Phosphorus-bridged [1.1]ferrocenophane with syn and anti conformations

Article abstract of DOI:10.1021/om049155w

Photolysis of PPh-bridged [1]ferrocenophane (1) in THF gave PPh-bridged [1.1]ferrocenophane (2) as a minor dimer along with major polymeric products. After subsequent sulfurization of the reaction mixture with elemental sulfur, both syn and anti isomers of P(S)Ph-bridged [1.1]ferrocenophane (3) were successfully isolated and characterized by X-ray analysis, syn-3 thus obtained was desulfurized stereoretentively to syn-2 with Si₂Cl₆ in refluxing benzene, while anti-3 primarily gave the isomerized product, syn-2. Stereoretentive desulfurization of anti-3 to anti-2 was achieved with CF ₃SO₃Me/P(NMe₂)₃ at room temperature. anti-2 thus obtained could be converted almost completely to syn-2 upon simple heating in toluene, indicative of the thermal instability of the anti isomer over the syn isomer. The yield of syn-2 was improved from 9% to 32% when THF used in the photolysis was replaced with ether and the reaction mixture was heated so as to isomerize anti-2, which had been formed concomitantly. A potential utility of syn-2 as a ligand was demonstrated by the formation of [CoCl₂(syre-2)] (5) through a reaction of syn-2 with CoCl ₂.

Full text of DOI:10.1021/om049155w

990
Organometallics 2005, 24, 990-996
Phosphorus-Bridged [1.1]Ferrocenophane with syn and
anti Conformations
Tsutomu Mizuta, Yuki Imamura, and Katsuhiko Miyoshi*
Department of Chemistry, Graduate School of Science, Hiroshima University,
Kagamiyama 1-3-1, Higashi-Hiroshima, Hiroshima 739-8526, Japan
Hideki Yorimitsu and Koichiro Oshima
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto-daigaku Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
Received October 30, 2004
Photolysis of PPh-bridged [1]ferrocenophane (1) in THF gave PPh-bridged [1.1]ferro-
cenophane (2) as a minor dimer along with major polymeric products. After subsequent
sulfurization of the reaction mixture with elemental sulfur, both syn and anti isomers of
P(S)Ph-bridged [1.1]ferrocenophane (3) were successfully isolated and characterized by X-ray
analysis. syn-3 thus obtained was desulfurized stereoretentively to syn-2 with Si2Cl6 in
refluxing benzene, while anti-3 primarily gave the isomerized product, syn-2. Stereoretentive
desulfurization of anti-3 to anti-2 was achieved with CF3SO3Me/P(NMe2)3 at room temper-
ature. anti-2 thus obtained could be converted almost completely to syn-2 upon simple heating
in toluene, indicative of the thermal instability of the anti isomer over the syn isomer. The
yield of syn-2 was improved from 9% to 32% when THF used in the photolysis was replaced
with ether and the reaction mixture was heated so as to isomerize anti-2, which had been
formed concomitantly. A potential utility of syn-2 as a ligand was demonstrated by the
formation of [CoCl2(syn-2)] (5) through a reaction of syn-2 with CoCl2.
Introduction
[1.1]Ferrocenophanes, in which two ferrocenes are
linked together via two ERn groups (Figure 1), have been
a subject of intensive study since the 1960s.1,2 Much
attention has been paid to their peculiar molecular
structures ever since the first X-ray structure was
reported for 1,12-dimethyl[1.1]ferrocenophane by Watts
et al.3 Many types of [1.1]ferrocenophanes bearing a
variety of ERn bridging groups have been synthesized
and characterized by X-ray analysis, as listed in Table
1.4 Among them, heteroatom bridges such as group 13
(B, Ga),5,6 group 14 (Si, Sn),7,8 and group 15 (P)9 have
Figure 1. Two conformations of ERn-bridged [1.1]ferro-
cenophane.
recently attracted interest. These ferrocenophanes take
either a syn- or anti-conformation, as shown in Figure
1.
It is known that whether a [1.1]ferrocenophane adopts
a syn- or anti-conformation depends on the balance of
the two types of intramolecular steric repulsions in it.2
One is that between the two hydrogen atoms at R- and
R′-positions. Molecular models demonstrate that the
* To whom correspondence should be addressed. Fax: +81-82-424-
0729. E-mail: kmiyoshi@sci.hiroshima-u.ac.jp.
(1) (a) Watts, W. E. J. Am. Chem. Soc. 1966, 88, 855-856. (b) Watts,
W. E. J. Organomet. Chem. 1967, 10, 191-192.
(2) Mueller-Westerhoff, U. T. Angew. Chem., Int. Ed. Engl. 1986,
25, 702-717.
(3) McKechnie, J. S.; Bersted, B. H.; Paul, I. C.; Watts, W. E. J.
Organomet. Chem. 1967, 8, P29-P31.
