Trialkylphosphine-stabilized copper(I) phenylchalcogenolate complexes - Crystal structures and copper-chalcogenolate bonding

Article abstract of DOI:10.1021/ic102249g

A series of trialkylphosphine-stabilized copper(I) phenylchalcogenolate complexes [(R₃P)_m(CuEPh)_n] (R = Me, Et, ⁱPr, ^tBu; E = S, Se, Te) has been prepared and structurally characterized by X-ray diffraction. Structures were found to be mono-, di-, tri-, tetra-, hexa-, hepta-, or decanuclear, depending mainly on size and amount of phosphine ligand. Several structural details were observed, including unusually long Cu-E bonds or secondary Cu-E connections, μ4-bridging, and planar bridging chalcogenolate ligands. Relatively rigid Cu-E-C angles were found to be of significant influence on the flexible molecular structures, especially for bridging chalcogenolate ligands, since in these cases a correlation results between the Cu-E-Cu angles and the inclination of the E-C bonds to their Cu-E-Cu planes. We further address some of these phenomena by means of density functional computations.

Full text of DOI:10.1021/ic102249g

ARTICLE
pubs.acs.org/IC
Trialkylphosphine-Stabilized Copper(I) Phenylchalcogenolate
Complexes - Crystal Structures and CopperꢀChalcogenolate Bonding
Oliver Kluge, Katharina Grummt, Ralf Biedermann, and Harald Krautscheid*
Institut f€ur Anorganische Chemie, Universit€at Leipzig, Johannisallee 29, 04103 Leipzig, Germany
S Supporting Information
b
ABSTRACT: A series of trialkylphosphine-stabilized copper(I) phenylchalcogenolate com-
i
t
plexes [(R3P)m(CuEPh)n] (R = Me, Et, Pr, Bu; E = S, Se, Te) has been prepared and
structurally characterized by X-ray diffraction. Structures were found to be mono-, di-, tri-,
tetra-, hexa-, hepta-, or decanuclear, depending mainly on size and amount of phosphine
ligand. Several structural details were observed, including unusually long CuꢀE bonds or
secondary Cu–E connections, μ4-bridging, and planar bridging chalcogenolate ligands.
Relatively rigid CuꢀEꢀC angles were found to be of significant influence on the flexible
molecular structures, especially for bridging chalcogenolate ligands, since in these cases a
correlation results between the CuꢀEꢀCu angles and the inclination of the EꢀC bonds to
their CuꢀEꢀCu planes. We further address some of these phenomena by means of density
functional computations.
’ INTRODUCTION
containing trigonal planar as well as tetrahedrally coordi-
nated copper atoms. The compound [(Ph3P)4(CuSPh)3] forms
a six-membered ring of alternating copper and sulfur atoms,12
and [(Ph3P)4(CuSPh)4] was described as a distorted step
structure.13 With diphenyl-ethyl-phosphine, the hexanuclear
complex [(Ph2EtP)5(CuTePh)6] could be obtained,14 forming
the same cage structure as the related silver compound
[(Ph3P)5(AgSC6H4Cl)6].15
Some trialkylphosphine-stabilized copperꢀphenyltellurolates
have already been reported,16 namely, [(Me3P)4(CuTePh)2]
and [(iPr3P)3(CuTePh)4], but while the report focused on the
photolysis of these substances to obtain mixed tellurolateꢀ
telluride systems, we reinvestigated the structures of the tell-
urolates and avoided any photolysis. We extended the study to
the lighter chalcogens sulfur and selenium, for which surprisingly
no structures were reported before. The systematic use of Me3P,
Et3P, iPr3P, and tBu3P allowed for determination of the sterical
influence of the phosphine ligand, since they span a wide range of
cone angles.17
Usually, the motivation for investigations of metal chal-
cogenolates1 is their importance in biological systems,2 or their
ability to act as precursor compounds in the generation of metal
chalcogenides.3 We use these binary compounds as starting
materials of definite composition for the synthesis of ternary
compounds. As it turned out, a big variety of compositions can be
obtained, and secondary copper--chalcogen connections and
extraordinarily long copperꢀchalcogen bonds occur in these
molecules. Therefore, we decided to perform a systematic X-ray
structural study in order to address this phenomena and explain
the molecular structures in terms of steric and electronic factors
with further information from quantum chemical calculations.
While copper(I) phenylthiolate forms polymeric chains, as
shown in a recent X-ray powder diffraction study,4 the structures
of the homologous selenium and tellurium compounds are still
unknown. Copper(I) phenylselenolate can be obtained as a
brownish yellow precipitate from cuprous oxide and phenyl-
selenol.5 Without the support of strongly coordinating ligands
(e.g., phosphines) several phenylchalcogenocuprates are acces-
sible. The ion [Cu(SPh)3]2ꢀ was reported in two different con-
formations,6,7 and coordination to a (CuSPh)3-ring leads to the
ion [Cu4(SPh)6]2ꢀ, which is built up by a tetrahedral arrange-
ment of trigonally coordinated copper atoms.6,8 The homolo-
gous ion with selenium is also known and was found to exhibit
the same structure.9
’ RESULTS AND DISCUSSION
1. Crystal Structures. Trialkylphosphine-stabilized copper(I)
phenylchalcogenolate complexes of the general formula
[(R3P)m(CuEPh)n] (E = S, Se, Te) can be obtained in high
yield by the reaction of copper(I) acetate with the silylated
phenylchalcogenolates under elimination of Me3SiOAc in the
presence of the appropriate amount of phosphine ligand
With triphenylphosphine as an additional ligand several
neutral polynuclear complexes of the general formula [(Ph3P)m
(CuEPh)n] (E = S, Se) are accessible. The dinuclear com-
pounds [(Ph3P)4(CuSPh)2]10 and [(Ph3P)3(CuSePh)2]11 have
been reported to form four-membered ring systems, the latter
Received: November 9, 2010
Published: May 06, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
(Scheme 1). Alternatively, cuprous oxide can be reacted with the
phenylchalcogenol, which requires higher temperatures and at
least 2 equiv of phosphine ligand. Complexes can be intercon-
verted into each other by addition of phosphine ligands, increas-
ing the ratio m/n, or by mixing with CuEPh (if accessible),
decreasing the ratio m/n.
