Kinetically stabilized 1,1'-bis[(E)-dipnosphenyl]ferrocenes: syntheses, structures, properties, and reactivity

Article abstract of DOI:10.1246/bcsj.80.1884

Kinetically stabilized 1,1'-bis[(E)-diphosphenyl]ferrocenes were synthesized by taking advantage of extremely bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)me

Full text of DOI:10.1246/bcsj.80.1884

1884 Bull. Chem. Soc. Jpn. Vol. 80, No. 10, 1884–1900 (2007)
ꢀ 2007 The Chemical Society of Japan
BCSJ Award Article
Kinetically Stabilized 1,10-Bis[(E)-diphosphenyl]ferrocenes:
Syntheses, Structures, Properties, and Reactivity#
Noriyoshi Nagahora,1;2 Takahiro Sasamori,1 Yasuaki Watanabe,3
ꢀ1
Yukio Furukawa,3 and Norihiro Tokitoh
1Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011
2Institute of Sustainability Science, Kyoto University, Gokasho, Uji, Kyoto 611-0011
3Department of Chemistry, School of Science and Engineering, Waseda University,
3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555
Received May 2, 2007; E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp
Kinetically stabilized 1,10-bis[(E)-diphosphenyl]ferrocenes were synthesized by taking advantage of extremely
bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (denoted as Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-
4-[tris(trimethylsilyl)methyl]phenyl (denoted as Bbt) groups, and characterized by the spectroscopic and X-ray crystallo-
graphic analyses. The electronic structures of the 1,10-bis[(E)-diphosphenyl]ferrocenes were determined by analyzing
electronic spectra, the transitions of which were reasonably assigned based on theoretical calculations. In the cyclic vol-
tammograms, there were two well-defined reversible one-electron reduction couples corresponding to the intramolecular
two diphosphene units. Furthermore, the 1,10-bis[(E)-diphosphenyl]ferrocene was found to undergo ligand-exchange
reactions with group 6 metal carbonyl complexes along with the E-to-Z isomerization of the diphosphene moieties, lead-
ing to the formation of the corresponding 1,10-bis[(Z)-diphosphenyl]ferrocene group 6 metal tetracarbonyl complexes,
[M(CO)4{(Z,Z)-(BbtP=PC5H4)2Fe}] (M ¼ Cr, Mo, and W). The molecular structures of these complexes were deter-
mined by spectroscopic analyses (1H, 13C, and 31P NMR spectra, and UV–vis spectra), and that of the tungsten complex
ꢀ
was determined by X-ray crystallographic analysis. Several types of d ! ꢀ
electron transitions due to the iron and
group 6 metals were detected by using UV–vis spectroscopy, and these results were supported by theoretical calculations.
P=P
The chemistry of heavier congeners of azo-compound
(–N=N–) has been studied extensively for more than 25
years,1 since the pioneering synthesis and isolation of the first
stable diphosphene bearing 2,4,6-tri-tert-butylphenyl groups
ꢀ
ꢀ
(Mes P=PMes ), reported by Yoshifuji and co-workers.2
Nowadays, it is well-known that diphosphenes, which have
ꢀ
relatively low-lying ꢀ orbitals, readily undergo one-electron
reduction to give their anion-radical species.3 We have report-
ed the synthesis of novel doubly bonded systems between
heavier group 15 elements (dipnictenes), that is, diphosphene,
distibene (–Sb=Sb–), dibismuthene (–Bi=Bi–), phosphabis-
muthene (–P=Bi–), and stibabismuthene (–Sb=Bi–), by taking
advantage of bulky protecting groups, such as 2,4,6-tris[bis-
(trimethylsilyl)methyl]phenyl (Tbt) and 2,6-bis[bis(trimethyl-
silyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl (Bbt) groups
(Fig. 1).4 Furthermore, the redox properties of (E)-BbtE=EBbt
(E ¼ P, Sb, and Bi) have been systematically elucidated based
on cyclic voltammetry and DFT calculations, and the solid-
state structure of the first stable anion radical species of (E)-
BbtSb=SbBbt has also been reported.4i,4k
Fig. 1. Effective steric protection groups.
ꢀ
attracted much interest due to their low-lying ꢀ levels
compared with diazenes (–N=N–) from two reasons: (i) their
electrochemical properties3 and (ii) coordination ability toward
transition metals.1a,5 Recently, unique ꢀ-conjugated systems
containing diphosphene unit(s) have been developed from the
former viewpoint (i). For example, a unique d(Fe)–ꢀ(P=P)
electron system, (E)-ferrocenyldiphosphene [(E)-FcP=PMes
(Fc = C5H4FeC5H5)], has been synthesized by Niecke and
Pietschnig for the first time (Fig. 2), and its absorption band
ꢀ
Low-coordinated species of heavier group 15 elements have
Published on the web October 12, 2007; doi:10.1246/bcsj.80.1884

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1885
Fig. 3.
Fig. 4. Possible structures of metal complexes for diphosphene.
biphosphorins10 and 3,4-bis(diphosphinidene)cyclobutenes
(DPCBs),11 has attracted great attention in recent years due
to their unique structures and strong ꢀ-acceptor abilities
(Fig. 3). Meanwhile, a diphosphene moiety is well-known to
work as a ligand for group 6 metals in several fashions of
coordination, that is, ꢁ1 (end-on), ꢁ2 (side-on), ꢂ2(ꢁ1:ꢁ1)
(end-on and end-on), ꢂ2(ꢁ1:ꢁ2) (end-on and side-on), and
ꢂ3(ꢁ1:ꢁ1:ꢁ2) (end-on, end-on, and side-on) types, using its
lone-pair electrons or ꢀ orbitals as the coordination site
(Fig. 4).1a,5 From the viewpoints of both (i) electrochemical
properties and (ii) coordination ability toward transition met-
als, 1,10-bis[(E)-diphosphenyl]ferrocenes should show attrac-
tive electrochemical behavior and be a good candidate as a bi-
dentate ligand in consideration of rotational flexibility of the
cyclopentadienyl ring in a ferrocene. In this paper, we report
the syntheses, structural characterization, and properties of
the first 1,10-bis[(E)-diphosphenyl]ferrocenes (E,E)-1a and
(E,E)-1b kinetically stabilized by the Tbt and Bbt groups,
respectively, and the ligand-exchange reactions of (E,E)-1b
with group 6 metal carbonyl complexes along with unique
E-to-Z isomerization of the diphosphene moieties.
Fig. 2.
corresponding to the electron transitions from d(Fe) to
ꢀ (P=P) orbitals has been reported.6 However, it readily
ꢀ
undergoes dimerization above ꢁ40 ꢂC under daylight leading
to the formation of the corresponding cyclotetraphosphane.6
Later on, we have determined the crystal structure of a kineti-
cally stabilized (E)-ferrocenyldiphosphene bearing a Tbt group
and its unique electrochemical behavior.4h On the other hand,
Protasiewicz and co-workers have synthesized 1,4-bis[(E)-
diphosphenyl]benzene derivatives (Fig. 2), in which the P=P
ꢀ electron systems are extended onto those of the conjugated
aromatic rings, and they have reported unique electrochemical
behavior for these ꢀ-conjugated diphosphenes.7 We have also
reported the synthesis of stable 1,10-bis[(E)-diphosphenyl]fer-
rocenes, which have unique d–ꢀ electron systems, by utilizing
Tbt ((E,E)-1a) and Bbt ((E,E)-1b) groups, and determined their
crystal structures and electrochemical properties (Fig. 2).8
Independently, Pietschnig and co-workers have reported the
synthesis of (E,E)-1a and the stable 1,10-bis[(E)-diphosphen-
yl]ferrocene bearing 2,6-dimesitylphenyl groups ((E,E)-1c).9
From viewpoint (ii), the chemistry of bidentate ligands
bearing low-coordinated phosphorus atoms, such as 2,20-
Results and Discussion
Syntheses of Kinetically Stabilized 1,10-Bis[(E)-diphos-
phenyl]ferrocenes. Synthetic route for the 1,10-bis[(E)-di-
phosphenyl]ferrocenes, (E,E)-1a and (E,E)-1b, is shown in
Scheme 1. Phosphines 4a and 4b having Tbt and Bbt groups,

