Sequential insertion of formaldehyde and carbon monoxide into a sulfide-bridged Pd-Ge bond followed by reductive elimination to form a [1,3,2] oxathiagermolan-4-one

Article abstract of DOI:10.1021/om049944d

The reaction of (Et₃P)₂Pd(μ-S)Ge[N(SiMe ₃)₂]₂ (2) with paraformaldehyde under photolytic conditions results in the insertion of formaldehyde into the Pd-Ge bond, with bond cleavage, to give (Et₃P)₂Pd(μ-S) (μCH₂O)Ge[N(SiMe₃)₂]₂ (3). Subsequent addition of CO to 3 results in migratory insertion into the Pd-C bond, followed by rapid reductive elimination to regenerate the Pd⁰ metal center and give a unique five-membered organic heterocycle, Ge[N(SiMe ₃)₂]₂-SC(O)CH₂O (6). The X-ray crystal structure of the dppe (dppe = bis(diphenylphosphino)-ethane) derivative of 3, (dppe)Pd(μ-S)(μCH₂O)Ge[N(SiMe₃) ₂]₂ (4), is reported.

Full text of DOI:10.1021/om049944d

2370
Organometallics 2004, 23, 2370-2375
Sequ en tia l In ser tion of F or m a ld eh yd e a n d Ca r bon
Mon oxid e in to a Su lfid e-Br id ged P d -Ge Bon d F ollow ed
by Red u ctive Elim in a tion To F or m a
[1,3,2]Oxa th ia ger m ola n -4-on e
Zuzanna T. Cygan,† J eff W. Kampf, and Mark M. Banaszak Holl*
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055
Received J anuary 21, 2004
The reaction of (Et3P)2Pd(µ-S)Ge[N(SiMe3)2]2 (2) with paraformaldehyde under photolytic
conditions results in the insertion of formaldehyde into the Pd-Ge bond, with bond cleavage,
to give (Et3P)2Pd(µ-S)(µCH2O)Ge[N(SiMe3)2]2 (3). Subsequent addition of CO to 3 results in
migratory insertion into the Pd-C bond, followed by rapid reductive elimination to regenerate
the Pd0 metal center and give a unique five-membered organic heterocycle, Ge[N(SiMe3)2]2-
SC(O)CH2O (6). The X-ray crystal structure of the dppe (dppe ) bis(diphenylphosphino)-
ethane) derivative of 3, (dppe)Pd(µ-S)(µCH2O)Ge[N(SiMe3)2]2 (4), is reported.
In tr od u ction
To study the potential for cooperative reactivity of the
M-Ge bond, we have explored the reactivity of the
stable germylene ligand Ge[N(SiMe3)2]2, first reported
by Lappert,34,35 bound to platinum. Various small
organic and inorganic molecules, including O2, CO2,
PhNO, and H2CO, will react with platinum germylenes
Germylenes are divalent germanium species. They
contain 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.1-4 In late-
metal-germylene complexes, the close proximity of the
electron-rich metal and the Lewis acidic GeII suggests
that a variety of addition reactions should be possible
across the metal-germylene bond. This bond-forming
reaction could occur with the addition of a substrate
molecule in whole or in part across the M-Ge moiety,
with oxidation of the metal and/or oxidation of the
germanium center, or with direct insertion into the
M-Ge moiety with M-Ge bond cleavage. Numerous
stable σ-bonded metal germylene complexes have been
synthesized in the last few decades;5-28,41 however,
comparatively fewer studies have emphasized the re-
activity of the metal-germylene bond.5,7,19,26,27,29-33,43,44
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* To whom correspondence should be addressed. E-mail: mbanasza@
umich.edu.
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F. R.; Bock, H.; Solouki, B.; Wagner, M. Angew. Chem., Int. Ed. Engl.
1992, 31, 1485-1488.
† Current address: National Institute of Standards and Technology,
100 Bureau Drive MS 8542, Gaithersburg, MD 20899-8542.
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10.1021/om049944d CCC: $27.50 © 2004 American Chemical Society
Publication on Web 04/15/2004

Formation of a [1,3,2]Oxathiagermolan-4-one
Organometallics, Vol. 23, No. 10, 2004 2371
reaction with the sulfide-bridged complex.44 The reactiv-
ity of the Pd-Ge bond in the sulfide-bridged complexes
was surprising, since none of the previous Pt-Ge
metallacycles had exhibited clean, cooperative reactivity
at the Pt-Ge bond nexus.
