X-ray crystallographic, luminescence and NMR studies of phenacyldiphenylphosphine oxide with the Ln(iii) ions Sm, Eu, Gd, Tb and Dy

Article abstract of DOI:10.1039/c7dt02678a

We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln(iii) ions (Sm, Eu, Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1:2 ratio between the Ln³⁺ ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate manner to the metal center. A fifth structure is reported for the 1:2 Eu(NO₃)₃-ligand complex showing bidentate binding between the two ligands and the metal center. The solution coordination chemistry of these metal complexes was probed by ¹H, ¹³C and ³¹P NMR, mass spectrometry, and luminescence experiments. The title ligand has the capability to sensitize Tb³⁺, Dy³⁺, Eu³⁺ and Sm³⁺ leading to metal-centered emission in solutions of acetonitrile and methanol and in the solid state.

Full text of DOI:10.1039/c7dt02678a

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X-ray crystallographic, luminescence and NMR
studies of phenacyldiphenylphosphine oxide
with the Ln(III) ions Sm, Eu, Gd, Tb and Dy†
Cite this: DOI: 10.1039/c7dt02678a
Erin G. Leach,a Justin R. Shady,a Adam C. Boyden,a Anne-lise Emig,a
a
Alyssa T. Henry,b Emily K. Connor,b Richard J. Staples,c Stephanie Schaertel,
Eric J. Wernerb and Shannon M. Biros
*
a
We report here the characterization in solution (NMR, luminescence, MS) and the solid-state (X-ray
crystallography, IR) of complexes between phenacyldiphenylphosphine oxide and five Ln(III) ions (Sm, Eu,
Gd, Tb, Dy). Four single crystal X-ray structures are described here showing a 1 : 2 ratio between the Ln3+
ions Eu, Dy, Sm and Gd and the ligand, where the phosphine oxide ligands are bound in a monodentate
manner to the metal center. A fifth structure is reported for the 1 : 2 Eu(NO3)3-ligand complex showing
bidentate binding between the two ligands and the metal center. The solution coordination chemistry of
these metal complexes was probed by 1H, 13C and 31P NMR, mass spectrometry, and luminescence
experiments. The title ligand has the capability to sensitize Tb3+, Dy3+, Eu3+ and Sm3+ leading to metal-
centered emission in solutions of acetonitrile and methanol and in the solid state.
Received 22nd July 2017,
Accepted 20th October 2017
DOI: 10.1039/c7dt02678a
rsc.li/dalton
Introduction
Research into the chemistry of lanthanide (Ln) metals has gen-
erated recent interest due to their incorporation into advanced
optical materials,1–8 biosensors,9–14 hybrid car batteries, and
magnets that exploit their unique magnetic and photophysical
properties.6 The need for additional insight into factors that
influence Ln coordination chemistry is further driven by the
growing desire to recycle materials utilizing Ln metals (e.g.,
hybrid car batteries, magnets, smart phones) combined with
an increased focus on the purification of Ln metals from raw Scheme 1 Synthesis of (a) β-ketophopshine oxide 4 and (b) mixtures of
sources (ground ores and minerals).15
1 : 2 and 1 : 3 Ln-ligand complexes.
A
well-known motif for chelating Ln metals is the
carbamoylmethylphopshine oxide (CMPO) group. This motif is
commonly used as a component of the TRUEX (transuranium
extraction) process for nuclear waste remediation.16 The
coordination chemistry of the related aryl ketone derivative, 4,
has been investigated with both lanthanide and actinide
metals by Platt and co-workers (Scheme 1).17–19 We add to this
body of work with five new crystal structures of
β-ketophosphine oxide 4 complexed with Tb3+, Eu3+, Dy3+ and
Gd3+, as well as NMR and luminescence studies to probe the
solution-state coordination chemistry.
aDepartment of Chemistry, Grand Valley State University, Allendale, MI 49401, USA.
