Effects of the intramolecular nh...s hydrogen bond in mononuclear platinum(ll) and palladium(ll) complexes with 2,2 -bipyridine and benzenethiol derivatives

Article abstract of DOI:10.1021/ic0490167

A series of complexes, [M(bpy)(SAr)₂] (M = platinum(ll) or palladium(ll), bpy = 2,2 -bipyridine, SAr = 2- or 4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the basis of ¹H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph₃CCONHC₆H₄)₂] (1) and [Pt(bpy)(S-2-f-BuNHCOC₆H₄)₂] (3) were determined by X-ray analysis. The complexes have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom. A weak NH-S hydrogen bond in these complexes and [Pd(bpy)(S-2-Ph₃CCONHC ₆H₄)₂] (4) is detected from the ¹H NMR spectra and the IR spectra in chloroform and in the solid state. [Pt(bpy)(S-2-Ph₃CCONHC₆H4)₂] (1) exhibits a remarkably high-energy-shifted lowest-energy band in UV-visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm and the positive shift of +0.24 V, as compared to those of [Pt(bpy)(SC₆H ₅)₂], are due to the effect of the NH-S hydrogen bond.

Full text of DOI:10.1021/ic0490167

Inorg. Chem. 2005, 44, 1966−1972
Effects of the Intramolecular NH‚‚‚S Hydrogen Bond in Mononuclear
Platinum(II) and Palladium(II) Complexes with 2,2
′-Bipyridine and
Benzenethiol Derivatives
Masahiro Kato, Taka-aki Okamura, Hitoshi Yamamoto, and Norikazu Ueyama*
Department of Macromolecular Science, Graduate School of Science, Osaka UniVersity,
Toyonaka, Osaka 560-0043 Japan
Received July 22, 2004
A series of complexes, [M(bpy)(SAr)2] (M
) platinum(II) or palladium(II), bpy ) 2,2′-bipyridine, SAr ) 2- or
4-(acylamino)benzenethiolate, or 2-(alkylcarbamoyl)benzenethiolate), were synthesized and characterized on the
basis of 1H NMR, IR, and electrochemical properties. The structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and
[Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3) were determined by X-ray analysis. The complexes have intramolecular NH‚‚‚
S
hydrogen bonds between the amide NH group and the sulfur atom. A weak NH‚‚‚S hydrogen bond in these
complexes and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) is detected from the 1H NMR spectra and the IR spectra in
chloroform and in the solid state. [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) exhibits a remarkably high-energy-shifted
lowest-energy band in UV−visible spectra and has a positively shifted oxidation potential. The blue-shift of 42 nm
and the positive shift of
hydrogen bond.
+0.24 V, as compared to those of [Pt(bpy)(SC6H5)2], are due to the effect of the NH‚‚‚
S
Introduction
) bipyridine, phenanthroline, and derivatives) have been of
increasing interest recently as chromophores in the light-
chemical energy conversion. These platinum(II) diimine
complexes feature long-lived charge-separated excited states.
The description of the low-energy excited states in this class
of complexes first requires the assignment of their frontier
orbitals, in particular, the HOMO and LUMO. The lowest
excited state in platinum(II)-diimine dithiolate complexes
was assigned as the charge transfer from the HOMO of
mixed S(pπ)-Pt(dπ) to the LUMO of diimine(π*) charac-
ter.6,8 In addition, for a flexible bis-thiolate complex, Pt(bpy)-
(4-X-C6F4S)2, it is reported that the HOMO is composed
of thiolate(π)/S(p)/Pt(d) orbitals and the LUMO is largely
localized on the π* (diimine) orbitals.2,7 Consequently, its
Platinum(II) diimine complexes Pt(diimine)L2 (L )
thiolate,1-8 acetylide,9-14 phenyl,15 and cyanide;16-18 diimine
* Author to whom correspondence should be addressed. E-mail:
ueyama@chem.sci.osaka-u.ac.jp.
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1966 Inorganic Chemistry, Vol. 44, No. 6, 2005
10.1021/ic0490167 CCC: $30.25
© 2005 American Chemical Society
Published on Web 02/22/2005

Effects of the NH‚‚‚S Hydrogen Bond in Pt(II) Complexes
energies are strongly dependent on the nature of the ligands
coordinated to platinum. More electron-withdrawing ligands
on platinum cause the bands to move to a higher energy level.
Previously, we reported that the NH‚‚‚S hydrogen bond
contributes to the positive shift in the redox potential in
benzenethiolate or Cys-containing oligopeptide Fe(II)
complexes19-26 as models of the Fe center of iron-sulfur
proteins and Fe(III) complexes27-31 as models of the Fe(III)
porphinate proteins such as P-450 and chloroperoxidase. The
NH‚‚‚S hydrogen bond has been found to shift the redox
potential in [MoVO(2-(acetylamino)benzenethiolate)4]-.32
Thus, NH‚‚‚S hydrogen bonding can conceivably produce a
positive shift in the redox potential in any metal thiolate
complex. The presence of such hydrogen bonds in Fe-
(II),19,21,23,26 Fe(III),27-31 Ga(III),30,31,33 Mo(V),32 Mo(IV), Co-
(II),21 Cu(I),34 Cd(II), and Hg(II)35 complexes has already
been reported.
