Enantioselective hydroamination/cyclization catalyzed by organolanthanide amides derived from a new chiral ligand, (S)-2-(pyrrol-2-ylmethyleneamino)- 2′-(dimethylamino)-1,1′-binaphthyl

Article abstract of DOI:10.1021/om701058k

A new series of bis-ligated organolanthanide amides, (1) ₂-LnN(SiMe₃)₂ · C₇H ₈ (Ln = Sm (2), Y (3), Yb (4)), have been prepared by the reaction of Ln[N(SiMe₃)₂]₃ with the ligand (S)-2-(pyrrol-2-ylmemyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl (1H) in good yields. They are active catalysts for the asymmetric hydroamination/cyclization reaction of aminoalkenes, affording cyclic amines in moderate to good conversions with moderate to good ee values.

Full text of DOI:10.1021/om701058k

1242
Organometallics 2008, 27, 1242–1246
Enantioselective Hydroamination/Cyclization Catalyzed by
Organolanthanide Amides Derived from a New Chiral Ligand,
(S)-2-(Pyrrol-2-ylmethyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl
Guofu Zi,*,† Li Xiang,† and Haibin Song‡
Department of Chemistry, Beijing Normal UniVersity, Beijing 100875, People’s Republic of China, and
State Key Laboratory of Elemento-Organic Chemistry, Nankai UniVersity,
Tianjin 300071, People’s Republic of China
ReceiVed October 21, 2007
A new series of bis-ligated organolanthanide amides, (1)2-LnN(SiMe3)2 · C7H8 (Ln ) Sm (2), Y (3),
Yb (4)), have been prepared by the reaction of Ln[N(SiMe3)2]3 with the ligand (S)-2-(pyrrol-2-
ylmethyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl (1H) in good yields. They are active catalysts
for the asymmetric hydroamination/cyclization reaction of aminoalkenes, affording cyclic amines in
moderate to good conversions with moderate to good ee values.
The hydroamination is a highly atom economical process in
number of highly enantioselective reactions (>90% ee) have
been reported.7a,10e,f Thus, alkene hydroamination remains an
open area of research.
which an amine N-H bond is added to an unsaturated
carbon-carbon bond. This reaction is of great potential interest
for the synthesis of nitrogen heterocycles that are found in
numerous biologically and pharmacologically active com-
pounds.1 Therefore, it is not surprising that recent efforts have
focused on the development of chiral catalysts for intramolecular
asymmetric alkene hydroamination.2–10 Over the years it has
been shown that the catalysts based on early transition metals
(group 4 and especially the lanthanides) are the most promising
for this purpose.3–10 However, even within this class only a small
Although many chiral lanthanide catalysts based on C1-
symmetric Cp ligands3 and chiral non-Cp ligands4–8 have been
studied, the development of new lanthanide catalysts for
asymmetric alkene hydroamination is still a desirable and
challenging goal. In recent years, we have developed a series
of chiral non-Cp multidentate ligands, and their Ir(I), Rh(I),
Ti(IV), Ag(I), Zn(II), Zr(IV), and lanthanide complexes
are useful catalysts for a wide range of transformations.11 More
recently, we have reported a new catalytic enantioselective
hydroamination/cyclization of aminoalkenes promoted by the
bis(pyrrolate) lanthanide amides [(R)-C20H12(NCHC4H3N)2]-
LnN(SiMe3)2(thf) (Ln ) Sm, Y, Yb) in which good yields but
low enantioselectivities (<24% ee) have been achieved.12 In
* To whom correspondence should be addressed. Tel: +86-10-5880 2237.
Fax: +86-10-5880 2075. E-mail: gzi@bnu.edu.cn.
† Beijing Normal University.
‡ Nankai University.
(1) For general hydroamination reviews, see: (a) Odom, A. L. Dalton
Trans. 2005, 225. (b) Doye, S. Synlett 2004, 1653. (c) Pohlki, F.; Doye, S.
Chem. Soc. ReV. 2003, 32, 104. (d) Bytschkov, I.; Doye, S. Eur. J. Org.
Chem. 2003, 935. (e) Seayad, J.; Tillack, A.; Hartung, C. G.; Beller, M.
AdV. Synth. Catal. 2002, 344, 795. (f) Nobis, M.; Driessen-Hölscher, B.
Angew. Chem., Int. Ed. 2001, 40, 3983. (g) Müller, T. E.; Beller, M. Chem.
ReV. 1998, 98, 675.
(8) (a) Riegert, D.; Collin, J.; Meddour, A.; Schulz, E.; Trifonov, A. J.
