Reactions of Palladium Germylene Complexes: Formation of Sulfide Bridges

Article abstract of DOI:10.1021/ic034613z

Reactivity of three novel Pd germylene species is presented. (Et ₃P)₂PdGe[N(SiMe₃)₂]₂ (1) and (dppe)PdGe[N(SiMe₃)₂]₂ (6) react with COS to give the sulfide bridged spe

Full text of DOI:10.1021/ic034613z

Inorg. Chem. 2003, 42, 7219−7226
Reactions of Palladium Germylene Complexes: Formation of Sulfide
Bridges
Zuzanna T. Cygan, Jeff W. Kampf, and Mark M. Banaszak Holl*
Department of Chemistry, UniVersity of Michigan, Ann Arbor, Michigan 48109-1055
Received June 3, 2003
Reactivity of three novel Pd germylene species is presented. (Et3P)2PdGe[N(SiMe3)2]2 (1) and (dppe)PdGe[N(SiMe3)2]2
(6) react with COS to give the sulfide bridged species (Et3P)2Pd(µS)Ge[N(SiMe3)2]2 (2) and (dppe)Pd(µS)Ge-
[N(SiMe3)2]2 (7) (dppe ) (diphenylphosphino)ethane). (Ph3P)2PdGe[N(SiMe3)2]2 (4) reacts with COS to give the
disulfide bridged complex (Ph P)2Pd(µS)2Ge[N(SiMe3)2]2 (5) resulting in Pd−Ge bond cleavage. This phos-
3
phine dependent reactivity is explored. Crystal structures of 2, 5, 7, and the dimeric form of complex 2, {(Et3P)-
Pd(µS)Ge[N(SiMe3)2]2}2 (8), are reported. In the presence of excess germylene, complexes 2 and 5 are shown to
partially regenerate their parent palladium germylene complexes, 1 and 4, respectively, via photolysis or heating.
Introduction
formation of Ge containing polymers,16-18 or cross coupling
reactions.19
Germylenes are divalent germanium species, containing
a singlet lone pair capable of interacting with metals in a
dative bonding sense, as well as an empty π-acidic p orbital
localized on the GeII center.1-7 The close proximity of the
electron rich metal and the Lewis acidic GeII suggests a
variety of addition reactions should be possible across the
metal-germylene bond. However, the majority of the
chemistry of the M-Ge bond has been studied in the context
of GeIV species: illustrative examples include germylation
reactions utilizing a metal catalyst,8-15 the metal catalyzed
Germanium has been explored as a promoter for pal-
ladium-based hydrogenation catalysts. A variety of interesting
activity and selectivity enhancements have been observed
for the hydrogenation of double bonds.20 The electrocatalytic
reduction of nitrate to hydroxylamine using germanium
promoters on a palladium electrode is also quite effective.21,22
In addition, germanium has been explored to develop sulfur-
resistant hydrogenation catalyst systems.23 The germanium
(12) Hayashi, T.; Yamashita, H.; Sakakura, T.; Uchimaru, Y.; Tanaka, M.
Chem. Lett. 1991, 245-248.
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Organometallics 1999, 18, 3764-3767.
* To whom correspondence should be addressed. E-mail:
mbanasza@umich.edu.
(14) Mochida, K.; Wada, T.; Suzuki, K.; Hatanaka, W.; Nishiyama, Y.;
Nanjo, M.; Sekine, A.; Ohashi, Y.; Sakamoto, M.; Yamamoto, A. Bull.
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10.1021/ic034613z CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/30/2003
Inorganic Chemistry, Vol. 42, No. 22, 2003 7219

Cygan et al.
stir for 2 h at 0 °C and slowly changed color to a yellow brown,
with the evolution of gas. The volatiles were evacuated leaving a
brown solid. The crude product was recrystallized from THF/
acetonitrile to give 589 mg (70% yield) of light yellow 2. 1H NMR
(C6D6) δ 0.59 (s, 36H, SiMe3), 0.90 (m, 18H, CH3) 1.62 (m, 12H,
CH2). Note: The ethyl groups of the phosphine ligands display
promoter for all of these cases is typically GeO2 or GeCl4;
however, spectroscopic studies indicate that these species
are readily reduced by the palladium metal to be Ge(0) or
Ge(II).20,24,25 The majority species present is generally
believed to be Ge(0);25 however, the state of the catalytically
active species has not been determined.
1
accidental overlap in their H NMR resonances. 31P NMR and13C
Despite a number of interesting catalysis studies, the role
of the germanium promoter is largely unknown, and the
chemical interactions of palladium, germanium, and sulfur
are not understood. Unfortunately, the catalytic work does
not have a substantial basis in solution phase chemistry to
provide a basis for comparisons and guidance regarding
anticipated structures or chemical conversions. Very little
structural chemistry of the Pd/Ge system has been explored;
just a handful of molecular species with Ge(II) have been
characterized,26-28 and no molecular species highlighting the
interactions of sulfur with Pd/Ge systems have been syn-
thesized.
In this report, we present an initial exploration of the
chemistry of Pd/Ge complexes of the general formula L2-
PdGe[N(SiMe3)2]2 where L represents monodentate or bi-
dentate phosphines. The reaction of COS displays a new
mode of heterocumulene reactivity with the M-Ge bond
vector, generating a class of molecules that highlight
cooperative reactivity with S by both the Pd and Ge metal
centers. We demonstrate the ability of the Ge(II) to sequester
S and reduce the Pd metal, illustrating the potential of Ge-
(II) to reverse the effect of sulfur poisoning of Pd catalysts.
