Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-(tert-butylthio)ethyl]amine

Article abstract of DOI:10.1016/S0020-1693(00)00333-9

Palladium(II) and platinum(II) complexes, [PdX(NS₃¹Bu)]BPh₄ (X = Cl, Br, I; NS₃¹Bu = tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS₃¹Bu)]BPh₄, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS₃¹Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The ¹H NMR spectrum of [PdCl(NS₃¹Bu)]BPh₄ in acetone-d₆ exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at -70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS₃¹Bu)]BPh₄ are in equilibrium in acetone-d₆. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The ¹H NMR spectra for [PdX(NS₃¹Bu)]BPh₄ (X = Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS₃¹Bu)]BPh₄ seems to occur more slowly than that of the palladium(II) analogue.

Full text of DOI:10.1016/S0020-1693(00)00333-9

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Inorganica Chimica Acta 312 (2001) 67–73
Crystal structures and coordination-site exchange reactions of
palladium(II) and platinum(II) complexes containing
tris[2-(tert-butylthio)ethyl]amine
Kiyohiko Nakajima a,*, Tomohiro Kajino a, Matsuo Nonoyama b, Masaaki Kojima c
a Department of Chemistry, Aichi Uni6ersity of Education, Igaya, Kariya 448-8542, Japan
b Department of Chemistry, Graduate School of Science, Nagoya Uni6ersity, Chikusa, Nagoya 464-8602, Japan
c Department of Chemistry, Faculty of Science, Okayama Uni6ersity, Tsushima, Okayama 700-8530, Japan
Received 8 July 2000; accepted 22 September 2000
Abstract
Palladium(II) and platinum(II) complexes, [PdX(NS31Bu)]BPh4 (X=Cl, Br, I; NS31Bu=tris[2-(tert-butylthio)ethyl]amine) and
[PtCl(NS31Bu)]BPh4, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium
and platinum atoms is square planar. The NS31Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated
to the metal. The H NMR spectrum of [PdCl(NS31Bu)]BPh4 in acetone-d6 exhibited a dynamic behavior. At 20°C the spectrum
1
showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were
observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the
tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm
can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically
equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The
square-planar and trigonal-bipyramidal species of [PdCl(NS31Bu)]BPh4 are in equilibrium in acetone-d6. The equilibrium was
shifted toward the square-planar species on decreasing the temperature. The 1H NMR spectra for [PdX(NS31Bu)]BPh4 (X=Cl, Br,
and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of
coexisting halogen ligand. The site exchange reaction of [PtCl(NS31Bu)]BPh4 seems to occur more slowly than that of the
palladium(II) analogue. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Variable-temperature 1H NMR spectra; Palladium(II) complexes; Platinum(II) complexes; Square-planar structure; Trigonal-bipyrami-
dal structure; Coordination-site exchange reaction; Five-coordinate intermediate
1. Introduction
determine the geometries of transition states, ab initio
calculations were applied to several square-planar plat-
inum(II) and rhodium(I) complexes, and pseudo-trigo-
nal-bipyramidal transition states were indicated [2].
In the coordination-site exchange reaction of the
tripodal ligand in square-planar complexes, the five-co-
ordinate trigonal-bipyramidal intermediate is presumed
(Scheme 1). Tripodal ligands seem to stabilize trigonal-
bipyramidal geometry. For example, [NiX(NS31Bu)]-
BPh4 (NS31Bu=tris[2-(tert-butylthio)ethyl]amine, X=
Cl, Br, I) [3] was prepared, and the existence of a
five-coordinate species was confirmed by the UV–vis
spectra in the solid state and in solution. The UV–vis
spectra of [NiX(N3P)]BPh4 (N3P=bis(2-diethyl-
A wide variety of square-planar d8 metal complexes
are known. Mechanisms for their substitution reaction
have been extensively studied on the basis of their
kinetic properties, and an associative mechanism has
been proposed in many cases [1]. There is an interest in
the geometry of the five-coordinate intermediate or the
activated complex. It is not easy, however, to determine
the structure of the intermediate directly. In order to
study the mechanism of substitution reactions and to
* Corresponding author. Tel.: +81-566-26 2355; fax: +81-566-26
2310.
