From a Transient 3-Germa-1-phosphabutadiene to a 1,2-Bis(phosphaalkenyl)-1,2-digermacyclobutane

Article abstract of DOI:10.1021/om981027i

Dehydrofluorination of the fluoro(fluorenyl)(phosphaalkenyl)germane 7 by tert-butyllithium in the presence of chlorotrimethylsilane affords the 1,2-bis(phosphaalkenyl)-1,2-digermacyclobutane 2. This reaction probably involves the prior formation of the transient 3-germa-1-phosphabutadiene 1, followed by its head-to-head dimerization. 2 contains a distorted four-membered ring with long intracyclic Ge-Ge (2.5567(8) ?), Ge-C(R₂) (2.058(4) ?), and (R₂)C-C(R₂) (1.592(6) ?) bonds; mesityl groups are trans in relation to this heterocycle.

Full text of DOI:10.1021/om981027i

1622
Organometallics 1999, 18, 1622-1628
F r om a Tr a n sien t 3-Ger m a -1-p h osp h a bu ta d ien e to a
1,2-Bis(p h osp h a a lk en yl)-1,2-d iger m a cyclobu ta n e
Isabelle Pailhous,† Henri Ranaivonjatovo,† J ean Escudie´,*,†
J ean-Paul Declercq,‡ and Antoine Dubourg§
He´te´rochimie Fondamentale et Applique´e, UPRES A 5069, Universite´ Paul Sabatier,
118 route de Narbonne, 31062 Toulouse Cedex 04, France, Laboratoire de Chimie Physique et
de Cristallographie, Universite´ Catholique de Louvain, Place Pasteur 1,
B-1348 Louvain-La-Neuve, Belgium, and LAMMI, Re´seau des Rayons X, Universite´ de
Montpellier II, 34095 Montpellier Cedex 5, France
Received December 17, 1998
Dehydrofluorination of the fluoro(fluorenyl)(phosphaalkenyl)germane 7 by tert-butyllithium
in the presence of chlorotrimethylsilane affords the 1,2-bis(phosphaalkenyl)-1,2-digerma-
cyclobutane 2. This reaction probably involves the prior formation of the transient 3-germa-
1-phosphabutadiene 1, followed by its head-to-head dimerization. 2 contains a distorted four-
membered ring with long intracyclic Ge-Ge (2.5567(8) Å), Ge-C(R2) (2.058(4) Å), and (R2)C-
C(R2) (1.592(6) Å) bonds; mesityl groups are trans in relation to this heterocycle.
In tr od u ction
Resu lts a n d Discu ssion
Attem p ted Syn th esis of 1. We chose as the sub-
stituent on phosphorus the very bulky 2,4,6-tri-tert-
butylphenyl group (Ar), which has served well in the
stabilization of dicoordinate P species3 and included the
carbon 4 in the fluorenylidene group which also is
known to stabilize germenes R′R′′GedCR2.4 Due to the
usual high reactivity of the GedC double bond, the Pd
C moiety was created first since, when phosphorus is
substituted by the very bulky Ar group, the PdC double
bond is generally almost inert. For the coupling of the
PdC moiety with the GeCHR2 moiety we used the
carbenoid ArPdC(Cl)Li (4),5 which is much more stable
than its bromo analogue.6
Treatment of carbenoid 4, obtained by reaction of
dichlorophosphaalkene 3 with n-butyllithium, with di-
fluoro(mesityl)(fluorenyl)germane 57 afforded the fluoro-
(phosphaalkenyl)germane 7 in good yield. In contrast,
the chloro analogue 8 was obtained only in very low
yield (∼10%). However, the chloro(phosphaalkenyl)-
germane 8 could be prepared in satisfactory yield by a
two-step procedure involving the prior reaction of 4 with
trichloromesitylgermane (9) (leading to 10), followed by
the addition of fluorenyllithium (Scheme 1).
Double-bonded compounds of germanium are now
well-known:1 thus, heavy homologues of many impor-
tant organic functions such as alkenes, imines, ketones,
thioketones, etc. have been synthesized and stabilized,
generally owing to a large steric hindrance allowing
their isolation as monomers. In contrast, heavy homo-
logues of dienes or heterodienes with a doubly bonded
germanium of type A (XdC(R)C(R′)dGe<) or B (Xd
C(R)Ge(R′)dC<) are still unknown. Such derivatives
should be interesting to study in order to determine if
they behave as germenes or as germadienes and, thus,
if the GedC and CdX double bonds react as two isolated
systems or if there is a conjugation between these two
double bonds. In this matter, B should be particularly
interesting since theoretical calculations on the 2,3-
digermabutadiene H2CdGeHGeHdCH2 predicted that
the conjugation through germanium atoms was higher
than expected and about half of that observed in 1,3-
butadiene.2 Thus, conjugation between the two double
bonds should exist in derivatives B, and a “diene”
behavior could be expected.
In this paper, we present the attempted synthesis of
a compound of type B, in which X is a phosphorus atom,
the 3-germa-1-phosphabutadiene ArPdC(Cl)Ge(Mes)d
CR2 (1).
(3) For reviews on -PdC< derivatives, see: (a) Lochschmidt, S.;
Schmidpeter, A. Phosphorus Sulfur Relat. Elem. 1986, 29, 73. (b)
Markovskii, L. N.; Romanenko, V. D. Tetrahedron 1989, 45, 6019. (c)
Appel, R. In Multiple Bonds and Low Coordination in Phosphorus
Chemistry; Regitz, M., Scherer, O. J ., Eds.; Georg Thieme Verlag:
Stuttgart, Germany, 1990; p 157. (d) Appel, R.; Knoll, F. Adv. Inorg.
Chem. 1989, 33, 259.
(4) (a) Couret, C.; Escudie´, J .; Satge´, J .; Lazraq, M. J . Am. Chem.
Soc. 1987, 109, 4411. (b) Lazraq, M.; Escudie´, J .; Couret, C.; Satge´, J .;
Dra¨ger, M.; Dammel, R. Angew. Chem., Int. Ed. Engl. 1988, 27, 828.
(c) Anselme, G.; Escudie´, J .; Couret, C.; Satge´, J . J . Organomet. Chem.