Sch em e 1
Herein we report the insertion of formaldehyde into
the Pd-Ge bond of complex 2 with bond scission to give
a five-membered metallacycle. Subsequent reaction of
this metallacycle with CO results in migratory insertion
into the newly generated Pd-C bond. Insertion is
followed by rapid, facile reductive elimination to form
a new C-S bond and generate 2,2-bis(1,1,1,3,3,3-hex-
amethyldisilazan-2-yl)[1,3,2]oxathiagermolan-4-one (6),
a novel five-membered organic heterocycle comprised of
four different elements.
such as (Et3P)2PtGe[N(SiMe3)2]2, without cleavage of the
Pt-Ge bond, to form four-membered metallocycles.7,29,30,36
Subsequent insertion chemistry of these rings at the
Pt-O or Pt-N bond leads to the formation of novel five-
and six-membered metallacyclic structures, demonstrat-
ing the ability to effect new bond-forming reactions with
metal-germylene complexes (Scheme 1).29,30,36 No in-
sertion chemistry was observed for the Pt-C bonds or
at the Pt-Ge bond. Reductive elimination of these
metallacycles could be used to generate novel hetero-
atomic ring systems. However, we were unsuccessful in
promoting such eliminations from the Pt complexes.
On the basis of the previous results using Pt, we
decided to explore the analogous Pd system. Metalla-
cycles formed from the analogous Pd complexes should
be more prone to reductive elimination,37 allowing the
heterocycles to detach from the metal. In addition, four-
membered metallacycles containing Pt-C bonds have
not been amenable to additional insertions, whereas
Pd-C bonds have a well-defined and facile insertion
chemistry.38-40 However, with the notable exception of
O2, the analogous Pd complexes failed to reproduce any
of the addition chemistry noted for Pt41 and the direct
reactions with various substrates, including CH2O, were
unsuccessful.42
Exp er im en ta l Section
All manipulations of metal-containing species were per-
formed using air-free techniques. Benzene, toluene, THF,
pentane, and benzene-d6 were dried over sodium benzophenone
ketyl and degassed. Acetonitrile was dried over 4 Å molecular
sieves and degassed. Paraformaldehyde, CuCl, dppe, and PPh3
were purchased commercially (Aldrich, Strem) and used as
43
received. (Et3P)2Pd(µ-S)Ge[N(SiMe3)2]2 (2) was made accord-
ing to literature procedures. Photolysis experiments were
performed using a Blak-Ray long-wave (365 nm) ultraviolet
lamp. 1H, 31P, and 13C NMR spectra were acquired on a Varian
400 MHz instrument (400, 161.9, and 100.6 MHz, respec-
tively). 31P NMR spectra are referenced to H3PO4 by using an
external secondary standard of PPh3 in benzene-d6 (assigned
to -5.0 ppm).45 Mass spectra were acquired on a VG (Micro-
mass) 70-250-S magnetic sector mass spectrometer. IR spectra
were acquired on a Perkin-Elmer Spectrum BX.
(Et3P )2P d (µ-S)(µ-CH2O)Ge[N(SiMe3)2]2 (3). Complex 2
(1.2 g, 1.6 mmol) and paraformaldehyde (600 mg, 20 mmol)
were added to 100 mL of THF. The light brown solution with
white precipitate was placed in a water bath and stirred under
a UV lamp for 4 days. The solution gradually darkened. The
volatiles were evaporated, and the resulting brown solid was
dissolved in toluene and filtered to remove excess formalde-
hyde. The toluene was evaporated, and the resulting brown
solid was recrystallized from THF/MeCN to give 725 mg (58%
yield) of 3 as a tan-brown solid. 1H NMR (C6D6): δ 0.68 (s,
36H, SiCH3), 0.75 (m, 9H, CH2CH3), 0.88 (m, 9H, CH2CH3),
1.13 (m, 6H, CH2CH3), 1.52 (m, 6H, CH2CH3), 5.01 (dd,
J H-P ) 8.4 and 0.8 Hz, 2H, CH2O). 31P{1H} NMR (C6D6): δ
We recently demonstrated the reactivity of (Et3P)2-
PdGe[N(SiMe3)2]2 (1) with COS to extrude S atoms and
form the sulfide-bridged species (Et3P)2Pd(µ-S)Ge[N-
(SiMe3)2]2 (2) (eq 1).43 Interestingly, the presence of the
2
2
7.07 (d, J P-P ) 42.1 Hz), 20.5 (d, J P-P ) 42.1 Hz). 13C{1H}
NMR (C6D6): δ 6.58 (s, SiCH3), 8.23 (s, CH2CH3), 8.34 (s,
CH2CH3), 15.66 (d, J P-C ) 24.4 Hz, CH2CH3), 17.31 (d, J P-C
)
14.5 Hz, CH2CH3), 74.41 (d, trans J P-C ) 107.5 Hz, cis-J P-C
too small to observe, CH2O). IR (KBr pellet): 1032 cm-1
(ν(C-O)). Anal. Calcd for C25H68GeN2OP2PdSSi4: C, 37.62; H,
8.59; N, 3.51. Found: C, 37.63; H, 8.61; N, 3.29.
