Cerium(III/IV) formamidinate chemistry, and a stable cerium(IV) diolate

Article abstract of DOI:10.1002/chem.201304582

Four new cerium(III) formamidinate complexes comprising [Ce(p-TolForm) ₃], [Ce(DFForm)₃(thf)₂], [Ce(DFForm) ₃], and [Ce(EtForm)₃] were synthesized by protonolysis reactions using [Ce{N(SiMe₃)₂}₃] and formamidines of varying functionality, namely N,N′-bis(4-methylphenyl) formamidine (p-TolFormH), N,N′-bis(2,6-difluorophenyl)formamidine (DFFormH), and the sterically more demanding N,N′-bis(2,6-diethylphenyl) formamidine (EtFormH). The bimetallic cerium lithium complex [LiCe(DFForm) ₄] was synthesized by treating a mixture of [Ce{N(SiHMe ₂)₂}₃(thf)₂] and [Li{N(SiHMe ₂)₂}] with four equivalents of DFFormH in toluene. Oxidation of the trivalent cerium(III) formamidinate complexes by trityl chloride (Ph₃CCl) caused dramatic color changes, although the cerium(IV) species appeared transient and reformed cerium(III) complexes and N′-trityl-N,N′-diarylformamidines shortly after oxidation. The first structurally characterized homoleptic cerium(IV) formamidinate complex [Ce(p-TolForm)₄] was obtained through a protonolysis reaction between [Ce{N(SiHMe₂)₂}₄] and four equivalents of p-TolFormH. [Ce{N(SiHMe₂)₂}₄] was also treated with DFFormH and EtFormH, but the resulting cerium(IV) complexes decomposed before isolation was possible. The new cerium(IV) silylamide complex [Ce{N(SiMe₃)₂}₃(bda)_0.5] ₂ (bda=1,4-benzenediolato) was synthesized by treatment of [Ce{N(SiMe₃)₂}₃] with half an equivalent of 1,4-benzoquinone, and showed remarkable resistance towards protonolysis or reduction. Figure ate: The reaction of ate complex [Li(thf)Ce{N(SiHMe ₂)₂}₄ with C₂Cl₆ gives straightforward access to the homoleptic complex [Ce{N(SiHMe₂) ₂}₄], which engages in protonolysis reactions (see scheme) with formamidines to afford the first Ce^IV formamidinate species [Ce(p-TolForm)₄] (p-TolForm=N,N′-bis(4-methylphenyl) formamidinato).

Full text of DOI:10.1002/chem.201304582

DOI: 10.1002/chem.201304582
Full Paper
&
Silylamine Elimination
Cerium(III/IV) Formamidinate Chemistry, and a Stable Cerium(IV)
Diolate
Daniel Werner,[a] Glen B. Deacon,*[a] Peter C. Junk,*[b] and Reiner Anwander*[c]
Abstract: Four new cerium(III) formamidinate complexes
comprising [Ce(p-TolForm)3], [Ce(DFForm)3(thf)2],
changes, although the cerium(IV) species appeared transient
and reformed cerium(III) complexes and N’-trityl-N,N’-diaryl-
formamidines shortly after oxidation. The first structurally
characterized homoleptic cerium(IV) formamidinate complex
[Ce(p-TolForm)4] was obtained through a protonolysis reac-
tion between [Ce{N(SiHMe2)2}4] and four equivalents of p-Tol-
FormH. [Ce{N(SiHMe2)2}4] was also treated with DFFormH
and EtFormH, but the resulting cerium(IV) complexes de-
composed before isolation was possible. The new cerium(IV)
silylamide complex [Ce{N(SiMe3)2}3(bda)0.5]2 (bda=1,4-benze-
nediolato) was synthesized by treatment of [Ce{N(SiMe3)2}3]
with half an equivalent of 1,4-benzoquinone, and showed re-
markable resistance towards protonolysis or reduction.
[Ce(DFForm)3], and [Ce(EtForm)3] were synthesized by proto-
nolysis reactions using [Ce{N(SiMe3)2}3] and formamidines of
varying functionality, namely N,N’-bis(4-methylphenyl)form-
amidine (p-TolFormH), N,N’-bis(2,6-difluorophenyl)formami-
dine (DFFormH), and the sterically more demanding N,N’-
bis(2,6-diethylphenyl)formamidine (EtFormH). The bimetallic
cerium lithium complex [LiCe(DFForm)4] was synthesized by
treating
a
mixture of [Ce{N(SiHMe2)2}3(thf)2] and
[Li{N(SiHMe2)2}] with four equivalents of DFFormH in toluene.
Oxidation of the trivalent cerium(III) formamidinate com-
plexes by trityl chloride (Ph3CCl) caused dramatic color
Introduction
tribution is highly dependent on ligand type, reaction environ-
ment, and solvent.[2,5–7] This is highlighted with the comparison
between the cerium bis(trimethylsilyl)amide complex (above)
and the slightly less bulky bis(dimethylsilyl)amide analogue.
When [Ce{N(SiHMe2)2}3(thf)2] was oxidized by chlorinating
agents PhICl2, Ph3CCl, or C2Cl6, the homoleptic species [Ce{N-
(SiHMe2)2}4] was isolated, in varying yields.[7] Of the oxidants
used, treatment with Ph3CCl showed the highest yield (60%
isolated) when compared with PhICl2 (20% crystal yield) or
C2Cl6, which reacted slowly compared with the other oxidants
(45% crystal yield). Furthermore, [Ce{N(SiHMe2)2}4] was pro-
duced by a redistribution process, making bulk purification dif-
ficult.[7] The presence of donor solvents dramatically affected
the synthesis of [Ce{N(SiHMe2)2}4]. In the absence of THF, oxida-
tion by the above chlorinating agents produced the cerium(III)
chloride cluster [Ce5{N(SiHMe2)2}8Cl7], instead of a tetravalent
complex. Such a subtle change to the system highlights the
many difficulties associated with the synthesis of organoceriu-
m(IV) complexes. Another example of the formation of a homo-
leptic complex occurred with the di(cyclohexyl)amido (NCy2)
ligand. The homoleptic cerium(IV) species [Ce(NCy)4] was gen-
erated by exposure of the trivalent precursors [Ce(NCy2)3]
(through redistribution) or [Li(thf)Ce(NCy2)4] to dry O2, and the
cerium(IV) complex generated showed stability in toluene.[8]
Although monoanionic amido ligands have allowed CeIV sta-
bilization to some degree, very few bidentate nitrogen-based
donors have been employed as CeIV supports. The oxidation of
cerium amidinates has not been widely studied, with [Ce(p-
MeOC6H4C(NSiMe3)2)3Cl] featuring as the only reported example
of a tetravalent amidinate species, which was isolated from the
Recent advances in cerium(IV) silylamide chemistry have
shown that [Ce{N(SiMe3)2}3] can be oxidized by TeCl4,[1]
Ph3CCl,[2] and PhICl2 to give the heteroleptic cerium(IV) com-
[3]
plex [Ce{N(SiMe3)2}3Cl], in varying yields. Notably, oxidation of
[Ce{N(SiMe3)2}3] by Ph3CCl appeared quantitative, with a good
isolated yield (81%). When initially synthesized by Lappert and
co-workers, [Ce{N(SiMe3)2}3Cl] was described as unstable, de-
composing after several hours at ambient temperature, pro-
ducing small amounts of [Ce{N(SiMe3)2}3] and a trivalent
chloro-bridged species [Ce{N(SiMe3)2}2(m-Cl)(thf)]2.[1,4] Such in-
stability of cerium(IV) species is not uncommon, with a multi-
tude of products generated upon decomposition.[1,2,4,5] Fur-
thermore, in the case of heteroleptic chlorides, ligand redistrib-
ution is possible forming homoleptic species, and, if the coor-
dination of four bulky ligands is too sterically demanding at
the cerium(IV) center, spontaneous reduction may occur. The
stability, or resistance of cerium(IV) compounds towards redis-
[a] D. Werner, Prof. Dr. G. B. Deacon
School of Chemistry, Monash University, Victoria 3800 (Australia)
E-mail: glen.deacon@monash.edu.au
[b] Prof. Dr. P. C. Junk
School of Pharmacy and Molecular Sciences, James Cook University
Townsville, Queensland 4811 (Australia)
E-mail: peter.junk@jcu.edu.au
[c] Prof. Dr. R. Anwander
Institut fꢀr Anorganische Chemie, Auf der Morgenstelle 18
72076 Tꢀbingen (Germany)
E-mail: reiner.anwander@uni-tuebingen.de
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oxidation of [Ce(p-MeOC6H4C(NSiMe3)2)3] with half an equiva-
lent of PhICl2.[3] Within the class of amidinato ligands, N,N’-dia-
rylformamidinato derivatives are of potential interest in ceriu-
m(IV) chemistry as the proligands are readily prepared and can
be electronically and sterically tuned. Such formamidinato li-
gands have been studied extensively in transition-metal[9] and
main-group chemistry.[10] One focus of the more recently devel-
oped rare-earth metal-derived chemistry[11] has been the mod-
(SiHMe2)2]. All cerium(III) formamidinate species [Ce(p-Tol-
Form)3] (1), [Ce(DFForm)3(thf)2] (2), [Ce(DFForm)3] (3), and [Ce-
(EtForm)3] (4; p-TolFormH: N,N’-bis(4-methylphenyl)formami-
dine,
DFFormH:
N,N’-bis(2,6-difluorophenyl)formamidine,
EtFormH: N,N’-bis(2,6-diethylphenyl)formamidine) were synthe-
sized by protonolysis reactions between [Ce{N(SiMe3)2}3] and
the stoichiometric amount of the corresponding formamidine,
whereas [LiCe(DFForm)4] (5) was synthesized by treating equiv-
ulation of steric effects of formamidinato ligands to induce Cꢀ alent amounts of [Ce{N(SiHMe2)2}3(thf)2] and [LiN(SiHMe2)2] with
F bond activation of a coordinating C6F5 group.[11a,b,12] Oxida-
tion studies of rare-earth metal formamidinate complexes have
so far only involved reactions of divalent Yb[11c] and Sm com-
plexes.[12,13] Currently there is only one example of a cerium
formamidinate complex, namely the trivalent [Ce(DippForm)2F-
four equivalents of DFFormH (Scheme 1).