Org. Chem. 2006, 71, 2514. (b) Collin, J.; Daran, J. C.; Jacquet, O.; Schulz,
E.; Trifonov, A. Chem. Eur. J. 2005, 11, 3455. (c) Collin, J.; Daran, J. C.;
Schulz, E.; Trifonov, A. Chem. Commun. 2003, 3048. (d) O’Shaughnessy,
P. N.; Scott, P. Tetrahedron: Asymmetry 2003, 14, 1979. (e) Meyer, N.;
Zulys, A.; Roesky, P. W. Organometallics 2006, 25, 4179. (f) Riegert, D.;
Collin, J.; Daran, J. C.; Fillebeen, T.; Schulz, E.; Lyubov, D.; Fukin, G.;
Trifonov, A. Eur. J. Inorg. Chem. 2007, 1159. (g) Kim, H.; Kim, Y. K.;
Shim, J. H.; Kim, M.; Han, M.; Livinghouse, T.; Lee, P. H. AdV. Synth.
Catal. 2006, 348, 2609. (h) Aillaud, I.; Wright, K.; Collin, J.; Schulz, E.;
Mazaleyrat, J.-P. Tetrahedron: Asymmetry 2008, 19, 82. (i) Aillaud, I.;
Collin, J.; Duhayon, C.; Guillot, R.; Lyubov, D.; Schulz, E.; Trifonov, A.
Chem. Eur. J. 2008, 14, 2189.
(2) For reviews of asymmetric hydroamination, see: (a) Roesky, P. W.;
Müller, T. E. Angew. Chem., Int. Ed. 2003, 42, 2708. (b) Hong, S.; Marks,
T. J. Acc. Chem. Res. 2004, 37, 673. (c) Hultzsch, K. C. Org. Biomol. Chem.
2005, 3, 1819. (d) Hultzsch, K. C. AdV. Synth. Catal. 2005, 347, 367. (e)
Hii, K. K. Pure Appl. Chem. 2006, 78, 341. (f) Aillaud, I.; Collin, J.;
Hannedouche, J.; Schulz, E. Dalton Trans. 2007, 5105.
(3) For selected papers for asymmetric hydroaminations using lanthanide
metal catalysts with chiral Cp ligands, see: (a) Giardello, M. A.; Conticello,
V. P.; Brard, L.; Sabat, M.; Rheingold, A. L.; Stern, C. L.; Marks, T. J.
J. Am. Chem. Soc. 1994, 116, 10241. (b) Gagné, M. R.; Brard, L.; Conticello,
V. P.; Giardello, M. A.; Stern, C. L.; Marks, T. J. Organometallics 1992,
11, 2003. (c) Vitanova, D. V.; Hampel, F.; Hultzsch, K. C. J. Organomet.
Chem. 2007, 69, 4690 and references therein.
(9) For asymmetric hydroamination using late metal catalysts, see: (a)
Löber, O.; Kawatsura, M.; Hartwig, J. F. J. Am. Chem. Soc. 2001, 123,
4366. (b) Patil, N. T.; Lutete, L. M.; Wu, H.; Pahadi, N. K.; Gridnev, I. D.;
Yamamoto, Y. J. Org. Chem. 2006, 71, 4270. (c) Hu, A.; Ogasaware, M.;
Sakamoto, T.; Okada, A.; Nakajima, K.; Takahashi, T.; Lin, W. AdV. Synth.
Catal. 2006, 348, 2051. (d) LaLonde, R. L.; Sherry, B. D.; Kang, E. J.;
Toste, F. D. J. Am. Chem. Soc. 2007, 129, 2452. (e) Zhang, Z.; Bender,
C. F.; Widenhoefer, R. A. Org. Lett. 2007, 9, 2887. (f) Zhang, Z.; Bender,
C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2007, 129, 14148.
(10) For examples of asymmetric hydroamination using other metal
catalysts, see: (a) Knight, P. D.; Munslow, I.; O’Shaughnessy, P. N.; Scott,
P. Chem. Commun. 2004, 894. (b) Gribkov, D. V.; Hultzcsh, K. C. Angew.
Chem., Int. Ed. 2004, 43, 5542. (c) Martinez, P. H.; Hultzsch, K. C.; Hampel,
F. Chem. Commun. 2006, 2221. (d) Watson, D. A.; Chiu, M.; Bergman,
R. G. Organometallics 2006, 25, 4731. (e) Wood, M. C.; Leitch, D. C.;
Yeung, C. S.; Kozak, J. A.; Schafer, L. L. Angew. Chem., Int. Ed. 2007,
46, 354. (f) Gott, A. L.; Clarke, A. J.; Clarkson, G. J.; Scott, P.
