CH/π interaction in nickel(n) complexes derived from 2-substituted benzothiazolines

Article abstract of DOI:10.1039/b002745f

By reaction of 2-(3,5-di-/e/7-butyl-4-hydoxyphenyl)benzothiazoline with nickel(n) acetate tetrahydrate, the complex bis[2-(3,5-di-/er/-butyl-4-hydroxyphenylmethyleneatnino)benzenethiolato] nickel(ii) 1 has been prepared. Its crystal structure has been elucidated, showing an intramolecular approach of the tert-buly group to the aromatic ring of the 2-aminobenzenethiol moiety. In addition, variable-temperature 'H NMR studies of 1 indicated the restriction of rotation of the pendant arm. Such behaviour is attributed to the existence of a CH/jt interaction between the tenbutyl group and the aromatic ring of another ligand. To provide further evidence for the CH/it interaction in nickel(il) complexes derived from 2-substituted benzothiazolines, we have also prepared a pair of nickel(n) complexes (2 and 3) with eta-substituted phenyl groups as pendant arms. A comparison between 2 with a methyl group and 3 with a chlorine atom on the pendant arm provided insight into the CH/Jt interaction that controls the orientation of the pendant arm. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b002745f

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CH/ꢀ interaction in nickel(II) complexes derived from 2-substituted
benzothiazolines
Tatsuya Kawamoto* and Yoshihiko Kushi
Department of Chemistry, Graduate School of Science, Osaka University, 1-16 Machikaneyama,
Toyonaka, Osaka 560-0043, Japan. E-mail: kaw@ch.wani.osaka-u.ac.jp
Received 6th April 2000, Accepted 14th July 2000
Published on the Web 8th August 2000
By reaction of 2-(3,5-di-tert-butyl-4-hydoxyphenyl)benzothiazoline with nickel() acetate tetrahydrate, the complex
bis[2-(3,5-di-tert-butyl-4-hydroxyphenylmethyleneamino)benzenethiolato]nickel() 1 has been prepared. Its crystal
structure has been elucidated, showing an intramolecular approach of the tert-butyl group to the aromatic ring of
the 2-aminobenzenethiol moiety. In addition, variable-temperature 1H NMR studies of 1 indicated the restriction of
rotation of the pendant arm. Such behaviour is attributed to the existence of a CH/π interaction between the tert-
butyl group and the aromatic ring of another ligand. To provide further evidence for the CH/π interaction in
nickel() complexes derived from 2-substituted benzothiazolines, we have also prepared a pair of nickel() complexes
(2 and 3) with meta-substituted phenyl groups as pendant arms. A comparison between 2 with a methyl group and 3
with a chlorine atom on the pendant arm provided insight into the CH/π interaction that controls the orientation of
the pendant arm.
Introduction
Experimental
2-Substituted benzothiazolines for several metal ions act as
Schiff base ligands with N,S donor atoms.1 Indeed, we have
reported that the reactions of a variety of metal ions with 2-
substituted benzothiazolines gave the corresponding Schiff
base metal complexes.2 Furthermore, we have demonstrated
that the formation of a carbon–carbon bond in the nickel()
complex derived from 2-phenylbenzothiazoline took place,
yielding a complex with a non-innocent ligand, even at room
temperature (Scheme 1).3 Our most recent contribution to this
General
All reactions were carried out under an atmosphere of argon or
nitrogen using standard Schlenk techniques. Reagents were
commercial samples and not purified further.
Infrared spectra were obtained on a Perkin-Elmer 983G
Infrared Spectrophotometer (4000–180 cmϪ1) using the Nujol
mulls, NMR spectra on a JEOL EX 270 instrument using
tetramethylsilane as internal standard (δ 0) and UV/VIS spectra
on a Hitachi U-3400 spectrophotometer. Elemental analyses
were performed at Osaka University.
