Rare-earth metal phenyl(trimethylsilyl)amide complexes

Article abstract of DOI:10.1002/ejic.201000220

The reactions of common rare-earth metal chloride, borohydride, and triflate precursors - LnCl₃(thf)_x, Ln(BH₄) ₃(thf)₃, and La(OTf)₃ - with alkali metal amide complexes M[N(SiMe₃)(C₆H₃iPr₂-2,6)] (M[NRR']; M = Li, K) were investigated in thf or hexane as a solvent. A. diverse range of products was obtained comprising alkali metal-free mono(rare-earth metal) complexes Y[NRR']Cl₂(thf)₃ and Ln[NRR']₂(BH₄)(thf) (Ln = Nd, La), as well as the mononeodymium ate complex [Nd[NRR']₂(BH₄) ₂}(Li(thf)₄} and polymeric ate complexes {La[NRR'] ₂(thf)(μ-Cl)K(thf)₂(n-Cl)}_n and {Nd[NRR']₂(μ-BH₄)Li(thf)₂(μ-BH ₄)}_n. All compounds were characterized by NMR ( ¹H and ¹³C) and FTIR spectroscopy, elemental and X-ray structure analyses. The lithium salts Li[NRR'](thf)₃ and Li ₄(OTf)₄(thf)₆ were isolated as side products and structurally characterized. The homoleptic complex La[NRR']₃ was prepared following two synthesis protocols in hexane, either by reacting Ln[NRR']₂(BH₄)(thf) with 1 equiv. of K[NRR'] or treatment of LaCl₃(thf)_1.25 with. 3 equiv. of K[NRR'].

Full text of DOI:10.1002/ejic.201000220

FULL PAPER
DOI: 10.1002/ejic.201000220
Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
Christoph Schädle,[a] Christian Meermann,[a,b] Karl W. Törnroos,[b] and
Reiner Anwander*[a,b]
Keywords: Rare earths / N ligands / Polymerization
The reactions of common rare-earth metal chloride, borohy-
{La[NRRЈ]2(thf)(µ-Cl)K(thf)2(µ-Cl)}n and {Nd[NRRЈ]2(µ-BH4)-
dride, and triflate precursors – LnCl3(thf)x, Ln(BH4)3(thf)3, and Li(thf)2(µ-BH4)}n. All compounds were characterized by NMR
La(OTf)3 – with alkali metal amide complexes M[N(SiMe3)-
(C6H3iPr2-2,6)] (M[NRRЈ]; M = Li, K) were investigated in thf
or hexane as a solvent. A diverse range of products was ob-
tained comprising alkali metal-free mono(rare-earth metal)
complexes Y[NRRЈ]Cl2(thf)3 and Ln[NRRЈ]2(BH4)(thf) (Ln =
Nd, La), as well as the mononeodymium ate complex
{Nd[NRRЈ]2(BH4)2}{Li(thf)4} and polymeric ate complexes
(1H and 13C) and FTIR spectroscopy, elemental and X-ray
structure analyses. The lithium salts Li[NRRЈ](thf)3 and Li4-
(OTf)4(thf)6 were isolated as side products and structurally
characterized. The homoleptic complex La[NRRЈ]3 was pre-
pared following two synthesis protocols in hexane, either by
reacting Ln[NRRЈ]2(BH4)(thf) with 1 equiv. of K[NRRЈ] or
treatment of LaCl3(thf)1.25 with 3 equiv. of K[NRRЈ].
Cl)(thf)]2. For the larger rare-earth metal center neodym-
ium, even a trimetallic cluster, [Nd{N(SiHMe2)2}(thf)]2-
Nd[N(SiHMe2)2]2(µ2-Cl)2(µ3-Cl)2[µ-N(SiHMe2)2], was ob-
tained. In order to avoid uncontrolled ligand redistribution
already at this early stage we set out to investigate the ac-
cessibility of well-defined mixed silylamide/chloride com-
plexes derived from the bulky phenylsilylamido ligand
[N(SiMe3)(C6H3iPr2-2,6)].[4–11] At the same time, we
wanted to further examine the effect of anions X different
Introduction
Heteroleptic rare-earth metal complexes bearing amido
and chloro ligands not only display useful synthesis precur-
sors according to protonolysis (that is amine elimination)
reactions,[1] but can also be directly converted into efficient
polymerization catalysts by reaction with organoaluminum
compounds.[2] Recently, we described such a silylamide-
based chlorination–alkylation sequence which led to the
precipitation and isolation of amorphous solids
[LnaAlbMecCld]n (a + b = 1, a Ͼ b; c + d = 3, d Ͼ c) suppos-
edly the active species in 1,3-diene polymerization.[3] In this
previous paper we also addressed the implications of the
rare-earth metal cation size – neodymium showing the high-
est activity – the solvent effect (toluene vs. hexane), and the
superior activation (“cis-directing”) behavior of the chloro
ligand to the borato ([B(C6F5)4]) ligand. Due to extensive
ligand redistribution reactions it was difficult to control the
Ln/Me/Cl ratio in the precipitates of such organoalumi-
num-mediated Ln-NR2 Ǟ Ln-alkyl transformations, which
crucially affects the polymer characteristics. Additionally,
occlusion of nitrogen- and aluminum-containing co-prod-
ucts was attributed to instant and rapid precipitation. The
originally used mixed silylamide/chloride complexes were
obtained by reaction of LnCl3(thf)x with 2 equiv. LiN-
(SiHMe2)2, which for scandium and yttrium, however, af-
–
from chloro, e.g., OTf– and BH4 . Scheme 1 summarizes
these ideas of new precursor complexes with fixed N/Ln/X
ratios of relevance for 1,3-diene polymerization according
to cationization–alkylation sequences.
forded
a
mixture of the tris(amido) derivatives
Ln[N(SiHMe2)2]3(thf)x and dimeric [Ln{N(SiHMe2)2}2(µ-
[a] Department of Inorganic Chemistry, University of Tübingen,
Auf der Morgenstelle 18, 72076 Tübingen Germany
Fax: +49-7071-292436
E-mail: reiner.anwander@uni-tuebingen.de
[b] Department of Chemistry, University of Bergen,
Allégaten 41, 5007 Bergen, Norway
Scheme 1. AmidoAnionAlkylation (AAA) interplay in rare-earth
metal precatalysts for isoprene polymerization.
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C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
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Figure 1. Structurally characterized rare-earth metal(III) complexes A,[5] B,[6] C,[7] D,[8] E,[8] F,[9] G,[5] H,[5] and I[10] featuring the [N(SiMe3)-
(C6H3iPr2-2,6)] ligand. Depicted are also two lanthanide(II) derivatives, J[5] and K.[11]
In 1995, Schumann et al. initially reported on lanthan- tic ate-free complex C (Figure 1). From the analogous reac-
ide(III) amide complexes featuring [N(SiMe3)(C6H3R2- tion of YbCl3 with 2 equiv. of Li[N(SiMe3)(C6H3iPr2-2,6)]
2,6)] (R = iPr, Me, H) ligands.[7] Bulky iPr goups in 2,6- compound G (Figure 1) was isolated and structurally char-
position of the aryl ligand facilitated the isolation of acterized.[5] The latter result confirmed that there is basi-
Nd[N(SiMe3)(C6H3iPr2-2,6)]2Cl(thf) (C, Figure 1) with a cally enough space around the Yb3+ ion to coordinate two
defined NR2/Cl ratio of 2:1 in high yield and free of ligand amido ligands. In our hands, the 2-equiv. reaction for the
redistribution products. It can be anticipated that this bulky larger Y3+, however, gave the mono(amido) derivative 2
amido ligand sterically saturates the large neodymium cat- (Scheme 2, Figure 2).
ion efficiently, making it less accessible for AlMe3. This
might slow down the alkylation reaction and facilitate the
formation of well-defined and aluminum-free [Me2Nd-
Cl]n. In the present work we studied the accessibility of
analogous phenyltrimethylsilylamide complexes Ln[N-
(SiMe3)(C6H3iPr2)]2X for several rare-earth metal centers
(Ln = Nd, La, Y) with varying anions (X = Cl, BH4, OTf).
Keeping in mind that the synthesis of such complexes is
hampered by salt incorporation (F and H, Figure 1) or even
C–H activation (E, Figure 1), the effect of solvent and dis-
tinct alkali metal amide precursors on the product forma-
tion was investigated.
Scheme 2. Reaction of YCl3(thf)3.5 with 2 equiv. of Li[N(SiMe3)-
(C6H3iPr2-2,6)].
