Mono-cyclopentadienyl complexes of lanthanum: Synthesis and characterization of anilido derivatives

Article abstract of DOI:10.1016/j.jorganchem.2004.03.042

Use of the bulky cyclopentadienyl ligand [η⁵ -C₅H₂ (SiMe₃)₃-1,2,4] ^- (Cp?) allows for the isolation of monomeric, mono-ring lanthanide species. As previously reported, (Cp?)K reacts with LaI₃(THF)₄ (THF=tetrahydrofuran) in THF/pyridine to form the mono-ring complex (Cp?) LaI₂(py)₃ (1) (py=pyridine); a minor product of this reaction is the bis-ring species (Cp?)₂LaI(py) (2). The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual intramolecular contacts. Addition of one equiv of KNHAr (Ar=2,6-ⁱPr₂C₆H₃) to complex 1 in THF generates the mono-anilido compound (Cp?) LaI(NHAr) (THF)₂ (3), which may be converted to the more stable pyridine adduct (Cp?)LaI(NHAr)(py)₂ (4) by the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group oriented trans to the iodide atom (N1-La1-I1=123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar C_s-symmetric structure with a slightly increased N_anilido-La-I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct (Cp?)LaI₂(bipy)(py) (5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp?)LaI(NHAr) (bipy)(py) (6) (bipy=2,2′-bipyridine); this compound may also be prepared by the addition of bipy to (Cp?)LaI(NHAr) (py)₂ (4). An X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp? ring, an iodide, an anilido group, a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis fashion (N_anilido-La-I=111.2(2)°), resulting in a complex with C₁ symmetry. Both (Cp?)LaI(NHAr)(py)₂ (4) and (Cp?)LaI(NHAr) (bipy)(py) (6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.

Full text of DOI:10.1016/j.jorganchem.2004.03.042

Journal of Organometallic Chemistry 689 (2004) 2177–2185
www.elsevier.com/locate/jorganchem
Mono-cyclopentadienyl complexes of lanthanum: synthesis
and characterization of anilido derivatives
*
Garth R. Giesbrecht , Gavin E. Collis, John C. Gordon, David L. Clark,
Brian L. Scott, Ned J. Hardman
Nuclear Materials Technology (NMT) Division, Chemistry (C) Division and the Glenn T. Seaborg Institute for Transactinium Science,
Los Alamos National Laboratory, Mailstop J514, Los Alamos, NM 87545, USA
Received 13 February 2004; accepted 29 March 2004
Abstract
Use of the bulky cyclopentadienyl ligand [g5-C5H2(SiMe3)3-1,2,4]ꢀ (Cp000) allows for the isolation of monomeric, mono-ring
lanthanide species. As previously reported, (Cp000)K reacts with LaI3(THF)4 (THF ¼ tetrahydrofuran) in THF/pyridine to form the
mono-ring complex (Cp000)LaI2(py)3 (1) (py ¼ pyridine); a minor product of this reaction is the bis-ring species (Cp000)2LaI(py) (2).
The solid state structure of 2 reveals a monomeric compound containing a pseudo-tetrahedral metal center exhibiting no unusual
intramolecular contacts. Addition of one equiv of KNHAr (Ar ¼ 2,6-iPr2C6H3) to complex 1 in THF generates the mono-anilido
compound (Cp000)LaI(NHAr)(THF)2 (3), which may be converted to the more stable pyridine adduct (Cp000)LaI(NHAr)(py)2 (4) by
the addition of pyridine to 3. An X-ray crystal structure of 3 indicated a trigonal bipyramidal metal center with the anilido group
oriented trans to the iodide atom (N1–La1–I1 ¼ 123.1(3)°). A structural study on the bis-pyridine adduct 4 revealed a similar Cs-
symmetric structure with a slightly increased Nanilido–La–I angle of 132.1(2)°. Addition of KNHAr to the di-iodo bipyridine adduct
(Cp000)LaI2(bipy)(py) (5), in which the two iodide atoms are cis-disposed, yields the mono-anilido complex (Cp000)LaI(NHAr)(bi-
py)(py) (6) (bipy ¼ 2,20-bipyridine); this compound may also be prepared by the addition of bipy to (Cp000)LaI(NHAr)(py)2 (4). An
X-ray diffraction study shows that the lanthanum center in 6 is octahedrally coordinated by a Cp000 ring, an iodide, an anilido group,
a pyridine molecule and two nitrogens of a bipy molecule. In this case, the anilido moiety and the iodide ligand are arranged in a cis
fashion (Nanilido–La–I ¼ 111.2(2)°), resulting in a complex with C1 symmetry. Both (Cp000)LaI(NHAr)(py)2 (4) and (Cp000)LaI(N-
HAr)(bipy)(py) (6) are inactive as catalysts for the hydroamination/cyclization of 2-amino-hex-5-ene.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Lanthanum; Bulky cyclopentadienyl; Anilido
1. Introduction
industry [7]. Early work by Marks et al. demonstrated
that high degrees of stereoselectivity were possible by
utilizing asymmetric catalysts incorporating chiral an-
cillary ligands; however, the organolanthanide com-
plexes often required lengthy and involved syntheses
[8–11]. Additionally, epimerization of C1-symmetric
lanthanide-based systems was often observed in the
presence of donor molecules, contributing to lowered
enantioselectivities. More recently, Livinghouse and co-
workers have revealed that non-cyclopentadienyl based
systems such as C2-symmetric bis-amides [12] and che-
lating bis-thiophosphinic amidates [13] result in im-
proved stereoselectivities and substantially increased
catalytic activities, suggesting that complicated multi-
step syntheses and separation of chiral ligand systems are
The recent renaissance of organolanthanide chemistry
may be directly attributed to the ability of many lan-
thanide complexes to catalyze organic reactions [1–3].
