Simple access to a 2,4-diphosphabicyclobutane

Article abstract of DOI:10.1021/om030548p

A 2-(phosphirenyl)ethylphosphinidene [W(CO)₅]₂ complex undergoes an original phosphinidene + phosphirene self-condensation to yield the tricyclic compound 5 with an unusual 2,4-diphosphabicyclobutane "butterfly" structure. The product has been characterized by X-ray crystal structure analysis and its formation studied from a theoretical standpoint at the B3LYP/6-311+G(d,p) level.

Full text of DOI:10.1021/om030548p

Organometallics 2003, 22, 4825-4828
4825
Notes
Sim p le Access to a 2,4-Dip h osp h a bicyclobu ta n e
Marcus White, Louis Ricard, and Franc¸ois Mathey*
Laboratoire “He´te´roe´le´ments et Coordination”, UMR CNRS 7653, DCPH, Ecole Polytechnique,
91128 Palaiseau Cedex, France
Received J uly 25, 2003
Sch em e 1
Summary: A 2-(phosphirenyl)ethylphosphinidene [W-
(CO)5]2 complex undergoes an original phosphinidene +
phosphirene self-condensation to yield the tricyclic com-
pound 5 with an unusual 2,4-diphosphabicyclobutane
“butterfly” structure. The product has been characterized
by X-ray crystal structure analysis and its formation
studied from a theoretical standpoint at the B3LYP/ 6-
311+G(d,p) level.
In tr od u ction
The long-known bicyclobutane structure has been of
special interest due to the similarity between the
chemical reactivity of its central bond and that of a
π-bond in alkenes. This similarity is underlined by the
recent development of original polycyclobutane polymers
obtained by radical or anionic polymerization of bicy-
clobutanes.1 In view of the fruitful analogy which exists
between phosphorus and carbon chemistry,2 it was
obviously tempting to synthesize and study phospha-
substituted bicyclobutanes. Adequate routes are known
for the synthesis of 1,3-diphospha structures.3 In con-
trast, as far as we know, only three 2,4-diphosphabicy-
clobutane derivatives, 1a -c, have been previously
approach has never been described in the literature, and
in our laboratory and others, numerous attempts to
condense a terminal phosphinidene complex with a
phosphirene complex have either failed or led to an
insertion into one of the P-C ring bonds to give a
diphosphetene derivative.5 A related chemistry has also
been developed with phosphirene imines and imino-
phosphanes.6 In the course of a program aiming at the
synthesis of new chelating ligands using the versatile
chemistry of electrophilic terminal phosphinidene com-
plexes,7 we have discovered the first case where a
phosphirene + phosphinidene condensation leads to a
reported and their syntheses involve nontrivial trans-
formations.4 We wish to describe in this paper a simpler
access to a 2,4-diphosphabicyclobutane and its charac-
terization by X-ray crystal structure analysis.
Resu lts a n d Discu ssion
An obvious approach to 2,4-diphosphabicyclobutanes
involves the cycloaddition of a phosphinidene unit onto
the CdC double bond of a phosphirene ring. Such an
(4) (a) Kobayashi, Y.; Fujino, S.; Hamana, H.; Hanzawa, Y.; Morita,
S.; Kumadaki, I. J . Org. Chem. 1980, 45, 4683. (b) Niecke, E.; Fuchs,
A.; Nieger, M. Angew. Chem., Int. Ed. 1999, 38, 3028. (c) J ones, C.;
Platts, J . A.; Richards, A. F. Chem. Commun. 2001, 663.
(5) Tran Huy, N. H.; Ricard, L.; Mathey, F. Organometallics 1997,
16, 4501. Tran Huy, N. H.; Ricard, L.; Mathey, F. J . Organomet. Chem.
1999, 582, 53. Wang, B.; Nguyen, K. A.; Srinivas, G. N.; Watkins, C.
L.; Menzer, S.; Spek, A. L.; Lammertsma, K. Organometallics 1999,
18, 796.