Results and Discussion
NMR investigations of the crude reaction product indi-
cated a mixture of compounds, from which complex 2 could
Heteroleptic Complexes with Amido and Chloro Ligands
Salt metathesis reactions of some lanthanide chlorides be isolated by extraction with hexane, and unequivocally
with Li[N(SiMe3)(C6H3R2-2,6)] (R = H, Me, iPr) have been characterized. The observed product mixture points toward
reported previously by Schumann et al.[7] Crucial for the the additional formation of ate complexes analog to com-
product formation and in particular for the number of Ln- pound G (Figure 1),[5] which considerably affects the repro-
coordinating amido ligands is hereby the type of substitu- ducibility of compound 2. In the same reaction, excess lith-
tion of the aryl moiety in the 2- and 6-positions. Hydrogen ium amide co-crystallized as the tris(thf) adduct Li[N-
substitutents led to the isolation of the tris(amido) com- (SiMe3)(C6H3iPr2-2,6)](thf)3 (1) (Scheme 2, Figure 2). In
plexes Ln[N(SiMe3)(C6H5)]3(thf)x, methyl groups gave the accordance with the previously reported ytterbium deriva-
ate species Nd[N(SiMe3)(C6H3Me2-2,6)]2(thf)(µ-Cl)2Li- tive (A, Figure 1) compound 2 can be synthesized in higher
(thf)2, while the bulkier iPr substituents afforded heterolep- yield by use of 1 equiv. of Li[N(SiMe3)(C6H3iPr2-2,6)].
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Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
thf, gave also a product mixture. Lithium complex 1 was the
only compound that crystallized from the hexane fractions.
Exchanging the lithium amide for the potassium congener
K[N(SiMe3)(C6H3iPr2-2,6)] according to the procedure for
the preparation of B (Figure 1)[6] did not yield the antici-
pated monomeric species. Instead, crystals of polymeric
{La[N(SiMe3)(C6H3iPr2-2,6)]2(thf)(µ-Cl)K(thf)2(µ-Cl)}n (3)
could be grown directly from the reaction mixture
1
(Scheme 3). H and 13C NMR spectroscopic measurements
of the crude reaction mixture further confirmed compound
3 as the main reaction product.
Figure 2. Solid-state structures of complexes Li[N(SiMe3)(C6H3-
iPr2-2,6)](thf)3 (1) and Y[N(SiMe3)(C6H3iPr2-2,6)]Cl2(thf)3 (2).
Non-H atoms are represented by atomic displacement ellipsoids at
the 50% level. Hydrogen atoms are omitted for clarity.
However, the obtained crystalline product 2 was still con-
taminated with small amounts of the lithium amide as indi-
cated by its microanalysis and NMR spectra.
X-ray structural data of Li[N(SiMe3)(C6H3iPr2-2,6)] de-
rivatives have been reported previously. When crystallized
from non-donor solvents such as hexane the dimeric species
{Li[N(SiMe3)(C6H3iPr2-2,6)]}2 was obtained featuring a
four-membered [Li-N]2 ring and close Li···H and Li···C
contacts.[12] Monomeric complex Li[N(SiMe3)(C6H3iPr2-
2,6)](py)(OEt2) features a lithium center which is coordi-
nated in an approximate trigonal-planar fashion exhibiting
additional short contacts to the ipso carbon atoms of the
phenyl ring.[13] In complex 1 the coordination sphere of the
lithium atom is fully saturated by three thf molecules. The
Li–N distances are comparable for all three complexes [1,
Scheme 3. Reaction of LaCl3(thf)1.25 with 2 equiv. of K[N(SiMe3)-
(C6H3iPr2-2,6)].
An X-ray structure analysis revealed that compound 3
crystallizes as bent polymer chains of alternating lantha-
num and potassium metal centers bridged via chlorido li-
gands. The geometry of the five coordinate lanthanum
metal center can best be described as heavily distorted tri-
gonal bipyramidal with O1 from thf and N1 from one
amido ligand at the apical positions and N2 of the second
amido as well as the two bridging chloro ligands Cl(1/2) in
the equatorial plane. A deviation of the ideal symmetry is
apparent from a bond angle of 145.46(8)° along the N1–
La–O1 axis and the bond angles of Cl1–La–Cl2
[132.08(3)°], Cl2–La–N2 [126.16(7)°], and Cl1–La–N2
[96.10(7)°] of the trigonal basis. The potassium centers are
coordinated by the two bridging chlorides [K–Cl(1/2),
2.997(2) and 3.059(2) Å] as well as two thf molecules [K–
O(2/3), 2.731(3) and 2.697(3) Å]. Furthermore an interac-
tion of K with the π-system of one phenyl ring (C3 and C4)
in the ligand backbone is indicated. Similar potassium
arene interactions were reported for K[La(OC6H3iPr2-
2,6)4][14] with K–C interatomic distances of 3.235(2) Å and
3.330(4) Å which are about the same as in 3 [K–C3,
3.212(4) Å and K–C4 3.366(4) Å]. In the latter publication
these interactions are described as rather modest compared
to the potassium–arene interactions in other systems rang-
1.986(4) Å;
Li[N(SiMe3)(C6H3iPr2-2,6)](py)(OEt2),[13]
1.916(9) Å; {Li[N(SiMe3)(C6H3iPr2-2,6)]}2, 1.961(4) Å],
and the Li–N–C angles lie in the range of 108.4(2)° (1) to
109.1(2)° ({Li[N(SiMe3)(C6H3iPr2-2,6)]}2).[12]
Compound 2 crystallizes in the monoclinic space group
P21/n (see Figure 2, Tables 1 and 7) and is isostructural to
the ytterbium compound A (Figure 1).[5] The coordination
geometry is best described as distorted octahedral. As ex-
pected the bond angles are all similar and the difference
in the Ln–N and Ln–Cl distances between the Yb and Y
derivatives follows the trend in the respective ionic radii
(Table 1).
Table 1. Selected bond lengths [Å] and angles [°] for 2 and A.
2 (Ln = Y)
A (Ln = Yb)
Ln–N
Ln–Cl1
Ln–Cl2
N–Ln–Cl1
N–Ln–Cl2
Cl1–Ln–Cl2
Ln–N–Si
2.260(2)
2.54945(5)
2.5793(5)
98.51(4)
98.97(4)
162.38(2)
124.1(3)
2.218(5)
2.550(2)
2.544(2)
97.8(2)
98.6(2)
163.40(6)
123.78(7)
Attempted preparation of the chloro analog of La[N- ing from 3.018(8) Å in K[Er(OC6H3iPr2-2,6)4][14] to 3.59 Å
(SiMe3)(C6H3iPr2-2,6)]2Br(thf) (B, Figure 1), following the [K(dibenzo-18-crown-6)](GaMe2NCS)(C6H6)2.[15] A section
same reaction procedure described for C (Figure 1) utilizing of the polymeric structure of 3 is shown in Figure 3 and
LaCl3(thf)1.25 and 2 equiv. of Li[N(SiMe3)(C6H3iPr2-2,6)] in selected bond lengths and angles are listed in Table 2.
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C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
FULL PAPER
Figure 3. Solid-state structure of complex {La[N(SiMe3)(C6H3iPr2-
2,6)]2(thf)(µ-Cl)K(thf)2(µ-Cl)}n (3). Non-H atoms are represented
by atomic displacement ellipsoids at the 50% level. Hydrogen
atoms are omitted for clarity.
Table 2. Selected bond lengths [Å] and angles [°] for 3.
Bond lengths
Bond angles
La–Cl1
La–Cl2
La–N1
La–N2
La–O1
K–Cl1
K–Cl2
K–C3
2.7449(8)
2.8479(8)
2.424(3)
2.367(3)
2.611(2)
2.997(2)
3.059(2)
3.212(4)
3.366(4)
Cl1–La–Cl2
N1–La–N2
O1–La–N1
O1–La–N2
Cl1–La–O1
Cl1–La–N2
Cl2–La–N2
La–Cl2–K
La–Cl1–K
132.08(3)
114.51(9)
145.46(8)
99.53(8)
80.73(6)
96.10(7)
126.16(7)
124.45(3)
157.37(4)
Scheme 4. Synthesis protocols for mixed amide/borohydride com-
plexes of neodymium and lanthanum.
