Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.12.008

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₂-symmetric ligands, (R)-2,2′-bis(pyridin-2-ylmethylamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), (R)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (3H₂), (R)-2,2′-bis(diphenylphosphinoylamino)-6,6′-dimethyl-1,1′-biphenyl (4H₂), (R)-2,2′-bis(methanesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (5H₂), (R)-2,2′-bis(p-toluenesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (6H₂), and C₁-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), which are derived from (R)-2,2′-diamino-6,6′-dimethyl-1,1′-biphenyl. Treatment of M(NMe₂)₄ with 1 equiv. of N₄-ligand, 2H₂ or 3H₂ gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2)Zr(NMe₂)₂ (9), (3)Zr(NMe₂)₂ (11), and titanium amide (3)Ti(NMe₂)₂ (10), respectively, in good yields. Reaction of Zr(NMe₂)₄ with 1 equiv of diphenylphosphoramide 4H₂ affords the chiral zirconium amide (4)Zr(NMe₂)₂ (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe₂)₄ with 1 equiv. of sulphonylamide ligand, 5H₂ or 6H₂ gives, after recrystallization from a toluene solution, the chiral titanium amides (5)Ti(NMe₂)₂·0.5C₇H₈ (13·0.5C₇H₈) and (6)Ti(NMe₂)₂ (15), respectively, in good yields, while reaction of Zr(NMe₂)₄ with 1 equiv. of 5H₂ or 6H₂ gives the bis-ligated complexes, (5)₂Zr (14) and (6)₂Zr (16). Treatment of M(NMe₂)₄ with 2 equiv. of diphenylthiophosphoramide ligand 7H or N₃-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)₂Zr(NMe₂)₂ (17) and (8)₂Zr(NMe₂)₂ (19), and bis-ligated chiral titanium amide (8)₂Ti(NMe₂)₂ (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with moderate ee values, while the titanium amides are not.

Full text of DOI:10.1016/j.jorganchem.2009.12.008

Journal of Organometallic Chemistry 695 (2010) 730–739
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV)
amides with chiral biphenyldiamine-based ligands
a
a
a
b
Guofu Zi a, , Furen Zhang , Xue Liu , Lin Ai , Haibin Song
*
a Department of Chemistry, Beijing Normal University, Beijing 100875, China
b State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 October 2009
Received in revised form 5 December 2009
Accepted 11 December 2009
Available online 16 December 2009
A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between
M(NMe2)4 (M = Ti, Zr) and C2-symmetric ligands, (R)-2,20-bis(pyridin-2-ylmethylamino)-6,60-dimethyl-
1,10-biphenyl (2H2), (R)-2,20-bis(pyrrol-2-ylmethyleneamino)-6,60-dimethyl-1,10-biphenyl (3H2), (R)-
2,20-bis(diphenylphosphinoylamino)-6,60-dimethyl-1,10-biphenyl (4H2), (R)-2,20-bis(methanesulphonyla-
mino)-6,60-dimethyl-1,10-biphenyl (5H2), (R)-2,20-bis(p-toluenesulphonylamino)-6,60-dimethyl-1,10-
biphenyl (6H2), and C1-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-20-(dimethylamino)-
6,60-dimethyl-1,10-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-20-(dimethylamino)-6,60-dimethyl-1,10-
biphenyl (8H), which are derived from (R)-2,20-diamino-6,60-dimethyl-1,10-biphenyl. Treatment of
M(NMe2)4 with 1 equiv. of N4-ligand, 2H2 or 3H2 gives, after recrystallization from an n-hexane solution,
the chiral zirconium amides (2)Zr(NMe2)2 (9), (3)Zr(NMe2)2 (11), and titanium amide (3)Ti(NMe2)2 (10),
respectively, in good yields. Reaction of Zr(NMe2)4 with 1 equiv of diphenylphosphoramide 4H2 affords
the chiral zirconium amide (4)Zr(NMe2)2 (12) in 85% yield. Under similar reaction conditions, treatment
of Ti(NMe2)4 with 1 equiv. of sulphonylamide ligand, 5H2 or 6H2 gives, after recrystallization from a tol-
uene solution, the chiral titanium amides (5)Ti(NMe2)2ꢀ0.5C7H8 (13ꢀ0.5C7H8) and (6)Ti(NMe2)2 (15),
respectively, in good yields, while reaction of Zr(NMe2)4 with 1 equiv. of 5H2 or 6H2 gives the bis-ligated
complexes, (5)2Zr (14) and (6)2Zr (16). Treatment of M(NMe2)4 with 2 equiv. of diphenylthiophosphora-
mide ligand 7H or N3-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chi-
ral zirconium amides (7)2Zr(NMe2)2 (17) and (8)2Zr(NMe2)2 (19), and bis-ligated chiral titanium amide
(8)2Ti(NMe2)2 (18), respectively, in good yields. All new compounds have been characterized by various
spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and
17–19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active cata-
lysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to
excellent yields with moderate ee values, while the titanium amides are not.
Keywords:
Chiral organo-titanium and zirconium
complexes
Synthesis
Crystal structure
Asymmetric hydroamination/cyclization
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
ing multidentate ligands, and their Ir(I), Rh(I), Ti(IV), Ag(I), Cu(II),
Zr(IV) and lanthanide complexes are useful catalysts for a wide
Ligand modification plays a key role in developing new cata-
lyst precursors for asymmetric synthesis. To meet the require-
ments of different purposes, a large number of chiral ligands
have been developed. Among these, the nitrogen-containing li-
gands have received increasing attention in recent years due to
their high complex stability and good availability in enantiomeri-
cally pure form, which are advantageous for practical applications
[1–5]. Although a variety of chiral nitrogen-containing ligands
have been studied, the development of new N-ligands for asym-
metric transformations is still a desirable goal. In recent years,
we have therefore developed a series of chiral nitrogen-contain-
range of transformations [6–21], and we found that the group 4
metal amides based on chiral binaphthyl-backbones are effective
catalysts for the asymmetric hydroamination/cyclization, in
which good enantioselectivities (up to 72% ee) have been ob-
tained [19–21]. In our endeavors to further explore the chiral
biaryl ligand system, we have recently extended our research
work to biphenyl-backbones, including C2-symmetric ligands,
(R)-2,20-bis(pyridin-2-ylmethylamino)-6,60-dimethyl-1,10-biphenyl
(2H2),
(R)-2,20-bis(pyrrol-2-ylmethyleneamino)-6,60-dimethyl-
1,10-biphenyl (3H2), (R)-2,20-bis(diphenylphosphinoylamino)-6,60-
dimethyl-1,10-biphenyl (4H2), (R)-2,20-bis(methanesulphonylami-
no)-6,60-dimethyl-1,10-biphenyl (5H2), and (R)-2,20-bis(p-toluene-
sulphonylamino)-6,60-dimethyl-1,10-biphenyl (6H2), and C1-
* Corresponding author. Tel.: +86 10 5880 2237; fax: +86 10 5880 2075.
E-mail address: gzi@bnu.edu.cn (G. Zi).
symmetric
ligands,
(R)-2-(diphenylthiophosphoramino)-20-
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.12.008

G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
731
(dimethylamino)-6,60-dimethyl-1,10-biphenyl (7H) and (R)-2-
(pyridin-2-ylamino)-20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl
(8H), which are derived from (R)-2,20-diamino-6,60-dimethyl-1,10-
biphenyl. Herein, we report the synthesis and properties of the
chiral ligands, their use in the coordination chemistry of tita-
nium(IV) and zirconium(IV), and the applications of the resulting
complexes as catalysts for the asymmetric hydroamination/cycli-
zation of aminoalkenes. For better understanding and compari-
son, the complex [(R)-(6-MeC6H3)2-2-{NCO(2,4,6-Me3C6H2)}2]-
Zr(NMe2)2 (20) [22–24] will be also discussed in this contribution.
biphenyl (1.06 g, 5.0 mmol) in dry toluene (25 mL). A few 4 Å
molecular sieves were added, and the solution was warmed up
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 red oily residue was washed with cold n-hexane
(30 mL ꢁ 3) to give 3H2 as a red solid. Yield: 1.15 g (63%). M.p.:
70–72 °C. 1H NMR (CDCl3): d 7.97 (s, 2H, N@CH), 7.23 (m, 2H, aryl),
7.08 (m, 2H, aryl), 6.83 (m, 4H, aryl), 6.50 (m, 2H, aryl), 6.22 (m, 2H,
aryl), 2.01 (s, 6H, CH3); protons of NH were not observed. These
spectroscopic data are in agreement with those reported in the lit-
erature [29].
