Study on synthesis and structure of sterically demanding 6-phosphafulvenes

Article abstract of DOI:10.1080/10426500902718240

t-Butylcyclopentadienyllithium was allowed to react with (2,4,6-tri-t-butylphenyl)phosphonous dichloride to afford the corresponding chloro-5-cyclopentadienylchlorophosphine as a mixture of diastereomers, the structure of one of which was determined by X-

Full text of DOI:10.1080/10426500902718240

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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Study on Synthesis and
Structure of Sterically
Demanding 6-Phosphafulvenes
Shigekazu Ito a , Hideaki Miyake a & Masaaki
Yoshifuji a
a Department of Chemistry, Graduate School of
Science , Tohoku University , Aoba, Sendai, Japan
Published online: 26 Mar 2009.
To cite this article: Shigekazu Ito , Hideaki Miyake & Masaaki Yoshifuji (2009)
Study on Synthesis and Structure of Sterically Demanding 6-Phosphafulvenes,
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:4, 917-927, DOI:
10.1080/10426500902718240
To link to this article: http://dx.doi.org/10.1080/10426500902718240
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Phosphorus, Sulfur, and Silicon, 184:917–927, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902718240
Study on Synthesis and Structure of Sterically
Demanding 6-Phosphafulvenes
Shigekazu Ito, Hideaki Miyake, and Masaaki Yoshifuji
Department of Chemistry, Graduate School of Science, Tohoku
University, Aoba, Sendai, Japan
t-Butylcyclopentadienyllithium was allowed to react with (2,4,6-tri-t-
butylphenyl)phosphonous dichloride to afford the corresponding chloro-5-
cyclopentadienylchlorophosphine as a mixture of diastereomers, the structure
of one of which was determined by X-ray crystallography. The mixture of 5-
cyclopentadienylchlorophosphine diastereomers was treated with a base to furnish
novel 2-t-butyl-6-(2,4,6-tri-t-butylphenyl)-6-phosphafulvenes, and each geometrical
isomer of them was fully characterized by X-ray crystallography. The E/Z ratio of
the 6-phosphafulvene obtained was considerably dependent on the diastereomeric
ratio of the chlorophosphine precursor.
Keywords Chlorophosphines; elimination; fulvenes; phosphaalkenes; steric protection;
X-ray crystallography
INTRODUCTION
Chemistry of kinetically stabilized phosphaalkenes [–P=C<] has re-
cently played an important role, not only in fundamental molecu-
lar science based on heavier low-coordinated main group elements,1
but also in several application fields such as synthetic catalysts2
and optoelectronic functions.3 Phosphaalkenes show basically similar
Received 30 November 2007; accepted 1 March 2008.
Dedicated to Professor Marian Mikolꢀajczyk from the CBMiM PAN in Lꢀ o´dz´, Poland,
on the occasion of his 70th birthday.
This work was supported in part by Grants-in-Aid for Scientific Research (No.
13304049 and 14044012) from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
The present affiliation for Shigekazu Ito is Tokyo Institute of Technology, Tokyo,
Japan and the present affiliation for Masaaki Yoshifuji is Department of Chemistry, The
University of Alabama, Tuscaloosa, Alabama, USA.
Address correspondence to Shigekazu Ito, Department of Applied Chemistry, Tokyo
Institute of Technology, Meguro, Tokyo 152-8552, Japan. E-mail: ito.s.ao@m.titech.ac.jp
or Masaaki Yoshifuji, Department of Chemistry, The University of Alabama, Tuscaloosa,
AL 35487-0336, USA. E-mail: myoshifuji@bama.ua.edu
917

