Synthesis and structural characterization of aryloxo-functionalized N-heterocyclic carbene complexes of nickel(II)

Article abstract of DOI:10.1016/j.jorganchem.2005.09.029

The reaction of Ni(PPh₃)₂Br₂ with two equivalents of anionic aryloxo-functionalized N-heterocyclic carbene [NaO-4,6-di-^tBu-C₆H₂-2-CH ₂{C(NCHCHNR)}] (R = ⁱPr, NaL¹

Full text of DOI:10.1016/j.jorganchem.2005.09.029

Journal of Organometallic Chemistry 690 (2005) 6227–6232
www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of aryloxo-functionalized
N-heterocyclic carbene complexes of nickel(II)
*
Wan-Fei Li, Hong-Mei Sun, Zhi-Guo Wang, Mu-Zi Chen, Qi Shen , Yong Zhang
The Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215006, China
Received 2 August 2005; received in revised form 13 September 2005; accepted 14 September 2005
Available online 26 October 2005
Abstract
The reaction of Ni(PPh3)2Br2 with two equivalents of anionic aryloxo-functionalized N-heterocyclic carbene [NaO-4,6-di-tBu-C6H2-
2-CH2{C(NCHCHNR)}] (R = iPr, NaL1; R = Bz, NaL2), which are generated in situ by the reaction of the corresponding salt H2LCl
with two equivalents of NaN(SiMe3)2, affords bis-ligand complexes of L12Ni (3) and L22Ni (4) in good yield, respectively. It is inter-
esting to note that still the bis-ligand one not the mono-ligand Ni(II) halide is obtained, even the molar ratio of NaL1or NaL2 to
Ni(PPh3)2Br2 is changed to 1:1. Complexes of 3 and 4 have been fully characterized including the X-ray structure determination.
The structural analysis shows that each nickel atom in 3 or 4 is bonded to two bidentate ligands L1 or L2, respectively, in a cis
arrangement.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Functionalized N-heterocyclic carbene; Bidentate ligand; Nickel
1. Introduction
tethered NHCs, have been designed and successfully ap-
plied in the synthesis of organometallic complexes, espe-
cially the early transition metal and lanthanide element
complexes, in which the anionic group acts as an anchor
and the tendency for ligand dissociation would be reduced
efficiently [4].
In recent years, tremendous efforts have been made
towards the synthesis of transition metal complexes con-
taining N-heterocyclic carbene (NHC) ligands [1]. N-
heterocyclic carbenes (NHCs), as appealing alternatives
to traditional phosphine ligands, have been widely used
in organometallic chemistry due to their strong donor
properties, easily tuned in electronic and steric effect by
the diversity of nitrogen substituents, and the excellent
catalytic behavior of their metal complexes in homoge-
neous catalysts [2]. The key point for new NHCs recently
has been paid to the designation of the functionalized
NHCs, since the introduction of pendant functional group
to an NHC could result both in diverse metal complexes,
and in an opportunity to better control the stability of ac-
tive centers in catalytic reactions [3]. Recently, the anionic
functionalized group, i.e., anionic amido, aryloxo, alkoxo-
NHCs becomes an important ligand in organometallic
chemistry of nickel, several kinds of Ni(II) NHC complexes
have been synthesized and some of them are excellent
precatalysts in organic reactions. However, no examples
to date of Ni(II) complex with an anionic functionalized
NHC is reported. In view of the lack of such kind of Ni(II)
complexes, the bidentate aryloxo-functionalized NHC
precursor [HO-4,6-di-tBu-C6H2-2-CH2{CH(NCHCHNiPr)}]-
Cl (iPr = CH(CH3)2, H2L1Cl, 1) and its analogue [HO-4,6-
di-tBu-C6H2-2-CH2{CH(NCHCHNBz)}Cl (Bz = CH2C6H5,
H2L2Cl, 2) were designed and synthesized. The corresponding
NHC of Ni(II) [O-4,6-di-tBu-C6H2-2-CH2{C(NCHCHN-
iPr)}]2Ni (L1Ni, 3) and [O-4,6-di-tBu-C6H2-2-CH2{C(NC-
2
HCHNBz)}]2Ni (L22Ni, 4) were synthesized by the reactions
of Ni(PPh3)2Br2 with 1 or 2 in the presence of NaN(SiMe3)2,
respectively. Here, we would like to report the results.
