Linked bis(β-diketiminato) yttrium and lanthanum complexes as catalysts in asymmetric hydroamination/cyclization of aminoalkenes (AHA)

Article abstract of DOI:10.1016/j.jorganchem.2010.09.051

Linked bis(β-diketiminato) rare-earth metal complexes based on the ethylene-bridged ligand [C₂H₄(BDI^DClP) ₂]H₂ [DClP = 2,6-Cl₂C₆H₃] and the cyclohexyl-bridged ligands [Cy(BDI^Ar)₂]H ₂ [Ar = PMP (= p-MeOC₆H₄), Mes (= 2,4,6-Me ₃C₆H₂), DIPP (= 2,6-iPr₂C ₆H₃)] were prepared via amine elimination starting from [Ln{N(SiMe₃)₂}₃] (Ln = La, Y). The three cyclohexyl-bridged complexes [{(R,R)-Cy(BDI^Mes)₂} YN(SiMe₃)₂] ((R,R)-3), [{(R,R)-Cy(BDI^Mes) ₂}LaN(SiMe₃)₂] ((R,R)-4), and [{(R,R)-Cy(BDI^DIPP)₂}LaN(SiMe₃)₂] ((R,R)-5) were obtained enantiomerically pure. The X-ray crystal structure analysis of the racemic variants of 3 and 4 revealed a distorted square pyramidal coordination geometry around the rare-earth metal, in which the amido ligand occupies the apical position and the two linked β-diketiminato moieties form the basis. The two aromatic substituents adopt a transoid arrangement and both β-diketiminato moieties are bound in a η⁵ coordination mode with close Ln?C contacts. Due to the smaller ionic radius of yttrium vs. lanthanum, the front side of the yttrium complex 3 is sterically more hindered than in the lanthanum complex 4, but there is much more empty coordination space on the rear side, which may rationalize the observed differences in selectivity of 3 in comparison to 4. The catalytic efficiency of the β-diketiminato complexes was strongly affected by steric factors such as ionic radius of the metal and the steric bulk of the aryl substituents, which is an indication for highly steric encumbered catalytic species. The complexes displayed good to moderate catalytic activity in the hydroamination/cyclization of aminoalkenes depending on the steric hindrance around the metal center. The sterically most demanding diisopropylphenyl- substituted complex (R,R)-5 displayed significantly higher enantioselectivities (up to 76% ee), but lower catalytic activity in comparison to the sterically more open mesityl-substituted complex (R,R)-4. The smaller yttrium metal center in complex (R,R)-3 led to reduced activity as well as a reversal in enantioselectivity, which may be rationalized by a change of the approach of the alkene moiety to the Ln-amido bond in the cyclization transition state.

Full text of DOI:10.1016/j.jorganchem.2010.09.051

Journal of Organometallic Chemistry 696 (2011) 321e330
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Linked bis(
b
-diketiminato) yttrium and lanthanum complexes as catalysts
in asymmetric hydroamination/cyclization of aminoalkenes (AHA)
,
Daniela V. Vitanova a, Frank Hampel a, Kai C. Hultzsch b
*
a Institut für Organische Chemie, Friedrich-Alexander Universität Erlangen-Nürnberg, Henkestr. 42, D-91054 Erlangen, Germany
b Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854-8087, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Linked bis(b-diketiminato) rare-earth metal complexes based on the ethylene-bridged ligand
[C2H4(BDIDClP)2]H2 [DClP ¼ 2,6-Cl2C6H3] and the cyclohexyl-bridged ligands [Cy(BDIAr)2]H2 [Ar ¼ PMP
(¼ p-MeOC6H4), Mes (¼ 2,4,6-Me3C6H2), DIPP (¼ 2,6-iPr2C6H3)] were prepared via amine elimination
starting from [Ln{N(SiMe3)2}3] (Ln ¼ La, Y). The three cyclohexyl-bridged complexes [{(R,R)-Cy(BDIMes)2}
YN(SiMe3)2] ((R,R)-3), [{(R,R)-Cy(BDIMes)2}LaN(SiMe3)2] ((R,R)-4), and [{(R,R)-Cy(BDIDIPP)2}LaN(SiMe3)2]
((R,R)-5) were obtained enantiomerically pure. The X-ray crystal structure analysis of the racemic variants
of 3 and 4 revealed a distorted square pyramidal coordination geometry around the rare-earth metal, in
Received 1 August 2010
Received in revised form
21 September 2010
Accepted 22 September 2010
Available online 1 October 2010
Keywords:
which the amido ligand occupies the apical position and the two linked
basis. The two aromatic substituents adopt a transoid arrangement and both
bound in a
5 coordination mode with close Ln/C contacts. Due to the smaller ionic radius of yttrium vs.
b
-diketiminato moieties form the
Asymmetric catalysis
Hydroamination
Rare-earth metals
b
-diketiminato moieties are
h
lanthanum, the front side of the yttrium complex 3 is sterically more hindered than in the lanthanum
complex 4, but there is much more empty coordination space on the rear side, which may rationalize the
b
-Diketiminato complexes
observed differences in selectivity of 3 in comparison to 4. The catalytic efficiency of the b-diketiminato
complexes was strongly affected by steric factors such as ionic radius of the metal and the steric bulk of the
aryl substituents, which is an indication for highly steric encumbered catalytic species. The complexes
displayed good to moderate catalytic activity in the hydroamination/cyclization of aminoalkenes
depending on the steric hindrance around the metal center. The sterically most demanding diisopropyl-
phenyl-substituted complex (R,R)-5 displayed significantly higher enantioselectivities (up to 76% ee), but
lower catalytic activity in comparison to the sterically more open mesityl-substituted complex (R,R)-4. The
smaller yttrium metal center in complex (R,R)-3 led to reduced activity as well as a reversal in enantio-
selectivity, which may be rationalized by a change of the approach of the alkene moiety to the Ln-amido
bond in the cyclization transition state.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
[2b,g,i,k] transition metals. Rare-earth metal-based catalysts [4],
pioneered by Marks and co-workers [2f,5], are still among the most
The hydroamination is a highly atom economical process in
which an amine NeH bond is added to an unsaturated carbon-
ecarbon bond. This reaction is of great potential interest for the
waste-free synthesis of basic and fine chemicals, pharmaceuticals
and other industrially relevant building blocks starting from inex-
pensive precursors [1,2].
Intensive research efforts from a growing number of research
group has led to the development of a variety of catalytic systems
based on alkali or alkaline-earth metals [2a,3], early (group 3e5, as
well as lanthanides and actinides) [2cef,h,j,l] and late (group 8e10)
reactive and versatile systems.
The generation of new stereogenic centers during the hydro-
amination process is an attractive application of this reaction and
the asymmetric hydroamination has found increased interest in
recent years [6], in particular for catalyst systems facilitating the
enantioselective cyclization of aminoalkenes [5bee,7e9]. Most of
these chiral catalyst systems have C2-symmetry, while the number
of catalysts with C1-symmetry is rather limited [5b,e,8e,9e].
We have previously investigated various C1 symmetric linked
bis(b-diketiminato) rare-earth metal complexes [10e12] as cata-
lysts in the epoxide/CO2-copolymerization and the catalytic activity
of related group IV metal complexes in ethylene polymerization
was recently reported [13,14]. Herein we want to disclose the
* Corresponding author. Fax: þ1 732 445 5312.
