Organoaluminum-assisted formation of rare-earth metal imide complexes

Article abstract of DOI:10.1021/om300443x

The μ₂-imide complexes [Ln(AlMe₄) (μ₂-Nmes*)]_x (mes* = C₆H ₂tBu₃-2,4,6) (Ln = Y, La, Nd, Lu) are synthesized from homoleptic heterobimetallic complexes Ln(AlMe₄)₃ utilizing two distinct protocols: reaction with 2,4,6-tri-tert-butylaniline in hexane via methane elimination or with potassium (2,4,6-tri-tert-butylphenyl)amide in toluene according to a salt metathesis-protonolysis tandem reaction. Complexes [Ln(AlMe₄)(μ₂-Nmes*)]₂ (Ln = Y, Nd, Lu) revealed isomorphous solid-state structures, featuring an asymmetrically bridged Ln₂N₂ core with very short Ln-N distances (2.071(1)-2.155(3) A). In the solid-state structure of the lanthanum derivative similar dimeric subunits assemble as La₄Al₄ oligomers through μ₂-η¹:η²-bridging tetramethylaluminato moieties. [La(AlMe₄)(μ₂- Nmes*)]₄ displays La - -arene interactions (2.702(6) A) that are considerably shorter than the La(μ-CH₃) _aluminato bond lengths.

Full text of DOI:10.1021/om300443x

Article
pubs.acs.org/Organometallics
Organoaluminum-Assisted Formation of Rare-Earth Metal Imide
Complexes
Dorothea Schadle,† Christoph Schadle,† Karl W. Tornroos,‡ and Reiner Anwander*,†
̈
̈
̈
†Institut fur Anorganische Chemie, Universitat Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany
̈
̈
̈
̈
‡Department of Chemistry, University of Bergen, Alleg
́
aten 41, 5007 Bergen, Norway
S
* Supporting Information
ABSTRACT: The μ2-imide complexes [Ln(AlMe4)(μ2-Nmes*)]x (mes* = C6H2tBu3-
2,4,6) (Ln = Y, La, Nd, Lu) are synthesized from homoleptic heterobimetallic complexes
Ln(AlMe4)3 utilizing two distinct protocols: reaction with 2,4,6-tri-tert-butylaniline in
hexane via methane elimination or with potassium (2,4,6-tri-tert-butylphenyl)amide in
toluene according to a salt metathesis−protonolysis tandem reaction. Complexes
[Ln(AlMe4)(μ2-Nmes*)]2 (Ln = Y, Nd, Lu) revealed isomorphous solid-state structures,
featuring an asymmetrically bridged Ln2N2 core with very short Ln−N distances
(2.071(1)−2.155(3) Å). In the solid-state structure of the lanthanum derivative similar
dimeric subunits assemble as La4Al4 oligomers through μ2-η1:η2-bridging tetramethylalu-
minato moieties. [La(AlMe4)(μ2-Nmes*)]4 displays La---arene interactions (2.702(6) Å)
that are considerably shorter than the La(μ-CH3)aluminato bond lengths.
25
shown that homoleptic tetramethylaluminates Ln(AlMe4)3
INTRODUCTION
■
Metal imido (MNR) moieties1 engage in a multitude of
chemical transformations,2 as evidenced for C−H bond
activation,3 metathesis of carbonyl and carbodiimide function-
alities,4 catalytic imine metathesis,5 hydroamination of alkynes,6
and metallacycle formation with alkenes and alkynes.6b,7
Moreover, imido ligands were utilized as ancillaries in transition
metal alkylidene complexes to promote stereoselective olefin
metathesis and polymerization.8 In contrast to the numerous
examples of transition metal and actinide imide complexes,9
lanthanide congeners remained scarce (Chart 1: A−H feature
lanthanide imide complexes structurally authenticated by X-ray
crystallography along with the synthesis protocols).10 This is
somewhat surprising since Bochkarev and Schumann et al.
provided structural evidence for LnNR moieties already in
1991 via the tetranuclear complex [Yb4(μ-η2:η2-Ph2N2)4(μ3-
PhN)2(thf)4] (A).11
react selectively with potassium (2,4,6-tri-tert-butylphenyl)-
amide in toluene via a salt metathesis−protonolysis tandem
reaction or with 2,4,6-tri-tert-butylaniline in hexane according
to a methane elimination reaction, affording complexes of the
type [Ln(AlMe4)(μ2-Nmes*)]x (mes* = C6H2tBu3-2,4,6) (Ln
= Y, La, Nd, Lu).