*
Corresponding author. Tel.: +86 512 6511 2513; fax: +86 512 6511
2371.
E-mail address: qshen@suda.edu.cn (Q. Shen).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.029

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W.-F. Li et al. / Journal of Organometallic Chemistry 690 (2005) 6227–6232
2. Experimental
2.1. General procedures
was gradually warmed to room temperature and then stir-
red for additional 12 h, filtered, and evaporated to dryness.
The residue was extracted with toluene. Crystals suitable
for elemental analysis and X-ray diffraction determination
were obtained by recrystallization from 1,4-dioxane/
CH2Cl2 (5:1) at room temperature (1.33 g, 75%). 1H
NMR (400 MHz, C6D6, 25 ꢁC) d 7.65 (1 H, s, Ph-H),
7.61 (1H, s, Ph-H), 7.49 (1H, s, Ph-H), 7.01 (1H, s, Ph-
H), 6.18 (2H, s, NCH), 5.73 (2H, s, NCH), 4.37 (2H, m,
CH(CH3)2), 4.30 (2H, s, CH2N), 4.27 (2H, s, CH2N) 3.39
(16H, s, OCH2CH2O), 1.90 (18H, s, C(CH3)3), 1.47(18H,
s, C(CH3)3), 1.10 (6H, d, CH(CH3)2), 0.27 (6H, d,
CH(CH3)2); 13C NMR (100 MHz, C6D6, 25 ꢁC): d 164.6,
162.3, 140.8, 132.8, 124.4, 123.2, 122.8, 121.3, 116.8, 67.6,
55.0, 51.8, 36.5, 34.6, 32.8, 30.9, 25.1, 21.4. Anal. Calc.
for C50H78N4O6Ni: C, 67.48; H, 8.84; N, 6.29. Found: C,
67.43; H, 8.81; N, 6.25%.
All manipulations were performed under pure argon
with rigorous exclusion of air and moisture using stan-
dard Schlenk techniques. Solvents were distilled from
Na/benzophenone ketyl under pure argon prior to use.
2-Chloromethyl-4,6-di-tert-butylphenol [5], (PPh3)2NiBr2
[6] and 1-benzyl-imidazole [7] was prepared by the litera-
ture methods, all other chemicals were obtained commer-
cially and used as received unless stated otherwise.
Elemental analysis was performed by direct combustion
1
on a Carlo-Erba EA-1110 instrument. H NMR spectra
were measured on a Unity Inova-400 spectrometer at
25 ꢁC.
2.2. Synthesis of H2LCl
2.3.2. Procedure B
2.2.1. Synthesis of H2L1Cl (1)
By the procedure analogous to that described above, the
reaction of 1 (0.36 g, 1 mmol) and NaN(SiMe3)2 (0.84 M,
2.4 mL) with Ni(PPh3)2Br2 (0.75 g, 1 mmol), 3 was ob-
tained in 40% yield (0.71 g).
To a solution of 2-chloromethyl-4,6-di-tert-butylphe-
nol (7.64 g, 30 mmol) in THF (20 mL) was added 1-iso-
propyl-imidazole (3.30 g, 30 mmol) in THF (30 mL).
After stirring about 2–3 h at room temperature, the reac-
tion mixture was filtered to collect the white powder,
which was dried in vacuo. Yield 9.20 g (85%). 1H
NMR (400 MHz, CDCl3, 25 ꢁC) d: 10.27(s, 1H, NCHN)
7.35 (s, 1H, Ph-H), 7.25 (s, 1H, Ph-H), 7.19 (s, 1H, Ph-
H), 7.09 (s, 1H, Ph-H), 5.84 (s, 2H, ArCH2N), 4.64 (m,
1H, CH(CH3)2), 1.59 (d, 6H, CH(CH3)2), 1.39 (s, 9H,
C(CH3)3), 1.29 (s, 9H, C(CH3)3). Anal. Calc. for
C21H33ClN2O: C, 69.11; H, 9.11; N, 7.67. Found: C,
68.18; H, 9.10; N, 7.62%.
