Bulky-hindrance-controlled ligand transformation from linked bis(amidinate) to linked imido-amidinate promoted by a mono(cyclopentadienyl)titanium group

Article abstract of DOI:10.1002/ejic.200600658

A novel class of silyl-linked bis(amidinate) ligands [SiMe ₂-{NC(Ph)N(2,6-R₂Ph)Li)₂] [L¹ (R = H), L² (R = Me), and L³ (R = iPr)] reacted with TiCl ₃(C₅H₅) to produce the half-sandwich titanium complexes 1,2, and 3. The molecular structures of 1-3 were confirmed successfully by X-ray crystallography. An unprecedented intramolecular ligand transformation from the linked bis(amidinate) configuration to the linked imido-amidinate configuration took place in the cases of L¹ and L². It was found that the rearrangement process was related to the steric hindrance of the terminal substituents. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600658

FULL PAPER
DOI: 10.1002/ejic.200600658
Bulky-Hindrance-Controlled Ligand Transformation from Linked
Bis(amidinate) to Linked Imido-Amidinate Promoted by a
Mono(cyclopentadienyl)titanium Group
Sheng-Di Bai,[a] Jian-Ping Guo,*[a] Dian-Sheng Liu,*[a] and Wai-Yeung Wong[b]
Keywords: Titanium / Bis(amidinate) / Bulky hindrance / Ligand transformation / Crystal structure / Steric hindrance
A novel class of silyl-linked bis(amidinate) ligands [SiMe2-
{NC(Ph)N(2,6-R2Ph)Li}2] [L1 (R = H), L2 (R = Me), and L3 (R
= iPr)] reacted with TiCl3(C5H5) to produce the half-sandwich
titanium complexes 1, 2, and 3. The molecular structures of
1–3 were confirmed successfully by X-ray crystallography.
An unprecedented intramolecular ligand transformation
from the linked bis(amidinate) configuration to the linked
imido-amidinate configuration took place in the cases of L1
and L2. It was found that the rearrangement process was re-
lated to the steric hindrance of the terminal substituents.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
of the substituents attached to the terminal nitrogen atoms,
which were less bulky, the N–C–N–Si–N–C–N backbone of
these dianionic ligands could be transformed to a new class
of linked imido-amidinate ligands. We believe that the metal
center of mono(cyclopentadienyl)titanium complexes pro-
moted the rearrangement reaction.
Introduction
Both cyclopentadienyl and amidinate ligands have been
extensively studied for decades because of their high adapt-
ability to a wide variety of metals in coordination chemistry.
The corresponding metal complexes have shown remark-
able utility as homogeneous catalysts for olefin polymeriza-
tion.[1,2] As a further step, systematic investigations on the
metal compounds with a mixed-ligand environment con-
taining these two types of ancillary ligands have been car-
ried out in the past few years, involving the new generation
of Ziegler–Natta catalysts, carbon mono- or dioxide reac-
tants, and Kharasch reaction catalysts.[3–9] These merits
have made the chemistry of half-sandwich compounds an
attractive research field. On the other hand, much attention
has recently been paid to metal compounds incorporated
with the linked bis(amidinate) ligands, as these unique dian-
ionic ligands have the advantage of affording dinuclear
complexes or mononuclear complexes analogous to “ansa-
metallocenes”, leading to valuable geometric structures and
properties. Nevertheless, there have been few reports on
linked bis(amidinate) half-sandwich compounds.[4a,9]
Result and Discussion
Synthesis and Structural Characterization
The analogous silyl-linked bis(amidinate) ligands L1, L2,
and L3 were prepared in our previous work. They demon-
strated a trend of increasing steric hindrance by variation of
the 2,6-substituents of the corresponding phenyl analogue.
Treatment of L1 with 1 equiv. of TiCl3(C5H5) in thf gave,
after extraction with CH2Cl2 and crystallization, compound
1 as red crystals in 82% yield. Complexes 2 and 3 were
prepared under similar synthetic procedures in yields of
48% and 65%, respectively (Scheme 1). These half-sand-
wich titanium compounds were characterized by NMR
spectroscopy, elemental analysis, and single-crystal X-ray
diffraction analysis.
