Synthesis of a sulfonate substituted β-diketimine ligand and its complexes of Co(II), Ni(II), Zn(II) and Pd(II)

Article abstract of DOI:10.1016/j.poly.2014.01.021

Deprotonation of the β-diketimine ligand [CH₂(C(Me)N-2,6- diisopropylphenyl)₂] using n-BuLi followed by treatment with SO ₃NMe₃ afforded the sulfonate substituted β-diketimine ligand Li(THF)₂[O₃SCH(C(Me)N-2,6-diisopropylphenyl) ₂] (1). Compound 1 is moderately soluble in water. It reacts with Ni(II) and Zn(II) chlorides to produce [LMCl] complexes (L = 1 without Li(THF)₂), in which the ligand coordinates to the metal in a tripodal fashion. Metal nitrate complexes [LM(O₂NO)] [M = Co(II), Ni(II) and Zn(II)] were also synthesized and structurally characterized. The reaction of 1 with [PdCl₂(CH₃CN)₂] was also explored. Depending on the reaction conditions, two dinuclear Pd complexes, [LPdCl ₂PdCl₂]^- and [LPdCl₂PdL], were formed. In both the cases the sulfonate group remained uncoordinated.

Full text of DOI:10.1016/j.poly.2014.01.021

Polyhedron 72 (2014) 27–34
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis of a sulfonate substituted b-diketimine ligand
and its complexes of Co(II), Ni(II), Zn(II) and Pd(II)
⇑
N.M. Rajendran, N. Dastagiri Reddy
Department of Chemistry, Pondicherry University, Pondicherry 605014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Deprotonation of the b-diketimine ligand [CH2(C(Me)@N-2,6-diisopropylphenyl)2] using n-BuLi followed
by treatment with SO3NMe3 afforded the sulfonate substituted b-diketimine ligand Li(THF)2
[O3SCH(C(Me)@N-2,6-diisopropylphenyl)2] (1). Compound 1 is moderately soluble in water. It reacts
with Ni(II) and Zn(II) chlorides to produce [LMCl] complexes (L = 1 without Li(THF)2), in which the ligand
coordinates to the metal in a tripodal fashion. Metal nitrate complexes [LM(O2NO)] [M = Co(II), Ni(II) and
Zn(II)] were also synthesized and structurally characterized. The reaction of 1 with [PdCl2(CH3CN)2] was
also explored. Depending on the reaction conditions, two dinuclear Pd complexes, [LPdCl2PdCl2]À and
[LPdCl2PdL], were formed. In both the cases the sulfonate group remained uncoordinated.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 22 October 2013
Accepted 12 January 2014
Available online 29 January 2014
Keywords:
Sulfonate substituted b-diketimine ligand
Co(II) complex
Ni(II) complex
Zn(II) complex
Pd(II) complex
1. Introduction
a Schlenk line and a glove box. MCl2Á6H2O (M = Ni, Co and Cu)
and M(NO3)2Á6H2O (M = Zn, Ni and Co) were procured from Hime-
The monoanionic bidentate b-diketiminate (NacNac) ligands
have emerged as one of the most versatile ligands in coordination
chemistry. They have been utilized in stabilizing a wide variety of
transition metals, main group elements and lanthanide metals
[1–9]. Incorporation of ligating groups into these ligands not only
provides additional binding modes but also changes the physical
properties, such as solubility. However, these kinds of modifica-
tions in b-diketiminate ligands are less explored in coordination
chemistry. Ligating groups like –CN, –NO2, –PPh2, N-aryloxy,
N-(hydroxyaryl), N-(thioalkoxyaryl), N-pendant amine and –NHAr
are integrated into the b-diketimine ligands resulting in the varia-
tion of their coordination mode and/or their donor ability [10–32].
Making b-diketiminate ligands water soluble would further
increase their potential as supporting ligands. With this view, we
dia Laboratories and used as received. [ZnCl2(CH3CN)2] [33] and
[PdCl2(CH3CN)2] [34] were prepared by following literature proce-
dures. Toluene, hexane and THF were distilled from Na/benzophe-
none ketyl as and when required. Acetonitrile was distilled from
CaH2. Benzene-d6 was condensed from Na/benzophenone ketyl
and CDCl3 was condensed from CaH2 and stored in a glove box.
Acetone-d6 was dried over molecular sieves. 1H and 13C NMR spec-
tra were recorded on a Bruker 400 MHz instrument. Elemental
analyses were performed using a Flash 2000 organic elemental
analyzer. IR spectra were recorded on a Smart Omni Transmission
analyzer. Thermogravimetric analyses were performed on a SDT
Q600V20.9 Build 20 instrument.
2.2. Single crystal X-ray experiments
À
designed a b-diketimine ligand bearing an ÀSO3 group and syn-
thesized NacNacSO3LiÁ2THF (Fig. 1) and its various metal com-
Data collection for all the compounds was done on an OXFORD
XCALIBUR diffractometer, equipped with a CCD area detector,
plexes. The results of these reactions are reported herein.
using graphite-monochromated Mo K
a (k = 0.71073 Å) radiation
2. Experimental
and a low temperature device. In order to avoid quality degrada-
tion, all the single crystals were coated with perfluoropolyalkyl
ether oil/paraffin oil and mounted on a glass fiber using cyanoacry-
late glue. All calculations were performed using SHELXS-97 and SHEL-
XL-97 [35]. The structures were solved by direct methods and
successive interpretation of the difference Fourier maps, followed
by full matrix least-squares refinement (against F2). All non-hydro-
gen atoms in the crystals were refined anisotropically. The contri-
bution of the hydrogen atoms, in their calculated positions, was
2.1. General considerations
All reactions and manipulations involving air/moisture sensi-
tive compounds were carried out under an N2 atmosphere using
⇑
Corresponding author. Tel.: +91 413 2654484.
E-mail address: ndreddy.che@pondiuni.edu.in (N.D. Reddy).
http://dx.doi.org/10.1016/j.poly.2014.01.021
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

28
N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
included in the refinement using a riding model. Upon conver-
gence, the final Fourier difference map of the X-ray structures
showed no significant peaks. All the datasets were collected to
2H values > 50°. Relevant data concerning crystallographic data,
data collection and refinement details are summarised in Table 1.
Fig. 1. NacNacSO3LiÁ2THF.
