Copper chalcogenide clusters stabilized with ferrocene-based diphosphine ligands

Article abstract of DOI:10.1021/ic3021854

The redox-active diphosphine ligand 1,1′-bis(diphenylphosphino) ferrocene (dppf) has been used to stabilize the copper(I) chalcogenide clusters [Cu₁₂(μ₄-S)₆(μ-dppf)₄] (1), [Cu₈(μ₄-Se)₄

Full text of DOI:10.1021/ic3021854

Article
pubs.acs.org/IC
Copper Chalcogenide Clusters Stabilized with Ferrocene-Based
Diphosphine Ligands†
Chhatra B. Khadka,‡ Bahareh Khalili Najafabadi,‡ Mahdi Hesari,‡ Mark S. Workentin,*,‡,§
and John F. Corrigan*,‡,§
‡Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7
§Centre for Advanced Materials and Biomaterials Research, The University of Western Ontario, London, Ontario, Canada N6A 3K7
S
* Supporting Information
ABSTRACT: The redox-active diphosphine ligand 1,1′-bis(diphenylphosphino)-
ferrocene (dppf) has been used to stabilize the copper(I) chalcogenide clusters
[Cu12(μ4-S)6(μ-dppf)4] (1), [Cu8(μ4-Se)4(μ-dppf)3] (2), [Cu4(μ4-Te)(μ4-η2-Te2)(μ-
dppf)2] (3), and [Cu12(μ5-Te)4(μ8-η2-Te2)2(μ-dppf)4] (4), prepared by the reaction of
the copper(I) acetate coordination complex (dppf)CuOAc (5) with 0.5 equiv of
E(SiMe3)2 (E = S, Se, Te). Single-crystal X-ray analyses of complexes 1−4 confirm the
presence of {Cu2xEx} cores stabilized by dppf ligands on their surfaces, where the
bidentate ligands adopt bridging coordination modes. The redox chemistry of cluster 1
was examined using cyclic voltammetry and compared to the electrochemistry of the free
ligand dppf and the corresponding copper(I) acetate coordination complex 5. Cluster 1
shows the expected consecutive oxidations of the ferrocene moieties, CuI centers, and
phosphine of the dppf ligand.
chalcogenolate ligands.7 To this end, the use of silylated
INTRODUCTION
■
chalcogen reagents [E(SiMe3)2 and Fc-R-ESiMe3, where E = S,
The metalloligand 1,1′-bis(diphenylphosphino)ferrocene
Se, R = spacer, and Fc = ferrocenyl] for the formation of
(dppf) has received significant research interest over last 4
structurally characterized ferrocenyl passivated copper and
decades in part because of its redox properties and flexible
silver chalcogen clusters has been well established.7 In principle,
coordination ability when ligated to metal centers.1 The
the “ancillary” phosphine and related ligands used to prepare
inherent properties of this ferrocene-containing ligand can be
nanoscopic metal chalcogenides can also be used to introduce
further manipulated by forming polyferrocenyl assemblies on
redox functionality onto these group 11 clusters. Herein, we
transition-metal clusters, whereby its electrochemical properties
report a probe of the utility of the bidentate phosphine-based
may be altered because of the metal−metal interactions
ferrocene ligand for the surface passivation of copper chalcogen
between the ferrocenyl unit and cluster metal centers.
frameworks with the synthesis and characterization of the
The intrinsic skeletal flexibility of the dppf ligand is manifest
clusters [Cu12(μ4-S)6(μ-dppf)4] (1), [Cu8(μ4-Se)4(μ-dppf)3]
through ring twisting and tilting, making it a valuable ligand in
(2), [Cu4(μ4-Te)(μ4-η2-Te2)(μ-dppf)2] (3), and [Cu12(μ5-
transition-metal cluster chemistry.1b,c,2 As such, it has been
Te)4(μ8-η2-Te2)2(μ-dppf)4] (4), each prepared from [CuOAc-
extensively utilized in cluster synthesis, most notably in the field
(dppf)] (5).
