Synthesis and structure of [{PhC(NtBu)2}2Ge 2(μ-S)2Cl2] and a germanium dithiocarboxylate analogue

Article abstract of DOI:10.1021/om101074j

LGeCl (L = PhC(NtBu)₂) was treated with elemental sulfur in THF to afford [{PhC(NtBu)₂}₂Ge₂(μ-S) ₂Cl₂] (2) in 44% yield instead of yielding a compound containing a Ge=S double bond. It was revealed by the X-ray single-crystal structure that there is no Ge=S unit in 2. Instead, 2 features a four-membered ring containing two germanium and two sulfur atoms. The four-membered Ge ₂S₂ ring is planar and is formed by a weak [2 + 2] cycloaddition interaction. Within the ring skeleton the two germanium atoms are arranged opposite to each other. Furthermore, 2 was reduced with 2 equiv of potassium graphite in THF to yield a potassium salt of a germathiocarboxylate analogue of composition [{PhC(NtBu)₂}Ge(S)SK(THF)]₂ (3). Compounds 2 and 3 were characterized by single-crystal X-ray diffraction studies, NMR spectroscopy, EI-MS spectrometry, and elemental analysis.

Full text of DOI:10.1021/om101074j

1030 Organometallics 2011, 30, 1030–1033
DOI: 10.1021/om101074j
Synthesis and Structure of [{PhC(NtBu)2}2Ge2(μ-S)2Cl2] and a
Germanium Dithiocarboxylate Analogue
Sakya S. Sen, Rajendra S. Ghadwal, Daniel Kratzert, Daniel Stern, Herbert W. Roesky,*
and Dietmar Stalke
€
Institut fu€r Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
€
€
Received November 15, 2010
LGeCl (L = PhC(NtBu)2) was treated with elemental sulfur in THF to afford [{PhC(NtBu)2}2-
Ge2(μ-S)2Cl2] (2) in 44% yield instead of yielding a compound containing a GedS double bond. It
was revealed by the X-ray single-crystal structure that there is no GedS unit in 2. Instead, 2 features a
four-membered ring containing two germanium and two sulfur atoms. The four-membered Ge2S2
ring is planar and is formed by a weak [2 þ 2] cycloaddition interaction. Within the ring skeleton the
two germanium atoms are arranged opposite to each other. Furthermore, 2 was reduced with 2 equiv
of potassium graphite in THF to yield a potassium salt of a germathiocarboxylate analogue of
composition [{PhC(NtBu)2}Ge(S)SK(THF)]2 (3). Compounds 2 and 3 were characterized by single-
crystal X-ray diffraction studies, NMR spectroscopy, EI-MS spectrometry, and elemental analysis.
Introduction
attention, due to the great variety of interesting chemical and
physical properties as well as applications.4 Several synthetic
approaches to this class of compounds have been developed.
Thiostannates have been synthesized through a solvother-
mal route using different amines as structure-directing
The chemistry of sulfur complexes shows a rich diversity.
Metal sulfur clusters are of considerable interest because
of their remarkable chemical and physical properties.1
Transition-metal clusters are among those which have
been intensely studied in recent years.2 In comparison to
that, main group sulfur clusters are less common in the
literature.3 Network compounds that consist of group 14
elements linked by sulfur atoms have received considerable
agents such as [SnS2 en] (en=ethylenediamine),5 (C6H20-
3
N4)2[SnS2] 2H2O,6 (C2H10N2)(C2H9N2)2[Sn2S6],7 R2Sn3S7
3
(R = tetramethylammonium (TMA),8 diazabicyclooctane
(DABCO),9 ammonium/tetraethylammonium (ATEA), tetra-
ethylammonium (TEA)10), R02Sn4S9 (R0 = tetrapropylammo-
nium (TPA), tetrabutylammonium (TBA)10), and (enH)4-
[Sn2S6].11 In this series of compounds thiogermanates were
neglected. Moreover, a well-known problem in solvothermal
syntheses is that many parameters such as temperature, time,
solvent, and concentration influence the product formation.
Although several efforts have been undertaken, chemists are
still far from achieving a deeper understanding of the reac-
tion mechanism occurring under solvothermal conditions.12
As a result, there has been a great quest for an alternative
*To whom correspondence should be addressed: E-mail: hroesky@
gwdg.de.