E-mail address: hultzsch@rci.rutgers.edu (K.C. Hultzsch).
catalytic activity of these linked bis(b-diketiminato) rare-earth
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.051

322
D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
metal complexes in hydroamination/cyclization reactions and their
effectiveness to perform enantioselective reactions.
SiMe3
N
Me3Si
N
N
N
N
H
[La{N(SiMe3)2}3]
H
N
N
N
La
Cl
2. Results and discussion
toluene, 65 °C, 3 h
Cl
Cl
N
Cl
Cl
Cl
Cl
2.1. Synthesis of linked bis(
complexes
b-diketiminato) lanthanum and yttrium
Cl
[C2H4(BDIDClP)2]H2
1 (98%)
2.1.1. Synthesis of linked bis(b-diketiminato) ligands
Scheme 2.
As reported previously [10], various linked bis(
b
-diketiminato)
ligands can be prepared through a two-step standard condensation
route (Scheme 1). Reaction of 2,4-pentadione and an aniline
time scale. The SiCH3 groups and the methine proton of the
derivative yields a b-enaminoketone. The carbonyl function of this
intermediate was activated using Meerwein’s salt, [Et3O]þ[BF4]ꢀ, in
order to introduce the ethylenediamine or trans-cyclohexane-1,2-
diamine linkers. Thus, utilization of resolved trans-(R,R)-1,2-dia-
minocyclohexane provides access to the enantiomerically pure
ligands [(R,R)-Cy(BDIMes)2]H2 and [(R,R)-Cy(BDIDIPP)2]H2. The
b
-diketiminato ligand each give rise to one signal and the ethylene
protons are split into two AA0BB0 doublets of triplets in the 1H NMR
spectrum.
As noted previously [10], the reactions of the more rigid cyclo-
hexyl-bridged ligands require commonly harsher reaction conditions
than the corresponding ethylene-bridged ligands. The reaction
conditions also depend significantly on the steric demand of the
aromatic substituent and the size of the rare-earth metal. The reac-
tion of the sterically least hindered p-methoxyphenyl-substituted
racemic ligand [Cy(BDIPMP)2]H2 with [La{N(SiMe3)2}3] proceeded
readily in refluxing hexanes within 2 h to form rac-2 in 68% yield
(Scheme 3). The sterically more congested mesityl- and 2,6-diiso-
propylphenyl-substituted ligands required increasingly higher reac-
tion temperatures to form the corresponding lanthanum complexes.
The enantiopure complexes (R,R)-4 (toluene, 100 ꢁC, 6 h) and (R,R)-5
(toluene, 110 ꢁC, 9 d) were prepared using slightly higher reaction
temperatures in comparison to the synthesis of their racemic coun-
terparts [10] in order to improve the yield. The smaller yttrium was
less reactive than lanthanum and the reaction of [(R,R)-Cy(BDIMes)2]-
H2 with [Y{N(SiMe3)2}3] required significant harsher reaction
conditions and longer reaction times to generate (R,R)-3 (toluene,
120 ꢁC, 8 d). The complexation of yttrium was also aided by the
addition of two equiv of THF, although the product was isolated as
a THF-free complex.
two new ligands [C2H4(BDIDClP)2]H2 (DClP ¼ 2,6-Cl2C6H3) and
PMP
[Cy(BDI
) ) ]H2 (PMP ¼ p-MeOC6H4) were prepared to probe the
2 2
electronic influence of the aromatic substituent on catalytic activity.
2.1.2. Complex synthesis and structural characterization
The rare-earth metal complexes are most conveniently prepared
via amine elimination starting from the homoleptic trisamide [Ln-
{N(SiMe3)2}3] (Ln ¼ La, Y). While the reaction of the sterically less
hindered trisamide [Ln{N(SiHMe2)2}3(THF)2] proceed generally
under milder reaction conditions [10b], the resulting bis(dime-
thylsilyl)amido complexes were considered less suitable for cata-
lytic hydroamination. Previous studies [7b,15] have shown that bis
(dimethylsilyl)amido complexes require higher reaction tempera-
tures and only a fraction of the complex is catalytically active
during the reaction. This hampered catalyst activation is a result of
the lower basicity of the bis(dimethylsilyl)amido ligand (pKa [HN-
(SiHMe2)2] ¼ 22.8 [16a]) compared to the bis(trimethylsilyl)amido
ligand (pKa [HN(SiMe3)2] ¼ 25.8 [16b]).
The reaction of the 2,6-dichlorophenyl-substituted ethylene-
The 1H and 13C NMR spectra of the cyclohexyl-bridged
complexes (R,R)-4 and (R,R)-5 are identical to their racemic coun-
terparts [10]. The spectra of the yttrium complex (R,R)-3 are in
accordance with a C1 symmetric structure in solution at room
linked bis(b
-diketiminato) ligand [C2H4(BDIDClP)2]H2 with [La{N-
(SiMe3)2}3] proceeded cleanly at 65 ꢁC in toluene within 3 h to
produce 1 in high yield (Scheme 2). In agreement to previously
characterized ethylene-linked bis(b-diketiminato) rare-earth metal
complexes [10], the 1H and 13C NMR spectra of complex 1 are in
accordance with a Cs symmetric structure in solution on the NMR
temperature based on the observation of two different
b-diketi-
minato groups and two diastereotopic aromatic rings. However, the
Scheme 1.

D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
323
Me3Si
SiMe3
N
R2
[Ln{N(SiMe3)2}3]
Ln = Y, La
N
N
H
R1
N
N
H
N
N
N
R1
N
Ln
rxn conditions:
R1
R1
R1
R1
R1
A hexanes, 68 °C, 2 h
B toluene, 110-120 °C,
8-9 d
R1
R2
R2
R1 R2
C toluene, 100 °C, 6 h
R2
[rac-Cy(BDIPMP)2]H2
[(R,R)-Cy(BDIMes)2]H2
[(R,R)-Cy(BDIDIPP)2]H2
Ln R1 R2 cond.
H
OMe
A
rac-2
La
Y
H
OMe
Me Me
B
C
B
(R,R)-3
(R,R)-4
(R,R)-5
Me Me
La Me Me
La iPr
iPr
H
H
Scheme 3.
SiCH3 groups of the amido ligand give rise of a single broad signal in
the 1H NMR spectrum, which is indicative of a slightly hindered
rotation around the YeN bond. These spectral features place the
fluxionality of complex 3 between that of the sterically more
hindered diisopropylphenyl-substituted lanthanum complex 5,
which displayed a C1 symmetric structure on the NMR time scale in
solution at room temperature, and the sterically more open mesi-
tyl-substituted lanthanum complex 4, which displayed substantial
fluxional behavior in solution at room temperature. A decoa-
lescence of the signals in accordance with a C1 symmetric structure
was observed for 4 at ꢀ20 ꢁC [10b]. As we will see later, the increase
in fluxionality in the order 5 < 3 < 4 correlates well with a decline
in the enantioselectivity in hydroamination/cyclization reactions of
aminoalkenes.
complex, the two b-diketiminato moieties are almost orthogonal
oriented to each other with an angle of 81.0ꢁ (in 3), respectively
82.8ꢁ (in 4), between the N2C2 planes. The two aromatic substitu-
ents are oriented in a transoid fashion, with one aromatic substit-
uent pointing away from the amido group and the other aromatic
substituent pointing towards the amido group. Both b-diketiminato
moieties in complexes 3 and 4 are bound in an h5 bonding mode,
ꢀ
with the metal being displaced by 1.38e1.42 A (in 3), respectively
ꢀ
1.84e1.88 A (in 4), out of the N2C3 planes and short Ln/C contacts.