Figure 1. Crystal structure of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1).
Thermal ellipsoids are drawn at 50% probability. The hydrogen atoms except
for the amide proton have been omitted for clarity.
This paper describes the presence of the intramolecular
NH‚‚‚S hydrogen bond in platinum(II) diimine complexes
containing bis(benzenethiolate) derivatives, 2-(acylamino)-
benzenethiolate, 4-(acylamino)benzenethiolate, and 2-(alky-
lcarbamoyl)benzenethiolate and related palladium(II) com-
plexes, and it also describes the influence of the hydrogen
bond in the sulfur atom coordinated to platinum on the UV-
visible spectra and the electrochemical properties of plati-
num(II) diimine complexes (Chart 1).
Chart 1
Results and Discussion
Crystal Structures of [Pt(bpy)(S-2-Ph3CCONHC6H4)2]
(1) and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3). Complexes 1
and 3 crystallized in the P21/n and P2/c space groups,
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Inorg. Chem. 1985, 24, 4700-4704.
respectively. ORTEP views of 1 and 3 are shown in Figures1
and 2, respectively. Selected bond distances and bond angles
for both complexes are listed in Table 1. Both complexes
show that the expected Pt coordination geometry is ap-
proximately square planar, with one 2,2′-bipyridine and two
thiophenolate ligands binding to the Pt(II) center. One of
the two thiophenol rings in 3 is disordered with Pt(1)-S(2)-
C(21)-C(22) dihedral angles of 177.6(5)° or -155.2(5)°.
The angle between the planes of the two thiophenol rings
coordinated to platinum in 1 is 165.2(2)°, and the two
thiophenol rings of 1 show intramolecular π-π stacking with
C(11)‚‚‚C(21) ) 3.49 Å and C(12)‚‚‚C(21) ) 3.52 Å. The
angles between the thiophenol rings and the PtS2 plane are
82.0(1)° and 86.0(1)°, and the structure of complex 1 is
analogous to Pt(bpy)(4-CN-C6F4S)2.2 In contrast, the two
thiophenol rings in 3 are in an anti configuration, thus
(26) Ueyama, N.; Nakata, M.; Fuji, M.; Terakawa, T.; Nakamura, A. Inorg.
Chem. 1985, 24, 2190-2196.
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Sakurai, H.; Nakamura, A. Inorg. Chem. 1998, 37, 2415-2421.
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A. Inorg. Chim. Acta 1998, 283, 91-97.
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A. J. Am. Chem. Soc. 1996, 118, 12826-12827.
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T.; Ueyama, N.; Nakamura, A. Inorg. Chem. 1999, 38, 1199-1210.
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Inorganic Chemistry, Vol. 44, No. 6, 2005 1967

Kato et al.
NH‚‚‚S hydrogen bond contained in a five-membered ring
and a six-membered ring for 3. The distances between the
nitrogen atom and the sulfur atom are 3.020(4) Å (N(1)-
S(1)), 2.949(4) Å (N(2)-S(2)) for 1 and 3.161(6) Å (N(1)-
S(1)), 3.10(2) Å or 3.01(2) Å (N(2)-S(2)) for 3 (Table 1).
In addition, the S(1)‚‚‚H(1) and S(2)‚‚‚H(2) distances in
complex 1 are 2.65 and 2.60 Å, whereas the S(1)‚‚‚H(1),
S(2)‚‚‚H(2), and S(2)‚‚‚H(2B) distances in complex 3 are
2.96, 2.83, and 2.51 Å, respectively. The previous structural
analyses in metalloproteins and model complexes suggest
that the distances forming an NH‚‚‚S hydrogen bond are ca.
3.0-3.5 Å at N‚‚‚S, and ca. 2.3-2.8 Å at S‚‚‚H.27,28,31,36-39
Therefore, complex 1 has two equal NH‚‚‚S hydrogen bonds,
and complex 3 has two distinct NH‚‚‚S hydrogen bonds
confirmed by the IR spectra in solid, as described later. The
crystal structure of the corresponding thiol compound, 2-t-
BuNHCOC6H4SH, shows the formation of the intramolecular
SH‚‚‚OdC hydrogen bond, not that of the intramolecular
NH‚‚‚S hydrogen bond.40 Consequently, this finding suggests
that the coordination of the sulfur atom to platinum results
in the rotation of the amide plane and the formation of the
intramolecular NH‚‚‚S hydrogen bond in complex 3.
Figure 2. Crystal structure of [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3).
Thermal ellipsoids are drawn at 50% probability. The hydrogen atoms except
for the amide proton have been omitted for clarity. The figure depicts only
one of two disordered sites corresponding to the 50:50 disordered thiophe-
nolate ligand.