2.3. Synthesis of NacNacSO3LiÁ2THF (1)
(15 mL) in a 50 mL round bottom flask. The resultant mixture
was stirred for 12 h to afford an off-white precipitate and filtered
To a solution of NacNacH (2.29 g, 5.48 mmol) in THF (20 mL) was
added n-BuLi (3.7 mL, 1.6 M in hexane, 5.92 mmol) slowly at
À78 °C, followed by stirring for one hour. The resultant mixture
was cannulated into a Schlenk flask containing a suspension of SO3-
NMe3 (0.84 g, 6.04 mmol) in THF (20 mL) at À78 °C. The reaction
mixture was allowed to warm to room temperature and stirred
overnight. The mixture was filtered using Celite; the volume of
the filtrate was reduced to 20 mL and kept at 0 °C to obtain colour-
less NacNacSO3LiÁ2THF (1) Crystals. Yield: 2.84 g, 80%. Mp: 215–
216 °C. 1H NMR (CD3OD, 400 MHz, ppm) d: 7.11 (6H, m, ArH), 5.09
through
a frit. The precipitate was washed with water
(10 mL Â 2) and dried under vacuum. The crude product was dis-
solved in THF (10 mL) and kept at room temperature to obtain col-
ourless crystals in a moderate yield. These crystals were found to
be the b-diketiminium bisulfate salt [CH(C(Me)@NHDipp)2][HSO4]
(2). 1H NMR (CDCl3, 400 MHz, ppm) d: 12.01 (2H, s, NH), 7.37 (6H,
m, ArH), 3.10 (4H, m, CHMe2), 2.10 (6H, s,
CHMe2).
a-Me), 1.25 (24H, t,
A similar procedure was used for the reactions with other metal
chlorides (Cu(II), Co(II) and Zn(II)) with NacNacSO3LiÁ2THF in aque-
ous medium. The b-diketiminium bisulfate was formed in all cases.
(1H, s,
a
c-CH), 3.76 (8H, m, THF), 3.08 (4H, m, CHMe2), 2.13 (6H, s,
-Me), 1.89 (8H, m, THF), 1.14 (24H, m, CHMe2). 13C NMR (CD3OD,
100 MHz, ppm) d: 170.75, 146.30, 138.38, 138.32, 125.23, 124.15,
124.02, 82.14, 68.87, 28.57, 28.48, 26.51, 24.58, 24.50, 24.10,
23.52, 20.64. IR (KBr, cmÀ1
)
m: 1050 (vs,
m
(SÀO)), 628 (m, (CÀS)).
m
2.4.2. In organic solvents
With [ZnCl2(CH3CN)2]: To a mixture of NacNacSO3LiÁ2THF (0.20 g,
0.31 mmol) and [ZnCl2(CH3CN)2] (0.07 g, 0.32 mmol) was added
THF (10 mL) in a 50 mL Schlenk flask. The resultant mixture was re-
fluxed under a nitrogen atmosphere for 12 h and allowed to cool to
room temperature, filtered through a frit, and then the volatiles
were removed from the filtrate under vacuum. The crude product
was dissolved in hot toluene and kept at room temperature to
2.4. Reactions of NacNacSO3LiÁ2THF with metal chlorides
2.4.1. In aqueous medium
With [NiCl2Á6H2O]: To a mixture of NacNacSO3LiÁ2THF (0.20 g,
0.31 mmol) and NiCl2Á6H2O (0.08 g, 0.34 mmol) was added water
Table 1
Crystal data and structure refinement parameters for compounds 2–5 and 7–9.
Compound
2ÁTHF
33H52N2O5S
3Á½Toluene
C65H90Cl2N4O6S2Zn2 C33H47ClN4NiO3S
4ÁCH3CN
5Á3CH2Cl2
C61H90Cl10N4O3Pd2S C33H47N5O6SZn
7ÁCH3CN
8ÁCH3CN
C33H47N5NiO6S
9ÁCH3CN
C33H47CoN5O6S
Empirical
formula
Formula
weight
C
588.83
1289.17
673.97
1526.73
707.19
700.53
700.75
Crystal system
T (K)
Space group
triclinic
150(2)
P1
monoclinic
150(2)
C2/c
triclinic
150(2)
P1
triclinic
150(2)
P1
monoclinic
150(2)
P21/c
monoclinic
150(2)
P21/n
triclinic
150(2)
P1
ꢀ
ꢀ
ꢀ
ꢀ
a (Å)
b (Å)
c (Å)
17.6035(3)
18.3194(3)
19.3040(3)
62.774(2)
70.396(2)
73.091(2)
5144.11(15)
6
27.530(3)
18.8528(6)
14.633(2)
90.00
118.805(18)
90.00
6655.1(12)
4
1.287
10.0210(3)
12.0069(4)
16.0509(5)
101.389(3)
99.856(3)
107.017(3)
1755.51(10)
2
15.9409(3)
16.6802(3)
16.7560(3)
60.206(2)
69.7452(18)
86.6039(17)
3592.39(11)
2
17.0819(7)
11.7913(3)
19.5109(7)
90.00
114.322(5)
90.00
3581.0(2)
4
1.312
16.1883(8)
13.1403(5)
17.5304(10)
90.00
105.081(5)
90.00
3600.6(3)
4
1.292
9.9943(3)
11.8217(4)
16.7399(4)
102.249(2)
97.665(2)
108.752(3)
1786.24(9)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg mÀ3
)
1.140
0.134
1.275
0.725
1.411
0.945
1.303
0.587
l
(mmÀ1
)
0.915
0.792
0.645
F(000)
1920.0
2728.0
716.0
1572.0
1496.0
1488.0
742.0
Crystal size
(mm)
0.30 Â 0.20 Â 0.20 0.30 Â 0.25 Â 0.25
0.30 Â 0.20 Â 0.20 0.31 Â 0.24 Â 0.20
0.38 Â 0.32 Â 0.28 0.30 Â 0.30 Â 0.25 0.40 Â 0.30 Â 0.30
h range (°)
No. of
2.72–25.00
57890/18102
2.68–25.00
15881/5877
3.93–25.00
21858/6126
2.75–25.00
40683/12623
2.68–29.23
18274/8336
3.78–29.17
38182/8738
2.64–29.33
23595/8514
collected/
Unique
(R(int) = 0.0473)
(R(int) = 0.0318)
(R(int) = 0.0236)
(R(int) = 0.0450)
(R(int) = 0.0366)
(R(int) = 0.0589)
(R(int) = 0.0375)
reflections
No. of data/
restraints/
params
18102/1/1143
5877/0/378
6126/0/400
12623/2/754
8336/0/427
8738/0/431
8514/0/427
Goodness-of-fit 1.045
1.045
1.076
1.048
0.996
1.037
1.047
(GOF) on F2
R1, wR2
(I > 2
0.0691, 0.1837
0.0312, 0.0738
0.0409, 0.0794
0.38 and À0.35
0.0303, 0.0785
0.0357, 0.0824
0.30 and À0.29
0.0536, 0.1295
0.0726, 0.1435
2.37 and À2.30
0.0363, 0.0814
0.0584, 0.0882
0.43 and À0.46
0.0525, 0.0976
0.0894, 0.1081
0.77 and À0.72
0.0373, 0.0882
0.0476, 0.0937
0.42 and À0.37
r
(I))a
R1, wR2 (all
0.1027, 0.2112
data)a
D
q
/
max Dqmin
1.13 and À0.85
(e ÅÀ3
)
R|Fo|. wR2 = [R R .
