Synthesis and reactivity of the five-membered cycloaurated complexes of 2-phenylthiazole

Article abstract of DOI:10.1016/S0020-1693(01)00432-7

2-Phenylthiazole (Hphtz) reacted with H[AuCl₄]·4H₂O to give the salt [H(Hphtz)][AuCl₄] (1), while the reaction of Hphtz with Na[AuCl₄]·2H₂O or AuCl₃·4H₂O afforded the adduct [AuCl₃(Hphtz-N)] (2). When the adduct 2 was heated in 1,2-dichloroethane in the presence of AgBF₄, cycloauration took place to produce [AuCl₂(phtz-C¹, N)] [phtz = 2-(2-thiazolyl)phenyl] (3). The reactivity of 3 towards Tl(acac) and PPh₃ was investigated.

Full text of DOI:10.1016/S0020-1693(01)00432-7

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Inorganica Chimica Acta 319 (2001) 203–206
Note
Synthesis and reactivity of the five-membered cycloaurated
complexes of 2-phenylthiazole
Hidenori Ieda, Hiroyuki Fujiwara, Yoshio Fuchita *
Department of Chemistry, Faculty of Sciences, Kyushu Uni6ersity at Ropponmatsu, Ropponmatsu, Chuo-ku, Fukuoka 810-8560, Japan
Received 23 October 2000; accepted 6 February 2001
Abstract
2-Phenylthiazole (Hphtz) reacted with H[AuCl4]·4H2O to give the salt [H(Hphtz)][AuCl4] (1), while the reaction of Hphtz with
Na[AuCl4]·2H2O or AuCl3·4H2O afforded the adduct [AuCl3(HphtzꢀN)] (2). When the adduct 2 was heated in 1,2-dichloroethane
in the presence of AgBF4, cycloauration took place to produce [AuCl2(phtzꢀC1, N)] [phtz=2-(2-thiazolyl)phenyl] (3). The
reactivity of 3 towards Tl(acac) and PPh3 was investigated. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Cyclometallation; Gold complexes; Thiazole complexes
fanyl)pyridine [11] or papaverine [12]. However, all the
above substrates, which give both types of cycloaurated
1. Introduction
complexes are definitely limited to the pyridine deriva-
tives. Recently we have finally succeeded in the cycloau-
ration of 1-ethyl-2-phenylimidazole, a ligand other than
Cyclometallation by gold(III) i.e. cycloauration is
believed to proceed through direct CꢀH bond activa-
tion of the heterosubstituted molecule. The first cy-
pyridine derivatives [13]. In this paper, we wish to
cloauration was established in 1989 with 2-phenyl-
report the cycloauration of 2-phenylthiazole, which is
pyridine by Constable and Leese [1]. However, in gen-
another example of cycloauration of a ligand other
eral this reaction is difficult to achieve and has not been
than pyridine derivatives.
widely explored. This is in sharp contrast to the well-es-
tablished chemistry on the cyclometallation by Pd(II) or
Pt(II) [2]. The cyclometallated complexes obtained so
2. Experimental
far by cycloauration can be classified into two cate-
gories. One is the complex having a terdentate N,N,C
chelate derived from 2,9-diphenyl-1,10-phenanthroline
[3], 4-(4-methoxyphenyl)-6-phenyl-2,2%-bipyridine [4], 6-
benzyl-2,2%-bipyridine [5] or 6-tert-butyl-2,2%-bipyridine
[5], and the other is the complex bearing a bidentate
N,C chelate formed by 2-benzylpyridine [6,7], 2-ben-
zoylpyridine [6], 2-anilinopyridine [8,9], 2-phenoxy-
pyridine [8], 2-(phenylsulfanyl)pyridine [8], 2-(2-thienyl)-
pyridine [10], 2-(3-thienyl) pyridine [10], 2-(alkylsul-
2.1. General procedures
The IR spectra were measured on a JASCO FT/IR-
420 spectrophotometer and 1H NMR spectra were
recorded on a JEOL JNM-GX-270 spectrometer using
tetramethylsilane as an internal standard. Melting
points were determined on a Yanaco MP-500D micro
melting-point apparatus and are uncorrected. Con-
ductivity measurements were carried out at 25°C on
a Toa Electronics CM-20E conductometer. 2-Phenyl-
thiazole was prepared according to the literature [14].