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Stammler, H.-G. Organometallics 2003, 22, 2766-2774. (b) Uhl, W.;
Hahn, I.; Jantschak, A.; Spies, T. J. Organomet. Chem. 2001, 637-
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Angew. Chem., Int. Ed. 2001, 40, 1424-1427
(7) (a) Berenbaum, A.; Lough, A. J.; Manners, I. Organometallics
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P.; Coche-Guerente, L. Organometallics 2001, 20, 4211-4215. (c)
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P.; Davidsson, O¨ .; Lo¨ewendahl, M.; Hilmersson, G.; Karlsson, A.;
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4741. (d) Ahlberg, P.; Davidsson, O¨ .; Hilmersson, G.; Lo¨ewendahl, M.;
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10.1021/om049155w CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/03/2005

Phosphorus-Bridged [1.1]Ferrocenophane
Organometallics, Vol. 24, No. 5, 2005 991
Table 1. Molecular Structures Determined by
X-ray Analysis for ERn-Bridged
[1.1]Ferrocenophanes
Scheme 1
bridging group
E-Cp length
conformation average (Å)
E
R1
R2
ref
C
H or dO
H or non
H
syn
1.50, 1.47
1.504
1.509
1.513
1.509
1.651
1.823
1.860
1.829
1.848
1.9449
1.963b
1.933
2.136
2.142
2.146
4a
C
C
C
C
H
H
H
H
syn
4f
Me
syn
syn
anti
syn
anti
anti
anti
anti
anti
anti
anti
anti
anti
anti
4c
Results and Discussion
Me
4h
4e
5
Me
B- Me
Me
Isolation of [1.1]Ferrocenophane. Phosphorus-
bridged [1]ferrocenophane is known to undergo a ring-
opening reaction driven by its highly strained ring
structure.11,12 We have previously reported that the
UV-vis irradiation of PhP-bridged [1]ferrocenophane,
1, induces a ring-opening reaction to give dimer 2 as
well as polymeric products, as shown in Scheme 1.10
Before the direct separation of 2 from the polymeric
products, the phosphorus centers were sulfurized by a
reaction with elemental sulfur in order to prevent
oxidation by air. The subsequent separation using silica
gel column chromatography afforded yellow and orange
dimers 3 in ca. 9% yield each. The X-ray structure of
the former yellow dimer is shown in Figure 2, where
two ferrocene units are linked through phosphorus
atoms to form a [1.1]ferrocenophane framework with a
centric symmetry. The two phosphorus bridging groups
are arranged in an anti-disposition, with two phenyl
groups located at exo-positions. The main structural
features of a [1.1]ferrocenophane molecule are usually
given by four essential angles: twist, rotation, tilt, and
bridge angles (see Figure 3).4c The small tilt angle of
2.91(7)° for anti-3 indicates that each ferrocene unit
consists of almost parallel Cp rings. The twist angle also
has a small value of 2.91(7)°, which is exactly the same
as the tilt angle due to the centric symmetry, thereby
P
Men
Men
Me
9
Si Me
Si Cl
Si Me
Ga Me
Ga Me
7c, 7d
7b
7a
6a
6a
6b
8b
8a
8a
Cl
CC-R
non
basea
Ga CH(SiMe3)2 non
Sn n-Bu
Sn t-Bu
Sn Mes
n-Bu
t-Bu
Mes
a Base: ether, pyridine, pyrimidine, quinoxaline, pyridine, and
dioxane. b An average value of all base adducts.
anti isomer is rigid and not able to relieve that repul-
sion, while the syn isomer is flexible and can easily twist
to relieve it. The other is the repulsion between the two
ERn groups, which is conceivable only in the syn isomer.
To take a CH2-bridged complex in Table 1 as an
example, the former repulsion in the anti isomer is
substantial because the two CH2 bridges form very short
Cp-ERn bonds, leading to a close approach of the R-
and R′-hydrogens. In contrast, the latter repulsion in
the corresponding syn isomer is subtle because it is
practically between the hydrogen atoms of the CH2
bridges. Therefore, the syn-conformation is preferable
for the CH2-bridged complex, as is actually the case
(Table 1). An example that exhibits the opposite prefer-
ence is an SnBu2-bridged complex, in which the SnBu2
bridges form fairly long Cp-ERn bonds and have bulky
butyl groups (see Table 1).
On the basis of the above perspective, a PR-bridged
complex is in a delicate situation because the Cp-P
bond length (ca. 1.80-1.84 Å) is in a range where the
syn-anti preference is switched, as shown in Table 1.
Brunner et al. have reported PMen-bridged [1.1]ferro-
cenophane (Men ) menthyl) adopting an anti-conforma-
tion, but they did not mention its relative stability in
comparison with the corresponding syn isomer, nor did
they try to prepare the syn isomer.9 However, the syn
isomer of phosphorus-bridged [1.1]ferrocenophane is
worth preparing because it can be utilized as a novel
bidentate chelate, which has two phosphorus donor
atoms that are doubly bridged by the two ferrocene
units, and thus can be expected to serve as a novel
supporting ligand for metal-catalyzed transformations.
(11) (a) Butler, I. R.; Cullen, W. R.; Einstein, F. W. B.; Rettig, S. J.;
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H. P., Jr.; Seyferth, D.; Fellmann, J. D.; Garrou, P. E.; Martin, S.
Organometallics 1982, 1, 1283-1288. (d) Osborne, A. G.; Whiteley, R.
H.; Meads, R. E. J. Organomet. Chem. 1980, 193, 345-357. (e) Stoeckli-
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194, 91-101.
(12) For example, see: (a) Hierso, J.-C.; Lacassin, F.; Broussier, R.;
Amardeil, R.; Meunier, P. J. Organomet. Chem. 2004, 689, 766-769.
