The effects of light lanthanoid elements (La, Ce, Nd) on (Ar)CF-Ln coordination and C-F activation in N,N-dialkyl-N′-2,3,5,6- tetrafluorophenylethane-1,2-diaminate complexes

Article abstract of DOI:10.1039/c2dt30604b

A new class of homoleptic organoamido rare earth complexes [Ln(L ^Me or L^Et)₃] (Ln = La, Ce, Nd; L ^Me/Et = p-HC₆F₄N(CH₂) ₂NMe₂/Et₂) exhibiting (Ar)CF-Ln interactions has been isolated from redox-transmetallation/protolysis (RTP) reactions between the free metals, Hg(C₆F₅)₂ and L ^Me/EtH in tetrahydrofuran, together with low yields of [Ln(L ^Me)₂F]₃ (Ln = La, Ce) or [Nd(L ^Et)₂F]₂ species, resulting from C-F activation reactions. The structures of the homoleptic complexes have eight-coordinate Ln metals with two tridentate (N,N′,F) amide ligands including (Ar)CF-Ln bonds and either a bidentate (N,F) ligand (Ln = La, Ce, Nd; L^Et) or a bidentate (N,N′) ligand (Ln = Nd; L^Me), in an unusual case of linkage variation. All (Ar)CF-Ln bond lengths are shorter than or similar to the corresponding Ln-NMe₂/Et₂ bond lengths. In [Ln(L ^Me)₂F]₃ (Ln = La, Ce) complexes, there is a six-membered ring framework with alternating F and Ln atoms and the metal atoms are eight-coordinate with two tridentate (N,N′,F) L^Me ligands, whilst [Nd(L^Et)₂F]₂ is a fluoride-bridged dimer.

Full text of DOI:10.1039/c2dt30604b

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PAPER
The effects of light lanthanoid elements (La, Ce, Nd) on (Ar)CF–Ln
coordination and C–F activation in N,N-dialkyl-N′-2,3,5,6-
tetrafluorophenylethane-1,2-diaminate complexes†
Glen B. Deacon,* Craig M. Forsyth, Peter C. Junk,* Rory P. Kelly, Aron Urbatsch and Jun Wang
Received 16th March 2012, Accepted 4th May 2012
DOI: 10.1039/c2dt30604b
A new class of homoleptic organoamido rare earth complexes [Ln(LMe or LEt)3] (Ln = La, Ce, Nd;
LMe/Et = p-HC6F4N(CH2)2NMe2/Et2) exhibiting (Ar)CF–Ln interactions has been isolated from redox–
transmetallation/protolysis (RTP) reactions between the free metals, Hg(C6F5)2 and LMe/EtH in
tetrahydrofuran, together with low yields of [Ln(LMe)2F]3 (Ln = La, Ce) or [Nd(LEt)2F]2 species, resulting
from C–F activation reactions. The structures of the homoleptic complexes have eight-coordinate
Ln metals with two tridentate (N,N′,F) amide ligands including (Ar)CF–Ln bonds and either a bidentate
(N,F) ligand (Ln = La, Ce, Nd; LEt) or a bidentate (N,N′) ligand (Ln = Nd; LMe), in an unusual case of
linkage variation. All (Ar)CF–Ln bond lengths are shorter than or similar to the corresponding
Ln–NMe2/Et2 bond lengths. In [Ln(LMe)2F]3 (Ln = La, Ce) complexes, there is a six-membered ring
framework with alternating F and Ln atoms and the metal atoms are eight-coordinate with two tridentate
(N,N′,F) LMe ligands, whilst [Nd(LEt)2F]2 is a fluoride-bridged dimer.
the spectacular cages [Ln28F68(SePh)16(py)4].30 These give
Introduction
intense near IR emissions, have a much higher F : Ln ratio (2.42)
than previously observed (1.67) in [Er3(C6H2But2-2,6-
Fluorine-mediated interactions between fluorocarbon groups and
metals, –CF–M,1 are attracting considerable and increasing atten-
tion both for intrinsic interest and also as possible precursors for
C–F activation reactions,2 since –F–M coordination weakens the
C–F bond.3 This is particularly relevant in lanthanoid chemistry
since the strength of the Ln–F bond4 makes it competitive with
the strong C–F bond.5 Reported examples of –CF–Ln coordi-
nation generally have an additional supporting donor atom, e.g.
C, N, O, S6–18 or a second –CF–Ln bond19 but discrete fluoro-
carbon-rare earth coordination has been observed in
[Sc(C5Me5)2(L)]BPh4 (L = PhF or o-C6H4F2).20 Complexes with
–CF–Ln bonds may undergo C–F activation reactions9,10,16,18
giving either LnF3 (potentially of atomic layer deposition inter-
est)16 or heteroleptic fluorides, e.g. [Ln(L)2F]9,10 or cages.18 In
other cases, where heteroleptic fluorides are formed by Ln-
induced C–F activation, intermediates with proven –CF–Ln
bonding have not been isolated but are likely.4,21–24 In further
examples of such activation reactions, the interest has been on
the organic products25,26 or on the mechanism of activation.27
As for alternative routes to lanthanoid heteroleptic fluorides,28–30
cleavage reactions of [LnL3] complexes with masked HF have
been the most widely applicable28,30 and have recently yielded
OMe-4)4F5]23 and defy rearrangement into insoluble and highly
stable LnF3. Heteroleptic lanthanoid fluorides should be useful
olefin polymerization catalysts in view of success with Group
4 metal amide fluorides.31 We have recently introduced the
bulky ethane-1,2-diaminate ligands [p-HC6F4N(CH2)2NR2]−
(R = Me or Et) (L = LMe or LEt) into lanthanoid metal–organic
chemistry with the syntheses of [Yb(LMe/Et)2(solv)2] (solv = thf
1
or dme) complexes, which exhibit tridentate (N,N′,F) coordi-
2
nation and undergo C–F activation reactions in solution on
standing or heating to give the attractive novel [Yb4(LMe/Et)6F6]
cages.18 In these, the ligands remain tridentate (N,N′,F) and
hence are poised for further activation reactions. The initial
choice of the ligands was based on their potential to form an
o-F–Ln interaction anchored in a five-membered chelate ring by
a charged amide nitrogen atom together with an amine nitrogen
atom in a further five-membered ring (Scheme 1). Two ortho
fluorine atoms increase the possibility of at least transitory Ln–F
interactions in solution, even with some rotation about the
p-HC6F4–N bond. With the probability that ortho fluorine reson-
ances might be broadened or shifted by Ln–F coordination (as
observed, see below), the meta fluorine atoms being further away
from the Ln atoms and characteristically shifted by the 4-H sub-
stituent,32 provide
a structural integration marker in the
19F NMR spectra. Although the ligands were initially prepared
in a template synthesis on platinum to give potential ‘rule-
breaker’ anticancer drugs,33,34 the amine ligand precursors
p-C6F4N(H)(CH2)2NR2 (R = Me, Et) are readily prepared by
School of Chemistry, Monash University, Clayton, VIC 3800, Australia.
E-mail: glen.deacon@monash.edu, peter.junk@monash.edu
†Electronic supplementary information (ESI) available. CCDC 859374
and 859380–859386. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2dt30604b
8624 | Dalton Trans., 2012, 41, 8624–8634
This journal is © The Royal Society of Chemistry 2012

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Results and discussion
Syntheses
Redox-transmetallation/protolysis (RTP) reactions between
lanthanum or cerium metals, bis(pentafluorophenyl)mercury and
N,N-dimethyl-N′-2,3,5,6-tetrafluorophenylethane-1,2-diamine
(LMeH) in thf at room temperature, yield the homoleptic com-
plexes [Ln(p-HC6F4N(CH2)2NMe2)3], [Ln(LMe)3] (Ln = La or
Ce) in good yield (Scheme 2, (i)), together with the correspond-
ing trimeric heteroleptic fluorides [Ln(LMe)2F]3 (Ln = La or Ce)
in low yield. The cerium complex [Ce(LMe)2F]3 was also
obtained from an analogous RTP reaction with Hg(CCPh)2
instead of Hg(C6F5)2. From a similar synthesis with La metal,
only [La(LMe)3] was isolated. By contrast, the corresponding
reactions with N,N-diethyl-N′-2,3,5,6-tetrafluorophenylethane-
1,2-diamine (LEtH) gave solely the homoleptic complexes
[Ln(LEt)3] (Ln = La or Ce) (Scheme 2, (ii)). Analogous reactions
with neodymium and either ligand gave the homoleptic com-
plexes [Nd(LMe)3] and [Nd(LEt)3] (Scheme 2, (iii), (iv)).
