Oxazolone copper(I) complexes inspired by the methanobactin active site

Article abstract of DOI:10.1016/j.ica.2011.03.070

Two oxazolone-derived potential ligands with enethioether substituents have been synthesized that differ by the terminal thioether moiety (S-Et in L ¹, S-C₆H₄(OMe)-2 in L²). Both L ¹ and L² behave as bidentate {NS} chelate ligands to form stable complexes with copper(I) triflate that crystallize as dimeric complexes [L₂Cu₂(OTf)₂] (4 and 5) featuring a central {Cu₂S₂} diamond core with distinctly different Cu-S bonds. L¹ as well as 4 and 5 have been characterized by single crystal X-ray diffraction. NMR spectroscopy including ¹H and ¹⁹F DOSY experiments reveals that 4 and 5 dissociate into monomeric species [LCu(OTf)] (4′ and 5′) in CDCl₃ solutions. 4′ and 5′ retain the {NS} binding motif of the oxazolone-derived ligands, but are in slow equilibrium with their {OS} isomers 4″ and 5″ that result from E/Z isomerization of the exocyclic enethioether double bond.

Full text of DOI:10.1016/j.ica.2011.03.070

Inorganica Chimica Acta 374 (2011) 601–605
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Oxazolone copper(I) complexes inspired by the methanobactin active site
⇑
Ann Christin Jahnke, Anastasia Herter, Sebastian Dechert, Michael John, Franc Meyer
Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstrasse 4, D-37077 Göttingen, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 7 April 2011
Two oxazolone-derived potential ligands with enethioether substituents have been synthesized that dif-
fer by the terminal thioether moiety (S-Et in L1, S–C6H4(OMe)-2 in L2). Both L1 and L2 behave as bidentate
{NS} chelate ligands to form stable complexes with copper(I) triflate that crystallize as dimeric complexes
[L2Cu2(OTf)2] (4 and 5) featuring a central {Cu2S2} diamond core with distinctly different Cu–S bonds. L1
as well as 4 and 5 have been characterized by single crystal X-ray diffraction. NMR spectroscopy includ-
Dedicated to Prof. Wolfgang Kaim on the
occasion of his 60th birthday
19
ing 1H and F DOSY experiments reveals that 4 and 5 dissociate into monomeric species [LCu(OTf)] (40
Keywords:
Copper
Bioinorganic chemistry
N ligands
and 50) in CDCl3 solutions. 40 and 50 retain the {NS} binding motif of the oxazolone-derived ligands, but are
in slow equilibrium with their {OS} isomers 400 and 500 that result from E/Z isomerization of the exocyclic
enethioether double bond.
S ligands
Oxazolone ligands
Methanobactin
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
cent of the chelating {NS} motif of methanobactin, and their
copper(I) complexes.
Mixed sulfur/nitrogen ligation is often encountered in biological
copper sites [1,2]. Prominent examples are the blue copper pro-
teins, the binuclear CuA center, or the CuZ cluster in nitrous oxide
reductase. A new copper binding motif has recently been discov-
ered in methanobactins (mb) [3–5], which are small peptide-de-
rived molecules that appear to be involved in various biological
processes in methanotrophic bacteria [6]. Methanobactins bind
copper(II) with subnanomolar affinity and reduce it to copper(I)
[7,8]. They use two oxazolone rings, each with an appended
enethiol group, to host the copper(I) ion in a distorted tetrahedral
{N2S2} coordination environment (Chart 1).
Many copper complexes with thioether-based ligands providing
an {N2S2} donor set have previously been investigated [9,10],
mostly with the aim of emulating certain features of the copper
binding sites of blue copper proteins. Such complexes exhibit the
expected high copper(II/I) redox potentials, as long as ligand flexi-
bility is sufficient for adapting to the stereoelectronic requirements
of copper(I). On the other hand, little is known about oxazolone
copper chemistry [11], and complexes of chelating oxazolone-
derived ligands that bear an appended S-donor are virtually
unknown. Here we report two potentially bidentate oxazolone
derivatives with an appended enethioether substituent, reminis-
2. Experimental
Oxazolone 3 was prepared as described in the literature [12,13].