2. Experimental
2.4. Preparation of (R)-2,20-bis(diphenylphosphinoylamino)-6,60-
dimethyl-1,10-biphenyl (4H2)
2.1. General methods
Diphenylphosphinoyl chloride (2.37 g, 10.0 mmol) was mixed
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 immedi-
ately prior to use. (R)-2,20-Diamino-6,60-dimethyl-1,10-biphenyl
(>98% ee) [25], (R)-2-amino-20-(dimethylamino)-6,60-dimethyl-
1,10-biphenyl [21], M(NMe2)4 [26], 2,2-dimethylpent-4-enylamine
[27], 2,20-dimethylhex-5-enylamine [27], and 1-(aminomethyl)-1-
allylcyclohexane [28] were prepared according to literature meth-
ods. All chemicals were purchased from Aldrich Chemical Co. and
Beijing Chemical Co., and 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 re-
corded on a Bruker AV 400 spectrometer at 400 and 100 MHz,
respectively. All chemical shifts are reported in d units with refer-
ence 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 anal-
yses were performed on a Vario EL elemental analyzer.
with
(R)-2,20-diamino-6,60-dimethyl-1,10-biphenyl
(1.06 g,
5.0 mmol) in dry toluene (30 mL). Pyridine (2 mL, 25.3 mmol)
was added, and the solution was refluxed for 2 days. The solvent
was removed and the residue was decomposed with H2O (20 mL)
and extracted with ethyl acetate (20 mL ꢁ 3) and washed with
brine (20 mL). The combined organic layers were dried with anhy-
drous Na2SO4 and the solvent was removed under reduced pres-
sure to give a white solid, which was further purified by flash
column chromatography (hexane/ethyl acetate = 2:1) to give 4H2
as a white solid. Yield: 2.91 g (95%). M.p.: 174–176 °C. 1H NMR
(CDCl3): d 7.68–7.57 (m, 8H, aryl), 7.42–7.38 (m, 2H, aryl), 7.34–
7.27 (m, 6H, aryl), 7.17–7.09 (m, 6H, aryl), 7.00 (t, J = 7.8 Hz, 2H,
aryl), 6.84 (d, J = 7.5 Hz, 2H, aryl), 5.11 (d, J = 10.2 Hz, 2H, NH),
1.98 (s, 6H, CH3). 13C NMR (CDCl3): d 137.2, 131.7, 131.1, 130.4,
130.3, 130.2, 127.7, 125.5, 123.1, 114.7, 18.9. IR (KBr, cmꢂ1):
m
3371 (s), 3052 (w), 1581 (s), 1463 (s), 1438 (s), 1372 (m), 1206
(s), 1122 (s), 1040 (m), 964 (m), 848 (m), 722 (s), 697 (s). Anal. Calc.
for C38H34N2O2P2: C, 74.50; H, 5.59; N, 4.57. Found: C, 74.29; H,
5.62; N, 4.50%.
2.2. Preparation of (R)-2,20-bis(pyridin-2-ylmethylamino)-6,60-
dimethyl-1,10-biphenyl (2H2)
2.5. Preparation of (R)-2,20-bis(methanesulphonylamino)-6,60-
dimethyl-1,10-biphenyl (5H2)
Modified method [29]. Pyridine-2-carboxaldehyde (1.07 g,
10.0 mmol) was mixed with (R)-2,20-diamino-6,60-dimethyl-1,10-
biphenyl (1.06 g, 5.0 mmol) in dry toluene (25 mL). A few 4 Å
molecular sieves were added, and the solution was warmed up to
70 °C and kept for 2 days at this temperature. The solution was fil-
tered and the solvent was removed under reduced pressure. The
resulting yellow oily residue (crude 1) was dissolved in methanol
(40 mL), NaBH4 (2.00 g, 52.6 mmol) was added in small portions
at 0 °C, then the solution was warmed up to 50 °C and kept for
2 h at this temperature. The solvent was removed and the residue
was decomposed with H2O (20 mL) and extracted with ethyl ace-
tate (20 mL ꢁ 3) and washed with brine (20 mL). The combined or-
ganic layers were dried with anhydrous Na2SO4 and the solvent was
removed under reduced pressure to give a yellow oil, which was
further purified by flash column chromatography (hexane/ethyl
acetate = 4:1) to give 2H2 as a colorless oil. Yield: 1.36 g (69%). 1H
NMR (CDCl3): d 8.38 (d, J = 4.6 Hz, 2H, aryl), 7.38 (m, 2H, aryl),
7.15 (d, J = 7.8 Hz, 2H, aryl), 7.02 (m, 4H, aryl), 6.61 (d, J = 7.4 Hz,
2H, aryl), 6.37 (d, J = 8.1 Hz, 2H, aryl), 4.34 (m, 4H, CH2), 1.90 (s,
6H, CH3); protons of NH were not observed. These spectroscopic
data are in agreement with those reported in the literature [29].
This compound was prepared as a white solid from the reaction
of methanesulphonyl chloride (1.15 g, 10.0 mmol) with (R)-2,20-
diamino-6,60-dimethyl-1,10-biphenyl (1.06 g, 5.0 mmol) in the
presence of pyridine (2 mL, 25.3 mmol) in dry toluene (30 mL) at
reflux and purification by flash column chromatography (hexane/
ethyl acetate = 4:1) using a similar procedure as in the synthesis
of 4H2. Yield: 1.82 g (99%). M.p.: 112–114 °C. 1H NMR (CDCl3): d
7.44 (d, J = 8.2 Hz, 2H, aryl), 7.31 (t, J = 8.0 Hz, 2H, aryl), 7.06 (d,
J = 7.4 Hz, 2H, aryl), 5.88 (s, 2H, NH), 2.98 (s, 6H, SO2CH3), 1.87 (s,
6H, CH3). 13C NMR (CDCl3): d 138.5, 135.5, 130.2, 126.6, 124.2,
115.9, 40.4, 19.8. IR (KBr, cmꢂ1):
m 3449 (m), 3274 (m), 2928 (w),
1582 (s), 1464 (s), 1377 (s), 1320 (vs), 1156 (vs), 1037 (s), 973
(s), 857 (s), 783 (s). Anal. Calc. for C16H20N2O4S2: C, 52.15; H,
5.47; N, 7.60. Found: C, 51.87; H, 5.15; N, 7.47%.
2.6. Preparation of (R)-2,20-bis(p-toluenesulphonylamino)-6,60-
dimethyl-1,10-biphenyl (6H2)
This compound was prepared as a white solid from the reaction
of p-toluenesulphonyl chloride (1.91 g, 10.0 mmol) with (R)-2,20-
diamino-6,60-dimethyl-1,10-biphenyl (1.06 g, 5.0 mmol) in the
presence of pyridine (2 mL, 25.3 mmol) in dry toluene (30 mL) at
reflux and purification by flash column chromatography (hexane/
ethyl acetate = 5:1) using a similar procedure as in the synthesis
of 4H2. Yield: 2.58 g (99%). M.p.: 150–152 °C. 1H NMR (CDCl3): d
7.59–7.57 (m, 4H, aryl), 7.48 (d, J = 8.2 Hz, 2H, aryl), 7.20 (m, 6H,
aryl), 6.92 (d, J = 7.6 Hz, 2H, aryl), 5.68 (s, 2H, NH), 2.33 (s, 6H,
2.3. Preparation of (R)-2,20-bis(pyrrol-2-ylmethyleneamino)-6,60-
dimethyl-1,10-biphenyl (3H2)
Modified method [29]. Pyrrole-2-carboxaldehyde (0.95 g,
10.0 mmol) was mixed with (R)-2,20-diamino-6,60-dimethyl-1,10-

732
G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
CH3), 1.50 (s, 6H, CH3). 13C NMR (CDCl3): d 144.5, 138.1, 136.0,
(w), 2747 (m), 1564 (s), 1438 (s), 1216 (s), 1109 (s), 1015 (s),
931 (s), 754 (s). Anal. Calc. for C30H36N6Zr: C, 63.01; H, 6.35; N,
14.70. Found: C, 62.83; H, 6.25; N, 14.40%.
135.2, 129.9, 129.8, 127.3, 126.2, 123.4, 115.7, 21.6, 19.3. IR (KBr,
cmꢂ1):
m 3331 (s), 2921 (m), 1598 (s), 1462 (s), 1385 (s), 1327
(s), 1164 (s), 1091 (s), 1034 (s), 959 (s), 847 (s). Anal. Calc. for
C28H28N2O4S2: C, 64.59; H, 5.42; N, 5.38. Found: C, 64.67; H,
5.20; N, 5.38%.