However, from some reactions involving LEtH, it was also poss-
ible to isolate the dimeric heteroleptic fluoride [Nd(LEt)2F]2 in
addition to [Nd(LEt)3]. Overall, the synthetic method readily
provides homoleptic [Ln(LMe/Et)3] complexes in good yield
but the concurrent formation of heteroleptic fluorides
[Ln(LMe/Et)2F]n is limited in extent and yield. Heating reaction
mixtures appeared to increase the complexity of the reactions
(see below for two examples of heat-induced transformations).
Scheme 1 Potential ligand binding mode.
nucleophilic substitution between the amines R2N(CH2)2NH2
(R = Me, Et) and pentafluorobenzene.18,35 So far, homoleptic
rare earth complexes of LMe/Et ligands have not been isolated but
formation of [Ln(LMe/Et)3] is favoured by charge balance for the
LnIII state. Because such complexes would have crowded coordi-
nation spheres, there is uncertainty over the coordination number
and whether N,N′,F-ligation and –CF–Ln bonding would be
possible for some or all ligands. The previous Ln-induced C–F
activation of LMe/Et involved an isolable YbII intermediate with
–CF–Ln bonding but is C–F activation possible for rare earths
with a much less stable LnII state?36 We have addressed these
issues by the synthesis and structure determination of homoleptic
[Ln(LMe/Et)3] (Ln = La, Ce, Nd) complexes, which exhibit a
fascinating linkage variation, by utilizing the largest Ln elements
to maximize the possibility of –CF–Ln coordination. In addition,
C–F activation products [Ln(LMe)2F]3 (Ln = La, Ce) and
[Nd(LEt)2F]2 have been isolated and structurally characterized,
albeit in low yields, with the elements having much less stable
LnII states than ytterbium.36
Analytical and spectroscopic characterization
Homoleptic [Ln(p-HC6F4N(CH2)2NR2)3] complexes (R = Me or Et)
Bulk samples of all six homoleptic complexes [Ln(LMe/Et)3]
(Ln = La, Ce, Nd) were characterized by microanalysis or metal
Scheme 2 Summary of syntheses.
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analyses. The larger sample used for the latter can provide a
good assessment of bulk purity. Analyses were consistent with
the single crystal compositions, except for [La(LEt)3]·C7H8 and
[Ce(LEt)3]·1/2C7H8 where the data indicated loss of toluene of
crystallization and this was confirmed by 1H NMR spectra of the
bulk samples. The 19F{1H} NMR spectra of diamagnetic
[La(LMe/Et)3] at room temperature show two equal intensity
broad singlets indicative of either free rotation of the polyfluoro-
phenyl groups and no (Ar)CF–Ln bonding in contrast to solid
[La(LEt)3] (below), or rapid exchange between coordination of
F2 and F6. At low temperatures, the 19F{1H} NMR spectrum of
[La(LEt)3] gives twelve separate resonances consistent with the
two different tridentate (N,N′,F) and one bidentate (N,F) LEt
ligands of the solid-state structure (below). Cooling [La(LMe)3]
also leads to multiple resonances also indicative of (Ar)CF–La
interactions. With less distinct resonances than [La(LEt)3], it is
possible that there are two tridentate (N,N′,F) ligands and one
bidentate (N,N′) ligand (the latter only giving two resonances
since free rotation of the fluorocarbon group is possible), as
observed in solid [Nd(LMe)3], but single crystals have not
yet been obtained. The 1H NMR spectra of paramagnetic
[Ce(LMe/Et)3] and [Nd(LMe/Et)3] at room temperature show res-
onances consistent with the compositions but with substantial
shifts and broadening and a chemical shift range of 23 ppm
([Ce(LEt)3]). In the 19F{1H} NMR spectrum of [Ce(LMe/Et)3]
and [Nd(LMe/Et)3] at room temperature, a single broad feature is
observed. This is close (ca. 5 ppm) to the expected value for F
ortho to H in diamagnetic systems. Cooling of representative
samples only caused broadening of this resonance. However,
spectra of [Ce(LMe/Et)3] and [Nd(LMe/Et)3] at 70 °C reveal two
resonances: one near the position in the room temperature spec-
trum, reasonably attributable to F3,5; and a very broad and sub-
stantially paramagnetically shifted signal at −180 to −200 ppm
for [Ce(LMe/Et)3] and [Nd(LMe/Et)3], attributable to F2,6 which
are nearer the paramagnetic centres. A detailed study of
[Nd(LMe)3] (as representative) from 30–70 °C shows that the
low frequency resonance is not clearly evident until 40 °C and is
broadened into the baseline at 30 °C. The substantial broadening
and paramagnetic shifting of F2,6 may suggest exchange
between different ligand coordination modes (see structures
[Ce(LEt)3] and [Nd(LMe/Et)3] below), possibly indicating
(Ar)CF–Ln interactions.
1H NMR spectrum, whereas isostructural [Ce(LMe)2F]3 analysed
with the single crystal composition of [Ce(LMe)2F]3·3/2C7H8
and resonances of C7H8 could be qualitatively distinguished
1
from residual proton resonances of C7D8 in the H NMR spec-
trum. Very low solubility required use of elevated temperatures
to obtain NMR spectra of [La(LMe)2F]3 and [Ce(LMe)2F]3,
whilst paramagnetism allied with low solubility precluded satis-
factory spectra for [Nd(LEt)2F]2. For diamagnetic [La(LMe)2F]3,
the spectra were consistent with the proposed composition
without toluene of crystallization and with free rotation of the
fluoroaryl groups but a little [La(LMe)3] was also observed,
presumably formed by rearrangement induced by heating to
achieve dissolution.
3½LaðLMeÞ2Fꢀ ! 2½LaðLMeÞ3ꢀ þ LaF3
The spectrum of paramagnetic [Ce(LMe)2F]3 is more compli-
cated, showing two sets of 1H resonances for the ligand at
100 °C. In the 19F{1H} NMR spectrum, two very close
(unequal) F3,5 resonances are evident at 50 °C, 70 °C and
100 °C but the corresponding F2,6 resonances are superimposed
in a very broad, paramagnetically shifted signal at −200 ppm. As
solid [Ce(LMe)2F]3 is trimeric, it is plausible that the features are
due to two species of different nuclearity e.g. the trimeric
species and a lower coordinate monomer. As the ratio of the
major to the minor resonance in the 19F{1H} NMR spectrum
(sample totally dissolved by prior heating) increases from 1.8 : 1
(50 °C) to 2.2 : 1 (70 °C) and 4.0 : 1 (100 °C), the major reson-
ance is reasonably attributable to a monomer and the minor res-
onance to the trimer. Resonances of the skeletal fluoride ligands
could not be resolved, a not unexpected result of low solubility
and expected broad signals, especially in view of the very broad
resonances for the aromatic fluorine atoms even for diamagnetic
[La(LMe)2F]3. With [Ln(DippForm)2F(thf)] (DippForm = N,N′-
bis(2,6-diisopropylphenyl)formamidinate) complexes, which
have terminal Ln–F bonds, fluoride resonances could only be
resolved for two of the compounds.24
Significant v(NH) or v(OH) absorptions are not detectable in
the infrared spectra and v(CF) bands are observed close to the
values for the corresponding homoleptic complexes. Comparison
of the far infrared spectra of [La(LMe)2F]3 with [La(LMe)3] and
of [Ce(LMe)2F]3 with [Ce(LMe)3] led to the assignment of bands
at 355 and 378 cm−1 respectively to v(Ln–F). A relatively strong
analogous band of [Nd(LEt)2F]2 (341 cm−1) is attributed to
v(Nd–F).
