Phospha[3]radialenes. Syntheses, structures, strain energies, and reactions

Article abstract of DOI:10.1021/ja002437c

In situ-generated terminal phosphinidene complex PhPW(CO) ₅ adds in a 1,2-fashion to the terminal double bond of tetramethylcumulene and cyclic 1,2,3-cyclodecatriene. The resulting alkenylidenephosphiranes 19A and 20A, which are three-membered

Full text of DOI:10.1021/ja002437c

J. Am. Chem. Soc. 2000, 122, 12507-12516
12507
Phospha[3]radialenes. Syntheses, Structures, Strain Energies, and
Reactions
Corine M. D. Komen,† Chris J. Horan,‡ Steffen Krill,‡ Gary M. Gray,‡ Martin Lutz,§
Anthony L. Spek,§ Andreas W. Ehlers,† and Koop Lammertsma*,†,‡
Contribution from the Department of Chemistry, Faculty of Sciences, Vrije UniVersiteit, De Boelelaan
1083, 1081 HV Amsterdam, The Netherlands, the Department of Chemistry, UniVersity of Alabama,
Birmingham, Alabama 35294, and the BijVoet Center for Biomolecular Research, Crystal and
Structural Chemistry, Utrecht UniVersity, Padualaan 8, 3584 CH Utrecht, The Netherlands
ReceiVed July 5, 2000. ReVised Manuscript ReceiVed September 29, 2000
Abstract: In situ-generated terminal phosphinidene complex PhPW(CO)5 adds in a 1,2-fashion to the terminal
double bond of tetramethylcumulene and cyclic 1,2,3-cyclodecatriene. The resulting alkenylidenephosphiranes
19A and 20A, which are three-membered phosphiranes containing an exocyclic allenic group, subsequently
rearrange to the corresponding phospha[3]radiales 19B and 20B, which are phosphiranes having two exocyclic
double bonds. All four organophosphorus compounds were characterized by single-crystal X-ray structure
determinations. Bicyclic 20A contains a significantly bent (171.5(7)°) and twisted (14.2(8)°) allenic unit in
contrast to 19A. The rearrangement to the thermodynamically favored radialenes is considered to occur by a
phosphirane ring opening/closure sequence. On using a second equivalent of PhPW(CO)5, insertion takes place
into a PC bond of 20B, but not of 19B, to give two new phospha[4]radialene isomers, viz. cis-20C and trans-
20C, both of which were characterized by crystal structure determinations. The PPCC ring in these systems
is significantly puckered (∼150°), causing the olefinic bonds of the butadiene unit to be much twisted from
planarity. Both phospha[3]radialenes undergo Diels-Alder reactions with methyl-1,2,4-triazole-3,5-dione
(MTAD), resulting in the case of the acyclic cumulene in the expected addition product 19D of which the
phosphirane ring easily hydrolyzes. Cycloaddition of MTAD to 20B does not occur at the radialene’s diene
unit but rather invokes one of its PC bonds, possibly in a concerted [(σ2 + π2) + π2] mechanism, to give the
unexpected adduct 20F. Ab initio theoretical studies on the parent systems, using the G3(MP2) method, show
phospha[3]radialene to be 3.6 kcal/mol more stable than ethenylidenephosphirane. Their strain energies (SE)
are calculated to be 32.3 and 29.7 kcal/mol, respectively. The 22.2 kcal/mol SE of phosphirane increases by
5.9 kcal/mol on introducing one exocyclic double bond and by another 4.2 kcal/mol on introducing the second
one. Still, the SE of phospha[3]radialene is less than the 39.0 kcal/mol of the more condensed phosphirene.
Introduction
contain three-membered heterocycles.3 This is especially the case
for organophosphorus compounds despite the close relationship
between carbon and phosphorus,4 and even though the three-
membered phosphiranes and the unsaturated phosphirenes are
well accessible, particularly as transition metal stabilized
complexes.5 Recently, we reported on the synthesis and proper-
ties of phosphiranes containing one6 and two spiroannelated
rings7 and those having one exocyclic double bond.8 In the
present study, we extend this work to phospha[3]radialenes and
also report on new diphospha[4]radialenes.
The interplay of small rings with unsaturated bonds has
yielded an array of intriguing hydrocarbons ranging from
radialenes to spiroannelated rotanes and triangulanes.1 The strain
energy and electronic properties of the cyclopropane ring are
prominent in these systems.2 Far fewer systems are known that
* To whom correspondence should be addressed at the Amsterdam
address.
† Vrije Universiteit.
‡ University of Alabama at Birmingham.
So far, phospha[3]radialenes have been reported by three
synthetic routes. Yoshifuji and co-workers9 used the CCl2
carbene addition to a heavily substituted terminal phosphacu-
mulene to generate ethenylidenephosphirane 1A, which rear-
§ Utrecht University.
(1) See, for example: (a) Greenberg, A.; Liebman, J. F. Strained Organic
Molecules; Academic Press: New York, 1978. (b) Wiberg, K. B. Angew.
Chem., Int. Ed. Engl. 1986, 25, 317. (c) The Chemistry of the Cyclopropyl
Group; Rappoport, Z., Ed.; Wiley: Chichester, 1987; 2 Vols. (d) Topical
issue, Strained Organic Compounds. Chem. ReV. 1989, 89 (5). (e) Pihlaja,
K.; Taskinen, E. Physical Methods in Heterocyclic Chemistry; Academic
Press: New York, 1978; Vol. 6, p 199. (f) Houben-Weyl; de Meijere, A.,
Ed.; Thieme: Stuttgart, 1997; Vol. E, pp 17a-c.
(2) For a recent review, see: (a) de Meijere, A.; Kozhushkov, S. In
AdVances in Strain in Organic Chemistry; Halton, B., Ed.; JAI Press Inc.:
London, 1995: Vol. 4, pp 225-282. See also: (b) de Meijere, A.;
Kozhushkov, S. I.; Khlebnikov, A. F. Zh. Org. Khim. 1996, 32, 1607; Russ.
J. Org. Chem. (Engl. Transl.) 1996, 32, 1555. (c) Zefirov, N. S.; Kuznetsova,
T. S.; Eremenko, O. V.; Kokoreva, O. V.; Zatonsky, G.; Ugrak, B. I. J.
Org. Chem. 1994, 59, 4087. (d) Eaton, P. E.; Lukin, K. A. J. Am. Chem.
Soc. 1993, 115, 11370. (e) Fitjer, L.; Conia, J. M. Angew. Chem., Int. Ed.
Engl. 1973, 12, 761.
(3) General three-ring heterocycles. Mathey, F. Chem. ReV. 1990, 90,
997.
(4) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon
Copy; Wiley: Chichester, 1998.
(5) Mathey, F. Angew. Chem., Int. Ed. Engl. 1987, 26, 275.
(6) Hung, J.-T.; Yang, S.-W.; Gray, G. M.; Lammertsma, K. J. Org.
Chem. 1993, 58, 6786.
(7) Lammertsma, K.; Wang, B.; Hung, J.-T.; Ehlers, A. W.; Gray, G.
M. J. Am. Chem. Soc. 1999, 121, 11650.
(8) Krill, S.; Wang, B.; Hung, J.-T.; Horan, C. J.; Gray, G. M.;
Lammertsma, K. J. Am. Chem. Soc. 1997, 119, 8432.
(9) Miyahara, I.; Hayashi, A.; Hirotsu, K.; Yoshifuji, M.; Yoshimura,
H.; Toyota, K. Polyhedron 1992, 11, 385.
10.1021/ja002437c CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/01/2000

12508 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Komen et al.
ranges to radialene 1B (eq 1). Maercker and Brieden10 used a
Scheme 1
condensation route in which dichlorophosphines were reacted
with a dynamic mixture11 of dilithio 2,5-dimethylhexadienes and
showed the ethenylidenephosphiranes to convert into the (sym-
metrically substituted) phospha[3]radialenes 2B-6B (eq 2). A
tane 136 and phospha[3]triagulene 14,7 which result from the
respective addition to alkylidenecyclopropane and bicyclopro-
pylidene (Scheme 1). These compounds are surprisingly stable
despite their significant strain energies (SE). Thus, calculations
with the G2(MP2) ab initio method showed the parent uncom-
plexed, nonsubstituted 15 to be 10.6 kcal/mol more strained
transition metal decomplexation route leading directly to 7B
was recently described by Marjoral and co-workers (eq 3).12 It
than the cumulative ring strain of the separate rings of which
phosphirane 16 has an SE of 21.3 kcal/mol.7 For parent phospha-
[3]radialene 18, a larger SE of 35.8 kcal/mol has been reported,
be it at the modest HF/6-31G* level of theory.19 In the present
study, we explore the reactivity of 11 toward cumulenes and
address the effect of unsaturation on the phosphirane ring strain
in 17 and 18 in more detail.
is noteworthy that the groups of both Yoshifuji and Maercker
observed rearrangements to the phospha[3]radialenes whereas
Breen and Stephan13 did not report such a rearrangement for
8A, which was synthesized from reaction of the nucleophilic
phosphinidene 914 with 1,4-dichloro-2-butyne (eq 4). It is evident
Results and Discussion
Two cumulenes were investigated, 2,5-dimethyl-2,3,4-
hexatriene (19) and cyclic 1,2,3-cyclodecatriene (20). The cyclic
system, which carries only two substituents, was considered to
be of interest also because of its anticipated influence of the
carbon ring-induced strain on the cumulenic unit. We first
discuss the phosphinidene addition reaction to the cumulenes,
then analyze the structures of the resulting organophosphorus
compounds, discuss their strain energies, and last present
insertion reactions, leading to 1,2-diphospha[4]radialenes and
to Diels-Alder addition reactions. Structures, energies, and
strain energies of parent systems (no substituents, no transition
metal complex) are based on ab initio theoretical calculations.