* Corresponding author. Tel./fax: +81-92-7264753.
E-mail address: fuchita@rc.kyushu-u.ac.jp (Y. Fuchita).
Starting
gold(III)
compounds,
H[AuCl4]·4H2O,
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00432-7

204
H. Ieda et al. / Inorganica Chimica Acta 319 (2001) 203–206
Na[AuCl4]·2H2O and AuCl3·4H2O were purchased
from Tanaka Kikinzoku Kogyo Co. Ltd. Other
reagents were obtained commercially and used without
purification.
pale yellowish white microcrystals, m.p. 231°C (dec.).
Anal. Found: C, 25.40; H, 1.42; N, 3.31. Calc. for
C9H6AuCl2NS: C, 25.25; H, 1.41; N, 3.27%. IR (KBr,
cm−1): 364, 310 (AuꢀCl). \M (1.0×10−3 mol dm−3
,
acetone): 0.1 S cm2 mol−1
.
2.2. Syntheses
2.2.4. [AuCl(phtzꢀC1,N)(acacꢀC3)] (4)
A dichloromethane solution (15 cm3) of Tl(acac)
(0.038 g, 0.124 mmol) was added to a suspension of 3
(0.050 g, 0.117 mmol) in the same solvent (15 cm3). The
resulting mixture was stirred for 13 h at r.t. under
shielding from the light and then filtered. The filtrate
was concentrated and diluted with hexane to give white
microcrystalline solids of complex 4 (0.047 g, 82%),
m.p. 176°C (dec.). Anal. Found: C, 34.15; H, 2.67; N,
2.83. Calc. for C14H13AuClNO2S: C, 34.20; H, 2.66; N,
2.85%. IR (KBr, cm−1): 1684 (CꢁO), 315 (AuꢀCl). \M
2.2.1. [H(Hphtz)][AuCl4] (1)
An ethanol solution (20 cm3) of 2-phenylthiazole
(Hphtz) (0.081 g, 0.502 mmol) was added to a solution
of H[AuCl4]·4H2O (0.100 g, 0.243 mmol) in the same
solvent (20 cm3). After the resulting yellow solution was
stirred at room temperature (r.t.) for 1 day, it was
concentrated and diluted with hexane to give yellow
microcrystals of complex 1 (0.108 g, 89%), m.p. 176°C.
Anal. Found: C, 21.71; H, 1.63; N, 2.83. Calc. for
C9H8AuCl4NS: C, 21.58; H, 1.61; N, 2.80%. IR (KBr,
cm−1): 355 (AuꢀCl). \M (1.0×10−3 mol dm−3, ace-
(1.0×10−3 mol dm−3, acetone): 0.6 S cm2 mol−1
.
tone): 163 S cm2 mol−1
.
2.2.5. [AuCl2(phtzꢀC1)(PPh3)] (5)
A solution of PPh3 (0.031 g, 0.118 mmol) in
dichloromethane (15 cm3) was added to a suspension of
3 (0.050 g, 0.117 mmol) in acetone (10 cm3). The
resulting suspension was stirred for 11 h. Then the
suspension was filtered off and the filter cake was
washed with acetone to give pale yellowish white solids
of 5 (0.068 g, 84%), m.p. 131°C. Anal. Found: C, 46.97;
H, 3.07; N, 2.03. Calc. for C27H21AuCl2NPS: C, 47.14;
H, 3.11; N, 2.01%. IR (KBr, cm−1): 319, 300 (AuꢀCl).