1991, 403, 93. (d) Lazraq, M.; Couret, C.; Escudie´, J .; Satge´, J .;
Soufiaoui, M. Polyhedron 1991, 10, 1153.
† Universite´ Paul Sabatier.
‡ Universite´ Catholique de Louvain.
§ Universite´ de Montpellier II.
(1) For reviews on >GedX derivatives, see: (a) Barrau, J .; Escudie´,
J .; Satge´, J . Chem. Rev. 1990, 90, 283. (b) Tsumuraya, T.; Batcheller,
S. A.; Masamune, S. Angew. Chem., Int. Ed. Engl. 1991, 30, 902. (c)
Escudie´, J .; Couret, C.; Ranaivonjatovo, H.; Satge´, J . Coord. Chem.
Rev. 1994, 130, 427. (d) Chaubon, M. A.; Ranaivonjatovo, H.; Escudie´,
J .; Satge´, J . Main Group Met. Chem. 1996, 19, 145. (e) Kandri Rodi,
A.; Ranaivonjatovo, H.; Escudie´, J .; Kerbal, A. Main Group Met. Chem.
1996, 19, 199. (f) Baines, K. M.; Stibbs, W. G. Adv. Organomet. Chem.
1996, 39, 275. (g) Tokitoh, N.; Okazaki, R. Main Group Chem. News
1995, 3, 4.
(5) Yoshifuji, M.; Kawanami, H.; Kawai, Y.; Toyota, K.; Yasunami,
M.; Niitsu, T.; Inamoto, N. Chem. Lett. 1992, 1053.
(6) (a) Goede, S. J .; Bickelhaupt, F. Chem. Ber. 1991, 124, 2677. (b)
Van der Sluis, M.; Wit, J . B.; Bickelhaupt, F. Organometallics 1996,
15, 174.
(2) J ouany, C.; Mathieu, S.; Chaubon-Deredempt, M. A.; Trinquier,
G. J . Am. Chem. Soc. 1994, 116, 3973.
(7) Anselme, G.; Couret, C.; Escudie´, J .; Satge´, J . Synth. React. Inorg.
Met.-Org. Chem. 1991, 21, 229.
10.1021/om981027i CCC: $18.00 © 1999 American Chemical Society
Publication on Web 03/27/1999

Synthesis of a (Phosphaalkenyl)germacyclobutane
Organometallics, Vol. 18, No. 9, 1999 1623
Sch em e 1
Sch em e 2
Only one isomer of 7 or 8 was formed, probably the E
isomer. The formation of E isomers can be reasonably
explained by the preferential substitution of chlorine at
the less hindered side of the PdC double bond to form
the Z carbenoid.6 This configuration was confirmed by
the X-ray structure of the compound derived from the
reaction between 7 and tert-butyllithium (see X-ray
Structure of 2).
Attempts to dehydrochlorinate 8 with n-butyllithium
failed; only the alkylation of germanium was observed,
leading to 11. In contrast, with the bulkier and more
basic tert-butyllithium, the expected lithium compounds
12 and 13 were formed immediately at low temperature.
Quenching with dimethyl sulfate afforded respectively
14 and 15. The Li/Cl exchange on sp2-hybridized carbon
to lead to 16, precursor of the germaphosphaallene 17,
did not occur, the formation of 12 and 13 being much
more rapid (Scheme 2).8
chlorotrimethylsilane was added. In contrast, addition
of chlorotrimethylsilane to 13 yielded the stable and
isolable silylfluorenyl derivative 18. The formation of 2
from 12 can be rationalized in terms of fluorine/chlorine
exchange at germanium, with the formation of the
(chlorogermyl)lithium compound 13. Such a reaction,
with further elimination of chlorotrimethylsilane, has
already been reported by Klingebiel in the synthesis of
(t-Bu)2SidNAr (Ar ) 2,4,6-tri-tert-butylphenyl).9 How-
ever, as 13 is stable under the experimental conditions
when directly formed from 8 and tert-butyllithium, such
a route seems to be ruled out. The transient formation
of 19 with a rapid elimination of fluorotrimethylsilane
(route a) also is a possibility. A similar elimination of
Me3SiF from Cp*Ge(X)(F)CR2SiMe3 has previously been
reported10 but occurred only after heating at 140 °C (or
at 100 °C in the presence of Et3N), which is not the case
here. In our experiment, a large lengthening of the
CR2-Si and Ge-F bonds due to the high steric hin-
drance could explain the very easy elimination of Me3-
SiF. However, the steric congestion in 1 is not too great,
since it can dimerize. Thus, for all these reasons, an
electrophilic assistance of chlorotrimethylsilane with a
concerted or nearly concerted six-center mechanism
(route b) seems the most likely. Such a mechanism was
postulated by Wiberg and Wagner for the formation of
The lithium compounds 12 and 13 are quite stable,
since they were recovered unchanged after some hours
at room temperature and 13 (X ) Cl) even survived in
refluxing Et2O. Heating 12 (X ) F) at 35 °C for 1 h led
to its partial decomposition with the formation of
dimeric 2 but only in low yield (∼10%) mixed with
unidentified products (Scheme 3).
The complete and nearly quantitative delithiofluori-
nation of 12 leading to 2 occurred when 1 equiv of
11
silene Me2SidC(SiMe3)SiMe(t-Bu)2 (Scheme 3).
Ch a r a cter iza tion of 1,2-Bis(p h osp h a a lk en yl)-1,2-
d iger m a cyclobu ta n e 2. 2 was isolated in the form of
(8) The first allenic derivative of germanium, the germaphosphaal-
lene Mes2GedCdPAr, has been prepared by a similar reaction from
Mes2Ge(F)C(Br)dPAr and n-butyllithium, via Mes2Ge(F)C(Li)dPAr by
a Br/Li exchange on the sp2 carbon: Ramdane, H.; Ranaivonjatovo,
H.; Escudie´, J .; Mathieu, S.; Knouzi, N. Organometallics 1996, 15,
3070.
(9) Hesse, M.; Klingebiel, U. Angew. Chem., Int. Ed. Engl. 1986,
25, 649.
(10) Chaubon, M. A.; Escudie´, J .; Ranaivonjatovo, H.; Satge´, J . J .
Chem. Soc., Dalton Trans. 1996, 893.