ꢀ
Remarkably, the Ln/C contacts are slightly closer in 4 (2.98e3.13 A)
ꢀ
than in 3 (3.04e3.30 A), despite the larger ionic radius of lanthanum
in 4 in comparison to yttrium in 3.
Due to the larger ionic radius of lanthanum, the front quadrant
in lanthanum complex
4
is more open (described by
The sterically less congested p-methoxyphenyl-substituted
N1eLaeN4 ¼132.01(7)ꢁ) in comparison to yttrium complex 3
complex 2 displayed also fluxional behavior in solution. The 1H NMR
spectrum showed only one set of signals for both b-diketiminato
moieties at 25 ꢁC, but the resonances for the cyclohexyl methine
protons were extremely broadened and practically undetectable at
this temperature. The complex displayed a Cs symmetric structure
on the NMR time scale at 80 ꢁC. Decoalescence of the signals for the
methine protons, the
b-diketiminato methyl groups and the
aromatic ring protons started at ꢀ10 ꢁC. At ꢀ30 ꢁC the 1H NMR
spectrum of the complex revealed the C1 symmetric structure
typical for cyclohexyl-linked complexes. Remarkably, the chemical
shifts for the b-diketiminate methine hydrogens were very close to
each other in 2 (4.63 and 4.61 ppm) in contrast to the large differ-
ence found in the spectra of 2,6-dialkylphenyl complexes (e.g. 5.10
and 4.14 ppm in 4 [10]), which can serve as an evidence for the
considerable influence of the steric demand of the aromatic
substituent on the overall ligand geometry.
X-ray crystallographic analyses of 3 and 4 are shown in Figs. 1
and 2, selected metrical parameters are tabulated in Table 1. The
coordination geometry around the metal centers in 3 and 4 show
strong resemblance to previously characterized cyclohexyl-linked
bis(b-diketiminato) lanthanum complexes [10], in which the two b-
diketiminato moieties and the amido ligand are coordinated in
a distorted square pyramidal geometry. For the purpose of the
catalytic studies presented later on in this study, we will focus
primarily on the similarities and differences in the structures of 3
and 4.
The N2-C-C-N3 torsion angle in 3 (ꢀ37.6(4)ꢁ) is smaller than in 4
(ꢀ40.3(3)ꢁ) or any other previously characterized cyclohexyl-linked
lanthanum complex (41.5e44.1ꢁ [10]) or ethylene-linked complex
(49.3e53.1ꢁ [10]). In order to minimize steric interactions in the
Fig. 1. ORTEP diagram of the molecular structure of rac-3. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of
clarity.

324
D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
2.2. Catalytic hydroamination/cyclization
The catalytic activity of the bis( -diketiminato) rare-earth metal
b
complexes was examined in hydroamination/cyclization reactions
of aminoalkenes (Table 2).
The structure of the linker unit in the bis(b-diketiminato)
complexes has considerable influence on the steric properties of
the complexes, but resulted only in minor effects on the catalytic
activity. Thus, the cyclohexyl- and ethylene-linked lanthanum
complexes 2, 4, and [{C2H4(BDIMes)2}LaN(SiMe3)2] (8) (Fig. 3) per-
formed the cyclization of 6a with similar activity at 25 ꢁC (Table 2,
entries 2, 4 and 7), however, the 2,6-dichlorophenyl-substituted
complex 1 was completely inactive under the same reaction
conditions. In agreement with the activating effect of larger gem-
dialkyl substituents in the substrate [17], the cyclizations of 6b and
6c proceed much faster than the reaction of 6a.
For a comparison, we also tested the sterically much less
hindered mono(b-diketiminato) complexes [(BDI)La{N(SiMe2X)2}2]
(BDI ¼ MesNC(Me)CHC(Me)NMes; X ¼ Me (9a), H (9b)) (Fig. 3)
[10b] in the catalytic cyclization of 6a. While the bis(trimethylsilyl)
amido complex 9a reacted readily at 25 ꢁC with high activity, the
analogous bis(dimethylsilyl)amido complex 9b reacted sluggish at
25 ꢁC and appreciable activity was observed only at 60 ꢁC (Table 2,
entry 8 vs. entry 9). As noted earlier, this observation is in
Fig. 2. ORTEP diagram of the molecular structure of rac-4. Thermal ellipsoids are drawn
at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity.
(N1eYeN4 ¼115.34(12)ꢁ). Additionally, the N1eLneN3 angle in 3
(145.62(12)ꢁ) is larger in comparison to 4 (134.00(7)ꢁ), which
suggests a more accessible back side in the yttrium complex 3 (vide
infra).
Table 2
Hydroamination reactions catalyzed by
b-diketiminato lanthanum and yttrium
complexes.a
Table 1
ꢁ
ꢀ
ꢀ
Selected bond lengths [A], atomic distances [A] and angles [ ] for rac-3 and rac-4.
rac-3 (Ln ¼ Y)
rac-4 (Ln ¼ La)
LneN1
LneN2
LneN3
LneN4
LneN10
Ln/Si2
Ln/Si1
Ln/C11
Ln/C12
Ln/C13
Ln/C16
Ln/C17
2.341(3)
2.344(3)
2.309(3)
2.295(3)
2.545(2)
2.465(2)
2.450(2)
2.503(2)
2.424(2)
3.572(2)
3.591(2)
3.105(3)
3.068(3)
2.976(3)
3.021(3)
3.134(3)
3.117(3)
72.77(7)
134.00(7)
132.01(7)
94.20(7)
64.40(7)
97.51(7)
129.15(7)
71.69(7)
99.81(7)
124.25(7)
119.59(11)
118.62(11)
121.78(12)
e40.3(3)
e94.8(3)
88.2(3)
2.288(3)
3.3413(11)
3.5661(13)
3.137(3)
3.298(3)
3.087(3)
3.041(4)
3.209(3)
3.067(3)
78.31(11)
145.62(12)
115.34(12)
102.31(12)
68.55(11)
96.04(12)
135.73(11)
78.05(12)
95.38(12)
121.56(12)
125.60(18)
112.78(16)
121.25(19)
e37.6(4)
71.2(5)
Entry Substrate
Product
Cat.