NMR spectra indicate that the two phosphine ligands are chemically
2
inequivalent. 31P{1H} NMR (C6D6) δ 6.11 (d, JP-P 42 Hz) 16.91
2
(d, JP-P 42 Hz). 13C {1H} NMR δ 6.78 (s, SiCH3), 8.23 (s,
CH2CH3), 9.04 (s, CH2CH3), 16.53 (d, CH2CH3, JP-C 14 Hz), 21.16
(d, CH2CH3, JP-C 16 Hz). Calcd for C24H66GeN2P2PdSSi4: C 37.52,
H 8.66, N 3.65. Found: C 37.13, H 8.30, N 3.32. UV-vis (pentane)
λmax 356 nm (ꢀ 12000 M-1 cm-1), 262 nm (ꢀ 20000 M-1 cm-1),
242 nm (ꢀ 21000 M-1 cm-1).
(Ph3P)2Pd(µS)2Ge[N(SiMe3)2]2 (5). In a 100 mL round-bottom
flask, 4 (150 mg, 0.14 mmol) was dissolved in 30 mL of toluene.
To the orange solution, 4.4 equiv of COS was added. The solution
gradually darkened to a brown color, and the evolution of gas was
observed. The solution was allowed to stir for 5 h. The volatiles
were evacuated leaving a yellow brown solid. The crude product
was recrystallized from THF/acetonitrile giving 67 mg (67%) of a
1
tan solid. H NMR (C6D6) δ 0.68 (s, 36H, SiMe3), 6.89 (m, 18H,
Ph), 7.56 (m, 12H, Ph). 31P{1H} NMR (C6D6) δ 31.28 (s). 13C {1H}
NMR δ 7.01 (s, SiCH3), 127.88 (s, Ph), 127.96 (s, Ph), 130.11 (s.
Ph), 135.25 (s, Ph). Calcd for C48H66GeN2P2PdS2Si4: C 52.96, H
6.11, N 2.57. Found: C 52.77, H 5.89, N 2.27. UV-vis (THF)
λmax 350 nm (ꢀ 11000 M-1 cm-1), 295 nm (ꢀ 26000 M-1 cm-1).
(dppe)Pd(µS)Ge[N(SiMe3)2]2 (7). A 100 mL round-bottom flask
was charged with 150 mg of 6 (0.17 mmol). Toluene (5 mL) was
distilled into the flask forming an orange solution. COS (3.2 equiv)
was added and the solution stirred at room temperature. The solution
was observed to liberate gas and slowly darkened to a brown color.
After 40 h of stirring, the volatiles were stripped leaving a light
brown solid. Crystals were grown by slow evaporation of THF and
were removed from the mother liquor giving 61 mg (37%) of
Experimental Section
All manipulations were performed using air-free techniques.
Benzene, toluene, THF, and benzene-d6 were dried over sodium
benzophenone ketyl and degassed. Acetonitrile was dried over 4
Å molecular sieves and degassed. COS (Aldrich, Pfaltz and Bauer)
was purchased commercially and used as received. Ge[N-
(SiMe3)2]2,29 (Et3P)2PdGe[N(SiMe3)2]2 (1),26 (Ph3P)2PdGe[N(SiMe3)2]2
(4),26 and (dppe)PdGe[N(SiMe3)2]2 (6)26 were prepared according
to published procedures. 1H, 31P, and 13C NMR spectra were
acquired on a Varian 400 MHz instrument (400, 161.9, and 100.6
MHz, respectively) or on a Varian 300 MHz instrument (300 MHz
1H, 121.5 MHz 31P). 31P NMR spectra are referenced to H3PO4 by
using an external secondary standard of PPh3 in benzene-d6
(assigned to -5.0 ppm).30 UV-vis spectra were acquired on a
Shimadzu UV-1601.
1
analytically pure 7. H NMR (C6D6) δ 0.50 (s, 36H, SiMe3), 1.69
(m, 1H, CH2), 1.74 (m, 1H, CH2), 1.95 (m, 1H, CH2), 2.02 (m,
1H,CH2), 6.98 (m, 2H, Ph) 7.03 (m, 10H, Ph), 7.51 (m, 4H, Ph),
7.95 (m, 4H, Ph). 1H NMR (THF-d8) δ 0.18 (s, 36H, SiMe3), 2.19
(m, 1H, CH2), 2.24 (m, 1H, CH2), 2.47 (m, 1H, CH2), 2.54 (m,
1H,CH2), 7.36 (m, 10H, Ph), 7.39 (m, 2H, Ph), 7.63 (m, 4H, Ph),
8.01 (m, 4H, Ph). 31P{1H} NMR (C6D6) δ 28.9 (d, JP-P 33 Hz),
44.16 (d, JP-P 33 Hz). 31P{1H} NMR (THF-d8) δ 34.1 (d, JP-P 35
Hz), 48.63 (d, JP-P 35 Hz). 13C NMR (THF-d8) δ 6.53 (s, SiMe3),
23.04 (d, CH2 JP-C 22 Hz), 25.54 (d, CH2 JP-C 21 Hz), 129.27 (d,
Ph JP-C 3 Hz), 129.37 (d, Ph JP-C 2 Hz), 130.86 (d, Ph JP-C 2 Hz),
131.22 (d, Ph JP-C 2 Hz), 134.02, 134.15, 134.42, 134.55, 134.65,
134.82, 134.91, 135.18 (s, Ph). EA was obtained on crystals grown
from THF solution. Calcd for C38H60GeN2O2P2PdSSi4‚C4H8O: C
50.32, H 6.84, N 2.79. Found: C 50.36, H 6.79, N 2.74.
(Et3P)2Pd(µS)Ge[N(SiMe3)2]2 (2). In a 250 mL round-bottom
flask, 1 (800 mg, 0.1 mmol) was dissolved in 70 mL of toluene
and cooled to 0 °C. To the orange solution, 1.4 equiv of COS was
added by measured gas bulb addition. The solution was allowed to
(24) Bodnar, Z.; Mallat, T.; Baiker, A. J. Electroanal. Chem. 1993, 358,
327-331.