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pubs.acs.org/Organometallics
Published on Web 02/18/2011
2011 American Chemical Society

Article
Organometallics, Vol. 30, No. 5, 2011 1031
Scheme 1. Preparation of 2
route. It has been found that the introduction of organic
ligands with a designed functionality is a convenient route to
prepare a variety of new main group sulfur clusters.4,13,14 In
view of these literature studies we were interested in synthe-
sizing a thiogermanate bound with terminal halide, because
the halide can easily be replaced to open a wide avenue to
various new compounds. We have been interested in germa-
nium polysulfides, due to their applicability as precursors for
novel heteropolynuclear sulfur complexes composed of ger-
manium and various transition metals. Earlier we treated the
β-diketaminato germanium halide [{HC(CMeNAr)2}GeX]
(Ar = 2,6-iPr2C6H3, X = Cl, F) with elemental sulfur and
obtained [{HC(CMeNAr)2}Ge(S)X]15 instead of a Ge2S2
four-membered ring. Very recently we reported on the
synthesis of a monomeric germanium(II) chloride of com-
position (PhC(NtBu)2GeCl) (1) with the support of a bulky
benzamidinato ligand with tBu substituents on the nitrogen
atoms.16 Furthermore, we were able to isolate a Ge(I) dimer
by the reduction of 1 with finely divided potassium metal.16
These results prompted us to study the oxidation reaction of
1 with elemental sulfur. Instead of obtaining the germathione
analogue (>GedS), we isolated [{PhC(NtBu)2}2Ge2(μ-S)2-
Cl2] (2), containing two germanium atoms bridged by two
sulfur atoms. Furthermore, each germanium atom is co-
ordinated by a terminal chlorine atom.
Figure 1. X-ray structure of 2 2THF. Hydrogen atoms and two
THF molecules are not shown for clarity. Selected bond distances
(A) andbondangles(deg):Ge(1)-N(2)=1.9245(11), Ge(1)-N(1)=
3
˚
2.0774(10), Ge(1)-S(1A) = 2.2090(4), Ge(1)-Cl(1) = 2.2096(4),
Ge(1)-S(1) = 2.2978(4); N(2)-Ge(1)-N(1) = 65.48(4), N(2)-
Ge(1)-S(1A)=118.27(3), N(1)-Ge(1)-S(1A) =90.37(3), N(2)-
Ge(1)-Cl(1) = 112.55(3), N(1)-Ge(1)-Cl(1) = 91.92(3), S(1A)-
Ge(1)-Cl(1)=124.808(14), N(2)-Ge(1)-S(1)=106.02(3), N(1)-
Ge(1)-S(1) =170.89(3), S(1A)-Ge(1)-S(1) =91.121(13), Cl(1)-
Ge(1)-S(1)=94.599(14), S(1A)-Ge(1)-C(1) =103.99(3), Cl(1)-
Ge(1)-C(1) =106.61(3), S(1)-Ge(1)-C(1) =138.95(3), Ge(1A)-
S(1)-Ge(1) = 88.881(13).
The X-ray structure of 2 2THF is shown in Figure 1. 2
3
crystallizes in the monoclinic space group P21/n.17 The
structure of 2 2THF consists of a Ge2S2 four-membered
3
ring, and each germanium atom exhibits a trigonal-bipyr-
amidal coordination polyhedron. Selected bond lengths and
bond angles are given in the legend of Figure 1. The four-
membered ring is planar, due to its inversion center. Two
germanium atoms are arranged opposite to each other in the
Ge2S2 four-membered ring. To explain the coordination
environment of the germanium atoms, Ge(1) is discussed in
detail. The three equatorial positions of the trigonal-bipyr-
amidal geometry are occupied by one nitrogen atom (N(2))
of the amidinato ligand, by one sulfur atom (S(1A)), and one
chlorine atom (Cl(1)). The axial positions are occupied by the
second sulfur atom (S(1)) and the remaining nitrogen atom
(N(1)) of the amidinato ligand. The most striking features are
the Ge-S bond lengths. The Ge-S bond distances of 2 are
Results and Discussion
The reaction of 1 with elemental sulfur in THF at ambient
temperature for 2 days smoothly afforded [{PhC(NtBu)2}2-
Ge2(μ-S)2Cl2] (2) in moderate yield (0.18 g, 44%) (Scheme 1).