(mol %) T (ꢁC) Nt
(hꢀ1
%ee
b
)
(config.)c
1
2
3
4
5
6
7
8
9
1
2.9
3
25
25
60
25
25
60
25
25
60
nr
e
rac-2
2.0
0.2
1.7
0.2
2.1
2.6
22.3
2.9
e
(R,R)-3 4.3
(R,R)-4 3.2
(R,R)-5 9.6
(R,R)-5 2.6
8
9a
9b
25 (S)
11 (R)
76 (R)
64 (R)
e
Ln/C18
N1eLneN2
N1eLneN3
N1eLneN4
N1eLneN10
N2eLneN3
N2eLneN4
N2eLneN10
N3eLneN4
N3eLneN10
N4eLneN10
LneN10eSi1
LneN10eSi2
Si1eN10eSi2
N2eCeCeN3
C11eN1/C31/C32
C11eN1eC31eC36
C18eN4eC41eC42
C18eN4eC41eC46
3.0
4.3
4.7
e
e
10
11
12
13
14
(R,R)-3 3.5
(R,R)-4 3.0
(R,R)-4 1.5
(R,R)-5 3.5
(R,R)-5d 2.7
60
25
25
25
25
2.6
11 (S)
36.4 11 (R)
50
2.7
2.9
14 (R)
61 (R)
64 (R)
15
(R,R)-3 3.0
60
2.6
42 (S)
16
17
18
a
(R,R)-4 2.6
(R,R)-5 3.0
25
25
25
26
2.3
32
5 (R)
53 (R)
e
e112.6(4)
e110.4(5)
73.9(5)
8
3.0
72.0(3)
e111.4(3)
Reaction conditions: 3e10 mol% cat., C6D6, Ar atm., >95% conversion.
Nt calculated from first half life.
b
c
Distances of Ln from N2C2 planes
Ln/Plane(1)
Ln/Plane(2)
Enantiomeric excess determined by 19F NMR spectroscopy of the Mosher
1.384
1.424
81.0
1.880
1.844
82.8
amides of the corresponding pyrrolidine products. The absolute configuration of the
hydroamination products was assigned based on 19F NMR spectroscopic data of the
Mosher amides reported in Ref. [8d].
:(Plane(1)/Plane(2))
d
Added 33 equiv of THF relative to catalyst. nr ¼ no reaction observed.
Plane(1) ¼ N1eC11eC13eN2, Plane(2) ¼ N3eC16eC18eN4.

D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
325
100
SiMe3
N
Me3Si
N
80
N(SiXMe2)2
N(SiXMe2)2
N
N
N
N
La
N
La
60
40
20
0
9a X = Me
9b X = H
8
Fig. 3. Additional
b-diketiminato lanthanum complexes [10] studied in catalytic
hydroamination/cyclization reactions of aminoalkenes.
0
200
00
600
800
1000
t (min)
agreement to previous studies [7b,15], in which the low activity of
bis(dimethylsilyl)amido complexes was ascribed to incomplete
catalyst activation as a result of the lower basicity of this amido
group in comparison to the bis(trimethylsilyl)amido ligand.
Catalytic experiments performed with chiral catalysts (R,R)-3,
(R,R)-4 and (R,R)-5 indicated that the enantioselectivity of these
systems is very sensitive to the identity/size of the rare-earth metal
and the steric demand of alkyl groups in 2,6-positions of the
aromatic substituents.
The methyl groups of a mesityl substituent are interacting in-
sufficiently with the substrate for effective transfer of stereochem-
ical information. The reaction of 6a-c catalyzed by (R,R)-4 gave
preferentially the (R)-pyrrolidine in low enantioselectivity (Table 2,
entries 4, 11, 12, and 16). Switching from lanthanum in (R,R)-4 to
yttrium in (R,R)-3 improved the stereoselectivities slightly for 6a
(25% ee; Table 2, entry 3) and for 6c (42% ee; Table 2, entry 15),
however, the yttrium complex was less reactive and the reaction
had to be performed at 60 ꢁC. Interestingly, the yttrium complex
(R,R)-3 produced the (S)-enantiomer, while both lanthanum
complexes (R,R)-4 and (R,R)-5 favor the (R)-enantiomer.
Fig. 4. Conversion of the substrate as a function of time for the hydroamination/
cyclization of 6b, using (R,R)-5 in C6D6 at 25 ꢁC. The line represents the least-square fit
to the linear part of the data.
reaction mediated by the sterically more encumbered complex
(R,R)-5 displayed zero order rate dependence on substrate
concentration for three half lifes (Fig. 4), the process catalyzed by
(R,R)-4 showed deviation from the linearity after approximately
one half life (Fig. 5). This observation is in agreement to previous
studies [5aed,8e] that sterically more open catalysts are prone to
product inhibition. In order to verify this hypothesis, a second batch
of substrate 6b was introduced to the catalytic system after the
cyclization of the first batch was finished. Kinetic plots of both
reactions clearly indicate more pronounced deviation for the
second catalytic cycle, as well as a depressed reaction rate.
As noted above, the catalytic efficiency of the present
b-diket-
iminato complexes was strongly affected by steric factors such as
ionic radius of the metal and the steric bulk of the aryl substituents,
which is an indication for highly steric encumbered catalytic
species. The enantioselectivity is expected to arise from non-
The increased steric demand of the bulky 2,6-diisopropylphenyl
moiety in the lanthanum complex (R,R)-5 improved the enantio-
selectivity significantly to 76% ee for 6a (Table 2, entry 5), 61% ee for
6b (Table 2, entry 13), and 53% ee for 6c (Table 2, entry 17). However,
this selectivity resulted also in a significant drop in reactivity when
comparing (R,R)-4 and (R,R)-5 (Table 2, entries 4, 11, 16 vs. entries 5,
13, 17). The temperature dependence of the enantioselectivity
100
irst catalytic cycle
80
seems to be slightly greater for (R,R)-5 (
range of 25e60 ꢁC; Table 2, entries 5 and 6), in comparison to
binaphtholate rare-earth metal complexes (
ee z 1.5% ee/10 ꢁC in
the range of 0e60 ꢁC [8d]), potentially as a result of the greater
fluxionality of the linked bis( -diketiminato)-ligand framework.
D
ee z 3.4% ee/10 ꢁC in the
D
60
b
Second catalytic cycle
Addition of a 33-fold excess of THF (with respect to the catalyst) did
not significantly diminish catalytic activity, but led to a slight
increase in enantioselectivity (Table 2, entry 13 vs. 14).
40
NMR spectroscopic analysis of the catalytic reaction mixture in
the cyclization of 6b with (R,R)-5 indicated a slow catalyst activa-
tion. With most catalysts, protonolysis of the bis(trimethylsilyl)
amido group by the aminoalkene substrate is rapid and takes place
immediately after mixing of the components. In the case of
complex (R,R)-5 the metal center seems to be strongly sterically
encumbered by the auxiliary ligand, resulting in a decreased rate of
catalyst activation (Fig. 4). The reaction showed an induction period
at the beginning (ꢂ2 h), which was then followed by a zero order
rate dependence on substrate concentration until 90% conversion.
Another interesting point here is the form of the kinetic plots for
the cyclization of 6b catalyzed by (R,R)-4 and (R,R)-5. While the
(
I cyle) = 33
.
7
h-1
h-1
N t
N t
20
0
(II cy e) = 25.5
l
0
20
40
60
80
t (min)
100
120
140
160
Fig. 5. Conversion of substrate as a function of time for the hydroamination/cyclization
of 6b, using (R,R)-4 (3 mol% in first catalytic cycle) in C6D6 at 25 ꢁC. Upon complete
consumption of the first batch of substrate, a second cycle was started by introducing
an additional aliquot of 6b. The lines represent least-squares fit to the linear part of the
data.

