Synthesis and characterization of mononuclear and tetranuclear palladium(II) complexes with 2-(phenylmethyleneamino)benzenethiolate

Article abstract of DOI:10.1016/S0020-1693(02)01474-3

Two palladium(II) complexes, [Pd(Hphbt-N,S)₂] (1; Hphbt=2-(phenylmethyleneamino)benzenethiolate) and [Pd₄(phbt-C,N,S)₄] (2), were newly prepared. X-ray and ¹H NMR studies indicated the presence of Pd?H-C interaction in the mononuclear 1, which is assumed to play an important role in the cyclometalation reaction leading to the tetranuclear structure in 2.

Full text of DOI:10.1016/S0020-1693(02)01474-3

Inorganica Chimica Acta 348 (2003) 217Á220
/
www.elsevier.com/locate/ica
Note
Synthesis and characterization of mononuclear and tetranuclear
palladium(II) complexes with 2-
(phenylmethyleneamino)benzenethiolate
Tatsuya Kawamoto *, Isoroku Nagasawa 1, Yoshihiko Kushi 2, Takumi Konno
Department of Chemistry, Graduate School of Science, Osaka University, 1-16 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
Received 1 July 2002; accepted 4 November 2002
Abstract
Two palladium(II) complexes, [Pd(Hphbt-N,S)2] (1; Hphbtꢀ2-(phenylmethyleneamino)benzenethiolate) and [Pd4(phbt-
/
C,N,S)4] (2), were newly prepared. X-ray and 1H NMR studies indicated the presence of PdÁ Á ÁHÃ
/
C interaction in the mononuclear
1, which is assumed to play an important role in the cyclometalation reaction leading to the tetranuclear structure in 2.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Palladium(II) complexes; C,N,S-ligand complexes; Crystal structures; MetalÁligand interaction
/
1. Introduction
In this context, it is worthwhile to investigate whether
a similar cyclometalation reaction could take place for
palladium(II) complexes with a flexible pendant arm,
instead of the rigid 1-naphthyl group in [Pd(H1-nabz-
N,S)2]. In this paper, we report on the synthesis and
structural characterization of the mononuclear palla-
dium(II) complex having phenyl groups as a pendant
arm, [Pd(Hphbt-N,S)2] (1), together with that of its
cyclometalation product [Pd4(phbt-C,N,S)4] (2).
The chemistry of the activation of CÃ
undoubtedly one of the most advanced areas. In the
field of CÃH activation, the importance of the three-
center two-electron agostic interaction has been well
recognized through many examples [1]. On the other
hand, recently, there is an increasing body of evidence
which shows interactions between electron-rich metal
centers and hydrogen atoms, being hydrogen bonding of
the three-center four-electron in character [2]. Pre-
viously, we reported that the hydrogen bonding-like
/
H bonds is
/
PdÁ Á ÁHÃ
/
C interaction in the mononuclear palladium(II)
2. Experimental
complex, [Pd(H1-nabz-N,S)2], which is the precursor of
the thiolato-bridged tetranuclear palladium(II) complex,
[Pd4(1-nabz-C,N,S)4], plays an important role in the
cyclometalation reaction [3]. However, the recognition
All manipulations were carried out under an argon
atmosphere using standard Schlenk techniques. Re-
agents were commercial samples and were not purified
further. The compound 2-phenylbenzothiazoline was
prepared by literature methods [4].
for the hydrogen bonding-like MÁ Á ÁHÃ
/C interaction in
cyclometalation reaction is still not enough.
The UVÁVis spectra were measured on a JASCO V-
/
570 spectrophotometer. The 1H NMR spectra were
measured on a JEOL EX 270 instrument using tetra-
* Corresponding author. Tel.: ꢂ
/
81-6-6850 5766; fax: ꢂ81-6-6850
/
5785.
methylsilane as the internal standard (dꢀ
were measured on a JASCO FT/IR-5000 instrument
(4000Á
400 cmꢁ1) using the Nujol mulls. Elemental
analyses were performed at Osaka University.