918
S. Ito et al.
characteristics to their carbon congeners, olefins, and thus it is rea-
sonable to expect that the substituents around the P C group might
modify their physicochemical properties.
We previously succeeded in preparation and isolation of a kineti-
cally stabilized 1,3,6-triphosphafulvene,5 and recently we have found
its unique electrophilic reactivity providing a number of exotic P-
heterocyclic compounds.6–8
Now we are interested in the chemistry of 6-phosphafulvene bearing
a cyclopentadienyl group and an exo P C double bond, which is one of
the typical phosphaalkene with an electronically perturbed P C moi-
ety. Indeed, electrochemistry and reduction generating radical anions
have been reported to elucidate the properties of 6-phosphafulvene.4
While synthetic procedures for 6-phosphafulvenes have been
established,4a structural studies on 6-phosphafulvenes as well as chem-
ical modifications leading to a series of novel exotic molecules have
been limited so far. Therefore, we needed to synthesize several 6-
phosphafulvene derivatives to carry out detailed studies in relation
to the 1,3,6-triphosphafulvene, and in this article we present prepa-
ration and structural characterization of novel 6-triphosphafulvenes.
Some electrophilic properties of the 6-phosphafulvenes are also
described.
RESULTS AND DISCUSSION
Compound 1 was lithiated to generate the corresponding cy-
clopentadienyl anion 2, and subsequently treated with (2,4,6-tri-t-
butylphenyl)phosphonous dichloride (Mes*PCl2; 3) at −78◦C to give
chlorophosphine 4 almost quantitatively as a 3:1 diastereomeric
[(R,S)/(S,R):(R,R)/(S,S)] ratio (Scheme 1). Compound 4 is an air sta-
ble solid, and one of the diastereomers was successfully recrystallized
to give single crystals suitable for X-ray diffraction. Figure 1 shows
an ORTEP drawing of the crystallized compound 4, which turned out
to possess the (R,S) configuration. Steric hindrance around the phos-
phorus atom causes distortion of the aromatic 6-membered ring to a
boat-like form, and correspondingly the ipso carbon atom in the Mes*
group is slightly pyramidalized [ꢀ(angles) = 354.1].9 The molecular
structure of 4 in the crystal is comparable to that of 3 showing distor-
tions around the phosphorus atom probably due to steric effects (Figure
2).10 However, in spite of the considerable steric encumbrance, the t-
butyl group at the cyclopentadienyl ring is not far from the Mes* moiety.
MM2 computations11 of the most stable conformer for the (R,S) isomer
(based on Figure 1) resulted in a conformation with a dihedral angle of

Sterically Demanding 6-Phosphafulvenes
919
SCHEME 1 Preparation of chlorophosphine 4 as a mixture of diastereomers.
120 degrees around the P–C1 bond [ꢁ(Cipso–P–C1–C2)] (Figure 3). This
sterically congested form of 4 would be affected by the CH-π interaction
between the Mes∗ and cyclopentadienyl groups12 and correspond to the
chemical shift at higher field of the proton at the C2 position and the
t-butyl group at the 5-membered ring. Accordingly, the major isomer of
4 could be assigned as the (R,S) configuration.
The diastereomeric mixture of 4 was allowed to react with DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene) at −78◦C to afford the corresponding
FIGURE 1 Molecular structure of 4 in the crystal; ellipsoids are drawn at
40% probability level. Hydrogen atoms except for H1 are omitted for clarity.
Selected distances (Å) and angles (◦): P–Cl 2.114(1), P–C1 1.867(3), P–C10
1.844(3), C1–C2 1.499(4), C1–C5 1.495(5), C2–C3 1.342(4), C3–C4 1.475(5),
C4–C5 1.339(5), C3–Ct-Bu 1.517(4), P–C10–C11 128.6(2), P–C10–C15 107.2(2),
ꢁ(C10–P–C1–C2) 61.1(2), ꢁ(Cmeta–Cortho–C10–P) 131.0(2), 136.7(2).