The IR spectra of all complexes are consistent with loss of the
NH proton of the reactant p-HC6F4NH(CH2)2NR2 and character-
istic v(CF) absorptions are observed at 954–957 cm−1 and
926–927 cm−1 for R = Me and 943–947 cm−1 for R = Et. The
close similarity between the infrared spectra of [Ln(LMe)3] (Ln =
La, Ce) and [Nd(LMe)3], the structure of which has been estab-
lished by X-ray crystallography (below), is consistent with the
complexes being isostructural.
Molecular structures
Homoleptic [Ln(p-HC6F4N(CH2)2NR2)3] complexes
Only one of the three [Ln(p-HC6F4N(CH2)2NMe2)3] complexes
(viz. [Nd(LMe)3]) could be obtained as single crystals suitable
for X-ray crystallography, whereas all three [Ln(p-HC6F4N-
(CH2)2NEt2)]3 complexes, [La(LEt)3], [Ce(LEt)3] and
[Nd(LEt)3], were structurally characterized. Unit cell and refine-
ment data are given in the Experimental section.
Organoamidolanthanoid fluorides [Ln(p-HC6F4N(CH2)2NR2)2F]n
(Ln = La, Ce; n = 3; Ln = Nd; n = 2)
Satisfactory microanalyses were obtained for the three hetero-
leptic fluorides [La(LMe)2F]3, [Ce(LMe)2F]3 and [Nd(LEt)2F]2.
In the case of [La(LMe)2F]3, the bulk sample had lost the toluene
of crystallization of the single crystals, as confirmed by the
All structures are eight-coordinate with two tridentate (N,N′,F)
ligands and one bidentate ligand but [Nd(LMe)3] differs from the
8626 | Dalton Trans., 2012, 41, 8624–8634
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Table 1 Selected bond lengths (Å) in [Nd(p-HC6F4N(CH2)2NMe2)3]
([Nd(LMe)3]), [La(p-HC6F4N(CH2)2NEt2)3]·C7H8 ([La(LEt)3]·C7H8),
[Ce(p-HC6F4N(CH2)2NEt2)3]·1/2C7H8
([Ce(LEt)3]·1/2C7H8)
and
[Nd(p-HC6F4N(CH2)2NEt2)3] ([Nd(LEt)3])
[Nd-
[La-
[Ce(LEt)3]·1/ [Nd-
(LMe)3]
(LEt)3]·C7H8 2C7H8
(LEt)3]
Ln(1)–N(1)
Ln(1)–N(3)
Ln(1)–N(5)
Ln(1)–N(2)
Ln(1)–N(4)
Ln(1)–F(1)
Ln(1)–F(5)
Ln(1)–N(6)
Ln(1)–F(9)
2.4163(16) 2.479(6)
2.4827(15) 2.473(6)
2.4092(16) 2.388(6)
2.6870(16) 2.731(6)
2.7273(16) 2.717(6)
2.5793(11) 2.773(4)
2.6138(11) 2.699(4)
2.452(8)
2.453(9)
2.363(9)
2.728(8)
2.687(8)
2.686(5)
2.779(6)
—
2.395(6)
2.412(6)
2.378(6)
2.709(6)
2.658(6)
2.647(4)
2.615(4)
—
2.7782(16)
—
2.765(4)
—
2.764(5)
2.705(4)
Fig. 1 Molecular diagram of [Nd(p-HC6F4N(CH2)2Me2)3] [Nd(LMe)3]
shown with 50% probability thermal ellipsoids. Hydrogen atoms have
been omitted for clarity.
[Ln(LEt)3] complexes in the mode of attachment of the third
ligand, in an unusual case of linkage variation.
[Nd(LMe)3]. The structure of the eight-coordinate Nd complex
is shown in Fig. 1 together with the numbering scheme. Selected
bond distances are given in Table 1. Two of the amido ligands
are tridentate (N,N′,F), as observed in [Yb(LEt)2(dme)] or
[Yb4(LMe/Et)6F6] complexes,18 whereas the third ligand is only
bidentate (N,N′) with the Ln–o-F contacts non-bonding
≥ 3.699(1) Å. In the absence of o-F bonding, the dihedral angle
for the bidentate (N,N′) ligand between the N(5)N(6)Nd plane
and the N(5) phenyl ring plane is 65.18(7)°, whereas for the
tridentate ligands, the corresponding angle is 22.07(8)° for
the N(1)(N2)Nd plane and the N(1) ring plane and 4.99(12)° of
the N(3)N(4)Nd plane and the N(3) aryl ring plane. Bonding
of the amide nitrogen is 0.20–0.34 Å shorter than the bonds to
the amine nitrogen and the Nd–NMe2(CH2–) bonds are some
0.1 Å longer than the corresponding Nd–o-F interactions for the
N(1) and N(3) ligands, as noted for YbII and YbIII complexes of
the tridentate (N,N′,F) ligands.18 Whether this shortening can be
attributed to stronger Nd–F than Nd–NMe2(CH2–) bonding is
arguable given that the third ligand prefers N,N′ over N,F chela-
tion, where both would give five-membered rings.
Fig. 2 Molecular diagram of [Nd(p-HC6F4N(CH2)2NEt2)3] [Nd(LEt)3]
shown with 50% thermal ellipsoids. Hydrogen atoms have been omitted
for clarity.
trigonal prismatic geometries with two capping atoms.
Atoms N(1)N(2)F(9) form one triangular face, while atoms
N(3)N(4)N(5) form the other face in the [Ln(LEt)3] complexes,
whereas N(1)N(2)N(5) and N(3)N(4)N(6) form the two triangu-
lar faces in the case of [Nd(LMe)3]; atoms F(1) and F(5) are
capping in both cases.
[La(LEt)3], [Ce(LEt)3] and [Nd(LEt)3]. The three complexes
are isostructural and the representative structure of [Nd(LEt)3] is
shown in Fig. 2 with selected bond distances in Table 1. All
three complexes are eight-coordinate with two tridentate (N,N′,F)
N,N-diethyl-N′-2,3,5,6-tetrafluorophenylethane-1,2-diaminate(1−)
ligands but the third ligand has N,F coordination with an uncoor-
dinated –(CH2)2NEt2 group (Nd–NEt2 contacts ≥5.502(6) Å for
[Nd(LEt)3]). This contrasts the preferred N,N′ binding of the
third ligand in [Nd(LMe)3]. This significant change vividly high-
lights the lower steric demands of the LMe ligand compared with
LEt. Coordination of the first two ligands results in less available
coordination space for the third ligand in [Ln(LEt)3] than in
[Ln(LMe)3] complexes, leading to the adoption of a less bulky
coordination mode by using chelating N,F donors. With
reduction in size from NEt2 to NMe2, the metal atom in
[Nd(LMe)3] is less crowded and can adopt the bulkier and
evidently more stable coordination mode of chelating N,N′ for
the third ligand. The structures feature bicapped distorted
In the [Ln(LEt)3] complexes, the Ln–N(amide) bonds are
shorter than the Ln–N(amine) bonds by 0.24–0.30 Å, similar to
[Nd(LMe)3] (above). For the La and Ce complexes, the shortest
Ln–N(amide) bond is for the bidentate ligand but this is not
observed in [Nd(LEt)3]. The Ln–F and Ln–N(amine) bonds are
of similar length, in contrast to [Nd(LMe)3] where the Ln–F
bond lengths are approximately 0.1 Å shorter than Ln–N(amine)
values. Comparison of the Nd complexes [Nd(LMe)3] and
[Nd(LEt)3] indicates longer Nd–N(amine) bonds in the former
and longer Nd–F bonds in the latter.
The Ln size range for the [Ln(LEt)3] complexes reveals some
interesting structural effects. Comparison of the La and Nd com-
plexes [La(LEt)3] and [Nd(LEt)3] shows that whilst three Ln–N
bonds decrease by at least the expected (from ionic radii differ-
ences) 0.05 Å, two, Ln–N(5) (amide) and Ln–N(2) (amine),
show no differences, i.e. they are effectively lengthened. By con-
trast, all three Ln–F bonds are shortened by more than 0.05 Å
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from [La(LEt)3] to [Nd(LEt)3]. Thus, in response to the smaller
size of Nd3+, all ligands bring the sterically undemanding C–F
unit relatively closer and two of the more crowded N donor
atoms are effectively further away.