2.2.2. [AuCl3(HphtzꢀN)] (2)
Method (a). An acetonitrile solution (5 cm3) of 2-
phenylthiazole (0.432 g, 2.68 mmol) was added to an
aqueous solution (7.5 cm3) of Na[AuCl4]·4H2O (0.504
g, 1.16 mmol) at r.t. After 10 min, the precipitated
solids were filtered off and recrystallized from CH2Cl2–
diethyl ether to give an orange powder of complex 2
(0.453 g, 84%), m.p. 157°C. Anal. Found: C, 23.43; H,
1.45; N, 3.04. Calc. for C9H7AuCl3NS: C, 23.27; H,
1.52; N, 3.02%. IR (KBr, cm−1): 368 (AuꢀCl). \M
\
(5.0×10−4 mol dm−3, acetone): 5.0 S cm2 mol−1
.
M
(1.0×10−3 mol dm−3, acetone): 4.0 S cm2 mol−1
.
Method (b). An acetonitrile solution (6 cm3) of 2-
phenylthiazole (0.219 g, 1.36 mmol) was added to an
aqueous solution (17%, 30 cm3) of AuCl3·4H2O (0.505
g, 1.35 mmol) at r.t. After stirring for 16 h, the precip-
itates were filtered off and recrystallized from
dichloromethane and diethyl ether to give 2 (0.537 g,
86%).
Method (c). An aqueous acetonitrile suspension
(17%, 30 cm3) of the salt 1 (0.050 g, 0.099 mmol) was
stirred at r.t. for 16 h. The suspension was filtered off,
and the yellow filter cake was washed with water and a
small volume of ethanol to give complex 2 (0.022 g,
48%).
2.2.6. [AuCl(phtzꢀC1)(PPh3)2]BF4 (6)
Method (a). To a suspension of 3 (0.050 g, 0.117
mmol) in acetone (10 cm3), an acetone solution (10
cm3) of PPh3 (0.063 g, 0.241 mmol) and then NaBF4
(0.064 g, 0.586 mmol) were added. The resulting sus-
pension was heated at 60°C for 1 day, and then evapo-
rated to dryness. The residue was extracted with
dichloromethane, and the extract was concentrated and
diluted with diethyl ether to give 6 as pale yellow white
microcrystals (0.110 g, 94%), m.p. 181°C. Anal. Found:
C, 53.83; H, 3.61; N, 1.40. Calc. for C45H36AuBClF4-
NP2S: C, 53.83; H, 3.61; N, 1.40%. IR (KBr, cm−1):
312 (AuꢀCl), 1068 (BF−4 ). \M (1.0×10−3 mol dm−3
acetone): 166 S cm2 mol−1
,
.
2.2.3. [AuCl2(phtzꢀC1,N)] (3)
[phtz=2-(2-thiazolyl)phenyl]
Method (b). An acetone solution (10 cm3) of PPh3
(0.016 g, 0.062 mmol) and then solid NaBF4 (0.033 g,
0.294 mmol) were successively added to a suspension of
5 (0.040 g, 0.059 mmol) in acetone (8 cm3). After the
resulting mixture was heated at 60°C for 2 days, the
volatile materials were evaporated off. The residue was
extracted with dichloromethane, and the extract was
concentrated and diluted with diethyl ether to give 6 as
pale yellow powder (0.043 g, 72%).
1,2-Dichloroethane solution (10 cm3) of silver(I) te-
trafluoroborate (0.139 g, 0.714 mmol) was added to 2
(0.318 g, 0.684 mmol) in the same solvent (40 cm3).