of carbonyl cluster chemistry. Although dppf has not found
similar widespread use in high-nuclearity metal chalcogen
EXPERIMENTAL SECTION
cluster chemistry,2 structurally characterized complexes such as
■
[(μ-Au2dppf){S(Au2dppf)2]2+, [Au5(C6F5)2(μ3-SC6F5)2(μ-
All experimental procedures were performed using standard double-
manifold Schlenk-line techniques under an atmosphere of dried
dppf)2]3+, [Ag4Mo2S8(μ-dppf)2], [Au6Se2(μ-dppf)3]2+, and
nitrogen gas or in nitrogen-filled gloveboxes. The nonchlorinated
[Ni6(μ3-Se2)(μ4-Se3)(dppf)3]2+ illustrate the potential for this
solvents [tetrahydrofuran (THF) and pentane] were dried and
flexible ligand to stabilize larger metal chalcogenide frame-
collected using a MBraun MB-SP Series solvent purification system
works.3 Indeed, dppf has been shown to play an integral role in
with tandem activated alumina (THF) and an activated alumina/
other branches of materials chemistry.4 In principle, dppf, like
other tertiary phosphine ligands, could be used to stabilize
nanoscopic assemblies of metal chalcogen materials5 but with
the added redox property that may ultimately be tailored and
developed for the generation of functional materials.4,6
copper redox catalyst (pentane).8 Chlorinated solvents (CDCl3,
CHCl3, and CH2Cl2) were dried and distilled over P2O5. Spectral-
grade solvent CH2Cl2 was purchased from Caledon. dppf was
purchased from Alfa and used as supplied. The reagents E(SiMe3)2
(E = S, Se, Te)9 and CuOAc10 were synthesized using literature
Recent research interests have focused on the incorporation
of multiple ferrocenyl units on the surface of the semiconductor
metal chalcogenide clusters via the design of ferrocene-based
Received: October 8, 2012
Published: May 24, 2013
© 2013 American Chemical Society
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Scheme 1. Synthesis of 1−4
procedures. Room temperature UV−visible absorption spectra were
recorded on a Varian Cary 100 spectrometer. Solution 1H NMR
spectra were recorded on a Varian Mercury 400 spectrometer with an
operating frequency of 400.08 MHz and referenced externally to
SiMe4 and internally to the residual proton peak in CDCl3. 31P{1H}
NMR spectra were recorded on the same instrument at 161.96 MHz
(C6D6, 23 °C): δp −17.4 (s). Anal. Calcd for C136H112Fe4P8S6Cu12: C,
51.49; H, 3.56; S, 6.06. Found: C, 51.39; H, 3.37; S, 6.16.
Synthesis of 2. CuOAc (0.065g, 0.530 mmol) was dissolved in 20
mL of THF by the addition of dppf (0.294g, 0.530 mmol), and the
yellow solution was cooled to −75 °C. Se(SiMe3)2 (0.06 mL, 0.265
mmol) was added to the yellow solution at −75 °C. The solution
changed color to red-orange after stirring for 2 h, while the reaction
temperature warmed to −10 °C. Red crystals were obtained after ca.
24 h by storing the reaction solution at −25 °C. Single-crystal X-ray-
quality crystals were obtained within a few days by dissolving the
crystals in CH2Cl2 and layering with pentane at room temperature.
Yield: 0.10 g (60%). 1H NMR (CDCl3, 23 °C): δH 7.67 (24H, m, Ph),
7.43−7.36 (36H, m, Ph), 4.37 (12H, s, Cp), 4.18 (12H, s, Cp).
31P{1H} NMR (C6D6, 23 °C): δp −20.4 (s). Anal. Calcd for
and were externally referenced to 85% H3PO4. Elemental analysis was
́
performed by Laboratoire d′Analyze Elementaire de l′Universite
́
de
Montrea
́ ́
l, Montreal, Canada, and Chemisar Laboratories, Guelph,
Canada.
An Autolab30 electrochemical workstation was equipped with GPES
4.9 software used for cyclic voltammetry (CV) experiments. A
homemade glassy carbon (GC; Tokai GC-20) working electrode (3
mm in diameter) was prepared by polishing over silicon carbide papers
(500, 1200, 2400, and 4000) and then over diamond pastes (Struers; 1
and 0.25 μm). The GC electrodes were stored in ethanol and always
polished before each set of experiments with a 0.25 mm diamond
paste, rinsed with dry ethanol (Commercial Alcohols), sonicated in dry
ethanol for 5 min and dried. Ag/AgCl (immersed silver wire in 0.1 M
tetramethyl chloride) and a platinum wire served as the reference and
counter electrodes, respectively.
The electrochemical samples were prepared in the glovebox using
dry dichloromethane (DCM) containing 0.1 M recrystallized
tetrabutylammonium perchlorate (TBAP) as the supporting electro-
lyte. Prior to each electrochemical experiment, the solution was
saturated with argon gas for 10 min, and the inert atmosphere was kept
for all CV measurements.
Single-crystal X-ray data were collected on Enraf-Nonius Kappa
CCD (1 and 4) and Bruker APEX-II CCD (2, 3, and 5)
diffractometers equipped with graphite-monochromated Mo Kα (λ =
0.71073 Å) radiation. Single crystals of the complexes were carefully
selected, immersed in paraffin oil and mounted on MiteGen
micromounts. Crystals were placed immediately in a cold stream of
dinitrogen to minimize desolvation. The structures were solved using
direct methods and refined by the full-matrix least-squares procedure
of SHELXTL.11 All non-hydrogen cluster atoms were refined
anisotropically, while hydrogen atoms were kept at their calculated
distances and refined using a riding model. For chiral 1, the TWIN
command in SHELXTL was used to refine the racemic twinning
[refined Flack parameter = 0.51(2)]. Crystallographic data for
structural analyses have been deposited with the Cambridge
Crystallographic Data Centre, CCDC 871936 and 871937 for
compounds 1 and 2 and CCDC 904597−904599 for 3−5. Copies
of this information may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. [fax (int. code)
+44(1223) 336-033 or e-mail deposit@ccdc.cam.ac.uk or http://www.
ccdc.cam.ac.uk].
C
102H84Fe3P6Se4Cu8: C, 49.21; H, 3.40. Found: C, 49.27; H, 3.29.