1886 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
Scheme 1. Syntheses of (E,E)-1a and (E,E)-1b.
Table 1. 31P NMR Data of Bis[(E)-diphosphene] Deriva-
tives
respectively, were prepared by the reaction of the correspond-
ing dichlorophosphines with lithium aluminum hydride in ex-
cellent yields. 1,10-Bis[bis(diethylamino)phosphino]ferrocene
(5) was quantitatively synthesized by the reaction of bis(dieth-
ylamino)chlorophosphine with 1,10-dilithioferrocene prepared
from 1,10-dibromoferrocene. The reaction of 5 with hydrogen
chloride in ether followed by the removal of inorganic salts
gave 1,10-bis(dichlorophosphino)ferrocene (6) in good yield.
The treatment of 6 with two molar amounts of LiP(H)Ar
(Ar ¼ Tbt (7a) or Bbt (7b)), which was prepared by the reac-
tion of H2PAr (Ar ¼ Tbt (4a) or Bbt (4b)) with an equimolar
amount of butyllithium in ether at ꢁ40 ꢂC, in benzene at room
temperature gave the corresponding chlorohydrodiphosphane
derivatives as diastereomixtures. Subsequently, the double-
dehydrochlorination reaction using 1,8-diazabicyclo[5.4.0]-
undec-7-ene (DBU) at room temperature afforded 1,10-bis[(E)-
diphosphenyl]ferrocenes, (E,E)-1a and (E,E)-1b in >90%
yields.12 Recrystallization from their hexane solution at ꢁ40
ꢂC gave purple powder of pure (E,E)-1a and (E,E)-1b, suitable
for chemical analyses, in 68% and 62% isolated yields, respec-
tively. Both (E,E)-1a and (E,E)-1b were thermally stable either
up to 260 ꢂC in the solid state or up to 120 ꢂC in toluene-d8
solution in a degassed and sealed tube. Upon exposure to day-
light, neither decomposition nor isomerization of the diphos-
phene moieties of (E,E)-1a and (E,E)-1b was observed in the
benzene-d6 solution.
ꢃP/ppm
1JPP/Hz
Ref.
(E,E)-1aa)
(E,E)-1ba)
(E,E)-1ca)
(E,E)-2b)
(E,E)-3ab)
(E,E)-3bb)
488.9, 497.3
491.1, 496.9
444.9, 470.3
476.7, 515.9
481.7, 525.5
479.7, 524.8
550
550
537
582.8
576
570
this work
this work
9
13
7a
7c
a) In C6D6. b) In CDCl3.
NMR Spectra of the 1,10-Bis[(E)-diphosphenyl]ferro-
cenes, (E,E)-1a and (E,E)-1b. The molecular structures of
(E,E)-1a and (E,E)-1b in solution were evaluated by their
Fig. 5. Conceivable resonance structures for 1,10-bis[(E)-
diphosphenyl]ferrocenes.
1
NMR spectra. The H NMR spectra of (E,E)-1a and (E,E)-1b
in benzene-d6 exhibited one set of A2B2 systems with 1JHH
bearing two different substituents. The 31P NMR spectral data
are summarized in Table 1 together with those of the pre-
viously reported bis[(E)-diphosphene] derivatives.7–9,13 The
observed coupling constants of (E,E)-1a and (E,E)-1b were
somewhat smaller than those of the reported (E)-diphosphenes
having two different bulky aryl groups,1a indicating their
characteristic polarized resonance structures similar to the case
of the reported (E)-ferrocenyldiphosphenes (Fig. 5).4h,6 The
31P NMR spectral data of several (E)-diphosphenes and (E)-
ferrocenyldiphosphenes are shown in Table 2 as references.
Crystal Structures of the 1,10-Bis[(E)-diphosphenyl]fer-
¼
1:8 Hz (both (E,E)-1a and (E,E)-1b) at 4.58 and 4.96 ppm (for
(E,E)-1a) and 4.58 and 4.93 ppm (for (E,E)-1b), which were
assigned to the protons of the cyclopentadienyl ring. The peaks
indicate that the fast rotation of the C(Cp ring)–P bonds occurs
at room temperature. The 31P NMR spectra of (E,E)-1a and
(E,E)-1b in benzene-d6 showed a diagnostic pair of doublets
at 497.3 and 488.9 ppm ((E,E)-1a) and 496.9 and 491.1 ppm
1
((E,E)-1b), respectively, with JPP ¼ 550 Hz (both (E,E)-1a
and (E,E)-1b), which are characteristic of (E)-diphosphenes

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1887
rocenes, (E,E)-1a and (E,E)-1b. Single crystals of (E,E)-1a
and (E,E)-1b suitable for X-ray diffraction study were obtained
from their benzene solutions in a degassed and sealed tube.
The molecular structures of (E,E)-1a and (E,E)-1b were deter-
mined by the X-ray crystallographic analyses (Fig. 6), and
their selected structural parameters are summarized in
Table 3. The conformations of (E,E)-1a and (E,E)-1b in the
solid states are curiously different from each other in spite of
the similarity between Tbt and Bbt groups. That is, (E,E)-1a
ꢀ
(triclinic, P1) has a crystallographic center of symmetry at
the central Fe atom, whereas (E,E)-1b (monoclinic, C2=c)
has a two-fold rotation axis through the Fe atom. The torsion
angle between the centroid(Cp)–P(2) moieties of (E,E)-1b (ꢄ
in the Fig. 6c) is 48.0ꢂ, whereas that of (E,E)-1a is inherently
180ꢂ. Both (E,E)-1a and (E,E)-1b has an (E)-conformation of
the diphosphene moieties with the C–P–P–C torsion angles
of 179.3(4) and 176.0(2)ꢂ, respectively, and their C–P–P–C
planes are almost coplanar with the adjacent Cp ring, suggest-
ing a conjugative interaction between the ꢀ-electrons of
Table 2. 31P NMR Data of (E)-Diphosphenes
R
ꢃP/ppm
1JPP/Hz
ꢀ
Diphosphenes, Mes P=PR
Tsia)
530.0, 533.1
467.6, 540.4
470, 535
620
574
572
548
Mesb)
Tipc)
Ph
455.5, 525.5
Ferrocenyldiphosphenes, FcP=PR
Fig. 6. ORTEP drawings of the major parts of (a) (E,E)-1a
and (b) (E,E)-1b with thermal ellipsoid plots (50% prob-
ability). Hydrogen atoms are omitted for clarity. (c) Mo-
lecular structure of (E,E)-1b without the CH(SiMe3)2
and C(SiMe3)3 groups and hydrogen atoms.
ꢀ
Mes
Tbt
442.6, 471.2
479.5, 501.7
532
546
a) Tsi; tris(trimethylsilyl)methyl. b) Mes; 2,4,6-trimethyl-
phenyl. c) Tip; 2,4,6-triisopropylphenyl.
Table 3. Observed and Calculated Structural Parameters for 1,10-Bis[(E)-diphosphenyl]ferrocenes
˚
Bond lengths/A
Bond angles/deg
Torsion angles/deg
1,10-Bis[(E)-diphosphenyl]ferrocene (E,E)-1a
C(1)–P(1)–P(2) 98.5(2)
C(1)–P(1)–P(2)–C(28) ꢁ179:3ð4Þ
C(28)–P(2)–P(1) 102.1(5)
P(1)–P(2) 2.015(3)
P(1)–C(1) 1.860(4)
P(2)–C(28) 1.797(9)
1,10-Bis[(E)-diphosphenyl]ferrocene (E,E)-1b
2.0398(18) C(1)–P(1)–P(2)
P(1)–P(2)
P(1)–C(1)
P(2)–C(31) 1.807(6)
103.25(15) C(1)–P(1)–P(2)–C(31) ꢁ176:0ð2Þ
1.854(4)
C(31)–P(2)–P(1) 101.9(3)
(E,E)-8a
P–P 2.055
P–C(Dmp) 1.860
C(Dmp)–P–P
C(Cp)–P–P
99.8
102.9
C(Dmp)–P–P–C(Cp)
C(Dmp)–P–P–C(Cp)
ꢁ179:2
ꢁ179:1
P–C(Cp)
P–P
1.819
(E,E)-8b
2.054
C(Dmp)–P–P
C(Cp)–P–P
99.7
103.1
P–C(Dmp) 1.860
P–C(Cp) 1.822