Table 1 gives an overview of the compounds we obtained.
After a brief description of the overall molecular structures and
noteworthy properties, a discussion of the structural parameters
(e.g., bond lengths and angles) will be given in a comparative
manner, focusing on unusual observations, supported by quan-
tum chemical calculations to understand and explain some of the
observed trends. Preparative and computational details as well as
structural data are part of the Supporting Information, and
relevant crystallographic data and refinement details are given
in Tables 2, 3, and 4.
By use of 3 equiv of triethylphosphine the copper atoms can be
shielded sterically and saturated electronically, leading to mono-
nuclear phenylchalcogenolates [(Et3P)3CuEPh] with E = S (1),
Se (2), and Te (3). The structures are shown in Figure 1. These
compounds melt between 15 and 20 °C, giving colorless oils at
room temperature. The copper atoms display a distorted tetra-
hedral environment, with PꢀCuꢀP angles somewhat larger than
109°. CuꢀE distances are 235.75(7) pm for E = S, 247.74(7) pm
for E = Se, and 268.9(2) pm for E = Te.
These compounds resemble the series [(Et3P)3CuESiMe3];18
the main differences are 2ꢀ5 pm shortened CuꢀE bonds and
about 10° smaller CuꢀEꢀR angles (R = Ph, SiMe3) in 1ꢀ3
compared with the analogous trimethylsilylchalcogenolates.
Both can be attributed to sterical reasons. A striking difference
is the 77Se-NMR shift, which is reported to be ꢀ570 ppm for
[(Et3P)3CuSeSiMe3] and is found to be þ74 ppm for 2.
If less than 1 equiv of triethylphosphine is used in the
synthesis, the hexanuclear compounds [(Et3P)5(CuEPh)6]
(E = S (4), Se (5), and Te (6)) can be isolated. These structures
are shown in Figure 2. The structure of 4 can be described as two
six-membered rings which are connected by three additional
CuꢀS bonds, Cu2ꢀS1, Cu4ꢀS5, and Cu5ꢀS4. The atoms Cu1,
Cu3, and Cu6 are coordinated in a trigonal planar fashion, each
by two sulfur atoms and one phosphorus atom. Cu2 is sur-
rounded by three sulfur atoms, and Cu4 and Cu5 are coordinated
tetrahedrally, each by three sulfur atoms and one phosphorus
Scheme 1. Summary of Reactions
Table 1. Trialkylphosphine-Stabilized Copper(I) Phenylchalcogenolate Complexes 1ꢀ18
E =
S
Se
Te
Me3P
[(Me3P)4(CuSPh)2] 15
[(Me3P)6(CuSPh)10] 18
[(Et3P)3CuSPh] 1
[(Me3P)4(CuSePh)2] 16
[(Me3P)4(CuTePh)2]a 17
Et3P
[(Et3P)3CuSePh] 2
[(Et3P)3CuTePh] 3
[(Et3P)5(CuSPh)6] 4
[(iPr3PCuSPh)3] 7
[(iPr3P)4(CuSPh)6] 8
[(tBu3PCuSPh)2] 13
[(Et3P)5(CuSePh)6] 5
[(iPr3P)4(CuSePh)6] 9
[(iPr3P)3(CuSePh)7] 10
[(tBu3PCuSePh)2] 14
[(Et3P)5(CuTePh)6] 6
[(iPr3P)3(CuTePh)4]a 11
iPr3P
tBu3P
[(tBu3P)3(CuTePh)4] 12
a Lit.16
Table 2. Crystallographic Data for Compounds [(Et3P)m(CuEPh)n]: [(Et3P)3CuEPh] E = S (1), Se (2), Te (3) and
[(Et3P)5(CuEPh)6] E = S (4), Se (5), Te (6)
1
2
3
4
5 0.5 C5H12
6
3
chemical formula
formula weight [g molꢀ1
C
24H50CuP3S
C24H50CuP3Se
574.05
C24H50CuP3Te
622.69
C66H105Cu6P5S6
1626.95
C68.5H111Cu6P5Se6
1938.38
C66H105Cu6P5Te6
2200.19
P21/n (No. 14)
21.6472(6)
15.5979(5)
24.1542(7)
90
]
527.15
Cc (No. 9)
16.550(1)
10.9479(9)
15.921(1)
90
3
space group
a [Å]
b [Å]
c [Å]
Cc (No. 9)
16.642(2)
10.9725(7)
16.005(1)
90
P21/n (No. 14)
8.9061(9)
33.255(3)
9.998(1)
90
P1 (No. 2)
13.1180(8)
13.8829(9)
23.449(1)
91.776(5)
94.983(5)
116.266(4)
3803.5(4)
2
P1 (No. 2)
13.6847(6)
14.9342(6)
22.375(1)
92.005(3)
103.197(3)
114.376(3)
4011.8(3)
2
R [°]
β [°]
γ [°]
V [Å3]
95.958(5)
90
95.508(7)
90
94.643(9)
90
98.176(2)
90
2869.1(3)
4
2909.1(4)
4
2951.3(5)
4
8072.8(4)
4
Z
Dcalcd [g cmꢀ3
]
1.220
1.311
1.401
1.421
1.605
1.810
3
μ [MoKR, mmꢀ1
R1 [I > 2σ(I)]
wR2 [all data]
]
1.011
2.176
1.881
1.953
4.419
3.811
0.0275
0.0697
0.0448
0.0908
0.0407
0.0321
0.0306
0.1199
0.2546
0.1003
0.0729
0.0763
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Table 3. Crystallographic Data for Compounds [(iPr3P)m(CuEPh)n]: [(iPr3PCuSPh)3] (7), [(iPr3P)4(CuEPh)6] E = S (8), Se (9),