sulfide bridge in complex 2 dramatically improved our
ability to observe cooperative reactivity of the Pd-Ge
bond. Clean insertion products can be isolated from
(dppe)P d(µ-S)(µ-CH2O)Ge[N(SiMe3)2]2 (4). A 25 mL round-
bottom flask was charged with 3 (50 mg, 0.06 mmol) and dppe
(25 mg, 0.06 mmol). An 8 mL portion of benzene was distilled
in, and the pale brown solution was stirred for 1 h. The
volatiles were then removed and the resulting brown oil was
left under dynamic vacuum for 1.5 h, while standing in a warm
water bath. The oil began to solidify gradually while under
vacuum. The product was dissolved in benzene and left to
evaporate slowly over several days, yielding 28 mg (47% yield)
(36) Litz, K. E.; Bender, J . E.; Sweeder, R. D.; Banaszak Holl, M.
M.; Kampf, J . W. Organometallics 2000, 19, 1186-1189.
(37) Macgregor, S. A.; Neave, G. W.; Smith, C. Faraday Discuss.
2003, 124, 111-127.
(38) Meijere, A. d.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994,
33, 2379-2241.
(39) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
(40) Elsevier, C. J . Coord. Chem. Rev. 1999, 185-186, 809-822.
(41) Cygan, Z. T.; Bender, J . E.; Litz, K. E.; Banaszak Holl, M. M.
Organometallics 2002, 21, 5373-5381.
(42) Cygan, Z. T. In Palladium Complexes with Germylene Ligands:
Synthesis, Structure, and Reactivity. Doctoral Thesis, University of
Michigan, Ann Arbor, MI, 2004; pp 1-131.
(43) Cygan, Z. T.; Kampf, J . W.; Banaszak Holl, M. M. Inorg. Chem.
2003, 42, 7219-7226.
1
of tan crystals of 4. H NMR (C6D6): δ 0.68 (s, 36H, SiCH3),
1.66 (m, 1H, CH2), 1.72 (m, 1H, CH2), 1.87 (m, 1H, CH2), 1.93
(44) Cygan, Z. T.; Kampf, J . W.; Banaszak Holl, M. M. Inorg. Chem.
2004, 43, 2057-2063.
(45) Lawson, H. J .; Atwood, J . D. J . Am. Chem. Soc. 1989, 111,
6223-6227.

2372 Organometallics, Vol. 23, No. 10, 2004
Cygan et al.
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 4
(m, 1H, CH2), 5.21 (dd, J H-P ) 8.0 and 1.4 Hz, 2H, CH2O),
7.00 (m, 8H, Ph), 7.10 (m, 4H, Ph), 7.42 (m, 4H, Ph), 7.91 (m,
empirical formula
formula wt
temp
cryst syst, space group
unit cell dimens
a
b
c
R
â
C39H62GeN2OP2PdSSi4
960.26
118(2) K
triclinic, P1h
2
4H, Ph). 31P{1H} NMR (C6D6): δ 34.0 (d, J P-P ) 33.8 Hz),
2
51.5 (d, J P-P ) 33.8 Hz). 13C{1H} NMR (C6D6): δ 6.54 (s,
SiCH3), 25.0 (m, CH2), 29.6 (m, CH2), 75.75 (d, trans-2J P-C
)
109.83 Hz, cis-2J P-C too small to observe, CH2O), 128.77,
128.86, 128.88, 128.98 (o or m, Ph), 129.77, 130.18 (i, Ph),
130.55, 130.58, 131.06, 131.08, (p, Ph) 132.82, 133.09 (i, Ph),
133.40, 133.52, 133.69, 133.82 (o or m, Ph). Ipso and para
assignments are based upon relative intensities. Anal. Calcd
for C39H62GeN2OP2PdSSi4: C, 48.78; H, 6.51; N, 2.92. Found:
14.115(2) Å
17.175(2) Å
21.180(3) Å
68.090(4)°
89.880(5)°
γ
88.499(5)°
C, 48.73; H, 6.33; N, 2.82. IR (KBr pellet): 1104 cm-1 (νasym
(C-O-Ge)).