For clarity and consistency we label alkenylidenephosphiranes
as A, phospha[3]radialenes as B, phospha[4]radialenes as C,
and Diels-Alder products as D-G.
that these approaches are somewhat limited by the choice of
starting materials. The only phospha[4]radialene we are aware
of was reported by Brieden and Kellersohn,15 who synthesized
4C via 4A and 4B (eq 2) and thereby illustrated that access to
the higher homologues is even more tedious.
Our approach toward the radialenes makes use of the carbene-
like reactivity of PhPW(CO)5 (10).5a,16 This phosphinidene is
generated in situ from thermal decomposition of phosphanor-
bornadiene 11 and adds to olefins to give phosphiranes in good
yield.17 Addition to cumulenes would then be a simple and
effective way to generate the desired compounds. 10 and even
i
the less electrophilic Pr2NPFe(CO)4 also react with allenes.18
An X-ray crystal structure was reported not only for methyl-
From Cumulene to Phospha[3]radialene. Reaction of
terminal phosphinidene complex PhPW(CO)5, generated in situ
from 7-phosphanorbornadiene precursor 10 in toluene at 55 °C
and catalyzed by CuCl,17,20 with the tetramethyl derivative 19
enephosphirane 128 but also for the strained phosphaspiropen-
(10) Maercker, A.; Brieden, W. Chem. Ber. 1991, 124, 933.
(11) Maercker, A.; Wunderlich, H.; Girreser, U. Tetrahedron 1996, 52,
6149.
(12) Mahieu, A.; Miquel, Y.; Igau, A.; Donnadieu, B.; Majoral, J.-P.
Organometallics 1997, 16, 3086.
(13) Breen, T. L.; Stephan, D. W. J. Am. Chem. Soc. 1995, 117, 11914.
(14) Hou, Z.; Breen, T. L.; Stephan, D. W. Organometallics 1993, 12,
3158.
(15) Brieden, W.; Kellersohn, T. Chem. Ber. 1993, 126, 845.
(16) Lammertsma, K.; Chand, P.; Yang, S.-W.; Hung, J.-T. Organome-
tallics 1988, 7, 1875.
(17) (a) Marinetti, A.; Mathey, F. Organometallics 1982, 1, 1488. 6. (b)
Marinetti, A.; Mathey, F.; Fischer, J.; Mitschler, A. J. Am. Chem. Soc. 1982,
104, 4484. (c) Marinetti, A.; Mathey, F. Organometallics 1984, 3, 456. (d)
Hung, J.-T.; Lammertsma, K. J. Org. Chem. 1993, 58, 1800.
(18) Wit, J. B. M.; van Eijkel, G. Th.; de Kanter, F. J. J.; Schakel, M.;
Ehlers, A. W.; Lutz, M.; Spek, A. L.; Lammertsma, K. Angew. Chem., Int.
Ed. Engl. 1999, 38, 2596.
(19) Bachrach, S. M. J. Phys. Chem. 1993, 97, 4996.

Phospha[3]radialenes
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12509
Table 1. 31P NMR Chemical Shifts of Alkenylidenephosphiranes
(A) and Phospha[3]radialenes (B)
gives in 70% isolated yield a 1:1 mixture of alkenylidenephos-
phirane 19A and phopha[3]radialene 19B (eq 5). Heating 19A
cmpd P-R R1 R2
R3 R4
M
A
B
ref
20 Ph
19 Ph
H
-(CH2)6-
H
W(CO)5 -131.4 -153.0
a
a
9
Me Me Me Me W(CO)5 -112.8 -155.0
1
7
6
5
4
3
2
8
Mes* Cl Cl
t-Bu Ph
Ph
t-Bu Me Me Me Me
i-Pr Me Me Me Me
Et
Me
Ph
Ph
Ph
H
-60.5 -115.7
H
-131.1 12
-139.8 -183.4 10
-149.3 10
Me Me Me Me
-124.5 -162.8 10
-137.2 -177.7 10
-152.8 -195.4 10
Me Me Me Me
Me Me Me Me
Mes* H
H
H
H
-149.6
13
a This work.
in toluene at 100 °C for 2 h gives full conversion to 19B.
Likewise, reaction of 10 with the cyclic triene 20 gives in 46%
isolated yield a 1:2 mixture of phospha[3]radialene 20B and
cyclic alkenylidenephosphirane 20A, which also fully converts
to the radialene on heating in toluene (eq 6). All products could
the C(3)BP bond. Radialene 18 is indeed more stable than
alkenylidenephosphirane 17 by 2.9 kcal/mol using the ab initio
G3(MP2) method. This relative stability order is also in accord
with the rearrangements of the uncomplexed systems of
Yoshifuji9 (1A f 1B) and of Maercker and Brieden10 (2A-
6A vs 2B-6B, respectively). Breen and Stephan13 synthesized
by a rather different route alkenylidenephosphirane 8A, which
was well identified by its characteristic 31P and 13C NMR
chemical shifts of δ -149.6 (P) and 200,5 (dCd) ppm,
respectively, but they did not report the presence of any radialene
in the reaction mixture.
(2) NMR Chemical Shifts. 31P NMR spectroscopy is ideally
suited for initial product identification and for monitoring the
conversion of the alkenylidenephosphiranes to the more stable
radialenes. Their 31P NMR chemical shifts are compiled in Table
1 together with literature data on uncomplexed products.
The phosphorus chemical shifts of the alkenylidenephos-
phiranes are in all cases deshielded by an average of 40 ppm
from those of the corresponding phospha[3]radialenes, which
have smaller CPC angles and therefore have more shielded
P-resonances. Only for 20 is this difference much less, i.e., 21.6
ppm, possibly indicating the presence of strain in 20A; the
W(CO)5 complexed phospha[3]radialenes 19B and 20B have
similar 31P chemical shifts of ∼-154 ppm. For comparison,
phosphirene complex 23 has a δ of -161.4 ppm.17b On the other
be separated by column chromatography, enabling spectroscopic
characterization of the four structures including single-crystal
X-ray structure determinations.
(1) Reactivities. The sequence of events indicates both 19A
and 20A to be the kinetic products which subsequently rearrange
to the corresponding radialenes 19B and 20B as the thermo-
dynamically more stable products. The electrophilic phosphin-
idene apparently has a higher affinity for the terminal, conju-
gated unsaturated bonds of the cumulenes than for their central
olefinic bonds. This intramolecular preference for a conjugated
diene over an isolated double bond was recently also observed
i
in the reaction of Pr2PFe(CO)4 with tetramethyldiallene, but
the resulting vinylphosphirane 21 could not be isolated as it
rearranges under the reaction conditions to phospholene 22 (eq
7).18 Other examples of similar 1,3-sigmatropic shifts have been
hand, the 31P NMR resonance of 20A of -112.8 ppm is at much
lower field than the δ of -134.8 ppm for the related 2-isopro-
pylidene-3,3-dimethylphosphirane (12-Me2),8 which may, how-
ever, illustrate an electronic effect of the allenic bond. The
chemical shifts listed in Table 1 show a sensitivity to the nature
of the P-substituent. Increasing its size from Me, Et, i-Pr, to
t-Bu in the respective uncomplexed radialenes 2, 3, 4, and 5
causes the phosphorus to deshield, by as much as 50 ppm.
Resonance stabilization by a Ph group (6), on the other hand,
has a significant shielding effect, while W(CO)5 complexation
(2B) causes a downfield shift of 30 ppm. Substituents at both
the olefinic bonds and the phosphirane ring also influence the
31P NMR chemical shift of A. We therefore decided to calculate
the 31P, 13C, 1H NMR chemical shifts (using the GIAO method)
for the parent molecules 17 and 18 using MP2/6-31G* optimized
reported recently, either concerted or biradicaloid,21 but such a
process is not feasible for 19A and 20A. However, vinylphos-
phiranes have also been shown to epimerize at the P-center,22
suggesting a CBP bond cleavage-closure sequence to give the
thermodynamically more stable isomer. A related pathway may
underlie the conversion of A into B.
