The first free 7λ3-phosphanorbornadiene

Article abstract of DOI:10.1021/ja9942944

The first uncoordinated 7λ³-phosphanorbornadiene 10 is reported. This missing member of the class of 7-heteranorbornadienes was prepared by decomplexation of its pentacarbonyltungsten complex 6 with iodine and N-methylimidazole. It is moderately stable at room temperature toward loss of the phosphinidene bridge (PhP:) because the aromatic fragment, [5]metacyclophane (5), is a highly strained compound. For this reason, 10 may be considered to be a hyperstable compound. An analysis of the energetics of the system by density functional calculations supports this rationalization.

Full text of DOI:10.1021/ja9942944

3386
J. Am. Chem. Soc. 2000, 122, 3386-3390
The First Free 7λ3-Phosphanorbornadiene
Maurice J. van Eis, Herman Zappey, Franciscus J. J. de Kanter, Willem H. de Wolf,
Koop Lammertsma,* and Friedrich Bickelhaupt*
Contribution from the Scheikundig Laboratorium, Vrije UniVersiteit, De Boelelaan 1083,
1081 HV Amsterdam, The Netherlands
ReceiVed December 7, 1999
Abstract: The first uncoordinated 7λ3-phosphanorbornadiene 10 is reported. This missing member of the class
of 7-heteranorbornadienes was prepared by decomplexation of its pentacarbonyltungsten complex 6 with iodine
and N-methylimidazole. It is moderately stable at room temperature toward loss of the phosphinidene bridge
(PhP:) because the aromatic fragment, [5]metacyclophane (5), is a highly strained compound. For this reason,
10 may be considered to be a hyperstable compound. An analysis of the energetics of the system by density
functional calculations supports this rationalization.
Introduction
Scheme 1a
In this study we report the first synthesis of a moderately
stable derivative of 7λ3-phosphanorbornadiene (1a) containing
trivalent, uncoordinated phosphorus (Scheme 1). Such com-
pounds have, despite considerable effort, so far remained
elusive.1,2 Only two types of stabilized derivatives have been
described in which the phosphorus bridge was either oxidized
to a phosphine oxide or protected by metal complexation.
Stille and co-workers2 demonstrated the accessibility of
phosphine oxides which are analogues of 1b, but only if they
are stabilized by benzoanellation.3,4 However, all attempts to
reduce their PdO bond proved futile, presumably because the
reduced compounds rapidly extrude the phosphorus bridge.2
So far, the only stable derivatives of 1a have been the
complexes 1c, prepared by Mathey and Marietti in 1982,5 in
which phosphorus is coordinated to Cr(CO)5, Mo(CO)5, or
W(CO)5 (Scheme 1). At temperatures around 100 °C, these
decompose by cheletropic elimination to give a substituted
benzene and a transient terminal complexed phosphinidene
:P(R)M(CO)5 (2), which behaves as a versatile carbene-like
synthon.5
a
M ) Cr, Mo, W.
decreasing element-carbon bond strength and the increasing
stability of the divalent hetero-fragment.
In Group 14, the parent norbornadiene (1d) is thermally rather
stable. In contrast, 7-norbornadienone (1e) decarbonylates above
-30 °C to give benzene and CO, for which a synchronous
concerted pathway was proposed based on the low activation
energy of 63 ( 10 kJ mol-1 (Scheme 2).6 Such elimination
reactions have even been exploited for the synthesis of unstable
and unusual molecules. Thus, the fragmentation of 7-nor-
bornadieneazine (1f) furnished, besides benzene, the two highly
unstable C2N2 isomers of cyanogen, isocyanogen (3),7 and
diisocyanogen (4).8
The failure to obtain (a derivative of) 1a with a free trivalent
phosphorus is all the more peculiar against the background that
many 7-heteranorbornadienes are known which contain elements
of Groups 14-16 in the bridge position. Their stability depends
critically on the tendency for cheletropic elimination of the
hetero-bridge to give a stable aromatic fragment. This tendency
increases for the heavier elements, presumably due to the
7-Silanorbornadienes 1g, first prepared by Gilman and co-
workers in 1964,9 decompose above 250 °C with loss of the
silylene bridge (Scheme 3), possibly via a radical mechanism.10
(1) Kashman, Y.; Wagenstein, I.; Rudi, A. Tetrahedron 1976, 32, 2427.