Table 2 Selected bond lengths (Å) in [La(p-HC6F4N(CH2)2NEt2)2F]3·
3/2C7H8
[La(LMe)2F]3·3/2C7H8,
[Ce(p-HC6F4N(CH2)2NEt2)2F]3·
3/2C7H8 [Ce(LMe)2F]3·3/2C7H8 and [Nd(p-HC6F4N(CH2)2NEt2)2F]2·
C6H14 [Nd(LEt)2F]2·C6H14
[La(LMe)2F]3·
3/2C7H8
[Ce(LMe)2F]3·
3/2C7H8
[Nd(LEt)2F]2·
C6H14
Although the <Nd–N(amide)> bond distances in [Nd(LEt)3]
and [Nd(LMe)3] are longer than in the six-coordinate Nd
complex, [Nd{N(SiMe3)C6H4(2-OCH3)}3] (2.37 Å),37 and the
<La–N(amide)> bond distance in [La(LEt)3] (2.45 Å) is longer
than in the six-coordinate La complex [La(NH-2,6-Pri2C6H3)3-
(thf)3] (2.39 Å),38 the increase is less than expected from ionic
radii for a change of two in the coordination number,39 indicative
of lower steric demands of the present amide ligands.
Ln(1)–N(1)
Ln(1)–N(3)
Ln(1)–N(2)
Ln(1)–N(4)
Ln(1)–F(1)
Ln(1)–F(5)
Ln(1)–F(9)
Ln(1)–F(9)#
Ln(1)–F(10)
2.510(6)
2.492(7)
2.701(7)
2.710(6)
2.628(4)
2.642(5)
2.339(4)
2.345(4)
—
2.484(8)
2.467(8)
2.673(8)
2.706(8)
2.642(5)
2.642(5)
2.325(5)
2.332(5)
—
2.428(2)
2.416(2)
2.723(2)
2.666(2)
2.6565(14)
2.6384(15)
2.2838(15)
—
2.3260(14)
Structures of the heteroleptic fluoride [Ln(p-HC6F4N-
(CH2)2NR2)2F]n complexes
bond distance (2.50 Å) is slightly longer than in [La(LEt)3]
(2.45 Å) and the average Ce–N(amide) bond distance (2.48 Å) is
somewhat longer than that in [Ce(LEt)3] (2.42 Å). Compensating
for this trend, the mean Ln–o-F bond lengths (La 2.64Å;
Ce 2.64 Å) are shorter than in [La(LEt)3] (2.74 Å) and [Ce(LEt)3]
(2.73 Å) respectively. As expected the framework Ln–F bonds
are considerably shorter (approximately 0.3 Å) than the (Ar)CF–
Ln bonds but they are ca. 0.2 Å longer than terminal Ln–F
bonds in six-coordinate [Ln(DippForm)2F(thf)] (Ln = La, Ce;
DippForm = N,N′-(2,6-diisopropylphenyl)formamidinate) com-
plexes.24 On the other hand, the framework La(1)–F(9)/F(9)#
bond lengths are very similar to the La–F bond length
(2.349(7) Å) of dimeric, eight-coordinate [La(C5H3(SiMe3)2-
Two isomorphous complexes [La(LMe)2F]3·3/2C7H8 and
[Ce(LMe)2F]3·3/2C7H8 crystallized from toluene in the R3 space
ˉ
group (Experimental section). Each compound has two similar
but crystallographically independent molecules, hence only one
is chosen to describe their structures (Fig. 3 and Table 2). Both
heteroleptic fluoride complexes are trinuclear species and the
metal centres are eight-coordinate. Each metal atom is ligated by
two tridentate (N,N′,F) N,N-dimethyl-N′-2,3,5,6-tetrafluoro-
phenylethane-1,2-diaminate(1−) ligands and two bridging fluoride
ions with a flat, distorted, hexagonal [Ln3F3] (Ln = La, Ce) core.
There is distorted bicapped trigonal prismatic coordination,
e.g. N(1)N(2)F(9) forms one triangular face while N(3)N(4)F(9#)
forms the other with bridging F(1) and F(5) as the capping
1,3)2F]2.28a These bond length similarities and structural
atoms for La(1). A similar [Ln3F3] core has been seen previously
21c
analogy with [YbCp2F]3
suggest that tridentate N,N-dialkyl-
21c
in [YbCp2F]3
and [ScCp2F]3.40 The average La–N(amide)
N′-2,3,5,6-tetrafluorophenylethane-1,2-diaminate(1−) ions may
be considered as Cp replacement ligands and the similarity is
supported by similar Ln–F bond lengths when ionic radii differ-
ences are considered.
The eight-coordinate heteroleptic neodymium fluoride
complex [Nd(p-HC6F4N(CH2)2NEt2)2F]2 was isolated as
[Nd(LEt)2F]2 from toluene and [Nd(LEt)2F]2·C6H14 from
hexane. Except for the absence/presence of hexane in the lattice,
both structures are very similar. Thus, data of the more precise
structure of [Nd(LEt)2F]2·C6H14 (Fig. 4 and Table 2) are dis-
cussed. The complex is dinuclear and the binding modes
between metal and LEt closely resemble those seen in the tri-
nuclear fluoride complexes [La(LMe)2F]3 and [Ce(LMe)2F]3.
Both metal atoms are bridged by two fluoride atoms, forming a
[Nd2F2] core. A similar core has been seen previously in five-
coordinate [Yb(OC6H2-2,6-tBu2-4-X)2F(thf)]2 (X
tBu),21c nine-coordinate [Yb(Cp or MeCp)2F(thf)]2
=
H
or
and
21b,c
eight-coordinate [Ln(C5H3(SiMe3)2-1,3)2F]2 (Ln = La, Nd, Sm,
Gd).28a In bicapped distorted trigonal prismatic coordination
geometry for Nd(1), N(1)N(2)F(9) forms one triangular face and
N(3)N(4)F(10) forms the other, with F(1) and F(5) as the
capping atoms, whilst for Nd(2), N(5)N(6)F(9) forms one tri-
angular face while N(7)N(8)F(10) forms the other, with F(11)
and F(15) as the capping atoms. The average Nd–N(amide) bond
distance (2.42 Å) is midway between those of [Nd(LEt)3]
(2.40 Å) and [Nd(LMe)3] (2.44 Å). The Nd–o-F contacts
(ave. 2.65 Å) are near those of [Nd(LMe)3] (ave. 2.60 Å) and
[Nd(LEt)3] (ave. 2.66 Å) but longer than the framework bonds
Fig. 3 Molecular diagram of [La(p-HC6F4N(CH2)2NMe2)2F]3·
3/2C7H8 [La(LMe)2F]3·3/2C7H8 shown with 50% probability thermal
ellipsoids. Hydrogen atoms and lattice C7H8 have been omitted for
clarity (symmetry code for F(9)#: −x + y, 1 − x, z).
8628 | Dalton Trans., 2012, 41, 8624–8634
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cannot be identified at this stage but a resonance in the −120 to
−130 ppm region suggests a fluorine with two ortho-H neigh-
bours, indicative of a defluorinated species.
The conversion of [Ce(LMe)3] into [Ce(LMe)2F]3 by C–F acti-
vation without apparent redox, in contrast to YbII(LMe/Et
)
2
species,18 has parallels in C–F activation of CF3 containing Ca
complexes.41 The contrast between the behaviour of [La(LMe)3]
and [Ce(LMe)3] raises the question of possible intervention of
+
CeIII ⇌ CeIV and m/z 432 [LMe − F]2 can be rationalized as
dimerization of a (p-HC6F3)N(CH2)2NMe2)2˙diradical, a poss-
ible product of such a process.
Apart from the observation of defluorinated ligand species,
the synthesis of [Ce(LMe)2F]3 using Hg(CCPh)2 establishes LMe
as a fluoride source. Implicitly, defluorination involves one (or
both) of the ortho-fluorine atoms, since these are involved in
–C–F–Ln coordination (Fig. 1 and 2). However, the low yields
of the multiple C–F activation organic products, compounded by
the difficulty in separating very small amounts of them, limit
probing the reaction paths but the species detected suggest more
than one path. Nevertheless, the reactions have provided well-
characterized organoamidolanthanoid fluorides, a rare compound
class, albeit in low yields.