The molecular structure of 1 is shown in Figure 1 and
the key bonding parameters are listed in Table 1. The ligand
coordinating to the titanium center does not keep the con-
figuration in L1. The original linked bis(amidinate) ligand
was expected to coordinate to the metal center in a tetra-
dentate mode. However, the ligand is tridentate in com-
pound 1. On both sides of the silyl bridge, the two amidin-
ate moieties exhibit different coordination styles to the Ti
ion. One is chelating and the other is monodentate. More-
over, the latter one adopts the opposite direction involving
a phenyl migration from N4 to N3. It gives a new imido
A novel class of linked bis(amidinate) ligands (L1, L2,
and L3) were developed in our laboratory. They displayed
close contact between the two amidinate moieties; that is in
contrast to other common examples reported in the litera-
ture.[10] We next attempted the preparation of the half-sand-
wich derivatives from the reactions of ligands with
TiCl3(C5H5). It was found, to our surprise, that in the cases
[a] Institute of Modern Chemistry, Shanxi University,
Taiyuan, Shanxi 030006, P. R. China
Fax: +86-351-7011743
E-mail: guojp@sxu.edu.cn
[b] Department of Chemistry, Hong Kong Baptist University,
Waterloo Road, Kowloon Tong, Hong Kong, P. R. China
Eur. J. Inorg. Chem. 2006, 4903–4907
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4903

S.-D. Bai, J.-P. Guo, D.-S. Liu, W.-Y. Wong
FULL PAPER
group [demonstrated by N3–C22 being 1.385(4) Å and N4–
C22 being 1.288(4) Å]. On the other hand, the five-mem-
bered skeleton of N4–C22–N3–Si1–N2 displays analogous
structural features, with an N2–Ti1–N4 angle of 84.70(13)°,
as in some reported titanium β-diketiminates, such
as [(Ar)NC(CH3)CHC(CH3)N(Ar)]Ti=NAr(OTf).[11] The
Ti–Nimido bond [1.847(3) Å] is much shorter than the
Ti–Namidinate bonds [2.220(3) and 2.111(3) Å]. The “unsym-
metrical” distribution of the two N–C–N moieties leads to
a difference of 0.09 Å between the silyl bridge and the
neighboring nitrogen atoms on either side.
Compound 2 was derived from L2, which was more
bulky than L1, by introducing 2,6-dimethyl groups onto the
terminal phenyl rings. Complex 2 is almost isostructural to
1 except for the presence of additional methyl groups. Struc-
tural analysis indicates that the increased steric bulk as-
cribed to the methyl groups plays no role in differentiating
Scheme 1.
Figure 1. ORTEP drawing (30% probability level) of the molecular structure of compound 1. Hydrogen atoms are omitted for clarity.
Table 1. Selected bond lengths [Å] and bond angles [°] for compounds 1, 2, and 3.
1
2
3
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(4)
Ti(1)–Cl(1)
Ti(1)–Cp(centroid)
N(1)–C(7)
N(2)–C(7)
Si(1)–N(2)
Si(1)–N(3)
2.220(3)
2.111(3)
1.847(3)
2.362(3)
2.050
1.313(4)
1.349(4)
1.709(3)
1.799(3)
1.385(4)
1.288(4)
60.91(12)
84.70(13)
116.6
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(4)
Ti(1)–Cl(1)
Ti(1)–Cp(centroid)
N(1)–C(9)
N(2)–C(9)
Si(1)–N(2)
Si(1)–N(3)
2.352(3)
2.061(3)
1.840(3)
2.3392(11)
2.043
1.297(4)
1.344(4)
1.709(3)
1.794(3)
1.381(4)
1.282(4)
59.54(10)
84.46(12)
116.9
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–Cl(1)
Ti(1)–Cp(centroid)
N(1)–C(13)
N(2)–C(13)
Si(1)–N(2)
Si(1)–N(3)
N(3)–C(22)
1.900(3)
1.911(3)
2.2921(14)
2.027
1.284(5)
1.397(4)
1.790(3)
1.791(3)
1.388(4)
1.278(5)
83.26(13)
116.4
N(3)–C(22)
N(4)–C(22)
N(3)–C(26)
N(4)–C(26)
N(4)–C(22)
N(2)–Ti(1)–N(3)
Cl(1)–Ti(1)–Cp(centroid)
C(21)–Si(1)–C(20)
N(1)–C(13)–N(2)
N(2)–Si(1)–N(3)
N(4)–C(22)–N(3)
N(2)–Ti(1)–N(1)
N(4)–Ti(1)–N(2)
Cl(1)–Ti(1)–Cp(centroid)
N(1)–C(7)–N(2)
N(2)–Si(1)–N(3)
N(4)–C(22)–N(3)
C(22)–N(4)–Ti(1)
N(2)–Ti(1)–N(1)
N(4)–Ti(1)–N(2)
Cl(1)–Ti(1)–Cp(centroid)
N(1)–C(9)–N(2)
N(2)–Si(1)–N(3)
N(4)–C(26)–N(3)
C(26)–N(4)–Ti(1)
116.9(2)
116.8(3)
90.01(14)
118.1(3)
111.2(3)
105.97(15)
122.5(3)
137.0(2)
113.3(3)
105.76(13)
121.5(3)
143.7(3)
4904
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4903–4907

Ligand Transformation from Linked Bis(amidinate) to Linked Imido-Amidinate
FULL PAPER
Figure 2. ORTEP drawing (30% probability level) of the molecular structure of compound 3. Hydrogen atoms are omitted for clarity.