326
D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
bonding interactions in the transition state of the rate-limiting
insertion of the double bond into the LneN bond. The experimental
results showed a significant increase in the enantiomeric excess for
complex (R,R)-5 (53e76% ee) in comparison to complex (R,R)-4
(5e14% ee), revealing the significant influence of the aryl groups in
these interactions. Another remarkable observation is the reversal
of the product configuration in going from lanthanum to the smaller
yttrium. The latter could result from a different approach of the
substrate molecule to the metal center and/or different geometry of
the ligand and consequently different steric interactions between
the substrate and the supporting ligand. Presumably, the combi-
nation of the smaller ionic radius of Y3þ and the relatively high steric
demand of the linked bis(b-diketiminato) ligands lead to an over-
crowded complex structure, which behaves differently in compar-
ison to the lanthanum complex. The crystallographic data of 3 and 4
revealed some differences in the geometry of the ancillary ligand
around the metal. Similar effects have been noted for lanthanocene
complexes, where an increase in enantioselectivity was observed in
the lanthanide series going from La3þ- through the smaller Sm3þ
-
complex, with the enantioselectivity decreasing thereafter and
ultimately favoring the opposite product antipode for Lu3þ [5b].
Analysis of the crystal structures of the catalysts amido
precursors supports a reasonable model explaining the different
behavior of the lanthanum and yttrium complexes. As shown in
Fig. 6 (top), the cleft between the two mesityl substituents is
significantly diminished in yttrium complex
3 compared to
ꢀ
ꢀ
lanthanum complex 4 (3.738 A vs. 4.292 A). On the other hand, the
rear side of the complexes also has a sizable cleft as depicted in
Fig. 6 (bottom), with a slightly larger gap for the yttrium complex 3
ꢀ
ꢀ
in comparison to the lanthanum complex 4 (4.887 A vs. 4.834 A).
The increase in the gap at the rear side is apparently limited by the
steric restraints inherent to the linked bis(
framework.
b-diketiminato) ligand
Fig. 7. Stereochemical models for intramolecular hydroamination/cyclization of 2,2-
dimethyl-pent-4-enylamine (6a) catalyzed by (R,R)-3 and (R,R)-4. The drawings show
an equatorial approach of the alkene to the Ln-amido bond from different sides d
frontal in case of the La-complex (A and B) and from the rear side in case of the Y-
complex (C and D), which could rationalize the observed reversal in the absolute
product configuration.
Therefore, the front side of yttrium complex 3 is sterically
significantly more hindered than in lanthanum complex 4. With
the frontal approach blocked, the more open coordination space on
the rear side of complex 3 is presumably better accessible for an
approach of the alkene moiety from that side. As shown in Fig. 7,
the approach of the alkene to the Ln-amido bond from the rear
favors the opposite enantiotopic face of the double bond in the
cyclization transition state. The present model is also in accordance
with the role of the 2,6-dialkylphenyl-substituents, since a more
demanding 2,6-diisopropylphenyl group will interact more effec-
tively than a mesityl group.
3. Conclusion
Herein we have reported the synthesis and catalytic application
of
a variety of linked bis(b-diketiminato) rare-earth metal
complexes. The complexes displayed good to moderate catalytic
activity in the hydroamination/cyclization of aminoalkenes
depending on the steric hindrance around the metal center. The
sterically most demanding and most rigid diisopropylphenyl-
substituted complex (R,R)-5 displayed significantly higher enan-
tioselectivities but lower catalytic activity in comparison to the
sterically more open and more fluxional mesityl-substituted
complex (R,R)-4. The smaller yttrium metal center in complex
(R,R)-3 led to reduced activity as well as a reversal in enantiose-
lectivity, which may be rationalized by a change of the approach of
Fig. 6. Space filling representation of the structure of rac-3 (left) and rac-4 (right). The
front view (top) shows the cleft for the frontal approach of the substrate, as defined by
the distance between the methyl groups of the two mesityl moieties
ꢀ
ꢀ
(C36a/C42a ¼ 3.738 A in rac-3, C32a$$$C46a ¼ 4.292 A in rac-4). The rear view
(bottom) shows the cleft for a potential approach of the substrate from the rear, as
defined by the distance between one of the mesityl methyl groups and the cyclohexyl
ꢀ
ꢀ
backbone (C32a/C21 ¼4.887 A in rac-3, C36a/C21 ¼4.834 A in rac-4).

D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
327
the alkene moiety to the Ln-amido bond in the cyclization transi-
tion state.
(100.6 MHz, CDCl3):
d
¼ 197.2 (CO), 161.3 (CH3CN), 135.0 (4-C6H3),
134.6 (aryl-Cipso), 128.7 (2,20-C6H3), 128.4 (3,30-C6H3), 97.3 (
29.3, 19.0 (CH3).
b-CH),
4. Experimental
4.4. [C2H4(BDIDClP)2]H2
4.1. General procedures
A solution of [Et3O]þ[BF4]ꢀ (1.578 g, 8.31 mmol) in CH2Cl2
(10 mL) was slowly added to a solution of 4-((2,6-dichlorophenyl)-
amino)-pent-3-en-2-one (1.736 g, 7.11 mmol) in CH2Cl2 (15 mL)
under an atmosphere of nitrogen. The mixture was stirred for 3 h at
room temperature. Then Et3N (0.8 g, 7.9 mmol) was added and the
mixture was stirred for another 5 min. Ethylenediamine (0.253 g,
4.21 mmol) in Et3N (5 mL) was added to the mixture and the stirring
was continued overnight. The solvent was removed in vacuo. The
product was extracted with toluene (3 ꢄ 25 mL). After removing the
solvent in vacuo the residue was treated with MeOH and kept in
a fridge at ꢀ20 ꢁC. The desired compound was obtained as a white
solid in 60% yield (1.094 g) after filtration and washing with MeOH.
All operations were performed under an inert atmosphere of
nitrogen or argon using standard Schlenk-line or glovebox tech-
niques. After drying over KOH, THF was distilled from sodium
benzophenone ketyl. Hexanes, pentane and toluene were purified by
distillation from sodium/triglyme benzophenone ketyl. Anhydrous
YCl3 (Aldrich) and LaCl3 (Strem) were used as received. [Ln{N-
(SiMe3)2}3] (Ln ¼ Y, La) [18], 2-(2,4,6-trimethylphenyl)-aminopent-
2-en-4-one [10], 4-((2,6-diisopropylphenyl)amino)pent-3-en-2-one
[10], 2,2-dimethyl-pent-4-enylamine (6a) [3f,19], 2,2-diphenyl-pent-
4-enylamine (6b) [3f,7c], and C-(1-allyl-cyclohexyl)-methylamine
(6c) [3f,20] were synthesized as described in the literature. The
racemic complexes [{Cy(BDIMes)2}LaN(SiMe3)2] (4), [{Cy(BDIDIPP)2}
LaN(SiMe3)2] (5), as well as complexes [{C2H4(BDIMes)2}LaN(SiMe3)2]
(8) and [(BDI)LnN(SiXMe2)2] (BDI ¼ MesNC(Me)CHC(Me)NMes;
X ¼ Me (9a), H (9b)) were prepared as reported previously [10].
