1,3-Digermacyclobutanes with exocyclic C=P and C=P=S double bonds

Article abstract of DOI:10.1039/b708308d

New 1,3-digermacyclobutanes, with two exocyclic C=PMes* bonds, and the corresponding first bis(methylenethioxo)phosphoranes with C=P(S)Mes* moieties have been synthesized. The Royal Society of Chemistry.

Full text of DOI:10.1039/b708308d

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1,3-Digermacyclobutanes with exocyclic CLP and CLPLS double
bonds{
Petronela Maria Petrar,ab Gabriela Nemes,a Ioan Silaghi-Dumitrescu,*a Henri Ranaivonjatovo,b
Heinz Gornitzkab and Jean Escudie´*b
Received (in Cambridge, UK) 1st June 2007, Accepted 6th July 2007
First published as an Advance Article on the web 3rd August 2007
DOI: 10.1039/b708308d
(Mes* = 2,4,6-tri-tert-butylphenyl) (2) and tBu2GeF2, affords the
New 1,3-digermacyclobutanes, with two exocyclic CLPMes*
2,4-diphosphinylidene-1,3-digermacyclobutane (3) in a near quan-
bonds, and the corresponding first bis(methylenethioxo)pho-
titative yield§ (Scheme 1).
sphoranes with CLP(S)Mes* moieties have been synthesized.
The cis and trans isomers, 3a and 3b are formed in a 3 : 1 ratio
…
1,3-Dimetallacyclobutanes featuring two exocyclic main group
element–carbon double bonds, I (Chart 1) are poorly documented
in the literature. This finding is illustrated by the relatively limited
number of such silicon heterocycles (I, M = Si, X = CR2,1a–c
CLCR2,1d NR,1e,f PR1g and PR31h) and turns out to be particularly
true for the germanium analogues, since only one example has
been reported so far (I, M = Ge, X = PR). Moreover, this sole
2,4-diphosphinylidene-1,3-digermacyclobutane was obtained in a
very low yield.2
(relative to the PLC CLP axis). An equilibrium between the two
geometrical isomers is established at room temperature in less than
1 h after dissolving crystals of either 3a or 3b. This kind of
geometrical isomerism has previously been described for similar
compounds.1g,2 DFT B3LYP/6-31G(d) calculations on several
model systems for 3 (see Table S2-1 in the ESI{) show the trans
isomer to be slightly lower in energy; unlike the trans isomer, the
cis isomer has a non-zero dipole moment and thus better solvation
in polar solvents (THF, CDCl3), explaining the reverse trend in
solution.
We have been successful in the synthesis of a new representative
(I, M = Ge, X = PMes*, R = R9 = tBu) and present the first
molecular X-ray structure of such a germanium heterocycle. This
molecule prompted us to investigate the accessibility of related
2,4-bis(thioxophosphoranylidene)-1,3-digermacyclobutane (I, M =
Ge, X = P(S)R). Since the report of the first stable thioxomethy-
lenephosphorane, a structure containing the P(LS)LC skeleton,3 no
counterpart featuring more than a single P(LS)LC unit has been
described. Here, we also detail the synthesis and the X-ray
structure of the first bis(thioxomethylenephosphorane) linked by
two germanium atoms. Such heterocycles could be interesting
building blocks in heterochemistry owing to the reactivity of their
PLC double bonds; these double bonds, next to the lone pairs of
phosphorus, oxygen or sulfur atoms, represent interesting
coordination sites for transition metals.
Both isomers 3a and 3b have been characterized by X-ray
diffraction." As they present approximately the same geometrical
data, only the structure of the trans isomer 3b is discussed (see
Fig. 1 for the molecular structure of 3b and the ESI for that of
3a{). The endocyclic Ge–C bond lengths lie slightly beyond the
upper limit of the standard range (1.93–1.97 s4) due to the high
steric hindrance, but are almost comparable to those reported for
1,3-digermacyclobutanes (2.009–2.010 s5a and 1.97–1.98 s5b). The
shape of the four-membered ring is rather different from that of
1,3-digermacyclobutanes without exocyclic double bonds since the
5
…
Ge Ge distance is longer (2.918 s vs. 2.77–2.80 s ) while the
5a
…
C
C distance is shorter (2.755 s vs. 2.904 s ) as a consequence
of the sp2 hybridization of the cyclic carbon atoms. The four-
membered ring is planar, in contrast to its silicon analogue with
The reaction of tBuLi with phosphagermapropene 1,{
prepared from C,C-dichlorophosphaalkene Mes*PLCCl2
two CLPMes* exocyclic bonds which is slightly folded by about 5u
along the C C or Si Si axes.
