First intramolecular aromatic substitution by gold(III) of a ligand other than pyridine derivatives. Synthesis and crystal structure of the novel five-membered cycloaurated complex of 1-ethyl-2-phenylimidazole

Article abstract of DOI:10.1039/a908048a

Reactions of gold(III) compounds, AuCl₃·4H₂O and HAuCl₄·4H₂O, with 2-phenyl-1H-imidazole (Hpi) and 1-ethyl-2-phenylimidazole (Hepi) have been performed under various reaction conditions: Hpi afforded only the salt [H(Hpi)][AuCl₄], while Hepi produced both the salt [H(Hepi)][AuCl₄] and the adduct [AuCl₃(Hepi)]. Cycloauration of Hepi, the first example of cycloauration of a substrate other than pyridine derivatives, has been established by the formation of [AuCl₂(epi-C¹,N)] [epi = 2-(1-ethyl-2-imidazolyl)phenyl] from the reaction between the adduct [AuCl₃(Hepi)] and AgBF₄. The cyclometallated structure of Hepi has been confirmed by the X-ray crystallographic study of a derivative [AuCl(epi-C¹,N)(PPh₃)]PF₆. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a908048a

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First intramolecular aromatic substitution by gold(III) of a ligand
other than pyridine derivatives. Synthesis and crystal structure of
the novel five-membered cycloaurated complex of 1-ethyl-2-phenyl-
imidazole
Yoshio Fuchita,*a Hidenori Iedaa and Mikio Yasutakeb
a Division of Molecular Chemistry, Graduate School of Science,
Kyushu University at Ropponmatsu, Chuo-ku, Fukuoka 810-8560, Japan.
E-mail: fuchita@rc.kyushu-u.ac.jp
b Institute for Fundamental Research of Organic Chemistry, Kyushu University, Hakozaki,
Higashi-ku, Fukuoka 812-8581, Japan
Received 6th October 1999, Accepted 3rd December 1999
Reactions of gold() compounds, AuCl3ؒ4H2O and HAuCl4ؒ4H2O, with 2-phenyl-1H-imidazole (Hpi) and
1-ethyl-2-phenylimidazole (Hepi) have been performed under various reaction conditions: Hpi afforded only
the salt [H(Hpi)][AuCl4], while Hepi produced both the salt [H(Hepi)][AuCl4] and the adduct [AuCl3(Hepi)].
Cycloauration of Hepi, the first example of cycloauration of a substrate other than pyridine derivatives, has
been established by the formation of [AuCl2(epi-C1,N)] [epi = 2-(1-ethyl-2-imidazolyl)phenyl] from the reaction
between the adduct [AuCl3(Hepi)] and AgBF4. The cyclometallated structure of Hepi has been confirmed by
the X-ray crystallographic study of a derivative [AuCl(epi-C1,N)(PPh3)]PF6.
Cyclometallation proceeds via direct C–H bond activation of
a heterosubstituted molecule to form a chelate ring composed
of a co-ordination bond and a covalent metal–carbon bond.1
This method of formation of a M–C σ bond is more convenient
than the classical one using organomagnesium or organo-
lithium compounds. Compared with the extensively studied
cyclopalladation or cycloplatination, the chemistry of cyclo-
auration has not been investigated so much.2 The first
cycloauration was performed in 1989 by Constable and
Leese3 using 2-phenylpyridine. Thereafter in this decade
cycloaurated complexes formed by C–H bond activation of
the following substrates have been reported: 2,9-diphenyl-
1,10-phenanthroline,4 4-(4-methoxyphenyl)-6-phenyl-2,2Ј-bi-
pyridine,5 2-benzylpyridine,6 6-benzyl-2,2Ј-bipyridine,7 6-tert-
butyl-2,2Ј-bipyridine,7 2-benzoylpyridine,8 2-anilinopyridine,9,10
2-phenoxypyridine,10 2-(phenylsulfanyl)pyridine,10 2-(alkyl-
sulfanyl)pyridine,11 papaverine (1-[(3,4-dimethoxyphenyl)-
methyl]-6,7-dimethoxyisoquinoline),12 2-(2-thienyl)pyridine13
and 2-(3-thienyl)pyridine.13 Recently, in connection with the
antitumor and luminescence properties of some cycloaurated
complexes, much more interest has been paid to the chemistry
of cycloauration. However, as shown above all the substrates
which underwent intramolecular C–H bond activation by
gold() are definitely limited to pyridine derivatives. In order
to break through this situation we have set out to investigate
the cycloauration of 2-phenylimidazole derivatives. Here we
report the first successful intramolecular aromatic substitution
1
–
Scheme 1 (i) AuCl3ؒ4H2O or HAuCl4ؒ4H2O; (ii) AuCl3ؒ4H2O; (iii)
of a substrate other than pyridine derivatives by gold(),
viz. cycloauration of 1-ethyl-2-phenylimidazole, and also the
crystal structure of a derivative [AuCl(epi-C1,N)(PPh3)]PF6
[epi = 2-(1-ethyl-2-imidazolyl)phenyl].