E-mail: biross@gvsu.edu; Fax: +1-616-331-3230; Tel: +1-616-331-8955
bDepartment of Chemistry, Biochemistry and Physics, The University of Tampa,
401 W. Kennedy Blvd., Tampa, FL 33606, USA
cCenter for Crystallographic Research, Department of Chemistry, Michigan State
University, 578 S. Shaw Lane, East Lansing, MI 48824, USA
Experimental
General considerations
†Electronic supplementary information (ESI) available: Further details are given
on the X-ray (all bond lengths and angles), NMR, IR and luminescence data
(solid state emission spectra, lifetime decay curves, excitation and absorption
spectra). CCDC 1484660–1484664 for 5–9. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c7dt02678a
All chemicals (including deuterated solvents) were used as pur-
chased from Sigma-Aldrich or Acros Chemicals and used
without further purification. 1H, 13C and 31P NMR spectral
data were recorded on either a Jeol Eclipse 300 or Varian Inova
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400 FTNMR spectrophotometer, as stated. For 1H and 13C tions were applied using SADABS23 multi-scan technique, sup-
NMR spectra, chemical shifts are expressed as parts per plied by George Sheldrick. The structures were solved by the
million (δ) relative to SiMe4 (TMS, δ = 0), and referenced direct method using the SHELXS-97 program and refined by
internally with respect to the protio solvent impurity. For least squares method on F2, SHELXL-2014,24 which are incor-
31P NMR spectra, chemical shifts are expressed as parts per porated in OLEX2.25,26 All non-hydrogen atoms were refined
million (δ) relative to H3PO4 (δ = 0). Both 13C and 31P NMR anisotropically. Hydrogen atom locations were calculated by
spectra were obtained as proton-decoupled data. IR spectra geometrical methods and refined as a riding model. The crys-
were acquired neat on a Jasco 4100 FTIR. Elemental (CHN) tals used for the diffraction study showed no decomposition
analyses were performed on a PerkinElmer 2400 Series II during data collection. Further crystallographic data and
CHNS/O Analyzer or by Atlantic Microlab Inc., Norcross, GA; experimental details for structural analysis of all the complexes
all CHN percentages calculated for lanthanide complexes are summarized in Table 1, and selected bond lengths and
assume 3 phosphine oxide ligands + Ln(NO3)3 + residual angles with their estimated standard deviations are given in
water/solvents as indicated. Mass spectrometry data were Tables 2 and 3. Complete tables for each structure reported
acquired on a Bruker Amazon speed ion trap instrument with here, along with diagrams depicting the thermal ellipsoids at
electrospray ionization (ESI). Absorption spectra were acquired 50%, are provided in the ESI.†
on a Shimadzu UV-2450 or Agilent 8453 UV-VIS spectrophoto-
meter. Luminescence data were collected on either a Horiba
Photophysical studies
Fluoromax 4 (emission spectra, luminescence lifetimes) or a
All luminescence studies were carried out with a 1 : 3 ratio of
Ln(NO3)3·xH2O to ligand 4 in chromasolv grade CH3CN, HPLC
grade CH3OH or 99.5% atom %D CH3OD. We prepared solu-
tions of complexes for absorption, emission and excitation
spectra by combining appropriate volumes of metal and ligand
Hitachi F-7000 spectrophotometer (77
quantum yields).
K measurements,
Single crystal X-ray crystallography
Crystals suitable for X-ray diffraction were mounted on a nylon stock solutions to give an overall 2.0 mM concentration of Ln-4
loop using a small amount of paratone oil. Data were collected complex.
using a Bruker CCD (charge coupled device) based diffract-
Quantum yields. Relative quantum yields of all Ln-4 com-
ometer equipped with an Oxford Cryostream low-temperature plexes were determined using the single-point method27,28
apparatus operating at 173(2) K. Data were measured using with quinine sulfate as the reference fluorophore. Metal
omega and phi scans of 0.5° per frame. The total number of complex samples were diluted to 1.0 × 10−5 M in CH3CN.