2.10. Preparation of (3)Ti(NMe2)2 (10)
This compound was prepared as red microcrystals from the
reaction of 3H2 (0.18 g, 0.5 mmol) with Ti(NMe2)4 (0.11 g,
0.5 mmol) in toluene (20 mL) and recrystallization from an n-hex-
ane solution by a similar procedure as in the synthesis of 9. Yield:
0.13 g (50%). M.p.: 128–130 °C (dec.). 1H NMR (C6D6): d 7.70 (m,
2H, aryl), 7.19 (m, 4H, aryl), 7.04 (d, J = 7.7 Hz, 2H, aryl), 6.91 (t,
J = 7.7 Hz, 2H, aryl), 6.83 (m, 2H, aryl), 6.47 (m, 2H, aryl), 3.41 (s,
12H, Ti(NMe2)2), 2.01 (s, 6H, CH3). 13C NMR (C6D6): d 159.2,
149.3, 137.9, 137.8, 133.1, 127.3, 127.0, 120.3, 116.8, 112.5, 47.3,
2.7. Preparation of (R)-2-(diphenylthiophosphoramino)-20-
(dimethylamino)-6,60-dimethyl-1,10-biphenyl (7H)
This compound was prepared as a white solid from the reaction
of diphenylthiophosphinic chloride (1.26 g, 5.0 mmol) with (R)-2-
amino-20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl
(1.20 g,
5.0 mmol) in the presence of pyridine (2 mL, 25.3 mmol) in dry tol-
uene (30 mL) at reflux and purification by flash column chroma-
tography (hexane/ethyl acetate = 50:1) using a similar procedure
as in the synthesis of 4H2. Yield: 1.62 g (71%). M.p.: 48–50 °C. 1H
NMR (CDCl3): d 7.74 (m, 2H, aryl), 7.60 (m, 2H, aryl), 7.34 (m,
1H, aryl), 7.26 (m, 3H, aryl), 7.20 (m, 4H, aryl), 6.92 (m, 2H, aryl),
6.81 (m, 2H, aryl), 5.37 (d, J = 8.6 Hz, 1H, NH), 2.39 (s, 6H, NMe2),
1.95 (s, 3H, CH3), 1.91 (s, 3H, CH3). 13C NMR (CDCl3): d 150.5,
137.2, 136.2, 133.6, 132.6, 130.2, 130.1, 129.9, 129.7, 127.1,
126.9, 126.6, 125.9, 122.6, 116.0, 114.4, 42.2, 18.9, 18.8. IR (KBr,
20.1. IR (KBr, cmꢂ1):
m 2948 (m), 1560 (s), 1433 (m), 1389 (s),
1292 (s), 1260 (s), 1091 (s), 1031 (s), 944 (s), 799 (s). Anal. Calc.
for C28H32N6Ti: C, 67.20; H, 6.44; N, 16.79. Found: C, 67.15; H,
6.24; N, 16.69%. Few red crystals suitable for X-ray diffraction anal-
ysis were picked up from the mixture.
2.11. Preparation of (3)Zr(NMe2)2 (11)
cmꢂ1):
m
3360 (m), 2940 (m), 1580 (s), 1463 (s), 1437 (s), 1289
This compound was prepared as orange microcrystals from the
reaction of 3H2 (0.18 g, 0.5 mmol) with Zr(NMe2)4 (0.14 g,
0.5 mmol) in toluene (20 mL) and recrystallization from an n-hex-
ane solution by a similar procedure as in the synthesis of 9. Yield:
0.20 g (75%). M.p.: 128–130 °C (dec.). 1H NMR (C6D6): d 7.60 (m,
2H, aryl), 7.33 (m, 2H, aryl), 7.13 (m, 2H, aryl), 6.92 (m, 4H, aryl),
6.62 (m, 2H, aryl), 6.49 (m, 2H, aryl), 3.27 (s, 12H, Zr(NMe2)2),
2.03 (s, 6H, CH3). 13C NMR (C6D6): d 158.9, 146.7, 138.7, 137.7,
136.2, 131.6, 128.1, 127.3, 119.7, 118.7, 112.3, 41.6, 21.8. IR (KBr,
(s), 1104 (s), 966 (s), 720 (s). Anal. Calc. for C28H29N2PS: C, 73.66;
H, 6.40; N, 6.14. Found: C, 73.67; H, 6.47; N, 5.89%.
2.8. Preparation of (R)-2-(pyridin-2-ylamino)-20-(dimethylamino)-
6,60-dimethyl-1,10-biphenyl (8H)
(R)-2-Amino-20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl
(1.20 g,
5.0 mmol),
tris(dibenzylideneacetone)dipalladium
(Pd2(DBA)3; 50.3 mg, 1.1 mol%), 1,3-bis(diphenylphosphino)pro-
pane (DPPP; 42.5 mg, 2 mol%), and tBuONa (680 mg, 7.0 mmol)
were loaded into a Schlenk flask with stirring. Toluene (50 mL)
was added followed by addition of 2-bromopyridine (0.78 mL,
8.0 mmol) via syringe. The solution was stirred at 80 °C for 2 days.
The solvent was removed under reduced pressure to give a pale
yellow oil, which was further purified by flash column chromatog-
raphy (hexane/ethyl acetate = 50:1) to give 8H as a colorless oil.
Yield: 1.54 g (97%). 1H NMR (C6D6): d 8.22 (m, 2H, aryl), 7.31 (t,
J = 7.8 Hz, 1H, aryl), 7.23 (t, J = 7.8 Hz, 1H, aryl), 7.04 (m, 2H, aryl),
6.95 (m, 2H, aryl), 6.79 (s, 1H, NH), 6.51 (d, J = 8.1 Hz, 1H, aryl), 6.42
(m,1H, aryl), 2.42 (s, 6H, NMe2), 2.11 (s, 3H, CH3), 2.02 (s, 3H, CH3).
13C NMR (C6D6): d 156.7, 152.7, 148.8, 138.9, 138.3, 137.5, 137.1,
130.9, 128.8, 124.7, 124.4, 117.9, 116.7, 114.7, 108.7, 43.5, 20.3,
cmꢂ1):
m 2959 (w), 1558 (s), 1432 (m), 1389 (s), 1288 (s), 1259
(s), 1032 (s), 934 (m), 732 (s). Anal. Calc. for C28H32N6Zr: C,
61.84; H, 5.93; N, 15.45. Found: C, 61.64; H, 5.83; N, 15.32%.
2.12. Preparation of (4)Zr(NMe2)2 (12)
This compound was prepared as yellow microcrystals from the
reaction of 4H2 (0.31 g, 0.5 mmol) with Zr(NMe2)4 (0.14 g,
0.5 mmol) in toluene (20 mL) and recrystallization from a benzene
solution by a similar procedure as in the synthesis of 9. Yield:
0.34 g (85%). M.p.: 250–252 °C (dec.). 1H NMR (C6D6): d 7.95 (m,
4H, aryl), 7.28 (m, 4H, aryl), 7.20 (m, 4H, aryl), 7.05–6.89 (m,
12H, aryl), 6.76 (m, 2H, aryl), 3.39 (s, 12H, Zr(NMe2)2), 1.79 (s,
6H, CH3). 13C NMR (C6D6): d 144.3, 136.3, 134.5, 133.4, 132.4,
20.0. IR (KBr, cmꢂ1):
m
3397 (m), 2943 (m), 1604 (s), 1582 (s),
131.4, 131.0, 126.7, 124.6, 124.1, 42.6, 20.3. IR (KBr, cmꢂ1):
m
1513 (s), 1464 (vs), 1440 (vs), 1318 (s), 1150 (s), 985 (w), 768
(s). Anal. Calc. for C21H23N3: C, 79.46; H, 7.30; N, 13.24. Found: C,
79.35; H, 7.61; N, 13.34%.
2961 (m), 2924.6 (m), 1589 (s), 1432 (s), 1364 (s), 1309 (m),
1260 (s), 1117 (vs), 1044 (vs), 932 (m), 788 (s), 719 (vs). Anal. Calc.
for C42H44N4O2P2Zr: C, 63.85; H, 5.61; N, 7.09. Found: C, 63.75; H,
5.53; N, 7.21%. Few yellow crystals suitable for X-ray diffraction
analysis were picked up from the mixture.
2.9. Preparation of (2)Zr(NMe2)2 (9)
A toluene solution (10 mL) of 2H2 (0.20 g, 0.5 mmol) was slowly
2.13. Preparation of (5)Ti(NMe2)2 (13)
added to
a toluene solution (10 mL) of Zr(NMe2)4 (0.14 g,
0.5 mmol) with stirring at room temperature. The solution was
stirred at room temperature for 1 day. The solution was filtered
and the solvent was removed under reduced pressure. The result-
ing orange solid was recrystallized from an n-hexane solution to
give 9 as orange microcrystals. Yield: 0.23 g (80%). M.p.: 124–
126 °C (dec.). 1H NMR (C6D6): d 8.23 (d, J = 4.8 Hz, 2H, aryl), 7.24
(m, 2H, aryl), 7.11 (d, J = 7.7 Hz, 2H, aryl), 6.90 (m, 4H, aryl), 6.54
(d, J = 7.4 Hz, 4H, aryl), 5.09 (d, J = 18.8 Hz, 2H, CH2), 4.69 (d,
J = 18.8 Hz, 2H, CH2), 3.05 (s, 12H, Zr(NMe2)2), 2.32 (s, 6H, CH3).
13C NMR (C6D6): d 167.2, 155.7, 148.2, 136.8, 136.1, 134.8, 126.6,
This compound was prepared as red microcrystals from the
reaction of 5H2 (0.18 g, 0.5 mmol) with Ti(NMe2)4 (0.11 g,
0.5 mmol) in toluene (20 mL) and recrystallization from a toluene
solution by a similar procedure as in the synthesis of 9. Yield:
0.20 g (78%). M.p.: 230–232 °C (dec.). 1H NMR (C6D6): d 7.58 (d,
J = 7.9 Hz, 2H, aryl), 7.12 (t, J = 7.7 Hz, 2H, aryl), 6.93 (d, J = 7.6 Hz,
2H, aryl), 3.40 (s, 12H, Ti(NMe2)2), 2.15 (s, 6H, CH3), 1.91 (s, 6H,
CH3). 13C NMR (C6D6): d 139.8, 137.4, 134.7, 129.0, 125.4 125.1,
45.5, 39.9, 19.6. IR (KBr, cmꢂ1):
m 2862 (m), 1445 (s), 1298 (vs),
1276 (vs), 1137 (vs), 1062 (s), 936 (s), 870 (vs), 807 (s). Anal. Calc.
for C20H30N4O4S2Ti: C, 47.81; H, 6.02; N, 11.15. Found: C, 47.72; H,
121.7, 120.7, 120.5, 119.9, 62.5, 43.8, 20.6. IR (KBr, cmꢂ1):
m 2921

G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
733
5.87; N, 11.35%. Few red crystals suitable for X-ray diffraction anal-
2.18. Preparation of (8)2Ti(NMe2)2 (18)
ysis were picked up from the mixture, which was identified as
13ꢀ0.5C7H8.