(2) Stille, J. K.; Eichelberger, J. L.; Higgins, J.; Freeburger, M. E. J.
Am. Chem. Soc. 1972, 94, 4761.
(3) A report (Schmidt, U.; Boie, I.; Osterroht, C.; Schro¨er, R.; Gru¨tz-
macher, H. F. Chem. Ber. 1968, 101, 1381) claiming the synthesis of a
derivative of 1b has been refuted.4
(4) Matsumoto, K,; Hashimoto, S.; Otani, S.; Uchida, T. Heterocycles
1984, 22, 2713.
(6) (a) Birney, D. M.; Berson, J. A. J. Am. Chem. Soc. 1985, 107, 4553.
(b) LeBlanc, B. F.; Sheridan, R. S. J. Am. Chem. Soc. 1985, 107, 4554. (c)
Birney, D. M.; Berson, J. A. Tetrahedron 1986, 42, 1561. (d) Birney, D.
M.; Wiberg, K. B.; Berson, J. A. J. Am. Chem. Soc. 1988, 110, 6631 and
references cited.
(5) (a) Marinetti, A.; Mathey, F.; Fischer, F.; Mitschler, A. J. Chem.
Soc., Chem. Commun. 1982, 667. (b) Marinetti, A.; Mathey, F.; Fischer,
F.; Mitschler, A. J. Am. Chem. Soc. 1982, 104, 4484. (c) Marinetti, A.;
Mathey, F. Organometallics 1982, 1, 1488. (d) Marinetti, A.; Charrier, C.;
Mathey, F.; Fischer, F. Organometallics 1985, 4, 2134. (e) For a review
see: Mathey, F. Angew. Chem. 1987, 97, 285; Angew. Chem., Int. Ed. Engl.
1987, 26, 275.
(7) (a) van der Does, T.; Bickelhaupt, F. Angew. Chem. 1988, 100, 998;
Angew. Chem., Int. Ed. Engl. 1988, 27, 936. (b) Stroh, F.; Winnewisser, B.
P.; Winnewisser, M.; Reisenauer, H. P.; Maier, G.; Goede, S. J.; Bickelhaupt,
F. Chem. Phys. Lett. 1989, 160, 105.
(8) Maier, G.; Reisenauer, H. P.; Eckwert, J.; Sierakowski, C.; Stumpf,
T. Angew. Chem. 1992, 104, 1287; Angew. Chem., Int. Ed. Engl. 1992, 31,
1218.
10.1021/ja9942944 CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/25/2000

The First Free 7λ3-Phosphanorbornadiene
J. Am. Chem. Soc., Vol. 122, No. 14, 2000 3387
Scheme 2
Scheme 4
fragments, but not by the usual elimination of the bridging
nitrene :NH; instead, a retro-Diels-Alder reaction furnishes
pyrrole and acetylene (Scheme 3).15j Again, the higher analogues
of Group 15 with a PR bridge proved to be too unstable for
isolation.1,2
Scheme 3a
Results and Discussion
Synthesis of 10. In pursuit of an uncomplexed 7-phospha-
norbornadiene, it occurred to us that the tremendous driving
force for cheletropic elimination of the phosphorus bridge can
be diminished by destabilizing the second fragment, the aromatic
compound. This may be accomplished by incorporation of strain
in the latter, e.g. by bending the aromatic ring as in small
cyclophanes.16 Recently, we reported the synthesis of the
transition metal complexed 7-phosphanorbornadiene 6 by the
unprecedented 1,4-addition of PhPW(CO)5 (2a) to the highly
bent [5]metacyclophane (5) (Scheme 4).17 The extraordinary
thermal stability of 6 was explained by the unfavorable
thermodynamics for the retro reaction as the strain in 5 is much
higher than that in 6. We therefore envisioned 6 to be a
promising candidate for generating the elusive uncomplexed
7-phosphanorbornadiene system.
For this purpose, we applied a decomplexation method
reported by Mathey and co-workers for the preparation of
phosphirenes from the corresponding complexes.18 In this
approach, the P-W bond is weakened and finally cleaved by
first oxidizing W(0) to W(II) with iodine, followed by exchange
of the CO ligands with N-methylimidazole (MeIm).
Monitoring the addition of 1 equiv of I2 to a solution of 6 in
CD2Cl2 at -30 °C by 31P NMR spectroscopy showed two new
resonances at 153.4 and 148.0 ppm to emerge in a 3:2 ratio
which are tentatively assigned to two stereoisomers of the W(II)
complex 7 (Scheme 5). These isomers exchange slowly as
indicated by broadening of the signals on warming, with
coalescence occurring at room temperature. The reduced
a MeIm ) N-methylimidazol.