RESULTS AND DISCUSSION
■
Clearly, the present study has been spurred by the isolation and
structural characterization of the trialkylaluminum adducts [(μ-
ArN)Sm(μ-NHAr)(μ-Me)AlMe2]2 (G)20 and LDoSc(μ-
NHAr)(μ-Me)AlMe2] (H, LDo = N[2-P(CHMe2)2-4-methyl-
phenyl]2, Ar = C6H3iPr2-2,6),21 obtained by treatment of
primary amide complexes with AlMe3. We have recently
embarked on the organoaluminum-assisted formation of rare-
earth metal methylene, methine, and carbide species involving
methyl group deprotonation as shown in Scheme 1 (XHR =
CH3).26,27 A more general applicability of this strategy might
implicate the formation of imido moieties as well (X = N).
Initially, we simply reacted homoleptic Ln(AlMe4)3 (Ln = Y
(1a), La (1b), Nd (1c), Lu (1d)) with bulky 2,4,6-tri-tert-
butylaniline 2. The envisaged protonolysis and consecutive
methylaluminum-assisted proton abstraction involving putative
transient primary amide complexes 4 did indeed occur.
However, such imido species [Ln(AlMe4)(μ2-Nmes*)]2 (5)
formed only for the smaller-sized rare-earth metals in moderate
yields (Scheme 2, route 1). Quantitative yields were obtained
Overall, four synthesis approaches for Ln imide complexes
seem feasible, comprising (a) the 1,2-addition of reactive Ln−X
bonds or redoxactive metals across NC unsaturated substrates
(e.g., azobenzene or nitriles; A−C),11−14 (b) salt metathesis
utilizing magnesium imides (D),15−17 (c) nucleophilic degra-
dation of a β-diketiminato ancillary (E),18 and (d) deprotona-
tion of rare-earth metal primary amides [Ln−NHR] (F−
I).19−22 By applying a Lewis base-assisted alkane elimination
Chen et al. recently synthesized the first scandium complexes
with terminal imido ligands (I),22 at the same time assessing
their reactivity.22b,23 Strikingly, the synthesis protocols applied
so far are exceedingly impaired by incomplete deprotonation,24
ate complexation, cluster formation, and incompatibility of the
entire Ln(III) size range. Here we report on imide synthesis
protocols that are feasible for a large Ln(III) size range. It is
Received: May 22, 2012
Published: July 11, 2012
© 2012 American Chemical Society
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Chart 1. Selected Examples of Rare-Earth Metal Imide Complexes
Scheme 1. Organoaluminum-Assisted Deprotonation
Reactions
Scheme 2. Synthesis of Donor-Free Rare-Earth Metal Imides
by applying a salt metathesis−protonolysis tandem reaction
using 1 and potassium salt 3 in toluene at ambient temperature
(Scheme 2, route 2).28 Most gratifyingly, even the lanthanum
derivative 5b was generated in moderate yield according to
route 2. It can be speculated that the concomitantly generated
extremely basic [K(AlMe4)] is involved in the transformation of
4 into 5 (Scheme 1).
Crystallized imide complexes 5 are insoluble in hexane, but
dissolve in toluene at elevated temperature. We assume that
complex G (Chart 1) is formed similarly by exploiting this
organoaluminum-assisted primary amido deprotonation and
involving intermediates such as those shown in Schemes 1 and
2. Treatment of homoleptic amide complexes [Ln(NR2)3],
however, can result in a multitude of alkylated species,29 which
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Article
is also indicated by the isolation of G in very low yields (ca.