{(Et3P)Pd(µS)Ge[N(SiMe3)2]2}2 (8). In a 250 mL round-bottom
flask, 1 (1 g, 1.35 mmol) was dissolved in ∼50 mL of toluene. To
the orange solution, 1.1 equiv of COS was added by measured gas
bulb addition. The solution quickly changed color to a light brown,
and the evolution of gas was observed. The solution was allowed
to stir for 46 h. The volatiles were evacuated leaving a brown solid.
A 200 mg portion of this solid was recrystallized from THF/
acetonitrile giving a brown solid. This solid was then recrystallized
from pentane giving a brown solid and darker brown filtrate. The
volatiles were evaporated from the filtrate giving a dark brown
residue. Benzene-d6 (ca 0.5 mL) was used to rinse out a small
(25) Pijpers, A. P.; Lefferts, L. Appl. Catal., A 1999, 185, 29-39.
(26) Cygan, Z. T.; Bender, J. E.; Litz, K. E.; Banaszak Holl, M. M.
Organometallics 2002, 21, 5373-5381.
(27) Hitchock, P. B.; Lappert, M. F.; Misra, M. C. J. Chem. Soc., Chem.
Commun. 1985, 863-865.
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Organomet. Chem. 1985, 289, C1-C4.
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P.; Riviere-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004-
2009.
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6227.
7220 Inorganic Chemistry, Vol. 42, No. 22, 2003

Reactions of Palladium Germylene Complexes
Table 1. Summary of Crystallographic Data for 2, 5, 7, and 8
2
5
7‚THF
8‚C6D6
empirical formula
fw
C24H66GeN2P2PdSSi4
768.14
C54H72GeN2P2PdS2 Si4
1166.55
C42H68GeN2OP2PdSSi4
1002.33
C42H108Ge2N4P2Pd2S2Si8
1378.08
temp
158(2) K
158(2) K
158(2) K
158(2) K
cryst syst, space group
unit cell dimensions
monoclinic, P21/n
a ) 16.064(3) Å
b ) 13.205(2) Å
c ) 36.708(7) Å
R ) 90°
orthorhombic, P212121
a ) 13.0526(14) Å
b ) 20.666(2) Å
c ) 22.719(2) Å
R ) 90°
monoclinic, C2/c
a ) 38.3831(19) Å
b ) 12.1176(5)Å
c ) 22.3611(11) Å
R ) 90°
triclinic, P1h
a ) 11.2870(13) Å
b ) 12.7506(15)Å
c ) 13.1569(15)Å
R ) 105.478(2)°
â ) 112.702(2)°
γ ) 90.475(2)°
1670.2(3) Å3
â)90.346(3)°
γ ) 90°
â ) 90°
â)106.421(2)°
γ ) 90°
γ ) 90°
V
7787(2) A3
6128.5(11) Å3
4, 1.264 Mg/m3
1.016 mm-1
9976.2(8) Å3
8, 1.335 Mg/m3
1.197 mm-1
Z, calcd d
abs coeff
8, 1.310 Mg/m3
1.509 mm-1
0.71073 Å
1, 1.370 Mg/m3
1.705 mm-1
λ
0.71073 Å
0.71073 Å
0.71073 Å
final R indices [I > 2σ(I)]
R1 ) 0.0392,
wR2 ) 0.0769
R1 ) 0.0486,
wR2 ) 0.0813
R1 ) 0.0352,
wR2 ) 0.0770
R1 ) 0.0432,
wR2 ) 0.0799
R1 ) 0.0229,
wR2 ) 0.0568
R1 ) 0.0279,
wR2 ) 0.0588
R1 ) 0.0214,
wR2 ) 0.0544
R1 ) 0.0253,
wR2 ) 0.0566
R indices (all data)
amount of the residue for NMR, and the remaining drops of benzene
were left in the flask to evaporate. Several red crystals of 8 were
collected after 3 days. 1H NMR (C6D6) δ 0.60 (s, 36H, SiMe3), 1.2
(m, 9H, CH3) 1.77 (m, 6H, CH2). 31P{1H} NMR (C6D6) δ 18.2 (s).
Structure Determination of 2. Yellow blocks of 2 were
crystallized from tetrahydrofuran at room temperature. A crystal
of dimensions 0.36 × 0.36 × 0.30 mm3 was mounted on a standard
Bruker SMART CCD-based X-ray diffractometer equipped with a
LT-2 low temperature device and normal focus Mo-target X-ray
tube (λ ) 0.71073 Å) operated at 2000 W power (50 kV, 40 mA).
The X-ray intensities were measured at 158(2) K; the detector was
placed at a distance 4.959 cm from the crystal. A total of 2490
frames were collected with a scan width of 0.3° in ω and æ with
an exposure time of 30 s/frame. The frames were integrated with
the Bruker SAINT software package31 with a narrow frame
algorithm. The integration of the data yielded a total of 86356
reflections to a maximum 2θ value of 56.62° of which 19850 were
independent and 16563 were greater that 2σ(I). The θ range for
data collection was 2.07-28.36°. The final cell constants (Table
1) were based on the xyz centroids of 7178 reflections above 10σ(I).
Analysis of the data showed negligible decay during data collection;
the data were processed with SADABS32 and corrected for
absorption. The crystals form as pseudo-orthorhombic merohedral
twins (twin law 1 0 0, 0 -1 0, 0 0 -1, twin fraction 0.0727(5)) and
two crystallographically independent molecules in the asymmetric
unit. The structure was solved and refined with the Bruker
SHELXTL software package,33 using the space group P21/n with
Z ) 8 for the formula C24H66N2P2Si4SGePd. All non-hydrogen
atoms were refined anisotropically with the hydrogen atoms placed
in idealized positions. The ethyl carbons of one triethylphosphine
ligand (P1) are rotationally disordered over two closely related
positions. Partial occupancy atoms and modest restraints allowed
for a chemically sensible modeling of the disorder. Limiting indices:
-21 e h e 21, -17 e k e 17, -48 e l e 48. See Table 1 for
additional details.
placed at a distance 4.959 cm from the crystal. A total of 2018
frames were collected with a scan width of 0.3° in ω and æ with
an exposure time of 30 s/frame. The frames were integrated with
the Bruker SAINT software package31 with a narrow frame
algorithm. The integration of the data yielded a total of 53009
reflections to a maximum 2θ value of 52.85° of which 12558 were
independent and 11204 were greater than 2σ(I). The θ range for
data collection was 3.26-26.41°. The final cell constants (Table
1) were based on the xyz centroids of 6734 reflections above 10σ(I).