1624 Organometallics, Vol. 18, No. 9, 1999
Pailhous et al.
F igu r e 1. PLATON view of 2. Ellipsoids are drawn at the 30% probability level.
Sch em e 3
air-stable yellow crystals after crystallization from
pentane. NMR spectra and the X-ray study proved that
2 was the head-to-head dimer of the expected 3-germa-
1-phosphabutadiene 1. A striking feature in the 1H
NMR spectrum was the large difference of chemical shift
(2.18 ppm) between the two o-methyl groups of the
mesityl, respectively at 0.87 and 3.05 ppm. Such a ∆δ
value proves the hindered rotation of the mesityl group
at 30 °C and the very different positions of these two
methyls in relation to the highly anisotropic fluore-
nylidene group. The X-ray structure of 2 confirms this
assessment, showing that one methyl is close to the
center of one aromatic group of the fluorenylidene, the
other one being rather far away. In the 13C NMR
spectrum, a doublet was observed at an unusually low
field for the carbon atom of the fluorenylidene group
which is bonded to the germanium atom (72.34 ppm,
3J CP ) 4.5 Hz). Such a doublet shows coupling with only
one phosphorus atom and proves the formation of the
head-to-head dimer 2 versus the head-to-tail dimer, in
which a triplet should be observed. Mass spectrometry
gives additional proof of the head-to-head structure,
since one of the main fragments (m/z 328) is the
difluorenylidene R2CdCR2.
X-r a y Str u ctu r e of 2. Figure 1 gives a PLATON view
and Figure 2 a stereoscopic view of 2; crystal data and
structure refinement details are given in Table 1, bond
lengths and bond angles in Table 2, and torsion angles
in Table 3.
As two independent molecules are present in the unit
cell, four ArPdC(Cl)Ge(Mes)CR2 moieties exist. Since
there are only slight differences in bond lengths, bond
angles, and torsion angles between them, we give
generally only average values for each of these data. The
molecule possesses an approximate C2 axis which
bisects both the (R2)C-C(R2) and Ge-Ge bonds of the
four-membered ring. The only lack of symmetry is
observed for the PdC-Cl moiety, since within the same
molecule, rather important differences are observed for
the P(1)-C(2)-Ge(3) and Cl-C(2)-Ge(3) bond angles;
e.g., they are respectively 125.8(2) and 118.1(2)° for
P(1A)-C(2A)-Ge(3A) and P(1B)-C(2B)-Ge(3B) and

Synthesis of a (Phosphaalkenyl)germacyclobutane
Organometallics, Vol. 18, No. 9, 1999 1625
F igu r e 2. Stereoscopic view of 2.
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
for 2
Ta ble 3. Tor sion An gles (d eg) for 2 (w ith Th eir
Esd ’s in P a r en th eses)a
empirical formula
fw
temp
wavelength
cryst syst, space group
unit cell dimensions
C82H96Cl2Ge2P2
1359.61
293(2) K
0.710 69 Å
triclinic, P1h
C(27)-P(1)-C(2)-Cl
0.5(4)
C(27)-P(1)-C(2)-Ge(3)
C(2)-Ge(3)-Ge(3)-C(2)
C(17)-Ge(3)-Ge(3)-C(17)
C(4)-Ge(3)-Ge(3)-C(4)
Ge(3)-Ge(3)-C(4)-C(4)
Ge(3)-C(4)-C(4)-Ge(3)
Ge(3)-Ge(3)-C(4)-C(4)
170.6(3)
139.7(11)
125.5(2)
14.11(16)
18.13(11)
22.5(2)
a ) 12.979(2) Å
b ) 16.464(3) Å
c ) 36.596(5) Å
R ) 87.92(1)°
â ) 89.19(1)°
γ ) 86.89(1)°
7803(2) Å3
18.2(2)
a
Average values are given; thus, the sign has been omitted.
The trapezoidal digermacyclobutane ring deviates
from planarity with folding angles of, respectively, 26.4
and 24.8° along the Ge(3)-C(4) axes in the two inde-
pendent molecules. The two mesityl groups as well as
the ArPdC(Cl) groups are trans in relation to the four-
membered ring. Long distances are observed for the
intracyclic Ge-Ge, Ge-C(R2), and (R2)C-C(R2) bonds:
2.5567(8) Å for Ge-Ge, at the upper limit of the range
which is 2.40-2.50 Å,12 2.058(4) Å for Ge-C(R2) (∼1.95-
1.99 Å for the classical Ge-C bond length),12 and 1.592
Å for the (R2)C-C(R2) bond length instead of 1.54 Å.
The increase in the bond lengths is due to the large
steric hindrance. A lesser lengthening of the Ge-C(2)
bond (2.002(4) Å) is also observed, whereas the Ge-
C(17) length (1.978(4) Å) lies almost in the normal
range. The arrangement around the PdC double bond
is nearly planar (C(27)P(1)C(2)Cl, -0.3(3)°; sum of
angles on C(2), 359.5°) with an E configuration. Normal
values are observed for C(27)-P(1), P(1)dC(2), and
C(2)-Cl bond lengths.
V
Z, calcd density
abs coeff
F(000)
cryst size
θ range for data collecn
limiting indices
4, 1.157 Mg/m3
0.920 mm-1
2864
0.32 × 0.28 × 0.25 mm
2.91-24.41°
0 e h e 15, -19 e k e 19,
-41 e l e 42
no. of rflns collected/
unique
completeness to θ )
24.41°
refinement method
no. of data/restraints/
params
60 716/23 772 (R(int) ) 0.045)
92.6%
full-matrix least squares on F2
23772/764/1585
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak and
hole
1.022
R1 ) 0.0496, wR2 ) 0.1317
R1 ) 0.0945, wR2 ) 0.1501
0.538 and -0.368 e Å-3
Ta ble 2. Bon d Len gth s (Å) a n d An gles (d eg) for 2
(w ith Th eir Esd ’s in P a r en th eses)
Bond Lengths
A 1,2-digermacyclobutane has been obtained by Apeloig
and co-workers13 by a head-to-head dimerization of
adamantylidenegermene (Me3Si)2GedAd (Ad ) 2-ada-
mantylidene).