[(iPr3P)3(CuSePh)7] (10) and [(iPr3P)3(CuTePh)4] (11)
7
8
9
9 C5H12
10
11
3
chemical formula
formula weight [g molꢀ1
C45H78Cu3P3S3
998.78
C72H114Cu6P4S6
1677.11
P21/n (No. 14)
14.8375(7)
15.7165(9)
18.4522(8)
90
C72H114Cu6P4Se6
1958.51
C77H114Cu6P4Se6
2018.56
C69H98Cu7P3Se7
2017.88
P21/n (No. 14)
16.8095(9)
21.8464(8)
21.450(1)
90
C51H83Cu4P3Te4
1553.64
]
3
space group
a [Å]
b [Å]
c [Å]
P21/n (No. 14)
14.0503(7)
13.4364(4)
26.985(1)
90
P1 (No. 2)
14.9051(7)
16.5766(9)
18.514(1)
102.399(4)
103.369(4)
100.992(4)
4205.3(4)
2
P1 (No. 2)
14.9225(7)
24.362(1)
27.153(1)
71.435(3)
88.298(4)
71.704(4)
8857.3(7)
4
P1 (No. 2)
11.8041(6)
15.1305(9)
18.503(1)
83.637(5)
80.377(5)
68.120(4)
3019.2(3)
2
R [°]
β [°]
γ [°]
V [Å3]
95.093(4)
90
112.584(3)
90
90.499(4)
90
5074.2(4)
4
3973.0(3)
2
7876.9(6)
4
Z
Dcalcd [g cmꢀ3
]
1.307
1.402
1.547
1.514
1.702
1.709
3
μ [Mo KR, mmꢀ1
R1 [I > 2σ(I)]
wR2 [all data]
]
1.490
1.850
4.199
3.989
5.186
3.393
0.0384
0.0377
0.0296
0.0473
0.0312
0.0310
0.1007
0.0858
0.0703
0.0984
0.0589
0.0786
t
t
t
n
Table 4. Crystallographic Data for Compounds [(R3P)m(CuEPh) ] (R = Me, Bu): [( Bu3P)3(CuTePh)4] (12), [( Bu3PCuEPh)2]
E = S (13), Se (14), [(Me3P)4(CuEPh)2] E = S (15), Se (16), [(Me3P)6(CuSPh)10] (18)
12
13
14
15
16
18 CH3OH
3
chemical formula
formula weight [g molꢀ1
C
60H101Cu4P3Te4
C36H64Cu2P2S2
750.01
C36H64Cu2P2Se2
843.81
C24H46Cu2P4S2
649.69
C24H46Cu2P4Se2
743.49
C79H107Cu10OP6S10
2214.47
C2/c (No. 15)
28.423(1)
13.5129(5)
25.2897(9)
90
]
1679.88
Pccn (No. 56)
18.1425(4)
23.7058(6)
31.4413(6)
90
3
space group
a [Å]
b [Å]
c [Å]
P21/c (No. 14)
13.0681(7)
25.049(1)
13.1012(8)
90
P212121 (No. 19)
10.8035(5)
16.1997(8)
22.5376(8)
90
P21/n (No. 14)
10.8449(6)
10.9060(6)
14.3336(9)
90
P21/c (No. 14)
17.0556(9)
13.6841(8)
14.0034(7)
90
R [°]
β [°]
γ [°]
V [Å3]
90
113.356(4)
90
90
102.679(5)
90
91.081(4)
90
105.633(3)
90
90
90
13522.4(5)
8
3937.2(4)
4
3944.4(3)
4
1654.0(2)
2
3267.7(3)
4
9353.7(6)
4
Z
Dcalcd [g cmꢀ3
]
1.650
1.265
1.421
1.305
1.511
1.570
3
μ [Mo KR, mmꢀ1
R1 [I > 2σ(I)]
wR2 [all data]
]
3.038
1.290
3.027
1.617
3.737
2.591
0.0323
0.0857
0.0264
0.0358
0.0255
0.0250
0.0271
0.0714
0.0672
0.0684
0.0504
0.0629
Figure 1. Molecular structures of compounds [(Et3P)3CuEPh], E = S (1), Se (2), Te (3). Hydrogen atoms omitted, 50% probability ellipsoids.
atom. Additionally, a secondary Cu--S connection between Cu1
and S2 is observed, their distance is 290.38(9) pm, and Cu1 is
31 pm out of the plane defined by P1, S1, and S6.
A different structure is found for compounds 5 and 6. In these
complexes the six chalcogen atoms form a distorted octahedron
with three faces capped by the atoms Cu4, Cu5, and Cu6. The
tetrahedral coordination sphere of these copper atoms is com-
pleted by one phosphine ligand each. Cu1 is coordinated by two
phosphine ligands and bridges the edge E1ꢀE2 of the octahe-
dron. The atoms Cu2 and Cu3 each lie on the center of opposite
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Figure 2. Molecular structures of compounds [(Et3P)5(CuEPh)6], E = S (4), Se (5), Te (6). Thermal ellipsoids are drawn at 50% probability level.
Hydrogen and carbon atoms are omitted; only carbon atoms bound to chalcogen atoms are shown.
Figure 3. Molecular structures of [(iPr3PCuSPh)3] (7) and [(iPr3P)4(CuSPh)6] (8). Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms and iPr-groups are omitted.
faces of the octahedron and therefore are trigonal planar. Note
that the trigonal planar coordination of Cu2 by E1, E2, and E3 is
the only structural similarity between 4 and 5 and 6. The cage
structure found for 5 and 6 is identical with that of the com-
pounds [(Ph2EtP)5(CuTePh)6]14 and [(Ph3P)5(AgSC6H4Cl)6].15
Interestingly, Corrigan and co-workers obtained the related ionic
compound [Et3PPh]þ[(Et3P)3Cu5(TePh)6]ꢀ.16 The anionic
part of this structure is identical with 6, if the (Et3P)2Cuþ-
moiety bridging Te1 and Te2 in 6 is removed.