10%).19 The synthesis of the lanthanum analogue of G from
[La(NHC6H3iPr2-2,6)3]2 and trimethylaluminum was not
successful.19 Also note that putative imide precursors [LLn-
(III)R(NHR)] featuring adjacent alkyl R and primary amido
ligands (L = ancillary ligand) do not readily undergo alkane
Table 1. Selected Bond Lengths [Å] and Angles [deg] of
Complexes 5a, 5c, and 5d
5a (Ln = Y)
5c (Ln = Nd)
5d (Ln = Lu)
Ln1−N1′
Ln1−N1
Ln1−C1
Ln1−C2
Ln1···C3
Ln1···C5
Ln1···C6
Ln1···Al1
2.1089(9)
2.2909(9)
2.515(1)
2.600(1)
4.164(2)
2.628(1)
2.718(1)
3.0909(4)
1.382(1)
84.87(4)
95.13(4)
176.20(8)
87.71(6)
82.41(4)
15.12(6)
2.155(3)
2.330(3)
2.786(6)
2.684(5)
3.701(7)
2.722(4)
2.071(1)
2.249(1)
2.456(2)
2.548(2)
4.132(2)
2.593(2)
2.680(2)
3.0306(5)
1.377(2)
85.42(5)
94.58(5)
176.8(1)
87.86(9)
84.44(6)
14.76(8)
elimination via the classical thermal pathways.24 The H NMR
1
and 13C NMR spectra of 5a (toluene-d8 at 50 °C) and 5b
(benzene-d6 at 26 °C) show the expected resonances for the
supermesityl substituents, meaning that only one set of signals
was observed (Figures S1−S4). In contrast, lutetium derivative
5d revealed two separate sets of resonances, which is ascribed
to restricted rotation around the Ar−N bond due to steric
repulsion of the supermesityl ligands at this smaller rare-earth
metal center (Figure S6). The tetramethylaluminato moiety of
5a displays a doublet at −0.33 ppm in the proton spectrum due
a
3.010(4)
3.124 (1)
1.388(4)
80.8(1)
N1−C5
N1′−Ln1−N1
Ln1′−N1−Ln1
Ln1′−N1−C5
Ln1−N1−C5
C1−Ln1−C2
C1−Ln1−C2−Al1
99.2(1)
168.8(3)
90.5(2)
1
to a two-bond H−89Y scalar coupling (2JYH = 2.51 Hz, δ(89Y)
75.27(17)
34.8(2)
= +396 ppm, T = 26 °C, 400.13 MHz, benzene-d6). The low
solubility of complexes 5 impeded the investigation of any
dynamic behavior at low temperatures. The proposed
a
Nd···C10.
1
intermediate 4a could not be detected by in situ H NMR
Å) and C13 (Ln = Y) (2.193(3)−2.342(3) Å), containing μ3-
capping imido ligands. The Nd−(μ3-N) distances in complex
[{Nd4(NPh)4I4(py)5(thf)2}·py]15 vary from 2.335(6) to
2.478(7) Å, being larger than the average Nd−N distance in
imide complex 5c. The Lu−N bond lengths in 5d are similar to
those in carboranyl complex [(ImDippN)Lu{η1:η5-
(Me2NCH2CH2)C2B9H10}(thf)]17e (2.068(2) Å) and com-
pound C13 (Ln = Lu) (2.192(4)−2.322(4) Å).
spectroscopic studies of the formation of 5a via [Y(AlMe4)3]
(1a) and H2Nmes* (2). A similar examination of the
corresponding lanthanum reaction indicated the disappearance
of the educt signals at the expense of a nonconclusive
multisignal NMR spectrum, corroborating that the lanthanum
imide complex 5b can be produced only via route 2. Efforts to
derivatize complexes 5 with pyridine or thf were unsuccessful,
leading to decomposition.
X-ray structure analyses revealed isomorphous dimeric
arrangements for the rare-earth metals Y (5a, Figure 1), Nd
The pronounced asymmetry of the Ln2N2 core most likely
originates from significant interactions between the ipso carbon
C5 as well as one ortho carbon (C6) of the bridging μ2-Nmes*
ligands and the rare-earth metal centers. As a consequence, the
anilido ligands coordinate in a η3 fashion. However, the
neodymium complex 5c rather displays a η2 coordination of the
Nmes* ligands with only one short Ln1···C5 contact. These
additional Ln···arene interactions are further evidenced by acute
Ln1−N1−C5 angles (87.71(6)−90.5(2)°), almost linear
Ln1′−N1−C5 angles (168.8(3)−176.8(1)°), and severe
distortions from planarity of the phenyl rings (5a: C7−C6−
C5−C10 19.2(2)°, C−C 1.381(2)−1.448(3) Å; cf., Table
S1).30 A similar T-shaped coordination geometry has been
previously observed in the bis(μ2-imido) samarium complex
G.19 Extensive interaction of the Ln(III) centers with the imido
ligand is also evident from close contacts to one of the methyl
groups of the tert-butyl substituents (Ln···C13: 5a, 2.838(1);
5d, 2.805(2) Å; Nd···C13: 5c, 2.984(4) Å). The Ln−C(μ2-Me)
bond lengths are slightly longer than reported for the
corresponding homoleptic complexes 1,25 which accounts for
the bending of the ligand. The latter deviation from planarity
increases with increasing metal size (Nd > Y ≈ Lu) (cf.,
interplanar angles C1−Ln1−C2−Al1, Table S1).31
Figure 1. ORTEP representation of the molecular structure of 5a with
atomic displacement parameters set at the 30% level. Hydrogen atoms
are omitted for clarity. Selected bond lengths [Å] and angles [deg] are
given in Table 1.