Synthesis of 3 and 4. CuOAc (0.045g, 0.367 mmol) was
dissolved in 20 mL of THF by the addition of dppf (0.205g, 0.367
mmol), and the yellow solution was cooled to −75 °C. Te(SiMe3)2
(0.06 mL, 0.185 mmol) was added to the yellow solution at this
temperature. The solution changed color to dark red after stirring for 1
h, while the reaction temperature warmed to −50 °C. The reaction
solution was slowly warmed to room temperature and stirred for an
additional 30 min to obtain a reddish-brown solution. The reaction
solution was stored at −25 °C for 2 days. Highly solvated, single X-ray-
quality crystals of 3 were obtained within a few days by layering with
hexanes at room temperature. Yield: 0.030 g (20%) based on CuOAc.
After the formation of 3, the crystals were isolated from the mother
liquor. Single X-ray-quality crystals of 4 formed within a few days at
room temperature from the reaction solution. Yield: 0.035 g (20%)
1
based on CuOAc. H NMR for 3 (CDCl3, 23 °C): δH 7.73 (16H, m,
Ph), 7.43−7.35 (24H, m, Ph), 4.36 (8H, s, Cp), 4.19 (8H, s, Cp).
31P{1H} NMR for 3 (CD2Cl2, 23 °C): δp −19.3 (s). Anal. Calcd for
1
C68H56Fe2P4Te3Cu4: C, 46.78; H, 3.23. Found: C, 46.80; H, 3.15. H
NMR for 4 (CD2Cl2, 23 °C): δH 7.73 (32H, m, Ph), 7.44−7.36 (48H,
m, Ph), 4.38 (16H, s, Cp), 4.20 (16H, s, Cp). 31P{1H} NMR (CD2Cl2,
23 °C): δp −20.2 (s). Anal. Calcd for C136H112Cu12Fe4P8Te8: C, 40.82;
H, 2.82. Found: C, 40.60; H, 2.56.
Synthesis of 5.12 CuOAc (0.030g, 0.245 mmol) was dissolved in
20 mL of THF by the addition of dppf (0.136g, 0.245 mmol), and the
yellow solution was obtained after stirring for 15 min at room
temperature. Yellow crystals were obtained after ca. 24 h by storing the
1
reaction solution at −25 °C. Yield: 0.140 g (85%). H NMR (CDCl3,
23 °C): δH 7.70 (8H, m, Ph), 7.37 (12H, m, Ph), 4.30 (4H, s, Cp),
4.19 (4H, s, Cp), 2.13 (3H, s, OAc). 31P{1H} NMR (CDCl3, 23 °C):
δp −18.1 (s). Anal. Calcd for C36H31FeP2O2Cu·THF: C, 64.14; H,
5.25. Found: C, 63.76; H, 5.23. Single-crystal X-ray data for 5,
including a thermal ellipsoid plot, are given in the Supporting
Information (Figure S1 and Table S1).
Synthesis of 1. CuOAc (0.059g, 0.481 mmol) was dissolved in 20
mL of THF by the addition of dppf (0.267g, 0.482 mmol), and the
yellow solution was cooled to −75 °C. S(SiMe3)2 (0.05 mL, 0.241
mmol) was added to the yellow solution at −75 °C. The solution
changed color to pale orange after stirring for 2 h, while the reaction
temperature warmed to −10 °C. Red crystals were obtained after ca.
24 h by storing the reaction solution at −25 °C. Single-crystal X-ray-
quality crystals were obtained within 2 days by redissolving crystals in
CHCl3 and layering with pentane at room temperature. Yield: 0.10 g
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Copper
Chalcogenide Complexes. The reaction of the coordination
complex 5, prepared in situ, with 0.5 equiv of the chalcogenide
reagent E(SiMe3)2 in THF afforded 1 and 2 as crystalline solids
after storing at −25 °C for ∼24 h (Scheme 1; E = S, Se). The
1
1
crystals obtained were not of X-ray-quality; however, H NMR
data indicated the formation of product with only one ferrocene
(80%). H NMR (CDCl3, 23 °C): δH 7.70 (32H, m, Ph), 7.44−7.32
(48H, m, Ph), 4.38 (16H, s, Cp), 4.20 (16H, s, Cp). 31P{1H} NMR
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Table 1. Crystal Data, Data Collection, and Refinement Parameters for Complexes 1−4
1·(CHCl3)10
2·(CH2Cl2)6
3·(OC4H8)4.5
4·(OC4H8)9
chemical formula
fw
C136H112P8Fe4S6Cu12·(CHCl3)10
4364.10
C102H84P6Fe3Se4Cu8·(CH2Cl2)6
2996.78
C68H56Cu4Fe2P4Te3·(OC4H8)4.5
2070.14
C136H112Cu12Fe4P8Te8·(OC4H8)9
4649.63
monoclinic
C2/c
cryst syst
space group
temp (K)
a (Å)
tetragonal
monoclinic
P2(1)/n
monoclinic
P2(1)/c
P42(1)/c
̅
150(2)
150(2)
150(2)
150(2)
21.4243(2)
21.4243(2)
17.8779(3)
16.7936(11)
22.2859(15)
30.1023(19)
98.220(2)
11150.4(13)
3.596
26.451(4)
18.553(2)
18.152(2)
109.966(3)
8372.7(18)
2.485
30.448(6)
16.561(3)
35.833(7)
101.85(3)
17684(6)
3.146
b (Å)
c (Å)
β (deg)
V (Å3)
8205.97(18)
2.551
μ (mm−1
)
Z
2
4
4
4
ρ (g cm−3
)
1.766
1.785
1.642
1.746
reflns collected
GOF
16417
339794
135064
106455
1.081
1.097
1.070
1.211
data/param
8347/461
0.0626
21522/1270
0.0485
14741/830
0.0797
15563/757
0.0896
R1 [I > 2σ(I)]
wR2 [I > 2σ(I)]
0.1717
0.1108
0.1963
0.2670
largest diff peak
1.213 and −1.428
2.046 and −1.487
2.630 and −1.135
2.554 and −3.539
and hole (e
Å−3
)
Figure 1. Molecular structure of 1. Thermal ellipsoids are drawn at the 40% probability level. Phenyl groups and hydrogen atoms are omitted for
clarity, and carbon atoms are not labeled. The molecule resides about a crystallographic 4 axis.