With triisopropylphosphine as a ligand we obtained two
phenylthiolate complexes [(iPr3PCuSPh)3] (7) and [(iPr3P)4-
(CuSPh)6] (8). These two structures are shown in Figure 3. The
trinuclear complex 7 consists of a nearly planar Cu3S3 ring with
a phosphine ligand coordinated to each copper atom. Not only
the copper atoms but also the sulfur atom S2 display a trigonal
planar environment, a rare case which will be addressed more
extensively in a later section.
The asymmetric unit of the hexanuclear complex 8 is again a
Cu3S3-ring. By the crystallographic inversion center the com-
plete molecule is created, which therefore has the point group
symmetry Ci. The two six-membered rings are connected by four
additional CuꢀS bonds (Cu2ꢀS10, Cu3ꢀS20, Cu20ꢀS1, and
Cu30ꢀS2). Atom Cu2 and its symmetry equivalent are tetra-
hedrally coordinated by three sulfur atoms and one phosphorus
atom. The bond Cu2ꢀS10 with 267.06(9) pm is extraordinarily
long, so one can state that this copper atom is intermediate
between tetrahedral and trigonal planar coordination. The other
copper atoms are trigonal planar, Cu1 is coordinated by one
phosphine ligand and two sulfur atoms, and Cu3 by three sulfur
atoms. Overall, the copper atoms as well as the sulfur atoms form
an octahedron each, both octahedra interpenetrating each other.
Compound 8 can be easily converted to compound 7 by adding
the necessary 2 equiv of triisopropylphosphine per mole of 8.
Accessible selenium compounds with triisopropylphosphine
ligands are [(iPr3P)4(CuSePh)6] (9) and [(iPr3P)3(CuSePh)7]
(10). Their structures are shown in Figure 4. The structure of
compound 9 can be described as a tetrahedron of selenium atoms
(Se3, Se4, Se5, and Se6). One tetrahedral face is capped by Cu6,
and four edges are bridged by Cu2, Cu3, Cu4, and Cu5,
respectively. The atoms Cu2 and Cu3 bind to Se1 and Se2,
which form further bonds to Cu1, giving a six-membered ring
together with Se3. The copper atoms are trigonal planar, except
Cu6 which is tetrahedrally coordinated but has a very long bond
of 270.15(5) pm to Se5 and is therefore intermediate between
tetrahedral and trigonal planar coordination. The atom Cu5 is 32
pm out of the plane defined by P3, Se4, and Se5, indicating a
weak secondary Cu--Se connection, since the distance between
Cu5 and Se2 is 363.69(5) pm. Compound 9 can also be crystal-
lized with pentane. The triclinic unit cell volume is doubled then,
and the asymmetric unit consists of two independent molecules,
which differ in their organic periphery; for example, the con-
formations of the phosphine ligands P3 and P4 are not identical.
The heavy atoms of the second molecule form nearly the same
framework as found in the solvent-free structure, but the long
bond Cu6ꢀSe5 appears to be somewhat shorter here (262.5(1)
pm). The secondary connection between Cu5 and Se2 is weaker
with a distance of 367.3(1) pm and an out-of-plane parameter of
26 pm for Cu5. In the first molecule a Cu5--Se2 distance of
413.0(1) pm and an out-of-plane parameter of only 13 pm is
observed. The bond between Cu6 and Se3 is replaced by a
secondary connection in the first molecule, the distance is
325.8(1) pm and Cu6 is 20 pm out of the plane defined by
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Figure 4. Molecular structures of [(iPr3P)4(CuSePh)6] (9) (left: solvent-free; middle: first molecule from 9 pentane) and [(iPr3P)3(CuSePh)7] (10).
3
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen and carbon atoms are omitted; only carbon atoms bound to chalcogen atoms
are shown.
Figure 5. Molecular structures of [(R3P)3(CuTePh)4], R = iPr (11, triclinic phase) and tBu (12, two independent molecules). Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms and carbon atoms of alkyl groups are omitted.
Se5, Se6, and P4. Instead, Cu4 is the tetrahedrally coordinated
atom then. Therefore, Se3 shows the tendency to bridge four
copper atoms.
asymmetric unit of compound 12 consists of two independent
half molecules, each containing a 2-fold rotation axis.
A significant difference going from iPr3P to tBu3P is the orienta-
tion of the phenyl groups attached to Te2 and Te3 in 11 and Te1
and Te10 in 12. The former are in syn-position, the latter in anti-
position. Further differences are slightly elongated Cu2ꢀTe
bonds in 12 due to the larger phosphine ligand. The most
striking differences are found in the opposite side of the ring
system, relative to Cu2. A schematic representation of the
CuꢀTe connectivities in this part of the molecules is given in
Figure 6.
The short bond between Cu4 and Te4 in 11 remains un-
changed when the phase transition occurs, while the very long
bond between Cu4 and Te1 is further elongated. The respective
bonds in 12 are equal by symmetry, and therefore the coordina-
tion of the central atom Cu4 is more tetrahedral in 12. In 11 the
atom Cu4 is only 22 pm (triclinic phase) or 19 pm (monoclinic
phase) out of the plane defined by Te2, Te3, and Te4, so the
coordination sphere is trigonal pyramidal rather than tetrahedral.
