Convenient Preparation of Lanthanide Aryloxides from Lanthanide Nitrate Polyether Complexes and the Crystal Structure of [La(OC6H3Me2-2,6)3(MeO(CH 2CH2O)4Me)]

Full text of DOI:10.1021/ic9507629

Inorg. Chem. 1996, 35, 255-257
255
Convenient Preparation of Lanthanide Aryloxides
from Lanthanide Nitrate Polyether Complexes
and the Crystal Structure of
[La(OC6H3Me2-2,6)3(MeO(CH2CH2O)4Me)]
Helen C. Aspinall* and Mark Williams
Department of Chemistry, University of Liverpool,
PO Box 147, Liverpool L69 3BX, U.K.
ReceiVed June 23, 1995
Introduction
The applications of lanthanide alkoxides and aryloxides are
diverse, ranging from homogeneous catalysis of organic
reactions1-3 to synthesis of high purity oxide materials.4
Preparative routes to alkoxides include reaction of the lanthanide
metal with an appropriate alcohol, reaction of the anhydrous
lanthanide chloride with an alkali metal alkoxide, and alco-
holysis of lanthanide tris(dialkylamides),5 all of which require
the use of starting materials which must be prepared and handled
under strictly anhydrous and/or anaerobic conditions. While
this is feasible on a laboratory scale, it is much less attractive
if preparation on an industrial scale is required. In this paper,
we describe the preparation of lanthanum and praseodymium
aryloxides from lanthanide nitrate polyether complexes, which
are easily prepared anhydrous starting materials.
Figure 1. PLUTO plot of 1.
[La(NO3)3(M2EO3)] gave [La(OC6H3Me2-2,6)3(M2EO3)], 3, also
in high yield. The mixed ligand complex [La(OC6H3Me2-
2,6)2(NO3)(M2EO4)], 4, was formed as the only product when
[La(NO3)3(M2EO4)] reacted with 2 equiv of Na(OC6H3Me2-2,6)
under similar conditions, and was found to be stable with respect
to ligand redistribution reactions. These preparations may be
carried out reasonably successfully without taking any rigorous
precautions to exclude moisture; however, the yields are higher
and the products easier to isolate when anhydrous conditions
are used.
Results and Discussion
All new complexes were characterized by elemental analysis
and NMR spectroscopy (1H and 13C); NMR data are given in
Table 1. We found it necessary to record NMR spectra in THF-
d8 as spectra recorded in less expensive noncoordinating solvents
(e.g. CDCl3) were very broad and poorly resolved, possibly due
to some degree of association in such solvents. The chemical
shifts of resonances due to the polyether ligands in the La
complexes are insensitive to the number or nature of the other
ligands, and are essentially indistinguishable from those found
Complexes of lanthanide nitrates with glycol and polyether
ligands were reported several years ago,6 and are among a small
number of anhydrous lanthanide complexes which may be
prepared readily from hydrated lanthanide salts without the use
of rigorously anhydrous conditions. When Ln ) La, [Ln-
(NO3)3(M2EOn)] is readily precipitated in high yields as an
analytically pure compound by addition of one equivalent of
M2EO4 to an ethylacetate solution of La(NO3)3‚nH2O (M2EOn
is MeO(CH2CH2O)nMe; n ) 3 is triglyme; n ) 4 is tetraglyme).
For the later lanthanides [Ln(NO3)3(M2EOn)] compounds
become increasingly hygroscopic and their precipitation from
ethyl acetate solution is effected by drying with molecular sieve.
Lanthanide trichlorides are the most widely used anhydrous
starting materials for lanthanide chemistry; they are extremely
hygroscopic and their preparation from the hydrated chlorides
can be a tedious procedure. The ready availability of [Ln(NO3)3-
(M2EO4)] for early lanthanides suggested that these complexes
may be convenient starting materials for the synthesis of
lanthanide alkoxides and aryloxides. We began our investiga-
tions with the preparation of 2,6-dimethylphenoxide complexes.
Reaction of a THF suspension of [Ln(NO3)3(M2EO4)] with
3 equiv of Na(OC6H3Me2-2,6) in THF at room temperature led
to rapid formation of [Ln(OC6H3Me2-2,6)3(M2EO4)] and pre-
cipitation of NaNO3. The product was obtained in high yield
as colorless (Ln ) La, 1) or pale green (Ln ) Pr, 2) prisms
from cold concentrated THF. An analogous reaction between
1
for [La(M2EOn)X3] (X ) NO3, CF3SO3) in CDCl3. The H
NMR spectrum of 2 at 298 K was extremely broad and
indecipherable due to the paramagnetism of the 4f2 Pr3+ ion.