Observation of C–F activation in the Nd/LEt system but not
for Ln/LEt (Ln = La, Ce), may in part relate to the considerable
shortening of <Ln–F> from La, Ce to Nd, far greater than
expected for the lanthanoid contraction (Table 2) and partly due
to isolation of a less crowded dimer for Nd than the trimers
observed for [Ln(LMe)2F]3 (Ln = La, Ce) (above).
Fig. 4 Molecular diagram of [Nd(p-HC6F4N(CH2)2NEt2)2F]2·C6H14
[Nd(LEt)2F]2·C6H14 shown with 50% probability thermal ellipsoids.
Hydrogen atoms and hexane of crystallization have been omitted for
clarity.
(ave. 2.30 Å) which are similar to those of [Nd(C5H3(SiMe3)2-
28a
1,3)2F]2
(2.337(1) Å). The similarity to this complex
reinforces the concept that LMe/Et are Cp replacement ligands.
Adoption of a dimeric structure for the smaller Nd in
[Nd(LEt)2F]2 rather than a trimer as in [Ln(LMe)2F]3 (Ln = La, Ce)
appears to reduce steric strain in response to the smaller size of
Nd3+. Repulsion between the two bulky amide ligands is the
biggest source of steric strain and in the dimeric Nd complex,
N(amide)–Nd–N(amide) is 118.79(16)°, far more open than in
the Ce or La complexes (110.4(3)° and 110.6(2)° respectively).
Although the F–Ln–F angles show the opposite trend
(67.78(11), 82.6(3) and 82.3(2) respectively, fluoride has very
low steric demand.
Conclusions
Coordination of the organoamide ligands p-HC6F4N-
(CH2)2NMe2/Et2(1−) to three light rare earth metals features
(Ar)CF–Ln coordination in the homoleptic complexes [Ln(LMe/Et)3]
(Ln = La, Ce, Nd) and the heteroleptic fluorides [Ln(LMe)3F]3
(Ln = La, Ce) and [Nd(LEt)2F]2. Tridentate (N,N′,F) coordi-
nation is mainly observed. However, in the eight-coordinate
[Ln(LMe/Et)3] complexes, one ligand is bidentate with either
N,N′-binding (LMe) or N,F-ligation (LEt) with a free –(CH2)2NEt2
group. This novel linkage variation appears to be driven by steric
factors. Although C–F activation giving heteroleptic fluorides
occurred, the extent of it was much lower than previously
observed for [Yb(LMe/Et)2(thf)2] complexes.18 Thus, less stable
LnII states (Ln = La, Ce, Nd)36 inhibit but do not prevent C–F
activation with these ligands.
Comments on C–F activation
From hydrolysis of the reaction mixture giving [La(LMe)3] and
[La(LMe)2F]3, species with m/z 298 [C12H2F8]+, 236 [LMeH]+,
233 [LMeH − 3H]+ and 384 [LMeH − F + C6F5]+ were identified,
the last being attributable to a defluorinated species and involve-
ment of a Ln(C6F5) species as well. By contrast, hydrolysis of
the reaction mixture giving [Ce(LMe)3] and [Ce(LMe)2F]3 yielded
Experimental
+
species with m/z 218 [LMeH − F + H]+ and 432 [LMe − F]2 , in
General: the compounds described herein were prepared and
handled using conventional inert atmosphere techniques. IR
spectra were recorded as Nujol mulls between NaCl plates using
either a Perkin Elmer 1600 Series FTIR instrument or a Perkin
Elmer Spectrum RX I FTIR Spectrometer within the range
4000–600 cm−1. Far IR spectra were obtained as Vaseline mulls
between polyethylene disks on a Bruker IFS120HR instrument
(with Mylar far IR optics). Multinuclear NMR spectra were
recorded on a Bruker DPX 300 spectrometer. Chemical shifts
(δ/ppm) were referenced to the residual 1H resonances of the
addition to m/z 384, 236 and 233 (above), providing clear evi-
dence of defluorination of LMe. An NMR scale experiment
showed significant conversion of [Ce(LMe)3] into the hetero-
leptic fluoride [Ce(LMe)2F]3 in 48 h in C7D8 at 110 °C but
[La(LMe)3] was much less reactive and [La(LMe)2F]3 was not
detected under similar conditions. On the contrary, heating
[La(LMe)2F]3 caused some rearrangement into [La(LMe)3]. The
formation of [Ce(LMe)2F]3 in C7D8 was accompanied by obser-
vation of additional low intensity 19F NMR resonances that
This journal is © The Royal Society of Chemistry 2012
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deuterated solvents (1H) or external CCl3F (19F). Melting points
were determined in sealed glass capillaries under nitrogen and
are not calibrated. Microanalyses were determined by the Camp-
bell Microanalytical Service, University of Otago (New
Zealand), whereas metal analyses were determined by
Na2H2edta titration following decomposition of the sample with
HNO3/H2SO4.42,43 GC/MS data were obtained with an Agilent
6890 series GC fitted with a 5% phenylmethylsiloxane capillary
column (Agilent 19091S-433HP-5mS) interfaced to an Agilent
5987 network mass selective detector. Dme, hexane and thf were
pre-dried over sodium metal and distilled over sodium benzophe-
none ketyl before being stored under an atmosphere of nitrogen.
Toluene, C7D8 and C6D6 were pre-dried over sodium and then
distilled under nitrogen from sodium metal before being stored
under an atmosphere of nitrogen. Absolute ethanol was used as
received. Pentafluorobenzene was stored over molecular sieves
(4 Å) but was otherwise used as purchased from Aldrich.
Lanthanoid metals were purchased from Santoku (America Int.)
or Tianjiao (Baotou, China) as ingots, powders or rods and
stored under nitrogen in a glove box. Hg(C6F5)2,44 Hg(CCPh)2,45
p-HC6F4NHC2H4NMe2 (LMeH)18,35 and p-HC6F4NHC2H4NEt2
(LEtH)18 were prepared by literature methods.
(C6D6, 282.4 MHz, 303 K): −143.5 (br, s, 6F; F3,5), −156.6
(br, s, 6F; F2,6); 19F{1H} NMR (C7D8, 282.4 MHz, 193 K):
−144.3 (s, 4F), −146.8 (s, 1F), −150.8 (s, 1F), −156.3 (s, 1F),
−157.2 (s, 2F), −162.7 (s, 1F), −163.7 (s, 2F).
Method 2: Freshly filed lanthanum metal (0.28 g, 2.0 mmol),
Hg(CCPh)2 (0.40 g, 1.0 mmol), LMeH (0.47 g, 2.0 mmol) and one
drop of Hg were stirred in thf (10 mL) for three days at room temp-
erature. The mixture was then filtered and the solvent removed
in vacuo leaving a pale solid crude product. Crystallization from
toluene (1 mL) gave a pale crystalline product [La(LMe)3] (0.34 g,
61%); identification by IR, 1H and 19F{1H} NMR spectroscopy.
GC/MS analyses of the reaction mixture from Method 1 forming
[La(LMe)3] and [La(LMe)2F]3
After the reaction from Method 1 was complete, some of the solu-
tion (0.5 mL) was transferred to a sample vial and EtOH (two
drops) was added. The insoluble materials were filtered off and
the solution was then diluted with EtOH (0.5 mL) and submitted
for analysis. GC/MS: Rt(m/z) = 10.483 (m/z 298) [C12H2F8]+,
11.677 (m/z 236) [LMeH]+, 13.306 (m/z 233) [LMeH − 3H]+,
16.152 (m/z 384) [LMeH − F + C6F5]+.
Attempted transformation of [La(LMe)3] into [La(LMe)2F]3
Synthesis of [La(p-HC6F4N(CH2)2NMe2)3] [La(LMe)3] and
[La(p-HC6F4N(CH2)2NMe2)2F]3 [La(LMe)2F]3
A solution of [La(LMe)3] (0.04 g) in C7H8 (0.7 mL) was heated
at 110 °C for 72 h. No appreciable transformation of [La(LMe)3]
into [La(LMe)2F]3 was detected by 19F{1H} NMR spectroscopy.