The formamidinate complexes 1–5 were isolated in high
yields (1, 96%; 2, 90%; 3, 95%; 4, 95%; 5, 72%). Considering
also the initial synthesis of [Ce{N(SiMe3)2}3], the yields are com-
parable with those of similar formamidinate complexes of
other rare-earth metals ([Ln(Form)3(thf)n], n=0–2), previously
synthesized by the one-pot redox transmetalation protonolysis
(RTP) using diarylmercury reagents.[11a,b] Complex 1, when syn-
thesized in Et2O or toluene, precipitates as an insoluble
powder allowing easier isolation compared with the synthesis
in THF, from which, upon vacuum drying, a mixture of unchar-
acterized solvated and unsolvated species was obtained. Com-
plex 1 is sparingly soluble in toluene and essentially insoluble
in hexane or Et2O at ambient temperature. When compared
with the other more soluble mononuclear complexes 2–4, it is
plausible that complex 1 is a multinuclear species. Once syn-
thesized in THF, 2 can be dried and crystallized from a hexane
solution as a solvated mononuclear complex: [Ce(DFForm)3-
(thf)2] (Figure 1, top). The complex is soluble in toluene and is
sparingly soluble in hexane at ambient temperature. The coor-
(thf)]
(DippForm=N,N’-bis(2,6-diisopropylphenyl)formamidi-
nate), and its possible oxidation was not examined.[11b] Thus,
trivalent and tetravalent cerium formamidinate chemistry is
still an unexplored area.
Herein we describe the synthesis of five new cerium(III) for-
mamidinate complexes utilizing three formamidinato ligands
of varying functionality, namely N,N’-bis(4-methylphenyl)forma-
midinato (p-TolForm), N,N’-bis(2,6-difluorophenyl)formamidina-
to (DFForm), and N,N’-bis(2,6-diethylphenyl)formamidinato
(EtForm). The complexes have been treated with the oxidizing
agent Ph3CCl in an attempt to isolate cerium(IV) formamidinate
complexes. Although oxidation was apparent, no stable ceriu-
m(IV) product was isolated with any ligand system, but some
decomposition products of the cerium(IV) transient species
were obtained, namely trityl-coupled formamidines and in
some cases cerium(III) products.
In an alternative approach,
[Ce{N(SiHMe2)2}4] was synthe-
sized by an improved route and
was subsequently used as a pro-
tonolysis precursor for reactions
with formamidines, thereby
giving the cerium(IV) formamidi-
nate complex [Ce(p-TolForm)4].
A
new cerium(IV) silylamide
complex, [Ce{N(SiMe3)2}3(bda)0.5]2
(bda=1,2-benzenediolato), was
synthesized by oxidation of
[Ce{N(SiMe3)2}3] with 1,4-benzo-
quinone, and shows remarkable
stability towards reduction and
protonolysis.
Results and Discussion
Synthesis and structural char-
acterization of cerium(III) for-
mamidinate complexes
All cerium(III) silylamide reagents
were synthesized by salt meta-
thesis reactions between [CeCl3-
Scheme 1. Synthesis of complexes 1–4, reaction time for each complex: 16 h. In each reaction three equivalents
of 3HN(SiMe3)2 were produced and removed by vacuum drying (2–5 h). a) 3p-TolFormH, toluene or diethyl ether;
b) 3DFFormH, THF; c) 3DFFormH, toluene; d) 3EtFormH, THF; e) reaction time 24 h in toluene, Ar=(2,6-difluoro-
(thf)2] and [KN(SiMe3)2] or [LiN- phenyl), four equivalents of HN(SiHMe2)2 were removed by vacuum drying.
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identical distance of 2.92 ꢁ, well within the sum (3.29 ꢁ) of the
Ce metallic radius (1.82 ꢁ)[14] and fluorine van der Waals radius
(1.47 ꢁ).[15] Thus, cerium has a formal coordination number of
ten. The CeꢀF distances in complex 3 are longer than those re-
ported for other ligand systems which also show o-FꢀCe coor-
dination,[16a,b] such as the eight-coordinate cerium diaminate
complex tris(N,N’-diethyl-N’-2,3,5,6-tetrafluorophenylethane-1,2-
diaminato)cerium(III), which displays three shorter CeꢀF inter-
actions at 2.686, 2.764, and 2.779 ꢁ and has good thermal sta-
bility.[16a] Investigations into a potential CꢀF bond activation of
the coordinating fluorine atoms in complex 3 has not yet been
undertaken. The CeꢀN bond lengths for 3 are shorter than
those observed in complex 2, and are more comparable with
those of the six-coordinate EtForm species 4, consistent with
weak o-FꢀCe interactions (Table 1). The absence of THF in com-
Table 1. Selected interatomic distances [ꢁ] for complexes 2, 3, and 4.
CeꢀX
2
3
4
CeꢀX
2
3
CeꢀN(1) 2.576(3) 2.486(2) 2.507(2) CeꢀF(1)
CeꢀN(2) 2.599(4) 2.489(2) 2.526(2) CeꢀF(3)
CeꢀN(3) 2.546(3) 2.479(2) 2.480(2) CeꢀF(5)
CeꢀN(4) 2.602(3) 2.580(2) 2.476(2) CeꢀF(11)
–
–
–
–
2.9186(13)
2.9189(13)
2.9189(13)
2.9206(13)
–
CeꢀN(5) 2.566(3) 2.581(2) 2.501(2) CeꢀO(1) 2.515(3)
CeꢀN(6) 2.595(4) 2.479(2) 2.499(2) CeꢀO(2) 2.508(3)
–
plex 3 allows closer CeꢀN distances and, consequently, fluorine
coordination. Although a weak interaction, the coordinating
fluorine has an influence on the Cipso-N-CH angle. For a phenyl
group containing a fluorine atom coordinating to cerium in 3,
the Cipso-N-CH angles are in the range 126.4(2)–128.3(2)8,
whereas for those with non-coordinating fluorine atoms, they
are in the range 121.68(19)–121.71(19)8 (Figure 2). The corre-
Figure 1. Crystal structures of complexes [Ce(DFForm)3(thf)2] (2, top) and
[Ce(DFForm)3] (3, bottom). Ellipsoids shown at 50% probability. Lattice sol-
vents and hydrogen atoms have been removed for clarity. Complex 2 crys-
tallized with two independent molecules in the asymmetric unit, only one is
depicted above.
sponding angles in complex
2 are significantly smaller
(116.1(4)–121.4(4)8). Furthermore, CeꢀF interactions have
a slight effect on the o-carbon fluorine bond length causing
slight elongation: 1.376(2) ꢁ, compared with the non-coordi-
nating fluorine atoms (1.359(2) ꢁ). Complex 2 has no CeꢀF in-
teractions, with the closest CeꢀF distance (3.67 ꢁ) far beyond
the sum of the van der Waals radii. Therefore, cerium has a co-
ordination number of eight and a geometry best described as
distorted dodecahedral and the THF ligands have a transoid
disposition (O(1)-Ce(1)-O(2)=153.60(11)8 O(3)-Ce(2)-O(4)=
157.34(11)8). The transoid THF coordination in 2 is comparable
to [La(o-TolForm)3(thf)2], which also displays transoid THF coor-
dinating THF on complex 2 cannot be removed readily. When
boiled in toluene and dried under vacuum, recrystallization
from hexane yielded only 2 in good yields. The unsolvated
DFForm complex 3 was prepared and isolated from a toluene
solution. It has a lower solubility in toluene than complex 2,
but much higher solubility than 1. From a toluene solution
under partial vacuum, 3 crystallized as the monomeric homo-
leptic species [Ce(DFForm)3]·PhMe (3·PhMe, Figure 1, bottom),
with a toluene of crystallization that is partly lost upon extend-
ed drying giving
a bulk solid with composition [Ce-
(DFForm)3]·0.5PhMe as determined by elemental analysis and
1H NMR spectroscopy. Complex 3 can be readily dissolved in
THF forming the THF solvated species 2, but this process, as in-
dicated above, appears irreversible (Scheme 1).
Because of the lack of solvent coordinating to cerium in
complex 3 and the relatively low bulk of the ligand, coordina-
tion saturation of the cerium atom is accomplished by the in-
teraction with four fluorine atoms, all weakly bonding at an
Figure 2. Increase in the Cipso-N-CH bond angle due to CeꢀF interactions.
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dination (O(1)-La(1)-O(1): 157.23(17)8).[11b] Complex 4, using the
bulkier EtForm ligand, crystallizes from toluene to afford the
six-coordinate homoleptic species [Ce(EtForm)3]·PhMe (4·PhMe,
not shown), mirroring the La, Nd, Sm, Ho and Yb species previ-
ously reported.[11b]
cerium nitrogen bonding brings three fluorine atoms into
close proximity to lithium. Complex 5 shows one terminal for-
mamidinato ligand bound to cerium and three formamidinato
ligands bridging between cerium and lithium. The bridging
formamidinato ligands have one m-k1,k1 nitrogen atom and
one k1. One of the bridging ligands is tetradentate, with four
sites of coordination (F, N, N’, F’), and two are tridentate (F, N,
N’) whereas the terminal ligand shows F, N, N’ chelation. The
structure is the first crystallographically characterized rare-
earth metal–lithium bimetallic amidinate complex, showing un-
solvated six-coordinate lithium encapsulation (three N and
three F donor atoms). Despite the close LiꢀF interactions, the
complex appeared stable at ambient temperature, with no
signs of CꢀF bond activation (compare with ref. [16]). In C6D6,
the 19F NMR spectrum of the complex shows only a single
ligand environment, indicating rapid formamidinato ligand (or
Li+) exchange at ambient temperature.