K–C4
Heteroleptic Complexes with Amido and
Borohydrido Ligands
Complexes Ln(BH4)3(thf)3 not only display versatile syn-
thesis precursors[16] but also are employed as precatalysts in
polymerization reactions.[17] Following the idea of em-
ploying anions different from chloride (Scheme 1) we
treated the neodymium tris(borohydride) complex Nd-
(BH4)3(thf)3 with 2 equiv. of Li[N(SiMe3)(C6H3iPr2-2,6)] (a,
Scheme 4).
Instant reaction was indicated by a color change of the
solution from purple to blue. Blue crystals of [Nd{N-
(SiMe3)(C6H3iPr2-2,6)}2(BH4)2][Li(thf)4] (4) could be har-
vested directly from the thf reaction mixture in high yield
and separated from co-crystallized colorless LiBH4(thf)x.[18]
The exact molecular composition of the obtained product
could be derived from a single crystal structure determi-
nation showing two [N(SiMe3)(C6H3iPr2-2,6)] ligands and
Figure 4. Solid-state structure of complex [Nd{N(SiMe3)-
(C6H3iPr2-2,6)}2(BH4)2][Li(thf)4] (4). Non-H atoms are represented
by atomic displacement ellipsoids at the 50% level. Hydrogen
atoms are except for the BH4 moieties omitted for clarity.
two BH4 anions coordinated to the neodymium metal cen- respectively (Table 3). Short contacts between the neodym-
ter. The anionic fragment {Nd[N(SiMe3)(C6H3iPr2-2,6)]2- ium center and the ipso carbon atoms of the aryl moiety
(BH4)2} of ate complex 4 is charge balanced by a Li(thf)4 were observed in C [2.814(2) Å, 3.129(2) Å] but do not pre-
ion (Figure 4).
vail in 4. A similar ate species was found for the neodymium
Previously reported Nd[N(SiMe3)(C6H3iPr2-2,6)]2Cl(thf) borohydride guanidinate complex [(Me3Si)2NC(N-Cy)2]2-
(C, Figure 1) is somewhat comparable to 4 featuring also a Nd(µ-BH4)2Li(thf)2.[19,20] However, in the latter complex
four-coordinate Nd metal center.[7] Both complexes display the BH4 ligands are bridging the neodymium and lithium
distorted tetrahedral coordination geometries as evidenced, metal centers giving rise to markedly longer Nd–B distances
e.g., by the large angle N1–Nd–N2 of 129.64(5)° in 4 [C: of 2.739(1) and 2.925(1) Å than in
4 [2.631(3) Å,
N1–Nd–N2 116.60(7)°, largest deviation: N2–Nd–O 2.631(2) Å]. The tridentate coordination mode of the BH4
121.03(6)°]. However, complexes 4 and C show distinct Nd– ligands is further corroborated by the IR spectrum of 4 (B–
N distances of 2.370(2)/2.350(2) Å and 2.276(2)/2.264(2) Å, Ht 2432 cm–1, strong singlet; B–Hb 2213 cm–1, broad).[21]
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Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
Table 3. Selected bond lengths [Å] and angles [°] for 4 and C.
4
C
Nd–N1
Nd–N2
Nd–B1
2.3700(15)
2.3498(15)
2.631(3)
2.276(2)
2.264(2)
–
Nd–B2
Nd–Cipso
2.631(2)
–
3.394(3); 3.387(2)
129.64(5)
115.45(7)
115.05(8)
124.9(2)
125.5(2)
129.64(5)
2.814(2); 3.129(2)
116.60(7)
125.7(1)
139.4(1)
113.4(1)
96.7(1)
N1–Nd–N2
Nd–N1–Si1
Nd–N2–Si2
Nd–N1–Cipso
Nd–N2–Cipso
N1–Nd–N2
116.60(7)
Having in mind that chloro complex C is hexane solu-
ble[7] we anticipated that performing the reaction of
Nd(BH4)3(thf)3 with Li[N(SiMe3)(C6H3iPr2-2,6)] in hexane
Figure 5. a) Section of the molecular structure of complex
might lead to an ate complex free species via precipitation {Nd[N(SiMe3)(C6H3iPr2-2,6)]2(µ-BH4)Li(thf)2(µ-BH4)}n (5). Non-
H atoms are represented by atomic displacement ellipsoids at the
of the lithium borohydride by-product. Moreover, the neo-
50% level. Hydrogen atoms except for the BH4 moiety are omitted
dymium precursor of choice already carries three molecules
for clarity. b) Borohydrido bridging modes in 5 as suggested by
of thf to a) enhance the solubility in hexane and b) make
FTIR spectroscopy.
further addition of thf, which would support ate complex
formation, unnecessary.
further evidenced by an acute angle Nd–N1–C1 of
Accordingly, Nd(BH4)3(thf)3 was treated with 2 equiv. of
97.03(9)° and by the markedly distorted tetrahedral bond-
the lithium amide salt Li[N(SiMe3)(C6H3iPr2-2,6)] in hex-
ing angles N1–Nd–B1 of 98.88(5)° and N2–Nd–B2 of
ane (b, Scheme 4). Again, color change of the suspension
99.25(5)°. The lithium metal centers also adopt a distorted
from pale purple to blue proved an instant reaction. Upon
tetrahedral geometry: two thf molecules and two bridging
separation of the precipitate and concentrating of the solu-
borohydrido ligands show bond angles ranging from
tion in vacuo, blue crystals of compound 5 could be grown
103.92(3)° to 122.2(2)° and average Li–O and Li–B bond
at –35 °C from the hexane solution. Due to the paramagne-
lengths of 1.936 Å and 2.510 Å, respectively. Selected bond
lengths and angles of 4 and 5 are listed and compared in
Table 4.
1
tism of the neodymium metal center the H and 13C NMR
spectra were not conclusive. Especially the proton reso-
nances appeared well separated within a signal range from
δ = 25 to –10 ppm, however, could not be assigned.
The solid-state structure of 5 consists of polymeric chains
of composition {Nd[N(SiMe3)(C6H3iPr2-2,6)]2(µ-BH4)Li-
(thf)2(µ-BH4)}n with alternating neodymium and lithium
metal centers bridged by borohydrido units (BH4) (Fig-
ure 5, a). The bridging mode of the BH4 moieties can be
derived from the pattern of the B–H stretching bands as
described by Marks et al.[21] Two medium bands at 2360
and 2338 cm–1 and a very weak band at 2430 cm–1 in the
IR spectrum of 5 are indicative of a mixed bridging mode.
This means that the borohydrido ligands bind to the neo-
dymium and lithium metal centers in a η2-η2 and a η2-η1
fashion (Figure 5, b).
Table 4. Selected bond lengths [Å] and angles [°] for 4 and 5.
4
5
Distances
Nd–N1
Nd–N2
Nd–B1
Nd–B2
Nd–C1
Nd–C16
Li–O1
Li–O2
Li–B1
2.370(2)
2.350(2)
2.631(2)
2.631(3)
3.394(2)
3.387(2)
2.297(2)
2.311(2)
2.720(2)
2.693(2)
2.847(2)
3.229(2)
1.944(3)
1.928(3)
2.600(4)
2.420(3)
Li–B2
Angles
Like in complex 4 (Figure 4) two borohydrido and two
amido ligands accomplish a distorted tetrahedral geometry
at the neodymium metal center in 5. The Nd–N bond
lengths are slightly shorter in 5 compared to 4 while the
Nd–BH4 distances are elongated due to the bridging nature
of these moieties in 5. Furthermore, in complex 5 the ipso-
carbon atoms C1 and C16 of the phenyl rings are in close
N1–Nd–B1
N2–Nd–B2
Nd–N1–C1
B2–Li–B1
O2–Li–O1
108.39(7)
108.22(7)
124.9(2)
98.88(5)
99.25(5)
97.03(9)
107.6(2)
105.5(2)
Since the choice of the alkali metal markedly affected
proximity to the neodymium center analogous to complex the reaction outcome for the amido–chloro derivatives (vide
C while this interaction is not observed in 4 [Nd–C1 supra), Nd(BH4)3(thf)3 was next treated with 2 equiv. of
2.847(2) Å, Nd–C16 3.229(2) Å in 5; Nd–C1 2.814(2) Å, K[N(SiMe3)(C6H3iPr2-2,6)] in thf or hexane at ambient
Nd–C16 3.129(2) Å in C; Nd–C1 3.394(2) Å, Nd–C16 temperature (c and d, Scheme 4). Both reactions produced
3.387(2) Å in 4]. The pronounced Nd···C1ipso interaction is pale purple suspensions, which turned green within a few
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C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
FULL PAPER
seconds indicating an immediate reaction. The green solid,
which was obtained from the “thf reaction” showed several
resonances for the trimethylsilyl groups in the 1H NMR
spectrum, clearly indicating a product mixture. However,
after dissolving the crude product mixture in a small
amount of thf and storing it at –35 °C for six weeks a few
blue single crystals formed. An X-ray structure analysis un-
equivocally proved the formation of the envisaged product
Nd[N(SiMe3)(C6H3iPr2-2,6)]2(BH4)(thf) (6). In contrast,
the “hexane reaction” (d, Scheme 4) afforded blue crystals
within one day at –35 °C in 64% crystallized yield. An X-
ray crystallographic study proved that complex 6 can be
reproducibly synthesized via this approach, however, under
these reaction conditions as the main product. The 1H
NMR spectrum revealed well separated peaks in a signal
range from 25 ppm to –8 ppm with a similar pattern as ob-
Figure 6. Molecular structure of Ln[N(SiMe3)(C6H3iPr2-2,6)]2-
served for 5. Using the same reaction protocol (d, (BH4)(thf) (Ln = Nd (6), La (7)) represented by complex Nd[N-
(SiMe3)(C6H3iPr2-2,6)]2(BH4)(thf). Non-H atoms are represented
by atomic displacement ellipsoids at the 50% level. Hydrogen
atoms except for the BH4 moiety are omitted for clarity.