(5c, Figure S7), and Lu (5d, Figure S8), featuring an Ln2N2
core on a crystallographic inversion center (Table 1). The
geometry about the four-coordinate metal centers can best be
described as distorted tetrahedral with two methyl groups and
two imido nitrogen atoms in the corners. The rare-earth metal
atoms are asymmetrically bridged by two μ2-imido nitrogen
atoms, displaying one short (Ln−N, 5a: 2.1089(9) Å; 5c:
2.155(3) Å; 5d: 2.071(2) Å) and one long contact (Ln−N, 5a:
2.2909(9) Å; 5c: 2.330(3) Å; 5d: 2.249(1) Å). The Y−N bond
lengths in 5a are comparable with the distances in imidazolin-2-
iminate complex [(ImDippN)Y(η5-C2B9H11)(thf)2]17e (2.083(2)
Imide complex 5b of the largest rare-earth metal lanthanum
revealed a solid-state structure distinct from those of yttrium,
neodymium, and lutetium. Two dimeric subunits are connected
by two (μ2-η1:η2-AlMe4) ligands to form a La4Al4 oligomer
(Figure 2). The internal lanthanum centers of the complex
[La4(η2-AlMe4)2(μ2-η1:η2-AlMe4)2(μ2-Nmes*)4] (5b) are five-
coordinate when neglecting any secondary interactions caused
by the imido ligands. Three methyl groups of the bridging
tetramethylaluminato ligands and two imido ligands accomplish
a distorted trigonal bipyramidal coordination geometry. The
outer lanthanum atoms are formally four-coordinate by two
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Figure 2. ORTEP representation of the molecular structure of 5b with atomic displacement parameters set at the 30% level. Hydrogen atoms are
omitted for clarity. Selected bond distances [Å] and angles [deg]: La1−N1 2.221(5), La1−N2 2.414(5), La2−N1 2.315(5), La2−N2 2.231(5), La1−
C1 2.814(7), La1−C2 2.862(7), La2−C23 2.957(7), La2−C24 2.867(8), La2−C25′ 3.056(7), La1...C3 3.302(8), La1···C27 2.702(6), La1···C32
3.120(7), La2···C5 3.013(6), La2...C6 3.699(7), La1···Al1 3.094(2), La2···Al2 3.452(2), N1−C5 1.415(8), N2−C27 1.402(8), La1−N1−La2
102.3(2), La1−N2−La2 98.9(2), N1−La1−N2 78.3(2), N1−La2−N2 80.3(2), La1−N1−C5 152.5(4), La2−N1−C5 105.2(4), La2−N2−C27
175.1(4), La2−C25′−Al2′ 165.0(4), C23−La2−C24−Al2 −0.1(2), La1C1C2−Al1C1C2 60.4(3), La2C23C24−Al2C23C24 0.2(4).
methyl groups of the peripheral aluminato ligands and the two
imido moieties.
EXPERIMENTAL SECTION
■
General Considerations. All operations were performed with
rigorous exclusion of air and water, using standard Schlenk, high-
vacuum, and glovebox techniques (MBraun 200B; <1 ppm O2, <1
ppm H2O). Hexane and toluene were purified by using Grubbs
columns (MBraun SPS, solvent purification system) and stored inside
a glovebox. Benzene-d6 and toluene-d8 were obtained from Aldrich,
degassed, dried over Na for 24 h, and filtered. Primary amine 2,4,6-tri-
tert-butylaniline (2) was obtained from Aldrich and used as received.
Potassium bis(trimethylsilyl)amide was received from Fluka and
sublimed prior to use. Homoleptic Ln(AlMe4)3 (Ln = Y, La, Nd,
Lu)25 (1) were synthesized according to literature procedures. The
NMR spectra of air- and moisture-sensitive compounds were recorded
by using J. Young valve NMR tubes at variable temperature on a
Bruker AVII+400 spectrometer (1H: 400.13 MHz; 13C: 100.61 MHz)
and a Bruker AVII+500 spectrometer (1H: 500.13 MHz; 13C: 125.76
MHz). 1H and 13C shifts are referenced to internal solvent resonances
and reported in parts per million relative to TMS. Coupling constants
are given in Hertz. DRIFT spectra were recorded on a Nicolet 6700
FTIR spectrometer using dried KBr and KBr windows. Elemental
analyses were performed on an Elementar Vario Micro Cube.
Caution: Complexes Ln(AlMe4)3 (1) and volatiles containing
trialkylaluminum react violently when exposed to air.