The isolation of a compound with a terminal >GedS moiety
is probably due to the reactivity of the >GedS unit, which
can be assumed as an intermediate, that rapidly undergoes a
[2 þ 2] cycloaddition to yield 2. Yellow crystals of 2 were
˚
2.2090(4)-2.2978(4) A; they match well with those found for
the Ge(IV) compound reported by Meller et al.18 and are
1
obtained from a THF solution at -32 °C. The H NMR
similar to those bond lengths reported for typical Ge-S
spectrum of 2 shows a singlet at δ 1.18 ppm for the 36 protons
of the four tBu groups and a multiplet resonance for the 10
aromatic protons (δ 6.86-7.26 ppm). The tBu protons
resonance in 2 exhibits a small downfield shift in comparison
with that of the precursor 1 (1 δ 1.08 ppm for tBu protons).
The most abundant peak in the EI-MS spectrum of 2
appeared with the highest relative intensity at m/z 371, which
corresponds to the half-fragment of 2. To understand the
bonding situation of 2, it was structurally characterized by
single-crystal X-ray diffraction studies.
single bonds (2.17-2.25 A).19 The Ge-S bond distances in 2
˚
are longer when compared with that of the germanethione
20
Tbt(Tip)GedS (2.049(3) A). Subsequently the GedS
˚
bond distance found in [{HC(CMeNAr)2}Ge(S)Cl] (Ar = 2,
6-iPr2C6H3)15 is 0.15 and 0.24 A shorter than those in 2,
˚
respectively. Recently Leung et al. reported the synthesis
of sulfur-bridged dimers of the germaketene analogues
(17) (a) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615–619.
(b) Stalke, D. Chem. Soc. Rev. 1998, 27, 171–178.
€
€
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(18) Ossig, G.; Meller, A.; Bronneke, C.; Muller, O.; Schafer, M.;
Herbst-Irmer, R. Organometallics 1997, 16, 2116–2120.
(19) (a) Veith, M.; Becker, S.; Huch, V. Angew. Chem. 1989, 101,
1287-1288; Angew. Chem., Int. Ed. Engl. 1989, 28, 1237-1238. (b)
Tokitoh, N.; Matsumoto, T.; Manmaru, K.; Okazaki, R. J. Am. Chem.
Soc. 1993, 115, 8855–8856.
(13) Gouzerh, P.; Proust, A. Chem. Rev. 1998, 98, 77–112.
(14) Peng, Z. Angew. Chem. 2004, 116, 948-953; Angew. Chem., Int.
Ed. 2004, 43, 930-935.
ꢀ
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Schmidt, H.-G. J. Am. Chem. Soc. 2002, 124, 8542–8543.
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H.; Pal, A.; Herbst-Irmer, R. Organometallics 2008, 27, 4259–4263.
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2317.
€

1032 Organometallics, Vol. 30, No. 5, 2011
Sen et al.
Scheme 2. Preparation of 3
Figure 2. X-ray structure of 3 at the 50% probability level.
Hydrogen atoms are not shown for clarity. Selected bond dis-
˚
tances (A) and bond angles (deg): Ge(1)-N(2)=1.9595(17),
21
[((TMS)NdPPh2)2CdGe(μ-S)]2. In this compound the
two Ge-S bond distances (2.230(2) and 2.236(2) A) are
almost identical, whereas those of 2 differ significantly.
Ge(1)-N(1)= 1.9744(16), Ge(1)-S(2)= 2.1601(10), Ge(1)-
S(20)=2.067(7), Ge(1)-S(1)=2.1184(6), K(1)-O(1)=2.852(12),
K(1)-O(10) = 2.74(2), K(1)-S(1) = 3.1743(7), K(1)-S(2) =
3.185(9), K(1)-S(20)=3.203(6); N(2)-Ge(1)-N(1)=66.83(7),
N(2)-Ge(1)-S(20) = 112.7(3), N(2)-Ge(1)-S(1) = 113.16(6),
N(1)-Ge(1)-S(1)=110.93(5), S(20)-Ge(1)-S(1)=123.10(18).