1888 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
Table 4. Reported Raman Shifts for (E)-Diphosphenes
(R1P=PR2)
Table 5. Observed and Calculated Vibrational Spectro-
scopic Data for 1,10-Bis[(E)-diphosphenyl]ferrocenes
R1, R2
ꢅ(P=P)/cmꢁ1
Ref.
Raman,
ꢅ(P=P)/cmꢁ1
Infrared,
ꢅ(P=P)/cmꢁ1
ꢀ
ꢀ
Mes , Mes
610
609
603
609
15
4f
4f
4h
Tbt, Tbt
Bbt, Bbt
Fc, Tbt
(E,E)-1a, obsda)
(E,E)-1b, obsda)
(E,E)-8a, calcdb)
(E,E)-8b, calcdb)
612
611
624
624
614
615
622
624
a) Measured with the excitation by He-Ne laser (532 nm).
b) Calculated at B3LYP/6-31G(d) level.
Fig. 7. Raman spectra of (top) (E,E)-1a and (bottom)
(E,E)-1b using He-Ne laser (532 nm) in the solid state.
Fig. 8. UV–vis spectra of (E,E)-1a (purple line) and (E,E)-
1b (blue line) in benzene.
Table 6. UV–Vis Spectral Data for 1,10-Bis[(E)-diphosphenyl]ferrocenes (E,E)-1a, (E,E)-
1b, and (E,E)-1c and 1,4-Bis[(E)-diphosphenyl]benzenes (E,E)-3a and (E,E)-3b
ꢀ
ꢀ
ꢀ
ꢆ1(ꢀ–ꢀ )/nm
ꢆ2(n–ꢀ )/nm
ꢆ3(d–ꢀ )/nm
Ref.
(E,E)-1aa)
(E,E)-1ba)
(E,E)-1ca)
(E,E)-3ab)
(E,E)-3bc)
384 (" 7300)
389 (" 7400)
351d)
390 (" 7550)
422 (" 19000)
480 (" 1800)
485 (" 1300)
—
539 (" 2200)
this work
this work
553 (" 2200)
e)
542d)
—
—
9
7a
7c
476 (" 870)
481 (" 2100)
a) In benzene. b) In hexane. c) In chloroform. d) The molar absorptivity was not
presented. e) The wavenumber of the absorption maximum was not mentioned.
the diphosphene units with those of the Cp rings of (E,E)-1a
˚
and (E,E)-1b. Their P=P bond lengths (2.015(3) A for (E,E)-
1a/(E,E)-1b were measured in the solid state with 532 nm ex-
citation in a degassed and sealed tube. In Fig. 7, the Raman
spectra of (E,E)-1a/(E,E)-1b are shown, and the most intense
signals were at 612/611 cmꢁ1, respectively, which were similar
to those of the (E)-diaryldiphosphenes4f,15 and (E)-ferrocenyl-
diphosphene (Tables 4 and 5).4h Interestingly, the Infrared
spectra of (E,E)-1a/(E,E)-1b in the solid state (KBr disks)
˚
1a and 2.0398(18) A for (E,E)-1b) are considerably shorter
14
˚
than the typical P–P single-bond lengths (ca. 2.19–2.24 A)
and are within the range of those found for the previously re-
ported (E)-diaryldiphosphenes (1.985–2.049 A).1a,4f Moreover,
˚
the P–P–C bond angles of (E,E)-1a and (E,E)-1b are 98.5(2)
and 102.1(5)ꢂ for (E,E)-1a and 103.25(15) and 101.9(3)ꢂ for
(E,E)-1b, respectively, and are within the range of those
for previously reported (E)-diaryldiphosphenes (97.8(1)–
114.9(1)ꢂ).2,4f,4l These results strongly indicated the P=P dou-
ble-bond character of (E,E)-1a and (E,E)-1b in the solid state.
Raman and Infrared Spectra of 1,10-Bis[(E)-diphosphen-
showed the characteristic signals for P=P at 614/615 cmꢁ1
,
respectively. The characteristic P=P vibrational frequencies
of (E,E)-1a/(E,E)-1b were found to be active for both Raman
(ꢅ ¼ 612=611 cmꢁ1) and IR (ꢅ ¼ 614=615 cmꢁ1) spectrosco-
py in the solid state due to the symmetric and asymmetric
stretching modes, the assignment of which was supported by
theoretical calculations on the model molecules (E,E)-8a/
(E,E)-8b (vide infra).
UV–Vis Spectra of 1,10-Bis[(E)-diphosphenyl]ferrocenes.
The UV–vis spectra of (E,E)-1a/(E,E)-1b in benzene showed
three absorption maxima at 384/389 (" ¼ 7300=7400), 480/
485 (sh, " ¼ 1800=1300), and 539/553 nm (" ¼ 2200=2200)
as shown in Fig. 8. The data are summarized in Table 6.
yl]ferrocenes.
Raman spectroscopy is a valuable tool to
evaluate the double-bond character of diphosphenes in the
solid sate.1c,4f,15 It is known that their intense Raman shifts
corresponding to the P=P stretching for the reported (E)-di-
phosphene compounds are in the range from 603 to 610
cmꢁ1 (Table 4),1c,4f,4l,15 while that of the diphosphane Ph2P–
16
PPh2 appeared at 530 cmꢁ1
.
The Raman spectra of (E,E)-

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1889
The first one (ꢆmax ¼ 384=389 nm), which was assigned to the
ꢀ
ꢀ ! ꢀ electron transitions based on the large ", was within
the range of those reported for (E)-diaryldiphosphenes (277–
418 nm),1a,4f showing a hypsochromic shift similar to those
for the 1,4-bis[(E)-diphosphenyl]benzenes (E,E)-3a/(E,E)-3b
(398/422 nm) reported by Protasiewicz’s group.7 The second
ꢀ
one (ꢆmax ¼ 480=485 nm) was assigned to the n ! ꢀ elec-
tron transitions for the diphosphene units, based on previous
reports of those for the (E)-diaryldiphosphenes (437–532
nm)1a,4f and (E,E)-3a/(E,E)-3b (476/481 nm).7 The third one
(ꢆmax ¼ 539=553 nm) was attributed to the metal-to-ligand
charge-transfer transitions (MLCT band) due to the electron
ꢀ
transitions from d orbitals of the iron atom to the ꢀ orbital
of the P=P moiety, where a subtle bathochromic shift was
observed as compared with those for (E)-FcP=PAr (Ar ¼
ꢀ
Mes ; 515 nm,6 Ar ¼ Tbt; 542 nm4h). In addition, the assign-
ment of the observed absorption maxima for (E,E)-1a/(E,E)-
1b was reasonably supported by theoretical calculations for
the excited states of their model molecules (vide infra).
Theoretical Calculations for 1,10-Bis[(E)-diphosphenyl]-
ferrocenes. In order to understand the electronic structures
of 1,10-bis[(E)-diphosphenyl]ferrocenes, we performed theo-
retical calculations for the model molecules, where the Tbt
and Bbt groups of (E,E)-1a and (E,E)-1b, respectively, were
replaced by 2,6-dimethylphenyl (denoted as Dmp) groups. In
the structural optimization of the model molecule [Fe(C5H4P=
PDmp)2] by using B3LYP at 6-31G(d) level, two local mini-
ma, which were named as (E,E)-8a and (E,E)-8b, were found
as geometries similar to the solid-state structures of (E,E)-1a
and (E,E)-1b, respectively. The selected structural parameters
and full theoretically optimized coordinates of (E,E)-8a and
(E,E)-8b are shown in Table 3 and the Supporting Information
(Tables S1 and S2), respectively. It was found that the SCF
energy of (E,E)-8a was smaller than that of (E,E)-8b by only
1.2 kJ molꢁ1, indicating the difference in the crystalline geo-
metries observed for (E,E)-1a and (E,E)-1b should be due to
the packing force. Theoretical calculations for the vibrational
frequencies of (E,E)-8a and (E,E)-8b showed the two charac-
teristic stretching vibrations for the P=P double-bonds arising
from the phase of the two intramolecular diphosphene units,
respectively. Namely, it was found that the symmetric and
asymmetric stretching vibrations for (E,E)-8a/(E,E)-8b ap-
peared at 624/624 and 622/624 cmꢁ1, respectively (Fig. 9
and Table 5). The former should be Raman active (624 nm
for (E,E)-8a and 622 nm for (E,E)-8b), whereas the latter
is Infrared active (624 nm for both (E,E)-8a and (E,E)-8b).
These calculated results are in good agreement with those
obtained from the Raman and IR spectra of (E,E)-1a and
(E,E)-1b. In addition, calculations on the excited states of
(E,E)-8a and (E,E)-8b were also performed by using TDDFT.
The results are shown in Table S3 (Supporting Information)
together with the UV–vis spectral data of (E,E)-1a and
(E,E)-1b. Calculations on (E,E)-8a and (E,E)-8b at B3LYP/
TZ(2d) for Fe, 6-311+G(2d) for P, and 6-31G(d) for C, H
level showed that the low-lying excitation energy for (E,E)-
Fig. 9. Schematic eigenvectors for the selected intense
(a) Raman-active symmetric and (b) infrared-active asym-
metric vibrations of (E,E)-8a and (E,E)-8b calculated at
the B3LYP/6-31G(d) level.
the iron atom (Fig. 10). Transitions from the nP=P (HOMOꢁ3
ꢀ
457.3 nm for (E,E)-8a and 463.6 nm for (E,E)-8b. Moreover, it
and HOMOꢁ4) to the ꢀ
orbitals were estimated to be at
P=P
was predicted that the high-energy region of singlet excitations
of (E,E)-8a and (E,E)-8b in the gas phase were the allowed
ꢀ
ꢀP=P ! ꢀ
transitions, which are in agreement with
P=P
the experimental results. Consequently, the assignment of the
observed UV–vis spectra of (E,E)-1a and (E,E)-1b were rea-
sonably supported by the TDDFT calculations for the model
molecule [Fe(C5H4P=PDmp)2].
Electrochemical Properties of 1,10-Bis[(E)-diphosphen-
yl]ferrocenes.
There have been a number of reports on
the electrochemical properties of diphosphenes, showing re-
versible one-electron reduction couples for (E)-diphosphenes
observed by cyclic voltammetry.3,4g–i,4k,4l,8 The redox behavior
of (E,E)-1a and (E,E)-1b was also analyzed by cyclic and
differential pulse voltammetries, and the voltammograms are
shown in Fig. 11. The observed redox potentials and the result-
ing comproportionation constants of (E,E)-1a and (E,E)-1b are
summarized in Table 7. In the THF solution, two reversible
one-electron redox waves due to the stepwise reduction of
the intramolecular two redox centers were observed at ꢁ1:84
and ꢁ2:19 V ((E,E)-1a) and ꢁ1:78 and ꢁ2:13 V ((E,E)-1b)
versus Ag/Agþ, respectively. The first reduction potentials
of (E,E)-1a and (E,E)-1b were similar to those of the reported
(E)-diphosphenes under similar conditions.3,4g–i,4k,4l,8 For
both (E,E)-1a and (E,E)-1b, the difference between the half-
potentials (ꢁE1=2 ¼ 0:35 V), which is commonly used as a
guide to an extent of electronic interaction between the two-
8a and (E,E)-8b predominantly corresponded to dFe
ꢀ
!
ꢀ
transitions. Thus, the low-lying vacant orbitals (LUMO
charac-
P=P
ꢀ
ter, whereas the HOMO orbital is localized on d orbitals of
and LUMO+1) for (E,E)-8a and (E,E)-8b have ꢀ
P=P