Syntheses
2-(3,5-Di-tert-butyl-4-hydroxyphenyl)benzothiazoline. 2-(3,5-
Di-tert-butyl-4-hydroxyphenyl)benzothiazoline was prepared
according to a literature procedure for 2-substituted benzothia-
zolines.6 2-Aminobenzenethiol (1.31 g, 10.5 mmol) and 3,5-
di-tert-butyl-4-hydroxybenzaldehyde (2.50 g, 10.3 mmol) in
ethanol (20 cm3) were refluxed for 20 min. The resulting
solution was reduced to approximately one half of the initial
volume under reduced pressure and allowed to cool in a
refrigerator overnight. The light yellow crystals were filtered off
and dried in vacuo. Yield 1.64 g, 47% (Found: C, 73.51; H, 7.99;
Scheme 1
area is the demonstration that the arrangement around the
metal centre is likely to be controlled by the steric effect of
the pendant arm of the ligand as well as by the properties of
the metal centre; in the case of the nickel() and palladium()
complexes with phenyl or 1-naphthyl groups as pendant arms
only cis isomers were formed,3,4 but the platinum() complex
with a ferrocenyl group was obtained as the trans and cis iso-
meric pair.5 We expected that introduction of the tert-butyl
group as a bulky substituent would improve the possibilities of
studying the influence of ligand modifications on the properties
of metal complexes.
In the present paper we describe the chemical properties of
nickel() complex obtained starting from 2-(3,5-di-tert-butyl-
4-hydroxyphenyl)benzothiazoline. Through an examination of
the nickel() complex with a tert-butyl group and a pair of
nickel() complexes with meta-substituted phenyl groups as
pendant arms, the work herein allows us to assess the signifi-
cance of CH/π interactions in altering the reactivity of the
metal complex and the orientation of the pendant arm.
N, 4.09. C21H27NOS requires C, 73.85; H, 7.97; N, 4.10%); νmax
cmϪ1 (Nujol) 3624s (OH), 3307m (NH) and 1574s (aromatic
C᎐C); δ (270 MHz, CDCl ) 7.40 (2 H, s, benzene), 7.05 (1 H,
/
᎐
H
3
dd, J = 7.6 and 1.0, benzene), 6.94 (1 H, dd, J = 7.7 and 1.2,
benzene), 6.75 (1 H, dt, J = 7.6 and 1.0, benzene), 6.64 (1 H, dd,
J = 7.6 and 0.7 Hz, benzene), 6.38 (1 H, s, 2-CH), 5.29 (1 H, s,
OH) and 1.43 (18 H, s, tert-butyl); δC(67.8 MHz, CDCl3) 154.0,
146.2, 135.8, 130.9, 127.2, 125.1, 123.6, 121.5, 120.4, 109.6,
71.4, 34.3 and 30.1.
Bis[2-(3,5-di-tert-butyl-4-hydroxyphenylmethyleneamino)-
benzenethiolato]nickel(II) 1. 2-(3,5-Di-tert-butyl-4-hydroxy-
phenyl)benzothiazoline (0.39 g, 1.1 mmol) and nickel(II) acetate
tetrahydrate (0.14 g, 0.56 mmol) were refluxed in ethanol (20
cm3) for 30 min. On standing the reaction mixture overnight, a
3022
J. Chem. Soc., Dalton Trans., 2000, 3022–3026
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b002745f

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Table 1 Crystallographic data for complexes 1 and 2
brown powder was formed and collected by filtration. The
brown product was recrystallized from CHCl3–n-hexane. Yield
0.24 g, 55%. Crystals of complex 1 suitable for a structure
determination were grown by slow diffusion of diethyl ether
into a CHCl3 solution of the brown product (Found: C, 65.61;
H, 6.84; N, 3.67. C42H52N2NiO2S2ؒ0.25CHCl3 requires C, 65.94;
H, 6.84; N, 3.64%); νmax/cmϪ1 (Nujol) 3606m (OH) and 1596s,
1
2
Formula
M
C42H52N2NiO2S2
739.71
C28H24N2NiS2
511.30
Crystal system
Space group
Monoclinic
C2/c
Triclinic
P1
¯
1572m and 1560w (C᎐N and aromatic C᎐C); δ (270 MHz,
᎐
᎐
CDCl ) 7.80 (2 H, s, CH᎐N), 7.30 (2 H, dd, J =H7.9 and 1.0,
a/Å
b/Å
c/Å
α/Њ
12.724(7)
21.161(10)
15.295(11)
12.163(5)
14.804(5)
7.028(6)
90.06(5)
106.80(5)
86.29(3)
1209(1)
2
᎐
3
benzene), 6.90 (2 H, t, J = 7.3, benzene), 6.58 (2 H, dt, J = 7.7
and 1.1, benzene), 6.30 (2 H, d, J = 7.9 Hz, benzene), 5.65 (2 H,
s, OH) and 1.40 (36 H, s, tert-butyl); δC(67.8 MHz, CDCl3)
167.9, 157.0, 150.3, 146.6, 136.9, 128.9, 128.4, 127.6, 126.9 (br),
121.4, 114.7, 34.5 and 30.2.