This compound was prepared as red crystals from the reaction
of 8H (0.16 g, 0.5 mmol) with Ti(NMe2)4 (0.06 g, 0.25 mmol) in tol-
uene (20 mL) and recrystallization from a benzene solution by a
similar procedure as in the synthesis of 9. Yield: 0.13 g (70%).
M.p.: 238–240 °C (dec.). 1H NMR (C6D6): d 8.10 (d, J = 5.0 Hz, 2H,
aryl), 7.54 (d, J = 7.8 Hz, 2H, aryl), 7.35 (t, J = 7.6 Hz, 2H, aryl),
7.09 (m, 4H, aryl), 6.94 (d, J = 7.4 Hz, 2H, aryl), 6.89 (t, J = 8.2 Hz,
2H, aryl), 6.81 (d, J = 7.9 Hz, 2H, aryl), 6.21 (d, J = 8.7 Hz, 2H, aryl),
5.94 (t, J = 6.2 Hz, 2H, aryl), 2.75 (s, 12H, Ti(NMe2)2), 2.15 (s, 6H,
CH3), 2.05 (s, 6H, CH3), 2.00 (s, 12H, NMe2). 13C NMR (C6D6): d
168.2, 153.0, 150.3, 142.3, 138.8, 138.1, 137.1, 136.4, 136.0,
128.3, 127.4, 127.3, 125.9, 125.0, 117.9, 107.2, 107.0, 45.6, 43.3,
2.14. Preparation of (5)2Zr (14)
This compound was prepared as yellow microcrystals from the
reaction of 5H2 (0.18 g, 0.5 mmol) with Zr(NMe2)4 (0.14 g,
0.5 mmol) in toluene (20 mL) and recrystallization from a toluene
solution by a similar procedure as in the synthesis of 9. Yield:
0.11 g (55%). M.p.: 260–262 °C (dec.). 1H NMR (C6D6): d 8.09 (d,
J = 8.0 Hz, 4H, aryl), 7.17 (t, J = 7.8 Hz, 4H, aryl), 6.99 (d, J = 7.5 Hz,
4H, aryl), 2.25 (s, 12H, CH3), 1.99 (s, 12H, CH3). 13C NMR (C6D6):
d 139.7, 136.8, 132.9, 129.0, 128.3, 124.6, 40.0, 19.8. IR (KBr,
20.6, 20.1. IR (KBr, cmꢂ1):
m 2802 (w), 1593 (s), 1467 (s), 1439
cmꢂ1):
m 2852 (m), 1567 (m), 1449 (s), 1277 (s), 1077 (m),
(s), 1355 (s), 1295 (s), 1020 (m), 940 (m), 759 (s), 732 (s). Anal.
Calc. for C46H56N8Ti: C, 71.86; H, 7.34; N, 14.57. Found: C, 72.11;
H, 7.06; N, 14.58%.
1040(s), 948 (m), 867 (s), 749(m). Anal. Calc. for C32H36N4O8S4Zr:
C, 46.64; H, 4.40; N, 6.80. Found: C, 46.99; H, 3.96; N, 7.12%.
2.15. Preparation of (6)Ti(NMe2)2 (15)
2.19. Preparation of (8)2Zr(NMe2)2 (19)
This compound was prepared as red microcrystals from the
reaction of 6H2 (0.26 g, 0.5 mmol) with Ti(NMe2)4 (0.11 g,
0.5 mmol) in toluene (20 mL) and recrystallization from a toluene
solution by a similar procedure as in the synthesis of 9. Yield:
0.21 g (63%). M.p.: 174–176 °C (dec.). 1H NMR (C6D6): d 7.79 (d,
J = 7.9 Hz, 2H, aryl), 7.30 (d, J = 8.0 Hz, 4H, aryl), 7.10 (t, J = 7.7 Hz,
2H, aryl), 6.73 (d, J = 7.5 Hz, 2H, aryl), 6.56 (d, J = 8.0 Hz, 4H, aryl),
3.52 (s, 12H, Ti(NMe2)2), 1.87 (s, 6H, CH3), 1.36 (s, 6H, CH3). 13C
NMR (C6D6): d 141.8, 139.9, 138.9, 138.5, 135.1, 128.9, 128.3,
This compound was prepared as orange crystals from the reac-
tion of 8H (0.16 g, 0.5 mmol) with Zr(NMe2)4 (0.07 g, 0.25 mmol) in
toluene (20 mL) and recrystallization from a benzene solution by a
similar procedure as in the synthesis of 9. Yield: 0.15 g (74%). M.p.:
261–263 °C (dec.). 1H NMR (C6D6): d 7.84 (m, 2H, aryl), 7.33 (m, 4H,
aryl), 7.08 (m, 4H, aryl), 6.94 (d, J = 7.4 Hz, 2H, aryl), 6.85 (m, 4H,
aryl), 6.23 (d, J = 8.8 Hz, 2H, aryl), 5.89 (t, J = 6.2 Hz, 2H, aryl),
2.52 (s, 12H, Zr(NMe2)2), 2.12 (s, 6H, CH3), 2.05 (s, 6H, CH3), 2.03
(s, 12H, NMe2). 13C NMR (C6D6): d 169.2, 152.9, 148.4, 142.6,
138.7, 138.0, 137.3, 137.0, 135.0, 128.3, 127.3, 125.8, 125.3,
127.6, 127.3, 124.6, 46.1, 20.7, 19.5. IR (KBr, cmꢂ1):
m 2854 (w),
1447 (m), 1274 (s), 1088 (s), 1041 (m), 933 (m), 868 (s), 734 (s).
Anal. Calc. for C32H38N4O4S2Ti: C, 58.71; H, 5.85; N, 8.56. Found:
C, 58.61; H, 5.82; N, 8.46%.
125.0, 117.6, 107.9, 107.6, 43.2, 41.1, 20.4, 19.9. IR (KBr, cmꢂ1):
2930 (w), 1596 (s), 1463 (s), 1438 (s), 1296 (s), 930 (s), 764 (s),
733 (s). Anal. Calc. for C46H56N8Zr: C, 68.02; H, 6.95; N, 13.80.
Found: C, 67.82; H, 6.85; N, 13.76%.
m
2.16. Preparation of (6)2Zr (16)
This compound was prepared as yellow microcrystals from the
reaction of 6H2 (0.26 g, 0.5 mmol) with Zr(NMe2)4 (0.14 g,
0.5 mmol) in toluene (20 mL) and recrystallization from a toluene
solution by a similar procedure as in the synthesis of 9. Yield:
0.16 g (55%). M.p.: > 300 °C (dec.). 1H NMR (C6D6): d 8.61 (d,
J = 7.9 Hz, 4H, aryl), 7.57 (d, J = 8.2 Hz, 8H, aryl), 7.25 (t, J = 7.8 Hz,
4H, aryl), 6.78 (d, J = 7.5 Hz, 4H, aryl), 6.44 (d, J = 8.2 Hz, 8H, aryl),
1.67 (s, 12H, CH3), 1.49(s, 12H, CH3). 13C NMR (C6D6): d 142.6,
140.2, 137.7, 137.6, 137.5, 133.7, 129.1, 128.9, 128.3, 125.2, 20.7,
2.20. General procedure for asymmetric hydroamination/cyclization
In a nitrogen-filled glove box, precatalyst (0.016 mmol), C6D6
(0.7 mL), and aminoalkene (0.16 mmol) were introduced sequen-
tially into a J. Young NMR tube equipped with Teflon screw cap.
The reaction mixture was subsequently kept at 120 °C to achieve
hydroamination, and the reaction was monitored periodically by
1H NMR spectroscopy. The cyclic amine was vacuum transferred
from the J. Young NMR tube into a 25 mL Schlenk flask which con-
tained 31 mg (0.16 mmol) of (S)-(+)-O-acetylmandelic acid. 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 [27].
19.5. IR (KBr, cmꢂ1):
m 2919 (w), 1568 (m), 1450 (s), 1283 (s),
1111 (s), 1074 (s), 1023 (s), 1008 (s), 865 (s), 798 (s), 730 (s). Anal.
Calc. for C56H52N4O8S4Zr: C, 59.60; H, 4.64; N, 4.96. Found: C,
59.53; H, 4.38; N, 4.87%.