̅
environment in solution. These NMR data obtained for 1 show
a downfield shift for the protons from the phenyl groups of the
free ligand, with peaks appearing as two sets of multiplets
between 7.70 and 7.32 ppm. The protons from the cyclo-
pentadienyl ring in 1 appear as broadened singlets at 4.38 and
4.20 ppm, which are again shifted slightly downfield compared
to free dppf in the same solvent (4.25 and 3.99 ppm). 1H NMR
data obtained for 2 show a downfield shift similar to that
observed for 1, with protons from the phenyl groups appearing
as multiplets between 7.67 and 7.36 ppm and protons from the
cyclopentadienyl ring as broadened singlets at 4.37 and 4.18
ppm. 31P{1H} NMR spectra of 1 and 2 display single
resonances at −17.4 and −20.4 ppm, respectively. The purity
of the clusters was further confirmed by elemental analysis.
Electrospray ionization mass spectrometry experiments (pos-
itive- and negative-ion modes) have been used to characterize
clusters 1 and 2. Unfortunately, only fragments were observed.
Products 1 and 2 are stable as solids and in solution for an
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Figure 2. Molecular structure of 2. Thermal ellipsoids are drawn at the 40% probability level. Phenyl groups and hydrogen atoms are omitted for
clarity, and carbon atoms are not labeled.
extended period of time under an inert atmosphere at room
temperature.
present in the asymmetric unit. The cluster resides about a
crystallographic 4 site, with each of the dppf ligands
̅
Highly solvated single crystals suitable for X-ray analysis were
obtained by redissolving the red solids in either CHCl3 (1) or
CH2Cl2 (2) and layering with pentane at room temperature.
Single crystals suitable for X-ray diffraction study for 3 and 4
were isolated from the layering of reaction solutions with a
hydrocarbon solvent. Diffraction data were collected for all
complexes, and a summary of the crystallographic, exper-
imental, and refinement data is listed in Table 1.
The generation of AcOSiMe3 is the driving force for these
reactions, which leads to the formation of metal−chalcogen
bonding interactions forming the copper chalcogenide cluster
core, {Cu2xEx}.5,13 The E2− ligands adopt bridging coordination
modes because of the high polarizabilty of these centers, which
often results in the formation of polynuclear species.13 The
lighter chalcogenide ligands in 1 and 2 adopt μ4-bridging
modes exclusively. The Cu−E cores of 1 and 2 are stabilized by
dppf ligands present on the surface of the complexes, which
protects the cluster from decomposition and/or further
condensation into bulk solids. Under similar reaction
conditions, the sulfur-containing cluster 1 formed a “Cu12S6”
core stabilized by four dppf ligands, while for the selenium-
containing cluster 2, a “Cu8Se4” core stabilized by three dppf
ligands was obtained. The phosphorus atoms of the dppf
ligands are exclusively bonded to a copper atom in a
monodentate fashion in both complexes, with each acting as
a bridging versus chelating ligand. The molecular structures of 1
and 2 are shown in Figures 1 and 2, respectively.
crystallographically equivalent. Eight of the copper centers are
bonded to two sulfur and one phosphorus atoms from the dppf
ligand to complete a distorted trigonal-planar coordination
geometry around Cu1−Cu2C. A distorted linear coordination
geometry is observed for the copper centers bonded to two
sulfide ligands (Cu3−Cu3C; Figure 1). The bond angles
around the three-coordinate copper atoms deviate significantly
from the ideal trigonal-planar coordination angles of 120°, with
smaller P−Cu−S angles ranging from 104.39(8)° to 116.19(9)°
and larger S−Cu−S angles ranging from 136.07(9)° to
139.41(9)° around copper (Table 2). The bond angle around
two-coordinate copper centers is 172.17(9)°. The average Cu−
P bond distance in 1 is 2.292(3) Å, and the average Cu−S bond
distance of 2.320(4) Å of three-coordinate copper atoms is
slightly longer than that observed for the two-coordinate
copper atoms [2.182(3) Å; Table 2]. For dppf, the torsion
angle between the two planes formed by Fe−C−P is 98.8° and
is, of course, equivalent for all four phosphine moieties in 1.
There is no short Fe···cluster contact observed in 1 or in any of
the clusters reported herein.