1890 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
Fig. 11. Cyclic and differential pulse voltammograms of
(a) (E,E)-1a and (b) (E,E)-1b in 0.1 M n-Bu4NBF4/THF
solution at room temperature.
the intramolecular diphosphene moieties of bis[(E)-diphos-
phene] 2 having an o-phenylene–ethylene–o-phenylene spacer
(Fig. 2).13 In CH2Cl2 solution, the reversible one-electron
oxidation waves due to the iron(II)/iron(III) of the ferrocene
moieties were observed at +0.14 V ((E,E)-1a) and +0.15 V
((E,E)-1b) versus Ag/Agþ, respectively. These potentials are
slightly lower than that of a ferrocene (+0.24 V versus Ag/
Agþ), indicating the influence of the polarized resonance
structures, depicted in Fig. 5.
Reactions of the 1,10-Bis[(E)-diphosphenyl]ferrocenes,
(E,E)-1a and (E,E)-1b, with Methanol. In order to elucidate
their reactivity, we reacted (E,E)-1a or (E,E)-1b with metha-
nol. A benzene-d6 solution of (E,E)-1a/(E,E)-1b was mixed
with methanol in a sealed tube affording H2PTbt (4a)/H2-
Fig. 10. Perspective views of the selected molecular orbi-
tals of (E,E)-8a (white; hydrogen, green; carbon, blue;
phosphorus, red; iron).
electron-transfer sites, afforded a comproportionation constant
(Kc) of 8:2 ꢃ 105 for the mixed-valence state, indicating
effective electronic interaction through the central ferrocene
unit to similar extent of the case of the previously reported
1,4-bis[(E)-diphosphenyl]benzene (E,E)-3a (ꢁE1=2 ¼ 0:34 V
and Kc ¼ 5:6 ꢃ 105 in THF–n-Bu4NBF4).7b By contrast, it
has been reported that no interaction is observed between

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1891
Scheme 2. Reactions of (E,E)-1a and (E,E)-1b with methanol in benzene-d6.
Scheme 3. Reactions of (E,E)-1b with group 6 metals carbonyl complexes.
Table 7. Redox Potentials (V vs. Ag/Agþ) of (E,E)-1a and
(E,E)-1b
Table 8. Reactions of 1,10-Bis[(E)-diphosphenyl]ferrocene
(E,E)-1b with Group 6 Metal Carbonyl Complexes
(E,E)-1a
(E,E)-1b
Isolated
yield/%
Entry
Metal reagent
Product
Oxidationa)
Reductionb)
Epa
Epc
+0.17
+0.10
+0.14
+0.18
+0.12
+0.15
1
2
3
4
5
[Cr(CO)5(CH3CN)]
[Mo(CO)4(nbd)]a)
[Mo(CO)5(CH3CN)] (Z,Z)-1b Mo(CO)4
[W(CO)4(cod)]b)
[W(CO)5(CH3CN)]
(Z,Z)-1b Cr(CO)4
81
74
70
89
92
ꢄ
E1=2
(Z,Z)-1b Mo(CO)4
ꢄ
ꢄ
Epc
Epa
ꢁ2:02, ꢁ2:35
ꢁ1:66, ꢁ2:02
ꢁ1:84, ꢁ2:19
0.35
8:2 ꢃ 105
ꢁ1:89, ꢁ2:24
ꢁ1:67, ꢁ2:02
ꢁ1:78, ꢁ2:13
0.35
8:2 ꢃ 105
(Z,Z)-1b W(CO)4
(Z,Z)-1b W(CO)4
ꢄ
ꢄ
E1=2
ꢁE1=2
Kcc)
a) nbd; 2,5-norbornadiene. b) cod; 1,5-cyclooctadiene.
around an axis through the iron atom and the centroid of the
cyclopentadienyl rings, indicating the possibility of forming
a new architecture of metal complexes.
a) 0.1 M n-Bu4NBF4 in CH2Cl2, E1=2(Cp2Fe/Cp2Feþ) =
+0.24 V vs. Ag/Agþ. b) 0.1 M n-Bu4NBF4 in THF. c) Com-
proportionation constant (Kc) was calculated by using the
equation of Kc ¼ expðꢁE1=2=25:69Þ at 298 K.17
After heating a benzene-d6 solution of 1,10-bis[(E)-diphos-
phenyl]ferrocene (E,E)-1b in the presence of a 10 molar
amount of [Mo(CO)4(nbd)] (nbd = 2,5-norbornadiene) at
50 ꢂC for 2 h under the dark conditions, the signals for
(E,E)-1b disappeared, and those for the molybdenum complex
PBbt (4b) and [Fe{C5H4PH(O)OMe}2] (9) in a ratio of 2:1
(Scheme 2). The regioselectivity observed for the addition of
methanol to the phosphorus–phosphorus double bonds of
(E,E)-1a/(E,E)-1b can be interpreted in terms of the polarized
resonance structure in solution as shown in Fig. 5.
1
(Z,Z)-1b Mo(CO)4 were exclusively observed in the H and
31P NMR spectra (Scheme 3 and Entry 2 in Table 8). Purifi-
cation of the reaction mixture by gel-permeation chromatog-
ꢄ
Reactions of the 1,10-Bis[(E)-diphosphenyl]ferrocene,
(E,E)-1b, with Group 6 Metal Complexes. Next, we fo-
cused on the coordination behavior of (E,E)-1b to group 6
metal carbonyl complexes. Although a number of reports on
diphosphene–group 6 metal carbonyl complexes have been
published, the coordination properties of bis(diphosphene) de-
rivatives have not been reported to the best of our knowledge.
Because of a variety of coordination modes in metal com-
plexes bearing a diphosphene unit (Fig. 4), 1,10-bis[(E)-di-
phosphenyl]ferrocene ligand has attracted much interest not
only in coordination chemistry but also in catalytic chemistry.
On the other hand, experimental results have shown that the
raphy afforded (Z,Z)-1b Mo(CO)4 as a purple solid in 74%
ꢄ
1
isolated yield. The H NMR spectrum of (Z,Z)-1b Mo(CO)4
ꢄ
in benzene-d6 showed A2B2 signals and a broad singlet for
the protons of the cyclopentadienyl and benzene rings of (Z,Z)-
1b Mo(CO)4 at 4.32, 4.62, and 6.92 ppm, respectively. The
spectral features indicated the symmetric molecular structure
ꢄ
of (Z,Z)-1b Mo(CO)4 with C2 axis passing through the iron
ꢄ
and molybdenum atoms. In the 31P NMR spectrum (Fig. 12),
(Z,Z)-1b Mo(CO)4 showed an AA0BB0 spin system at 358.7
ꢄ
2
and 304.3 ppm with 1JðPA{PBÞ ¼ ꢅ606:7, JðPA{PA Þ ¼
0
4
3
0
0
ꢅ29:7,
JðPA{PB Þ ¼ ꢆ14:9, and j JðPB{PB Þj < 4:0 Hz
(Table 9), showing a higher field chemical shifts and a larger
1
rotation energy of the cyclopentadienyl rings in ferrocene is
18
coupling constant JPP as compared to those for (E,E)-1b
1
about 4.6–9.6 kJ molꢁ1
occurs at room temperature in solution. Thus, the diphosphene
,
and therefore, free rotation readily
(491.1 and 496.9 ppm and JPP ¼ 550 Hz). On the basis of
the spectroscopic properties of the previously reported com-
ꢀ
units of the 1,10-bis[(E)-diphosphenyl]ferrocene can move
plexes, [M(CO)5{(Z)-RP=PMes }] (M ¼ Cr, Mo, or W, R ¼