˚
Therefore we assume that 2 forms a weak [2 þ 2] cycloaddi-
16
˚
tion product. The Ge-Clav bond length of 2.2096(4) A in 2
is marginally shorter than that of 1 (2.2572(13) A) and
˚
comparable to the GeIV-Cl bond distance reported by
Willey et al.22
Recently, we were able to isolate a silicon thioester analo-
gue, [{PhC(NtBu)2}Si(S)StBu], with a Si(dS)-S skeleton
from the reduction of [{PhC(NtBu)2}SiCl2StBu] with finely
divided potassium metal.23 Following this, we successfully
isolated the germanium carboxylic acid analogue [{HC-
(CMeNAr)2}Ge(E)OH] (E = S, Se) by oxidative addition
of elemental sulfur and selenium to the corresponding
Ge-OH compound24a and also the germanium thiocar-
boxylic acid [{HC(CMeNAr)2}Ge(S)SH] (Ar=2,6-iPr2C6-
H32)24b by insertion of elemental sulfur into the germylene-
hydrogen bond and simultaneous oxidative addition with
elemental sulfur. In view of these results, we became inter-
ested to see whether benzamidinato-stabilized 2 is also capa-
ble of forming the thiocarboxylate analogue or the LGe-
(S)-Ge(S)L compound.
Treatment of 2 with 2 equiv of KC8 in THF afforded a
potassium salt of a germanium thiocarboxylic acid analogue,
[{PhC(NtBu)2}Ge(S)SK(THF)] (3), in 39% yield (Scheme 2)
instead of forming the anticipated LGe(S)-Ge(S)L (L=
PhC(NtBu)2). 3 is stable in solution and in the solid state
at room temperature under an inert atmosphere. It is soluble
in solvents such as toluene, THF, and diethyl ether. 3 was
characterized by NMR spectroscopy, EI-MS spectrometry,
elemental analysis, and single-crystal X-ray studies. The 1H
and 13C NMR spectra of 3 display two sets of resonances
from the benzamidinate ligand. In the 1H NMR spectrum a
downfield shift of the tBu protons (δ 1.39 ppm) is observed
in comparison with those of 2 (δ 1.18 ppm). In addition, 3
displays two more resonances at δ 1.72 and 3.56 ppm,
which indicates the existence of coordinated THF in the
complex. This was further confirmed by the 13C NMR
Figure 3. Molecular structure of 3 in the solid state, elucidating
the head-to-tail connection between the dimers to give the
overall coordination polymer.
spectrum, which exhibits resonances at δ 26.8 and 67.8
ppm. The molecular ion was not observed in the EI-MS
spectrum, although it exhibited a fragment at m/z 479 as the
ion with the highest mass, which indicates the half-frag-
ment of 3.
In order to elucidate the bonding situation in 3, it was
further structurally characterized by single-crystal X-ray
diffraction studies.17 The molecular structure of 3 is shown
in Figure 2. Selected bond lengths and angles are given in the
caption to the figure. 3 crystallizes in the monoclinic space
group P21/c. The solid-state structure consists of
the dimer [LGeS2K THF]2, generated by a center of inver-
sion in the middle of the K2O2 four-membered ring. The
two potassium atoms are slightly asymmetrically bridged
(21) Leung, W.-P.; So, C.-W.; Wang, Z.-X.; Wang, J.-Z.; Mak,
T. C. W. Organometallics 2003, 22, 4305–4311.
(22) Willey, G. H.; Somasunderam, U.; Aris, D. R.; Errington, W.
Inorg. Chim. Acta 2001, 315, 191–195.
(23) So, C.-W.; Roesky, H. W.; Oswald, R. B.; Pal, A.; Jones, P. G.
Dalton Trans. 2007, 5241–5244.