Metallocene based derivatives have been shown to be
effective catalysts for ethylene polymerization, hydroge-
nation, hydroboration and hydrosilylation. One of the
most well studied reactions is the intramolecular hydro-
amination of alkenes and alkynes to form nitrogen-
containing heterocycles [4], which are of interest in
natural products synthesis [5,6] and the pharmaceutical
* Corresponding author. Tel.: +505-667-4431; fax: +505-667-9905.
E-mail address: garth@lanl.gov (G.R. Giesbrecht).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.042

2178
G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
not necessary. Similarly promising results have been
communicated for lanthanide systems bearing polyden-
tate Schiff base ligands such as salicylaldimine [14], and
this chemistry has recently been extended to include the
binaphthyl diamine [15], biphenolate and binaphtholate
families [16]. In fact, the cyclization efficiency of many
amino-olefins in the presence of the simple tris-amide
Ln[N(SiMe3)2]3 (Ln ¼ lanthanide) is directly comparable
to cyclizations conducted under identical conditions us-
ing yttrocene catalysts [17].
We have been interested in the synthesis of lanthanide
species complexed by a single bulky cyclopentadienyl ring
[18], reasoning that much useful chemistry may have been
overlooked by concentrating on the bis-cyclopentadienyl
derivatives, Cp#2 LnX (Cp# ¼ substituted cyclopentadie-
nyl; X ¼ halide, alkyl, hydride, etc.). In the course of our
studies, we realized that simple chiral organolanthanide
compounds (A) could be readily synthesized by the ad-
dition of a bidentate chelating ligand such as 2,20-bipyri-
dine to a Cs-symmetric precursor such as Cp#LnIR(L)2
(B) (R ¼ anilido; L ¼ Lewis base). In this manner, chiral
species could be obtained without the need for synthe-
sizing chiral auxillary ligands and subsequent separation
of enantiomers by derivitization and/or chiral chroma-
tography. Here we report the synthesis of new mono-ring
organolanthanide species and discuss the possible impli-
cations on enantioselective hydroamination.
Complex 2 is soluble in pentane and diethyl ether, in
contrast to the mono-ring compound 1, which is insolu-
ble in these solvents. The H NMR spectrum of 2 in
1
d5-pyridine is similar to that of complex 1 in the same
solvent, with a single peak arising from the four equiva-
lent CpH protons and two singlets in a 2:1 ratio as a result
of the SiMe3 groups. The bis-ring compound 2 likely
arises from a small excess of Cp000K used in the reaction.
Thermolysis of a d5-pyridine solution of (Cp000)LaI2(py)3
(1) (80 °C, 48 h) does not result in the formation of 2,
suggesting that the steric bulk of the C5H2(SiMe3)3
ligands is enough to discourage redistribution reactions
to form bis-ring and unsubstituted products, although it
is possible that such reactions could occur in more weakly
coordinating solvents such as THF.
2.1.1. Solid state and molecular structure of (Cp000)2LaI
(py) (2)
Single crystals of 2 that were suitable for an X-ray
diffraction study were grown by slow evaporation of a
saturated hexanes solution. Selected bond lengths and
angles are presented in Table 1. A thermal ellipsoid plot
giving the atom-numbering scheme used in the tables is
shown in Fig. 1; complete details of the structural anal-
yses of compounds 2, 3, 4 and 6 are listed in Table 3. The
molecule is monomeric in the solid state, with the La(III)
ion coordinated by two C5H2(SiMe3)3 ligands, a single
R'
R'
Table 1
000
ꢀ
Selected bond distances (A) and angles (°) for (Cp )2LaI(py) (2)
La
La
La1–Cp1
La1–N1
2.579
La1–Cp2
La1–I1
2.573
3.1272(9)
110.51
L
R
L
R
L
2.643(4)
100.28
134.37
108.53
L
I
I
Cp1–La1–N1
Cp1–La1–Cp2
N1–La1–Cp2
Cp1–La1–I1
N1–La1–I1
I1–La1–Cp2
94.79(11)
101.62
chiral, C1-symmetry
achiral, Cs-symmetry
A
B
2. Results and discussion
2.1. Synthesis and characterization of (Cp000)2LaI(py) (2)
We previously reported the synthesis of the mono-
ring compound (Cp000)LaI2(py)3 (1) from the reaction of
Cp000K with LaI3(THF)4 in THF, followed by the addi-
tion of pyridine [19]. We have recently discovered that
the bis-ring complex (Cp000)2LaI(py) (2) is also formed in
this reaction, albeit in low yield (Eq. (1)). Compounds 1
and 2 are easily separated due to their differing solu-
bilities in common organic solvents.