/
0). IR spectra
E-mail address: kaw@ch.wani.osaka-u.ac.jp (T. Kawamoto).
1
Present address: Department of Chemistry, Fukuoka University
of Education, Akama 729-1, Munakata, Fukuoka 811-4192, Japan.
/
2
Emeritus Professor of Osaka University.
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01474-3

218
T. Kawamoto et al. / Inorganica Chimica Acta 348 (2003) 217Á220
/
2.1. Synthesis
2.2. X-ray structure determination
Intensity data were collected on a Mac Science MXC3
diffractometer with Mo Ka radiation at r.t. u Á
/
2u scans
2.1.1. Synthesis of bis[2-
(phenylmethyleneamino)benzenethiolato]palladium(II)
[Pd(Hphbt-N,S)2] (1)
To an ethanol solution (20 cm3) of 2-phenylben-
zothiazoline (0.43 g, 2.0 mmol) was added palladium(II)
acetate (0.22 g, 1.0 mmol). The reaction mixture was
refluxed for 20 min and cooled in a refrigerator over-
were employed; no significant decomposition of the
crystal occurred during the data collection. The struc-
tures of complexes 1 and 2 were solved by direct
methods using SIR 92 [5] and refined anisotropically
for all non-hydrogen atoms with full-matrix least-
squares calculations. The solution and refinement pro-
cedures were made by the use of the CRYSTAN-GM
night. The redÁbrown precipitate, which was spectro-
/
software package [6]. Crystallographic data: for 1×
3C5H12; C29.3H28N2PdS2, fwꢀ578.71, monoclinic,
space group C2/c, aꢀ27.82(2), bꢀ18.269(6), cꢀ
118.70(4)8, Vꢀ7446(6) A , Zꢀ
1.55 g cmꢁ3, m(Mo Ka)ꢀ1.22 mmꢁ1, crystal
size 0.45ꢃ0.40ꢃ0.40 mm, 4380 observed reflections
[I ꢀ2.0s(I)] used in the refinement, Rꢀ0.045, Rwꢀ
0.051 and goodness-of-fitꢀ2.76. For 2×Et2O;
C56H46N4OPd4S4, fwꢀ1344.95, monoclinic, space
group P21/n, aꢀ19.928(3), bꢀ17.526(2), cꢀ14.583(2)
4, Dcalc 1.76 g
1.57 mmꢁ1, crystal size 0.45ꢃ
0.20 mm, 7433 observed reflections [I ꢀ2.0s(I)]
used in the refinement, Rꢀ0.050, Rwꢀ0.053 and
goodness-of-fitꢀ2.46.
/2/
scopically pure (1H NMR), was collected by filtration
and dried in vacuo. Yield, 0.34 g (64%). This crude
/
/
/
/
precipitate (0.10 g) was recrystallized from chloroformÁ
/
3
˚
˚
16.699(6) A, bꢀ
/
/
/12,
diethyl ether (yield, 0.04 g). Crystals suitable for X-ray
diffraction were grown by slow diffusion of pentane into
a 1,2-dichloroethane solution of 1. Found: C, 55.06; H,
Dcalc
ꢀ
/
/
/
/
/
/
/
3.68; N, 4.97%. Calc. for C26H20N2PdS2×
/
1/3CHCl3: C,
55.41; H, 3.59; N, 4.91%. IR: nmax cmꢁ1 (Nujol): 1599
/
/
/
1
(CÄ
Jꢀ
7.4, Caryl
7.27 (4H, t, Jꢀ
1.2, Caryl H), 6.83 (2H, dt, Jꢀ
/
N). H NMR (CDCl3, 270 MHz): dꢀ
/
7.95 (4H, d,
N), 7.50 (2H, t, Jꢀ
7.9 and 1.3, Caryl H),
H), 7.05 (2H, dt, Jꢀ7.5 and
7.7 and 1.3, Caryl H)
Vis:
/
/
/
/
7.3, Caryl
H), 7.43 (2H, dd, Jꢀ
7.7, Caryl
Ã
/
H), 7.80 (2H, s, CHÄ
/
/
3
˚
˚
A, bꢀ
cmꢁ3, m(Mo Ka)ꢀ
0.35ꢃ
/
94.68(1)8, Vꢀ
/
5076(1) A , Zꢀ
/
ꢀ
/
Ã
/
/
Ã
/
/
/
/
Ã
/
/
/
/
Ã
/
/
Ã
/
/
/
and 6.57 (2H, d, Jꢀ
/
8.2 Hz, Caryl
Ã
/
H). UVÁ
/
/
nmax(CHCl3) 103 cmꢁ1 [log(o dm3 molꢁ1 cmꢁ1)]: 22.6
(3.61).
