Synthesis and reactivity of a novel palladium germylene system

Article abstract of DOI:10.1021/om0204134

The synthesis of three novel Pd germylene complexes is reported. (Ph₃P)₂PdGe[N(SiMe₃)₂]₂ (1) was synthesized by ligand substitution of (Ph₃P)₄Pd, whereas (Et₃P)PdGe[N(SiMe₃)₂]₂ (2) and {appePdGe[N(SiMe₃)₂]₂}₂ (3b) (dppe = (diphenylphosphino)ethane) were synthesized by photolytic reduction of their corresponding phosphine oxalato complexes followed by addition of the germylene ligand. In solution, 3b exists in equilibrium with the monomeric dppePdGe[N(SiMe₃)₂]₂ (3a). The germylene ligand of 2 was found to be 1 order of magnitude more labile than the analogous Pt system and 2 orders of magnitude less labile than the analogous Ni system. The reactivity of these new palladium germylenes toward O₂ is described.

Full text of DOI:10.1021/om0204134

Organometallics 2002, 21, 5373-5381
5373
Syn th esis a n d Rea ctivity of a Novel P a lla d iu m
Ger m ylen e System
Zuzanna T. Cygan, J ohn E. Bender IV,† Kyle E. Litz,‡ J eff W. Kampf, and
Mark M. Banaszak Holl*
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055
Received May 24, 2002
The synthesis of three novel Pd germylene complexes is reported. (Ph3P)2PdGe[N(SiMe3)2]2
(1) was synthesized by ligand substitution of (Ph3P)4Pd, whereas (Et3P)PdGe[N(SiMe3)2]2
(2) and {dppePdGe[N(SiMe3)2]2}2 (3b) (dppe ) (diphenylphosphino)ethane) were synthesized
by photolytic reduction of their corresponding phosphine oxalato complexes followed by
addition of the germylene ligand. In solution, 3b exists in equilibrium with the monomeric
dppePdGe[N(SiMe3)2]2 (3a ). The germylene ligand of 2 was found to be 1 order of magnitude
more labile than the analogous Pt system and 2 orders of magnitude less labile than the
analogous Ni system. The reactivity of these new palladium germylenes toward O2 is
described.
In tr od u ction
possible across the metal-germylene bond. This bond-
forming reaction could occur with the breaking of the
M-Ge bond, oxidation of the metal, and/or oxidation of
the germanium center.
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.1-6 The
majority of the chemistry of the M-Ge bond has been
studied in the context of GeIV species: germylation
reactions utilizing a metal catalyst,7-14 the metal-
catalyzed formation of Ge-containing polymers,15 or
cross-coupling reactions.16 However, the close proximity
of the electron-rich metal and the Lewis acidic GeII
suggests a variety of addition reactions should be
To study these addition reactions, we have explored
the reactivity of the stable germylene ligands Ge-
[N(SiMe3)2]2 and Ge[CH(SiMe3)2]2, first reported by
Lappert,17,18 bound to nickel and platinum. Various
small organic and inorganic molecules will react with
platinum germylenes such as (Et3P)2PtGe[N(SiMe3)2]2
to form four-membered rings. Subsequent insertion
chemistry of these rings leads to the formation of novel
five- and six-membered metallacyclic structures.19,20
Reductive elimination of these metallacycles could be
used to generate novel heteroatomic ring systems;
however, thus far we have been unsuccessful in promot-
ing such eliminations in the Pt system. We have also
studied the reactivity of the analogous Ni germylene
complexes. In this system the germylene ligand was
found to be extremely labile.21 This lability generally
resulted in reagents reacting directly with the ger-
mylene ligand.22
On the basis of previous results using Pt and Ni, we
decided to explore the analogous Pd system. Metalla-
cycles formed from Pd complexes of the general struc-
ture (R3P)2PdGeR′2 should be more prone to reductive
elimination, allowing the heterocycles to be removed
from the metal. In addition, four-membered metalla-
cycles containing Pt-C bonds have not been amenable
to additional insertions, whereas Pd-C bonds have a
* To whom correspondence should be addressed. E-mail: mbanasza@
umich.edu.
† Current address: Grand Valley State University, Allendale, MI.
‡ Current address: General Electric, Schenectady, NY.
(1) Schriewer, M.; Neumann, W. P. J . Am. Chem. Soc. 1983, 105,
897-901.
(2) Barthelat, J . C.; Roch, B. S.; Trinquier, G.; Satge, J . J . Am. Chem.
Soc. 1980, 102, 4080-4086.
(3) Petz, W. Chem. Rev. 1986, 86, 1019-1047.
(4) Lappert, M. F.; Rowe, R. S. Coord. Chem. Rev. 1990, 100, 267-
292.
(5) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J . Am. Chem. Soc.
2001, 123, 11162-11167.
(6) Knorr, M.; Hallauer, E.; Huch, V.; Veith, M.; Braunstein, P.
Organometallics 1996, 15, 3868-3875.
(7) Mitchell, T. N.; Schneider, U.; Frohling, B. J . Organomet. Chem.
1990, 384, C53-C56.
(8) Chatani, N.; Horiuchi, N.; Hanafusa, T. J . Org. Chem. 1990, 55,
3393-3395.
(9) Reddy, N. P.; Hayashi, T.; Tanaka, M. Chem. Lett. 1991, 677-
680.
(10) Tsumuraya, T.; Ando, W. Organometallics 1990, 9, 869-871.
(11) Ikenaga, K.; Matsumoto, S.; Kikukawa, K.; Matsuda, T. Chem.
Lett. 1990, 185-188.
(12) Hayashi, T.; Yamashita, H.; Sakakura, T.; Uchimaru, Y.;
Tanaka, M. Chem. Lett. 1991, 245-248.
(17) Harris, D. H.; Lappert, M. F. J . Chem. Soc., Chem. Commun.
1974, 895-896.
(18) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert, M. F.;
Thorne, A. J . J . Chem. Soc., Dalton Trans. 1986, 1551-1556.
(19) Litz, K. E.; Banaszak Holl, M. M.; Kampf, J . W.; Carpenter, G.
B. Inorg. Chem. 1998, 37, 6461-6469.
(20) Litz, K. E.; Kampf, J . W.; Banaszak Holl, M. M. J . Am. Chem.
Soc. 1998, 120, 7484-7492.
(21) Litz, K. E.; Bender, J . E.; Sweeder, R. D.; Banaszak Holl, M.