Formation of radialenes from 19B and 20B would require
rupture of the C(1)BP distal bond and subsequent closure of
(21) van Eis, M. J.; Nijbacker, T.; de Kanter, F. J. J.; de Wolf, W. H.;
Lammertsma, K. Bickelhaupt, F. J. Am. Chem. Soc. 2000, 122, 3033.
(22) Wang, W.; Lake, C. H.; Lammertsma, K. J. Am. Chem. Soc. 1996,
118, 1690.
(20) Marinetti, A.; Mathey, F.; Fischer, J.; Mitschler, J. J. Chem. Soc.
Chem. Commun. 1984, 45. Marinetti, A.; Fischer, J.; Mathey, F. J. Am.
Chem. Soc. 1985, 107, 5001.

12510 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Komen et al.
Figure 1. 31P, 13C, and 1H NMR computed chemical shifts using MP2/
6-31G* geometries for 17 (left) and 18.
Figure 3. ORTEP presentation scaled to 50% probability ellipsoids
of 20A.
Table 2. Selected Bond Distances (in Å) and CPC Angles (in deg)
for the X-ray Structures of 19A, 20A, 12, and 13, the Theoretical
Structures of 17 and 25, and the Microwave Structure of 16
bond
19A
20A
12a
13b
17
25a
16c
P-C(1)
P-C(2)
1.881(8) 1.855(6) 1.85(1) 1.855(7) 1.888 1.905 1.867
1.784(8) 1.791(6) 1.776(8) 1.794(6) 1.824 1.818 1.867
C(1)-C(2) 1.505(12) 1.506(9) 1.47(1) 1.508(9) 1.466 1.460 1.502
C(2)-C(3) 1.291(11) 1.288(9) 1.31(1) 1.470(1) 1.294 1.330
1.475(10)
Figure 2. ORTEP presentation scaled to 50% probability ellipsoids
of 19A.
C(3)-C(4) 1.303(12) 1.283(9)
1.315
P-C(6)
1.818(7) 1.809(6) 1.799(7) 1.819(7)
C(1)PC(2) 48.4(4)
48.8(3) 47.8(4) 48.6(3)
46.5 51.2 47.4
geometries and Me3PO and Me4Si as references, respectively.
These data are displayed in Figure 1. They illustrate that the
31P NMR chemical shifts of the parent systems are, as expected,
at higher field but, maybe surprisingly, that they hardly differ
from each other. The 31P upfield shift of radialene 18 as
compared to 2B is due to the PBH vs PBMe substituent effect.
We attribute the observed general downfield shift of ∼40 ppm
for the alkenylidene phosphiranes to the presence of substituents
on the PCC ring. The calculated 13C NMR chemical shift of
188 ppm for the allenic carbon (C3) of 17 agrees nicely with
the δ of 200.5 ppm observed by Breen and Stephan for 8A.
Alkenylidenephosphiranes. The single-crystal X-ray struc-
tures of 19A and 20A are the first of their kind. They are shown
in Figures 2 and 3, respectively. Of the heterocyclic systems
only a crystal structure of the sulfur analogue 24 has been
b
c
a Reference 8. Reference 6. Bowers, M.; Baudet, R. A.; Goldwhite,
H.; Tang, R. J. Am. Chem. Soc. 1969, 91, 17.
that are not. This rather long and presumably weaker distal bond
is fully in line with its suggested cleavage and subsequent
C(3)-P bond formation sequence for the observed rearrange-
ment that leads to 19B. Slightly smaller differences in phos-
phirane PC bond lengths of ∼0.07 Å were reported for 12 and
13; the difference in SC bonds of 24 is 0.11 Å. MP2(fc)/6-
31G* parent structure 17 also has a 0.064 Å longer distal than
proximal PC bond; a similar difference in PC bond lengths of
0.087 Å for 25 has been explained to result from conjugative
effects.8 The olefinic bond lengths of 19A are similarly as short
as those calculated for 17, but the experimental phosphirane
C(1)BC(2) bond of 1.505(11) Å is distinctly longer (by ∼0.05
Å) also compared to that of 12 (and its parent 25).
Cyclic alkenylidenephosphirane 20A has a strikingly different
X-ray crystal structure, particularly with respect to the allenic
C(2)dC(3)dC(4) unit, which is significantly bent at C(3) with
an angle of 171.5(7)°, suggesting ring-induced strain. This
bending contrasts the near allenic linearity in the acyclic
structures 19A (179.1(10)°), episulfide 24 (178.3°),23 and several
cyclopropane derivatives (178.0-179.4°).24 Not only is the
allene unit in 20A bent, it is also twisted by 14.2(8)°; the
dihedral angle between the C(1)C(2)C(3) and C(3)C(4)C(5)
planes amounts to 75.8(8)°. Bending and twisting has been
reported.23 Selected bond lengths and angles are listed in Table
2, which also contains crystal structure data for 128 and 136
and MP2/6-31G* geometrical parameters of 17, 25, and C2H5P
(16).
Structure 19A has distinctly different PC bond lengths of
which the 1.881(8) Å distal C(1)-P bond is ∼0.1 Å longer
than the proximal one; we refer to proximal P-C bonds as those
attached to the allene unit and to distal PBC bonds as those
(23) Toyota, K.; Yoshimura, H.; Uesugi, T.; Yoshifuji, M. Tetrahedron
Lett. 1991, 32, 6879.

Phospha[3]radialenes
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12511
Figure 4. ORTEP presentation scaled to 50% probability ellipsoids
of 19B.
Figure 5. ORTEP presentation scaled to 50% probability ellipsoids
of 20B.
G3MP2 Strain Energies. To what extent does unsaturation
increase the strain of the phosphirane ring? Recently, we
evaluated the effect of spiroannulation (for 26 and 15) and
showed that the strain energy of 21.3 kcal/mol for the parent
C2H5P system increases by 5.3 kcal/mol per spiro carbon as
calculated with the G2(MP2) method.7 Because of the electronic
relationship between the cyclopropyl ring and the olefinic bond,
a similar increase in SE may be anticipated for phosphiranes
with exocyclic double bonds and this is indeed confirmed. SE
values for 25, 17, and 18 of 28.1, 29,7, and 32.3 kcal/mol,
respectively, are obtained with the more advanced G3(MP2)
method31,32 using the homodesmotic reactions a-c. At the same
level of theory, phosphirane has a SE of 22.2 kcal/mol. Thus,
its strain increases by 5.9 kcal/mol on introducing one exocyclic
double bond and by another 4.2 kcal/mol on introducing the
recorded in the10-membered ring allene 28, which has a similar
bend angle of 170.7(4)°, but a smaller twist; its dihedral angle
is 80.0(4)°.25 These angles are larger in the corresponding 11-
membered ring and smaller in the 9-membered ring, thereby
illustrating the effect of ring strain.25,26 On the basis of these
arguments, we conclude that the strain in cyclic 20A is higher
than in acyclic 19A. Additionally, this may also be reflected in
the shorter olefinic bonds of 20A and the reduced hypercon-
jugation with its PBC(1) bond, although these differences are
within the experimental margins of error.
Phospha[3]radialenes. The single-crystal X-ray structures
of 19B and 20B are shown in Figures 4 and 5, respectively.
Selected bond lengths and angles are summarized in Table 3
together with those of the previously reported phospha[3]radia-
lenes 1B and 7B, phosphatriangulene 14, and phosphirene 23.17b
This table also contains MP2/6-31G* geometrical data for the
parent 18 and phosphirene (27) structures. The data presented
complements the already impressive set of diverse hetero[3]-
radialenes, of which crystal structures have been reported for
silicon,27 germanium,28 titanium,29 and two sulfur30 derivatives.
The phospha[3]radialenes 19B and 20B have slightly more
contracted PC bonds (1.800(5)-1.815(6) Å) than 1B (1.816 Å)
and 7B (1.826 Å) due to the stabilizing influence of the transition
metal group. Also, the phosphorus substituents cause a signifi-
cant reduction of the PC bond length, which is 1.845 Å at MP2/
6-31G* for the parent molecule 18. The phosphirane CC bond
in 18 is consequently longer than in the experimental structures.
Possible effects of strain from the hydrocarbon ring are not
evident in cyclic 20B. It is noteworthy that the P-phenyl of 20B
is oriented orthogonally to its PCC ring.
(26) Interestingly, the bend (178.3(1)°) and twist (88.0(8)°) are hardly
evident in the 10-membered allene 29, which contains two carbonyl carbons.
See: Carrell, H. L.; Glusker, J. P.; Covey, D. F.; Batzold F. H.; Robinson,
C. H. J. Am. Chem. Soc., 1978, 100, 4282.
(27) Yamamoto, T.; Kabe, Y.; Ando, W. Organometallics 1993, 12, 1996.