2.4. Synthesis of L22Ni ꢀ 2ðC4H8O2Þ (4)
2.4.1. Procedure A
A Schlenk flask was charged with 2 (0.42 g, 1 mmol),
THF (20 mL) and a stir bar. To this suspension was
added dropwise two equivalents of NaN(SiMe3)2(0.84 M,
2.4 mL) in THF at ꢁ78 ꢁC. The reaction was stirred for
30 min and gradually warmed to room temperature for
additional 10 min. Then, the resulted solution was added
slowly to a suspension of Ni(PPh3)2Br2(0.38 g, 0.5 mmol)
in THF at ꢁ78 ꢁC under stirring. The resulting solution
was gradually warmed to room temperature and then
stirred for additional 12 h, filtered, and evaporated to
dryness. The residue was extracted with toluene. Crystals
suitable for elemental analysis and X-ray diffraction
determination were obtained by recrystallization from
1,4-dioxane/CH2Cl2 (5:1) at room temperature (0.68 g,
2.2.2. Synthesis of H2L2Cl (2)
1-Benzyl-imidazole (4.74 g, 30 mmol) was treated in a
procedure similar to that for 1 to yield 2 (9.91 g, 80%).
1H NMR (400 MHz, CDCl3, 25 ꢁC) d: 10.27(s, 1H,
NCHN) 7.36 (d, 6H, Ph-H), 7.20 (s, 1H, Ph-H), 7.07 (d,
1H, Ph-H), 7.04 (s, 1H, Ph-H), 5.81 (s, 2H, ArCH2N),
5.40 (s, 2H, PhCH2N), 1.39 (s, 9H, C(CH3)3), 1.28 (s,
9H, C(CH3)3). Anal. Calc. for C25H33ClN2O: C, 72.71;
H, 8.05; N, 6.78. Found: C, 72.77; H, 8.03; N, 6.75%.
1
70%). H NMR (400 MHz, C6D6, 25 ꢁC) d 7.55 (2H, s,
Ph-H), 7.51 (2H, s, Ph-H), 7.06 (10H, m, Ph-H), 5.96
(2H, s, NCH), 5.59 (2H, s, NCH), 4.39 (4H, d, CH2N),
4.09 (4H, m, CH2Ph), 3.39 (16H, s, OCH2CH2O), 1.87
(18H, s, C(CH3)3), 1.47(18H, s, C(CH3)3), 13C NMR
(100 MHz, C6D6, 25 ꢁC): d 164.3, 162.2, 140.6, 136.3,
132.7, 129.6, 127.8, 124.5, 123.1, 122.3, 121.7, 121.3,
67.6, 55.2, 53.1, 36.6, 34.5, 32.9, 31.2. Anal. Calc. for
C58H70N4NiO6: C, 71.23; H, 7.22; N, 5.73. Found: C,
71.24; H, 7.23; N, 5.70%.
2.3. Synthesis of L12Ni ꢀ 2ðC4H8O2Þ (3)
2.3.1. Procedure A
A Schlenk flask was charged with 1 (0.73 g, 2 mmol),
THF (20 mL) and a stir bar. To this suspension was added
dropwise two equivalents of NaN(SiMe3)2 (0.84 M,
4.8 mL) in THF at ꢁ78 ꢁC. The reaction was stirred for
30 min and gradually warmed to room temperature for
additional 10 min. Then the resulted solution was added
slowly to a suspension of Ni(PPh3)2Br2 (0.75 g, 1 mmol)
in THF at ꢁ78 ꢁC under stirring. The color of the solution
from green to orange was immediately observed and indi-
cated the occurrence of the reaction. The resulting solution
2.4.2. Procedure B
By the procedure analogous to that described above, the
reaction of 2 (0.42 g, 1 mmol) and NaN(SiMe3)2(0.84 M,
2.4 mL) with Ni(PPh3)2Br2(0.75 g, 1 mmol), 4 was obtained
in 42% yield (0.41 g).

W.-F. Li et al. / Journal of Organometallic Chemistry 690 (2005) 6227–6232
6229
Table 2
Selected bond lengths (A) and angles (ꢁ) for 3 and 4
2.5. Structure determination
˚
3
Suitable single crystals of complexes 3 and 4 were each
sealed in a thin-walled glass capillary for X-ray structural
analysis. Diffraction data were collected on a Rigaku Mer-
cury CCD area detector at 193(2) K. The structure was
solved by direct methods and refined by full-matrix least-
squares procedures based on F2. All non-hydrogen atoms
were refined with anisotropic displacement coefficients.