1g
…
…
When the germanium atom was substituted by bulky Tip (2,4,6-
triisopropylphenyl) and tBu groups, the analogous reaction led to
the stable phosphagermaallene Mes*PLCLGe(Tip)tBu.6 With two
Chart 1
aBabes-Bolyai University, 1, Kogalniceanu Street, Cluj-Napoca,
Romania. E-mail: isi@chem.ubbcluj.ro; Fax: +40 264 590818;
Tel: +40 264 590482
bHe´te´rochimie Fondamentale et Applique´e (UMR CNRS 5069),
Universite´ Paul Sabatier, 118 Rte de Narbonne, 31062 Toulouse Cedex
9, France. E-mail: escudie@chimie.ups-tlse.fr; Fax: +33 561558204;
Tel: +33 561558347
{ Electronic supplementary information (ESI) available: S1 includes full
physicochemical data for 1, 3a, 3b, 5a and 5b, and X-ray data for 3a, 3b,
5a and 5b. S2 includes the calculated energies for 3a, 3b, 5a and 5b.
Scheme 1
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Chem. Commun., 2007, 4149–4151 | 4149

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Scheme 3
thermal stability and did not undergo valence isomerization to give
the corresponding thiaphosphirane via a [1 + 2] cycloaddition of
sulfur with the PLC double bond; the further addition of sulfur to
give a thiaphosphirane P-sulfide derivative was not observed. The
high steric congestion in 5 might be responsible for its stability
since, in other instances, depending on the substituents at C and P,
the CLPLS moieties are either stable, rearrange to a thiapho-
sphirane or further add sulfur.3
Fig. 1 Molecular structure of 3b (50% probability ellipsoids). Hydrogen
atoms, solvent molecules and rotation disorder of the p-tBu moieties on
the aryl groups are omitted for clarity. ‘‘A’’ letters in the atom labels
correspond to the symmetry operation K 2 x, K 2 y, 2z. Selected bond
lengths (s) and bond/torsion angles (u): Ge(1)–C(1) 2.005 (3), C(1)–P(1)
Both 5a and 5b have been characterized by X-ray diffraction"
(see Fig. 2 for the molecular structure of 5b and the ESI for that of
5a{). Close similarities in geometry between 5a and 5b, and the
starting 3a and 3b were noticed.
…
1.665(3), P(1)–C(10) 1.872(3), Ge(1)–C(2) 2.016(3), Ge(1) Ge(1A) 2.918,
…
C(1) C(1A) 2.755, C(1)–Ge(1)–C(1A) 86.71(11), Ge(1)–C(1)–Ge(1A)
93.29(11), Ge(1)–C(1)–P(1) 117.45(15), C(1)–Ge(1)–C(1A)–Ge(1A) 0.
The presence of sulfur atoms and the PLC double bonds makes
derivatives 5a and 5b of interest in the synthesis of novel transition
metal complexes. Their ability to act as versatile ligands is
currently under investigation. Theoretical calculations that could
give us insight into the electronic structure of the SLPLC unit and
its potential coordinative properties, the likely mechanism of the
cis–trans isomerisation and a study into the possible interactions
between the two coordinative moieties are now in progress.