Scheme 4), the lanthanum analog La[N(SiMe3)(C6H3iPr2-
2,6)]2(BH4)(thf) (7) was synthesized. In comparison to the
1
potassium amide precursor the H and 13C NMR spectra
of diamagnetic 7 show two distinct features: a) two sets of
dymium or lanthanum metal center could be assigned by
signals for the methyl groups of the isopropyl substituents
FTIR spectroscopy and verified through the crystal struc-
due to the hindered rotation around the C–N axis of the
ture. The terminal hydrogen–boron stretching mode was
2,6-diisopropylphenyl moiety; b) a broad quartet (w1/2
≈
found at 2454 cm–1 for the neodymium complex and at
2448 cm–1 for the lanthanum complex. Bands at 2204/
2144 cm–1 (6) as well as at 2201/2143 cm–1 (7) could be as-
signed to the two bridging hydrogen–boron stretching
208 Hz) for the borohydrido ligand, showing H–B coupling
[I(11B) = 3/2].
Complexes 6 (Nd) and 7 (La) are isostructural, constitut-
ing monomeric species in the solid state (Figure 6), quite
different from ate complex 4 (Nd) and polymeric complex
5 (Nd). The overall structural features are closely related to
those of B and C (Figure 1). A comparison of important
bond lengths and angles of all four complexes 6, 7, B, and
C is presented in Table 5.
modes. Using the criteria published by Marks et al.[21]
a
tridentate coordination of the tetrahydroborate is sug-
gested.
Interactions between the lanthanide centers and the ipso-
carbon atoms of the phenyl ring in the ligand backbone
were reported for chloro derivative C and are also observ-
able for borohydride complexes 6 and 7. This is documented
by close Ln···Cipso contacts and acute angles Ln1–N–Cipso
(Table 5).
The geometry around the four coordinate neodymium
and lanthanum metal centers is again distorted tetrahedral
with bond angles ranging from 96.35(5)° to 121.84(4)° in
6 and 99.1(2)° to 122.03(4)° in 7, respectively. While this
distortion from ideal symmetry is more pronounced than
in complex Nd[N(SiMe3)(C6H3iPr2-2,6)]2Cl(thf) (C),[7] the
bond lengths match well for isostructural complexes B, C,
6, and 7, considering the difference in ion size.[22] The coor-
Attempted Synthesis of Heteroleptic Complexes
with Amido and Triflate Ligands
Lanthanide triflates have been exploited for the synthesis
dination mode of the BH4 moieties to the respective neo- of various organolanthanide compounds.[23] Belot et al.
Table 5. Selected bond lengths [Å] and angles [°] for 6, 7, B, and C.
6 (Ln = Nd, X = B)
7 (Ln = La, X = B)
B (Ln = La, X = Br)
C (Ln = Nd, X = Cl)
Ln–N1
Ln–N2
Ln–O1
Ln–X1
Ln–C1
Ln–C16
N1–Ln–N2
N1–Ln–X1
N1–Ln–O1
N2–Ln–X1
N2–Ln–O1
O1–Ln–X1
Ln–N1–C1
Ln–N2–C16
2.303(2)
2.282(2)
2.450(2)
2.603(2)
2.927(2)
2.853(2)
121.83(4)
100.63(5)
114.78(4)
96.35(5)
116.39(4)
99.66(5)
100.94(8)
98.10(8)
2.358(2)
2.345(2)
2.510(2)
2.675(2)
2.959(2)
2.883(2)
122.03(4)
99.22(6)
115.83(4)
95.40(6)
116.59(4)
99.10(6)
100.18(9)
97.104(9)
2.335(3)
2.332(3)
2.508(3)
2.8664(7)
3.181(3)
2.876(5)
115.1(2)
109.62(8)
97.5(2)
102.14(9)
117.5(2)
115.5(2)
113.3(2)
97.0(3)
2.276(2)
2.264(2)
2.445(1)
2.617(1)
3.129(2)
2.814(2)
116.60(7)
103.98(5)
102.12(7)
103.24(6)
121.03(6)
108.61(5)
113.4(1)
96.7(1)
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Eur. J. Inorg. Chem. 2010, 2841–2852

Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
stated explicitly the high yield synthesis of archetypal sil- (OTf)(thf)]n, and 1.449 Å, 1.329 Å, and 1.833 Å for the free
ylamide complexes Ln[N(SiMe3)2]3 (Ln = La, Nd, Sm, Er) acid, respectively. Also the average O–S–C angles of 103.25°
employing Ln(OTf)3.[24] Our comprehensive studies on (8), 103.3 ([Li(OTf)(thf)]n), and 104.0° (HOTf) are similar.
bis(dimethylsilyl)amide complexes Ln[N(SiHMe2)2]3(thf)2
revealed that the synthesis of pure compounds is extremely
dependent on the solvent, the nature of the alkali metal
salt, and choice of the rare-earth metal precursor.[25,26] For
example, use of La(OTf)3 and LiN(SiHMe2)2 gave compli-
cated product mixtures, while the corresponding reaction
with Y(OTf)3 yielded the tris(amido) derivative Y[N-
(SiHMe2)2]3(thf)2 only contaminated with LiOTf[25] and the
donor solvent-free ate complex {Y[N(SiHMe2)2]4Li}2.[26]
Use of the bulkier [N(SiMe3)(C6H3iPr2-2,6)] ligand might
counteract ligand scrambling and allow the isolation of
putative complexes Ln[N(SiMe3)(C6H3iPr2-2,6)]2(OTf)-
(thf). However, 1H NMR spectroscopic investigations of the
crude products obtained from the reactions of Ln(OTf)3
(Ln = Y, Nd) with 2 equiv. of Li[N(SiMe3)(C6H3iPr2-2,6)]
in thf showed mixtures of several species, which could not
be unambiguously identified. The chemical shift of the
SiMe3 moiety of the neodymium congener (δ = –2.13 ppm)
was found to be almost identical to that of Nd[N-
(SiMe3)(C6H5)]3(thf) (δ = –2.14 ppm) and gave an indica-
tion of the formation of a neodymium amide species (for
comparable compound C, Figure 1, no NMR spectroscopic
Figure 7. Structural motifs in lithium trifluoromethanesulfonates:
[Li(OTf)(thf)]n and Li4(OTf)4(thf)6 (8).
data were given).[7] Fractionate crystallization from thf
[27]
solutions yielded only colorless crystals of side product Li4-
(OTf)4(thf)6 (8), allowing for a partial enrichment of the
rare-earth metal containing complexes. The putative yt-
trium or neodymium derivatives were nevertheless not ac-
cessible in pure form and unfortunately did so far not crys-
tallize.
The high-yield formation of compound 8 is reproducible.