Analysis of the data showed negligible decay during data collection;
the data were processed with SADABS32 and corrected for
absorption. The structure was solved and refined with the Bruker
SHELXT software package,33 using the space group P212121 with
Z ) 4 for the formula C54H72N2S2Si4P2GePd which includes the
contribution of a benzene lattice solvate molecule. All non-hydrogen
atoms were refined anisotropically with the hydrogens placed in
idealized positions. Limiting indices: -16 e h e 16, -25 e k e
25, -28 e l e 28. See Table 1 for additional details.
Structure Determination of 7. Yellow plates of 7 were
crystallized from a THF/benzene solution at room temperature. A
crystal of dimensions 0.58 × 0.44 × 0.40 mm3 was cut from a
larger plate and mounted as for 2. The X-ray intensities were
measured at 158(2) K; the detector was placed at a distance 4.959
cm from the crystal. A total of 2937 frames were collected with a
scan width of 0.3° in ω and æ with an exposure time of 20 s/frame.
The frames were integrated with the Bruker SAINT software
package31 with a narrow frame algorithm. The integration of the
data yielded a total of 126271 reflections to a maximum 2θ value
of 56.71° of which 12918 were independent and 10918 were greater
than 2σ(I). The final cell constants (Table 1) were based on the
xyz centroids of 6751 reflections above 10σ(I). The θ range for
data collection was 3.30-28.30°. Analysis of the data showed
negligible decay during data collection; the data were processed
with SADABS32 and corrected for absorption. The structure was
solved and refined with the Bruker SHELXTL software package,33
using the space group C2/c with Z ) 8 for the formula C38H60N2P2-
SSi4PdGe‚(THF). All non-hydrogen atoms were refined anisotro-
pically with the hydrogen placed in idealized positions. Limiting
indices: -51 e h e 49, -16 e k e 16, -29 e l e 29. The THF
lattice solvate is disordered over two orientations. See Table 1 for
additional details.
Structure Determination of 5. Yellow plates of 5 were grown
from a benzene-d6 solution at room temperature. A crystal of
dimensions 0.26 × 0.26 × 0.16 mm3 was mounted as for 2. The
X-ray intensities were measured at 158(2) K; the detector was
(31) Saint Plus, V. 6.02; Bruker Analytical X-ray: Madison, WI, 1999.
(32) Sheldrick, G. M. SADABS. Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
Crystal Structure Determination of 8. Orange blocks of 8 were
crystallized from a benzene-d6 solution at room temperature. A
crystal of dimensions 0.60 × 0.48 × 0.32 mm3 was mounted as
(33) Sheldrick, G. M. SHELXTL, V. 5.10; Bruker Analytical X-ray:
Madison, WI, 1997.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7221

Cygan et al.
is formed without cleavage of the Pd-Ge bond. The 31P
NMR spectrum of 2 reveals unsymmetrical phosphine ligands
appearing as a pair of doublets at 6.11 and 16.91 ppm. In
for 2. The X-ray intensities were measured at 158(2) K; the detector
was placed at a distance of 4.939 cm from the crystal. A total of
3008 frames were collected with a scan width of 0.3° in ω and æ
with an exposure time of 10 s/frame. The frames were integrated
with the Bruker SAINT software package31 with a narrow frame
algorithm. The integration of the data yielded a total of 21115
reflections to a maximum 2θ value of 56.65° of which 8130 were
unique and 7375 were greater than 2σ(I). The final cell constants
(Table 1) were based on the xyz centroids of 7856 reflections above
10σ(I). The θ range for data collection was 3.42-28.32°. Analysis
of the data showed negligible decay during data collection; the data
were processed with SADABS32 and corrected for absorption. The
structure was solved and refined with the Bruker SHELXTL
software package,33 using the space group P1h with Z ) 1 for the
formula C36H102N4P2S2Si8Ge2Pd2‚(C6D6). The Pd-Ge complex and
the benzene solvate are both located on inversion centers in the
crystal lattice. All non-hydrogen atoms were refined anisotropically
with the hydrogen atoms located on a difference Fourier map and
allowed to refine isotropically. Limiting indices: -15 e h e 13,
-16 e k e 16, -17 e l e 17. Additional details are presented in
Table 1.
1
the H NMR spectrum, the trimethylsilyl protons of the
germylene ligand appear at 0.59 ppm, downshifted ap-
proximately 0.1 ppm from the starting material resonance.