P(1)-C(2)
P(1)-C(27)
C(2)-Cl
C(2)-Ge(3)
Ge(3)-C(17)
1.664(4)
1.851(4)
1.744(4)
2.002(4)
1.978(4)
Ge(3)-C(4)
Ge-Ge
C(4)-C(16)
C(4)-C(5)
(R2)C-C(R2)
2.058(4)
2.5567(8)
1.520(5)
1.528(5)
1.592(6)
This molecule has longer Ge-C and C-C bonds than
2 (respectively 2.097(7) and 1.63(1) Å) but a much
shorter Ge-Ge bond (2.422(2) Å). Other 1,2-digerma-
cyclobutanes14,15 and 1,4-digermabicyclo[2.2.0]hexanes15,16
(thus, including two 1,2-digermacyclobutane rings) have
been prepared from germylenes and alkenes. Such
heterocycles also display long intracyclic Ge-Ge, Ge-
C, and C-C bonds; however, these are not as long as
those bonds in 2.
Bond Angles
C(2)-P(1)-C(27)
105.4(2)
P(1)-C(2)-Cl
122.9(2)
P(1A)-C(2A)-Ge(3A) 125.8(2)
P(1C)-C(2C)-Ge(3C) 118.2(2)
Cl(A)-C(2A)-Ge(3A) 111.1(2)
Cl(C)-C(2C)-Ge(2C) 118.4(2)
P(1B)-C(2B)-Ge(3B) 118.1(2)
P(1D)-C(2D)-Ge(3D) 126.7(2)
Cl(B)-C(2B)-Ge(3B) 117.6(2)
Cl(D)-C(2D)-Ge(2D) 110.3(2)
C(17)-Ge(3)-C(2)
C(17)-Ge(3)-C(4)
C(2)-Ge(3)-C(4)
C(17)-Ge-Ge
C(2)-Ge-Ge
C(4)-Ge-Ge
99.36(16)
C(16)-C(4)-C(5)
101.6(3)
112.6(3)
112.7(3)
103.6(3)
124.4(3)
101.8(2)
114.79(16) C(16)-C(R2)-C(R2)
120.62(16) C(5)-C(R2)-C(R2)
125.17(12) C(16)-C(4)-Ge(3)
121.48(13) C(5)-C(4)-Ge(3)
The isolation of the head-to-head dimer 2 proves the
intermediate formation of the transient 3-germa-1-
75.33(11)
C(R2)-C(R2)-Ge(3)
111.2(2) and 117.6(2)° for Cl(A)-C(2A)-Ge(3A) and Cl-
(B)-C(2B)-Ge(3B). This also is observed in all the
torsion angles around the C(2)-Ge(3) bond; e.g., P(1A)-
C(2A)-Ge(3A)-C(17A) ) 111.5(3)° and P(1B)-C(2B)-
Ge(3B)-C(17B) ) -57.9(3)°. The second independent
molecule displays the same differences.
(11) Wiberg, N.; Wagner, G. Chem. Ber. 1986, 119, 1467.
(12) Baines, K. M.; Stibbs, W. G. Coord. Chem. Rev. 1995, 145, 157.
(13) Bravo-Zhivotovskii, D.; Zharov, I.; Kapon, M.; Apeloig, Y. J .
Chem. Soc., Chem. Commun. 1995, 1625.
(14) Ohgaki, H.; Kabe, Y.; Ando, W. Organometallics 1995, 14, 2139.
(15) Ohtaki, T.; Ando, W. Organometallics 1996, 15, 3103.
(16) Ohgaki, H.; Fukaya, N.; Ando, W. Organometallics 1997, 16,
4956.

1626 Organometallics, Vol. 18, No. 9, 1999
Pailhous et al.
Sch em e 4
Sch em e 6
Sch em e 5
disilacyclobutanes are formed from silenes by a process
believed to be initiated by silicon-silicon bond forma-
tion. Thus, in our case, we can postulate the preliminary
formation of a Ge-Ge bond involving the 1,4-diradical
species 22, whose radical centers are located on carbon.
This diradical then couples to give dimer 2 (Scheme 6).21
The dimerization is stereoselective, since only the dimer
is formed in which the same groups on germanium are
trans in relation to the four-membered ring. This could
be due to the large difference of steric hindrance
between Mes and ArPdC(Cl). However, other mecha-
nisms cannot be excluded.
phosphabutadiene 1. Even though this intermediate has
not been obtained, the lithium compounds 12 and 13
can be considered, to some extent, as synthetic equiva-
lents of 1, since addition of methanol affords quantita-
tively the methoxygermane 20 (Scheme 4).
Our efforts are now directed toward substitution on
phosphorus and germanium by bulkier groups in order
to stabilize such germaphosphabutadienes against dimer-
ization.
The facile dimerization of 3-germa-1-phosphabutadi-
ene 1 is surprising since the germene Mes2GedCR2 (21),
with the same group on carbon and two mesityl sub-
stituents on germanium instead of one mesityl and a
ArPdC(Cl) group, is very thermally stable and resistant
to dimerization.4a It is recovered unchanged after heat-
ing at 150 °C for a few hours (Scheme 5). The behavior
of 1 could be due to the lesser steric hindrance of ArPd
C(Cl) group (vs that of the mesityl group) as well as the
less polarized GedC double bond in this molecule.
In the absence of a trapping reagent, the most
common pathway of transient germenes is head-to-tail
dimerization, which is consistent with the polarization
Exp er im en ta l Section
Gen er a l Exp er im en ta l Con sid er a tion s. All experiments
were carried out in flame-dried glassware under an atmo-
sphere of nitrogen. Et2O and THF were distilled from sodium/
benzophenone prior to use. NMR spectra were recorded on the
following spectrometers: 1H, Bruker AC 80 (80.13 MHz) and
Bruker AC 200 (200.13 MHz); 13C, Bruker AC 200 (50.32 MHz)
and Bruker AC 250 (62.89 MHz) (reference TMS); 19F, Bruker
AC 80 (75.39 MHz) (reference CF3COOH); 31P, Bruker AC 200
(80.01 MHz) (reference 85% H3PO4). The NMR solvent was
always CDCl3. Melting points were determined on a Leitz 350
apparatus. Mass spectra were collected on a Hewlett-Packard
5989 A spectrometer by EI at 70 eV referenced to 74Ge.
Elemental analyses were performed by the “Service de Mi-
croanalyse de l’Ecole de Chimie de Toulouse”.