All other chemicals were purchased from commercial sources and
used as received. Solvents were dried by standard procedures be-
fore use. NMR spectra were recorded on either a Bruker Avance
III 300 MHz, a Bruker Avance III 400 MHz or a Bruker DRX
500 MHz spectrometer. Chemical shifts were calibrated to the
residual proton and carbon signal of the solvent (CDCl3:
dH = 7.27, dC = 77.2 ppm) and to external CH3NO2 and CFCl3 for
15N and 19F NMR, respectively. ESI mass spectra were recorded
with an Applied Biosystems API 2000 and a BRUKER (HCT ultra).
IR spectra from KBr pellets were recorded on a Digilab Excalibur
Series FTS 3000 spectrometer. UV/Vis spectra were collected with
a Varian Cary 5000. Elemental analyses were performed by the
analytical laboratory of the Institute of Inorganic Chemistry at
Georg-August-University using an Elementar Vario EL III
instrument.
2.1. Synthesis of L1
L1 was prepared following the method described in literature
[14], starting from 3.00 g (14.49 mmol) of 3. Yield: 2.23 g
(9.57 mmol, 66%). Pale yellow single crystals of the Z-isomer suit-
able for X-ray crystallography were obtained by slow diffusion of
⇑
Corresponding author. Fax: +49 551 393063.
E-mail address: franc.meyer@chemie.uni-goettingen.de (F. Meyer).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.070

602
A.C. Jahnke et al. / Inorganica Chimica Acta 374 (2011) 601–605
O
product was dried under reduced pressure to obtain an orange pow-
O
der (88.2 mg, 0.10 mmol, 40%). Orange crystals for X-ray crystallog-
raphy were obtained by slow diffusion of Et2O in a benzene solution
O
3
of the product. 1H NMR (300 MHz, CDCl3): d 1.56 (t, JH,H = 7.4 Hz,
N
3H, CH3), 3.29 (q, 3JH,H = 7.4 Hz, 2H, CH2), 7.66 (t, 3JH,H = 7.7 Hz, 2H,
S
3
CHmeta), 7.79 (t, JH,H = 7.5 Hz, 1H, CHpara), 7.85 (s, 1H, CHvinyl), 8.42
Cu
S
3
(d, JH,H = 7.4 Hz, 2H, CHortho) ppm. 13C NMR (75 MHz, CDCl3): d
15.7 (CH3), 32.2 (CH2), 122.3 (Cipso), 127.3 (C@CH), 129.3 (Cortho),
130.1 (Cmeta), 136.2 (Cpara), 141.8 (C@CH), 158.6 (C@O), 165.8 (C-
Ph) ppm. 15N NMR (40 MHz, CDCl3): d ꢀ199.0 ppm. 19F NMR
(376 MHz, CDCl3): d ꢀ77.1 ppm. MS (ESI): m/z (%) = 743 (15)
[L2Cu2(SO3CF3)]+, 529 (100) [L2Cu]+, 296 (18) [LCu]+. IR (KBr):
~
N
O
O
Chart 1. Copper-binding site of methanobactin.
m
= 3044 (w), 2982 (w), 2936 (w), 1803 (s), 1621 (s), 1555 (m),
1489 (m), 1450 (m), 1344 (s), 1308 (vs) 1268 (s), 1236 (vs), 1202
(s), 1173 (vs), 1117 (w), 1049 (w), 1021 (vs), 986 (m) 847 (m), 836
(m), 783 (w), 700 (s), 637 (s), 514 (m) cmꢀ1. UV/Vis (DCM): k [nm]
Et2O into a MeCN solution of the product. After 5 days at 60 °C both
isomers could be observed in NMR experiments, ratio of E/Z 1:10.
M.p. 107 °C. 1H NMR (400 MHz, CDCl3): Z-isomer: d 1.48 (t,
(e
rel/L molꢀ1 cmꢀ1) = 243 (0.10), 263 (0.20), 359 (0.43), 376 (0.37).
3
3JH,H = 7.4 Hz, 3H, CH3), 3.12 (q, JH,H = 7.4 Hz, 2H, CH2), 7.45–7.51
Elemental Anal. Calc. for C26H22Cu2F6-N2O10S4 (889.87 g/mol): C,
35.06; H, 2.49; N, 3.15; S, 14.37. Found: C, 35.15; H, 2.67; N, 3.24;
S, 14.19%.