images was based on results from the program COSMO20 Quinine sulfate solutions were diluted to 1.0 × 10−5 M in 0.1 M
where redundancy was expected to be 4.0 and completeness of H2SO4. Integrated emission intensities (I) were collected with
100% out to 0.83 Å. Cell parameters were retrieved using APEX the Hitachi F-7000 instrument as noted above, exciting all
II software21 and refined using SAINT on all observed reflec- samples at 300 nm with a scan speed of 240 nm min−1 and
tions. Data reduction was performed using the SAINT soft- excitation/emission slit widths of 2.5 nm. Absorbance (A)
ware,22 which corrects for Lp. Scaling and absorption correc- values were recorded at 300 nm using an Agilent 8453 UV-Vis
Table 1 Crystal data and structure refinement for complexes 5–9
5
6
7
8
9
Structure number
Eu(4)2(NO3)3H2O
Gd(4)2(NO3)3H2O
Tb(4)2(NO3)3H2O
Dy(4)2(NO3)3H2O
Eu(4)2(NO3)3
Empirical formula
CCDC number
Formula weight
Temperature/K
C40H36EuN3O14P2
1484663
996.62
C40H36GdN3O14P2
1484664
1001.91
C40H36TbN3O14P2
1484662
1003.58
C40H36DyN3O14P2
1484660
1007.16
C40H34EuN3O13P2·(CHCl3)2
1484661
1217.34
173(2)
173(2)
173(2)
173(2)
173(2)
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
ˉ
ˉ
ˉ
ˉ
ˉ
a/Å
b/Å
c/Å
α/°
11.2311(19)
11.6325(19)
18.480(3)
72.083(2)
75.706(2)
66.718(2)
2088.3(6)
2
11.23800(10)
11.6353(2)
18.4819(2)
72.0301(6)
75.7452(6)
66.7376(6)
2090.38(5)
2
11.2287(12)
11.6265(12)
18.433(2)
72.0460(10)
75.8340(10)
66.6960(10)
2081.6(4)
11.2313(7)
11.6143(7)
18.4094(11)
72.0480(10)
75.8590(10)
66.6400(10)
2076.6(2)
12.5305(12)
14.0929(14)
16.2116(16)
71.5480(10)
80.1730(10)
72.0490(10)
2575.0(4)
β/°
γ/°
Volume/Å3
Z
2
2
2
Reflections collected
Independent reflections
21 495
30 211
34 436
29 641
51 489
7660 [Rint = 0.0483,
Rsigma = 0.0523]
R1 = 0.0452,
wR2 = 0.1178
R1 = 0.0511,
wR2 = 0.1246
7956 [Rint = 0.0389,
Rsigma = 0.0359]
R1 = 0.0242,
wR2 = 0.0603
R1 = 0.0257,
wR2 = 0.0613
7587 [Rint = 0.0518,
Rsigma = 0.0428]
R1 = 0.0293,
wR2 = 0.0618
R1 = 0.0371,
wR2 = 0.0654
7902 [Rint = 0.0512,
Rsigma = 0.0508]
R1 = 0.0321,
wR2 = 0.0656
R1 = 0.0435,
wR2 = 0.0702
9820 [Rint = 0.1507,
Rsigma = 0.1278]
R1 = 0.0730,
wR2 = 0.1540
R1 = 0.1287,
wR2 = 0.1769
Final R indexes [I ≥ 2σ(I)]
Final R indexes [all data]
Dalton Trans.
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18
Table 2 Selected bond distances (Å) for Ln-4 structures 5–9 reported here, as well as the Er(NO3)342(H2O)17 (10) and Ce(NO3)343 (11) data
reported previously
Ten-coordinate Ln(III)
Nine-coordinate Ln(III)
1118
Ce(4)3(NO3)3
9
5
6
7
8
1017
Er(4)2(NO3)3H2O
Eu(4)2(NO3)3
Eu(4)2(NO3)3H2O
Gd(4)2(NO3)3H2O
Tb(4)2(NO3)3H2O
Dy(4)2(NO3)3H2O
Monodentate ligand
Ln–O1(P)
2.401
2.410
—
—