However, on cooling the sample to 253 K, three resonances in
the ratio 1:2:6 were resolved due to the three dimethylphenoxide
ligands which were equivalent on an NMR time scale at this
temperature. When the temperature was lowered to 233 K, two
sets of resonances were observed for the dimethylphenoxide
ligands; these sets of resonances were in the ratio 2:1 and
demonstrate the freezing out of a structure analogous to that
found in the solid state for 1. It is perhaps surprising that the
resonances due to the M2EO4 ligand in 2 show only a very small
paramagnetic shift. This must be due to geometrical factors
rather than dissociation from the metal as, at room temperature,
these resonances as well as those from the dimethylphenoxide
ligands are very broad.
X-ray Crystal Structure of 1. Crystals suitable for X-ray
diffraction were grown from a mixture of THF and diethyl ether.
A PLUTO plot of the complex is shown in Figure 1; fractional
atomic coordinates are given in Table 2, and selected bond
lengths and angles are given in Table 3. The compound
crystallizes with a non-stoichiometric quantity of sovent (prob-
ably diethyl ether) which occupies a disordered position in the
crystal. This solvent is very readily lost from the crystal as it
does not appear either in NMR spectra or in elemental analysis.
(1) Makioka, Y.; Nakagawa, I.; Taniguchi, Y.; Takaki, K.; Fujiwara, Y.
J. Org. Chem. 1993, 58, 4771-4774.
(2) Ohno, H.; Mori, A.; Inoue, S. Chem. Lett. 1993, 375-378.
(3) Sasai, H.; Suzuki, T.; Arai, S.; Arai, T.; Shibasaki, M. J. Am. Chem.
Soc. 1992, 114, 4418-4420.
(4) Bradley, D. C. Chem. ReV. 1989, 89, 1317-1322.
(5) Mehrotra, R. C.; Singh, A.; Tripathi, U. M. Chem. ReV. 1991, 91,
1287-1303.
(6) Hirashima, Y.; Shiokawa, J. Chem. Lett. 1979, 463-464.
0020-1669/96/1335-0255$12.00/0 © 1996 American Chemical Society

256 Inorganic Chemistry, Vol. 35, No. 1, 1996
Table 1. 1H and 13C NMR Data
Notes
1H NMR
C6H3Me2
13C NMR
C6H3Me2
compound
C6H3Me2
polyether
C6H3Me2
polyether
La(OC6H3Me2-2,6)3(M2EO4)
2.24 (s, 18H) 6.20 (t,3H, J)7.2Hz);
6.72 (d, 6H, J)7.2Hz)
3.28 (s, 6H); 3.48 (m); 19.78 115.20; 126.93;
59.09; 72.84;
73.10; 74.33
3.60 (m)
129.72
Pr(OC6H3Me2-2,6)3(M2EO4)a
Pr(OC6H3Me2-2,6)3(M2EO4)b
26.35(s, 18H) 15.75 (s, 3H); 19.85 (s, 6H)
2.90; 2.99; 3.47; 3.72;
4.21
2.75, 2.86, 3.31, 3.55,
4.14
57.55 (br, s,
6H); 29.26
(br, s, 12H)
49.92 (s, 2H); 39.57 (s, 1H);
21.12 (s, 4H); 16.59 (s, 2H)
La(OC6H3Me2-2,6)2(NO3)(M2EO4) 2.26 (s, 12H) 6.46 (t, 2H); 6.84 (d, 4H)
La(OC6H3Me2-2,6)3(M2EO3) 2.23 (s, 18H) 6.25 (t, 3H); 6.74 (d, 6H)
3.37 (s, 6H); 3.56 (m); 18.77 126.42; 129.79
60.46; 72.57;
72.72; 74.10
60.45; 72.76;
130.19; 156.76 72.99; 74.39
3.72 (m)
3.37 (s, 6H); 3.59 (m); 18.30 120.16; 126.30;
3.63 (m)
a Recorded at 253 K. b Recorded at 233 K.