(28) Ando, W.; Ohgaki, H.; Kabe, Y. Angew. Chem. 1994, 106, 723.
(29) Maercker, A.; Groos, A. Angew. Chem. 1996, 108, 216.
(30) Ando, W.; Hanyu, Y.; Kumamoto Y.; Takata, T. Tetrahedron 1986,
42, 1989. Tokitoh, N.; Hayakawa, H.; Goto, M.; Ando, W. Chem. Lett.
1988, 961.
(31) G3(MP2): Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.;
Rassolov, V. Pople, J. A. J. Chem. Phys. 1999, 110, 4703. G3: Curtiss, L.
A.; Raghavachari, K.; Redfern, P. C.; Rassolov, V.; Pople, J. A. J. Chem.
Phys. 1998, 109, 7764.
(32) Gaussian 98 (Revision A.7). Frisch, M. J.; Trucks, G. W.; Schlegel,
H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;
Montgomery, J. A.; 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. G.; Chen, W.; Wong, M.
W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian,
Inc., Pittsburgh, PA, 1998.
(24) (a) Learned, A. E.; Arif, A. M.; Stang, P. J. J. Org. Chem. 1988,
53, 3122. (b) Eckert-Maksic, M.; Zollner, S.; Gothling, W.; Boese, R.;
Maksimovic, L.; Machinek, R.; de Meijere, A. Bergakademie 1991 124,
1591. (c) Manhart, S.; Schier, A.; Paul, M.; Riede J.; Schmidbaur, H. Chem.
Ber. 1995 128, 365.
(25) Luche, J.-L.; Damiano J.-C.; Cohen-Addad, C. J. Am. Chem. Soc.
1980, 102, 5370.

12512 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Komen et al.
Table 3. Selected Bond Distances (in Å) and CPC Angles (in deg) for the X-ray Structures of 19B, 20B, 1B, 7B, 14, and 23, and the
Theoretical Structures of 18 and 27
bonda
19B
20B
1Bb
7Bc
14d
23e
18
27
P-C(1)
1.815(6)
1.810(6)
1.432(9)
1.319(9)
1.800(5)
1.809(5)
1.434(6)
1.334(7)
1.816
1.816
1.422
1.344
1.827
1.825
1.413
1.330
1.807(8)
1.820(8)
1.48(1)
1.48(1)
1.49(1)
1.50(1)
1.51(1)
1.833(8)
48.1(4)
1.790(4)
1.787(4)
1.307(6)
1.453(6)
1.845
1.845
1.412
1.335
1.845
1.845
1.303
P-C(2)
C(1)-C(2)
C(1)-C(R)
C(2)-C(â)
1.319(9)
1.327(6)
1.320
46.1
9.9
1.327
1.474(6)
1.335
P-C(Ph)
1.822(6)
46.5(3)
148.0(6)
151.0(6)
-1(2)
1.825(5)
46.8(2)
146.2(5)
146.7(5)
-10.9(14)
1.831(4)
42.8(2)
150.0(4)
149.5(4)
C(1)PC(2)
C(1)C(2)C(â)
C(2)C(1)C(R)
torsion
45.5
45.0
146.2
146.2
41.4
2.6(17)
3.7(16)
b
c
d
e
a C(R) and C(â) are respectively C(3) and C(6) for 19B and C(10) and C(3) for 20B. Reference 9. Reference 12. Reference 7. Reference 17b.
Table 4. G3MP2 Enthalpies (-au) and Strain Energies SE
(kcal/mol)
structure
17
495.966 00 495.970 58 457.956 20 418.707 15
29.3 32.3 28.3 39.0
18
25
27
energy
SEa
a The GMP2 enthalpies (-au) used in eqs a-e are as follows:
CH3PH2, 381.92320; CH3CH3, 79.646 71; CH2CH2, 78.430 77;
CH3PHCH3, 421.162 24; PH2CH2CH3, 421.155 35; PH2C(CH3)CH2,
459.176 42; PH2C(CH3)CH2,, 497.188 85; PH2CHCH2, 419.942 15.
PhPW(CO)5 with cyclic 20 (leading to 20A and 20B) showed
second double bond, rendering the incremental SE per unsatur-
ated ring carbon slightly less than that for a spiro carbon. We
reemphasize that ethenylidenephosphirane 17 is less strained
(by 3.6 kcal/mol) than the thermodynamically more stable
radialene 18. It is further noteworthy that of the two three-
membered rings with unsaturated ring carbons 18 has a 6.7 kcal/
mol smaller SE than phosphirene 27 (39.0 kcal/mol, eq d). This
difference is due not only to the 0.110 Å shorter ring CC bond
of phosphirene but also to the unsaturation within the ring. This
effect is further evident from the 14 kcal/mol difference in SEs
between phosphirene and cyclopropene (30, 53 kcal/mol, eq e,
same level) as the increase in SE on introducing an endocyclic
CdC bond is less for phosphirane f phosphirene (∆SE ) 16.8
kcal/mol) than for cyclopropane f cyclopropene (∆SE ) 27
kcal/mol). For clarity, all ring SEs are summarized in Table 4.
the formation of small amounts of the two unique 1,2-diphospha-
[4]radialenes, cis-20C and trans-20C. These also result from
radialene 20B (in addition to the common side product 33)33
but the corresponding products could not be identified in the
reaction with acyclic 19 nor with 19B. Repetitive chromatog-
raphy and crystallization yielded the isomeric diphospha[4]-
radialenes in pure form. We assume that these products are
formed by a formal PhPW(CO)5 insertion into a PC bond as
was recently also observed in some, but not all, phosphirene
complexes. The formation of the [4]radialenes was confirmed
by determination of their single crystal X-ray structures, shown
in Figures 6 and 7. We are aware of only one other crystal
structure for a 1,2-diphospha[4]radialene, namely, uncomplexed
trans-4C, reported by Brieden and Kellersohn.15 Selected bond
lengths and angles of these three crystal structures are sum-
marized in Table 5.
25 + 2CH3PH2 + CH3CH3 f
CH3PHCH3 + PH2CH2CH3 + PH2C(CH3)dCH2 (a)
17 + 2CH3PH2 + CH2CH2 f
CH3PHCH3 + PH2CH2CH3 + PH2C(CH3)dCdCH2 (b)
The central four-membered ring in the 1,2-diphospha[4]-
radialenes are similarly puckered with angles (defined by the
P(1)P(2)C(1) and P(2)C(2)C(1) planes) of 148.3(3)° and 129.6-
(4)° for trans-20C and cis-20C, respectively. The extend of
puckering appears not to be influenced by the two transition
metal groups as the P(1)C(1)C(2)P(2) torsion angles of 26.0-
(3)° for cis-20C and 27.7(3)° for trans-20C are similar to the
23.2° angle for uncomplexed trans-4C. As a result of ring
puckering, the butadiene unit is rather twisted with a dihedral
angle of 47.0(10)° for cis-20C and a still larger angle of 61.9-
(9)° for trans-20C. Also phospha[3]radialene 20B shows torsion
between the double bonds of the butadiene unit, be it only by
-10.9(14)°, which in this case is solely due to the 10-membered
ring-induced conformational twist. It is then not surprising that
18 + 2CH3PH2 + CH3CH3 f
CH3PHCH3 + PH2C(CH3)dCH2 (c)
27 + 2CH3PH2 + CH2CH2 f
CH3PHCH3 + 2PH2CHdCH2 (d)
30 + 2CH3CH3 + CH2CH2 f
CH3CH2CH3 + 2CH3CHdCH2 (e)
B. 1,2-Diphospha[4]radialenes. Attempts to synthesize bis-
phosphirylidenes 31 and spirodiphosphapentanes 32, either from
the cumulenes 19 and 20 directly or from their “primary”
products A and B, respectively, proved to be unsuccessful.
Instead, careful analysis of the above-discussed reaction of
(33) Marinetti, A.; Charrier, C.; Mathey, F.; Fischer, J. Organometallics
1985, 4, 2134.

Phospha[3]radialenes
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12513
(DA) cycloadditions as was demonstrated by Ando for the
reactions of the sila- and germa[3]radialenes 34 with 4-methyl-
and 4-phenyl-1,2,4-triazoline-3,5-dione (MTAD, PTAD) (eq
9).27,28 To examine whether the phospha derivatives 19B and
Figure 6. ORTEP presentation scaled to 50% probability ellipsoids
of cis-20C.
20B behave analogously, we used MTAD for the DA reactions
(eq 10).