Likewise, 7-germanorbornadienes 1h extrude germylenes al-
ready around 150 °C.11 This trend of decreasing stability for
the heavier elements continues for 7-stannanorbornadienes 1i
which have not been isolated yet as they decompose on
attempted synthesis.12
7-Heteranorbornadienes of Group 16 are accessible by Diels-
Alder reactions of alkynes with furan13 and thiophene.14 The
heavier analogues with the 7-thia bridge are too unstable to
survive the (drastic) conditions required for their formation.
So far, only the nitrogen derivatives were known from the
Group 15 7-heteranorbornadienes.15 The parent system 1j was
prepared in 1982 by Vogel and co-workers. Above 80 °C, 1j
(15) (a) Wittig, G. Angew. Chem. 1957, 69, 245. (b) Mandell, L.;
Blanchard, W. A. J. Am. Chem. Soc. 1957, 79, 2343. (c) Mandell, L.;
Blanchard, W. A. J. Am. Chem. Soc. 1957, 79, 6198. (d) Wittig, G.;
Behnisch, W. Chem. Ber. 1958, 91, 2358. (e) Wittig, G.; Reichel, B. Chem.
Ber. 1963, 96, 2851. (f) Kitzing, R.; Fuchs, R.; Joyeux, M.; Prinzbach, H.
HelV. Chim. Acta 1968, 51, 888. (g) Bansal, R. C.; McCulloch, A. W.;
McInnes, A. G. Can. J. Chem. 1970, 48, 1472. (h) Anderson, P. S.; Christy,
M. E.; Lundell, G. F.; Ponticello, G. S. Tetrahedron Lett. 1975, 2553. (i)
Prinzbach, H.; Babsch, H. Heterocycles 1978, 11, 113. (j) Altenbach, H.
J.; Blech, B.; Marco, J. A.; Vogel, E. Angew. Chem. 1982, 94, 789; Angew.
Chem., Int. Ed. Engl. 1982, 21, 772. (k) Prinzbach, H.; Bingmann, H.; Fritz,
H.; Markert, J.; Knothe, L.; Eberbach, W.; Brokatzky-Geiger, J.; Sekutowski,
J. C.; Kru¨ger, C. Chem. Ber. 1986, 119, 616. (l) Altenbach, H. J.; Constant,
D.; Martin, H. D.; Mayer, B.; Mu¨ller, M.; Vogel, E. Chem. Ber. 1991, 124,
791.
(9) (a) Gilman, H.; Cottis, S. G.; Atwell, W. H. J. Am. Chem. Soc. 1964,
86, 1596. (b) Gilman, H.; Cottis, S. G.; Atwell, W. H. J. Am. Chem. Soc.
1964, 86, 5584.
(10) (a) Barton, T. J.; Goure, W. F.; Witiak, J. L.; Wulff, W. D. J.
Organomet. Chem. 1982, 225, 87. (b) Appler, H.; Gross, L. W.; Mayer,
B.; Neumann, W. P. J. Organomet. Chem. 1985, 291, 9.
(11) Neumann, W. P.; Schriewer, M. Tetrahedron Lett. 1980, 21 3273.
(12) Grugel, C.; Neumann, W. P.; Schriewer, M. Angew. Chem. 1979,
91, 577; Angew. Chem., Int. Ed. Engl. 1979, 18, 543.
(13) (a) Diels, O.; Alder, K. Liebigs Ann. Chem. 1931, 490, 243. (b)
Weis, C. D. J. Org. Chem. 1962, 27, 3520. (c) Eberbach, W.; Perroud-
Argu¨elles, M.; Achenbach, H.; Druckrey, E.; Prinzbach, H. HelV. Chim.
Acta 1971, 54, 2579. (d) Prinzbach, H.; Babsch, H. Angew. Chem. 1975,
87, 772; Angew. Chem., Int. Ed. Engl. 1975, 14, 753.
(14) (a) Helder, R.; Wynberg, H. Tetrahedron Lett. 1972, 605. (b) Kuhn,
H. J.; Gollnick, K. Chem. Ber. 1973, 106, 674.
(16) Bickelhaupt, F.; de Wolf, W. H. J. Phys. Org. Chem. 1998, 11,
362 and references cited.