920
S. Ito et al.
FIGURE 2 Molecular structure of 3 in the crystal; ellipsoids are drawn at 40%
probability level. Hydrogen atoms are omitted. Bond angle (◦): P–Cipso–Cortho
130.8(9), 111.9(9).
6-phosphafulvene 5 as an E/Z isomeric mixture. The E/Z ratio of 5 at
−78◦C (1:3) corresponded to the diastereomeric ratio of the employed
4, and furthermore the E/Z ratio of 5, determined by 31P NMR spec-
troscopy, depended on the reaction temperatures as summarized in
Scheme 2.13 Taking into account the fact that HCl elimination afford-
ing 5 generally proceeds in the anti-type manner, the (R,S) isomer of
4 would afford E-5. However, our results (Scheme 2) indicate that the
FIGURE 3 Most stable conformation for the (R,S) isomer of 4a (optimized by
MM2 based on the molecular structure in Figure 1). Hydrogen atoms except
for that on the C(sp3) atom in the 5-membered ring are omitted.

Sterically Demanding 6-Phosphafulvenes
921
SCHEME 2 Preparation of 6-phosphafulvenes 5.
(R,S) isomers afford Z-5 via the syn-type HCl elimination of 4.14 Figure
4 displays calculated anti- and syn-periplanar conformations for 4, 4b
and 4c, which were obtained on the basis of the X-ray structure of 4
(Figure 1). It is likely that the reaction in Scheme 2 involves the inter-
mediacy of conformer 4a permitting the syn elimination solely at low
temperatures. On the other hand, at higher temperatures, the reaction
course may be dependent not only on conformational composition of
4, but also on changes in elimination rates, and correspondingly the
E/Z ratio would be varied. As for the (R,R) or (S,S) isomer of 4, the syn
elimination predominantly affords E-5 at low temperatures.
The geometrical isomerism of 5 corresponds to different melting
points. Both the E and Z isomers of 5 show almost the same rela-
tively low-field δP shifts as well as similar 13C NMR data and photo-
1
absorption properties. Alternatively, in the H NMR spectrum of Z-5,
the t-butyl group at the cyclopentadienyl ring indicates a ring-current
effect of the Mes* group, which might correspond to the NMR properties
of 4.
FIGURE 4 Anti-periplanar conformation (4b, left) and syn-periplanar confor-
mation (4b, right) for 4 (based on the structure in Figure 1). Hydrogen atoms
except for that on the C(sp3) atom in the 5-membered ring are omitted.

922
S. Ito et al.
FIGURE 5 Molecular structure of Z-5 in the crystal; ellipsoids are drawn at
50% probability level. One of the two independent molecules is shown. Hydro-
gen atoms are omitted for clarity. Selected distances (Å) and angles (◦): P1–C1
1.688(5), P1–CMes∗ 1.843(5), C1–C2 1.469(7), C1–C5 1.465(7), C2–C3 1.334(7),
C3–C4 1.465(7), C4–C5 1.358(7), C4–Ct-Bu 1.510(7), C1–P1–CMes∗ 100.2(2).
The E and Z isomers of 5 show different solubility in hexane, and
both of the E and Z isomers of 5 were successfully purified by recrystal-
lization. The structures were unambiguously determined by X-ray crys-
tallography, and Figures 5 and 6 display the structures of E-5 and Z-5,
respectively. The E isomer shows normal P C bond lengths and Mes*–
P–C angle together with an almost planar cyclopentadienyl ring. The
Mes* aromatic ring is almost perpendicular to the 6-phosphafulvene
plane to minimize steric congestion.
Similarly to fulvene derivatives,15 Z- and E-5 showed regioselec-
tive reactivity to nucleophiles. Both Z- and E-5 were allowed to re-
act with reagents such as alkyllithiums and hydrido lithium reagents
to generate the corresponding phosphinocyclopentadienyl anions 6 as
room-temperature stable species (Scheme 3). According to our previ-
ous report on the 1,3,6-triphosphafulvene,8 we attempted preparation
of a phosphorus ylide bearing a P–H bond (7). However, the desired
compound 7 was not observed in the reaction mixture; instead phos-
phinocyclopentadiene derivative 8 was observed as a mixture of iso-
mers due to protonation at the cyclopentadienyl group. Less steric