(b) Paquet, C.; Cyr, P. W.; Kumacheva, E.; Manners, I. Chem. Commun.
2004, 234-235. (c) Mizuta, T.; Onishi, M.; Nakazono, T.; Nakazawa,
H.; Miyoshi, K. Organometallics 2002, 21, 717-726. (d) Wang, X. S.;
Winnik, M. A.; Manners, I. Macromolecules 2002, 35, 9146-9150. (e)
Cao, L.; Massey, J. A.; Peckham, T. J.; Winnik, M. A.; Manners, I.
Macromol. Chem. Phys. 2001, 202, 2947-2953. (f) Stepnicka, P.; Base,
T. Inorg. Chem. Commun. 2001, 4, 682-687. (g) Cao, L.; Manners, I.;
Winnik, M. A. Macromolecules 2001, 34, 3353-3360. (h) Evans, C. E.
B.; Lough, A. J.; Grondey, H.; Manners, I. New J. Chem. 2000, 24,
447-453. (i) Cao, L.; Winnik, M. A.; Manners, I. J. Inorg. Organomet.
Polym. 1998, 8, 215-224. (j) Herberhold, M.; Hertel, F.; Milius, W.;
Wrackmeyer, B. J. Organomet. Chem. 1999, 582, 352-357. (k) Peck-
ham, T. J.; Massey, J. A.; Honeyman, C. H.; Manners, I. Macromol-
ecules 1999, 32, 2830-2837. (l) Honeyman, C. H.; Peckham, T. J.;
Massey, J. A.; Manners, I. J. Chem. Soc., Chem. Commun. 1996, 2589-
2590. (m) Mizuta, T.; Yamasaki, T.; Nakazawa, H.; Miyoshi, K.
Organometallics 1996, 15, 1093-1100. (n) Podlaha, J.; Stepnicka, P.;
Ludvik, J.; Cisarova, I. Organometallics 1996, 15, 543-550. (o)
Honeyman, C. H.; Foucher, D. A.; Dahmen, F. Y.; Rulkens, R.; Lough,
A. J.; Manners, I. Organometallics 1995, 14, 5503-5512. (p) Butler, I.
R.; Cullen, W. R.; Rettig, S. J.; White, A. S. C. J. Organomet. Chem.
1995, 492, 157-164. (q) Cullen, W. R.; Rettig, S. J.; Zheng, T. C. J.
Organomet. Chem. 1993, 452, 97-103. (r) Butler, I. R. Polyhedron
1992, 11, 3117-3121. (s) Butler, I. R.; Cullen, W. R.; Rettig, S. J.
Organometallics 1987, 6, 872-880. (t) Butler, I. R.; Cullen, W. R.; Kim,
T. J.; Rettig, S. J.; Trotter, J. Organometallics 1985, 4, 972-980. (u)
Butler, I. R.; Cullen, W. R.; Einstein, F. W. B.; Willis, A. C. Organo-
metallics 1985, 4, 603-604. (v) Butler, I. R.; Cullen, W. R. Organo-
metallics 1984, 3, 1846-1851.
Our group has recently reported the ring-opening
polymerization of PPh-bridged [1]ferrocenophane in-
duced by UV-vis irradiation.10 In addition to polymeric
products, dimers were isolated from the reaction mix-
ture, though their yields were low. Here we report the
details of their molecular structures, syn-anti prefer-
ence, and coordination behavior to a metal fragment.
(10) Mizuta, T.; Onishi, M.; Miyoshi, K. Organometallics 2000, 19,
5005-5009.

992 Organometallics, Vol. 24, No. 5, 2005
Mizuta et al.
Figure 2. ORTEP drawing of anti-3 with 50% thermal
ellipsoids. Selected bond distances (Å) and angles (deg):
S-P 1.9549(5), P-C1, 1.794(1), P-C6* 1.800(1), P-C11
1.824(1), S-P-C1 114.23(5), S-P-C6* 113.30(5), C1-P-
C6* 110.88(6). Symmetry transformation used to generate
equivalent (asterisked) atoms: (-x, -y+1, -z).
Figure 4. ORTEP drawing of syn-3 with 50% thermal
ellipsoids. Selected bond distances (Å) and angles (deg):
S-P 1.9421(6), P-C1, 1.803(2), P-C6* 1.782(2), P-C11
1.825(2), S-P-C1 114.28(7), S-P-C6* 114.63(6), C1-P-
C6* 109.21(8). Symmetry transformation used to generate
equivalent (asterisked) atoms: (-x, y, -z+0.5).
ppm. The syn structure of the product was confirmed
by X-ray analysis, as shown in Figure 5. Similar
treatment was also applied to the desulfurization of
anti-3 in the hopes of getting the corresponding anti-2.