Tetrameric 8 crystallizes in the monoclinic space group
P21/n (see Figures 7 and 8), with four Li(OTf) moieties as-
sembled to three annelated eight-membered rings. For com-
parison, from the salt metathesis reaction of CpLu(OTf)2-
(thf)3 with LiCH2SiMe3 a polymeric side product, [Li(OTf)-
(thf)]n, could be isolated.[27] Crystals of the latter compound
were grown from toluene solutions at ambient temperature
(cf., 8: thf, –35 °C) and an X-ray structure analysis showed
an oligomeric two-dimensional network, in which the indi-
vidual oligomers are further arranged in layers. Again are
eight-membered rings the prevailing structural motif, four
Figure 8. Solid-state structure of complex Li4(OTf)4(thf)6 (8). Non-
H atoms are represented by atomic displacement ellipsoids at the
of which are connected via Li···O=S bonds to form a 16-
membered ring (Figure 7). Apparently, the different struc-
tural motifs of Li4(OTf)4(thf)6 (8) and [Li(OTf)(thf)]n origi-
nate from the different number of coordinating thf mole-
cules. In [Li(OTf)(thf)]n each of the lithium atoms carries
one thf molecule, whereas in 8 two molecules thf are coordi-
50% level. Hydrogen atoms are omitted for clarity.
A Homoleptic Lanthanum Amide
Homoleptic amide complexes of the rare-earth metals are
nated to the lithium cations in the outer eight-membered considered valuable synthesis precursors and the synthesis
rings and only one to the lithium atoms in the inner ring. and characterization of such species is pursued for amides
The formation of two different thf adducts of [Li(OTf)] is of the entire lanthanide series.[4] Within the class of LnIII
most likely caused by a solvent effect, i.e., toluene vs. thf. tris(amide) complexes, donor-solvent free derivatives are of
All bonds in 8 compare relatively well to those in [Li(OTf)- particluar interest.[29] Schumann et al.[7] reported that
(thf)]n and trifluoromethanesulfonic acid HOTf.[27,28] The homoleptic amide complexes of neodymium and lutetium
average S–O, C–F, and C–S distances are 1.430 Å, 1.321 Å, bearing the bulky amido ligand [N(SiMe3)(C6H3iPr2-2,6)]
and 1.808 Å in 8, 1.430 Å, 1.313 Å, and 1.821 Å in [Li- were not accessible by reacting three equivalents of Li[N-
Eur. J. Inorg. Chem. 2010, 2841–2852
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2847

C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
FULL PAPER
(SiMe3)(C6H3iPr2-2,6)] with the respective lanthanide chlo- C38, lie as well in the N1N2N3 plane, while the lanthanum
rides LnCl3 (Ln = Nd, Lu). Instead the bis(amido) deriva- metal center is displaced from this plane by 0.665 Å
tives Ln[N(SiMe3)(C6H3iPr2-2,6)]2Cl(thf) [Ln = Lu, Nd (C: towards the phenyl rings. This results in N–La–N bond
Figure 1)] were isolated. So far homoleptic species Ln[N- angles ranging from 111.86(9)° to 113.10(9)°. The average
(SiMe3)(C6H3R2-2,6)]3 (Ln = Y, La, Nd, Sm, Eu, Tb, Dy, La–N bond length of 2.373 Å is marginally elongated com-
Er, Yb, Lu) were isolable for the less sterically demanding pared to those in 7 (2.351 Å) and B (2.334 Å). However, the
amido ligand where R = H. Herein the first successful syn- interatomic La1···Cipso distances 3.130(3) Å (C1),
thesis of homoleptic La[N(SiMe3)(C6H3iPr2-2,6)]3 is pre- 3.110(3) Å (C16), and 3.129(3) Å (C31) appear in average
sented.
elongated compared to those observed in B[6] [3.181(3)/
Contrary to Schumanns reaction protocol based on 2.876(5) Å], in C[7] [3.129(2)/2.814(2) Å] as well as in com-
LnCl3 (Ln = Nd, Lu)[7] and lithium amide in thf, we ini- plex 7 (2.959(2)/2.883(2) Å]. These pronounced secondary
tially utilized the heteroleptic complex La[N(SiMe3)(C6H3- interactions are also indicated by more obtuse bond angles
iPr2-2,6)]2(BH4)(thf) (7) in a consecutive ligand exchange La–N–Cipso
.
reaction with another equiv. of K[N(SiMe3)(C6H3iPr2-2,6)]
in hexane (Scheme 5). After stirring at ambient temperature
for 24 h the cloudy suspension was filtered, the solvent re-
duced, and the remaining solution stored at –35 °C. Color-
less crystals formed within another 24 h and were examined
by IR and NMR spectroscopy, elemental analysis, and X-
1
ray crystallography. Both H and 13C NMR spectroscopy
as well as elemental analysis pointed toward the successful
synthesis of putative La[N(SiMe3)(C6H3iPr2-2,6)]3 (9). The
proton resonances are in the expected regions similar to
those of the potassium amide K[N(SiMe3)(C6H3iPr2-2,6)].
As in the spectrum of La[N(SiMe3)(C6H3iPr2-2,6)]2(BH4)-
(thf) (7) two sets of signals are observed for the methyl
groups of the isopropyl substituents indicating a rigid struc-
ture even in solution due to a hindered rotation around the
C–N axis of the 2,6-diisopropylphenyl moieties. Compound
9 could be also obtained from the reaction of La(BH4)3-
(thf)3 with 3 equiv. of K[N(SiMe3)(C6H3iPr2-2,6)] in hexane
(Scheme 5).
Figure 9. Molecular structure of complex La[N(SiMe3)(C6H3iPr2-
2,6)]3 (9). Non-H atoms are represented by atomic displacement
ellipsoids at the 50% level. Hydrogen atoms are omitted for clarity.
Table 6. Selected bond lengths [Å] and angles [°] for 9.
Bond lengths
Bond angles
La–N1
La–N2
La–N3
La–C1
La–C16
La–C31
2.379(3)
N1–La1–N2
N2–La1–N3
N3–La1–N1
La1–N1–C1
La1–N2–C16
Si3–N3–C31
La1–N1–Si1
La1–N2–Si2
La1–N3–Si3
111.86(9)
112.43(9)
113.10(9)
108.2(2)
107.4(2)
120.7(2)
128.5(1)
129.5(1)
129.5(1)
2.369(3)
2.372(3)
3.130(3)
3.110(3)
3.129(3)
Scheme 5. Synthesis of the homoleptic lanthanum amide 9.
The solid-state structure of 9 was determined by X-ray
crystallography (Figure 9, Table 6), albeit twinned, twofold
around direct axis 1 0 1 in a ratio 2:1. Refinement was per-
formed on the main component only. A hoax electron den-
Conclusions
Heteroleptic rare-earth metal complexes bearing the
sity in close proximity to the metal center (4.26 e/Å3) re- bulky amido ligand [N(SiMe3)(C6H3iPr2-2,6)] and the an-
flects the anomalous effects of the twinning. The lanthanum ionic coligands [Cl] or [BH4] are readily accessible via salt
metal center in 9 is coordinated by three amido ligands in metathesis reactions, employing LnCl3(thf)x or Ln(BH4)3-
a distorted trigonal planar fashion. All three amido ligands (thf)3 as precursors. The product composition, be it the en-
are tilted in such a way that the trimethylsilyl groups are visaged monomeric alkali metal-free complexes or any un-
located above and the 2,6-diisopropylphenyl moieties be- desired ate derivatives, crucially depends on the solvent and
neath the N1N2N3 plane. Two of the isopropyl carbon choice of alkali metal amide precursor. For the larger rare-
atoms of each phenyl ring, namely C10/C11, C22/C23, C37/ earth metal centers, use of Li[N(SiMe3)(C6H3iPr2-2,6)] in
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Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
2,6) in thf or as a side product in the synthesis of 2. Colorless
thf as a solvent clearly favors the formation of ate com-
plexes and polymeric coligand-bridged compounds. The
combination K[N(SiMe3)(C6H3iPr2-2,6)]/hexane gives ac-
cess to alkali metal-free monolanthanide complexes
Ln[N(SiMe3)(C6H3iPr2-2,6)]2(BH4)(thf) and Ln[N(SiMe3)-
(C6H3iPr2-2,6)]3 while conducting the reaction in thf cannot
impede salt contamination. Using lanthanide triflates as
rare-earth metal precursors yielded mixtures of products
from which only the side product Li4(OTf)4(thf)6 could be
isolated and characterized. The large lanthanum centers can
accommodate three bulky amido ligands accomplishing the
homoleptic complex La[N(SiMe3)(C6H3iPr2-2,6)]3. Current
studies address the reactivity of such heteroleptic amide
complex toward alkylating reagents such as trimethylalumi-
num and the potential of the activated species in polymeri-
zation reactions, according to Scheme 1.
crystals were grown from saturated thf solutions. 1H NMR
3
(400.13 MHz, [D6]benzene): δ = 7.21 (d, JH,H = 6.8 Hz, 2 H,
3
C6H3), 6.94 (t, JH,H = 7.2 Hz, 1 H, C6H3), 4.19 (br. s, 2 H, CH),
3.35 (m, 12 H, thf), 1.35 (s, 12 H, iPr), 1.31 (m, 12 H, thf), 0.40 (s,
9 H, SiMe3) ppm. 13C{1H} NMR (100.61 MHz, [D6]benzene): δ =
143.1, 124.2, 123.4, 68.0 (thf), 28.5, 27.4, 25.5, 25.0, 23.8, 0.8
(SiMe3) ppm. C27H50LiNO3Si (471.72 gmol–1): calcd. C 68.75, H
10.68, N 2.97; found C 67.57, H 11.21, N 3.43.