The coordination spheres of the atoms Cu1 and Cu3 in 11 are
intermediate between trigonal planar and tetrahedral, since all
the distances to Te4 are large. In the triclinic phase Cu3 is more
tetrahedrally coordinated, with a very long bond of 289.83(6) pm
to Te4, while Cu1 is better described as trigonal planar with
a secondary connection (337.88(6) pm) to Te4, resulting in an
out-of-plane parameter of 31 pm for Cu1 based on P1, Te1, and
Te2. After phase transition to the monoclinic crystal system, the
connections between Te4 and copper atoms Cu1 and Cu3 both
The structure of 10 is related to that of 9 by replacing the
phosphine ligand at Cu5 with an CuSePh moiety, which forms
additional bonds to Se1 and Se2. The result is an octahedron of
selenium atoms (Se1 to Se5 and Se7) and a tetrahedron of
trigonal planar copper atoms (Cu2, Cu3, Cu5, and Cu7). This
central core resembles the ion [Cu4(SePh)6]2ꢀ.9 The Se1ꢀSe2
edge of the octahedron is bridged by Cu1 and the Se3ꢀSe5 edge
by Cu6. The bond length of Cu6ꢀSe3 is 281.69(6) pm, which is
a borderline case between a bond and a secondary connection, so
Cu6 is intermediate between tetrahedral and trigonal planar
coordination. A secondary Cu--Se connection is observed be-
tween Cu4 and Se3, their distance is 324.63(6) pm and Cu4 is 35
pm out of the plane defined by P2, Se4, and Se6, so Cu4 is on the
way to tetrahedral coordination, too. This leads to approximate
Cs-symmetry for the heavy atom framework, and Se3 shows the
tendency to bridge four copper atoms.
The monoclinic phase of [(iPr3P)3(CuTePh)4] (11) has been
reported before.16 If synthesis and crystallization are performed at
low temperatures, a metastable triclinic phase is obtained, which
converts to the reported monoclinic phase at room temperature.
The compound [(tBu3P)3(CuTePh)4] (12) exhibits a very
similar structure. The two structures are shown in Figure 5.
These tetranuclear complexes consist of a centered [(R3P)3
Cu4(TePh)3]þ ring system, which is also part of compound 6.
An additional TePhꢀ ligand completes these molecules. The
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Figure 6. Schematic representation of different CuꢀTe distances [pm] in [(R3P)3(CuTePh)4], R = iPr (11) and tBu (12).
Figure 7. Molecular structures of compounds [(tBu3PCuEPh)2], E = S (13) and Se (14). Hydrogen atoms omitted, 50% probability ellipsoids.
are secondary. It was stated that the phenyltellurolate ligand Te4
is perhaps best described as “pseudo-terminal”,16 a statement we
agree with, since the bond Cu4ꢀTe4 is even 13 pm shorter than
the CuꢀTe bond in compound 3, where the phenyltellurolate
ligand is terminal. In the first molecule of 12, one bond is of usual
length (Cu1ꢀTe2) and a secondary connection of 308.26(6) pm
is observed between Cu1 (47 pm out of plane) and Te20. In
the second molecule, the respective atoms are all connected
by bonds, with the overall longest CuꢀTe bond distance of
291.6(1) pm between Cu1 and Te2. In fact, this bond shows
some properties of a secondary Cu--Te connection and may
therefore be described as a borderline case.
15 consists of half a molecule. The complete molecules are
centrosymmetric. For 16 there are two independent half mol-
ecules in the asymmetric unit, generating two different molecules
with inversion symmetry. Therefore, the four-membered rings
are exactly planar and the phenyl groups are in anti-position. The
copper atoms are coordinated tetrahedrally by two phosphine
ligands and two bridging phenylchalcogenolates. In 15 the two
independent CuꢀS bonds have the same length (238.83(5) pm
and 238.93(4) pm) and the planes of the phenyl groups are
approximately perpendicular to the plane defined by the two
sulfur atoms and C1, so the molecule has approximately
C2h-symmetry. In 16 a short and a long CuꢀSe bond can be
distinguished for each molecule, and the difference is about 5 pm.
Interestingly, the shorter bond is found with the phenyl ring in
plane, which is contrary to what one would expect from sterical
considerations. As was found for 17,16 the two independent
molecules differ in their CuꢀEꢀCu angles. The difference for 17
was reported to be about 8°, and in 16 it is 6°. A 77Se-NMR signal
at ꢀ39 ppm could be observed for compound 16. Note that the
homologous oxygen compound [(Me3P)4(CuOPh)2] was also
characterized structurally.19 In contrast to 15, 16, and 17 the
phenyl rings are in plane with the Cu2O2 ring.
t
With Bu3P and the lighter chalcogens, we obtained the
dinuclear complexes [(tBu3PCuEPh)2] with E = S (13) and
E = Se (14). The structures are shown in Figure 7. The copper
atoms are trigonal planar with two bonds to the chalcogen atoms
and one to phosphorus. Because of the bulky phosphine ligands
these systems are sterically crowded, resulting in one EPhꢀ-
moiety coordinating with elongated bond lengths. The max-
imum difference between CuꢀE bond lengths is 16 pm in 13 and
13 pm in 14, showing some relaxation due to the larger Cu2E2-
core in 14. The angle P2ꢀCu2ꢀS1 in 13 is 146.35(2)°, which is
nearly half way to linear coordination. The phenyl groups are in
anti-position and the four-membered rings are folded along the
vector Cu1ꢀCu2 (44° in 13 and 52° in 14).
A further phenylthiolate compound coordinated by trimethyl-
phosphine could be isolated. The structure of the decanuclear
complex [(Me3P)6(CuSPh)10] (18) is shown in Figure 9. The
asymmetric unit contains half a molecule, and the complete
molecules have the point group symmetry Ci. The inner core
containing the atoms Cu1, Cu2, Cu5, S1, S2, S3 and their
symmetry equivalents resemble the structure of the hexanuclear
complex 8, with two interpenetrating octahedra of sulfur and
Other dinuclear complexes can be obtained with 2 equiv of
trimethylphosphine. The structures of [(Me3P)4(CuEPh)2]
with E = S (15) and E = Se (16) are shown in Figure 8. The
homologous tellurium compound (17) has been described
already16 and is isomorphous with 16. The asymmetric unit of
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Figure 8. Molecular structures of compounds [(Me3P)4(CuEPh)2], E = S (15) and Se (16, two independent molecules). Hydrogen atoms are omitted,
50% probability ellipsoids.
Figure 9. Molecular structure of [(Me3P)6(CuSPh)10] (18). Thermal ellipsoids are drawn at the 50% probability level. Left: hydrogen atoms omitted;
right: only the heavy atom framework with carbon atoms bound to sulfur atoms is shown.