(17) Van Eis, M. J.; Komen, C. M. D.; de Kanter, F. J. J.; de Wolf, W.
H.; Lammertsma, K.; Bickelhaupt, F.; Lutz, M.; Spek, A. L. Angew. Chem.
1998, 110, 1656; Angew. Chem., Int. Ed. Engl. 1998, 37, 1547.
(18) Marinetti, A.; Mathey, F.; Fischer, F.; Mitschler, A. J. Chem. Soc.,
Chem. Commun. 1984, 45.

3388 J. Am. Chem. Soc., Vol. 122, No. 14, 2000
Van Eis et al.
Scheme 5
coupling constants of 7 (major isomer: 1J (P,W) ) 142 Hz) as
compared to that of 6 (1J (P,W) ) 227 Hz) may signal a
weakened P-W bond.
C1 and C10 resonate at 57.60 and 50.16 ppm, respectively.
1
Whereas their coupling constants J(C,P) ) 62.1 and 52.4 Hz
confirm an intact norbornadiene structure, they are strikingly
To accomplish a stepwise exchange of the metal ligands of
7, we first added 1 equiv of MeIm at -30 °C. The resulting
new 31P NMR resonance at 179.5 ppm (1J(P,W) ) 172 Hz) is
tentatively assigned to 8. On addition of a second equivalent of
MeIm at -30 °C, 8 was converted to a new compound,
presumably 9 (δ(31P) ) 173.5 ppm, 1J(P,W) ) 127 Hz), which
is extremely air sensitive, but stable at room temperature under
inert conditions. Only upon addition of a third equivalent of
MeIm did a slow decomposition take place (at 298 K, first-
order kinetics with a half-life time of 6 h) under formation of
a new organophosphorus compound having a 31P NMR reso-
nance at 112 ppm without P,W coupling. To this compound,
we assign the structure of the uncomplexed 7λ3-phosphanor-
bornadiene 10.
Characterization of 10. Attempts to isolate 10 were unsuc-
cessful because it decomposes at room temperature and did not
survive attempted chromatographic purification. However, its
structure was corroborated by NMR spectroscopy and by direct
inlet HR-MS.
The phosphorus nucleus of 10 is strongly deshielded for a
tertiary phosphine, but similar shifts in the range of 60-150
ppm have been reported for related 7-phosphanorbornenes.19
A theoretical study20 attributed this deshielding to anisotropy
effects and predicted that incorporation of a second double bond,
as in the corresponding 7-phosphanorbornadiene, would cause
stronger shielding of the phosphorus. However, in the present
case we find this effect on the chemical shift to be small.
The identity of 10 is further supported by its 1H and 13C NMR
spectra, which are closely related to those of its W(CO)5
complex 6.17 Indicative are the olefinic protons, which appear
as two doublets at 6.20 and 5.87 ppm. The bridgehead carbons
different from those of 6 (1J(C,P) ) 26.2 and 20.2 Hz). An
1
analogous increase of J(C,P) on decomplexation is found in
the couple (pentacarbonyltungsten)phosphirane ([C2H4PH]W-
(CO)5, 1J(C,P) ) 10.4 Hz21) and phosphirane (C2H4PH:, 1J(C,P)
) 33 Hz22).23
At room temperature, 10 slowly fragments (half-life time of
about 1 day) into [5]metacyclophane (5) and presumably
phenylphosphinidene (11), which, however, did not form
products detectable by 31P NMR spectroscopy. The recovery
of 5 was estimated at 80%, based on the appearance of its
characteristic 1H NMR resonance at 0.25 ppm. Attempted
analysis by GCMS revealed that under these conditions, 10 is
also completely converted to 5 as the sole detectable product.
Calculational Analysis. We were struck by the ease of
formation of 5 in view of its high strain energy of 174 kJ mol-1
(DFT)24 and because 7-azanorbornadienes disproportionate by
a different pathway yielding pyrroles and alkynes (cf. 1j, Scheme
3).15j We therefore applied density functional calculations
(B3LYP/6-31G*[25]) to distinguish between the two decomposi-
tion modes for the parent systems 1j and 1a, namely either by
a retro cycloaddition giving the five-membered heterocycles
[pyrrole (12j) and phosphole (12a), respectively] together with
acetylene (Scheme 6, pathway a) or by a chelotropic elimination
of the bridge [as singlet nitrene (13) or phosphinidene (14),
respectively] furnishing benzene as the second fragment (path-
way b).