w(Fo2–Fc2)2/ w(Fo2)2]0.5
a
R1
=
R
||Fo| À |Fc||/

N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
29
obtain colourless [NacNacSO3ZnCl] (3) crystals. Even after drying
the crystals under high vacuum for several hours, toluene could
not be removed completely from crystals. Yield: 0.14 g, 70%. Mp:
167–168 °C dec. 1H NMR (C6D6, 400 MHz, ppm) d: 7.06 (4H, m,
ArH), 6.95 (2H, m, ArH), 5.39 (1H, s, b-CH), 3.58 (2H, m, CHMe2),
reaction mixture was warmed slowly to room temperature and
stirred for 12 h. The resultant suspension was filtered through a
frit. The volume of the filtrate was reduced to 10 mL and kept at
À20 °C to obtain crystals in almost quantitative yield.
With [Zn(NO3)2Á6H2O]: NacNacSO3Li (0.21 g, 0.32 mmol) and
Zn(NO3)2Á6H2O (0.10 g, 0.34 mmol). White crystals of [NacNacSO3-
Zn(O2NO)] (7) were obtained. The crystals were dried under high
vacuum to obtain the complex without acetonitrile. Mp: 138–
139 °C dec. 1H NMR (CDCl3/acetone-d6, 400 MHz, ppm) d: 7.20
(6H, m, ArH), 5.50 (1H, s, b-CH), 3.15 (2H, m, CHMe2), 2.57 (2H,
2.53 (2H, m, CHMe2), 1.84 (6H, s,
a-Me), 1.39 (6H, d, J = 6.8 Hz,
CHMeMe), 1.27 (6H, d, J = 6.8 Hz, CHMeMe), 1.17 (6H, d, J = 6.8 Hz,
CHMeMe), 0.87 (6H, d, J = 6.8 Hz, CHMeMe). 13C NMR (CDCl3,
100 MHz, ppm) d: 179.17, 142.28, 139.53, 138.66, 129.34, 125.79,
124.10, 71.89, 29.29, 27.54, 25.51, 24.86, 24.61, 24.15, 24.04. IR
(KBr, cmÀ1
)
m: 1022 (m,
m
(SÀO)), 661 (m,
m
(CÀS)).
m, CHMe2), 2.29 (6H, s, a
-Me), 1.16 (24H, m, CHMeMe). 13C NMR
(CDCl3, 100 MHz, ppm) d: 178.79, 141.70, 139.25, 138.81, 128.39,
125.45, 124.27, 71.64, 29.16, 27.29, 26.24, 24.46, 24.32, 24.23. Anal.
Calc. for C29H41N3O6SZn: C, 55.72; H, 6.61; N, 6.72. Found: C, 55.89;
With [NiCl2Á6H2O]: To a mixture of NacNacSO3LiÁ2THF (0.21 g,
0.32 mmol) and NiCl2Á6H2O (0.08 g, 0.34 mmol) was added CH3CN
(15 mL) in a 50 mL Schlenk flask. The resultant mixture was stirred
for 24 h and then filtered through a frit. The volume of the filtrate
was reduced to 10 mL under vacuum and kept at À20 °C to obtain
green coloured crystals of [NacNacSO3NiCl] (4). The crystals were
dried under high vacuum to yield the complex without acetoni-
trile. Yield: 0.10 g, 52%. Mp: 228–229 °C dec. Anal. Calc. for C29H41
ClN2O3SNi: C, 58.85; H, 6.98; N, 4.73. Found: C, 58.68; H, 6.72; N,
H, 6.72; N, 6.81%. IR (KBr, cmÀ1
)
m
: 1008 (s,
m
(SÀO)), 661 (s, (CÀS)).
m
With [Ni(NO3)2Á6H2O]: NacNacSO3Li (0.20 g, 0.31 mmol) and
Ni(NO3)2Á6H2O (0.09 g, 0.31 mmol). Blue coloured crystals of [Nac-
NacSO3Ni(O2NO)] (8) were obtained. The crystals were dried under
high vacuum to obtain the complex without acetonitrile. Mp: 143–
144 °C dec. Anal. Calc. for C29H41N3O6SNi: C, 56.32; H, 6.68; N, 6.79.
4.84%. IR (KBr, cmÀ1
)
m
: 1013 (m,
m(SÀO)), 662 (m,
m
(CÀS)).
Found: C, 56.24; H, 6.54; N, 6.96%. IR (KBr, cmÀ1
) m: 1017 (vs
With [PdCl2(CH3CN)2] in dichloromethane: To a stirred solution of
[PdCl2(CH3CN)2] (0.09 g, 0.35 mmol) in dichloromethane (10 mL)
was added dropwise a solution of NacNacSO3Li (0.21 g, 0.32 mmol)
in dichloromethane (10 mL) at room temperature. The resultant
mixture was stirred for 18 h to obtain an orange precipitate, which
was filtered through a frit. The precipitate was washed with
dichloromethane and dried under vacuum. The crude material
was recrystallized from a mixture of dichloromethane and acetone
at room temperature to obtain orange crystals (5). Yield: 0.22 g,
51%. Mp: 231–232 °C dec. In the following NMR data, [NacNacSO3
Pd2Cl4]À is represented by a and [NacNacH2]+ is represented by b.
1H NMR (acetone-d6, 400 MHz, ppm) d: 9.81 (2H, s, NH) (b), 7.29
(6H, m, ArH) (b), 7.15 (6H, m, ArH) (a), 5.76 (1H, s, b-CH) (a),
4.55 (1H, s, b-CH) (b), 3.99 (2H, m, CHMe2) (a), 3.54 (2H, m, CHMe2)
m
(SÀO)), 661 (s, (CÀS)).
m
With [Co(NO3)2Á6H2O]: NacNacSO3Li (0.22 g, 0.34 mmol) and
Co(NO3)2Á6H2O (0.10 g, 0.34 mmol). Pink coloured crystals of [Nac-
NacSO3Co(O2NO)] (9) were obtained. The crystals were dried under
high vacuum to obtain the complex without acetonitrile. Mp: 116–
117 °C dec. Anal. Calc. for C29H41N3O6SCo: C, 56.30; H, 6.68; N, 6.79.