THF/py
LaI3(THF)4 + Cp'''K
(Cp''')LaI2(py)3 + (Cp''')2LaI(py)
-KI
1
2
74%
5%
Fig. 1. Thermal ellipsoid view of (Cp000)2LaI(py) (2) drawn with 30%
probability ellipsoids.
ð1Þ

G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
2179
Table 2
Selected
iodide ion and a pyridine molecule. The geometry about
the lanthanum center is best described as pseudo-tetra-
hedral, with the largest distortion from idealized geom-
etry found between the two bulky C5H2(SiMe3)3 ligands
(Cp1–La1–Cp2 ¼ 134.37°). As found in the less sterically
hindered mono-ring derivative, the SiMe3 groups in 2 are
bent back approximately 14° from the plane of the cy-
ꢀ
bond
distances
(A)
and
angles
(°)
for
(Cp000)LaI(NHAr)(THF)2 (3), (Cp000)LaI(NHAr)(py)2 (4) and
(Cp000)LaI(NHAr)(bipy)(py) (6)
3
4
6
La1–Cp1
La1–I1
2.596
3.1628(18)
2.577
3.1980(14)
2.612
3.2219(13)
2.397(9)
2.712(10)
2.701(10)
2.777(10)
–
La1–N1
La1–N2
2.324(12)
–
2.351(10)
2.694(9)
ꢀ
clopentadienyl ring. The La–I bond length of 3.1272(9) A
is slightly shorter than those found for complex 1
ꢀ
(3.1934(15) and 3.2289(14) A) [19] as well as other mono-
La1–N3
La1–N4
–
2.721(9)
–
–
2.544(11)
La1–O1
La1–O2
–
ring lanthanum di-iodide complexes (3.1974(4) and
1
2.575(11)
113.95
–
120.37
–
5
1
ꢀ
3.2287(4) A for (g :g :g C5H3(CH2CH2NMe2)2-1,2)-
Cp1–La1–I1
Cp1–La1–N1
Cp1–La1–N2
Cp1–La1–N3
Cp1–La1–N4
Cp1–La1–O1
Cp1–La1–O2
I1–La1–N1
I1–La1–N2
I1–La1–N3
I1–La1–N4
I1–La1–O1
I1–La1–O2
N1–La1–N2
N1–La1–N3
N1–La1–N4
N1–La1–O1
N1–La1–O2
N2–La1–N3
N2–La1–N4
N3–La1–N4
O1–La1–O2
107.88
104.63
98.43
99.46
167.66
–
5
1
1
ꢀ
LaI2(THF); 3.1696(4) and 3.2681(4) A for (g :g :g -
C5H3(CH2CH2NMe2)2-1,3)LaI2(THF)) [20]. The La–C
and La–N distances are unremarkable and are similar to
those ascribed to other similar complexes.
122.47
–
107.37
110.11
–
104.17
–
–
100.59
–
101.95
123.1(3)
–
132.1(2)
–
2.2. Synthesis and characterization of (Cp000)LaI(NHAr)
(THF)2 (3) and (Cp000)LaI(NHAr)(py)2 (4)
111.1(2)
90.3(2)
137.9(2)
77.3(2)
–
–
83.6(2)
80.6(2)
–
–
84.2(3)
–
The addition of one equiv of KNHAr (Ar ¼ 2,6-
iPr2C6H3) to a THF solution of (Cp000)LaI2(py)3 (1)
produces the mono-anilido complex (Cp000)LaI(NHAr)
(THF)2 (3) as a light yellow solid in low yield (Scheme 1).
Compound 3 is soluble in toluene, producing an effective
avenue for separating the mono anilido complex from
unreacted di-iodo species 1, which is toluene insoluble.