2
1
–
HAuCl4ؒ4H2O; (iv) CH3CN–water (1:5); (v) AgBF4; (vi) PPh3, NaBF4
2(5) or NH4PF6 (6).
correlation spectroscopy (COSY) and the data are summarized
in Table 1.
Results and discussion
Synthesis and characterization of the gold(III) complexes of Hpi
and Hepi
The methods for preparation of the new gold() complexes
derived from 2-phenyl-1H-imidazole (Hpi) and 1-ethyl-2-
phenylimidazole (Hepi) are shown in Scheme 1. Assignment of
The reaction of AuCl3ؒ4H2O with an equimolar amount of
2-phenyl-1H-imidazole (Hpi) or 1-ethyl-2-phenylimidazole
1
1
the H NMR spectra was performed with the aid of H–1H
J. Chem. Soc., Dalton Trans., 2000, 271–274
This journal is © The Royal Society of Chemistry 2000
271

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Table 1 Proton NMR spectral data of the new gold() complexesa
Imidazolyl moietyb
Complex
H4Ј or H5Ј
CH2
CH3
Benzene ringb
Phosphine
1 [H(Hpi)][AuCl4]
2 [H(Hepi)][AuCl4]
3 [AuCl3(Hepi)]
7.81 (s, 2 H)
—
—
8.0 (m, 2 H, o-H)
7.8–7.65 (m, 5 H)
7.75–7.7 (m, 5 H)
7.85 (d, 1 H)e
7.66 (m, 3 H, m, p-H)
—
—
—
—
7.97 (d),c 7.86 (d)c
7.91 (d),c 7.78 (d)c
7.77 (d),c 7.56 (d)c
4.17 (q)d
4.05 (q)d
4.52 (q)d
1.38 (t)d
1.30 (t)d
1.46 (t)d
4 [AuCl2(epi-C1,N)]
7.68 (d, 1 H)e
7.48 (t, 1 H)e
7.34 (t, 1 H)e
5 [AuCl(epi-C1,N)(PPh3)]BF4
6 [AuCl(epi-C1,N)(PPh3)]PF6
7.5–7.9 (c, 2 H) f
7.6–7.95 (c, 2 H) f
4.57 (q)d
4.55 (q)d
1.47 (t)d
1.48 (t)d
7.5–7.9 (1 H, H3)f
6.78 (t, 1 H, H5)e
7.6–7.95 (1 H, H3)f
6.78 (t, 1 H, H5)e
7.34 (br t, 1 H, H4)e
6.62 (br d, 1 H, H6)e
7.34 (t, 1 H, H3)e
6.60 (br d, 1 H, H6)e
7.5–7.9 (c, 15 H)
7.6–7.95 (c, 15 H)
a Measured in DMSO-d6 at 270 MHz and at 23 ЊC; δ in ppm with respect to SiMe4; s = singlet, d = doublet, t = triplet, q = quartet, br = broad,
m = multiplet, c = complex. b For numbering see Scheme 1. c 3J(HH) = 2.0 Hz. d 3J(HH) = 7.3 Hz. e 3J(HH) = 8.0 Hz. f Overlapping with triphenyl-
phosphine signals.
(Hepi) carried out in dichloromethane did not afford the addi-
tion complex [AuCl3(L)] (L = Hpi or Hepi), giving only the
corresponding salt [H(Hpi)][AuCl4] 1 or [H(Hepi)][AuCl4] 2,
respectively. It is not clear whether the hydrated water molecule
in AuCl3ؒ4H2O is the proton source for the formation of the
salts, but a similar result has been reported for the synthesis of
2-(α,α-dimethylbenzyl)pyridinium tetrachloroaurate() from
the reaction between 2-(α,α-dimethylbenzyl)pyridine and AuCl3ؒ
2H2O.6 Previously, we achieved the conversion of the tetra-
chloroaurate salts of 2-phenoxy- and 2-(phenylsulfanyl)-
pyridine into corresponding adducts in acetonitrile–water (1:5)
mixed solvent.10 The addition complex [AuCl3(Hepi)] 3 was
obtained by the above method and also by the reaction of
HAuCl4ؒ4H2O with two molar equivalents of Hepi in ethanol.