The cerium–lithium bimetallic complex 5 is the first reported
trivalent rare-earth complex with four coordinating formamidi-
nato ligands, with all previous derivatives having only two or
three (Figure 3). The cerium atom is ten-coordinate, with eight
The trivalent formamidinate complexes showed typical para-
magnetic shifting in their NMR spectra and with complexes
1
1 and 2 no coherent H NMR spectra could be obtained. In this
regard, the contrast between 2 with THF coordination and un-
solvated 3 is noteworthy. However, both gave clear but differ-
ing 19F NMR spectra. Elemental analyses for complexes 1–5
were obtained from the bulk material, after hexane washing
and drying, and all values are within acceptable limits for air-
sensitive rare-earth metal complexes.
Figure 3. Crystal structure of [LiCe(DFForm)4] (5); ellipsoids shown at 50%
probability; hydrogen atoms removed for clarity. See Scheme 1 for a simpli-
fied drawing. Relevant interatomic distances [ꢁ]: CeꢀN(1) 2.694(2), CeꢀN(3)
2.805(3), CeꢀN(5) 2.900(2), CeꢀN(2) 2.498(3), CeꢀN(4) 2.543(3), CeꢀN(6)
2.528(2), CeꢀN(7) 2.490(2), CeꢀN(8) 2.731(2), CeꢀF(3) 2.962(2), CeꢀF(7)
3.276(2),[a] CeꢀF(11) 3.127(2),[a] CeꢀF(13) 3.009(2), LiꢀN(1) 2.199(6), LiꢀN(3)
2.136(6), LiꢀN(5) 2.128(6), LiꢀF(1) 2.053(6), LiꢀF(5) 2.012(6), LiꢀF(9) 2.023(6).
[a] Non-bonding.
Oxidation of trivalent cerium formamidinate complexes 1–5
The cerium(III) complexes 1–5 were tested as precursors for
cerium(IV) formamidinate complexes. Initially each complex
was treated with either TeCl4, Hg(C6F5)2, perfluorodecalin or
C2Cl6, but showed no signs of oxidation upon reagent addition.
When trityl chloride was added, each complex 1–5 showed
signs of oxidation by dramatic color changes, typically from
light yellow to darker colors (dark brown/deep green). Each
cerium(IV) species was short lived decomposing soon after for-
nitrogen and two fluorine donor atoms. The CeꢀF distances
are somewhat longer than for complex 3 but still well within
the sum of the appropriate radii
(above). Longer CeꢀF(7) and Ceꢀ
F(11) distances have less signifi-
cance. The encapsulated lithium
atom is six-coordinate, with
closer lithium fluorine interac-
tions than the bridging lithium
nitrogen bond lengths. The pref-
erential interaction with fluorine
over nitrogen is in contrast to
the N,N’-bis(2-fluorophenyl)for-
mamidinate (FForm) derivative
[Li(FForm)(Et2O)]2,[10c]
which
shows closer LiꢀN bonding than
LiꢀF. The inability of the lithium
metal to bind to the nitrogen
atoms at a closer distance is
probably due to the bridging of
the ligands to the larger, higher
Scheme 2. Attempted synthesis of CeIV formamidinate complexes from trivalent formamidinate complexes by oxi-
dation with trityl chloride: a) [Ce(p-TolForm)3] (1), THF; b) [Ce(DFForm)3(thf)2] (2), THF; c) [Ce(DFForm)3] (3), tolu-
charged cerium atom. The ene; d) [Ce(EtForm)3] (4), THF; e) [LiCe(DFForm)4] (5), THF, ꢀLiCl.
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III
C
mation (from near instantaneous to several hours, see the Ex-
perimental Section), with no cerium(IV) products isolated
before decomposition (Scheme 2). It appears that when trityl
chloride is used as an oxidant for 1, the initially formed ceriu-
m(IV) complex is reduced by the trityl radical co-product, pro-
ducing N,N’-bis(4-methylphenyl),N’-(triphenylmethyl)-formami-
dine (6a, Scheme 2, a; Figure 4, top). Likewise N,N’-bis(2,6-di-
fluorophenyl),N’-(triphenylmethyl)formamidine (6b) was ob-
tained from oxidation of complexes 2, 3, and 5 (Scheme 2, b,
c, e; Figure 4, middle). All reactions appear to follow the reac-
Ph3C ”![Ce (Form)2Cl]+Form(CPh3). Cerium(III) products then
arise from the degradation of [CeIII(Form)2Cl].
With the oxidation of complexes 1 and 3, isolation of the
cerium-containing product was not possible. The trimetallic
pentachloride complex [Ce3Cl5(DFForm)4(thf)4] (7a) was ob-
tained from the oxidation of complex 2, and identified by X-
ray crystallography of very small crystals (Figure 5). However
7a was not the sole product of decomposition, and the pres-
ence of other species caused difficulty in characterizing the
product by other means. Complex 4, with the bulky EtForm
ligand, was the least stable transient cerium(IV) complex, dis-
coloring from dark green to light gold within seconds after for-
mation. Small crystals were grown from the reaction mixture
revealing the formation of the formamidinatocerium dichloride
species [Ce(EtForm)Cl2(thf)3] (7b, Figure 5, bottom). A small
tion
pathway:
[CeIII(Form)3]+Ph3CCl!“[CeIV(Form)3Cl]+
Figure 5. Crystal structures of [Ce3Cl5(DFForm)4(thf)4]·4THF (7a, top) and [Ce-
(EtForm)Cl2(thf)3] (7b, bottom). Ellipsoids shown at 50% probability. Lattice
solvents (7a), and hydrogen atoms have been omitted for clarity. Selected
interatomic distances [ꢁ] and angles [8]: 7a: Ce1ꢀCl1 2.8323(15), Ce1ꢀCl2
2.9870(15), Ce1ꢀCl3 2.9585(14), Ce1ꢀCl4 2.8027(13), Ce1ꢀN1 2.521(5), Ce1ꢀ
N2 2.547(5), Ce1ꢀO1 2.482(5), Ce1ꢀO2 2.496(4), Ce2ꢀCl1 2.8526(15), Ce2ꢀCl2
3.0053(14), Ce2ꢀCl3 2.9151(14), Ce2ꢀCl5 2.8075(14), Ce2ꢀN3 2.525(5), Ce2ꢀ
N4 2.549(5), Ce2ꢀO3 2.472(4), Ce2ꢀO4 2.518(5), Ce3ꢀCl2 2.9191(14), Ce3ꢀCl3
3.0527(14), Ce3ꢀCl4 2.8990(14), Ce3ꢀCl5 2.9095(14), Ce3ꢀN5 2.565(5), Ce3ꢀ
N6 2.534(4), Ce3ꢀN7 2.563(5), Ce3ꢀN8 2.566(5); Ce1-Cl1-Ce2 97.28(4), Ce1-
Cl2-Ce2 90.81(4), Ce1-Cl3-Ce2 93.81(4), Ce1-Cl4-Ce3 97.46(4), Ce2-Cl2-Ce3
92.76(4), Ce2-Cl3-Ce3 91.87(4), Ce2-Cl5-Ce3 97.21(4). 7b: Ce1-Cl1 2.7224(12),
Ce1-Cl2 2.7308(12), Ce1-N1 2.500(3), Ce1-N2 2.523(3), Ce1-O1 2.488(3), Ce1-
O2 2.551(3), Ce1-O3 2.518(3); Cl1-Ce1-Cl2 165.68(4), Cl1-Ce1-O1 95.69(8), Cl1-
Ce1-O2 80.55(8), Cl1-Ce1-O3 87.14(8), Cl2-Ce1-O1 83.46(8), Cl2-Ce1-O2
85.44(9), Cl2-Ce1-O3 86.60(8).
Figure 4. Crystal structures of compounds 6a (top), 6b (middle), and 6c
(bottom). Ellipsoids shown at 50% probability, hydrogen atoms and lattice
solvent were removed for clarity.
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amount of reaction mixture was hydrolyzed by D2O in C6D6
[Ce{N(SiHMe2)2}4] as a precursor for cerium(IV) formamidi-
nates
1
and analyzed by H NMR spectroscopy, indicating the presence
of N,N’-bis(2,6-diethylphenyl),N’-(triphenylmethyl)formamidine
(6c) by the chemical shift of the N=CHꢀN backbone
The homoleptic CeIV bis(dimethylsilyl)amide (9) has formerly
(8.54 ppm) distinctive from that of EtFormH (6.92 ppm, N=CHꢀ been synthesized from a redistribution process (see the Intro-
N). Crystals of 6c were not obtained directly from the reaction
mixture. However, treatment of the residue from evaporation
of the reaction mixture with hot acetonitrile gave small crystals
of 6c·CH3CN (Figure 4, bottom). Treatment of complex 5 with
Ph3CCl gave a deep red solution within hours of stirring. How-
ever, upon evaporation and addition of hexane only crystals of
complex 2 and compound 6b
duction).[7] Therefore, a new synthesis route that eliminated
the redistribution step was sought.[21] A trivalent cerium–lithi-
um bimetallic complex with four silylamido ligands, [Li-
(thf)Ce{N(SiHMe2)2}4] (8), was synthesized by treatment of
[CeCl3(thf)2] with four equivalents of [Li{N(SiHMe2)2}] in toluene
(Scheme 3). The crystal structure of complex 8 mirrors the
were obtained. The 19F NMR
spectrum of a reaction mixture
showed the presence of only 2
and 6b.