Hydrogen atoms were treated as idealized contributions.
The structures were solved and refined using SHELXS-97
and SHELXL-97 programs, respectively. Crystal data and
collection and main refinement parameters are given in
Ni(1)–O(1)
Ni(1)–C(8)
C(8)–Ni(1)–O(1)
C(29)–Ni(1)–O(2)
C(8)–Ni(1)–C(29)
1.885(5)
1.854(6)
91.9(2)
91.3(2)
91.5(3)
Ni(1)–O(2)
Ni(1)–C(29)
C(29)–Ni(1)–O(1)
C(8)–Ni(1)–O(2)
O(2)–Ni(1)–O(1)
1.882(4)
1.861(6)
176.6(2)
177.0(2)
85.3(2)
4
Ni(1)–O(1)
Ni(1)–C(8)
C(8)–Ni(1)–O(1)
C(8A)–Ni(1)–O(1A)
C(8)–Ni(1)–C(8A)
1.893(2)
1.864(3)
92.40(1)
92.40(1)
89.73(2)
Ni(1)–O(1A)
Ni(1)–C(8A)
C(8A)–Ni(1)–O(1)
C(8)–Ni(1)–O(1A)
O(1A)–Ni(1)–O(1)
1.893(2)
1.864(3)
177.86(9)
177.86(9)
85.51(1)
˚
Table 1. Selected bond lengths (A) and angles (ꢁ) for 3
and 4 are given in Table 2.
corresponding precursors H2L1Cl (1) or H2L2Cl (2) in
85% or 80% yields, respectively. The characterization of 1
and 2 were supported by elemental analysis and 1H
3. Results and discussion
1
NMR spectroscopy. The H NMR spectra of compounds
3.1. Syntheses and characterizations of 1 and 2
1 and 2 exhibit the characteristic resonances of imidazo-
lium C2-H signals at 10.27 ppm for 1 and 10.27 ppm for
2, the tert-butyl protons signals in the region d 1.29–
1.39 ppm for 1 and d 1.28–1.39 ppm for 2, respectively.
Our aim was to understand the application of anionic-
functionalized NHCs in organometallic chemistry of Ni(II).
Taking into consideration that anionic aryloxo-functional-
ized NHCs are capable of binding metal atom through the
aryloxide oxygen and the carbene carbon to provide an [O,
tBu
OH
tBu
OH
Cl
C
carbene]-type chelation, we designed aryloxo-functional-
THF
tBu
ized NHC ligands L1 and L2. Their precursors, H2L1Cl
and H2L2Cl, were synthesized conveniently in high yields
via nucleophilic attack of a 1-alkylimidazole on a benzyl
chloride by the method shown in Scheme 1. Thus, the
reactions of 2-chloromethyl-4,6-di-tert-butylphenol with
1-isopropyl-imidazole or 1-benzyl-imidazole yielded the
tBu
+
N
N R
Cl-
N
N
R
R = iPr (1), Bz (2)
Scheme 1. Synthesis of 1 and 2.
Table 1
X-ray crystallographic data for 3 and 4
3
4
Empirical formula
Formula weight
Temperature (K)
k (Mo Ka) (A)
Crystal system
C
889.87
193(2)
42H62N4NiO2 Æ 2(C4H8O2)
C50H54N4NiO2 Æ 2(C4H8O2)
977.89
193(2)
0.71070
Monoclinic
c2/c
31.636(1)
10.892(3)
22.620(8)
90.00
134.002(5)
90.00
5607.0(3)
4
1.159
0.396
˚
0.71070
Monoclinic
P2(1)/n
15.611(2)
21.220(3)
16.428(2)
90.00
111.015(3)
90.00
5080.1(1)
4
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalcd (g/cm3)
1.164
0.430
1928
Absorption coefficient (mmꢁ1
F(000)
)
2088
Crystal size (mm)
2hmax (ꢁ)
Number of reflections collected
0.44 · 0.43 · 0.28
55.0
56366
0.45 · 0.40 · 0.30
50.7
56366
Number of independent reflections
11619
26659
(Rint = 0.0413)
1.121
(Rint = 0.0594)
1.094
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
0.0755
0.0640

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W.-F. Li et al. / Journal of Organometallic Chemistry 690 (2005) 6227–6232
3.2. Synthesis and characterizations of 3 and 4
melt at 165 ꢁC for 3 and at 180 ꢁC for 4, respectively. It is
worth mentioning that complexes 3 and 4 are much less
sensitive to air and moisture, and both of them can even re-
main unchanged for a few days in open air.