Y[N(SiMe3)(C6H3iPr2-2,6)]Cl2(thf)3 (2): To
a suspension of
YCl3(thf)3.5 (147 mg, 0.33 mmol) in thf, LiN(SiMe3)(C6H3iPr2-2,6)
(168 mg, 0.66 mmol) dissolved in thf was slowly added. After hav-
ing been stirred for several minutes a colorless solution formed
which was further reacted at ambient temperature overnight. The
solvent was removed in vacuo and the remaining solid extracted
with hexane. The crude product (164 mg, 0.26 mmol, 80%) was re-
dissolved in a hexane/thf mixture. Colorless crystals formed under
slow evaporation of the solvents and were identified as 2 (the crys-
tallized yield was not determined). The reaction was rerun with
equimolar amounts of YCl3(thf)3.5 (212 mg, 0.47 mmol) and Li[N-
(SiMe3)(C6H3iPr2-2,6)] (121 mg, 0.47 mmol) yielding 52% of 2
(154 mg, 0.25 mmol) after extraction with hexane. 1H NMR
Experimental Section
General Information and Material: All of the manipulations of
metal complexes were performed under rigorous exclusion of air
and moisture in an argon-filled glovebox (MB Braun MB150B-G-
II; Ͻ1 ppm O2, Ͻ1 ppm H2O). Solvent pretreatment/purification
was performed with Grubbs columns (MBraun SPS, solvent purifi-
cation system). [D6]benzene was obtained from Aldrich, degassed,
dried with Na for 24 h, filtered, and stored in a glovebox.
Y(OTf)3 and Nd(OTf)3 were ordered from Aldrich and dried at
180 °C under high vacuum for 24 h before use. Nd[N(SiMe3)(C6H3-
iPr2-2,6)]2Cl,[7] HN(SiMe3)(C6H3iPr2-2,6)[30] and LiN(SiMe3)(C6H3-
iPr2-2,6)[30] were synthesized according to literature procedures.
Nd(BH4)3(thf)3 was synthesized by treating NdCl3(thf)1.75 with
NaBH4 in thf at ambient temperature for 48 h; similar procedures
have been presented previously.[31] NMR spectroscopic data were
obtained in [D6]benzene solution at 25 °C on a Bruker DMX-400
Avance (1H: 400.13 MHz; 13C: 100.61 MHz) and a Bruker-BIO-
SPIN-AV600 (5 mm cryo probe, 1H: 600.13 MHz; 13C:
3
(500.13 MHz, [D6]benzene): δ = 7.17 (d, JH,H = 7.2 Hz, 2 H,
3
C6H3), 7.02 (t, JH,H = 7.6 Hz, 1 H, C6H3), 4.31 (br. s, 2 H, iPr),
3
3.67 (s, thf), 1.54 (d, JH,H = 6.4 Hz, 6 H, iPr), 1.41 (s, thf), 1.37
3
(d, JH,H = 6.8 Hz, 6 H, iPr), 0.56 (s, 9 H, SiMe3) ppm. 13C{1H}
NMR (125.77 MHz, [D6]benzene): δ = 146.5, 144.6, 124.2, 123.3,
72.2 (thf), 27.5, 26.6 (thf), 25.9, 23.8, 4.1 ppm. IR (Nujol): ν = 1422
˜
(s), 1311 (m), 1244 (m), 1230 (m), 1179 (m), 1105 (w), 1040 (w),
1008 (w), 895 (s), 874 (s), 844 (s), 780 (s), 747 (w), 671 (w), 623 (vw),
526 (w), 439 (w), 405 (w) cm–1. C27H50Cl2NO3SiY (624.59 gmol–1):
calcd. C 51.92, H 8.07, N 2.24; found C 49.74, H 8.56, N 1.83.
{La[N(SiMe3)(C6H3iPr2-2,6)]2(thf)(µ-Cl)K(thf)2(µ-Cl)}n (3): LaCl3-
(thf)1.25 (50 mg, 0.15 mmol) and 2 equiv. of K[N(SiMe3)(C3H6iPr2-
2,6)] (86 mg, 0.30 mmol) were suspended in thf and stirred at ambi-
ent temperature overnight. Upon filtration the slightly yellow solu-
tion was reduced in volume by evaporation of the solvent under
vacuum and stored at –35 °C. Colorless crystals of 3 formed in 60%
1
150.91 MHz). H and 13C shifts are referenced to internal solvent
1
yield (87 mg, 0.09 mmol). H NMR (400.13 MHz, [D6]benzene): δ
resonances and reported relative to TMS. IR spectra were recorded
on a Nicolet Impact 410 FTIR spectrometer using Nujol mulls
sandwiched between CsI plates. Elemental analyses were performed
on an Elementar Vario EL III.
= 7.09 (br., 4 H, C6H3), 6.86 (br., 2 H, C6H3), 3.81 (br., CHMe2),
3.49 (br., thf), 1.37 (br., CHMe2), 1.20 (br., thf), 1.18 (br., CHMe2),
0.49 (br., SiMe3) ppm. 13C{1H} NMR (100.61 MHz, [D6]benzene):
δ = 124.7 (ortho-C C6H3), 123.3 (para-C C6H3), 68.1 (thf), 28.5
(CHMe ), 25.7 (thf), 23.8 (CHMe ), 4.1 (SiC) ppm. IR (Nujol): ν
˜
K[N(SiMe3)(C3H6iPr2-2,6)]: To a solution of HN(SiMe3)(C6H3-
iPr2-2,6) (125 mg, 0.50 mmol) in 10 mL hexane a suspension of po-
tassium bis(trimethylsilyl)amide (100 mg, 0.50 mmol) in hexane
was added and the reaction mixture stirred at ambient temperature
overnight. Then the solvent was decanted off and the remaining
white solid was washed 3 times with equal amounts of hexane
(5 mL). K[N(SiMe3)(C3H6iPr2-2,6)] (115 mg, 0.40 mmol) formed
with 81% yield. 1H NMR (400.13 MHz, [D6]benzene): δ = 6.99 (d,
2
2
= 1308 (w), 1243 (m), 1197 (w), 1110 (w), 1042 (w), 922 (m), 876
(w), 840 (m), 783 (m), 721 (m), 654 (w), 612 (w), 574 (w) cm–1.
C42H76Cl2KLaN2O3Si2 (962.14 gmol–1): calcd. C 52.43, H 7.96, N
2.91; found C 52.14, H 7.94, N 3.06.
[Nd{N(SiMe3)(C6H3iPr2-2,6)}2(BH4)2][Li(thf)4] (4): Nd(BH4)3(thf)3
(91 mg, 0.22 mmol) was dissolved in thf and a solution of Li[N-
(SiMe3)(C6H3iPr2-2,6)] (115 mg, 0.45 mmol) in thf added. The blue
solution was stirred at ambient temperature for 48 h. Then the vol-
ume was reduced by evaporation of the solvent and the reaction
mixture stored at –35 °C. Blue crystals formed which were iden-
tified as 4 by X-ray structure analysis (193 mg, 0.20 mmol, 91%).