Table 1. Selected Bond Distances (Å), Intramolecular NH‚‚‚S Contacts
(Å), and Bond Angles (deg) of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and
[Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3)
1H NMR Spectra. The amide NH signal in 2-Ph3-
CCONHC6H4SH appears at 8.28 ppm of normal chemical
1
3
+
Pt(1)-S(1)
Pt(1)-S(2)
Pt(1)-N(31)
Pt(1)-N(41)
2.284(1)
2.289(1)
2.045(3)
2.071(4)
2.283(3)
2.285(3)
2.067(3)
2.059(4)
shift. This signal in (NEt4 )(2-Ph3CCONHC6H4S-) is shifted
downfield by 2.04 ppm to 10.32 ppm, due to the formation
of an intramolecular NH‚‚‚S hydrogen bond. The amide NH
signal in 1 appears at 8.74 ppm and shifts downfield by 0.46
ppm as compared to that of the thiol form. This small shift
in 1 as compared to that of the thiolate anion suggests that
the intramolecular NH‚‚‚S hydrogen bond is weak. It was
previously revealed that the increase of covalency between
metal and thiolate decreases the electron density of S
coordinated to metal and weakens the intramolecular NH‚‚
‚S hydrogen bond.35 The small shift in 1 is ascribed to the
lower acidity of amide NH through the formation of
hydrogen bond as compared to the thiolate anion. Conse-
quently, these findings predict that the intramolecular NH‚
‚‚S hydrogen bond between the sulfur atom binding to Pt(II)
and the amide NH is weaker than that in the thiolate anion
N(1)‚‚‚S(1)
N(2)‚‚‚S(2)
3.020(4)
2.949(4)
3.161(6)
3.01(2), 3.10(2)a
Pt(1)-S(1)-C(11)
Pt(1)-S(2)-C(21)
111.9(1)
107.3(2)
107.3(1)
111.6(1)
S(1)-Pt(1)-S(2)
N(41)-Pt(1)-S(1)
N(31)-Pt(1)-S(2)
N(31)-Pt(1)-N(41)
93.79(4)
92.8(1)
94.6(1)
78.9(1)
88.4(1)
94.2(1)
98.2(1)
79.3(2)
Pt(1)-S(1)-C(11)-C(12)
Pt(1)-S(2)-C(21)-C(22)
91.7(4)
163.2(3)
133.0(2)
177.6(5), -155.2(5)a
a Atoms N(2) and C(22) are disordered.
+
form, (NEt4 )(2-Ph3CCONHC6H4S-). This prediction is
eliminating the possibility of intramolecular π-π stacking
as observed in 1, and are nearly perpendicular to the PtS2
planes (dihedral angle ) 74°, 109°). The dihedral angle
between the amide groups and the thiophenol ring for 1,
C(17)-N(1)-C(12)-C(13), is -38.4(6)° and another ring,
C(27)-N(2)-C(22)-C(23), is -42.5(6)°, and that between
the carbamoyl groups and the thiophenol ring for 3, N(1)-
C(17)-C(12)-C(11), is -49.9(4)° and another disordered
ring, N(2)-C(27)-C(22)-C(21), is 48(1)° or -48(1)°,
values that are not favorable for spreading the π-conjugated
systems. Accordingly, we carried out computations with
Gaussian03 (B3LYP/LanL2DZ) on the energy changes for
complex 1 by altering the angle between the planes of the
amide group and thiophenol ring. The result of our computa-
tions shows that the structure of 1 (dihedral angle ) 38.4°
and 42.5°) is stabilized by ca. 2.0 kcal/mol-1 relative to the
model structure in which these dihedral angles are 0°. The
amide NH groups for 1 are directed to form an intramolecular
supported by the IR spectra in solution, as described later.
The chemical shifts of the amide NH for other complexes
are summarized in Table 2. The amide NH signal in [Pt-
(bpy)(S-2-t-BuNHCOC6H4)2] (3) shifts downfield by 1.62
ppm as compared to the corresponding thiol compound. This
shift is smaller than that in the thiolate anion (6.47 ppm),40
and complex 3 also forms a weak intramolecular NH‚‚‚S
hydrogen bond. The amide NH signal in a palladium
complex, [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4), which has
the same coordination structure as platinum complexes, shifts
(36) Adman, E.; Watenpaugh, K. D.; Jensen, L. H. Proc. Natl. Acad. Sci.
U.S.A. 1975, 72, 4854-4858.
(37) Watenpaugh, K. D.; Sieker, L. C.; Jensen, L. H. J. Mol. Biol. 1979,
131, 509-522.
(38) Baker, E. N. J. Mol. Biol. 1988, 203, 1071-1095.
(39) Kissinger, C. R.; Sieker, L. C.; Adman, E. T.; Jensen, L. H. J. Mol.
Biol. 1991, 219, 693-715.
(40) Kato, M.; Kojima, K.; Inohara, M.; Okamura, T.; Yamamoto, H.;
Ueyama, N., submitted for publication.
