Synthesis of novel organonickel(II) complexes with thiosalicylaldehyde as a chelate ligand

Article abstract of DOI:10.1016/j.ica.2014.05.001

Two sulfur-coordinated acyl nickel(II) complexes 3 and 4 Ni(?CO)(PMe₃)₃ (? = phenyl (3), 5-methylphenyl (4)) were synthesized by reactions of thiosalicylaldehyde (1) and 5-methylthiosalicylaldehyde (2) with NiMe₂(PMe₃) ₃. Complex 3 reacted with excess iodomethane affording (2-methyl-mercapto-phenyl)nickel(II) complex 5. The mechanisms of formation of 3-5 were proposed and discussed. The molecular structures of 4 and 5 were determined by X-ray diffraction.

Full text of DOI:10.1016/j.ica.2014.05.001

Accepted Manuscript
Synthesis of novel organonickel(II) complexes with thiosalicylaldehyde as a
chelate ligand
Wenbo Zhang, Xiaoyan Li, Hongjian Sun
PII:
S0020-1693(14)00247-3
http://dx.doi.org/10.1016/j.ica.2014.05.001
ICA 15981
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Accepted Date:
28 March 2014
3 May 2014
Please cite this article as: W. Zhang, X. Li, H. Sun, Synthesis of novel organonickel(II) complexes with
thiosalicylaldehyde as a chelate ligand, Inorganica Chimica Acta (2014), doi: http://dx.doi.org/10.1016/j.ica.
2014.05.001
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Synthesis of novel organonickel(II) complexes with thiosalicylaldehyde as a
chelate ligand
Wenbo Zhang, Xiaoyan Li, Hongjian Sun*
School of Chemistry and Chemical Engineering, Key Laboratory of Special
Functional Aggregated Materials, Ministry of Education, Shandong University,
Shanda Nanlu 27, 250199 Jinan, PR China
Abstract:
Two sulfur-coordinated acyl nickel(II) complexes 3 and 4 Ni(S^C=O)(PMe3)3 (^ =
phenyl (3), 5-methylphenyl (4)) were synthesized by reactions of thiosalicylaldehyde
(1) and 5-methylthiosalicylaldehyde (2) with NiMe2(PMe3)3. Complex 3 reacted with
excess iodomethane affording (2-methyl-mercapto-phenyl)nickel(II) complex 5. The
mechanisms of formation of 3 - 5 were proposed and discussed. The molecular
structures of 4 and 5 were determined by X-ray diffraction.
Keywords: thiosalicylaldehyde, trimethylphosphine , nickel complex, C,S-coupling
*Corresponding author. Tel.: + 86 531 88361350; fax: + 86 531 88564464.
E-mail: hjsun@sdu.edu.cn.
1

1. Introduction
In comparison with the chemistry of salicylaldehyde, the development of the
chemistry of thiosalicylaldehyde through the replacement of an oxygen atom (hard
base) by a sulfur atom (soft base) is greatly restricted because it is much more
difficult to prepare the derivatives of thiosalicylaldehyde and their odors are
unpleasant. Recently, we reported the synthesis of sulfur-coordinated
acyl(hydrido)cobalt(III) complex by the reaction of thiosalicylaldehyde with
CoMe(PMe3)4
[1].
The
reactivity
of
mer-hydrido(2-mercaptobenzoyl)tris(trimethylphosphine)cobalt(III) complex was
intensively studied and a series of sulfur-coordinated organocobalt complexes were
obtained [2]. We found out that the properties of the sulfur-coordinated
organocobalt(III) complexes are far different from those of organocobalt(III)
complexes with salicylaldehyde as pre-ligand. Comparing with the combination of
Co(III)(hard)/O(hard), the combination Co(III)(hard)/S(soft) makes the
sulfur-coordinated
complexes
unstable.
It
was
confirmed
that
mer-hydrido(2-mercaptobenzoyl)tris(trimethylphosphine)cobalt(III) complex is an
excellent catalyst for hydrosilylation of aldehydes and ketones under mild condition
[1] while mer-hydrido(benzoyl)tris(trimethylphosphine)cobalt(III) complex could not
catalyze this reduction reaction under the similar reaction conditions [3]. Klein
reported the synthesis and reactivity of (acylphenolato)nickel(II) complexes supported
by trimethylphosphine ligands [4-7]. Several stable diorganonickel(IV) compounds
were isolated through the oxidation addition reactions of (acylphenolato)nickel(II)
2

