM) and L6 (0.268 g, 0.93 mM)], UO2(NO3)2(L1)2
[UO2(NO3)2·6H2O (0.202 g, 0.402 mM) and L1 (0.26 g, 1.2 mM)], UO2(NO3)2(L2)2 [UO2
(NO3)2·6H2O (0.188 g, 0.374 mM) and L2 (0.289 g, 1.12 mM)], UO2(NO3)2(L3)2 [UO2
(NO3)2·6H2O (0.196 g, 0.39 mM) and L3 (0.263g, 1.17mM)], UO2(NO3)2(L4)2 [UO2(NO3)2·
6H2O (0.146 g, 0.291 mM) and L4 (0.227 g, 0.873 mM)], and UO2(NO3)2(L5)2
[UO2(NO3)2·6H2O (0.226 g, 0.45 mM) and L5 (0.412 g, 1.35 mM)] were prepared. The
uranium complexes were synthesized by the reaction of CH2Cl2 solutions of uranyl nitrate
and the ligands. The products obtained were recrystallized from CH2Cl2/Et2O mixture after
removing the solvent. The unreacted ligands were collected from the worked-up solvent mix-
tures and this indirectly supports the metal–ligand stoichiometries. The metal–complexes
were dried in vacuo over anhydrous calcium chloride. The complete list of isolated metal
complexes is given in tables 1 and 2.
3.2.3. Preparation of [UO2(NO3)2(dppeO2)]. DppeO2 (0.270 g, 0.627 mM) was added
into a hot ethanol solution (15 mL) of UO2(NO3)2·6H2O (0.302 g, 0.614 mM). The mixture
was refluxed for 4 h. The resulting solid was then filtered, washed with ethanol
(2 ꢀ 10 mL), and dried in vacuo. The product was recrystallized from a methanol–CH2Cl2
mixture as a yellow crystalline solid. Yield: 0.282 g, 57%. IR (Nujol mull/cmꢁ1): 1524 (s),
1
1308 (s), 1276 (w) (NO3); 1141(s) [P=O]; 930 (O=U=O). H NMR (CDCl3, ppm): δ 7.42–
7.79 (m, phenyl), 2.82 (m, CH2). 31P{1H} NMR (CDCl3, ppm): δ 23.4, s.
3.3. Computational details
All calculations were carried out using the DMol3 density functional theory (DFT) code as
implemented in the Accelrys Material Studio® 5.0 software package [21]. The non-local
generalized gradient approximation (GGA) using the PW91 exchange-correlation functional
was used for geometry optimization in all cases [22]. A double numeric, polarized split
valence (DNP) basis set was used in this study with a DFT semi-core pseudopotential to
account for the core electrons of P. The size of the DNP basis set is comparable to Gaussian
6-31 G⁄⁄, but the DNP is more accurate than the Gaussian basis set of the same size [23].
Geometry optimizations were performed without symmetry constraints. The convergence
criteria for these optimizations consisted of the following threshold values: 1 ꢀ10ꢁ5 Ha for
energy; 0.002 Ha Åꢁ1 for gradient and 0.005 Å for displacement convergence, while a self-
consistent field density convergence threshold of 1 ꢀ10ꢁ6 Ha was specified. All optimized
geometries were subjected to a full frequency analysis at the same level of theory (GGA/
PW91/DNP) to verify the nature of the stationary points. Optimized geometries were char-
acterized by the absence of imaginary frequencies.
4. Conclusion
As phosphine oxides are important ligand systems and are versatile extractants in the
nuclear waste treatment plants, the present paper describes the synthesis and coordination

Aminophosphine oxides
2657
chemistry of multidentate aminophosphine oxides (AmPOs). The presence of multi-donor
sites did not show any influence on the phosphoryl coordination towards lanthanum,
thorium, and uranium salts. Theoretical calculations clearly reveal an increase in nucleo-
philicity of the phosphoryl group with an increase in ‘N’ character. The changes in chemi-
cal shifts can be attributed to variations in the extent and intensity of coordination of
donors to metal. TGA studies revealed that all the metal complexes decompose by either
single-step or multi-step elimination of ligand species, whereas the free ligands showed
single-step decomposition only. Preliminary investigations proved the extractability of
hydrated metal salts from aqueous solutions in the presence of AmPOs in chloroform.
Various factors including aqueous phase ionic strength, AmPOs concentration in the
organic phase, temperature, type of mineral acid, and strength of mineral acid can affect
the efficiency of extraction.