However, the 31P{1H} NMR spectrum of the product
showed a chemical shift almost identical to that of syn-
2, suggesting that an anti-to-syn isomerization had
taken place during the desulfurization reaction in
refluxing benzene. To confirm that the product was not
anti-2 but syn-2, the desulfurized product of anti-3 was
sulfurized again. The 31P{1H} NMR chemical shift of
the resulfurized product was found identical to that of
syn-3. Since refluxing in benzene probably induced the
isomerization, desulfurization of anti-3 was also carried
out at room temperature using CF3SO3Me/P(NMe2)3.14
However, because of the poor solubility of the product
in the usual laboratory solvents, its spectroscopic char-
acterization was unsuccessful as it was. Thus, the
product was characterized as the resulfurized form,
which turned out to give spectroscopic data identical to
those of anti-3, demonstrating that the anti-conforma-
tion is retained during the present desulfurization of
anti-3.
Figure 3. Description of the four essential angles in a [1.1]-
ferrocenophane molecule.4c
indicating the coplanarity of the two Cp rings bonding
to the same phosphorus center.
A molecular structure for the other dimer 3 is shown
in Figure 4, where the dimer adopts a syn-conformation
with C2 symmetry. A significant steric repulsion is
anticipated at first glance between both sulfur atoms
of syn-3, but actually syn-3 avoids it by adopting a
significantly large twist angle of 42.5(1)° to sufficiently
separate the sulfur atoms from each other. In addition,
the two Cp rings of each ferrocene unit are tilted by 8.2-
(1)° so as to enlarge the separation of the two sulfur
atoms.
syn-3 thus obtained was desulfurized by treatment
with Si2Cl6 in refluxing benzene.13 The 31P NMR signal
of the desulfurized product, 2, was observed at -29.7
Improvement of the Yield of syn-2. The molecular
structure of syn-2 shown in Figure 5 suggests a potential
utility as a novel diphosphine chelate in which two lone
(13) (a) Naumann, K.; Zon. G.; Mislow, K. J. Am. Chem. Soc. 1969,
91, 7012-7023. (b) Naumann, K.; Zon. G.; Mislow, K. J. Am. Chem.
Soc. 1969, 91, 7023-7030.
(14) Omelankzuk, J.; Mikolajczyk, M. Tetrahedron. Lett. 1984, 25,
2493-2496.

Phosphorus-Bridged [1.1]Ferrocenophane
Organometallics, Vol. 24, No. 5, 2005 993
Scheme 2
therefore expected that high-dilution conditions may
enhance the latter intramolecular ring-closure of 4. THF
in Scheme 2 acts as a strongly donating solvent that
facilitates formation of the ring-opened intermediates,
primarily leading to polymeric products. Conversely, if
a less donating solvent is employed, formation of the
ring-opened intermediates is suppressed to lead to a low
concentration of the intermediate 4, which has a greater
chance of undergoing the intramolecular ring-closure of
4. Ether was chosen as such a less donating solvent.
Actually, the photolysis in ether proceeded slowly,
taking a few hours for complete consumption of the
starting 1, while the reaction in THF was completed
within 10 min. Separation of the sulfurized dimer
following the procedures described above gave a syn-
anti mixture of 3 in about 2 times the yield. In addition,
the desulfurization in refluxing benzene has been
confirmed to accompany the anti-to-syn isomerization.
Thus, a crude mixture of syn- and anti-2 obtained by
the above modified photolysis was heated overnight in
toluene at a higher temperature to further improve the
yield of syn-2. In this case, without sufurization, syn-2
could be isolated directly by an Al2O3 column in 32%
yield.
Figure 5. ORTEP drawing of syn-2 with 50% thermal
ellipsoids. Selected bond distances (Å) and angles (deg):
P-C1, 1.826(1), P-C6* 1.810(1), P-C11 1.849(1), C1-
P-C6* 105.96(6), C1-P-C11 98.29(6), C6*-P-C11
100.63(6). Symmetry transformation used to generate
equivalent (asterisked) atoms: (-x+1, y, -z+1.5).
pairs on the phosphorus atoms are nicely disposed for
coordination to a metal. However, the yield of syn-2 in
the photolysis described above is too low to perform
preparative scale studies. For SiR2-bridged [1]ferro-
cenophane, a transition-metal-catalyzed ring-opening
reaction gives [1.1]ferrocenophane in high to moderate
yields.7a,15-17 However, the addition of a palladium(0)
complex such as Pd(PPh3)4 to a solution of 1 did not give
any desired products, probably because of the strong
metal coordination expected for the starting 1 as well
as for the products derived from it.
Preparation of Cobalt Complex. To explore the
structural properties of syn-2 coordinated to a transition
metal fragment, Co(II) was selected as a tetrahedral
metal center that tolerates a relatively wide range of
bite angles formed by diphosphine chelates, 96.3(1)°
for [CoCl2(dppp)],19 107.87(3)° for [CoCl2(dppf)],20 and
114.57(6)° for [CoCl2{MeN(CH2CH2PPh2)2}].21
syn-2 was allowed to react with CoCl2 in THF to give
green CoCl2(syn-2) (5) in an almost quantitative yield.
