The phosphorus version of the oxaspiropentene-cyclobutenone rearrangement

Article abstract of DOI:10.1021/om900983k

The phosphatriafulvene complex 1 is sulfurized at phosphorus by reaction with propylene sulfide at room temperature. The X-ray crystal structure of 2 shows a long P-S bond (2.0039(5) A) compatible with a zwitterionic formulation. The reaction of 1 with propylene oxide takes place at 110 °C and leads to the ring-expanded 1-phosphacyclobutenone 3. DFT calculations support the intermediacy of a phosphatriafulvene epoxide and its rearrangement to a four-membered ring, paralleling the oxaspiropentene-cyclobutenone conversion.

Full text of DOI:10.1021/om900983k

1302 Organometallics 2010, 29, 1302–1304
DOI: 10.1021/om900983k
The Phosphorus Version of the Oxaspiropentene-Cyclobutenone
Rearrangement
Ngoc Hoa Tran Huy,*,†,‡ Bruno Donnadieu,† Guy Bertrand,*,† and Franc-ois Mathey*,‡
†UCR-CNRS Joint Research Chemistry Laboratory, Department of Chemistry, University of California
Riverside, Riverside, California 92521-0403, and ‡Nanyang Technological University, Division of Chemistry
& Biological Chemistry, 21 Nanyang Link, Singapore 637371
Received November 10, 2009
˚
Summary: The phosphatriafulvene complex 1 is sulfurized at
phosphorus by reaction with propylene sulfide at room tempera-
ture. The X-ray crystal structure of 2 shows a long P-S bond
is no bond between C1 and S1 (distance 3.138 A), the three-
membered ring remains essentially aromatic, and the P1-C1
bond is just slightly elongated by the sulfurization
˚
˚
˚
(2.0039(5) A) compatible with a zwitterionic formulation. The
(1.8293(14) A in 2 vs 1.806(8) A in 1). More drastic condi-
tions are needed to perform the reaction with the corre-
sponding epoxide. At 110 °C, the primary product
rearranges to give the four-membered-ring species 3 (eq 3),
whose structure was established by X-ray analysis (Figure 2).
reaction of 1 with propylene oxide takes place at 110 °C and
leads to the ring-expanded 1-phosphacyclobutenone 3. DFT
calculations support the intermediacy of a phosphatriafulvene
epoxide and its rearrangement to a four-membered ring, paral-
leling the oxaspiropentene-cyclobutenone conversion.
In spite of their low stability, it has proven possible to
characterize a few oxaspiropentenes1 and to demonstrate
that they rearrange easily into the corresponding cyclobute-
nones (eq 1).1a,b
Similar compounds have already been obtained by inser-
tion of carbon monoxide into phosphirenes (e.g., 4).4 How-
ever, the presence of the amino substituents in 3 induces a
significant change in the structure of the four-membered
ring. Indeed, the C2-C3 bond has no significant double-
While studying the chemistry of phosphatriafulvenes ob-
tained by condensation of stable nucleophilic carbenes with
electrophilic terminal phosphinidene complexes,2 we have
discovered a rearrangement that appears to be the phos-
phorus version of this oxaspiropentene rearrangement. As
for any phosphaalkenes with inverse electron density,3 the
negatively charged phosphorus of phosphatriafulvenes is
easily oxidized. We have found that a controlled oxidation
takes place upon reaction with epoxides or episulfides. In the
case of episulfides, the reaction stops at the primary sulfuri-
zation product (eq 2).
˚
˚
bond character at 1.417(6) A (vs. 1.36(1) A in 4) and one of
P
the nitrogens (N2) is planar ( (angles)=359.7°), hence the
zwitterionic formulation. A related rearrangement has been
found by Regitz on studying the reaction of azides with
noncomplexed phosphatriafulvenes.5 Taking into account
the carbon case and the fact that the controlled oxidation of
phosphaalkene complexes is known to produce oxapho-
sphiranes,6 we were obliged to consider the possible forma-
tion of a spirooxaphosphirane as a precursor for 3 instead of
(4) Marinetti, A.; Fischer, J.; Mathey, F. J. Am. Chem. Soc. 1985, 107,
5001.
€
(5) Eisfeld, W.; Slany, M.; Bergstrasser, U.; Regitz, M. Tetrahedron
Lett. 1994, 35, 1527.
(6) Bauer, S.; Marinetti, A.; Ricard, L.; Mathey, F. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 1166.
(7) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; , Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision B.05; Gaussian, Inc.,
Pittsburgh, PA, 2003.
Compound 2 was characterized by X-ray crystal structure
analysis (Figure 1). The most significant features of the
structure concern its zwitterionic formulation. At 2.0039(5)
˚
A, the P1-S1 bond has clearly a single-bond character, there
*To whom correspondence should be addressed. E-mail: fmathey@
ntu.edu.sg (F.M.).
(1) (a) Halton, B.; Cooney, M. J.; Wong, H. J. Am. Chem. Soc. 1994,
116, 11574. (b) Bickers, P.; Halton, B; Kay, A. J.; Northcote, P. T. Aust. J.
Chem. 1999, 52, 647. (c) Billups, W. E.; Litosh, V. A.; Saini, R. K.; Daniels,
A. D. Org. Lett. 1999, 1, 115.
(2) Tran Huy, N. H.; Donnadieu, B.; Bertrand, G.; Mathey, F. Chem.
Asian J. 2009, 4, 1225.
(3) Weber, L. Eur. J. Inorg. Chem. 2000, 2425.
r
pubs.acs.org/Organometallics
Published on Web 01/25/2010
2010 American Chemical Society