β/Њ
108.70(5)
γ/Њ
V/Å3
3901(4)
4
0.637
1905
Z
µ/mmϪ1
0.989
4654
No. unique reflections
2-(m-Toluyl)benzothiazoline.
2-(m-Toluyl)benzothiazoline
measured
No. reflections in
was prepared according to a literature procedure for 2-
substituted benzothiazolines.6 2-Aminobenzenethiol (1.25 g,
9.99 mmol) and m-tolualdehyde (1.20 g, 9.99 mmol) in ethanol
(20 cm3) were refluxed for 1 h. The resulting solution was
reduced to approximately one half of the initial volume under
reduced pressure and allowed to cool in a refrigerator over-
night. The light yellow crystals were filtered off and dried in
vacuo. Yield 2.07 g, 91% (Found: C, 73.65; H, 5.83; N, 6.22.
C14H13NS requires C, 73.97; H, 5.76; N, 6.16%); νmax/cmϪ1
1482 (I > 1.5σ(I))
3826 (I > 2.0σ(I))
refinement
R
0.068
0.065
0.085
0.098
RЈ
benzene), 6.73 (2 H, t, J = 7.6, benzene) and 6.30 (2 H, d, J = 7.9
Hz, benzene); δC(67.8 MHz, DMSO-d6, using the solvent
resonances as the internal reference standard) 168.1, 149.0,
145.2, 136.4, 134.0, 130.7, 130.1, 128.7, 128.6, 127.9, 127.5,
121.5 and 117.3.
(Nujol) 3380m (NH) and 1576s (aromatic C᎐C); δ (270 MHz,
᎐
H
CDCl3) 7.37 (1 H, s, benzene), 7.33 (1 H, d, J = 7.6, benzene),
7.24 (1 H, t, J = 7.6, benzene), 7.14 (1 H, d, J = 7.3, benzene),
7.04 (1 H, dd, J = 7.6 and 1.0, benzene), 6.95 (1 H, dt, J = 7.8
and 1.3, benzene), 6.76 (1 H, dt, J = 7.5 and 1.2, benzene), 6.66
(1 H, dd, J = 7.9 and 1.0 Hz, benzene), 6.36 (1 H, s, 2-CH), 4.33
(1 H, s, NH) and 2.35 (3 H, s, CH3); δC(67.8 MHz, CDCl3) 146.2,
141.3, 138.4, 129.4, 128.5, 127.1, 126.5, 125.3, 123.5, 121.5,
120.5, 109.6, 70.0 and 21.5.
X-Ray crystallography
X-Ray crystallographic data were collected on a Mac Science
MXC3 diffractometer with Mo-Kα (λ = 0.71073 Å) radiation at
room temperature. θ–2θ scans were employed; no significant
decomposition of the crystal occurred during the data collec-
tion. The solution and refinement procedures made use of the
CRYSTAN-GM software package.7 The structures of com-
plexes 1 and 2 were solved by direct methods using SIR 928 and
refined anisotropically for all non-hydrogen atoms with full-
matrix least-squares calculations. Hydrogen atoms were calcu-
lated with a C–H distance of 0.96 Å and refined isotropically.