Organometallics 2007, 26, 1729. (g) Ogata, T.; Ujihara, A.; Tsuchida, S.;
Shimizu, T.; Kaneshige, A.; Tomioka, K. Tetrahedron Lett. 2007, 48, 6648.
(4) Hong, S.; Tian, S.; Metz, M. V.; Marks, T. J. J. Am. Chem. Soc.
2003, 125, 14768.
(5) (a) O’Shaughnessy, P. N.; Knight, P. D.; Morton, C.; Gillespie,
K. M.; Scott, P. Chem. Commun. 2003, 1770. (b) O’Shaughnessy, P. N.;
Gillespie, K. M.; Knight, P. D.; Munslow, I. J.; Scott, P. Dalton Trans.
2004, 2251.
(6) Kim, J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 1737.
(7) (a) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. J. Am. Chem. Soc.
2006, 128, 3748. (b) Gribkov, D. V.; Hultzsch, K. C. Chem. Commun. 2004,
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2004, 4091. (d) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. Chem. Eur. J.
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2007, 268, 163.
10.1021/om701058k CCC: $40.75
2008 American Chemical Society
Publication on Web 02/28/2008

Catalysis by Organolanthanide Amides
Organometallics, Vol. 27, No. 6, 2008 1243
Table 1. Selected Bond Distances (Å) and Bond Angles (deg) for 2–4
2 (Ln ) Sm)
3 (Ln ) Y)
4 (Yb)
2 (Ln ) Sm)
3 (Ln ) Y)
4 (Ln ) Yb)
Ln(1)-N(1)
2.476(2)
2.497(2)
2.258(2)
142.6(1)
106.8(1)
119.1(1)
69.8(1)
122.7(1)
121.1(1)
69.2(1)
2.419(3)
2.425(3)
2.208(3)
144.3(1)
106.7(1)
122.2(1)
72.2(1)
120.9(1)
121.4(2)
69.6(3)
2.385(3)
2.389(3)
2.169(3)
145.1(1)
108.7(1)
123.2(1)
72.9(1)
116.1(1)
118.5(2)
69.0(2)
Ln(1)-N(3)
Ln(1)-N(6)
2.376(2)
2.402(2)
69.6(1)
94.4(1)
88.4(1)
118.2(1)
110.2(1)
122.2(1)
116.8(1)
2.300(3)
2.319(3)
71.8(1)
92.2(1)
89.3(1)
116.9(1)
108.9(1)
120.3(2)
118.3(2)
2.283(3)
2.266(4)
72.8(1)
89.6(1)
91.4(1)
120.8(1)
106.2(1)
119.7(2)
121.7(2)
Ln(1)-N(4)
Ln(1)-N(7)
N(1)-Ln(1)-N(3)
N(1)-Ln(1)-N(6)
N(3)-Ln(1)-N(4)
N(3)-Ln(1)-N(7)
N(4)-Ln(1)-N(7)
Si(1)-N(7)-Si(2),
Si(2)-N(7)-Ln(1)
N(1)-Ln(1)-N(4)
N(1)-Ln(1)-N(7)
N(3)-Ln(1)-N(6)
N(4)-Ln(1)-N(6)
N(6)-Ln(1)-N(7)
Si(1)-N(7)-Ln(1)
torsion (aryl-aryl)
76.1(1)
76.6(3)
76.6(2)
Scheme 1. Synthesis of Organolanthanides
Experimental Section
General Methods. All experiments were performed under an
atmosphere of dry dinitrogen with rigid exclusion of air and
moisture, using standard Schlenk or cannula techniques, or in a
glovebox. All organic solvents were freshly distilled from sodium
benzophenone ketyl immediately prior to use. (S)-2-amino-2′-
dimethylamino-1,1′-binaphthyl,14 Ln[N(SiMe3)2]3,15 2,2-dimethyl-
pent-4-enylamine (5a),6 pent-4-enylamine (6a),6 2,2-dimethylhex-
5-enylamine (7a),6 and 1-(aminomethyl)-1-allylcyclohexane (8a)8a
were prepared according to literature methods. All chemicals were
purchased from Aldrich Chemical Co. and Beijing Chemical Co.
and were used as received unless otherwise noted. Infrared spectra
were obtained from KBr pellets on an Avatar 360 Fourier transform
spectrometer. 1H and 13C NMR spectra were recorded on a Bruker
AV 500 spectrometer at 500 and 125 MHz, respectively. All
chemical shifts are reported in δ units with reference to the residual
protons of the deuterated solvents for proton and carbon chemical
shifts. Melting points were measured on an X-6 melting point
apparatus and were uncorrected. Elemental analyses were performed
on a Vario EL elemental analyzer.
