835
solubility in solution. This is different from the corresponding
reaction with a mixture of gold(I) and silver(I), in which a single
species of [Au2Ag2(L)4] with an AuAgAuAg-type arrangement
is selectively formed in solution.4,8 The affinity of an imine
group to a CuI center, which is much higher than to an AgI
center, seems to prevent the conversion of some kinetic products
to the thermodynamically stable product of 1 in solution.
To obtain a homometallic CuI4 metalloring compound, a
chloroform solution of 2-(4-dimethylaminophenyl)benzothiazo-
line was treated with an acetonitrile solution of tetraaceto-
nitrilecopper(I) perchlorate in a 1:1 ratio. However, this reaction
did not give [Cu4(L)4] but produced a brown compound of
[Cu8(L)8](ClO4) that has been obtained by the 2:1 reaction of
2-(4-dimethylaminophenyl)benzothiazoline with copper(II) ace-
tate in 1,2-dichloroethane.3c After several trials, an orange
compound 2, which is assignable to have a neutral formula of
[CuI(L)]n based on the elemental analysis and IR spectrum that is
essentially the same as that of 1 (Figure S2),5 was obtained by
the reaction of 2-(4-dimethylaminophenyl)benzothiazoline with
copper(II) acetate in a 2:1 ratio in toluene.5,9 Although the
characterization of 2 by means of the NMR spectroscopy was
precluded owing to its poor solubility in common solvents
and its instability in solution,10 an expected CuI4 metalloring
structure was established by single-crystal X-ray analysis.11 In 2,
four Cu atoms are bridged by four S atoms from four L ligands
to form a tetranuclear metalloring structure with an S4 symmetry
(Figure 2). Each Cu atom in 2 is in a +1 oxidation state, as
evidenced by the lack of any counter cations. Thus, it is seen that
2-(4-dimethylaminophenyl)benzothiazoline acts not only as a
ligand precursor but also as a reducing agent for copper(II).3c
The successful isolation of 2 by the use of toluene as a reaction
medium, instead of 1,2-dichloroethane, is most likely due to the
insolubility of 2 in this solvent, which leads to the precipitation
of 2 prior to its conversion into [Cu8(L)8]+ in solution. Each L
ligand in 2 also adopts a ¯2-κ1S:κ2N,S coordination mode (av
Cu-S = 2.211(4) ¡, av Cu-N = 2.140(9) ¡), like in 1. However,
in 2, four imine groups from four L ligands bind to four different
CuI atoms, and each CuI atom is situated in an NS2 trigonal-
planar geometry (S-Cu-S = 146.59(8)°, N-Cu-S = 117.9(3)
and 87.8(3)°). Thus, the four bridging S atoms in 2 are situated
in a square arrangement, which is distinct from an arrangement
of parallelogram found in 1.
Figure 1. Perspective views of (a) 1 and (b) its core structure;
AuI: purple, CuI: brown, N: blue, S: yellow, C: gray. H atoms are
omitted for clarity.
rather than to an AuI center, accounts for the formation of this
metalloring structure. Despite the Ci symmetric structure in
crystal 1, the 1H NMR spectrum of 1 in CDCl3 gave only a
single set of signals for four L ligands (Figure S1a),5 suggestive
of the flexible nature of its AuI2CuI2S4 metalloring framework
with an averaged C2h symmetry in solution.
It is possible that three heterometallic species, [Au3Cu1(L)4],
[Au2Cu2(L)4], and [Au1Cu3(L)4], besides two homometallic
species, [Au4(L)4] and [Cu4(L)4], are formed from L ligands in
combination with a 1:1 mixture of AuI and CuI ions. In addition,
two isomeric forms that are discriminated by the arrangement
of AuI and CuI ions, AuAuCuCu-type and AuCuAuCu-type,
are possible for [Au2Cu2(L)4]. However, the present reaction
exclusively produced [Au2Cu2(L)4] with an AuCuAuCu-type
arrangement in a moderate yield of ca. 50%. Since the 1H NMR
spectrum of a reaction mixture of 2-(4-dimethylaminophenyl)-
benzothiazoline, triethylamine, chloro(tetrahydrothiophene)-
gold(I), and tetraacetonitrilecopper(I) perchlorate in a 2:2:1:1
ratio in CDCl3/CD3CN is indicative of the formation of a
complex mixture with no obvious preference for a single species
(Figure S1b),5 the selective isolation of 1 is attributed to its less
Previously, we have shown that the homometallic AuI4 and
AgI4 compounds, [Au4(L)4] and [Ag4(L)4], also have a metal-
loring structure, in which four metal atoms are bridged by four S
atoms from four L ligands, as in the case of [Cu4(L)4] (2).4
However, in [Au4(L)4], all four AuI atoms adopt a two-
coordination geometry, whereas two of four AgI atoms adopt a
two-coordination geometry and the other AgI atoms have a four-
coordination geometry in [Ag4(L)4] (Figure S3).5 The 2,2,2,2-
coordination in [Au4(L)4] and the 2,4,2,4-coordination in
[Ag4(L)4] are both different from the 3,3,3,3-coordination found
in 2, in which four CuI atoms are unified to have a three-
coordination geometry. It should be noted that the 2,4,2,4-
coordination pattern in [Ag4(L)4] is the same as that in
[Au2Cu2(L)4] (1). In addition, the four bridging S atoms in
[Ag4(L)4] are in an arrangement of parallelogram like in 1,
whereas those in [Au4(L)4] are in a square arrangement like in 2.
Thus, the overall metalloring structure in [Ag4(L)4] is well
comparable with that in [Au2Cu2(L)4] (1), rather than those in
Chem. Lett. 2012, 41, 834-836
© 2012 The Chemical Society of Japan
Takino, Yusuke
