Synthesis and lanthanide coordination chemistry of 2-[(phosphinoyl)methyl- 4,5-dihydrooxazole and 2-[(phosphinoyl)methylbenzoxazole ligands

Article abstract of DOI:10.1016/j.poly.2011.08.012

Syntheses for [(diphenylphosphinoyl)methyl-4,5-dihydrooxazole (2) and [(diarylphosphinoyl)methylbenzoxazoles [aryl = phenyl (3), tolyl (4), 2-trifluoromethylphenyl (5) and 3,5-bis(trifluoromethyl)phenyl (6) have been developed. Each ligand has been charac

Full text of DOI:10.1016/j.poly.2011.08.012

Polyhedron 30 (2011) 2746–2757
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and lanthanide coordination chemistry of 2-[(phosphinoyl)methyl]-
4,5-dihydrooxazole and 2-[(phosphinoyl)methyl]benzoxazole ligands
⇑
Sylvie Pailloux, Cornel Edicome Shirima, Eileen N. Duesler, Karen Ann Smith, Robert T. Paine
Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM 87131, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Syntheses for [(diphenylphosphinoyl)methyl]-4,5-dihydrooxazole (2) and [(diarylphosphinoyl)methyl]
benzoxazoles [aryl = phenyl (3), tolyl (4), 2-trifluoromethylphenyl (5) and 3,5-bis(trifluoromethyl)phenyl
(6)] have been developed. Each ligand has been characterized by spectroscopic methods and single crys-
tal X-ray diffraction analyses have been completed for 2, 3, 4 and 5. The coordination chemistry of the
ligands with Nd(NO3)3 and Yb(NO3)3 has been examined and structure determinations for [Nd(2)2
(NO3)3(CH3OH)], [Nd(2)2(NO3)3], [Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH), [Nd(3)2(NO3)3]ꢀ3(CHCl3), [Nd(4)2
(NO3)3(H2O)], [Yb(4)2(NO3)3(H2O)] and [Yb(5)2(NO3)3(H2O)]ꢀ0.5(CH3CN) are reported. Depending upon
conditions, the ligands act as monodentate PO or bidentate, chelating PO,N donors.
Received 22 June 2011
Accepted 10 August 2011
Available online 23 August 2011
Keywords:
Oxazole
Benzoxazole
Phosphine oxide
Lanthanide complexes
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Despite the expansive options available for functionalization of
A and B, relatively few reports of attempts to prepare ligands
The synthesis and reactivity of organic molecules containing 2-
oxazoline (A) and 2-benzoxazole (B) ring fragments have been
actively studied due, in part, to their appearance in natural systems
and their use as platforms for the construction of hybrid, hemila-
bile ligands. In the latter case, A and B have been decorated with,
for example, hydroxyphenyl [1–3], pyridine [3–11], quinolinyl
[12,13], thiol [14], phosphine [15–25] and phosphine oxide
[26–29] donor groups. The coordination chemistry of the ligands
has been elaborated largely by using late, soft, d-block metal ions
in efforts to obtain asymmetric catalysts for various organic trans-
formations. Portions of that coordination chemistry for the oxazo-
line-based ligands have been thoroughly reviewed [30,31]. In all
cases where molecular structures have been determined by crys-
tallographic methods, the hybrid ligands have been observed to
chelate to metal cations by using the oxazoline or benzoxazole ring
that effectively bind with f-block metal ions have appeared
[5,6,9,11,33–37]. In our group, we have been engaged in ligand de-
sign efforts for lanthanide and actinide ions, and that work has led
to development of bifunctional ligand classes C–E [38–51]. In each
case, the hybrid PO,CO and PO,NO ligands were expected to form
bidentate chelate complexes with hard metal cations by using both
available O-atom donor centers, and it was anticipated that the
phosphoryl oxygen atom would provide the stronger interaction.
Indeed, in all structurally characterized examples except one, C–
E were found to form bidentate chelates [38–48]. In the exception,
[Er(C)2(NO3)3(H2O)], both C (R = iPr, R0 = Et) ligands were observed
to bind with Er(III) through monodentate PO interactions while the
amide carbonyl groups interacted, via hydrogen bonds, with an in-
ner sphere water molecule [39]. These results led us to examine re-
lated N,CO and NO,CO hybrid ligand architectures including those
of type F–H [49–51]. Ligands G and H were observed to form
bidentate complexes although a derivative of G with a hydroxyl
group on the methylene carbon atom was found to chelate through
the amide carbonyl O-atom and the hydroxyl O-atom [50]. In con-
trast, spectroscopic data suggested that examples of F behaved
only as monodentate CO donor ligands with the pyridine N-atom
hydrogen bonded to inner sphere solvent (H2O or MeOH). Unfortu-
nately, efforts to confirm this bonding mode by crystallographic
analyses have, so far, been unsuccessful. Nonetheless, these find-
ings suggested the possibility that new ligands of types I and J, con-
taining a very hard PO donor center and a softer Nring donor site,
might produce complexes with both monodentate and bidentate
coordination modes. Herein, we report the syntheses of methyl-
phosphoryl decorated derivatives of I (R = Ph) and J (R = Ph, Tol,
Noxaz-atom and one or two exo-donor atom(s). The Ooxaz-atom has
not been found to participate in the coordination chemistry. This
observation is consistent with photoelectron spectroscopic analy-
ses and quantum mechanical computations that indicate that the
Noxaz-atom lone pair lies at lower energy than the Ooxaz-atom lone
pair [32].
O
O
N
X
X
N
A
B
⇑
Corresponding author. Tel.: +1 505 277 1661; fax: +1 505 277 2609.
E-mail address: rtpaine@unm.edu (R.T. Paine).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.012

S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
2747
(CF3)C6H4 and (CF3)2C6H3) and structurally characterized coordina-
tion compounds of each ligand that show evidence for hemilabile
interactions on lanthanide cations.
(100 mL), concentrated, then vacuum evaporated over several days
leaving a yellow solid, 1. Yield: 3.8 g, 47%. Mp 58–60 °C. HRESI-MS:
m/z 270.1058 [M+H+] (C16H17NOP requires 270.0970). 31P NMR
(CDCl3): d = ꢁ16.9. 1H NMR (250 MHz, CDCl3): d = 3.0 (s, 2H, H1),
3
3
3.6 (t, 2H, H3, JHH = 9.2 Hz), 3.9 (t, 2H, H4, JHH = 9.5 Hz), 7.2 (m,
6H, Ar), 7.3–7.4 (m, 4H, Ar).
O
P
O
C
R
R
The crude sample of 1 was dissolved in Et2O and oxygen was
bubbled through the solution (23 °C, 2d). The solvent was evapo-
rated and the yellow oily residue purified by column chromatogra-
phy (silica gel, 70–230 mesh, elution by CH2Cl2/MeOH 95/5
followed by CH2Cl2/MeOH 90/10). Compound 2 was obtained as
a yellow solid. Yield: 5.1 g, 58%. Mp 128–130 °C. Recrystallization
from EtOAc gave colorless single crystals. HRESI-MS: m/
z = 286.0993 [M+H+] (C16H17NO2P requires 286.0997); 308.0818
R
R
NR'2
N
O
P
N
O
E
R
R
O
P
O
C
D
N
O
N
N
[M+Na+]. IR (KBr, cmꢁ1):
m = 1659 (s, mCN), 1188 (s, m
PO). 31P NMR
C
NR2
C
NR2
O
O
C
(CDCl3): d = 28.1. 1H NMR (500 MHz, CDCl3): d = 3.4 (d, 2H, H1,
NR2
O
2JHP = 14.6 Hz), 3.7 (dt, 2H, H3, JHH = 9.4 Hz, JHP = 3.6 Hz), 4.0 (t,
3
5
G
H
F
3
2H, H4, JHH = 9.5 Hz), 7.4–7.5 (m, 6H, Ar), 7.7–7.8 (m, 4H, Ar).
1H{31P} NMR (500 MHz, CDCl3): d = 3.4 (s, 2H, H1), 3.7 (t, 2H, H3,
3JHH = 9.5 Hz), 4.0 (t, 2H, H4, JHH = 9.5 Hz), 7.4–7.5 (m, 6H, Ar),
3
O
O
N
7.8 (d, 4H, Ar). 13C{1H} NMR (62.9 MHz, CDCl3): d = 32.5 (d, C1,
R
R
R
1JCP = 64.2 Hz), 54.8 (s, C3), 68.2 (s, C4), 128.9 (d, Ar, JCP = 12.2 Hz),
N
P
P
R
O
O
1
131.5 (d, Ar, JCP = 9.7 Hz), 132.4 (d, i-Ar, JCP = 100.9 Hz), 132.5 (d,
Ar, JCP = 2.5 Hz), 161.4 (d, C2, JCP = 7.4 Hz).
2
I
J
R = Ph ; 2
R = Ph ; 3
= Tolyl ; 4
= 2-CF3C6H4 ; 5
= 3,5-(CF3)2C6H3 ; 6
2.2.1.2. 2-[(Diphenylphosphinoyl)methyl]benzoxazole (3). Method 1.