E-mail address: knakajim@auccc.aichi-edu.ac.jp (K. Nakajima).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(00)00333-9

68
K. Nakajima et al. / Inorganica Chimica Acta 312 (2001) 67–73
Scheme 1.
aminoethyl)(2-diphenylphosphinoethyl)amine, X=Cl,
Br, I) [4] indicated that the square-planar and trigonal-
bipyramidal species existed in equilibrium for X=Cl or
Br, and for X=I, only the square-planar species was
formed. Although, an equilibrium between the trigonal-
bipyramidal and square-planar species of [PdCl-
an ethanol solution (10 cm3) of NaBPh4 (0.035 g,
0.10 mmol) was added to give a yellow precipitate,
which was filtered, washed three times with ethanol
(3×10 cm3), and dried. It was recrystallized by diffu-
sion of hexane into an acetone solution of the complex
at room temperature to yield yellow crystals. Yield
90%. Anal. Found: C, 61.13; H, 7.22; N, 1.84. Calc. for
[PdCl(NS31Bu)]BPh4=C42H59BClNPdS3: C, 61.01; H,
7.19; N, 1.69%. PdCl2 and [PdCl2(cod)] were also used
instead of [PdCl2(PhCN)2] to give the same product,
but the yields were lower.
(trenMe6)]+
(trenMe6=tris[2-(dimethylamino)ethyl]-
amine) was suggested on the basis of the 1H NMR
spectra in solution [5], a detailed study has not been
performed.
Thus, we are interested in the coordination-site ex-
change reaction of palladium(II) and platinum(II) com-
plexes containing
a
tripodal ligand. The coor-
2.1.2. [PdBr(NS31Bu)]BPh4 (2) and [PdI(NS31Bu)]BPh4
(3)
dination-site exchange reaction rates for these com-
plexes will be slower than those for the corresponding
nickel(II) complex. Therefore, we expect that the five-
coordinate intermediate may be detected as an isolated
Complexes 2 and 3 were prepared according to the
same procedure as that described for complex 1, except
that [PdBr2(PhCN)2] and [PdI2(PhCN)2] were used in-
stead of [PdCl2(PhCN)2] to yield orange and brown
crystals respectively. Yield for 2 93%. Anal. Found for
2: C, 56.64; H, 6.74; N, 1.84. Calc. for
[PdBr(NS31Bu)]BPh4·H2O1=C42H61BBrNOPdS3 (2): C,
56.73; H, 6.91; N, 1.58%. Yield for 3 73%. Anal. Found
for 3: C, 54.19; H, 6.54; N, 1.38. Calc. for
[PdI(NS31Bu)]BPh4=C42H59BINPdS3 (3): C, 54.94; H,
6.48; N, 1.53%.
1
signal in the H NMR spectra for palladium(II) and
platinum(II) complexes.
In this work, we have used the tripodal ligand,
tris[2-(tert-butylthio)ethyl]amine (NS31Bu), and pre-
pared [PdX(NS31Bu)]BPh4 (X=Cl, Br, I) and
[PtCl(NS31Bu)]BPh4. The structures of the complexes
have been characterized by X-ray analyses, and the
coordination-site exchange reaction of the ligand has
been studied by the variable-temperature 1H NMR
spectra in the range 183–293 K.
2.1.3. [PtCl(NS31Bu)]BPh4 (4)
To an ethanol solution (20 cm3) of NS31Bu (0.220 g,
0.60 mmol)
was
added
[PtCl2(cod)]
(0.188 g,
0.50 mmol). The solution was refluxed for 3 h, and an
ethanol solution (10 cm3) of NaBPh4 (0.172 g,
0.50 mmol) was added to give a pale yellow precipitate,
which was filtered, washed three times with ethanol
(3×10 cm3), and dried. It was recrystallized by diffu-
sion of hexane into a solution of the complex in acetone
at room temperature to yield pale yellow crystals. Yield
33%. Anal. Found: C, 54.77; H, 6.63; N, 1.64. Calc. for
[PtCl(NS31Bu)]BPh4=C42H59BClNPtS3: C, 55.10; H,
6.50; N, 1.53%.
2. Experimental
The tripodal ligand (NS31Bu) [6], [PdCl2(PhCN)2] [7],
and [PtCl2(cod)] (cod=1,5-cyclooctadiene) [8] were
prepared according to the literature procedures.