(24) (a) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Herbst-Irmer,
R. Angew. Chem. 2004, 116, 5650-5652; Angew. Chem., Int. Ed.
2004, 43, 5534-5536. (b) Pineda, L. W.; Jancik, V.; Oswald, R. B.;
Roesky, H. W. Organometallics 2006, 25, 2384–2387. (c) Ding, Y.;
3
˚
(K-O = 2.85 vs 2.75 A) by the two THF molecules in
the dimer. This bridging is quite rare in THF coordina-
tion to potassium.25 The potassium atom is five-coordi-
nate. Two oxygen atoms of the THF molecules and three
ꢀ
Ma, Q.; Roesky, H. W.; Uson, I.; Noltemeyer, M.; Schmidt, H.-G.
Dalton Trans. 2003, 1094–1098. (d) Jana, A.; Ghoshal, D.; Roesky,
H. W.; Objartel, I.; Schwab, G.; Stalke, D. J. Am. Chem. Soc. 2009,
131, 1288–1293. (e) Nagendran, S.; Roesky, H. W. Organometallics
2008, 27, 457–492.
(25) (a) Dippel, K.; Klingebiel, U.; Kottke, T.; Pauer, F.; Sheldrick,
G. M.; Stalke, D. Chem. Ber. 1990, 123, 237–242. (b) Brooker, S.;
Edelmann, F. T.; Kottke, T.; Roesky, H. W.; Sheldrick, G. M.; Stalke,
D.; Whitmire, K. H. J. Chem. Soc., Chem. Commun. 1991, 144–146.

Article
Organometallics, Vol. 30, No. 5, 2011 1033
˚
sulfur atoms (K(1)-S0(1) = 3.1743(7) A, K(1)-S(2) =
under vacuum to remove the two noncoordinated THF mole-
cules. Anal. Calcd for C30H46Cl2Ge2N4S2 (743.1): C, 48.49; H,
6.24; N, 7.54. Found: C, 47.66; H, 6.63; N, 7.36. 1H NMR (200
MHz, C6D6, 25 °C): δ 1.18 (s, 36H, tBu), 6.86-7.26 (m, 10H, Ph)
ppm. 13C{1H} NMR (125.75 MHz, C6D6, 25 °C): δ 29.6 (CMe3),
42.8 (CMe3), 128.8, 131.8, 133.0, 137.2 (Ph), 164.4 (NCN) ppm.
EI-MS: m/z (%) 371 [(M/2)þ] (100).
˚
˚
3.1208(69) A, K(1)-S(2 ) = 3.2030(6) A) reside in its co-
ordination environment. The symmetry equivalent of S(1)
˚
([þx, 1 þ y, þz] at a distance of 3.17 A) of the closest
neighboring dimer provides the link to give a coodination
polymer along the b axis, depicted in Figure 3.
The potassium (K(1)), the two sulfur atoms (S(1) and
S(2)), and the germanium atom (Ge(1)) form another four-
membered ring, which is oriented perpendicularly to the
neighboring GeN2C unit. The central Ge atom is almost
ideally tetrahedrally coordinated by the two nitrogen atoms
of the amidinato ring and two sulfur atoms.
The structure is disordered with respect to the bridging
THF molecule, one of the tBu groups, and one of the sulfur
atoms (S(2)) bridging the potassium and germanium atoms.
Nevertheless, this disorder could successfully be modeled
and all non-hydrogen atoms were refined anisotropically.
The site occupation factors were refined to 0.59/0.41 (tBu),
0.66/0.34 (THF), and 0.57/0.43 (S2), respectively.
Preparation of 3. THF (50 mL) was added to a mixture of 2
(1.09 g, 2.94 mmol) and potassium graphite (0.59, 4.41 mmol)
at -78 °C. The resulting red mixture was stirred overnight. The
solvent was then removed in vacuo, and the residue was
extracted with THF (50 mL). The insoluble precipitate was
filtered off, and the colorless filtrate was concentrated to yield
colorless crystals of 3, suitable for an X-ray structure determi-
nation (0.46 g, 38.65%). Mp: 192-198 °C. Anal. Calcd for
C38H62Ge2K2N4O2S4 (960.15): C, 47.61; H, 6.52; N, 5.84.