(6) Averin, A. D.; Lukashev, N. V.; Kazankova, M. A.; Beletskaya,
I. P. Mendeleev Commun. 1993, 68; Link, M.; Niecke, E.; Nieger, M.
Chem. Ber. 1994, 127, 313.
(7) Reviews: Mathey, F.; Tran Huy, N. H.; Marinetti, A. Helv. Chim.
Acta 2001, 84, 2938. Lammertsma, K.; Vlaar, M. J . M. Eur. J . Org.
Chem. 2002, 4, 1127.
(1) Chen, X.-P.; Padias, A. B.; Hall, H. K., J r. Macromolecules 2001,
34, 3514. Kitayama, T.; Kawauchi, T.; Chen, X.-P.; Padias, A. B.; Hall,
H. K., J r. Macromolecules 2002, 35, 3328.
(2) Dillon, K. B.; Mathey, F.; Nixon, J . F. Phosphorus: The Carbon
Copy; Wiley: Chichester, U.K., 1998. Mathey, F. Angew. Chem., Int.
Ed. 2003, 42, 1578.
(3) Binger, P.; Biedenbach, B.; Kru¨ger, C.; Regitz, M. Angew. Chem.,
Int. Ed. Engl. 1987, 26, 764. Barron, A. R.; Cowley, A. H.; Hall, S. W.;
Nunn, C. M. Angew. Chem., Int. Ed. Engl. 1988, 27, 837. Niecke, E.;
Metternich, H. J .; Streubel, R. Chem. Ber. 1990, 123, 67.
10.1021/om030548p CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/15/2003

4826 Organometallics, Vol. 22, No. 23, 2003
Notes
Ta ble 2. Geom etr y a n d En er gy of
1,2-Dip h osp h eten es
product
E
F
G
P-C (Å)
1.846
1.341
2.289
1.851
1.338
2.313
1.845-1.926
1.342-1.536
2.316
100.8
-838.688407
C-C (Å)
P-P (Å)
folding (deg)
energy (au)
-761.296253
-761.293270
phabicyclobutane moiety explains the abnormal 31P
chemical shift, as shown previously.4c
At this point, we were wondering why, in this precise
case, the phosphinidene + phosphirene condensation
leads to a butterfly structure 5 instead of the more
conventional 1,2-diphosphetene structure 6. The study
was carried out at the B3LYP/6-311+G(d,p) level10 on
the noncomplexed parent structures A-G. The results
F igu r e 1. Crystal structure of complex 5. Significant bond
distances (Å) and angles (deg): W(1)-P(1) ) 2.4541(8),
P(1)-C(2) ) 1.821(3), P(1)-C(2a) ) 1.802(3), P(1)-C(1) )
1.843(3), C(1)-C(1a) ) 1.532(6), C(2)-C(2a) ) 1.570(6);
C(2)-P(1)-C(2a) ) 51.3(2), C(2)-P(1)-C(1) ) 103.7(1),
C(2)-P(1)-W(1) ) 127.9(1), P(1)-C(2)-P(1a) ) 97.8(2),
C(1)-P(1)-W(1) ) 122.5(1); folding angle P(1)C(2)C(2a)/
P(1a)C(2)C(2a) 113.44.
are summarized in Tables 1 and 2 (energy and geom-
etry). Compound B has already been studied at the
MP2/6-31G* level, and our geometrical parameters are
very similar to those reported for 1b4b and those found
in the earlier theoretical study.11 The endo,exo (B) and
endo,endo (A) 2,4-diphosphabicyclobutane isomers are
almost isoenergetic, while the exo,exo isomer (C) is the
least stable by 2.2 kcal mol-1. In the same vein, the
trans form (E) is favored over the cis-diphosphetene (F)
Ta ble 1. Geom etr y a n d En er gy of
2,4-Dip h osp h a bicyclobu ta n es
product
A
B
C
D
P-C (Å) 1.836
C-C (Å) 1.507
P‚‚‚P (Å) 2.996
1.841-1.850 1.861
1.832b
1.484
2.902
118.4
1.465
2.856
113.1
1.516b
2.882
119.6
folding
126.9
by 1.9 kcal mol-1 12
This result agrees nicely with the
.