However, in the case of Hpi the corresponding adduct
[AuCl3(Hpi)] could not be prepared by either method, recover-
ing or forming only the salt 1, implying the higher stability of
the 2-phenylimidazolium cation.
Different from the chemical behavior of the adducts of
2-phenoxy- and 2-(phenylsulfanyl)-pyridine,10 the adduct of
Hepi 3 did not change into the corresponding cycloaurated
complex [AuCl2(epi-C1,N)] [epi = 2-(1-ethyl-2-imidazolyl)-
phenyl] 4 by heating in acetonitrile–water (1:5) solvent. The
novel cycloaurated complex 4 was finally obtained in 20%
yield when the adduct 3 was refluxed with AgBF4 in CH2Cl2.
However, the yield of 4 did not increase under several reaction
conditions using other silver salts such as AgO2CMe and
AgO2CCF3 in the presence or absence of Na2CO3 in CH2Cl2 or
acetone. This is the first example of intramolecular aromatic
substitution of a ligand other than pyridine derivatives, which
we believe could throw new light upon the development of
cycloauration chemistry. It should be added that by transmetal-
lation from the corresponding organomercury() compounds
or by bromination of gold() complexes, [AuBr(L)] [L = PPh2-
Fig. 1 An ORTEP view of complex [AuCl(epi-C1,N)(PPh3)]PF6
6
(molecule A). Hydrogen atoms and the hexafluorophosphate anion are
omitted for clarity.
from the cycloaurated structure, the far-IR spectrum of 4
showed two bands at 351 and 296 cmϪ1 characteristic of ν(Au–
Cl) frequencies trans to the imidazolyl nitrogen atom and trans
to the phenylene carbon atom, respectively.18
Synthesis and structural analysis of [AuCl(epi-C1,N)(PPh3)]PF6
Complex 4 reacted with an equimolar amount of PPh3 in the
presence of an excess of NaBF4 or NH4PF6 to give cationic
complexes 5 (ΛM 138 S cm2 molϪ1 in acetone) or 6 (ΛM 141 S
cm2 mol Ϫ1 in acetone), respectively. The IR spectra of 5 and 6
exhibited only one band assignable to the ν(Au–Cl) frequency
trans to the phenylene group at 315 and 311 cmϪ1, respectively,18
Ϫ
)
besides a strong band due to counter anion at 1055 (5 BF4
and 834 cmϪ1 (6 PF6Ϫ). In the 1H NMR spectrum of 5 and 6 the
H6 signal appeared at considerably higher field [δ 6.62 (5), 6.60
(6)] which is caused by the ring current of the adjacent benzene
ring of the triphenylphosphine co-ordinated cis to the C–Au
bond. On the basis of these data together with elemental
analysis, 5 and 6 were assigned to cationic four-co-ordinate
complexes [AuCl(epi-C1,N)(PPh3)]BF4 and [AuCl(epi-C1,N)-
(PPh3)]PF6, respectively.
(C H CH᎐CH ) or PPh (C H CH CH᎐CH )], cycloaurated
᎐
᎐
6
4
2
2
6
4
2
2
complexes of azobenzene,14,15 benzylamine,15–17 2-phenyl-
oxazoline,17 benzylideneamine18 and diphenylphosphine19
derivatives have been prepared.