1892 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
Table 9. 31P NMR Data (Chemical Shifts in ppm and Coupling Constants in Hz) of (Z,Z)-1b Cr(CO)4,
(Z,Z)-1b Mo(CO)4, and (Z,Z)-1b W(CO)4 in Benzene-d6
ꢄ
ꢄ
Complex
ꢄ
Spin
system
4
2
3
1J(PA–PB)
J(PA–PB ) j JðPB{PB Þj
0
J(PA–PA )
0
0
ꢃP
(Z,Z)-1b Cr(CO)4
ꢄ
AA0BB0 386.4, 295.9
ꢅ620:1
ꢅ606:7
ꢅ604:6
ꢅ37:3
ꢅ29:7
ꢅ29:0
ꢆ18:7
ꢆ14:9
ꢆ14:5
<4:0
<4:0
<4:0
(Z,Z)-1b Mo(CO)4 AA0BB0 358.7, 304.3
(Z,Z)-1b W(CO)4
ꢄ
ꢄ
AA0BB0 307.2a), 283.7
a) The resonance with the satellite signals of J(183W–31P) = 245.1 Hz.
1
Fig. 12. (a) 31P NMR spectrum of molybdenum complex
(Z,Z)-1b Mo(CO)4 in benzene-d6. (b) The simulated
Fig. 13. (a) 31P NMR spectrum of tungsten complex (Z,Z)-
ꢄ
1b W(CO)4 in benzene-d6. The asterisk indicates the
resonance of an AA0BB0 spin system at 358.7 and 304.3
ꢄ
tungsten–phosphorus satellite signals of 1J(183W–31P)
(245.1 Hz). (b) The simulated resonance of an AA0BB0
spin system at 307.2 and 283.7 ppm with 1JðPA{PBÞ ¼
2
ppm with 1JðPA{PBÞ ¼ ꢅ606:7, JðPA{PA Þ ¼ ꢅ29:7,
0
4
3
0
0
JðPA{PB Þ ¼ ꢆ14:9, j JðPB{PB Þj < 4:0 Hz (line width
of 8.0 Hz).
Table 10. 31P NMR Data of [M(CO)5{(Z)-RP=PRMes }]
2
3
0
0
ꢅ604:6,
JðPA{PA Þ ¼ ꢅ29:0,
JðPA{PB Þ ¼ ꢆ14:5,
4
0
j JðPB{PB Þj < 4:0 Hz (line width of 8.0 Hz).
ꢀ
(Scheme 3 and Entry 4 in Table 8). A 31P NMR spectrum
R
M
ꢃP/ppm
1JPP
of (Z,Z)-1b W(CO)4 in benzene-d6 showed characteristic sig-
nals of an AA0BB0 spin system at 307.2 and 283.7 ppm with
ꢄ
Mes
Mes
Mes
Cp
Cp
Cr
Mo
W
Cr
Mo
W
384.9, 393.9
359.0, 398.4
322.4a), 393.1
421, 385
396, 391
394, 362
603.0
585.9
576.8
603
583
581
2
3
1JðPA{PBÞ ¼ ꢅ604:6,
JðPA{PA Þ ¼ ꢅ29:0,
JðPA{PB Þ ¼
0
0
4
0
ꢆ14:5, and j JðPB{PB Þj < 4:0 Hz (Fig. 13 and Table 9). It
ꢀ
ꢀ
should be noted that the former resonance (ꢃP ¼ 307:2) of
(Z,Z)-1b W(CO)4 has satellite signals with 1J(183W–31P) =
ꢀ
ꢄ
Cp
245.1 Hz, which lies within the range of the reported values
for the tungsten complexes coordinated to a low-coordinated
phosphorus atom,10d,11a,11d–f,13,19b,19c,21–23 suggesting that the
two diphosphene units should coordinate to the tungsten metal
in an ꢁ1-fashion (end-on) in solution.
a) The resonance with the satellite signals of 1J(183W–
31P) = 231.9 Hz.
Mes or Cp ) (Table 10),19 these spectral features suggest that
ꢀ
(Z,Z)-1b Mo(CO)4 possesses (Z)-configurated P=P units in
spite of the (E)-configuration of the staring material (E,E)-
Finally, a systematic method for the synthesis of group
6 metal complexes of (E,E)-1b was established by using of
[M(CO)5(CH3CN)] (M ¼ Cr, Mo, and W), which can be
readily prepared from the commercially available reagents,
[M(CO)6].24,25 That is, the treatment of (E,E)-1b with an ex-
cess amount (at least 10 molar amount) of [M(CO)5(CH3CN)]
ꢄ
2
0
1b. Furthermore, the observed J(PA–PA ) (ꢅ29:7 Hz) and
3
0
J(PA–PB ) (ꢆ14:9 Hz) values suggested that only two phos-
phorus atoms of (Z,Z)-1b Mo(CO)4 coordinate to the molyb-
denum metal with a cis conformation, based on the former
ꢄ
2
0
coupling constant J(PA–PA ). The values are close to those
(M ¼ Cr, Mo, and W) afforded (Z,Z)-1b Cr(CO)4, (Z,Z)-
ꢄ
of the reported compounds cis-[Mo(CO)4(PR3)(PR03)] (23–
1b Mo(CO)4, and (Z,Z)-1b W(CO)4 in 81%, 70%, and 92%
isolated yields, respectively (Scheme 3 and Entries 1, 3, and
ꢄ
ꢄ
33 Hz).20
Similarly, in the case of (Z,Z)-1b Mo(CO)4, the novel
tungsten complex (Z,Z)-1b W(CO)4, [W(CO)4{(Z,Z)-(BbtP=
5 in Table 8). A 31P NMR spectrum of (Z,Z)-1b Cr(CO)4 is
shown in Fig. 14 together with its simulated one. All 31P NMR
data of (Z,Z)-1b Cr(CO)4, (Z,Z)-1b Mo(CO)4, and (Z,Z)-
1b W(CO)4 are summarized in Table 9. The features of
these complexes in the 31P NMR spectra agreed with those
ꢄ
ꢄ
ꢄ
PC5H4)2Fe}], was obtained as purple crystals in 89% isolated
yield, when a 10 molar amount of [W(CO)4(cod)] (cod = 1,5-
cyclooctadiene) was used as the metal source in benzene-d6
ꢄ
ꢄ
ꢄ