The complexation of linear and cyclic carboxylates and polyaminocarboxylates [24]
provided more insight into the role of steric differences between the ligands and different
donor groups, which can affect complexation strength. In light of this, it is very important to
fine-tune the ligand properties toward better solubility and extractability into an organic
phase. The functionalization of ligands can be done either by inserting additional groups in
the ligand backbone, or by inserting appropriate bulky groups in substituents on phosphorus
introducing new properties into a ligand; it can make it more selective toward a metal ion
and increase the thermodynamic stability and the kinetic inertness. We are currently working
on the coordination behavior of AmPOs having different electronic and steric properties.
Acknowledgments
Dr ASRK is highly thankful to DAE-BRNS (No. 2012/37C/6/ BRNS/623), India, for the
financial assistance. EVSG and BBPK thank VIT University for the facilities. We thank
Prof. M.N. Sudheendra Rao (IITM, Chennai, India) and Prof. John R. Moss (University of
Cape Town, South Africa) for their encouragement and support. Dr. ASRK and his group
members thank DST-VIT-FIST for NMR and SAIF-VIT Universiy for other
instrumentation facilities.
References
[1] (a) A. Lemos. Molecules, 14, 4098 (2009); (b) M.J. Glazier, W. Levason, M.L. Matthews, P.L. Thornton,
M. Webster. Inorg. Chim. Acta, 357, 1083 (2004); (c) R.J. Puddephatt. Chem. Soc. Rev., 12, 99 (1983);
(d) I. Haiduc, I.S. Dumitrescu. Coord. Chem. Rev., 77, 127 (1986); (e) B. Chaudret, B. Delavaux, R. Poil-
blanc. Coord. Chem. Rev., 86, 191 (1988); (f) C.A. McAuliffe. In Comprehensive Coordination Chemistry,
G. Wilkinson, R.D. Gillard, J.A. McCleverty (Eds.), pp. 989–999, Pergamon Press, Oxford, Vol. 2 (1987);
(g) V.M.R. dos Santos, C.L. Donnici, J.B.N. DaCosta, J.M.R. Caixeiro. Quim. Nova, 30, 159 (2007); (h)
M. Vysvaril, D. Dastych, J. Taraba, M. Necas. Inorg. Chim. Acta, 362, 4899 (2009); (i) J.S. Harvey,
S.J. Malcolmson, K.S. Dunne, S.J. Meek, A.L. Thompson, R.R. Schrock, A.H. Hoveyda, V. Gouverneur.
Angew. Chem. Int. Ed., 48, 762 (2009).
[2] (a) H. Iwanaga, F. Aiga. J. Lumin., 130, 812 (2010); (b) U. Casellato, S. Sitran, S. Tamburini, P.A. Vigato,
R. Graziani. Inorg. Chim. Acta, 95, 37 (1984); (c) S.S. Krishnamurthy. Proc. Ind. Acad. Sci. Chem. Sci.,
108, 111 (1996); (d) F.A. Hart. In Comprehensive Coordination Chemistry, G. Wilkinson, R.D. Guillard,
J.A. McCleverty (Eds.), p. 245, Pergamon, Oxford, Vol. 3 (1987); (e) N. Tetsuhiro, M. Takamasa,
M. Takayoshi, H. Yasumasa. J. Org. Chem., 70, 7172 (2005); (f) G. Ionova, S. Ionov, C. Rabbe, C. Hill,
C. Madic, R. Guillaumont, G. Modolo, K.C. Jean. New J. Chem., 25, 491 (2001); (g) L.Y. Jung, S.H. Tsai,
F.E. Hong. Organometallics, 28, 6044 (2009); (h) D. Rosario-Amorin, E.N. Duesler, R.T. Paine, B.P. Hay,
L.H. Delmau, S.D. Reilly, A.J. Gaunt, B.L. Scott. Inorg. Chem., 51, 6667 (2012).

2658
E.V. Goud et al.
[3] (a) N.J. Farrer, R. McDonald, T. Piga, J.S. McIndoe. Polyhedron, 29, 254 (2010); (b) H.H. Dam,
D.N. Reinhoudt, W. Verboom. Chem. Soc. Rev., 36, 367 (2007) and references therein; (c) R. Engel,
J.I. Rizzo. Curr. Org. Chem., 10, 2393 (2006); (d) D. Leca, L. Fensterbank, E. Locate, M. Malacria. Chem.