Method 1: Freshly filed lanthanum metal (0.80 g, 6.0 mmol),
Hg(C6F5)2 (1.60 g, 3.0 mmol), LMeH (1.42 g, 6.0 mmol) and
one drop of Hg were stirred in thf (30 mL) for three days at
room temperature. The reaction mixture was filtered and then the
solvent was removed in vacuo leaving a small amount of dark
brown oil. Toluene (10 mL) was then added and overnight
storage of the solution at −30 °C yielded colourless crystals of
[La(LMe)2F]3·3/2C7H8 (0.14 g, 10%). M.p. 235 °C (dec.);
(Found C 38.62, H 3.65, N 8.40; C60H66F27La3N12 requires
(loss of C7H8 of solvation, 1884.92) C 38.23, H 3.53, N 8.92%);
IR (Nujol): v = 1640 (s), 1572 (m), 1525 (w), 1495 (s), 1406
(w), 1354 (m), 1296 (w), 1275 (w), 1154 (w), 1139 (s), 1072
(m), 1056 (m), 1037 (m), 952 (m), 926 (m), 869 (w), 784 (w),
756 (w), 726 (w) cm−1; far IR (Vaseline): v = 547 (s), 497 (w),
473 (s), 447 (m), 398 (s), 379 (w), 355 (m), 319 (w), 279 (m),
Synthesis of [La(p-HC6F4N(CH2)2NEt2)3] [La(LEt)3]
Freshly filed lanthanum metal (0.84 g, 6.0 mmol), Hg(C6F5)2
(1.60 g, 3.0 mmol), LEtH (1.59 g, 6.0 mmol) and one drop of
Hg were stirred in thf (30 mL) for three days at room tempera-
ture. The solvent was then removed in vacuo and replaced with
toluene (20 mL). The mixture was filtered and the volume of the
solution was reduced in vacuo to 3 mL. The solution was stored
at ambient temperature for two days yielding colourless crystals
[La(LEt)3]·C7H8 (0.84 g, 45%). M.p. 138 °C (dec.); (Found
C 46.61, H 5.02, N 8.86; C36H45F12N6La requires (loss of C7H8
of solvation, 928.67) C 46.56, H 4.88, N 9.05%); IR (Nujol):
v = 1646 (s), 1578 (m), 1498 (m), 1295 (m), 1263 (w),
1246 (w), 1200 (w), 1182 (w), 1140 (s), 1064 (m), 1046 (w),
1006 (w), 977 (m), 944 (m), 918 (w), 873 (w), 826 (w), 796 (w),
1
250 (m), 184(s) cm−1; H NMR (C6D6, 300 MHz, 343 K): loss
of C7H8 of solvation: 1.93 (s, 36H; Me2N), 1.96 (s, br, 12H;
CH2NMe2, 3.59 (s, br, 12H; CH2NAr), 5.80 (m, 6H; HC6F4);
19F{1H} NMR (C6D6, 282.4 MHz, 343 K): −142.4 (br, s, 12F;
F3,5), −154.6 (br, s, 12F; F2,6); the spectra also show the pres-
ence of a small amount of the homoleptic complex [La(LMe)3].
Further concentration of the filtrate to 2 mL gave colourless crys-
talline [La(LMe)3] (1.04 g, 62%). M.p. 180 °C (dec.); (Found
C 42.70, H 3.99, N 9.69; C30H33F12LaN6 (844.51) requires:
C 42.67, H 3.94, N 9.95%); IR (Nujol): v = 1640 (s), 1573 (s),
1353 (m), 1284 (m), 1264 (w), 1238 (w), 1160 (w), 1134 (m),
1059 (m), 1039 (m), 954 (s), 926 (s), 872 (m), 791 (m), 760 (m)
cm−1; far IR (Vaseline): v = 576 (s), 545 (s), 498 (m), 474 (s),
453 (br, s), 401 (m), 376 (m), 330 (w), 276 (m), 227 (w),
1
761 (m), 752 (m), 691 (w), 656 (w), 614 (w) cm−1; H NMR
(C6D6, 300 MHz, 303 K): loss of C7H8 of solvation, 0.71 (t,
18H; Me), 2.45 (m, 18H; CH2Me + CH2NEt2), 3.67 (m, 6H;
CH2NAr), 5.78 (m, 3H; HC6F4); 19F{1H} NMR (C6D6,
282.4 MHz, 303 K): −142.8 (s, 6F; F3,5), −155.7 (s, br, 6F;
F2,6); 19F{1H} NMR (C7D8, 282.4 MHz, 203 K): −139.0
(s, 1F), −139.5 (s, 1F), −139.9 (s, 1F), − 143.9 (s, 1F), −144.5
(s, 1F), −145.3 (s, 1F), −145.5 (s, 1F), −146.7 (s, 1F), −154.7
(s, br, 1F), −163.0 (s, 1F), −163.7 (s, 1F), −164.0 (s, 1F).
Synthesis of [Ce(p-HC6F4N(CH2)2NMe2)3] [Ce(LMe)3] and
[Ce(p-HC6F4N(CH2)2NMe2)2F]3 [Ce(LMe)2F]3
195 (w), 168 (s) cm−1
;
1H NMR (C6D6, 300 MHz, 303 K):
3
1.85 (s, 18H; Me2N), 2.11 (t, JH,H = 6.0 Hz, 6H; CH2NMe2,
Method 1: Freshly filed cerium metal (0.84 g, 6.0 mmol),
3.55 (br, s, 6H; CH2NAr, 5.86 (m, 3H; HC6F4); 19F{1H} NMR
Hg(C6F5)2 (1.60 g, 3.0 mmol), LMeH (1.42 g, 6.0 mmol) and
8630 | Dalton Trans., 2012, 41, 8624–8634
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one drop of Hg were stirred in thf (30 mL) for three days at
room temperature. The reaction mixture was filtered and then the
solvent was removed in vacuo leaving a pale brown solid.
Toluene (10 mL) was then added and concentration of the solu-
tion in vacuo to 5 mL overnight deposited colourless crystals of
[Ce(LMe)2F]3·3/2C7H8 (0.20 g, 15%). M.p. 248 °C (dec.);
(Found C 41.32, H 4.03, N 8.36; C70.5H78F27N12Ce3 (2026.76)
requires C 41.78, H 3.88, N 8.29%); IR (Nujol): v = 1644 (vs),
1574 (vs), 1407 (vs), 1354 (vs), 1295 (s), 1275 (s), 1294 (w),
1200 (m), 1139 (vs), 1088 (w), 1073 (s), 1056 (s), 1035 (w),
951 (vs), 926 (vs), 870 (s), 786 (s), 762 (sh), 752 (s), 727 (vs),
707 (w), 658 (s), 653 (w), 577 (m) cm−1; far IR (Vaseline):
and then the solution was diluted with EtOH (0.5 mL) and sub-
mitted for analysis. Rt: 11.872 (m/z 236) [LMeH]+, 12.552
(m/z 218) [LMeH − F + H]+, 12.923 (m/z 233) [LMeH − 3H]+,
15.570 (m/z 384) [LMeH − F + C6F5]+, 19.690 (m/z 408), 20.348
+
(m/z 432) [LMeH − F − H]2 .
Transformation of [Ce(LMe)3] into [Ce(LMe)2F]3
A solution of [Ce(LMe)3] (0.030 g) in C7D8 (0.7 mL) was heated
1
at 110 °C for 48 h. The H and 19F{1H} NMR spectra indicate
40% transformation of [Ce(LMe)3] into [Ce(LMe)2F]3 based on
576 (m), 546 (m), 378 (s), 322 (m), 254 (s), 201 (s) cm−1
;
integration values.
1H NMR (C7D8, 300 MHz, 373 K): proposed monomer (see
Results and discussion): −0.86 (br, s, 12H; Me2N), 2.13
(s; MePh), 3.07 (br, s, 2H; HC6F4), 7.08 (m; C7H8), 8.16 (br, s,
4H; CH2NMe2), 15.91 (br, s, 4H; CH2NAr); proposed trimer:
−2.55 (br, s, 36H; Me2N), 2.80 (br, s, 12H; CH2NMe2), 10.95
(br, s, 6H; HC6F4), 19.85 (br, s, 12H; CH2NAr). Both species
are evident at 323 K (trimer : monomer 0.55 : 1 by integration),
343 K (trimer : monomer 0.45 : 1) and at 373 K (trimer :
monomer 0.25 : 1); 19F{1H} NMR: (C7D8, 282.4 MHz, 373 K):
monomer and trimer indistinguishable: −147.7 (s, F3,5), −199.8
(vvbr, s, F2,6) (1 : 1 integration ratio).