Table 2. Positional Parameters for 1
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 1
atom
x
y
z
La(1)-O(1)
La(1)-O(2)
La(1)-O(3)
La(1)-O(4)
2.28(2)
2.30(2)
2.30(2)
2.70(2)
La(1)-O(5)
La(1)-O(6)
La(1)-O(7)
La(1)-O(8)
2.69(2)
2.74(2)
2.64(2)
2.80(2)
La(1)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0.5365(2)
0.434(1)
0.681(1)
0.395(1)
0.362(2)
0.479(2)
0.659(1)
0.693(2)
0.730(2)
0.359(1)
0.405(1)
0.330(2)
0.208(1)
0.162(1)
0.238(2)
0.185(2)
0.533(3)
0.769(1)
0.887(2)
0.978(1)
0.951(1)
0.833(2)
0.742(1)
0.617(3)
0.918(2)
0.309(1)
0.323(1)
0.234(2)
0.131(1)
0.117(1)
0.206(2)
0.428(2)
0.180(3)
0.260(3)
0.333(2)
0.450(2)
0.562(2)
0.590(2)
0.689(3)
0.763(3)
0.755(4)
0.719(4)
0.846(3)
0.22600(7)
0.2998(7)
0.272(1)
0.1449(7)
0.285(1)
0.170(1)
0.1108(7)
0.1660(9)
0.295(1)
0.3385(8)
0.4004(8)
0.4400(6)
0.4178(8)
0.3559(8)
0.3163(6)
0.252(1)
0.426(1)
0.3034(8)
0.2750(6)
0.3120(8)
0.3774(8)
0.4059(6)
0.3689(8)
0.403(1)
0.207(1)
0.1005(7)
0.0759(8)
0.0293(8)
0.0074(7)
0.0320(8)
0.0785(8)
0.102(1)
0.107(1)
0.330(2)
0.256(1)
0.214(1)
0.118(1)
0.074(1)
0.069(1)
0.108(1)
0.204(2)
0.270(3)
0.317(2)
0.96189(9)
0.8841(9)
1.0486(8)
0.9203(8)
1.0517(8)
1.0947(8)
1.001(1)
0.867(1)
0.885(1)
0.8404(8)
0.8201(9)
0.7715(9)
0.7433(8)
0.7636(9)
0.8122(9)
0.833(1)
0.851(2)
1.0929(8)
1.1182(9)
1.1603(9)
1.1770(8)
1.1517(9)
1.1096(9)
1.080(2)
1.096(1)
0.890(1)
0.8176(9)
0.7889(7)
0.8331(9)
0.9060(8)
0.9346(7)
0.770(1)
1.011(2)
1.028(2)
1.122(1)
1.153(1)
1.123(2)
1.057(1)
0.938(2)
0.884(2)
0.809(2)
0.810(2)
0.911(1)
O(1)-La(1)-O(2)
O(1)-La(1)-O(3)
O(1)-La(1)-O(4)
O(1)-La(1)-O(8)
O(2)-La(1)-O(3)
O(2)-La(1)-O(4)
O(2)-La(1)-O(5)
O(2)-La(1)-O(6)
O(2)-La(1)-O(7)
O(2)-La(1)-O(8)
O(3)-La(1)-O(4)
O(3)-La(1)-O(5)
114.4(6)
90.4(5)
76.3(5)
71.9(6)
152.9(6)
81.1(5)
74.8(6)
84.3(6)
103.0(6)
71.2(6)
95.4(5)
80.0(5)
O(3)-La(1)-O(6)
O(3)-La(1)-O(7)
O(3)-La(1)-O(8)
O(4)-La(1)-O(5)
O(4)-La(1)-O(8)
O(5)-La(1)-O(6)
O(6)-La(1)-O(7)
O(7)-La(1)-O(8)
La(1)-O(1)-C(1)
La(1)-O(2)-C(9)
La(1)-O(3)-C(17)
74.9(5)
81.2(6)
130.3(6)
60.9(5)
122.9(5)
61.4(5)
59.2(5)
58.7(6)
172(1)
173(2)
175(1)
The other structurally characterized rare earth dimethylphe-
noxides are [Y(OC6H3Me2-2,6)3(THF)2]2, 5,7 and [Ln(OC6H3-
Me2-2,6)2(THF)(µ-OC6H3Me2-2,6)2AlMe2], 6 (Ln ) Nd, Yb).8
The La-O-C bond angles for the dimethylphenoxide ligands
of 1 are all somewhat larger than those found for the terminal
phenoxides of 5 (162.6(5)°) and 6 (165.5(12)° for Yb; 169(8)°
for Nd). Allowing for differences between the ionic radii of
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
Y
3+, Nd3+, Yb3+, and La3+, the Ln-O distances for the
dimethylphenoxide ligands of 1 are similar to those for the
terminal dimethylphenoxide ligands of 5 (2.075(6) and 2.046-
(6) Å) and 6 (2.057(11) Å for Yb and 2.153(9) Å for Nd).