1968 Inorganic Chemistry, Vol. 44, No. 6, 2005

Effects of the NH‚‚‚S Hydrogen Bond in Pt(II) Complexes
Table 2. Chemical Shifts (ppm) and Temperature Coefficients (ppb/K)
of Amide NHs of M(bpy)(bis)thiolates (M ) PtII, PdII) Complexes and
Related Compounds in Chloroform-d1 and Acetonitrile-d3 (10 mM)
in
in
a
a
compound
chloroform-d1
acetonitrile-d3
[Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1)
[Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2)
[Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3)
[Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4)
2-Ph3CCONHC6H4SH
8.74/0.8
8.84/0.0
7.55/-4.0c
7.47/-0.7
8.91/0.0
8.67/-8.2
10.72/-0.5
6.78/-9.0
12.72/-1.2
b
7.40/-1.3
8.75/1.1
8.28/-0.7
10.32/-0.7
5.78/-2.0
12.25/-3.1
(NEt4+)(2-Ph3CCONHC6H4S-)
2-t-BuNHCOC6H4SH
(NEt4+)(2-t-BuNHCOC6H4S-)
a Chemical shift [ppm]/temperature coefficient [ppb/K]. b The amide
signal is not detected to overlap with the signal of chloroform or triphenyl
group. c Complex concentration ≈ 1 mM.
downfield by 0.47 ppm as compared to that of the thiol
compound. This shift value is almost the same as that of the
corresponding platinum complex, thus indicating that the
palladium complex 4 forms the weak intramolecular NH‚‚
‚S hydrogen bond as well as the platinum complex 1.
Figure 3. IR spectra of (a) [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1), (b) 2-Ph3-
CCONHC6H4SH, and (c) (NEt4+)(2-Ph3CCONHC6H4S-) in chloroform.
1
The temperature coefficients of the amide NH H NMR
signals in platinum complexes 1 and 3, the palladium
complex 4, and the corresponding thiol and thiolate anion
compounds are summarized in Table 2. The temperature
coefficients of the amide NH signals in the thiol compounds
2-Ph3CCONHC6H4SH and 2-t-BuNHCOC6H4SH are -0.7
and -2.0 ppb/K in chloroform-d1 and -8.2 and -9.0 ppb/K
in acetonitrile-d3, respectively. On the other hand, those in
(NEt4 )(2-Ph3CCONHC6H4S-), exhibits a broad NH band
+
at 3150 cm-1 and CO band at 1654 cm-1. This large ∆ν-
(NH) value (-193 cm-1) for the thiolate anion compound
as compared to that of the thiol compound is ascribed to the
intramolecular NH‚‚‚S hydrogen bond and is detected by the
formation of the NH‚‚‚O hydrogen bond in the corresponding
carboxylate anion compounds.44 Complex 1 exhibits two NH
bands at 3288 and 3325 cm-1 and a CO band at 1673 cm-1,
as shown in Figure 3a. The ∆ν(NH) for 1 can be estimated
to be -55 and -18 cm-1 when the stretching of the free
NH in the thiol state, 2-Ph3CCONHC6H4SH, is employed
as a standard. Table 3 lists the IR data in the amide region
ν(NH) and ν(CdO) bands for the other platinum and
palladium complexes, free ν(NH) and ν(CdO) bands of the
corresponding thiol compounds, and the shift values. The
amide ν(NH) values in [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3)
and [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4) were observed at
3305 and 3281 cm-1 by a shift of -126 and -62 cm-1,
respectively, as compared to the corresponding thiol com-
pounds. The corresponding ∆ν(CdO) shifts are somewhat
small (-22, -10, and -13 cm-1) due to the free state of
the amide CdO group. The combined data indicate the
presence of the intramolecular NH‚‚‚S hydrogen bond in
complexes 1, 3, and 4. On the other hand, [Pt(bpy)(S-4-Ph3-
CCONHC6H4)2] (2) and the corresponding thiol and thiolate
the thiolate anion compounds (NEt4 )(2-Ph3CCONHC6H4S-)
+
+
and (NEt4 )(2-t-BuNHCOC6H4S-) are -0.7 and -3.1 ppb/K
in chloroform-d1 and -0.5 and -1.2 ppb/K in acetonitrile-
d3, respectively. The temperature coefficients of the amide
signal in the thiolate anion compounds are very small as
compared to those of the thiol compounds in acetonitrile-
d3. The observation of the small temperature coefficients has
been established for the presence of the intramolecular NH‚
‚‚OdC hydrogen bond in peptides.41-43 Obviously, the amide
NH’s in the thiolate anion compounds are involved in an
intramolecular hydrogen bond like the NH‚‚‚S hydrogen
bond. The temperature coefficients of the amide NH signals
in 1, 3, and 4 are 0.8, -1.3, and 1.1 ppb/K in chloroform-d1
and 0.0, -0.7, and 0.0 ppb/K in acetonitrile-d3, respectively.
In contrast, the value in 2 without the intramolecular
NH‚‚‚S hydrogen bond is -4.0 ppb/K in acetonitrile-d3.
Consequently, the small temperature coefficients in com-
plexes 1, 3, and 4 as compared to complex 2 suggest the
formation of the intramolecular NH‚‚‚S hydrogen bond.
IR Spectra in Solution and in the Solid State. The
presence of an NH‚‚‚S hydrogen bond was established by
IR spectroscopy. Figure 3 shows the IR spectra of [Pt(bpy)-
(S-2-Ph3CCONHC6H4)2] (1) and the corresponding thiol and
thiolate anion compounds, 2-Ph3CCONHC6H4SH and
+
anion compounds, 4-Ph3CCONHC6H4SH and (NEt4 )(4-Ph3-
CCONHC6H4S-), exhibit an NH band at 3410, 3409, and
3409 cm-1 and a CO band at 1677, 1683, and 1675 cm-1,
respectively. These ν(NH) values exhibit somewhat similar
values because the intramolecular NH‚‚‚S hydrogen bond
cannot form in 4-acylaminobenzenethiol derivatives.