Complex 7a has two different
cerium coordination environ-
ments. Ce(3) is ligated by two
formamidinato ligands and four
chloro anions, whereas Ce(1)
and Ce(2) are coordinated by
one formamidinato ligand, two
THF molecules and four chloro
anions. Thus, each cerium atom
is eight-coordinate. The complex
crystallized with four THF mole-
cules within the lattice. This pen-
tachloro bridging motif is known
for other rare-earth metal com-
Scheme 3. Synthesis of homoleptic complex [Ce{N{SiHMe2)2}4] (9) from CeIII bis(dimethylsilyl)amide ate complex 8
and formamidine-promoted protonolysis reactions.
plexes, with similar examples for diketiminate[17] and cyclopen-
tadienyl complexes.[18] Other similar motifs have four bridging
chloro ligands and another bridging species, such as
[N(SiHMe2)2] or [CH2].[19] A similar fluoro-bridged moiety is
known in the bulky aryloxide complex [Er3F5(thf)4(OArOMe)4]
(OArOMe=2,6-di-tert-butyl-4-methoxy-phenolato),[20] which has
the same asymmetry of ligand attachment, but each erbium
atom is six- or seven-coordinate, opposed to the eight-coordi-
nate cerium atoms in complex 7a. Complex 7b contains two
terminal chloro anions coordinating trans to each other with
bond lengths of CeꢀCl(1)=2.7224(12) and CeꢀCl(2)=
2.7308(12), which, as expected, are shorter than the bridging
CeꢀCl bonds of complex 7a. The closest CeꢀCl interaction in
7a is 2.8027(13) between Ce(1) and Cl(4), with the other CeꢀCl
distances ranging between 2.8075 (14) and 3.0527 (14).
cerium di(cyclohexyl)amide complex [Ce(NCy2)4Li(thf)].[8] Two
terminal bis(dimethylsilyl)amido ligands coordinate to cerium
while the remaining two bridge between the Ce and Li metal
atoms (Figure 6). The presence of THF impacts the solubility
and reactivity of 8 dramatically.
Other reagents were examined for cerium(III) formamidinate
oxidation, such as dry O2, benzoquinone, and PhICl2. Each oxi-
dant showed signs of oxidizing the trivalent cerium complexes
1–5, as indicated by a dramatic color change, but each species
decomposed to lighter colored species, with NMR analyses
showing paramagnetic peak broadening, all indicative of the
formation of trivalent cerium complexes. Currently no products
have been isolated. It should also be noted that treatment of
complex 2 with Ph3SiCl showed no signs of reactivity, even
with extended heating.
Figure 6. Crystal structure of [Li(thf)Ce{N(SiHMe2)2}4] (8). Ellipsoids shown at
35% probability. Hydrogen atoms and atom disorder removed for clarity. Se-
lected bond (ꢁ) lengths and angles (o) for (8): Ce1ꢀN1 2.388(5), Ce1ꢀN2
2.386(4), Ce1ꢀN3 2.523(4), Ce1ꢀN4 2.532(5), Li1ꢀN3 2.087(11), Li1ꢀN4
2.094(12), Li1ꢀO1B 1.83(3); N1-Ce1-N2 98.19(16), N1-Ce1-N3 110.76(15), N1-
Ce1-N4 134.64(16), N2-Ce1-N3 131.98(15), N2-Ce1-N4 107.21(15), Ce1-N3-Li1
90.04(3), Ce1-N4-Li1 90.0(3), O1B-Li1-Ce1 167.1(7), N3-Li-O1B 134.9(10), N3-Li-
N4 100.3, N4-Li-O1B 124.1(9).
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Ate complex 8 proved to be an excellent precursor for
[Ce{N(SiHMe2)2}4] (9), when treated with half an equivalent of
1
C2Cl6 in toluene. The H NMR analysis of the reaction mixture
indicated quantitative oxidation. Complex 9 was separated
from LiCl by filtration and was isolated as sticky red crystals by
evaporation of solvent and C2Cl4 under vacuum. The oxidation
of 8 was repeated several times under different conditions and
the major factors which adversely affected reaction times were
(determined by time taken for color change) 1) oxidation in
THF instead of toluene and 2) the use of stronger oxidants,
such as PhICl2 or TeCl4 (caused the sample to fume and form
a black viscous oil in toluene). The first cerium(IV) formamidi-
nate complex was then synthesized by treating 9 with four
equivalents of p-TolFormH producing [Ce(p-TolForm)4] (10) in
high isolated yield (72%; Scheme 3).
When 9 was treated with DFFormH in THF or toluene, the
solution initially remained dark red, but completely discolored
to white after 16 h of stirring. Clear colorless crystals were
grown from a THF/hexane mixture, with X-ray crystallography
revealing the formation of the trivalent complex 2. When Et-
FormH was added to 9 in toluene the solution turned dark
green but discolored completely to a golden yellow after mi-
nutes of stirring. Crystals of complex 4 were grown from the
reaction solution. The formation of the trivalent derivatives in-
dicates that the corresponding cerium(IV) formamidinate com-
plexes are unstable. Similarly, Lappert’s [Ce{N(SiMe3)2}3Cl] also
reformed [Ce{N(SiMe3)2}3] upon decomposition.[4] Evidently,
steric effects govern the stability of cerium(IV) formamidinates,
as stability declines in the series p-TolForm>DFForm>EtForm,
namely, in the order of increasing steric bulk.
Figure 7. Crystal structure of [Ce(p-TolForm)4] (10). Ellipsoids shown at 50%
probability, hydrogen atoms removed for clarity. Selected bond distances
and angles (o): Ce1ꢀN1 2.452(2), Ce1ꢀN2 2.456(2), Ce1ꢀN3 2.407(2), Ce1ꢀN4
2.462(2), Ce1ꢀN5 2.427(2), Ce1ꢀN6 2.477(2), Ce1ꢀN7 2.434(2), Ce1ꢀN8
2.459(2); C8-Ce1-C23 119.30(8), C8-Ce1-C38 90.81(7), C8-Ce1-C53 117.46(7).
Et2O or THF than in toluene or hexane, from which a brown
colored solution was obtained, but no products could be iden-
tified.
Despite the shielding of the cerium(IV) center by the
[N(SiHMe2)2] ligands, complex 9 underwent protonolysis reac-
tions with each formamidine, affording CeIV formamidinates of
differing stabilities. In the following, another cerium(IV) silyl-
amide species was generated which showed a complete con-
trast in protonolysis reactivity. [Ce{N(SiMe3)2}3] was treated with
half an equivalent of 1,4-benzoquinone forming the dinuclear
cerium(IV) complex [Ce{N(SiMe3)2}3(bda)0.5]2 (11, bda=1,4-ben-
zenediolato, Scheme 4). A similar redox protocol was previous-
ly applied for the synthesis of CeIV alk(aryl)oxide complexes of
Complex 10, unlike the trivalent derivative, is dark green in
color and readily soluble in toluene, C6D6, Et2O, and THF
1
(Figure 7). The H NMR spectrum of 10 showed no indication
of a paramagnetic species or impurities upon synthesis. The
1H NMR resonance (9.83 ppm) of the N=CHꢀN backbone of 10
is comparable with that of the diamagnetic potassium complex
[K(p-TolForm)(18-crown-6)] (9.15 ppm)[10e] notably shifted from
the p-TolFormH value: (7.88 ppm). Typically for paramagnetic
systems, the backbone hydrogen resonance is shifted exten-
sively, as shown by the paramagnetic complexes 3, 4, and 5
(20.82, 14.38, 12.76 ppm, respectively).
type
{(BINOLate)6Ce}2(m2-O2C6H4)]·Et2O.[23]
[{(tBu3CO)3Ce}2(m2-O2C6H4)][22]
and
[{Li3(Et2O)3.5}-
Complex 11 was isolated from toluene as dark brown crys-
tals. The crystal structure shows [Ce{N(SiMe3)2}3(bda)0.5] in the
asymmetric unit, with CeꢀN bond lengths ranging from
2.2386(14) to 2.2486(14) ꢁ (average: 2.24 ꢁ), values slightly
Complex 10 is the first cerium(IV) formamidinate complex
and only the second cerium(IV) amidinate complex known (see
the Introduction). The coordination number of cerium in 10 is
eight, showing stereochemistry best described as distorted do-
decahedral. The CeꢀN bond lengths average 2.44 ꢁ, with
a range of 2.407(2) (N3)–2.477(2) ꢁ (N6). As expected these are
shorter on average than those of the cerium(III) formamidinate
precursors (Table 1 and Figure 3, caption), such differences
owing to the larger ionic radii of Ce3+. The bond lengths of 10
are comparable with those of the bulky N,N’-bis(trimethylsilyl)-
4-methoxybenzeneimidamide
complex
[Ce(p-MeOC6H4C-
(NSiMe3)2)3Cl], which has CeꢀN bond lengths averaging 2.43 ꢁ
with a wider range of 2.3583(19)–2.5019(19) ꢁ.[3] Although iso-
lated, 10 was still unstable, completely decomposing within
days of formation, thereby explaining the somewhat deviant
microanalysis. The decomposition of 10 occurred quicker in
Scheme 4. Synthesis of heteroleptic CeIV complex [Ce{N(SiMe3)2}3(bda)0.5
(11, bda=1,4-benzenediolato).
]
2
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longer than those of [Ce{N(SiMe3)2}3Cl] (2.22 ꢁ),[1] and compara-
ble with [Ce{N(SiHMe2)2}4] (2.25 ꢁ; Figure 8).[7] The CeꢀN bond
lengths in 11 are much shorter than in 10, which has a much
higher coordination number. The benzoquinone reagent upon
reduction becomes aromatized, which is evident in the crystal
structure parameters. The bda ligand coordinates in a near
lent of benzoquinone, instead of putative [Ce{N(SiHMe2)2}3-
(bda)0.5] only crystals of 9 were isolated with the other species
of redistribution unidentified.