We thank the French Ministry of Foreign Affairs (AI Brancusi
no 08581TK (Fr) and 18015 (Ro), and Eiffel grant to P. M. P.), the
CNRS, and the French and Romanian Ministry of Education and
less bulky Mes (2,4,6-trimethylphenyl) groups, the transient
2
phosphagermaallene Mes*PLCLGeMes2 could be observed by
31P NMR experiments. The latter readily lead to the corresponding
1,3-digermacyclobutane derivative I (M = Ge, X = PMes*, R = R9
= Mes). The same phenomenon could be observed in the silicon
series since the 1,3-disilacyclobutanes I (M = Si, X = PMes*, R =
Ph, R9 = Tip) were also formed via the phosphasilaallene
intermediate Mes*PLCLSi(Ph)Tip.1g In the case of 1, monitoring
the reaction by 31P NMR spectroscopy between 280 uC and room
temperature showed the initial formation of 4 (Scheme 2) (dP
=
381.6, 3JPF = 10.1 Hz), leading to a new asymmetric intermediate
(dP = 286.7 and 443.8, 4JPP = 38.5 Hz), and finally to 3 at 240 uC;
no phosphagermaallene could be observed. These preliminary
results seem to indicate that at least one stabilizing aryl group on
the group 14 metal atom favours the observation of the
phosphametallaallene.
The reaction of 3 with an excess of sulfur in refluxing THF
affords a new type of bis(methylenethioxophosphoranes),3 5a (cis)
and 5b (trans), bridged by two germanium atoms (Scheme 3). The
two isomers are also in equilibrium, and at the room temperature
the ratio 5a : 5b is 3 : 1. The electropositive germanium atoms (2.0–
2.1 on the Pauling scale) bonded to the thioxophosphaalkene
carbons cause the phosphorus nuclei in compound 5 to resonate at
low fields (dP 5a = 184.4, 5b = 183.7), as in the case of
MesP(S)LC(SiMe3)2 (190.9 pm)3i bearing two electropositive
silicon atoms. The 31P NMR spectra of such compounds
substituted by alkyl or aryl groups generally exhibit chemical
shifts between 107 and 160 ppm.3f–m
Fig. 2 Molecular structure of 5b (50% probability ellipsoids). Hydrogen
atoms, solvent molecules, rotation disorder of the p-tBu on the aryl groups
and disorder of the whole tBu group on the germanium atom over two
positions are omitted for clarity. ‘‘A’’ letters in the atom labels correspond
to the symmetry operation 1 2 x, 2y, z. Selected bond lengths (s) and
bond/torsion angles (u): Ge(1)–C(1) 2.008(6), C(1)–P(1) 1.652(6), P(1)–S(1)
Derivatives 5I are the first examples of compounds containing
two CLPLS units in a same molecule. They showed very good
…
1.937(2), P(1)–C(6) 1.827(6), Ge(1)–C(2) 2.105(19), Ge(1) Ge(1A) 2.956,
…
C(1) C(1A) 2.712, C(1)–Ge(1)–C(1A) 85.1(3), Ge(1)–C(1)–Ge(1A)
94.9(3), Ge(1)–C(1)–P(1) 121.9(3), C(1)–P(1)–S(1) 124.8(2), C(1)–Ge(1)–
C(1A)–Ge(1A) 0.
Scheme 2
4150 | Chem. Commun., 2007, 4149–4151
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added 3 equivalents of sulfur; the reaction mixture was refluxed for 3 h. An
NMR study showed the quantitative formation of 5. After removal of
THF, 20 mL of pentane was added and the reaction mixture was filtered to
eliminate the excess sulfur; a mixture of 5a/5b was isolated (0.52 g, 81%).
Crystals of the trans isomer were obtained from the THF solution at
220 uC while the cis isomer crystallized from pentane. dP (121.5 MHz):
184.4 (5a), 183.7 (5b).
Research (CEEX project SUPRACOM) for their financial support
of this work.
Notes and references
{ Synthesis of phosphagermapropene 1. To 1.0 g (2.7 mmol) of
dichlorophosphaalkene 2 in 30 mL of THF cooled at 290 uC was added
dropwise 1.9 mL of 1.6 M nBuLi in hexane (1 equiv.). After half an hour at
285 uC, 0.62 g (2.7 mmol) of tBu2GeF2 in 20 mL of THF were canulated.