Cu···Cu interactions in 1 vary from 2.5609(14) to
2.9235(14) Å. The molecular arrangement of the core atoms
in 1 has previously been described for copper sulfide clusters
containing “Cu12S6” with different surface ligands, namely,
[Cu12S6(PR3)8] (R = Et, nPr, nPrPh2, Et2Ph).14 This also
includes structural isomers where PR3 ligate to different copper
atoms in the cluster frame than those observed in 1. The
structure of the “Cu12S6” core in 1 can be derived from a Cu12
cubeoctahedron, which is itself derived from a S6 octahedron
Cluster 1 crystallizes in the tetragonal space group P42(1)/c
̅
with Z = 2, and there are three CHCl3 solvent molecules
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bond distance found in 1. The range of Cu−Se bond distances
for the six three-coordinate copper atoms is 2.4030(10)−
2.5526(10) Å; the Cu−Se bond lengths for the two two-
coordinate copper atoms are markedly shorter [avg. 2.278(4)
Å]. The Cu···Cu interactions in 2 vary from 2.5021(11) to
3.0218(11) Å. The cluster 2 shares some structural features
with the polynuclear copper telluride [Cu8Te4(PPh3)7].15 The
molecular structure of 2 can be described as consisting of a
central (nonbonded) Se4 tetrahedron with copper bridging
edges of the tetrahedron by ligating with the selenide atoms
(two of the edges being doubly bridged). The dppf ligands are
bonded to alternating copper atoms on the edges of the
tetrahedron.
Table 2. Selected Bond Distances (Å) and Bond Angles
(deg) for Complex 1
Cu1−S1
Cu1−P1
Cu1−S2
Cu2−P2
Cu2−S1B
2.280(2)
2.296(2)
2.3392(15)
2.287(2)
2.356(2)
Cu2−S1
Cu3−S1C
Cu3−S2
Cu3A−S2
2.304(2)
2.183(2)
2.180(2)
2.180(2)
S1−Cu1−P1
S1−Cu1−S2
P1−Cu1−S2
P2−Cu2−S1
P2−Cu2−S1B
S1−Cu2−S1B
S2−Cu3−S1
C1−P1−Cu1
Cu3B−S1−Cu2C 70.637
113.90(9)
136.07(9)
110.02(10)
116.19(9)
104.39(8)
139.41(9)
172.17(9)
114.7(3)
C6−P2−Cu2
115.2(3)
70.63(7)
83.10(12)
76.38(8)
135.47(14)
107.10(9)
72.51(7)
79.25(7)
Cu3−S2−Cu1
Cu3−S2−Cu3A
Cu3−S2−Cu1A
Cu1−S2−Cu1A
Cu3B−S1−Cu1
Cu3B−S1−Cu2
Cu1−S1−Cu2
The utility of dppf in stabilizing copper−tellurium frame-
works was also probed with reactions of 5 with Te(SiMe3)2.
The two clusters 3 and 4 were isolated, both of which contain a
mixture of telluride and ditelluride ligands in their CuTe
68.57(6)
2−
architectures. The generation of Te2 from Te(SiMe3)2 in
CuTe cluster chemistry has been previously described and can
occur when these cluster-forming reactions are brought up to
room temperature.16
with 12 copper atoms bridging the sulfur atoms along these
edges (Figure 1). The polyhedron is distorted because of the
coordination of copper atoms to phosphorus and sulfur atoms.
Copper atoms coordinated to one phosphorus and two sulfur
atoms move slightly outward from the cluster center, while
copper atoms coordinated to only two sulfur atoms move
slightly toward the cluster core.14b dppf acts as a bridging ligand
in 1, where the phosphorus atoms are bonded to two
alternating copper atoms that themselves lie along the edges
of the S6 octahedron. For racemic 1, both enantiomers are
observed in the unit cell (via twinning), with a refined Flack
parameter of 0.51(2).
Red-brown, rapidly desolvating single crystals of 3 were
obtained by layering reaction solutions with hexanes. After
numerous attempts at low-temperature mounting onto a
micromount, a suitable data set was obtained from a crystal
displaying only modest visual signs of desolvation. Although the
R(int) and final agreement factors are relatively high (Table 1),
a satisfactory solution and refinement was able to be completed
in the monoclinic space group P2(1)/c.
The structure of 3 (Figure 3 and Table 4) consists of a four-
phosphine-ligated copper(I), with Cu2 and Cu3 displaying
tetrahedral coordination and Cu1/Cu4 being three-coordinate.
The two dppf ligands in 3 each bridge these two different
copper centers. The lone telluride ligand symmetrically bridges
the four copper atoms [2.539(2)−2.679(2) Å], with the μ4-
Te22−CuI bonding distances spanning a greater range of
2.554(2)−2.841(2) Å and a Te−Te bond length of 2.819(1) Å
(Table 4).