(deg)
energy
(au)a
-761.265 872 -761.265 990 -761.262 330 -838.690 238
slow isomerization of the cis-diphosphetene into the
corresponding trans-diphosphetene upon heating.13 How-
ever, the most significant result is that both cis- and
trans-1,2-diphosphetenes are substantially more stable
than the 2,4-diphosphabicyclobutanes. Isomer B is
higher in energy than E and F by 19.0 and 17.1 kcal
mol-1, respectively. This explains why the isolation of
a 2,4-diphosphabicyclobutane is normally difficult. In
contrast, the introduction of the P-CH2CH2-P bridge
leads to an inversion of stability. The tricyclic structure
D becomes slightly more stable than the bicyclic struc-
ture G by 1.15 kcal mol-1. Even though the experiments
a
b
ZPE correction included. P-CH2 1.878 Å, H2C-CH2 1.541 Å.
2,4-diphosphabicyclobutane structure. Our starting point
has been the 1-(â-chloroethyl)phosphirene complex 2.8
The lithium 3,4-dimethylphospholide-pentacarbonyl-
tungsten complex9 reacts with 2 as a weak base and a
good nucleophile to give the substitution product 3.
Complex 3 then reacts with dimethyl acetylenedicar-
boxylate via its phosphole dienic system to give the
intermediate 7-phosphanorbornadiene complex 4, which
collapses in situ to give the final product 5 (Scheme 1).
Product 5 displays a 31P resonance at -6.9 ppm, and
thus, we initially believed that it had the expected
bicyclic structure 6. However, its 13C spectrum shows
two sp3-carbon resonances at 34.01 (s, CH2) and 33.35
ppm (pseudo-triplet, C-Ph), and a X-ray analysis
demonstrated that it has in fact the tricyclic “butterfly”
structure 5 (Figure 1). This structure is characterized
by a long C-C bridge bond at 1.570(6) Å and a high
folding (as measured by the angle between the two PCC
planes) around that bond at 113.4°. Otherwise, the
structure of the phosphirane rings appears to be normal.
Finally, the endo,endo configuration of the 2,4-diphos-
(10) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.11; Gaussian, Inc.: Pittsburgh,
PA, 1998.
(11) Nguyen, M. T.; Van Praet, E.; Vanquickenborne, L. G. Inorg.
Chem. 1994, 33, 1153.
(12) E and F have already been studied at the MP2/6-31G* level:
Bachrach, S. M.; Liu, M. J . Org. Chem. 1992, 57, 2040.
(13) Maigrot, N.; Ricard, L.; Charrier, C.; Le Goff, P.; Mathey, F.
Bull. Soc. Chim. Fr. 1992, 129, 76.
(8) Deschamps, B.; Mathey, F. Tetrahedron Lett. 1985, 26, 4595.
(9) Holand, S.; Mathey, F.; Fischer, J . Polyhedron 1986, 5, 1413.

Notes
Organometallics, Vol. 22, No. 23, 2003 4827
proposed in our earlier work. It must be stressed,
however, that the actual reaction takes place on the
W(CO)5-complexed species under mild conditions (60 °C)
with a catalyst (CuCl) and a alkynyl activating group
on C3. The role of the activating group is to weaken the
P4-C3 bond as already established.5 We think that the
role of CuCl is to facilitate the cleavage of the P2-C1
bond by inserting into this bond. The insertion of d10
metallic centers into the P-C ring bonds of phos-
phiranes is indeed a well-known process.15
Exp er im en ta l Section
NMR spectra were recorded on a multinuclear Bruker
AVANCE 300 MHz spectrometer operating at 300.13 MHz for
1H, 75.47 MHz for 13C, and 121.50 MHz for 31P. Chemical shifts
are expressed in parts per million (ppm) downfield from
internal tetramethylsilane (1H and 13C) and external 85%
aqueous H3PO4 (31P). Elemental analyses were performed by
the Service de microanalyse du CNRS, Gif-sur-Yvette, France.