The molecular structure of 5 determined by X-ray
analysis is shown in Figure 6, where syn-2 coordinates
to CoCl2 to form a tetrahedral coordination sphere. The
two phosphorus donor atoms of syn-2 are doubly linked
with two ferrocene units, which occupy the front and
back spaces of the coordination plane defined by a CoP2
core. The bite angle P-Co-P is 95.62(2)°, which is much
smaller than the ideal tetrahedral angle of 109.5°. It is
noteworthy that the bite angle of syn-2 in 5 is also much
smaller than the 107.87(3)° angle found in the corre-
sponding dppf complex possessing a single ferrocene
linker. For dppf coordinating to the CoCl2 fragment, two
Cp rings of the ferrocene unit are approximately eclipsed
Formation of the cyclic dimer 2 from 1 is a side
reaction of the polymerization (Scheme 1). We have
demonstrated that the photolytic ring-opening reaction
proceeds through the cleavage of the Cp-Fe bond, as
shown in Scheme 2.18 The major reaction that follows
is a successive intermolecular coupling between some
sorts of ring-opened intermediates, leading eventually
to the polymeric products. On the other hand, the dimer
2 is probably formed through an intramolecular head-
to-tail ring-closure of the dimeric intermediate 4. It is
(15) Reddy, N. P.; Choi, N.; Shimada, S.; Tanaka, M. Chem. Lett.
1996, 649-650.
(16) (a) Ni, Y.; Rulkens, R.; Pudelski, J. K.; Manners, I. Macromol.
Rapid Commun. 1995, 16, 637-641. (b) Zechel, D. L.; Hultzsch, K. C.;
Rulkens, R.; Balaishis, D.; Ni, Y.; Pudelski, J. K.; Lough, A. J.;
Manners, I. Organometallics 1996, 15, 1972-1978. (c) Gomez-Elipe,
P.; Resendes, R.; Mcdonald, P. M.; Manners, I. J. Am. Chem. Soc. 1998,
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(19) dppp ) 1,3-bis(diphenylphosphino)propane. Heinze, K.; Hutt-
ner, G.; Zsolnai, L.; Schober, P. Inorg. Chem. 1997, 36, 5457-5469.
(20) dppf ) 1,1′-bis(diphenylphosphino)ferrocene. Park, T.-J.; Huh,
S.; Kim, Y.; Jun, M.-J. Acta Crystallogr. Sect. C 1999, C55, 848-850.
(21) Wang, M.; Yu, X.; Shi, Z.; Qian, M.; Jin, K.; Chen, J.; He, R. J.
Organomet. Chem. 2002, 645, 127-133.
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18, 1030-1040.
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125, 2068-2069.

994 Organometallics, Vol. 24, No. 5, 2005
Mizuta et al.
Table 2. Geometrical Parameters of
Phosphorus-Bridged [1.1]Ferrocenophanes
anti-3
syn-3
syn-2
5
Angles (deg)
bridge angle
twist angle
tilt angle
110.88(6) 109.21(8) 105.96(6) 107.5(2) 109.4(2)
2.91(7)
2.91(7)
50.3
42.47(10) 24.81(7) 21.1(2) 20.9(2)
8.2(1)
-34.8
3.68(7)
-17.6
3.0(2)
16.1
5.7(2)
-10.4
rotation angle
Distances (Å)
1.793
C(Cp)-Pa
1.797
1.818
2.05
2.22
1.791
1.95d
2.36f
H(C5)‚‚‚H(C10*)b,c 1.82
2.49
2.05e
H(C5)‚‚‚H(C5*)b,c
2.08
P‚‚‚P*c
4.847(1) 4.623(1) 3.758(1) 3.532(1)
a An average value. b Distances are estimated assuming an ideal
geometry with a C-H length of 1.08 Å. c Symmetry transforma-
tions used to generate equivalent (asterisked) atoms: (-x, -y+1,
-z) for anti-3, (-x, y, -z+0.5) for syn-3, and (-x+1, y, -z+1.5)
for syn-2. d A distance between H(C5) and H(C15). e A distance
between H(C10) and H(C20). f A distance between H(C5) and
H(C20).
of anti-3 and of syn-2 are given in Table 2. The small
twist angle of 2.91(7)° for anti-3 indicates that the two
Cp rings bound to the same phosphorus bridge are
almost coplanar, with the two R-H(Cp) atoms, H(C5) and
H(C10*), being in close proximity. Moreover, the short
C(Cp)-bridge distance of 1.797 Å also contributes to their
short H(C5)‚‚‚H(C10*) separation of 1.82 Å, which
suggests a substantial steric repulsion present between
them.4,22-24
On the other hand, syn-2 adopts a wider twist angle
of 24.81(7)° and therefore has a longer R-H‚‚‚R-H
distance of 2.05 Å, leading in turn to a smaller H‚‚‚H
repulsion than that of anti-2. In addition, the steric
repulsion between the two PPh bridging groups is
expected to be small in syn-2 because their endo-
positions are occupied with lone pairs (see Figure 5),
the bulkiness of which is negligible from a stereochem-
ical point of view, though with a slight electrostatic
repulsion being anticipated between the lone pairs.25,26
Consequently, the observed thermodynamic preference
of syn-2 over anti-2 can be understood rationally.
Figure 6. ORTEP drawing of 5 with 50% thermal el-
lipsoids. Selected bond distances (Å) and angles (deg): Co-
Cl1 2.221(1), Co-Cl2 2.2381(9), Co-P1 2.3947(9), Co-P2
2.3728(9), P1-C1 1.806(3), P1-C11, 1.791(3), P1-C21,
1.818(3), P2-C6 1.775(3), P2-C16 1.793(3), P2-C27
1.820(3), P1-Co-P2 95.62(3), Cl1-Co-Cl2 111.38(4),
Co-P1-C1 112.9(1), Co-P1-C11 109.3(1), Co-P1-C21
119.3(1), C1-P1-C11 107.5(2), Co-P2-C6 110.6(1), Co-
P2-C16 109.8(1), C6-P2-C16 109.4(2).