the configuration of 2 from that of 1. However, the steri-
The proposed mechanism for the formation of 1 and 2 is
cally more demanding isopropyl groups do make com- outlined in Scheme 2. Combination of the linked bis(amid-
pound 3 saliently different from 1 and 2. The ligand frame- inate) ligands and titanium salt gives the expected com-
work of 3 (Figure 2) is identical to that of ligand L3. It pounds with the tetradentate coordination environment (a).
should be pointed out that the ligand of 3 adopts the di- Induced by the electronically deficient metal center, one am-
amido configuration rather than the linked bis(amidinate) idinate moiety is polarized, and its C–N double bond is
configuration. The Ti–Namido bonds in 3 are much shorter located at the outer position because of the electronic with-
than the Ti–Namidinato bonds in 1 and 2. The two terminal drawal from the aromatic group. The electronically rich
nitrogen atoms have no bonding contacts with the metal imino nitrogen atom then attacks the silicon atom (b). It
center and they are converted into imino groups. The re- forms an N–C–N–Si four-membered ring and a notable
sulting diamido ligand bites the titanium ion at a right an- five-coordinate silicon transition state. The original N–Si
gle and it exhibits a planar Ti–N–Si–N tetragonal core. The bond is then weakened (c). Rearrangement is completed af-
tetragonal square is perpendicular to another coincident ter electron transfer to form an imido group (d). It should
plane composed of C20–Si1–C21 and Cl1–Ti1–Cp(cen- be pointed out that the N–C–N–Si–N–C–N fragment in
troid) (with a dihedral angle of 89.8°).
Intramolecular Rearrangement Reaction
The tetradentate bonding mode between the ligands and
the Ti center is not preferred because the common electron
count of the titanium ion is 12 or 14. Apparently, the steric
bulk of the terminal group plays an important role in the
determination of the resulting configuration of compounds
1, 2, and 3. In the absence of sterically demanding substitu-
ents, such as in L1 and L2, one amidinate moiety of the
ligand tends to take the end-contact mode rather than the
general chelating mode in order to obtain 14 outer electrons
for the Ti ion. The initial terminal nitrogen atom is linked
to a phenyl group, which decreases the electronegativity of
that N atom and the bond strength of the corresponding
N–Ti edge. Comparatively, N4 in 1 or 2 becomes an imido
nitrogen atom after rearrangement and the new N–Ti bond
is greatly reinforced. These factors in combination drive the
ligand transformation process in 1 and 2.
Scheme 2.
Eur. J. Inorg. Chem. 2006, 4903–4907
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4905

S.-D. Bai, J.-P. Guo, D.-S. Liu, W.-Y. Wong
FULL PAPER
7.61–6.99 (m, 20 H, phenyl), 6.67, 6.50, 6.13 (t, 5 H, Cp), 0.57,
–0.47 (d, 6 H, SiMe2) ppm. 13C NMR (75 MHz, CDCl3): δ = 174.7,
163.4 (N-C-N), 148.9–125.9 (phenyl), 120.5, 118.9, 116.7 (Cp), 4.7,
2.9 (SiMe2) ppm. C33H31ClN4SiTi·CH2Cl2 (679.98): calcd. C 60.06,
H 4.89, N 8.24; found C 59.82, H 4.90, N 8.18.
these ligands is quite flexible. The intramolecular N–Si
coupling could be fulfilled without shielding from sterically
demanding substituents. This is the crucial step for the
transformation. On the contrary, the isopropyl groups in L3
are bulky enough to stop that terminal N atom from being
bonded to the Ti center or approaching the silyl bridge.
This gives compound 3 with the ligand remaining intact
and the Ti center with 12 outer electrons.