(m, 2H, CHmeta), 7.52 (s, 1H, CHvinyl), 7.54–7.60 (m, 1H, CHpara),
3
8.06–8.08 (m, 2H, CHortho); E-isomer: d 1.47 (t, JH,H = 7.4 Hz, 3H,
3
CH3), 3.01 (q, JH,H = 7.4 Hz, 2H, CH2), 7.45–7.51 (m, 2H, CHmeta),
7.54–7.60 (m, 1H, CHpara), 7.71 (s, 1H, CHvinyl), 8.00–8.03 (m, 2H,
CHortho) ppm. 13C NMR (75 MHz, CDCl3): d 15.7 (CH3), 29.3 (CH2),
125.9 (C@CH), 128.0 (Cortho), 129.0 (Cmeta), 130.9 (Cipso), 132.9
(Cpara), 139.7 (C@CH), 161.4 (C-Ph), 164.3 (C@O) ppm. 15N NMR
2.4. Synthesis of [L2Cu(SO3CF3)]2 (5)
Ligand L2 (78 mg, 0.25 mmol, 1.00 eq) and CuSO3CF3ꢁ½ C6H6
(63.0 mg, 0.25 mmol, 1.00 eq) were dissolved in dried and deoxy-
genated benzene (5 mL). The reaction mixture was stirred for 3 h.
After filtering off the insoluble material, the solvent was removed
and the product was dried under reduced pressure to obtain a yellow
powder (102 mg, 0.10 mmol, 39%). Yellow crystals for X-ray crystal-
lography were obtained by slow diffusion of Et2O in a solution of the
product in toluene. 1H NMR (500 MHz, CDCl3): d 3.94 (s, 3H, OCH3),
6.96–7.11 (m, 2H, CH5, CH6), 7.41–7.56 (m, 2H, CH3, CH4), 7.68 (t,
3JH,H = 7.9 Hz, 2H, CHmeta), 7.79 (t, 3JH,H = 7.4 Hz, CHpara), 7.88 (s, 1H,
CHvinyl), 8.46 (d, 3JH,H = 7.6 Hz, 2H, CHortho) ppm. 13C NMR (75 MHz,
CDCl3): d 56.5 (OCH3), 112.3 (C5), 116.6 (C1), 122.0 (C6), 122.4 (Cipso),
126.9 (C@CH), 129.4 (Cortho), 130.1 (Cmeta), 132.8 (C3), 133.8 (C4),
136.2 (Cpara), 142.5 (C@CH), 158.4 (C2), 159.0 (C@O), 165.7 (C-Ph)
ppm. MS (ESI): m/z (%) = 899 (5) [L2Cu2(SO3CF3)]+, 685 (100)
~
(40 MHz, CDCl3):
d
-145.0 ppm. MS (ESI): m/z (%) = 272 (18)
[M+K]+, 256 (24) [M+Na]+, 234 (100) [M+H]+. IR (KBr):
m
= 3026
~
(m), 2966 (w), 2858 (w), 1799 (m), 1782 (s), 1638 (s), 1550 (m),
1447 (m), 1327 (m), 1265 (m), 1164 (s), 992 (m), 859 (vs), 840
(s), 804 (m), 692 (s), 608 (w) cmꢀ1. UV/Vis (DCM): k [nm] (erel
/
L molꢀ1 cmꢀ1) = 243 (0.11), 263 (0.28), 359 (0.71), 376 (0.62). Ele-
mental Anal. Calc. for C12H11NO2S (233.05 g/mol): C, 61.78; H, 4.75;
N, 6.00; S, 13.74. Found: C, 61.52; H, 4.74; N, 5.95; S, 13.71%.
2.2. Synthesis of L2
L2 was prepared in close analogy to a method described in litera-
ture [14], starting from 3.00 g (14.49 mmol) of 3. To a solution of 3
and 2-methoxybenzenethiol (1.76 mL, 14.49 mmol) in CH2Cl2
(120 mL) was added triethylamine (2.01 mL, 14.49 mmol). The reac-
tion was stirred for 1.5 h. The organic layer was washed with aque-
ous HCl (10%, 120 mL) and water (120 mL) and dried over Na2SO4.