Scheme 3
The conversion of anti-2 to syn-2 proceeds upon
heating, while the syn-anti interconversion is reported
to be very rapid for the CH2-bridged [1.1]ferrocenophane
at room temperature.23,24 The energy barrier for the
latter is estimated to be 28 kJ/mol by low-temperature
NMR measurements,24 and it is supported by a molec-
ular mechanics calculation.23 On the other hand, for the
conversion of anti-2 to syn-2, one of the two phosphorus
centers must invert its configuration, as shown in
Scheme 3. An energy barrier for the inversion of a
trivalent phosphorus center is reported to be ca. 125-
146 kJ/mol,27 which is responsible for the prolonged
heating necessary for the anti-2 to syn-2 conversion.
and tilted by 6.1°, with their spacing increasing toward
the P atoms. The latter tilting in a slightly opened
“clam” contributes to the bite angle being closer to the
ideal tetrahedral angle. On the other hand, because the
two phosphorus atoms of syn-2 are doubly linked with
the two ferrocene units, the clam-like tilting is expected
to be rather difficult for syn-2. Actually, the two fer-
rocene units of 5 adopt smaller tilt angles of 3.0° and
5.7°.
syn-anti Preference of 2. anti-2 was almost com-
pletely converted to syn-2 upon simple heating in
toluene, while syn-2 gave a trace amount of anti-2 under
similar conditions (Scheme 3). These results indicate
thermodynamic stability of syn-2 over anti-2. Although
the molecular structure of anti-2 has not yet been
determined, its structure is expected to be similar to
that of anti-3. The twist, rotation, tilt, and bridge angles
(22) Karlsson, A.; Lo¨ewendahl, M.; Hilmersson, G.; Davidsson, O¨ .;
Ahlberg, P. J. Phys. Org. Chem. 1996, 9, 436-438.
(23) Rudzinski, J. M.; Osawa, E. J. Phys. Org. Chem. 1993, 6, 107-
112.
(24) Lo¨ewendahl, M.; Davidsson, O¨ .; Ahlberg, P. J. Chem. Res.,
Synop. 1993, 40-41.
(25) Sztaray, B.; Szalay, P. G. J. Am. Chem. Soc. 1997, 119, 11926.
(26) Becker, G.; Golla, W.; Grobe, J.; Klinkhammer, K. W.; Le Van,
D.; Maulitz, A. H.; Mundt, O.; Oberhammer, H.; Sachs, M. Inorg. Chem.
1999, 38, 1099.
(27) Quin, L. D. A Guide to Organophosphorus Chemistry; John
Wiley & Sons: New York, 2000; pp 272-306.

Phosphorus-Bridged [1.1]Ferrocenophane
Organometallics, Vol. 24, No. 5, 2005 995
Table 3. Crystallographic Data
Experimental Section
anti-3
syn-3
General Remarks. All reactions were carried out under
an atmosphere of dry nitrogen using Schlenk tube techniques.
All solvents were dried and purified by distillation: CH2Cl2
was distilled from P2O5; benzene, toluene, ether, and THF were
distilled from sodium/benzophenone; and hexane was distilled
from sodium metal. These purified solvents were stored under
an N2 atmosphere. Other reagents were used as received. PPh-
bridged [1]ferrocenophane 1 was prepared according to previ-
ously described methods.9d,12l,28
formula
cryst color, habit
cryst syst
space group
a (Å)
C
32H26Fe2P2S2
orange, plate
triclinic
C32H26Fe2P2S2
orange, plate
monoclinic
C2/c (#15)
11.729(3)
12.655(3)
19.330(4)
P1h (#2)
7.7460(2)
8.6840(4)
10.7830(4)
72.269(2)
80.518(3)
75.220(2)
665.03(4)
1
b (Å)
c (Å)
R (deg)
â (deg)
104.86(2)
γ (deg)
NMR spectra were recorded on a JEOL LA-300 spectrom-
1
V (Å3)
2773.0(10)
4
eter. H and 13C NMR chemical shifts were reported relative
Z
to Me4Si and were determined by reference to the residual
solvent peaks. 31P NMR chemical shifts are reported relative
to H3PO4 (85%), which was used as an external reference.
Elemental analyses were performed with a Perkin-Elmer
2400CHN elemental analyzer.
Photolysis was carried out with Pyrex-glass-filtered emis-
sion from a 400 W mercury arc lamp (Riko-Kagaku Sangyo
UVL-400P). The emission lines (nm) used and their relative
intensities (in parentheses) were as follows: 577.0 (69), 546.1
(82), 435.8 (69), 404.7 (42), 365.0 (100), 334.1 (7), 312.6 (38),
and 302.2 (9).
temp (K)
200
13.90
300
µ(Mo KR) (cm-1
)
13.33
MacScience
MXC3-κ
diffractometer
MacScience
DIP2030 Imaging Plate
no. of reflns
measd
obsd
2917
2830
4470
3355
(I > 3.00σ(I))
no. variables
p-factor
225
0.1050
225
0.0670
0.029; 0.043
residualsa:
0.025; 0.054
c
Rb; Rw
Preparation of Sulfurized Dimers anti-3 and syn-3. A
solution of 1 (508 mg, 1.74 mmol) in THF (40 mL) was
irradiated with a mercury arc lamp. To the suspension thus
obtained was added elemental sulfur (276 mg). After the
suspension was stirred for a day, the solvent was removed.