The copper selenide cluster 2 crystallizes in the monoclinic
space group P2(1)/n with six molecules of CH2Cl2. Selected
bond distances for 2 are summarized in Table 3. Six copper
Table 3. Selected Bond Distances (Å) for Complex 2
Cu1−P1
Cu1−Se2
Cu1−Se1
Cu2−P2
Cu2−Se1
Cu2−Se4
Cu3−P3
Cu3−Se3
Cu3−Se4
Cu4−P4
Cu4−Se4
2.305(2)
Cu4−Se1
Cu5−P5
Cu5−Se3
Cu5−Se2
Cu6−P6
Cu6−Se2
Cu6−Se3
Cu7−Se2
Cu7−Se4
Cu8−Se1
Cu8−Se3
2.5271(10)
2.215(2)
2.4271(9)
2.4343(9)
2.2114(17)
2.4290(10)
2.4778(10)
2.287(2)
2.4277(10)
2.5350(10)
2.196(2)
The larger copper−tellurium 4 isolated contains four dppf
ligands on the surface and a mixture of Te2− and Te22− ligands
(Figure 4 and Table 5). In contrast to the more open
framework displayed in the dodecacopper sulfide cluster 1, the
larger and more polarizable tellurium ligands in 4 result in
higher coordination numbers around the copper(I) sites (3 and
4 vs 2 and 3). The telluride ligands each bridge five copper(I)
atoms [2.535(2)−2.736(2) Å], and each of the tellurium sites
2.4083(10)
2.5526(10)
2.2752(9)
2.2869(9)
2.2737(10)
2.2747(10)
2.4030(10)
2.4355(9)
2.215(2)
2−
2.4376(9)
in the Te2 is bonded to four copper(I) atoms [2.642(2)−
2.778(2) Å] with a Te−Te bond distance of 2.911(2) Å. As in
1, the four dppf ligands bridge two copper sites, with each of
these copper atoms adopting (distorted) tetrahedral coordina-
tion geometry. The other four copper atoms are each bonded
to three tellurium atoms. Clusters 3 and 4 are stable as solids
and in solution under an inert atmosphere at room temper-
ature.
Room temperature (solution) UV−visible absorption spectra
were recorded for solutions of dppf, 1, and 2 and are illustrated
in Figure 5. Cluster 1 displays a discrete absorption maximum
around 475 nm along with a weak shoulder centered at ∼540
nm. The absorption profile for cluster 2 shows an absorption
maximum at ∼540 nm and a shoulder centered at ∼460 nm.
The absorptions observed at ∼475 nm (1) and ∼460 nm (2)
are in a region similar to that observed for the d−d transitions
in free dppf but of much stronger intensity and consistent with
atoms (Cu1−Cu6) are each coordinated with one phosphorus
atom from the dppf ligand and two selenium atoms to form a
distorted trigonal-planar coordination geometry around the
metal centers. The other two copper atoms (Cu7−Cu8) are
coordinated by two selenium atoms in an almost linear fashion
(Figure 2). P−Cu−Se angles range from 107.36(5)° to
132.42(5)°, and Se−Cu−Se angles range from 109.55(3)° to
138.14(4)° around the three-coordinate copper atoms. The
average bond angle around two-coordinate copper centers is
176.66(6)°, which is closer to linear values than that observed
in 1. The Fe−C−P torsion angle of the dppf ligand bridging
Cu1 and Cu2 is 86.9°, which for the dppf ligand bridging Cu3−
Cu4 is 82.7° and that bridging Cu5−Cu6 is 106.0°, illustrating
the torsional flexibility of the bidentate ligand.1 The average
Cu−P bond distance of 2.238(2) Å in 2 is similar to the Cu−P
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Figure 3. Molecular structure of 3. Thermal ellipsoids are drawn at the 40% probability level.
Table 4. Selected Bond Distances (Å) for Complex 3
Cu1−Te1
Cu2−Te2
Cu2−Te3
Cu3−Te3
Cu4−Te1
Te2−Te3
2.539(2)
2.662(2)
2.838(2)
2.659(2)
2.554(2)
2.819(1)
Cu1−Te3
Cu2−Te1
Cu3−Te1
Cu3−Te2
Cu4−Te2
2.554(2)
2.679(2)
2.656(2)
2.841(2)
2.560(2)
spectra reported for other copper(I) chalcogenide clusters
(Figure 5).15,17 The solution-state absorption data for the
telluride complexes 3 and 4 display similar features but with less
well-pronounced maxima (Figure S2 in the Supporting
Information).
Electrochemical Study. The CV of complexes 1−5 was
investigated in 1 mM oxygen-free DCM solutions of a complex
containing 0.1 M TBAP. Parts A and B of Figure 6 show the
cyclic voltammograms of 1 and 3. The cyclic voltammograms of
these two complexes show a number of similar oxidation
features labeled as I−III. In order to better interpret the
electrochemistry observed for these complexes, the CV of both
the dppf-free ligand (Figure 6C) and CuOAc(dppf) 5 (Figure
6D) was also studied under similar conditions. The CV of the
dppf-free ligand shown in Figure 6C shows a quasi-reversible
one-electron oxidation with a peak potential of 1.02 V, which
becomes reversible [the anodic-to-cathodic peak current ratio
(Ipa/Ipc) reaches 1] with a E0 = 0.93 V at higher scan rates
(demonstrated in the figure as overlapping cyclic voltammo-
grams, corresponding to cyclic voltammograms at increasing
scan rate between 50 to 200 mV s−1). This peak is assigned to
oxidation of the ferrocene moiety, and its electrochemical
behavior is consistent with that reported previously for the dppf
ligand, where the irreversibility at lower scan rates is due to a
competing electrochemical−chemical mechanism of the oxi-
Figure 4. Molecular structure of 4. Thermal ellipsoids are drawn at the
40% probability level. Phenyl groups and hydrogen atoms are omitted
for clarity. The molecule resides about a crystallographic 2-fold
rotation axis.