2.17. Preparation of (7)2Zr(NMe2)2 (17)
This compound was prepared as yellow crystals from the reac-
tion of 7H (0.23 g, 0.5 mmol) with Zr(NMe2)4 (0.07 g, 0.25 mmol) in
toluene (20 mL) and recrystallization from a benzene solution by a
similar procedure as in the synthesis of 9. Yield: 0.17 g (63%). M.p.:
210–212 °C (dec.). 1H NMR (C6D6): d 8.63 (m, 4H, aryl), 7.27–7.07
(m, 10H, aryl), 6.99 (m, 10H, aryl), 6.82 (m, 4H, aryl), 6.70 (m,
4H, aryl), 2.73 (s, 12H, Zr(NMe2)2), 2.40 (s, 6H, CH3), 1.89 (s, 6H,
CH3), 1.66 (s, 12H, NMe2). 13C NMR (C6D6): d 150.9, 149.7, 138.8,
134.7, 134.6, 134.4, 132.2, 131.2, 129.0, 128.3, 126.4, 125.4,
2.21. X-ray crystallography
Single-crystal X-ray diffraction measurements were carried out
on a Rigaku Saturn CCD diffractometer at 113(2) K using graphite
monochromated Mo Ka radiation (k = 0.71070 Å). An empirical
absorption correction was applied using the SADABS program [30].
All structures were solved by direct methods and refined by full-
matrix least squares on F2 using the SHELXL-97 program package
[31]. All the hydrogen atoms were geometrically fixed using the
riding model. The crystal data and experimental data for 10, 12,
13, and 17–19 are summarized in Table 1. Selected bond lengths
and angles are listed in Table 2.
124.3, 122.7, 118.6, 116.0, 43.8, 42.7, 20.4, 20.0. IR (KBr, cmꢂ1):
m
2865 (m), 1574 (m), 1434 (s), 1234 (vs), 1105 (s), 1042 (s), 1024
(s), 931 (s), 849 (s), 796 (s), 743 (s). Anal. Calc. for C60H68N6P2S2Zr:
C, 66.08; H, 6.29; N, 7.71. Found: C, 66.21; H, 6.15; N, 7.65%.

734
G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
Table 1
Crystal data and experimental parameters for compounds 10, 12, 13, and 17–19.
Compound
10
12
13ꢀ0.5C7H8
17
18
19
Formula
C28H32N6Ti
500.50
C42H44N4O2P2Zr
789.97
Monoclinic
P12/c1
20.435(2)
10.781(1)
19.361(2)
90
115.85(1)
90
C23.5H34N4O4S2Ti
548.57
C60H68N6P2S2Zr
1090.48
Monoclinic
P21
12.687(1)
14.226(1)
15.850(2)
90
90.08(3)
90
2860.4(5)
2
C46H56N8Ti
768.89
C46H56N8Zr
812.21
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Monoclinic
P12/n1
9.685(1)
11.784(1)
11.984(1)
90
108.50(1)
90
1297.1(2)
2
Triclinic
Orthorhombic
P212121
14.846(3)
15.661(3)
18.290(4)
90
Orthorhombic
P212121
14.856(2)
15.638(2)
18.287(2)
90
90
90
4248.5(8)
4
1.270
ꢀ
P1
9.605(1)
9.842(1)
15.707(2)
73.44(1)
80.63(1)
69.56(1)
1330.2(3)
2
a
(°)
b (°)
90
90
c
(°)
V (Å3)
3838.7(6)
4
1.367
4252.4(15)
4
1.201
Z
Dcalc. (g/cm3)
1.281
0.358
1.370
0.515
1.266
0.364
l
(Mo K
a
)
calc
(mmꢂ1
)
0.411
0.243
0.300
Size (mm)
F(0 0 0)
0.22 ꢁ 0.16 ꢁ 0.14
0.22 ꢁ 0.20 ꢁ 0.18
0.26 ꢁ 0.20 ꢁ 0.16
0.22 ꢁ 0.18 ꢁ 0.14
0.26 ꢁ 0.24 ꢁ 0.22
0.36 ꢁ 0.34 ꢁ 0.30
528
1640
578
1144
1640
1712
2h Range (°)
4.74–55.74
15 917
3088 (0.0532)
2861
4.22–54.58
25 985
8405 (0.0448)
7250
4.54–55.74
16 664
6298 (0.0244)
5421
2.86–54.20
26 776
10 511 (0.0634)
9438
3.42–56.00
21 964
9594 (0.0303)
9323
3.54–55.74
41 654
10 124 (0.0336)
9811
Number of reflections collected
Number of unique reflections [Rint
Number of observed reflections
]
Absorbed corrections (Tmax, Tmin
R
)
0.95, 0.93
0.053
0.93, 0.92
0.044
0.92, 0.88
0.034
0.95, 0.92
0.032
0.95, 0.94
0.042
0.92, 0.90
0.026
wR
0.119
0.111
0.086
0.056
0.100
0.061
wR2 (all data)
Goodness-of-fit (GOF)
0.131
1.15
0.117
1.05
0.089
1.04
0.058
0.90
0.101
1.09
0.062
1.03
(4H2),
(R)-2,20-bis(methanesulphonylamino)-6,60-dimethyl-1,10-
Table 2
Selected bond distances (Å) and bond angles (°) for compounds 10, 12, 13, and 17–19.
biphenyl (5H2), and (R)-2,20-bis(p-toluenesulphonylamino)-6,60-di-
methyl-1,10-biphenyl (6H2), respectively, in good yields (Scheme
1). Under similar reaction conditions, reaction of (R)-2-(amino)-
20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl with 1 equiv. of
diphenylthiophosphinic chloride in the presence of an excess of
pyridine in toluene at reflux, after purification by flash column
chromatography, gives C1-symmetric ligand, (R)-2-(diphenylthio-
phosphoramino)-20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl
(7H) in 71% yield (Scheme 2). Treatment of (R)-2-(amino)-20-
(dimethylamino)-6,60-dimethyl-1,10-biphenyl with an excess of 2-
bromopyridine in the presence of catalytic amount of tris(diben-
zylideneacetone)dipalladium (Pd2(DBA)3) and 1,3-bis(diphenyl-
phosphino)propane (DPPP) in toluene at 80 °C, after purification
by flash column chromatography, gives C1-symmetric N3-ligand,
(R)-2-(pyridin-2-ylamino)-20-(dimethylamino)-6,60-dimethyl-1,10-
biphenyl (8H) in 97% yield (Scheme 2).
Compound 10 (Ti) 12 (Zr) 13 (Ti) 17 (Zr) 18 (Ti) 19 (Zr)
M–N (av.)
M–N
(NMe2)
2.109(2) 2.171(2) 1.961(1) 2.171(3) 2.098(2) 2.209(1)
1.903(2) 2.071(2) 1.861(1) 2.035(3) 1.912(2) 2.029(1)
1.903(2) 2.071(2) 1.879(1) 2.052(3) 1.913(2) 2.043(1)
M–X (av.)
M–O
2.249(2) 2.194(1) 2.754(1)
Zr–P Ti–S Zr–P
M–O
Zr–S
2.912(1) 2.797(1) 3.106(1)
Sum
angles
of N
359.9(2) 359.7(2) 358.7(1) 359.5(3) 356.9(2) 356.6(2)
359.9(2) 359.7(2) 359.8(1) 359.1(3) 359.5(2) 359.9(2)
(NMe2)
Torsion
(aryl–
aryl)
67.8(3)
72.1(2)
68.5(2)
85.4(5)
81.6(5)
71.7(2)
71.1(2)
71.0(2)
70.7(2)
All ligands are air-stable, and are soluble in CH2Cl2, CHCl3, tolu-
ene and benzene, and slightly soluble in n-hexane. They have been
fully characterized by various spectroscopic techniques, and ele-
mental analyses. The 1H and 13C NMR spectra of 2H2, 3H2, 4H2,
5H2 and 6H2 indicate that they are symmetrical on the NMR time-
scale, which are consistent with their C2-symmetric structures.
And the 1H and 13C NMR spectra of 7H and 8H confirm that they
are non-symmetrical on the NMR timescale consistent with their
C1-symmetric structures. The infrared spectra of these compounds
exhibit peaks corresponding to aromatic stretches in addition to
3. Results and discussion
3.1. Synthesis and characterization of ligands
The C2-symmetric pyridine ligand, (R)-2,20-bis(pyridin-2-ylm-
ethylamino)-6,60-dimethyl-1,10-biphenyl (2H2), is readily prepared
in 69% yield by condensation of the starting material (R)-2,20-dia-
mino-6,60-dimethyl-1,10-biphenyl with 2 equiv. of pyridine-2-car-
boxaldehyde in the presence of molecular sieves in toluene at
70 °C, followed by reduction with an excess of NaBH4 in methanol
(Scheme 1). Of course, the C2-symmetric Schiff base ligand, (R)-
2,20-bis(pyrrol-2-ylmethyleneamino)-6,60-dimethyl-1,10-biphenyl
(3H2), is also readily prepared in 63% yield by condensation of (R)-
2,20-diamino-6,60-dimethyl-1,10-biphenyl with 2 equiv. of pyrrole-
2-carboxaldehyde in the presence of molecular sieves in toluene at
70 °C (Scheme 1). Treatment of (R)-2,20-diamino-6,60-dimethyl-
N–H stretches at about 3360 cmꢂ1
.