A change in the phosphine ligands of the parent palladium
germylene complex has a pronounced effect on the reactivity
with COS. The reaction of excess COS with (Ph3P)2PdGe-
[N(SiMe3)2]2 (4) resulted in the formation of only one
product: (Ph3P)2Pd(µS)2Ge[N(SiMe3)2]2 (5), a disulfide
bridged species with a cleaved Pd-Ge bond (see eq 2). The
symmetric phosphines appear as a singlet at 31.28 ppm in
the 31P NMR. The trimethylsilyl protons of the germylene
1
appear at 0.68 ppm in the H NMR, a shift of 0.2 ppm
Reaction of 2 and 5 with Excess Germylene. NMR tubes fitted
with Teflon valves were used. Each tube was filled with a benzene-
d6 solution containing 15 mg (0.02 mmol) of 2 and 38 mg (0.10
mmol) of Ge[N(SiMe3)2]2, or 10 mg (0.009 mmol) of 5 and 18 mg
(0.046 mmol) of Ge[N(SiMe3)2]2. For photolysis experiments, the
tubes were placed in a water bath beneath a Blak-Ray long wave
(365 nm) ultraviolet lamp. For heating experiments, the NMR tubes
were first degassed by freezing and opening to vacuum, and then
placed in an oil bath maintained at 63 ( 4 °C. A set of NMR tubes
was also left out on the benchtop in ambient light at room
temperature for comparison to photolyzed and heated samples. 1H
NMR, 31P NMR, and 13C NMR spectra were acquired periodically
to monitor reaction progress. Percentages of conversion were
calculated by comparing integrations of resonances in the 31P NMR
spectra. Control reactions were carried out with NMR tubes
containing solutions of 1 or 4 without added germylene which were
heated, photolyzed, or left out on the bench alongside the other
experiments. Control reactions containing excess phosphine were
run under the same conditions as already described with solutions
containing 12 mg (0.015 mmol) of 2 and 11 µL (0.078 mmol) of
PEt3 or 9 mg (0.008 mmol) of 5 and 11 mg (0.04 mmol) of PPh3.
downfield from the starting material.
We have also synthesized a palladium germylene complex
that contains a bidentate ligand. (Dppe)PdGe[N(SiMe3)2]2
exists in equilibrium in solution between its dimeric (6a)
and monomeric (6b) forms (eq 3).26 The addition of 3 equiv
of COS to a ∼1:1 mixture of 6a and 6b resulted in the
formation of only one product, (dppe)Pd(µ-S)Ge[N(SiMe3)2]2
(7). The 31P NMR spectrum contains a pair of doublets at
44.16 and 28.8 ppm, and the trimethylsilyl resonance appears
Results and Discussion
Formation of µ-S Complexes. Addition of 1.6 equiv
of COS to a room temperature toluene solution of (Et3P)2-
PdGe[N(SiMe3)2]2 (1) results in the rapid darkening of
the orange solution to a brown color with the evolution of
a gas, presumably CO. The resulting metal complex,
1
at 0.5 ppm in the H NMR. There is no spectroscopic
evidence for the formation of products with the dimeric form
of the starting material, 6a. This reactivity out of the
monomeric form is similar to previously reported behavior
of these complexes with O2.26
(Et3P)2Pd(µ-S)Ge[N(SiMe3)2]2 (2), contains a S atom bridg-
ing the Pd center and Ge center (see eq 1). The sulfide bridge
In order to further investigate the differing reactivity of 1
and 4 with COS, an isolated sample of 2 was allowed to
1
react with one more equivalent of COS (eq 1). H NMR
and 31P NMR spectra are consistent with the formation of
the doubly bridged species (Et3P)2Pd(µS)2Ge[N(SiMe3)2]2 (3).
A large singlet is present in the trimethylsilyl region at 0.75
ppm. Additionally, a singlet at 18.4 ppm in the 31P NMR is
consistent with equivalent phosphines. Although all of the
starting material is consumed, 3 only represents 45% of the
products formed as indicated by trimethylsilyl peaks in the
1H NMR spectrum.
7222 Inorganic Chemistry, Vol. 42, No. 22, 2003

Reactions of Palladium Germylene Complexes
The formation of the first sulfide bridge to form 2 occurs
within 15 min for 30 mM solutions of 1 in room temperature
C6D6 in the presence of 1.1 equiv of COS. During this time
period, conversion to disulfide-bridged 3 remains under 5%
of the products formed. Formation of the second sulfide
bridge to give 3 requires several hours and is not quantitative
in contrast to the high yield reaction observed to form 5
Pd metal centers38 and the insertion of COS into two of the
Pd ligand bonds.39 The formation of [PdS(COS)]2 from the
reaction of COS with PdCl2 has been proposed on the basis
of IR assignments.40 It is interesting that, in the presence of
phosphine ligands, the reaction of COS with the palladium
germylene complexes does not proceed via the carbonylation
route. It is likely that the loss of CO drives this reaction, as
attempts to make similar products from 1 using other sulfur
sources such as S8, CS2, and ethylene sulfide were unsuc-
cessful.
Previous work in our group with the Pt analogue of 1,
(Et3P)2PtGe[N(SiMe3)2]2, demonstrated the cooperative re-
activity of the transition metal and Ge center. Small
molecules such as CO2,41 O2,42 and arylnitroso compounds43
add across the Pt-Ge bond to form metallocyclic structures.
In all cases, the Pt-Ge bond is preserved. The bridging
molecule remains intact, and it simply adds the site of
unsaturation to the Pt and Ge centers to make a four-
membered ring. The complexes reported here differ in terms
of the fragmentation of the substrate molecule, the size of
the resulting metallocycle, and in the case of 5, the cleavage
of the M-Ge bond.
1
(>90% H NMR yield).
Complex 2 can be synthesized without the formation of
complex 3 if the reaction is performed at low temperatures.
A toluene solution of 2 was cooled to 0 °C, and 1.1 equiv
of COS was added. After stirring for 2 h at 0 °C, the volatiles
were stripped, and NMR spectra revealed the formation of
2, without the formation of 3. For comparison, room
temperature experiments with 1.1-1.6 equiv of COS gener-
ated ∼5% 3 over a 2 h period.
In order to compare to the conversion of 1 to 2, (Ph3P)2-
PdGe[N(SiMe3)2]2 (4) was allowed to react with 1 equiv of
COS for approximately 4 h (eq 4). Although all the starting
Complexes 2 and 7 also provide rare examples of a three-
membered ring formed by the M-Ge bond and another atom.