Geδ+dCδ- 1
. The head-to-head dimerization is a less
common mode of dimerization.1 The same behavior was
observed for some silenes >SidC<,17,18 but until now
only head-to-tail dimerization has been observed for
stannenes >SndC<.19
ArPdCCl2 was prepared according to the procedure of
Bickelhaupt from ArPCl2, CHCl3, and n-BuLi at low temper-
ature (-90 °C).6a
The mechanisms by which silenes dimerize have been
the subject of intense interest and controversy for
theoreticians.20 According to most of the papers, 1,2-
Syn th esis of Ar P dC(Cl)Ge(Mes)(F )CHR 2 (7). ArPd
C(Li)Cl (4) was prepared by adding n-BuLi (1.80 mL, 1.6 M
in hexane) to ArPdCCl2 (3; 1.00 g, 2.78 mmol) in THF (15 mL),
cooled to -78 °C. To this brown reaction mixture was added a
solution of MesGe(F)2CHR2 (5; 1.09 g, 2.78 mmol) in THF (15
mL) cooled to -78 °C. After 30 min of stirring at this
temperature, the brown reaction mixture was gradually
warmed to room temperature. After removal of THF in vacuo,
pentane (40 mL) was added and LiF was removed by filtration.
Recrystallization from pentane afforded 1.50 g (77%) of 7 as a
light yellow powder (mp 177 °C).
(17) For a review on >SidC<, see: (a) Brook, A. G.; Brook, M. A.
Adv. Organomet. Chem. 1996, 39, 71. (b) Raabe, G.; Michl, J . Chem.
Rev. 1985, 85, 419.
(18) Schmohl, K.; Blach, M.; Reinke, H.; Kempe, R.; Oehme, H. Eur.
J . Inorg. Chem. 1998, 1667.
(19) (a) Anselme, G.; Ranaivonjatovo, H.; Escudie´, J .; Couret, C.;
Satge´, J . Organometallics 1992, 11, 2748. (b) Anselme, G.; Declercq,
J .-P.; Dubourg, A.; Ranaivonjatovo, H.; Escudie´, J .; Couret, C. J .
Organomet. Chem. 1993, 458, 49.
(20) (a) Seidl, E. T.; Grev, R. S.; Schaefer, H. F., III. J . Am. Chem.
Soc. 1992, 114, 3643. (b) Bernardi, F.; Bottoni, A.; Olivucci, M.; Robb,
M. A.; Venturini, A. J . Am. Chem. Soc. 1993, 115, 3322. (c) Bernardi,
F.; Bottoni, A.; Olivucci, M.; Venturini, A.; Robb, M. J . Chem. Soc.,
Faraday Trans. 1994, 90, 1617. (d) Venturini, A.; Bernardi, F.; Olivucci,
M.; Robb, M. A.; Rossi, I. J . Am. Chem. Soc. 1998, 120, 1912.
(21) In the dimerization of silenes involving the preliminary forma-
tion of a Si-Si bond, various types of dimers (head-to-head, disilanaph-
thalene, or linear) are obtained, depending on the substituents on the
silene carbon.18

Synthesis of a (Phosphaalkenyl)germacyclobutane
Organometallics, Vol. 18, No. 9, 1999 1627
1H NMR: δ 1.32 (s, 9H, p-t-Bu), 1.39 (s, 18H, o-t-Bu), 2.05
(d, 5J HF ) 2.3 Hz, 6H, o-Me of Mes), 2.17 (s, 3H, p-Me of Mes),
4.88 (broad s, 1H, CHR2), 6.66 (s, 2H, arom H of Mes), 7.18-
Syn th esis of Ar P dC(Cl)Ge(Mes)(Bu )CHR2 (11). To a
solution of 8 (1.00 g, 1.40 mmol) in Et2O/toluene (10 mL/10
mL) cooled to -78 °C was added n-BuLi (0.96 mL, 1.6 M in
hexane, 1.54 mmol). The brown reaction mixture was stirred
for 20 min at -78 °C and then warmed to room temperature.
After removal of solvents and addition of pentane (30 mL),
the lithium salts were removed by filtration. 11 could not be
obtained in pure form by crystallization from various solvents
but was identified by its spectroscopic data.
4
7.85 (m, 8H, CR2), 7.39 (d, J HP ) 1.5 Hz, 2H, arom H of Ar).
4
13C NMR: δ 21.2 (p-Me of Mes), 23.6 (d, J CF ) 5.1 Hz, o-Me
4
of Mes), 31.4 (p-CMe3), 32.9 (d, J CP ) 6.6 Hz, o-CMe3), 35.1
2
(p-CMe3), 37.8 and 37.9 (o-CMe3), 44.7 (dd, J CF ) 11.9 Hz,
3J CP ) 5.1 Hz, CHR2), 120.1 and 120.2 (C4C5), 122.1 and 122.2
(m-C of Ar), 124.8, 125.7 and 126.6 (C1C2C3C6C7C8), 128.3
1
1H NMR: δ 0.35-1.05 (m, 9H, GeBu), 1.38, 1.43 and 1.50
(3 × 9H, o- and p-t-Bu), 2.32, 2.39 and 2.50 (3 × 3H, o- and
p-Me of Mes), 5.00 (s, 1H, CHR2), 6.66 (s, 2H, arom H of Mes),
7.10-7.95 (m, 8H, CR2), 7.44 (d, 4J HP ) 1.4 Hz, 2H, arom H of
(ipso-C of Mes), 129.0 (m-C of Mes), 134.0 (d, J CP ) 64.9 Hz,
ipso-C of Ar), 140.3, 140.9, 141.4, 142.3, 142.4 and 142.5 (p-C
of Mes, C10C11C12C13), 143.7 (o-C of Mes), 151.0 (p-C of Ar),
1
2
153.5 (o-C of Ar), 165.6 (dd, J CP ) 87.7 Hz, J CF ) 9.0 Hz,
PdC). 19F NMR: δ -100.1 (d, J FP ) 26.8 Hz).31P NMR: δ
3
3
Ar). 13C NMR: δ 13.4 (Me of Bu), 19.6 (d, J CP ) 7.4 Hz, CH2-
305.1 (d, 3J PF ) 26.8 Hz). MS (m/z): 700 (M, 10), 665 (M - Cl,
7), 535 (M - CHR2, 40), 499 (M - CHR2 - Cl - 1, 20), 287
(ArPdC - 1, 45), 165 (CHR2, 82), 57 (t-Bu, 100). Anal. Calcd
for C41H49ClFGeP: C, 70.36; H, 7.06. Found: C, 70.41; H, 7.22.