Diglyme has been used to stabilize monomeric rate earth
alkoxides and coordinates facially in the 6-coordinate complex
[Y{OCMe(CF3)2}3(diglyme)],9 but there are no reported ex-
amples of rare earth alkoxide complexes containing triglyme
or tetraglyme ligands. Bridged complexes of the type [GdL3]2(µ-
M2EOn) with M2EOn bonded through two O atoms to each Gd
have been reported for n ) 3 or 4 where L is the sterically
demanding bidentate ligand 2,2,6,6-tetramethyl-3,5-heptanedi-
onate.10
Conclusions
We have prepared rare earth dimethylphenoxides with poly-
ether ligands M2EOn (n ) 3 or 4) from [Ln(NO3)3(M2EO3)]
and [Ln(NO3)3(M2EO4)], respectively, demonstrating that these
polyether complexes of lanthanide nitrates are valuable anhy-
drous starting materials for synthetic lanthanide chemistry.
1 is 8-coordinate; the five oxygen donors of the M2EO4 ligand
are approximately coplanar with the La atom (La(1) lies 0.46
Å out of the least-squares plane defined by O(4)-O(8)), and
the dimethylphenoxide ligands occupy meridional sites in a
plane perpendicular to that defined by the M2EO4 oxygen atoms.
The dihedral angle between the phenyl groups attached to O(1)
and O(2) is 40.24°; the corresponding angle for O(1) and O(3)
is 73.73°, and for O(2) and O(3) it is 104.50°. Inspection of
space-filling diagrams of 1 indicate that there is sufficient room
for coordination of an additional small ligand, and we are
investigating the Lewis acid activity of 1, 3, 4, and related
compounds.
(7) Evans, W. J.; Olofson, J. M.; Ziller, J. W. Inorg. Chem. 1989, 28,
4308-4309.
(8) Evans, W. J.; Ansari, M. A.; Ziller, J. W. Inorg. Chem. 1995, 34,
3079-3082.
(9) Bradley, D. C.; Chudzynska, H.; Hursthouse, M. B.; Motevalli, M.
Polyhedron 1993, 12, 1907-1918.
(10) Baxter, I.; Drake, S. R.; Hursthouse, M. B.; Abdul Malik, K. M.;
McAleese, J.; Otway, D. J.; Plakatouras, J. C. Inorg. Chem. 1995, 34,
3079-3082.

Notes
Inorganic Chemistry, Vol. 35, No. 1, 1996 257
Table 4. Crystallographic Data for 1
spectroscopy was distilled from CaH2. All solvents were stored under
N2 and over 4 Å molecular sieves prior to use. Samples for NMR
spectroscopy were sealed under vacuum, and spectra were recorded
on Bruker WM250 and AC200 spectrometers. Elemental analyses were
performed in duplicate by Mr. S. Apter of this Department.
Crystal Data
formula
fw
crystal syst
space group
lattice paras
a, Å
C34H49O8La
724.66
monoclinic
P21/c (No. 14)
Preparation of [Ln(OC6H3Me2-2,6)3(M2EO4)], Ln ) La, Pr. A
solution of 2,6-dimethylphenol (1.015 g, 8.31 mmol) was dissolved in
THF (20 cm3), and NaH (80 % in mineral oil, 0.43 g, 17.8 mmol) was
added, resulting in vigorous effervescence. The resulting colorless
solution of Na(OC6H3Me2-2,6) was separated by decantation from the
unreacted NaH and added, with stirring, to a suspension of Ln-
(NO3)3(M2EO4) (2.77 mmol) in THF (100 cm3), which had been dried
by refluxing for 2 h through a Soxhlet thimble containing 4 Å molecular
sieves. Stirring at room temperature was continued for 1.5 h, and then
the precipitated NaNO3 was allowed to settle out. The clear, colorless
solution of [Ln(OC6H3Me2-2,6)3(M2EO4)] was separated by decantation.
The solution was concentrated to ca. 20 cm3 and diethyl ether (ca. 20
cm3) was added; prisms were formed (colorless for La; very pale green
for Pr) on cooling to -10 °C. Yield ) 85% (La), 75% (Pr). Anal.