Preparation of (S)-2-(Pyrrol-2-ylmethyleneamino)-2′-(di-
methylamino)-1,1′-binaphthyl (1H). Pyrrole-2-carboxaldehyde
(0.95 g, 10.0 mmol) was mixed with (S)-2-amino-2′-(dimethyl-
amino)-1,1′-binaphthyl (3.12 g, 10.0 mmol) in dry toluene (50 mL).
A few 4 Å molecular sieves were added, and the solution was
warmed to 70 °C and kept for 2 days at this temperature. The
solution was filtered, and the solvent was removed under reduced
pressure. The resulting brown solid was recrystallized from
methanol (40 mL) to give 1H · CH3OH as yellow crystals. Yield:
3.58 g (85%). Mp: 82–84 °C. 1H NMR (C6D6): δ 8.03 (s, 1H, aryl
H), 7.77–7.70 (m, 4H, aryl H), 7.44 (d, J ) 8.4 Hz, 2H, aryl H),
7.26–6.96 (m, 6H, aryl H), 6.39 (d, J ) 2.4 Hz, 1H, aryl H), 6.07
(s, 1H, aryl H), 6.02 (m, 1H, aryl H), 2.87 (s, 3H, CH3OH), 2.30
(s, 6H, N(CH3)2); protons of OH and NH were not observed. 13C
NMR (C6D6): δ 151.0, 150.6, 148.8, 134.6, 134.5, 132.3, 131.1,
130.3, 129.2, 129.1, 128.5, 128.4, 128.2, 127.8, 127.0, 126.8, 126.5,
126.4, 124.9, 124.0, 123.2, 120.4, 119.9, 116.6, 110.0, 49.8, 43.6.
IR (KBr, cm-1): ν 3407 (br, m), 3052 (m), 2934 (m), 2780 (w),
1625 (vs), 1609 (vs), 1586 (vs), 1503 (s), 1418 (s), 1032 (s), 747
(s). Anal. Calcd for C28H27N3O: C, 79.8; H, 6.46; N, 9.97. Found:
C, 79.8; H, 6.52; N, 9.83. The solvate methanol can be easily
removed under vacuum at 50 °C overnight to give pure compound
1H.
our ongoing research, we are now focusing on the preparation
of lanthanide catalysts coordinated by a new chiral C1-symmetric
versatile ligand, (S)-2-(pyrrol-2-ylmethyleneamino)-2′-(di-
methylamino)-1,1′-binaphthyl (1H), which contains three σ-do-
nating nitrogen atoms that can act in a bidentate or tridentate
fashion.13 In contrast to organolanthanides with C2-symmetric
ligands,4–8,12 as far as we know, no organolanthanide with a
C1-symmetric non-Cp ligand for the hydroamination/cyclization
has been reported yet. We report here the synthesis and
properties of the new chiral ligand, its use in the coordination
chemistry of lanthanide, and the applications of the resulting
complexes as catalysts for the hydroamination/cyclization
reaction.
(11) (a) Zi, G.-F.; Yin, C.-L. Acta Chim. Sin. 1998, 56, 484. (b) Zi,
G.-F.; Yin, C.-L. J. Mol. Catal. A: Chem. 1998, 132, L1. (c) Zi, G.; Xiang,
L.; Zhang, Y.; Wang, Q.; Yang, Y.; Zhang, Z. J. Organomet. Chem. 2007,
692, 3949. (d) Zhang, Z.; Li, M.; Zi, G. Chirality 2007, 19, 802. (e) Zhang,
Y.; Xiang, L.; Wang, Q.; Duan, X.-F.; Zi, G. Inorg. Chim. Acta 2008, 361,
1246. (f) Wang, Q.; Xiang, L.; Zi, G. J. Organomet. Chem. 2008, 693, 68.
(g) Xiang, L.; Song, H.; Zi, G. Eur. J. Inorg. Chem. 2008, 1135.
(12) Xiang, L.; Wang, Q.; Song, H.; Zi, G. Organometallics 2007, 26,
5323.