This mixture was refluxed for 13 h and then evaporated
to dryness. The residue was extracted with acetonitrile
(100 cm3) and the extract was concentrated and diluted
with diethyl ether to afford complex 3 (0.193 g, 66%) as

H. Ieda et al. / Inorganica Chimica Acta 319 (2001) 203–206
205
3 showed only six and well-separated aromatic protons
(Table 1). This fact indicated that metallation occurred
on the 2-phenylthiazole moiety in 3. It has been known
that gold(III) species sometimes attack carbon atoms in
the heterocycles of 1-phenylpyrazole [17], 2-(2-
thienyl)pyridine [10] and 6-(2-thienyl)-2,2%-bipyridine
[18] to produce aurated heterocycles. However, the
1H–1H COSY spectrum of 3 revealed that two thiazole-
ring protons H4% and H5% appeared at l 8.38 (d) and
8.19 (d) as an AB pattern. Moreover, in the far-IR
spectrum two strong bands due to the stretching mode
of AuꢀCl bond trans to nitrogen and carbon atoms
were observed at 364 and 310 cm−1, respectively. These
results and the elemental analysis confirmed the five-
membered cycloaurated structure of 2-phenythiazole in
3 as shown in Scheme 1.
3. Results and discussion
The reaction procedures in this study are summarized
1
in Scheme 1. The H NMR spectral data of the new
compounds are listed in Table 1.
2-Phenylthiazole (Hphtz) reacted with H[AuCl4]·
4H2O in ethanol to give the salt [H(Hphtz)][AuCl4],
whereas the reaction of Hphtz with Na[AuCl4]·2H2O or
AuCl3·4H2O in aqueous acetonitrile afforded the ad-
duct [AuCl3(Hphtz–N)] (2). The adduct 2 was also
obtained from the salt 1 in aqueous acetonitrile. Such
the conversion has already been found in the similar
salts of 2-phenoxy- and 2-(phenylsulfanyl)-pyridine [8],
and 1-ethyl-2-phenylimidazole [13]. In the far-IR spec-
trum, the adduct 2 showed only one strong band at 368
cm−1, attributable to the overlapping w(AuꢀCl) fre-
quency trans to the thiazole–nitrogen and chloro ligand
[15]. The absence of the characteristic band owing to
w(AuꢀCl) frequency of the band trans to sulfur (which
appears around 310 cm−1) [16], excludes the possibility
of thiazole–sulfur coordination.
The cycloaurated complex 3 reacted with thallium(I)
acetylacetonate to give [AuCl(phtzꢀC1, N)(acacꢀC3)]
1
(4). In the H NMR spectrum of 4, besides the signals
due to the cycloaurated 2-phenylthiazole moiety, both
methyl and methine protons of the acac ligand ap-
peared as singlets at l 2.44 and 4.58, respectively. As
far as the IR spectrum of 4 is concerned, w(CꢁO)
frequency of the acac ligand appeared as only one band
at 1684 cm−1 and a w(AuꢀCl) frequency trans to car-
bon atom was observed at 315 cm−1. On the basis of
these data, together with the conductivity measurement
(\M 0.6 S cm2 mol−1), complex 4 was assigned to the
four-coordinate neutral complex where the acac ligand
is metallated at C3 as illustrated in Scheme 1.
When the adduct 2 was heated in 1,2-dichloroethane
in the presence AgBF4, coordinated 2-phenylthiazole in
2 cyclometallated with the central gold(III) to give
[AuCl2(phtzꢀC1, N)] [phtz=2-(2-thiazolyl)phenyl] (3)
1
in 66% yield. While the H NMR spectrum of adduct 2
exhibited seven protons in the aromatic region, that of
Complex 3 reacted with an equimolar amount of
PPh3 to give [AuCl2(phtzꢀC1)(PPh3)] (5). In the far-IR
spectrum of 5, two bands characteristic of w(AuꢀCl)
frequencies trans to PPh3 and trans to phenylene carbon
were observed at 319 and 300 cm−1, respectively. The
molar conductivity (\M 5.0 S cm2 mol−1) showed that
5 is a neutral complex. These facts clearly showed that
with an equimolar amount of PPh3 the CꢀN chelate
ring in 5 easily opens. Such the easy opening of the
chelate ring was also found in the five-membered cy-
cloaurated complexes [AuCl2(CꢀN)] (CꢀN denotes cy-
cometallated ligand) derived from azobenzene [19] and
4-butyl-N-(2,3,4-trimethoxybenzylidene)aniline
[15],
whereas the chelate rings formed from 2-(2-thienyl)-
and 2-(3-thienyl)-pyridine, 1-ethyl-2-phenylimidazole
and N,N-dimethylbenzylamine remained unchanged af-
fording cationic species [AuCl(CꢀN)(PPh3)]+ [10,13,19].