M.; Kampf, J . W. Organometallics 2000, 19, 1186-1189.
(22) Litz, K. E.; Banaszak Holl, M. M. Unpublished work.
(13) Furukawa, N.; Kourogi, N.; Seki, Y.; Kakiuchi, F.; Murai, S.
Organometallics 1999, 18, 3764-3767.
(14) Mochida, K.; Wada, T.; Suzuki, K.; Hatanaka, W.; Nishiyama,
Y.; Nanjo, M.; Sekine, A.; Ohashi, Y.; Sakamoto, M.; Yamamoto, A.
Bull. Chem. Soc. J pn. 2001, 74, 123-137.
(15) Gomez, F. J .; Wagener, K. B. J . Organomet. Chem. 1999, 592,
271-277.
(16) David-Quillot, F.; Thibonnet, J .; Marsacq, D.; Abarbri, M.;
Duchene, A. Tetrahedron Lett. 2000, 41, 9981-9984.
10.1021/om0204134 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/01/2002

5374 Organometallics, Vol. 21, No. 24, 2002
Cygan et al.
well-defined and facile insertion chemistry.23-25 Finally,
the Pd-Ge bond should be less labile than the Ni-Ge
bond of the Ni complex, thus improving the chances for
observing reactivity at the Pd-Ge nexus.
mylene-containing complexes are air and moisture sensitive
to hydrolysis of the Ge-N bonds of the ligand.
tr a n s-(Et3P )2P d Cl2. (cod)PdCl2 (4.75 g, 0.017 mol) was
dissolved in 200 mL of methylene chloride. PEt3 (5 mL, 0.034
mol) was then added to the orange solution, which rapidly
became yellow. The solution was stirred for 2 h, and then the
volume was reduced in half. The solution was filtered, and the
volatiles were evaporated from the filtrate, giving 6.28 g (92%)
of shiny yellow microcrystals. 1H NMR (CDCl3): δ 1.19 (m,
18H, CH3) 1.86 (m, CH2). 31P{1H} NMR (CDCl3): δ 18.16 (s).
(P h 3P )2P d Ge[N(SiMe3)2]2 (1). (Ph3P)4Pd (0.5 g, 0.43 mmol)
and Ge[N(SiMe3)2]2 (0.170 g, 0.43 mmol) were stirred in 20
mL of benzene for 5 h. The volatiles were then evaporated,
giving an orange-brown solid. Additional Ge[N(SiMe3)2]2 (0.08
g, 0.20 mmol) was added to the crude product, and the mixture
was then recrystallized from THF/acetonitrile to give 313 mg
(71%) of orange microcrystalline 1. 1H NMR (C6D6): δ 0.48 (s,
36H, SiMe3), 7.01 (m, 18H, Ph) 7.47 (m, 12H, Ph). 31P{1H}
NMR (C6D6): δ 28.84 (s). 13C{1H} NMR (C6D6): δ 5.95 (s,
SiMe3), 128.86 (s, Ph), 134.25 (t, J C-P ) 8.7 Hz), 138.02, (s,
Ph). Anal. Calcd for C48H66GeN2P2PdSi4: C, 56.28; H, 6.49;
N, 2.73. Found: C, 56.15; H, 6.53; N, 2.59.
No direct Pd analogues of three-coordinate (R3P)2-
MGeR′2 systems exist. In fact, complexes of palladium
with a germylene ligand are extremely rare, with only
two examples in the literature. Lappert and co-workers
reported the homoleptic complex Pd{Ge[N(SiMe3)2]2}3,
which was found to react with CO to form the trinuclear
cluster Pd3(CO)3(µ-Ge[N(SiMe3)2]2)3.26,27 However, no
additional reactivity of these species has been reported.
There are no crystallographically characterized ex-
amples of palladium germylene complexes in the litera-
ture.
Herein the synthesis and spectroscopic and structural
characterization of three novel palladium germylene
complexes are reported. Two of the complexes are of the
general formula (R3P)2PdGe[N(SiMe3)2]2. The third
contains a bidentate phosphine ligand. Such complexes
may ultimately be important for controlling the desired
reductive-elimination and insertion chemistry. As an
initial test of the chemistry of these new complexes, the
lability of the germylene ligand and the reactivity of the
complexes with dioxygen was explored. These results
were compared to previous studies using analogous Ni
and Pt systems.19,21
(Et3P )2P d Ge[N(SiMe3)2]2 (2). A two-necked 250 mL round-
bottom flask was charged with (Et3P)2PdC2O4 (2.0 g, 4.6 mmol)
and 80 mL of benzene. Excess PEt3 (10 mL) was then added,
and the flask was sealed with a rubber septum and a needle
valve. The clear liquid with off-white solid suspension was
frozen and the flask evacuated. After thawing the flask was
irradiated while the contents were stirred in a water bath for
7 h. The solution gradually became yellow, with a yellow solid
suspension. The solution was degassed three times during the
photolysis and again at the end. A solution of Ge[N(SiMe3)2]2
(2.012 g, 5.1 mmol) in 12 mL of benzene was then added via
steel cannula. The solution was stirred for 16 h and gradually
became red with no solids present. The solvent was evaporated,
and the crude red-brown solid was recrystallized from THF/
acetonitrile to yield orange microcrystalline 2 (2.38 g, 70%
Exp er im en ta l Section
All manipulations of air-sensitive complexes 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.
PdCl2, (PPh3)4Pd, PPh3, PEt3, and dppe were purchased from
Strem and used as received. (cod)PdCl2,28 (dppe)PdCl2,29
(dppe)PdC2O4,30 and Ge[N(SiMe3)2]231 were prepared according
to the literature procedures. An improved preparation for
trans-(Et3P)2PdCl2 is included.32 The preparation for (Et3P)2-
PdC2O4 was based upon the approach of Landis et al.,33
omitting the refluxing step. Ag2C2O4 (Caution! explosive when
heated) was made by reaction of K2C2O4 and AgCl2 in water.30
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 and 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).34 Photolysis experiments were performed using
a Blak-Ray long-wave (365 nm) ultraviolet lamp. All ger-
1
yield). H NMR (C6D6): δ 0.51 (s, 36H, SiMe3), 1.05 (m, 18H,
CH3) 1.40 (m, 12H, CH2). 31P{1H} NMR (C6D6): δ 15.31 (s).