+
(NEt4 )(2-Ph3CCONHC6H4S-), in chloroform-d1. 2-Ph3-
The IR data in the amide region ν(NH) and ν(CdO) bands
in the solid state for the platinum and palladium complexes,
free ν(NH) and ν(CdO) bands of the corresponding thiol
CCONHC6H4SH exhibits a free NH band at 3343 cm-1 and
a free CO band at 1685 cm-1. The thiolate anion compound,
(41) Patel, D. J. Biochemistry 1973, 12, 667-676.
(42) Patel, D. J. Biochemistry 1973, 12, 677-688.
(43) Gellman, S. H.; Dado, G. P.; Liang, G. B.; Adams, B. R. J. Am. Chem.
Soc. 1991, 113, 1164-1173.
(44) Onoda, A.; Yamada, Y.; Takeda, J.; Nakayama, Y.; Okamura, T.; Doi,
M.; Yamamoto, H.; Ueyama, N. Bull. Chem. Soc. Jpn. 2004, 77, 321-
329.
Inorganic Chemistry, Vol. 44, No. 6, 2005 1969

Kato et al.
Table 3. IR Spectral Data (cm-1) for M(bpy)(bis)thiolates (M ) PtII, PdII) Complexes and Related Compounds in Chloroform (10 mM) and in the
Solid State
chloroform
solid state
compound
ν(NH)
ν(CO)
1673
1677
1636, 1648
1672
1685
1654
1683
1675
ν(NH)
3278
ν(CO)
1675
1681
1634, 1648
1675
1696
1644
1681
1675
[Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1)
[Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2)
[Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3)
[Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4)
2-Ph3CCONHC6H4SH
3288, 3325
3410
3305
3281, 3323
3343
3150
3409
3409
3431
3153
3404
3241, 3298
3280, 3333
3348
3140
3398
3411
3303
3154
(NEt4+)(2-Ph3CCONHC6H4S-)
4-Ph3CCONHC6H4SH
(NEt4+)(4-Ph3CCONHC6H4S-)
2-t-BuNHCOC6H4SH
1658
1618
1632
1618
(NEt4+)(2-t-BuNHCOC6H4S-)
Table 4. IR Shift ∆ν(NH) of the Amide NH Band by the NH‚‚‚S
Hydrogen Bond in Various Metal Complexes with
2-(Acylamino)benzenethiolate Ligands (SAr)
between NH and S pπ against the strongly covalent Pt-S
and Pd-S bonds.
UV-Visible Spectra. The absorption spectra of the
platinum complexes [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) and
[Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2) at 298 K exhibit a broad
asymmetric absorption band with medium intensity in the
visible region (400-600 nm) (Figure 4). This lowest energy
compound
∆ν(NH)/cm-1
ref
[Pt(bpy)(SAr)2]a
-55
-62
this work
this work
34
[Pd(bpy)(SAr)2]a
(NEt4)[CuI(SAr)3]b
(NEt4)2[CoII(SAr)4]b
(NEt4)2[CdII(SAr)4]b
(NEt4)[MoVO(SAr)4]c
[HgII(SAr)2]b
-171
-114
-126
-67
21
32
35
29
33
-52
[FeIII(OEP)(SAr)]d
[GaIII(OEP)(SAr)]b
-66
-143
a S-2-Ph3CCONHC6H4. b S-2-t-BuCONHC6H4. c S-2-CH3CONHC6H4. d S-
2-CF3CONHC6H4.
compounds, and the shift values are all summarized in Table
3. The thiol forms, 2-Ph3CCONHC6H4SH and 4-Ph3-
CCONHC6H4SH, in the solid state exhibit NH bands at 3348
and 3398 cm-1 and CO bands at 1696 and 1681 cm-1,
respectively. These bands ν(NH) and ν(CdO) in the solid
state are similar to those in solution and different from those
of 2-t-BuNHCOC6H4SH. This result suggests that these
compounds do not have an intermolecular NH‚‚‚OdC
hydrogen bond in the solid state as does 2-t-BuNHCOC6H4-
SH.40 Complexes 1 and 4 exhibit NH bands at 3278, 3280,
and 3333 cm-1, and CO bands at 1675 and 1675 cm-1,
respectively. The ∆ν(NH) values for 1 and 4 can be estimated
to be -70 and -68 cm-1 when the stretching of the free
NH in the thiol compound is employed as a standard, and
the shifts are ascribed to an NH‚‚‚S hydrogen bond as well
as occurring in solution. These ∆ν(NH) values are smaller
than that of the thiolate anion, (NEt4+)(2-Ph3CCONHC6H4S-)
(3140 cm-1). This finding suggests that these NH‚‚‚S
hydrogen bonds are weak, as would be expected from the
X-ray analysis. Complex 3 exhibits NH bands at 3241 and
3298 cm-1 and CO bands at 1634 and 1648 cm-1. The two
separate NH and CO bands are tentatively assigned to those
with two distinct NH‚‚‚S hydrogen bonds detected by the
X-ray analysis. Complex 2 exhibits an NH band at 3404 cm-1
and a CO band at 1681 cm-1, without a hydrogen bond.