[PdBr2(PhCN)2] and [PdI2(PhCN)2] were prepared in an
approximately 30% yield by treating [PdCl2(PhCN)2] in
acetone with an excess amount of KBr and KI in water
respectively. 1H NMR spectra were measured at
400 MHz on a JEOL JNM LA-400 spectrometer with
TMS as an internal reference.
2.1. Preparation of compounds
2.1.1. [PdCl(NS31Bu)]BPh4 (1)
1 The elemental analysis suggested that complex 2 contains a water
of crystallization; however, the water molecule was not found in the
X-ray structure. The apparent discrepancy may be caused because
these samples were taken from different batches.
To an ethanol solution (20 cm3) of NS31Bu (0.039 g,
0.11 mmol) was added [PdCl2(PhCN)2] (0.040 g,
0.10 mmol). The solution was refluxed for 10 min, and

K. Nakajima et al. / Inorganica Chimica Acta 312 (2001) 67–73
69
2.2. Collection of X-ray data and structure
determination
Absorption correction was applied based on „ scan
data for complex 1, and by the numerical integration
method from crystal shape for complex 3. A numerical
absorption correction using the program NUMABS [9]
was applied for complexes 2 and 4. The structures were
solved by direct methods (SIR92 [10]) and expanded
using Fourier techniques (DIRDIF94 [11]). All non-hy-
drogen atoms were refined anisotropically. Hydrogen
atoms were placed at idealized positions and included
in the refinement with fixed isotropic thermal parame-
ters. All calculations were performed using the teXsan
crystallographic software package [12] of Molecular
Science Corporation.
A summary of the crystallographic data and experi-
mental details for complexes 1, 2, 3, and 4 is given in
Table 1. Single crystals of complexes 1 and 3 were
mounted on glass fibers and the measurements were
made on a Rigaku AFC7R four-circle diffractometer
with graphite-monochromated Mo Ka radiation (u=
,
0.710 69 A). Unit cell dimensions were determined by
least-squares refinement of the best angular positions
for 25 carefully centered reflections in the range 29.0B
2qB30.0° The data were collected using ꢀ–2q scan
mode. The intensities of three standard reflections mon-
itored after every 150 reflections remained constant
throughout the data collection. Single crystals of com-
plexes 2 and 4 were mounted on glass fibers and the
measurements were made on a Rigaku RAXIS-RAPID
diffractometer with graphite-monochromated Mo Ka
3. Results and discussion
3.1. Structures of the complexes
,
radiation (u=0.710 69 A). A total of 44 images was
The structures of complexes 1, 2, 3, and 4 were
almost the same as one another. Fig. 1 shows a perspec-
tive view of the complex cation, [PdCl(NS31Bu)]+ (1),
representatively, and selected bond distances and angles
are listed in Table 2 for all the complexes. The distances
collected with two different goniometer settings
(2qmax=55°). The camera radius was 127.40 mm. Ex-
posure time was 5.00 min per degree. Readout was
performed in the 0.100 mm pixel mode. For all the
complexes, the diffraction data were processed by the
PROCESS-AUTO program package. After removal of re-
dundant data, a set of 4814 reflections for 1, 7197 for 2,
6548 for 3 (I\2|(I)), and 9697 for 4 (all observed
unique data) were used for the structure determination.
,
of Pd(1)ꢀS(3) and Pt(1)ꢀS(3) were 5.584(2) A (averaged)
,
and 5.604(2) A respectively, and there was no bonding
interaction. Thus, the coordination geometry around
the palladium and platinum atoms is square planar, the
donor atoms being the nitrogen, two sulfur, and halo-
Table 1
Crystallographic data and experimental details
Complex
1
2
3
4
Formula
M
C42H59BClNPdS3
826.78
C42H59BBrNPdS3
871.23
C42H59BINPdS3
918.23
C42H59BClNPtS3
915.47
Crystal system
Space group
triclinic
triclinic
triclinic
triclinic
(
(
(
(
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
,
a (A)
14.595(8)
15.276(7)
11.980(5)
110.64(3)
95.17(2)
116.51(4)
2
15.1625(5)
15.2824(4)
12.0159(4)
110.6804(8)
109.8762(9)
107.4746(9)
2
14.817(4)
15.167(4)
12.106(3)
109.35(2)
96.54(2)
116.38(2)
2
15.1501(6)
15.2654(4)
12.0401(3)
110.608(2)
110.549(2)
106.681(2)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Z
3
,
V (A )
2136(3)
6.72
2152.1(1)
15.37
2187(1)
13.02
2156.1(1)
34.76
v(Mo Ka) (cm−1
)
Transmission factor
Crystal color
0.93–1.00
yellow
1.285
0.82–0.92
orange
1.344
0.66–0.88
brown
1.394
0.48–0.57
pale yellow
1.410
Dcalcd (g cm−3
)
2q
(°)
50
55
55
55
max
R1 (R)a
Rw
0.031
0.043
0.048
0.050 (0.085)
0.048b
1.53
0.064b
0.061b
1.61
0.137c
Sd
1.25
1.82
a R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ, R is obtained for all observed unique data.