Phenyl magnesium bromide (30 mL, 2.0 M solution in THF,
20 mL) was added dropwise, with stirring, under dry nitrogen to
freshly distilled diethyl phosphite (1.0 mL, 6.5 mmol) in dry THF
(10 mL). The temperature rose during the addition and the result-
ing mixture was refluxed (60 °C, 1 h). A sample of 2-chloromethyl-
benzoxazole (1.1 g, 6.5 mmol) [28] in dry THF (10 mL) was added
(23 °C), and the mixture refluxed (60 °C, 12 h) during which time
the color turned from yellow to dark red. The THF was vacuum
evaporated and the residue treated with saturated aqueous NH4Cl
(100 mL). The resulting mixture was extracted with CHCl3
(3 ꢂ 10 mL) and the filtrate evaporated to dryness leaving a yellow
solid, 3. Further purification was accomplished by column chroma-
tography (silica gel 70–230 mesh, MeOH/CH2Cl2, 5/95). Yield: 2.1 g,
96%. Mp 160–161 °C. Method 2. This method is similar to that de-
scribed by Minami [27]. Diisopropylamine (2.2 mL, 16 mmol) and
BuLi (1.6 M solution in hexane, 10.2 mL, 16 mmol) were combined
in dry THF (15 mL), stirred (ꢁ78 °C, 10 min), and the solution
added with stirring (ꢁ78 °C, 15 min) to 2-methylbenzoxazole
(1.1 g, 8 mmol) in THF (10 mL). The resulting yellow solution was
combined with diphenylphosphinic chloride (1.5 mL, 8 mmol)
and stirred (ꢁ78 °C, 1.5 h). The mixture was then quenched with
aqueous 1.2 M HCl (ꢁ78 °C, 100 mL), extracted with CHCl3
(3 ꢂ 20 mL), the combined organic layers washed with saturated
aqueous brine solution (100 mL) and dried over Na2SO4. The recov-
ered organic phase was vacuum evaporated leaving a yellow resi-
due that was initially purified by column chromatography (silica
gel, 70–230 mesh, with elution by CH2Cl2 followed by 2.5%
MeOH/CH2Cl2, 5% MeOH/CH2Cl2 and 10% MeOH/CH2Cl2). The pale
yellow solid, 3, was vacuum-dried and crystallized from MeOH/
CH2Cl2 (5:95) or from hot ethyl acetate. Yield: 2.3 g, 84%. Method
3. A solution of LDA prepared from diisopropylamine (4.5 mL,
32 mmol) and BuLi (1.6 M in hexane, 20.5 mL, 33 mmol) in THF
(15 mL) was added to a solution of 2-methylbenzoxazole (2.1 g,
16 mmol) in THF (10 mL, ꢁ78 °C). The combination was stirred
(ꢁ78 °C, 15 min) and diphenylphosphine chloride (3.3 mL,
17.6 mmol) was added (ꢁ78 °C, 1.5 h, ꢁ78 °C). The resulting cold
mixture was quenched with aqueous 1.2 M HCl (100 mL), warmed
to 23 °C and extracted with CHCl3 (3 ꢂ 20 mL). The combined or-
ganic phases were washed with saturated brine solution
(100 mL) and dried over Na2SO4. This solution was left exposed
2. Experimental
2.1. Materials and characterization
Organic solvents were purchased from VWR and synthetic re-
agents were obtained from Aldrich Chemical Co. Infrared spectra
were recorded on a Bruker Tensor 27 benchtop spectrometer and
NMR spectra were measured with Bruker FX-250 and Avance
300 and 500 spectrometers using Me4Si (1H, 13C) and 85%
H3PO4 (
31P) as external standards. Downfield shifts were given
+d values. Mass spectra were obtained from the UNM Mass
Spectrometry Center. Elemental analyses were obtained from
Galbraith Laboratories. The preparations of N-(2-hydroxy-
phenyl)chloroacetoamide [28] and polyphosphate ester (PPE)
[52] used in the synthesis of 2-chloromethylbenzoxazole were
taken from the literature. A threefold excess of PPE was used
to drive the reaction to completion.
2.2. Experimental procedures
2.2.1. Ligand syntheses
2.2.1.1. 2-[(Diphenylphosphinoyl)methyl]-4,5-dihydrooxazole (2).
The precursor phosphane, 2-[(diphenylphosphanyl)methyl]-
4,5-dihydrooxazole (1), was prepared in a fashion similar to that
described in the literature [18]. A sample of 2-methyl-2-oxazoline
(2.6 g, 30.8 mmol, Aldrich) in dry THF (5 mL) was added dropwise
with stirring (10 min, ꢁ78 °C) under dry nitrogen to BuLi in hexane
(19.4 mL, 1.6 M, 30.8 mmol) in dry THF (50 mL). Stirring was con-
tinued (ꢁ78 °C, 1 h) wherein the solution changed from colorless
to yellow. A sample of degassed Me3SiCl (4.0 mL, 30.8 mmol) was
added (ꢁ78 °C), stirred (1 h) and then Ph2PCl (5.5 mL, 30.8 mmol)
in dry THF (10 mL) was added. The resulting mixture was stirred
and allowed to slowly warm to 23 °C (12 h). The volatiles were re-
moved in vacuo leaving a yellow oil that was extracted with CH2Cl2

2748
S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
to air (24 h) in order to complete the oxidation of the intermediate
phosphine. The product was vacuum evaporated and the crude
product purified by column chromatography as described above
leading to a pale yellow solid, 3. Yield: 3.8 g, 72%. HRESI-MS: m/
z = 334.1003 [M+H+] (C20H17NO2P requires 334.0997), 356.0815
from EtOAc/hexane solution provided colorless crystals of 5. Yield:
2.7 g, 74%. Mp 140–141 °C. HRESI-MS: m/z = 470.0743 [M+H+]
(C22H15F6NO2P requires 470.0744. IR (KBr, cmꢁ1):
m = 1616 (s,
m
CN), 1176 (vs
m
PO). 31P NMR (CDCl3): d = 28.4. 1H NMR (250 Mz,
2
CDCl3): d = 4.3 (d, 2H, H1, JPH = 14.5 Hz), 7.2 (m, 2H, Ar), 7.3–7.4
(m, 1H, Ar), 7.5–7.6 (m, 5H, Ar), 7.7–7.8 (m, 2H, Ar), 8.2–8.3 (m,
2H, Ar). 13C{1H} NMR (125.7 MHz, CDCl3): d = 34.0 (d, C1,
[M+Na+]. IR (KBr, cmꢁ1):
m = 1610 (s, mCN), 1196 (vs m
PO). 31P NMR
(CDCl3): d = 27.7. 1H NMR (250 MHz, CDCl3): d = 4.1 (d, 2H, H1,
2JHP = 14.5 Hz), 7.2 (m, 2H, Ar), 7.3–7.5 (m, 8H, Ar), 7.7–7.8 (m,
4H Ar). 13C{1H} NMR (125.7 MHz, CDCl3): d = 32.8 (d, C1,
1JCP = 63.2 Hz), 110.4 (s), 119.6 (s), 123.9 (s), 124.7 (s), 128.5 (d,
1JCP = 89.7 Hz), 110.4 (s), 119.7 (s), 123.4 (q, CF3, JCF = 273.0 Hz),
1
1
124.2 (s), 124.9 (s), 127.6 (s), 130.6 (d, C9, JCP = 99.3 Hz), 131.5
(d, JCP = 13.8 Hz), 131.8 (qd, C10
2
,
2JCP = 6.5 Hz, JCF = 33.5 Hz), 132.4
C10
,
2JCP = 12.5 Hz), 130.9 (d, C11
,
3JCP = 9.6 Hz), 131.3 (d, C9,
(s), 134.2 (d, JCP = 8.9 Hz), 141.0 (s) 150.9 (s), 158.3 (d, C2,
2JCP = 9.6 Hz. Anal. Calc. for C22H14F6NO2P: C, 56.30; H, 3.01; N,
2.98. Found: C, 55.79; H, 2.89; N, 2.98%.
1JCP = 104.3 Hz), 132.1 (d, C12
,
4JCP = 2.8 Hz), 141.0 (s), 150.9(s),
158.6 (d, C2, JCP = 9.1 Hz). 13C{1H, 31P}NMR (125.7 MHz, CDCl3):
d = 32.8, 110.4, 119.6, 124.1, 124.7, 128.5, 130.9, 131.3, 132.2,
141.0, 150.9, 158.6. Anal. Calc. for C20H16NO2P: C, 72.07; H, 4.84;
N, 4.20. Found: C, 71.16; H, 4.85; N, 3.89%.
2
2.2.1.5. 2-[Bis(3,5-bis-trifluoromethylphenyl)phosphinoylmethyl]ben-
zoxazole (6).