1H NMR (600.13 MHz, [D6]benzene): δ = 34.44 (BH4), 22.82,
16.37, 13.54, 12.89, 11.87, 10.49, 5.23, 4.68, 4.54, 4.31, 3.60, –4.44,
–5.82 br, –20.28 ppm. 13C{1H} NMR (150.91 MHz, [D6]benzene):
δ = 145.5, 144.6, 143.0, 124.2, 123.3, 65.7, 40.4, 29.7, 28.4, 27.5,
3
3JH,H = 7.3 Hz, 2 H, C6H3), 6.51 (t, JH,H = 7.2 Hz, 1 H, C6H3),
3
3
3.81 (sept, JH,H = 6.9 Hz, 2 H, CHMe2), 1.24 (d, JH,H = 6.7 Hz,
12 H, CHMe2), 0.36 (s, 9 H, SiMe3) ppm. 13C{1H} NMR
(100.61 MHz, [D6]benzene): δ = 141.7 (ortho-C C6H3), 122.9 (meta-
C C6H3), 111.8 (para-C C6H3), 27.0 (CHMe2), 23.8 (CHMe2), 5.2
(SiC) ppm. IR (Nujol): ν = 1880 (w), 1842 (w), 1801 (w), 1578 (m),
˜
1417 (s), 1344 (s), 1295 (m), 1260 (m), 1227 (m), 1153 (w), 1132
(w), 1118 (w), 1102 (w), 1045 (m), 980 (s), 939 (w), 925 (w), 838
(s), 805 (s), 756 (s), 745 (m), 647 (m), 609 (w), 468 (w) cm–1.
25.2, 24.2, 23.9, 18.8, 3.4, 0.8 ppm. IR (Nujol): ν = 2432 (vs) cm–1
˜
LiN(SiMe3)(C6H3iPr2-2,6)(thf)3 (1): Compound 1 could be ob-
tained by dissolving the donor-free species LiN(SiMe3)(C6H3iPr2-
(BH4), 2213 (vs), br. (BH4), 1900 (vw), 1845 (vw), 1585 (m), 1421
(s), 1359 (m), 1309 (s), 1251 (vs), 1178 (vs), 1104 (s), 1043 (vs), 892
Eur. J. Inorg. Chem. 2010, 2841–2852
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2849

C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
FULL PAPER
(vs), 838 (vs), 774 (s), 741 (m), 667 (m), 615 (m), 569 (w), 522 (m),
suspension stirred at ambient temperature until a clear solution
426 cm–1 (m). C46H92B2LiN2NdO4Si2 (966.21 gmol–1): calcd. C developed. The solvent was evaporated and the product mixture
57.18, H 9.60, N 2.90; found C 57.11, H 10.73, N 2.78.
repeatedly extracted with hexane. The remaining white solid
(90 mg, 0.09 mmol, 72%) was dissolved in a hexane/thf mixture,
affording 8 as colorless crystals.
{Nd[N(SiMe3)(C6H3iPr2-2,6)]2(µ-BH4)Li(thf)2(µ-BH4)}n (5): Solid
Nd(BH4)3(thf)3 (81 mg, 0.2 mmol) and Li[N(SiMe3)(C6H3iPr2-2,6)]
(102 mg, 0.40 mmol) were mixed and suspended in 10 mL hexane.
The slurry turned blue after a few minutes and was stirred over-
night at ambient temperature. After filtration, the remaining blue
solution was reduced in volume by evaporation of the solvent. Stor-
age at –35 °C produced crystals which were identified as 5 by X-
ray crystallography (100 mg, 0.12 mmol, 61%). 1H NMR
(400.13 MHz, [D6]benzene): δ = 21.85, 20.03, 18.73, 16.17 (br),
12.56, 9.49, 9.02, 7.88, 7.13, 7.02, 4.80, 1.94, 0.07, –0.59, 0.88,
–2.20, –8.63 ppm. 13C{1H} NMR (100.61 MHz, [D6]benzene): δ =
216.4, 145.5, 123.3, 114.6 (vbr), 63.9, 40.3, 28.4, 22.2, 19.2,
Route II: Nd(OTf)3 (159 mg, 0.27 mmol) was suspended in thf and
Li[N(SiMe3)(C6H3iPr2-2,6)] (137 mg, 0.46 mmol) dissolved in thf
added, resulting in a green solution with a fine precipitate. The
reaction mixture was stirred overnight and the solvent removed un-
der vacuum giving a green oil. Extraction with 2ϫ5 mL hexane
gave 8 as white hexane insoluble powder (99 mg, 0.09 mmol, 70%).
Route III: Upon stirring at ambient temperature, the reaction
mixtures of route I/II were reduced in volume and stored at
–35 °C, giving colorless crystals of
8
exclusively. 1H NMR
(400.13 MHz, [D6]benzene): δ
= 3.53 (thf), 1.32 (thf) ppm.
2.0 ppm. IR (Nujol): ν = 2430 (w, BH ), 2360 (m, BH ), 2338 (m,
˜
4
4
C28H48F12Li4O18S4·C4H8O (1128.78 gmol–1): calcd. C 34.05, H
BH4), 1423 (m), 1360 (m), 1238 (m), 1175 (m), 1102 (m), 1047 (m),
922 (m), 890 (w), 835 (m), 778 (m), 656 (w), 618 (w), 566 (w), 514
(w) cm–1. C38H76B2LiN2NdO2Si2 (821.97 gmol–1): calcd. C 55.53,
H 9.32, N 3.41; found C 55.56, H 8.81, N 3.28.
5.00; found C 34.6, H 4.6.
La[N(SiMe3)(C6H3iPr2-2,6)]3 (9): Route I: Compound 7 (78 mg,
0.11 mmol) and K[N(SiMe3)(C6H3iPr2-2,6)] (31 mg, 0.11 mmol)
were stirred in hexane at ambient temperature for 24 h. Any insolu-
ble parts of the slightly green, cloudy solution were filtered off. The
volume was reduced by evaporation of the solvent and the solution
stored at –35 °C to yield colorless crystals (41 mg, 0.05 mmol,
43%).
Nd[N(SiMe3)(C6H3iPr2-2,6)]2(BH4)(thf) (6): Solid Nd(BH4)3(thf)3
(162 mg, 0.40 mmol) and K[N(SiMe3)(C3H6iPr2-2,6)] (230 mg,
0.80 mmol) were combined and suspended in 10 mL of hexane. The
green suspension was stirred at ambient temperature for 24 h in
order to drive the reaction to completion. After filtration the green
solution was concentrated by evaporation of the solvent and sub-
sequently stored at –35 °C yielding blue crystals of 6 in 64% yield
(186 mg, 0.26 mmol). 1H NMR (400.13 MHz, [D6]benzene): δ =
20.88, 17.64, 8.73, 7.15, 4.67, 1.23, 0.88, 0.10, –1.92 ppm. 13C{1H}
NMR (100.61 MHz, [D6]benzene): δ = 152.8, 123.3, 31.9, 28.5,
Route II: To a suspension of La(BH4)3(thf)3 (80 mg, 0.2 mmol) in
10 mL hexane was slowly added a suspension of K[N(SiMe3)(C6H3-
iPr2-2,6)] (172.5 mg, 0.6 mmol) in 5 mL hexane. The reaction mix-
ture was stirred at ambient temperature for 24 h, then reduced in
volume, and finally the insoluble parts filtered off. Colorless crys-
tals of 9 were obtained at –35 °C (97 mg, 0.11 mmol, 55%). 1H
23.9, 23.0, 15.9, 14.3, 0.8 ppm. IR (Nujol): ν = 3044 (m), 2454 (m,
˜
3
BH4), 2343 (w), 2204 (m, BH4), 2144 (m, BH4), 1915 (w), 1856 (w),
1586 (w), 1415 (s), 1308 (m), 1246 (s), 1230 (s), 1189 (s), 1110 (m),
1097 (m), 1044 (m), 1012 (m), 909 (s), 884 (s), 833 (s), 775 (s), 746
(s), 675 (w), 653 (m), 615 (w), 585 (w), 569 (w), 503 (s), 429 (m)
cm–1. C34H64BN2NdOSi2 (728.08 gmol–1): calcd. C 56.09, H 8.86,
N 3.85; found C 56.33, H 9.26, N 3.87.