Found: C, 56.23; H, 6.57; N, 6.68%. IR (KBr, cmÀ1
) m: 1016 (s,
m
(SÀO)), 660 (s, (CÀS)).
m
3. Results and discussion
3.1. Synthesis of the NacNacSO3LiÁ2THF ligand
À
It has been reported in the literature that an ÀSO3 group was
introduced into the tripodal ligand tris(1-pyrazoyl)methane by
treating it with n-BuLi followed by SO3NMe3Àin THF [36]. This pro-
cedure was adopted to incorporate an ÀSO3 group into NacNacH
(a), 2.98 (6H, s, a-Me) (b), 2.82 (4H, m, CHMe2) (b), 2.28 (6H, s, a-
Me) (a), 1.74 (6H, d, J = 6.8 Hz, CHMeMe) (a), 1.30 (6H, d, J = 6.8 Hz,
CHMeMe) (a), 1.22 (6H, d, J = 6.8 Hz, CHMeMe) (a), 1.15 (6H, d,
J = 6.8 Hz, CHMeMe) (a), 1.07 (12H, d, J = 6.8 Hz, CHMeMe) (b),
0.93 (12H, d, J = 6.8 Hz, CHMeMe) (b). The 13C NMR spectrum could
not be recorded due to the poor solubility of the compound in com-
at the central carbon (c position). Deprotonation of NacNacH with
n-BuLi followed by treatment with SO3NMe3 (Scheme 1) afforded
NacNacSO3LiÁ2THF (1) in good yield. The compound was character-
ized by IR and 1H NMR spectroscopy. The IR spectrum showed
mon deuterated solvents. IR (KBr, cmÀ1
(CÀS)).
With [PdCl2(CH3CN)2] in acetonitrile: To a stirred solution of
)
m: 1034 (s,
m
(SÀO)), 630 (s,
m
bands associated with
m
(SÀO) and
m
(CÀS) at 1050 and 628 cmÀ1
respectively. The 1H NMR spectrum confirmed the presence of
two THF molecules in the ligand. Diffraction quality crystals could
not be obtained for single crystal X-ray diffraction studies. The
compound showed moderate solubility in water.
[PdCl2(CH3CN)2] (0.04 g, 0.15 mmol) in acetonitrile (10 mL) was
added dropwise a solution of NacNacSO3Li (0.10 g, 0.15 mmol) in
acetonitrile (10 mL) at room temperature. The resultant mixture
was stirred for 18 h and then filtered through a frit. The filtrate
was evaporated under vacuum and washed with dichloromethane
to remove any unreacted ligand. Attempts to grow single crystals
were unsuccessful. Yield: 0.12 g, 61%. Mp: 224–225 °C dec. 1H
NMR acetone-d6, 400 MHz, ppm) d: 7.10 (6H, m, ArH), 5.58 (1H,
s, b-CH), 4.01 (2H, m, CHMe2), 3.45 (2H, m, CHMe2), 2.18 (6H, s,
3.2. Reactions of NacNacSO3LiÁ2THF with metal chlorides in water
(metal = ZnII, NiII, CoII and CuII)
The moderate solubility of the ligand in water gave us an oppor-
tunity to explore the reactions of this ligand with metal salts in
aqueous medium. A mixture of NacNacSO3LiÁ2THF and NiCl2Á6H2O
was dissolved in water and stirred for 12 h to afford an off-white
precipitate (Scheme 2). Single crystal X-ray diffraction studies
a-Me), 1.53 (6H, d, J = 6.8 Hz, CHMeMe), 1.30 (6H, d, J = 6.4 Hz,
CHMeMe), 1.17 (6H, d, J = 7.2 Hz, CHMeMe), 1.13 (6H, d,
J = 6.8 Hz, CHMeMe). The 13C NMR spectrum could not be recorded
due to the poor solubility of the compound in common deuterated
solvents. Anal. Calc. for C58H82Cl2N4O6S2Pd2: C, 54.46; H, 6.46; N,
4.38. Found: C, 54.32; H, 6.35; N, 4.32%. IR (KBr, cmÀ1
) m: 1033
(m,
m
(SÀO)), 627 (m, (CÀS)).
m
2.5. General procedure for the synthesis of metal nitrate complexes
An equimolar mixture of NacNacSO3LiÁ2THF and M(NO3)2Á6H2O
was taken in a 50 mL Schlenk flask. Acetonitrile (ꢀ15 mL) was
condensed onto the mixture at liquid nitrogen temperature, the
Scheme 1. Synthesis of NacNacSO3Li.2THF.

30
N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
Scheme 2. Reaction of NacNacSO3Li.2THF with metal chlorides in aqueous
medium.
Fig. 3. Crystal structure of [NacNacSO3ZnCl] (3). Hydrogen atoms and the solvent
molecule toluene are omitted for clarity. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond distances (Å): C2–N1 1.282(3), C4–N2 1.286(3), C3–
S1 1.840(2), S1–O1 1.4865(15), S1–O2 1.4343(15), O1–Zn1 2.0195(14), N1–Zn1
2.0400(17), N2–Zn1 2.0393(17), Zn1–Cl1 2.1485(7). Selected bond angles (°): C2–
N1–Zn1 115.06(13), C4–N2–Zn1 114.24(13), C3–S1–O1 103.51(9), S1–O1–Zn1
119.68(8), O1–Zn1–Cl1 122.38(4), N1–Zn1–N2 96.18(7), N1–Zn1–Cl1 121.82(5),
N2–Zn1–Cl1 125.03(5), N1–Zn1–O1 90.87(6), N2–Zn1–O1 91.82(6).
Zn complex [NacNacSO3ZnCl] (3) in good yield (Scheme 3). The for-
mation of the NacNacSO3ZnCl complex was confirmed by single
crystal X-ray analysis and NMR spectra. An ORTEP diagram of its
molecular structure, important bond lengths and bond angles are
given in Fig. 3. [NacNacSO3ZnCl] crystallizes in the C2/c space group
of the monoclinic system. The Zn atom adopts a distorted tetrahe-
dral geometry with the ligand coordinating to the metal in an
N,N,O chelating fashion, similar to tripodal ligands, and the chloride
ion occupies the fourth position. The N1–Zn–N2 bond angle
[96.18(7)°] is the smallest of all the bond angles around the Zn
centre. The average imine C@N distance found in 3 (1.284(3) Å) is
typical of C@N double bond distance, which indicates the absence
Fig. 2. Crystal structure of [CH(C(Me)@NH(Dipp)2][HSO4] (2). Hydrogen atoms, the
counter anion [HSO4]À and the solvent molecule THF are omitted for clarity (except
on the N atoms and
c-carbon atom). Thermal ellipsoids are drawn at the 50%
probability level. Selected bond distances (Å): N1–C2 1.328(4), N2–C4 1.333(4), C1–
C2 1.500(4), C4–C5 1.496(4), C2–C3 1.395(4). Selected bond angles (°): C1–C2–N1
114.8(2), C5–C4–N2 114.6(3), N1–C2–C3 119.8(3) N2–C4–C3 119.9(3), C4–C3–C2
126.8(3).
of
p-delocalization in the backbone of the b-diketimine ligand.