The solvent was removed and the product was recrystallized from
CH2Cl2/Et2O. Yield: 3.75 g (12.06 mmol, 83%). M.p. 155 °C. 1H NMR
(300 MHz, CDCl3): d 3.92 (s, 3H, OCH3), 6.99 (dd, 3JH,H = 1.6, 7.6 Hz,
[L2Cu]+, 374 (37) [LCu]+. IR (KBr):
m = 3062 (w), 2965 (w), 1847
(m), 1811 (m), 1629 (s), 1549 (m), 1479 (m), 1344 (m), 1306 (s),
1263 (m), 1232 (s), 1217 (vs), 1175 (s), 1098 (s), 1023 (vs), 859
(m), 839 (m), 798 (s), 765 (s), 699 (m), 630 (m), 462 (m) cmꢀ1. UV/
Vis (DCM): k [nm] (e
rel/L molꢀ1 cmꢀ1) = 261 (0.31), 281 (0.25), 363
(0.63), 376 (0.67). Elemental Anal. Calc. for C36H26Cu2F6N2O12S4
(1045.89 g/mol): C, 41.26; H, 2.50; N, 2.67; S, 12.24. Found: C,
41.81; H, 2.43; N, 2.66; S, 12.10%.
1H, CH5), 7.05 (dd, JH,H = 1.1, 7.9 Hz, 1H, CH6), 7.42 (dt, JH,H = 1.6,
7.9 Hz, 1H, CH3), 7.47–7.62 (m, 4H, CH4, CHmeta, CHpara), 7.66 (s, 1H,
CHvinyl), 8.09–8.13 (m, 2H, CHortho) ppm. 13C NMR (75 MHz, CDCl3):
d 56.1 (OCH3), 111.6 (C5), 119.9 (C1), 121.5 (C6), 125.7 (C@CH),
128.2 (Cortho), 128.9 (Cmeta), 130.6 (Cipso), 131.3 (Cpara), 133.0 (C3),
133.1 (C4), 140.0 (C@CH), 158.2 (C2), 161.6 (C-Ph), 164.3 (C@O)
ppm. MS (ESI): m/z (%) = 645 (39) [M2+Na]+, 350 (17) [M+K]+, 334
3
3
2.5. X-ray crystallography
X-ray data for L1, 4, and 5 were collected on a STOE IPDS II dif-
fractometer (graphite monochromated Mo
k = 0.71073 Å) by use of
K
a
radiation,
+
+
x
scans at ꢀ140 °C (Table 1). The struc-
~
(98) [M+Na] , 312 (100) [M+H] . IR (KBr):
m = 3055 (w), 3015 (w),
tures were solved by direct methods and refined on F2 using all
reflections with SHELX-97 [15]. The non-hydrogen atoms were re-
fined anisotropically. Hydrogen atoms were placed in calculated
positions and assigned to an isotropic displacement parameter of
0.08 Å2. Face-indexed absorption corrections were performed
numerically with the program X-RED [16].
1770 (vs), 1629 (s), 1581 (m), 1477 (m), 1453 (m), 1325 (m), 1294
(m), 1246 (s), 1156 (m), 1070 (m), 1020 (m), 992 (m), 860 (s), 836
(s), 754 (s), 695 (s), 612 (w) cmꢀ1. UV/Vis (DCM): k [nm]
(e
rel/L molꢀ1 cmꢀ1) = 262 (0.20), 281 (0.14), 363 (0.60), 376 (0.65).
Elemental Anal. Calc. for C17H13NO3S (311.06 g/mol): C, 65.58; H,
4.21; N, 4.50; S, 10.30. Found: C, 64.38; H, 4.10; N, 4.41; S, 10.39%.
2.3. Synthesis of [L1Cu(SO3CF3)]2 (4)
3. Results and discussion
To a solution of ligand L1 (58.1 mg, 0.25 mmol, 1.00 eq) in dried
and deoxygenated benzene (5 mL) was added CuSO3CF3ꢁ½ C6H6
(63.0 mg, 0.25 mmol, 1.00 eq). The reaction was stirred for 3 h. After
filtering off the insoluble material, the solvent was removed and the
3.1. Synthesis and characterization of ligands
The oxazolone-based ligands L1 and L2 (Scheme 1) were synthe-
sized in three steps starting from commercially available hippuric

A.C. Jahnke et al. / Inorganica Chimica Acta 374 (2011) 601–605
603
Table 1
Crystal data and refinement details for L1, 4, and 5.