3. Results and discussion
2.1.2. Synthesis of tetrakis[2-
(phenylmethyleneamino)benzenethiolato-
The reaction of 2-phenylbenzothiazoline with palla-
dium(II) acetate in a molar ratio of 2:1 in ethanol gave a
red-brown complex, [Pd(Hphbt-N,S)2] (1) (Scheme 1).
When 1 was treated with an equimolar amount of
palladium(II) acetate in ethanol, a brown powder was
precipitated. This powder was purified by a silica gel
C,N,S]tetrapalladium(II) [Pd4(phbt-C,N,S)4] (2)
To a suspension of crude complex 1 (0.22 g, 0.41
mmol) in ethanol (20 cm3) was added an equimolar
amount of palladium(II) acetate (0.092 g, 0.41 mmol).
The mixture was refluxed for 1 h and cooled to room
temperature (r.t.). The fine brown precipitate (0.16 g)
was collected by filtration and dissolved in CH2Cl2 (20
cm3). The solution was purified by chromatography on
a silica gel (230Á400 mesh) column, eluting with
/
CH2Cl2. The first band, which corresponds to 2, was
collected, and removal of CH2Cl2 under reduced pres-
sure yielded a red powdery solid. This product was then
washed with diethyl ether. Yield, 0.03 g (22% based on
Pd). Crystals suitable for X-ray diffraction were grown
by slow diffusion of diethyl ether into a chloroform
solution of 2. Found: C, 49.64; H, 3.41; N, 4.44%. Calc.
for C52H36N4Pd4S4×
4.17%. IR: nmax cmꢁ1 (Nujol): 1586 (CÄ
(CDCl3, 270 MHz): dꢀ7.65Á7.60 (4H, m, Caryl
7.34 (4H, s, CHÄN), 7.11 (4H, d, Jꢀ6.9 Hz, Caryl
7.03Á6.97 (16H, m, Caryl H), and 6.90Á
Caryl
/
C4H10O: C, 50.01; H, 3.45; N,
1
/N). H NMR
/
/
Ã
/
H),
/
/
Ã
/
H),
/
Ã
/
/
6.82 (8H, m,
Ã
/
H). UVÁ
/
Vis: nmax(CHCl3) 103 cmꢁ1 [log(o dm3
molꢁ1 cmꢁ1)]: 19.8(sh) (3.84), 21.8 (3.97) and 29.4
(4.85).
Scheme 1. Synthetic scheme of complexes.

T. Kawamoto et al. / Inorganica Chimica Acta 348 (2003) 217Á
/
220
219
column chromatography to isolate a red complex,
[Pd4(phbt-C,N,S)4] (2). Complexes 1 and 2 were char-
plexes. However, the lower-field shift for 1 is not so
large as the shift (d 9.28) observed for [Pd(H1-nabz-
N,S)2] [3]. Thus, it is considered that 1 has a weaker
1
acterized by H NMR, IR and UVÁ
/
Vis spectroscopies,
besides elemental analyses, and their molecular struc-
tures were determined by single-crystal X-ray analyses.