The structure of complex 6 was established by X-ray dif-
fraction. The crystal consists of two crystallographically
independent molecules A and B, the structures of which are
almost identical. Selected bond distances and angles are
summarized in Table 2. Fig. 1 shows an ORTEP22 view of the
cationic moiety of the molecule A. In molecules A and B the
gold atoms have essentially square-planar AuCNClP co-
ordination with the mean deviation from the best planes of
0.1016 and 0.1264 Å, respectively. The Au–C and Au–P
1
In the H NMR spectrum of complex 4 two imidazole-ring
protons resonated as an AB quartet at δ 7.56 (d) and 7.77 (d). It
has been reported that gold() sometimes attacks on carbon
atoms in heterocycles rather than those in the benzene ring, e.g.,
C-4 metallation of the pyrazole ring in 1-phenylpyrazole20 or
C-5 auration of the thiophene ring in 2-(2-thienyl)pyridine13
or 6-(2-thienyl)-2,2Ј-bipyridine.21 However, in complex 4 the
detection of two imidazole-ring protons completely excludes
the possibility of formation of aurated imidazole species. On
the contrary, the benzene-ring protons of 4 appeared as a well
separated ABCD pattern typical for an o-phenylene group
(Table 1). On the basis of these results it was concluded that in
complex 4 metallation occurs at the ortho position of the phenyl
ring of Hepi, forming a cycloaurated chelate ring. As expected
bond distances in
6 are as in other gold() com-
plexes.4,6–8,10,17,18,23 The bite angle of the cycloaurated ligand is
80.8(2)Њ (molecules A and B), whose value is comparable to
those in five-membered auracycles derived from 4,4Ј-dimethyl-
azobenzene [80.1(2)Њ],24 4-butyl-N-(trimethoxybenzylidene)-
aniline [81.41(14)Њ],18 4,4-dimethyl-2-phenyl-1,3-oxazoline
272
J. Chem. Soc., Dalton Trans., 2000, 271–274

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Table 2 Selected bond distances (Å) and angles (Њ) with estimated
standard deviations (e.s.d.s) in parentheses for complex 6
Syntheses
[H(Hpi)][AuCl4] 1. Method (a). A dichloromethane (10 cm3)
solution of 2-phenylimidazole (0.083 g, 0.576 mmol) was added
to a solution of AuCl3ؒ4H2O (0.214 g, 0.569 mmol) in the same
solvent (10 cm3). After the resulting mixture was stirred over-
night at room temperature, it was evaporated to dryness and
the residue extracted with acetonitrile. The extract was concen-
trated under reduced pressure and diluted with diethyl ether
to give yellow microcrystals of complex 1 (0.125 g, 45%), mp
210 ЊC (Found: C, 22.5; H, 1.9; N, 5.65. C9H8AuCl4N2 requires
C, 22.4; H, 1.65; N, 5.8%); νmax/cmϪ1 (KBr) 3290 (br, NH) and
Molecule A
Molecule B
Au–C(1)
Au–N(2)
Au–Cl
2.049(6)
2.045(5)
2.365(1)
2.300(2)
1.422(8)
1.461(8)
1.342(8)
1.367(7)
1.369(8)
1.390(8)
1.362(7)
2.055(6)
2.047(5)
2.362(1)
2.307(2)
1.431(7)
1.446(8)
1.340(8)
1.391(7)
1.360(8)
1.379(7)
1.347(7)
Au–P
C(1)–C(6)
C(6)–C(7)
C(7)–N(2)
N(2)–C(9)
C(9)–C(8)
C(8)–N(1)
N(1)–C(7)
359 (Au–Cl); ΛM(1 × 10Ϫ3 M, acetone) 152 S cm2 molϪ1
.
Method (b). An ethanol (3 cm3) solution of 2-phenyl-
imidazole (0.147 g, 1.02 mmol) was added to a solution of
HAuCl4ؒ4H2O (0.205 g, 0.498 mmol) in the same solvent (5
cm3). The resulting yellow solution was stirred at room tem-
perature for 20 h. After similar work-up to that described in
method (a), complex 1 was obtained in 36% yield.
C(1)–Au–N(2)
C(1)–Au–P
N(2)–Au–P
P–Au–Cl
N(2)–Au–Cl
C(1)–Au–Cl
80.8(2)
95.9(2)
172.7(1)
93.26(6)
90.6(1)
80.8(2)
96.4(2)
167.3(1)
93.83(6)
90.4(1)
[H(Hepi)][AuCl4] 2. A dichloromethane (20 cm3) solution of
1-ethyl-2-phenylimidazole (0.059 g, 0.343 mmol) was added to
a solution of AuCl3ؒ4H2O (0.110 g, 0.292 mmol) in the same
solvent (20 cm3) and the resulting mixture stirred at room tem-
perature. After 12 h the yellow solution was concentrated and
diluted with hexane to give yellow microcrystals of complex 2
(0.077 g, 55%), mp 116 ЊC (Found: C, 26.15; H, 2.6; N, 5.5.