L1
4
5
Empirical formula
Formula weight
Crystal size (mm3)
Crystal system
Space group
a (Å)
C
12H11NO2S
C26H22Cu2F6N2O10S4
891.78
C36H26Cu2F6N2O12S4
1047.91
233.28
0.50 ꢂ 0.09 ꢂ 0.07
monoclinic
P21/n (no. 14)
15.1194(7)
4.92240(10)
15.5644(8)
90
105.488(4)
90
1116.30(8)
4
0.50 ꢂ 0.41 ꢂ 0.19
0.32 ꢂ 0.30 ꢂ 0.27
monoclinic
P21/n (no. 14)
9.5809(4)
13.5532(5)
15.0458(7)
90
94.067(3)
90
1948.81(14)
2
triclinic
ꢀ
P1 (no. 2)
8.6228(5)
9.8383(7)
10.1432(7)
105.164(5)
103.241(5)
94.360(5)
799.94(9)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
q
(g cmꢀ3
)
1.388
1.851
1.786
F(0 0 0)
l
488
0.273
448
1.684
1056
1.402
(mmꢀ1
)
Tmin/Tmax
h Range (°)
hkl Range
Measured reflections
Unique reflections (Rint
0.7651/0.9173
1.67–26.71
19, ꢀ6–5, 19
13070
2367 (0.0497)
2135
0.4832/0.6135
2.15–26.76
10, ꢀ12–10, 12
10572
3382 (0.0474)
3117
0.5101/0.7419
2.02–26.74
12, 17, 19
25693
4119 (0.0501)
3830
)
Observed reflections (I > 2r(I))
data/restraints/parameters
2367/0/146
1.072
3382/0/227
1.032
4119/0/281
1.047
Goodness-of-fit (F2)
R1, wR2 (I > 2
r
(I))
0.0335, 0.0887
0.0380, 0.0910
ꢀ0.267/0.325
0.0313, 0.0806
0.0337, 0.0819
ꢀ0.725/0.805
0.0298, 0.0719
0.0325, 0.0732
ꢀ1.009/1.132
R1, wR2 (all data)
Residual electron density (e Åꢀ3
)
1)HC(OEt)
OAc2
HO
N
3
O
OH
4-DMAP
Ph
Ph
N
H
O
O
2) HCl
O
1
2
O
Cl
Cl
Fig. 1. ORTEP plot (30% probability thermal ellipsoids) of the molecular structure of
L1. Selected bond lengths [Å] and angles [°]: S1–C10 1.7122(15), S1–C11 1.8107(16),
N1–C1 1.2839(19), N1–C3 1.4011(18); C1–N1–C3 105.45(12), C10–S1–C11
100.86(7).
O
SR
O
Cl
O
N
O
HSR, NEt3
N
O
3
Ph
Ph
only the Z-isomer is found, which seems to be the preferred config-
uration of L1. This is supported by NMR experiments: starting from
crystalline material of the Z-isomer slow isomerization is observed
in CDCl3 solution, and after 5 days at 60 °C both isomers could be
observed at an equilibrated ratio of Z/E 10:1.
1
L : R = Et
2
L : R = C H (OMe)-2
6
4
Scheme 1. Synthesis of the oxazolone ligands L1 and L2 with appended enethioe-
ther group.
3.2. Structural and spectroscopic characterization of copper(I)
complexes
acid (1), in close analogy to procedures reported previously [12–
14]. Reaction of key intermediate oxazolone 3 with two different
thiols in the presence of triethylamine leads to L1 and L2 in 66%
or 83% yield, respectively.
Copper complexes of the enethioether–oxazolone ligands L1
and L2 could be obtained by their reaction with CuSO3CF3ꢁ½C6H6
in dried and deoxygenated benzene; the products 4 and 5 were iso-
lated in around 40% yield. Complex formation is evidenced by ESI-
MS measurements, which show dominant signals for species
[L2Cu]+ (at m/z = 529 for [L12Cu]+ and 685 for [L22Cu]+, respectively)
as well as additional peaks characteristic for [LCu]+ and
[L2Cu2(OTf)]+. The IR resonances usually assigned to the C@N
stretch show only minor or even negligible shifts upon complexa-
tion (1638 cmꢀ1 for L1, 1622 cmꢀ1 for 4; 1629 cmꢀ1 for L2 and 5).1
In case of complex 4 orange crystals were obtained by slow diffusion
L1 has already been mentioned in a previous report [17], and its
constitution is now confirmed by X-ray crystallography; the new
compound L2 has been fully characterized by spectroscopic meth-
ods. Pale yellow crystals of L1 were obtained by slow diffusion of
Et2O into a MeCN solution of the crude product. The molecular
structure of L1 along with selected atoms distances and angles is
displayed in Fig. 1.