Sterically Demanding 6-Phosphafulvenes
923
FIGURE 6 Molecular structure of E-5 in the crystal; ellipsoids are drawn at
50% probability level. Selected distances (Å) and angles (◦): P1–C1 1.693(6),
P1–CMes∗ 1.858(6), C1–C2 1.462(8), C1–C5 1.453(8), C2–C3 1.348(8), C3–C4
1.462(8), C4–C5 1.333(9), C4–Ct-Bu 1.510(8), C1–P–CMes∗ 102.0(3).
encumbrance and stability of the cyclopentadienyl ring compared with
the 1,3,6-triphosphafulvene derivative, which bears three Mes* groups
and three P=C bonds,8 might be prone to cause protonation on the
cyclopentadienyl ring of 6.
SCHEME 3 Reaction of 5 with nucleophiles.

924
S. Ito et al.
In conclusion, we have described the synthesis of novel 6-
phosphafulvene derivatives 5 via HCl elimination of chlorophosphine
4. Structure elucidation of 4 gave information to explain the reac-
tion mechanism from 4 to 5. The structures of the Z- and E-isomers
of 5 were unambiguously determined by X-ray crystallography, and
their electrophilicity affording phosphinocyclopentadienyl anions was
characterized.
EXPERIMENTAL
Preparation of 4
To a solution of t-butylcyclopentadiene16 (1, 5.6 mmol) in THF (20 mL),
–3
butyllithium (5.6 mmol, 1.6 M solution in hexane, 1 M = 1 mol dm
)
at −78◦C was added, and the mixture was stirred for 5 min to fur-
nish 2. A solution of (2,4,6-tri-t-butylphenyl)phosphonous dichloride (3,
2.1 g, 6.0 mmol)17 in THF (20 mL) was added dropwise to the THF
solution of 2, and the mixture was stirred for 5 min. The reaction mix-
ture was allowed to warm up to room temperature, and the volatile
materials were removed in vacuo. The residue was washed with ace-
tonitrile to afford 2.2 g of 4 (3:1 mixture of diastereomers, 98% yield) as
colorless solid. Single crystals were obtained by recrystallization from
dichloromethane at 0◦C. Mp 95–97◦C (decomp); H NMR (400 MHz,
1
CDCl3): major isomer: δ = 7.40 (s, 2H, Mes∗), 6.71 (s, 1H, CH), 6.70 (s,
2
1H, CH), 4.45 (d, JPH = 15.1 Hz, 1H, PCH), 3.94 (s, 1H, H-C2), 1.60
(brs, 18H, o-t-Bu), 1.37 (s, 9H, p-t-Bu), 0.97 (s, 9H, t-Bu); minor isomer:
δ = 7.40 (s, 2H, Mes∗), 6.43 (s, 1H, CH), 6.27 (s, 1H, CH), 4.47 (s, 1H,
H-C2), 4.45 (d, 2JPH = 14.8 Hz, 1H, PCH), 1.60 (brs, 18H, o-t-Bu), 1.37
(s, 9H, p-t-Bu), 1.16 (s, 9H, t-Bu). 13C{ H} NMR (151 MHz, CDCl3):
1
major isomer: δ = 160.1 (d, JPC = 6.0 Hz, Ct-Bu), 157.7 (s, o-Mes∗),
3
152.4 (s, p-Mes∗), 140.0 (d, 1JPC = 81.1 Hz, ipso-Mes∗), 137.2 (d, 2JPC
=
14.3 Hz, CH), 134.8 (d, 3JPC = 5.0 Hz, CH), 122.7 (s, m-Mes∗), 120.2 (d,
2JPC = 13.1 Hz, CH), 59.3 (d, JPC = 43.9 Hz, PCH), 39.4 (s, o-CMe3),
1
34.3 (s, o-CMe3), 32.1 (s, p-CMe3), 31.2 (s, p-CMe3), 29.7 (s, CMe3), 29.3
3
(s, CMe3); minor isomer: δ = 159.8 (d, JPC = 6.2 Hz, Ct-Bu), 157.7 (s,
o-Mes∗), 152.3 (s, p-Mes∗), 139.5 (d, JPC = 81.0 Hz, ipso-Mes∗), 135.4
1
(d, 3JPC = 4.8 Hz, CH), 130.6 (d, JPC = 11.9 Hz, CH), 126.4 (d, JPC
=
2
2
12.0 Hz, CH), 122.7 (s, m-Mes∗), 59.3 (d, 1JPC = 43.9 Hz, PCH), 39.4 (s,
o-CMe3), 34.3 (s, o-CMe3), 32.1 (s, p-CMe3), 31.2 (s, p-CMe3), 29.7 (s,
CMe3), 29.3 (s, CMe3). 31P{ H} NMR (162 MHz, CDCl3): major isomer:
1
δ = 69.2; minor isomer: δ = 72.1. EI-MS (70 eV) m/z (rel. intensity): 432
(M+, 19 %), 311 (Mes∗PCl, 100 %). ESI-MS found: 471.2553, calcd for
C27H42ClP·ONa 471.2554.