The phosphono Grignard reagent was prepared in the same
fashion as described for the synthesis of 5 by using 3,5-bis(trifluo-
romethyl)bromobenzene (3.5 mL, 20.5 mmol) and diethyl phos-
phite (1.0 mL, 7.5 mmol). The resulting solution was combined
with 2-chloromethylbenzoxazole (1.3 g, 7.5 mmol) in THF
(10 mL) and refluxed (50–60 °C, 12 h). The dark red solution was
vacuum evaporated and the residue treated with saturated aque-
ous NH4Cl (100 mL), extracted with CHCl3 (3 ꢂ 40 mL), the com-
bined organic phases dried (Na2SO4) and vacuum evaporated
leaving an orange solid. The solid was crystallized from EtOAc/hex-
ane solution leaving colorless crystals of 6. Yield 2.6 g, 55%. Mp
209–211 °C. HRESI-MS: m/z = 606.0496 [M+H+] (C24H13F12NO2P re-
2.2.1.3. 2-[(Di-o-tolylphosphinoyl)methyl]benzoxazole (4). A sample
of o-tolylmagnesium bromide (2.0 M solution in Et2O, 6.5 mL,
13.0 mmol) in THF (15 mL) was added dropwise to freshly distilled
diethyl phosphite (0.6 g, 4.4 mmol) in THF (10 mL). The tempera-
ture rose during the addition and the resulting mixture was
refluxed (70 °C, 1 h). The mixture was then cooled (23 °C) and
2-chloromethylbenzoxazole (0.7 g, 4.4 mmol) [28] in THF (10 mL)
was added with stirring. The resulting mixture was refluxed
(70 °C, 12 h), then cooled (23 °C) and the volatiles removed by vac-
uum evaporation leaving a yellow residue. The residue was treated
with saturated aqueous NH4Cl (100 mL), extracted with CHCl3
(3 ꢂ 20 mL), the combined organic phases dried over Na2SO4 and
vacuum evaporated. The recovered yellow solid was purified by
column chromatography (silica gel 70–230 mesh, elution with
EtOAc/hexane (50:50) and then EtOAc (100%)). This left a pale yel-
low oil that was washed with CH2Cl2/hexane mixture and vacuum
dried leaving a white solid, 4. Yield: 1.0 g, 67%. Mp 161–162 °C.
HRESI-MS: m/z = 362.1304 [M+H+] (C22H21NO2P requires
quires 606.0492. IR (KBr, cmꢁ1): 1616 (s,
PO). 31P NMR (CDCl3): d = 23.4. 1H NMR (250 Mz, CDCl3): d = 4.2
mCN), 1175 (sh), 1140 (s,
m
2
(d, 2H, H1, JHP = 16.2 Hz), 7.2–7.3 (m, 3H, Ar), 7.6 (m, 1H, Ar), 8.1
(s, 2H, H13), 8.4 (d, 4H, H10
Mz, CDCl3): d = 32.7 (d, C1, JCP = 67.6 Hz), 110.4 (s), 120.0 (s),
122.5 (q, CF3, JCF = 273.5 Hz), 124.9 (s), 125.8 (s), 126.8 (s), 131.5
,
3JHP = 11.8 Hz). 13C{1H} NMR (125.7
1
1
2
(d, C10
,
2JCP = 8.4 Hz), 132.7 (qd, C11
,
3JCP = 12.4 Hz, JCF = 34.6 Hz),
1
362.1310. IR (KBr, cmꢁ1): 1607 (s,
m
CN), 1178 (vs
m
PO). 31P NMR
133.5 (d, C9, JCP = 102.3 Hz), 140.7 (s), 150.7 (s), 156.4 (d, C2,
2JCP = 7.7 Hz). Anal. Calc. for C24H12F12NO2P: C, 47.62; H, 2.00; N,
2.31. Found: C, 47.70; H, 2.05; N, 2.28%.
(CDCl3) d = 31.1. 1H NMR (500 MHz, CDCl3): d = 2.4 (s, 6H, H11),
2
4.2 (d, 2H, H1, JPH = 14.2 Hz), 7.2 (m, 6H, Ar), 7.3–7.4 (m, 3H, Ar),
7.5–7.6 (m, 1H, Ar), 7.7–7.8 (d, 2H, H15,
3JPH = 13.8 Hz). 1H{31P}
NMR (500 MHz, CDCl3): d = 2.4 (s,6H, H11), 4.2 (s, 2H, H1), 7.1–7.2
(m, 6H, Ar), 7.3–7.4 (m, 3H, Ar), 7.5 (m, 1H, Ar), 7.7 (s, 2H, H15).
2.2.2. Synthesis of lanthanide complexes
2.2.2.1. [Nd(2)2(NO3)3(CH3OH)]. A sample of 2 (0.5 g, 1.7 mmol) in
MeOH (5 mL) was combined with Nd(NO3)3ꢀ6H2O (0.26 g,
0.58 mmol) in MeOH (2 mL), stirred (10 min), and a white precipi-
tate formed. Stirring was continued (1 h) and the solid collected by
filtration, washed with cold MeOH and dried (0.44 g, 54%). The
complex was isolated as [Nd(2)(NO3)3(MeOH)] by dissolving a
sample in a minimum of hot MeOH followed by slow cooling. This
provided X-ray quality crystals of the complex. IR (KBr, cmꢁ1):
13C{1H} NMR (125.7 MHz, CDCl3): d = 21.0 (d, C11
,
3JCP = 15.3 Hz),
1
32.3 (d, C1, JCP = 64.8 Hz), 110.4 (s), 119.5 (s), 123.9 (s), 124.6 (s),
125.6 (d, C15,
2JCP = 12.8 Hz), 130.2 (d, C9, JCP = 100.3 Hz), 131.6
1
(d, JCP = 11.8 Hz),131.7 (d, JCP = 11.1 Hz), 132.0 (s), 141.0 (s), 141.9
(d, C14, 3JCP = 9.7 Hz), 151.1 (s), 159.0 (d, C2, 2JCP = 8.5 Hz). Anal.Calc.
for C22H20NO2P: C, 73.12; H, 5.58; N, 3.88. Found: C, 72.83; H, 5.66;
N, 3.86%.
m
= 1646 (s, mCN), 1160 (s, mPO). Anal. Calc. for C33H36N2NdO14P2: C,
2.2.1.4. 2-[Bis(2-trifluoromethylphenyl)phosphinoylmethyl]benzoxaz-
ole (5). Magnesium turnings (0.5 g, 20.5 mmol) and THF (10 mL)
were placed in a nitrogen purged 250 mL Schlenk vessel. 2-Bromo-
benzotrifluoride (2.8 mL, 20.5 mmol) in THF (10 mL) was added
dropwise (23 °C) with stirring. The temperature rose during the
addition and the mixture was refluxed (60 °C, 1 h) to complete
the reaction. Freshly distilled diethyl phosphite (1.0 mL, 7.5 mmol)
in dry THF (10 mL) was added dropwise to the cooled Grignard
solution (23 °C) and the mixture was refluxed (60–70 °C, 1 h).
The reaction mixture was cooled (23 °C) and freshly distilled 2-
chloromethylbenzoxazole (1.3 g, 7.5 mmol) in dry THF (10 mL)
was added. This mixture was refluxed (12 h) and the progress of
the reaction monitored by TLC (95% CH2Cl2/5% MeOH). Volatiles
were removed by vacuum evaporation and the residue was treated
with saturated aqueous NH4Cl (100 mL) and extracted with CHCl3
(3 ꢂ 40 mL). The combined organic phases were dried (Na2SO4)
and evaporated leaving an orange solid. Crystallization of the solid
42.49; H, 3.89; N, 7.51; Nd, 15.46; P, 6.64. Found: C, 42.32; H, 3.73;
N, 7.47; Nd, 15.60; P, 6.27%.
2.2.2.2. [Nd(2)2(NO3)3]. A sample of [Nd(2)(NO3)3(CH3OH)] was
dissolved in CH3CN, stirred (12 h) and the volatiles removed by
vacuum evaporation. The remaining white solid was dissolved in
a minimum of CH3CN and the solution allowed to slowly evaporate
(5 d) leaving colorless crystals of [Nd(2)2(NO3)] suitable for X-ray
diffraction analysis.
2.2.2.3. [Nd(3)2(NO3)3 ]ꢀ3(CHCl3). A sample of 3 (0.1 g, 0.3 mmol)
was dissolved in MeOH (5 mL) and combined with Nd(NO3)3ꢀ6H2O
(0.06 g, 0.15 mmol) in MeOH (2 mL). The mixture was stirred
(12 h) resulting in a clear solution which was allowed to slowly
evaporate (4 d). A white solid formed and this was crystallized
from hot CHCl3 from which colorless single crystals were isolated
(0.15 g, 79%). IR (KBr, cmꢁ1):
m = 1155 (s, mPO). Anal. Calc. for

S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
2749
[Nd(3)2(NO3)3]ꢀ3(CHCl3), C42.5H34.5Cl7.5N5NdO13P2: C, 38.11; H,
(CH 3OH), Nd(4)(NO3)3(H2O)], [Yb(4)2(NO3)3(H2O)], [Yb (5)2(NO3)3
(H2O)]ꢀ0.5(CH3CN) and [Nd(3)2(NO3)3]ꢀ3(CHCl3), were placed in
glass capillaries and sealed. Crystal data were collected on a Bruker
X8 Apex 2 CCD-based X-ray diffractometer, outfitted with an
2.60; N, 5.17. Found: C, 42.33; H, 3.04; N, 6.21%.