Syn th esis of Ar P dC(Cl)Ge(Cl2)Mes (10). To a solution
of ArPdCCl2 (3; 1.20 g, 3.35 mmol) in THF (15 mL) cooled to
-78 °C was added n-BuLi (2.30 mL, 1.6 M in hexane, 3.68
mmol). After 45 min of stirring at this temperature, a solution
of ArPdC(Li)Cl (4) was slowly added to a solution of MesGeCl3
(1.00 g, 3.35 mmol) in THF (15 mL) cooled to -78 °C. The
reaction mixture turned black-brown. It was stirred for 30 min
at this temperature and then gradually warmed to 20 °C. After
removal of solvents in vacuo, pentane (30 mL) was added and
LiCl was filtered off. Elimination of pentane in vacuo afforded
1.56 g (80%) of 10 (mp 165 °C) as a light brown oil which slowly
solidified.
Ge), 21.1 (p-Me of Mes), 25.1 (o-Me of Mes), 26.5 and 26.9
4
(CH2CH2CH3), 31.5 (p-CMe3), 32.8 (d, J CP ) 6.5 Hz, o-CMe3),
4
33.0 (d, J CP ) 6.7 Hz, o-CMe3), 35.1 (p-CMe3), 37.9 and 38.0
(o-CMe3), 42.9 (d, 3J CP ) 5.2 Hz, CHR2), 119.8 and 120.1 (C4C5),
122.0 and 122.1 (m-C of Ar), 124.5-126.8 (C1C2C3C6C7C8),
1
129.5 (m-C of Mes), 135.6 (d, J CP ) 67.1 Hz, ipso-C of Ar),
138.7-145.6 (o- and p-C of Mes, C10C11C12C13), 150.5 (p-C of
1
Ar), 153.5 (o-C of Ar), 173.7 (d, J CP ) 91.4 Hz, PdC). 31P
NMR: δ 286.4. MS (m/z): 682 (M - Bu + 1, 3), 573 (M -
CHR2, 84), 517 (M - CHR2 - t-Bu +1, 37), 461 (M - CHR2 -
2t-Bu + 2, 23), 287 (ArPdC - 1, 21), 165 (CHR2, 100), 57 (t-
Bu, 27).
Syn th esis of Ar P dC(Cl)Ge(Mes)(F )C(Me)R2 (14). To a
solution of 7 (0.68 g, 0.97 mmol) in Et2O (15 mL) cooled to
-60 °C was added via syringe t-BuLi (0.60 mL, 1.7 M in
pentane, 1.02 mmol). The dark red reaction mixture was
stirred for 15 min at this temperature and then warmed to
-50 °C. One equivalent of Me2SO4 (124 mg) was added. The
resulting solution was dark brown. After removal of solvents
and addition of pentane (30 mL), the lithium salts were
removed by filtration; recrystallization from pentane afforded
0.60 g (87%) of a yellow-orange powder of 14 (mp 166 °C).
1H NMR: δ 1.38 (s, 9H, p-t-Bu), 1.43 and 1.47 (2s, 2 × 9H,
o-t-Bu), 1.97 (broad s, 6H, o-Me of Mes), 2.16 and 2.20 (2s, 2
× 3H, p-Me of Mes and CMeR2), 6.66 (s, 2H, arom H of Mes),
7.10-8.20 (m, 8H, CR2), 7.43 (d, 4J HP ) 2.0 Hz, arom H of Ar).
13C NMR: δ 20.6 (d, 3J CF ) 4.2 Hz, MeCR2), 21.2 (p-Me of Mes),
1H NMR: δ 1.38 (s, 9H, p-t-Bu), 1.52 (s, 18H, o-t-Bu), 2.33
(s, 3H, p-Me of Mes), 2.68 (s, 6H, o-Me of Mes), 6.95 (s, 2H,
arom H of Mes), 7.48 (d, 4J HP ) 1.6 Hz, 2H, arom H of Ar). 13
C
NMR: δ 22.5 (p-Me of Mes), 25.9 (o-Me of Mes), 31.7 (p-CMe3),
4
33.0 (d, J CP ) 6.8 Hz, o-CMe3), 35.2 (p-CMe3), 38.0 (o-CMe3),
1
122.5 (m-C of Ar), 130.2 (m-C of Mes), 132.7 (d, J CP ) 63.3
Hz, ipso-C of Ar), 142.0 (p-C of Mes), 143.5 (o-C of Mes), 151.5
2
1
(p-C of Ar), 153.8 (d, J CP ) 3.0 Hz, o-C of Ar), 164.5 (d, J CP
) 91.2 Hz, PdC). 31P NMR: δ 301.9. MS (m/z): 586 (M, 16),
571 (M - Me, 92), 537 (M - Me - Cl + 1, 17), 529 (M - t-Bu,
14), 323 (ArPdCCl, 16), 275 (ArP - 1, 38), 119 (Mes, 21), 57
(t-Bu, 100). Anal. Calcd for C28H40Cl3GeP: C, 57.34; H, 6.87.
Found: C, 57.50; H, 6.95.