Conclusion
Utilizing three formamidinato ligands of varying steric bulk
and functionality five new cerium(III) formamidinate complexes
were prepared. Each species was treated with various oxidants,
mainly with Ph3CCl and showed evidence of successful oxida-
tion. However, rapid reductive decomposition was prevalent
giving trityl formamidines and chlorinated trivalent cerium
complexes with the two isolated examples [Ce3Cl5(DFForm)4-
(thf)4] and [Ce(EtForm)Cl2(thf)3] (DFForm=N,N’-bis(2,6-difluoro-
phenyl)formamidinato and EtForm=N,N’-bis(2,6-diethylphe-
nyl)formamidinato) revealing the structural variety of such het-
eroleptic complexes. The synthesis of homoleptic [Ce{N-
(SiHMe2)2}4] was improved by treating ate complex [Li(thf)Ce{N-
(SiHMe2)2}4] with C2Cl6 in toluene. Crucially, [Ce{N(SiHMe2)2}4]
can be used successfully as a precursor in CeIV!CeIV transfor-
mations as shown for the synthesis, via protonolysis, of the
first cerium(IV) formamidinate species [Ce(p-TolForm)4] (p-Tol-
Form=N,N’-bis(4-methylphenyl)formamidinato). The stability
of such tetravalent formamidinate species, however, seems to
be quite sensitive to the type of formamidinato ligand. Tetrava-
lent [Ce{N(SiMe3)2}3(bda)0.5]2 (bda=1,4-benzenediolato) was
synthesized by oxidation of [Ce{N(SiMe3)2}3] with 1,4-benzoqui-
none, but unlike [Ce{N(SiHMe2)2}4], [Ce{N(SiMe3)2}3(bda)0.5]2 did
not engage in protonolysis reactions.
Figure 8. Crystal structure of [Ce{N(SiMe3)2}3(bda)0.5]2 (11, bda=1,4-benzene-
diolato). Ellipsoids shown at 50% probability, hydrogen atoms and lattice
solvents removed for clarity. Selected bond distances (ꢁ) and angles (o):
Ce1ꢀN1 2.2388(14), Ce1ꢀN2 2.2398(15), Ce1ꢀN3 2.2487(14), Ce1ꢀO1
2.0895(13), O1ꢀC19 1.356(2), C19ꢀC20 1.399(2), C20ꢀC21 1.387(3); N1-Ce1-
O1 97.19(5), N2-Ce1-O1 99.58(5), N3-Ce1-O1) 105.69(5), Ce1-O1-C19
173.13(11), O1-C19-C20 120.55(16), O1-C19-C21’ 120.93(16).
linear fashion to the cerium atom, (Ce-O-C(19) 173.148, CeꢀO
2.0895(13) ꢁ. The CꢀC bond distances within the reduced bda
ring are C(19)ꢀC(20)=1.399(2), C(19)ꢀC(21)’=1.396(3), and
C(20)ꢀC(21)=1.388(3) ꢁ, all indicating aromaticity. The ceri-
um(IV) atom is four-coordinate and the stereochemistry is best
Experimental Section
General
1
described as distorted tetrahedral. The H NMR spectrum also
All manipulations were performed using glovebox (MBraun 200B;
<0.1 ppm O2, <0.1 ppm H2O) or Schlenk line techniques under an
atmosphere of purified argon gas or nitrogen, in oven-dried glass-
ware. Formamidine proligands (DFFormH, p-TolFormH, and Et-
FormH) were synthesized according to a published procedure.[26]
Anhydrous CeCl3 was purchased from ABRC chemicals and was ac-
tivated by Soxhlet extraction with THF, giving [CeCl3(thf)2].
[K{N(SiMe3)2}] was purchased from Sigma–Aldrich and purified by
high-vacuum sublimation before use. [Li{N(SiHMe2)2}] was synthe-
sized according to published procedures.[27] Cerium(III) silylamide
complexes were synthesized by treatment of [CeCl3(thf)2] with
three equivalents of [Li{N(SiHMe2)2}] or [K{N(SiMe3)2}] in hexane and
were purified by filtration, evaporation to dryness and crystalliza-
tion from fresh hexane. [Li(p-TolForm)] was synthesized by treat-
ment of p-TolFormH with [Li{N(SiHMe2)2}]. Benzoquinone, perfluor-
odecalin, Cl2Cl6, Ph3CCl, Ph3SiCl, and TeCl4 were purchased from
Sigma–Aldrich, whereas C6H5ICl2 was synthesized according to
a published procedure.[28] Solvents used (THF, Et2O, hexane, and
toluene) were purified with Grubbs columns (MBraun SPS, solvent
purification system) and stored in a glovebox. Acetonitrile was pu-
rified by distillation over CaH2 and stored over molecular sieves
(3 ꢁ). C6D6 was purchased from Sigma–Aldrich, degassed, and
dried by being stirred over Na metal for 12 h. The NMR spectra of
air and moisture-sensitive compounds in C6D6 were recorded with
J. Young valve NMR spectroscopy tubes at 258C with a Bruker 266
Avance DMX400 (1H: 400.13 MHz; 19F: 282.0 MHz) spectrometer. In-
supports the aromaticity of the benzene-1,4-diolato ligand,
with one resonance in the aromatic region (7.28 ppm) and one
signal for the {N(SiMe3)2} ligands at 0.43 ppm (ꢀ3.39 ppm for
[Ce{N(SiMe3)2}3]). The dark color, aromaticity of the bda, and
1
the H NMR spectrum all support the successful formation of
a cerium(IV) species. Complex 11 shows remarkable stability,
with no signs of decomposition weeks after formation unlike
the other cerium(IV) silylamide or formamidinate complexes.
This stability, however, made 11 a poor reagent as a protonoly-
sis precursor. When one or three equivalents of DFFormH, p-
TolFormH, or EtFormH were added to 11, no color change oc-
curred, even after several days of stirring. Large crystals of
both the protonated ligand (FormH) and 11 were isolated from
all reaction mixtures. Complex 11 also showed no reactivity to-
wards AlMe3, HAlMe2, and HN(SiHMe2)2, even when excess
amounts were used. Complex 11 also resisted reduction when
treated with SmI2(thf)2, showing no sign of reaction after days
of stirring. The inert behavior of 11 can be related to the mark-
edly decreased reactivity of [Ln-{N(SiMe3)2}] moieties, as com-
pared to [Ln-{N(SiHMe2)2}] (steric effect)—complex 9 readily
reacts with formamidines, even with the bulky EtFormH—[24] or
to the presence of the aromatic bda ligand. For comparison,
when [Ce{N(SiHMe2)2}3(thf)2] was treated with half an equiva-
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frared spectra were recorded on either: a Nicolet 6700 FTIR spec-
trometer (v˜ =4000–400 cmꢀ1) by using a DRIFT chamber with dry
KBr/sample mixtures and KBr windows or a Perkin–Elmer 1600
Fourier transform infrared spectrometer (v˜ =4000–500 cmꢀ1) as
a Nujol mull. Micro-elemental analysis (C, H, N) was performed
with an Elementar Vario Micro cube by Mr. S. Bock (Tꢂbingen Uni-
versity), with the exception of complex 8b, which was analyzed by
the elemental analysis service of London Metropolitan University.
trated (1 mL), then stored at ꢀ308C affording large light yellow
block crystals of [Ce(EtForm)3]·PhMe (4·PhMe).
[LiCe(DFForm)4] (5): DFFormH (0.20 g, 0.75 mmol) was added to
[Ce{N(SiHMe2)2}3(thf)2] (0.11 g, 0.16 mmol) and [Li{N(SiHMe2)2}]
(0.025 g, 0.18 mmol) and stirred in toluene (5 mL) for 1 day. The
solvent was removed in vacuo. The resulting white powder was
washed with cold toluene, redissolved in toluene (4 mL) and con-
centrated in vacuo producing crystals of 5. Yield: 0.15 g, (76%);
1H NMR (C6D6, 300 K): d=6.43 (brs, 8H; H4-Ar), 6.64 (brs, 16H;
H3,5-Ar), 12.76 ppm (s, 4H; NC(H)N); 19F{1H} NMR(C6D6, 300 K): d=
ꢀ133.7 ppm (brs); IR (DRIFT): v˜ =2934 (vw), 1622 (m), 1541 (vs),
1480 (s), 1471 (vs), 1394 (vw), 1312 (vs), 1262 (w), 1234 (vs), 1210
(vs), 1149 (w), 1062 (w), 1016 (vw), 998 (s), 933 (w), 826 (w), 771 (s),
743 (s), 732 (m), 714 (m), 687 (vw), 618 cmꢀ1 (m); elemental analy-
sis calcd (%) for C52H28CeF16LiN8 (1215.86): C 51.37, H 2.32, N 9.22;
found: C 51.25, H 2.39, N 9.02.
General synthesis of cerium(III) formamidinate complexes 1–
4
[Ce{N(SiMe3)2}3] (0.16 g, 0.26 mmol) and 3 equivalents of formami-
dine (0.77 mmol) were added to a preweighed sample vial and dis-
solved in a solvent: (1: Et2O or toluene, 2: THF, 3: toluene, 4: THF,
3–6 mL). The solution was stirred for 16 h then evaporated in
vacuo. Each complex was washed with small amounts of cold
hexane, redried, and weighed. Elemental analysis, infrared, and
1H NMR and 19F NMR spectra were determined on the bulk sample.
1H NMR spectra of complexes 1 and 2 were examined but due to
paramagnetism, no interpretable spectra were obtained at ambient
temperature or on heating.