2.2.2.4. [Yb(3)2(NO3)3(H2 O)]ꢀ0.5(CH3OH). A sample of 3 (0.13 g,
0.39 mmol) dissolved in MeOH (5 mL) and Yb(NO3)3ꢀ5H2O
(0.08 g, 0.2 mmol) in MeOH (5 mL) were combined and stirred
(23 °C, 12 h). The solution was then evaporated and the colorless
residue dissolved in CHCl3/hexane which led to the formation of
Oxford Cryostream 700 low temperature device, by using Mo K
a
radiation (0.71073 Å). The data frames were integrated with
Bruker SAINT [53] and processed with SADABS [54]. In all cases, a full
sphere of data was collected with negligible decay. Lattice param-
eters and data collection details are presented in Tables 1 (ligands)
and Table 2 (complexes). The structures were solved and refined
with Bruker SHELXTL [55]. All non-hydrogen atoms were refined
anisotropically and H-atoms were placed in ideal positions and
refined with Uiso = 1.2 Ueq of the parent atom except as noted other-
wise. In compound 4 the hydrogen atoms on aromatic C atoms
were included in ideal positions with fixed Uiso = 1.2 Ueq while
the H-atoms on the terminal methyl groups were placed in ideal
positions with Uiso = 1.5 Ueq. For [Nd(2)2(NO3)3(CH3OH)] the non-
hydrogen atoms were refined anisotropically except for C33 of
the inner coordination sphere CH3OH. The atom was disordered
over three positions, and it was refined isotropically with fixed
occupancies (C33, 39%, C330, 34%, C3300, 27%). The CH3OH OH-atom
was located and refined in position and Uiso, and the methyl H-
atoms were refined with Uiso = 1.5 Ueq. The other H-atoms were
placed in idealized positions and refined with Uiso = 1.2 Ueq of the
parent atom. For [Nd(2)2(NO3)3] the H-atoms were placed in ideal-
ized positions and refined isotropically with Uiso = 1.2 Ueq of the
parent atom except for the H-atoms on C1 and C21. These were al-
lowed to vary in position and Uiso. In [Yb(3)2(NO3)3]ꢀ0.5(CH3OH)
there is a disordered outer sphere CH3OH molecule that resides
close to a center of symmetry and is at half occupancy. The methyl
H-atoms and the OH H-atom were fixed in ideal positions with
Uiso = 1.2 Ueq and 1.5 Ueq, respectively. The H-atoms on the water
molecule were located in the difference maps and refined with
variable position and Uiso. In [Nd(3)2(NO3)3]ꢀ3(CHCl3)there are
three CHCl3 solvent molecules in the asymmetric unit. Two are
ordered but the third is disordered over two sites [C43–Cl7, Cl8,
Cl9 and C44–Cl10, Cl11, Cl12] with occupancies 0.47 and 0.53.
The H-atoms were included in ideal positions with fixed Uiso = 1.2
Ueq of the parent atom. For [Nd(4)2(NO3)3(H2O)] one tolyl ring
[C38–C44] showed signs of disorder that could not be adequately
modeled, and it was constrained as a regular hexagon with the
yellow crystals (0.11 g, 52%). IR (KBr, cmꢁ1):
m = 1159 (s, mPO). Anal.
Calc. for [Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH), C42.5H36N5O14.5P2Yb: C,
45.90; H, 3.42; N, 6.61. Found: C, 47.90; H, 3.83; N, 5.79%.
2.2.2.5. [Yb(4)2(NO3)3(H2O)]. A sample of 4 (0.2 g, 0.55 mmol) in
MeOH (10 mL) and Yb(NO3)3ꢀ5 H2O (0.12 g, 0.28 mmol) in MeOH
(2 mL) were combined and stirred (23 °C, 12 h). The solution was
evaporated leaving a yellow solid that was recrystallized from
MeCN/MeOH solution leaving colorless crystals (0.26 g, 85%). IR
(KBr, cmꢁ1):
C
m
= 1151 (s,
44H42N5O14P2Yb: C, 48.04; H, 3.81; N, 6.36. Found: C, 44.73; H,
3.67; N, 6.38%.
mPO). Anal. Calc. for [Yb(4)(NO3)3(H2O)],
2.2.2.6. [Nd(4)2(NO3)3(H2O)]. A sample of 4 (0.2 g, 0.55 mmol) in
MeOH (10 mL) and Nd(NO3)3ꢀ6H2O in MeOH (10 mL) were com-
bined and stirred (23 °C, 12 h). Solvent was evaporated leaving a
pale yellow solid. X-ray quality crystals were obtained by slow
evaporation of a MeOH/EtOAc solution. IR (KBr, cmꢁ1):
m
= 1152
(s,
mPO). Anal. Calc. for [Nd(4)(NO3)3(H2O)], C44H42N5NdO14P2: C,
49.34; H, 3.92; N, 6.53. Found: C, 44.74; H, 3.63; N, 6.83%.
2.2.2.7. [Yb(5)2(NO3)3(H2 O)]ꢀ0.5(CH3CN). A sample of
5
(0.2 g,
0.43 mmol) in MeOH (10 mL) and Yb(NO3)3ꢀ5H2O in MeOH
(2 mL) were combined and stirred (23 °C, 12 h). The solution was
evaporated leaving a white solid that was crystallized from MeCN
(0.18 g, 64%). IR (KBr, cmꢁ1):
[Yb(5)2(NO3)3(H2O)]ꢀ0.5(CH3CN),
m
= 1176 (s,
C45H31.5
m
PO). Anal. Calc. for
F12N5.5O14P2Yb:
C,40.44; H, 2.35; N, 5.76. Found: C, 37.53; H, 2.63; N, 5.84%.
2.3. Single crystal X-ray diffraction analyses
Single crystals of the ligands, 2, 3, 4 and 5, and complexes
[Nd(2)2(NO3)3(CH3OH)], [Nd(2)2(NO3)3], [Yb(3)2(NO3)3(H2O)]ꢀ0.5
Table 1
Crystallographic data for ligands 2–5.
2
3
4
5
Empirical formula
Color, habit
Crystal size (mm)
Formula weight
Crystal system
Space group
Unit cell dimension
a (Å)
C
16H16NO2P
C20H16NO2P
colorless plate
0.16 ꢂ 0.41 ꢂ 0.46
333.31
monoclinic
P21/n
C22H20NO2P
colorless prism
0.23 ꢂ 0.35 ꢂ 0.47
361.36
monoclinic
P21/c
C22H14F6NO2P
colorless prism
0.25 ꢂ 0.39 ꢂ 0.41
469.31
monoclinic
P21/n
colorless block
0.46 ꢂ 0.44 ꢂ 0.42
285.27
orthorhombic
P212121
8.3623(6)
11.2530(8)
15.539(1)
90
90
90
8.7818(3)
18.4043(6)
10.7928(3)
90
109.015(2)
90
8.4150(5)
18.982(1)
11.5290(6)
90
98.419(2)
90
13.9184(7)
9.2015(5)
15.9039(8)
90
99.313(2)
90
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Volume
Z
1462.3(2)
4
1649.18(9)
4
1821.7(2)
4
2010.0(2)
4
T (K)
223(2)
1.296
0.188
223(2)
1.342
0.178
225(2)
1.318
0.167
225(2)
1.551
0.212
Density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
)
Minimun/maximum transmission
Reflection collected
0.910/0.920
39 352
0.920/0.970
40 488
0.920/0.960
74 096
0.916/0.946
54 342
Independent reflections [Rint
Final R indices [I > 2 (I)] R1 (wR2)
Final R indices (all data) R1(wR2)
]
4691[0.0182]
0.0275(0.0649)
0.0287(0.0657)
6066[0.0225]
0.0406(0.1149)
0.0495(0.1239)
6263[0.0243]
0.0384(0.1076)
0.0440(0.1141)
6777[0.0196]
0.0415(0.1194)
0.0507(0.1296)
r

Table 2
Crystallographic data for coordination complexes.