The reaction of Ni(PPh3)2Br2 with two equivalents of 1
or 2 in the presence of two equivalents of NaN(SiMe3)2
each yielded an orange Ni(II) complex in ca. 75% or 70%
yield, respectively. Both of them were characterized to be
the desired bis-ligand ones (3 and 4) by elemental analysis
3.3. Crystal structures of 3 and 4
1
and H NMR spectra (Scheme 2, Eq. 1). Attempt to syn-
Crystals of 3 and 4 suitable for an X-ray crystal struc-
ture determination were grown from 1,4-dioxane/CH2Cl2
at room temperature. The solid structures for 3 and 4 were
shown in Figs. 1 and 2, respectively. The crystallographic
data and selected bond distances and angles are listed in
Tables 1 and 2, respectively.
thesize mono-ligand complex by the same reactions at the
molar ratio of 1:1 is unsuccessful (Scheme 2, Eq. 2). After
workup, the same bis-ligand complexes 3 and 4 were iso-
lated in reasonable lower yields of 40% and 42%, respec-
tively. The results might be due to the additional of the
second ligand being faster than the first one or the dispro-
portionation of mono-ligand Ni(II) halide to a more stable
bi-ligand complex [8]. The formations of 3 and 4 were sup-
ported by elemental analysis and NMR spectroscopy. In
13C NMR spectra the signals for carbene carbon atoms
of complexes 3 and 4 appear at d 164.6, 162.3 ppm for 3
and d 164.3, 162.2 ppm for 4, respectively. These Ccarbene
signals are comparable to those observed in Ni(II)-based
NHC complexes [9]. However, it was noticed that two sing-
lets, not one singlet, were observed for the peak of Ccarbene
in each 13C NMR spectrum, although the structure analysis
of 3 or 4 showed them to be a C2 symmetry at the center
nickel atom of each complex (as shown in 3.3) [10]. Such
characteristics of 13C NMR spectra of 3 and 4 might be
contributed to the existence of an equilibrium between a
cis and trans isomer in solution of 3 and 4, respectively.
In fact, it was really observed that the signal of the carbene
carbon in 3 or 4 was firstly appeared as a singlet
(162.3 ppm for 3 and 162.2 ppm for 4), and then another
singlet (164.6 ppm for 3 and 164.3 ppm for 4) gradually ap-
peared nearly in the process of monitoring. In additional, it
was also noticed that the signals of methylene protons of 3
The X-ray structural analysis revealed the complexes 3
and 4 have the similar solid-state structure. The center
nickel atom of each complex coordinated to two bidentate
ligands to form a distorted square-planar geometry (Figs. 1
and 2). The two chelating rings adopt a cis arrangement
around the nickel atom, such that there is a C2 symmetry
at the nickel center. The two chelating rings slightly distort
the coordination geometry of the nickel atom with the
C–Ni–O bite angle being reduced to 85.3(2)ꢁ for 3 and
85.5(1)ꢁ for 4. The two cis Ni–Ccarbene bonds of (1.854(6)
˚
˚
and 1.861(6) A for 3; 1.864(3) and 1.864(3) A for 4) are
very close to these found in a bi-ligand picolyl-functional-
ized NHC supported Ni(II) complex [1.851(4) and
˚
1.861(4) A] reported by Jin and co-workers [10]. The
Ni–O bond distances in 3 and 4 are comparable to those
in known Ni(II) complexes [11]. In complex 3, the dihedral
angles of N-heterocyclic carbene planes (N1–N2–C8–C9–
C10 and N3–N4–C29–C30–C31) with the plane formed
by O1–O2–C8–C29 are 58.4ꢁ and 59.0ꢁ, respectively, while
O1–O1A–C8–C8A in complex 4 both are 54.9ꢁ, which is
smaller as compared with those in 3 and is somewhat more
similar to those in the bis(bidentate)nickel(II) complexes
(Ni(3-methyl-1-picolylimidazolin-2-ylidene)2Cl2, 44.6ꢁ; Ni-
(3-benzyl-1-picolylimidazolin-2-ylidene)2Cl2, 46.7ꢁ) [10].