Preparation of 2: A solution of L2 (2.51 mmol) in thf (20 mL) was
added to a solution of TiCl3(C5H5) (0.55 g, 2.51 mmol) in thf
(10 mL) at 0 °C. The red solution was stirred at room temperature
for 12 h and then concentrated under vacuum. The residue was
extracted with CH2Cl2 (20 mL) and the solution filtered. The fil-
trate was concentrated to give compound 2 as red crystals. Yield:
1
Conclusions
0.79 g (48%); m.p. 179–180 °C. H NMR (300 MHz, CDCl3): δ =
7.60–6.68 (m, 16 H, phenyl), 6.55, 6.48 (d, 5 H, Cp), 2.74–2.04 (m,
12 H, methyl), 0.70, –0.24, –0.95 (t, 6 H, SiMe2) ppm. 13C NMR
(75 MHz, CDCl3): δ = 179.3, 17.6, 168.5 (N-C-N), 149.8–124.2
(phenyl), 120.6, 117.1 (Cp), 27.1–24.9 (methyl), 9.5, 4.5 (SiMe2)
ppm. C37H39ClN4SiTi·(CH2Cl2)0.25 (672.37): calcd. C 66.54, H
5.92, N 8.33; found C 66.89, H 5.97, N 8.31.
A novel intramolecular rearrangement of linked bis-
(amidinate) ligands was demonstrated. It was promoted by
the active titanium ion but could be tuned by the bulky
hindrance of terminal substituents. We are currently
exploring the reactions between the ligands and other metal
salts so as to investigate the generalization of this type of
chemical transformation.
Preparation of 3: A solution of L3 (1.55 mmol) in thf (20 mL) was
added to a solution of TiCl3(C5H5) (0.34 g, 1.55 mmol) in thf
(10 mL) at 0 °C. The red solution was stirred at room temperature
for 12 h and then concentrated under vacuum. The residue was
extracted with CH2Cl2 (20 mL) and the solution filtered. The fil-
trate was concentrated to give compound 3 as red crystals. Yield:
Experimental Section
1
General Procedures: All reactions were carried out under nitrogen
in flame-dried Schlenk-type glassware on a dual-manifold Schlenk
line. Solvents were dried prior to use. The ligand transfer reagents
L1, L2, and L3 were prepared according to the reported methods.[10]
0.77 g (65%); m.p. 186–187 °C. H NMR (300 MHz, CDCl3): δ =
7.50–6.87 (m, 16 H, phenyl), 6.44, 5.83 (d, 5 H, Cp), 3.49, 2.78 (d,
4 H, CH of iPr), 1.36–0.86 (m, 24 H, methyl of iPr), 0.56, 0.18, (d,
6 H, SiMe2) ppm. 13C NMR (75 MHz, CDCl3): δ = 166.7 (N-C-
N), 143.8–123.6 (phenyl), 117.5 (Cp), 28.6, 27.8, 25.1, 22.8 (iPr on
phenyl), 2.3, –0.6 (SiMe2) ppm. C45H55ClN4SiTi (763.37): calcd. C
70.80, H 7.26, N 7.34; found C 70.41, H 7.25, N 7.27.
TiCl3(C5H5) was prepared according to literature procedures.[12] 1
H
and 13C NMR spectra were recorded with a Bruker DRX-300 spec-
trometer. Elemental analyses were performed with a Vario EL-III
instrument. Melting points were taken with a Sanyo Gallenkamp
Variable Heater.
X-ray Crystallography: Single crystals of 1, 2, and 3 suitable for X-
ray diffraction studies were obtained by crystallization from
CH2Cl2. X-ray diffraction data were collected using graphite-mo-
nochromated Mo-Kα radiation (λ = 0.71073 Å) with a Bruker
Smart Apex CCD diffractometer, equipped with an Oxford Cryosy-
stems CRYOSTREAM device. The collected frames were processed
with the proprietary software SAINT and an absorption correction
was applied (SADABS) to the collected reflections.[13,14] The struc-
tures of these molecules were solved by direct methods and ex-
Preparation of 1: A solution of L1 (1.88 mmol) in thf (20 mL) was
added to a solution of TiCl3(C5H5) (0.41 g, 1.88 mmol) in thf
(10 mL) at 0 °C. The red solution was stirred at room temperature
for 12 h and then concentrated under vacuum. The residue was
extracted with CH2Cl2 (20 mL) and the solution filtered. The fil-
trate was concentrated to give compound 1 as red crystals. Yield:
1
1.05 g (82%); m.p. 171–172 °C. H NMR (300 MHz, CDCl3): δ =
Table 2. Crystal data and refinement results for compounds 1, 2, and 3.