Figure 4. Electronic absorption spectra of [Pt(bpy)(S-2-Ph3CCONHC6H4)2]
(1) (-) and [Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2) (- - -) in tetrahydrofuran
at 298 K.
absorption band at 530 nm in Pt(bpy)(SC6H5)2 is assigned
as the transition from the HOMO composed of thiolate(π)/
S(p)/Pt(d) orbitals to the LUMO largely localized on the π*
(bipyridine) orbital and shifts to a lower energy level with
an increase of the thiolate ligand donor ability.2 The lowest
energy absorption band in complex 2 is detected at 537 nm
(ꢀ ) 1020 M-1 cm-1), which is only slightly shifted as
compared to that in Pt(bpy)(SC6H5)2 (530 nm, ꢀ ) 2140 M-1
cm-1).7 Because the electronic effect of the amide group at
the 2- or 4-position of the benzene ring is known not to be
significant for organic disulfide molecules,45 that of acy-
lamino group in these complexes is not significant. However,
this band in complex 1 is detected at 488 nm (ꢀ ) 2410
M-1 cm-1), consistent with a significant shift to higher
energy. In the case of the Fe(II), Co(II),21 Mo(V), and Mo-
(IV)32 complexes, the local electron-withdrawing ability of
the amide group through the NH‚‚‚S hydrogen bond results
in a decrease in the electron density of S(pπ). Consequently,
this finding suggests that the intramolecular NH‚‚‚S hydrogen
bond decreases the electron density of S(pπ) coordinated to
platinum in this case and the lowest energy absorption band
largely shifts to a higher energy level.
The ∆ν(NH) values in the platinum complex 1, the
palladium complex 4, and the reported complexes are
summarized in Table 4. As compared to other metal
complexes, the relatively small ∆ν(NH) values in complexes
1 and 4 are similar to each other as the Mo(V),32 Hg(II),35
or Fe(III)29 complex and are ascribed to a weak interaction
(45) Jaffe, H. H. Chem. ReV. 1953, 53, 191-261.
1970 Inorganic Chemistry, Vol. 44, No. 6, 2005

Effects of the NH‚‚‚S Hydrogen Bond in Pt(II) Complexes
lecular NH‚‚‚S hydrogen bond decreases the electron density
of S(pπ) coordinated to platinum as well as the result of
UV-visible spectra.
Conclusions
2-(Acylamino)benzenethiolate and 2-(alkylcarbamoyl)-
benzenethiolate complexes of Pt(bpy) and Pd(bpy) having
an intramolecular NH‚‚‚S hydrogen bond, Pt(bpy)(S-2-Ph3-
CCONHC6H4)2 (1) and Pt(bpy)(S-2-t-BuNHCOC6H4)2 (3),
were synthesized, and their crystal structures were deter-
mined. The presence of a weak NH‚‚‚S hydrogen bond in
both complexes and Pd(bpy)(S-2-Ph3CCONHC6H4)2 (4) is
established by the observation of the temperature coefficients
of the NH signal in the 1H NMR spectra and the shifted NH
stretching of the amide groups in the IR spectra in chloroform
and in the solid state. The lowest energy absorption band in
complex 1 shows the high-energy shift by the effect of the
NH‚‚‚S hydrogen bond. In addition, the oxidation potential
in complex 1 shows the positive shift with a decrease of the
electron density for S(pπ) coordinated to platinum correlated
to the HOMO due to the NH‚‚‚S hydrogen bond.
Figure 5. Cyclic voltammograms of a 1.0 mM solution of (a) [Pt(bpy)-
(S-2-Ph3CCONHC6H4)2] (1) and (b) [Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2)
in tetrahydrofuran at room temperature. Scan rate: 100 mV/s.
Table 5. Cyclic Voltammetric Data of Pt(bpy)(Bis)thiolates Complexes
and Related Compoundsa
compound
Ep,a/V
E1/20/-/V E1/2-/2-/V
[Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1) +1.04
[Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2) +0.69(sh),
+0.79
-1.20
-1.05
-1.84
-1.88c
[Pt(bpy)(SC6H5)2]b
[Pt(bpy)Cl2]b
+0.80
+1.24
-1.14
-1.07
-1.79
-1.73
Experimental Section
a Measured in tetrahydrofuran (0.2 M NBu4PF6) versus SCE at 298 K
and a scan rate of 100 mV/s. b From ref 7. c Irreversible. Cathodic peak
potential.