This structural motif is unprecedented in transition metal
germylene complexes; however, there has been one report4
of an unusually close interaction between a germylene and
a chloride ligand in cis-[RhCl(Ge[N(SiMe3)2]2)(PPh3)2]. The
Ge‚‚‚Cl distance was found to be 2.723(4) Å in the crystal
structure of this complex.
material was consumed, the only identifiable product was
doubly bridged species 5 which formed in 20% yield. Several
other unidentified products are also formed in this reaction
although none had resonances assignable to a monobridged
structure analogous to 2. Most notably, there were no pairs
of doublets in the 31P NMR as expected for the two
inequivalent phosphines present in a singly bridged species.
This difference in reactivity between complexes 1 and 4
can be rationalized in terms of the steric constraints of the
phosphine ligands. PPh3 is the largest of the three ligands,
with a cone angle of 145° compared to 132° for PEt3, and
125° for dppe.34 A space filling model of 5 indicates that
the second sulfide relieves steric interaction between the
phosphine aryl groups and the germylene trimethylsilyl
groups. A single sulfide bridge may result in greater steric
crowding leading to enhanced lability of one of the PPh3
ligands. The open site would provide an opportunity for
reaction with the second equivalent of COS.
Common COS reactivity modes with transition metal
complexes include σ complexes, π complexes, bridging of
two metal centers, and insertion into various metal-
heteroatom bonds.35,36 If fragmentation of the COS molecule
occurs, it usually acts as a carbonylation agent to deliver a
CO ligand to the metal center. The S fragment can then react
with another part of the metal complex, often a phosphine
ligand, leaving as the phosphine sulfide. The formation of a
sulfide complex and loss of CO is much rarer. Such a reaction
was observed with [(C5H4Me)3U]‚THF, which formed [(C5H4-
Me)3U]2(µ-S).37 Reactions of Pd complexes with COS have
yielded the addition of both a S and a CO fragment to the
An alternative bonding model for complexes 2 and 7
would be that of a germanethione bound to Pd via π
donation, as shown in eq 5. Very few R2GedS species are
known in the literature. Only four such species have been
isolated, three stabilized by intramolecular coordination.44
Only Tbt(Tip)GedS (Tbt ) 2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl, Tip ) 2,4,6-triisopropylphenyl) is kinetic-
ally stable.45 Typical GesS single bond lengths range from
2.21 to 2.29 Å,46 whereas the GedS bond length of
Tbt(Tip)GedS is 2.049(3) Å,45 and the calculated value for
(38) Tarlton, S. V.; Choi, N.; McPartlin, M.; Mingos, D. M. P.; Vilar, R.
J. Chem. Soc., Dalton Trans. 1999, 653-654.
(39) Werner, H.; Bertleff, W.; Schubert, U. Inorg. Chim. Acta 1980, 43,
199-204.
(40) Datta, S.; Agarwala, U. C. Indian J. Chem., Sect. A: Inorg., Phys.,
Theor. Anal. 1981, 20, 1190-1195.
(41) Litz, K. E.; Henderson, K.; Gourley, R. W.; Banaszak Holl, M. M.
Organometallics 1995, 14, 5008-5010.
(42) Litz, K. E.; Banaszak Holl, M. M.; Kampf, J. W.; Carpenter, G. B.
Inorg. Chem. 1998, 37, 6461-6469.
(43) Litz, K. E.; Kampf, J. W.; Banaszak Holl, M. M. J. Am. Chem. Soc.
1998, 120, 7484-7492.
(44) Lin, C. L.; Su, M. D.; Chu, S. Y. Chem. Phys. Lett. 2001, 339, 147-
(34) Tolman, C. A. Chem. ReV. 1977, 77, 313-348.
(35) Pandey, K. K. Coord. Chem. ReV. 1995, 140, 37-114.
(36) Pandey, K. K.; Nigam, H. L. ReV. Inorg. Chem. 1984, 6, 69-94.
(37) Brennan, J. G.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1986, 25,
1761-1765.
153.
(45) Matsumoto, T.; Tokitoh, N.; Okazaki, R. J. Am. Chem. Soc. 1999,
121, 8811-8824.
(46) Baines, K. M.; Stibbs, W. G. Coord. Chem. ReV. 1995, 145, 157-
200.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7223

Cygan et al.
Figure 1. ORTEP representation (50% probability) of (Et3P)2Pd(µS)Ge[N(SiMe3)2]2 (2) and (dppe)Pd(µS)Ge[N(SiMe3)2]2 (7).