Crystallographic data for 1 and 2 are listed in Table 1.
CCDC reference number 186/2091.
Bis[2-(m-toluylmethyleneamino)benzenethiolato]nickel(II) 2.
2-(m-Toluyl)benzothiazoline (0.34 g, 1.5 mmol) and nickel(II)
acetate tetrahydrate (0.19 g, 0.75 mmol) were refluxed in
ethanol (20 cm3) for 20 min. A brown powder of the product
precipitated upon cooling to room temperature and was iso-
lated by filtration. Yield 0.30 g, 78%. Crystals of complex 2
suitable for a structure determination were grown by slow diffu-
sion of diethyl ether into a CHCl3 solution of the brown pro-
duct (Found: C, 65.69; H, 4.85; N, 5.56. C28H24N2NiS2 requires
C, 65.77; H, 4.73; N, 5.48%); νmax/cmϪ1 (Nujol) 1590m and
See http://www.rsc.org/suppdata/dt/b0/b002745f/ for crystal-
lographic files in .cif format.
Results and discussion
The nickel() complex 1 was prepared from the 2-(3,5-di-tert-
butyl-4-hydroxyphenyl)benzothiazoline and nickel() acetate
tetrahydrate (Scheme 2). The IR spectrum shows the absence of
1570m (C᎐N and aromatic C᎐C); δ (270 MHz, CDCl ) 9.60
᎐
᎐
H
3
(2 H, s, benzene), 7.75 (2 H, s, CH᎐N), 7.59 (2 H, d, J = 6.9,
᎐
benzene), 7.40 (2 H, dd, J = 7.8 and 1.2, benzene), 7.17–7.24
(4 H, m, benzene), 7.00 (2 H, dt, J = 7.4 and 1.2, benzene), 6.69
(2 H, dt, J = 7.6 and 1.3, benzene), 6.24 (2 H, d, J = 7.6 Hz,
benzene) and 1.93 (6 H, s, Me); δC(67.8 MHz, CDCl3) 166.6,
149.9, 146.8, 140.0, 134.8, 132.1, 130.6, 128.8, 128.7, 128.2,
126.4, 121.4, 116.3 and 20.6.
ν(NH) vibration and the presence of multiplets of ν(C᎐N) and
᎐
ν(aromatic C᎐C) vibrations near 1600 cmϪ1 as observed for
᎐
nickel() complexes derived from 2-substituted benzothiazo-
lines previously studied.2–5 This indicates that the complex
contains the ligand in Schiff base form. However, a part of
the resonances due to the pendant arm of 1 were not observed
Bis[2-(3-chlorophenylmethyleneamino)benzenethiolato]-
nickel(II) 3. 2-Aminobenzenethiol (0.47 g, 3.8 mmol) was added
to an ethanolic solution (30 cm3) containing 3-chlorobenzal-
dehyde (0.53 g, 3.8 mmol). The mixture was refluxed for 1 h and
then nickel() acetate tetrahydrate (0.46 g, 1.9 mmol) was
added [2-(3-chlorophenyl)benzothiazoline was not isolated
because it is a liquid at room temperature]. The mixture was
refluxed for 20 min and then cooled to room temperature. The
red-brown precipitate was isolated by filtration and dried in
vacuo. Yield 0.81 g, 79%. (Found: C, 56.39; H, 3.42; N, 5.18.