Materials. All operations were performed under an argon
atmosphere. All solvents were dried and distilled under argon before
use. 2,2′-Dithiobis(N-phenyl-2,2,2-triphenylacetamide) and 2,2′-
dithiobis[N-(1,1-dimethyl ethyl)benzamide] were prepared by lit-
erature procedures. The syntheses of 2-triphenylacetylaminoben-
zenethiol, tetraethylammonium 2-triphenylacetylaminobenzenethiolate,
4-triphenylacetylaminobenzenethiol, and tetraethylammonium 4-t-
riphenylacetylaminobenzenethiolate were carried out using the same
previously reported procedure.40
Synthesis of [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1). Bis[2-(triph-
enylacetylamino)phenyl] disulfide (79 mg, 0.10 mmol) and NBu4-
BH4 (64 mg, 0.25 mmol) were suspended in tetrahydrofuran (5
mL). To the solution was added dropwise Pt(bpy)Cl2 (42 mg, 0.1
mmol) in dimethyl sulfoxide (DMSO, 3 mL). The yellow solution
changed to dark brown. Stirring was continued for an hour at room
temperature. The reaction mixture was acidified with HCl aqueous
solution and extracted with chloroform. The solution was washed
with 2% HCl aqueous solution, NaCl-saturated aqueous solution,
saturated NaHCO3 aqueous solution, and NaCl-saturated aqueous
solution. The organic layer was dried with anhydrous sodium sulfate
and concentrated under pressure. The obtained brown powder was
washed diethyl ether and dried under vacuo. The crude product
was reprecipitated from hot methanol and recrystallized from
acetone. Yield 53.7 mg (47%). mp 175 °C. Anal. Calcd for
C62H48N4O2PtS2‚CH3OH: C, 64.54; H, 4.47; N, 4.78. Found: C,
64.54; H, 4.25; N, 4.81. ESI-MS: m/z 1163 [M + Na]+. 1H NMR
(chloroform-d1): δ 9.33 (dd, 2H), 8.74 (s, 2H), 8.10 (td, 2H), 8.00-
8.02 (m, 4H), 7.46 (td, 2H), 7.40 (dd, 2H), 7.28 (m, 12H), 7.15
(m, 12H), 7.06 (tt, 6H), 6.83 (td, 2H), 6.51 (td, 2H).
Electrochemical Properties. The cyclic voltammograms
of the platinum complexes [Pt(bpy)(S-2-Ph3CCONHC6H4)2]
(1) and [Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2) in tetrahydro-
furan are shown in Figure 5. The redox potentials are listed
in Table 5. The first reduction is a one-electron process,
which is reversible for complexes 1 and 2. The value of the
first reduction potential is largely unaffected by the nature
of the thiolate and is close to the value of the first reduction
for Pt(bpy)Cl2. This suggests that the LUMO is mainly
localized on the bpy ligand.2 The values of the second
reduction potentials of complexes 1 and 2 are very similar
to each other and are close to that for Pt(bpy)Cl2 (Table 5).
These second reductions are a quasi-reversible process.
On the other hand, the oxidation is irreversible for
complexes 1 and 2. The value of the oxidation potential is
largely affected and in a manner different from that of the
reduction potential because the HOMO is mainly composed
of thiolate (π)/S(p)/Pt(d) orbital. The value of the oxidation
potential for complexes 1 and 2 manifests at +1.04 and
+0.79 V (versus SCE), respectively. The value for complex
2 is the same as that for Pt(bpy)(SC6H5)2 (+0.80 V versus
SCE).7 In contrast, the value for complex 1 shifts to largely
positive (∆E ) +0.2 V). The observed remarkable positive
shift is attributed to the intramolecular NH‚‚‚S hydrogen
bond. The contribution of NH‚‚‚S hydrogen bonding to the
positive shift of redox potential was proposed for native
metalloproteins as early as 1975,36,46 and this hypothesis is
supported by the model complexes. The oxidation potential
Ep,a values shift very positively with decreasing donor
capacity of the thiolate ligand. Consequently, the intramo-
Synthesis of [Pt(bpy)(S-4-Ph3CCONHC6H4)2] (2). The com-
plex was synthesized by the same method described above for the
synthesis of [Pt(bpy)(S-2-Ph3CCONHC6H4)2]. The crude complex
was precipitated from acetone. Yield 71%. mp > 250 °C. ESI-
1
MS: m/z 1163 [M + Na]+. H NMR (chloroform-d1): δ 9.85 (d,
2H), 8.07 (td, 2H), 8.01 (d, 2H), 7.54 (dt, 4H), 7.51 (td, 2H), 7.17-
7.34 (m, 30H), 6.99 (4H, dt).
Synthesis of [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3). The complex
was synthesized by the same method described above for the
(46) Carter, C. W., Jr. J. Biol. Chem. 1977, 252, 7802-7811.
Inorganic Chemistry, Vol. 44, No. 6, 2005 1971

Kato et al.
Table 6. Crystallographic Data for [Pt(bpy)(S-2-Ph3CCONHC6H4)2] (1)
and [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (3)
diffractometer using graphite-monochromated Mo KR radiation (λ
) 0.71075 Å) at 200 K. The basic crystallographic parameters for
1 and 3 are listed in Table 6. The structures were solved by direct
method with SIR9247 and expanded using Fourier techniques. The
absorption correction for both complexes was performed by
multiscan method. All non-hydrogen atoms were refined anisotro-
pically by the full-matrix least-squares method on F2 using
SHELXL-97.48 Hydrogen atoms were not refined. In complex 3,
one thiophenol ligand and a solvent acetone molecule are disordered
into two positions with site occupancy factors of each 0.500. All
calculations were carried out on SGI workstation using the teXsan49
crystallographic software package of the Molecular Structure Corp.
Molecular Orbital Calculations. Density functional theory
(DFT) calculations at Becke’s three-parameter hybrid functional
with the correlation functional of Lee, Yang, and Parr (B3LYP)
level50-52 for Pt(bpy)(S-2-t-BuCONHC6H4)2 were carried out on
the basis of the crystal structure of Pt(bpy)(S-2-Ph3CCONHC6H4)2
(1) and with the assumption of an idealized coplanar structure
between amide plane and thiophenol plane using the Gaussian 03
system of programs.53 The effective core potentials (ECP) of Hay
and Wadt with double-ú valence basis set (LanL2DZ)54 were used.