The Zn–N and Zn–O bond distances [Zn1–N1 = 2.0400(17),
Zn1–N2 = 2.0393(17) and Zn1–O1 = 2.0195(14) Å] are similar to
those found in tris(pyrazoyl)methane sulfonate zinc complexes
[Zn–N = 2.0484(2)–2.152(2) and Zn–O = 2.017(2)–2.0858(18) Å]
[37,38].
Scheme 3. Synthesis of Zn and Ni complexes of [NacNacSO3]À.
performed on the crystals grown from the precipitate revealed that
it was a b-diketiminium bisulfate salt [CH(C(Me)@NH(Dipp)2]
[HSO4] (Dipp = 2,6-diisopropylphenyl). The structure was further
supported by a 1H NMR spectrum. An ORTEP diagram, along with
important bond lengths and bond angles, is given in Fig. 2. The
same product was obtained when NacNacSO3LiÁ2THF was treated
with CuCl2Á6H2O, CoCl2Á6H2O and ZnCl2 under similar conditions.
Fig. 4. Crystal structure of [NacNacSO3NiCl(CH3CN)] (4). Hydrogen atoms and the
solvent molecule acetonitrile are omitted for clarity. Thermal ellipsoids are drawn
at the 50% probability level. Selected bond distances (Å): C2–N1 1.276(2), C4–N2
1.277(2), C3–S1 1.8236(18), S1–O1 1.4683(14), S1–O2 1.4322(16), O1–Ni1
2.0744(13), N1–Ni1 2.0447(15), N2–Ni1 2.0960(14), Ni1–Cl1 2.2539(5), N3–Ni1
2.053(18). Selected bond angles (°):C2–N1–Ni1 117.46(13), C4–N2–Ni1 117.00(12),
C3–S1–O1 103.31(8), S1–O1–Ni1 122.56(8), N2–Ni1–N3 161.59(7), O1–Ni1–Cl1
158.56(4), N1–Ni1–N2 91.61(6), N1–Ni1–Cl1 111.98(5), N2–Ni1–Cl1 93.77(4), N1–
Ni1–O1 89.36(6), N2–Ni1–O1 87.41(6).
3.3. Reactions of NacNacSO3LiÁ2THF with metal chlorides in organic
solvents (metal = ZnII, NiII and CoII)
Since the attempts to prepare metal complexes of [NacNacSO3]À
in aqueous medium were unsuccessful, the reactions were explored
in organic solvents. An equimolar mixture of NacNacSO3LiÁ2THF and
[ZnCl2(CH3CN)2] in THF under reflux conditions afforded a tripodal

N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
31
Unlike [ZnCl2(CH3CN)2], NiCl2Á6H2O upon treatment with Nac-
NacSO3LiÁ2THF in THF produced a white crystalline material which
was found to be insoluble in common organic solvents. Due to its
insoluble nature, further characterization could not be carried
out. This product is presumed to be a coordination polymer. None-
theless, when the reaction was carried out in acetonitrile, a green
coloured penta-coordinated Ni complex was obtained in moderate
yield (Scheme 3). The single crystal X-ray structure of complex 4
(Fig. 4) reveals that the Ni center adopts a distorted square-pyra-
midal geometry [s = (161.59–158.56)/60 = 0.05] [39]. The base of
the square-pyramid contains one chloride ion, one nitrogen atom
from acetonitrile, one nitrogen atom and one oxygen atom from
the ligand. The base is almost planar and the Ni atom lies slightly
above (0.349 Å) the mean plane. The apex is occupied by another
nitrogen atom from the ligand. Since the ligand coordinates to
the metal in a tripodal fashion, the apex is tilted towards the li-
gand. Important bond lengths and bond angles are listed in
Fig. 4. The average imine C@N distance found in 4 (1.277(2) Å) is
typical of a C@N double bond distance. The Ni–N and Ni–O bond
distances [Ni1–N1 = 2.0447(15), Ni1–N2 = 2.0960(14) and Ni1–
O1 = 2.0744(13) Å] are found to be in the range of those reported
Fig. 5. Crystal structure of [SO3NacNacPd2Cl4][CH(C(Me)@NHDipp)2] (5). Hydrogen
atoms, the counter cation [CH(C(Me) @NHDipp)2]+ and three solvent molecules of
dichloromethane are omitted for clarity. Thermal ellipsoids are drawn at the 50%
probability level. Selected bond distances (Å): C2–N1 1.295(7), C4–N2 1.298(7), C3–
S1 1.856(5), S1–O1 1.454(4), S1–O2 1.428(5) N1–Pd1 2.017(4), Pd1–Cl1 2.3323(13),
Cl1–Pd2 2.3057(13), Pd2–Cl3 2.2742(13). Selected bond angles (°): C2–N1–Pd1
126.0(4), C4–N2–Pd1 125.7(4), C2–C3–S1 108.3(3), C3–S1–O1 104.0(2), C3–S1–O2
103.9(3), N1–Pd1–Cl1 93.36(12), N1–Pd2–N2 91.85(17), Pd1–Cl1–Pd2 92.03(4),
Cl1–Pd2–Cl283.26(5), Cl3–Pd2–Cl4 92.97(5).
for
a tris(pyrazoyl)methane sulfonate nickel complex [Ni–
N = 2.0964(17) and Ni–O = 2.0438(14) Å] [37,38]. When this green
coloured Ni complex was dried under high vacuum, a yellow col-
oured material was produced, which showed no C„N stretching
frequency in its IR spectrum. This observation indicates that the
acetonitrile is loosely held to Ni. This was further confirmed by ele-
mental analysis. Treatment of NacNacSO3LiÁ2THF with CoCl2Á6H2O
in acetonitrile, afforded a blue coloured Co complex in moderate
yield. Attempts to grow the X-ray quality crystals were unsuccess-
ful. The IR spectrum of the complex is similar to that of the Ni com-
plex and further characterization is under progress.