L1 shows the expected heterocyclic ring structure and the antic-
ipated disposition of the oxazolone-N and thioether-S atoms (Z
configuration of the exocyclic double bond), which thus should
be well suited for binding copper ions in a {NS}-chelating mode.
All metrical parameters of L1 are in the usual range. In the crystals
1
These IR bands may also comprise components from the conjugated exocyclic
C@C bond.

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A.C. Jahnke et al. / Inorganica Chimica Acta 374 (2011) 601–605
to the inversion symmetry the {Cu2S2} units are flat and the sum
of the S–Cu–S and Cu–S–Cu angles is 360°. All copper atoms can
be described as having strongly distorted tetrahedral coordination
geometries in which two sulfur atoms and one nitrogen atom from
the oxazolone ligands and one oxygen atom from the triflate coun-
ter ion coordinate the respective metal center. The two Cu–S dis-
tances are quite different, however, so that the coordination
geometry around the copper atom may also be described as trigo-
nal pyramidal with an additional weak Cu–S interaction. The dif-
ference between the two Cu-S bonds is particularly pronounced
in complex 5 (2.37 versus 2.84 Å), which thus is reminiscent of
the rather rare seesaw type arrangement of donor atoms. Although
the additional oxygen-donor from the anisole group of the L2 li-
gand in 5 is too far away from the metal center to be considered
as a copper-oxygen interaction (dCuꢁꢁꢁO = 3.06 Å) it seems to prevent
the formation of a more regular tetrahedral geometry.
Interestingly complexes 4 and 5 are only the second and third
structurally characterized examples in which a thioether group
(R–S–R0) acts as a bridging ligand in a {Cu2S2} diamond core in
the solid state. More common for RS-based ligands are compounds
with carbothioyl (e.g. thiourea), thiolato- or thiocyanato-bridged
copper atoms. The Cu–S bond lengths and CuꢁꢁꢁCu distances in 4
and 5 are comparable to those reported for the only other com-
Fig. 2. ORTEP plot (30% probability thermal ellipsoids) of the molecular structure of 4.
Hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles
[°]: Cu1–N1 1.9681(16), Cu1–O3 1.9914(16), Cu1–S10 2.3720(6), Cu1–S1 2.5967(6),
S1–Cu10 2.3720(6), Cu1ꢁꢁꢁCu10 3.2663(5); N1–Cu1–O3 140.47(7), N1–Cu1–S10
107.06(5), O3–Cu1–S10 111.97(5), N1–Cu1–S1 82.15(5), O3–Cu1–S1 98.22(5), S1–
Cu10–S10 97.937(19), Cu1–S10–Cu10 82.063(18). Symmetry operation used to
generate equivalent atoms: (0) 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
pound with a {Cu2(
3,5,7-tetramethyl-2,4,6,8-tetrathia-adamantane)-bis(
bis( -chloro)-tetracopper) [18]. In the latter complex the Cu–S
l
-R–S–R0)2} core, namely catena-(bis(
3 -chloro)-
l3-1,
l
l
bonds show only slight differences (2.37 versus 2.40 Å) and the
CuꢁꢁꢁCu0 distance is somewhat longer (3.47 Å), which probably orig-
inates from the otherwise different bonding situation.
The triflate counter ion acts as a co-ligand in 4 and 5. The Cu–O
bond distance of about 2 Å agrees with those reported for related
copper(I) compounds containing triflate ions such as, e.g.
[(Ph3P)2Cu(NCMe)(O3SCF3)] (2.18 Å) [19] or
g
2-cyclo-octene
(2.05 Å) or bis(pyrazolyl)methane-based CO-complexes of cop-
per(I) (ꢃ2.1 Å) [20]. The Cu–O distances, however, seem to depend
on the type of other coordinating ligands. For example, in a series
of copper(I) triflate complexes with 4,7-phenanthroline Cu–O dis-
tances ranging from 2.3 Å to 2.6 Å have been observed [21].