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1893
of the previously reported ꢁ1-complexes of (Z)-diphosphene
atom from coordination to the chromium atom due to its ex-
treme hindrance, and (ii) the isomerization of the diphosphene
moiety having a ferrocenyl group proceeds at room tempera-
ture during the ligand-exchange reaction in the presence of
an excess amount of [Cr(CO)5(thf)].
The observed E-to-Z isomerization process of the diphos-
phene units of (E,E)-1b in the dark is probably due to the
use of an excess molar amount of the metal reagents and the
contribution of the polarized resonance structure of (E,E)-1b
(Fig. 5), which should make the rotation barrier of the P=P
double bond lower than those of diaryldiphosphenes having
no ꢀ-conjugation system between the diphosphene and the
aryl groups.
with a group 6 metal, as shown in Table 10.5,19,26 Moreover,
1
the observed JPP values (620.1 Hz for (Z,Z)-1b Cr(CO)4,
606.7 Hz for (Z,Z)-1b Mo(CO)4, and 604.6 Hz for (Z,Z)-
ꢄ
ꢄ
1b W(CO)4) were larger than that of (E,E)-1b (550 Hz), indi-
ꢄ
cating the enhanced s-character of the double bond in the
diphosphene moieties.
Although (E)-diphosphene ꢁ1-metal complexes have been
reported to undergo photochemical isomerization leading to
the formation of the corresponding (Z)-diphosphene ꢁ1-metal
complexes,1a,5,19 the thermal isomerization has been hitherto
unknown. Therefore, we tried to explore the isomerization
process depending on the amount of the metal reagents in
the ligand-exchange reactions. Treatment of (E,E)-1b with a 5
molar amount of [W(CO)5(CH3CN)] in benzene-d6 at 50 ꢂC
for 2 h resulted in the formation of the mixture of two isomers
in the ratio (E,Z)-1b W(CO)4:(Z,Z)-1b W(CO)4 = 1:3 as
Infrared Spectra of the 1,10-Bis[(Z)-diphosphenyl]ferro-
cene–Group 6 Metal Complexes. There have been numer-
ous reports for the IR spectra of group 6 metal carbonyl com-
plexes, and the studies using IR spectroscopy give useful infor-
mation to understand the electronic structure of the complexes.
On the other hand, a combination of IR spectroscopy and
theoretical calculations can be a powerful tool for investigating
the molecular structure and bonding properties of the com-
plexes.28 In general, local C2v symmetry in cis-[M(CO)4L2]
(M = group 6 metals, L = ligands) leading to four carbonyl
stretching modes (2A1, B1, and B2).29 The IR spectra of (Z,Z)-
1b Cr(CO)4, (Z,Z)-1b Mo(CO)4, and (Z,Z)-1b W(CO)4 were
ꢄ
ꢄ
judged by the 1H and 31P NMR spectra (Fig. 15). Consequent-
ly, these results suggest that the unique E-to-Z isomerization
process of the diphosphene moieties in (E,E)-1b depends on
the ratio of the metal reagents. Moreover, in order to investi-
gate the effect of the ferrocenyl group, the ligand-exchange
reaction of (E)-FcP=PTbt, with [Cr(CO)5(thf)] was also exam-
ined in the dark.27 It is interesting that the reaction of (E)-
FcP=PTbt with an excess molar amount of [Cr(CO)5(thf)] at
room temperature afforded only [Cr(CO)5{(Z)-FcP=PTbt}]
in 73% yield along with E-to-Z isomerization. The results
indicate: (i) the Tbt group prevents the adjacent phosphorus
ꢄ
ꢄ
ꢄ
recorded as Nujol samples and the results are summarized in
Table 11 together with those of the previously reported tetra-
carbonyl complexes cis-[M(CO)4L2]. The IR spectra of (Z,Z)-
1b Cr(CO)4, (Z,Z)-1b Mo(CO)4, and (Z,Z)-1b W(CO)4
ꢄ
ꢄ
ꢄ
showed four strong absorptions attributable to the CꢇO
stretching frequency in the range of 2030–1900 cmꢁ1, indicat-
ing a cis geometry around the metal moieties in (Z,Z)-1b
ꢄ
Cr(CO)4, (Z,Z)-1b Mo(CO)4, and (Z,Z)-1b W(CO)4. These
ꢄ
ꢄ
bands were similar to those of 2,20-biphosphorin molybdenum
1010e and di(phosphaalkene) complexes 11–1311e and found
to be shifted toward higher frequencies by 6–34 cmꢁ1 as com-
pared to those of cis-[M(CO)4{(PPh2CH2)2}] (M ¼ Cr, Mo,
and W)30 (Fig. 16). These results indicate the ꢇ-donor and
ꢀ-acceptor abilities of the (Z,Z)-1b ligand may resemble those
of 2,20-biphosphorin and di(phosphaalkene) ligands having
low-coordinated phosphorus atoms.
Fig. 14. (a) 31P NMR spectrum of chromium complex
(Z,Z)-1b Cr(CO)4 in benzene-d6. (b) The simulated
Crystal Structure of (Z,Z)-1b W(CO) . Since only one
4
example [Cr(CO)5{(Z)-MesP=PMes }] has been reported
for the solid-state structure of the diphosphene mono-metal
ꢁ1-complex bearing group 6 metal so far,19a the structural
features of the group 6 metal complex of the 1,10-bis[(Z)-di-
phosphenyl]ferrocene are of great interest. The molecular
ꢀ
ꢀ
ꢄ
resonance of an AA0BB0 spin system at 386.4 and
2
295.9 ppm with 1JðPA{PBÞ ¼ ꢅ620:1, JðPA{PA Þ ¼
0
4
3
0
0
ꢅ37:3, JðPA{PB Þ ¼ ꢆ18:7, j JðPB{PB Þj < 4:0 Hz (line
width of 8.0 Hz).
Fig. 15. 31P NMR spectrum of (E,Z)-1b W(CO)4 (open circle) and (Z,Z)-1b W(CO)4 (solid triangle) in benzene-d6.
ꢄ
ꢄ

1894 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
Table 11. IR Data of cis-Group 6 Metal Tetracarbonyl Complexes
Complex
ꢅ/cmꢁ1
Ref.
a)
(Z,Z)-1b Cr(CO)4
ꢄ
2015, 1954, 1935, 1910
2028, 1958, 1942, 1906
2024, 1951, 1932, 1896
2030, 1935, 1900
2013, 1957, 1923, 1892
2025, 1928, 1892
2019, 1919, 1888
2009, 1914, 1899, 1877
2020, 1919, 1907, 1881
2016, 1912, 1901, 1876
this work
this work
this work
11e
a)
(Z,Z)-1b Mo(CO)4
ꢄ
a)
(Z,Z)-1b W(CO)4
ꢄ
10a)
11b)
12b)
13b)
12e
12e
12e
28
28
28
cis-[Cr(CO)4{(PPh2CH2)2}]c)
cis-[Mo(CO)4{(PPh2CH2)2}]c)
cis-[W(CO)4{(PPh2CH2)2}]c)
a) Nujol method. b) KBr method. c) 1,2-Dichloroethane solution.
Table 12. Selected Structural Parameters of (Z,Z)-1b W(CO)4
ꢄ
˚
Bond lengths/A
Bond angles/deg
C(1)–P(1)–P(2)
C(15)–P(2)–P(1) 113.9(5) C(6)–P(3)–P(4)–C(45) 4.1(8)
116.7(5)
1.776(16) C(45)–P(4)–P(3) 119.3(4)
Torsion angles/deg
P(1)–P(2)
2.038(6)
2.046(5)
1.775(14) C(6)–P(3)–P(4)
118.2(5) C(1)–P(1)–P(2)–C(15) 9.7(7)
P(3)–P(4)
P(1)–C(1)
P(3)–C(6)
P(2)–C(15) 1.800(16) C(1)–P(1)–W(1)
P(4)–C(45) 1.830(13) P(2)–P(1)–W(1)
124.2(5)
117.6(2)
125.3(5)
118.0(2)
W(1)–P(1)
W(1)–P(3)
2.414(4)
2.422(4)
C(6)–P(3)–W(1)
P(4)–P(3)–W(1)
Fig. 16.
structure of (Z,Z)-1b W(CO)4 was determined by X-ray crys-
ꢄ
tallographic analysis. An ORTEP drawing of the major part of
the disordered molecules and the selected structural pa-
rameters of (Z,Z)-1b W(CO)4 are described in Fig. 17 and
ꢄ
Table 12, respectively. Based on spectroscopic analyses with
the almost planar C–P–P–C torsion angles (4.1(8) and 9.7(7)ꢂ),
it was found that the two diphosphene moieties of (Z,Z)-
1b W(CO)4 has a Z-configuration as expected and the two
phosphorus atoms adjacent to the central ferrocene moiety co-
ordinated to the tetracarbonyl tungsten are in a cis form. The
ꢄ
Fig. 17. ORTEP drawing of the major part of (Z,Z)-
1b W(CO)4 with thermal ellipsoid plots (30% probabili-
ty). Hydrogen atoms are omitted for clarity.
ꢄ
phosphorus–phosphorus bond lengths of (Z,Z)-1b W(CO)4
ꢄ
˚
(2.038(6) and 2.046(5) A) are substantially shorter than the
14
˚
typical P–P single-bond length (ca. 2.19–2.24 A), whereas
1b W(CO)4 were slightly longer than that of (E,E)-1b, sug-
gesting relatively weak dW–ꢀ
ꢄ
ꢀ
they are within the range of the reported P=P double-bond
1a,4f,4h,4l
back donation from d orbi-
Pꢀ=P
˚
lengths (1.985–2.049 A) for (E)-diphosphenes,
and
very close to that (2.039(3) A) of the (Z)-diphosphene–chro-
tals of the tungsten atom to ꢀ orbitals of the P=P bonds.
Moreover, the six P–W–C and four C–W–C angles are in the
range from 88.3(5) to 93.5(4)ꢂ and from 87.9(7) to 93.3(6)ꢂ,
˚
ꢀ
mium complex [Cr(CO)5{(Z)-MesP=PMes }].19a These re-
sults show that (Z,Z)-1b W(CO)4 retains considerable P=P
double-bond character with a Z-configuration in the solid
state. The phosphorus–phosphorus bond lengths of (Z,Z)-
respectively, where the tungsten center of (Z,Z)-1b W(CO)4
adopts an octahedral geometry with a P–W–P angle of
90.60(12)ꢂ. This indicates low steric strain around the tungsten
ꢄ
ꢄ