dized ferrocene ligand.18 This is followed by additional
irreversible peaks at more positive potentials (at 1.63 and
1.86 V vs Ag/AgCl) due to oxidation of the phosphorus of the
phosphine ligands.18 The electrochemistry of CuOAc(dppf) 5
(Figure 6D) shows a one-electron oxidation of the ferrocene
moiety (which also becomes reversible at higher scan rates, vide
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Table 5. Selected Bond Distances (Å) for Complex 4
Te1−Cu6
Te1−Cu5
Te1−Cu4
Te2−Cu3
Te2−Cu4A
Te3−Cu6
Te3−Cu3
Te3−Te3A
Te4−Cu1
Te4−Cu2
Cu1−Cu5
Cu1−Cu2
Cu2−Cu5A
Cu3−Te3A
Cu4−Te2A
Cu5−Te4A
2.535(2)
2.599(2)
2.723(2)
2.570(2)
2.666(2)
2.642(2)
2.660(2)
2.911(2)
2.646(2)
2.757(2)
2.623(3)
2.670(3)
2.703(3)
2.648(2)
2.666(2)
2.648(2)
Te1−Cu1
Te1−Cu2
Te2−Cu5A
Te2−Cu6
Te2−Cu2
Te3−Cu3A
Te3−Cu4
Te4−Cu1A
Te4−Cu5A
Te4−Te4A
Cu1−Te4A
Cu2−Cu6
Cu3−Cu6
Cu3−Cu4A
Cu5−Te2A
2.580(2)
2.669(2)
2.541(2)
2.605(2)
2.736(2)
2.648(2)
2.778(2)
2.645(2)
2.648(2)
2.913(2)
2.645(2)
2.664(3)
2.635(3)
2.666(3)
2.541(2)
Figure 5. Room temperature (solution) UV−visible absorption
spectra of clusters 1 (), 2 (···), and dppf ligand (− −) in DCM.
infra) at 0.94 V followed by a reversible one-electron process at
1.17 V due to oxidation of the copper(I) center to copper(II).19
Complex 5 also shows additional peaks at higher potentials due
to oxidation of the phosphorus centers (not shown).
By comparing the cyclic voltammograms of compounds 1
and 3 to those measured for the dppf ligand and model
copper(I) acetate complex 5, we can better assign the redox
chemistry of 1 (Figure 6A). In the case of 1 and 3, we assign
the peak labeled I to oxidation of ferrocene moieties; in the case
of 1, this has a peak potential (Ep) of 1.15 V, but it is not well-
resolved from the copper oxidation because it overlaps with
peak II due to oxidation of the copper(I) centers (each has
their corresponding reduction peaks I′ and II′). For 3, the first
two waves are resolved enough to show the reversibility of the
first due to the ferrocene moiety, which has a Ep = 1.16 and E0
= 1.12 V vs quasi-Ag/AgCl. The peak III in each is assigned to
oxidation of the phosphorus centers. In the case of 3, there is a
reduction peak at 0.36 V, which is observed only after scanning
through the irreversible phosphorus oxidations (this peak also
appeared in complex 4 at Ep = 0.23 V). The cyclic
voltammograms of clusters 2 and 4 are similar, although the
electrochemistry is not as well-resolved and difficult to
reproduce because these larger clusters are less soluble and
less stable, leading to electrode fouling. However, each cyclic
voltammogram shows a reversible peak from the ferrocene
Figure 6. (A) Cyclic voltammograms of a 1 mM solution of 1 at short
and wide potential range (scan rate 50 mV s−1). (B) Cyclic
voltammograms of a 1 mM solution of compound 3 in DCM (scan
rate 50 mV s−1). The reversibility of the peak I was examined by
applying different scan rates: 25, 50, 100, and 200 mV s−1 (E0 = 1.09 V
vs Ag/AgCl). (C) Cyclic voltammograms of a 1 mM solution of the
dppf ligand in a short potential window, with varying scan rates, 50,
100, and 200 mV s−1 (···), and a wider potential range scan rate (),
50 mV s−1. (D) Cyclic voltammograms of a 1 mM solution of complex
5 in short (− −) and wide potential () ranges (scan rate 50 mV
s−1). All experiments were done in DCM with 0.1 M TBAP. T = 25
°C.
moiety, which can overlap (appears to be more broad) because
of the subsequent oxidation of the copper(I) centers. These are
followed by peaks due to oxidation of the phosphorus sites
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(6) (a) Astruc, D.; Daniel, M.-C.; Ruiz, J. Chem. Commun. 2004,
2637. (b) Daniel, M.-C.; Ruiz, J.; Nlate, S.; Blais, J.-C.; Astruc, D. J.
Am. Chem. Soc. 2003, 125, 2617.
(Figures S3 and S4 in the Supporting Information). No
noticeable color change was observed during the electro-
chemical experiments.
(7) (a) MacDonald, D. G.; Corrigan, J. F. Philos. Trans. R. Soc. A
2010, 368, 1455.. (b) MacDonald, D. G.; Eichhofer, A.; Campana, C.