Sterically Demanding 6-Phosphafulvenes
925
Preparation of 5
To a solution of 4 (3:1 mixture of diastereomers, 2.2 g, 5.5 mmol) in
hexane (30 mL), DBU (8.4 mmol) was added, and the mixture was
stirred for 0.5 h. The reaction mixture was monitored by 31P NMR
spectroscopy, and both Z-5 and E-5 were observed in a 3:1 ratio. The
solvent was removed in vacuo, and the residue was purified by silica
gel column chromatography (hexane) to afford a mixture of Z-5 and
E-5 as deep red solids. Recrystallization from hexane afforded pure E-5
1
at first and Z-5 subsequently. Z-5: 770 mg (35%). Mp 104–106◦C. H
NMR (400 MHz, CDCl3): δ = 7.41 (s, 2H, Mes∗), 6.45 (s, 2H, H3 and
H4), 4.49 (s, 1H, H1), 1.43 (s, 18H, o-t-Bu), 1.38 (s, 9H, p-t-Bu), 0.99
1
1
(s, 9H, t-Bu). 13C{ H} NMR (151 MHz, CDCl3): δ = 182.3 (d, JPC
=
40.2 Hz, P=C), 156.9 (d, 3JPC = 22.0 Hz, C2), 155.3 (s, o-Mes∗), 150.8 (s,
p-Mes∗), 137.8 (d, 1JPC = 55.7 Hz, ipso-Mes∗), 130.5 (d, 3JPC = 25.3 Hz,
C3), 127.6 (d, JPC = 37.0 Hz, C4), 121.3 (s, m-Mes∗), 113.0 (d, JPC
=
2
2
4
11.4 Hz, C1) 38.5 (s, o-CMe3), 35.5 (s, p-CMe3), 34.3 (d, JPC = 7.2 Hz,
o-CMe3), 32.3 (s, CMe3), 31.9 (s, p-CMe3), 29.9 (s, CMe3); 31P{ H} NMR
1
–3
(162 MHz, CDCl3): δ = 296.0. UV (hexane) λmax (ε x 10
M
–1cm–1):
380 (2.0), 324 (21.0), 237 (10.0) nm. EA Calcd for C27H41P: C 81.77, H
10.42; found: C 81.42, H 10.44. E-5: 370 mg (17%). Mp 179–181◦C. H
1
NMR (400 MHz, CDCl3): δ = 7.48 (s, 2H, Mes∗), 6.36 (s, 1H, H3), 6.23
(s, 1H, H4), 4.98 (s, 1H, H1), 1.53 (s, 18H, o-t-Bu), 1.42 (s, 9H, p-t-Bu),
1.25 (s, 9H, t-Bu). 13C1H NMR (151 MHz, CDCl3) δ = 182.3 (d, JPC
=
1
40.2 Hz, P C), 157.3 (d, JPC = 27.0 Hz, C2), 155.1 (s, o-Mes∗), 150.7
3
(s, p-Mes∗), 137.3 (d, JPC = 97.2 Hz, ipso-Mes∗), 130.6 (d, JPC = 18.7
1
3
Hz, C3), 121.2 (s, m-Mes∗) 121.0 (d, 2JPC = 7.0 Hz, C4), 118.1 (d, 2JPC
=
4
34.1 Hz, C1) 38.5 (s, o-CMe3), 35.5 (s, p-CMe3), 34.3 (d, JPC = 7.0 Hz,
o-CMe3), 32.6 (s, CMe3), 31.9 (s, p-CMe3), 30.1 (s, CMe3). 31P{ H} NMR
1
–3
(162 MHz, CDCl3): δ = 295.0. UV (hexane) λmax (ε x 10
M
–1cm–1):
380 (2.2), 323 (22.0), 236 (11.0) nm. EA Calcd. for C27H41P: C 81.77, H
10.42; found: C 81.82, H 10.34.
Reaction of Z/E-5 with Alkyllithiums: Typical Procedures
To a solution of Z-5 (10 mg, 2.5 µmol) in THF (0.5 mL), methyllithium
(5.0 µmol) at −78◦C was added and was monitored by 31P NMR spec-
troscopy after warming up to room temperature. The corresponding
anion 6 was observed at δP –40 (R = Me) or –26 (R = n-Bu). The re-
action solution was treated with acetic acid to give 8 as a mixture of
diastereomers at δP –38, –39, and –42 (R = Me) or δP –24, –25, and –28
(R = n-Bu). Almost the same results were obtained in the reaction of
E-5.