À
hybridized with one hydrogen atom and an –SO3 group attached
to it. The –SO3À group is almost perpendicular to the square plane
of the Pd atom that is attached to the ligand. It is not involved in
coordination with Pd. The Pd–N and Pd–Cl bond distances
[Pd1–N1 = 2.017(4) and Pd1–Cl1 = 2.333(13) Å] and N1–Pd1–N2
bond angle [91.85(17)°]are similar to those reported for a similar
Pd(II) complex [Pd–N1 = 2.013(3), Pd–Cl1 = 2.323(1) Å and N1–
Pd–N2 = 89.85(15)°] [41]. The complex is insoluble in common
deuterated solvents, such as chloroform-d, and is sparingly soluble
3.4. Reactivity of NacNacSO3LiÁ2THF with palladium(II) chloride
When [PdCl2(CH3CN)2] was treated with NacNacSO3LiÁ2THF in
dichloromethane at room temperature for 18 h, an orange coloured
precipitate was formed. This was later characterized as
[CH(C(Me)@NH(Dipp)2][SO3NacNacPd2Cl4] (Scheme 4). The crys-
tals, obtained from a mixed acetone and dichloromethane solution
of this solid, were subjected to single crystal X-ray diffraction stud-
ies. The crystal structure shows a dinuclear anionic complex with a
diketiminium ion as the counter cation. To the best of our knowl-
edge, there are only two more examples containing a Pd2Cl4 unit
with NacNac based ligands reported in the literature [40,41]. An
ORTEP diagram showing the complex anionis is given in Fig. 5. Both
the Pd centers have a square-planar geometry with two chloride
ions bridging the metals. These planes are not coplanar and the
dihedral angle between them is 33.25°. This is relatively high com-
pared to that of the reported complexes [19.06° and 5.39°] [40,41].
The central carbon atom of the diketimine ligand is essentially sp3
in acetone-d6 and methanol-d4. Because of its poor solubility, a 13
C
NMR spectrum could not be obtained.
Interestingly, when the reaction was carried out only for 12 h, a
yellow coloured compound was produced. Diffraction quality crys-
tals could not be obtained for this complex. The 1H NMR spectrum
of this compound looks essentially the same as that of the anionic
portion of the dinuclear Pd complex 5. No resonances for a counter
cation, as in 5, were observed. The m(S–O) and m(C–S) stretching
frequency bands, which appear at 1033 and 627 cmÀ1, respec-
tively, in the IR spectrum confirm the presence of free –SO3À, as
in 5. These bands appear at 1034 and 627 cmÀ1 in the IR spectrum
of 5. Based on these facts and the elemental analysis, this yellow
solid was characterized as [SO3NacNacPd-
l-Cl]2 (6), in which the
Pd centers are bridged by two ClÀ ions. The yield was only 36%.
Scheme 4. Reactivity of PdCl2(CH3CN)2 with NacNacSO3LiÁ2THF.

32
N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
However, when the reaction was carried out in acetonitrile, a good
yield (61%) of 6 was achieved. Interestingly, even after 18 h of stir-
ring in acetonitrile, only the formation of 6 was observed. There
were no traces of 5. Our efforts to obtain single crystals from solu-
tions of 6 in acetone, methanol or tetrahydrofuran always yielded a
white precipitate, which was found (by NMR) to be the b-diketi-
minium bisulfate salt [CH(C(Me)@NH(Dipp)2][HSO4]. From these
observations, it can be concluded that in the reactions of [PdCl2
(CH3CN)2] with NacNacSO3LiÁ2THF in dichloromethane or acetoni-
trile, formation of complex 6 occurs, which decomposes to 5 in
dichloromethane on standing.
3.5. Reactions of NacNacSO3LiÁ2THF with metal nitrates (metal = ZnII,
NiII and CoII)
Fig. 7. Crystal structure of [NacNacSO3Ni(O2NO)(CH3CN)] (8). Hydrogen atoms and
the solvent molecule acetonitrile are omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.
We further explored the coordination behavior of the tripodal
ligand NacNacSO3LiÁ2THF with metal nitrates. All the reactions of
1 with metal nitrates were carried out in acetonitrile. Stirring an
equimolar mixture of 1 and M(NO3)2Á6H2O (M = Zn, Ni and Co) at
room temperature afforded a quantitative yield of the correspond-
ing metal complex with the general formula [NacNacSO3M(O2
NO)(CH3CN)] (M = Zn = 7, M = Ni = 8, M = Co = 9) (Scheme 5).
All the complexes were characterized by single crystal X-ray
analyses and the ORTEP diagrams of the molecular structures are
given in Figs. 6–8. The crystal structures reveal that the metal cen-
ters adopt a distorted octahedral geometry. The ligand, which coor-
dinates in a tripodal fashion, occupies a face of the octahedron. The
remaining corners are occupied by the nitrate ion and one acetoni-
trile molecule. It is noticed that the coordinated acetonitrile mole-
cule exhibits a positional variation. In the Zn and Co complexes it
occupies a position trans to one of the imino groups, whereas in
the Ni complex, it coordinates to the metal from a position trans
to the sulfonate group.
Fig. 8. Crystal structure of [NacNacSO3Co(O2NO)(CH3CN)] (9). Hydrogen atoms and
the solvent molecule acetonitrile are omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.
The dihedral angles between the three planes of the tripodal
structure are listed in Table 2. The angles, which are expected to
be 120° for an ideal tripodal chelation, deviate significantly due
to the difference in the steric crowding on the coordinating atoms.
The dihedral angle between the planes passing through the imine
groups is significantly higher than the other two angles due to
the presence of large isopropyl groups on the imine N atoms, and
also due to the absence of a substituent on the sulfonate O atom.
Scheme 5. Syntheses of Zn, Ni and Co nitrate complexes.
Table 2
A comparison of the torsion angles.
Complex
Z (°)
X (°)
Y (°)
[NacNacSO3ZnCl]
114.57
116.84
113.34
115.01
114.32
114.59
114.24
114.90
115.71
117.28
130.84
128.92
131.76
129.28
128.40
[NacNacSO3NiCl(CH3CN)]
[NacNacSO3Zn(O2NO)(CH3CN)]
[NacNacSO3Ni(O2NO)(CH3CN)]
[NacNacSO3Co(O2NO)(CH3CN)]
Fig. 6. Crystal structure of [NacNacSO3Zn(O2NO)(CH3CN)] (7). Hydrogen atoms and
the solvent molecule acetonitrile are omitted for clarity. Thermal ellipsoids are
drawn at the 50% probability level.

N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
33
Table 3
Selected bond lengths and bond angels for the Zn, Ni and Co nitrate complexes.