Oxidations
Oxidations of 1: a) Oxidation in THF: 1 (0.10 g, 0.12 mmol) was
stirred in THF (3–5 mL) until dissolved. Trityl chloride (0.033 g,
0.12 mmol) was added and the mixture turned dark brown almost
immediately. The solution discolored to a light orange/gold color
after 20 min of stirring. The solvent was removed and the residue
was analyzed by 1H NMR spectroscopy showing no identifiable
single species. The experiment was repeated with the addition of
1 equivalent of Li(p-TolForm) (0.027 g, 0.12 mmol). The solution
turned a dark brown/green on addition of Ph3CCl, but discolored
to red after minutes of stirring. The solvent was removed in vacuo,
toluene (2 mL) was added, and the sample was quickly filtered pro-
ducing a light red solution and yellow precipitate. Once filtered
from the precipitate (light yellow insoluble unidentified products),
the solution was concentrated (1 mL) in vacuo affording small
yellow block crystals of N,N’-bis(4-methylphenyl)-N’-(triphenylme-
[Ce(p-TolForm)3] (1): Yield: 0.20 g (96%); DRIFT (KBr): v˜ =3026 (m),
2918 (m), 2860 (m), 2729 (vw), 1653 (m), 1608 (w), 1513 (vs), 1506
(vs), 1456 (w), 1419 (w), 1375 (vw), 1302 (s), 1218 (m), 1177 (w),
1112 (vw), 1036 (vw), 1015 (vw), 993 (w), 943 (m), 818 (s), 731 (vw),
711 (w), 644 (vw), 586 (w), 519 (w), 464 cmꢀ1 (w); elemental analysis
calcd (%) for C45H45CeN6 (810.01): C 66.72, H 5.59, N 10.37; found: C
67.19, H 5.54, N 10.11.
[Ce(DFForm)3(thf)2] (2): Yield: 0.25 g (90%); 19F{1H} NMR (C6D6,
300 K): d=ꢀ135.9 ppm (brs); 19F{1H} NMR (THF, 300 K): d=
ꢀ129.0 ppm (brs); IR (Nujol): v˜ =1667 (w), 1617 (s), 1576 (vs), 1545
(vs), 1315 (vs), 1269 (s), 1214 (vs), 1149 (w), 1098 (w), 1063 (s), 1000
(vs), 942 (m), 871 (s), 830 (m), 804 (vw), 774 (vs), 742 cmꢀ1 (m); ele-
mental analysis calcd (%) for C47H37CeF12N6O2 (1085.93): C 51.98, H
3.43, N 7.74; found: C 51.55, H 3.08, N 7.81. Small amounts of THF
and 2 mL of hexane were added to 2. Colorless block crystals
formed at ambient temperature suitable for X-ray diffraction. Boil-
ing 2 in toluene and evaporation to dryness whilst hot (under
vacuum) did not remove coordinating THF but, after crystallization
from hexane, yielded complex 2.
[Ce(DFForm)3]·0.5PhMe (3): Yield: 0.23 g (95%); 1H NMR (C6D6,
300 K): d=2.11 (s, 1.5H; CH3, PhMe), 5.58 (m, 12H; H 3,5, DFForm),
5.77 (m, 6H; H 4, DFForm) 7.03 (m, 2.5H; Ar-H, PhMe), 20.82 ppm
(s, 3H, NC(H)N); 19F{1H} NMR (C6D6, 300 K): d=ꢀ138.2 ppm (brs); IR
(Nujol): v˜ =2722 (m), 1652 (s), 1616 (s), 1582 (vs), 1540 (vs), 1309
(vs), 1261 (s), 1234 (m), 1209 (s), 1148 (m), 1060 (s), 989 (s), 937 (m),
825 (w), 769 (m), 715 (m), 688 cmꢀ1 (vw); elemental analysis calcd
(%) for C42.5H25CeF12N6 (3·0.5PhMe, 987.79): C 51.68, H 2.55, N 8.50;
found: C 51.58, H 2.34, N 7.70. Toluene (5 mL) was added to the
sample and the mixture was stirred until completely dissolved. The
solution was concentrated in vacuo (1–2 mL) and allowed to stand
affording colorless block crystals of [Ce(DFForm)3]·PhMe (3·PhMe)
suitable for X-ray diffraction.
[Ce(EtForm)3] (4): Yield: 0.26 g (95%); 1H NMR (C6D6, 300 K): d=
ꢀ14.82 (brs, 3H; NC(H)N), 0.36 (brs, 24H; CH2), 0.71 (brs, 36H;
CH3), 6.56 (m, 6H; H4-Ar), 6.72 ppm (m, 12H; 3,5H-Ar); IR (DRIFT):
v˜ =3063 (w), 3063 (w), 2965 (s), 2931 (m), 2872 (m), 1592 (w), 1521
(vs), 1448 (vs), 1375 (w), 1321 (w), 1290 (vs), 1234 (vw), 1195 (s),
1106 (w), 1059 (vw), 1011 (vw), 940 (m), 869 (vw), 808 (w), 767 (m)
756 cmꢀ1 (m); elemental analysis calcd (%) for C63H81CeN6
(1062.47): C 71.22, H 7.68, N 7.91; found: C 71.03, H 7.20, N 7.85.
The sample was redissolved in a toluene/hexane mixture, concen-
1
thyl)formamidine (6a), identified by X-ray crystallography. H NMR
(C6D6, 300 K): d=1.73–1.95 (brm, 6H, CH3), 6.58–6.99 (brm, 23H,
Ar-H), 8.11 ppm (s, 1H, NC(H)N). b) Oxidation in toluene: 1 (0.10 g,
0.12 mmol) was added and rapidly stirred in toluene (5 mL). Ph3CCl
(0.033 g, 0.12 mmol) was added with stirring and the mixture
slowly turned dark green. The compound decomposed after
30 min of stirring. No species was conclusively identified in the de-
composed sample.
Oxidation of 2: a) Oxidation in THF: 2 (0.10 g, 0.18 mmol) was dis-
solved in THF (3 mL) and Ph3CCl (0.05 g, 0.18 mmol) was added
slowly with stirring. The solution slowly changed color to dark red/
brown. The solution completely discolored after 12 h, forming
a white precipitate and a colorless solution. Small amounts of the
solution were extracted and analyzed by 19F NMR spectroscopy.
The spectrum indicated the formation of several species.
19F{1H} NMR (THF, 300 K): d=ꢀ128.8 (brs, 6F), ꢀ127.6 (brs, 4F),
ꢀ127.0 (s, 2F, F2,6-Ar(N), 6b), ꢀ113.8 ppm (s, 2F, F2,6-Ar(N’), 6b).
The sample was dried in vacuo leaving a white powder. THF was
added to the powder and the solution was filtered and concentrat-
ed under vacuum producing small crystals of [Ce3Cl5(DFForm)4-
(thf)4]·4THF (7a) identified by X-ray crystallography, elemental anal-
ysis was tried from three separate samples all giving similar but un-
satisfactory results. The filtrate was refiltered and concentrated,
producing small yellow crystals of N,N’-bis(2,6-difluorophenyl)-N’-
(triphenylmethyl)formamidine (6b), identified by X-ray crystallogra-
phy. The sample mixture was dried and C6D6 was added, producing
a slightly yellow solution and a white precipitate. The 19F NMR
spectrum showed only two peaks, identified as compound 6b;
19F{1H} NMR (C6D6, 300 K): d=ꢀ125.19 (s, 2F, F2,6-Ar(N)),
Chem. Eur. J. 2014, 20, 4426 – 4438
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ꢀ112.05 ppm (s, 2F, F2,6-Ar(N’)). No cerium complexes could be
elemental analysis calcd (%) for C20H64CeLiN4OSi8 (748.49): C 32.18,
identified by NMR spectroscopy. b) Oxidation in toluene: 2 (0.056 g, H 8.56, N 7.49; found: C 31.98, H 7.91, N 7.18.
0.052 mmol) was dissolved in toluene (3 mL). Ph3CCl (0.013 g,
[Ce{N(SiHMe2)2}4] (9): a) Synthesis in toluene: hexachloroethane
0.052 mmol) was added and the sample turned dark brown after
5 min of stirring. The solution discolored after 2 h and a small
amount of sample was examined by NMR spectroscopy:
19F{1H} NMR (toluene, 300 K): d=ꢀ139.2–136.2 (brs, 10 F), ꢀ130.5
(s, 1F), ꢀ128.6 (s, 1F), ꢀ126.6 (s, 2F, F2,6-Ar(N), 6b), ꢀ113.5 ppm
(s, 2F, F2,6-Ar(N’) 6b). An additional 2 equivalents of Ph3CCl
(0.023 g, 0.10 mmol) were added to the NMR tube, forming
a white precipitate and yellow solution. Further analysis by
19F NMR spectroscopy indicated only the presence of 6b.
19F{1H} NMR (toluene, 300 K): d=ꢀ126.0 (s, 2F, F2,6-Ar(N)),
ꢀ112.8 ppm (s, 2F, F2,6-Ar(N’)).
(0.023 g, 0.10 mmol) was added to a Schlenk flask charged with 8
(0.15 g, 0.20 mmol). Toluene (5 mL) was added and the mixture re-
acted immediately producing a dark red color. The solution was so-
nicated for 6 h leaving a deep red solution and white precipitate
of LiCl. The solution was centrifuged and filtered from the insolu-
ble LiCl (LiCl was washed, dried and weighed: ~0.0060 g, ~75%).
The dark red solution was dried under vacuum removing C2Cl4 and
excess solvent leaving 9 as sticky red crystals (0.12 g, 92%). The
1H NMR spectrum of the bulk sample gave data consistent with
the literature.[7] b) Attempted synthesis in THF: Upon addition of
THF (5 mL) to 8 (0.15 g, 0.20 mmol) and C2Cl6 (0.023 g, 0.10 mmol)
the mixture slowly changed color to dark red after 72 h of stirring,
Oxidation of 3: Complex 3 (0.02 g, 0.02 mmol), was dissolved in
toluene (2 mL) and transferred to an NMR tube, Ph3CCl (0.006 g, with no observable precipitate. c) Treating 8 with TeCl4 or PhICl2 in
0.02 mmol) was added and the white solution turned bright yellow toluene caused violent oxidation, causing the sample to fume in
and produced a white powder immediately. A small amount of so- the drybox, leaving a thick black oil..
lution was extracted and analyzed by 19F NMR spectroscopy, which
showed only the presence of 6b; 19F{1H} NMR (toluene, 300 K): d=
[Ce(p-TolForm)4] (10): p-TolFormH (0.17 g, 0.75 mmol) was added
with stirring to 9 (0.12 g, 0.18 mmol) dissolved in toluene (5 mL).