926
S. Ito et al.
X-Ray Crystallography
3: C18H29Cl2P: M = 347.31, monoclinic, P21/a (No. 14), a = 16.707(2),
b = 11.678(2), c = 9.780(2) Å, β = 90.511(4)◦, V = 1908.1(5) Å3, Z = 4,
T = 143 K, ρcalcd = 1.209 g cm–3, µ(MoKα) = 0.417 mm–1, 2θmax = 55.0◦,
13538 observed reflections, 13031 unique reflections (Rint = 0.067), R1
= 0.250 (I > 2σ(I)), Rw = 0.530 (all data) (CCDC-668729). The high R
value might be due to the crystal of low quality. 4: C27H42ClP: M =
433.06, monoclinic, P21/n (No. 14), a = 8.9814(3), b = 17.6217(5), c =
16.5341(5) Å, β = 93.331(1)◦, V = 2612.4(1) Å3, Z = 4, T = 140 K, ρcalcd
=
1.101 g cm–3, µ(MoKα) = 0.218 mm–1, 2θmax = 55.0◦, 21012 observed re-
flections, 12116 unique reflections (Rint = 0.050), R1 = 0.056 (I > 2σ(I)),
Rw = 0.068 (all data) (CCDC-667900). Z-5: C27H41P: M = 396.59, mon-
oclinic, P21/c (No. 14), a = 16.369(1), b = 16.3314(5), c = 19.3928(5) Å,
β = 91.235(2)◦, V = 5142.1(4) Å3, Z = 8, T = 153 K, ρcalcd = 1.025 g
cm–3, µ(MoKα) = 0.116 mm–1, 2θmax = 55.0◦, 38939 observed reflec-
tions, 13891 unique reflections (Rint = 0.124), R1 = 0.105 (I > 2σ(I)),
Rw = 0.194 (all data) (CCDC-667901). E-5: C27H41P: M = 396.59, mon-
oclinic, P−1 (No. 2), a = 11.387(3), b = 11.533(3), c = 9.558(2) Å, α =
88.20(2), β = 90.28(2), γ = 88.75(1)◦, V = 1254.2(5) Å3, Z = 2, T = 143
K, ρcalcd = 1.050 g cm–3, µ(MoKα) = 0.119 mm–1, 2θmax = 55.0◦, 8189
observed reflections, 3525 unique reflections (Rint = 0.078), R1 = 0.138
(I > 2σ(I)), Rw = 0.288 (all data) (CCDC-667902).
The high R values for Z- and E-5 might be due to the presence of
unsolved molecular structures. Attempts to solve the structures with
either lower symmetrical space groups or larger crystal lattices failed.
REFERENCES
[1] (a) M. Yoshifuji and S. Ito, Top. Curr. Chem., 223, 67 (2003); (b) M. Regitz and O.
J. Scherer, Eds., Multiple Bonds and Low Coordination in Phosphorus Chemistry
(Thieme, Stuttgart, 1990); (c) K. B. Dillon, F. Mathey, and J. F. Nixon, Phosphorus:
The Carbon Copy, (Wiley, Chichester, 1998).
[2] F. Ozawa and M. Yoshifuji, Dalton Trans., 4987 (2006).
[3] T. Baumgartner and R. Re´au, Chem. Rev., 106, 4681 (2006).
[4] (a) G. Ma¨rkl and K. M. Raab, Tetrahedron Lett., 30, 1077 (1989); (b) A. Al Badri,
M. Chentit, M. Geoffroy, and A. Jouaiti, J. Chem. Soc., Faraday Trans., 93, 3631
(1997).
[5] S. Ito, H. Sugiyama, and M. Yoshifuji, Angew. Chem., Int. Ed., 39, 2781 (2000).
[6] S. Ito, H. Miyake, H. Sugiyama, and M. Yoshifuji, Tetrahedron Lett., 45, 7019 (2004).
[7] S. Ito, H. Miyake, H. Sugiyama, and M. Yoshifuji, Heterocycles, 63, 2591 (2004).
[8] S. Ito, H. Miyake, M. Yoshifuji, T. Ho¨ltzl, and T. Veszpre´mi, Chem. Eur. J., 11, 5960
(2005).
[9] (a) M. Yoshifuji, I. Shima, N. Inamoto, and T. Aoyama, Tetrahedron Lett., 32, 3057
(1981); (b) M. Freytag, P. G. Jones, R. Schmutzler, and M. Yoshifuji, Heteroatom