Found: C, 47.12; H, 6.42; N, 6.27. 1H NMR (500 MHz, C6D6,
25 °C): δ 1.39 (br, 36H, tBu), 1.72 (br, 8H, THF), 3.56 (br, 8H,
THF), 6.93-7.14 (m, 10H, Ph) ppm. 13C{1H} NMR (125.75
MHz, C6D6, 25 °C): δ 26.8 (THF), 32.1 (CMe3), 53.7 (CMe3),
67.8 (THF), 128.9 129.83, 136.68, 143.2 (Ph), 166.6 (NCN) ppm.
EI-MS: m/z (%) 479 [Mþ - C19H31GeKN2OS2] (100).
Crystal Structure Determination. Shock-cooled crystals were
selected and mounted under a nitrogen atmosphere using the
X-TEMP device.17 Data were collected at 100(2) K. Those for 2
were measured on a Bruker TXS-Mo rotating anode with Helios
mirror optics and APEX II detector on a D8 goniometer, while
those for 3 were collected on a INCOATEC Mo Microsource26
with Quazar mirror optics and APEX II detector on a D8
goniometer. Both diffractometers were equipped with a low-
Conclusion
In summary, [{PhC(NtBu)2}2Ge2(μ-S)2Cl2] (2) has been
prepared and fully characterized. It was reduced with po-
tassium graphite to afford a potassium salt of a dithiocar-
boxylate analogue of composition [{PhC(NtBu)2}Ge(S)-
SK(THF)]2 (3). The potassium cation was introduced from
the reducing agent KC8, to give a coordination polymer.
˚
temperature device and used Mo KR radiation (λ = 0.7173 A).
The data for 2 and 3 were integrated with SAINT,27 and an
empirical absorption correction (SADABS) was applied.28 The
structures were solved by direct methods (SHELXS-97) and
refined by full-matrix least-squares methods against F2
(SHELXL-97).29 All non-hydrogen atoms were refined with
anisotropic displacement parameters. The hydrogen atoms were
refined isotropically on calculated positions using a riding
model with their Uiso values constrained to equal to 1.5 times
the Ueq values of their pivot atoms for terminal sp3 carbon atoms
and 1.2 times these values for all other carbon atoms. Disor-
dered moieties were refined using bond length restraints and
isotropic displacement parameter restraints.
Experimental Section
All manipulations were carried out under an inert gas
atmosphere of dinitrogen using standard Schlenk techniques
and in a dinitrogen-filled glovebox. Solvents were purified by
a MBRAUN MB SPS-800 solvent purification system. All
chemicals purchased from Aldrich were used without further
purification. Compound 1 was prepared according to the
literature method.16 1H and 13C NMR spectra were recorded
using a Bruker Avance DPX 200 or a Bruker Avance DRX 500
spectrometer. The NMR spectra were recorded in C6D6. The
chemical shifts δ are given relative to SiMe4. EI-MS spectra
were obtained using a Finnigan MAT 8230 instrument. Ele-
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft, the DNRF, and the Center
for Materials Crystallography for supporting this work.
€
mental analyses were performed by the Institut fur Anorga-
nische Chemie, Universitat Gottingen. Melting points were
€
€
€
measured in a sealed glass tube on a Buchi B-540 melting point
apparatus.
Supporting Information Available: A table and CIF files
giving crystal data for 2 and 3. This material is available free
of charge via the Internet at http://pubs.acs.org.
Preparation of 2. A solution of 1 (0.40 g, 1.02 mmol) in THF
(20 mL) was added to a stirred suspension of sulfur (0.038 g, 1.02
mmol) in THF (10 mL). The reaction mixture was stirred at
room temperature for 2 days until the solution became trans-
parent. Storage of the reaction mixture at -32 °C in a freezer for
(26) Schulz, T.; Meindl, K.; Leusser, D.; Stern, D.; Ruf, M.; Sheldrick,
G. M.; Stalke, D. J. Appl. Crystallogr. 2009, 42, 885–891.
(27) SAINT v 7.68A; Bruker AXS Inc., Madison, WI, 2009.
€
(28) Sheldrick, G. M. SADABS 2008/2; University of Gottingen,
7 days afforded the crystals of 2 2THF, suitable for a X-ray
3
structure determination (yield 0.18 g, 43.42%). Mp: 165-
€
Gottingen, Germany, 2008.
(29) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.
170 °C. For the elemental analysis 2 2THF was kept overnight
3