2.306(3)
2.301(3)
2.2914(16)
2.2882(15)
2.281(2)
2.273(2)
2.264(2)
2.263(2)
2.246
2.253
Ln–O1a(P)
Bidentate ligand
Ln–O1(P)
Ln–O2(C)
Ln–O1a(P)
Ln–O2a(C)
2.446
2.609
—
2.345(5)
2.496(6)
2.372(5)
2.536(6)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Water and bidentate nitrates
Ln–O1w
—
—
2.392(3)
2.486(3)
2.475(4)
2.482(3)
2.513(3)
2.500(3)
2.498(3)
2.3739(15)
2.4797(16)
2.4608(19)
2.4827(18)
2.5068(18)
2.5007(17)
2.4908(17)
2.358(2)
2.470(2)
2.445(3)
2.464(2)
2.488(2)
2.485(2)
2.472(2)
2.344(2)
2.453(2)
2.429(3)
2.443(2)
2.478(3)
2.477(2)
2.458(3)
2.323
2.431
2.410
2.420
2.443
2.472
2.432
Ln–O3b(N)
Ln–O4b(N)
Ln–O3c(N)
Ln–O4c(N)
Ln–O3d(N)
Ln–O4d(N)
2.630
2.623
2.672
2.526
2.753
2.580
2.620(5)
2.535(5)
2.494(6)
2.454(6)
2.605(6)
2.504(5)
18
Table 3 Selected bond angles (°) for Ln-4 structures 5–9 reported here, as well as the Ce(NO3)343
and Er(NO3)342(H2O)17 data reported
previously
Ten-coordinate Ln(III)
1118
Nine-coordinate Ln(III)
9
5
6
7
8
1017
Ce(4)3(NO3)3 Eu(4)2(NO3)3 Eu(4)2(NO3)3H2O Gd(4)2(NO3)3H2O Tb(4)2(NO3)3H2O Dy(4)2(NO3)3H2O Er(4)2(NO3)3H2O
Monodentate ligand
O1–Ln–O1a
O1–Ln–O3b
O1–Ln–O3d
O1–Ln–O4d
O1–Ln–O1w
O1a–Ln–O3b
O1a–Ln–O4b
O1a–Ln–O4c
O1a–Ln–O4d
O1a–Ln–O1w
Bidentate ligand
O1–Ln–O2
O1a–Ln–O2a
O1–Ln–O3d
O2–Ln–O4b
O1a–Ln–O3b
O2a–Ln–O4d
83.724
72.096
66.575
77.661
—
74.434
88.035
79.816
73.151
—
—
—
—
—
—
—
—
—
—
—
84.39(11)
72.52(10)
75.64(12)
80.04(12)
82.81(11)
79.20(10)
80.86(12)
77.56(11)
76.23(11)
152.05(11)
84.18(6)
72.49(6)
75.77(6)
79.82(6)
83.00(6)
78.95(6)
81.04(7)
77.69(6)
76.35(6)
151.68(6)
84.21(8)
72.63(8)
75.70(8)
80.14(8)
83.04(8)
78.95(8)
80.94(9)
77.41(8)
76.47(8)
151.55(8)
84.20(8)
72.62(8)
75.95(9)
80.57(9)
83.30(8)
78.92(8)
81.20(9)
77.22(8)
76.68(8)
151.60(9)
83.718
73.480
75.938
80.608
83.883
78.982
81.505
77.259
76.674
151.959
68.125
—
72.03(18)
71.60(18)
69.02(17)
73.31(19)
71.19(18)
73.41(17)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
74.482
74.084
—
—
Water and bidentate nitrates
O3b–Ln–O4b
O3c–Ln–O4c
O3d–Ln–O4d
O1w–Ln–O3b
O1w–Ln–O4b
O1w–Ln–O3c
O1w–Ln–O3d
47.266
48.069
47.542
—
—
—
49.07(18)
51.8(2)
49.22(17)
—
—
—
51.14(11)
50.83(11)
50.89(10)
73.29(10)
85.66(12)
72.57(11)
74.70(10)
51.62(6)
50.98(6)
51.07(5)
73.14(6)
85.36(6)
72.48(6)
74.76(6)
51.90(8)
51.35(8)
51.35(7)
72.99(8)
85.43(8)
72.44(8)
74.63(8)
52.14(9)
51.52(8)
51.46(8)
73.04(8)
85.10(9)
72.21(9)
74.55(8)
51.975
52.023
51.719
73.405
85.305
71.475
74.023
—
—
spectrophotometer. The quantum yield of each Ln-4 (Φx) is taken as 0.54. The relative quantum yield of each Ln-4
complex was calculated using the following equation:
complex was measured in triplicate to yield the reported
average values and standard deviations.