Table 5. Minimal, Average, and Maximal CuꢀE Bond
Lengths [pm] Found in Compounds 1ꢀ18
Table 6. Distances for Secondary Cu--E Connections in
Compounds 1ꢀ18, Out-of-Plane Parameters (o. o. p. p.) for
the Respective Copper Atom and Cu--E-C Angles
E
minimal
average
maximal
E
compound
Cu--E [pm]
oopp [pm]
Cu--E-C [deg]
Cu(3-fold coordinated)-E [pm]
S
4
290.38(9)
324.63(6)
325.8(1)
31.15(6)
34.80(4)
20.13(9)
32.32(4)
25.75(8)
45.38(6)
47.17(5)
49.15(5)
30.80(5)
129.2(1)
140.8(1)
152.9(2)
122.05(9)
122.7(2)
120.4(1)
137.3(1)
132.3(1)
134.1(1)
S
219
232
251
227
241
261
246
257
267
Se
10
Se
9 pentane
3
Te
9
363.69(5)
367.3(1)
Cu(4-fold coordinated)-E [pm]
9 pentane
3
S
232
243
255
240
254
268
267
282
292
Te
11
12
11
11
305.58(7)
308.28(6)
314.83(7)
337.88(6)
Se
Te
copper atoms, respectively. In 18 the atoms Cu4 and S5 bind to
the Cu6S6-core and are connected by Cu3 and S4, giving a six-
membered ring together with Cu5 and S2. Atoms Cu1 and Cu2
are coordinated tetrahedrally by one phosphorus and three sulfur
atoms, and the other three copper atoms are trigonal planar.
Atom S2 bridges four copper atoms, which is a rare case. As a
result, the CuꢀS bonds in this structure span a wide range from
219.29(7) pm for Cu4ꢀS4 to 245.79(6) pm for Cu4ꢀS2. The
coordination of Cu4 can be stated to be intermediate between
trigonal planar and linear, as the bond angle S3ꢀCu4ꢀS4 is
155.61(3)°.
1ꢀ18. For 4-fold coordinated copper the maximal bond lengths
represent cutoff values chosen to separate bonds and secondary
connections (compare Table 6). Especially in the case of tell-
urium compounds this separation is somewhat arbitrary. Count-
ing all secondary connections as bonds would result in
unreasonably long bonds and distorted mean values.
There is a clear dependency of the CuꢀE bond length on the
coordination mode of the copper atom. For E = S this depen-
dency causes nearly a separation into two groups, as CuꢀS bond
lengths for 3-fold coordinated copper rarely exceed 230 pm,
while 4-fold coordinated copper has exclusively CuꢀS bonds
2. Comparison of Structural Data. Table 5 gives minimal,
average, and maximal CuꢀE bond lengths found in compounds
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longer than 230 pm. This is also illustrated in Figure 10. This
separation is somewhat less clear for E = Se and Te, the latter
showing a much smaller difference of the average values (13 pm
for S and Se, 7 pm for Te). Intermediate cases in coordina-
tion mode result in one extremely large bond length. All the
long bonds for tetrahedral coordination correspond to a begin-
ning transition toward trigonal planar coordination. The two
longest CuꢀS bonds for 3-fold coordinated copper are related
to intermediate cases between trigonal planar and linear
coordination.
For 3-fold coordinated copper, we observed secondary Cu--E
connections with even longer distances. They represent a begin-
ning transition from trigonal planar to tetrahedral coordination
and usually express in enlarged out-of-plane parameters (20ꢀ
50 pm) and strongly deformed thermal ellipsoids at the affected
copper atom, giving rise to large Hirshfeld differences.20
The CuꢀP bonds are less flexible, as can be seen in Figure 10.
Average values are 223 and 226 pm for 3-fold and 4-fold
coordinated copper, respectively. No dependence on the size
of the alkyl groups could be found, and it seems that steric and
electronic effects (increased donor capability for larger alkyl
groups) cancel out. The longest CuꢀP bonds are found in the
phosphine-rich mononuclear complexes 1ꢀ3. The EꢀC bonds
are rigid. Average values are 177, 193, and 213 pm for E = S, Se,
and Te, respectively. The largest deviations from these values are
found for the overall shortest EꢀC bonds in complexes 1ꢀ3
(174.6(3) pm, 190.4(6) pm, and 211(1) pm).
The coordination spheres of the copper atoms are generally
distorted. As illustrated in Figure 11, angles EꢀCuꢀP and
EꢀCuꢀE span a wide range for both 3-fold and 4-fold coordi-
nated copper. Ideal values of 120° and 109° are matched only
occasionally. At least for the smaller phosphine ligands, the
average angles EꢀCuꢀP are close to ideal values with 122°
and 111° for both Me3P and Et3P. For the larger phosphines,
these average values exceed the ideal values with 126° and 120°
for iPr3P and 127° and 119° for tBu3P. Angles EꢀCuꢀE tend to
be smaller than ideal, as the average values for 3-fold coordinated
copper are 113°, 116°, and 111° for E = S, Se, and Te. For 4-fold
coordinated copper, these values are 100° for S and Se and 105°
for Te. Note that the average values for tellurium are much closer
to each other than for sulfur and selenium.
Extremely large variations are observed for CuꢀEꢀCu angles,
which show values between 50° and 140° (Figure 11). The
increasing range going from sulfur to tellurium can be attributed
Figure 10. Plot of CuꢀE and CuꢀP bond lengths in compounds
1ꢀ18. Values for 3-fold coordinated copper are shown in the left and for
4-fold coordinated copper in the right columns, respectively.
Figure 11. Plot of bond angles at copper and chalcogen atoms in compounds 1ꢀ18. In the case of EꢀCuꢀP and EꢀCuꢀE angles values for 3-fold
coordinated copper are shown in the left and for 4-fold coordinated copper in the right columns, respectively.