[NacNacSO3Zn (O2NO)(CH3CN)]
[NacNacSO3Ni (O2NO)(CH3CN)]
[NacNacSO3Co (O2NO)(CH3CN)]
Bond distances (Å)
C2–N1
C4–N2
C3–S1
1.281(2)
1.278(2)
1.283(3)
1.275(3)
1.824(2)
1.4740(17)
1.4444(19)
2.0760(16)
2.0888(17)
2.1423(18)
1.281(3)
1.271(3)
1.218(3)
2.069(2)
2.062(2)
1.276(2)
1.284(3)
1.8249(18)
1.4709(14)
1.4422(14)
2.1975(13)
2.4580(15)
2.0785(14)
1.261(2)
1.285(2)
1.217(2)
2.0510(17)
2.0810(15)
1.8268(17)
1.4763(12)
1.4398(13)
2.0861(11)
2.2028(13)
2.0812(12)
1.257(2)
1.287(2)
1.212(2)
2.0946(16)
2.1528(13)
S1–O1
S1–O2
O1–M1
M1–O4
M1–O5
O4–N3
O5–N3
N3–O6
M1–N4
M1–N1
Bond angles (°)
C2–N1–M1
C4–N2–M1
C3–S1–O1
117.61(13)
117.74(13)
103.73(8)
105.33(8)
126.78(5)
169.21(5)
116.46(15)
87.98(5)
91.05(5)
92.20(6)
122.56(17)
85.02(5)
87.27(5)
117.5(16)
117.86(17)
103.92(10)
104.70(11)
89.82(7)
87.67(7)
115.37(19)
99.67(7)
107.23(7)
91.68(8)
121.9(2)
88.22(7)
88.55(7)
117.08(11)
117.94(11)
104.32(7)
104.35(8)
113.67(5)
172.90(5)
115.28(14)
88.12(5)
98.21(5)
90.04(5)
123.06(17)
86.60(5)
88.21(5)
C3–S1–O2
O1–M1–O4
O1–M1–O5
O4–N3–O5
N1–M1–O4
N2–M1–O5
N1–M1–N2
O4–N3–O6
O1–M1–N1
O1–M1–N2
Selected bond angles and distances are listed in Table 3. The N1–M–
N2 bond angle around the metal center in the three complexes vary
slightly (Zn = 92.20(6)°, Ni = 91.68(8)° and Co = 90.04(5)°). All the
three complexes exhibit similar M1–N1, M1–N2 and M1–O1 bond
distances (Table 3). The M–O1 bond distances [Zn1–O1
2.1975(13), Ni1–O1 2.0760(16) and Co1–O1 2.0861(11) Å] are
found to be in the same range as for tris(pyrazoyl)methane sulfo-
nate metal complexes [Zn1–O1 2.0858(18)–2.017(2), Ni1–O1
2.0438(14) and Co1–O1 2.0861(11) Å] [37,38].
in coordination. In the case of the Pd complexes the
stretching frequency is higher than the other transition metal com-
plexes, but lower than the ligand. A reverse trend was observed in
m(S–O)
case of the
m
(C–S) stretching frequency. All the complexes in which
À
–SO3 coordinates to the metal show higher
m(C–S) stretching
frequencies.
4. Conclusion
The average imine C@N bond distance found in the three com-
plexes (av.1.2795 Å) is in the range for a typical C@N double bond.
Surprisingly, there are no structural reports in the CCDC on transi-
tion metal nitrate complexes of b-diketimine or its anion. The NMR
spectra recorded for vacuum dried crystals of 7 did not show an
acetonitrile peak. The absence of a stretching frequency band for
The water soluble tripodal NacNacSO3LiÁ2THF ligand has been
synthesized. However, it could not be used in aqueous medium be-
cause of the ready cleavage of its sulfonate group. When the ligand
was treated with divalent chlorides of Ni, Co, Cu and Zn in aqueous
À
medium, the –SO3 group was cleaved and produced the b-diketi-
minium salt [CH(C(Me)@NHDipp)2][HSO4]. Nonetheless, reactions
carried out in organic solvents produced the complexes
[NacNacSO3Zn(Cl)] and [NacNacSO3Ni(Cl)(CH3CN)], in which the
C„N (
m
ꢀ 2200 cmÀ1) in the IR spectra, in all cases, indicates that
acetonitrile can easily be removed from these complexes by apply-
ing a vacuum.
À
NacNacSO3 ligand shows a typical tripodal coordination mode.
An interesting observation was made in the reaction of the ligand
with [PdCl2(CH3CN)2] in dichloromethane. When the reaction was
3.6. IR data for all SO3 substituted compounds
carried out for 18 h, a
Pd2Cl4 core was formed, whereas, when the reaction was stopped
after 12 h of stirring, a -Cl bridged Pd2Cl2 complex was obtained.
l-Cl bridged, boat shaped complex with a
The
m(S–O) and m(C–S) stretching frequencies in the IR spectra of
l
the ligand [NacNacSO3LiÁ2THF] and all its metal complexes are
The NacNacSO3Li ligand formed the distorted octahedral com-
plexes [NacNacSO3Zn(O2NO)(CH3CN)], [NacNacSO3Ni(O2NO)(CH3-
CN)] and [NacNacSO3Co(O2NO)(CH3CN)] when it was treated
with divalent metal nitrates in acetonitrile. Most of the complexes
were characterized by single crystal X-ray diffraction studies.
listed in Table 4. It is noteworthy that the m(S–O) stretching fre-
quency is lower in all the cases where the –SO3À group is involved
Table 4
À
The IR stretching frequencies for SO3 substituted compounds.
Compound
m
(S–O) cmÀ1
m
(C–S) cmÀ1
NacNacSO3LiÁ2THF
[NacNacSO3ZnCl]
[NacNacSO3NiCl
[NacNacSO3Zn(O2NO)]
[NacNacSO3Ni(O2NO)]
[NacNacSO3Co(O2NO)]
[SO3NacNacPd2Cl4]
[SO3NacNacPdCl]2
1050 (vs)
1022 (m)
1013 (m)
1008 (s)
1017 (vs)
1016 (s)
1034 (s)
1033 (m)
628 (m)
661 (m)
662 (m)
661 (s)
661 (s)
660 (s)
630 (s)
627 (m)
Acknowledgements
We gratefully acknowledge the Council of Scientific and Indus-
trial Research (CSIR) and the Department of Science and Technol-
ogy (DST), New Delhi for financial support and Alexander von
Humboldt Stiftung of Germany for the donation of a glove box.
We thank Pondicherry University for NMR and IR spectra, and

34
N.M. Rajendran, N.D. Reddy / Polyhedron 72 (2014) 27–34
[17] P.J. Ragogna, N. Burford, M. D’eona, R. McDonald, Chem. Commun. (2003)
1052.