A similar structural motif was observed previously in
complexes [Cp*6La6{(μ-Me)3AlMe}4(μ3-Cl)2(μ2-Cl)6] (av
2.795 versus 2.950(3) Å).32 The nonbridging AlMe4 ligands
show a markedly bent η2-coordination (C1−La1−C2−Al1
32.1(2)°). Such bending is characteristic for tetramethylalumi-
nato ligands bonded to sterically unsaturated Ln centers and
was observed before in half-sandwich complexes.31 The La−
C(μ-Me) bond lengths of av 2.838 Å are shorter than the bond
lengths of the nonbent bridging AlMe4 ligand and longer than
those in [Cp*La(AlMe4)2] (av 2.798 Å).30 The dimeric
subunits are asymmetrically bridged with La−N bond lengths
averaging 2.295 Å. As observed for 5a, 5c, and 5d, the formally
four-coordinate lanthanum centers show short La···Cipso
contacts, which enforce acute La1−N2−C27 angles
(85.8(3)°), hence affording a pronounced η2 coordination of
one of the two arylimido ligands. Strikingly, the La···C27ipso
contact (2.702(6) Å) is shorter than the shortest La−C(μ-
Me)aluminato bond length.
Potassium (2,4,6-Tri-tert-butylphenyl)amide (3). A solution of
2,4,6-tri-tert-butylaniline (265 mg, 1.01 mmol) in hexane (7 mL) was
added to a suspension of potassium bis(trimethylsilyl)amide (200 mg,
1.00 mmol) in hexane (1 mL). The reaction mixture was stirred for 2 d
at ambient temperature. The product was separated by centrifugation,
washed with hexane (3 × 5 mL), and dried in vacuo. Anilide 3 was
obtained as an off-white powder (292 mg, 0.97 mmol, 97%). The low
solubility of 3 in noncoordinating solvents did not allow for
characterization by 1H NMR and 13C{1H} NMR spectroscopy.
DRIFT IR (KBr): 2956s, 2900m, 2867m, 1596w, 1474w, 1463w,
1412s, 1386w, 1377w, 1359m, 1335w, 1273vs, 1237m, 1204w, 1126w,
883w, 825w, 787w, 727w, 699w, 627w, 514w cm−1. Anal. Calcd (%)
for C18H30KN (299.54 g mol−1): C 72.18, H 10.10, N 4.68. Found: C
71.82, H 9.82, N 4.69.
General Procedures for the Synthesis of [Ln(AlMe4)-
(Nmes*)]x (5). Route 1. A solution of 2,4,6-tri-tert-butylaniline
(H2Nmes*, 2) in hexane (3 mL) was added to a solution of
Ln(AlMe4)3 (1) in hexane (2 mL). The reaction mixture was stirred
for 8 h at 70 °C. The solution turned yellow (Y, Lu), and a precipitate
formed. The mixture was cooled to ambient temperature, upon which
the solid product was separated by centrifugation and washed with
CONCLUSIONS
■
The organoaluminum-assisted deprotonation reaction displays
a viable route for the synthesis of rare-earth metal imide
complexes. A salt metathesis−protonolysis tandem reaction
utilizing Ln(AlMe4)3 and [K(HNmes*)] (mes* = C6H2tBu3-
2,4,6) turned out to be particularly successful. Clearly, the
AlMe4 ligand demonstrates its highly flexible and ionic bonding
characteristics as well as its capability to adapt to new ligand
environments. Current work addresses the scope of these
reaction protocols, e.g., use of other primary amines or
applicability to other protic substrates such as primary
phosphines. It can be anticipated that the isolation and in-
depth characterization of these long-time elusive complexes in
combination with their derivatization and/or reactivity will
disclose a better understanding of the nature of such LnXR
bonding.