1
2
3
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C34H33Cl3N4SiTi
679.98
C37H39ClN4SiTi
651.16
C45H55ClN4SiTi
763.37
monoclinic
P21/c (no. 14)
11.000(9)
15.650(19)
19.278(17)
102.70(6)
3237(5)
monoclinic
P21/n (no. 14)
11.4269(19)
24.534(4)
12.329(2)
103.438(2)
3361.9(10)
4
monoclinic
P21/n (no. 14)
18.187(6)
9.818(3)
24.152(8)
96.464(6)
4285(3)
β [°]
V [Å3]
Z
4
4
F(000)
1408
1.395
0.580
13119
5696
3774
0.951
1368
1.286
0.402
13786
5864
4109
1.030
1624
1.183
0.325
20142
7544
4490
1.029
Dcalcd. [gcm–3]
µ(Mo-Kα) [mm–1]
Reflections collected
Unique reflections
Observed reflections
Gof (for F2)
R1, wR2 [I Ͼ 2σ(I)]
R1, wR2 (all data)
Largest diff. peak/hole [eÅ–3]
0.0580, 0.1090
0.0927, 0.1203
0.492/–0.344
0.0605, 0.1184
0.0913, 0.1296
0.465/–0.286
0.0645, 0.1415
0.1182, 0.1670
0.445/–0.281
4906
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4903–4907

Ligand Transformation from Linked Bis(amidinate) to Linked Imido-Amidinate
FULL PAPER
M. Gondo, S. Masuda, H. Kondo, Y. Yamaguchi, K. Matsub-
ara, Chem. Commun. 2003, 442–443; d) Y. Motoyama, M.
Gondo, S. Masuda, Y. Iwashita, H. Nagashima, Chem. Lett.
2004, 33, 442–443; e) J. Terasawa, H. Kondo, T. Matsumoto,
K. Kirchner, Y. Motoyama, H. Nagashima, Organometallics
2005, 24, 2713–2721.
panded by standard difference Fourier syntheses using the software
SHELXTL.[15] Structure refinements were made on F2 using the
full-matrix least-squares technique. All non-hydrogen atoms were
refined with anisotropic displacement parameters. Hydrogen atoms
were placed in their idealized positions and allowed to ride on the
respective parent atoms. Pertinent crystallographic data and other
experimental details are summarized in Table 2. CCDC-295090 (for
1), -295091 (for 2), and -295092 (for 3) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
[7] W. J. van Meerendonk, K. Schröder, E. A. C. Brussee, A.
Meetsma, B. Hessen, J. H. Teuben, Eur. J. Inorg. Chem. 2003,
427–432.
[8] A. Xia, H. M. El-Kaderi, M. J. Heeg, C. H. Winter, J. Or-
ganomet. Chem. 2003, 682, 224–232.
[9] a) J. R. Hagadorn, M. J. McNevin, Organometallics 2003, 22,
609–611; b) J. R. Hagadorn, M. J. McNevin, G. Wiedenfeld,
R. Shoemaker, Organometallics 2003, 22, 4818–4824; c) M. J.
McNevin, J. R. Hagadorn, Inorg. Chem. 2004, 43, 8547–8554;
d) J. R. Hagadorn, Chem. Commun. 2001, 2144–2145.
[10] S.-D. Bai, J.-P. Guo, D.-S. Liu, Dalton Trans. 2006, 2244–2250;
and for examples of other kinds of linked bis(amidinate)com-
pounds, see: a) H. A. Jenkins, D. Abeysekera, D. A. Dickie,
J. A. C. Clyburne, J. Chem. Soc., Dalton Trans. 2002, 3919–
3922; b) J. Grundy, M. P. Coles, P. B. Hitchcock, J. Organomet.
Chem. 2002, 662, 178–187; c) C.-T. Chen, L. H. Rees, A. R.
Cowley, M. L. H. Green, J. Chem. Soc., Dalton Trans. 2001,
1761–1767; d) C.-T. Chen, C.-A. Huang, Y.-R. Tzeng, B.-H.
Huang, Dalton Trans. 2003, 2585–2590; e) J.-F. Li, L.-H. Weng,
X.-H. Wei, D.-S. Liu, J. Chem. Soc., Dalton Trans. 2002, 1401–
1405; f) J.-F. Li, S.-P. Huang, L.-H. Weng, D.-S. Liu, Eur. J.