The dihedral angles between the two carbene planes are
76.3ꢁ for 3 and 68.6ꢁ for 4, respectively, suggesting that a
benzyl group is less steric demanding than an isopropyl
group. The structure differences between the two complexes
1
and 4 appeared in H NMR spectra both as a singlet at
room temperature, even these signals should be doublets
if the solid-state structures of 3 and 4 were retained in solu-
tion. These features might be related to the testꢀs tempera-
ture. It was expected that the singlets could turn into the
doublets at a temperature low enough.
Complexes 3 and 4 are soluble in protic solvents
CH2Cl2, DME, THF, 1,4-dioxane, diethyl ether and tolu-
ene, insoluble in hexane. They are thermally stable and will
tBu
tBu
O
2NaN(SiMe3)2
Ni
tBu
2
N R
0.5NiBr2(PPh3)2
(1)
(2)
N
tBu
OH
N
Cl-
N R
2NaN(SiMe3)2
NiBr2(PPh3)2
tBu
O
Br
tBu
Ni PPh3
N
N R
R = iPr (3), Bz (4)
Fig. 1. The crystal structures of complex 3 showing 30% probability
Scheme 2. Synthesis of 3 and 4.
ellipsoids. The hydrogen atoms are omitted for clarity.

W.-F. Li et al. / Journal of Organometallic Chemistry 690 (2005) 6227–6232
6231
Fig. 2. The crystal structures of complex 4 showing 30% probability ellipsoids. The hydrogen atoms are omitted for clarity.
(c) L. Jafarpour, S.P. Nolan, J. Organomet. Chem. 617 (2001) 17;
(d) L.D. Vasquez-Serrano, B.T. Owens, J.M. Buriak, Chem. Com-
mun. (2002) 2518;
might be due to the steric hindrance of the substituent
group of the ligand: an isopropyl group exerts greater steric
hindrance than a benzyl group.
`
´
(e) I.E. Marko, S. Sterin, O. Buisine, G. Mignani, P. Branlard, B.
Tinant, J.P. Declerq, Science 298 (2002) 204;
4. Conclusions
(f) M.C. Perry, K. Burgess, Tetrahedron: Asymmetry 14 (2003) 951;
(g) O. Navarro, R.A. Kelly III, S.P. Nolan, J. Am. Chem. Soc. 125
(2003) 16194.
In summary, a novel kind of bidentate aryloxo-function-
alized imidazium chloride 1 and 2 was synthesized and the
bis-ligand Ni(II) complexes 3 and 4 were obtained using 1
and 2 as the reactants. Further investigation on the appli-
cations of such complexes and the functionalized-NHC
ligands in other metals is in progress.
[2] (a) D. Bourissou, O. Guerret, F.P. Gabba¨ı, G. Bertrand, Chem. Rev.
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(b) W.A. Herrmann, Angew. Chem., Int. Ed. 41 (2002) 1290;
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Acknowledgments
(f) C.M. Crudden, D.P. Allen, Coord. Chem. Rev. 248 (2004) 2247.
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Chem. Soc. 125 (2003) 12716;
We are grateful to the Ph.D. Foundation of the Depart-
ment of Education, the Department of Education of Jiang-
su Province, the National Natural Science Foundation of
China and Key Laboratory of Organic Chemistry, Jiangsu
Province, for the financial support.
(c) D.S. McGuinness, V.C. Gibson, J.W. Steed, Organometallics 23
(2004) 6288;
(d) S. Gischig, A. Togni, Organometallics 23 (2004) 2479;
(e) A.E. Wang, J. Zhong, J.H. Xie, K. Li, Q.L. Zhou, Adv. Synth.
Catal. 346 (2004) 595;
Appendix A. Supplementary data
(f) S. Winston, N. Stylianides, A.A.D. Tulloch, J.A. Wright, A.A.
Danopoulos, Polyhedron 23 (2004) 2813;
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC nos. 279472 and 279473 for complexes 3
and 4, respectively. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK, fax: +44 1223 336 033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
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