3.2. Synthesis and characterization of complexes
Group 4 metal amide complexes can be efficiently prepared via
amine elimination reaction between M(NMe2)4 and protic reagents
[32–43]. It is rational to propose that the acidic proton in the li-
gands 2H2, 3H2, 4H2, 5H2, 6H2, 7H and 8H would allow the similar
amine elimination to occur between 2H2, 3H2, 4H2, 5H2, 6H2, 7H or
8H and metal amides. In fact, treatment of M(NMe2)4 with 1 equiv.
of N4-ligand, (R)-2,20-bis(pyridin-2-ylmethylamino)-6,60-dimethyl-
1,10-biphenyl (2H2) or (R)-2,20-bis(pyrrol-2-ylmethyleneamino)-
1,10-biphenyl with
2 equiv. of diphenylphosphinoyl chloride,
methanesulphonyl chloride, or p-toluenesulphonyl chloride in
the presence of an excess of pyridine in toluene at reflux gives,
after purification by flash column chromatography, (R)-2,20-
bis(diphenylphosphinoylamino)-6,60-dimethyl-1,10-biphenyl

G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
735
O
O
R
N
N
N
S
H
N
H
RSO2Cl
NH2
O
N
N
H
pyridine
NH2
O
N
C7H8/m.s.
S
O
R
O
H
N
1
5
6
R = Me ( H2), p-tolyl ( H2)
H
Ph2POCl
pyridine
NaBH4
MeOH
M[NMe2]4
C7H8
C7H8/m.s.
N
Ph
Ph
O
R
H
N
P
NH
N
H
S
O
O
N
N
N
O
O
NMe2
NMe2
H
H
N
M
S
N
P
N
O
NH
Ph
Ph
R
N
3H2
4H2
Zr[NMe2]4
C7H8
2
H2
M = Ti
R = Me ( ), p-tolyl ( )
M[NMe2]4
C7H8
Zr[NMe2]4
C7H8
13
15
Ph
Ph
O
O
R
N
P
N
S
NMe2
N
N
N
O
N
N
M
NMe2
NMe2
NMe2
NMe2
Zr
Zr
N
NMe2
Zr
N
O
N
N
P
N
O
2
S
Ph
Ph
O
R
M = Ti (10), Zr (11)
9
14 16
R = Me ( ), p-tolyl( )
12
Scheme 1.
6,60-dimethyl-1,10-biphenyl (3H2) gives, after recrystallization
from an n-hexane solution, the chiral zirconium amides
(2)Zr(NMe2)2 (9), (3)Zr(NMe2)2 (11), and titanium amide
(3)Ti(NMe2)2 (10), respectively, in good yields (Scheme 1). Reaction
enesulphonylamino)-6,60-dimethyl-1,10-biphenyl (6H2) gives, after
recrystallization from a toluene solution, the chiral titanium
amides (5)Ti(NMe2)2ꢀ0.5C7H8 (13ꢀ0.5C7H8), (6)Ti(NMe2)2 (15),
respectively, in good yields (Scheme 1), while reaction of
Zr(NMe2)4 with 1 equiv. of 5H2 or 6H2 does not give the expected
complex (5)Zr(NMe2)2 or (6)Zr(NMe2)2, instead, the bis-ligated
complexes, (5)2Zr (14) and (6)2Zr (16), have been isolated, respec-
tively, in good yields (Scheme 1). Under similar reaction condi-
of Zr(NMe2)4 with
1 equiv. of diphenylphosphoramide (R)-
2,20-bis(diphenylphosphinoylamino)-6,60-dimethyl-1,10-biphenyl
(4H2) affords, after recrystallization from a benzene solution, the
chiral zirconium amide (4)Zr(NMe2)2 (12) in 85% yield (Scheme
1). Under similar reaction conditions, treatment of Ti(NMe2)4 with
1 equiv. of sulphonylamide ligand, (R)-2,20-bis(methanesulpho-
nylamino)-6,60-dimethyl-1,10-biphenyl (5H2) or (R)-2,20-bis(p-tolu-
tions,
diphenylthiophosphoramide ligand, (R)-2-(diphenylthiophospho-
ramino)-20-(dimethylamino)-6,60-dimethyl-1,10-biphenyl
(7H)
treatment
of
Zr(NMe2)4
with
2
equiv.
of
Ph
S
Ph
Ph2PSCl
pyridine
N
Br
P
N
H
N
NH2
N
H
Pd(dba)3,DPPP
tBuONa
NMe2
NMe2
NMe2
8H
M[NMe2]4
C7H8
7H
Zr[NMe2]4
C7H8
Ph
Ph
N
S
NMe2
NMe2
NMe2
Zr
P
N
Me2N
M
Me2N
N
2
2
NMe2
M=Ti(18),Zr(19)
17
Scheme 2.

736
G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
gives, after recrystallization from a benzene solution, the bis-li-
gated chiral zirconium amide (7)2Zr(NMe2)2 (17) in 63% yield
(Scheme 2). Reaction of M(NMe2)4 with 2 equiv. of N3-ligand
(R)-2-(pyridin-2-ylamino)-20-(dimethylamino)-6,60-dimethyl-1,10-
biphenyl (8H) also gives, after recrystallization from a benzene
solution, the bis-ligated chiral titanium amide (8)2Ti(NMe2)2
(18), and zirconium amide (8)2Zr(NMe2)2 (19), respectively, in
good yields (Scheme 2).
These complexes are stable in dry nitrogen atmosphere, while
they are very sensitive to moisture. They are soluble in organic sol-
vents such as THF, DME, pyridine, toluene, and benzene, and only
slightly soluble in n-hexane. They have been characterized by var-
ious spectroscopic techniques, and elemental analyses. The 1H
NMR spectra of 9, 10, 11, 12, 13 and 15 support that the ratio of
amino group NMe2 and ligand anion 2, 3, 4, 5 or 9 is 2:1, and estab-
lish that half toluene molecule for 13 co-crystallized. Unlike the
zirconium amides 9, 11 and 12, the 1H NMR spectra of 14 and 16
do not exhibit a singlet resonance at about 3.30 ppm attributable
to the NMe2 groups, supporting the formation of the bis-ligated
complexes 14 and 16. The 1H NMR spectra of 17, 18 and 19 support
that the ratio of amino group NMe2 and ligand anion 7 or 8 is 1:1,
supporting the formation of the bis-ligated complexes 17, 18 and
19. These results are consistent with their 13C NMR spectra. The so-
lid-state structures of the complexes 10, 12, 13 and 17–19 have
further been confirmed by X-ray diffraction analyses.
Fig. 2. Molecular structure of 12 (thermal ellipsoids drawn at the 35% probability
level).
The solid-state structure of 10 shows that the Ti4+ is
r-bound to
four nitrogen atoms from the ligand anion 3 and two nitrogen
atoms from amino groups NMe2 in a distorted-octahedron geome-
try (Fig. 1) with the average distance of Ti–N (2.109(2) Å). The short
Ti–N(3) and Ti–N(3A) bond distances (1.903(2) and 1.903(2) Å) and
the planar geometry around the N(3) and N(3A) nitrogen atoms
indicate that both nitrogen atoms with sp2 hybridization are en-
The solid-state structure of 13 shows that there are two mole-
cules (5)Ti(NMe2)2 and one solvate benzene in the lattice. In each
molecule of (5)Ti(NMe2)2, the Ti4+ is
r-bound to two nitrogen
atoms and one oxygen atom from the ligand 5 and two nitrogen
atoms from amino groups NMe2 in a distorted-trigonal–bipyrami-
dal geometry (Fig. 3) with the average distance of Ti–N (1.961(1) Å)
and the distance of Ti–O (2.194(1) Å), respectively. The short
distances of Ti–NMe2 (1.861(1) and 1.879(1) Å) and the planar
geometry around the nitrogen atoms of N(3) and N(4) indicate that
the nitrogen atoms with sp2 hybridization are engaged in
N(p )?Ti(d ) interactions. The twisting between the phenyl rings
gaged in N(p ) ? Ti(d ) interactions. These structural data are
p
p
close to those found in [(R)-C20H12(NCHC4H3N)2]Ti(NMe2)2 [20].
The twisting between the phenyl rings of torsion angle is 67.8(3)°.
The solid-state structure of 12 shows that there are two mole-
cules (4)Zr(NMe2)2 in the lattice. In each molecule of (4)Zr(NMe2)2,
the Zr4+ is
r-bound to two nitrogen atoms and two oxygen atoms
from the ligand 4 and two nitrogen atoms from amino groups
NMe2 in a distorted-octahedron geometry (Fig. 2) with the average
distance of Zr–N (2.171(2) Å) and the average distance of Zr–O
(2.249(2) Å), respectively. The short distances of Zr–NMe2
(2.071(2) and 2.071(2) Å) and the planar geometry around the
nitrogen atoms of N(2) and N(2A) indicate that the nitrogen atoms
with sp2 hybridization are engaged in N(p ) ? Zr(d ) interactions.
p
p
of torsion angle is 68.5(2)°, which is comparable to those found in
10 (67.8(3)°) and 12 (72.1(2)°).
The solid-state structure of 17 shows that the substituted Me2N
group is far away from the metal center, and the Zr4+ is
r-bound to
p
p
The twisting between the phenyl rings of torsion angle is 72.1(2)°,
which is slightly larger than that found in 10 (67.8(3)°).
Fig. 1. Molecular structure of 10 (thermal ellipsoids drawn at the 35% probability
Fig. 3. Molecular structure of 13 (thermal ellipsoids drawn at the 35% probability
level).
level).