13C{1H} NMR (C6D6): δ 5.95 (s, SiMe3) 9.48 (s, CH3) 21.84 (t,
CH2). Anal. Calcd for C24H66GeN2P2PdSi4: C, 39.16; H, 9.04;
N, 3.81. Found: C, 39.28; H, 9.14; N, 3.61.
{(d p p e)P d Ge[N(SiMe3)2]2}2 (3b). A 100 mL round-bottom
flask was charged with dppePdC2O4 (120 mg, 0.23 mmol) and
Ge[N(SiMe3)2]2 (81 mg, 0.21 mmol) in 20 mL of benzene. The
solution was frozen and the flask evacuated. The solution was
then thawed and irradiated for 6 h. The solution was degassed
several times during photolysis. The volatiles were evaporated,
leaving a sticky red-brown solid. The crude product was
recrystallized from THF/acetonitrile, yielding 42 mg of a brown
solid (23% yield). In benzene-d6 solution, both the dimeric 3b
and the monomeric species (dppe)Pd Ge[N(SiMe3)2]2 (3a ) are
observed. 3a : 1H NMR (C6D6) δ 0.48 (s, 36H, SiMe3), 2.00 (d,
4H, CH2, 2J P-H ) 14.7 Hz), 7.11 (m, Ph), 7.58 (m, Ph); 31P{1H}
NMR (C6D6) δ 33.35 (s). 3b: 1H NMR (C6D6) δ 0.56 (s, 36H,
SiMe3), 2.71 (s, 4H, CH2) 7.00 (m, Ph), 7.58 (m, Ph); 31P{1H}
NMR (C6D6) δ 22.47 (s). Elemental analysis was obtained on
a crystal of 3b grown from benzene-d6 solution. Anal. Calcd
for C76H120Ge2N4P4Pd2Si8‚C6D6: C, 52.37; H, 7.07; N, 2.98.
Found: C, 52.37; H, 6.61; N, 2.74.
(23) Meijere, A. D.; Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994,
33, 2379-2411.
(24) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663-681.
(25) Elsevier, C. J . Coord. Chem. Rev. 1999, 185-186, 809-822.
(26) Hitchock, P. B.; Lappert, M. F.; Misra, M. C. J . Chem. Soc.,
Chem. Commun. 1985, 863-865.
(27) Campbell, G. K.; Hitchcock, P. B.; Lappert, M. F.; Misra, M. C.
J . Organomet. Chem. 1985, 289, C1-C4.
(28) Drew, D.; Doyle, J . R. Inorg. Synth. 1990, 28, 346-349.
(29) Broadwood-Strong, G. T.; Chaloner, P. A.; Hitchcock, P. B.
Polyhedron 1993, 12, 721-729.
Ben zil Tr a p p in g Exp er im en ts. A benzene-d6 solution
containing 2 (20 mg, 0.027 mmol) and 4 equiv of benzil (22.7
mg, 0.1 mmol) was placed in an NMR tube fitted with a Teflon
valve. For experiments protected from light, the two solids
were added to a tube containing frozen benzene-d6. The tube
was then sealed with a Teflon valve and immediately wrapped
(30) Paonessa, R. S.; Prignano, A. L.; Trogler, W. C. Organometallics
1985, 4, 647-657.
(31) Gynane, J . J . S.; Harris, D. H.; Lappert, M. F.; Power, P. P.;
Riviere, P.; Riviere-Baudet, M. J . Chem. Soc., Dalton Trans. 1977,
2004-2009.
1
(32) Alcock, N. W.; Kemp, T. J .; Wimmer, F. L. J . Chem. Soc., Dalton
Trans. 1981, 635-638.
in foil. H NMR spectra of the solutions were acquired over a
period of several hours. The progress of the trapping reactions
(33) Schaad, D. R.; Landis, C. R. Organometallics 1992, 11, 2024-
1
was followed by the growth of a singlet at 0.36 ppm in the H
2029.
NMR, the resonance for the trimethylsilyl protons of the
product of the reaction of free germylene and benzil. The extent
(34) Lawson, H. J .; Atwood, J . D. J . Am. Chem. Soc. 1989, 111,
6223-6227.

A Novel Palladium Germylene System
Organometallics, Vol. 21, No. 24, 2002 5375
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 1, 2, a n d 3b
1
2
3b‚1/2THF
empirical formula
fw
temp, K
C
48H66GeN2P2PdSi4
C
24H66GeN2P2PdSi4
C
78H124Ge2N4 O0.50P4Pd2 Si8
1024.32
178(2)
736.08
158(2)
1832.39
158(2)
wavelength, Å
cryst syst
space group
unit cell dimens
a, Å
0.710 73
monoclinic
P21/c (No. 14)
0.710 73
monoclinic
C2/c (No. 15)
0.710 73
triclinic
P1h (No. 2)
13.9430(10)
15.9735(15) Å
13.437(2)
R, deg
b, Å
90
90
114.446(3)
19.872(3)
18.3100(10)
21.595(2)
â, deg
c, Å
107.330(10)
21.383(2)
91.851(2)
11.1049(11)
90.181(3)
20.924(3)
γ, deg
90
90
109.656(2)
4723.4(13); 2
1.288
1.214
1904
V, Å3; Z
5211.2(7); 4
1.306
1.108
2128
3828.7(6); 4
1.277
1.479
1552
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
cryst size, mm
θ range, deg
limiting indices
0.20 × 0.20 × 0.18
0.04 × 0.24 × 0.34
0.18 × 0.06 × 0.01
2.70-26.00
1.59-26.39
1.22-23.25
-17 e h e 16, 0 e k e 22,
0 e l e 26
12 674/10 236(R(int) ) 0.0459)
ψ scans
-19 e h e 19, -26 e k e 26,
-13 e l e 13
37 605/3914 (R(int) ) 0.0426)
semiempirical from
equivalents
-14 e h e 14, -22 e k e 20,
-3 e l e 23
no. of rflns collected/unique
abs cor
42 030/13 562 (R(int) ) 0.1343)
semiempirical from
equivalents
refinement method
full-matrix least squares on F2
10 232/0/537
0.848
full-matrix least squares on F2
3914/0/167
full-matrix least squares on F2
13 562/30/936
0.999
no. of data/restraints/params
goodness of fit on F2
1.068
final R indices (I > 2σ(I))
R1
0.0342
0.0718
0.0287
0.0701
0.0625
0.1330
wR2
R indices (all data)
R1
0.0613
0.0372
0.1456
wR2
0.0759
0.0738
0.1659
largest diff peak and hole,
0.672 and -0.698
0.358 and -0.409
0.904 and -0.548
e Å-3
of conversion to trapped product was determined by comparing
the integration of this singlet with the resonance of the
trimethylsilyl protons of the remaining 2 at 0.51 ppm.