[1-(2-Ch lor oeth yl)-2,3-d ip h en ylp h osp h ir en e]p en ta ca r -
bon yltu n gsten (2). [1-(2-Chloroethyl)-3,4-dimethylphosphole]-
pentacarbonyltungsten8 (6.0 g, 12 mmol), dimethyl acetylene-
dicarboxylate (3.0 mL, 24 mmol), and diphenylacetylene (5 g,
28 mmol) were dissolved in toluene (35 mL) and heated to 110
°C for 48 h. The solvent was then removed under reduced
pressure and the residue separated by flash chromatography
(2% diethyl ether in hexane). Recrystallization from dichlo-
F igu r e 2. Computed structure of the (B-F) transition
state. Significant bond distances (Å) and angles (deg):
P(2)-C(1) ) 2.511, P(2)‚‚‚P(4) ) 2.780, P(2)-C(3) ) 1.823,
P(4)-C(3) ) 2.033, P(4)-C(1) ) 1.804, C(1)-C(3) ) 1.406;
P(2)-C(3)-P(4) ) 92.1, P(2)-C(3)-C(1) ) 101.3, P(2)-
C(3)-C(1)-P(4) ) -81.9, H(6)-P(2)‚‚‚P(4)-H(8) ) -66.7.
have been carried out on the W(CO)5-complexed species,
the trend revealed by the calculations is consistent with
the successful isolation of complex 5.
romethane/hexane gave the product 2 as pale yellow crystals
We were eager to shed some light on a curious feature
of the insertion of phosphinidenes into phosphirenes.
In the complexed series, it gives exclusively or predomi-
nantly the cis-diphosphetenes.5 The proposed explana-
tion involved the attack of the phosphinidene at the
CdC double bond of the phosphirene from the less
hindered side of the ring opposite to the P substituent.
This type of condensation corresponds to a endo,exo
stereochemistry, as in B. Thus, we decided to investigate
the potential rearrangement of B into F. The QST2
procedure yielded a transition state (B-F) (one imagi-
nary frequency), which is depicted in Figure 2. The
optimized structure of this transition state is remark-
ably similar to that of the transient geometry proposed
for the formation of cis-1,2-diphosphetenes in our earlier
paper.5 One of the P-C bonds of B is broken (P‚‚‚C
separation 2.511 Å), while the other P-C bond into
which the phosphinidene will insert is already elongated
at 2.037 Å. At 1.406 Å, the C-C bond lies halfway
between a single and a double bond, and the P‚‚‚P
separation has decreased from 2.902 in B to 2.780 Å in
the TS. The folding is reduced from 118.4° in B to 81.9°
in the TS. Finally, the (B-F) transition state lies 46.3
kcal mol-1 above B, which shows that the reaction is
not easy under purely thermal conditions. It must be
stressed here that bicyclobutanes are known to rear-
range thermally to give the corresponding butadienes
via one disrotatory and one conrotatory opening of the
two three-membered rings.14 Cyclobutenes are not
intermediates in this rearrangement. In the 2,4-diphos-
phabicyclobutane series, however, the 1,4-diphospha-
butadienes are certainly destabilized by comparison
with 1,2-diphosphetenes, except when very bulky sub-
stituents are bonded to the two phosphorus atoms.4b In
any event, these results give some credence to the
mechanism of formation of cis-1,2-diphosphetenes, as
1
(3.4 g, 47%). 31P NMR (CDCl3): δ -161.98 ppm (d, J P-W
)
265.3 Hz). 1H NMR (CDCl3): δ 2.33 (2H, t, J ) 7.3 Hz, P-CH2),
3.35 (2H, dt, 3J P-H ) 13.3, J ) 7.3 Hz, CH2Cl), 7.43-7.53 (6H,
m, Ph), 7.84 (4H, d, J ) 6.9 Hz, Ph). 13C NMR (CDCl3): δ 40.57
1
2
(d, J C-P ) 1.7 Hz, P-CH2), 40.98 (d, J C-P ) 7.0 Hz, CH2-
1
Cl), 127.95 (d, J C-P ) 6.8 Hz, P-C), 128.94 (d, J C-P ) 11.0
Hz, Ph), 129.79 (s, Ph), 130.62 (d, J C-P ) 5.3 Hz, Ph), 131.25
1
2
(s, Ph), 196.15 (dt, J C-W ) 108.7 Hz, J C-P ) 8.3 Hz, cis-CO),
198.05 (d, 2J C-P ) 30.9 Hz, trans-CO) MS (EI; m/z (ion, relative
abundance)): 596 (M+, 87), 512 (M+ - (CO)3, 46), 484 (M+
-
-
(CO)4, 93), 748 (M+ - (CO)5 + 1, 100). Anal. Calcd for C21H14
ClO5PW: C, 42.48; H, 2.37. Found: C, 42.42; H, 2.31.