[Nd(2)2(NO3)3(CH3OH)] [Nd(2)2(NO3)3]
[Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH) [Yb(4)2(NO3)3(H2O)] [Nd(4)2(NO3)3(H2O)] [Yb(5)2(NO3)3(H2O)]ꢀ0.5(CH3CN) [Nd(3)2(NO3)3]ꢀ3(CHCl3)
Empirical formula
Color, habit
Crystal size (mm)
Formula weight
Crystal system
Space group
Unit cell dimension
a (Å)
C
33H36N5NdO14P2
C32H32N5NdO13P2
colorless prism
C40.5H36N5O14.5P2Yb
pink block
C44H42N5O14P2Yb
colorless prism
0.46 ꢂ 0.25 ꢂ 0.14
1099.81
orthorhombic
P212121
C44H42N5NdO14P2
pale blue prism
0.53 ꢂ 0.37 ꢂ 0.0.35
1071.01
orthorhombic
P212121
C45H31.5F12N5.5O14P2Yb
colorless prism
0.19 ꢂ 0.35 ꢂ 0.39
1336.24
monoclinic
P21/c
C43H35Cl9N5NdO13P2
colorless prism
0.09 ꢂ 0.26 ꢂ 0.30
1354.99
colorless plate
0.27 ꢂ 0.23 ꢂ 0.21
932.85
monoclinic
P21/n
0.15 ꢂ 0.46 ꢂ 0.52 0.32 ꢂ 0.32 ꢂ 0.50
900.81
1059.72
monoclinic
P21/n
triclinic
triclinic
ꢀ
ꢀ
P1
P1
16.0073(9)
12.3024(7)
19.197(1)
90
97.846(2)
90
12.1596(4)
13.5689(4)
13.8678(5)
63.326(1)
76.159(1)
64.092(1)
1836.4(1)
2
10.0465(8)
20.238(2)
21.291(2)
90
94.132(3)
90
10.6206(6)
11.6896(7)
37.538(2)
90
90
90
10.698(1)
11.714(1)
37.928(5)
90
90
90
11.8234(6)
15.7990(8)
26.812(1)
90
92.062(2)
90
13.1425(3)
13.8228(3)
17.8614(5)
96.368(1)
110.695(2)
111.438(1)
2715.9(1)
2
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Volume
Z
3745.0(4)
4
4317.6(6)
4
4660.4(5)
4
4753(1)
4
5005.2(4)
4
T (K)
223(2)
1.654
1.546
228(2)
1.629
1.571
223(2)
1.630
2.314
225(2)
1.567
2.146
225(2)
1.497
1.229
225(2)
1.773
2.049
223(2)
1.657
1.521
Density (g cmꢁ3
)
Absorption coefficient
(mmꢁ1
)
Minimum/maximum
transmission
0.660/0.720
0.464/0.796
0.391/0.525
0.430/0.750
0.560/0.650
0.501/0.698
0.659/0.876
Reflection collected
Independent reflections [Rint
99906
10925[0.0216]
0.0175(0.0435)
60847
14894[0.0187]
0.0203(0.0492)
158885
19173[0.0317]
0.0312(0.0736)
183428
18864[0.0505]
0.0366(0.0829)
150752
18473[0.0441]
0.0400(0.1004)
178785
21100[0.0263]
0.0310/0.0708
93947
20616[0.0458]
0.0408(0.10940)
]
Final R indices [I > 2r (I)] R1
(wR2)
Final R indices (all data)
R1(wR2)
0.0199(0.0457)
0.0242(0.0526)
0.0397(0.0793)
0.0415(0.0851)
0.0431(0.1022)
0.0471/0.0822
0.0575(0.1028)

S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
2751
methyl group allowed to vary in position. The H-atoms on the
water molecule were located in the final difference map but they
were fixed in position with an O–H distance 0.83 Å. All H-atoms
were included in ideal positions with fixed Uiso = 1.2 Ueq of the par-
ent atom except for the H-atoms on the water and the terminal
methyl with Uiso = 1.5. The Flack parameter for [Yb(4)2(NO3)3(-
H2O)] converged to 0.349(6) suggesting that the complex is a race-
mic twin. There are no signs of disorder; however, the tolyl ring has
a large range of C–C bond lengths so the ring was constrained as a
regular hexagon in the final refinement. The H-atoms were in-
cluded in ideal positions with fixed Uiso = 1.2 Ueq of the parent atom
except for the hydrogen atoms on the terminal methyl and water
which were set to Uiso = 1.5 Ueq of the parent atom. In [Yb(5)2(-
NO3)3(H2O)]ꢀ0.5(CH3CN), the CH3CN molecule is close to a center
of symmetry and is at half-occupancy. The H-atoms were placed
in ideal positions and refined with Uiso = 1.2 Ueq of the parent atom.
as a pale yellow solid via column chromatography. The CHN ana-
lytical data and 1H NMR spectra suggest the presence of a minor
impurity that displays at least one unique proton resonance at
7.28 ppm. Compound 2 may be obtained analytically pure by
recrystallization from hot EtOAc. The compound displays an in-
tense [M+H+] ion in the HRESI-MS and strong infrared bands at
1659 and 1188 cmꢁ1 that are assigned to
mCN and mPO, respectively.
The 31P NMR spectrum of 2 shows a single resonance at d 28.1 that
is, as expected, downfield of the resonance for the phosphine 1, d
ꢁ16.9. Preparation of 2 in a one-step procedure by use of Ph2P(O)Cl
in place of Ph2PCl was explored, but 2 was obtained only in low
yield along with several unidentified species.
Although we were initially interested in preparing several orga-
nyl derivatives of 2, the sensitivity of the molecule to aqueous acid
led us to shift attention to the preparation of previously unre-
ported 2-[(phosphinoyl)methyl]benzoxazoles, J, that were ex-
pected to be more robust. The synthesis of J (R = Ph, 3) was
accomplished via three methods summarized in Scheme 2.
Although it requires preparation of commercially unavailable 2-
(chloromethyl)benzoxazole (two steps from 2-aminophenol [28]),
the phosphino-Grignard approach (method 1) proved to be the
most efficient of the three procedures. Furthermore, since a variety
of phosphino-Grignard reagents are easily prepared from diet-
hylphosphite and RMgCl or RMgBr reagents [56–61], method 1
was also used to prepare 4–6. The optimized yield of 3 was 96%
while the unoptimized yields for 4–6 were 55–74% based on 2-
(chloromethyl)benzoxazole. The one-step synthesis of 3 via meth-
od 2 (Scheme 2) is related to a reaction reported by Minami and
coworkers [27] for the synthesis of the diethyl phosphonate, J
(R = OEt). The yield of 3 by this route is good (84%); however, appli-
cation of the chemistry for the synthesis of other derivatives re-
quires preparation of the respective R2P(O)Cl reagents. Method 3
employs chlorodiphenyl phosphine and 2-(methylbenzoxazole in
a Minami-like synthesis related to the procedure shown in Scheme
1. The yield of 3 from this approach is good (72%), but its applica-
tion to other derivatives requires chlorodiorganyl phosphines that
are generally expensive or commercially unavailable. Lastly, it is
noted that Kosaka and Wakabayashi [28] reported the formation
of J (R = OEt) from an Arbusov reaction of 2-(chloromethyl)benzox-
azole and P(OEt)3 at 150 °C. In our hands, the Arbusov methodol-
ogy did not provide a good approach for synthesis of 3–6.
3. Results and discussion
3.1. Ligand syntheses and characterization
The synthesis of I (R = Ph, 2) was accomplished in a manner de-
scribed by Braunstein and coworkers [18] as summarized in
Scheme 1. The intermediate phosphine, 1, was recovered in lower
yield (47%) than previously described, but the physical properties
and spectroscopic data are identical to those reported. No evidence
for the formation of the bis-(phosphinomethyl)oxazoline was
noted. The P-oxidation of 1 to form 2 was initially attempted by
addition of aqueous H2O2 and m-CPBA/CHCl3 solutions at 23 °C.
However, these conditions proved to be too harsh, and phosphine
oxidation was accompanied by oxazoline ring opening. As a result,
oxidation was performed by bubbling oxygen gas through an Et2O
solution of 1. The reaction is slow but efficient when performed on
a 2 g scale. The product 2 was isolated and purified, with some loss,
1
1
1. BuLi, THF, -78°C
2. (CH3)3SiCl
2
2
O
O
O
PPh2
PPh2
O
O2, ether
2 days
4
4
N
N
N
3. Ph2PCl
3
3
1
2
Scheme 1.
O
MgBr
O
THF, 60°C
THF, 60°C
Ph
MgBr
H
O
method 1
3
P
P
Ph
O
O
Ph
MgBr
O
N
O
N
P
Ph
Ph
Ph
Cl
P
O
3
O
N
O
N
2 eq. LDA
Ph2POCl
method 2
method 3
Ph
Ph
P
O
3
O
N
O
N
O
N
LDA
air
24 h in CHCl3
Ph
Ph
Ph
Ph
Ph2PCl
P
P
O
3
Scheme 2.

2752
S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
The new ligands, 3–6, were obtained as analytically pure solids
that exhibit strong parent, [M+H+], and sodium complex, [M+Na+],
ions in the HRESI-MS. Infrared spectra display strong adsorptions
in the regions 1616–1607 and 1196–1175 cmꢁ1 that are tenta-
tively assigned to mCN and mPO stretching vibrations, respectively.
The decrease in mCN relative to the value recorded for
2
(1659 cmꢁ1) is expected as a result of C@N bond delocalization
with the fused aromatic ring system. The 31P NMR spectra show
a single resonance in the region d 23.4–31.1. This chemical shift re-
gion is characteristic for aryl phosphine oxides [41,44,56] and CF3
decorated aryl phosphine oxides [48,59,60]. The 1H and 13C NMR
spectra are complex, but a majority of the observed resonances
were assigned in detail by a combination 1H and 31P coupled and
decoupled experiments along with comparisons with spectra for
related [(phosphinoyl)methy]pyridine N-oxides compounds
[45,48,56,59]. The spectra for 3–6 are included in Supplementary
material. It is noted that the ‘‘elbow’’ methyl groups spanning
the R2P(O) group and the benzoxazole ring show little variation
with R group modifications: 1H d 4.1–4.2, JPH = 14.2–16.2 Hz;
13C{1H} d 32.3–34.0, JCP = 63.2–69.4 Hz.
Fig. 2. Molecular structure and atom labeling scheme for 3. Thermal ellipsoids are
shown at the 20% level.