2
2 1/2
b Rw=[SwꢀꢀFoꢀ−ꢀFcꢀꢀ /SwꢀFoꢀ ]
.
2
2 2
2 2 1/2
c Rw=[SwꢀꢀFoꢀ −ꢀFcꢀ ꢀ /Sw(ꢀFoꢀ ) ]
.
d S=[SwꢀꢀFoꢀ−ꢀFcꢀꢀ /(m−n)]1/2 (m is the no. of reflections used; n is the no. of refined parameters).
2

70
K. Nakajima et al. / Inorganica Chimica Acta 312 (2001) 67–73
Fig. 1. Perspective ORTEP drawing of [Pd(NS31Bu)Cl]+ cation in complex 1 with the atom labeling scheme. All non-hydrogen atoms are
represented by their thermal displacement vibrational ellipsoids at 30% probability.
Table 2
,
Selected bond distances (A) and bond angles (°)
1 (M=Pd, X=Cl)
2 (M=Pd, X=Br)
3 (M=Pd, X=I)
4 (M=Pt, X=Cl)
Bond distances
M(1)ꢀX(1)
M(1)ꢀS(1)
M(1)ꢀS(2)
M(1)ꢀN(1)
2.3006(9)
2.320(1)
2.305(1)
2.068(3)
2.4256(5)
2.321(1)
2.303(1)
2.079(3)
2.5796(5)
2.317(2)
2.309(2)
2.102(4)
2.312(2)
2.301(2)
2.288(2)
2.097(5)
Bond angles
X(1)ꢀM(1)ꢀS(1)
X(1)ꢀM(1)ꢀS(2)
X(1)ꢀM(1)ꢀN(1)
S(1)ꢀM(1)ꢀS(2)
S(1)ꢀM(1)ꢀN(1)
S(2)ꢀM(1)ꢀN(1)
93.38(4)
93.06(4)
178.00(8)
166.67(4)
86.92(9)
87.05(9)
93.33(3)
92.92(3)
177.68(8)
166.36(4)
86.9(1)
93.36(4)
92.60(4)
178.3(1)
166.15(6)
86.8(1)
93.24(6)
93.08(6)
178.4(1)
166.34(6)
87.1(2)
87.4(1)
87.6(1)
86.9(2)
gen atoms. The potentially tetradentate NS31Bu ligand is
coordinated to the palladium and platinum atoms as a
tridentate ligand having an uncoordinated pendant 2-
(tert-butylthio)ethyl group. For example, no large devi-
ation from a square-planar angle was observed at the
palladium atom for complex 1, but the chelate angles of
S(1)ꢀPd(1)ꢀN(1) (86.92(9)°) and S(2)ꢀPd(1)ꢀN(1)
(87.05(9)°) are slightly smaller than the bond angles of
Cl(1)ꢀPd(1)ꢀS(1) (93.38(4)°) and Cl(1)ꢀPd(1)ꢀS(2)
(93.06(4)°). The palladium and platinum atoms are
the uncoordinated pendant arm from the least-squares
plane defined by the four donor atoms. Although we
cannot give a clear explanation for the displacement, it
may reduce the steric repulsion among the two Bu and
uncoordinated pendant 2-(tert-butylthio)ethyl groups.