-
V
4761.9(11) Å3
4, 1.339 Mg/m3
1.251 mm-1
Z, calcd density
abs coeff
Ge[N(SiMe3)2]2SC(O)CH2O (6). A Pyrex bomb reactor was
charged with 3 (400 mg, 0.5 mmol) and PPh3 (523 mg, 2.0
mmol) and evacuated. Toluene (∼40 mL) was distilled in, and
1 atm of CO was added. The solution was stirred vigorously
and changed color slowly from a dark brown to a lighter brown.
After 8 days the volatiles were evaporated and NMR spectra
indicated that the reaction was less than half complete. The
NMR solution was returned to the bomb, and the volatiles were
removed. Toluene (∼40 mL) was again distilled in and 1 atm
of CO added. The solution was stirred vigorously for another
12 days, and the volatiles were removed. Pentane (∼40 mL)
was then added. The resulting slurry was filtered to separate
the green-yellow solid (PPh3)4Pd from the pale yellow filtrate.
The volatiles were removed from the filtrate, giving a pale
yellow oil that contained 6 and free PPh3. This oil was
redissolved in 15 mL of benzene, and CuCl (260 mg, 2.6 mmol)
was added to precipitate the PPh3. The solution was stirred
for 15 min and slowly became more reddish. The volatiles were
removed, and the resulting solid was suspended in 15 mL of
pentane. The solution was filtered, and the volatiles were
removed from the filtrate, leaving a yellow oil. This oil was
redissolved in benzene and passed through a silica gel column,
giving a faintly yellow eluent. The volatiles were removed,
λ
0.710 73 Å
R1 ) 0.0583, wR2 ) 0.1534
R1 ) 0.0785, wR2 ) 0.1735
final R indices (I > 2σ(I))
R indices (all data)
above 10σ(I). Analysis of the data showed negligible decay
during data collection; the data were processed with SADABS47
and corrected for absorption. The structure was solved and
refined with the Bruker SHELXTL software package,48 using
the space group P1h with Z ) 4 for the formula C39H62N2OSi4P2-
SGePd. All non-hydrogen atoms were refined anisotropically
with the hydrogen atoms placed in idealized positions. Full-
matrix least-squares refinement based on F2 converged at
R1 ) 0.0583 and wR2 ) 0.1534 (based on I > 2σ(I)); R1 )
0.0785 and wR2 ) 0.1735 for all data. A summary of crystal-
lographic data is given in Table 1.
Resu lts
Photolysis of THF solutions of (Et3P)2Pd(µ-S)Ge-
[N(SiMe3)2]2 (2) in the presence of paraformaldehyde
yields the insertion of formaldehyde into the Pd-Ge
bond to give (Et3P)2Pd(µ-S)(µ-CH2O)Ge[N(SiMe3)2]2 (3)
(eq 2). Characterization of this complex by 31P NMR and
1
giving 31 mg of 6 as a faintly yellow oil (13% yield). H NMR
(C6D6): δ 0.24 (s, 36H, SiCH3), 4.12 (s, 2H, CH2O). 13C{1H}
NMR (C6D6): δ 5.23 (s, SiCH3), 71.55 (s, CH2O), 203.06 (s,
CdO). IR (thin film on NaCl plate): 1706 cm-1 (ν(CdO)), 1111
cm-1 (νasym(C-O-Ge)). EI/MS (m/z): [M]+ 484.5, [M
OdCCH2O]+ 426.4. EI/HRMS (m/z): [M]+ 484.0941.