We [19,21] and others [20,22,23] have previously shown
that reacting potassium salts with iodo lanthanide
species is a facile method for the sequential introduction
–
86.5(3)
–
–
84.1(3)
–
145.3(3)
88.1(3)
87.8(3)
–
–
84.2(3)
–
–
85.3(4)
–
83.6(4)
–
–
145.6(3)
–
58.9(3)
70.0(3)
66.0(3)
–
–
–
–
–
–
158.4(3)
Table 3
Crystallographic data
Compound
2
3
4
6
Formula
C33H63ILaNSi6
C34H63ILaNO2Si3
867.94
203(2)
C36H57ILaN3Si3
881.92
203(2)
C41H60ILaN4Si3
959.01
203(2)
Molecular weight
Temperature (K)
Crystal system
Space group
908.18
203(2)
Triclinic
Orthorhombic
P212121
0.40 ꢁ 0.36 ꢁ 0.30
15.006(6)
15.006(6)
38.061(17)
90
Monoclinic
P21=c
0.45 ꢁ 0.22 ꢁ 0.20
10.188(4)
19.174(8)
24.476(11)
90
Monoclinic
P21=n
0.30 ꢁ 0.22 ꢁ 0.16
11.337(3)
22.703(8)
17.694(6)
90
ꢁ
P1
Crystal size (mm)
ꢀ
0.40 ꢁ 0.30 ꢁ 0.20
10.527(3)
13.180(4)
17.667(5)
94.223(7)
101.430(6)
107.708(5)
2265.2(12)
2
a (A)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
90
90
100.762(9)
90
92.801(7)
90
3
ꢀ
V (A )
8570(6)
8
1.345
4697(3)
4
1.247
4549(3)
4
1.400
Z
Dcalc (g/mL)
Absorption coefficient (mmꢀ1
1.332
1.804
924
)
1.827
3536
1.666
1784
1.728
1944
F ð000Þ
H range (°)
Total reflections
1.64–27.87
16,072
8770
1.07–23.27
45,329
12130
1.36–22.46
22,098
5614
1.46–22.46
22,994
5886
Independent reflections
GOF
1.100
0.0489
0.1053
1.775
0.0586
3.726
0.0771
1.408
0.1118
0.1238
R1
wR2
0.1623
1=2
0.1670
2
P
P
P
P
2
2
R1 ¼ jjFoj ꢀ jFcjj= jFoj and R2w ¼ ½ ½xðFo2 ꢀ Fc2Þ ꢂ= ½xðFo2Þ ꢂꢂ ; x ¼ 1=½r2ðFo2Þ þ ðaPÞ ꢂ, where a ¼ 0:0394; 0:0711; 0:027 and 0.0315.

2180
G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
THF
(Cp''')LaI2(py)3 + KNHAr
(Cp''')LaI(NHAr)(THF)2
-KI
1
3
py
15%
THF/py
(Cp''')LaI2(py)3 + KNHAr
(Cp''')LaI(NHAr)(py)2
-KI
4
1
54%
Scheme 1.
of ligands of interest without unwanted redistribution
reactions. In this case, there is no evidence for the for-
mation of the bis-anilido or bis-ring species,
(Cp000)La(NHAr)2 or (Cp000)2La(NHAr). This synthetic
method also circumvents the formation of salt or ‘‘ate’’
complexes, which is a pervasive problem in f-element
chemistry [24–34].
Fig. 2. Thermal ellipsoid view of (Cp000)LaI(NHAr)(THF)2 (3) drawn
with 30% probability ellipsoids. Isopropyl methyl groups omitted for
clarity.
The formulation of 3 with two molecules of coordi-
nated THF was based on the X-ray crystal structure
determination (see later); 1H NMR spectroscopy was
consistent with less than two molecules per metal center.
We were unable to obtain a suitable microanalysis for
this compound, which we ascribe to the extreme sensi-
tivity of this material. As reported for the parent di-iodo
species [19], a more stable, higher yielding derivative was
obtained by synthesizing the pyridine analog. If the
metathesis reaction to form the mono-anilido derivative
was performed in the presence of pyridine, the thermally
stable, less fluxional bis-pyridine adduct (Cp000)LaI-
(NHAr)(py)2 (4) was isolated in moderate yield. Com-
pound 4 may also be formed by the addition of pyridine
to a toluene solution of 3; the pyridine adduct 4 is iso-
lable as golden yellow needles following evaporation of
a saturated hexanes solution. The 1H NMR spectra of 3
and 4 were consistent with the presence of one anilido
group per metal center; additionally, the thermal sta-
bility of the pyridine adduct 4 was reflected in the sat-
isfactory microanalysis obtained for this compound.
the expected 120°. Due to the steric bulk of the
C5H2(SiMe3)3 ligand, the O1–La1–O2 angle deviates
from ideal (158.4(4)°). An additional indication of the
extent of steric crowding around the metal center is the
bending back of the SiMe3 groups from the plane of
the Cp ring (ꢃ15°). This has been a common feature of
all of the mono-ring La complexes we have investi-
gated. Overall, the molecule has Cs symmetry, with a
mirror plane containing La1, I1, N1 and the cyclo-
pentadienyl centroid. The La1–I1 distance of 3.1628(18)
ꢀ
A is intermediate between those determined for com-
plexes 1 and 2 and is similar to La–I parameters
reported for related cyclopentadienyl-supported com-
ꢀ
pounds. The La–Nanilido bond length of 2.324(12) A
may be compared with values of 2.347(4) and 2.360(3)
ꢀ
A for the terminal metal–anilido linkages in dimeric
La2(NHAr)6 and are in agreement with those found in
the monomeric base adducts La(NHAr)3(THF)3 and
ꢀ
La(NHAr)3(py)2 (2.360(3)–2.434(3) A) [35]. The La–
2.2.1. Solid state and molecular structures of
(Cp000)LaI(NHAr)(THF)2 (3) and (Cp000)LaI(NHAr)
(py)2 (4)
O(THF) distances do not differ greatly from those
observed in La(O-2,6-iPr2C6H3)3(THF)2 (2.52(1) A
ꢀ
Colorless crystals of 3 that were amenable to X-ray
diffraction studies were grown by slow evaporation of a
saturated toluene solution. The solid state molecular
structure of 3 is presented in Fig. 2. A comparative
listing of relevant bond lengths and angles for the
anilido derivatives 3, 4 and 6 is available in Table 2.