Reaction in benzene of acyclic 19B with the reddish MTAD
occurs with rapid loss of color to give the expected tricyclic
phosphirene 19D. Characteristic are the 31P and 13C NMR
chemical shifts of the phosphirene ring atoms at -75.9 and
144.0 ppm, respectively. This DA product, however, reacts with
the moisture in chloroform over a period of 2 weeks at 5 °C to
fully convert into 19E, which was identified by its 31P, 13C,
and 1H NMR and HRMS spectroscopic data. Characteristic are
its olefinic CHdC group and its phosphine 31P NMR resonance
at 114 ppm. This H2O induced ring-opened product 19E is
similar to 34E, which Ando reported to result from hydrolysis
of a germa[3]radialene (eq 9).28 Also Marinetti and Mathey34
reported similar nucleophilic-induced ring openings of substi-
tuted phosphirenes.
The reaction of cyclic 20B with MTAD is slower and behaves
differently. The 31P NMR spectrum of the reaction mixture
showed the appearance of two new resonances at 52.6 and -84.1
ppm in a ratio of 9 to 1. We assume the minor product to be
tricyclic structure 20D, because of the similarity of its 31P NMR
resonance to that of 19D, but too little material was obtained
to establish this with certainty. However, the major product
could be isolated, and on the basis of its 31P, 13C, and 1H NMR
data with supporting APT and CH-COSY measurements and a
HRMS exact mass measurement, we assign it tricyclic structure
20F; characteristic is its allenic 13C NMR resonance at δ 204
ppm. While selected phosphiranes and azaphosphiranes are
known to react with alkenes17b and imines35 to give stable five-
membered ring structures, we are unaware of a similar process
for phosphirenes. Product 20F must result from an interaction
of the NdN bond of MTAD with the phosphirene ring, but a
Figure 7. ORTEP presentation scaled to 50% probability ellipsoids
of trans-20C.
the endocyclic CC bond of the PCC ring in 20B (1.434(6)°)
and of the PPCC ring in cis-20C (1.475(8)°) and trans-20C
(1.487(7)°) appears to increase with increased twisting of the
butadiene component.
The 31P NMR spectrum of the trans isomer shows a single
resonance at 63.4 ppm suggesting a C2-like symmetrical (or
rapidly equilibrating) structure, but we were unable to confirm
this by 13C NMR due to a lack of adequate pure material. The
crystal structure, however, gives slightly different PC bond
lengths, albeit within the margins of error. Due to the ring
puckering, the 31P NMR spectrum of the cis isomer shows two
dissimilar and more shielded resonances (δ ) 58.2 and 37.1
1
ppm, JPP ) 55 Hz), which compare well with those of di-
W(CO)5 complexed 1,2-dihydro-1,2-diphosphetes.
The 31P NMR spectrum of the reaction mixture of 20C also
contains small resonances δ 24.1 (d), 10.3 (d), and -27.9 ppm
1
(t, JPP ) 240 Hz), which we speculatively attribute to the
(34) Marinetti, A.; Mathey, F. Tetrahedron 1989, 45, 3061. Marinetti,
A.; Mathey, F. J. Am. Chem. Soc. 1985, 107, 4700.
(35) Huy, N. H. T.; Ricard, L.; Mathey, F. Heteroatom Chem. 1998, 9,
597.
presence of a minute amount of a triphospha[5]radialene.
C. Diels-Alder Reactions. Phospha[3]radialenes contain a
diene unit and hence could be susceptible to [2+4] Diels-Alder

12514 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Komen et al.
Table 5. Selected Bond Distances (in Å) and CPC Angles (in deg) for the X-ray Structures of 1,2-diphospha[4]radialenes cis-20C, trans-20C,
and 4C
cis-20C
trans-20C
trans-4Ca
cis-20C
trans-20C
trans-4C
P1-C1
P2-C2
C1-C2
P1-P2
CdC1
C2dC
1.835(5)
1.820(6)
1.475(8)
2.284(2)
1.334(8)
1.335(8)
1.840(5)
1.825(5)
1.487(7)
2.2891(18)
1.321(7)
1.333(8)
1.847(3)
1.847(3)
1.468(3)
2.245(1)
1.336(4)
1.336(4)
P1-C1-C2
C1-C2-P2
C2-P2-P1
P2-P1-C1
101.1(4)
99.8(4)
76.4(2)
74.89(19)
352.2
47.0(10)
26.0(3)
100.0(3)
99.9(4)
75.99(18)
75.20(17)
351.1
61.9(9)
27.7(3)
100.1(2)
100.1(2)
76.6(1)
76.6(1)
352.4
57.8(3)
23.2(1)
∑
(4-ring)
CdC1sC2dC
P1-C1-C2-P2
a Reference 15.
direct PC insertion would, however, result in 20G, in analogy
with the insertion of phosphinidenes to give 1,2-dihydro-1,2-
diphosphetes.36 The unexpected formation of 20F suggests a
MTAD-induced (nucleophilic) ring opening of phospha[3]-
triangulene 20B with subsequent ring closure to the apparently
thermodynamically more stable 20F. However, 20F can also
be explained to result from a concerted [(σ2 + π2) + π2]
mechanism. Such a mechanism has been extensively investi-
gated by Pasto for the cycloaddition reactions of alkenylidenecy-
clopropanes with dienophiles such as MTAD to give related
five-membered ring structures.37 We conclude that the difference
in reactivity between 19B and 20B for cycloaddition has its
origin in the torque of the diene unit of the cyclic radialene
enabling it to follow a different cycloaddition path.
Phospha[3]radialenes 19B and 20B undergo different Diels-
Alder reactions with methyl-1,2,4-triazole-3,5-dione. The “nor-
mal” 4+2 cycloaddition product 19D is formed in the reaction
with the acyclic radialene 19B. The ring-induced strain in this
compound is evident from the rather high sensitivity of the
phosphirane ring toward hydrolysis, resulting in 19E. An
alternative [(σ2 +π2) + π2] cycloaddition occurs with cyclic
radialene 20B that involves the participation of one of its PC
bonds. Because of the presence of an allenic unit, 20F cannot
be formed by a simple insertion of MTAD into the phosphirane
ring. The formation of product 20F is reminiscent to the similar
reactions of alkenylidenecyclopropanes with dienophiles such
as TMAD.
Ab initio theoretical studies on the parent systems, using the
G3(MP2) method, show phospha[3]radialene to be 3.6 kcal/
mol more stable than ethenylidenephosphirane. Their strain
energies are 32.3 and 29.7 kcal/mol, respectively, as obtained
from isodesmotic equations using G3(MP2) calculated heats of
formation for the molecules of these equations. Phospha[3]-
radialene illustrates that the SE of 22.2 kcal/mol of phosphirane
increases by 5.9 and 4.2 kcal/mol on subsequently introducing
exocyclic double bonds. Still, the SE of phospha[3]radialene is
less than the 39.0 kcal/mol of the more condensed phosphirene.
Optimized MP2(fc) geometries of the parent molecules
compare well with the X-ray crystal structures of 19A and 19B,
taking substituent effects into account. Their GIAO calculated
13C and 31P NMR chemical shifts compare well with available
literature data on derivatized uncomplexed systems.
Conclusions
Phospha[3]radialenes can be conveniently synthesized from
the 1,2-cycloaddition of in situ-generated phosphinidene com-
plex PhPW(CO)5 to readily available cumulenes. Alkenylidene-
phosphiranes are obtained as intermediate products as PhPW-
(CO)5 has a preference for the terminal double bond of the
cumulene. However, these products cleanly rearrange to the
phospha[3]radialene complexes, supposedly by a phosphirane
ring opening/closure sequence. The reaction has been demon-
strated for the simple tetramethylcumulene and the strained
cyclic 1,2,3-cyclodecatriene. Single-crystal X-ray structures were
obtained both for the kinetic products 19A and 20A and for the
thermodynamically preferred radialenes 19B and 20B. The
structural and NMR spectroscopic properties of the radialenes
compare well with literature data on related systems. The crystal
structures of 19A and 20A are the first of their kind. They show
the distal PC bond to the allenic group to be significantly
elongated. The higher reactivity of the more strained bicyclic
20A is evident from the significant bending (172.1°) and twisting
(15°) that is present in its allenic unit.
Phosph[4]radialenes result from the reaction of an additional
equivalent of PhPW(CO)5 with phospha[3]radialene 20B. Two
isomers are formed, i.e., cis-20C and trans-20C. X-ray crystal
structures were obtained for both, which is also a first. Both
isomers have puckered PPCC rings (∼150°), and as a result,
the olefinic bonds of their butadiene units are substantially
twisted from planarity. No phospha[4]radialenes are obtained
in the reaction of PhPW(CO)5 with 19B. The higher reactivity
of 20B toward the phosphinidene is considered to originate from
the influence of the 10-membered hydrocarbon ring on the
phosphirane ring.