The oily residue was dissolved in CH2Cl2 and loaded into a
silica gel column (3 cm i.d. × 18 cm). Elution with CH2Cl2 gave
light yellow anti-3 as the first band and orange syn-3 as the
third band. After the solvent was removed in vacuo, anti-3 (52
mg, 9%) and syn-3 (52 mg, 9%) were obtained from their
respective fractions.
largest diff peak/
0.28/-0.45
0.45/-0.24
hole (e/Å3)
syn-2
5
formula
cryst color, habit
cryst syst
space group
a (Å)
b (Å)
c (Å)
C
32H26Fe2P2
C35H32CoCl5Fe2P2
green, cubic
monoclinic
P21/n (#14)
11.4290(1)
17.2090(2)
18.3380(1)
yellow, plate
monoclinic
C2/c (#15)
24.5570(3)
6.1060(1)
19.1840(3)
R (deg)
â (deg)
1
anti-3. H NMR (300.4 MHz, CDCl3): δ 4.54 (br, 4H, fc),
121.140(1)
102.922(1)
4.79 (br, 4H, fc), 4.92 (br, 4H, fc), 5.56 (br, 4H, fc), 7.13-7.23
(m, 6H, Ph), 7.46 (m, 4H, Ph). 13C{1H} NMR (75.45 MHz,
CDCl3): δ 71.8 (d, JPC ) 11 Hz, fc), 73.5 (d, JPC ) 9 Hz, fc),
73.8 (d, JPC ) 15 Hz, fc), 74.7 (d, JPC ) 9 Hz, fc), 78.9 (d, JPC
γ (deg)
V (Å3)
2462.05(7)
4
3515.41(6)
4
Z
temp (K)
200
200
µ(Mo KR) (cm-1
)
13.28
MacScience
17.76
) 97 Hz, ipso-fc), 128.0 (d, JPC ) 12 Hz, Ph), 129.4 (d, JPC
)
diffractometer
MacScience
11 Hz, Ph), 130.2 (d, JPC ) 3 Hz, Ph). 31P{1H} NMR (121.5
MHz, in CDCl3): δ 40.5. Anal. Calcd for C32H26Fe2P2S2: C,
59.28; H, 4.04. Found: C, 59.36; H, 3.75.
DIP2030 Imaging Plate
no. of refls
measd
obsd
3184
2748
8080
7358
syn-3. 1H NMR (300.4 MHz, CDCl3): δ 4.56 (br, 4H, fc), 4.67
(br, 8H, fc), 5.42 (br, 4H, fc), 7.15-7.30 (m, 6H, Ph), 7.40 (m,
(I > 3.00σ(I))
no. variables
p-factor
4H, Ph). 13C{1H} NMR (75.45 MHz, CDCl3): δ 71.6 (d, JPC
)
216
425
0.1020
0.029; 0.052
0.2000
11 Hz, fc), 72.0 (d, JPC ) 9 Hz, fc), 74.9 (d, JPC ) 11 Hz, fc),
76.7 (d, JPC ) 11 Hz, fc), 79.4 (d, JPC ) 97 Hz, ipso-fc), 128.0
(d, JPC ) 12 Hz, Ph), 129.8 (d, JPC ) 11 Hz, Ph), 130.3 (d, JPC
) 3 Hz, Ph), 139.3 (d, JPC ) 88 Hz, ipso-Ph). 31P{1H} NMR
(121.5 MHz, in CDCl3): δ 37.7. Anal. Calcd for C32H26-
Fe2P2S2: C, 59.28; H, 4.04. Found: C, 58.84; H, 3.80.
Desulfurization of syn-3. An excess amount of Si2Cl6 was
added to syn-3 (125 mg, 0.193 mmol) dissolved in benzene (100
mL). The mixture was refluxed for a day, then cooled to room
temperature, and a 30% aqueous NaOH solution (20 mL) was
added. The organic layer was washed with water, then dried
over anhydrous magnesium sulfate and filtered. The solvent
was removed, and the residue was recrystallized from CH2-
Cl2/hexane. The product was washed with hexane and ether
and then dried in vacuo to give yellow syn-2 (96 mg, 85%). 1H
NMR (300.4 MHz, CDCl3): δ 4.42 (br, 4H, fc), 4.46 (br, 4H,
fc), 4.57 (br, 4H, fc), 4.80 (br, 4H, fc), 7.10 (m, 6H, Ph), 7.18-
7.24 (m, 4H, Ph). 13C{1H} NMR (75.45 MHz, CDCl3): δ 70.8
(s, fc), 71.1 (d, JPC ) 4 Hz, fc), 72.0 (s, fc), 75.3 (t, JPC ) 18 Hz,
fc), 127.8 (s, Ph), 127.9 (t, JPC ) 3 Hz, Ph), 131.6 (t, JPC ) 11
Hz, Ph). 31P{1H} NMR (121.5 MHz, in CDCl3): δ -29.7. Anal.
residualsa:
0.055; 0.139
c
Rb; Rw
largest diff peak/
0.38/-0.48
1.11/-0.79
hole (e/Å3)
a Function minimized: ∑w(|Fo| - |Fc|)2 where w ) 1/[σ2(Fo)] )
[σc (Fo) + p2Fo2/4]-1. σc(Fo) ) esd based on counting statistics, p )
2
p-factor. b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw ) [(∑w(|Fo| - |Fc|)2/
∑wFo2)]1/2
.