The bond length of PdꢀX increases with respect to the
t
,
ligand in the order Cl (2.3006(9) A)BBr
X
,
,
(2.4256(5) A)BI (2.5796(5) A). These bond lengths are
acceptable when the ionic radii for halogens and Pd2+
are taken into consideration. The bond length of
Pd(1)ꢀN(1) also increases with respect to the X ligand in
,
displaced by 0.196(1) (averaged) and 0.192(1) A toward

K. Nakajima et al. / Inorganica Chimica Acta 312 (2001) 67–73
71
the order ClBBrBI, which is consistent with the order
of trans influence of the X ligand as an electron donor
toward Pd. The lengths of PdꢀS(1) and PdꢀS(2) and
angles at the palladium atom are similar irrespective of
the X ligand in complexes 1, 2, and 3. It is notable that
the averaged bond length of Pt(1)ꢀS(1) and Pt(1)ꢀS(2)
assignable to the tert-butyl protons. The ethylene pro-
tons were observed at 3.33 and 3.66 ppm, and the
aromatic protons of BPh4− at 6.7–7.4 ppm. This spec-
trum is not consistent with the square-planar structure
determined by X-ray analysis. Complex 1 has two kinds
of tert-butyl group in the square-planar structure, i.e.
the two tert-butyl groups on the coordinated sulfur
atoms and the other one on the uncoordinated sulfur
atom. Accordingly, a dynamic motion was suggested,
and the 1H NMR spectra were measured at low temper-
ature. The variable-temperature 1H NMR spectra of
the tert-butyl signals are shown in Fig. 2. The singlet
signal at 1.60 ppm (293 K) became broad with a de-
crease in temperature, and split into two broad signals
(1.38 and 1.69 ppm) at 223 K. Another broad singlet
signal emerged at 1.61 ppm at 203 K, and its intensity
reduced at lower temperatures. The intensity ratio of
the two signals at 1.70 and 1.36 ppm below 203 K was
2:1. We attributed these two signals to the tert-butyl
protons on the coordinated and uncoordinated sulfur
atoms of the square-planar complex as presented in
Fig. 3(a), although the structure is not frozen even at
183 K. Holm and coworkers characterized the structure
of [NiCl(NS31Bu)]BPh4 by X-ray analysis to be trigonal-
bipyramidal [13]. According to these results, we de-
duced that [PdCl(NS31Bu)]+ is in equilibrium between
the square-planar and trigonal-bipyramidal forms in
acetone-d6. Therefore, the signal at 1.61 ppm observed
at low temperature (183–203 K) was assigned to the
tert-butyl protons in the trigonal-bipyramidal structure
(Fig. 3(b)), where three tert-butyl groups are magneti-
cally equivalent. Thus, the trigonal-bipyramidal form
has a sufficiently long lifetime to be detected by 1H
,
(2.295(2) A) is smaller than that of Pd(1)ꢀS(1) and
,
Pd(1)ꢀS(2) (2.313(1) A), although the Pt(1)ꢀCl(1) bond
,
length (2.312(2) A) is slightly larger than that for
,
Pd(1)ꢀCl(1) (2.3006(9) A). It seems that the sulfur atom
has a strong affinity toward Pt(II).
Several complexes containing the NS31Bu ligand or its
analogue have been prepared, and X-ray structure anal-
ysis was applied to some of them. The geometry around
the metals of [CoBr(NS31Bu)]PF6 [4], [NiCl(NS31Bu)]-
BPh4 [13], and [CuCl(NS3Et)]ClO4 [14] was trigonal-
bipyramidal in the solid state. It seems that the com-
plexes of first-row transition metals with the NS3R
(R=alkyl; tris[2-(alkylthio)ethyl]amine) ligand prefer
the trigonal-bipyramidal structure. However, the struc-
tures of [NiX(NS3Et)]BPh4 (X=Cl, Br, I) [4] were
assigned to be octahedral in the solid state based on
their reflectance spectra. The structure of [HgCl-
(NSi3Pr)]2(Hg2Cl6) [15] has also been reported and the
geometry around mercury was intermediate between a
trigonal-bipyramid and a tetrahedron. Thus, the coor-
dination mode of the NS3R ligand depends upon the
metal ion and the substituent on sulfur.
3.2. Coordination-site exchange reaction
The 1H NMR spectrum of complex 1 in acetone-d6 at
room temperature showed
a singlet at 1.60 ppm
Fig. 2. Temperature-dependent 1H NMR spectra due to the tert-butyl protons in acetone-d6. (a) Complex 1 in the region of 183–293 K. (b)
Complex 4 at 293 K. (c) Complex 2 at 223 K. (d) Complex 3 at 223 K.