Soc. Rev., 34, 858 (2005); (e) L. Ackermann. Synthesis, 1557 (2006); (f) L. Ackerman, R. Born, J.H. Spatz,
A. Althammer, C.J. Gschrei. Pure Appl. Chem., 78, 209 (2006); (g) V.V. Grushin. Chem. Rev., 104, 1629
(2004); (h) B. Allen, S. Kuldip, W.G.P. Andrew. Polyhedron, 42, 30 (2012).
[4] M. Kim, F. Sanda, T. Endo. Polym. Bull., 46, 277 (2001).
[5] (a) J.G. Verkade, K.J. Coskram. In Organophosphorus Compounds, G.M. Kosolapoff, L. Maier (Eds.),
pp. 1–53, Wiley, New York, Vol. 2 (1972); (b) A.H. Cowley, R.E. Davies, K. Remadna. Inorg. Chem.,
20, 2146 (1981); (c) S. Priya, M.S. Balakrishna, S.M. Mobin. Polyhedron, 24, 1641 (2005); (d) S.A. Katz,
V.S. Allured, A.D. Norman. Inorg. Chem., 33, 1762 (1994); (e) G. Ewart, D.S. Payne, A.L. Porte,
A.P. Lane. J. Chem. Soc., 3984 (1962); (f) D.S. Payne, A.P. Walker. J. Chem. Soc., 498 (1966); (g)
P.W. Dyer, M.J. Hanton, R.D.W. Kemmitt, R. Padda, N. Singh. Dalton Trans., 104 (2003); (h) M.R.I.
Zubiri, J.D. Woollins. Comments Inorg. Chem., 24, 189 (2003).
[6] (a) X. Fu, W.T. Loh, Y. Zhang, T. Chen, T. Ma, H. Liu, J. Wang, C.H. Tan. Angew. Chem. Int. Ed., 48, 7387
(2009); (b) J.J. Brunet, R. Chauvin, J. Chiffre, S. Huguet, P. Leglaye. J. Organomet. Chem., 566, 117 (1998);
(c) N.R. Price, J. Chambers. In The Chemistry of Organophosphorus Compounds, F.R. Hartley (Ed.), p. 649,
Wiley, Chichester, Vol. 1 (1990); (d) J. Ansell, M. Wills. Chem. Soc. Rev., 31, 259 (2002); (e) M.C.B. Dolinsky,
W.O. Lin, M.L. Dias. J. Mol. Catal. A: Chem., 258, 267 (2006); (f) M.S. Rahman, M. Oliana, K.K. Hii.
Tetrahedron: Asymmetry, 15, 1835 (2004); (g) J. Andrieu, J.M. Camus, R. Poli, P. Richard. New J. Chem.,
25, 1015 (2001); (h) R.A. Cherkasov, A.R. Garifzyanov, A.S. Talan, R.R. Davletshin, N.V. Kurnosova. Russ.
J. Gen. Chem., 79, 1835 (2009); (i) S. Singh, K.M. Nicholas. Chem. Commun., 149 (1998); (j) J.M. De
Santos, R. Ignacio, D. Aparicio, F. Palacios. J. Org. Chem., 72, 5202 (2007).
[7] M.M. Reinoso-Garcia, W. Verboom, D.N. Reinhoudt, F. Brisach, F. Arnaud-Neu, K. Liger. Solvent Extr. Ion
Exch., 23, 425 (2005).
[8] (a) Y. Masuda, M.H. Zahir. Talanta, 42, 93 (1995); (b) M.F.P. da Silva, J. Zukerman-Schpector, G. Vicentini,
P.C. Isolani. Inorg. Chim. Acta, 358, 796 (2005); (c) A.R. de Aquino, G. Bombieri, P.C. Isolani, G. Vicentini,
J. Zukerman-Schpector. Inorg. Chim. Acta, 306, 102 (2000) and the references therein.
[9] J.T. Donoghue, E. Fernandez. Bull. Chem. Soc. Jpn., 43, 271 (1970); (b) J.T. Donoghue. Bull. Chem. Soc. Jpn.,
43, 932 (1970).