complexes with iodomethane [5-6]. In this paper we extended our research from
cobalt to nickel complexes with thiosalicylaldehyde as chelate ligand. Two
sulfur-coordinated acyl nickel(II) complexes 3 - 4 were synthesized through reaction
of
thiosalicylaldehydes
with
dimethyltris(trimethylphosphine)nickel(II),
NiMe2(PMe3)3. The reaction of complex 3 with iodometane was studied and
(2-methyl-mercapto-phenyl)nickel(II) complex 5 was obtained. The mechanism of
formation of 5 was discussed.
2. Results and discussion
The reaction of NiMe2(PMe3)3 with thiosalicylaldehydes (1 - 2) afforded two
nickel(II) complexes 3 - 4 via both C-H and S-H bond activation reaction of
thiosalicylaldehydes according to Eq. (1).
O
O
R
Et2O
3-4 h
R
H
PMe3
PMe3
NiMe (PMe )
+
(1)
2 CH
2
3 3
+
Ni
4
SH
1 - 2
S
PMe3
3 - 4
R = H Me
2
1
3
4
Nickel(II) complexes 3 and 4 were obtained as red crystals in the yields of 47 %
and 38 % by crystallization from Et2O at -20 °C. Crystals of 3 and 4 remain stable at
room temperature for more than 10 h but they quickly decompose when dissolved and
1
exposed to the air. Complexes 3 and 4 were characterized by IR, H NMR and 31P
NMR spectroscopy. Both complexes are penta-coordinate nickel(II) species
containing a five-membered chelate ring with [C,S]-coordination. In the IR spectra of
3

complexes 3 and 4, the bands of ν(C=O) are shifted to 1593 (3) and 1602 (4) cm−1
from 1690 cm−1 of thiosalicylaldehyde [8] owing to the coordination of the acyl group.
This indicates that the C=O double bond is weakened after coordination to the nickel
1
centre. In the H NMR spectra of complexes 3 – 4, three PMe3 ligands were recorded
as one broade singlet at 1.07 (3) and 1.00 (4) ppm. In the 31P NMR spectra, one signal
at -7.1 (3) and -6.5 (4) ppm suggests that the three phosphorus atoms have the same
chemical environments in solution.
Figure 1. Molecular structure of 4: selected bond lengths (Å) and angles (0): Ni1-C10
1.952(6), Ni1-S1 2.312(2), Ni1-P1 2.235(2), Ni1-P2 2.228(2), Ni1-P3 2.223(2),
C10-O1 1.223(8); C10-Ni1-S1 88.2(2), P1-Ni1-S1 85.74(7), P2-Ni1-S1 115.54(8),
P3-Ni1-P2 125.70(7), P3-Ni1-S1 117.49(7), P1-Ni1-P2 96.55(7), C10-Ni1-P2 84.8(2),
C10-Ni1-P3 85.8(2), C10-Ni1-P1 173.8(2).
The molecular structure of complex 4 with the selected bond distances and angles
is shown in Fig. 1. In the molecular structure of 4, the nickel atom attains a distorted
trigonal bipyramid with C10 and P1 atoms in the axial positions. The axial angle is
C10-Ni1-P1 (173.8(2)0). The S1 and the other two phosphorus atoms (P2 and P3) are
4

in the triangular plane. The sum of three bond angles (P2-Ni1-S1 = 115.54(8),
P3-Ni1-S1 117.49(7) and P3-Ni1-P2 = 125.70(7)0) around the nickel center in the
triangular plane is 358.730. It implies that the four atoms [Ni1, P2, P3, and S1] are not
exactly in a plane. The Ni1 deviates from the plane defined by [P2, P3 and S1] by
0.1279 Å. The bite angle S1-Ni1-C10 is 88.2(2)0. This value is remarkably larger than
that
(85.5(2)0)
of
(3-tert-butyl-5-methyl-2-oxobenzoyl)tris(trimethylphosphine)nickel(II) [4] because
the atomic radius of S is observably larger than that of O atom. Ni1-S1 distance
(2.312(2) Å) is in the normal region while Ni1-C10 (1.952(6) Å) in complex 4 is
significantly longer than the related bond (Ni-C9 (1.904(4) Å) in the corresponding
(acylphenolato)nickel(II) complex [4]. This is also caused by the replacement of O
atom by the bigger S atom in the molecular structure. The metal chelate ring and the
phenyl ring are coplanar. This result is similar to the report in the literature [4].
O
O
R
Me
Ni
Me
R
CHO
S
PMe3
PMe3
R
H
H
NiMe (PMe )
+
2
3
3
Ni
PMe3
CH4
SH
PMe3
PMe3
S
PMe3
1 - 2
A
B
PMe
+
3
CH4
O
R
PMe3
PMe3
Ni
S
PMe3
3 - 4
Scheme 1
The mechanism of formation of complexes 3 and 4 is proposed in Scheme 1 [4].
The initial step is the reaction of the acidic hydrogen atom of the mercapto group of
2-mercaptobenzaldehyde with the basic methyl group of complex NiMe2(PMe3)3 with
5