1
in the H NMR spectrum at room temperature. Furthermore,
in an attempt to synthesize a nickel complex with a non-
innocent ligand through carbon–carbon bond formation, a
toluene solution of complex 1 was stirred, but no reaction
occurred, even at higher temperature. This is in contrast to the
behaviour of the nickel() complex with non-substituted phenyl
group as pendant arm in Scheme 1.3
To determine unambiguously the structure of complex 1 an
X-ray crystallographic study was undertaken. The molecular
structure together with the atomic labeling scheme is shown in
Fig. 1. In the molecule the metal atom lies on a crystallographic
2-fold axis. Selected bond distances and angles for 1 are given in
Table 2. Though strong interligand steric interactions occur, the
complex has a slightly distorted square planar geometry in
C26H18Cl2N2NiS2 requires C, 56.55; H, 3.29; N, 5.08%); νmax
/
cmϪ1 (Nujol) 1592s, 1570m and 1552w (C᎐N and aromatic
᎐
C᎐C); δ (270 MHz, CDCl ) 8.86 (2 H, d, J = 7.3, benzene), 8.62
᎐
H
3
(2 H, s, benzene), 7.82 (2 H, s, CH᎐N), 7.36–7.43 (4 H, m,
᎐
benzene), 7.15 (2 H, t, J = 7.9, benzene), 7.06 (2 H, t, J = 6.9,
J. Chem. Soc., Dalton Trans., 2000, 3022–3026
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Table 2 Selected bond distances (Å) and angles (Њ) of complexes 1
and 2
1
2
Ni1–S1
Ni1–S2
Ni1–N1
Ni1–N2
S1–C1
S2–C21
N1–C2
N1–C7
N2–C14
N2–C22
2.163(8)
1.928(19)
1.76(3)
2.182(2)
2.184(2)
1.925(5)
1.912(5)
1.762(7)
1.761(7)
1.427(8)
1.296(8)
1.286(8)
1.431(8)
1.43(4)
1.28(3)
S1–Ni1–S1*
S1–Ni1–S2
S1–Ni1–N1
S2–Ni1–N2
N1–Ni1–N1*
N1–Ni1–N2
Dihedral angle between
NiNS planes
89.7(4)
87.5(6)
95.8(9)
8(4)
93.9(1)
87.5(2)
87.0(2)
96.0(2)
23(3)
Fig. 1 (a) An ORTEP9 drawing of complex 1 with 50% probability
ellipsoids. (b) Side view. H atoms are omitted for clarity.
Scheme 2
which the nitrogen and sulfur donor atoms are cis to each
other. The dihedral angle between the S–Ni–N planes is
8(4)Њ. The steric repulsion between ligands is decreased by a
stepped conformation (Fig. 1(b)). Consequently, 1 shows a
molecular helicity like analogous nickel() complexes. The bond
parameters around the nickel atom are within the normal
values.2–5
The steric bulk of the ligand through the tert-butyl group did
not provide new significant information regarding the arrange-
1
ment around the metal centre. However, why did a H NMR
spectrum of complex 1 at room temperature reveal no reson-
ances for the ortho phenyl protons of the pendant arm? This
should be manifested as fluxional behaviour in variable-
temperature NMR spectra. The variable-temperature 1H NMR
of 1 from ϩ20 to Ϫ50 ЊC as shown in Fig. 2 confirmed the
1
fluxionality of the ligand. Although H NMR spectrum of the
2-(3,5-di-tert-butyl-4-hydroxyphenyl)benzothiazoline starting
material reveals one resonance at δ 7.40 due to equivalent ortho
phenyl protons, interestingly the spectrum of 1 at Ϫ50 ЊC
contains two sharp singlets at δ 7.04 and 9.86 due to inequiva-
lent ortho phenyl protons. Especially, one ortho proton appears
to be shifted downfield, showing the interaction between it
and the metal centre.4 This inequivalence of the protons in the
ortho position of the 3,5-di-tert-butyl-4-hydroxyphenyl group
Fig. 2 Variable-temperature 1H NMR spectra of complex 1 in CDCl3
from ϩ20 to Ϫ50 ЊC (o = ortho protons of pendant arm).
of complex 1 indicates that the pendant arm is held fixed in
space or moves very slowly relative to the NMR timescale.