Pathway a is strongly favored for the 7-azanorbornadiene 1j
(∆H298(a) ) +1.0 kJ mol-1, ∆H298(b) ) +237 kJ mol-1), in
agreement with experimental observations.15j In contrast, the
(21) Deschamps, B.; Ricard, L.; Mathey, F. Polyhedron 1989, 8, 2671.
(22) Goldwhite, H.; Rowsell, D.; Vertal, L. E.; Bowers, M. T.; Cooper,
M. A.; Manatt, S. L. Org. Magn. Reson. 1983, 21, 494.
(23) We thank a referee for pointing out this analogy.
(24) van Eis, M. J.; de Wolf, W. H.; Bickelhaupt, F.; Boese, R. J. Chem.
Soc., Perkin Trans. 2. In press.
(19) Quin, L. D. In ReViews on Heteroatom Chemistry Compounds; Oae,
F. S., Ed.; Ohno, A., Furukawa, N., Associate Eds.; MYU: Tokyo, 1990;
Vol. 3, pp 39-74.
(20) Wilcox, C. F., Jr.; Gleiter, R. J. Org. Chem. 1989, 54, 2688.

The First Free 7λ3-Phosphanorbornadiene
J. Am. Chem. Soc., Vol. 122, No. 14, 2000 3389
Scheme 6
7-phosphanorbornadiene 1a slightly favors pathway b, i.e., the
elimination of phosphinidene (14) (∆H298(a) ) +113 kJ mol-1
,
∆H298(b) ) +108 kJ mol-1). This preference becomes more
pronounced on phenyl substitution at phosphorus (1k) as it
stabilizes the resulting phenylphosphinidine (11) considerably
(∆H298(a) ) +112 kJ mol-1, ∆H298(b) ) +42 kJ mol-1).26 It
is clear that the elimination of a phosphinidene is the preferred
reaction channel for a 7-phosphanorbornadiene, in accordance
with our experimental observation.
While a comprehensive analysis of the different reaction
channels available to 10 was beyond our resources, the
computed enthalpy for dissociation into 5 and 11 amounts to
∆H298(b) ) +201 kJ mol-1. The impressive difference of
∆∆H298(b) ) +159 kJ mol-1 for the fragmentations of 10 and
1k largely reflects the strain in [5]metacyclophane 5 (∆H(SE))
174 kJ mol-1),24 and explains the stability of 10 relative to that
of “normal” derivatives of 1a that do not contain a pentameth-
ylene bridge.
Figure 1. Calculated structure of 10. Selected bond lengths [Å] and
angles [deg]: P11-C13 1.853, P11-C1 1.913, P11-C10 1.919, C1-
C2 1.535, C1-C12 1.540, C2-C3 1.340, C3-C10 1.529, C9-C12
1.344, C9-C10 1.534; C13-P11-C1 106.7, C13-P11-C10 105.8,
C1-P11-C10 76.9, C2-C1-C12 107.2, C2-C1-P11 103.8, C12-
C1-P11 94.6, C3-C2-C1 110.5, C2-C3-C10 109.2, C12-C9-C10
109.0, C9-C10-C3 106.0, C9-C10-P11 96.1, C3-C10-P11 105.1,
C9-C12-C1 110.5, C3-C4-C5 113.6, C4-C5-C6 118.8, C5-C6-
C7 118.0, C6-C7-C8 118.8, C7-C8-C9 113.2; C1-C2-C3-C4
165.8, C8-C9-C12-C1 167.6.
Finally, we note that the calculated structure of 10 (Figure
1) closely resembles the X-ray crystal structure of 6.17 Decom-
plexation has only a minor influence on the 7-phosphanorbor-
nadiene skeleton. The differences between 10 and the unbridged
analogue 1k (Figure 2) are more striking. For example, the
C1-P bond of 10 (1.913 Å) is shorter than that of 1k (1.941
Å), reflecting a tighter binding of the phosphorus bridge. Also
in contrast to 1k, but similar to the W(CO)5 complex 6,17 the
double bonds in 10 are strongly twisted (-165.8° [C1-C2-
C3-C4] and 167.6(4)° [C8-C9-C12-C1]). This, together with
the large C-C-C angles in the pentamethylene bridge (118.0-
118.8°), signals a significant degree of strain in 10, though much
less than that in 5.