Table 2. Selected Bond Lengths (Å) and Angles (deg)
2
Pd-Ge 2.4092(5)
Pd1-P1 2.2911(11)
Ge1-N1 1.875(3)
Pd-S 2.3769(10)
Ge-S 2.1830(1)
N-Ge-N 107.64(13)
P-Pd-P 105.95(4)
Pd-Ge-N2 125.69(9)
P2-Pd-Ge 143.78(3)
S-Pd-Ge 54.27(2)
Ge-S-Pd 63.62(3)
S-Ge-Pd 62.11(3)
5
7
8
Pd1-P1 2.3213(10)
Pd1-S1 2.3453(10)
Pd1‚‚‚Ge1 3.17
Ge1-N1 1.862(3)
P1-Pd1-P2 98.91(3)
N1-Ge1-N2 111.64(15)
P1-Pd1-S1 171.44(3)
S1-Pd1-S2 87.19(3)
S1-Ge1-S2 95.26(4)
Pd-S1-S2-Ge 171.04(2)
Ge1-S1 2.1925(10)
S1-Ge1-N2 113.74(13)
Pd-Ge 2.4043(2)
Pd1-P1 2.2648(4)
Ge1-N1 1.8701(13)
Pd-S 2.3685(4)
Ge-S 2.1996(4)
P-Pd-P 85.887(14)
N-Ge-N 108.75(6)
Ge-S-Pd 63.390(11)
P2-Pd-Ge 155.312(12)
S-Ge-Pd 61.732(12)
S-Pd-Ge 54.878(10)
Pd-Ge-N2 128.32(4)
Pd1-S1 2.5055(5)
S1-Ge1 2.2169(5)
P1-Pd1-Ge1A 107.971(14)
N1-Ge1-N2 111.00(6)
Ge1A-Pd1-S1A 54.784(12)
Ge1A-S1A-Pd1-S1 179.9(3)
S1-Pd1-S1A 107.304(14)
Pd1A-S1-Ge1 59.951(11)
Pd1A-Ge1-S1 65.256(12)
Ge1-Pd1A-S1-Pd1 179.9(3)
Pd1-P1 2.2674(4)
Pd1-S1A 2.4645(4)
Ge1-N1 1.8621(13)
S1A-Pd1-Pd1A-S1 180.00(2)
Pd1-Ge1A 2.3488(3)
Pd1-S1-S1A-Pd1A 180.00(2)
H2GedS is 2.042 Å.45 The GesS lengths of 2 and 7 are
2.1830(1) and 2.1996(4) Å, respectively. While this is slightly
shorter than many previously reported values for GesS
single bonds, there appears to be very little double bond
character present. The PdsS bond lengths of 2.3769(10) and
2.3685(4) Å also fall in the range of PdsS single bonds that
have been crystallographically characterized. A search of the
Cambridge Structural Database System returned 1003 Pds
S single bonds averaging 2.32 ( 0.06 Å. Thus, σ donation
through the S atom is the better bonding model for this
interaction.
sulfur bridge and Pd-Ge bond is clearly evident. The PdII
metal centers takes on a distorted square planar geometry
with a S-Pd-Ge angles of approximately 54°, and P2-Pd-
Ge angles of 143.78(3)° and 155.312(12)° (see Table 2 for
selected bond lengths and angles). The Ge centers are also
distorted substantially from their preferred tetrahedral ge-
ometry with S-Ge-Pd angles of 62° and Pd-Ge-N2 angles
of 125.69(9)° and 128.32(4)°. In both structures, the Pd-
Ge bond length is approximately 0.07 Å longer than that of
the original palladium germylene complex.26
Unlike structures 2 and 7, the ORTEP of 5 (Figure 2)
shows a much less strained geometry about both the Pd and
Ge metal centers. The Pd-Ge bond has been completely
severed with a Pd‚‚‚Ge distance of greater than 3.1 Å. This
allows the Pd center to adopt a nearly square planar
conformation. The S1-Pd1-S2 angle is 87.19(3)°, and the
P1-Pd1-S1 angle is 171.44(3)°. The environment about the
Ge center is also more tetrahedral than that in the other two
structures, with S1-Ge1-S2 and S1-Ge1-N2 angles of
95.26(4)° and 113.74(13)°, respectively.
There is also no evidence for the formation of [(Me3-
Si)2N]2GedS free in solution. The reaction of Ge[N-
(SiMe3)2]2 with elemental S results in a four-membered ring
{[(Me3Si)2N]2GeS}2.47 Such a structure would be essentially
the dimeric structure of [(Me3Si)2N]2GedS. No such products
1
are observed in the H NMR or 13C NMR spectra of the
reactions with COS.
Crystal Structures. The crystal structures of 2 and 7 are
shown in Figure 1. In both structures, the constraint on the
preferred geometry of the metal centers imparted by the
The Pd1-S1-S2-Ge1 dihedral angle of 5 is 171.04(2)°,
indicating a slight hinging of the {M2S2}core on the S‚‚‚S
axis. Similar puckering has been found in X-ray diffraction
(47) Wegner, G. L.; Jockisch, A.; Schier, A.; Schmidbaur, H. Z. Natur-
forsch. 2000, 55, 347-351.
7224 Inorganic Chemistry, Vol. 42, No. 22, 2003

Reactions of Palladium Germylene Complexes
The fate of the S atom in these reactions is not clear. NMR
spectra reveal the growth of several other products throughout
the course of these reactions. Several new singlets appear in
1
the trimethylsilyl region of the H NMR and 13C NMR
spectra in addition to the singlet associated with 1 or 4. This
indicates that several new germanium-containing species are
formed. It is possible that thiadigermiranes are among these
new species as these structures are known to be stable.51
However, only the reaction of 5 heated with excess ger-
mylene showed evidence for the formation of the dimeric
germanesulfanone, {[(Me3Si)2N]2GeS}2. Both 1H NMR and
13C NMR show a singlet resonances at 0.50 and 7.02 ppm,
respectively, consistent with the formation of this dimer.
These resonances were not observed in the NMR spectra of
any other reactions in this series.
To confirm that the removal of S was dependent on the
presence of excess germylene and was not mediated by the
formation of phosphine sulfide, solutions containing 2 or 5
and 5 equiv of PEt3 or PPh3, respectively, were also
examined. With one exception, no reaction occurred in
ambient light, heating, or photolytic conditions over the 48
h time course of the experiments. A small amount of
phosphine sulfide and 1 (2%) were observed for the reaction
of 2 with excess phosphine after 48 h of photolysis.
Figure 2. ORTEP representation (50% probability) of (Ph3P)2Pd(µS)2Ge-
[N(SiMe3)2]2 (5).
studies and ab initio calculations of complexes containing
the {Pt2S2}core where terminal ligands on the Pt are small
enough. Thus, Pt-S-S-Pt dihedral angles of 121° and 140°
were found for [Pt2(PMe2Ph)4(µ-S)2]48 and [Pt2(dppe)2(µ-
S)2]49, respectively, and calculated to be as low as 119° for
[Pt2(H2PCH2CH2PH2)2(µ-S)2].49 However, the very bulky
2-diphenylphosphanopyridine (dppy) ligand forces complete
planarity in [Pt2(dppy)4(µ-S)2].50 The near planar structure
of 5 suggests a substantial steric constraint imparted not only
by the phosphine ligand but by the bulky germylene as well.