Oxygen Exp er im en ts. A solution of 1-3 or 5 in benzene-
d6 was added to an NMR tube fitted with a Teflon valve. The
solution was degassed and then frozen. One equivalent of O2
was then added. The tubes were either kept in ambient light
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 a power of 2000 W (50 kV, 40 mA). The X-ray
intensities were measured at 158(2) K. The detector was placed
at a distance 4.939 cm from the crystal. A total of 2322 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 software package37 with a narrow-frame
algorithm. The integration of the data yielded a total of 37 605
reflections to a maximum 2θ value of 52.80°, of which 3914
were independent and 3377 were greater that 2σ(I). The final
cell constants (Table 1) were based on the xyz centroids of 4245
reflections above 10σ(I). Analysis of the data showed negligible
decay during data collection; the data were processed with
SADABS38 and corrected for absorption. The structure was
solved and refined with the Bruker SHELXTL software
package,39 using the space group C2/c with Z ) 4 for the
formula C24H66N2Si4P2GePd. The molecule occupies a 2-fold
rotation axis in the crystal lattice coincident with the Pd-Ge
bond. 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
) 0.0287 and wR2 ) 0.0701 (based on I > 2σ(I)) and at R1 )
0.0372 and wR2 ) 0.0738 for all data. Additional details are
presented in Table 1.
1
or wrapped in foil to protect them from ambient light. H and
31P NMR spectra were acquired periodically over several days
to monitor the progress of the reactions.
Str u ctu r e Deter m in a tion of 1. A colorless, rectangular
block of 1 of dimensions 0.20 × 0.20 × 0.18 mm was coated
with Paratone-N oil and transferred directly to the cold stream
of the diffractometer. Single-crystal X-ray diffraction experi-
ments were performed on a Siemens R3/v automated diffac-
tometer equipped with an LT-2 low-temperature apparatus at
-95 °C and graphite-monochromated Mo KR radiation (λ )
0.710 73 Å). Additional details: scan method θ/2θ, scan rate
variable 2-5° min-1, background-to-scan ratio 0.5, 2θ scan
range 5-52° (h, -17 to +16; k, 0-22; l, 0-26), 12 674
reflections measured, merged to 10 236 unique reflections, Rint
) 0.0459, absorption correction via ψ scans. The structure was
solved by direct methods, and 537 parameters were refined
in a full matrix with the program SHELXTL PLUS.35 All non-
hydrogen atoms were refined anisotropically with hydrogen
atoms placed in idealized positions. Neutral atom scattering
factors and corrections for anomalous dispersion were taken
from published values.36 See Table 1 for additional details.
Str u ctu r e Deter m in a tion of 2. Yellow plates of 2 were
crystallized from THF/acetonitrile at 10 °C. A crystal of
dimensions 0.34 × 0.24 × 0.04 mm was cut from a larger
crystal and mounted on a standard Bruker SMART CCD based
Str u ctu r e Deter m in a tion of 3b. Yellow plates of 3b were
crystallized from a THF/acetonitrile solution at room temper-
ature. A crystal of dimensions 0.18 × 0.06 × 0.01 mm was
mounted as for 2. A total of 2408 frames were collected with
a scan width of 0.3° in ω and ψ with an exposure time of 30
(37) Saint Plus, v. 6.02; Bruker Analytical X-ray, Madison, WI, 1999.
(38) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen, Gottingen,
Germany, 1996.
(39) Sheldrick, G. M. SHELXTL, v. 5.10; Bruker Analytical X-ray,
Madison, WI, 1997.
(35) Sheldrick, G. M. SHELXTL-PLUS Structure Determination
Programs; Nicolet Instrument Corp., Madison, WI, 1988.
(36) Ibers, J . A.; Hamiltion, W. C. International Tables for Crystal-
lography; Kynoch Press: Birmingham, U.K., 1974; Vol. 4.

5376 Organometallics, Vol. 21, No. 24, 2002
Cygan et al.
s/frame. The frames were integrated with the Bruker SAINT37
software package with a narrow-frame algorithm. The integra-
tion of the data yielded a total of 42 030 reflections to a
maximum 2θ value of 49.8°. Due to the lack of high-angle data,
resolution was limited during refinement to 0.90 Α, which
yielded 13 562 unique data and 7461 data greater that 2σ(I).
The final cell constants (Table 1) were based on the xyz
centroids of 2347 reflections above 10σ(I). Analysis of the data
showed negligible decay during data collection; the data were
processed with SADABS38 and corrected for absorption. The
structure was solved and refined with the Bruker SHELXTL
software package,39 using the space group P1h with Z ) 2 for
the formula C76H120N4P4Si8Ge2Pd2‚0.5THF. All non-hydro-
gen atoms were refined anisotropically with the hydrogen
atoms located on a difference Fourier map and refined isotro-
pically or placed in idealized positions. Full-matrix least-
squares refinement based on F2 converged at R1 ) 0.0625 and
wR2 ) 0.1330 (based on I > 2σ(I)) and at R1 ) 0.1456 and
wR2 ) 0.1659 for all data. Additional details are presented in
Table 1.
It appears that, under these conditions, the germylene
ligand is labile enough to separate from the metal in
the solid state and is then volatile enough to be re-
moved in vacuo. The tetrakis(phosphine) complex is
subsequently re-formed from the remaining excess
phosphine present, either in the solid state or upon
dissolution in the NMR solvent. Addition of more
germylene to this material resulted in complete conver-
sion of the (Ph3P)4Pd present to complex to 1 and free
PPh3. Recrystallization of crude 1 from THF and aceto-
nitrile removed PPh3 and also resulted in the formation
of 10-20% (Ph3P)4Pd. This is likely due to the lability
of the germylene ligand (see discussion below), leading
to it being separated from 1 in solution as the less
soluble Pd species precipitate out. The remaining
“-(Ph3P)2Pd0” fragment can then be stabilized by some
of the remaining excess PPh3. Recrystallization in the
presence of excess germylene eliminated this problem,
generating analytically pure 1.