Enantiomerically enriched (ꢃ98% ee) trans-(R,R)-1,2-diaminocyclo-
hexane was obtained from the L-(þ)-tartrate salt, after hydrolysis
1H NMR (400 MHz, C6D6):
d
¼ 10.54 (br s, 2H, NH), 7.12 (d,
3JH,H ¼ 8 Hz, 4H, C6H3), 6.40 (t, 3JH,H ¼ 8.0 Hz, 2H, C6H3), 4.59 (s, 2H,
b
-CH), 2.54 (m, 4H, CH2), 1.69 (s, 6H, CH3), 1.63 (s, 6H, CH3); 13C{1H}
NMR (100.6 MHz, C6D6):
123.1, 128.2 (aryl), 94.2 (
d
¼ 168.9, 157.7 (CH3CN), 147.4 (aryl-Cipso),
b
-CH), 44.3 (CH2), 21.2, 19.3 (CH3). Anal.
Calcd for C24H26N4Cl4 (512.308): C, 56.27; H, 5.12; N,10.94. Found: C,
56.09; H, 5.02; N, 10.79.
with 20% solution of NaOH [21]. (R)-(þ)-
a-Methoxy-a-trifluoro-
methylphenylacetic acid (>99% ee, from Reuter Chemische Appara-
tebau KG (RCA), Freiburg, Germany) was transformed to its acid
chloride using oxalyl chloride/DMF in hexanes [22]. All other chem-
4.5. [Cy(BDIPMP)2)2]H2
icals were commerciallyavailable and usedasreceived.1H,13C and19
F
A solution of [Et3O]þ[BF4]ꢀ (4.201 g, 22.11 mmol) in CH2Cl2
(10 mL) was slowly added to a solution of 4-((p-methoxyphenyl)
amino)-pent-3-en-2-one (4.105 g, 20.00 mmol) in CH2Cl2 (15 mL)
under a nitrogen atmosphere. The mixture was stirred for 3 h at
room temperature. Then Et3N (2.8 mL, 20 mmol) was added and the
mixture was stirred for another 5 min. Racemic trans-1,2-dia-
minocyclohexane (1.213 g, 10.62 mmol) in Et3N (10 mL) was added
to the mixture and the stirring was continued overnight. The solvent
was removed in vacuo. The product was extracted with pentane
(3 ꢄ 25 mL). After removing the solvent, the residue was dissolved in
NMR spectra were recorded on Bruker Avance 300 or Avance 400
spectrometer. The enantiomeric excess of the hydroamination/
cyclization reactions were determined via 19F NMR spectroscopy of
the Mosher amides as described earlier [3f,8d].
4.2. 4-((p-Methoxyphenyl)amino)-pent-3-en-2-one
2,4-Pentadione (84.134 g, 840 mmol) and p-methoxyaniline
(19.51 g, 158.4 mmol) were added to a 250 mL round-bottom flask
equipped with a stir bar. A simple distillation apparatus was
attached to collect water and the neat solution was heated to
130e140 ꢁC for 24 h. The excess of 2,4-pentadione was removed in
vacuo, and the residue was distilled under vacuum (94e101 ꢁC,
0.2 mmHg) to give a yellowish liquid, which solidified at ꢀ20 ꢁC.
Washing with hexanes and drying in vacuo, produced the title
MeOH and stored in a fridge at ꢀ20 ꢁC. Crystallization afforded [Cy
PMP
(BDI
) ) ]H2 in form of white crystals, which were filtered off,
2 2
washed with hexanes and dried in vacuo to give 0.741 g (15%) of
spectroscopically pure product. 1H NMR (400 MHz, C6D6):
¼ 11.46
(br s, 2H, NH), 6.86 (s, 8H, C6H4), 4.67 (s, 2H, -CH), 3.30 (s, 6H, OCH3),
d
b
3.02 (br m, 2H, ring-CH),1.91 (s, 6H, CH3),1.81 (s, 6H, CH3),1.78 (br m,
2 H, ring-CH2), 1.38 (br m, 2 H, ring-CH2), 1.10 (br m, 2 H, ring-CH2),
compound in 97% (31.7 g) yield. 1H NMR (400 MHz, CDCl3):
3
d
¼ 12.26 (br s, 1H, NH), 7.00 (2 overlapping dd, JH,H ¼ 8.8 Hz,
0.90(br m, 2 H, ring-CH2); 13C{1H} NMR (100.6 MHz, C6D6):
d
¼ 166.4
4JH,H ¼ 2.6 Hz, 2H, 2,6-C6H4), 6.84 (2 overlapping dd, 3JH,H ¼ 8.8 Hz,
(4-C6H4), 155.9, 155.7 (CH3CN), 145.5 (aryl-Cipso), 122.8, 114.5 (aryl),
94.9(CH), 58.1 (ring-CH), 55.0(OCH3), 33.2, 24.3 (ring-CH2), 21.1,19.4
(CH3). Anal. Calcd for C30H40N4O2 (488.66): C, 73.74; H, 8.25; N,11.47.
Found: C, 73.64; H, 8.26; N, 11.69.
4JH,H ¼ 2.6 Hz, 2H, 3,5-C6H4), 5.12 (s, 1H,
b-CH), 3.77 (s, 3H, OCH3),
2.06 (s, 3H, CH3), 1.87 (s, 3H, CH3); 13C{1H} NMR (100.6 MHz,
CDCl3):
d
¼ 195.8 (CO), 161.2 (CH3CN), 157.7 (4-C6H4), 131.5 (aryl-
Cipso), 126.6 (2,20-C6H4), 114.2, (3,30-C6H4), 96.8
(OCH3), 29.0, 19.6 (CH3).
(b-CH), 55.4
4.6. [(R,R)-Cy(BDIMes)2]H2
4.3. 4-((2,6-Dichlorophenyl)amino)-pent-3-en-2-one
The enantiopure ligand was synthesized in a procedure analo-
gous to that for the racemic compound [10]. A solution of
[Et3O]þ[BF4]ꢀ (4.250, 22.37 mmol) in CH2Cl2 (20 mL) was slowly
added to a solution of 2-(2,4,6-trimethylphenyl)-aminopent-2-en-
4-one (4.382 g, 20.16 mmol) in CH2Cl2 (10 mL) under a nitrogen
atmosphere. The mixture was stirred for 2.5 h at room temperature.
Et3N (2.8 mL, 20 mmol) was added to the clear pale yellow solution
and the mixture was stirred for another 5 min. Then trans-(R,R)-1,2-
diaminocyclohexane (1.14 g, 10 mmol) in Et3N (10 mL) was added
to the mixture and the stirring was continued overnight. Volatiles
were removed in vacuo and the residue was extracted with pentane
(2 ꢄ 20 mL) and toluene (20 mL). [NEt3H]þ[BF4]ꢀ was separated as
A mixture of 2,6-dichloraniline (4.07 g, 25.12 mmol), 2,4-pen-
tadione (10-fold excess, 25.1 g, 251 mmol) and p-toluenesulfonic
acid (3.95 g, 20 mmol) was refluxed for 24 h in a Dean-Stark
apparatus. After removing the excess of pentadione a brown liquid
product was obtained. Distillation in vacuo gave a pale yellow solid,
which was crystallized from a hexanes/methanol-mixture (5:1) at
ꢀ20 ꢁC. The aimed compound was obtained in 29% yield (1.761 g).