3.2. Ligand X-ray crystal structure determinations
The molecular structures for the ligands 2–5 have been con-
firmed by single crystal X-ray diffraction analyses. Views of the
molecules are shown in Figs. 1–4 and selected bond lengths are
summarized in Table 3. The molecular structure of 2 consists of a
planar 4,5-dihydroxazole ring bonded at the 2-position (C3) to a
diphenylmethyl phosphine oxide arm. The P@O bond vector is
twisted out of the ring plane as indicated by the torsion angle
O1–P–C4–C3, 60.8(1)°. The P–O1 bond length, 1.4865(8) Å, is com-
parable with related distances in 2-[(diphenylphosphinoyl)methyl]
pyridine and pyridine N-oxide ligands [45,59], and it is consistent
with a localized P@O double bond. The C–N bond lengths, C3–N,
1.253(2) Å and C2–N, 1.475(2) Å, indicate a localized C@N double
bond and a C–N single bond, respectively, in the dihydrooxazoline
ring. The shorter distance is comparable with the C@N bond length
in the phosphine ligand, 2-[1-(diphenylphosphanyl)ethyl]-4,4-di-
methyl-4,5-dihydrooxazole, 1.259(3) Å [25]. The difference be-
tween the two C–O bond lengths in the dihydrooxazole ring is
less pronounced but still significant: C3–O2, 1.344(2) Å and C1–
O2, 1.448(2) Å. It is noted that in the unit cell the molecular units
of 2 show alignment along the b-axis probably as a result of weak
hydrogen bonding between the phosphoryl O-atom and dihydro-
oxazoline O-atom in each molecule with aryl ring C–H H-atoms
in neighboring molecules, e.g., in C6–H6ꢀ ꢀ ꢀO2(#1): H6ꢀ ꢀ ꢀO2(#1),
Fig. 3. Molecular structure and atom labeling scheme for 4. Thermal ellipsoids are
shown at the 20% level.
Fig. 1. Molecular structure and atom labeling scheme for 2. Thermal ellipsoids are
Fig. 4. Molecular structure and atom labeling scheme for 5. Thermal ellipsoids are
shown at the 20% level.
shown at the 20% level.

S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
2753
Table 3
Selected bond lengths (Å) in ligands 2–5.
Bond Type
2
3
4
5
P–O
P–C
P–O1 1.4865(8)
P–C4 1.823(1)
P–C5 1.804(1)
P–C11 1.799(1)
C3–N 1.253(2)
C2–N 1.475(1)
C3–O2 1.344(2)
C1–O2 1.448(2)
C1–C2 1.514(2)
C3–C4 1.489(2)
P1–O1 1.4831(8)
P1–C8 1.823(1)
P1–C9 1.798(1)
P1–C15 1.806(1)
C1–N1 1.293(2)
C7–N1 1.397(1)
C1–O2 1.357(1)
C2–O2 1.383(1)
C2–C7 1.379(2)
C1–C8 1.481(2)
P1–O2 1.4892(8)
P1–C8 1.833(1)
P1–C9 1.807(1)
P1–C16 1.807(1)
C7–N1 1.293(1)
C1–N1 1.400(1)
C7–O1 1.363(1)
C3–O1 1.380(1)
C1–C6 1.383(2)
C7–C8 1.481(1)
P–O2 1.4714(9)
P– C8 1.830(1)
P–C9 1.828(1)
P–C16 1.817(1)
C7–N1 1.291(2)
C6–N1 1.400(2)
C7–O1 1.352(2)
C1–O1 1.384(1)
C1–C6 1.479(2)
C7–C8 1.482(2)
C–N
C–O
C–C
2.58 Å, C6ꢀ ꢀ ꢀO2(#1), 3.437(2) Å, C6–H6–O2(#1), 151.1°; in C16–
H16ꢀ ꢀ ꢀO1(#2): H16ꢀ ꢀ ꢀO1(#2), 2.49 Å, C16ꢀ ꢀ ꢀO1(#2), 3.403(1) Å,
C16–H16ꢀ ꢀ ꢀO1(#2), 165.4°.
containing ligand 6 are not presented due to poor crystal quality
and/or severe unresolved disorder in the CF3 groups and outer
sphere solvent molecules.
The molecular structures of the benzoxazole-based ligands, 3–
5, are similar to each other and to the structure of 2. Each contains
a planar benzoxazole ring fragment with the diarylmethylphos-
phine oxide ‘‘arm’’ bonded at the 2-position (2, C1; 3, C7, 4, C7).
The P@O bond vector is rotated out of the benzoxazole ring plane
with O–P–C–C torsion angles similar to that found in 2:3, O1–P1–
C8–C1, 60.4(1)°; 4, O2–P1–C8–C7, 30.03(9)° and 5, O2–P–C8–C7,
50.6(1)°. The P@O bond lengths in 3 and 4, 1.4831(8) and
1.4892(8) Å, are similar to the P@O bond length in 2 while the
P@O bond length in 5 is noticeably shorter, P–O2, 1.4714(9) Å.
We have observed similar P@O bond shortening in other 2-CF3 dec-
orated aryl phosphine oxides [48,59,60]. Furthermore, there are
two nonbonded Pꢀ ꢀ ꢀF distances in 5, 2.934 and 3.080 Å, that are
shorter than the sum of covalent radii: 3.27 Å [63], and similar
interactions at the backside of the phosphoryl P-atom have been
observed previously [48,59,60]. It is not clear whether nonbonded
Pꢀ ꢀ ꢀF interactions or through-bond electron withdrawal or a com-
bination of both effects are responsible for the shorter P@O bond
distances in the 2-CF3 aryl decorated ligands. As found in the struc-
ture of 2, the C–N and C–O bond lengths in 3–5 fall into short and
long groups, but the differences are much smaller consistent with
greater electron delocalization in the benzoxazole systems. Lastly,
it is mentioned that a crystal structure determination for 6 was
completed; however, the molecule shows severe disorder in one
CF3 group so the data are not included, in full, in this report. It is
noted that the P@O bond length, 1.482(1) Å, is more similar to
those in 3 and 4, and short backside Pꢀ ꢀ ꢀF interactions involving
the ordered meta-CF3 groups are absent.
The 2:1 combination of methanol solutions of 2 and
Nd(NO3)3ꢀ6H2O at 23 °C led to the formation of a slightly soluble
white solid. Dissolution of the solid in hot methanol followed by
slow cooling resulted in the deposition of crystallographic quality
single crystals for which CHN analyses suggest a composition
[Nd(2)2(NO3)3(CH3OH)]. Infrared spectra for the complex in KBr
pellets show bands at 1646 and 1160 cmꢁ1 that are tentatively as-
signed to
m
CN and
m
PO, respectively. The down-frequency coordina-
tion shift for the phosphoryl stretching mode,
D
m
PO = 28 cmꢁ1, is
consistent with Nd(III) ion binding to the phosphoryl oxygen atom
and the value is comparable to shifts observed for lanthanide ion
binding with ligand types C–E [38–46,56]. The small perturbation
of the mCN mode,
Dm
CN = 12 cmꢁ1, suggests that the oxazoline ring
N-atom may not be bonded or is weakly bonded to the Nd(III).
An X-ray crystal structure determination for the complex con-
firmed the composition proposed from the elemental analysis. A
view of the complex is shown in Fig. 5 and selected bond lengths
are summarized in Table 4. The structure solution reveals an unex-
pected and somewhat unusual coordination condition for two
identical neutral ligands bonded to a Nd(III) ion. One ligand is
bonded in a bidentate mode, via P@O and Noxa-ring/Nd interac-
tions, while the second ligand is coordinated with a monodentate,
P@O/Nd interaction. The Noxa-ring atom in the second ligand mol-
ecule, however, is hydrogen bonded with the H-atom of an inner
sphere methanol molecule. The resulting O14–H14ꢀꢀꢀN2 interaction
is nearly linear, 175(3)°, with distances O14–H14, N2ꢀꢀꢀH14, and
O14ꢀꢀꢀN2 0.71(2), 1.96(2) and 2.667(2) Å, respectively. This
3.3. Lanthanide ion coordination chemistry and X-ray crystal structure
determinations
As mentioned in the Introduction, our primary interest in I and J
rests on the nature of the binding interactions displayed by each
ligand with hard lanthanide ion acceptors. Namely, do these li-
gands act only as monodentate PO donors or do they form biden-
tate PO,N chelate interactions? Therefore, the coordination
chemistry of 2–5 toward an early lanthanide, Nd(NO3)3ꢀ6H2O,
and a late lanthanide, Yb(NO3)3ꢀ6H2O, was explored with 1:1–3:1
ligand:Ln reactant ratios in methyl alcohol solution. The resulting
complexes were then crystallized under various conditions (see
Section 2). In all cases, even with a deficiency of ligand, the analyt-
ical data for the isolated complexes best fit a 2:1 ligand/Ln(III)
composition although in some cases the agreement between
proposed and experimental compositions is not within 3%. This
appears to be due to the loss of outer sphere solvent during
handling. The 2:1 composition for the crystalline complexes was
confirmed ultimately by X-ray crystal structure determinations,
vide infra. It is noted that crystal structures for complexes
Fig. 5. Molecular structure and atom labeling scheme for [Nd(2)2(NO3)3(MeOH)].