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Table 2. Crystallographic Data for Compounds 5a, 5b, 5c, and 5d
5a
5b
5c
5d
formula
color
C44H82Al2N2Y2
yellow
C88H164Al4La4N4
yellow
C44H82Al2Nd2N2
green
C44H82Al2Lu2N2
yellow
Mr [g mol−1
cryst syst
space group
a [Å]
]
870.90
1941.79
981.56
1043.02
monoclinic
C2/c
monoclinic
C2/c
triclinic
triclinic
P1
̅
P1
̅
24.1086(8)
11.7699(4)
20.4463(7)
90
10.5291(9)
14.5921(13)
17.0337(15)
76.6860(10)
80.847(2)
74.7430(10)
2443.4(4)
1
9.6377(15)
11.643(2)
12.2647(15)
62.306(12)
85.093(11)
88.038(13)
1214.1(3)
1
23.9903(9)
11.7282(5)
20.4162(8)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
Z
111.6504(4)
90
111.435(2)
90
5392.5(3)
4
5347.0(4)
4
F(000)
1856
1000
506
2112
T [K]
103(2)
1.073
123(2)
173(2)
100(2)
1.296
ρcalcd [g cm−3
]
1.320
1.342
μ [mm−1
]
a
2.200
1.789
2.179
3.729
R1 (obsd)
0.0227
0.0495
0.0448
0.0171
b
wR2 (all)
0.0605
0.1165
0.079
0.0384
c
S
1.083
0.983
1.041
1.065
a
b
c
2
2
2
R1 = ∑(|Fo| − |Fc|)/∑|Fo|, Fo > 4σ(Fo). wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2. S = [∑w(Fo − Fc2)2/(no − np)]1/2
.
hexane (2 × 2 mL). Compounds 5 were dried in vacuo and obtained as
yellow (Y, Lu) powders.
1276s, 1238m, 1186s, 1111w, 1044w, 999w, 869m, 838m, 789w, 777w,
749w, 711vs, 694vs, 619m, 579m, 548m, 509w, 481m, 454m, 411w
cm−1. Anal. Calcd (%) for C88H164Al4N4La4 (1941.82 g mol−1): C
54.43, H 8.51, N 2.89. Found: C 54.34, H 8.45, N 2.72.
Route 2. A solution of Ln(AlMe4)3 (1) in 3 mL of toluene was
added to a vigorously stirred suspension of potassium (2,4,6-tri-tert-
butylphenyl)amide ([K(HNmes*)]) (3) in 2 mL of toluene. The
reaction mixture was stirred for 2 h at ambient temperature, and the
toluene solution then separated by centrifugation, decanted, and
filtrated. The solid residue (product and [K(AlMe4)]) was extracted
with additional toluene (5 × 2 mL). The extract was dried under
vacuum and triturated with hexane (2 × 2 mL). Then the solid was
washed with hexane (2 × 2 mL), followed by drying under reduced
pressure. Compounds 5 were obtained as powders or by crystallization
from the mother liquor at ambient temperature.
[Y(AlMe4)(Nmes*)]2 (5a). Following route 1, Y(AlMe4)3 (1a, 133
mg, 0.38 mmol) and H2Nmes* (2, 99 mg, 0.38 mmol) yielded 5a as a
yellow powder (58 mg, 0.13 mmol, 35%). Following route 2,
Y(AlMe4)3 (1a, 35 mg, 0.10 mmol) and [K(HNmes*)] (3, 30 mg,
0.10 mmol) yielded [Y(AlMe4)(Nmes*)]2 as yellow crystals (44 mg,
0.10 mmol, quant.). 1H NMR (500 MHz, toluene-d8, 50 °C, TMS): δ
7.43 (s, 4H, HAryl), 1.48 (s, 36H, (C(CH3)3)ortho), 1.36 (s, 18H,
(C(CH3)3)para), −0.42 (s, 24H, Al(CH3)4) ppm. 13C NMR (126 MHz,
toluene-d8, 50 °C) δ 154.5 (Ar, Cipso), 139.0 (Ar, Cpara), 138.3 (Ar,
Cortho), 126.0 (Ar, Cmeta), 37.0 ((C(CH3)3)ortho), 34.6 ((C(CH3)3)para),
31.8 ((C(CH3)3)para), 31.6 ((C(CH3)3)ortho), −0.2 (Al(CH3)4) ppm.
89Y NMR from 1H−89Y HSQC, benzene-d6, 26 °C: δ 396 ppm.
DRIFT IR (KBr): 3015w, 2963s, 2886m, 2774w, 1589w, 1477m,
1460m, 1394m, 1377m, 1361m, 1340w, 1275m, 1245s, 1226m, 1200s,
1108w, 917w, 894w, 874w, 856m, 785w, 856m, 785m, 755m, 717s,
695vs, 664m, 638w, 610w, 580m, 547m, 506m, 477m, 460m, 440m
cm−1. Anal. Calcd (%) for C44H82Al2N2Y2 (870.91 g mol−1): C 60.68,
H 9.49, N 3.22. Found: C 60.79, H 9.46, N 3.10.