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to the higher polarizability for the heavier chalcogens. CuꢀEꢀC
angles are more rigid (Figure 11). Their mean values are 111°,
109°, and 105° for S, Se, and Te, respectively. CuꢀEꢀC angles
do not only span a relatively sharp range but are approximately
normal distributed around their mean values, emphasizing their
rigidity. Usually, deviations are found to be less than 15°, and
outliers are related to borderline cases between CuꢀE bonds and
secondary Cu--E connections. The two largest values for E = Se
are 126° and 136°. Both are found in compound 10 and
correspond to the long Cu6ꢀSe bonds (264.08(7) pm and
281.69(6) pm, respectively). The largest value for E = Te is 122°
and corresponds to the long bond between Cu1 and Te2 in
the second molecule of compound 12 (291.6(1) pm). Note that
the respective Cu--Te distance is 308.28(6) pm in the first
molecule and results in a Cu--TeꢀC angle of 137.3(1)°. In
Table 6, the secondary Cu--E connections are listed together
with the respective Cu--E-C angles. Obviously, the rigidity gets
lost when the respective CuꢀE distance is elongated. So it may
be concluded that the CuꢀEꢀC angles can help to distinguish
between long CuꢀE bonds and secondary Cu--E connections.
3. DFT Calculations. We performed DFT(B3LYP) calcula-
tions on simple model systems to get a deeper insight in the
electronic structure, which may be helpful to explain the observed
phenomena. At first, it is useful to take a look into the system
SPhꢀ. In terms of molecular orbital theory, the two highest
occupied molecular orbitals (Figure 12) are located mainly at the
sulfur atom and are of p-character, pointing perpendicular to the
SꢀC bond. Regarding these orbitals as sulfur lone-pairs, there is a
charge delocalization toward the phenyl π-system in the highest
occupied molecular orbital (HOMO).
In terms of charge density analysis, the charge distribution
around the chalcogen atom is rather asymmetrical. As shown in
Figure 13, the charge density F(r) is distinctly higher in directions
perpendicular to the SꢀC bond. This can be seen even more
clearly in the second derivative (Laplacian) of the charge density,
which can beinterpreted ascharge concentration wherenegative.21
Introducing a Cuþ ion in this system, one can expect a
(covalent) CuꢀS σ-bond to be formed along the directions of
the two highest occupied MOs to obtain an effective overlap.22
As a result, the CuꢀSꢀC bond angle can be expected to be
highly bent. Calculations for the systems CuEPh (E = S, Se) give
a minimum on the potential energy surface for a bent CuꢀEꢀC
arrangement (point group symmetry Cs) with bond angles of
103° and 100° for S and Se, respectively, while the linear
CuꢀEꢀC arrangement (point group symmetry C2v) is found
to be a second-order saddle point, 126 and 144 kJ/mol above the
minimum for S and Se, respectively. Similar results were obtained
for systems CuESiH3 (E = O, S, Se), and a detailed bond and
charge density analysis revealed that bending of the CuꢀEꢀSi
angle reduces Pauli repulsion and leads to an increased covalent
interaction between the copper and the chalcogen atom.23 It has
been shown further that the bending potential of the CuꢀOꢀSi
angle is much flatter than for the heavier chalcogens, since the
CuꢀO bond is more ionic anyhow. Other related examples are
the terminally bonded phenylchalcogenolates in Cp*2Zr(EPh)2
(E = O, S, Se, Te), which show the same trend.24 For the
structures presented here, it may be concluded that the second-
ary Cu--E connections are more electrostatic (ionic) in nature,
since the respective Cu--EꢀR angles are not bent in the usual
way, which would be a precondition for effective orbital overlap
and therefore for a covalent bond.
Regarding bridging phenylchalcogenolate ligands, one can
expect that all CuꢀEꢀC bond angles will be bent in a similar
manner, but it may be more convenient to consider the inclina-
tion angle φ of the EꢀC vector toward the respective CuꢀEꢀCu
plane (Figure 14).
For a simple Cs-symmetrical system Cu2EPhþ we define τ as
the angle CuꢀEꢀC and υ as half the angle CuꢀEꢀCu. As can be
derived from the definition of the cosine in a rectangular triangle
and the scalar product of vectors EꢀCu and EꢀC, these three
angles are related by their cosines as given in eq 1:
cos φ ¼ cos τ=cos υ
ð1Þ
Figure 12. The two highest occupied orbitals in the system SPhꢀ as
derived from DFT(B3LYP) calculations. The surface represents the
isovalue of 0.02.
For a given (rigid) CuꢀEꢀC angle τ, the inclination angle φ is
then simply a function of υ. Therefore, one can expect a
Figure 13. Plots of charge density F(r) and its second derivative (Laplacian) in the system SPhꢀ as derived from DFT(B3LYP) calculations. The z-axis
coincides with the SꢀC bond. Left: one-dimensional plots dependent on the distance from the sulfur atom. Right: two-dimensional plots of the
Laplacian in a plane with the phenyl ring and perpendicular to this plane.
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correlation between φ and the CuꢀEꢀCu angle 2υ. And in fact,
despite their flexibility, CuꢀEꢀCu angles 2υ are correlated to
inclination angles φ (Figure 15). In 1ꢀ18, the worst correlation
is obtained for two data pairs involving the borderline case bond
Cu6ꢀSe3 of 281.69(6) pm in compound 10.
one obtains two different minima in Cs-symmetry, according to
the rotational angle of the phenyl ring. Chalcogen atoms are
pyramidal and data pairs 2υ, φ are 76.1°, 69.9° and 101.7°, 65.7°
for E = S and 71.1°, 74.2° and 96.9°, 71.1° for E = Se. The
respective minima differ less than 3 kJ/mol in energy and the
respective transition state was found to be less than 5 kJ/mol
above the lowest minimum, so phenyl rings can rotate nearly free
in this system. Optimizations for planar chalcogen atoms (φ = 0°,
point group symmetry C2v) gave transition states with 2υ =
134.3° and 135.3° for E = S and Se. The phenyl ring is
perpendicular to the CuꢀEꢀCu plane in this case, and these
systems are 23 and 39 kJ/mol above the lowest minimum for
Cu2EPhþ with E = S and Se, respectively. In compound 7, we
observed a μ2-bridging phenylthiolate ligand which matches
approximately this trigonal planar geometry at the sulfur atom
with φ = 4° and 2υ = 131.13(3)°. Obviously, the energy needed
to force this atom to planarity is overcome by steric effects.