Sterically Demanding 6-Phosphafulvenes
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Chem., 12, 300 (2001); 12, 457 (2001); (c) S. Ito and M. Yoshifuji, Sci. Rep. Tohoku
University Ser. 1, 79, 9 (2002); (d) M. Unno, Y. Kawai, and H. Matsumoto, Heteroatom
Chem., 12, 238 (2001).
[10] (a) R. J. Wehmschulte, M. A. Khan, and S. I. Hossain, Inorg. Chem., 40, 2756
(2001); (b) C. Overla¨nder, J. J. Tirre´e, M. Nieger, E. Niecke, C. Moser, S. Spirk, and
R. Pietschnig, Adv. Organometal. Chem., 21, 46 (2007).
[11] J.-H. Lii, S. Gallion, C. Bender, H. Wikstrom, N. L. Allinger, K. M. Flurchick, and
M. M. Teeter, J. Comp. Chem., 10, 503 (1989).
[12] S. Tsuzuki, K. Honda, T. Uchimaru, M. Mikami, and K. Tanabe, J. Am. Chem. Soc.,
122, 3746 (2000).
[13] No E/Z isomerization of 5 was observed upon heating.
[14] R. W. Carling and A. B. Holmes, J. Chem. Soc., Chem. Commun., 325 (1986).
[15] K. Ziegler, H.-G. Gellert, H. Martin, K. Nagel, and J. Schneider, Liebigs Ann. Chem.,
589, 91 (1954).
[16] (a) D. L. Compton and T. B. Rauchfuss, Organometallics, 13, 4367 (1994); (b) D.
Tews and P. E. Gaede, Tetrahedron Lett., 45, 9029 (2004).
[17] M. Yoshifuji, I. Shima, N. Inamoto, K. Hirotsu, and T. Higuchi, J. Am. Chem. Soc.,
103, 4587 (1981).