the escape of methane to form an intermediate A. With the S atom as an anchoring
group, the C-H bond of the aldehyde group was activated. The oxidative addition of
the C-H bond at the nickel(II) center delivered the unstable nickel(IV) species B. In
the presence of PMe3, the reductive elimination of Ni-H and Ni-Me bonds afforded
the final product with the formation of another molecule of methane.
In the past two decades, the research on the nickel-catalyzed C,C-coupling
reactions and the related reaction mechanisms has received much more attention [9].
The mechanism usually consists of an oxidative addition / reductive elimination
reaction sequence. This requires the presence of nickel(IV) intermediates [10 - 13].
Such scheme was proposed in early times, but it was not accepted by the chemical
researcher until the diorganonickel(IV) compounds were isolated in the labor of Klein
[5 - 7]. Due to the instability of diorganonickel(IV) species, only few of them have
been experimentally confirmed until now. Recently, a few more diorganonickel(IV)
compounds have been reported, such as silylnickel(IV) compounds [14], homoleptic
anion [Ni(SnB11H11)6]8- [15 - 16] and tetrahedral alkylnickel(IV) complexes [17 - 18].
According to the related work by Klein [5 - 7], we expected to prepare the new
diorganonickel(IV) compound through the reaction of complex 3 with MeI because
the analogous relationship between thiosalicylaldehyde and salicylaldehyde. But
under similar reaction conditions, no expected Ni(IV) compound was found. As an
unexpected Ni(II) complex, 5 was isolated as yellow crystals (Scheme 2). Complex 5
1
was fully characterized through IR and NMR spectra. In the H NMR spectrum, the
resonance of the methylthio group was recorded at 1.19 ppm as a singlet while the
6

resonance of the six methyl groups of the two PMe3 ligands appears at 0.92 ppm as a
singlet. One 31P NMR signal at 0.0 ppm indicates that two trimethylphosphine ligands
are in trans-orientation.
O
PMe3
Me
O
S
Ni
I
S
PMe3
PMe3
PMe3
Ni
(excess)
MeI
+
Me3P
PMe3
I
CO
Ni
3
PMe3
[Me4P]I
SMe
5
Scheme 2
The molecular structure of complex 5 was determined by X-ray single crystal
diffraction (Fig. 2). The molecular structure of complex 5 confirms that the nickel(II)
center has a square-planar coordination geometry with two trans-trimethylphosphine
ligands. The sum of the bond angles around the Ni atom is 359.980. This indicates that
the four coordination atoms [C6, P1, P2, I1] and central Ni atom are almost in a plane.
Ni1-C6 distance (1.917(2) Å) and Ni1-I1 distance (2.5875(5) Å) are within the normal
ranges of the corresponding bond lengths.
7

Figure 2. Molecular structure of 5: selected bond lengths (Å) and angles (0): I1-Ni1
2.5875(5), Ni1-C6 1.917(2), Ni1-P1 2.2137(8), Ni1-P2 2.2202(8), S2-C1 1.787(3),
S2-C13 1.801(3); C6-Ni1-P1 88.98(8), C6-Ni1-P2 88.49(8), P1-Ni1-P2 177.47(3),
C6-Ni1-I1 175.46(7), P1-Ni1-I1 91.30(2), P2-Ni1-I1 91.21(2), C1-S2-C13 103.5(1).
According to the mechanism of formation of diorganonickel(IV) complexes
[5-6], a similar mechanism of formation of 5 could be proposed in Scheme 3. The
first step is the oxidative addition reaction of iodomethane at the Ni(II) center of
complex 3 to form a diorganonickel(IV) intermediate C. In comparison with the
analogous Ni(IV) complexes of salicylaldehyde, intermediate
C
of
thiosalicylaldehyde is not stable from the perspective of the HSAB theory. The former
is a combination of Ni(IV) (hard base) / O (hard acid) while the latter is a grouping of
Ni(IV) (hard base) / S (soft acid). Therefore, intermediate C is not as stable as the
Ni(IV) complexes of salicylaldehyde [5-6 ]. D as an intermediate was formed through
the reductive elimination between Ni-Me and Ni-S bonds via C,S-coupling process.
Subsequent decarbonylation of the acyl nickel(II) intermediate D afforded complex 5
as end product.
O
O
Me3P
SMe O
PMe3
Me
Ni
PMe3
I
I
PMe3
PMe3
MeI
+
Ni
Ni
Ni
CO
PMe3
I
S
S
PMe3
PMe3
SMe
PMe3
3
C
D
5
Scheme 3
3. Conclusions
8