H-atoms, except on the O-atom of MeOH, omitted for clarity. Thermal ellipsoids are
shown at the 20% level.

Table 4
Selected bond lengths (Å) in complexes.
Bond type
M–OP
[Nd(2)2(NO3)3(CH3OH)]
[Nd(2)2(NO3)3]
[Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH)
Yb–O1 2.228(1)
Yb–O3 2.213(1)
[Yb(4)2(NO3)3(H2O)]
[Nd(4)2(NO3)3(H2O)]
[Yb(5)2(NO3)3(H2O)]ꢀ0.5(CH3CN)
Yb–O1 2.269(1)
Yb–O3 2.249(1)
[Nd(3)2(NO3)3]ꢀ3(CHCl3)
Nd–O1 2.404(2)
Nd–O3 2.420(2)
Nd–O1 2.4274(9)
Nd–O3 2.4136(9)
Nd–O1 2.3803(9)
Nd–O2 2.4189(9)
Yb–O1 2.233(2)
Yb–O3 2.234(2)
Nd–O1 2.3531(9)
Nd–O3 2.350(1)
M–N
Nd–N1 2.655(1)
Nd–N1 2.660 (1)
Nd–N2 2.691(1)
Nd–N1 2.665(2)
Nd–N2 2.672(2)
M–Onitrate
2.601
2.584
2.426
2.431
2.541
2.414
2.579
avg range
2.549(1)–2.649(1)
2.502(1)–2.703(1)
2.363(2)–2.509(2)
2.369(3)–2.513(3)
2.500(3)–2.579(3)
2.354(2)–2.447(2)
2.530(2)–2.617(3)
M–Osolvent
P–O
Nd–O14 2.447(1)
Yb–O5 2.278(2)
Yb–O14 2.285(3)
Nd–O14 2.427(5)
Yb–O5 2.311(2)
P1–O1 1.497(1)
P2–O3 1.497(1)
P1–O1 1.496(1)
P2–O3 1.5015(9)
P1–O1 1.491(1)
P2–O3 1.496(2)
P1–O1 1.494(2)
P2–O3 1.495(2)
P1–O1 1.498(2)
P2–O3 1.504(2)
P1–O1 1.497(2)
P2–O3 1.494(2)
P1–O1 1.498(2)
P2–O3 1.496(2)
P–C
P1–C1 1.811(1)
P1–C5 1.793(1)
P1–C11 1.793(2)
P2–C17 1.819(1)
P2–C21 1.797(1)
P2–C27 1.794(1)
P1–C1 1.799(1)
P1–C5 1.785(1)
P1–C11 1.796(2)
P2–C17 1.812(1)
P2–C21 1.788(1)
P2–C27 1.792(1)
P1–C8 1.817(2)
P1–C9 1.794(2)
P1–C15 1.781(2)
P2–C28 1.813(2)
P2–C29 1.791(2)
P2–C35 1.781(2)
P1–C8 1.839(3)
P1–C9 1.787(3)
P1–C16 1.799(3)
P2–C30 1.826(3)
P2–C31 1.794(4)
P2–C38 1.785(2)
P1–C8 1.834(3)
P1–C9 1.784(3)
P1–C16 1.804(3)
P2–C30 1.826(3)
P2–C31 1.799(4)
P2–C38 1.775(2)
P1–C8 1.833(3)
P1–C14 1.811(2)
P1–C21 1.822(2)
P2–C30 1.828(2)
P2–C36 1.820(2)
P2–C43 1.813(2)
P1–C8 1.815(2)
P1–C9 1.792(2)
P1–C15 1.789(3)
P2–C28 1.818(2)
P2–C29 1.787(2)
P2–C35 1.785(2)
N–C
O–C
C–C
N1–C2 1.271(2)
N1–C3 1.484(2)
N2–C18 1.264(2)
N2–C19 1.472(2)
N1–C2 1.275(2)
N1–C4 1.476(2)
N2–C18 1.274(2)
N2–C20 1.482(2)
N1–C1 1.286(3)
N1–C7 1.401(3)
N2–C21 1.291(3)
N2–C27 1.407(3)
N1–C7 1.279(4)
N1–C6 1.402(5)
N2–C29 1.290(5)
N2–C28 1.385(5)
N1–C7 1.288(4)
N1–C6 1.399(4)
N2–C29 1.287(4)
N2–C28 1.394(4)
N1–C7 1.275(4)
N1–C6 1.414(4)
N2–C29 1.290(3)
N2–C28 1.399(3)
N1–C7 1.289(3)
N1–C6 1.404(3)
N2–C27 1.291(3)
N2–C26 1.404(3)
O2–C2 1.347(2)
O2–C4 1.460(2)
O4–C18 1.343(2)
O4–C20 1.460(2)
O3–C2 1.337(2)
O3–C3 1.455(3)
O4–C18 1.344(2)
O4–C19 1.457(2)
O2–C1 1.363(3)
O2–C2 1.383(3)
O4–C21 1.359(2)
O4–C22 1.376(3)
O2–C1 1.380(5)
O2–C7 1.357(4)
O4–C23 1.384(4)
O4–C29 1.355(4)
O2–C1 1.384(5)
O2–C7 1.352(4)
O4–C23 1.377(4)
O4–C29 1.362(4)
O2–C7 1.361(3)
O2–C1 1.371(4)
O4–C29 1.363(3)
O4–C23 1.376(3)
O2–C1 1.372(3)
O2–C7 1.354(3)
O4–C27 1.356(3)
O4–C21 1.377(3)
C1–C2 1.491(2)
C3–C4 1.529(2)
C17–C18 1.491(2)
C19–C20 1.511(3)
C1–C2 1.489(2)
C3–C4 1.515(2)
C17–C18 1.482(2)
C19–C20 1.516(3)
C1–C8 1.485(3)
C2–C7 1.377(3)
C21–C28 1.483(3)
C22–C27 1.377(3)
C7–C8 1.481(5)
C1–C6 1.364(6)
C29–C30 1.489(5)
C23–C28 1.368(5)
C7–C8 1.483(4)
C1–C6 1.375(6)
C29–C30 1.486(5)
C23–C28 1.381(5)
C7–C8 1.474(4)
C1–C6 1.366(4)
C29–C30 1.479(3)
C23–C28 1.382(4)
C7–C8 1.482(3)
C1–C6 1.378(3)
C27–C28 1.478(3)
C21–C26 1.381(3)
Coord. No.
Polyhedron
10
10
9
9
9
9
10
BCSAPa
SCb
MCSAPc
MCSAP
MCSAP
MCSAP
CId
a
b
c
BCSAP = bicapped square antiprism.
SC = sphenocorona.
MCSAP = monocapped square antiprism.
CI = cubicosahedron.
d

S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
2755
hydrogen bonding interaction is consistent with theꢁsmall infrared
mCN value. There are also three inner sphere NO3 counter-ions
Yb(NO3)3 also forms a 2:1 complex with 2 in CH3OH and CH3CN, at-
tempts to obtain X-ray quality crystals were unsuccessful. There-
fore, it is not possible at this point to determine if a related
monodentate/bidentate to bis-bidentate transformation takes
place with the smaller lanthanide.
D
bonded to the Nd(III) ion in an asymmetric, bidentate fashion.
These atoms generate a 10-membered distorted bicapped square
antiprism coordination polyhedron. The Nd–O(P) bond lengths,
2.4274(9) and 2.4136(9) Å, are typical of related coordination
interactions involving neutral organophosphine oxide ligands
[37–48,56,57]. It is noted that the shorter distance is associated
with the monodentate (P)O–Nd interaction. The Nd–Noxa-ring
bond length, Nd–N1 2.655(1) Å, is significantly longer. Several in-
tra-ligand bond lengths also show modifications with metal bind-
ing. For example, the P–O bond lengths, P1–O1 and P2–O3 bond
lengths are identical, 1.497(1) Å, and they are longer than the free
ligand bond length, 1.4865(8) Å. The ring C@N bond lengths in the
complex, C2–N1 1.271(2) and C18–N2 1.264(2) Å are also both
longer than the distance in the free ligand, 1.253(2) Å, and the
bond lengthening is slightly greater for the ring that is involved
in bidentate coordination to the Nd(III).
The 2:1 combinations of 3–5 with Nd(NO3)3ꢀ6H2O and Yb(-
NO3)3ꢀ6H2O in methanol solutions led to formation of solid com-
plexes following solvent evaporation. In general, CHN analytical
data for the resulting powders matched best with 2:1 ligand/Ln
compositions, but agreement in every instance was not within 3%
relative to the assumed theoretical Ln(L)2(NO3)3 compositions. This
suggested that the solids contained labile inner and/or outer
sphere water and/or methanol molecules, and this was confirmed
by infrared spectra. The crude solid complexes were subsequently
crystallized under different conditions in order to obtain single
crystals suitable for X-ray diffraction analyses. Once more, the
agreements of experimental CHN elemental analysis data with
compositions deduced from the crystal structure analyses were
unsatisfactory. The infrared spectra are complicated in the finger-
The unusual mixed monodentate/bidentate coordination condi-
tion found in [Nd(2)2(NO3)3(CH3OH)] suggested that it might be
possible to displace the coordinated, inner sphere CH3OH molecule
and produce a bis-bidentate coordination field with 2. Indeed, when
the complex was dissolved in CH3CN at 23 °C and the volatiles al-
lowed to slowly evaporate, a white powder formed whose IR spec-
tra (KBr) no longer showed evidence for CH3OH. Furthermore, the
print region, but a band due to
and the
mPO was identified in each complex
D
mPO values appear in a range 25–30 cmꢁ1. Overlapping
bands in the region 1650–1550 cmꢁ1 precluded confident assign-
ment of mCN and therefore the data do not allow for a clear identi-
fication of ligand denticity.