Solutions of 4 and 5 in CDCl3 remain yellow even under aerobic
conditions for several hours and only gradually turn green due to
formation of CuII species, showing that the oxazolone-based {NS}
ligands impart significantly stability to CuI. However, according
to NMR experiments the speciation of the CUI complexes in solu-
tion turned out to be more complicated than expected. All NMR
experiments were carried out under anaerobic conditions. Dissolv-
ing crystals of 4 in CDCl3 gives a clean 1H NMR spectrum of a spe-
cies 40, where differences in chemical shifts compared to the free
ligand L1 are most pronounced for the vinylic proton (7.52 ppm
in the free ligand versus 7.85 ppm in 40) and the ortho protons of
the phenyl group (8.08 ppm in the free ligand versus 8.42 ppm in
40). 1H DOSY experiments gave diffusion coefficients
(1.58 ꢂ 10ꢀ10 m2 sꢀ1 for the free ligand, 1.38 ꢂ 10ꢀ10 m2 sꢀ1 for
40) that are at variance with a dimeric structure 4 but in agreement
with a monomeric [L1Cu(OTf)] composition with tightly bound OTf
group (19F DOSY: 2.09 ꢂ 10ꢀ10 m2 sꢀ1 for the free OTfꢀ anion,
1.38 ꢂ 10ꢀ10 m2 sꢀ1 for 40).2 Furthermore, within several days at
60 °C a new set of signals appears. The new compound 400 shows sig-
nificant changes for the resonances of the vinylic proton (singlet at
8.66 ppm) and the phenyl ortho protons (doublet at 8.23 ppm), but
an only slightly different diffusion coefficient (1.29 ꢂ 10ꢀ10 m2 sꢀ1).
Equilibrium is reached after ten days with a ratio 40:400 of around
Fig. 3. ORTEP plot (30% probability thermal ellipsoids) of the molecular structure of 5.
Hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles
[°]: Cu1–N1 1.9558(16), Cu1–O4 1.9738(14), Cu1–S10 2.3561(6), Cu1–S1 2.8398(5),
Cu1ꢁꢁꢁO3 3.0634(14), Cu1ꢁꢁꢁCu10 3.3874(4); N1–Cu1–O4 135.96(7), N1–Cu1–S10
111.55(5), O4–Cu1–S10 112.48(5), N1–Cu1–S1 79.91(5), O4–Cu1–S1 93.80(4), S1–
Cu10–S10 99.205(16), Cu1–S10–Cu10 80.795(16). Symmetry operation used to
generate equivalent atoms: (0) 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
of Et2O into a benzene solution of the product. Complex 5 forms yel-
low crystals by slow diffusion of Et2O into a toluene solution of the
product. Molecular structures of 4 and 5 are shown in Figs. 2 and 3,
respectively; selected atoms distances and angles are collected in
Table 1.
In contrast to expectation, the molecular structures of 4 and 5 in
the solid state consist of two dimerized [LCu(O3SCF3)] units instead
of the anticipated species [L2Cu](O3SCF3), even if an excess of the
ligand is used. Within the dimeric compounds, which feature crys-
tallographically imposed inversion symmetry, the copper atoms
are bridged by two sulfur atoms of the respective thioether side
arms of the ligands. Cu1ꢁꢁꢁCu10 separations in the resulting dis-
torted {Cu2S2} diamond cores are 3.27 Å (4) and 3.39 Å (5). Due
2
For spherical particles of a given mass density and solvent viscosity the diffusion
coefficient D is proportional to the inverse cubic root of the mass of the particle. Data
for 40 and 400 give effective radii of 3.9 0.1 and 4.2 0.1 Å, which is much smaller
than the value of ꢃ5.8 Å estimated for 4.

A.C. Jahnke et al. / Inorganica Chimica Acta 374 (2011) 601–605
605
Ph
Acknowledgment
O
Ph
O
O
N
Financial support by the Fonds der Chemischen Industrie is
gratefully acknowledged.
O
N
Cu
Cu
OTf
OTf
S
Et
S
Et
Appendix A. Supplementary material
4''
4'
CCDC 813638, 813639 and 813640 contain the supplementary
crystallographic data for compounds L1, 4 and 5, respectively.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.2011.03.070.
Scheme 2. Slow equilibrium between monomeric species 40 and 400 in CDCl3
solution.
1:0.25. Cooling the solution to 243 K leads to broadening of the sig-
nals for 400 (at 223 K also the signals of 40 become broader due to in-
creased viscosity), but no change of the signal ratio is observed,
presumably because of slow interconversion between 40 and 400.
15N chemical shifts (ꢀ145 ppm in the free ligand, ꢀ199 ppm in 40)
References
3
and three-bond coupling constants (3JHCO = 3.5 Hz, JHN = 4.5 Hz in
3
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4. Conclusions
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{N2S2} coordination environment found in methanobactins are
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