The lanthanum metal center is best described as trigo-
nal bipyramidal, with the oxygen atoms of the THF
donors occupying axial sites. The Cp ring centroid, N1
and I1 reside in the equatorial plane, with all of the
angles anchored by the lanthanum center being close to
ave) [36] as well as other THF adducts of La such as
5
ꢀ
La(g -C5Me5)[CH(SiMe3)2]2(THF) (2.547(6) A) [37],
5
5
1
1
ꢀ
La(g -C5H5)3(THF) (2.57(1) A) [38], (g :g :g -C5-
ꢀ
H3(CH2- CH2NMe2)2-1,2)LaI2(THF) (2.558(3) A) [20]
and (g5:g1:g1-C5H3(CH2CH2NMe2)2-1,3)LaI2(THF)
ꢀ
(2.593(3) A) [20]. The distances between the metal
center and the carbon atoms of the Cp ring are within
the expected range for such compounds.
Crystals of 4 were obtained by the slow evaporation
of a concentrated hexanes solution. The molecular
structure is depicted in Fig. 3 and a partial list of bond

G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
2181
Compound 6 is soluble in diethyl ether and common
organic solvents such as benzene and toluene. Alter-
nately, 6 may be synthesized by the addition of a
toluene solution of 2,20-bipyridine to a toluene solution
of the bis-pyridine adduct (Cp000)LaI(NHAr)(py)2 (4)
(Eq. (3))
toluene
(Cp''')LaI(NHAr)(py)2 + bipy
(Cp''')LaI(NHAr)(bipy)(py)
-py
4
6
75%
ð3Þ
1
The H NMR spectrum of 6 in d5-pyridine confirms
the presence of a single bipyridine molecule per lantha-
num center, although NMR spectroscopy was not
helpful in determining the stereochemistry of the prod-
uct. In order to establish the configuration of 6, we
turned to X-ray crystallography.
Fig. 3. Thermal ellipsoid view of (Cp000)LaI(NHAr)(py)2 (4) drawn with
30% probability ellipsoids. Isopropyl methyl groups omitted for clar-
ity.
2.3.1. Solid State and Molecular Structure of
(Cp000)LaI(NHAr)(bipy)(py) (6)
X-ray quality crystals of 6 were collected after cooling
a concentrated diethyl ether solution to –30 °C. The
solid state structure is available in Fig. 4; selected bond
lengths and angles are presented in Table 2. Compound
6 exhibits a distorted octahedral geometry, with the
cyclopentadienyl centroid and the nitrogen atom of the
pyridine molecule occupying axial positions (Cp1–La1–
N4 ¼ 167.66°). The iodide ligand resides significantly
below the equatorial plane, likely a result of the steric
bulk of the iodide, anilido and bipyridine units, as well
as an attempt to alleviate any interaction with the SiMe3
groups of the cyclopentadienyl ring. The crowding of
the coordination sphere is also evidenced by the La1–I1
lengths and angles can be found in Table 2. The overall
structural features of 4 are the same as those determined
for 3, although the slightly more rigid pyridine donors
result in a more distorted coordination sphere (N1–La1–
N2 ¼ 145.6(3)°). The bond lengths and angles in 4 are
not dissimilar to those established for 3 and will not be
discussed in detail aside from the La–Npyridine distances
ꢀ
(2.694(9) and 2.721(9) A), which compare favorably
with those in (Cp000)LaI2(py)3 (1) [19], (Cp000)2LaI(py) (2)
and La(NHAr)3(py)2 [35].
2.3. Synthesis and characterization of (Cp000)LaI(N-
HAr)(bipy)(py) (6)
We and others have previously reported that the
stereochemistry of mono-ring lanthanide complexes
may be controlled by the addition of a bidentate Lewis
base such as 1,2-dimethoxyethane [39] or 2,20-bipyridine
[19]. We reasoned that the relative orientation of the
iodide and anilido groups may be important in catalytic
processes such as intramolecular hydroamination/cycli-
zation reactions, where the catalyst structure plays an
important role in determining the stereochemistry of the
organic product. Thus, addition of KNHAr to a THF
solution of (Cp000)LaI2(bipy)(py) (5), in which the two
iodide atoms are cis-disposed, yields the mono-anilido
complex (Cp000)LaI(NHAr)(bipy)(py) (6) as an orange
solid in moderate yield (Eq. (2))
THF/py
(Cp''')LaI2(bipy)(py) + KNHAr
(Cp''')LaI(NHAr)(bipy)(py)
-KI
5
6
56%
Fig. 4. Thermal ellipsoid view of (Cp000)LaI(NHAr)(bipy)(py) (6)
drawn with 30% probability ellipsoids.