Furthermore, the X-ray study of 1 shows that the tert-butyl
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J. Chem. Soc., Dalton Trans., 2000, 3022–3026

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Table 3 Interatomic contacts (Å) in complexes 1 and 2
1
C17 ؒ ؒ ؒ C1a
C17 ؒ ؒ ؒ C2a
C17 ؒ ؒ ؒ C3a
C17 ؒ ؒ ؒ C4a
4.40(4)
4.26(4)
3.87(4)
3.64(4)
C17 ؒ ؒ ؒ C5a
C17 ؒ ؒ ؒ C6a
C17 ؒ ؒ ؒ ring
centrea
3.87(4)
4.25(4)
3.81
2
C28 ؒ ؒ ؒ C1
C28 ؒ ؒ ؒ C2
C28 ؒ ؒ ؒ C3
C28 ؒ ؒ ؒ C4
C28 ؒ ؒ ؒ C5
C28 ؒ ؒ ؒ C6
C28 ؒ ؒ ؒ ring
centre
3.875(12)
3.928(12)
3.936(12)
3.919(13)
3.910(13)
3.866(13)
3.65
C27 ؒ ؒ ؒ C21
C27 ؒ ؒ ؒ C22
C27 ؒ ؒ ؒ C23
C27 ؒ ؒ ؒ C24
C27 ؒ ؒ ؒ C25
C27 ؒ ؒ ؒ C26
C27 ؒ ؒ ؒ ring
centre
3.891(13)
3.948(13)
3.943(13)
3.911(14)
3.886(14)
3.872(14)
3.66
Fig. 3 An ORTEP drawing of complex 2 with 50% probability
ellipsoids.
a Interatomic contact related to the twofold axis.
substituent of the pendant arm is close to the 2-amino-
benzenethiol moiety; the distance between C17 and the centre
of the benzene ring C1*–C6* is 3.81 Å (Table 3). It seems
reasonable to assume that the tert-butyl group in the meta
position of the pendant arm prevents the observation of the
resonances for the ortho phenyl protons at room temperature
through an attractive interligand interaction between it and the
2-aminobenzenethiol moiety. Such an attractive interaction
between CH (soft acids) and π groups (soft bases) is called a
CH/π interaction.10 It has reported that the CH/π interaction
plays an important role in determining the conformation of
organic compounds,11 in host–guest complexation12 and in
protein structures.13 Okawa also suggested the presence of a
CH/π interaction in co-ordination compounds.14 Thus, dynamic
1
Fig. 4 1H NMR spectra of complexes 2 (a) and 3 (b) in CDCl3
(o = ortho protons of pendant arm).
behaviour in the H NMR spectra of complex 1 can be corre-
lated to the interligand CH/π interaction. Furthermore, these
facts allow us to suggest that the difference in reactivity for
carbon–carbon bond formation owing to the substituent group
of the pendant arm is also caused by this CH/π interaction.
To probe the presence of the CH/π interaction between
ligands in nickel() complexes with meta-substituted phenyl
groups like 1, complex 2 with a methyl group and 3 with
a chlorine atom at the meta position have been prepared.
Complex 2 was characterized by NMR spectroscopy as well as
by crystal structure determination. The molecular structure is
shown in Fig. 3. The geometry around nickel is distorted square
planar and the two ligands are co-ordinated in a cis fashion.
Three possible structures accompanying the restriction of
rotation of the pendant phenyl group can be anticipated for
the cis isomer as shown in Scheme 3. Complex 2 has the
structure (I) in Scheme 3 and the methyl group of pendant arm
lies over the aromatic ring of another ligand with separations of
3.65 and 3.66 Å, which are comparable to those reported
for complexes showing CH/π interactions (Table 3).14 The
1H NMR resonance of the methyl group of complex 2 shows
an upfield shift when compared with that of the 2-(m-
toluyl)benzothiazoline starting material. This is explained in
terms of an additional ring-current effect caused by an
approach of the methyl group to the aromatic ring of the
2-aminobenzenethiol moiety. In addition, the neighbouring
ortho proton for the methyl group shows a downfield shift
(δ 9.60) which is illustrative of the interaction between the
proton and the metal centre4 and a doublet for another
ortho phenyl proton appears at δ 7.59, which corresponds to
a normal phenyl proton (Fig. 4). These results suggest that
the structure (I) is also predominant in solution.