The reaction mixture was then allowed to warm to room temperature, and
the solvent was removed under vacuum and replaced by pentane. Lithium
salts were removed by filtration. 1 precipitated from methanol as a white
solid (1.47 g, 78%, mp = 118 uC). Only the E-isomer was obtained. NMR
data for 1 (solvent CDCl3). dH (300 MHz): 1.23 (d, 4JHF = 1.2 Hz, tBuGe),
1.29 (s, p-tBu), 1.47 (s, o-tBu), 7.38 (d, 4JPH = 1.4 Hz, ArH); dC (75.5 MHz):
1 (a) (X = CR2) M. Ishikawa, S. Matsuzawa, K. Hirotsu, S. Kamitori and
T. Higuchi, Organometallics, 1984, 3, 1930; (b) T. J. Barton, J. Lin,
S. Ijadi-Maghsoodi, M. D. Power, X. Zhang, Z. Ma, H. Shimizu and
M. S. Gordon, J. Am. Chem. Soc., 1995, 117, 11695; (c) D. Ostendorf,
L. Kirmaier, W. Saak, H. Marsmann and M. Weidenbruch, Eur. J.
Inorg. Chem., 1999, 2301; (d) (X = CLCR2) N. Auner and M. Grasmann,
J. Organomet. Chem., 2001, 621, 10; (e) (X = NR) M. Weidenbruch,
B. Brand-Roth, S. Pohl and S. Saak, Angew. Chem., Int. Ed. Engl., 1990,
29, 90; (f) M. Weidenbruch, J. Hamann, H. Piel, D. Lentz, K. Peters and
H. G. Von Schnering, J. Organomet. Chem., 1992, 426, 35; (g) (X = PR)
L. Rigon, H. Ranaivonjatovo, J. Escudie´, A. Dubourg and J.-P. Declercq,
Chem.–Eur. J., 1999, 5, 774; (h) (X = PR3) H. Schmidbaur, R. Pichl and
G. Mueller, Chem. Ber., 1987, 120, 789.
1
2
165.27 (dd, JCP = 91.0 Hz, JCF = 4.5 Hz, CLP); dF (188.3 MHz,
CF3COOH): 2135.4; dP (121.5 MHz): 293.5 (d, JPF = 45.8 Hz).
3
§ Synthesis of 2,4-diphosphinylidene-1,3-digermacyclobutane (3). To 1.0 g
(1.89 mmol) of 1 in 20 mL of THF cooled at 295 uC was added dropwise
1.38 mL of 1.5 M tBuLi in hexane (10% excess). The reaction mixture was
left at low temperature for 15 min and then allowed to warm slowly to
room temperature. After removal of the lithium salts and solvents, 20 mL
of pentane was added. A mixture of 3a/3b precipitated (0.67 g, 75%). The
yellow mixture was dissolved in 20 mL of THF. Yellow acicular crystals of
the trans isomer of 3 were obtained after a few days, while the cis isomer
crystallized from pentane through slow evaporation. mp = 309 uC (3a),
mp = 301 uC (3b).
2 H. Ramdane, H. Ranaivonjatovo, J. Escudie´, S. Mathieu and
N. Knouzzi, Organometallics, 1996, 15, 3070.
3 (a) Some mono(methylenethioxophosphoranes) have already been
evidenced by trapping reactions3b–e or stabilized as monomers;3f–m for a
review, see: I. L. Odinets, N. M. Vinogradova and T. A. Mastryukova,
Russ. Chem. Rev., 2003, 72, 787; (b) E. Deschamps and F. Mathey,
J. Chem. Soc., Chem. Commun., 1984, 1214; (c) C. D. Cox and
M. J. P. Harger, J. Chem. Res. (S), 1998, 578; (d) H. Qian, P. P. Gaspar
and N. P. Rath, J. Organomet. Chem., 1999, 585, 167; (e) M. J. P. Harger,
J. Chem. Soc., Perkin Trans. 2, 2002, 489; (f) E. Niecke and
D.-A. Wildbredt, J. Chem. Soc., Chem. Commun., 1981, 72; (g) Th.