4
23.8 (d, J CF ) 5.6 Hz, o-Me of Mes), 31.5 (p-CMe3), 33.0 (d,
4J CP ) 6.7 Hz, o-CMe3), 35.2 (p-CMe3), 37.9 and 38.0 (o-CMe3),
2
52.4 (d, J CF ) 10.8 Hz, CR2), 120.0 and 120.3 (C4C5), 122.0
Syn th esis of Ar P dC(Cl)Ge(Mes)(Cl)CHR2 (8). To a
solution of 10 (1.95 g, 3.33 mmol) in Et2O (15 mL) cooled to 0
°C was added 1 equiv of R2CHLi (prepared from fluorene (0.55
g, 3.31 mmol) and n-BuLi (2.20 mL, 1.6 M in hexane, 3.52
mmol)). After the end of the addition, the brown reaction
mixture was warmed to room temperature and stirred for 30
min. The solvents were removed in vacuo, 30 mL of pentane
was added, and LiCl was removed by filtration. Crystallization
from pentane afforded 2.02 g (85%) of 8 as a yellow powder
(mp 188 °C).
and 122.3 (m-C of Ar), 124.5-127.2 (C1C2C3C6C7C8), 127.8
1
(ipso-C of Mes), 129.1 (m-C of Mes), 134.5 (d, J CP ) 65.6 Hz,
ipso-C of Ar), 139.8, 139.9, 148.2 and 148.5 (o-C and p-C of
2
Mes, C10C11C12C13), 150.9 (p-C of Ar), 153.2 (d, J CP ) 2.2 Hz,
1
2
o-C of Ar), 153.8 (o-C of Ar), 166.0 (dd, J CP ) 88.7 Hz, J CF
)
9.0 Hz, PdC). 19F NMR: δ -102.9 (d, J FP ) 27.5 Hz). 31P
NMR: δ 303.1 (d, 3J PF ) 27.5 Hz). MS (m/z): 714 (M, 20), 695
(M - F, 7), 535 (M - CMeR2, 93), 479 (M - CMeR2 - t-Bu +
1, 41), 423 (M - CMeR2 - 2t-Bu + 2, 59), 287 (ArPdC - 1,
3
1H NMR: δ 1.30 (s, 27H, t-Bu), 2.24 (s, 3H, p-Me of Mes),
2.30 (s, 6H, o-Me of Mes), 4.90 (broad s, 1H, CHR2), 6.77 (broad
77), 179 (CMeR2, 92), 57 (t-Bu, 100). Anal. Calcd for C42H51
-
ClFGeP: C, 70.66; H, 7.20. Found: C, 70.85; H, 7.35.
4
Syn t h esis of Ar P dC(Cl)Ge(Mes)(Cl)C(Me)R 2 (15). 15
was obtained by the same process as 14 using (1.23 g, 1.71
mmol) of 8, t-BuLi (1.11 mL, 1.7 M in pentane, 1.89 mmol),
and 215 mg of Me2SO4 in THF/Et2O (10 mL/10 mL). A 0.88 g
(70%) amount of an orange powder of 15 was obtained by
crystallization from pentane (mp 150 °C).
s, 2H, arom H of Mes), 7.10-7.90 (m, 8H, CR2), 7.33 (d, J HP
) 1.6 Hz, 2H, arom H of Ar). 13C NMR: δ 21.1 (p-Me of Mes),
4
24.8 (o-Me of Mes), 31.4 (p-CMe3), 33.0 (d, J CP ) 7.0 Hz,
3
o-CMe3), 35.0 (p-CMe3), 37.8 (o-CMe3), 46.3 (d, J CP ) 5.1 Hz,
CHR2), 120.0 and 120.1 (C4C5), 122.0 and 122.2 (m-C of Ar),
124.8-126.8 (C1C2C3C6C7C8), 128.5 (ipso-C of Mes), 129.8 (m-C
1
of Mes), 133.9 (d, J CP ) 57.0 Hz, ipso-C of Ar), 140.3, 141.6,
1H NMR: δ 1.39 (s, 9H, p-t-Bu), 1.44 and 1.52 (2s, 2 × 9H,
o-t-Bu), 2.08 (broad s, 6H, o-Me of Mes), 2.24 and 2.26 (p-Me
of Mes and CMeR2), 6.70 (s, 2H, arom H of Mes), 7.20-8.30
(m, 10H, arom H of Ar and CR2). 13C NMR: δ 21.1 and 21.2
(p-Me of Mes and CMeR2), 24.9 (o-Me of Mes), 31.4 (p-CMe3),
33.2 (d, 4J CP ) 6.8 Hz, o-CMe3), 33.4 (d, 4J CP ) 6.6 Hz, o-CMe3),
35.1 (p-CMe3), 37.9 and 38.2 (o-CMe3), 53.3 (CR2), 120.0 and
120.4 (C4C5), 121.8 and 122.5 (m-C of Ar), 124.6-127.3
141.9, 142.4, and 142.8 (p-C of Mes, C10C11C12C13), 143.8 (o-C
of Mes), 150.8 (p-C of Ar), 153.3 and 153.8 (o-C of Ar), 164.8
1
(d, J CP ) 91.7 Hz, PdC). 31P NMR: δ 299.7. MS (m/z): 716
(M, 3), 681 (M - Cl, 12), 551 (M - CHR2, 78), 515 (M - CHR2
- Cl - 1, 35), 495 (M - CHR2 - t-Bu + 1, 26), 459 (M - CHR2
- t-Bu - Cl, 65), 423 (M - CHR2 - 2Cl - t-Bu -1, 36), 287
(ArPdC - 1, 56), 165 (CHR2, 75), 119 (Mes, 16), 57 (t-Bu, 100).
Anal. Calcd for C41H49Cl2GeP: C, 68.75; H, 6.89. Found: C,
68.78; H, 6.92.
1
(C1C2C3C6C7C8), 129.5 (m-C of Mes), 134.2 (d, J CP ) 68.1 Hz,
ipso-C of Ar), 139.8-148.4 (o- and p-C of Mes, C10C11C12C13),

1628 Organometallics, Vol. 18, No. 9, 1999
Pailhous et al.
2
150.6 (p-C of Ar), 153.2 (d, J CP ) 2.5 Hz, o-C of Ar), 154.4
were removed in vacuo and replaced by pentane (30 mL). After
removal of lithium salts, 2 was recrystallized from pentane to
afford 1.46 g (75%) of yellow crystals (mp 270 °C).
(o-C of Ar), 165.8 (d, 1J CP ) 92.4 Hz, PdC). 31P NMR: δ 294.7.
MS (m/z): 551 (M - CMeR2, 7), 515 (M - CMeR2 - Cl - 1, 5),
459 (M - CMeR2 - Cl - t-Bu + 1, 6), 287 (ArPdC - 1, 39),
179 (CMeR2, 26), 57 (t-Bu, 100). Anal. Calcd for C42H51Cl2-
GeP: C, 69.07; H, 7.04. Found: C, 69.21; H, 7.26.