C11H13AuCl4N2 requires C, 25.8; H, 2.55; N, 5.45%); νmax/cmϪ1
(KBr) 367 (Au–Cl); ΛM(1 × 10Ϫ3 mol dmϪ3, acetone) 158 S cm2
169.1(2)
168.3(2)
molϪ1
.
[AuCl3(Hepi)] 3. Method (a). An ethanol (5 cm3) solution of
1-ethyl-2-phenylimidazole (0.522 g, 3.03 mmol) was added to a
solution of HAuCl4ؒ4H2O (0.610 g, 1.48 mmol) in the same
solvent (7.5 cm3). The resulting mixture became a yellow sus-
pension after stirring at room temperature for 1 h. After 1 d the
yellow precipitates were collected and washed thoroughly with
ethanol to give complex 3 (0.6667 g, 95%), mp 162 ЊC (Found:
C, 27.85; H, 2.55; N, 5.85. C11H12AuCl4N2 requires C, 27.8; H,
2.55; N, 5.9%); ν max/cmϪ1 (KBr) 367 (Au–Cl); ΛM(1 × 10Ϫ3 mol
Fig. 2 Orientation of ethyl group in molecules A and B of complex 6.
[81.7(3)Њ]17 and N,N-dimethylbenzylamine [82.2(4)Њ],25 and
smaller than the values found in the six-membered auracycles
[AuCl(C6H4NHC5H4N-C1,N)(PPh3)]BF4 [85.2Њ],10 [AuCl2(C6-
H4CMe2C5H4N-C1,N)] [85.7(1)Њ],7 [AuCl(C6H4CH2C5H4N-
C1,N)(PPh3)]BF4 [85.8(4)Њ],8 [AuCl2(C6H4OC5H4N-C1,N)]
[86.6Њ],10 [AuCl2(C6H4SC5H4N-C1,N)] [88.3Њ]10 and [AuCl2-
(C6H4COC5H4N-C1,N)] [89.5(3)Њ].8 The slightly longer Au–Cl
[2.365(1) (molecule A) and 2.362(1) Å (molecule B)] and Au–N
bond distances [2.045(5) (molecule A) and 2.047(5) Å (molecule
B)] are caused by the greater trans influences of the carbon
donor and phosphine ligand, respectively. In the chelated epi
moiety the plane of benzene ring slightly twists against the
plane of imidazole, resulting in dihedral angles of 16.4 (mole-
cule A) and 16.7Њ (molecule B). The main difference between
molecules A and B is the orientation of the ethyl group in the
imidazole ring as shown in Fig. 2: in molecule A the plane
composed of N(1), C(10) and C(11) is nearly co-planar with the
best plane of the imidazole ring (dihedral angle 5.4Њ), while in B
the plane is nearly perpendicular to the imidazole ring (dihedral
angle 90.8Њ).
dmϪ3, acetone) 3.0 S cm2 molϪ1
.
Method (b). The salt 2 (0.051 g, 0.099 mmol) was stirred at
room temperature in acetonitrile–water (1:5) for 3 d. The pre-
cipitated microcrystals were filtered off and washed thoroughly
with ethanol to give complex 3 (0.0384 g, 81%).
[AuCl2(epi-C 1,N)] 4. A dichloromethane (25 cm3) solution of
[AuCl3(Hepi)] (0.341 g, 0.716 mmol) was added to a dichloro-
methane (25 cm3) suspension of AgBF4 (0.141 g, 0.724 mmol).
The resulting mixture was refluxed for 6 h and then the volatile
materials were removed in vacuo. The residue was extracted
with acetonitrile to remove unreactive adduct 3. The extract
was evaporated to dryness and the residue extracted with
dichloromethane. The dichloromethane extract was dried
in vacuo and the resulting white residue washed successively
with a small amount of acetonitrile and diethyl ether to give
complex 4 (0.063 g, 20%), mp 270 ЊC (decomp.) (Found: C,
29.95; H, 2.55; N, 6.2. C11H11AuCl2N2 requires C, 30.1; H, 2.55;
N, 6.4%); νmax/cmϪ1 (KBr) 351 and 296 (Au–Cl).