In conclusion,
the reaction of 2-mercaptobenzaldehyde
1
(or
2-mercapto-5-methylbenzaldehyde 2) with NiMe2(PMe3)3 delivered the
corresponding (acylthiophenolato)nickel(II) complexes 3 (or 4). Treatment of
complex 3 with excess iodomethane afforded (2-methyl-mercapto-phenyl)nickel(II)
complex 5 and no related Ni(IV) complex was found. This result can be interpreted by
the HSAB theory. However, an instable diorganonickel(IV) intermediate might exist
in this decarbonylation process. The related mechanisms of formation of complexes 3
– 5 were proposed. The molecular structures of complexes 4 and 5 were determined
by X-ray single crystal diffraction.
4. Experimental
4.1. General Procedures and Materials
Standard vacuum techniques were used in manipulations of volatile and air
sensitive materials. Solvents were dried by known procedures and distilled under
nitrogen before use. Literature methods were used in the preparation of
NiMe2(PMe3)3.[19] Infrared spectra (4000 - 400 cm-1), as obtained from Nujol mulls
1
between KBr disks, were recorded on a Bruker ALPHA FT-IR Spectrometer. H, and
31P spectra (300 and 121 MHz, respectively) were recorded on a Bruker Avance 300
spectrometer. 31P NMR resonances were obtained with broadband proton decoupling.
X-ray crystallography was performed with a Bruker Smart 1000 diffractometer.
Elemental analyses were carried out on an Elementar Vario EL III.
4.2. Synthesis of complex 3
9

A sample of NiMe2(PMe3)3 (1.08 g, 3.41 mmol) in 30 mL of diethyl ether was
slowly combined
with a solution of 2-mercaptobenzaldehyde (0.47 g, 3.41mmol)
in 20mL diethyl ether at -80°C This mixture was allowed to warm to 20 oC and stirred
for 16 h to form a orange red solution. The reaction solution was then filtered.
o
Crystallization at -20 C afforded dark red crystals of 3 (0.60 g, 47.1%). Anal. Calcd
for 3, C16H31NiOP3S (423.08 g mol-1): C, 45.42; H, 7.38; S, 7. 58. Found: C, 45.27; H,
7.69; S, 7. 87. IR (Nujol mull, cm-1): 1593 ν(C=O), 942 ρ(PMe3). 1H NMR (300 MHz,
31
C6D6, 297 K): δ 1.17 (br, 27H, PCH3), 6.72-7.66 (m, 4H, Ar-H) ppm. P NMR (121
MHz, C6D6, 297 K): δ -7.1 (s, PCH3) ppm．
4.3. Synthesis of complex 4
Complexes 4 were synthesized according to the method given above for complex 3.
Complex 4: Yield: 37.6%. Anal. Calcd for 4, C17H33NiOP3S (437.11 g mol-1): C,
46.71; H, 7.61; S, 7.34. Found: C, 47.01; H, 7.69; S, 7. 22. IR (Nujol mull, cm-1):
1602 ν(C=O), 940 ρ(PMe3). 1HNMR (300 MHz, C6D6, 297 K): δ 1.00 (br, 27H,
PCH3), 2.14 (s, 3H, C-CH3), 6.60-8.02 (m, 3H, Ar-H) ppm . 31P NMR (121 MHz,
C6D6, 297 K): δ -6.5 (s, PCH3) ppm．
4.4. Synthesis of complex 5
A sample of complex 3 (0.30 g, 0.70 mmol) in 20 mL of acetonitrile at -80 °C
was combined with a solution of CH3I (0.20 g, 1.4 mmol) in 10 mL of acetonitrile
under vigorous stirring. In the process of warming up to room temperature, the color
of the solution changed quickly from dark red to light yellow in 30 minutes. The
volatiles were transferred under vacuum, and the residue was extracted with pentane
10