The cyclometallated ring finally opened when 3 was
treated with two molar equivalents of PPh3. Thus in the
presence of NaBF4 [AuCl(phtzꢀC1)(PPh3)2]BF4 (6) was
obtained. The AuꢀCl stretching band at 312 cm−1
indicated the trans arrangement of the carbon and the
chloride atoms.
In conclusion, here we have showed the second ex-
ample of the cycloauration of a ligand other than
pyridine derivatives.
Scheme 1. (i) H[AuCl4]·4H2O; (ii) Na[AuCl4]·2H2O or AuCl3·4H2O;
(iii) aqueous CH3CN (17%); (iv) AgBF4; (v) T1(acac); (vi) PPh3; (vii)
2PPh3, NaBF4; (viii) PPh3, NaBF4.

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H. Ieda et al. / Inorganica Chimica Acta 319 (2001) 203–206
Table 1
1H NMR spectral data of the new complexes a
Complex
Thiazolyl moiety b
Phenyl moiety
Others
1
7.80 (d, 1H, H5%) c
7.55–7.5 (c, 3H, m, p-Ph)
7.95–8.0 (c, 2H, o-Ph) d
7.95–8.0 (c, 1H, H4%) d
2
3
7.79 (d, 1H, H5%) e
8.07 (d, 1H, H4%) e
7.6–7.75 (c, 3H, m, p-Ph)
7.95–8.0 (c, 2H, o-Ph) d
8.19 (d, 1H, H5%) c
8.38 (d, 1H, H4%) c
7.39 (dt, 1H, H4) f,g
7.47 (dt, 1H, H5) f,g
7.76 (d, 1H, H3) f
7.89 (dd, 1H, H6) f,g
4
7.54 (d, 1H, H5%) e
8.40 (d, 1H, H4%) e
7.35–7.45 (c, 2H, H4, H5)
7.62 (dd, 1H, H3) g,h
7.80 (dd, 1H, H6) g,h
2.44 (s, 6H, acacꢀMe)
4.58 (s, 1H, acacꢀCH)
5
6
7.80 (d, 1H, H5%) c
8.19 (d, 1H, H4%) c
7.0–7.05 (c, 2H, H4, H5)
7.3–7.35 (c, 2H, H3, H6)
7.4–7.65 (c, 15H, PPh3)
7.35–7.65 (c, 30H, PPh3)
7.87 (d, 1H, H5%) c
8.49 (d, 1H, H4%) c
6.8–6.85 (m, 1H, H5)
6.9–7.0 (c, 2H, H3 and H4)
7.2–7.25 (m, 1H, H6)
a Measured in DMSO-d6 except for 2 and 4 (CDCl3) at 270 MHz and at 23°C; l in ppm with respect to SiMe4; s, singlet; d, doublet; dd, double
doublet; dt, double triplet; m, multiplet; c, complex.
1
1
b Lower field resonance was tentatively assigned to H4% in consideration of the H NMR data of thiazole or 2-aminothiazole [20]. H NMR data
of free 2-phenylthiazole in CDCl3 are as follows; l 7.33 [d, H5%, 3J(HH)=3.4 Hz], 7.4–7.5 [c, m, p-H’s of Ph], 7.87 [d, H4%, 3J(HH)=3.4 Hz],
7.95–8.0 [c o-H’s of Ph].
c 3J(HH)=3.5 Hz.
d Overlapping to each other.
e 3J(HH)=4.0 Hz.
f 3J(HH)=7.7 Hz.
g 3J(HH)=1.5 Hz.
h 3J(HH)=7.3 Hz.