Synthesis of [Ce(p-HC6F4N(CH2)2NEt2)3] [Ce(LEt)3]
Freshly filed cerium metal (0.84 g, 6.0 mmol), Hg(C6F5)2
(1.60 g, 3.0 mmol), LEtH (1.59 g, 6.0 mmol) and one drop of
Hg were stirred in thf (30 mL) for three days at room tempera-
ture. The reaction mixture was filtered and then the solvent was
removed in vacuo leaving a small amount of dark orange/brown
oil. Toluene (10 mL) was then added and concentration of the
solution in vacuo to 3 mL and storage for three weeks deposited
large colourless plates [Ce(LEt)3]·1/2C7H8 (0.69 g, 37%).
M.p. 190–194 °C; (Found Ce 14.67; C36H45F12N6Ce (loss of C7H8
of solvation, 929.88) requires Ce 15.07%); IR (Nujol): v =
1644 (s), 1576 (m), 1497 (m), 1398 (w), 1378 (w), 1368 (w),
1350 (w), 1296 (w), 1138 (s), 1076 (w), 1048 (m), 1003 (w),
946 (s), 904 (w), 874 (w), 788 (w), 760 (w), 748 (w), 728 (w),
The filtrate following isolation of [Ce(LMe)2F]3 was further
concentrated in vacuo to 1 mL and stored overnight. The solu-
tion was decanted to collect [Ce(LMe)3] as a pale brown solid
(0.91 g, 54%). M.p. 157–161 °C; (Found C 42.64, H 4.12,
N 9.65; C30H33F12N6Ce (845.72) requires C 42.61, H 3.93,
N 9.94%); IR (Nujol): v = 1642 (s), 1573 (m), 1494 (vs), 1355
(vs), 1284 (m), 1201 (vw), 1137 (s), 1057 (s), 1040 (s), 955 (m),
926 (s), 871 (w), 790 (w), 763 (w), 722 (m), 690 (vw),
652 (vw), 578 (w) cm−1; far IR (Vaseline): v = 630 (m), 578 (s),
545 (m), 474 (m), 454 (s), 402 (s), 374 (w), 324 (m), 276 (w),
1
657 (w) cm−1; H NMR (C6D6, 300 MHz, 343 K): loss of most
C7H8 of solvation, −3.00–3.60 (br, m, 36H; Me + CH2Me +
CH2NEt2), 2.50 (t, 3H; HC6F4), 19.24 (br, s, 6H; CH2NAr); 19F
{1H} NMR (C6D6, 282.4 MHz, 303 K): −150.3 (br, s, Δν1/2
=
1
228 (m), 197 (w), 168 (m) cm−1; H NMR (C7D8, 300 MHz,
1099 Hz, 6F; F3,5); T = 343 K: −148.1 (s, 6F; F3,5), −201.5
(vvbr, s, Δν1/2 = 2015 Hz, 6F; F2,6).
303 K): −10.32 (br, s, ≈18H; Me2N), −2.38 (vbr, s, ≈6H;
CH2NMe2), 8.64 (s, 3H; HC6F4), 17.79 (br, s, ≈6H; CH2NAr);
considerable broadening of some resonances prevented accurate
integration but better resolution was obtained by heating; T =
343 K: −7.81 (br, s, 18H; Me2N), 0.14 (br, s, 6H; CH2NMe2),
7.68 (br, m, 3H; HC6F4), 15.75 (br, s, 6H; CH2NAr); 19F{1H}
NMR (C7D8, 282.4 MHz, 303 K): −142.0 (m; F3,5); T = 343 K:
−141.8 (s, 6F; F3,5), −180.1 (s, br, 6F; F2,6).
Method 2: Freshly filed cerium metal (0.28 g, 2.0 mmol),
Hg(CCPh)2 (0.40 g, 1.0 mmol), LMeH (0.47 g, 2.0 mmol) were
stirred in thf (10 mL) for five days at room temperature. The
mixture was then filtered and the solvent removed in vacuo
leaving a brown solid. Toluene (10 mL) was added and a small
amount of dark residue settled out overnight. The solution was
filtered and from it, [Ce(LMe)2F]3 was identified by 19F{1H}
NMR spectroscopy; [Ce(LMe)3] was also present.
Synthesis of [Nd(p-HC6F4N(CH2)2NMe2)3] [Nd(LMe)3]
Neodymium powder (1.73 g, 12.0 mmol), Hg(C6F5)2 (1.60 g,
3.0 mmol), LMeH (1.42 g, 6.0 mmol) and one drop of Hg were
stirred in thf (30 mL) for three days at room temperature. The
reaction mixture was filtered and then the solvent was removed
in vacuo leaving a small amount of dark brown oil. Hexane
(5 mL) was then added and the solution was stored overnight at
room temperature yielding [Nd(LMe)3] as pale blue crystals
(0.70 g, 41%). M.p. 174–178 °C; (Found C 42.44, H 3.88,
N 9.65; C30H33F12N6Nd (849.84) requires C 42.40, H 3.91,
N 9.89%); IR (Nujol): v = 1645 (s), 1573 (m), 1494 (vs), 1411
(w), 1399 (w), 1379 (w), 1300 (w), 1286 (m), 1264 (w), 1200
(vw), 1159 (w), 1136 (s), 1098 (vw), 1057 (sh), 1043 (vs), 1017
(sh), 957 (m), 927 (vs), 874 (m), 786 (m), 770 (m), 736 (sh),
716 (m), 690 (w), 641 (w), 578 (w), 543 (w) cm−1; H NMR
1
GC/MS analyses of the reaction mixture forming [Ce(LMe)3] and
[Ce(LMe)2F]3
(C7D8, 300 MHz, 303 K): −11.44 (br, s, 18H; Me2N), 3.95 (br,
s, 6H; CH2NMe2), 7.44 (s, 3H; HC6F4), 29.23 (br, s, 6H;
CH2NAr); 19F{1H} NMR (C6D6, 282.4 MHz, 303 K): −142.9
(br, s; F3,5); 19F{1H} NMR (C6D6, 282.4 MHz, 343 K): −143.5
(s, 6F; F3,5), −190.1 (s, br, 6F; F2,6).
After the reaction detailed in Method 1 was complete, some of
the solution (0.5 mL) was transferred to a sample vial and EtOH
(two drops) was added. The insoluble materials were filtered off
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 8624–8634 | 8631

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Synthesis of [Nd(p-HC6F4N(CH2)2NEt2)3] [Nd(LEt)3]
Synthesis of [Nd(p-HC6F4N(CH2)2NEt2)2F]2 [Nd(LEt)2F]2
Neodymium powder (0.86 g, 6.0 mmol), Hg(C6F5)2 (1.07 g,
2.0 mmol), LEtH (1.59 g, 6.0 mmol) and one drop of Hg were
stirred in thf (30 mL) for three days at room temperature. The
reaction mixture was filtered and then the solvent was removed
in vacuo and replaced with toluene (10 mL). The solution was
concentrated in vacuo (2 mL) and stored overnight at room temp-
erature yielding pale blue plates [Nd(LEt)3] (0.67 g, 36%). Crys-
tals suitable for X-ray crystallography were obtained by
crystallization from hexane. M.p. 132–140 °C; (Found Nd
14.91; C36H45F12N6Nd (934.01) requires Nd 15.44%); IR
(Nujol): v = 1647 (vs), 1579 (s), 1524 (sh), 1499 (vs), 1352 (w),
1297 (s), 1263 (m), 1247 (w), 1201 (m), 1182 (w), 1140 (vs),
1071 (s), 1048 (w), 1034 (w), 1008 (vw), 979 (s), 947 (vs),
919 (w), 876 (w), 825 (vw), 797 (w), 764 (s), 727 (s), 708 (vw),
A similar reaction procedure for the synthesis of [Nd(LEt)3] was
used but the solution was concentrated in vacuo to 5 mL. The
solution was stored at ambient temperature for four weeks giving
dichroic blue/orange crystals (yield: 0.34 g, 25%). Crystals suit-
able for X-ray crystallography were obtained from crystallization
from either toluene or hexane. (Found C 42.24, H 4.70, N 8.21;
C48H60F18N8Nd2 (1379.49) requires C 41.79, H 4.38, N 8.12%);
IR (Nujol): v = 1645 (s), 1576 (m), 1522 (w), 1498 (s),
1400 (w), 1369 (w), 1350 (w), 1296 (m), 1261 (w), 1246 (w),
1199 (w), 1139 (s), 1076 (w), 1048 (w), 946 (s), 904 (w),
875 (w), 791 (w), 760 (w), 748 (w), 728 (w), 668 (w), 657 (w)
cm−1; far IR (Vaseline): v = 574 (s), 553 (w), 533 (m), 510 (w),
482 (s), 462 (w), 441 (m), 427 (w), 397 (w), 381 (m), 341 (s),
272 (w), 239 (w), 196 (m), 176 (vs) cm−1
.