-
Rea ction of 2 w ith [CH 2O]3 P r otected fr om Ligh t. Two
round-bottomed flasks were charged with a THF solution of
complex 2 (20 mg, 0.026 mmol) and paraformaldehyde (8 mg,
0.26 mmol). One flask was wrapped in foil and left stirring
inside of a cabinet to protect the reaction from ambient light.
For a direct comparison to this dark reaction, the other flask
was placed in a water bath and stirred under a UV lamp. After
23 h the volatiles were removed from both flasks and the
products were dissolved in benzene-d6 for NMR analysis.
1H NMR spectroscopy indicates the presence of two
inequivalent phosphine ligands. The 13C NMR spectrum
contains a resonance at 74.1 ppm with a trans-J P-C
coupling constant of 107 Hz, consistent with a Pd-bound
methylene.49 The trimethylsilyl protons of the ger-
mylene appear as a singlet at 0.68 ppm, shifted down-
field from the starting material, and the methylene
protons appear as a doublet of doublets at 5.01 ppm.
The IR spectrum of this complex contains a ν(C-O-
Str u ctu r e Deter m in a tion of 4. Colorless plates of 4 were
grown from a benzene/toluene solution at 22 °C. A crystal of
dimensions 0.36 × 0.24 × 0.16 mm was mounted as on a
standard Bruker SMART CCD-based X-ray diffractometer
equipped with an LT-2 low-temperature device and normal
focus Mo-target X-ray tube (λ ) 0.710 73 Å) operated at 2000
W power (50 kV, 40 mA). The X-ray intensities were measured
at 118(2) K; the detector was placed at a distance 4.980 cm
from the crystal. A total of 2223 frames were collected with a
scan width of 0.3° in ω and ψ with an exposure time of 30
s/frame. The frames were integrated with the Bruker SAINT
Ge) band at 1032 cm-1
.
We wished to confirm the presence of the sulfide
bridge and the connectivity of the formaldehyde bridge
software package46 with
a narrow frame algorithm. The
(47) Sheldrick, G. M. SADABS. Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen, Gottingen,
Germany, 1996.
(48) Sheldrick, G. M. SHELXTL, v. 5.10; Bruker Analytical X-ray,
Madison, WI, 1997.
(49) Campora, J .; Lopez, J . A.; Palma, P.; Rio, D. d.; Carmona, E.;
Valerga, P.; Graiff, C.; Tiripicchio, A. Inorg. Chem. 2001, 40, 4116-
4126.
integration of the data yielded a total of 40 894 reflections to
a maximum 2θ value of 43.94°, of which 11 581 were inde-
pendent and 9725 were greater than 2σ(I). The final cell
constants were based on the xyz centroids of 6467 reflections
(46) Saint Plus v 7.01; Bruker Analytical X-ray, Madison, WI, 2003.

Formation of a [1,3,2]Oxathiagermolan-4-one
Organometallics, Vol. 23, No. 10, 2004 2373
1H NMR spectrum of 6 contains a singlet in the
trimethylsilyl region at 0.24 ppm, consistent with
similar GeIV species.53-55 The two methylene protons
appear as a singlet at 4.12 ppm. The presence of the
carbonyl moiety is evident in the 13C NMR spectrum
with a resonance at 203.1 ppm and in the IR with a
ν(CdO) band at 1706 cm-1. The asymmetric C-O-Ge
stretch is also observed at 1111 cm-1. High-resolution
mass spectroscopy gives a parent peak at m/z 484.1 with
isotopic distribution pattern matching the calculated
spectrum for 6. The next heaviest fragment at m/z 426.4
is consistent with the loss of a OdCCH2O moiety from
the parent complex. Complex 4 is stable in the presence
of CO and does not form an analogous insertion product.
The formation of 6 occurs cleanly and quantitatively,
as long as the solution contains ligands to trap the free
Pd0 fragment also formed in the reaction. Once the
overpressure of CO is removed from the reaction, the
Pd metal center is no longer stabilized and partial
decomposition of the product is observed. However,
reactions run in the presence of PPh3 result in clean
conversion to 6 and (Ph3P)4Pd with no subsequent
decomposition observed upon removal of volatiles.