Note
Organometallics, Vol. 29, No. 5, 2010 1303
Figure 3. Computed structure of oxaphosphirane 5. Main dis-
˚
tances (A) and angles (deg): P11-W12 = 2.4944, P11-C1 =
1.7843, P11-O2 = 1.7148, C1-O2 = 1.4525, C1-C7 =
1.4591, C1-C9 = 1.4584, C7-C9 = 1.3151; C1-O2-P11 =
Figure 1. X-ray crystal structure of sulfide 2. Main distances
˚
(A) and angles (deg): P1-S1 = 2.0039(5), P1-C1 = 1.8293(14),
67.99, C1-P11-O2
=
49.00, C7-C1-C9
=
53.58,
P1-C4 = 1.8385(14), P1-W1 = 2.5282(4), C1-C2 =
1.3865(18), C1-C3 = 1.3857(19), C2-C3 = 1.4096(18);
C1-P1-S1 = 109.80(5), C4-P1-S1 = 105.42(5), S1-P1-
W1 = 115.873(18), C1-P1-C4 = 96.60(6), C1-P1-W1 =
108.54(5), C4-P1-W1 = 118.79(5).
C2-C1-C7-C9 = 113.94.
earlier for the triphenyl-substituted species 44 but are rather
different from those of 3.
In terms of energy, 5 is higher than 6 by 46.0 kcal mol-1 but
the transition state for a concerted rearrangement is higher
than 5 by 36.2 kcal mol-1 (ZPE included). This last value is too
high for a ready rearrangement at 110 °C. Our conclusion
is that the rearrangement probably proceeds in a stepwise
manner. Thus, the introduction of phosphorus in the cycle
does not block the oxaspiropentene-cyclobutenone rearran-
gement but seems to significantly alter its mechanism.
Experimental Section
Figure 2. X-ray crystal structure of phosphetene 3. Main dis-
˚
tances (A) and angles (deg): P1-C1 = 1.886(4), P1-C3 =
Synthesis of the Sulfurization Product 2. A solution of 1
(70 mg, 1 mmol) in THF (5 mL) and propylene sulfide (0.1
mL) was stirred overnight at room temperature and then
evaporated under vacuum. The light yellow precipitate was
washed with pentane and dried under vacuum. Light yellow
microcrystals were isolated (50 mg, 70% yield). 1P NMR
1.838(5), P1-C4 = 1.817(4), P1-W1 = 2.5004(12), C1-C2 =
1.431(7), C2-C3 = 1.417(6), C2-N1 = 1.416(5), C3-N2 =
1.321(6), C1-O1 = 1.220(5); C1-P1-C3 = 71.82(19),
P1-C1-C2 = 92.4(3), C1-C2-C3 = 100.2(3), P1-C3-C2
= 95.0(3), C2-N1-C10 = 116.0(4), C2-N1-C13 = 112.8(4),
1
(CDCl3): δ 32.7 ppm (1JPW=249.5 Hz). H NMR (CDCl3): δ
C10-N1-C13
=
119.8(4), C3-N2-C16
=
119.2(4),
1.32, 1.34 (2s, 24 H, Me), 4.04 (m, 4 H, CH), 7.43, 8.03 (2 m, 5H,
Ph). The 13C NMR spectrum in CDCl3 appears to be very
complex: all the resonances corresponding to phenyl and car-
bonyl carbons are doubled, suggesting blocked rotations of the
phenyl and W(CO)5 groups around their bonds with phos-
phorus. Exact mass: m/z calcd for C26H33N2O5PSW [M þ H]
701.143, found 701.1431. Single crystals suitable for X-ray study
were obtained from CH2Cl2 at -20 °C.
Synthesis of the Phosphacyclobutenone 3. A solution of 1
(prepared from 245 mg (0.4 mmol) of the 7-phosphanorbornadiene
precursor2 and 110 mg (0.4 mmol) of diisopropylcyclopropenyli-
dene carbene2 in diglyme (2 mL)) and an excess of propylene oxide
(2 mL) were heated in a pressure tube at 110 °C for 4 h. The product
C3-N2-C19 = 117.8(4), C16-N2-C19 = 122.7(4).
the oxygen analogue of the zwitterionic sulfide 2. In order to
check this hypothesis, we decided to perform DFT calcula-
tions at the B3LYP/6-31G(d)-Lanl2dz (W) level7 on the
model compound 5. We were delighted to find that it
corresponds to a genuine minimum (no negative frequency).
Its computed structure is shown in Figure 3. As expected, the
three-membered ring is highly localized. The parameters of
the O-cyclopropene unit are very close to those computed for
the parent oxaspiropentene.1c Similarly, the computed para-
meters for 6 are in good agreement with those reported