To generate complexes with phosphine ligands other
than PPh3, a synthetic procedure involving the reduc-
tion of a PdII species similar to the synthesis of the
analogous Pt complex was followed.42 Photolysis of
(R3P)2PdC2O4 generates a “(R3P)2Pd0” fragment as well
as 2 equiv of CO2.30 Attempts to perform the photolysis
of (Et3P)2PdC2O4 in the presence of germylene ligand
produced very low yields of 2 due to much of the
germylene being consumed by a side reaction with
CO2.43 Many other side products were generated by the
in situ photolysis, presumably the result of the highly
reactive “(Et3P)2Pd” fragment having no other ligands
to stabilize it. Pure 2 could not be isolated from this
mixture. The photolysis was then performed without
germylene, but in the presence of a large excess of PEt3
to trap the Pd0 species as it was being formed. The
reaction mixture was then degassed before addition of
a germylene solution (eq 2). The excess PEt3 could then
Resu lts a n d Discu ssion
Syn th esis of (R3P )2P d Ge[N(SiMe3)2]2. Several dif-
ferent approaches were used to synthesize and isolate
Pd germylene complexes. The first was simple ligand
substitution using a Pd0 species. The commercial avail-
ability of Pd0 is limited to (Ph3P)4Pd and Pd2(dba)3 (dba
) dibenzylidineacetone). The latter was found to be an
undesirable starting material, due to the tendency of
the germylene to preferentially react with the dba ligand
in solution. Germylenes are known to undergo 2 + 4
additions with unsaturated systems, including R,â-
unsaturated ketones.40,41 NMR and IR spectra of the
reaction of Ge[N(SiMe3)2]2 with Pd2(dba)3 are consistent
with the addition of the germylene to the carbonyl and
one of the double bonds of the dba ligand. However, the
reaction of the germylene ligand with (Ph3P)4Pd re-
sulted in the displacement of two PPh3 ligands to
generate complex 1 quantitatively by NMR (eq 1).
be removed in vacuo. This method cleanly generated
high yields of 2 after recrystallization.
Separation of the 2 equiv of free PPh3 from this
reaction mixture without also causing the decomposition
of 1 proved to be quite challenging. Attempts to use
CuCl to precipitate out copper phosphines did not
remove all of the PPh3 and caused decomposition upon
extended stirring with crude 1. An interesting result
was observed in our attempts to sublime away the PPh3
under vacuum. At temperatures above 55 °C, PPh3 was
deposited on the cold finger of the sublimator; however,
NMR spectroscopy of the material left in the bottom of
the apparatus revealed a mixture of 1 and newly formed
(PPh3)4Pd, with no free germylene present. The white
solid on the cold finger was found to contain only PPh3.
To the best of our knowledge, there is only one
example of a terminal germylene ligand bound to
palladium in the literature. In 1985, Lappert and co-
workers reported the formation of the homoleptic Pd
26
germylene Pd[Ge[N(SiMe3)2]2]3 from the reaction of
Pd(cod)Cl2 (cod ) 1,5 cyclooctadiene) with 5 equiv of
germylene. The complex was characterized as being red
with a melting point of 210-212 °C. Crude 2 is some-
times red, but recrystallization removes a red oil com-
prised of various unidentified germylene side products.
Pure 2 is then obtained as a bright orange microcrys-
(42) Litz, K. E.; Henderson, K.; Gourley, R. W.; Banaszak Holl, M.
M. Organometallics 1995, 14, 5008-5010.
(43) Sita, L. R.; Babcock, J . R.; Xi, R. J . Am. Chem. Soc. 1996, 118,
10912-10913.
(40) Neuman, W. P. Chem. Rev. 1991, 91, 311-334.
(41) Barrau, J .; Rima, G. Coord. Chem. Rev. 1998, 178-180, 593-
622.

A Novel Palladium Germylene System
Organometallics, Vol. 21, No. 24, 2002 5377
talline powder. Complexes 1 and the 3a /3b mixture
discussed below are also observed to be orange to brown.
The approaches toward the generation of Pd ger-
mylene species presented here have not yielded any
complexes containing multiple germylene ligands bound
to one metal. In the ligand substitution reaction utilized
to make 1, the only products of the reaction are 1 and
free PPh3, as observed in the 1H NMR and 31P NMR
spectra of this reaction. There is no evidence for further
displacement of PPh3 to generate a bis- or tris(ger-
mylene) complex. Furthermore, the 31P NMR spectra
do not show any broadening or shifting as might be
expected in the event of an equilibrium with (PPh3)4-
Pd. Likewise, complex 2 also appears to be stable in
solution for several days, without any further rear-
rangement. Addition of 10 equiv of germylene to a
solution of 2 did not result in any displacement of the
phosphine ligands on the Pd. This implies that a bis-
(phosphine) mono(germylene) configuration is electroni-
cally favored and/or that there may be a significant
steric barrier to the addition of more germylene ligands.
The reaction of 2 and CO was also attempted. One
atmosphere of the gas was added to a benzene-d6
solution of the palladium germylene; however, no reac-
tion was observed over a period of 24 h at 20 °C.
Syn th esis of {(d p p e)P d Ge[N(SiMe3)2]2}2 (3b). We
are interested in studying the effects of bidentate
phosphine ligands on these palladium germylene sys-
tems. The more constrained geometry about the Pd
center afforded by the bidentate ligand could bring
about a greater reactivity toward activations, and also
a greater propensity toward reductive elimination of
activated metallacycles. No such bidentate analogues
have been made in the Pt or Ni systems.
chemical shifts of the trimethylsilyl protons on the
germylene ligand. Two main products appeared in this
region. The first is a large singlet at 0.48 ppm, assigned
to the monomeric form of the product, 3a . A much
smaller peak corresponding to the dimeric form 3b grew
in more slowly at 0.56 ppm. After recrystallization, the
two species could be observed in the NMR spectra with
their relative concentrations varying as a function of the
concentration of the NMR sample. At a concentration
of 8.8 mM, the ratio of dimer to monomer was 2:3. The
relative percentage of 3b was observed to decrease as
the sample was diluted, though traces of the dimer could
be observed until the solution was so dilute that the
NMR signal was too weak to be a reliable measure of
the species in solution. Crystals grown from this mixture
were those of 3b.
The 31P NMR chemical shifts of the monomeric versus
the dimeric species are consistent with expected values.