F igu r e 1. ORTEP representation (50% probability) of
(dppe)Pd(µ-S)(µ-CH2O)Ge[N(SiMe3)2]2 (4). Selected bond
lengths (Å) and angles (deg): Pd1-S1 ) 2.389(3), Pd1-
C1 ) 2.166(11), O1-C1 ) 1.383(14), Ge1-O1 ) 1.785(6),
Ge1-S1 ) 2.182(3), Pd(1)-P(1) ) 2.230(3), Ge(1)-N(2) )
1.848(8), P(2)-Pd(1)-S(1) ) 97.10(10), O(1)-Ge(1)-N(2)
) 101.3(3), C(1)-O(1)-Ge(1) ) 114.6(6), O(1)-C(1)-Pd-
(1) ) 115.2(7), S1-Pd1-C1 ) 91.7(3), Ge1-S1-Pd1 )
95.72(10), S1-Ge1-O1 ) 103.7(3), N2-Ge1-N1 ) 116.0(3),
P2-Pd1-P1 ) 85.57(10).
of 3 crystallographically. However, suitable crystals
could not be grown. To facilitate crystallization, the
bis(diphenylphosphino)ethane (dppe) derivative was
prepared by ligand substitution. NMR spectroscopy
confirmed the displacement of the two PEt3 ligands of
3 with the dppe to give (dppe)Pd(µ-S)(µ-CH2O)Ge[N(Si-
Me3)2]2 (4) (eq 2).
Discu ssion
The crystal structure of 4 (Figure 1) confirms the
presence of the sulfide bridge and the binding mode of
the inserted formaldehyde. Attempts to refine the
structure with the C-O moiety reversed, Pd-O-CH2-
Ge, resulted in nonpositive-definite thermal displace-
ment parameters for C and unrealistically large thermal
displacement for O. The Ge-O bond length of 1.785(6)
Å and the Pd-C bond length of 2.166(11) Å are
consistent with literature values.50,51 The C-O bond
length of the bridge is 1.383(14) Å. The palladium metal
center is square planar, and the Ge center has a
tetrahedral geometry.
The reactivity of the Pd-Ge bond with formaldehyde
differs markedly from the chemistry observed in our
studies of Pt-Ge chemistry. (Et3P)2PtGe[N(SiMe3)2]2
reacts with paraformaldehyde to give a four-membered
metallacycle (eq 4).36 Reactions of the Pd analogue,
The insertion of CH2O into the Pd-Ge bond of 2 is
observed to require photolytic conditions.52 THF solu-
tions of 2 with excess [CH2O]3 that were protected from
light showed no reaction after 1 day of stirring. By way
of contrast, 60% conversion to 3 can be observed in
solutions that have been stirring for 1 day with UV
irradiation. Very slow conversion to 3 can also be
observed under ambient (fluorescent) light, with ap-
proximately 15% conversion to 3 after 5 days of stirring.
(Et3P)2PdGe[N(SiMe3)2]2 (1), with paraformaldehyde
were unsuccessful and decomposition of the Pd complex
was observed.42 The presence of a sulfide bridge between
the Pd and Ge centers was necessary in order to observe
cooperative reactivity of the Pd-Ge bond with CH2O.
The addition of 1 atm of CO to benzene solutions of 3
results in the formation of [1,3,2]oxathiagermolan-4-one
(6), with reduction of the Pd metal center (eq 3). The
(53) Kobayashi, S.; Iwata, S.; Abe, M.; Shoda, S. J . Am. Chem. Soc.
1995, 117, 2187-2200.
(50) Baines, K. M.; Stibbs, W. G. Coord. Chem. Rev. 1995, 145, 157-
200.
(54) Miller, K. A.; Bartolin, J . A.; O’Neill, R. M.; Sweeder, R. D.;
Owens, T. M.; Kampf, J . W.; Banaszak Holl, M. M.; Wells, N. J . J .
Am. Chem. Soc. 2003, 125, 8986-8987.
(51) A search of the Cambridge Structrual Database for Pd-C(sp3)
bond lengths found an average length of 2.1 ( 0.1 Å.
(52) For UV-vis data for complex 2, see ref 43.
(55) Sweeder, R. D.; Gdula, R. L.; Ludwig, B. J .; Banaszak Holl, M.
M.; Kampf, J . W. Organometallics 2003, 22, 3222-3229.

2374 Organometallics, Vol. 23, No. 10, 2004
Cygan et al.