Ligand triplet state energy. The triplet state energy of com-
pound 4 in acetonitrile was determined by recording emission
2
ΦrIxArnx
Φx ¼
2
IrAxnr
where subscripts r and x denote the quinine sulfate reference spectra of the 1 : 3 Gd(NO3)3-4 complex at 77 K. Separate stock
standard and Ln-4 sample, respectively, n denotes the refrac- solutions of the ligand and metal nitrate salt were prepared
tive index of each solution (nr = 1.3340 and nx = 1.344), and Φr and combined to give a solution of the 1 : 3 (M : L) complex at
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1.0 × 10−4 M. Low temperature spectra were recorded with the to give an off-white powder in reasonable yield (2.89 g, 56%
Hitachi F-7000 spectrophotometer running in both fluo- from 3.18 g starting bromoacetophenone). 1H NMR (CDCl3,
rescence and phosphorescence mode (scan rate
= 240 300 MHz) δ: 7.98 (m, 2H), 7.83–7.76 (m, 4H), 7.54–7.38 (m,
nm min−1, λex = 350 nm, SW = 5 nm for fluorescence and scan 9H), 4.12 (d, JP–H = 15 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ
rate = 240 nm min−1, λex = 350 nm, SW = 10 nm for phosphor- 193.0 (d, JP–C = 5.9 Hz, CvO), 137.2 (s), 133.8 (m), 132.7 (s),
escence), with phosphorescence emission being collected fol- 132.4 (m), 131.6 (s), 131.3 (m), 129.4 (s), 128.8 (m), 43.4 (d,
lowing a 1 ms delay time after initial excitation. The triplet JP–C = 58 Hz, CH2); 31P NMR (CDCl3, 121 MHz) δ: 28.1; 1H NMR
state energy value was obtained from deconvolution of the (CD3CN, 400 MHz): δ 7.98 (m, 2H), 7.80 (m, 4H), 7.40–7.60 (m,
phosphorescence spectrum into its Gaussian components 9H), 4.25 (d, JP–H = 14.8 Hz, 2H, CH2); 13C NMR (CD3CN,
(OriginPro 2017). The peak corresponding to the highest 100 MHz): δ 194.1 (d, JC–P = 6.2 Hz, CvO), 138.3 (s), 134.1 (d,
energy vibrational level obtained from deconvolution was used JC–P = 134 Hz), 131.7 (m), 130.0 (s), 129.6 (m), 129.3 (m), 40.5
to calculate the ligand triplet state energy.29
(d, JC–P = 60.1 Hz, CH2); 31P NMR (CD3CN, 121 MHz): δ 26 (s);
FT-IR ν (cm−1): 1680 (CvO), 1440 (CH2), 1179 (PvO); UV-VIS
(6.0 mM, CH3CN): λmax = 317 nm.
Synthesis
iPrOPPh2 in diethyl ether (2). The procedure of Shintou and
Metal–ligand complex synthesis. General procedure for Ln
co-workers30 was followed for the preparation of the iso-pro- (NO3)3 (Ln = Sm, Eu, Tb, Dy) complexes described here.
poxydiphenyl phosphine 2; we varied only the isolation pro- Phosphine oxide 4 (50 mg, 0.156 mmol) and 1/3 molar equi-
cedure, which is described here. After the pyridinium hydro- valent of Ln(NO3)3·6H2O were dissolved in acetonitrile
chloride salt was removed using a Hirsch funnel, the solid was (∼15 mL) and stirred at room temperature for thirty minutes.
rinsed with diethyl ether. The filtrate was concentrated on a The volatiles were removed under reduced pressure, and the
rotary evaporator under reduced pressure, with the water bath resultant clear film was triturated two to three times with
at room temperature, until the majority of the solvent was diethyl ether to give off-white powders. The characterization
removed. If care is not taken with this step it is possible to data for each of the metal–ligand complexes are given below.
1
evaporate the desired product along with solvent diethyl ether.