A. Van Der Knaap, Th. C. Klebach, R. Lourens, M. Vos and
F. Bickelhaupt, J. Am. Chem. Soc., 1983, 105, 4026; (h) Th. A. Van Der
Knaap and F. Bickelhaupt, Tetrahedron, 1983, 39, 3189; (i) M. Caira,
R. H. Neilson, W. H. Watson, P. Wisian-Neilson and Z. M. Xie, J. Chem.
Soc., Chem. Commun., 1984, 698; (j) K. Toyota, K. Shimura,
H. Takahashi and M. Yoshifuji, Chem. Lett., 1994, 1927; (k)
K. Toyota, H. Takahashi, K. Shimura and M. Yoshifuji, Bull. Chem.
Soc. Jpn., 1996, 69, 141; (l) M. Yoshifuji, H. Takahashi, K. Shimura,
K. Toyota, K. Hirotsu and K. Okada, Heteroat. Chem., 1997, 8, 375; (m)
A. Nakamura, S. Kawasaki, K. Toyota and M. Yoshifuji, J. Organomet.
Chem., 2007, 692, 70.
4 K. M. Baines and W. G. Stibbs, Coord. Chem. Rev., 1995, 145,
147.
5 (a) N. P. Toltl, M. Stradiotto, T. L. Morkin and W. J. Leigh,
Organometallics, 1999, 18, 5643; (b) N. Wiberg, T. Passler, S. Wagner and
K. Polborn, J. Organomet. Chem., 2000, 598, 292.
6 Y. El Harouch, H. Gornitzka, H. Ranaivonjatovo and J. Escudi´e,
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7 G. M. Sheldrick, SHELXS-97, Program for solution of crystal structures,
University of Go¨ttingen, Germany, 1997.
NMR data for 3 (solvent CDCl3). 3a dH (300 MHz): 0.56 (s, tBuGe),
1.23 and 1.32 (2 s, p-tBu and tBuGe), 1.47 (s, o-tBu), 7.07 (s, ArH); dC
1
3
(75.5 MHz): 204.0 (dd, JCP = 96.6 Hz, JCP = 25.7 Hz, CLP); dP
(121.5 MHz): 367.4.
3b dH (300 MHz): 0.94, 1.19 and 1.50 (3 s, tBu), 7.13 (s, ArH); dC
1
3
(75.5 MHz): 204.3 (dd, JCP = 92.0 Hz, JCP = 24.9 Hz, CLP); dP
(121.5 MHz): 367.7.
" Crystal data for 3b and 5b.
3b: C58H104Ge2O1P2, M = 1024.54, monoclinic, a = 35.416(2), b =
10.6099(7), c = 16.2868(11) s, b = 101.109(1)u, V = 6005.3(7) s3, T =
173(2) K, space group C2/c, Z = 4, 14909 reflections measured, 5077
unique (Rint = 0.0577). The final R1 (for I . 2s(I)) was 0.0386 and wR2 (all
data) was 0.0847 with R1 = S||Fo| 2 |Fc||/S|Fo| and wR2 = (Sw(Fo2 2 Fc2)2/
Sw(Fo2)2)0.5
.
5b: C62H110Ge2O2P2S2, M = 1158.74, orthorhombic, a = 20.440(3), b =
16.670(2), c = 19.133(3) s, V = 6519.2(15) s3, T = 173(2) K, space group
Ibam, Z = 4, 14548 reflections measured, 2491 unique (Rint = 0.1131). The
final R1 (for I . 2s(I)) was 0.0504 and wR2 (all data) was 0.1217.
Data for all structures represented in this paper were collected at low
temperatures using an oil coated shock cooled crystal on a Bruker-AXS
CCD 1000 diffractometer with Mo-Ka radiation (l = 0.71073 s). The
structures were solved by direct methods7 and all non-hydrogen atoms were
refined anisotropically using the least-squares method on F2.8 CCDC
649323 (3a), 649324 (3b), 649325 (5a) and 649326 (5b). For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b708308d
I Synthesis of 2,4-bis(thioxophosphoranylidene)-1,3-digermacyclobutane
(5). To 0.60 g (0.63 mmol) of a mixture of cis/trans 3 in 10 mL of THF were
8 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
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Chem. Commun., 2007, 4149–4151 | 4151