Sch em e 2
not observed in NMR spectra of these reactions, sug-
gesting that conversion from 3b to 5 and from 5 to 6 is
rapid. Thus, the loss of PEt3 from 3 is most likely the
rate-determining step in this reaction.
Because species 5 has not been observed spectroscopi-
cally, we have no direct evidence as to its structure. We
believe that migratory insertion of CO into the Pd-C
bond and not the Pd-S bond is most likely occurring.
Insertions of CO into Pd-C bonds are well prece-
dented.60,61 Pd is used industrially to polymerize CO and
alkenes to make polyketones.62
In contrast, there are very few examples of CO
insertion into M-S bonds in the literature. CO has been
observed to desulfurize thiols on Co to give Co-alkyl
complexes and COS.63-67 There has been one report in
which the insertion of CO into Pd-S-Ar bonds has been
proposed as a possible intermediate in the Pd-catalyzed
transformation of sulfenamides (RSNR′2) to thiocar-
bamates (RSC(O)NR′2).68 However, in this example the
two possible migratory insertion pathways are into the
Pd-S bond versus into the Pd-N bond and not a Pd-S
bond versus a Pd-C bond. In our system we have
observed that the reaction of (Et3P)2PdGe[N(SiMe3)2]2
(1) with COS generates complex 2 and CO (eq 1).43
Complex 2 is stable for days in the presence of excess
CO at room temperature and does not undergo subse-
quent insertion or desulfurization. Thus, the Pd-S-Ge
moiety appears to be unreactive to carbonylation of the
Pd-S bond under our conditions.
Reductive elimination to generate C-S bonds has
been reported in the literature.69-71 Insertions of CO
into S-C bonds followed by C-S bond forming reductive
eliminations can be used to catalytically generate
thioesters on Co, Rh, and Pd. However, these reactions
require forcing conditions (∼60 atm of CO, 125-180
°C).69 Stoichiometric C-S-forming reductive elimina-
tions on Pd have been reported under milder conditions
(50-95 °C).71 In our system, the precursor to reductive
elimination, complex 5, is not observed spectroscopically,
indicating that reductive elimination is rapid and facile
at room temperature. The rates of C-S bond-forming
reductive eliminations on Pd are accelerated by an
electron-deficient carbon center and by the presence of
a π system in the product that can coordinate and
stabilize the reductive elimination transition state.71
Both of these elements are present in the carbonyl
moiety of 5 that gives rise to the cyclic thioester 6 and
may be facilitating reductive elimination.
This cooperative reactivity exhibited in the formation
of 3 is different from any of the addition and insertion
reactions observed in the Pt system. The Pd-Ge bond
is broken in the formation of the insertion product. In
the Pt chemistries, reaction of (Et3P)2PtGe[N(SiMe3)2]2
with various substrate molecules resulted in four-
membered metallacycles with preservation of the Pt-
Ge bond.7,29,30,36 Subsequent reactivity (Scheme 1) re-
sulted in insertions into the Pt-X bond (X ) O, N),
without the Pt-Ge bond cleavage. The reactions with
the Pt-Ge and Pd-Ge bonds are similar in that the
connectivities of the insertion products are the same,
M-CH2-O-Ge.
The formation of complex 3 is, to our knowledge, the
first example of an insertion of formaldehyde into a
M-Ge bond with concomitant M-Ge bond cleavage.
Formaldehyde is known to insert into M-C56-58 and
M-Si59 bonds. The metal carbon insertion products
display a M-O-CH2-R connectivity for both early
transition metals (Ta) and late transition metals (Ni,
Cu). Insertions of formaldehyde into early-metal (Ta)
silicon bonds also give this connectivity.59 However,
aldehyde insertions into M-Si bonds of electron-rich or
low-valent metals generate M-CR2-O-Si insertion
isomers.59 This latter connectivity is observed in 3 and
is consistent with the trend observed for M-Si inser-
tions.
Complex 3 reacts further with CO to form a new
organic heterocycle and a Pd0 fragment (eq 3). A formal
mechanism for this reaction can be postulated (see
Scheme 2). The first step is ligand substitution of PEt3
with CO, to give the cis coordination necessary for
concerted migration.60 In complex 4, where a bidentate
phosphine ligand blocks access to this coordination site,
no reactivity with CO is observed. Species 3b and 5 are
The insertion of CO into the Pd-C bond of 3 and
subsequent reductive elimination illustrates two desir-
able modes of reactivity of the Pd-Ge system not
observed in the Pt-Ge heterocyclic chemistry. The first
(61) Yamamoto, A. J . Chem. Soc., Dalton Trans. 1999, 1027-1037.