[18] N.D. Reddy, A. Jana, H.W. Roesky, P.P. Samueland, C. Schulzke, Dalton Trans. 39
(2010) 234.
elemental and TG/DSC analysis. NMR thanks UGC and CSIR for pro-
viding a fellowship.
[19] N. Burford, M. D’eon, P.J. Ragogna, R. McDonald, M.J. Ferguson, Inorg. Chem. 43
(2004) 734.
Appendix A. Supplementary data
[20] A.P. Dove, V.C. Gibson, E.L. Marshall, A.J.P. White, D.J. Williams, Dalton Trans.
(2004) 570.
CCDC 966290–966296 contain the supplementary crystallo-
graphic data for compounds 2–5 and 7–9 respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.poly.2014.01.021.
[21] X. Shang, X. Liu, D. Cui, J. Polym. Sci., Part A: Polym. Chem. 45 (2007) 5662.
[22] M.H. Chisholm, J.C. Gallucci, K. Phomphrai, Inorg. Chem. 43 (2004) 6717.
[23] J. Takaichi, K. Ohkubo, H. Sugimoto, M. Nakano, D. Usa, H. Maekawa, N. Fujieda,
N. Nishiwaki, S. Seki, S. Fukuzumi, S. Itoh, Dalton Trans. 42 (2013) 2438.
[24] F. Dulong, O. Bathily, P. Thuéry, M. Ephritikhine, T. Cantat, Dalton Trans. 41
(2012) 11980.
[25] F. Dulong, P. Thueery, M. Ephritikhine, T. Cantat, Organometallics 32 (2013)
1328.
[26] N.W. Aboelella, B.F. Gherman, L.M.R. Hill, J.T. York, N. Holm, V.G. Young, C.J.
Cramer Jr., W.B. Tolman, J. Am. Chem. Soc. 128 (2006) 3445.
[27] S. Pfirrmann, C. Limberg, E.Z. Hoppe, Anorg. Allg. Chem. 635 (2009) 312.
[28] X. Xu, X. Xu, Y. Chen, S. Jie, Organometallics 27 (2008) 758.
[29] E. Lu, W. Gan, Y. Chen, Organometallics 28 (2009) 2318.
[30] H. Hu, C. Cui, Organometallics 31 (2012) 1208.
[31] D. Neculai, H.W. Roesky, A.M. Neculai, J. Magull, H.-G. Schmidt, M. Noltemeyer,
J. Organomet. Chem. 643–644 (2002) 47.
[32] D. Barnes, G.L. Brown, M. Brownhill, I. German, C.J. Herbert, A. Jolleys, A.R.
Kennedy, B. Liu, K. McBride, F.S. Mair, R.G. Pritchard, A. Sanders, J.E. Warren,
Eur. J. Inorg. Chem. (2009) 1219.
References
[1] L. Bourget-Merle, M.F. Lappert, J.S. Severn, Chem. Rev. 102 (2002) 3031.
[2] S. Harder, Angew. Chem., Int. Ed. 43 (2004) 2714.
[3] C.J. Cramer, W.B. Tolman, Acc. Chem. Res. 40 (2007) 601.
[4] P.L. Holland, Acc. Chem. Res. 41 (2008) 905.
[5] P.B. Hitchcock, A.V. Khvostov, M.F. Lappert, A.V. Protchenko, Dalton Trans.
(2009) 2383.
[6] S.K. Mandal, H.W. Roesky, Acc. Chem. Res. 43 (2010) 248.
[7] R. Jiao, M. Xue, X. Shen, Y. Zhang, Y. Yao, Q. Shen, Eur. J. Inorg. Chem. (2011)
1448.
[33] V.K. Bel’sky, N.R. Streltsova, B.M. Bulychev, P.A. Storozhenko, L.V. Ivankina, A.I.
Gorbunov, Inorg. Chim. Acta 164 (1989) 211.
[34] F.R. Hartley, S.G. Murray, C.A. McAuliffe, Inorg. Chem. 18 (1979) 1394.
[35] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[36] W. Klaui, M. Berghahn, G. Rheinwald, H. Lang, Angew. Chem., Int. Ed. 39 (2000)
2464.
[37] E.T. Papish, M.T. Taylor, F.E. Jernigan III, M.J. Rodig, R.R. Shawhan, G.P.A. Yap,
F.A. Jove, Inorg. Chem. 45 (2006) 2242.
[38] W. Kläui, M. Berghahn, W. Frank, G.J. Reiß, T. Schönherr, G. Rheinwald, H. Lang,
Eur. J. Inorg. Chem. (2003) 2059.
[39] A.W. Addison, T.N. Rao, J. Reedijk, J.V. Rijn, G.C. Verschoor, J. Chem. Soc., Dalton
Trans. (1984) 1349.
[40] E.K. Cope-Eatough, F.S. Mair, R.G. Pritchard, J.E. Warren, R.J. Woods,
Polyhedron 22 (2003) 1447.
[41] D. Domin, D. Benito-Garagorri, K. Mereiter, J. Frohlich, K. Kirchner,
Organometallics 24 (2005) 3957.
[8] Y.-C. Tsai, Coord. Chem. Rev. 256 (2012) 722.
[9] S.K. Mandal, H.W. Roesky, Acc. Chem. Res. 45 (2012) 298.
[10] S. Yokota, Y. Tachi, N. Nishiwaki, M. Ariga, S. Itoh, Inorg. Chem. 40 (2001) 5316.
[11] C. Shimokawa, S. Itoh, Inorg. Chem. 44 (2005) 3010.
[12] A.R. Cabrera, Y. Schneider, M. Valderrama, R. Frohlich, G. Kehr, G. Erker, R.S.
Rojas, Organometallics 29 (2010) 6104.
[13] S.D. Allen, D.R. Moore, E.B. Lobkovsky, G.W. Coates, J. Organomet. Chem. 683
(2003) 137.
[14] C. Shimokawa, Y. Tachi, N. Nishiwaki, M. Ariga, S. Itoh, Bull. Chem. Soc. Jpn. 79
(2006) 118.
[15] R.S. Rojas, B.C. Peoples, A.R. Cabrera, M. Valderrama, R. Frohlich, G. Kehr, G.
Erker, T. Wiegand, H. Eckert, Organometallics 30 (2011) 6372.
[16] R.S. R.S. Rojas, A.R. Cabrera, B.C. Peoples, K. Spannhoff, M. Valderrama, R.
Frohlich, G. Kehr, G. Erker, Dalton Trans. 41 (2012) 1243.