ð2Þ

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G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
ꢀ
bond length of 3.2219(13) A, which is longer than the
equivalent bonds in 2, 3 and 4. A slight lengthening of
the La–Nanilido bond is also observed. The presence of a
chelating bipyridine molecule also serves to force the
iodide and anilido moieties into closer proximity. In the
di-iodo species 1 and 5, the addition of 2,20-bipyridine
results in a reduction of the I1–La1–I2 angle from
153.90(3)° in 1 to 99.53(4)° in 5, a change of ꢃ55° [19].
Although the analogous change in I1–La1–Nanilido bond
angle between the bis-pyridine adduct 4 and the bi-
pyridine adduct 6 is less pronounced (132.1(2)° in 4,
111.2(2)° in 6), more important is the formation of a
chiral metal center in complex 6 upon the addition of a
simple bidentate ligand to 4.
4. Experimental
4.1. General considerations
All manipulations were carried out under an inert
atmosphere of oxygen-free UHP grade argon using
standard Schlenk techniques or under oxygen-free he-
lium in a Vacuum Atmospheres glovebox. 2,20-Bipyri-
dine was purchased from Aldrich and used as received.
Pyridine was purchased from Aldrich and distilled over
sodium benzophenone prior to use. [g5-C5H2(SiMe3)3-
1,2,4]K [40,41], LaI3(THF)4 [21], KNHAr [42],
(Cp000)LaI2(py)3 (1) [19], (Cp000)LaI2(bipy)(py) (5) [19]
and 2-amino-hex-5-ene (7) [43,44] were prepared ac-
cording to literature procedures. Hexanes, toluene,
tetrahydrofuran and diethyl ether were de-oxygenated
by passage through a column of supported copper
redox catalyst (Cu-0226 S) and dried by passing
through a second column of activated alumina [45]. d8-
THF and d5-pyridine were distilled over sodium ben-
3. Conclusions
We have shown that mono-cyclopentadienyl com-
plexes of lanthanum are readily accessible via simple,
high-yielding reactions, and the relative orientation of
the iodide and anilido groups is easily controlled by the
appropriate choice of Lewis base, allowing for the iso-
lation of both achiral C2-symmetric and chiral C1-
symmetric species. All anilido derivatives presented here
are inactive for the hydroamination/cyclization of
2-amino-hex-5-ene, which is predicted based on the
relative pKa’s of the parent amines (HN(SiMe3)2 > 2-
amino-hex-5-ene ꢄ 2,6-di-iso-propyl-aniline). Our ini-
tial selection of the [g5-C5H2(SiMe3)3-1,2,4]ꢀ ligand
system for this chemistry was based on the ability of
bulky cyclopentadienyl ligands to stabilize mono-ring
lanthanide complexes, and limit redistribution reactions
to generate the more common bis-cyclopentadienyl
compounds. Additionally, the presence of three trim-
ethylsilyl groups on the cyclopentadienyl ring increased
solubility and provided a convenient NMR handle.
From a retrosynthetic perspective, a more suitable tar-
get complex for the hydroamination/cyclization of
amino-olefins would be the bis(trimethylsilyl)amido
species, (Cp000)LaI- (N(SiMe3)2)(py)2 and (Cp000)LaI(N-
(SiMe3)2)(bipy)(py). However, these compounds have
proven to be too soluble to isolate as discrete species,
and structural information has not been forthcoming
due to their extreme solubility even in aliphatic solvents
at –40 °C. In order to investigate the catalytic potential
of mono-ring lanthanide species, the [g5-C5H2(SiMe3)3-
1,2,4]ꢀ ligand will have to be replaced with a compa-
rably bulky, but less soluble derivative, such as the
fluorenyl or indenyl group. This study has revealed a
general approach to the synthesis of mono-cyclopenta-
dienyl, mono-anilido lanthanide species; modification of
the complexes with related bulky cyclopentadienyl-
based ligands should allow for the generation of viable
catalysts for the hydroamination/cyclization of a variety
of amino-olefins.
zophenone and degassed prior to use. H and 13C{1H}
1
NMR spectra were recorded on a Bruker AMX 300
spectrometer at ambient temperature unless otherwise
1
noted. H chemical shifts are given relative to residual
C4D7HO (d ¼ 3:58 ppm) or C5D4HN (d ¼ 8:74 ppm).
13C chemical shifts are given relative to C4D8O
(d ¼ 67:57 ppm) or C5D5N (d ¼ 150:35 ppm). Infrared
spectra were recorded on a Nicolet Avatar 360 FT-IR
spectrometer as Nujol mulls between KBr plates.
Elemental analyses were performed by the Micro-
Mass Facility at the University of California,
Berkeley.