̈
CONCLUSION
F.; Corrigan, J. F. Chem.Eur. J. 2011, 17, 5890. (c) MacDonald, D.
■
G.; Kubel, C.; Corrigan, J. F. Inorg. Chem. 2011, 50, 3252. (d) Ahmar,
̈
In summary, silylated chalcogen reagents have been used to
isolate copper(I) chalcogenide clusters containing multiple
dppf ligands on the cluster surface. X-ray crystallographic
analyses of 1−4 show that the dppf ligands exclusively adopt
bridging coordination modes on these frameworks. CV
demonstrates the consecutive oxidations of the ferrocene
centers, followed by copper(I) and phosphorus, respectively.
S.; MacDonald, D. G.; Vijayaratnam, N.; Battista, T. L.; Workentin, M.
S.; Corrigan, J. F. Angew. Chem. 2010, 49, 4422. (e) Ahmar, S.;
Nitschke, C.; Vijayaratnam, N.; MacDonald, D. G.; Fenske, D.;
Corrigan, J. F. New J. Chem. 2011, 35, 2013.
(8) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(9) (a) DeGroot, M. W.; Taylor, N. J.; Corrigan, J. F. J. Mater. Chem.
2004, 14, 654. (b) So, J.; Boudjouk, P. Synthesis 1989, 306.
(10) Edwards, D. A.; Richards, R. J. J. Chem. Soc., Dalton Trans. 1973,
2463.
(11) (a) Sheldrick, G. M. SHELXTL PC: An Integrated System for
Solving, Refining, and Displaying Crystal Structures from Diffraction Data,
version 6.1; Bruker Analytical X-ray Systems: Madison, WI, 2000.
(b) Sheldrick, G. M. Acta Crystallogr. 2008, 64A, 112.
(12) Liu, X.; Zhang, S.; Ding, Y. J. Mol. Struct. 2012, 1018, 185.
(13) (a) DeGroot, M. W.; Corrigan, J. F. In Comprehensive
Coordination Chemistry II; Fujita, M., Powell, A., Creutz, C., Eds.;
Pergamon: Oxford, U.K., 2004; Vol. 7, pp 57−123. (b) Fenske, D. In
Clusters and Colloids, From Theory to Applications; Schmid, G., Ed.;
VCH: Weinheim, Germany, 1994; pp 212−297. (c) Fenske, D.;
Corrigan, J. F. In Metal Clusters in Chemistry; Braunstein, P., Oro, L. A.,
Raithby, P. R., Eds.; VCH: Weinheim, Germany, 1999; pp 1302−1324.
(d) Corrigan, J. F.; Fuhr, O.; Fenske, D. Adv. Mater. 2009, 21, 1867.
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic data for complexes 1−5 in CIF format,
molecular structure of 5, crystal data of 5, UV−visible
absorption spectra, and cyclic voltammograms. This material
is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: mworkent@uwo.ca (M.S.W.), corrigan@uwo.ca
(J.F.C.). Phone: 1-519 661-2111 ext 86319 (M.S.W.), 1-519
661-2111 ext 86387 (J.F.C.).
Notes
(14) (a) Dehnen, S.; Schafer, A.; Fenske, D.; Ahlrichs, R. Angew.
̈
The authors declare no competing financial interest.
Chem., Int. Ed. Engl. 1994, 33, 746. (b) Dehnen, S.; Fenske, D.;
Deveson, A. C. J. Cluster Sci. 1996, 7, 351. (c) Dehnen, S.; Eichhofer,
̈
A.; Fenske, D. Eur. J. Inorg. Chem. 2002, 279.
ACKNOWLEDGMENTS
■
(15) Eichhofer, A.; Corrigan, J. F.; Fenske, D.; Troster, E. Z. Anorg.
̈
̈
We gratefully acknowledge the Natural Sciences and Engineer-
ing Research Council of Canada for financial support of this
research and equipment funding. The Government of Ontario,
The University of Western Ontario, and the Canada
Foundation for Innovation are thanked for equipment funding.
Allg. Chem. 2000, 626, 338.
(16) Fenske, D.; Steck, J.-C. Angew. Chem., Int. Ed. Engl. 1993, 32,
238.
(17) (a) Corain, B.; Longato, B.; Favero, G. Inorg. Chim. Acta 1989,
157, 259. (b) Trivedi, M.; Nagarajan, R.; Kumar, A.; Rath, N. P.;
Valerga, P. Inorg. Chim. Acta 2011, 376, 549.
(18) (a) Park, D.; Jabbar, M. A.; Park, H.; Lee, H. M.; Shin, S.; Shim,
Y. Bull. Korean Chem. Soc. 2007, 28, 1996. (b) Nataro, C.; Campbell,
A. N.; Ferguson, M. A.; Incarvito, C. D.; Rheingold, A. L. J. Organomet.
Chem. 2003, 673, 47.
DEDICATION
■
†Dedicated to Prof. Dieter Fenske on the occasion of his 70th
birthday.
(19) Kuang, S. M.; Cuttell, D. G.; McMillin, D. R.; Fanwick, P. E.;
Walton, R. A. Inorg. Chem. 2002, 41, 3313.
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