G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
737
3.3. Asymmetric hydroamination/cyclization
To examine the catalytic ability of the complexes 9–19, the
asymmetric hydroamination/cyclization of unactivated terminal
aminoalkenes has been evaluated under the conditions given in Ta-
ble 3. The results of the hydroamination/cyclization of 2,2-dimeth-
ylpent-4-enylamine clearly show that the zirconium amides are
active catalysts for this transformation (Table 3, entries 1, 3, 4, 9
and 11), and the mono-ligated complex 11 shows the most effective
catalyst for this transformation, but the enantioselectivity is mod-
erate (only up to 21%; Table 3, entry 3). When more bulky ligand
4 is used, both the rate and ee value decrease significantly (Table
3, entry 4). However, the bis-ligated complex 17 gives a noticeably
better ee value (38%; Table 3, entry 9), but the rate is slow. When
the less bulky ligand 8 is used, the rate increases while the ee value
decreases slightly (Table 3, entry 11). Under similar reaction condi-
tions, no detectable hydroamination activity is observed for tita-
nium complexes 10, 13, 15 and 18 (Table 3, entries 2, 5, 7 and
10), and bis-ligated zirconium complexes 14 and 16 (Table 3, en-
tries 6 and 8) even heated at 120 °C for one week, and none of the
complexes described above is effective catalysts for the cyclization
of 1-aminopent-4-ene into 2-methylpyrrolidine, presumably due to
a lack of a Thorpe–Ingold effect [44,45] from the unsubstituted
aminoalkene. Substrate 22a reacts fast but the ee values are moder-
ate (Table 3, entries 13–17). We are pleased to find that the forma-
tion of six-membered ring can also be performed with our
zirconium catalysts (Table 3, entries 18–22), and a moderate
enantioselectivity (up to 24%), mediated by the catalyst 17, has
been obtained (Table 3, entry 21). The catalytic activities of the
bis-ligated zirconium complexes 17 and 19 are more effective than
C2-symmetric zirconium amides 9, 11 and 12, but less than
bis(amidate) zirconium amide [(R)-(6-MeC6H3)2-2-{NCO(2,4,6-
Me3C6H2)}2]Zr(NMe2)2 (20) (Table 3, entry 12) [22]. Although the
enantiomeric excesses obtained remain moderate, it should be
noted that there are only few group four catalysts for these reac-
tions that give a significant ee (>90%) at all [19–23,46–53].
The stereochemical outcome of the asymmetric hydroamina-
tion/cyclization of aminoalkene 21a catalyzed by C2-symmetric zir-
conium amides can be rationalized by the transition state pictures
(Fig. 6) similar to those proposed by Hultzsch and others [23,54],
which may well explain the experimental observations that the
substituted groups on the biphenyl backbone have considerable
influence on the enantioselectivity of the catalysts and the configu-
ration of the resulting products. For example, the more sterically
unfavorable interactions between the carbon chain of the substrate
and the mesitoylamido groups of complex [(R)-(6-MeC6H3)2-2-
{NCO(2,4,6-Me3C6H2)}2]Zr(NMe2)2 (20) lead to the product 2,4,4-
trimethylpyrrolidine with a significantly preferentially (up to 93%
ee) with (S)-configuration (Table 3, entry 12) [22,23], while the less
sterically unfavorable interactions between the carbon chain of the
substrate and the diphenylphosphinoylamido groups of complex 12
result in a poor enantioselectivity (only up to 6.8% ee; Table 3, entry
4), indicating that highly enantioselective catalyst for this transfor-
mation requires very precise control of the metal coordination
sphere. The enantioselectivity induced by C2-symmetric zirconium
amides could be roughly ruled out, however, it is difficult to draw a
conclusion from the different enantioselectivity between the bis-li-
gated zirconium complexes and the C2-symmetric zirconium
amides. For example, the bis-ligated diphenylphosphoramidate
[(R)-2-(Ph2PON)-20-(Me2N)-(6-MeC6H3)2]2Zr(NMe2)2 [21] is more
selective than C2-symmetric diphenylphosphoramidate 12, while
the bis-ligated mesitoylamidate [(R)-2-{NCO(2,4,6-Me3C6H2)}-20-
(Me2N)-(6-MeC6H3)2]2Zr(NMe2)2 [21] is less selective than the
C2-symmetric mesitoylamidate [(R)-(6-MeC6H3)2-2-{NCO(2,4,6-
Me3C6H2)}2]Zr(NMe2)2 (20) [22]. Although the reasons for the
different enantioselectivity between the bis-ligated zirconium
Fig. 4. Molecular structure of 17 (thermal ellipsoids drawn at the 35% probability
level).
two nitrogen atoms and two sulfur atoms from the two ligands 7
and two nitrogen atoms from amino groups NMe2 in a distorted-
octahedron geometry (Fig. 4) with the average distance of Zr–N
(2.171(3) Å) and the average distance of M–S (2.754(1) Å). The
short Zr–N(5) and Zr–N(6) bond distances (2.035(3) and
2.052(3) Å) and the planar geometry around the N(5) and N(6)
nitrogen atoms indicate that the nitrogen atoms with sp2 hybrid-
ization are engaged in N(p ) ? Zr(d ) interactions. The twisting
p
p
between the phenyl rings of torsion angles are 85.4(5) and
81.6(5)°, which are close to those found in [(R)-2-(Ph2PON)-20-
(Me2N)-(6-MeC6H3)2]2Zr(NMe2)2 (85.4(3) and 86.8(3)°) [21].
The single-crystal X-ray diffraction analysis shows that 18 and
19 are isostructural. In each molecule (8)2M(NMe2)2, the substi-
tuted Me2N group is far away from the metal center, and the M4+
is
r-bound to four nitrogen atoms from the two ligands 8 and
two nitrogen atoms from amino groups NMe2 in a distorted-octa-
hedron geometry (Fig. 5) with the average distance of M–N
(2.098(2) Å) for Ti and (2.209(1) Å) for Zr, respectively. The short
distances of M–NMe2 1.912(2) and 1.913(2) Å for Ti and 2.029(1)
and 2.043(1) Å for Zr and the planar geometry around the nitrogen
atoms N(7) and N(8) indicate that the nitrogen atoms with sp2
hybridization are engaged in N(p ) ? M(d ) interactions. The
p
p
twisting between the phenyl rings of torsion angle is 71.7(2)°
and 71.1(2)° for 18 and 71.0(2)° and 70.7(2)° for 19, which are
smaller than those found in 17 (85.4(5)° and 81.6(5)°).
Fig. 5. Molecular structure of 18 (M = Ti) and 19 (M = Zr) (thermal ellipsoids drawn
at the 35% probability level).

738
G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
Table 3
Enantioselective hydroamination/cyclization of aminoalkenes.a
Entry
Catalyst (M)
Substrate
Product
Time (h)
Conv. (%)b
Ee (%)c
1
2
3
4
5
6
7
8
9 (Zr)
24
160
24
96
24 (S)d
NA
NH2
H
N
10 (Ti)
11 (Zr)
12 (Zr)
13 (Ti)
14 (Zr)
15 (Ti)
16 (Zr)
17 (Zr)
18 (Ti)
19 (Zr)
(R)-20 (Zr)e
9 (Zr)
NR
100
86
NR
NR
NR
NR
92
NR
100
>98
100
100
93
21 (S)d
6.8 (S)d
NA
24
160
160
160
160
24
160
24
3
16
16
16
16
NA
NA
NA
21a
21b
9
38 (S)d
NA
10
11
12
13
14
15
16
17
32 (S)d
93 (S)
19
NH2
NH
11 (Zr)
12 (Zr)
17 (Zr)
19 (Zr)
17
8.9
28
24
100
94
16
22b
NH
22a
NH2
18
19
20
21
22
9 (Zr)
24
24
24
24
24
100
100
95
100
100
18
16
11
24
20
11 (Zr)
12 (Zr)
17 (Zr)
19 (Zr)
23b
23a
a
b
c
Conditions: C6D6 (0.70 mL), aminoalkene (0.16 mmol), catalyst (0.016 mmol), at 120 °C.
Determined by 1H NMR based on p-xylene as the internal standard. NR = no reaction.
Determined by 1H NMR of its diastereomeric (S)-(+)-O-acetylmandelic acid salt [27]. NA = not applicable.
d
e
Absolute configuration of the major enantiomer was assigned by the comparison of optical rotation with literature data [54].
See Refs. [22,23].
M(NMe2)4 (M = Ti, Zr) and chiral ligands, 2H2, 3H2, 4H2, 5H2, 6H2,
7H and 8H. The zirconium amides have displayed good to excellent
catalytic activity for the asymmetric hydroamination/cyclization of
representative aminoalkenes, while the titanium amides have not.