NMR (400.13 MHz, [D6]benzene): δ = 7.00 (d, JH,H = 7.1 Hz, 6
3
3
H, C6H3), 6.91 (t, JH,H = 7.5 Hz, 3 H, C6H3), 3.44 (sept, JH,H
=
6.9 Hz, 3 H, CHMe2), 3.36 (br., 3 H, CHMe2) 1.23 (br., 36 H,
CHMe2), 0.39 (s, 27 H, SiMe3) ppm. 13C{1H} NMR (100.61 MHz,
[D6]benzene): δ = 125.5 (ipso-C C6H3), 124.2 (ortho-C C6H3), 123.3
(meta-C C6H3), 123.0 (para-C C6H3), 27.5 (CHMe2), 23.0
(CHMe ), 3.9 (SiC) ppm. IR (Nujol): ν = 1583 (w), 1420 (m), 1333
˜
2
La[N(SiMe3)(C6H3iPr2-2,6)]2(BH4)(thf) (7): Solid La(BH4)3(thf)3
(136 mg, 0.34 mmol) and 2 equiv. of K[N(SiMe3)(C3H6iPr2-2,6)]
(195 mg, 0.68 mmol) were mixed and suspended in hexane. The
slightly yellow suspension was stirred at ambient temperature over-
night. The solution was then filtered, reduced in volume, and stored
at –35 °C. Colorless crystals formed which were identified as 7
(crystallized yield 129 mg, 0.18 mmol 52%). 1H NMR
(w), 1303 (m), 1246 (m), 1227 (m), 1181 (s), 1148 (w), 1104 (m),
1050 (w), 1037 (w), 914 (s), 876 (m), 840 (s), 772 (s), 745 (m), 731
(m), 659 (m), 617 (w), 568 (w), 508 (m), 443 (w), 424 (m) cm–1.
C45H78LaN3Si3 (884.3 gmol–1): calcd. C 61.12, H 8.89, N 4.75;
found C 60.98, H 7.96, N 4.68.
Crystallographic Data Collection and Refinement: Crystals of 1–8
were grown by standard techniques from saturated solutions using
thf (1, 3, 4), hexane/thf (2, 8), or hexane (5, 6, 7, 9) at –35 °C.
Suitable single crystals of 1–5, 7 and 8 were selected in a glovebox,
coated with Paratone-N, fixed in a nylon loop, and measured on a
Bruker SMART 2K CCD diffractometer. Compounds 6 and 9 were
measured on an APEXII Ultra rotating anode diffractometer. All
data were collected using graphite monochromated Mo-Kα radia-
tion (λ = 0.71073 Å) performing ω-scans in four φ positions. Raw
data were reduced and scaled with program SAINT.[32] Corrections
for absorption effects were applied using SADABS[33] or
SHELXTL.[34] The structures were solved by a combination of di-
rect methods (SHELXS-97[34]) and difference-Fourier syntheses
(SHELXL97).[34] Final model refinement was done using
SHELXL97.[34] All plots were generated using the program OR-
TEP-3.[35] Further details of the refinement and crystallographic
data are listed in Tables 7 and 8 and in the CIF files.
3
(400.13 MHz, [D6]benzene): δ = 7.02 (d, JH,H = 7.5 Hz, 4 H,
C6H3), 6.84 (t, 3JH,H = 7.5 Hz, 2 H, C6H3), 3.77 (br., 4 H, CHMe2),
1
2.63 (br., 4 H, thf), 1.82 (br. q, JB,H = 80.3 Hz, 4 H, BH4) 1.22
3
(br., 12 H, CHMe2), 1.20 (br., 4 H, thf), 1.18 (d, JH,H = 6.5 Hz,
12 H, CHMe2), 0.50 (s, 18 H, SiMe3) ppm. 13C{1H} NMR
(100.61 MHz, [D6]benzene): δ = 147.2 (ipso-C C6H3), 143.9 (ortho-
C C6H3), 125.0 (meta-C C6H3), 123.1 (para-C C6H3), 70.4 (thf),
27.6 (CHMe2), 25.7 (thf), 23.0 (CHMe2), 4.1 (SiC) ppm. IR (Nu-
jol): ν = 2448 (w, BH ), 2201 (w, BH ), 2143 (w, BH ), 1415 (m),
˜
4
4
4
1312 (w), 1243 (m), 1197 (w), 1170 (w), 1110 (w), 1091 (w), 1042
(w), 1012 (w), 925 (m), 838 (m), 776 (m), 656 (w), 620 (w), 501 (w)
cm–1. C34H64BLaN2OSi2 (722.77 gmol–1): calcd. C 56.50, H 8.93,
N 3.88; found C 56.55, H 9.20, N 3.88.
Li4(OTf)4(thf)6 (8): Colorless crystals of 8 were obtained from the
reaction of Ln(OTf)3 (Ln = Y, Nd) with 2 equiv. of Li[N(SiMe3)-
(C6H3iPr2-2,6)] in thf.
Route I: To Y(OTf)3 (123 mg, 0.23 mmol) in thf Li[N(SiMe3)(C6H3-
iPr2-2,6)] (117 mg, 0.46 mmol) dissolved in thf was added and the
CCDC-767394 (for 1), -767395 (for 2), -767396 (for 3), -767397 (for
4), -767398 (for 5), -767399 (for 6), -767400 (for 7), -767401 (for
2850
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2841–2852

Rare-Earth Metal Phenyl(trimethylsilyl)amide Complexes
Table 7. Summary of crystallographic data and structure refinement for compounds 1–5.
1
2
3
4
5
Chemical formula C27H50LiNO3Si C27H50Cl2NO3SiY C42H76Cl2KLaN2O3Si2 C46H92B2LiN2NdO4Si2 C38H76B2LiN2NdO2Si2
Mr [gmol–1]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
471.71
monoclinic
P21/n
10.7559(4)
16.2830(6)
16.3705(6)
90.00
92.265(1)
90.00
2864.86(18)
4
624.58
monoclinic
P21/n
11.4046(4)
24.1927(9)
11.6362(4)
90.00
91.145(1)
90.00
3209.9(2)
4
962.14
orthorhombic
Pbca
14.8094(4)
15.7724(5)
42.7869(13)
90
90
90
9994.2(5)
8
966.20
821.99
monoclinic
Cc
22.0482(8)
14.1974(5)
14.4931(5)
90
94.447(1)
90
4523.1(3)
4
triclinic
¯
P1
13.1483(5)
13.5289(5)
15.2514(5)
85.522(1)
80.881(1)
83.362(1)
2655.76(17)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
F(000)
T [K]
1040
100(2)
1.094
0.108
0.0636
0.1448
1.050
1320
123(2)
1.292
2.047
0.0297
0.0779
1.092
4032
123(2)
1.279
1030
123(2)
1.208
1.061
0.0305
0.0833
1.109
1740
123(2)
1.207
ρcalcd [gcm–3]
µ [mm–1]
R1 (obsd.)[a]
wR2 (all)[b]
S[c]
1.128
1.231
0.0427
0.1069
1.285
0.0169
0.0432
1.071
2
2 2
2
2 2
[a] R1 = Σ(|Fo| – |Fc|)/Σ|Fo|, Fo Ͼ 4σ(Fo). [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2. [c] S = [Σw(Fo – Fc ) /(no – np)]1/2
.
Table 8. Summary of crystallographic data and structure refinement for compounds 6–9.
6
7
8
9
Chemical formula
Mr [gmol–1]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C34H64BN2NdOSi2
728.10
C34H64BLaN2OSi2
722.77
C28H48F12Li4O18S4
1056.70
monoclinic
P21/n
9.5804(7)
19.1727(14)
13.0298(10)
90.00
99.640(2)
90.00
2359.5(3)
2
C45H78LaN3Si3
884.28
triclinic
triclinic
triclinic
¯
¯
¯
P1
P1
P1
9.7535(3)
12.5334(4)
17.6518(8)
105.622(2).
92.834 (1)
109.715(1)
1932.76(12)
2
9.7900(2)
12.5642(2)
17.6846(3)
105.83(1)
92.40(1)
109.86(1)
1946.3(2)
2
13.0718(12)
13.1192(12)
15.0994(14)
99.759(1)
99.609(1)
103.273(1)
2425.9(4)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
F(000)
T [K]
766
123(2)
1.251
1.431
0.0166
0.0438
1.062
760
123(2)
1.233
1.185
0.0252
0.0532
1.055
1088
123(2)
1.487
0.313
0.0698
0.1758
1.096
936
123(2)
1.211
0.986
0.0413
0.1090
1.035
ρcalcd [gcm–3]
µ [mm–1]
R1 (obsd.)[a]
wR2 (all)[b]
S[c]
2
2 2
2
2 2
[a] R1 = Σ(|Fo| – |Fc|)/Σ|Fo|, Fo Ͼ 4σ(Fo). [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2. [c] S = [Σw(Fo – Fc ) /(no – np)]1/2
.
[4]
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for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[5]
[6]
[7]
[8]
[9]
[10]
Acknowledgments
We thank the Norwegian Research Council (Project No. 171245/
V30) and the University of Bergen for generous support.
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2851

C. Schädle, C. Meermann, K. W. Törnroos, R. Anwander
FULL PAPER
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Received: February 24, 2010
Published Online: April 23, 2010
2852
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Eur. J. Inorg. Chem. 2010, 2841–2852