Preparation of (1)2-SmN(SiMe3)2 · C7H8 (2). A toluene solution
(10 mL) of 1H (0.19 g, 0.5 mmol) was slowly added to a toluene
solution (10 mL) of Sm[N(SiMe3)2]3 (0.32 g, 0.5 mmol) with stirring
at room temperature. The resulting solution was refluxed overnight
to give a yellow solution. The solution was filtered, and the filtrate
was concentrated to about 5 mL. 2 was isolated as yellow crystals
(13) For selected recent reviews for N-based ligands, see: (a) Lemaire,
M.; Mangeney, P. Chiral Diazaligands for Asymmetric Synthesis. In Topics
in Organometallic Chemistry; Springer-Verlag: Berlin, Heidelberg, Ger-
many, 2005; Vol. 15. (b) Knight, P. D.; Scott, P. Coord. Chem. ReV. 2003,
242, 125. (c) Che, C.-M.; Huang, J.-S. Coord. Chem. ReV. 2003, 242, 97.
(14) (a) Wang, C.-J.; Shi, M. J. Org. Chem. 2003, 68, 6229. (b) Wang,
J.; Li, H.; Duan, W.; Zu, L.; Wang, W. Org. Lett. 2005, 7, 4713.
(15) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton
Trans. 1973, 1021.

1244 Organometallics, Vol. 27, No. 6, 2008
Zi et al.
188–190 °C dec. IR (KBr, cm-1): ν 3055 (w), 2961 (m), 2924
(m), 1617 (m), 1594 (m), 1571 (s), 1502 (s), 1390 (s), 1301 (s),
1260 (vs), 1093 (s), 1033 (vs), 801 (s). Anal. Calcd for
C67H70N7Si2Yb: C, 66.9; H, 5.87; N, 8.15. Found: C, 67.2; H, 5.68;
N, 7.83.
This complex can also be prepared in 64% yield (0.19 g) from
the reaction of 1H (0.19 g, 0.5 mmol) with Yb[N(SiMe3)2]3 (0.33
g, 0.5 mmol) in toluene (20 mL).
GeneralProcedureforAsymmetricHydroamination/Cycliza-
tion. The cyclization of 2,2-dimethylpent-4-enylamine (5a) cata-
lyzed by 2 is representative. In a nitrogen-filled glovebox, (1)2-
Sm[N(SiMe3)2] · C7H8 (2; 18.9 mg, 0.016 mmol), C6D6 (0.7 mL),
and 2,2-dimethylpent-4-enylamine (36 mg, 45.2 µL, 0.32 mmol)
were introduced sequentially into a J. Young NMR tube equipped
with a Teflon screw cap. The reaction mixture was subsequently
kept at 21 °C or heated to 60 or 120 °C to achieve hydroamination,
and the reaction was monitored periodically by 1H NMR spectros-
copy. The cyclic amine 2,4,4-trimethylpyrrolidine was vacuum-
transferred from the J. Young NMR tube into a 25 mL Schlenk
flask which contained 62 mg (0.32 mmol) of (S)-(+)-O-acetylman-
delic acid. This transfer was quantitated by washing the NMR tube
with a small amount of CDCl3. The resulting mixture was stirred
at room temperature for 2 h, and the volatiles were removed in
vacuo. The resulting diastereomeric salt was then dissolved in
CDCl3, and the enantiomeric excesses were determined by 1H NMR
spectroscopy.6
Figure 1. Molecular structure of 1H (35% probability ellipsoids).
Selected distances (Å) and angles (deg): N(2)-C(5), 1.286(4);
torsion (aryl-aryl), 75.6(3).
X-ray Crystallography. Single-crystal X-ray diffraction mea-
surements of compounds 1H and 2-4 were carried out on a Rigaku
Saturn CCD diffractometer at 113(2) K using graphite-monochro-
mated Mo KR radiation (λ ) 0.710 70 Å). An empirical absorption
correction was applied using the SADABS program.16 All structures
were solved by direct methods and refined by full-matrix least
squares on F2 using the SHELXL-97 program package.17 All of
the hydrogen atoms were geometrically fixed using the riding model.
Crystal data for 1H · CH3OH: C28H27N3O, fw 421.53, monoclinic,
P21, a ) 8.893(2) Å, b ) 14.556(3) Å, c ) 9.416(2) Å, ꢀ )
107.08(1)°, V ) 1165.0(4) Å3, Z ) 2, R1 ) 0.042 for 2470
reflections (I > 2σ(I)), wR2 ) 0.112 (all data). Crystal data for 2:
C67H70N7Si2Sm, fw 1179.83, orthorhombic, P212121, a ) 11.515(2)
Å, b ) 21.460(4) Å, c ) 24.200(5) Å, V ) 5980(2) Å3, Z ) 4, R1
) 0.032 for 14 236 reflections (I > 2σ(I)), wR2 ) 0.069 (all data).