[Nd(AlMe4)(Nmes*)]2 (5c). Following route 1, [Nd(AlMe4)3 (1c,
81 mg, 0.20 mmol) and H2Nmes* (2, 52 mg, 0.20 mmol, in hexane (5
mL) yielded a green solution. The mixture was filtered and
concentrated in vacuo. After cooling to −35 °C a precipitate was
formed. The solid product was separated by centrifugation, washed
with hexane (2 × 2 mL), and dried in vacuo to give 5c as a green solid.
Crystallization from a hexane solution at −35 °C gave single crystals of
5c suitable for X-ray diffraction analysis (14 mg, 0.03 mmol, 14%
cryst). Following route 2, Nd(AlMe4)3 (1c, 203 mg, 0.50 mmol) and
[K(HNmes*)] (3, 150 mg, 0.50 mmol) yielded 5c as a green powder
1
(72 mg, 0.15 mmol, 29%). H NMR (400 MHz, benzene-d6, 26 °C,
TMS): δ 8.45 (brs, Δν1/2 =19 Hz, Al(CH3)4), 7.41 (s, HAryl), 1.41 (s,
54H, (C(CH3)3)ortho/para) ppm. DRIFT (KBr): 2963s, 2927s, 2886s,
2833m, 1569s, 1475m, 1431m, 1394w, 1364m, 1310vw, 1190s, 1122m,
1100m, 1031m, 880m, 800w, 700vs, 577m, 525m, 475m cm−1. Anal.
Calcd (%) for C44H82Al2N2Nd2 (981.58 g mol−1): C 53.84, H 8.42, N
2.85. Found: C 53.60, H 8.38, N 2.86.
[Lu(AlMe4)(Nmes*)]2 (5d). Following route 1, Lu(AlMe4)3 (1d,
44 mg, 0.10 mmol) and H2Nmes* (2, 26 mg, 0.10 mmol) yielded 5d
as a yellow powder (31 mg, 0.06 mmol, 60%). Following route 2,
Lu(AlMe4)3 (1d, 87 mg, 0.20 mmol) and [K(HNmes*)] (3, 60 mg,
0.20 mmol) yielded 5d as yellow crystals (104 mg, 0.20 mmol, quant.).
1H NMR (400 MHz, benzene-d6, 26 °C, TMS): δ 7.44 (s, 4H, HAryl),
1.51 (s, 36H, (C(CH3)3)ortho), 1.38 (s, 18H, (C(CH3)3)para), −0.10 (s,
24H, Al(CH3)4) ppm. 13C NMR (126 MHz, toluene-d8, 50 °C, TMS):
δ 157.3 (Ar, Cipso), 138.6 (Ar, Cpara), 137.0 (Ar, Cortho), 126.3 (Ar,
Cmeta), 37.2 ((C(CH3)3)ortho), 34.5 ((C(CH3)3)para), 31.8 ((C-
(CH3)3)para), 31.4 ((C(CH3)3)ortho), 1.9 (Al(CH3)4) ppm. DRIFT
(KBr): 3020w, 2989w, 2963s, 2869m, 2777w, 1590w, 1477m, 1463w,
1395m, 1376m, 1361m, 1341w, 1278m, 1246s, 1225m, 1202s, 1142w,
1108w, 918w, 895w, 874w, 585m, 784w, 755w, 717s, 695s, 663w,
637w, 611w, 577m, 548m, 504m, 477m, 460m, 441 m cm−1. Anal.
Calcd (%) for C44H82Al2N2Lu2 (1043.03 g/mol): C 50.67, H 7.92, N
2.69. Found: C 50.30, H 7.93, N 2.65.
[La(AlMe4)(Nmes*)]4 (5b). Route 1 led to degradation products.
Following route 2, La(AlMe4)3 (1b, 120 mg, 0.30 mmol) and
[K(HNmes*)] (3, 90 mg, 0.30 mmol) yielded 5b as a yellow powder
(53 mg, 0.11 mmol, 36%). The crystals were grown from a saturated
1
toluene solution at −35 °C. H NMR (400 MHz, benzene-d6, 26 °C,
TMS): δ 7.51 (s, 8H, HAryl), 1.46 (s, 72H, (C(CH3)3)ortho), 1.39 (s,
36H, (C(CH3)3)para), −0.36 (s, 48H, Al(CH3)4) ppm. 13C NMR (101
MHz, benzene-d6, 26 °C): δ 151.5 (Ar, Cipso), 142.1 (Ar, Cortho), 140.5
(Ar, Cpara), 125.7 (Ar, Cmeta), 36.9 ((C(CH3)3)ortho), 35.0
((C(CH3)3)para), 32.1 ((C(CH3)3)ortho/para), 1.6 (Al(CH3)4) ppm.