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1895
center, in contrast to those found for the reported tungsten
complexes bearing a bidentate phosphorus ligand.22,23 The
P(1) and P(3) atoms coordinated toward the tungsten atom
were found to have completely planar geometries (the sum
of the angles around the P(1) and P(3) atoms are 360.0ꢂ) as
Mo(CO)4, and 363 nm (sh, " ¼ 4400) for (Z,Z)-1b W(CO)4)
ꢄ
ꢀ
phosphene units taking into account those for the previously
can be assigned to the ꢀ ! ꢀ electron transitions for the di-
ꢀ
reported (E)-diaryldiphosphenes (ꢀ ! ꢀ band; 277–418
nm)1a and [Cr(CO)5{(Z)-FcP=PTbt}] (ꢆmax ¼ 352 nm).27 The
ꢀ
in the case of [Cr(CO)5{(Z)-MesP=PMes }] (359.9ꢂ). The
absorption maxima observed at longer wavelength (ꢆmax
¼
P(2)–P(1)–C(1) and P(4)–P(3)–C(6) bond angles (116.7(5)
and 118.2(5)ꢂ) of (Z,Z)-1b W(CO)4 are larger than those of
492 (" ¼ 5400), 640 (sh, " ¼ 1300) for (Z,Z)-1b Cr(CO)4,
ꢄ
488 (" ¼ 4100), 627 (sh, " ¼ 640) for (Z,Z)-1b Mo(CO)4,
ꢄ
ꢄ
(E,E)-1b (102.6(3)ꢂ) and similar to that of [Cr(CO)5{(Z)-
and 492 (" ¼ 5700), 620 (sh, " ¼ 1500) nm for (Z,Z)-1b
ꢄ
ꢀ
MesP=PMes }] (118.7(3)ꢂ), indicating a large amount of
W(CO)4), which were very broad, can be attributed to the
mixture of several types of d ! ꢀ (MLCT) bands due to the
sp2-hybridized character in the P–P bonds (P(1)–P(2) and
ꢀ
electron transitions from the d orbitals of the iron and group 6
P(3)–P(4)) in (Z,Z)-1b W(CO)4 as compared to that in
(E,E)-1b. To our best knowledge, the phosphorus–tungsten(0)
ꢄ
ꢄ
ꢀ
metal atoms to the ꢀ orbitals of the P=P moieties, respective-
˚
bond lengths of (Z,Z)-1b W(CO)4 [2.414(4) and 2.422(4) A]
ly. Moreover, the MLCT bands exhibited a bathochromic shift
as compared to that for the 1,10-bis[(E)-diphosphenyl]ferro-
cene (E,E)-1b (ꢆmax ¼ 553 nm).
are considerably shorter than those of the reported tungsten
complexes coordinated by sp3- and sp2-type phosphorus
atoms,11d–f,13,20c,22,23 except for the tungsten complex of
Theoretical Calculations for 1,10-Bis[(Z)-diphosphenyl]-
ferrocene–Chromium Tetracarbonyl Complex. Structural
optimization on [Cr(CO)4{(Z,Z)-(HP=PC5H4)2Fe}] ((Z,Z)-
14), as a model molecule, was performed at B3LYP/6-31G(d)
level using an initial geometry referred to the solid-state
tris(tetramethyl-2,20-biphosphorin) (2.3552(9), 2.361(1), and
10d
˚
2.3640(6) A).
These results of the structural properties in
(Z,Z)-1b W(CO)4 indicate the following: (i) a good ꢇ-donat-
ꢄ
ing ability of the lone-pair electrons in the diphosphene units
with complexation in a ꢁ1-fashion (end-on), (ii) a flexible
1,10-ferrocenylene moiety and selective formation of the bi-
dentate complexes due to the two extremely bulky Bbt groups,
(iii) complexation of the diphosphene moieties with an sp2-
hydridized geometry, and (iv) a slightly longer P=P bond
structure of (Z,Z)-1b W(CO)4. The theoretically optimized
ꢄ
coordinates and selected molecular orbitals of (Z,Z)-14 are
summarized in the Supporting Information (Tables S4 and
S6). The optimized structure of (Z,Z)-14 was found to have a
geometry similar to the solid-state structure of (Z,Z)-1b
W(CO)4. The low-lying LUMO and LUMO+1 for (Z,Z)-14
ꢄ
ꢀ
lengths indicating their relatively weak d–ꢀ back donation
from the central tungsten atom.
ꢀ
had ꢀ
character as in the case of [Fe(C5H4P=PDmp)2]
P=P
UV–Vis Spectra of (Z,Z)-1b Cr(CO) , (Z,Z)-1b Mo(CO) ,
4
(E,E)-8a (Table S6). Furthermore, the HOMO, HOMOꢁ1,
and HOMOꢁ2 of (Z,Z)-14 were localized on the d orbitals
of the chromium atom, whereas all of the orbitals from the
HOMOꢁ3 to the HOMOꢁ6 should be d orbitals of the iron
atom of the ferrocene unit. In addition, TDDFT calculations
on (Z,Z)-14 were also performed at TD-B3LYP/6-31G(d)
level. The calculated low-lying singlet excitation energies of
(Z,Z)-14 are shown in the Supporting Information (Table S5).
The lowest energy part (between 617.3 and 357.3 nm) of the
calculations on (Z,Z)-14 originated from electron transitions
from the d orbitals of the iron and group 6 metals into the
ꢀ ꢀ
4
and (Z,Z)-1b W(CO) .
ꢀ
UV–vis spectra of (Z,Z)-1b
4
ꢄ
Cr(CO)4, (Z,Z)-1b Mo(CO)4, and (Z,Z)-1b W(CO)4 were
ꢄ
ꢄ
measured in hexane (Fig. 18), showing approximately two
characteristic absorption maxima in the range from 300 to
800 nm. Since there has been no report for the electronic
spectral data of group 6 metal complexes of (Z)-diphosphenes
and it is difficult to make an assignment for their electronic
transitions, the assignment were estimated based on TDDFT
calculations on a model molecule, [Cr(CO)4{(Z,Z)-(HP=
PC5H4)2Fe}] ((Z,Z)-14) (vide infra). The absorption maxima
observed at shorter wavelength (ꢆmax ¼ 360 (sh, " ¼ 4400)
for (Z,Z)-1b Cr(CO)4, 362 (sh, " ¼ 5400) for (Z,Z)-1b
ꢀ
low-lying ꢀ
citations in the range of 354.6 to 291.4 nm were due to allowed
orbitals (MLCT transitions), whereas the ex-
P=P
ꢄ
ꢄ
ꢀ
orbitals. The computational
transitions from the ꢀP=P to the ꢀ
and forbidden transi-
P=P
ꢀ
tions from the nP=P to the ꢀ
P=P
results indicate that the predicted energies of the singlet exci-
tations of (Z,Z)-14 are in good agreement with the experimen-
tal results.
Conclusion
We synthesized the first stable 1,10-bis[(E)-diphosphenyl]-
ferrocenes (E,E)-1a and (E,E)-1b by taking advantage of bulky
protecting groups, Tbt and Bbt. Compounds (E,E)-1a and
(E,E)-1b are very robust in an inert atmosphere. The 31P NMR
spectra of (E,E)-1a and (E,E)-1b showed diagnostic AB sys-
tems in a characteristic low-field region, suggesting the forma-
tion of phosphorus–phosphorus double bonds with the asym-
metric substituents. Solid-state Raman and IR spectra of
(E,E)-1a and (E,E)-1b also indicated characteristic stretching
vibrations of the P=P units as well as their NMR spectra in so-
lution. The molecular structures of (E,E)-1a and (E,E)-1b were
Fig. 18. UV–vis spectra of (Z,Z)-1b Cr(CO)4 (red line),
(Z,Z)-1b Mo(CO)4 (gray line), and (Z,Z)-1b W(CO)4
(blue line) in hexane and the calculated electron transi-
tions (black bars) for the excited state of [Cr(CO)4{(Z,Z)-
(HP=PC5H4)2Fe}] ((Z,Z)-14).
ꢄ
ꢄ
ꢄ