Experimental Section
NMR spectra were recorded on a Bruker MSL 400 and a Bruker
AC 200. Chemical shifts are referenced in ppm to internal Me4Si for
1
the H and 13C NMR spectra and to external 85% H3PO4 for the 31P
NMR spectra. Downfield shifts are reported as positive. Toluene was
dried by distillation from sodium and Et2O from LiAlH4. The oxygen-
sensitive 2,5-dimethyl-2,3,4-hexatriene (2)38 was prepared from the
reaction of 3,4-diiodo-2,5-di-methyl-2,4-hexadiene39 (synthesized from
2,5-dimethyl-3-hexyne-2,5-diol with hydriodic acid) and butyllithium
in diethyl ether at -50 °C. 1,2,3-Cyclodecatriene (20)40 was synthesized
from cyclooctene in a four steps, starting with its conversion into 1,2-
cyclononadiene41 via a dibromocarbene addition (by means of phase-
transfer catalysis in aqueous medium)42 followed by treatment with
MeLi in diethyl ether at -40 °C. Repetition of the carbene addition
and the ring expansion reactions gives the very oxygen sensitive 1,2,3-
cyclodecatriene via 10,10-dibromobicyclo[7.1.0]decene. Each com-
pound was purified by a vacuum distillation, except for 1,2,3-
(38) Iyoda, M.; Tanaka, S.; Otani, H.; Nose, M.; Oda, M. J. Am. Chem.
Soc. 1988, 110, 8494.
(39) Zalkind, Y. S.; Rubin, B.; Kruglov, A. Russ. Phys.-Chem. Soc. 1926,
58, 1044; Chem. Abstr. 1928, 22, 1137.
(40) Moore, W. R.; Ozretich, T. M. Tetrahedron Lett. 1967, 33, 3205.
(41) Skattebøl, L.; Solomon, S. Organic Syntheses; Wiley: New York,
1973: Collect. Vol. V, p 306.
(42) Williamson, K. L. Macroscale and Microscale Organic Experiments;
D. C. Heath and Co.: Lexington, 1989; p 590.
(36) Wang, B.; Nguyen, K. A.; Srinivas, G. N.; Watkins, C. L.; Menzer,
S.; Spek, A. L.; Lammertsma, K. Organometallics 1999, 18, 796. Huy, N.
H. T.; Richard, L.; Mathey, F. Organometallics 1997, 16, 4501.
(37) Pasto, D. J.; Chen, A. F.-T.; Binsch, G. J. Am. Chem. Soc., 1973,
95, 1553. Pasto, D. J.; Scheidt, W. R. J. Org. Chem. 1975, 40, 1444. Pasto,
D. J. J. Org. Chem. 1976, 41, 4012. Pasto, D. J. J. Am. Chem. Soc. 1979,
101, 37. Pasto, D. J.; Chen, A. F.-T. Tetrahedron Lett. 1972, 30, 2995.
Pasto, D. J.; Chen, A. J. Am. Chem. Soc. 1971, 93, 2562.

Phospha[3]radialenes
J. Am. Chem. Soc., Vol. 122, No. 50, 2000 12515
cyclodecatriene. The synthesis of the phosphinidene precursor 10 is
described in ref 17. The reaction of 10 with the cyclic cumulene is
described first because of its more diverse product composition.
PhPW(CO)5 Addition to 1,2,3-Cyclodecatriene (20). Freshly
prepared and carefully dried 20 (0.8 g, 6 mmol) and 10 (3.5 g, 5.4
mmol) were heated for 3 h at 55 °C in 15 mL of toluene with CuCl
(0.11 g). Monitoring of the reaction mixture, using 31P NMR, showed
the appearance of both alkenylidenephosphirane 20A (δ -131.4 ppm)
and phospha[3]radialene 20B (δ -153.0 ppm) in a ratio of ∼1:2. The
reaction mixture was evaporated to dryness and chromatographed on
silica gel with hexane. The first fraction (0.3 g, 10%) contains mostly
alkenylidenephosphirane 20A (20A:20B ) 3:1), fractional crystalliza-
tion from hexane gave 20A as colorless crystals. The second fraction
(1.1 g, 36%), a mixture of alkenylidenephosphirane 20A and phospha-
[3]radialene 20B (20A:20B ) 1:3), was converted completely to 20B
by heating in toluene at 100 °C during 2 h. Crystallization from hexane
gave 20B as colorless crystals. Minor amounts of yellow-green crystals
trans-20C and cis-20C were obtained from fractions 3 and 4,
respectively.
cis-CO), 198.3 (d, 2JCP ) 29.9 Hz, trans-CO); 1H NMR (C6D6) δ 1.08
(d, 3JHP ) 13.1 Hz, 3H, CH3), 1.46 (d, 3JHP ) 19.4 Hz, 3H, CH3), 1.79
5
5
(d, JHP ) 4.9 Hz, 3H, CdCsCH3), 1.85 (d, JHP ) 5.0 Hz, 3H, Cd
CsCH3), 7.29-7.47 (m, 5H, Ar-H); MS (m/e; relative intensity) 540
(M+, 35.0), 512 (M - CO, 2.0), 484 (M - 2CO, 13.8), 456 (M -
3CO, 25.2), 428 (M - 4CO, 17.1), 400 (M - 5CO, 100), 348 (PhP -
W(CO)2, 33.4), 320 (PhPW(CO), 56.8), 292 (PhPW, 51.4), 108 (C8H12,
24.3), 77 (C6H5, 79.2).
19B: mp 110-111 °C; 31P NMR (CDCl3) δ -155.0 (1JPW ) 246.2
Hz); 13C NMR (CDCl3) δ 24.4 (d, 3JCP ) 10.3 Hz, CH3), 25.5 (d, 3JCP
) 8.8 Hz, CH3), 116.6 (s, CdCMe2), 128.5 (d, 3JCP ) 10.4 Hz, m-Ar),
129.9 (d, 4JCP ) 2.6 Hz, p-Ar), 131.0 (d, 2JCP ) 13.9 Hz, o-Ar), 133.9
2
1
(d, JCP ) 2.2 Hz, CdCMe2), 135.2 (d, JCP ) 17.9 Hz, i-Ar), 195.7
2
2
1
(d, JCP ) 8.0 Hz, cis-CO), 198.2 (d, JCP ) 28.2 Hz, trans-CO); H
NMR (CDCl3) δ 2.12 (s, 6H, CH3), 2.21 (s, 6H, CH3), 7.32-7.50 (m,
5H, ArH); MS (m/e; relative intensity) 540 (M+, 29.4), 512 (M - CO,
2.5), 484 (M -2CO, 11.8), 456 (M - 3CO, 26.6), 428 (M - 4CO,
16.6), 348 (PhP - W(CO)2, 31.2), 320 (PhPW(CO), 60.1), 292 (PhPW,
51.4), 108 (C8H12, 18.8), 77 (C6H5, 76.9). Anal. Calcd for C16H13-
PWO5: C, 42.25; H, 3.17. Found: C, 42.22; H, 3.04.
20A: mp 118 °C; 31P NMR (C6D6) δ -131.4 (1JPW ) 250.5 Hz);
13C NMR (C6D6) δ 25.7 (d, JCP e 2.5 Hz, CH2), 26.0 (d, JCP ) 4.8 Hz,
CH2), 26.9 (s, CH2), 27.3 (s, CH2), 27.5 (d, JCP ) 8.9 Hz, CH2), 30.4
Phospha[4]radialenes 20C. Phospha[3]radialene 20B (0.18 g, 0.3
mmol) and 10 (0.2 g, 0.3 mmol) were heated for 3 h at 55 °C in 2 mL
of toluene with CuCl (0.11 g). Monitoring of the reaction mixture using
31P NMR showed the appearance of phospha[4]radialene cis-20C and
33.33 Extra phosphinidene precursor (0.15 g) was added, and the reaction
mixture was heated until no starting materials were detected by
monitoring with 31P NMR. The reaction mixture was evaporated to
dryness and purified by column chromatography on silica gel with
pentane/benzene (4:1). The first fraction (0.12 g) contains, according
to the 31P NMR spectrum, both phospha[4]radialene cis-20C (δ ) 63.9
ppm (s), 1JPW ) 201.6 Hz)and triphospholane (δ ) 24.1 ppm (d), 10.3
2
(d, JCP ) 2.8 Hz, CdCdCH-CH2), 30.8 (d, JCP ) 10.5 Hz, CH-
ring), 83.3 (d, 1JCP ) 7.4 Hz, CdCdCH), 95.4 (d, 3JCP ) 6.9 Hz, Cd
CdCH), 128.8 (d, 3JCP ) 10.0 Hz, m-Ar), 130.7 (d, 4JCP e 2 Hz, p-Ar),
2
1
132.5 (d, JCP ) 12.0 Hz, o-Ar), 132.2 (d, JCP ) ( 24 Hz, i-Ar),
195.9 (d, 2JCP ) 7.9 Hz, cis-CO), 198.3 (d, 2JCP ) 30.2 Hz, trans-CO),
202.0 (s, CdCdC); 1H NMR (C6D6) δ 0.82-1.23 (m, 7H, CH2), 1.38-
1.5 (m, 2H, CH2), 1.55-1.7 (m, 1H, CdCdCHsCH2), 1.7-1.8 (m,
1H, CH2) 2.05-2.15 (m, 1H, CdCdCHsCH2), 2.15-2.22 (m, 1H
3+3+5
4
CH-ring), 5.3-5.4 (d pseudo q,
J
) 7.5 and JHP ) 4.7, 1H,
HH
1
CdCsH), 6.85-6.98 (m, 3H, Ar-H), 7.35-7.45 (m, 2H, o-Ar-H).
ppm (d), -27.9 ppm (t), JPP ) 240 Hz, 5:3). These products could
20B: mp 110 °C; 31P NMR (C6D6) δ -153.0 (1JPW ) 248.2 Hz);
not be separated, and it was not possible to convert the mixture
completely to the triphospholane. The second fraction was diphosphene
33.