72
K. Nakajima et al. / Inorganica Chimica Acta 312 (2001) 67–73
the analogous palladium(II) complex. The strong
affinity of platinum toward sulfur, which is evidenced
by the short PtꢀS bond, may make a conformational
change of complex 4 difficult.
4. Conclusions
We prepared palladium(II) and platinum(II) com-
plexes containing tris[2-(tert-butylthio)ethyl]amine, and
the structures were determined by X-ray analysis. The
geometry around the palladium and platinum atoms
was square planar in the solid state. However, the
structure was not rigid and the coordination-site ex-
change reaction occurred in acetone-d6. In this study,
we could detect the five-coordinate intermediate of the
reaction. The reaction proceeded via a trigonal-bipyra-
midal intermediate, which was identified by the vari-
Fig. 3. Square-planar (a) and trigonal-bipyramidal (b) structures of
complex 1. In the trigonal-bipyramidal structure all three Bu groups
t
are magnetically equivalent, whereas in the square-planar structure
t
t
t
the BuC group is not equivalent to the BuA and BuB groups.
NMR spectroscopy at low temperature (183–203 K).
However, it seems that the inversion at the sulfur donor
atoms is too fast to be observed even at 183 K. Accord-
ingly, the singlet signal at 1.60 ppm observed at 293 K
was interpreted as an averaged signal of the tert-butyl
protons under the fast site-exchange conditions. This
chemical shift (1.60 ppm) is very close to the weighted
average (1.59 ppm) of the two signals (1.70 and
1.36 ppm).
able-temperature
1H
NMR
spectra.
The
variable-temperature NMR spectra of complex 1 can be
interpreted as follows. (1) T\243 K: the complex is
stereochemically non-rigid, and fast site-exchange reac-
tion occurs; (2) 203BTB243 K: site-exchange rates
are comparable to the NMR time scale; (3) TB203 K:
the complex exists mainly in a square-planar structure,
but not frozen even at 183 K. The presence of a trigo-
nal-bipyramidal intermediate was indicated.
The geometry around the nickel atom of
[NiBr(N3P)]BPh4 was confirmed by an X-ray analysis
to be square-planar in the solid state [3]. On the other
hand, the UV–vis spectra of [NiX(N3P)]BPh4 (X=Cl,
Br) indicated that both the diamagnetic square-planar
and paramagnetic trigonal-bipyramidal species exist in
equilibrium in solution. It seems that the structural
characteristics of [NiX(N3P)]BPh4 (X=Cl, Br) are sim-
ilar to those of complex 1 in the solid state and in
5. Supplementary material
Tables of non-hydrogen atom coordinates and an-
isotropic thermal parameters, coordinates of the hydro-
gen atoms and bond lengths and angles have been
deposited (nos 149231, 149232, 149233, and 149234 for
complexes 1, 2, 3, and 4 respectively) at the Cambridge
Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
1
solution. However, the signals of H NMR spectra for
[NiX(N3P)]BPh4 (X=Cl, Br) shifted continuously from
the diamagnetic positions and at the same time became
broader by decreasing the temperature. This means that
the equilibrium between the square-planar and trigonal-
bipyramidal species is shifted toward the latter on
decreasing the temperature. On the contrary, in our
1
case the relative ratio of the H NMR signal intensities
of the trigonal-bipyramidal species to that of the
square-planar one decreased with a decrease in temper-
ature. The stable form of complex 1 is a square-planar
structure over the entire temperature region (183–
293 K). Although the variable-temperature 1H NMR
spectra (Fig. 2(a)) were so complicated that we could
not estimate the thermodynamic parameters, the reso-
nances of the 1H NMR spectra of tert-butyl protons for
complexes 2 and 3 at 223 K resemble those of complex
1 very closely (Fig. 2). These results suggest that there
is little difference in the rate of the coordination-site
exchange reaction among these complexes. However,
Acknowledgements
The present work was partially supported by a
Grant-in Aid for Scientific Research No. 10640543
from the Ministry of Education, Science, and Culture.
We express our thanks to the Institute for Molecular
Science, Okazaki, for allowing the use of facilities for
X-ray diffraction measurements.
References
1
the resonance of the H NMR spectrum for complex 4
at 293 K is similar to those of complexes 1, 2, and 3 at
243 K (Fig. 2). The coordination-site exchange reaction
of complex 4 seems to occur more slowly than that of
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