Figure 2. Calculated structure of 1k. Selected bond lengths [Å] and
angles [deg]: P7-C8 1.852, P7-C1 1.941, P7-C4 1.925, C1-C2
1.526, C1-C6 1.532, C2-C3 1.336, C3-C4 1.531, C4-C5 1.535,
C5-C6 1.340; C8-P7-C1 106.4, C8-P7-C4 106.5, C1-P7-C4
76.9, C2-C1-C6 108.5, C2-C1-P7 103.1, C6-C1-P7 93.9, C1-
C2-C3 110.5, C2-C3-C4 110.3, C3-C4-C5 108.3, C4-C5-C6
110.3, C3-C4-P7 103.4, C5-C4-P7 94.1, C5-C6-C1 110.3.
Conclusion
The first free 7λ3-phosphanorbornadiene derivative 10 has
been prepared by decomplexation of its pentacarbonyltungsten
(25) All B3LYP/6-31G* calculations were performed with the Gaussian
98 suite of programs: Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria,
G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J.
A., Jr.; 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.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A.; Gaussian, Inc.: Pittsburgh,
PA, 1998.
complex 6. On one hand, the propensity of 10 toward elimina-
tion of the bridging group is in line with the trend observed for
other 7-heteranorbornadienes with heavier elements in the
bridge. On the other hand, its stability at room temperature, be
it only moderate, is remarkable because all previous attempts
to obtain a simple, unbridged 7λ3-phosphanorbornadiene had
failed.
Obviously, 10 owes its kinetic stabilization to the overall
increase in strain that results on dissociation. Normally, the
stability of the aromatic fragment is the thermodynamic driving
force for the fragmentation process. In the present case, the
considerable energy content of the highly strained aromatic
fragment, [5]metacyclophane (5), reduces the rate of this
(26) Note that these reaction enthalpies do not take into account
stabilization in the condensed phase, which should further reduce the
endothermicities for elimination of the high energy species nitrene and
phosphinidene.

3390 J. Am. Chem. Soc., Vol. 122, No. 14, 2000
Van Eis et al.
certainty and which are of essence for the identity of 9 are listed. 31P
NMR (162.0 MHz, CD2Cl2, 298 K): δ 173.6 (1J(P,W) ) 127 Hz). 1H
NMR (400.13 MHz, CD2Cl2, 298 K): δ 8.25 (bs; 2H), 7.64 (s; 2H),
7.56 (s; 2H), 7.17-7.09 (m; 4H), 6.88 (dd, 3J(H,P) ) 20.8 Hz, 3J(H,H)
) 4.2 Hz; o-Ar), 6.20 (dd, 3J(H,P) ) 11.1 Hz, 3J(H,H) ) 4.1 Hz; H12),
fragmentation. In this respect, 10 can be considered to be a
hyperstable derivative.
We feel that the strategy applied for the preparation of 10,
i.e., making the 7-heteranorbornadiene skeleton hyperstable
through bridging of the 2- and 6-positions by a short (oligo-
methylene) chain, will give access to other hitherto unknown
representatives of this class, notably those of sulfur and tin.
3
3
6.01 (dd, J(H,P) ) 8.6 Hz, J(H,H) ) 4.0 Hz; H2), 4.25 (m; H1),
4.07 (bs; H10), 3.79 (s, 6H), 3.10-0.75 (m; 10H). 13C{1H} NMR
(100.64 MHz, CD2Cl2, 298 K): δ 203.2 (s; CO), 198.3 (s; CO), 158.2
2
2
(d, J(C,P) ) 10.2 Hz; C3), 156.2 (d, J(C,P) ) 19.4 Hz; C9), 61.60
(d, 1J(C,P) ) 34.2 Hz; C1), 52.10 (d, 1J(C,P) ) 25.9 Hz; C10), 37.49
(s; CH3), 37.00 (s; CH3), 35.55 (s; CH2), 35.47 (s; CH2), 35.44 (s; CH2),
34.77 (s; CH2), 26.50 (s; C6).