Although the geometry about the Pd and Ge centers is less
strained, the steric constraints imparted by the large ger-
mylene and phosphine ligands are evident at the S bridges.
Regeneration of Parent Three-Coordinate Pd-Ge
Complexes from Bridged Sulfide Complexes. The addition
of 5 equiv of free germylene to a benzene-d6 solution of 2
results in the reformation of the parent complex 1 as
Formation of {(Et3P)Pd(µS)Ge[N(SiMe3)2]2}2 (8). If the
reaction of 1 with COS is allowed to stir for several days, a
black precipitate deposits, and NMR spectra reveal the
growth of several new products in addition to 2. One of these
new products crystallized out of the mixture, and X-ray
diffraction revealed a dimeric form of 2, {(Et3P)Pd(µS)Ge-
[N(SiMe3)2]2}2 (8). Each Pd center has lost one phosphine
1
monitored by H NMR, 31P NMR, and 13C NMR spectros-
copy. This transformation occurs slowly in ambient light at
room temperature, resulting in 6% conversion to 1 after 2
days. Heating of the solutions to 63 °C speeds up the rate of
the conversion to 32%. The greatest degree of conversion
occurred under photolytic conditions with 63% of 1 being
formed after 48 h of UV exposure. The presence of excess
germylene is critical for the regeneration of 1, as solutions
of 2 that did not contain excess germylene showed no
reaction under these conditions.
Solutions of 5 to which 5 equiv of germylene was added
regenerated 4. Heating of the solution resulted in 32%
conversion to 4 after 48 h. Photolytic conditions were less
effective giving 12% conversion to 4 after the same length
of time. The presence of excess germylene is necessary to
obtain conversion; however, unlike complex 2, solutions kept
in ambient light at room temperature did not react over the
time frame of the experiments.
ligand, and the empty coordination site is being filled by
coordination to the bridging S atom. The NMR chemical
shifts of the germylene trimethylsilyl groups of 8 are
coincident with those of 2 at 0.60 ppm, suggesting that the
electronic environment around the Ge center is similar. The
crystal structure of 8 (Figure 3) reveals that the Pd, Ge, and
S atoms form an unusual and almost completely planar
arrangement (see Table 2 for relevant dihedral angles). The
Pd-Ge bond length of 8 is slightly shorter at 2.3488(3) Å,
while the Pd1-S1A bond length is 2.4645(4) Å, 0.1 Å longer
than in 2. The length of the new bond formed from the
bridging S1 to the Pd1 center is even longer at 2.5055(5) Å.
The development of a high-yield synthesis for 8 has eluded
us. It is not present in reaction mixtures of 1 and COS that
have only stirred for several hours. Complex 8 does not
appear to form simply from the dimerization of 2. A THF
solution of 2 was allowed to stir for 5 days without any
apparent formation of 8, and benzene solutions of 2 also do
(48) Fong, S. W. A.; Hor, T. S. A. J. Chem. Soc., Dalton Trans. 1999,
639-651.
(49) Capdevila, M.; Carrasco, Y.; Clegg, W.; Coxall, R. A.; Gonzalez-
Duarte, P.; Lledos, A.; Sola, J.; Ujaque, G. Chem. Commun. 1998,
597-598.
(50) Yam, V. W. W.; Yeung, P. K. Y.; Cheung, K. K. Chem. Commun.
1995.
(51) Tsumuraya, T.; Sato, S.; Ando, W. Organometallics 1988, 7, 2015-
2019.
Inorganic Chemistry, Vol. 42, No. 22, 2003 7225

Cygan et al.
has not been developed, we report the structure of this
complex here because of its intrinsic novelty and its
relationship to the other complexes reported.
Conclusions
We have described new modes of cooperative reactivity
for transition metal germylene complexes. Sulfide bridges
form via extrusion of the S atom from COS and addition
across the Pd-Ge bond without cleavage of the bond. A
second sulfide bridge and cleavage of the Pd-Ge bond
occurs upon reaction with a second equivalent of COS. The
formation of a single or double-bridged sulfide is phosphine
dependent. A unique dimeric product is also formed by these
reactions. These complexes are the first molecular Pd/Ge/S
species to be isolated and characterized, representing a class
of complexes that serve as model systems for considering
the interactions of S with Pd-Ge heterogeneous catalysts.
We have demonstrated the ability of germylene to sequester
S in these systems and to regenerate the original Pd0 metal
center, providing insight into potential mechanisms of action
of Ge promoters in sulfur resistant catalysis systems.
Figure 3. ORTEP representation (50% probability) of {(Et3P)Pd(µS)Ge-
[N(SiMe3)2]2}2 (8).
not appear to react on their own, even after heating or
photolysis (vide supra). The addition of the phosphine trap,
CuCl, or stoichiometric amounts of H2O or O2 as phosphine
oxidants to solutions of 2 failed to generate 8. We have also
explored the possibility that the CO gas liberated in the
reaction may be involved in the formation of the dimer. The
addition of CO to solutions of 2, as well as addition of an
equivalent of CO and an equivalent of COS to solutions of
1 or 2, also failed to generate 8. Thus far, we have only
been able to generate 8 in trace amounts by extending stirring
of the reaction that forms 2. Crystals can be isolated from
benzene as part of the purification process for 2. Although
a well-defined method for high-yield isolation of this material
Acknowledgment. This work was funded by the Re-
search Corporation and the Petroleum Research Fund. Z.T.C.
thanks the National Science Foundation for a graduate
research fellowship.
Supporting Information Available: X-ray crystallographic data
and files in CIF format for 2, 5, 7, and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC034613Z
7226 Inorganic Chemistry, Vol. 42, No. 22, 2003