Calcd for C32H26Fe2P2: C, 65.79; H, 4.49. Found: C, 65.53; H,
4.78.
Desulfurization of anti-3 with Si2Cl6. anti-3 (129 mg,
0.199 mmol) was treated similarly with Si2Cl6 in the manner
described for syn-3 to give a yellow product. The spectroscopic
data of the product were identical to those of syn-2, indicating
that the major product is syn-2 (91 mg, 78%).
Desulfurization of anti-3 with CF3SO3Me/P(NMe2)3. To
anti-3 (244 mg, 0.376 mmol) dissolved in CH2Cl2 (30 mL) was
added CF3SO3Me (120 µL, 1.06 mmol). The mixture was stirred
for 3 h at room temperature. The volatiles were removed in
vacuo. Next, P(NMe2)3 (170 µL, 0.935 mmol) was again added
to the residue dissolved in CH2Cl2 at room temperature. The
mixture was stirred for 3 h, and the volatiles were then
(28) Seyferth, D.; Withers, H. P., Jr. J. Organomet. Chem. 1980,
185, C1.

996 Organometallics, Vol. 24, No. 5, 2005
Mizuta et al.
removed in vacuo. The residue was washed with CH2Cl2/ether
and with pure ether and dried in vacuo to give anti-2 (214
mg, 97.4%). Anal. Calcd for C32H26Fe2P2: C, 65.79; H, 4.49.
Found: C, 65.74; H, 4.83.
Since the product was almost insoluble in common organic
solvents, spectroscopic data could not be obtained at all. Its
characterization was therefore performed as the sulfide of anti-
2. anti-2 suspended in CH2Cl2 was treated with excess sulfur.
After stirring, the solution became homogeneous. 31P{1H} NMR
spectrum of this solution gave only one singlet at 40.5 ppm,
which was identical to that of the starting anti-3.
55° for syn-2, anti-3, and 5 and 60° for syn-3. Cell parameters
and intensities for the reflection were estimated using the
program packages of MacDENZO.29 The structure was solved
by direct methods and expanded using Fourier techniques.
Non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included for all crystals and refined except for 5.
All calculations were performed using the teXsan crystal-
lographic software package from the Molecular Structure
Corporation.30 Crystal data and refinement details are sum-
marized in Table 3.
Improved Method for the Synthesis of syn-2. A solution
of 1 (972 mg, 3.33 mmol) in ether (100 mL) was irradiated
with a mercury arc lamp for 3 h. The precipitate was washed
with toluene/ether (1:2) and then dried in vacuo. The product
suspended in toluene (80 mL) was refluxed overnight. After
the solvent was removed in vacuo, the residue was dissolved
in CH2Cl2 and then loaded into an Al2O3 column. syn-2 eluted
with CH2Cl2 was collected, and the solvent was removed in
vacuo to give syn-2 as a yellow powder (314 mg, 32%).
Preparation of Cobalt Complex with syn-2. syn-2 (354
mg, 0.606 mmol), CoCl2 (98 mg, 0.755 mmol), and THF (30
mL) were placed into a Schlenk tube and stirred for 1 day.
The green precipitate formed was washed with THF and ether
and then dried in vacuo to give CoCl2(syn-2) (417 mg, 96%).
Anal. Calcd for C32H26Cl2CoFe2P2: C, 53.83; H, 3.67. Found:
C, 53.45; H, 3.37.
Acknowledgment. This work was supported by
Grants-in-Aid for Scientific Research (Nos. 15350035,
15550051, and 160332450) from the Ministry of Educa-
tion, Culture, Sports, Science, and Technology, Japan.
We would like to thank Mrs. Haino of the Natural
Science Center for Basic Research and Development
(N-BARD), Hiroshima University, for the measurement
of elemental analyses.
Supporting Information Available: Tables giving bond
lengths and angles, and positional and thermal parameters
for syn-2, syn-3, anti-3, and 5. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM049155W
X-ray Crystallography. A suitable crystal was mounted
on a glass fiber for syn-2, syn-3, anti-3, and 5. Measurements
were made on a Mac Science DIP2030 imaging plate area
detector for syn-2, anti-3, and 5 and on a Mac Science MXC3-κ
for syn-3. The data were collected to a maximum 2θ value of
(29) Gewirth, D. (with the cooperation of the program authors
Otwinowski, Z. and Minor, W.) MacDENZO in The MacDenzo Manual-A
Description of the Programs DENZO, XDISPLAYF, and SCALEPACK;
Yale University: New Haven, CT, 1995.
(30) teXsan, Single-Crystal Structure Analysis Software, Version 1.6;
Molecular Structure Corporation: The Woodlands, TX, 1993.