4.2. (Cp000)2LaI(py) (2)
An orange THF solution of [g5-C5H2(SiMe3)3-
1,2,4]K (1.00 g, 3.12 mmol) was added dropwise to a
solution of LaI3(THF)4 (2.50 g, 3.10 mmol) in THF,
forming an orange/brown slurry. This was stirred at
room temperature overnight. The reaction mixture was
then filtered through a frit lined with Celite to remove
insoluble KI, yielding an orange solution. The solvent
was removed under vacuum and the off-white residue
dissolved in toluene. Approximately 1 mL pyridine was
added and the slightly cloudy orange solution was stir-
red for 1 h. The solution was filtered through a frit lined
with Celite, and the toluene removed under vacuum.
The solid was washed with hexanes to yield
(Cp000)LaI2(py)3 (1) as an off-white solid. The hexanes
washings were combined and left to evaporate to give 2
as colorless plates (140 mg, 5% yield). H NMR (d5-
1
pyridine): d 8.74 (m, o-pyridine), 7.58 (m, p-pyridine),
7.30 (s, 4H, CpH), 7.22 (m, m-pyridine), 0.46 (s, 18H,
SiMe3), 0.39 (s, 36H, SiMe3). 13C{1H}NMR (d5-pyri-
dine): d 145.47 (Cp000), 138.78 (Cp000), 129.12 (Cp000), 3.24
(SiMe3), 2.52 (SiMe3) (pyridine peaks obscured by sol-

G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
2183
vent resonances). IR (Nujol, cmꢀ1): 1340 (sh), 1304 (m),
1250 (m), 1220 (m), 1170 (m), 1150 (s), 1090 (m), 1073
(m), 1037 (s), 1005 (s), 992 (m), 967 (w), 933 (m), 891
(m), 842 (s), 753 (m), 723 (s), 623 (w). Anal. Calc. for
C33H63ILaNSi6: C, 43.64; H, 6.99; N, 1.54. Found: C,
42.73; H, 7.23; N, 1.58.
(s, 18H, SiMe3), 0.34 (s, 9H, SiMe3). 13C{1H}NMR (d5-
pyridine): d 152.83 (NHAr), 137.16 (NHAr), 136.44
(Cp000), 134.18 (NHAr), 129.86 (Cp000), 129.12 (Cp000),
31.61 (CHMe2), 24.67 (CHMe2), 2.58 (SiMe3), 1.33
(SiMe3), (one NHAr peak and pyridine peaks obscured
by solvent resonances). IR (Nujol, cmꢀ1): 3173 (w), 1598
(w), 1305 (m), 1250 (w), 1152 (w), 1089 (m), 1064 (w),
1034 (m), 1002 (w), 935 (m), 838 (s), 723 (s), 621 (w).
Anal. Calc. for C36H57ILaN3Si3: C, 49.03; H, 6.51; N,
4.76. Found: C, 48.73; H, 6.74; N, 4.38.
4.3. (Cp000)LaI(NHAr)(THF)2 (3)
Solid [g5-C5H2(SiMe3)3-1,2,4]K (320 mg, 1.00 mmol)
was added to a solution of LaI3(THF)4 (810 mg, 1.00
mmol) in THF, forming an orange/brown slurry. After
stirring overnight, a THF solution of KNHAr was ad-
ded (215 mg, 1.00 mol). The reaction mixture was then
stirred overnight and filtered through a frit lined with
Celite to remove insoluble KI. The THF was removed
under vacuum and the solid extracted with a minimum
of toluene and filtered. The yellow toluene solution was
left to evaporate, resulting in large colorless blocks (130
mg, 15% yield). 1H NMR (d8-THF): d 6.98 (s, 2H,
4.5. (Cp000)LaI(NHAr)(bipy)(py) (6)
Method 1. A THF solution of KNHAr (170 mg,
0.76 mmol) was added to a THF/pyridine solution of
(Cp000)LaI2(bipy)(py) (5) (660 mg, 0.76 mmol), forming
a yellow/orange slurry. The reaction mixture was then
stirred overnight and filtered through a frit lined with
Celite to remove insoluble KI. The solvent was re-
moved under vacuum to give an orange solid. The
solid was extracted with diethyl ether, filtered, and
cooled to –30 °C to give orange crystals of 5 (810 mg,
56% yield).
3
CpH), 6.79 (d, JH–H ¼ 7:5 Hz, 2H, m-H), 6.36 (t,
3JH–H ¼ 7:5 Hz, 1H, p-H), 5.27 (s, 1H, NH), 3.62 (br m,
3
a-THF), 2.80 (sept, JH–H ¼ 7:2 Hz, 2H, CHMe2), 1.77
3
(br m, b-THF), 1.17 (d, JH–H ¼ 7:2 Hz, 12H, CHMe2),
Method 2. A toluene solution of 2,20-bipyridine (110
mg, 0.70 mmol) was added to a yellow toluene solution
of 4 (620 mg, 0.70 mmol), forming a deep red solution.