1304 Organometallics, Vol. 29, No. 5, 2010
Tran Huy et al.
was purified by chromatography on silica gel with 1/4 hexane/
dichloromethane as the eluent; 170 mg of light yellow crystals was
obtained (62% yield). 31P NMR (CDCl3): δ 37.24 (1JP-W=226.2
Hz). 1H NMR (CDCl3): δ 1.16, 1.18 (2s, 12 H, Me), 1.38 (br, 12 H,
Me), 3.54 (m, 4H, CH), 7.50, 7.79 (2 m, 5H, Ph). 13C NMR
(CDCl3): δ 22.59, 23.24 (s br, CH3); 51.43, 62.01 (s br, CH), 126.19
(d, 1JCP=66.5 Hz, ipso C(Ph)), 128.99 (d, 3JCP=9.2 Hz meta CH
Ph), 130.99 (d, 2JCP=12.7 Hz, N-Cd), 131.65 (s, para CH Ph),
133.16 (d, 2JCP=11.4 Hz, ortho CH Ph), 176.27 (s, 1JCP=43.6 Hz,
N-Cd), 184.49 (d, 1JPC=25.2 Hz, CdO), 195.60 (d, 1JPC=5.8Hz,
cis CO), 198.24 (d, 2JPC=24.1 Hz, trans CO). Exact mass: m/z calcd
for C26H34N2O6PW (M þ H) 685.1664, found 685.1668. Single
crystals suitable for X-ray study were obtained from CH2Cl2/
hexane at -20 °C.
Acknowledgment. We thank the University of California
Riverside and Nanyang Technological University in
Singapore for financial support of this work.
Supporting Information Available: CIF files giving details of
the X-ray crystal structure analysis of compounds 2 and 3. This
material is available free of charge via the Internet at http://
pubs.acs.org.