[9] M. Nonoyama, K. Nakajima, Polyhedron 16 (1997) 4039.
[10] Y. Fuchita, H. Ieda, S. Wada, S. Kameda, M Mikuriya, J.
Acknowledgements
Chem. Soc., Dalton Trans. (1999) 4431.
[11] J. Vicente, M.T. Chicote, M.I. Lozano, S. Huertas,
H.I. was supported by the Sasakawa Scientific Re-
search Grant for The Japan Science Society.
Organometallics 18 (1999) 753.
[12] M. Nonoyama, Synth. React. Inorg. Met.-Org. Chem. 29 (1999)
119.
[13] Y. Fuchita, H. Ieda, M Yasutake, J. Chem. Soc., Dalton Trans.
(2000) 271.
References
[14] H. Erlenmeyer, C. Becker, E. Sorkin, H. Block, E. Suter, Helv.
Chim. Acta 30 (1947) 2058.
[15] J. Vicente, M.D. Bermudez, F.J. Carrion, P.G. Jones, Chem.
Ber. 129 (1996) 1301.
[16] (a) K.S. Liddle, C. Parkin, J. Chem. Soc., Chem. Commun.
(1976) 26;
(b) D. Rasala, Bull. Soc. Chim. Fr. 129 (1992) 79;
(c) R.J. Puddephatt, in: G. Wilkinson (Ed.), Comprehensive
Coordination Chemistry, vol. 5, Pergamon, Oxford, 1987, p. 861.
[17] G. Minghetti, M.A. Cinellu, M.V. Pinna, S. Stoccoro, A. Zucca,
M. Manessero, J. Organomet. Chem. 568 (1998) 225.
[18] (a) E.C. Constable, R.P.G. Henny, P.R. Raithby, L.R. Sousa,
Angew. Chem. Int., Ed. Engl. 30 (1991) 1363;
(b) E.C. Constable, L.R. Sousa, J. Organomet. Chem. 427 (1992)
125.
[19] J. Vicente, M.T. Chicote, M.D. Bermudez, J. Organomet. Chem.
268 (1984) 191.
[20] N.S. Bhacca, D.P. Hollis, L.F. Johnson, E.A. Pier (Eds.), NMR
Catalog, High Resolution NMR Spectra of Organic Com-
pounds, vol. 2, The National Press, USA, 1963.
[1] E.C. Constable, T.A. Leese, J. Organomet. Chem. 363 (1989)
419.
[2] (a) M.I. Bruce, Angew. Chem., Int. Ed. Engl. 16 (1977) 73;
(b) I. Omae, Chem. Rev. 79 (1979) 287;
(c) I. Omae, Coord. Chem. Rev. 32 (1980) 235;
(d) G.R. Newkome, W.E. Puckett, V.K. Gupta, G.E. Kiefer,
Chem. Rev. 86 (1986) 451.
[3] C.W. Chan, W.T. Wong, C.M. Che, Inorg. Chem. 33 (1994)
1266.
[4] H.O Liu, T.C. Cheung, S.M. Peng, C.M. Che, J. Chem. Soc.,
Chem. Commun. (1995) 1787.
[5] M.A. Cinellu, A. Zucca, S. Stoccoro, G. Minghetti, M. Man-
assero, M. Sansoni, J. Chem. Soc., Dalton Trans. (1996) 4217.
[6] Y. Fuchita, H. Ieda, Y. Tsunemune, J. Kinoshita-Kawashima,
H. Kawano, J. Chem. Soc., Dalton Trans. (1998) 791.
[7] M.A. Cinellu, A. Zucca, S. Stoccoro, G. Minghetti, M. Man-
assero, M. Sansoni, J. Chem. Soc., Dalton Trans. (1995) 2865.
[8] Y. Fuchita, H. Ieda, A. Kayama, J. Kinishita-Nagaoka, H.
Kawano, S. Kameda, M. Mikuriya, J. Chem. Soc., Dalton
Trans. (1998) 4095.
.