The reaction mixture was stirred overnight and the
solvent removed under vacuum. The residue was washed
with hexanes and dried under vacuum to give 6 as an
0.38 (s, 18H, SiMe3), 0.34 (s, 9H, SiMe3). 13C{1H} NMR
(d8-THF): d 152.81 (NHAr), 136.63 (NHAr), 136.12
(Cp000), 133.73 (NHAr), 129.81 (Cp000), 129.04 (Cp000),
123.52 (NHAr), 68.38 (a-THF), 31.04 (CHMe2), 26.52
(b-THF), 24.63 (CHMe2), 2.68 (SiMe3), 1.33 (SiMe3). IR
(Nujol, cmꢀ1): 3177 (w), 1597 (w), 1305 (w), 1248 (m),
1168 (w), 1018 (m), 890 (m), 837 (m), 722 (m). We were
unable to obtain a suitable microanalysis for this
compound.
1
orange solid (510 mg, 75% yield). H NMR (d5-pyri-
dine): d 8.74 (m, o-pyridine), 8.72 (m, 4H, 3,6-bipy), 7.77
(d of t, 2H, 5-bipy), 7.58 (m, p-pyridine), 7.38 (s, 2H,
CpH), 7.25 (m, 2H, 4-bipy), 7.22 (m, m-pyridine), 7.11
3
3
(d, JH–H ¼ 7:5 Hz, 2H, m-H), 6.80 (t, JH–H ¼ 7:5 Hz,
3
1H, p-H), 6.39 (s, 1H, NH), 3.09 (sept, JH–H ¼ 7:2 Hz,
4.4. (Cp000)LaI(NHAr)(py)2 (4)
3
2H, CHMe2), 1.22 (d, JH–H ¼ 7:2 Hz, 12H, CHMe2),
0.37 (s, 18H, SiMe3), 0.34 (s, 9H, SiMe3). 13C{1H} NMR
(d5-pyridine): d 156.93 (bipy), 152.80 (NHAr), 137.55
(bipy), 137.15 (NHAr), 136.70 (Cp000), 134.18 (NHAr),
129.86 (Cp000), 129.11 (Cp000), 124.62 (bipy), 121.63
(bipy), 31.60 (CHMe2), 24.66 (CHMe2), 2.57 (SiMe3),
1.33 (SiMe3), (one NHAr peak and pyridine peaks ob-
scured by solvent resonances). IR (Nujol, cmꢀ1): 3168
(w), 1598 (m), 1311 (m), 1250 (m), 1211 (w), 1167 (w),
1157 (w), 1088 (m), 995 (m), 935 (m), 834 (s), 723 (s), 640
(m), 623 (m). Anal. Calc. for C36H55ILaN3Si3: C, 49.14;
H, 6.30; N, 4.78. Found: C, 47.62; H, 6.18; N, 4.95.
To a THF solution of 1 (1.50 g, 1.70 mmol) was
added a solution of KNHAr (350 mg, 1.70 mmol) in
THF, forming a yellow/orange slurry. The reaction
mixture was then stirred overnight and filtered through
a frit lined with Celite to remove insoluble KI. The THF
was removed under vacuum and the solid dissolved in
toluene. Approximately 1 mL of pyridine was added,
and the reaction mixture stirred for 1 h, after which time
the slightly cloudy solution was filtered through a frit
lined with Celite. The solvent was then removed under
vacuum, and the yellow solid was extracted with hex-
anes. The remaining insolubles were filtered off, and the
bright yellow hexanes solution left to evaporate, yielding
4 as bright yellow needles (810 mg, 54% yield). 1H NMR
(d5-pyridine): d 8.74 (m, o-pyridine), 7.58 (m, p-pyri-
dine), 7.37 (s, 2H, CpH), 7.22 (m, m-pyridine), 7.11 (d,
4.6. General procedures for hydroamination/cyclization
In the glovebox, a screw-cap NMR tube was charged
with catalyst (0.015 mmol), C6D6 (ꢃ0.5 mL) and 2-
amino-hex-5-ene (7) (0.30 mmol). The NMR tube was
then placed in an oil bath maintained at 80 °C, and the
3
3JH–H ¼ 7:5 Hz, 2H, m-H), 6.78 (t, JH–H ¼ 7:5 Hz, 1H,
3
p-H), 6.40 (s, 1H, NH), 3.09 (sept, JH–H ¼ 7:2 Hz, 2H,
3
1
CHMe2), 1.22 (d, JH–H ¼ 7:2 Hz, 12H, CHMe2), 0.37
conversion followed by H NMR spectroscopy.

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G.R. Giesbrecht et al. / Journal of Organometallic Chemistry 689 (2004) 2177–2185
4.7. Crystallographic studies
gram. Los Alamos National Laboratory is operated by
the University of California for the U.S. Department of
Energy under Contract W-7405-ENG-36.
Crystals of 2, 3, 4 and 6 were mounted on glass fibers
using a spot of silicone grease. Due to air sensitivity, the
crystals were mounted from a pool of mineral oil under
argon gas flow. The crystals were placed on a Bruker P4/
CCD diffractometer, and cooled to 203 K using a Bru-
ker LT-2 temperature device. The instrument was
equipped with a sealed, graphite monochromatized Mo
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