13C NMR (C6D6) δ 27.1 (s, CH2), 30.1 (s, CH2), 32.1 (d, JCP ) 11.0
4
Hz, CdCHsCH2), 122.3 (s, CdCH), 128.9 (d, 3JCP ) 10.7 Hz, m-Ar),
130.6 (d, 4JCP ) 2.6 Hz, p-Ar), 131.7 (d, 2JCP ) 14.3 Hz, o-Ar), 134.0
Reaction of 19B with MTAD. To a solution of 27.5 mg (0.05 mmol)
of 19B in benzene was added 6.1 mg (0.05 mmol) of MTAD. The
reaction mixture was stirred at room temperature until it fully
decolorized. The solution was filtered, and the solvent was removed
in vacuo. The crude product was dissolved in CDCl3.
1
2
(s, CdCH), 135.0 (d, JCP ) 18.5 Hz, i-Ar), 196.0 (d, JCP ) 8.1 Hz,
cis-CO), 198.4 (d, 2JCP ) 28.8 Hz, trans-CO); 1H NMR (C6D6) δ 1.4-
1.78 (m, 8H, CH2), 2.5-2.65 (m, 4H, CdCsCH2), 6.49-6.60 (d t,
3JHP ) 17.5 Hz and 3JHH ) 7.7 Hz, 2H, CdCsH), 7.35-7.42 (m, 3H,
Ar-H), 7.48-7.57 (m, 2H, o-Ar-H); HRMS (EI) (m/e) for C21H19-
19D: 31P NMR (CDCl3) δ -75.9 (1JPW ) 284.1 Hz); 13C NMR
(CDCl3) δ 23.7 (s, CH3), 24.4 (s, CH3), 25.3 (s, NCH3), 62.7 (d,
PO5182W2: calcd 564.0453, found 564.0454 ( 0.0010.
trans-20C: mp 248 °C (dec); 31P NMR (C6D6) δ 63.4 (s, JPW
)
2JCP ) 5.8 Hz, CMe2), 129.1 (d, JCP ) 10.7 Hz, m-Ar), 131.2 (d,
1
3
1
4
201.6 Hz); H NMR (C6D6) δ 1.05-1.24 (m, 4H, CH2), 1.50-1.70
(m, 4H, CH2), 1.55-1.92 (m, 2H, CH2), 2.22-2.35 (m, 2H, CH2),
6.18-6.28 (m, 2H, CdCsH), 7.06-7.14 (m, 2H, Ar-H), 7.22-7.28
(m, 4H, Ar-H), 7.62-7.72 (m, 4H, Ar-H); HRMS (EI) (m/e) for
C32H24P2O10184W2: calcd 997.9865, found 997.986 ( 0.003.
2JCP ) 16.9 Hz, o-Ar), 131.9 (d, JCP ) 2.3 Hz, p-Ar), 139.3 (d,
1
1JCP ) 5.6 Hz, i-Ar), 144.0 (s, JCP ) 7.1 Hz, CdC), 153.9 (s,
N-CdO), 195.9 (d, 2JCP ) 8.4 Hz, cis-CO), 197.0 (d, 2JCP ) 33.6 Hz,
1
trans-CO); H NMR (CDCl3) δ 1.75 (s, 6H, CH3), 1.80 (s, 6H, CH3),
3.08 (s, 3H, NCH3) 7.42-7.56 (m, 5H, ArH); HRMS (EI) (m/e) for
C22H20N3O7P182W: calcd 653.0549 found 653.0550 ( 0.0002.
19E: 31P NMR (CDCl3) δ 114.0 (1JPW ) 280.8 Hz); 13C NMR
(CDCl3) δ 23.6 (s, CH3), 24.0 (s, CH3), 24.4 (s, CH3), 24.9 (s, NCH3),
25.2 (s, CH3), 58.8 (d, 3JCP ) 16.7 Hz, CMe2), 63.3 (d, 2JCP ) 4.2 Hz,
cis-20C: mp 210 °C (dec); 31P NMR (C6D6) δ 58.22 (d, JPP ) 55
1
1
1
Hz), 37.05 (d, JPP ) 55 Hz); H NMR (C6D6) δ 1.23-1.58 (m, 8H,
CH2), 2.02-2.26 (m, 4H, CH2), 5.9-6.3 (m, 2H, CdCsH), 6.76-
6.68 (m, 4H, Ar-H), 6.86-6.76 (m, 2H, Ar-H), 6.86-6.96 (m, 4H,
Ar-H); HRMS (EI) (m/e) for C32H24P2O10184W2: calcd 997.9865,
found 997.986 ( 0.005.
2
3
CMe2), 128.0 (d, JCP ) 13.5 Hz, o-Ar), 128.5 (d, JCP ) 10.0 Hz,
m-Ar), 130.4 (d, 4JCP ) 2.3 Hz, p-Ar), 130.7 (d, 1JCP ) 31.8 Hz, i-Ar),
141.7 (s, 1JCP ) 7.1 Hz, H-C)C), 145.9 (s, 2JCP ) 29.2 Hz, H-CdC),
PhPW(CO)5 Addition to 2,5-Dimethyl-2,3,4-hexatriene (19). The
reaction was executed as described for 20 giving a crude mixture of
alkenylidenephosphirane 19A and phospha[3]radialene 19B in a 1:1
ratio. After column chromatography, a 370 mg (70%) yield of a
colorless solid was obtained containing mostly alkenylidenephosphirane
19A and a small amount of phospha[3]radialene 19B; fractional
crystallization from hexane gave 19A as colorless crystals. Part of the
crude mixture of 19A and 19B was converted completely to 19B by
heating in toluene at 100 °C during 2 h. Crystallization from hexane
gave 19B as colorless crystals.
2
153.5 (s, N-CdO), 153.7 (s, N-CdO), 196.5 (d, JCP ) 7.5 Hz, cis-
2
1
CO), 198.5 (d, JCP ) 33.6 Hz, trans-CO); H NMR (CDCl3) δ 1.45
(s, 3H, CH3), 1.55 (s, 3H, CH3), 1.65 (s, 3H, CH3) 1.79 (s, 3H, CH3),
3
2.79 (s, 3H, NCH3), 6.30 (d, JHP ) 23.6 Hz, 1H, H-CdC), 7.4-7.6
(m, 5H, ArH); HRMS (EI) (m/e) for C22H22N3O8P182W: calcd 671.0654,
found 671.0654 ( 0.0003.
Reaction of 20B with MTAD. The reaction was executed on a 0.20-
mmol scale in a fashion similar to that described for 19B. The 31P NMR
spectrum of the crude reaction mixture showed two resonances at 52.6
and -84.1 ppm (9:1). The main product (20F) was isolated as a yellow
solid by means of column chromatography (pentane/benzene) in a yield
of 59% (79.6 mg).
20F: 31P NMR (CDCl3) δ 52.6 (1JPW ) 288.5 Hz); 13C NMR (CDCl3)
δ 19.7 (s, CH2), 21.2 (s, CH2), 24.5 (s, CH2), 24.9 (s, CH2), 25.6 (s,
NCH3), 26.9 (d, 3JCP ) 1.4 Hz, N-CH-CH2), 27.0 (d, 4JCP ) 4.3 Hz,
CdCdCHsCH2), 60.2 (s, N-CH), 101.2 (d, 3JCP ) 12.8 Hz, CdCd
19A: mp 93-94 °C; 31P NMR (CDCl3) δ -112.8 (1JPW ) 279.1
Hz); 13C NMR (C6D6) δ 20.7 (d, 2JCP ) 3.8 Hz, CH3), 21.1 (d, 2JCP
)
5
5
3.9 Hz, CH3), 22.6 (d, JCP ) 2.5 Hz, CH3), 26.3 (d, JCP ) 5.6 Hz,
1
CH3), 32.2 (d, JCP ) 10.6 Hz, PCMe2) 88.7 (s, CdCdCMe2), 101.6
(d, 3JCP ) 7.3 Hz, CdCdCMe2), 128.5 (d, 3JCP ) 9.7 Hz, m-Ar), 130.2
4
2
(d, JCP ) 2.2 Hz, p-Ar) 132.2 (d, JCP ) 11.7 Hz, o-Ar), 134.9 (d,
1JCP ) 21.6 Hz, i-Ar), 195.2 (s, CdCdC), 195.8 (d, JCP ) 8.0 Hz,
2

12516 J. Am. Chem. Soc., Vol. 122, No. 50, 2000
Komen et al.