3b appears as a singlet at 22.5 ppm, which is interme-
diate between complex 1 (δ 28.8 ppm) and 2 (δ 15.3
ppm). However, the monomeric species has a resonance
markedly downfield at 33.3 ppm, suggesting a very
different electronic environment about the P in 3a . Such
a downfield shift is expected for ethyl-bridged phos-
phines upon a change in binding mode from bridging
two metals to chelating one metal center.44
The formation of the dimeric species 3b clearly
relieves the steric strain that would arise from a small-
bite-angle bidentate ligand chelated to the metal. Port-
noy and Milstein have reported the P-Pd-P angle for
(dippe)2Pd (dippe ) 1,2-bis(diisopropylphosphino)et-
hane) to be 87.05(3)°.45 Hitchcock and co-workers re-
ported the P-Pd-P angle for the depe ligand of
Pd(depe)(dppe) to be 85.7(2)° (dppp ) bis(diphenylphos-
phino)propane).29 It is likely that the bite angle of dppe
in 3a would be very similar. The P-Pd-P angle of the
dimer 3b is 111.6(1)°. This is very close to that of 1,
giving a steric environment similar to that of the
monodentate phosphine complex. However, if this dimer-
ic species were substantially lower in energy than the
monomeric form, a monomer-dimer equilibrium should
not be observed. The presence of this equilibrium
suggests that neither species 3a nor 3b is significantly
more thermodynamically favored than the other. It is
also an indication of the lability of the phosphine ligands
in these complexes.
Attempts to perform photolysis of (dppe)PdC2O4 in the
presence of excess PEt3, analogous to the synthesis of
2, were unsuccessful. The resulting product mixtures
contained Pd species with different combinations of
phosphine ligands, including (dppe)2Pd, with no forma-
tion of the desired palladium germylene complex. For-
tunately, photolysis of (dppe)PdC2O4 in the presence of
slightly less than 1 equiv of germylene (eq 3) was
somewhat cleaner than for the synthesis of 2, and clean
products could be isolated from these reaction mixtures,
albeit in relatively low yields.
Attempts to synthesize bidentate phosphine pal-
ladium germylene species by displacing monodentate
phosphine ligands of 1 and 2 with a bidentate phosphine
were unsuccessful. Though the germylene ligand is
observed to displace PPh3 and PEt3, as noted above, to
give the three-coordinate bis(phosphine) complexes, the
germylene itself can be quickly displaced by a bidentate
phosphine ligand. Reaction of 1 with depe (depe ) 1,2-
bis(diethylphosphino)ethane) resulted in the formation
of the bis bidentate species (depe)2Pd and the liberation
of free germylene and free PPh3, as observed by 1H and
31P NMR spectroscopy. This germylene displacement is
also observed in the slow conversion of the 3a /3b
mixture to (dppe)2Pd. Stirring of this mixture for several
days in tetrahydrofuran gave rise to free germylene, as
(44) Garrou, P. E. Chem. Rev. 1981, 81, 229-266.
(45) Portnoy, M.; Milstein, D. Organometallics 1993, 12, 1655-
1664.
The progress of the photolysis of (dppe)PdC2O4 in the
presence of germylene was monitored by the NMR

5378 Organometallics, Vol. 21, No. 24, 2002
Cygan et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 1, 2, a n d 3b
1
2
3ba
Pd-Ge
2.3281(4)
2.3013(9)
1.867(2)
2.330(5)
2.3173(7)
1.893(2)
2.337(2)
2.307(4)
1.89(1)
Pd-P1
Ge-N1
P1-Pd-P2
N1-Ge-N2
Ge-Pd-P1
P1-Pd-Ge-N1
P1-Pd-Ge-N2
112.85(3)
106.09(11)
125.66(2)
-74.68(11)
103.43(11)
119.45(4)
105.59(12)
120.276(19)
99.60(8)
111.6(1)
106.2(4)
124.0(1)
71.3(4)
-80.40(8)
-108.3(4)
a
For 3b average values are provided from the two crystallo-
graphically independent molecules.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) of Oth er Gr ou p 10 Meta l Ger m ylen e
Com p lexes
F igu r e 1. ORTEP diagram of (Et3P)2PdGe[N(SiMe3)2]2 (2)-
(50% probability).
448
542
M-Ge
M-P
2.2064(6)
2.304(1)
2.157(1), 2.164(1)
1.867(2), 1.885(3)
113.81(4)
2.263(3), 2.261(3)
1.867(7), 1.874(7)
115.0(1)
Ge-N
P-M-P
N-Ge-N
105.05(11)
106.3(3)
1
judged by the H NMR spectrum, and a small amount
of a new species, (dppe)2Pd, at 31.24 ppm in the 31P
NMR spectrum. The basicities of these bidentate phos-
phines should be very similar to those of their mono-
dentate analogues; therefore, it is likely that the chelate
effect plays an important role in this displacement
phenomenon.
F igu r e 2. ORTEP diagram of {(dppe)PdGe[N(SiMe3)2]2}2
(3b) (50% probability). Only ipso carbons of the phenyl
rings are shown for clarity.
Cr yst a l St r u ct u r es. The crystal structures of the
complexes presented here appear to be the first crystal-
lographic documentation of a germylene bound to pal-
ladium. A search of the Cambridge Crystallographic
Database found only one complex containing a Pd-Ge
bond. Ito and co-workers have reported the structure
of a bis(organogermyl)palladium(II) complex containing
two palladium-germyl bonds, with Pd-Ge distances of
2.427(2) and 2.404(2) Å.46 The three structures pre-
sented here all have similar Pd-Ge bond lengths (see
Table 2 for selected bond lengths and angles). These
lengths are somewhat shorter than those reported for
the germyl ligands. With no other crystal structures for
comparison, it is unclear how much of this shortening
is due to some double-bond character of the metal-
ligand bond47 or due to the change in coordination
number of the Pd from 4 to 3. There is also the potential
for a competitive Fisher type interaction of the N atoms
bound to the Ge center. These Pd-Ge lengths are
somewhat longer than the Pt-Ge bond of (Et3P)2PtGe-
[N(SiMe3)2]2 (5) (2.3039(10) Å)42 and the Ni-Ge bond
of (Ph3P)NiGe[N(SiMe3)2]2 (4) (2.2064(6) Å) (Table 3).48
In addition to the Pd-Ge bond length, the P-Pd-P
angle is an important parameter to analyze. Crystal
structures of complexes 1, 2, and 3b show a trigonal
geometry about the Pd metal center (Figures 1 and 2).