[1-(2-(2,3-Dip h en ylp h osp h ir en -1-yl)eth yl)-3,4-d im eth -
ylp h osp h ole]bis(p en ta ca r bon yltu n gsten ) (3). Lithium 3,4-
dimethylphospholide-pentacarbonyltungsten9 (2.2 mmol) in
THF (5 mL) was cooled to 0 °C, and [1-(2-chloroethyl)-2,3-
diphenylphosphirene]pentacarbonyltungsten (2; 1.25 g, 2.1
mmol) was added. The solution was allowed to warm to room
temperature and then the solvent was removed under reduced
pressure. The resulting residue was separated by flash chro-
matography (3% diethyl ether in hexane), and recrystallization
from dichloromethane/hexane gave the product 3 as pale
yellow crystals (0.6 g, 28%). 31P NMR (CDCl3): δ -153.41 ppm
(dd, 3J P-P ) 25.2 Hz, 1J P-W ) 262.8 Hz), 6.80 ppm (dt, 3J P-P
)
1
1
25.2 Hz, J P-W ) 211.7 Hz). H NMR (CDCl3): δ 1.97 (4H, br
2
s, P-CH2), 2.23 (6H, s, Me), 6.24 (2H, d, J P-H ) 37.2 Hz, 2 ×
CH-P), 7.4-7.7 (6H, m, Ph), 7.97 (4H, d, J ) 8.0 Hz, Ph). 13
C
3
NMR (CDCl3): δ 17.73 (d, J C-P ) 11.1 Hz, Me), 27.03 (dd,
1
2
2J C-P ) 3.8 Hz, J C-P ) 19.6 Hz, P-CH2), 33.88 (dd, J C-P
)
1
1
4.5 Hz, J C-P ) 8.7 Hz, P-CH2), 127.82 (d, J C-P ) 40.8 Hz,
1
P-CH), 128.16 (s, Ph), 129.49 (d, J C-P ) 11.5 Hz, Ph-C),
129.86 (s, Ph), 130.52 (d, J C-P ) 5.0 Hz, Ph), 131.28 (s, Ph),
2
152.81 (d, J C-P ) 5.8 Hz, Me-C), 196.17 (m, cis-CO), 196.26
(m, trans-CO). MS (EI; m/z (ion, relative abundance)): 996 (M+,
4), 828 (M+ - (CO)6, 9), 772 (M+ - (CO)8, 34), 744 (M+ - (CO)9,
100), 716 (M+ - (CO)10, 40), 532 (M+ - W(CO)10, 19). Anal.
Calcd for C32H22O10P2W2: C, 38.58; H, 2.23. Found C, 38.45;
H, 2.25.
(15) Carmichael, D.; Hitchcock, P. B.; Nixon, J . F.; Mathey, F.;
Ricard, L. J . Chem. Soc., Dalton Trans. 1993, 1811.