1H NMR (400 MHz, CDCl3):
d
¼ 12.03 (br s, 1H, NH), 7.35 (d,
3
3JH,H ¼ 8.1 Hz, 2H, C6H3), 7.17 (pt, JH,H ¼ 8.1 Hz, 1H, C6H3), 5.28 (s,
1H,
b
-CH), 2.11 (s, 3H, CH3), 1.71 (s, 3H, CH3); 13C{1H} NMR

328
D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
an oily precipitate. Toluene was removed in vacuo and the residue
was dissolved in EtOH. Crystallization at ꢀ20 ꢁC afforded 1.481 g
(29%) of [(R,R)-Cy(BDIMes)2]H2. The spectroscopic data of the
product were identical with the data of the racemic compound [10].
1.89e1.83 (m, 2H, ring-CH2), 1.80 (s, 3H, CH3), 1.78 (m, 1H, ring-
CH2), 1.73 (s, 3H, CH3), 1.67 (s, 6H, CH3), 1.56 (m, 2H, ring-CH2), 1.43
(m, 1H, CH2), 1.10 (m, 1H, ring-CH2), 0.34 (s, 9H, SiCH3), 0.32 (s, 9H,
13
SiCH3); C{1H} NMR (100.6 MHz, toluene-d8, ꢀ30 ꢁC):
d
¼ 165.1,
162.1 (4-C6H4), 160.8, 158.9, 157.5, 157.0 (CH3CN), 139.7, 139.4 (aryl-
4.7. [(R,R)-Cy(BDIDIPP)2]H2
Cipso), 126.8, 125.4 (2-C6H4), 115.8, 115.4 (3-C6H4), 101.1, 98.7 (b-CH),
65.3, 62.3 (ring-CH), 54.71, 54.66 (OCH3), 34.8, 32.8 (ring-CH2), 27.5,
25.6 (ring-CH2), 24.3, 23.85, 23.82, 21.6 (CH3), 4.9, 4.8 (SiCH3). Anal.
Calcd for C36H56N5LaO2Si2 (785.95): C, 55.02; H, 7.18; N, 8.91.
Found: C, 54.85; H, 7.16; N, 8.41.
A 100 mL Schlenk flask was charged with 4-((2,6-diisopropyl-
phenyl)-amino)-pent-2-en-3-one (3.900 g, 15.04 mmol). This was
dissolved in CH2Cl2 (10 mL) and a solution of [Et3O]þ[BF4]ꢀ
(3.135 g, 16.50 mmol) in CH2Cl2 (20 mL) was slowly added under
a nitrogen atmosphere. After stirring for 3 h at room temperature
Et3N (2.1 mL, 15 mmol) was added slowly. The mixture was stirred
for another 15 min and then trans-(R,R)-1,2-diaminocyclohexane
(0.856 g, 7.50 mmol) in Et3N (10 mL) was added to the mixture.
After stirring at room temperature for 18 h, the volatiles were
removed in vacuo and the residue was treated with pentane
(3 ꢄ 15 mL) and subsequently toluene (2 ꢄ 25 mL) to extract the
product. Finally, crystallization from MeOH at ꢀ20 ꢁC afforded
[(R,R)-Cy(BDIDIPP)2]H2 in 34% yield (1.521 g). The spectroscopic
data of the product were identical with those of the racemic
compound [10].
4.10. [{(R,R)-Cy(BDIMes)2}YN(SiMe3)2] ((R,R)-3)
A
Schlenk flask was charged with [(R,R)-Cy(BDIMes)2]H2
(256.2 mg, 0.50 mmol) and [Y{N(SiMe3)2}3] (285 mg, 0.50 mmol).
Toluene (5 mL) and THF (74 mg, 1.0 mmol) were added and the
mixture was stirred for 8 days at 120 ꢁC. Volatiles were removed in
vacuo to give a pale yellow powder of (R,R)-3 in quantitative yield
(372 mg, 98%), which was pure by NMR spectroscopy. The racemic
complex was obtained in an analogous mannerand gave identical 1H
and 13C NMR spectra. 1H NMR (400 MHz, C6D6):
C6H2), 6.78 (s,1H, C6H2), 6.76 (s, 1H, C6H2), 6.71 (s, 1H, C6H2), 5.97 (s,
1H, -CH), 4.53 (m, 1H, ring-CH), 4.27 (s, 1H,
-CH), 3.10, (ddd, 3Jax-
d
¼ 6.89 (s, 1H,
b
b
3
4.8. [{C2H4(BDIDClP)2}LaN(SiMe3)2] (1)
¼ 14 Hz, Jax-eq ¼ 3.6 Hz, 1H, ring-CH), 2.56 (s, 3H, CH3), 2.42 (m,
ax
1H, ring-CH2), 2.39 (s, 3H, CH3), 2.19 (s, 3H, CH3), 2.16 (s, 3H, CH3),
2.03 (s, 3H, CH3), 2.01 (s, 3H, CH3),1.77 (s, 3H, CH3),1.73 (m, 2H, ring-
CH2),1.65 (m,1H, ring-CH2),1.594 (s, 3H, CH3),1.590 (s, 3H, CH3),1.38
(s, 3H, CH3), 1.50 (m, 1H, CH2), 1.20e1.36 (m, 2H, ring-CH2), 1.09 (m,
1H, CH2), 0.1e0.6 (br s,18H, SiCH3); 13C{1H} NMR (100.6 MHz, C6D6):
A Schlenk flask was charged with [C2H4(BDIDClP)2]H2 (512.3 mg,
1.00 mmol) and [La{N(SiMe3)2}3] (620.1 mg, 1.00 mmol). Toluene
(10 mL) was added and the reaction mixture was stirred at 65 ꢁC for
3 h. The solvent and volatiles were removed in vacuo. A waxy
material was obtained, which contained residual free amine and
a small amount toluene. After addition of hexanes (10 mL) a white
solid precipitated. All volatiles were removed in vacuo to give a pale
yellow powder of 1 (796.7 mg, 98%), which was pure according to
d
¼ 164.2, 164.1, 163.5, 162.3 (CH3CN), 147.4, 145.3 (aryl-Cipso), 133.5,
132.92, 132.88, 132.80 (2C), 131.6 (2,4,6-C6H2), 130.0, 129.6, 129.4,
128.97 (3,5-C6H2),101.8, 97.5, ( -CH), 69.9, 65.3 (ring-CH), 33.4, 33.1,
b
26.7, 25.4 (ring-CH2), 25.3, 24.4, 24.0, 22.0, 21.6, 21.0 (3C), 18.9, 18.7
(CH3), 5.8 (SiCH3). Anal. Calcd for C40H64N5YSi2 (760.05): C, 63.21; H,
8.49; N, 9.21. Found: C, 63.12; H, 8.35; N, 8.61.