o
(40 mL). Crystallization from pentane at -20 C afforded light yellow single crystals
of 5 (0.10 g, 40%) suitable for X-ray analysis. Anal. Calcd for 5, C13H25INiP2S
(460.94 g mol-1): C, 33.87; H, 5.47; S, 6.96. Found: C, 34.17; H, 5.69; S, 6.92. IR
(Nujol mull, cm-1): IR (Nujol mull, cm-1): 1550 ν(C=C), 940 ρ(PMe3). 1HNMR (300
MHz, C6D6, 297 K): δ 0.92 (br, 18H, PCH3), 1.91 (s, 3H, S-CH3), 6.42-7.53 (m, 4H,
Ar-H) ppm. 31P NMR (121 MHz, C6D6, 297 K): δ 0.0 (s, PCH3) ppm．
4.5.Crystallographic data of complex 4
C13H33NiOP3S, Mr. =437.11, monoclinic, space group P2(1)/c,, a=10.626(2) Å,
b=29.839(6) Å, c=13.742(3) Å, β=90.04(3)°, V=4357.2(15) Å3, T=273 K, Z=8,
Dc=1.333 g cm−3, µ=1.208 mm−1. A total of 34738 reflections were collected, 9387
unique (Rint = 0.0663), R1 = 0.0780 (for 9387 reflections with I > 2 sigma(I)), wR2 =
0.2027 (all data).
4.6.Crystallographic data of complex 5
C13H25INiP2S, Mr. =460.94, monoclinic, space group P2(1)/n, a=9.2133(18) Å,
b=11.937(2) Å, c=17.615(4) Å, β=98.57(3)°, V=1915.7(7) Å3, T=293 K, Z=4,
Dc=1.598 g cm−3, µ=2.885 mm−1. A total of 10763 reflections were collected, 4226
unique (Rint = 0.0280), R1 = 0.0259 (for 4226 reflections with I > 2 sigma(I)), wR2 =
0.0645 (all data).
Acknowledgement
We gratefully acknowledge the financial support by NSF China No. 21372143 and
the support from Prof. Dr. Dieter Fenske and Dr. Olaf Fuhr (Karlsruhe Nano-Micro
Facility) on the determination of the crystal structures.
11

Appendix A. Supplementary material
CCDC 980515 (4) and 979646 (5) contain the supplementary crystallographic data.
These
data
can
be
obtained
free
or
of
from
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html,
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.
References
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5235-5238.
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[3] H.-F. Klein, S.Haller, H. Sun, X. Li, Naturforsch , 53 b(1998), 587-598.
[4] H.-F. Klein, A. Bickelhaupt, B. Hammerschmitt, Organometallics 13(1994),
2944-2950.
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Flörke, H.-J. Haupt, Organometallics 16(1997), 668-676.
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467-468.
[8] Q. Niu, X. Xu, H. Sun, X. Li, Chin. J. Chem. 30(2012), 2495-2550.
[9] For a recent review of Ni-catalyzed C−C coupling, see: J. Yamaguchi, K. Muto, K.
Itami, Eur. J. Org. Chem. 1 (2013) 19-30.
12

[10] M. F. Semmelhack, P. M. Helquiat, L. D. Jones, J. Am. Chem. Soc. 93 (1971),
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13

Graphical abstract
Pictogram:
Synthesis of novel organonickel(II) complexes with thiosalicylaldehyde as a
chelate ligand
Wenbo Zhang, Xiaoyan Li, Hongjian Sun*
_____________________________________________________________________
O
O
Me3P
SMe O
PMe3
Me
Ni
PMe3
I
I
PMe3
PMe3
MeI
+
Ni
Ni
Ni
CO
PMe3
I
S
S
PMe3
PMe3
SMe
PMe3
3
C
D
5
___________________________________________________________________________
14

Synopsis：
________________________________________
Synthesis of novel organonickel(II) complexes with thiosalicylaldehyde as a
chelate ligand
Wenbo Zhang, Xiaoyan Li, Hongjian Sun*
The reaction of 2-mercaptobenzaldehyde 1 (or 2-mercapto-5-methylbenzaldehyde 2)
with NiMe2(PMe3)3 delivered the corresponding (acylthiophenolato)nickel(II)
complexes 3 (or 4). Treatment of complex 3 with excess iodomethane afforded
(2-methyl-mercapto-phenyl)nickel(II) complex 5 and no related Ni(IV) complex was
found. The related mechanisms of formation of complexes 3 – 5 were proposed. The
molecular structures of complexes 4 and 5 were determined by X-ray single crystal
diffraction.
15

Highlights
synthesis and characterization of sulfur-coordinated acyl nickel(II) complexes ► C-H
bond activation ► trimethylphosphine ligands ► C,S-coupling