The bis-ligated zirconium complexes 17 and 19 are more effective
chiral catalysts for the enantioselective hydroamination/cycliza-
tion reaction than C2-symmetric zirconium amides 9, 11 and 12,
but less than bis(amidate) zirconium amide [(R)-(6-MeC6H3)2-2-
{NCO(2,4,6-Me3C6H2)}2]Zr(NMe2)2 (20) [22–24]. How to fully opti-
mize both the rate and selectivity remains a question for asymmet-
ric hydroamination, it seems that very precise control of the metal
coordination sphere is required for this transformation to be a real-
istic prospect. Our ligand set using peripheral biphenyl-based N4,
N3 or N2O2-ligand in multidentate systems does not provide a suc-
cessful suitable coordination sphere to achieve a significant enanti-
oselectivity, however, this modification should significantly
expand the range of possibilities in designing catalysts not only
for hydroamination but also for many other reactions [1–4]. Fur-
ther optimization of the ligand architecture to improve the enan-
tiomeric excess for this transformation and the exploration of
these catalysts toward other types of transformations are still
underway.
Me
Me
Me
Me
N
N
Zr
Zr
N
N
N
N
favored
disfavored
H
N
H
N
(
S
)
(R
)
Me
Me
Me
Me
Fig. 6. Proposed transition states.
Acknowledgements
complexes (17 and 19) and the C2-symmetric zirconium amides (9,
11 and 12) are not clear at this time, the coordination environment
around the metal center seems to be a major reason for this differ-
ent olefin switch approach. Further computational investigation of
the ligand architecture for this transformation is currently
underway.
This work was supported by the National Natural Science Foun-
dation of China (20972018), Beijing Municipal Commission of Edu-
cation, and Excellent Doctoral Dissertation Fund of Beijing Normal
University.
4. Conclusions
Appendix A. Supplementary material
In conclusion, a new series of chiral titanium(IV) and zirco-
nium(IV) amides have been prepared from the reactions between
CCDC 749372, 749373, 749374, 749375, 749376, and 749377
contain the supplementary crystallographic data for 10, 12, 13,

G. Zi et al. / Journal of Organometallic Chemistry 695 (2010) 730–739
[27] J.Y. Kim, T. Livinghouse, Org. Lett. 7 (2005) 1737–1739.
739
17, 18 and 19. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.12.008.
[28] D. Riegert, J. Collin, A. Meddour, E. Schulz, A. Trifonov, J. Org. Chem. 71 (2006)
2514–2517.
[29] M. Kettunen, C. Vedder, F. Schaper, M. Leskelä, I. Mutikainen, H.-H. Brintzinger,
Organometallics 23 (2004) 3800–3807.
[30] G.M. Sheldrick, SADABS, Program for Empirical Absorption Correction of Area
Detector Data, University of Göttingen, Göttingen, Germany, 1996.
[31] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structure from
Diffraction Data, University of Göttingen, Göttingen, Germany, 1997.
[32] G.M. Diamond, R.F. Jordan, J.L. Petersen, Organometallics 15 (1996) 4045–
4053.
[33] A.K. Hughes, A. Meetsma, J.H. Teuben, Organometallics 12 (1993) 1936–
1945.
[34] D.W. Carpenetti, L. Kloppenburg, J.T. Kupec, J.L. Petersen, Organometallics 15
(1996) 1572–1581.
[35] G. Zi, H.-W. Li, Z. Xie, Organometallics 21 (2002) 3850–3855.
[36] Z.J. Tonzetich, R.R. Schrock, A.S. Hock, P. Müller, Organometallics 24 (2005)
3335–3342.
[37] E.J. Crust, A.J. Clarke, R.J. Deeth, C. Morton, P. Scott, Dalton Trans. (2004) 4050–
4058.
[38] S. Majumder, A.L. Odom, Organometallics 27 (2008) 1174–1177.
[39] J.A. Bexrud, C. Li, L.L. Schafer, Organometallics 26 (2007) 6366–6372.
[40] Z. Zhang, D.C. Leitch, M. Lu, B.O. Patrick, L.L. Schafer, Chem. Eur. J. 13 (2007)
2012–2022.
[41] R.K. Thomson, J.A. Bexrud, L.L. Schafer, Organometallics 25 (2006) 4069–4071.
[42] R.K. Thomson, F.E. Zahariev, Z. Zhang, B.O. Patrick, Y.A. Wang, L.L. Schafer,
Inorg. Chem. 44 (2005) 8680–8689.
[43] P.N. O’Shaughnessy, K.M. Gillespie, C. Morton, I. Westmoreland, P. Scott,
Organometallics 21 (2002) 4496–4504.
[44] R.M. Beesley, C.K. Ingold, J.F. Thorpe, J. Chem. Soc. 107 (1915) 1080–1106.
[45] C.K. Ingold, J. Chem. Soc. 119 (1921) 305–329.
[46] P.D. Knight, I. Munslow, P.N. O’Shaughnessy, P. Scott, Chem. Commun. (2004)
894–895.
[47] D.V. Gribkov, K.C. Hultzcsh, Angew. Chem., Int. Ed. 43 (2004) 5542–5546.
[48] F. Pohlki, I. Bytschkov, H. Siebeneicher, A. Hertling, W.A. König, S. Doye, Eur. J.
Org. Chem. (2004) 1967–1972.
[49] J.M. Hoover, J.R. Petersen, J.H. Pikul, A.R. Johnson, Organometallics 23 (2004)
4614–4620.
[50] D.A. Watson, M. Chiu, R.G. Bergman, Organometallics 25 (2006) 4731–4733.
[51] A.L. Gott, A.J. Clarke, G.J. Clarkson, P. Scott, Chem. Commun. (2008) 1422–1424.
[52] A.L. Gott, G.J. Clarkson, R.J. Deeth, M.L. Hammond, C. Morton, P. Scott, Dalton
Trans. (2008) 2983–2990.
References
[1] M. Lemaire, P. Mangeney, Chiral Diazaligands for Asymmetric Synthesis in
Topics in Organometallic Chemistry, vol. 15, Springer-Verlag, Berlin,
Heidelberg, 2005.
[2] P.D. Knight, P. Scott, Coord. Chem. Rev. 242 (2003) 125–143.
[3] C.-M. Che, J.-S. Huang, Coord. Chem. Rev. 242 (2003) 97–113.
[4] F. Fache, E. Schulz, M.L. Tommasino, M. Lemaire, Chem. Rev. 100 (2000) 2159–
2232.
[5] G. Zi, Dalton Trans. (2009) 9101–9109.
[6] G.F. Zi, C.L. Yin, Acta Chim. Sinica 56 (1998) 484–488.
[7] G.F. Zi, C.L. Yin, J. Mol. Catal. A: Chem. 132 (1998) L1–L4.
[8] G. Zi, L. Xiang, Y. Zhang, Q. Wang, Y. Yang, Z. Zhang, J. Organomet. Chem. 692
(2007) 3949–3956.
[9] Y. Zhang, L. Xiang, Q. Wang, X.-F. Duan, G. Zi, Inorg. Chim. Acta 361 (2008)
1246–1254.
[10] L. Xiang, Q. Wang, H. Song, G. Zi, Organometallics 26 (2007) 5323–5329.
[11] Q. Wang, L. Xiang, H. Song, G. Zi, Inorg. Chem. 47 (2008) 4319–4328.
[12] G. Zi, L. Xiang, H. Song, Organometallics 27 (2008) 1242–1246.
[13] Q. Wang, L. Xiang, G. Zi, J. Organomet. Chem. 693 (2008) 68–76.
[14] Z. Zhang, M. Li, G. Zi, Chirality 19 (2007) 802–808.
[15] R. Liu, X. Bai, Z. Zhang, G. Zi, Appl. Organomet. Chem. 22 (2008) 671–685.
[16] Z. Zhang, X. Bai, R. Liu, G. Zi, Inorg. Chim. Acta 362 (2009) 1687–1691.
[17] Q. Wang, L. Xiang, H. Song, G. Zi, J. Organomet. Chem. 694 (2009) 691–696.
[18] H. Song, L.-N. Gu, G. Zi, J. Organomet. Chem. 694 (2009) 1493–1502.
[19] Q. Wang, L. Xiang, H. Song, G. Zi, Dalton Trans. (2008) 5930–5944.
[20] L. Xiang, H. Song, G. Zi, Eur. J. Inorg. Chem. (2008) 1135–1140.
[21] G. Zi, X. Liu, L. Xiang, H. Song, Organometallics 28 (2009) 1127–1137.
[22] M.C. Wood, D.C. Leitch, C.S. Yeung, J.A. Kozak, L.L. Schafer, Angew. Chem. Int.
Ed. 46 (2007) 354–358.
[23] M.C. Wood, D.C. Leitch, C.S. Yeung, J.A. Kozak, L.L. Schafer, Angew. Chem. Int.
Ed. 48 (2009) 6937.
[24] A.L. Gott, A.J. Clarke, G.J. Clarkson, P. Scott, Organometallics 26 (2007) 1729–
1737.
[25] S. Kanoh, S. Goka, N. Murose, H. Kubo, M. Kondo, T. Sugino, M. Motoi, H. Suda,
Polym. J. 19 (1987) 1047–1065.
[26] G.M. Diamond, R.F. Jordan, J.L. Petersen, J. Am. Chem. Soc. 118 (1996) 8024–
8033.
[53] A.J. Hickman, L.D. Hughs, C.M. Jones, H. Li, J.E. Redford, S.J. Sobelman, J.A.
Kouzelos, A.R. Johnson, Tetrahedron: Asymmetry 20 (2009) 1279–1285.
[54] D.V. Gribkov, K.C. Hultzsch, F. Hampel, J. Am. Chem. Soc. 128 (2006) 3748–
3759.