1
692 (vw), 658 (w), 617 (m), 576 (w) cm−1; H NMR (C6D6,
300 MHz, 343 K): −3.37 (br, s, 30H; Et), 0.82 (s, 3H; HC6F4),
1.40 (br, s, 6H; CH2NEt2), 22.89 (br, s, 6H; CH2NAr); 19F{1H}
NMR (C6D6, 282.4 MHz, 303 K): −144.0 (br, s, F3,5); 19F{1H}
NMR (C6D6, 282.4 MHz, 343 K): −146.8 (s, 6F; F3,5), −192.5
(br, s, 6F; F2,6).
Concurrent synthesis of [Nd(LEt)3] and [Nd(LEt)2F]2
Neodymium powder (0.86 g, 6.0 mmol), Hg(C6F5)2 (1.60 g,
3.0 mmol), LEtH (1.59 g, 6.0 mmol) and one drop of Hg were
Table 3 Crystal data and structure refinement for complexes [La(LEt)3]·C7H8 –[Nd(LMe)2F]2·C6H14
[La(LEt)3]·C7H8
[Ce(LEt)3]·1/2C7H8
[Nd(LMe)3]
[Nd(LEt)3]
Formula
Mr
Space group
a (Å)
b (Å)
c (Å)
α (°)
C
43H53F12N6La
C39.5H49F12N6Ce
975.97
P1
C30H33F12N6Nd
849.86
P1
C36H45F12N6Nd
934.02
P21/c
21.120(4)
10.559(2)
17.562(4)
90
103.42(3)
90
1020.82
ˉ
ˉ
ˉ
P1
10.168(2)
11.251(2)
20.709(4)
102.76(3)
99.50(3)
92.84(3)
2269.9(8)
2
10.233(2)
11.421(2)
18.757(4)
81.03(3)
78.85(3)
85.71(3)
2122.2(7)
2
9.7596(3)
9.7779(3)
17.8383(6)
89.367(2)
75.192(2)
81.488(2)
1626.98(9)
2
β (°)
γ (°)
V (Å3)
Z
3809.4(13)
4
1.457
μ (mm−1
)
1.028
1.494
1.161
1.527
1.697
1.735
ρcalc (g cm−3
)
1.629
Nτ
N(Rint
28 485
23 644
28 652
42 892
)
7800(0.0515)
0.0667/0.1517
0.0750/0.1561
1.221
7417(0.2295)
0.0726/0.1097
0.2101/0.1474
0.970
7464(0.0194)
0.0202/0.0511
0.0217/0.0522
1.069
6723(0.1969)
0.0622/0.1305
0.1184/0.1557
1.030
R1/wR2 (I > 2σ(I))
R1/wR2 (all data)
GOF
max/min Δe (e Å−3
)
3.669/−3.018
0.919/−0.928
1.251/−0.364
1.499/−1.034
[La(LMe)2F]3·3/2C7H8
[Ce(LMe)2F]3·3/2C7H8
[Nd(LEt)2F]2
[Nd(LEt)2F]2·C6H14
Formula
Mr
Space group
a (Å)
b (Å)
c (Å)
α (°)
C70.5H78F27N12La3
2023.18
R3
22.6999(3)
22.6999(3)
53.1241(12)
90
90
120
23 706.6(7)
12
1.705
C70.5H78F27N12Ce3
2026.81
R3
22.712(3)
22.712(3)
53.514(11)
90
90
120
23 907 (7)
12
1.796
C48H60F18N8Nd2
1379.52
P1
C54H70F18N8Nd2
1461.66
Pbca
18.5793(5)
22.1566(6)
28.3427(7)
90
ˉ
ˉ
ˉ
12.115(2)
12.644(3)
20.204(4)
72.95(3)
76.68(3)
68.60(3)
2728.4(9)
2
β (°)
90
90
γ (°)
V (Å3)
Z
11 667.4(5)
8
1.861
μ (mm−1
)
1.985
1.679
ρcalc (g cm−3
)
1.701
1.689
1.664
Nτ
N (Rint
178 448
9264(0.0625)
0.0559/0.1352
0.0978/0.1780
1.156
42 852
23 861
86 381
)
9362(0.1634)
0.0641/0.1428
0.1573/0.1894
1.074
9087(0.0618)
0.0503/0.1370
0.0550/0.1415
1.047
13 399 (0.0439)
0.0308/0.0713
0.0463/0.0803
1.039
R1/wR2 (I > 2σ(I))
R1/wR2 (all data)
GOF
max/min Δe (e Å−3
)
2.361/−2.137
3.109/−0.961
1.312/−1.322
1.336/−0.571
8632 | Dalton Trans., 2012, 41, 8624–8634
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stirred in thf (30 mL) for two days at room temperature. Filtration
and evaporation of the solvent in vacuo gave a small amount of
dark brown oil. Hexane (30 mL) was added to the oil and a
small amount of dark solid precipitated. After filtration and con-
centration in vacuo to 10 mL and storage at −30 °C for two
days, a brownish solid precipitated, to which hexane (10 mL)
was added. After heating and cooling twice, the solution was
filtered to remove a small amount of orange-brown solid. The
filtrate was concentrated in vacuo to 5 mL and left at ambient
temperature, giving a large amount of non-crystalline solid.
Hexane (20 mL) was added and the mixture was again heated
and filtered to remove some blue solid (a) which was dissolved
in toluene (10 mL) and the solution concentrated to 5 mL and
layered with hexane. Some small blue crystals formed and the
mixture was gently heated and left at ambient temperature. After
three days, light blue solid precipitated and isolation by decanta-
tion and washing with cold hexane and drying in vacuo gave
[Nd(LEt)3] (0.17 g, 9%); identification by 1H, 19F{1H} NMR
and IR spectroscopy. The filtrate obtained from the isolation of
(a) deposited orange needles and blue-green blocks. Sufficient
needles were separated manually and identified by X-ray crystal-
lography as [Nd(LEt)2F]2·C6H14. The IR spectrum of the bulk
dried product corresponded to that of unsolvated [Nd(LEt)2F]2,
consistent with ready loss of C6H14.
Science for a Faculty of Science Dean’s Scholarship to RPK,
and Dr Samar Beaini for X-ray crystallography assistance.
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Single crystals coated with viscous hydrocarbon oil were
mounted on glass fibres. Data were obtained at −150 °C (123 K)
on a Bruker X8 APEX II CCD diffractometer ([La(LEt)3]·C7H8,
[La(LMe)2F]3·3/2C7H8, [Nd(LMe)3], [Nd(LEt)2F]2·C6H14) or an
Enraf-Nonius Kappa CCD diffractometer ([Ce(LEt)3]·1/2C7H8,
[Ce(LMe)2F]3·3/2C7H8, [Nd(LEt)3], [Nd(LEt)2F]2); all are
equipped with graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å). Each data set was empirically corrected for absorp-
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were solved by conventional methods and refined by full-matrix
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crystallographic data for this paper.†
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(moiety formula C70.50H78Ce3F27N12, Z = 12) of the unit cell.
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