DRIFT (KBr): 2951vs, 2883s, 2787w, 1475w, 1404s, 1384m, 1361w,
X-ray Crystallography and Crystal Structure Determination
of Complexes 5. Crystals of 5a, 5b, 5c, and 5d were grown by
standard techniques from solutions using toluene/−40 °C (5a, 5b, 5d)
and hexane/−40 °C (5c). Suitable single crystals were selected in a
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Organometallics
Article
glovebox and coated with Paratone-N (Hampton Research) and fixed
in a nylon loop (5b) or on a glass fiber (5a, 5c, 5d). Data of 5a and 5b
were collected on a Bruker AXS TXS Ultra system using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å) performing 182°
ω-scans in four orthogonal ϕ positions. Raw data were collected using
the program APEX33 and integrated and reduced with the program
SAINT.34 Corrections for absorption effects were applied using
SHELXTL and/or SADABS.35 The scattering factor contribution for
one disordered toluene molecule was removed from the structure
factors by the use of the Squeeze routine in PLATON.36 Data of 5c
were collected on a STOE IPDSII system. The structure was solved by
direct methods using the Stoe X-Area and WinGX suite of programs
including SHELXS and SHELXL for structure solution and refine-
ment.37 Data of 5d were collected on a Bruker AXS APEXII system.
The scattering factor contribution for one disordered toluene molecule
was removed from the structure factors by the use of the Squeeze
routine in PLATON.36 Further details of the refinement and
crystallographic data are listed in Table 2 and in CIF files; CCDC
reference numbers 876146 (5a), 876147 (5b), 876148 (5c), and
876149 (5d). These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Hubregtse, T.; Dam, J.; Meetsma, A.; Teuben, J. H.; Hessen, B.
Organometallics 2008, 27, 4071.
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ASSOCIATED CONTENT
■
(10) Giesbrecht, G. R.; Gordon, J. C. Dalton Trans. 2004, 2387.
(11) Trifonov, A. A.; Bochkarev, M. N.; Schumann, H.; Loebel, J.
Angew. Chem., Int. Ed. Engl. 1991, 30, 1149.
(12) Beetstra, D. J.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Organometallics 2003, 22, 4372.
(13) (a) Cui, D.; Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2005,
44, 959. (b) Cui, D.; Tardif, O.; Hou, Z. J. Am. Chem. Soc. 2004, 126,
1312.
(14) Pan, C.-L.; Chen, W.; Song, S.; Zhang, H.; Li, X. Inorg. Chem.
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S
* Supporting Information
CIF files giving full crystallographic data for complexes of 5a,
5b, 5c, and 5d, 1H NMR spectra of compounds 5a (Figures S1
S2, and S3), 5b (Figure S4), 5c (Figure S5), and 5d (Figure
S6), ORTEP representations of 5c (Figure S7) and 5d (Figure
S8), and selected bond lengths and torsion angles of the phenyl
rings of complexes 5 (Table S1). This material is available free
of charge via the Internet at http://pubs.acs.org.
(15) Berthet, J.-C.; Thuer
2008, 5455.
(16) Hascall, T.; Ruhlandt-Senge, K.; Power, P. P. Angew. Chem., Int.
Ed. Engl. 1994, 33, 356.
́
y, P.; Ephritikhine, M. Eur. J. Inorg. Chem.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: (+49) 70171 29 2436. E-mail: reiner.anwander@uni-
tuebingen.de.
(17) Rare-earth metal complexes carrying imidazolin-2-iminato
ligands as ancillaries show also very short Ln−N bonds: (a) Panda,
T. K.; Randoll, S.; Hrib, C. G.; Jones, P. G.; Bannenberg, T.; Tamm,
M. Chem. Commun. 2007, 5007. (b) Panda, T. K.; Trambitas, A. G.;
Bannenberg, T.; Hrib, C. G.; Randoll, S.; Jones, P. G.; Tamm, M.
Inorg. Chem. 2009, 48, 5462. (c) Trambitas, A. G.; Panda, T. K.; Jenter,
J.; Roesky, P. W.; Daniliuc, C.; Hrib, C. G.; Jones, P. G.; Tamm, M.
Inorg. Chem. 2010, 49, 2435. (d) Trambitas, A. G.; Panda, T. K.;
Tamm, M. Z. Anorg. Allg. Chem. 2010, 636, 2156. (e) Trambitas, A. G.;
Yanf, J.; Melcher, D.; Daniliuc, C.; Jones, P. G.; Xie, Z.; Tamm, M.
Organometallics 2011, 30, 1122.
Notes
The authors declare no competing financial interest.
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