However only 2 exhibits a near-perfect trigonal plane
with P-Pd-Ge and P-Pd-P angles of 120.276(19) and
119.45(4)°, respectively. In complexes 1 and 3b the
P-Pd-P angles are approximately 112°. This does not
follow the simple trend of cone angles (PPh3,145°; PEt3,
132°; dppe, 125°)49 of the three phosphine ligands and
is an indication of the influence of the substantial steric
bulk of the germylene ligand. The trimethylsilyl groups
of the germylene extend forward on both sides in the
plane of the Pd-Ge bond, where they approach the alkyl
groups attached to the phosphine ligand that are also
protruding forward. In both 1 and 3b, the two phenyl-
substituted phosphine ligands are squeezed closer to-
gether to accommodate the germylene, resulting in a
smaller P-Pd-P angle. In complex 2, the ethyl groups
also protrude forward but are themselves much smaller
than the phenyl rings of the other complexes, and thus
a more trigonal conformation can be attained.
A similar trend is observed in the dihedral angles of
these complexes. Complex 2 displays an almost orthogo-
nal arrangement of the P-Pd-P plane versus the
N-Ge-N plane with a dihedral angle of 80.40(8)°
(P1-Ge-Pd-N2). There is substantially less orthogo-
nality present for complexes 1 and 3b, with dihedral
angles of 74.68(11) and 71.3(4)°, respectively. This is
also due to steric constraints. A view of these structures
down the Pd-Ge bond reveals that, in 1 and 3b, the
phenyl rings of the phosphine are staggered with respect
to the alkyl groups of the germylene. A rotation of the
ligands toward greater orthogonality would lead to a
more eclipsed conformation and greater steric repul-
sions.
(46) Suginome, M.; Oike, H.; Shuff, P. H.; Ito, Y. J . Organomet.
Chem. 1996, 521, 405-408.
(47) Bender, J . E., IV; Shusterman, A. J .; Banaszak Holl, M. M.;
Kampf, J . W. Organometallics 1999, 18, 1547-1552.
(48) Litz, K. E.; Bender, J . E.; Kampf, J . W.; Banaszak Holl, M. M.
Angew. Chem., Int. Ed. 1997, 36, 496-498.
La bility of th e Ger m ylen e Liga n d . Free germylene
ligand can be trapped with benzil as shown in eq 4.21
(49) Tolman, C. A. Chem. Rev. 1977, 77, 313-348.

A Novel Palladium Germylene System
Organometallics, Vol. 21, No. 24, 2002 5379
Ta ble 4. 31P NMR Ch em ica l Sh ifts (p p m ) for
Rea ction s of 1-3 a n d 5 w ith O2
δ(starting
material)
δ(6)
[J P-P, Hz]
δ(oxidized
phosphine)
complex
δ(7)
1
28.8
15.3
16.4 (d),
41.5 (d) [33]
23.2 (d),
26.7 (d) [40]
45.3 (d),
50.9 (d) [34]
-5.0 (d),
16.5 (d) [11]
26.4 (s)
25.2 (s)
2
3
5
25.3 (s)
44.0 (s)
2.1 (s)
45.8 (s),
53.1 (s)
29.5 (s)
33.4 (3a ),
22.5 (3b)
38.2
The length of time necessary to completely trap the
ligand is used as an indicator of the lability of the
germylene ligand in a particular complex. The addition
of 4 equiv of benzil to a solution of (Ph3P)NiGe-
[N(SiMe3)2]2 (4) resulted in complete trapping of the
germylene ligand in less than a few minutes in ambient
light. When a frozen solution of 4 and benzil was thawed
in a darkened room and placed into an NMR spectrom-
eter, 40% conversion to trapped product could be
observed. When the NMR tube was exposed to ambient
light for 20 s, the reaction immediately proceeded to
completion.21 Reaction of (Et3P)PtGe[N(SiMe3)2]2 (5)
with benzil showed 91% conversion to the trapped form
after 94 h in ambient light and 50% conversion after
113 h for a solution that had been shielded from light.21
The lability of the germylene ligand bound to Pd
appears to follow the expected trend of being intermedi-
ate between its two group 10 neighbors. A solution of 2
with 4 equiv of benzil was allowed to react in ambient
light. After 30 min, ∼50% of the germylene had been
trapped, and after 4 h, ∼90% had been converted to
trapped product. Thus, in ambient light the germylene
ligand bound to 2 is 1 order of magnitude more labile
than on the analogous Pt system and 2 orders of
magnitude less labile than the similar Ni system.
Trapping reactions that were protected from light
resulted in ∼30% conversion to trapped product after
30 min and ∼75% conversion after 4 h. These results
suggest that the Pd germylene system will display
reactivity closer to that observed for the Pt germylene
complex and that the germylene ligand may not be too
labile for reactivity across the Pd-Ge bond. Thus, the
lability of the germylene ligand in the Pd system in the
dark is not substantially greater than in the presence
of ambient light, indicating that the thermal and
photochemical labilities are on the same order of
magnitude.
not obsd
generating species 7a .19 Both species 6a and 7a are
stable complexes that have been isolated and crystal-
lographically characterized. To probe the reactivity of
the palladium germylene system with oxygen, reactions
of complexes 1, 2, and the 3a /3b mixture with 1 equiv
of O2 were followed by NMR.
The Pd species formed orange solutions in benzene-
d6. Upon addition of oxygen, they slowly changed color
over a period of several hours to a dark brown and
eventually turned black. In all three reactions, the
starting materials are completely consumed and appear
to form both a peroxide species (6) and germanate
species (7). Both of these products could be observed in
the 31P NMR (see Table 4). Peaks corresponding to
oxidized phosphine ligands were also observed within
minutes of O2 addition for reactions with 2 and 3 and
within the first 1 h for reaction with 1. 31P NMR spectra
were generally clean, with only the two products 6 and
7 and the oxidized phosphine resonances. The reaction
with 2 produced trace amounts of other P-containing
complexes. The reaction with 1 was the only reaction
to generate another substantial P-containing species
with some, though not all, spectra, displaying a broad
1
resonance at approximately 22 ppm. H NMR spectra
contained downfield-shifted singlets in the trimethylsilyl
region, consistent with shifts observed in the Pt system.
1
The H NMR also contained other smaller peaks in this
region that were difficult to assign and grew as the
reactions progressed and the products decomposed.
1
However, none of the H NMR spectra contained peaks
at 0.47 ppm, the resonance for [Ge[N(SiMe3)2]2(µ-O)]2,
which is the product of the reaction of free germylene
with O2.50 This indicates that free germylene did not
react directly with oxygen.