The crystal structures for five complexes containing 3, 4 and 5
were determined. Four of these, [Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH),
[Yb(4)2(NO3)3(H2O)], [Nd(4)2(NO3)3(H2O)] and [Yb(5)2(NO3)3(-
H2O)]ꢀ0.5(CH3CN), were found to have basically the same 2:1 li-
gand/metal composition differing only by the presence or
absence of different outer sphere solvent molecules. Furthermore,
the molecular structures are very similar. A view of one of the com-
plexes, [Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH) is shown in Fig. 7 and se-
lected metrical parameters for each complex are summarized in
Table 4. In each case, the lanthanide inner coordination sphere
geometry approximates a mono-capped square antiprism gener-
ated by two oxygen atoms from two monodentate, (P)O bonded
benzoxazole ligands, six oxygen atoms from three asymmetric,
bidentate nitrate anions and one oxygen atom from an inner
sphere water molecule. The two Ln–O(P) bond lengths in each
complex are similar to each other within 0.03 Å, and, as expected,
the Nd–O(P) bond lengths are longer than the Yb–O(P) bond
lengths due primarily to the difference in lanthanide ionic radii
[62]. In addition, the P@O bond length in each of the ligand
spectrum showed bands at
m (Dm
CN = 1637 cmꢁ1 CN = 22 cmꢁ1) and
m
PO = 1158 cmꢁ1 PO = 31 cmꢁ1), and these coordination shifts
(Dm
are more in-line with bidentate ligand–metal interactions. It is
noted that an identical IR spectra were obtained from solids iso-
lated from 2:1 and 3:1 combinations of 2 with Nd(NO3)3 in CH3CN
solutions. The solid was crystallized from CH3CN solution and sin-
gle crystals suitable for X-ray diffraction analysis were obtained.
A view of the molecule is shown in Fig. 6 and selected bond lengths
are presented in Table 4. The complex contains two molecules of 2
both bonded to the Nd(III) ion in a bidentate PO,Noxa mode. The
remaining inner sphere coordination positions are occupied by six
O-atoms from three asymmetric, bidentate nitrate anions. It is
noted that one of the two neutral ligand molecules appears to be
more tightly bound than the other as indicated by the distances
Nd–O1 2.3803(9) Å vs. Nd–O2 2.4189(9) Å and Nd–N1 2.660(1) Å
vs. Nd–N2 2.691(1) Å. Both of the Nd–N distances are longer than
the bidentate coordination interaction in the monodentate/biden-
tate structure described above: 2.655(1) Å. The changes in the
intra-ligand bond lengths in the bis-bidentate complex upon
coordination are similar to those observed in the monodentate/
bidentate complex: P1–O1 1.496(1), P2–O2 1.5015(9), C2–N1
1.275(2) and C18–N2 1.274(2) Å. Although the late lanthanide
Fig. 7. Molecular structure and atom labeling scheme for [Yb(3)2(NO3)3(-
H2O)]ꢀ0.5MeOH. Outer sphere MeOH and H-atoms, except on inner sphere water
omitted for clarity. Thermal ellipsoids are shown at the 20% level.
Fig. 6. Molecular structure and atom labeling scheme for Nd(2)2(NO3)3. H-atoms
omitted for clarity. Thermal ellipsoids are shown at the 20% level.

2756
S. Pailloux et al. / Polyhedron 30 (2011) 2746–2757
fragments elongates relative to the free ligand upon coordination
to the lanthanide ions while the remaining bond lengths show lit-
tle change. It is noted that there are hydrogen bond interactions
between the inner sphere water molecule H-atoms and the benz-
oxazole ring N-atom involving each monodentate ligand, and these
orient the benzoxazole fragment N-atom toward the Ln(III) ion.
The resulting O–HꢀꢀꢀN interactions are slightly more bent (range
161–173°) than observed with the complex containing 2 and
MeOH, and the heavy-atom NꢀꢀꢀO separations fall in a range
2.709(4)–2.849(3) Å with the longer distances appearing in the
complex containing ligand 5.
the counter-anions. This is not unexpected since many related
observations have been reported in the lanthanide coordination
chemistry literature [63], and similar behavior has been observed
in our studies of ligands C–H bonded to Ln(III) cations [38–
51,56–59]. A unique feature in the present study is that we have
been able to isolate and structurally characterize complexes where
the ligand reveals both its partial and full chelation potential in the
solid state structures. A particularly relevant, parallel multifunc-
tional phosphine oxide donor system involving dynamic chelation
has been reported by Ziessel and coworkers [64]. By using a com-
bination of X-ray crystallography, solution absorption and emis-
sion spectroscopy and computational analyses, the interactions of
a potentially pentadentate bis(bipyridine) phosphine oxide ligand,
PhP(O)[CH2bipyr(CH3)]2, were thoroughly characterized, and the
ligand denticity in solution was found to be dependent upon sol-
vent and anion coordinating ability. In both systems it appears that
hydrogen bonding between coordinated solvent and ligand also
plays a role in stabilizing structures.
The bis-monodentate PO-coordination conditions found with
the complexes of 3–5 suggested that, like ligand 2, it might be pos-
sible drive off the inner sphere water molecule and convert these
complexes to bis-bidentate PO,N coordination complexes. Several
different approaches to accomplish this conversion were exam-
ined. Based upon IR spectra, it appears that performing the synthe-
ses of the complexes initially in hot MeOH or by heating the
isolated bis-monodentate complexes in MeOH leads to replace-
ment of the water, but MeOH probably remains O-bonded, in the
inner coordination sphere. Attempts were made to expel the meth-
anol by crystallization of the solids in hydrophilic and hydrophobic
solvent combinations, but in only one case were X-ray crystallo-
graphic quality single crystals obtained: [Nd(3)2(NO3)3]ꢀ3CHCl3. A
view of this molecule is shown in Fig. 8 and selected bond lengths
are presented in Table 4. In parallel with the observations with li-
gand 2 in its Nd complex, the inner sphere water molecule in the
complex [Nd(3)2(NO3)3(H2O)], and likely MeOH in an intermediate
composition, are displaced by the benzoxazine ring N-atom of both
PO-bonded ligands. The two bidenate ligands and three bidentate
nitrate groups generate a 10-coordinate cubicosahedron inner
sphere geometry. The Nd–O(P) and Nd–Nring bond lengths are sim-
ilar to those observed in the [Nd(2)2(NO3)3] complex. The intrali-
gand bond lengths for 3 in the bidentate condition are essentially
identical to the bond lengths for monodentate 3 in [Yb(3)2(NO3)3(-
H2O)]ꢀ0.5(CH3OH) which suggests that the electronics in the ligand
framework are not significantly perturbed by metal binding.
The results described here indicate that the inner sphere com-
positions and molecular structures of the coordination complexes
formed by ligands of type I and J with Ln(III) cations are variable
and dependent upon at least, the competing coordinating abilities
of the ligands, the solvent molecules, H2O, MeOH and MeCN, and
4. Conclusion
Unlike ligands of types C, E and G, ligands of types I and J prob-
ably hold little practical potential as solvent extraction reagents for
f-block elements. However, their coordination chemistry is inter-
esting and provides fundamental information about the outcome
of competing interactions between various donor centers as well
as additional examples of dynamic hemilabile interactions on
Ln(III) cations. In the present examples, it is apparent that the
phosphine oxide provides the stable ligand–metal interaction
while the ring N-atom acts as the labile center in competition with
solvent and anion donors. These initial results suggest that further
studies of the solution phase ligand–metal interactions should be
explored by detailed absorption and emission spectroscopies.
Acknowledgements
Financial support for this study was provided by the US Depart-
ment of Energy (DoE), Chemical Sciences, Geosciences and Biosci-
ences Office, Office of Basic Energy Sciences (Grant DE-FG02-
03ER15419) (RTP). In addition, funds from the National Science
Foundation assisted the purchase of the X-ray diffractometer
(CHE-0443580) and NMR spectrometers (CHE-0840523 and
0946690).
Appendix A. Supplementary data
CCDC 740145 (2), 793390 (3), 793391 (4), 793392 (5), 740146,
740147, 793393, 793394, 793395, 793680, 793396 contain the
supplementary crystallographic data for [Nd(2)2(NO3)3(CH3OH)],
[Nd(2)2(NO3)3], [Yb(3)2(NO3)3(H2O)]ꢀ0.5(CH3OH), [Nd(3)2(NO3)3]ꢀ3
(CHCl3), [Yb(4)2(NO3)3(H2O)], [Nd(4)2(NO3)3(H2O)], [Yb(5)2(NO3)3
(H2O)]ꢀ0.5(CH3CN). These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2011.08.012.
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