(62) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
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Soc. 1997, 119, 4669-4677.
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(65) Antebi, S.; Alper, H. Tetrahedron Lett. 1985, 26, 2609-2612.
(66) Shim, S. C.; Antebi, S.; Alper, H. Tetrahedron Lett. 1985, 26,
1935-1938.
(56) Luinstra, G. A.; Vogelzang, J .; Teuben, J . H. Organometallics
1992, 11, 2273-2281.
(57) Carmona, E.; Palma, P.; Paneque, M.; Poveda, M. L.; Gutier-
rezpuebla, E.; Monge, A. J . Am. Chem. Soc. 1986, 108, 6424-6425.
(58) Leoni, P.; Pasquali, M. J . Organomet. Chem. 1983, 255, C31-
C33.
(59) Arnold, J .; Tilley, T. D. J . Am. Chem. Soc. 1987, 109, 3318-
3322.
(60) Kayaki, Y.; Tsukamoto, H.; Kaneko, M.; Shimizu, I.; Yamamoto,
A.; Tachikawa, M.; Nakajima, T. J . Organomet. Chem. 2001, 622, 199-
209.
(67) Luh, T.-Y.; Ni, Z.-J . Synthesis 1990, 89-103.
(68) Sugoh, K.; Kuniyasu, H.; Sugae, T.; Ohtaka, A.; Takai, Y.;
Tanaka, A.; Machino, C.; Kambe, N.; Kurosawa, H. J . Am. Chem. Soc.
2001, 123, 5108-5109.
(69) Kondo, T.; Mitsudo, T. Chem. Rev. 2000, 100, 3205-3220.
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I. A. J . Am. Chem. Soc. 1998, 120, 9205-9219.

Formation of a [1,3,2]Oxathiagermolan-4-one
Organometallics, Vol. 23, No. 10, 2004 2375
Sch em e 3
Con clu sion s
Novel cooperative reactivity of the Pd-Ge bond is
reported. A sulfide bridging the Pd and Ge centers
enables insertion of formaldehyde into the Pd-Ge bond
with bond cleavage. The resulting metallacycle under-
goes further insertion chemistry with the migratory
insertion of CO into the newly formed Pd-C bond.
Subsequent reductive elimination generates a unique
organic heterocycle. These reactions demonstrate the
capacity of the Pd system to couple multiple organic and
inorganic substrates together in a controlled manner on
one metal center.
The chemistries reported here further develop the
chemistry of group 10 metal germylene and germyl
complexes. Three novel modes of reactivity not observed
in the Pt-Ge chemistry are reported. Direct insertion
of a substrate into the M-Ge bond with bond cleavage
is observed. This is followed by insertion of a substrate
molecule into the M-C bond and reductive elimination
of metallacycles from the metal center.
is the insertion into a M-C bond. Although insertions
into Pt-N and Pt-O bonds could be observed,29,30 we
have been unsuccessful in effecting insertions into the
Pt-C bond of complexes such as (Et3P)2Pt(µCH2O)Ge-
Ack n ow led gm en t. This work was funded by the
Research Corporation and the donors of the Petroleum
Research Fund, administered by the American Chemi-
cal Society. Z.T.C. thanks the National Science Founda-
tion for a graduate research fellowship. Dr. A. C.
Gottfried is thanked for numerous helpful conversa-
tions.
36
[N(SiMe3)2]2 (eq 4) and (Et3P)2Pt(µC(O)O)Ge[N(Si-
Me3)2]2.7,36 Finally, reductive elimination of Pt metal-
lacycles could not be induced, yet elimination is rapid
and facile for Pd.
Scheme 3 summarizes the overall process for the
synthesis of 6 beginning from complex 1.41 Three
different substrate molecules can be coupled together
in a controlled manner to generate four new bonds: Ge-
S, Ge-O, C-C, and C-S. Compound 6 is a unique
heterocyclic ring, in which only two atoms are of the
same type.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data and files in CIF form for 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM049944D