Crystal data for 3: C67H70N7Si2Y, fw 1118.39, orthorhombic,
P212121, a ) 11.444(2) Å, b ) 21.508(2) Å, c ) 24.216(2) Å, V
) 5960.6(8) Å3, Z ) 4, R1 ) 0.066 for 12 997 reflections (I >
2σ(I)), wR2 ) 0.114 (all data). Crystal data for 4: C67H70N7Si2Yb,
fw 1202.52, orthorhombic, P212121, a ) 11.438(3) Å, b ) 21.506(5)
Å, c ) 24.243(7) Å, V ) 5963.3(3) Å3, Z ) 4, R1 ) 0.041 for
14 022 reflections (I > 2σ(I)), wR2 ) 0.080 (all data). Selected
bond lengths and angles for complexes 2–4 are given in Table 1.
Figure 2. Molecular structures of 2 (Ln ) Sm), 3 (Ln ) Y), and
4 (Ln ) Yb) (35% probability ellipsoids).
after this solution stood at room temperature for 3 days. Yield:
0.23 g (78%). Mp: 186–188 °C (dec). IR (KBr, cm-1): ν 3056
(w), 2961 (m), 2846 (w), 1615 (w), 1594 (m), 1567 (s), 1503 (s),
1434 (m), 1390 (m), 1300 (s), 1259 (s), 1093 (s), 1034 (vs), 801
(s). Anal. Calcd for C67H70N7Si2Sm: C, 68.2; H, 5.98; N, 8.31.
Found: C, 67.9; H, 6.24; N, 8.52.
Preparation of (1)2-YN(SiMe3)2 · C7H8 (3). This compound was
prepared as yellow crystals from the reaction of 1H (0.19 g, 0.5
mmol) with Y[N(SiMe3)2]3 (0.28 g, 0.5 mmol) in toluene (20 mL)
under reflux for 2 days and recrystallization from a toluene solution
by a procedure similar to that used in the synthesis of 2. Yield,:
1
0.21 g (74%). Mp: 216–218 °C dec. H NMR (C6D6): δ 8.50 (m,
Results and Discussion
2H, aryl H), 8.13 (d, J ) 8.6 Hz, 2H, aryl H), 7.83 (m, 6H, aryl
H), 7.55–7.04 (m, 21H, aryl H), 6.71 (s, 2H, aryl H), 6.20 (d, J )
3.1 Hz, 2H, aryl H), 5.94 (m, 2H, aryl H), 2.23 (s, 3H, C6H5CH3),
2.13 (s, 12 H, N(CH3)2), 0.43 (s, 18H, Si(CH3)3). 13C NMR (C6D6):
δ 158.6, 150.0, 143.4, 139.9, 136.7, 135.5, 129.9, 129.3, 129.0,
128.5, 128.3, 127.8, 127.6, 127.4, 127.1, 125.9, 125.4, 125.1, 124.7,
123.9, 120.4, 113.1, 43.7, 21.2, 4.4; other carbon resonances were
not observed. IR (KBr, cm-1): ν 3056 (w), 2960 (m), 2823 (w),
1617 (m), 1595 (m), 1564 (vs), 1504 (s), 1392 (s), 1258 (s), 1035
(vs), 814 (s). Anal. Calcd for C67H70N7Si2Y: C, 72.0; H, 6.31; N,
8.77. Found: C, 71.7; H, 6.36; N, 9.12.
Preparation of (1)2-YbN(SiMe3)2 · C7H8 (4). This compound
was prepared as yellow crystals from the reaction of 1H (0.19 g,
0.5 mmol) with Yb[N(SiMe3)2]3 (0.17 g, 0.25 mmol) in toluene
(20 mL) and recrystallization from a toluene solution by a procedure
similar to that used in the synthesis of 2. Yield: 0.21 g (70%). Mp:
Ligand. The C1-symmetric pyrrole imine ligand (S)-2-(pyrrol-
2-ylmethyleneamino)-2′-(dimethylamino)-1,1′-binaphthyl (1H)
is readily prepared by condensation of pyrrole-2-carboxaldehyde
with 1 equiv of (S)-2-amino-2′-(dimethylamino)-1,1′-binaphthyl,
which is derived from (S)-1,1′-binaphthyl-2,2′-diamine by a five-
step procedure,14 in the presence of molecular sieves in toluene
at 70 °C (Scheme 1). The product is isolated in 85% yield after
recrystallization from a methanol solution.
(16) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Göttingen, Göttingen,
Germany, 1996.
(17) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structure from Diffraction Data; University of Göttingen, Göttingen,
Germany, 1997.

Catalysis by Organolanthanide Amides
Organometallics, Vol. 27, No. 6, 2008 1245
Table 2. Enantioselective Hydroamination/Cyclization of Aminoalkenesa
a Conditions: C6D6 (0.70 mL), aminoalkene (0.32 mmol). b Determined by 1H NMR with p-xylene as the internal standard. N.R. ) no reaction.
c Determined by 1H NMR of its diastereomeric (S)-(+)-O-acetylmandelic acid salt.6 N.A. ) not applicable.
Ligand 1H is air-stable, but sensitive to hydrolysis, is soluble
in CH2Cl2, CHCl3, toluene, and benzene, and is only slightly
soluble in n-hexane. It has been fully characterized by various
spectroscopic techniques, elemental analyses, and single-crystal
X-ray diffraction analysis. The 1H and 13C NMR spectra of 1H
indicate that it is nonsymmetrical on the NMR time scale, which
is consistent with its C1-symmetric structure. The IR spectrum
of 1H shows typical characteristic N-H and NdC absorptions
at 3407 and 1625 cm-1, respectively.
The molecular structure of 1H · CH3OH shows there is one
1H molecule and one methanol molecule in the lattice. The 1H
crystallizes in a C1-symmetric distorted-tetrahedral geometry
(Figure 1). As expected, the distance (1.286(4) Å) of CdN is
in agreement with a CdN double bond. The twisting between
the naphthyl rings gives a torsion angle of 75.6(3)°, which is
larger than that (63.9(6)°) found in (R)-2,2′-diamino-1,1′-
binaphthyl.18
treatment of 1H with 1 or 0.5 equiv of Ln[N(SiMe3)2]3 in toluene
under reflux, followed by recrystallization from a toluene
solution, gives the bis-ligated organolanthanide amides (1)2-
LnN(SiMe3)2 · C7H8 (Ln ) Sm (2), Y (3), Yb (4)) (Scheme 1),
in good yields. These amides are stable under a dry nitrogen
atmosphere, while they are very sensitive to moisture. They are
soluble in organic solvents such as THF, DME, pyridine,
toluene, and benzene and only slightly soluble in n-hexane. They
have been characterized by various spectroscopic techniques,
elemental analyses, and single-crystal X-ray diffraction analyses.
The 1H NMR spectrum of 3 supports a ratio of toluene, amino
group N(SiMe3)2, and ligand 1 of 1:1:2, and the 1H NMR spectra
of the hydrolytic products of 2 and 4 support that the ratio of
toluene, amido group N(SiMe3)2, and ligand 1 is also 1:1:2 for
2 and 4. Their IR spectra exhibit a weak characteristic NdC
absorption at about 1617 cm-1
.
The solid-state structures of 2–4 confirm that they are
isostructural and show one toluene molecule of solvent in the
lattice. The substituted Me2N groups are far away from the metal
center, and the Ln3+ is σ-bound to four nitrogen atoms from
the ligand 1 and one nitrogen atom from amido group N(SiMe3)2
in a distorted-tetragonal-pyramidal geometry (Figure 2) with
average Ln-N distances of 2.402(2) Å for Sm, 2.334(3) Å for
Y, and 2.298(4) Å for Yb. The average N-Ln(1)-N angles
are 104.2(1)° for Sm, 104.5(1)° for Y, and 104.7(1)° for Yb,
respectively. The average Si-N(7)-Ln(1) angles are 121.7(1)°
forSm,120.9(2)°forY,and119.1(2)°forYb.TheSi(1)-N(7)-Si(2)
Organolanthanide Amides. Our previous work has shown
12
that interaction between (R)-C20H12(NCHC4H4N)2 or (S)-2-
(pyrrol-2-ylmethyleneamino)-2′-hydroxy-1,1′-binaphthyl11f and
Ln[N(SiMe3)2]3 in toluene results in the clean formation of the
corresponding organolanthanide amide compounds. The acidic
proton in the ligand 1H would allow a similar silylamine
elimination to occur between 1H and metal amides. In fact,
(18) Jones, M. D.; Almeida Paz, F. A.; Davies, J. E.; Johnson, B. F. G.
Acta Crystallogr. 2003, E59, o910.

1246 Organometallics, Vol. 27, No. 6, 2008
Zi et al.
angles are 122.2(1)° for Sm, 120.3(2)° for Y, and 119.7(2)° for
Yb. These structural data are comparable to those found in [(R)-
C20H12(NCHC4H3N)2]LnN(SiMe3)2(thf).12 The Ln-N(SiMe3)2
distances of 2.258(2) Å for Sm, 2.208(3) Å for Y, and 2.169(3)
Å for Yb are very close to the corresponding values of 2.284(5)
Å for Sm, 2.223 Å for Y, and 2.183 Å for Yb found in the
starting materials Sm[N(SiMe3)2]3,19 Y[N(SiMe3)2]3,20 and
Yb[N(SiMe3)2]3.21 The twisting between the naphthyl rings give
torsion angles of 69.2(1) and 76.1(1)° for Sm, 69.6(3) and
76.6(3)° for Y, and 69.0(2) and 76.6(2)° for Yb, which are
comparable to that found in 1H of 75.6(3)°.
plexes can mediate the cyclization of the representative ami-
noalkenes, but the conversion ceases after 1 or 2 days due to
the decomposition of the complexes by the intermediacy of the
metal alkyl species via 1,2-migratory insertion at the imine
unit,5a which makes the determination of kinetic data infeasible.
Although the enantiomeric excesses obtained remain moderate
to good, it should be noted that there are only a small number
of catalysts for these reactions that give a significant ee (>90%)
at all.7a,9d,f,10e–g
Conclusions
Asymmetric Hydroamination. Compounds 2–4 have been
used as the catalysts in the intramolecular hydroamination/
cyclization reaction of nonactivated terminal aminoalkenes
(Table 2). All substrates are converted to the cyclic product at
room temperature or elevated temperature in moderate to good
conversions. The results of the hydroamination/cyclization of
2,2-dimethylpent-4-enylamine (5a) show that the samarium
amide 2 (Table 2, entry 1) is noticeably good at room
temperature. Not surprisingly, given a more open coordination
sphere, the reaction is faster, but the ee value remains moderate.
When the smaller Y3+ ion is used (Table 2, entry 2), the rate
increases and the ee also improves slightly. However, under
similar reaction conditions, the smaller Yb3+ ion (Table 2, entry
3) gives a rather low conversion (only 7.0%) but affords a good
ee value (up to 71%), which is commensurate with the smaller
metal ion radius.22 When the temperature is increased, the rate
increases but the ee value falls slightly (Table 2, entry 4). We
are encouraged to find that the formation of six-membered rings
can also be achieved with our catalysts 2 and 3 (Table 2, entries
8 and 9), and a moderate enantioselectivity (25%), mediated
by the catalyst 3, has been obtained (Table 2, entry 9). It can
be concluded that the rate of cyclization for aminoalkenes
follows the order 5 > 6, consistent with classical, stereoelec-
tronically controlled cyclization processes.8e The three com-
The bis-ligated lanthanide amides (1)2-LnN(SiMe3)2, prepared
from the C1-symmetric monopyrrole-substituted ligand 1H, have
been found to be more effective chiral catalysts for the
enantioselective hydroamination/cyclization reaction than the
C2-symmetric bis(pyrrolate) lanthanide amides [(R)-C20H12-
(NCHC4H3N)2]LnN(SiMe3)2(thf) (Ln ) Sm, Y, Yb).12 In some
cases, the corresponding heterocyclic products have been
obtained with good ee values (up to 71%) by this modified chiral
1,1′-binaphthyl-2,2′-diamine ligand. Although this modification
using peripheral binaphthalene coupled with pyrrole and dim-
ethylamine ligation in multidentate systems does not provide
sufficient rigidity of the dative N-donor ligand to achieve a
significant enantioselectivity (ee >90%), in contrast to the case
for the binaphtholate system,7a the present results should
significantly expand the range of possibilities in designing
catalysts not only for hydroamination but also for many other
reactions.13 We are planning to synthesize a similar tridentate
chiral binaphthyl embedded in a C1-symmetric chiral scaffold
in order to obtain more effective and stereoselective chiral
ligands and to utilize those novel chiral ligands in this
transformation and other catalytic asymmetric reactions. Work
along these lines is in progress.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China (Grant No.
20602003).
(19) Brady, E. D.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D. W.;
Poli, R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 42, 6682.
(20) Westerhausen, M.; Hartmann, M.; Pfitzner, A.; Schwarz, W. Z.
Anorg. Allg. Chem. 1995, 621, 837.
Supporting Information Available: X-ray crystallographic data,
in CIF format, for 1H, 2, 3 and 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
(21) Niemeyer, M. Z. Anorg. Allg. Chem. 2002, 628, 647.
(22) For the ionic radius of yttrium (Y3+ ) 0.88 Å), samarium (Sm3+
) 0.964 Å), and ytterbium (Yb3+ ) 0.858 Å), see: Cotton, F. A.; Wilkinson,
G. AdVanced Inorganic Chemistry, 4th ed.; Wiley: New York, 1980; p 982.
OM701058K