Rea ction w ith O2. Complex 5 will react with O2 to
give a side-bridged peroxide species (6a ), as shown in
eq 5.19 Complex 6a will photochemically rearrange in
The reactivity of O2 with the Pt system was also
followed by NMR for comparison to the Pd reactions.
Complex 5 forms a bright yellow solution in benzene-
d6 that slowly becomes lighter in color after addition of
O2. The pale yellow color of the solution remains
unchanged for several weeks with no metallic precipita-
tion and no observed decomposition in solution. This
reaction produced products 6a and 7a cleanly without
any observed formation of oxidized phosphine species
even after many days in solution. The 31P NMR spec-
trum contained only the signals for the two products
with no other resonances observed.
Unlike the fairly stable Pt system, the Pd reactions
with O2 resulted in the steady decomposition of the Pd
species in solution as time progressed. This decomposi-
tion was characterized by the decrease in the amount
(50) Ellis, D.; Hitchcock, P. B.; Lappert, M. F. J . Chem. Soc., Dalton
Trans. 1992, 3397-3398.
ambient light to insert oxygen across the Pt-Ge bond,

5380 Organometallics, Vol. 21, No. 24, 2002
Cygan et al.
Sch em e 1
of material present in solution, as gauged by the
decrease in the signal-to-noise ratio of the 31P NMR
spectra over time. Visually, the solutions darkened over
the course of a few hours, and eventually precipitated
black solid coated the walls of the NMR tube with a
black metallic material, presumably metallic Pd. De-
composition of these species is related to the formation
of phosphine oxide, which serves to remove the phos-
phine ligands required to stabilize the Pd metal center.
In the 31P NMR spectrum the resonances corresponding
to oxidized phosphine grew and the signals from the
products decreased over a period of several days, and
in the case of 3, the oxidized phosphine eventually
became the only P species in solution. To test if these
oxidized phosphines were the result of a side reaction
of dissociated phosphine ligand with O2, a solution of 1
was stirred with 1 equiv of O2 and then the volatiles
were removed. NMR spectra showed that all of 1 had
been consumed, though no signal for oxidized phosphine
was yet present. This material was redissolved in
benzene, and stirring was continued. Unlike the chem-
istry observed for Pt, species 6b does not convert cleanly
under thermal or photolytic conditions to 7b. Instead,
slow decomposition to form OPPh3 and insoluble black,
Pd-containing precipitates occurred.
The reactions of 1 and 2 were also performed shielded
from light, to study the influence of photolytic reactions
on this system. No significant differences were observed
in the rates of reactivity or of decomposition of the
species in solution for the reactions kept in the dark.
Both species 6b and 7b and 6c and 7c were observed
in the solution, indicating that conversion from 6 to 7
occurs even in the absence of light. This result is
markedly different than what is observed for the Pt
system. Complex 6a can be isolated without the forma-
tion of 7a if the reaction with oxygen is performed in
the absence of light.19 The peroxide product converted
cleanly to 7a with prolonged stirring in the light or by
UV irradiation. In the Pd system, the thermal reaction
dominates and protection from light does not prevent
rearrangement of peroxide 6 to germanate 7.
the formation of products 6d and 7d (see Scheme 1).
The reaction with O2 appears to occur solely with 3a ,
on the basis of the rapid disappearance of the mono-
meric species as the reaction progresses. An initial
solution concentration of approximately 30 mM contain-
ing a 1:1 ratio of 3a and 3b was exposed to 1 equiv of
O2. After 10 min the solution contained no 3a , as
assessed by 1H and 31P NMR spectroscopy. Products 6d
and 7d had formed in a 1:1 ratio and together comprised
∼70% of the P-containing species in solution. Complex
3b could also be observed and accounted for ∼20% of
the P species in solution, whereas oxidized phosphine
was integrated to be ∼10% of the P present. After 30
min, a small amount of 3b (∼5% of the P species)
remained in solution. The products 6d and 7d together
were ∼75% of the species in solution, and the amount
of oxidized phosphine had grown to ∼20%. All of the
starting materials were consumed after 1.5 h. Thus, 3a
was consumed rapidly, and 3b persisted in solution,
presumably converting slowly to 3a . The monomer was
then consumed as it was being formed, to give the two
oxidized products.
Species 6d and 7d should have a more constrained
geometry about the Pd center and, thus, would be
expected to be more reactive than the analogous mono-
dentate phosphine complexes. Of the three Pd reactions,
the products 6d and 7d were the fastest to decompose,
with only oxidized phosphine observed in the NMR after
4 days. In contrast, for the reactions with 1 and 2, the
oxygen products were still approximately 20% and 57%,
respectively, of the P-containing species in solution after
4 days.
Con clu sion s
Three novel palladium germylene complexes contain-
ing monodentate and bidentate phosphine ligands have
been synthesized. The crystal structures of these com-
plexes show a trigonal geometry about the metal with
the germylene ligand tilted orthogonally to the plane
of the phosphines. The lability of the germylene on Pd
was found to be intermediate between similar Ni and
Pt systems, though more similar to Pt. Unlike the Pt
and Ni systems, the photochemical lability of the Pd
system does not dramatically affect the overall lability
of the ligand. Initial studies of the reactivity of the Pd
system with O2 suggest that these complexes react in a
The reactivity of the 3a /3b mixture with O2 is
particularly interesting. This reaction begins with both
monomeric and dimeric starting materials, but only two
products are observed in the 31P NMR spectrum: one
singlet and one pair of doublets. These are assigned to

A Novel Palladium Germylene System
Organometallics, Vol. 21, No. 24, 2002 5381
manner similar to that of the Pt system, only with
increased reactivity. However, unlike the Pt system,
shielding the reactions from light does not affect the
reactivity. The use of bidentate phosphine ligands
appears to increase reactivity, possibly enabling reac-
tions to be tuned. The increased reactivity and differing
photochemistry of the Pd system as well as the use of
bidentate ligands could be exploited in future reactions
to give products that could not be attained with the Pt
complexes. We are currently investigating other reactiv-
ity of this novel system.
Ack n ow led gm en t. This work was funded by the
Research Corporation. Z.T.C. thanks the National Sci-
ence Foundation for a graduate research fellowship.
M.M.B.H. is grateful for support as an Alfred P. Sloan
Research Fellow.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data for 1, 2, and 3b. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM0204134