Experimental Section
Tetracarbonyliodo[11-phenyl-11-phosphatricyclo[7.2.1.03,10)dodeca-
2,9(12)-diene]tungsten Iodide (7). Under nitrogen a solution of 617
(28.9 mg, 0.050 mmol) in CD2Cl2 (400 µL) was prepared in a 5 mm
NMR tube. After the mixture was cooled to -30 °C, a solution of I2
(12.7 mg) in 200 mL of CD2Cl2 was added. The NMR tube was capped
with a Teflon cap and slowly warmed to room temperature. At this
point, the extrusion of CO was indicated by gas evolution. After the
evolution of CO had ceased, NMR spectra of the solution were recorded
at -30 °C. 31P NMR (162.0 MHz, CD2Cl2, 243 K): δ 153.4 (1J(P,W)
) 142 Hz), major isomer (59.4%); δ 148.0 (the signal was too broad
to determine 1J(P,W)), minor isomer (41.6%). 1H NMR (400.13 MHz,
11-Phenyl-11-phosphatricyclo[7.2.1.03,10)dodeca-2,9(12)-diene (10).
To an NMR tube containing a solution of 9 (vide supra) in CD2Cl2
(700 µL) was added under nitrogen at room temperature N-methyl-
imidazole (16.4 mg, 0.20 mmol). The tube was tightly capped with a
Teflon cap and the decomposition of 9 was monitored by 31P NMR
spectroscopy. The complexity of the reaction mixture prevented the
complete identification of all resonances of 10. The most revealing
signals are listed below. 31P NMR (162.0 MHz, CD2Cl2, 298 K): δ
112.5. 1H NMR (400.13 MHz, CD2Cl2, 298 K): δ 6.20 (dd, 3J(H,P) )
12.7 Hz, 3J(H,H) ) 4.4 Hz; H12), 5.87 (dd, 3J(H,P) ) 13.0 Hz, 3J(H,H)
) 4.6 Hz; H2). 13C{1H} NMR (100.64 MHz, CD2Cl2, 298 K): δ 57.60
3
CD2Cl2, 298 K): δ 7.43-7.18 (m, 5H), 6.33 (dd, J(H,P) ) 6.3 Hz,
3
3
3J(H,H) ) 4.0 Hz; H12), 6.02 (dd, J(H,P) ) 4.2 Hz, J(H,H) ) 4.2
Hz; H2), 4.25 (bs; H1), 3.93 (bs; H10), 2.80-0.80 (m; 10H).
Tricarbonyliodo(N-methylimidazole)[11-phenyl-11-phosphatricyclo-
[7.2.1.03,10]dodeca-2,9(12)-diene]tungsten Iodide (8). To an NMR tube
containing a solution of 7 (vide supra) in CD2Cl2 (600 µL) was added
under nitrogen at - 30 °C a solution of N-methylimidazole (4.1 mg,
0.050 mmol) in CD2Cl2 (50 µL). The solution immediately changed
color from deep orange to pale yellow. 31P NMR (162.0 MHz, CD2Cl2,
243 K): δ 179.5 (1J(P,W) ) 172 Hz).
1
1
(d, J(C,P) ) 62.1 Hz; C1), 50.16 (d, J(C,P) ) 52.4 Hz; C10); MS-
DI (70 eV) m/z (%): 256 (variable, only at higher pressures) [M +
2)+), 254 (3.8) [M+], 252 (8.4), 250 (4.4), 236 (27.0), 234 (34.9), 173
(77.0), 155 (100), 153 (57.1), 141 (17.1), 128 (37.3), 115 (52.4), 91
(30.2), 82 (94.9), 77 (35.7), 58 (65.1); HR-MS (direct inlet) C19H19P
(M+) Calcd.: m/z 254.1224. Found: 254.1231 ( 0.0009. Due to the
instability of 10 at room temperature, an elemental analysis was not
obtained.
Dicarbonyliodobis(N-methylimidazole)[11-phenyl-11-phospha-
tricyclo[7.2.1.03,10]dodeca-2,9(12)-diene]tungsten Iodide (9). To an
NMR tube containing a solution of 8 (vide supra) in CD2Cl2 (650 µL)
was added under nitrogen at - 30 °C a solution of N-methylimidazole
(4.1 mg, 0.050 mmol) in CD2Cl2 (50 µL). The tube was tightly capped
with a Teflon cap and transferred to the NMR probe. Unfortunately
some signals in the 13C NMR spectrum of 9 were obscured by
impurities. Therefore, only those signals which could be assigned with
Acknowledgment. The authors thank the Section of Theo-
retical Chemistry, Vrije Universiteit, for computing time. These
investigations have been supported by the Council for Chemical
Sciences (GCW) with financial aid from The Netherlands
Organization for Scientific Research (NWO).
JA9942944