We could not grow X-ray-quality crystals of complex 3, but
its identity was confirmed by microanalysis and NMR spec-
troscopy. In the 1H NMR spectrum the azomethine protons are
observed as a sharp singlet at δ 7.82. Its spectroscopic proper-
ties are in accord with C2 symmetry. A singlet at δ 8.62 and
a doublet at δ 8.86 assigned to the ortho protons of the 3-
chlorophenyl pendant arm are shifted downfield relative to the
phenyl group, which indicates the interaction between these
protons and the metal centre (Fig. 4).4 This behaviour is
unexpected for a trans isomer5 and shows the formation of the
cis isomer for 3. In addition, such similar chemical shifts (δ 8.62
and 8.86) of two ortho phenyl protons indicate that these
protons are in similar environments in contrast to the ortho
protons of complex 2. Consequently, it can be assumed that
Scheme 3
J. Chem. Soc., Dalton Trans., 2000, 3022–3026
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6 P. J. Palmer, R. B. Trigg and J. V. Warrington, J. Med. Chem., 1971,
14, 248.
7 CRYSTAN-GM, A Computer Program for the Solution and
Refinement of Crystal Structures for X-ray Diffraction Data, MAC
Science Corporation, Yokohama, 1994.
8 SIR 92, A. Altomare, G. Cascarano, C. Giacovazzo and A.
Guagliardi, J. Appl. Crystallogr., 1993, 26, 343.
complex 3 with no CH/π interaction is in equilibrium (structure
(II)) between structures (I) and (III) in solution. Thus the
results presented here for complexes 2 and 3 reveal that such
an anomalous arrangement of 2 with respect to the methyl
group (structure (I)) is enforced by the CH/π interaction.
In conclusion, through an examination of complexes 2 and 3,
the reactivity towards carbon–carbon bond formation and
dynamic behaviour in the 1H NMR spectra of 1 is interpreted in
terms of an interligand CH/π interaction.15
9 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
10 M. Nishio and M. Hirota, Tetrahedron, 1989, 45, 7201; M. Nishio,
M. Hirota and Y. Umezawa, The CH/π Interaction. Evidence, Nature
and Consequences, John Wiley & Sons, Inc., New York, 1998.
11 J. A. Dickinson, P. W. Joireman, R. T. Kroemer, E. G. Robertson
and J. P. Simons, J. Chem. Soc., Faraday Trans., 1997, 1467.
12 T. Fujimoto, R. Yanagihara, K. Kobayashi and Y. Aoyama, Bull.
Chem. Soc. Jpn., 1995, 68, 2113.
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70, 1599.
14 H. Okawa, Coord. Chem. Rev., 1988, 92, 1; K. Yamanari, T. Nozaki,
A. Fuyuhiro, Y. Kushi and S. Kaizaki, J. Chem. Soc., Dalton Trans.,
1996, 2851; K. Jitsukawa, K. Iwai, H. Masuda, H. Ogoshi and
H. Einaga, J. Chem. Soc., Dalton Trans., 1997, 3691.
4 T. Kawamoto, I. Nagasawa, H. Kuma and Y. Kushi, Inorg. Chem.,
1996, 35, 2427.
5 I. Nagasawa, T. Kawamoto, H. Kuma and Y. Kushi, Bull. Chem.
Soc. Jpn., 1998, 71, 1337.
15 Complexes 2 and 3 lead to the corresponding nickel complexes with
non-innocent ligands in contrast to 1. This result can be attributed
to a multiple CH/π interaction by the tert-butyl group of 1 (CH/π
interaction; tert-butyl group > methyl group).
3026
J. Chem. Soc., Dalton Trans., 2000, 3022–3026