Calcd for C34H49LaO8: C, 56.38; H, 6.81. Found: C, 56.25; H, 7.12%.
Calcd for C34H49O8Pr: C, 56.20; H, 6.80%. Found: C, 53.09; H, 6.69.
Preparation of [La(OC6H3Me2)2(NO3)(M2EO4). The preparation
was carried out in a manner analogous to that described above for [Ln-
(OC6H3Me2-2,6)3(M2EO4)], using 2 equiv of Na(OC6H3Me2-2,6) instead
of 3. The product was obtained as colorless needles by crystallization
from CH2Cl2 and petroleum ether at -10 °C. Yield ) 67%. Anal.
Calcd for C26H40NLaO10: C, 46.92; H, 6.06; N, 2.11. Found: C, 42.00;
H, 5.74; N, 2.30.
Preparation of [La(OC6H3Me2-2,6)3(M2EO3)]. [La(OC6H3Me2-
2,6)3(M2EO3)] was prepared by a method analogous to that for
[La(OC6H3Me2-2,6)3(M2EO4)], using La(NO3)3(M2EO3) as a starting
material. The product was crystallised as colourless needles from THF/
diethyl ether at -10 °C. Yield ) 84%.
X-ray Data Collection, Structure Determination, and Refinement
for [La(OC6H3Me2-2,6)3(M2EO4)]. Crystals of [La(OC6H3Me2-
2,6)3(M2EO4)] suitable for X-ray diffraction were grown from THF/
diethyl ether at -10 °C. An air sensitive colorless prism, approximate
dimensions 0.5 × 0.1 × 0.5 mm, was mounted on a glass fiber in
Nujol oil and cooled to -120 °C in a stream of N2 gas. The cell
constants were obtained from nine carefully centered reflections in the
range 7.39 < 2θ < 12.66°. Crystal data and details of data collection
and structure solution are summarized in Table 4.
10.16(3)
20.38(2)
17.71(4)
91.5(2)
3667
b, Å
c Å
â, deg
V, Å3
Z
D
4
calc, g cm-3
1.312
1496
12.10
F000
µ(Mo KR), cm-1
Intensity Measurements
Rigaku AFC6S
diffractometer
radiation
MoKR (λ ) 0.710 69 Å)
temp, °C
-120
take-off angle, deg
detector aperture, mm
horizontal
6.0
6.0
6.0
40
vertical
cryst to detector dist, cm
scan type, deg min-1
scan width, deg
2θmax, deg
no. of reflcns
tot.
4.0 (in ω) (2 rescans)
(1.42 + 0.30 tan θ)
50.0
7028
unique
corrections
6615 (Rint ) 0.301)
Lorentz-polarization
Structure Solution and Refinement
structure solution
hydrogen atom treatment
direct methods
included in calculated
positions (dC-H ) 0.95 Å)
refined as rigid groups
full-matrix least-squares
∑w(|Fo| - |Fc|)2
phenyl rings
refinement
function minimized
least-squares weights
p-factor
anomolous dispersion
no. of observns (I > 3.00σ(I))
no. of variables
2
2
4Fo /σ2(Fo )
0.03
all non-hydrogen atoms
2181
237
Acknowledgment. We are grateful to SERC for a student-
ship (M.W.), to Glaxo Process Development for Additional
financial support, to Mr. J. V. Barkley for assistance with the
crystal structure determination and to Mr. S. Apter for elemental
analyses.
reflection/param ratio
residuals: R; Rw
goodness of fit indicator
max shift/error in final cycle
max peak in final difference map,
e/Å3
9.20
0.082; 0.078
1.37
0.73
1.17
min peak in final difference map,
-1.68
Supporting Information Available: Tables of positional and
thermal parameters, intramolecular bond distances and angles, and
torsion angles (18 pages). Ordering information is given on any current
masthead page.
e/Å3
Experimental Section
Ln(NO3)3(M2EO4) and Ln(NO3)3(M2EO3) were prepared using the
published procedure.11 Preparations of aryloxide complexes were
carried out using standard Schlenk techniques. Solvents for preparative
work were distilled from sodium benzophenone ketyl; THF-d8 for NMR
IC9507629
(11) Hirashima, Y.; Kanetsuki, K.; Yonezu, I.; Kamakura, K.; Shiokawa,
J. Bull. Chem. Soc. Jpn. 1983, 56, 738-743.