The charge distribution around the chalcogen atom also
affects the rotational angles of the phenyl group. As mentioned
above, there is some charge delocalization from the chalcogen
atom to the phenyl π-system in the HOMO. This can be
interpreted as a þM-effect in terms of substituted aromatic
Note that this correlation has been observed by Dance
and co-workers for μ2-bridging SPh-groups in the system
[(Ph3P)4(CuSPh)3].12 Examination of related systems, like the
planar Fe3(SPh)3 core25 in [Fe3(SPh)3Cl6]3ꢀ, indicated that this
correlation may be of general interest for transition metal thiolates
and therefore also for metalloꢀcystein proteins. To our knowl-
edge, this relationship was not extended to higher bridging modes
or heavier chalcogens, nor was an explanation given.
Not surprising, this phenomena can be reproduced on DFT-
(B3LYP) level of theory. For the simple model system Cu2EPhþ
1
systems. As can be seen from the phenyl region in the H
NMR spectra, this charge delocalization decreases for heavier
chalcogens, since chemical shifts increase for ortho- and para-
protons going from sulfur to tellurium, comparing homologous
compounds such as 1ꢀ3 or 15ꢀ17.
As a result of this charge delocalization, the donor capability of
the EPhꢀ ligand is somewhat larger in the plane of the phenyl
ring (compare Figure 13), and CuꢀE bonds can be expected to
be somewhat stronger in this direction. It should be noted that
this effect does show structural consequences only if the CuꢀE
bond is relatively long (e.g., for tetrahedrally coordinated copper
Figure 14. Bridging chalcogenolate ligand, definition of angles φ, τ, and
υ in this system, and a short derivation of eq 1.
Figure 15. Plot of inclination angles φ against the respective CuꢀEꢀCu angles 2υ for compounds 1ꢀ18. Lines represent eq 1 for CuꢀEꢀC angles
τ = 105°, 110°, and 115°.
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atoms), since it is contrary to sterical effects, meaning the
repulsive interaction between the copper atom and the ortho-
hydrogen atom. We noted that for compound 16 a short and a
long CuꢀSe bond is observed, with the short one in plane with
the phenyl ring. We suggest that this a manifestation of the
charge delocalization. The same is true for the isostructural
compound 17.
Jiang, J.-J.; Sommer, H.; Weigend, F.; Fuhr, O.; Fenske, D.; Su, C.-Y.;
Buth, G. Eur. J. Inorg. Chem. 2010, 410–418.
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’ SUMMARY
(8) Baumgartner, M.; Bensch, W.; Hug, P.; Dubler, E. Inorg. Chim.
Acta 1987, 136, 139–147.
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(11) Kampf, J.; Kumar, R.; Oliver, J. P. Inorg. Chem. 1992,
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We isolated 18 different trialkylphosphine-stabilized copper-
(I) phenylchalcogenolate complexes and characterized them by
X-ray crystallography. The nuclearity of the complexes is mainly
influenced by the size and amount of the phosphine ligand. In
most cases, different phosphines result in different copper-
chalcogen frameworks. In addition, the change of the chalcogen
atom can also cause different structures, which is at least partly a
steric effect, due to different atomic radii for different chalcogens.
The CuꢀEꢀC angles τ were found to be relatively rigid, and
electronic reasons were pointed out. As a result, for bridging
chalcogenolate ligands a correlation between the inclination angle
φ of the EꢀC vector toward the respective CuꢀEꢀCu plane and
the CuꢀEꢀCu angle 2υ is observed, since these three angles are
related by their cosines: cos φ = cos τ/cos υ. Charge delocaliza-
tion from the chalcogen atom to the phenyl π-system is only of
minor importance for the overall molecular structure but has
influence on bond lengths in the copper-chalcogen core.
(14) Corrigan, J. F.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1997,
36, 1981–1983.
(15) Dance, I. G.; Fitzpatrick, L. J.; Scudder, M. L. Inorg. Chem. 1984,
23, 2276–2281.
(16) DeGroot, M. W.; Cockburn, M. W.; Workentin, M. S.;
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(19) Tasker, P.; Parkin, A.; Coventry, D.; Parsons, S.; Messenger, D.
Private communication, 2005, CCDC deposition number 276810.
(20) Hirshfeld, F. L. Acta Crystallogr. 1976, A32, 239–244.
(21) Bader, R. F. W. Atoms in Molecules; Clarendon Press: Oxford,
U.K., 1990.
’ ASSOCIATED CONTENT
S
Supporting Information.
Experimental and computa-
b
tional details, tables of selected bond lengths and angles, histo-
grams of distribution for CuꢀEꢀC angles, crystallographic
information in cif-file format. This material is available free of
charge via the Internet at http://pubs.acs.org.
(22) For
a MO-theoretical DFT study of (CuSMe)n ring
systems, see Howell, J. A. S. Polyhedron 2006, 25, 2993–3005.
(23) (a) Medina, I.; Jacobsen, H.; Mague, J. T.; Fink, M. J. Inorg.
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’ AUTHOR INFORMATION
Corresponding Author
*E-mail: krautscheid@rz.uni-leipzig.de.
(25) Hagen, K. S.; Holm, R. H. J. Am. Chem. Soc. 1982,
104, 5496–5497.
’ ACKNOWLEDGMENT
Financial support by the University of Leipzig (PbF-1) and the
graduate school BuildMoNa is gratefully acknowledged. We thank
URZ Leipzig for computational resources.
’ DEDICATION
Dedicated to Professor Hansgeorg Schn€ockel on the occasion
of his 70th birthday
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