Table 6. Crystal Data and Data Collection Procedures for 19A, 19B, 20A, 20B, cis-20C, and trans-20C
19A
19B
20A
20B
cis-20C
trans-20C
formula
fw
C19H17O5PW
540.15
C19H17O5PW
540.15
C21H19O5PW
566.18
C21H19O5PW
566.18
C32H24O10P2W2
998.15
C32H24O10P2W2
998.15
cryst syst
space gp
a (Å)
b (Å)
c (Å)
triclinic
P1 (No. 2)
7.031(2)
9.599(2)
15.959(3)
86.30(2)
78.29(2)
83.37(2)
1046.7(4)
2
triclinic
P1 (No. 2)
8.541(2)
10.498(2)
12.943(3)
66.21(2)
81.63(2)
72.12(2)
1010.3(4)
2
monoclinic
P21/c (No. 14)
9.910(3)
31.360(10)
6.826(3)
90
103.95(3)
90
2058.8(12)
4
monoclinic
P21/c (No. 14)
10.8902(12)
9.8451(11)
20.6783(17)
90
112.802(7)
90
2043.8(4)
4
triclinic
triclinic
P1 (No. 2)
10.2375(11)
10.6317(9)
15.3774(15)
85.707(7)
86.277(9)
82.092(8)
1650.6(3)
2
P1 (No. 2)
9.5208(4)
11.1008(7)
16.0527(12)
90.116(6)
95.543(5)
97.452(4)
1674.21(18)
2
R (deg)
â (deg)
γ (deg)
V (Å)3
Z
density (g/cm3)
1.714
5.62
colorless
1.776
5.82
colorless
1.827
1.840
5.76
colorless
2.008
7.12
yellowish
1.980
7.02
yellowish
µ (mm-1
)
5.72
cryst color
colorlessa
cryst size (mm-3
transmission
sin(θ/2θ)max
)
0.49 × 0.30 × 0.23 0.47 × 0.29 × 0.17 0.53 × 0.18 × 0.18 0.33 × 0.25 × 0.25 0.50 × 0.37 × 0.25 0.45 × 0.30 × 0.18
0.11-0.58
0.65
0.12-0.59
0.65
4971/4618
0.048
0.12-0.59
0.65
8685/4716
0.107
0.30-0.74
0.65
4878/4669
0.042
0.28-0.72
0.63
6523/6278
0.040
0.24-0.70
0.65
9358/7684
0.034
refl measd/unique 5349/4804
Rint
0.068
params/restraints
R (obs/all refl)
wR2 (obs/all refl) 0.1202/0.1289
239/0
0.0468/0.0660
239/0
261/0
253/0
415/0
415/0
0.0378/0.0532
0.0949/0.1013
1.057
0.0448/0.0585
0.1104/0.1187
1.030
0.0314/0.0470
0.0623/0.0669
1.038
0.0309/0.0391
0.0714/0.0748
1.040
0.0340/0.0449
0.0788/0.0838
1.030
GooF
1.058
resid e
-2.13/1.34
-1.68/1.46
-2.63/2.23
-0.81/0.65
-2.38/2.35
-1.86/2.17
density (e/A3)
a Crystal turns orange during X-ray exposure.
1
2
CH), 108.3 (d, JCP ) 50.0 Hz, PsCdCdC), 127.7 (d, JCP ) 13.5
PLATON package.46 Details of the crystal data and structure solution
procedures are summarized in Table 6.
3
4
Hz, o-Ar), 128.8 (d, JCP ) 10.2 Hz, m-Ar), 131.1 (d, JCP ) 2.1 Hz,
1
3
p-Ar), 137.9 (d, JCP ) 32.8 Hz, i-Ar), 150.8 (d, JCP ) 5.2 Hz, Ps
X-ray Crystal Structure Determination of 20A, 20B, cis-20C, and
trans-20C. Diffraction data of single crystals, mounted on a glass fiber
with perfluoropolyether oil, were collected at a temperature of 150 K
on an Enraf-Nonius CAD4T diffractometer using Mo KR radiation (λ
) 0.710 73 Å, rotating anode, graphite monochromator). Data reduction
was performed with the HELENA program.43 The structures were
solved with Patterson methods using the program DIRDIF.47 Refinement
was done on F2 of all reflections using SHELXL-97.45 In structure trans-
20C, the disorder of atoms C7 and C8 could not be resolved. Absorption
correction (routine DELABS), checking for higher symmetries and
structure calculations were performed with the PLATON package.46
Details of the crystal data and structure solution procedures are
summarized in Table 6.
2
NsNsCdO), 152.7 (s, PsNsCdO), 194.8 (d, JCP ) 7.4 Hz, cis-
2
2
CO), 197.5 (d, JCP ) 30.2 Hz, trans-CO), 204.2 (d, JCP ) 16.0 Hz,
CdCdC); 1H NMR (CDCl3) δ 0.7-2.4 (m, 12H, CH2), 3.10 (s, NCH3),
3
3
3
5
4.78 (dddd, JHP ) 5.8 Hz, JHH ) 3.8 Hz, JHH ) 3.7 Hz, JHH ) 4.0
Hz, 1H, N-C-H), 5.98 (dddd, 4JHP ) 9.8 Hz, 3JHH ) 6.8 Hz, 3JHH
)
5
4.0 Hz, JHH ) 4.0 Hz, 1H, CdCsH), 7.41-7.48 (m, 5H, Ar-H);
HRMS (EI) (m/e) for C24H22N3O7P182W: calcd 679.0705, found
679.0704 ( 0.0003.
Computations. All electronic structure calculations were carried out
using the GAUSSIAN 98 suite of programs.32 Geometries were
optimized at the HF and MP2(fc) levels of theory using the 6-31G*
basis set. The Hessian index, which is the number of negative
eigenvalues of the force constant matrix, was determined for all species
at the SCF level to be 0. Geometrical MP2(fc) parameters for selected
Acknowledgment is made to the National Science Founda-
tion and The Netherlands Organization for Scientific Research
(NWO/CW) for support of this research. We thank Dr. F. J. J.
de Kanter for the NMR measurements, Drs. B. L. M. van Baar
and H. Zappey for the HRMS measurements, and Drs. S.
Menzer and W. J. J. Smeets for preliminary crystal structure
investigations.
systems are shown in Figure 1. This figure also shows the 31P and 13
C
NMR chemical shifts for structures 17 and 18 as calculated with the
GIAO method at MP2(fc)/6-31G* and referenced against Me3PO and
Me4Si, respectively. G3(MP2) theory was used to obtain more accurate
absolute energies for the optimized structures. Heats of formation
(∆Hf298) for the systems in eqs a-e were estimated from their heats of
atomization calculated at G3MP2.31 The resulting strain energies are
listed in Table 4 together with the ∆Hf298 values and absolute energies
for selected molecules.
X-ray Crystal Structure Determination of 19A and 19B. Dif-
fraction data of single crystals, mounted on a glass fiber with epoxy
cement, were collected at room temperature on an Enraf-Nonius CAD4
diffractometer using Mo KR radiation (λ ) 0.710 73 Å, sealed tube,
graphite monochromator). Data reduction was performed with the
HELENA program.43 The structures were solved using the MolEN
package.44 Refinement was done on F2 of all reflections using SHELXL-
97.45 Absorption correction (routine DELABS), checking for higher
symmetries, and structure calculations were performed with the
Supporting Information Available: Position and thermal
parameters and a complete listing of bond lengths, angles, and
torsion angles for 19A, 19B, 20A, 20B, cis-20C, trans-20C
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
JA002437C
(45) Sheldrick, G. M. SHELXL-97. Program for crystal structure
refinement. University of Go¨ttingen, Germany, 1997.
(46) Spek, A. L. PLATON. A multipurpose crystallographic tool. Utrecht
University, The Netherlands, 2000.
(43) Spek, A. L. HELENA. Program for X-ray data reduction. Utrecht
University, The Netherlands 1998.
(44) Fair, C. K. MolEN, an interactive intelligent system for crystal
structure analysis, Enraf-Nonius, Delft, The Netherlands, 1990.
(47) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M. Smykalla, C. The
DIRDIF97 program system, Technical Report of the Crystallography
Laboratory, University of Nijmegen, The Netherlands, 1997.