ꢀ125.2 (s, 2F, F2,6-Ar(N)), ꢀ112.01 ppm (s, 2F, F2,6-Ar(N’)).
Oxidation of 4: Complex 4 (0.14 g, 0.13 mmol) was dissolved in
The solution turned dark green within seconds and a light yellow
precipitate slowly formed. The solution was filtered, concentrated,
THF (3 mL), Ph3CCl (0.037 g, 0.13 mmol) and was added with stir- and hexane was added (1 mL) producing dark green block crystals
ring producing a dark green solution immediately on addition.
Within a minute of stirring the sample completely changed to light
of [Ce(p-TolForm)4] (10), formula identified by X-ray crystallography.
Crystal yield: 0.050 g, 25%. Total yield of dried sample: 0.14 g,
gold. The sample mixture was concentrated (0.5 mL), and hexane 72%; 1H NMR (C6D6, 300 K): d=2.28(s, 24H; -C(H)3), 6.96 (s, 32H;
was added (1 mL) producing a thick off white oil and small crystals
Ar-H), 9.77 ppm (s, 4H; NC(H)N),; IR (DRIFT): v˜ =3022 (w), 2917 (w),
of [Ce(EtForm)Cl2(thf)3] (7b), overnight (0.02 g, 20%). Elemental 1652 (w), 1607 (w), 1534 (v s), 1521 (v s), 1285 (s), 1217 (m), 1109 (v
analysis calcd (%) for: C33H51CeCl2N2O3 (734.79): C 53.94, H 7.00, N w), 981 (w), 942 (m), 810 cmꢀ1 (m); elemental analysis (bulk prod-
3.81; found: C 54.16, H 6.89, N 3.94. The mixture was evaporated
to dryness and acetonitrile was added. The mixture was heated to found: C 67.33, H 6.26, N 9.65. Repeated analyses were also devi-
608C and cooled producing small white crystals of N,N’-bis(2,6-di-
ant. The sample decomposed completely upon storage at ꢀ308C
ethylphenyl)-N’-(triphenylmethyl)formamidine as the acetonitrile with no identified products from decomposition.
uct) calcd (%) for C60H60CeN8 (1033.29): C 69.74, H 5.85, N 10.84;
solvate 6c·CH3CN (0.03 g, 41%), as identified by X-ray crystallogra-
phy.
[Ce{N(SiMe3)2}3(bda)0.5
] (11): [Ce{N(SiMe3)2}3] (0.22 g, 0.35 mmol)
2
was dissolved in toluene (3 mL) and benzoquinone (0.02 g,
0.17 mmol) was added with stirring. The solution turned dark
purple immediately. After being stirred for 2 h the solution was
Oxidation of 5: Complex 5 (0.10 g, 0.080 mmol) was dissolved in
THF. Ph3CCl (0.022 g, 0.080 mmol) was added slowly and the solu-
tion turned a dark gold color immediately. The color changed to concentrated (1–2 mL) and stored at ꢀ308C for 2 weeks. Large
red over several hours of stirring. The solution was filtered from dark brown block crystals suitable for X-ray analysis were isolated,
the precipitated LiCl and the THF removed in vacuo. Hexane yielding: [Ce{N(SiMe3)2}3(bda)0.5]2·2PhMe (11·2PhMe). The sample
(4 mL) was added to the mixture and two small sets of crystals
was dried under vacuum, removing toluene of crystallization;
were grown and hand-picked for analysis by X-ray crystallography. yield: 0.23 g (96%). 1H NMR (C6D6, 300 K): d=0.10 (s, 14H;
Small cube crystals of complex 2 and block crystals of 6b, were {N(SiMe3)2}), 0.43 (s, 94H; {N(SiMe3)2}), 7.28 ppm (s, 4H; bda); IR
identified by unit cell comparisons with the authentic compounds.
(DRIFT): v˜ =2925 (m), 2898 (w), 1486 (s), 1249 (vs), 1212 (s), 913
19F NMR analysis of an NMR scale reaction mixture indicated the (vs), 836 (vs), 770 (s), 654 (s), 604 cmꢀ1 (vs); elemental analysis (%)
presence of only 6b and 2 after 2 h of reaction.
calcd for C42H112Ce2N6O2Si12 (1350.64): C 37.34, H 8.36, N 6.22;
found: C 37.35, H 8.40, N 5.96. Complex 11 was treated separately
with one equivalent of DFFormH, p-TolFormH, AlMe3, HAlMe2, and
EtFormH and no color change was observed after several days of
stirring when treated in either THF or toluene. Two additional
equivalents of reagents were added, and in each case the sample
was stirred for 2 days without showing any signs of reaction, and
crystals of 11·2PhMe were isolated from concentrated toluene sol-
utions. When an excess of SmI2(thf)2 was added to 11, the reaction
mixture was stirred for 4 days showing no color change or indica-
tion of any reaction.
Synthesis of 8–11
[Li(thf)Ce{N(SiHMe2)2}4] (8): [Li{N(SiHMe2)2}] (0.17 g,1.23 mmol) was
added to [CeCl3(thf)2] (0.12 g, 0.31 mmol) in toluene (4 mL). The
mixture was stirred for 16 h and then centrifuged, filtered and the
solvent was removed in vacuo yielding a light yellow oil; yield:
0.19 g. The complex was redissolved in toluene (3 mL) and, after
one day, small yellow block crystals were grown in vacuo. The su-
pernatant solution was decanted from the crystals (yield: 0.10 g,
43%). (Note: in situ yield appears quantitative. Once separated
from insoluble products, 8 can be treated with C2Cl6 without prior
isolation to give 9.) 1H NMR (C6D6, 300 K): d=ꢀ17.70 (brs, 6H; SiH),
ꢀ0.04 (brs, 48H; Me), 2.71 (s, 2H; SiH), 5.73 (brs, 4H; THF),
Attempted synthesis of [Ce(DFForm)4] and [Ce(EtForm)4]
a) DFForm/DFFormH (0.11 g, 0.40 mmol) was added with stirring to
12.18 ppm (brs, 4H; THF); IR (DRIFT): v˜ =2951 (s), 2896 (m), 2046 9 (0.07 g 0.10 mmol) dissolved in THF (5 mL). The solution re-
(vs, nSi-H), 1943 (vs, nSi-H), 1504 (w), 1417 (w), 1246 (vs), 1019 (s), mained red upon addition but slowly discolored with stirring. After
1019 (vs), 836 (vs), 787 (vs), 765 (vs), 700 (s), 683 (m), 624 cmꢀ1 (w); 16 h of stirring the solution completely discolored to colorless. The
Chem. Eur. J. 2014, 20, 4426 – 4438
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sample was dried and large colorless block crystals of complex 2
(identified by unit cell comparison), were isolated from a hexane
solution. b) EtForm/EtFormH (0.13 g, 0.41 mmol) was added with
stirring to 9 (0.07 g, 0.10 mmol) in toluene (3 mL). The solution
turned dark green immediately on addition of EtFormH. The color
completely dissipated to light gold after 3 min of stirring. Crystalli-
zation from concentrated toluene yielded crystals of 4·PhMe identi-
fied by unit cell determination; other products of decomposition
were not identified.
0.0287 (I>2s(I)) and wR2 was 0.0642 (all data). Refinement details:
toluene solvate was disordered over two positions, and refined
with PART (50:50) refinement. The hydrogen atoms on the disor-
dered toluene were not assigned.
[Ce(EtForm)3]·PhMe (4·PhMe): Using Olex2,[31] the structure was
solved with the ShelXS[32] structure solution program using Direct
Methods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C70H89CeN6 (Mr =1154.59):
monoclinic, space group P21/c (no. 14), a=12.4367(4), b=
23.7877(8), c=21.8256(8) ꢁ, b=105.336(2)8, V=6227.0(4) ꢁ3, Z=4,
T=100.15 K, m(MoKa)=0.776 mmꢀ1, 1calcd =1.232 gmmꢀ3, 147942
reflections measured (3.4ꢁ2qꢁ57.64), 16126 unique (Rint =0.0554)
which were used in all calculations. The final R1 was 0.0370
(I>2s(I)) and wR2 was 0.0792 (all data). Refinement details: toluene
disordered over two positions, and was refined with PART (50:50)
refinement. Disordered ethyl groups on EtForm were modeled
with PART refinement (FVAR).
[LiCe(DFForm)4] (5): Using Olex2,[31] the structure was solved with
the ShelXS[32] structure solution program using Patterson method
and refined with the XL[32] refinement package using least squares
minimization. Crystal data for C52H28CeF16LiN8 (Mr =1215.88): mono-
clinic, space group P21/n (no. 14), a=13.1871(3), b=18.7513(5), c=
19.3773(4) ꢁ, b=98.8570(10)8, V=4734.39(19) ꢁ3, Z=4, T=
100.15 K, m(MoKa)=1.073 mmꢀ1, 1calcd =1.706 gmmꢀ3, 64875 reflec-
tions measured (3.04ꢁ2qꢁ56.724), 11727 unique (Rint =0.0342)
which were used in all calculations. The final R1 was 0.0275
(I>2s(I)) and wR2 was 0.1188 (all data).
[p-TolForm(CPh3)] (6a): Using Olex2,[31] the structure was solved
with the ShelXS[32] structure solution program using Direct Meth-
ods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C34H30N2 (Mr =466.60): mono-
clinic, space group P21/c (no. 14), a=9.6383(3), b=13.1289(4), c=
20.3550(6) ꢁ, b=98.5740(10)8, V=2546.94(13) ꢁ3, Z=4, T=
100.15 K, m(MoKa)=0.071 mmꢀ1, 1calcd =1.217 gmmꢀ3, 21622 reflec-
tions measured (3.704ꢁ2qꢁ52.756), 5197 unique (Rint =0.0447)
which were used in all calculations. The final R1 was 0.0432
(I>2s(I)) and wR2 was 0.1328 (all data).