Syn th esis of Ar P dC(Cl)Ge(Mes)(OMe)CHR2 (20). To a
solution of 7 (1.08 g, 1.54 mmol) in THF (15 mL) cooled to -100
°C was added n-BuLi (1.00 mL, 1.6 M in hexane, 1.54 mmol).
To the black-brown resulting solution was added at -100 °C
after 20 min of stirring a slight excess of methanol. The
reaction mixture became immediately light orange. After the
usual workup, 20 was recrystallized from pentane as white
crystals (mp 189 °C).
1H NMR (200 MHz): δ 0.87 (s, 6H, o-Me of Mes), 1.26 (s,
18H, p-t-Bu), 1.28 (s, 36H, o-t-Bu), 2.15 (s, 6H, p-Me of Mes),
3.05 (s, 6H, o-Me of Mes), 6.25 and 6.77 (2s, 2 × 2H, arom H
3
of Mes), 6.54, 6.92, 6.92, and 7.21 (4t, J HH ) 7.1 Hz, 4 × 2H,
3
H on C2C3C6C7), 6.75, 7.25, 7.43, and 8.16 (4d, J HH ) 7.1 Hz,
4 × 2H, H on C1C4C5C8). 13C NMR: δ 21.0 (p-Me of Mes), 24.0
4
and 28.0 (o-Me of Mes), 31.4 (p-CMe3), 32.8 and 33.0 (2d, J CP
) 7.2 Hz, o-CMe3), 35.0 (p-CMe3), 37.7 and 37.8 (o-CMe3), 72.3
3
(d, J CP ) 4.5 Hz, CR2), 117.8 and 118.6 (C4C5), 121.9 (m-C of
1
Ar), 124.5-128.7 (C1C2C3C6C7C8, m-C of Mes), 135.8 (d, J CP
) 71.0 Hz, ipso-C of Ar), 137.4-150.4 (o- and p-C of Mes, p-C
of Ar, C10C11C12C13), 153.4 and 153.5 (o-C of Ar), 173.1 (d, 1J CP
) 96.4 Hz, PdC). 31P NMR: δ 304.8. MS (m/z): 328 (R2Cd
1H NMR: δ 1.31 (s, 9H, p-t-Bu), 1.33 (s, 18H, o-t-Bu), 2.24
(s, 3H, p-Me of Mes), 2.31 (s, 6H, o-Me of Mes), 3.44 (s, 3H,
OMe), 4.76 (broad s, 1H, CHR2), 6.77 (s, 2H, arom H of Mes),
7.11-7.92 (m, 8H, CR2), 7.35 (d, 4J HP ) 1.5 Hz, 2H, arom H of
Ar). 13C NMR: δ 21.2 (p-Me of Mes), 23.9 (o-Me of Mes), 31.5
CR2, 45), 165 (CHR2, 18), 57 (t-Bu, 100). Anal. Calcd for C82H96
-
Cl2Ge2P2: C, 72.44; H, 7.12. Found: C, 72.51; H, 7.26.
Cr ysta l Str u ctu r e Deter m in a tion . The data were col-
lected on a MAR345 image plate with graphite-monochro-
mated Mo KR radiation. The structure was solved by direct
methods and refined using the program SHELX-97.22 Hydro-
gen atoms were placed in calculated positions, and all other
atoms were refined with anisotropic thermal parameters. Since
each of the two independent molecules in the asymmetric unit
is a dimer, there are four chemically equivalent “monomers”
in the asymmetric unit. Restraints with a standard deviation
of 0.02 Å were applied to equivalent bond distances (1-2
distances) and angles (1-3 distances) between the four
“monomers”. The largest residual densities are close to the
germanium atoms.
4
4
(p-CMe3), 33.0 (d, J CP ) 6.3 Hz, o-CMe3), 33.1 (d, J CP ) 6.6
Hz, o-CMe3), 35.1 (p-CMe3), 37.8 and 37.9 (o-CMe3), 43.6 (d,
3J CP ) 3.5 Hz, CHR2), 54.0 (OMe), 120.0 and 120.1 (C4C5), 122.0
and 122.2 (m-C of Ar), 125.2-126.6 (C1C2C3C6C7C8), 129.4
1
(m-C of Mes), 134.7 (d, J CP ) 67.6 Hz, ipso-C of Ar), 139.7-
144.4 (o-C and p-C of Mes, C10C11C12C13), 150.6 (p-C of Ar),
153.4 (d, 2J CP ) 2.3 Hz, o-C of Ar), 153.6 (d, 2J CP ) 2.1 Hz, o-C
of Ar), 166.7 (d, J CP ) 91.3 Hz, PdC). 31P NMR: δ 299.2. MS
1
(m/z): 677 (M - Cl, 3), 589 (M - Cl - OMe - t-Bu, 2), 547 (M
- CHR2, 37), 515 (M - CHR2 - OMe - 1, 35), 459 (M - CHR2
- t-Bu - OMe, 17), 287 (ArPdC - 1, 41), 165 (CHR2, 100), 57
(t-Bu, 85). Anal. Calcd for C42H52ClGeOP: C, 70.86; H, 7.36.
Found: C, 70.92; H, 7.45.
Syn th esis of Dim er 2. To a solution of 7 (1.10 g, 1.57
mmol) in Et2O (15 mL) cooled to -60 °C was added t-BuLi (1
mL, 1.7 M in pentane, 1.70 mmol). When the resulting red-
brown mixture was warmed to room temperature, no change
was observed. A 31P NMR spectrum displayed the signal of 12
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
coordinates, anisotropic displacement parameters, bond dis-
tances and angles, and torsion angles and stereoviews of 2.
This material is available free of charge via the Internet at
http://pubs.acs.org.
3
(δ 295.71 ppm, d, J PF ) 18.8 Hz). 12 was recovered almost
unchanged after 1 h in refluxing Et2O, since only ∼10% of 2
was formed. The solution of 12 was cooled again to -50 °C,
and 1 equiv of Me3SiCl (0.17 g) was added. The reaction
mixture was then warmed to room temperature; the solvents
OM981027I
(22) Sheldrick, G. M.; Schneider, T. R.; SHELXL: High-Resolution
Refinement. Methods Enzymol. 1997, 277, 319.