NMR spectroscopy. 1H NMR (400 MHz, C6D6):
d
¼ 6.85 (dd,
3JH,H ¼ 8.0 Hz, 4JH,H ¼ 1.4 Hz, 4H, 3-C6H3), 6.25 (t, 3JH,H ¼ 8.0 Hz, 2H,
4-C6H3), 4.84 (s, 2H,
b
-CH), 3.74 (dt, 2JH,H ¼ 13 Hz, 3JH,H ¼ 6.3 Hz, 2H,
CH2), 3.21 (dt, 2JH,H ¼ 13 Hz, 3JH,H ¼ 6.3 Hz, 2H, CH2),1.67 (s, 6H, CH3),
4.11. [{(R,R)-Cy(BDIMes)2}LaN(SiMe3)2] ((R,R)-4)
1.63 (s, 6H, CH3), 0.34 (s, 18H, SiCH3); 13C{1H} NMR (100.6 MHz,
C6D6):
123.7 (aryl), 100.0 (
d
¼ 165.0, 160.5 (CH3CN), 146.1 (aryl-Cipso), 131.6, 131.2, 128.8,
A
Schlenk flask was charged with [(R,R)-Cy(BDIMes)2]H2
b
-CH), 51.2 (CH2), 24.3, 21.6 (CH3), 4.4 (SiCH3).
(513 mg, 1.00 mmol) and [La{N(SiMe3)2}3] (621.6 mg, 1.00 mmol).
Toluene (10 mL) was added and the mixture was stirred for 6 h at
100 ꢁC. All volatiles were removed in vacuo to give an orange
powder of the product in quantitative yield. The 1H NMR spectrum
showed the presence of some impurities. Therefore, pentane
(10 mL) was added and, after filtration, the clear solution was
stored at ꢀ30 ꢁC for crystallization. The mother liquor was dec-
anted via cannula to leave 680 mg (84%) of (R,R)-4 as white crystals.
1H and 13C NMR spectra of the complex were identical with those of
the racemic compound [10].
Anal. Calcd for C30H42N5Cl4LaSi2 (809.58): C, 44.51; H, 5.23; N, 8.65.
Found: C, 44.38; H, 5.38; N, 8.24.
4.9. [{Cy(BDIPMP)2}LaN(SiMe3)2] (2)
A Schlenk flask was charged with [Cy(BDIPMP)2]H2 (489.2 mg,
1.00 mmol) and [La{N(SiMe3)2}3] (620.1 mg, 1.00 mmol). Hexanes
(10 mL) were added and the reaction mixture was stirred at reflux
(68 ꢁC) for 2 h. The solvent and volatiles were removed in vacuo. A
waxy material was obtained and addition of pentane (5 mL) caused
precipitation of a white solid material. After filtration the residue
was washed with additional pentane (5 mL). The solid product was
dried in vacuo to give 531 mg, (68%) of 2. 1H NMR (400 MHz, C6D6,
4.12. [{(R,R)-Cy(BDIDIPP)2}LaN(SiMe3)2] ((R,R)-5)
A
Schlenk flask was charged with [(R,R)-Cy(BDIDIPP)2]H2
80 ꢁC):
d
¼ 6.74 (m, 4H, aryl), 6.51 (m, 4H, aryl), 4.63 (s, 2H,
b
-CH),
(569.6 mg, 1.0 mmol) and [La{N(SiMe3)2}3] (620 mg, 1.0 mmol).
Toluene (5 mL) was added and the mixture was stirred for 9 days at
110 ꢁC. Volatiles were removed in vacuo to give a pale yellow foam-
like product, which was dissolved in pentane (15 mL). After filtra-
tion volatiles were removed to give the title compound in 96% yield
(863 mg), which was pure by NMR spectroscopy. 1H and 13C NMR
are identical with those of the racemic compound [10].
3.89 (m, 2H, ring-CH), 3.40 (s, 6H, OCH3), 2.10 (m, 2H, ring-CH2),
1.86 (s, 3H, CH3), 1.77e1.75 (m, 2H, ring-CH2), 1.71 (s, 6H, CH3), 1.70
(m, 2H, ring-CH2), 1.34 (m, 2H, ring-CH2), 0.22 (s, 18H, SiCH3); 13C
{1H} NMR (100.6 MHz, C6D6, 80 ꢁC):
d
¼ 163.7 (4-C6H4), 160.4, 157.8
(CH3CN), 140.7 (aryl-Cipso), 126.3, 116.1 (aryl), 99.3 ( -CH), 64.6
b
(ring-CH), 55.4 (OCH3), 34.0, 26.5 (ring-CH2), 23.3, 22.7 (CH3), 4.8
1
(SiCH3); H NMR (400 MHz, toluene-d8, ꢀ30 ꢁC):
d
¼ 6.64 (d,
3JH,H ¼ 9.6 Hz, 2H, aryl), 6.68 (d, JH,H ¼ 9.3 Hz, 2H, aryl), 6.52 (d,
4.13. X-ray crystal structure analysis of rac-3 and rac-4
3
3JH,H ¼ 8.6 Hz, 2H, aryl), 6.24 (br m, 2H, aryl), 4.63 (s, 1H,
b-CH), 4.61
3
3
(s, 1H,
b
-CH), 4.30 (dt, JH,H ¼ 2.3 Hz, JH,H ¼ 10.8 Hz, 1H, ring-CH),
Clear, slight yellow plates of rac-3, C40H64N5Si2Y, 760.05 g molꢀ1
,
3.39 (m, 1H, ring-CH), 3.15 (s, 6H, OCH3), 2.14 (m, 1H, ring-CH2),
were obtained from a cold hexanes solution at ꢀ35 ꢁC. Crystal size

D.V. Vitanova et al. / Journal of Organometallic Chemistry 696 (2011) 321e330
329
ꢀ
0.20 ꢄ 0.20 ꢄ 0.20 mm, orthorhombic, P212121, a ¼ 11.698(2) A,
Acknowledgment
3
ꢀ
ꢀ
ꢀ
b ¼ 11.855(2) A, c ¼ 30.412(6) A, V ¼ 4217.5(15) A , Z ¼ 4, Dcalc
¼
1.197 Mg/m3,
m
¼ 1.472 mmꢀ1. Data were collected on a Nonius
Generous financial support by the Deutsche Forschungs-
gemeinschaft (Emmy Noether Programme) and the National
Science Foundation (NSF CAREER Award CHE 0956021) is gratefully
acknowledged.
KappaCCD area detector at 173(2) K up to 2qmax ¼ 55.0ꢁ (Mo-K
a
radiation). 9431 reflections were collected for rac-3, 9431 were
unique [R(int) ¼ 0.0000] of which 7452 were observed [I > 2
s(I)].
R1 ¼0.0478, wR2 ¼ 0.1323 (obsd. data), goodness-of-fit on F2 ¼ 1.044;
ꢀꢀ3
residual electron density (max/min) 0.426/e0.381 e A
. Clear,
Appendix A. Supplementary material
slight yellow plates of rac-4, C40H64LaN5Si2, 810.05 g molꢀ1
,
were obtained from a cold hexanes solution at ꢀ35 ꢁC. Crystal
size 0.20 ꢄ 0.20 ꢄ 0.20 mm, monoclinic, P21/c, a ¼ 13.0912
CCDC-785394 and CCDC-785395 contains the supplementary
crystallographic data 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.
(3) A, b ¼ 11.9471(1) A, c ¼ 27.3710(6) A,
¼ 96.318(1)ꢁ, V ¼ 4254.88
ꢀ
ꢀ
ꢀ
b
(14) A , Z ¼ 4, Dcalc ¼ 1.265 Mg/m3,
m
¼ 1.092 mmꢀ1
. Data were
3
ꢀ
collected on a Nonius KappaCCD area detector at 173(2) K up to
2
qmax ¼ 55.0ꢁ (Mo-K
a radiation). 17,137 reflections were collected
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