(14) Closs, G. L.; Pfeffer, P. E. J . Am. Chem. Soc. 1968, 90, 2452.

4828 Organometallics, Vol. 22, No. 23, 2003
Notes
[1,6-Dip h en yl-2,5-d ip h osp h a tr icyclo(3.1.0.02,6)h exa n e]-
bis(p en ta ca r bon yltu n gsten ) (5). [1-(2-(2,3-Diphenylphos-
phiren-1-yl)ethyl)-3,4-dimethylphosphole]bis(pentacarbonyl-
tungsten) (3; 0.55 g, 0.55 mmol) and dimethyl acetylene-
dicarboxylate (0.27 mL, 2.2 mmol) were dissolved in toluene
(35 mL) and heated to 110 °C for 24 h. The solution was then
cooled to room temperature, and the solvent was removed
under vacuum. The residue was extracted with hexane (2 × 8
mL), and the combined extracts were filtered, concentrated to
approximately 5 mL under vacuum, and left to stand under
nitrogen, whereupon the product 5 precipitated as colorless
crystals (60 mg, 12%). 31P NMR (CDCl3): δ -6.93 ppm (dd,
In ter m ed ia te Com p ou n d 4 (Not Isola ted ). 31P NMR
3
1
(toluene): δ -152.62 (dd, J P-P ) 19.9 Hz, J P-W ) 261.7 Hz),
3
1
212.63 (dt, J P-P ) 19.0 Hz, J P-W ) 236.6 Hz).
Cr ysta llogr a p h ic Da ta for 5: 26H14O10P2W2: Mr
C
)
916.01; orthorhombic; space group Pbcn; a ) 10.450(1) Å, b )
15.079(10) Å, c ) 18.567(1) Å, V ) 2925.7(4)Å3; Z ) 4; D )
2.080 g cm-3; µ ) 8.019 cm-1; F(000) ) 1712; crystal dimen-
sions 0.20 × 0.20 × 0.20 mm; 17 413 total reflections collected
and 3412 with I >2σ(I); goodness of fit on F2 1.056; R1 ) 0.0285
(I > 2σ(I)), wR2 ) 0.0814 (all data); maximum/minimum
residual density 2.522(0.147)/-1.538(0.147) e Å3. Data were
collected on a KappaCCD diffractometer at 150.0(1) K with
Mo KR radiation (λ ) 0.710 73 Å). Full details of the crystal-
lographic analysis are described in the Supporting Informa-
tion.
3J P-W ) 31.2 Hz, J P-W ) 235.3 Hz). H NMR (CDCl3): δ 2.20
(4H, t, J ) 4.4 Hz, CH2), 7.2-7.3 (10H, m, Ph). 13C NMR
(CDCl3): δ 33.35 (pseudo-t, Ph-C), 34.01 (s, CH2), 128.51 (s,
Ph), 128.69 (t, J C-P ) 10.9 Hz, Ph), 129.22 (s, Ph), 131.47 (t,
J C-P ) 7.3 Hz, Ph), 194.11 (m, cis-CO), 196.2 (m, trans-CO).
MS (EI; m/z (ion, relative abundance)): 916 (M+, 39), 805
(M+ - (CO)4 + 1, 76), 776 (M+ - (CO)5, 55), 748 (M+ - (CO)6,
1
1
Ack n ow led gm en t. We thank J ohnson Matthey
Catalysts for the financial support of M.W. and of this
research program.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data for 5 and Z matrixes for A-G and the (B-
F) transition state. This material is available free of charge
via the Internet at http://pubs.acs.org.
54), 720 (M+ - (CO)7, 100), 692 (M+ - (CO)8, 47), 636 (M+
-
(CO)10, 84), 451 (M+ - W(CO)10 - 1, 63), 268 (M+ - W2(CO)6,
36). Anal. Calcd for C26H14O10P2W2: C, 34.09; H, 1.54. Found:
C, 34.14; H, 1.57.
OM030548P