1‚2(CH3)2CO‚H2O
3‚(CH3)2CO
chemical formula
formula weight
C68H62N4O5S2Pt
1274.47
C35H42N4O3S2Pt
825.95
T/K
200(1)
200(1)
crystal system
monoclinic
monoclinic
lattice parameter
a/Å
b/Å
c/Å
â/deg
V/Å3
Z
16.522(4)
19.518(5)
17.644(3)
95.624(9)
5662(2)
4
30.881(4)
14.258(2)
19.371(2)
124.109(6)
7061(1)
8
space group
P21/n (No. 14)
1.495
25.99
C2/c (No. 15)
1.559
41.31
D
calc/g cm-3
µ/cm-1
reflns collected
38 690
32 649
ind reflns (Rint
R1 for I > 2σ(I)
wR2 for all data
)
12 689 (0.106)
0.0460
0.0545
8028 (0.031)
0.0219
0.0504
synthesis of [Pt(bpy)(S-2-Ph3CCONHC6H4)2]. The crude complex
was precipitated from acetone. Yield 80%. mp 200 °C. Anal. Calcd
for C32H36N4O2PtS2: C, 50.05; H, 4.73; N, 7.30. Found: C, 49.73;
H, 4.60; N, 7.31. ESI-MS: m/z 634.1 [M + Na]+. 1H NMR
(chloroform-d1): δ 9.77 (d, 2H), 8.14 (td, 2H), 8.09 (d, 2H), 7.92
(dd, 2H), 7.59 (td, 2H), 7.53 (dd, 2H), 7.40 (s, 2H), 6.96 (td, 2H),
6.86 (td, 2H), 1.35 (s, 18H).
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Area (A) (No.
12304040) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan. M.K. expresses his special
thanks for the center of excellence (21COE) program
“Creation of Integrated EcoChemistry of Osaka University”.
Synthesis of [Pd(bpy)(S-2-Ph3CCONHC6H4)2] (4). To a sus-
pension of Pd(bpy)Cl2 (47 mg, 0.14 mmol) and 2-triphenylacety-
laminobenzenethiol (112.3 mg, 0.28 mmol) in acetonitrile (12 mL)
was added triethylamine (40 µL). The solid slowly turned dark red.
After the mixture was stirred overnight, the solid was filtered off,
washed with methanol, and suction dried. The crude complex was
recrystallized from tetrahydrofuran. Yield 65%. mp 170 °C. Anal.
Calcd for C62H48N4O2PdS2‚1.5H2O: C, 69.04; H, 4.77; N, 5.19.
Found: C, 68.96; H, 4.76; N, 5.03. ESI-MS: m/z 1073 [M + Na]+.
1H NMR (chloroform-d1): δ 8.77 (d, 2H), 8.75 (s, 2H), 8.03 (dd,
2H), 7.93-8.00 (m, 4H), 7.39 (td, 2H), 7.35 (dd, 2H), 7.22 (m,
12H), 7.08 (m, 12H), 6.98 (tt, 6H), 6.80 (td, 2H), 6.44 (td, 2H).
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0490167
(47) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A. SIR92-A
program for crystal structure solution. J. Appl. Crystallogr. 1993, 27,
435.
(48) Sheldrick, G. M. SHELXL-97: Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1997.
(49) teXsan: Crystal Structure Analysis Program; Molecular Corp.: The
Woodlands, TX, 1985 and 1992.
1
Physical Measurements. H NMR spectra was obtained on a
JEOL GSX-400 spectrometer in chloroform-d1 or acetonitrile-d3
solution at 303 K. Tetramethylsilane (TMS) was used as the internal
reference for proton resonance. IR spectra were taken on a Jasco
FT/IR-8300 spectrometer. Samples were prepared as chloroform-
d1 solutions or KBr pellets. ESI-mass spectrometric analyses were
performed on a Finniganmat LCQ-MS instrument in methanol or
acetonitrile. Absorption spectra were recorded on a Shimadzu UV-
3100PC spectrophotometer using a 1-cm cell. The cyclic voltam-
mograms were recorded on a BAS 100B/W instrument with a three-
electrode system consisting of a glassy carbon working electrode,
a platinum-wire counter electrode, and a saturated calomel electrode
(SCE). The scan rate was 100 mV/s. The sample concentration was
1 mM in tetrahydrofuran, containing 0.2 M NBu4BF4 as supporting
electrolyte. Potentials were determined at room temperature versus
SCE as a reference.
(50) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100.
(51) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.
(52) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-789.
(53) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. C.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P.
Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J.
B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian03, revision
B.5; Gaussian, Inc.: Pittsburgh, PA, 2003.
Structure Determinations. The data collections for Pt(bpy)(S-
2-Ph3CCONHC6H4)2 (1) and Pt(bpy)(S-2-t-BuNHCOC6H4)2 (3)
were carried out on a Rigaku RAXIS-RAPID Imaging Plate
(54) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310.
1972 Inorganic Chemistry, Vol. 44, No. 6, 2005