Inorg. Chem. 2003, 810–813; g) H. Kawaguchi, T. Matsuo,
Chem. Commun. 2002, 958–959; h) J. R. Hagadorn, J. Arnold,
Angew. Chem. 1998, 110, 1813–1815; Angew. Chem. Int. Ed.
1998, 37, 1729–1731; i) G. D. Whitener, J. R. Hagadorn, J. Ar-
nold, J. Chem. Soc., Dalton Trans. 1999, 1249–1255; j) J. R.
Babcock, C. Incarvito, A. L. Rheingold, J. C. Fettinger, L. R.
Sita, Organometallics 1999, 18, 5729–5732; k) S. Bambirra, A.
Meetsma, B. Hessen, J. H. Teuben, Organometallics 2001, 20,
782–785.
[11] a) F. Basuli, J. C. Huffman, D. J. Mindiola, Inorg. Chem. 2003,
42, 8003–8010; b) F. Basuli, B. C. Bailey, J. Tomaszewski, J. C.
Huffman, D. J. Mindiola, J. Am. Chem. Soc. 2003, 125, 6052–
6053.
[12] R. D. Gorsich, J. Am. Chem. Soc. 1958, 80, 4744–4744.
[13] SAINT, Reference Manual, Siemens Energy and Automation,
Madison, WI, 1994–1996.
[14] G. M. Sheldrick, SADABS, Empirical Absorption Correction
Program, University of Göttingen, Germany, 1997.
[15] G. M. Sheldrick, SHELXTL, Reference Manual, version 5.1,
Siemens, Madison, WI, 1997.
Acknowledgments
This work was supported by grants from the Natural Science Foun-
dation of China (20472046 to D.-S. L. and 50443001 to J.-P. G.).
[1] a) A. Togni, R. L. Halterman, Metallocenes, Wiley-VCH Ver-
lag GmbH, Weinheim, Germany, 1998; b) S. Arndt, J. Okuda,
Chem. Rev. 2002, 102, 1953–1976; c) Y. Qian, J. Huang, M. D.
Bala, B. Lian, H. Zhang, H. Zhang, Chem. Rev. 2003, 103,
2633–2690.
[2] a) J. Barker, M. Kilner, Coord. Chem. Rev. 1994, 133, 219–300;
b) F. T. Edelmann, Coord. Chem. Rev. 1994, 137, 403–481.
[3] a) A. N. Chernega, R. Gómez, M. L. H. Green, J. Chem. Soc.,
Chem. Commun. 1993, 1415–1417; b) R. Gómez, R. Duch-
ateau, A. N. Chernega, J. H. Teuben, F. T. Edelmann, M. L. H.
Green, J. Organomet. Chem. 1995, 491, 153–158; c) C.-T. Chen,
L. H. Doerrer, V. C. Williams, M. L. H. Green, J. Chem. Soc.,
Dalton Trans. 2000, 967–974.
[4] a) J. R. Babcock, C. Incarvito, A. L. Rheingold, J. C. Fettinger,
L. R. Sita, Organometallics 1999, 18, 5729–5732; b) Y. Zhang,
L. R. Sita, Chem. Commun. 2003, 2358–2359; c) Y. Zhang, R. J.
Keaton, L. R. Sita, J. Am. Chem. Soc. 2003, 125, 8746–8747;
d) Y. Zhang, E. K. Reeder, R. J. Keaton, L. R. Sita, Organome-
tallics 2004, 23, 3512–3520; e) M. B. Harney, R. J. Keaton,
L. R. Sita, J. Am. Chem. Soc. 2004, 126, 4536–4537; f) Y.
Zhang, L. R. Sita, J. Am. Chem. Soc. 2004, 126, 7776–7777.
[5] a) P. J. Stewart, A. J. Blake, P. Mountford, J. Organomet. Chem.
1998, 564, 209–214; b) A. E. Guiducci, A. R. Cowley, M. E. G.
Skinner, P. Mountford, J. Chem. Soc., Dalton Trans. 2001,
1392–1394; c) C. L. Boyd, E. Clot, A. E. Guiducci, P. Mount-
ford, Organometallics 2005, 24, 2347–2367.
[6] a) H. Kondo, Y. Yamaguchi, H. Nagashima, J. Am. Chem. Soc.
2001, 123, 500–501; b) H. Kondo, K. Matsubara, H. Nagash-
ima, J. Am. Chem. Soc. 2002, 124, 534–535; c) H. Nagashima,
Received: July 13, 2006
Published Online: October 5, 2006
Eur. J. Inorg. Chem. 2006, 4903–4907
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4907