Crystal 1 contains two crystallographically indepen-
dent, yet nearly identical, complex molecules. One has a
palladium atom (Pd(1)) in a general position, while the
palladium atom (Pd(2)) of the other molecule locates on
a twofold axis; the former molecule is selected in Fig. 1.
The coordination geometry at the palladium atom in 1 is
a slightly distorted square planar with a cis arrangement
of the sulfur and nitrogen atoms. The dihedral angles
between the two PdNS planes are 7(6)8 for Pd(1) and
PdÁ Á ÁHÃ
/
C interaction compared with [Pd(H1-nabz-
N,S)2], owing to the increase of freedom of the pendant
arm, which is compatible with the X-ray analytical
result.
The asymmetric unit of 2 consists of one formula unit,
and all palladium atoms are crystallographically inequi-
valent. As shown in Fig. 2, the core of 2 consists of an
eight-membered ring of alternating Pd and S atoms.
This structure is the same as that of [Pd4(1-nabz-
C,N,S)4], but both complexes are not isomorphous
[3]. The coordination environment about each palla-
dium atom can be described as a square planar having
two sulfur, one imine nitrogen, and one aryl carbon
donor atoms. Consequently, the Schiff base ligand acts
7(5)8 for Pd(2). The PdÃ
/
S and PdÃ
/
N distances, which
˚
range from 2.256(4) to 2.267(4) A and from 2.089(9) to
˚
2.096(8) A, respectively, compare well with those
observed in the related square planar palladium(II)
complexes [3,7]. A closer examination of the structure
as a rare C,N,S-chelate. The PdÃ
/
C distances being from
2.003(12) to 2.027(13) A and the PdÃN distances being
from 2.032(10) to 2.036(10) A are quite normal [3,9].
The PdÃSchelating distances trans to carbon are longer
than the PdÃSbridging distances trans to nitrogen (av.
PdÃSchelating
˚
/
of 1 reveals the interesting intramolecular PdÁ Á ÁHÃ
interaction between the metal center and the ortho
aromatic CÃH with the average PdÁ Á ÁH distance of
2.65(6) A, though it is slightly longer than the corre-
/C
˚
/
/
/
˚
˚
A
/
ꢀ
/
2.371(4)
and av. PdÃ
/
Sbridging
ꢀ
/
˚
sponding distance (2.57(7) A) in the closely related
˚
2.303(4) A), which is attributed to trans influence of
[Pd(H1-nabz-N,S)2] having 1-naphthyl groups as a
pendant arm [3].
1
The H NMR spectrum of 1 in CDCl3 shows a half-
the coordinated carbon of the cyclometalated ligand.
The Pd(1)Ã
/
Pd(2) and Pd(3)Ã
/
Pd(4) distances are 3.299(2)
and 3.334(2) A, respectively, showing the absence of any
Pd bonding. These distances are longer than the
˚
set of protons corresponding to its C2 symmetrical
structure. The resonances for the ortho protons of
phenyl groups of 1 are observed at relatively lower-field
(d 7.95) in the aromatic region [8]. This means the
PdÃ
/
˚
corresponding distances (3.180(1) A) found in [Pd4(1-
1
nabz-C,N,S)4] [3]. In the H NMR spectrum of 2 in
CDCl3, only one set of well-resolved resonances is
observed for the four phbt ligands in the complex.
This result suggests that the D2 symmetrical tetranuclear
found in crystal is retained in solution.
presence of a weak PdÁ Á ÁHÃ
/
C interaction (three-center
four-electron), rather than an agostic interaction (three-
center two-electron), which may influence the reactivity
of mononuclear complexes leading to tetranuclear com-
Fig. 1. Molecular structure of one of the independent molecules of
[Pd(Hphbt-N,S)2] (1) (30% probability ellipsoids). Selected bond
Fig. 2. Molecular structure of [Pd4(phbt-C,N,S)4] (2) (30% prob-
˚
distances (A) and angles (8): Pd(1)Ã
/
S(1) 2.267(4), Pd(1)Ã
N(2) 2.095(8); S(1)ÃPd(1)Ã
N(1) 84.0(3), S(1)ÃPd(1)Ã
N(1) 172.4(3), S(2)ÃPd(1)ÃN(2) 83.8(3), N(1)Ã
102.3(4).
/
S(2)
S(2)
ability ellipsoids). Hydrogen atoms are omitted for clarity. Selected
˚
2.256(4), Pd(1)Ã
90.3(2), S(1)ÃPd(1)Ã
Pd(1)Ã
/
N(1) 2.089(9), Pd(1)Ã
/
/
/
bond distances (A) and angles (8) (average): PdÃ
/
Schelating 2.371(4), PdÃ
/
/
/
/
/
N(2) 172.4(3), S(2)Ã
/
Sbridging 2.303(4), PdÃ
Sbridging 99.8(2), Schelating
Sbridging N 175.6(4), Sbridging
PdÃ
/
N 2.034(11), PdÃ
PdÃN 84.6(4), Schelating
PdÃC 93.7(4), NÃ
/
C 2.011(13); Schelating
PdÃC 165.4(4),
PdÃC 82.0(5).
Ã
/
PdÃ
/
/
/
/
/
Pd(1)ÃN(2)
/
Ã
/
/
Ã
/
/
Ã
/
/
Ã
/
/
/
/

220
T. Kawamoto et al. / Inorganica Chimica Acta 348 (2003) 217Á220
/
1
1789;
In summary, it was found based on X-ray and H
NMR studies that there exists the hydrogen bonding-
like interaction between palladium atom and ortho
(b) I.C.M. Wehman-Ooyevaar, D.M. Grove, H. Kooijman, P.
van der Sluis, A.L. Spek, G. van Koten, J. Am. Chem. Soc. 114
(1992) 9916;
aromatic CÃ
converted to the tetranuclear structure in 2 having
PdÃC bonds, it is reasonable to assume that the
C interaction plays an important role in the
/H in the mononuclear 1. Since 1 was
(c) A. Albinati, F. Lianza, P.S. Pregosin, B. Muller, Inorg. Chem.
¨
33 (1994) 2522;
/
(d) L. Brammer, D. Zhao, F.T. Ladipo, J. Braddock-Wilking,
Acta Crystallogr., B 51 (1995) 632;
PdÁ Á ÁHÃ
/
cyclometalation reaction even in the present flexible
system. The results presented here may be deeply
(e) E. Bouwman, R.K. Henderson, A.K. Powell, J. Reedijk,
W.J.J. Smeets, A.L. Spek, N. Veldman, S. Wocadlo, J. Chem.
Soc., Dalton Trans. (1998) 3495.
correlated to the studies on understanding the CÃ
/
H
activation during the cyclometalation reaction in palla-
[3] T. Kawamoto, I. Nagasawa, H. Kuma, Y. Kushi, Inorg. Chem.
35 (1996) 2427.
dium(II) complexes [10].
[4] T. Kawamoto, H. Kuma, Y. Kushi, Bull. Chem. Soc. Jpn. 70
(1997) 1599.
[5] SIR 92, A. Altomare, G. Cascarano, C. Giacovazzo, A. Gua-
gliardi, J. Appl. Crystallogr. 26 (1993) 343.
[6] CRYSTAN-GM, A Computer Program for the Solution and
4. Supplementary material
Refinement of Crystal Structures for X-ray Diffraction Data,
MAC Science Corporation, Yokohama, 1994.
[7] T. Kawamoto, Y. Kushi, J. Chem. Soc., Dalton Trans. (1992)
3137.
Tables of all final coordinates and thermal para-
meters, bond lengths, bond angles, hydrogen atom
coordinates and tables of observed and calculated
structure factors are available from the authors.
[8] The value of dꢀ7.95 (4H) is considered the average of chemical
/
shifts of two ortho-hydrogens of the pendant phenyl
groups.
[9] B. Schreiner, R. Urban, A. Zografidis, K. Sunkel, K. Polborn, W.
¨
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