[DFForm(CPh3)] (6b): Using Olex2,[31] the structure was solved with
the ShelXS[32] structure solution program using Direct Methods and
refined with the olex2.refine[32] refinement package using Gauss–
Newton minimization. Crystal data for C32H22F4N2 (Mr =511.52):
monoclinic, space group P21/n (no. 14), a=9.7606(1), b=
21.0993(3), c=13.2290(2) ꢁ, b=92.882(1)8, V=2720.96(6) ꢁ3, Z=4,
T=100.15 K, m(MoKa)=0.092 mmꢀ1, 1calcd =1.2462 gmmꢀ3, 26041
reflections measured (4.94ꢁ2qꢁ56.9), 6770 unique (Rint =0.0209)
which were used in all calculations. The final R1 was 0.0843
(I>2s(I)) and wR2 was 0.2720 (all data). Refinement details: unac-
counted for electron density within crystal lattice, could be mod-
eled as disordered THF or disordered hexane with no conclusive
preference, therefore density left unassigned.
Reactions of benzoquinone and [Ce{N(SiHMe2)2}3(thf)2]
Compound [Ce{N(SiHMe2)2}3(thf)2] (0.10 g, 0.15 mmol) and benzo-
quinone (0.010 g, 0.10 mmol) were dissolved in THF (5 mL) produc-
ing a dark red colored complex immediately. Crystallization from
hexane at ꢀ308C, produced small red crystals matching the unit
cell of 9. Upon storage of the filtrate for several days, small white
crystals of another material formed. However, the crystals melted
in paratone crystallography oil, silicon grease and solvents C6D6,
Et2O, and toluene. When exposed to air the material fumed. The
material also decomposed in the cryo-stream of the diffractometer,
producing highly twinned diffraction data with poor intensity, no
unit cell could be determined.
X-ray crystallography
Compounds 2, 5, 6a, 6b, and 11 were examined on a Bruker
APEX-II CCD diffractometer at 100.15 K, mounted on a fiber loop in
paratone crystallography oil. Complexes 3, 4, 7a, 8, and 10 were
examined on a Bruker P4 diffractometer at 100.15 K, mounted on
a glass fiber in viscous paratone crystallography oil. Compounds
6b and 7b were examined on an Oxford Gemini ultra diffractome-
ter at 100.15 K, the crystals were mounted on a fiber loop in vis-
cous paratone oil. Absorption corrections were completed using
SADABS,[29] or for complexes 6b and 7b SORTAV[30] was used. Data
for complexes 2–11 were obtained with MoKa radiation (l=
0.71073 ꢁ). CCDC 973018 (10), 973019 (11), 973020 (2), 973021 (3),
973022 (4), 973023 (5), 973024 (6a), 973025 (6b), 973026 (6c),
973027 (7a), 973028 (7b), and 973029 (8) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[Ce(DFForm)3(thf)2] (2): Using Olex2,[31] the structure was solved
with the ShelXS[32] structure solution program using Direct Meth-
ods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C47H37CeF12N6O2 (Mr =
¯
1085.94): triclinic, space group P1 (no. 2), a=12.7538(3), b=
18.9692(4), c=20.3546(5) ꢁ, a=111.8920(10)8, b=103.2860(10)8,
g=94.5130(10)8, V=4372.69(18) ꢁ3, Z=4, T=100.15 K, m(MoKa)=
, , 63787 reflections measured
1.140 mmꢀ1 1calcd =1.650 gmmꢀ3
(2.246ꢁ2qꢁ61.428), 26142 unique (Rint =0.0295) which were used
in all calculations. The final R1 was 0.0504 (I>2s(I)) and wR2 was
0.1625 (all data). Refinement remarks: disordered coordinating THF
molecules were modeled with PART (50:50) refinement where ap-
plicable.
[EtForm(CPh3)]·CH3CN (6c·CH3CN): Using Olex2,[31] the structure
was solved with the olex2.solve[32] structure solution program
using Charge Flipping[32] and refined with the XL[32] refinement
package using least squares minimization. Crystal data for C42H45N3
(Mr =591.81): monoclinic, space group Pc (no. 7), a=11.0933(5),
b=9.6838(4), c=15.8730(8) ꢁ, b=103.798(5)8, V=1655.97(13) ꢁ3,
[Ce(DFForm)3]·PhMe (3·PhMe): Using Olex2,[31] the structure was
solved with the ShelXS[32] structure solution program using Direct
Methods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C46H29CeF12N6 (Mr =1033.86):
monoclinic, space group P21/n (no. 14), a=13.1454(2), b=
13.4738(2), c=23.3893(4) ꢁ, b=90.0280(10)8, V=4142.68(11) ꢁ3,
Z=2, T=123.00(16) K, m(MoKa)=0.069 mmꢀ1, 1calcd =1.187 gmmꢀ3
,
10302 reflections measured (4.968ꢁ2qꢁ61.886), 6439 unique
(Rint =0.0218) which were used in all calculations. The final R1 was
0.0372 (I>2s(I)) and wR2 was 0.0927 (all data).
[Ce3(DFForm)4Cl5(thf)4]·4THF (7a): Using Olex2,[31] the structure
was solved with the ShelXS[32] structure solution program using
Z=4, T=100.15 K, m(MoKa)=1.195 mmꢀ1
, ,
1calcd =1.645 gmmꢀ3
67194 reflections measured (3.488ꢁ2qꢁ58.828), 11408 unique
(Rint =0.0254) which were used in all calculations. The final R1 was
Chem. Eur. J. 2014, 20, 4426 – 4438
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4436
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Direct Methods and refined with the XL[32] refinement package
using least squares minimization. Crystal data for
Council (ARC Discovery: DP 130100152) and an Australian Post-
graduate Award to D.W.
C84H92Ce3Cl5F16N8O8 (Mr =2243.26): monoclinic, space group Cc (no.
9), a=13.6723(5), b=34.9623(11), c=19.2700(6) ꢁ, b=103.694(2)8,
V=8949.5(5) ꢁ3, Z=4, T=100.15 K, m(MoKa)=1.741 mmꢀ1, 1calcd
=
Keywords: cerium · formamidinate · oxidation · protonolysis ·
silylamide
1.665 gmmꢀ3
,
77968 reflections measured (3.188ꢁ2qꢁ58.91),
22076 unique (Rint =0.0463) which were used in all calculations.
The final R1 was 0.0354 (I>2s(I)) and wR2 was 0.0743 (all data). Re-
finement details: THF solvates indicated slight disorder, left un-
modeled.
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, , 62412 reflections measured
1.465 mmꢀ1 1calcd =1.373 gmmꢀ3
(3.76ꢁ2qꢁ54.994), 8145 unique (Rint =0.1114) which were used in
all calculations. The final R1 was 0.0470 (I>2s(I)) and wR2 was
0.1037 (all data).
[Li(thf)Ce{N(SiHMe2)2}4] (8): Using Olex2,[31] the structure was
solved with the ShelXS[32] structure solution program using Direct
Methods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C20H64CeLiN4OSi8 (Mr =
748.49): monoclinic, space group P21/c (no. 14), a=19.1228(5), b=
11.4421(3), c=37.2808(11) ꢁ, b=92.328(2)8, V=8150.5(4) ꢁ3, Z=8,
T=100.15 K, m(MoKa)=1.370 mmꢀ1, 1calcd =1.207 gmmꢀ3, 55375 re-
flections measured (3.116ꢁ2qꢁ52.816), 16592 unique (Rint
=
0.0555) which were used in all calculations. The final R1 was 0.0499
(I>2s(I)) and wR2 was 0.1141 (all data). Refinement details: disor-
dered SiH(CH3)2 groups were modeled with PART disorder (50:50,
or FVAR), coordinating THF appeared disordered to several posi-
tions and was modeled to two, NPD were restrained with the ISOR
command. Due to disorder SiꢀH atoms were not assigned.
[Ce(p-TolForm)4] (10): Using Olex2,[31] the structure was solved
with the ShelXS[32] structure solution program using Direct Meth-
ods and refined with the XL[32] refinement package using least
squares minimization. Crystal data for C60H60CeN8 (Mr =1033.28):
monoclinic, space group P21/n (no. 14), a=16.5452(2), b=
18.3467(2), c=16.9889(2) ꢁ, b=96.7900(10)8, V=5120.81(10) ꢁ3,
Z=4, T=100.15 K, m(MoKa)=0.936 mmꢀ1
, ,
1calcd =1.340 gmmꢀ3
43509 reflections measured (3.28ꢁ2qꢁ52.944), 10562 unique
(Rint =0.0498) which were used in all calculations. The final R1 was
0.0338 (I>2s(I)) and wR2 was 0.1104 (all data).
[Ce{N(SiMe3)2}3(bda)0.5]2·2PhMe (11·2PhMe): Using Olex2,[31] the
structure was solved with the ShelXS[32] structure solution program
using Patterson method and refined with the XL[32] refinement
package using least squares minimization. Crystal data for
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¯
C56H128Ce2N6O2Si12 (Mr =1534.96): triclinic, space group P1 (no. 2),
a=11.1102(6), b=11.5965(6), c=18.6253(10) ꢁ, a=72.7870(10)8,
b=75.1860(10)8, g=63.9770(10)8, V=2037.55(19) ꢁ3, Z=1, T=
100.15 K, m(MoKa)=1.317 mmꢀ1, 1calcd =1.251 gmmꢀ3, 41571 reflec-
tions measured (4ꢁ2qꢁ58.296), 10955 unique (Rint =0.0345)
which were used in all calculations. The final R1 was 0.0248
(I>2s(I)) and wR2 was 0.0569 (all data).
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Acknowledgements
We gratefully acknowledge support from the German Science
Foundation (Grant AN 238/16-1) and the Australian Research
Chem. Eur. J. 2014, 20, 4426 – 4438
www.chemeurj.org
4437
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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Received: November 22, 2013
Revised: January 30, 2014
Published online on March 18, 2014
Chem. Eur. J. 2014, 20, 4426 – 4438
www.chemeurj.org
4438
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim