Synthesis and structures of novel chiral lithium amidinates and mono- and di-lithium (1R,2R)-(-)-1,2-(NHSiMe3)2C6H10

Article abstract of DOI:10.1039/b106992f

Four lithium salts derived from (1R,2R)-1,2-diaminocyclohexane are described. After the resolution of 1,2-diaminocyclohexane (DACH), (1R,2R)-(-)-1,2-(NHSiMe₃)₂C₆H₁₀ (1) was prepared from the (R,R) enatiomer by r

Full text of DOI:10.1039/b106992f

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Synthesis and structures of novel chiral lithium amidinates and
mono- and di-lithium (1R,2R)-(؊)-1,2-(NHSiMe3)2C6H10
Jian-Feng Li,a Lin-Hong Weng,b Xue-Hong Weia and Dian-Sheng Liu*a
a Department of Chemistry, The Shanxi University, Shanxi, P.R.China.
E-mail: dsliu@mail.sxu.edu.cn
b Department of Chemistry, The Fudan University, Shanghai, P.R.China
Received 1st August 2001, Accepted 4th January 2002
First published as an Advance Article on the web 26th February 2002
Four lithium salts derived from (1R,2R)-1,2-diaminocyclohexane are described. After the resolution of
1,2-diaminocyclohexane (DACH), (1R,2R)-(Ϫ)-1,2-(NHSiMe3)2C6H10 (1) was prepared from the (R,R)
enatiomer by reaction with LiBun and Me3SiCl. Treatment of 1 with one equiv. of LiBun gave the single
lithium salt (1R,2R)-(Ϫ)-1-Li(NSiMe3)-2-(NHSiMe3)C6H10 (2). Double deprotonation of 1 with two
equiv. of LiBun yielded the dilithium salt Li2[(1R,2R)-(Ϫ)-1,2-(NSiMe3)2C6H10] (3). The addition
reaction of 2 or 3 with PhCN gave (1R,2R)-(Ϫ)-1-Li[NC(Ph)N(SiMe3)]-2-(NHSiMe3)C6H10 (4)
and Li2[(1R,2R)-(Ϫ)-1,2-{NC(Ph)N(SiMe3)}2C6H10] (5) respectively. Crystallographic studies
and comparison of these lithium salts with β-diketiminates exhibit some noteworthy features.
Introduction
trans-1,2-Diaminocyclohexane (DACH) as its (R,R) or (S,S)
enatiomer has been utilised as a broad-range chiral reagent in
the field of asymmetric synthesis and molecular recognition.1
The (R,R) enatiomer when exposed to the known Jacobsen’s
catalysts2 or other chiral metal catalysts3 has been proved to be
a very useful building block. The parent chiral DACH has been
modified to give variants which bear appropriate structural and
electronic features for intended specific reactions and its lithium
salt derivatives are used as ligand transfer agents for metal
complexes.4 The mono- and di-lithium anions derived from
(1R,2R)-(Ϫ)-1,2-(NHSiMe3)2C6H10 are very useful parent sys-
tems for generating a variety of chiral derivatives. Surprisingly,
such parent alkali metal anions seem not to have been charac-
terized by X-ray diffraction so far, although the lithium salts
have been prepared as mixtures of enatiomers in trans form.5
For a detailed understanding and comparison, we therefore
prepared mono- and di-lithium (1R,2R)-(Ϫ)-1,2-(NHSiMe3)2-
C6H10 (2 and 3) and grew suitable single crystals for X-ray dif-
fraction. Derived from compounds 2 and 3 two novel amidinate
anions 4 and 5 were synthesized via an addition reaction with
PhCN. The molecular structure of complex 4 shows that the
central metal has a tridentate coordination environment similar
to the alkylamidinate anions [CyNC(R)NCy]Ϫ (Cy = cyclo-
hexane, R = alkyl).6 Especially as a ligand transfer agent
for metal complexes it will be interesting to investigate the
efficiency of the chiral reagent in asymmetric synthesis.
Scheme 1 Synthesis of 1, 2, 3, 4 and 5. Reagents and conditions:
i. LiBun in Et2O, 0 to 20 ЊC, then Me3SiCl in C6H14, 0 to 20 ЊC; ii,
1 equiv. LiBun in C6H14, 0 to 20 ЊC; iii, 2 equiv. LiBun in C6H14, 0 to
20 ЊC; iv, 1 equiv. PhCN in C6H14, 0 to 20 ЊC; v, 2 equiv. of PhCN in
Et2O, 0 to 20 ЊC.
Results and discussion
Synthesis of 2, 3, 4 and 5
The resolution of ( )-trans-DACH was carried out using -(ϩ)-
tartaric acid.7 Treatment of (1R,2R)-DACH with 2 equiv. of
LiBun and 2 equiv. of Me3SiCl gave (1R,2R)-(NHSiMe3)2C6H10
(1), which was purified by distillation, yielding a colorless oil
(1 mmHg, bp 62–64 ЊC).8 The mono- and di-lithium anion
complexes (1R,2R)-(Ϫ)-1-Li(NSiMe3)-2-(NHSiMe3)C6H10 (2)
and Li2[(1R,2R)-(Ϫ)-1,2-(NSiMe3)2C6H10] (3) were obtained by
carefully controlling the molecular ratio of LiBun added
(Scheme 1). Single crystals suitable for X-ray diffraction were
obtained by crystallization from a concentrated solution of
hexane at Ϫ30 ЊC for 7 days. Compounds 2 and 3 appeared as
spiculate and hexagonal crystals, respectively.
The reaction of LiNR1R2 with R3CN is a fascinating area in
organometallic chemistry.9 In our earlier publications we have
DOI: 10.1039/b106992f
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Table 1 Selected bond distances (Å) and bond angles (Њ) for 2
shown that the interaction of a trimethylsilylmethyllithium
reagent Li[CHR2] (R = SiMe3) with an α-hydrogen-free nitrile
R3CN can yield a 1-azaallyl- (A),10 β-diketiminato- (B)11 or 1,3-
diazaallyl-lithium (C)12 resulting from the 1,3-migration of an
SiMe3 group from carbon to nitrogen (Scheme 2).
Li1–N1
Li1–N3
N3–Li2
Li2–N1
Li2–Li1
Li1–N2
Li2–N4
2.008(7)
1.980(8)
2.019(8)
1.985(7)
2.363(10)
2.050(8)
2.112(8)
N3–C13
C13–C18
C18–N4
C1–N1
C6–C1
1.470(5)
1.550(6)
1.474(5)
1.474(4)
1.556(5)
1.477(5)
N2–C6
N1–Li1–N3
Li1–N3–Li2
N3–Li2–N1
Li2–N1–Li1
C6–Li1–N1
Li1–N1–C1
107.7(3)
N1–Li1–N2
C1–C6–Li1
N3–C13–C18
C13–C18–Li2
C18–Li2–N3
Li2–N3–C13
91.2(3)
79.0(2)
110.9(3)
82.3(3)
68.0(2)
147.1(4)
72.4(3)
107.1(3)
72.5(3)
66.5(2)
100.8(3)
Scheme 2
Table 2 Selected bond distances (Å) and bond angles (Њ) for 3
Herein we have designed chiral tridentate and tetradentate
ligands using mono- and di-lithium anions as nucleophiles via
an addition reaction with benzonitrile (Scheme 1). However
when using the nonaromatic nitrile ButCN there was no reac-
Li1–Li4
Li1–Li3
N2–Li3
Li1–N2
Li1–N1
2.362(11)
2.365(10)
2.094(8)
2.021(9)
2.072(8)
N3–Li4
Li4–N1
N1–Li2
N2–C6
N1–C1
1.984(8)
2.087(8)
2.048(8)
1.477(5)
1.487(5)
1
tion, as proved by H NMR spectroscopy. Treatment of com-
pound 2 with one equiv. of PhCN in hexane at 0 ЊC gave
(1R,2R)-(Ϫ)-1-Li[NC(Ph)N(SiMe3)]-2-(NHSiMe3)C6H10 (4) in
90% yield. The molecular structure of complex 4 shows that
the reaction involved a silicotropic rearrangement resulting in a
η3-NCN conjugate anion, and another terminal N atom
also provides a coordination site, Fig 3. However the addition
reaction of compound 3 with two equiv. of PhCN yielded
Li2[(1R,2R)-(Ϫ)-1,2-{NC(Ph)N(SiMe3)}2C6H10] (5), confirmed
by 1H NMR and 13C NMR. Ensuing work, especially using the
anions as chiral ligands for transition metals, is under way.
Li4–N1–Li2
N1–Li2–N3
N1–Li1–N2
N3–Li4–N1
69.4(3)
108.9(4)
88.1(3)
N4–Li1–N2
Li1–N2–Li3
N2–Li3–N4
Li3–N4–Li1
109.3(4)
70.1(3)
109.5(3)
70.5(3)
109.5(4)
Table 3 Selected bond distances (Å) and bond angles (Њ) for 4
Li1–N23
Li1–N22
Li1–N12
Li2–N22
Li2–Li1
N21–Li2
N13–Li2
C11–Li1
2.115(5)
2.056(5)
2.133(5)
2.151(5)
2.572(6)
2.036(5)
2.180(5)
2.400(5)
Li1–N11
N23–C43
C11–N11
C11–N12
C18–C23
N13–C23
C31–Li2
2.018(5)
1.486(3)
1.319(3)
1.340(3)
1.536(4)
1.485(4)
2.424(5)
NMR spectroscopy
The 1H NMR spectra showed characteristic resonances for the
protons of the cyclohexane groups in the region δ 1.00–2.12 (1),
δ 1.24–2.63 (2), δ 1.34–2.70 (3), δ 0.82–2.78 (4), δ 0.59–3.06 (5).
In the two asymmetric compounds 2 and 4, the protons of the
SiMe3 groups appear as two separate peaks (δ 0.22 and 0.37 for
2, δ 0.26 and 0.33 for 4). Additional support for the identi-
fication of the products was provided by the 13C NMR spectra.
It was observed that the 13C NMR spectra of 2 and 4 showed
all of the expected resonances for the carbon atoms and the
symmetric complexes 1, 3 and 5 showed half of them.
N12–Li1–N22
Li1–N12–Li2
N12–Li2–N22
Li2–N22–Li1
C43–Li1–N22
Li1–N22–C38
103.3(2)
75.31(19)
102.0(2)
75.34(19)
60.72(14)
106.16(19)
N11–Li1–N12
C38–C43–Li1
N12–C18–C23
C18–C23–Li2
C23–Li2–N12
Li2–N12–C18
66.92(16)
79.51(16)
110.7(2)
78.79(16)
59.46(14)
107.7(2)
from 1.980(8) to 2.019(8) Å). Two of the five-membered Li–N–
C–C–N rings adopt an envelope conformation.
Crystal structures of complexes 2, 3 and 4
The molecular structure of 3 is shown in Fig. 2; it has rigor-
ous C2-symmetry. Dimeric aggregation is revealed, which is
built around two (LiN)2 rhombi consisting of N3–Li4–N1–
Li2 and N4–Li1–N2–Li3. Between these two (LiN)2 rhombi
there are distorted Li4-tetrahedra with N atoms capping the
triangular faces.
The crystal structures of the three lithium complexes 2, 3 and 4
were determined by X-ray diffraction. Selected bond distances
and angles are listed in Tables 1–3.
The molecular structure of 2 is shown in Fig. 1. A centro-
symmetric dimeric aggregation is observed which is built
around a strict (LiN)2 rhombus (with the Li–N bonds ranging
Fig. 1 Molecular structure of compound 2.
Fig. 2 Molecular structure of compound 3.
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Table 4 Some important geometric data (bond lengths in Å, angles in Њ) on compounds 2, 3, 4, 6 and 7
2
3
4
6
7
Li–N(1)
Li–N(2)
Li–N(1)Ј
N(1)–C(1)
2.008(7)
2.050(8)
1.980(8)
1.474(4)
1.477(5)
2.072(8)
2.021(9)
2.087(8)
1.487(5)
1.477(5)
2.133(5)
2.018(5)
2.056(5)
1.319(3)
1.340(3)
1.97(2)
2.04(2)
2.17(2)
1.27(1)
1.33(1)
1.965(9)
1.952(10)
2.095(9)
1.337(6)
1.299(6)
N(2)–C(2)
N(1)–Li–N(2)
Co-ordination number at Li
Aggregation
91.2(3)
3
Dimer
88.1(3)
3
Dimer
66.92(16)
4
Dimer
100.0(7)
3
Dimer
103.0(4)
3
Dimer
Fig. 3 Molecular structure of compound 4.
The dinuclear lithium complex 4 (Fig. 3) presents a nearly
planar (LiN)2 ring. The N–C–N fragment is in the form of a
η3-anion and has some degree of π-electron delocalisation
providing a lithium coordinate site [Li–C distance, 2.424(5) Å;
Li–N distances, 2.151(5) and 2.036(5)Å]. Interestingly, the
other nitrogen atom on the cyclohexane provides another
coordination site having an intermolecular Li–Nsp2 bond [Li–N
distance, 2.115(5) Å].
A study of the key bond angles and distances in these com-
plexes reveals some noteworthy trends. A comparison of the
structural data for complexes 2, 3, and 4 with the dinuclear
β-diketiminates [Li{N(R)C(Ph)C(H)C(But)NR}]2 (6)9a and
[Li{N(R)C(Ph)C(H)C(Ph)NR}]2 (7)9b (prepared in our earlier
work and shown schematically in Scheme 3) is given in Table 4.
It should be noted that the N(1)–Li–N(2) angles broaden with
increasing length of the carbon chain of the distorted or planar
fragments NCN [66.92(16)Њ (4)], NCCN [91.2(3)Њ (2) and
88.1(3)Њ (3)] and NCCCN [100.0(7)Њ (6) and 103.0(4)Њ (7)]. All
the N–Li–N angles at the lithium atom of the (LiN)2 cores in 2,
3, 4, 6 and 7 [107.7(3)Њ (2), 109.5(4)Њ (3), 103.3(2)Њ (4), 103.8(7)Њ
(6) and 105.0(4)Њ (7)] are wider than the Li–N–Li angle at nitro-
gen [72.5(3)Њ (2), 69.4(3)Њ (3), 75.34(19)Њ (4), 76.2(6)Њ (6) and
75.0(4)Њ (7)]. The addition products 4 and 5 are interesting for
us due to their η3-electron delocalisation and possible utiliz-
ation as chiral ligands. The intramolecular distance from the
lithium to the chiral center Li–C(chiral) in 4 [4.122(5) and
3.474(9) Å] is longer than the intermolecular distance [2.674(5)
Å]. As a ligand it might be more useful to prepare the catalyst
of the dinuclear metal complex in an asymmetrical syntheses.
As a comparison of the mono-lithium salts, the β-diketiminato
ligands 6 and 7 with different substituents (Ph, But in 6, Ph, Ph
in 7) have shorter intramolecular Li–Nsp3 bonds [2.04(2) (6) and
Scheme 3
1.965(9) Å (7)] than the intermolecular Li–Nsp3 bond [2.17(2)
(6) and 2.095(9) Å (7)]; however, amide and amidinate com-
plexes 2 and 4 have longer intramolecular Li–Nsp3 bonds
[2.008(7) (2) and 2.133(5) Å (4) than intermolacular Li–Nsp3
bonds 1.980(8) (2) and 2.056(5) Å (4)]. In addition, the N–C
bond distances in 2 and 3 are around 1.477 0.001 Å, but the
pairs of N–C bonds in 4 [1.319(3) and 1.340(3) Å], 6 [1.27(1)
and 1.33(1) Å] and 7 [1.337(6) and 1.299(6) Å] having some
degree of π-electron delocalisation are far from being identical.
It is observed that for the mono-lithium salts 2, 4, 6 and 7,
anionic nitrogen N(1) is four-co-ordinate and bridging, and the
other N(2) three-co-ordinate; for di-lithium salt 3, all nitrogen
atoms are four-co-ordinate and bridging. All the cyclohex-
anyl groups of the three complexes 2, 3 and 4 adopt chair
conformations.
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Table 5 Summary of crystallographic data for 2, 3 and 4
Compounds
2
3
4
Formula
M
Temperature/K
Crystal system
C24H54Li2N4Si4
524.95
298 (2)
Monoclinic
P21
C24H56Li4N4Si4
540.85
293 (2)
Trigonal
P31
C19H34LiN3Si2
367.61
173 (2)
Monoclinic
P21
Space group
a/Å
b/Å
c/Å
α/Њ
9.778(3)
18.113(5)
10.387(3)
90
10.5111(14)
10.5111(14)
27.891(5)
90
9.9459(4)
20.6507(9)
11.0775(4)
90
β/Њ
103.643(5)
90
1787.7(8)
2
90
120
2668.7(7)
3
0.184
96.703(1)
90
2259.7(2)
4
γ/Њ
U/Å3
Z
µ/mmϪ1
0.183
0.163
Reflections collected
Independent reflections
R1 (I > 2σ(I ))
wR2 (all data)
8423
6875
0.0570
0.1525
11141
6280
0.0591
0.1536
16443
5212
0.0373
0.0814
solution was concentrated and left to stand for one week, allow-
Experimental
ing the isolation of colorless crystals of compound 3 (0.34 g,
1
General procedures
41%). H NMR (C6D6): δ 0.31 (s, NSiMe3), 1.34 (m, CH, 4H),
1.69 (m, CH, 2H), 2.43 (m, CH, 2H), 2.70 (m, CH, 2H).
13C{1H} NMR (C6D6): δ 3.7 (s, SiMe3), 26.8 (s, NCCC), 40.0
(s, NCC), 67.4 (s, CN).
All manipulations were carried out under argon, using standard
high-vacuum, Schlenk techniques. Hexane, Et2O, benzene-d6
were distilled from Na/K alloy. Optical rotation was recorded
using a standard cell with a 10 cm pass on a Perkin-Elmer 241
polarimeter. 1H (300 MHz) and 13C (75.47 MHz) NMR spectra
were recorded on a Bruker DRX-300 spectrometer at ambient
temperature.
(1R,2R)-(؊)-1-Li[NC(Ph)N(SiMe3)]-2-(NHSiMe3)C6H10 4.
PhCN (0.16 cm3, 1.58 mmol) was added by syringe to a solution
of 2 (0.417 g, 1.58 mmol) in hexane (ca. 25 cm3) at 0 ЊC. The
mixture was slowly warmed to ambient temperature and stirred
for 12 h. The clear solution was concentrated and allowed to
stand for one week; crystalline products were obtained (0.52 g,
90%) (Found: C, 63.05; H, 9.22; N, 11.10. C19H34N3LiSi2
requires C, 62.08; H, 9.32; N, 11.43%). 1H NMR (C6D6): δ 0.26
(s, NSiMe3), 0.33 (s, NSiMe3), 0.82 (m, CH, 2H), 1.20 (m, CH,
2H), 1.48 (m, CH, 2H), 1.96 (m, CH, 2H), 2.66 (m, CH, 1H),
2.78 (m, CH, 1H), 7.19 (m, Ph, 2H), 7.50 (m, Ph, 3H). 13C{1H}
NMR (C6D6): δ 2.26 (s, SiMe3), 4.55 (s, SiMe3), 26.06
(s, NCCC), 27.02 (s, NCCC), 38.59 (s, NCC), 38.71 (s, NCC),
60.73 (s, CN), 65.73 (s, CN), 129.07–127.624 (m, C5H5), 143.80
(s, CC5H5), 180.68 (s, CPh).
Preparations
(1R,2R)-(؊)-1,2-(NHSiMe3)2C6H10 1. A commercially avail-
able mixture of cis- and trans-1,2-diaminocyclohexane was
dealt with by the reported procedure to give (1R,2R)-DACH;
[α]2D0 = Ϫ25Њ (c = 5, 1 N HCl). LiBun (14.2 cm3, 1.23 M in
hexane) was added by syringe to a stirred solution of (1R,2R)-
DACH (1.00g, 8.76 mmol) in Et2O (ca. 20 cm3) at 0 ЊC. The
mixture was warmed to room temperature slowly, stirred for
12 h, and filtered. The white precipitate isolated was dried in
vacuum to give (1R,2R)-(Ϫ)-1,2-(LiNH)2C6H10, (0.98 g, 89%).
To this compound was added Me3SiCl (15.5 mmol, 1.96 cm3)
in hexane (ca. 20 cm3) at 0 ЊC. The mixture was warmed to
ambient temperature, stirred for 12 h, and then filtered. The
filtrate was distilled at reduced pressure, and a fraction was
collected at 1 mmHg, bp 62–64 ЊC to give a colorless compound
(1.97 g, 87%). 1H NMR (CDCl3): δ Ϫ0.04 (s, NSiMe3), 0.65 (br,
NH, 2H), 1.00 (m, CH, 2H), 1.15 (m, CH, 2H), 1.55 (m, CH,
2H), 1.81 (m, CH, 2H), 2.12 (m, CH, 2H), 13C{1H} NMR
(C6D6): δ 1.7 (s, SiMe3), 26.5 (s, NCCC), 37.6 (s, NCC), 59.7
(s, CN).
Li2[(1R,2R)-(؊)-1,2-{NC(Ph)N(SiMe3)}2C6H10] 5. PhCN
(0.18 cm3, 1.77 mmol) was added by syringe to a solution of 3
(0.240 g, 0.89 mmol) in Et2O (ca. 25 cm3) at 0 ЊC. The mixture
was slowly warmed to ambient temperature and stirred for 12 h.
The solution was concentrated and a solid product obtained
(0.38 g, 89%) (Found: C, 66.13; H, 8.18; N, 11.42. C26H38N4-
Li2Si2 requires C, 65.51; H, 8.04; N, 11.76%). 1H NMR (C6D6):
δ 0.03 (s, NSiMe3), 0.59 (m, CH, 2H), 0.97 (m, CH, 4H), 1.71
(m, CH, 2H), 3.06 (m, CH, 2H), 6.59 (m, Ph, 2H), 6.97 (m, Ph,
3H). 13C{1H} NMR (C6D6): δ 4.29 (s, SiMe3), 26.77 (s, NCCC),
37.07 (s, NCC), 64.80 (s, CN), 128.85–132.83 (m, C5H5), 143.49
(s, CC5H5), 181.68 (s, CPh).
(1R,2R)-(؊)-1-Li(NSiMe3)-2-(NHSiMe3)C6H10 2. LiBun (2.0
cm3,1.61 M in hexane) was added to a solution of 1 (0.851 g,
3.30 mmol) in hexane (15 cm3) carefully by syringe at 0 ЊC, The
mixture was warmed to ambient temperature slowly and stirred
overnight. The clear solution was concentrated to ca. 8 cm3, to
give colorless spiculate crystals (0.31 g, 36%). 1H NMR (C6D6):
δ 0.22 (s, NSiMe3), 0.37 (s, NSiMe3), 1.24 (m, CH, 4H), 1.72 (m,
CH, 2H), 2.08 (m, CH, 2H), 2.63 (m, CH, 2H). 13C{1H} NMR
(C6D6): δ 1.8 (s, SiMe3), 2.9 (s, SiMe3), 26.9 (s, NCCC), 27.2
(s, NCCC), 38.6 (s, NCC), 45.0 (s, NCC), 61.6 (s, CN), 65.8
(s, CN).
Crystal data and refinement details
Single crystals of complexes 2, 3 and 4 were mounted in
Lindemann capillaries under argon. Data were collected on
an Bruker Smart 1000 diffractometer utilizing graphite-
monochromatized Mo-Kα radiation (λ = 0.71073 Å) at room
temperature. A total of N reflections were collected using
an ω scan mode. Corrections were applied for Lorentz and
polarization effects as well as absorption using multi-scans
(SADABS).13 The structure was solved by direct methods
(SHELXS97).14 Then the remaining non-hydrogen atoms were
obtained from the successive difference fourier map. All non-H
atoms were refined with anisotropic displacement parameters,
Li2[(1R,2R)-(؊)-1,2-(NSiMe3)2C6H10] 3. LiBun (3.8 cm3, 1.61
M in hexane) was added to a solution of 1 (0.796 g, 3.08 mmol)
in hexane (ca. 25 cm3) at 0 ЊC. The mixture was warmed to
ambient temperature slowly and stirred for 12 h. The resulting
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P. Knochel, J. Org. Chem., 1994, 59, 4143; (d ) X. Zhang and
while the H atoms were constrained to parent sites, using a
riding model (SHELXTL).15 Further details are given in Table 5.
CCDC reference numbers 161938–161940.
See http://www.rsc.org/suppdata/dt/b1/b106992f/ for crystal-
lographic data in CIF or other electronic format.
C. Guo, Tetrahedron Lett., 1995, 36, 4947.
4 Y. L. Bennani and S. Hanessian, Chem. Rev., 1997, 97, 3161.
5 B. Tsuie, D. C. Swenson, R. F. Jordan and J. L. Peterson,
Organometallics, 1997, 16, 1392.
6 (a) Y. Zhou and D. S. Richeson, Inorg. Chem., 1997, 36, 501; (b)
M. P. Coles, D. C. Swenson and R. F. Jordan, Organometallics, 1997,
24, 5183; (c) S. R. Foley, C. Bensimon and D. S. Richeson, J. Am.
Chem. Soc., 1997, 119, 10359.
Acknowledgements
7 J. F. Larrow and E. N. Jacobsen, J. Org. Chem., 1994, 59, 1939.
8 Jordan and co-workers have reported work including the synthesis
of ( )-trans-1,2-(NHSiMe3)2C6H10 whose boiling point is different
(10Ϫ3 mmHg, bp 92.9–96.0 ЊC) to that given here (see ref. 5).
9 (a) P. B. Hitchcock, M. F. Lappert, M. Layh, D.-S. Liu, R. Sablong
and T. Shun, J. Chem. Soc., Dalton Trans., 2000, 2301; (b) P. B.
Hitchcock, M. F. Lappert and D.-S. Liu, J. Chem. Soc., Chem.
Commun., 1994, 1699; (c) M. F. Lappert and D.-S. Liu,
J. Organomet. Chem., 1995, 203.
We thank the Natural Science Foundation of China and Shanxi
Province (20171030, 29872024 and 20011008, D.-S. L.).
References
1 (a) S. Kobayashi and H. Ishitani, Chem. Rev., 1999, 99, 1069;
(c) R. O. Duthaler and A. Hafner, Chem. Rev., 1992, 92, 807; (d )
F.-y. Zhang, C.-C. Pai and A. S. C. Chan, J. Am. Chem. Soc., 1998,
120, 5808; (e) K. Ishimaru, K. Monda, Y. Yamamoto and K.-y.
Akiba, Tetrahedron, 1998, 54, 727.
10 P. B. Hitchcock, M. F. Lappert and M. Layh, Chem. Commun., 1998,
201.
2 (a) S. E. Schaus, J. Branalt and E. N. Jacobsen, J. Org. Chem., 1998,
63, 403; (b) W. Zhang, J. L. Loebach, S. R. Wilson and E. N.
Jacobsen, J. Am. Chem. Soc., 1990, 112, 2801; (c) M. S. Sigman and
E. N. Jacobsen, J. Am. Chem. Soc., 1998, 120, 5315; (d ) L. Deng
and E. N. Jacobsen, J. Org. Chem., 1992, 57, 4320; (e) J.-X. Gao,
T. Ikariya and R. Noyori, Organometallics, 1996, 15, 1087.
3 (a) M. J. Rozema, C. Eisenberg, H. Lütjens, R. Ostwald, K. Belyk
and P. Knochel, Tetrahedron Lett., 1993, 34, 3115; (b) B. M. Trost,
M. J. Krische, R. Radinov and G. Zanoni, J. Am. Chem. Soc., 1996,
118, 6297; (c) R. Ostwald, P.-Y. Chavant, H. Stadtmüller and
11 F. Antolini, P. B. Hitchcock and M. F. Lappert, Chem. Commun.,
2000, 1301.
12 P. B. Hitchcock, M. F. Lappert, W.-P. Leung, D.-S. Liu, T. C. W.
Mak and Z.-X. Wang, J. Chem. Soc., Dalton Trans., 1999, 1263.
13 G. M. Sheldrick, Correction Software, University of Göttingen,
Germany, 1996.
14 G. M. Sheldrick, Program for the solution of Crystal Structures,
University of Göttingen, Germany, 1997.
15 Program for Crystal Structure Refinement, Bruker Analytical X-ray
Instruments Inc., Madison, Wisconsin, USA, 1998.
J. Chem. Soc., Dalton Trans., 2002, 1401–1405
1405