Sm-(4)3(NO3)3. H NMR (CD3CN, 400 MHz): δ 8.28 (m, 4H),
1
The crude reaction mixture was analyzed by H NMR, and the 7.72 (m, 2H), 7.57 (m, 3H), 7.34 (m, 6H), 4.93 (d, JP–H = 14.8
relative amount of product to solvent ether was determined by Hz, 2H, CH2); 13C NMR (CD3CN, 100 MHz): δ 193.8 (d, JP–C
=
integration. If remaining pyridinium chloride was detected in 5.6 Hz, CvO), 136.5 (d, JP–C = 3.6 Hz), 134.4 (s), 133.2 (s), 131.6
the product, it was precipitated out by placing the solution in (d, JP–C = 10.7 Hz), 130.3 (d, JP–C = 107 Hz), 129.1 (m), 42.9 (d,
the refrigerator overnight. The product was then decanted the JP–C = 68.2 Hz, CH2); 31P NMR (CD3CN, 162 MHz): δ 35 (broad
following day and reanalyzed by 1H NMR. The resultant iso- s); FT-IR ν (cm−1): 2869 (CH), 1677 (CvO), 1138 (PvO);
propoxydiphenylphosphine 2 is stable for months if stored in ESI-LRMS (M+, m/z): calcd for Sm(C20H17O2P)3(NO3)2: 1236.2,
the refrigerator as a solution in diethyl ether. Typically, we found 1236.3; calcd for Sm(C20H17O2P)2(NO3)2: 916.1, found
carried forward a ∼65% solution of iPrOPPh2 in diethyl ether 916.1; anal. calcd for Sm(C20H17O2P)3(NO3)3 (found): C, 55.55
to the procedure described below.
Phenacyldiphenylphosphine oxide (4). Compound 4 was pre-
(55.47); H, 3.96 (4.06); N, 3.24 (3.27).
Eu-(4)3(NO3)3. FT-IR ν (cm−1): 1676 (CvO), 1138 (PvO);
pared in two steps following slightly modified procedures of ESI-LRMS (M+, m/z): calcd for Eu(C20H17O2P)3(NO3)2: 1235.2,
Böhmer31 and Gandelman.32 Isopropoxy ether 2 (as an ethe- found 1235.1; calcd for Eu(C20H17O2P)2(NO3)2: 915.1, found
real solution, typically 5–10 gram scale) and 2-bromoaceto- 915.1; anal. calcd for Eu(C20H17O2P)3(NO3)3(CH3CN)(H2O)3
phenone 3 (10% molar excess) were mixed, without additional (found): C, 53.42 (53.46); H, 4.34 (3.90); N, 4.02 (3.71).
solvent, in an open 50 mL round bottom flask at room temp-
Tb-(4)3(NO3)3. FT-IR ν (cm−1): 1677 (CvO), 1141 (PvO);
erature. After approximately 5–10 minutes, the reaction ESI-LRMS (M+, m/z): calcd for Tb(C20H17O2P)3(NO3)2: 1243.2,
mixture warmed rapidly and a gaseous byproduct was evolved. found 1243.3; calcd for Tb(C20H17O2P)2(NO3)2: 923.6, found
When the reaction had cooled to room temperature, the 923.6; anal. calcd for Tb (C20H17O2P)3(NO3)3(CH3CN)(H2O)4
mixture was heated to 100 °C for thirty minutes at which point (found): C, 52.48 (52.07); H, 4.40 (3.82); N, 3.95 (3.91).
the solution became quite viscous. The reaction mixture was
Dy-(4)3(NO3)3. FT-IR ν (cm−1): 1676 (CvO), 1140 (PvO);
allowed to cool to room temperature, and the viscous oil was ESI-LRMS (M+, m/z): calcd for Dy(C20H17O2P)3(NO3)2: 1248.2,
dissolved in CHCl3 (30 mL) and added drop wise to a solution found 1248.4; calcd for Dy(C20H17O2P)2(NO3)2: 928.1, found
of saturated NaHCO3 (45 mL). The solution was transferred to 928.3; anal. calcd for Dy (C20H17O2P)3(NO3)3(CH3CN)(H2O)2
a separatory funnel, and the organic layer was drained off. The (found): C, 53.71 (53.46); H, 4.22 (3.90); N, 4.04 (3.71).
aqueous phase was extracted with CHCl3 (2 × 30 mL). The com-
bined chloroform layers were washed with saturated sodium
bicarbonate (2 × 25 mL), brine (1 × 25 mL), dried over MgSO4
and concentrated under reduced pressure. The resulting
orange-red oil was placed under high vacuum overnight to
Results and discussion
Synthesis of ligand and Ln-ligand complexes
remove any remaining volatile impurities. The product was Phosphine oxide ligand 4 was readily prepared in two steps
purified by trituration with Et2O and EtOAc (three times each) using Arbuzov chemistry (Scheme 1a).31 Diphenylchloro-
Dalton Trans.
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