[10] (a) A.N. Turanov, V.K. Karandashev, A.N. Yarkevich, V.E. Baulin. Radiochem., 51, 359 (2009);
(b) A.N. Turanov, V.K. Karandashev, V.E. Baulin, A.N. Yarkevich, Z.V. Safronova. Solv. Extr. Ion Exch., 27,
551 (2009); (c) T.W. Hayton, G. Wu. J. Am. Chem. Soc., 130, 2005 (2008); (d) I.V. Smirnov. Radiochemistry,
49, 44 (2007); (e) H. Iwanaga, A. Amano, F. Aiga, K. Harada, M. Oguchi. J. Alloys Compd., 408, 92 (2006);
(f) S. Kannan, N. Rajalakshmi, K.V. Chetty, V. Venugopal, M.G.B. Drew. Polyhedron, 23, 1527 (2004);
(g) A.N. Turanov, V.K. Karandashev, A.N. Yarkevich, Z.V. Safronova. Solv. Extr. Ion Exch., 22, 391 (2004);
(h) Z. Spichal, M. Necas, J. Pinkas, J. Novosad. Inorg. Chem., 43, 2776 (2004); (i) X. Liu, X.J. Yang,
P. Yang, Y. Liu, B. Wu. Inorg. Chem. Commun., 12, 481 (2009).
[11] G. Bandoli, G. Bortolozzo, D.A. Clemente, U. Croatto, C. Panattoni. Inorg. Nucl. Chem. Lett., 7, 401 (1971).
[12] (a) L. Peisen, L. Huanyong, J. Wanqi. J. Rare Earths, 29, 317 (2011); (b) B.S. Sekhon, L. Gandhi. Int. J.
ChemTech Res., 2, 1057 (2010); (c) K.J. Paluch, L. Tajber, T. McCabe, J.E. O’Brien, O.I. Corrigan,
A.M. Healy. Eur. J. Pharm. Sci. 42, 928 (2011), published as an advanced article, doi: 10.1016/j.
ejps.2010.11.012
[13] For uranyl phosphates: (a) J.M. Schaekers. J. Therm. Anal., 6, 145 (1974); (b) V. Brandel, N. Dacheux,
M. Genet. J. Solid State Chem., 121, 467 (1996); (c) J. Ling, J. Qiu, G.E. Sigmon, M. Ward, J.E.S. Szymanowski,
P.C. Burns. J. Am. Chem. Soc., 132, 13395 (2010); For lanthanum phosphates: (d) P. Chen, T.-I. Mah. J. Mat.
Sci., 32, 3863 (1997); (e) H. Onoda, T. Funamoto. J. Mat. Sci. Res., 2, 75 (2013); For thorium phosphates: (f) P.
Bénard, V. Brandel, N. Dacheux, M. Genet, D. Louër, S. Jaulmes, S. Launay, M. Quarton, C. Lindecker. Chem.
Mater., 8, 181 (1996); (g) V. Brandel, N. Dacheux, M. Genet. Radiochemistry, 43, 16 (2001).
[14] W.L.F. Armarego, D.D. Perrin. Purification of Laboratory Chemicals. p. 186, 4th Edn. Butterworth and
Heinemann, Boston, MA (1996).
[15] K.A. Petrov, A.I. Gavrilova, V.P. Korotkova. Z. Obshch. Khim, 32, 915 (1962).
[16] A.M.Z. Slawin, J. Wheatley, J.D. Woollins. Eur. J. Inorg. Chem., 713 (2005).
[17] (a) L.A. Cates, V.S. Li, B.H. Saddawi, K.A. Alkadhi. J. Med. Chem., 28, 595 (1985); (b) R.P. Nielsen,
H.H. Sisler. Inorg. Chem., 2, 753 (1963).
[18] H.H. Sisler, R.P. Nielsen. Inorg. Synth., 8, 7406 (1966).
[19] W. Levason, R. Patel, G. Reid. J. Organomet. Chem., 688, 280 (2003).
[20] J.T. Donoghue, E. Fernandez, D.A. Peters. Inorg. Chem., 8, 1191 (1969); (b) C. Rømming, J. Songstad. Acta
Chem. Scand. Ser. A, 32, 689 (1978).
[21] B. Delley. J. Chem. Phys., 113, 7756 (2000); (b) B. Delley. J. Chem. Phys., 92, 508 (1990).
[22] J.P. Perdew, Y. Wang. Phys. Rev., B45, 13244 (1992).
[23] N.A. Benedek, I.K. Snook, K. Latham, I. Yarovsky. J. Chem. Phys., 122, 144102 (2005).
[24] P. Thakur, J.L. Conca, G.R. Choppin. J. Coord. Chem., 64, 3214 (2011).