Experimental
General
[AuCl(epi-C 1,N)(PPh3)]BF4 5. To a suspension of [AuCl2-
(epi-C1,N)] 4 (0.060 g, 0.138 mmol) in dichloromethane (5 cm3)
was added a solution of PPh3 (0.038 g, 0.44 mmol) in dichloro-
methane (10 cm3). After a few minutes NaBF4 (0.077 g, 0.700
mmol) was added to the resulting pale yellow solution and the
mixture stirred for 11 h at room temperature. Precipitated solids
were removed by filtration and the filtrate was evaporated to
dryness. The residue was extracted with ethanol and diluted
with diethyl ether to give pale yellowish white microcrystals of
complex 5 (0.061 g, 59%), mp 131 ЊC (Found: C, 46.15; H, 3.55;
The IR spectra were measured on a JASCO FT/IR-420
spectrophotometer, 1H NMR spectra 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. Conductivity
measurements were carried out at 25 ЊC on a Toa Electronics
CM-20E conductometer. 1-Ethyl-2-phenylimidazole26 was pre-
pared according to the literature. Other reagents were obtained
commercially and used without purification.
J. Chem. Soc., Dalton Trans., 2000, 271–274
273

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acetone) 138 S cm2 molϪ1
.
[AuCl(epi-C 1,N)(PPh3)]PF6 6. This complex was similarly
prepared as described for 5 using NH4PF6. Yield 56%, mp
200 ЊC (Found: C, 43.1; H, 3.3; N, 3.45. C29H26AuClF6N2P2
requires C, 42.95; H, 3.25; N, 3.45%); νmax/cmϪ1 (KBr) 834 (PF6)
and 311 (Au–Cl); ΛM(1 × 10Ϫ3 M, acetone) 141 S cm2 molϪ1
.
X-Ray crystallography
Suitable crystals of [AuCl(epi-C1,N)(PPh3)]PF6 6 were grown
from dichloromethane–diethyl ether.
Crystal data. C29H26AuClF6N2P2, M = 810.90, monoclinic,
space group Cc, a = 27.831(1), b = 9.6282(3), c = 23.3900(7) Å,
β = 115.012(1)Њ, U = 5679.9(3) Å3, Dc = 1.896 g cmϪ3, Z = 8,
µ(Mo-Kα) = 54.68 cmϪ1, λ = 0.71069 Å.
A yellow prismatic crystal having approximate dimensions
of 0.10 × 0.25 × 0.10 mm was mounted on a glass fiber. All
measurements were made on a Rigaku RAXIS-RAPID
Imaging Plate diffractometer with graphite monochromated
Mo-Kα radiation. The data were collected at Ϫ180 1 ЊC
and processed by the PROCESS-AUTO program package.27
Of the 27031 reflections 6507 were unique (Rint = 0.043). An
asymmetry-related absorption correction using the program
ABSCOR28 was applied. The data were corrected for Lorentz-
polarization effects. The structure was solved by direct
methods29 and expanded using Fourier techniques.30 The non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were included but not refined. The final cycle of full-matrix
least-squares refinement was based on 6051 observed reflections
(I > 3.00σ(I )) and 740 variable parameters and converged with
unweighted and weighted agreement factors of R = 0.019 and
RЈ = 0.017.
CCDC reference number 186/1764.
24 J. Vicente, M. D. Bermudez, M. P. Carrillo and P. G. Jones, J. Chem.
Soc., Dalton Trans., 1992, 1975.
Acknowledgements
25 J. Vicente, M. T. Chicote, M. D. Bermudez, P. G. Jones and G. M.
Sheldrick, J. Chem. Res., 1985, (S) 72; (M) 954.
26 H. J. J. Loozen, J. J. M. Drouen and O. Piepers, J. Org. Chem., 1975,
40, 3279.
We thank Professor Teruo Shinmyozu of the Institute for
Fundamental Reseach of Organic Chemistry, Kyushu
University for the use of the crystallographic facility.
27 PROCESS-AUTO, Automatic Data Acquisition and Processing
Package for Imaging Plate Diffractometer, Rigaku Corporation,
Tokyo, 1998.
28 T. Higashi, ABSCOR, Program for Absorption Correlation, Rigaku
Corporation, Tokyo, 1995.
29 A. Altomare, M. C. Burla, M. Camalli, M. Cascarano, C.
Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr.,
1994, 27, 435.
30 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. De
Gelder, R. Israel and J. M. M. Smits, The DIRDIF 94 program
system, Technical Report of the Crystallography Laboratory,
University of Nijmegen, 1994.
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