1896 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
and Ag/0.01 M (1 M = 1 mol dmꢁ3) AgNO3 reference electrode.
established by X-ray crystallographic analyses, and the dou-
ble-bond character of (E,E)-1a and (E,E)-1b was elucidated.
The UV–vis spectra of (E,E)-1a and (E,E)-1b showed three
The measurements were carried out in CH2Cl2 and THF solution
containing 0.1 M n-Bu4NBF4 as a supporting electrolyte with scan
rates of 10–200 mV sꢁ1 in a glovebox filled with argon at ambient
temperature. All melting points were determined on a Yanaco
micro melting point apparatus and were uncorrected. Elemental
analyses were performed by the Microanalytical Laboratory of
the Institute for Chemical Research, Kyoto University.
Materials. Hydrogen chloride in ether was purchased from
Aldrich Co., Ltd. Celiteꢁ (diatomacenous earth) was purchased
from KANTO CHEMICAL Co., Inc. and dried at 200 ꢂC for
24 h before use. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) was
purchased from Aldrich Co., Ltd. and was distillated form sodium
hydroxide prior to use. 2,4,6-Tris[bis(trimethylsilyl)methyl]phenyl-
phosphine, H2PTbt (4a),4h 1,10-dibromoferrocene,32 bis(diethyl-
amino)chlorophosphine,33 1,10-bis(dichlorophosphino)ferrocene,34
and [M(CO)5(CH3CN)] (M ¼ Cr, Mo, and W)24,25 were prepared
according to the procedures reported in the literatures. [Mo(CO)4-
(nbd)] (nbd = 2,5-norbornadiene) and [W(CO)4(cod)] (cod =
1,5-cyclooctadiene) were purchased from Aldrich Co., Ltd. and
purified by recrystallization from toluene before use.
ꢀ
types of absorptions, which corresponded to the ꢀ ! ꢀ , n !
ꢀ
ꢀ
ꢀ , and d ! ꢀ electron transitions of (E,E)-1a and (E,E)-1b.
The electrochemical properties of (E,E)-1a and (E,E)-1b were
revealed by cyclic and differential pulse voltammetries. It is
interesting that the two reversible one-electron redox waves
due to the stepwise reductions of the P=P units of (E,E)-1a
and (E,E)-1b were found in the range from about ꢁ1:8 to
ꢁ2:2 V versus Ag/Agþ. These results pointed out the elec-
tronic interaction between the diphosphene moieties through
the central ferrocene units of (E,E)-1a and (E,E)-1b.
Furthermore, we observed unique ligand-exchange reactions
of 1,10-bis[(E)-diphosphenyl]ferrocene (E,E)-1b as a bidentate
ligand having sp2-type phosphorus atoms with group 6 metals
leading to the formation of novel 1,10-bis[(Z)-diphosphenyl]-
ferrocene–metal complexes [M(CO)4{(Z,Z)-(BbtP=PC5H4)2-
Fe}] (M ¼ Cr, Mo, or W). The molecular structure of the tung-
sten complex was determined by X-ray crystallographic analy-
sis, showing that the diphosphene units have Z-configurations
and coordinated to the tungsten metal with ꢁ1-fashion. It
should be noted that the diphosphene units of (E,E)-1b under-
went an E-to-Z isomerization during complexation. It was
also found that the progress of the ligand-exchange reactions
depended on the ratio of the metal reagents. These results will
stimulate further interest to understand the interactions be-
tween diphosphene units and group 6 metals. Several types
Preparation of 2,6-Bis[bis(trimethylsilyl)methyl]-4-[tris(tri-
methylsilyl)methyl]phenylphosphine (4b). To a solution of 2,6-
[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyldi-
chlorophosphine (2.00 g, 2.75 mmol) in THF (50 mL) was added
lithium aluminum hydride (104 mg, 2.75 mmol) at 0 ꢂC. The solu-
tion was stirred at 0 ꢂC for 1 h and warmed to room temperature.
After the solvent was removed, hexane was added to the residue.
The suspension was filtered through Celiteꢁ, the resulting solution
was filtered through a pad of silica gel to afford 2,6-bis[bis(tri-
methylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenylphosphine
(1.73 g, 2.63 mmol, 96%) as colorless solids. 4b: mp 152.5–153.5
ꢂC. 1H NMR (300 MHz, CDCl3, 23 ꢂC) ꢃ 0.05 (s, 27H, Si(CH3)3),
0.24 (s, 36H, Si(CH3)3), 2.49 (s, 1H, CH), 2.51 (s, 1H, CH), 3.68
ꢀ
of d ! ꢀ
metals were detected by UV–vis spectroscopy, and these
electron transitions due to the iron and group 6
P=P
results were supported by theoretical calculations.
Experimental
1
(brd, 2H, JPH ¼ 190 Hz, PH2), 6.76 (s, 1H, C6H2), 6.77 (s, 1H,
General Comments. All experiments were performed under
an argon atmosphere unless otherwise noted. All solvents were
purified by standard methods and then dried by using an Ultimate
Solvent System (Glass Contour Company).31 All solvents used
in the spectroscopy (benzene, benzene-d6, and hexane) were dried
by using a potassium mirror. Preparative thin-layer chromatogra-
phy (PTLC) was performed with Merck Kieselgel 60 PF254.
Preparative gel-permeation liquid chromatography (GPLC) was
performed on an LC-908 or LC-918 apparatus equipped with
JAI-gel 1H and 2H columns (Japan Analytical Industry Co., Ltd.)
with toluene as an eluent. 1H NMR (400 or 300 MHz) and
13C NMR (100 or 75 Hz) spectra were measured in C6D6 with a
JEOL AL-400 or -300 spectrometer using C6HD5 (ꢃ 7.15) and
C6D6 (ꢃ 128.0) as internal standards for 1H and 13C NMR spectra,
respectively. 31P NMR (120 MHz) spectra were measured in C6D6
with a JEOL AL-300 spectrometer using 85% H3PO4 in water
(ꢃ 0) as an external standard. High-resolution EI- and FAB-mass
spectral data were obtained on a JEOL SX-270 mass spectrometer
(matrix: 2-nitrophenyl octyl ether). Electronic spectra were re-
corded on a JASCO V-570 UV/Vis spectrometer. Infrared spectra
were obtained on a JASCO FT/IR-460 plus spectrometer. Raman
spectra were measured on a Raman spectrometer consisting of
an Spex 1877 Triplemate and an EG&G PARC 1421 intensified
photodiode array detector. An NEC GLG 108 He-Ne laser was
used for Raman excitation. The electrochemical experiments were
carried out with an ALS 602A electrochemical analyzer using a
glassy carbon disk working electrode, a Pt wire counter electrode,
C6H2). 13C{1H} NMR (75 MHz, CDCl3, 24 ꢂC) ꢃ 1.08 (s, CH3),
5.31 (s, CH3 ꢃ 2), 21.78 (s, C(SiMe3)3), 30.65 (s, CH(SiMe3)2),
30.78 (s, CH(SiMe3)2), 122.62 (d, 2JPC ¼ 3:1 Hz, o-C6H2), 126.30
3
(d, JPC ¼ 1:9 Hz, m-C6H2), 143.98 (s, p-C6H2), 148.47 (d,
1JPC ¼ 11:7 Hz, ipso-C6H2). 31P NMR (120 MHz, CDCl3, 24 ꢂC)
1
ꢃ ꢁ142:4 (t, JHP ¼ 190 Hz, PH2). HRMS (FAB): m=z found
656.3543 (½M þ Hꢈþ), calcd for C30H69PSi7: 656.3522. Anal.
Calcd for C30H69PSi7: C, 54.81; H, 10.58%. Found: C, 54.58;
H, 10.37%.
Preparation of 1,10-Bis[bis(diethylamino)phosphino]ferro-
cene (5). To a solution of 1,10-dibromoferrocene (902 mg, 2.62
mmol) in ether (20 mL) was added butyllithium in hexane (1.50
mol dmꢁ3, 3.84 mL, 5.76 mmol) at ꢁ78 ꢂC. The solution was
warmed to room temperature for 30 min and was cooled to ꢁ78
ꢂC. After bis(diethylamino)chlorophosphine (1.21 mL, 5.76 mmol)
was added to the solution at ꢁ78 ꢂC, the reaction mixture was
allowed to be warmed to room temperature for 30 min and was
stirred for 14 h. After removal of the solvents, hexane was added
to the residue and the mixture was filtered through Celiteꢁ. The
solvent of the filtrate was removed to afford 1,10-bis[bis(diethyl-
amino)phosphino]ferrocene (5) (1.37 g, 2.56 mmol, 98%) as an
orange oil. 5: 1H NMR (300 MHz, C6D6, 25 ꢂC) ꢃ 1.03 (t,
1JHH ¼ 6:8 Hz, CH3, 24H), 3.00–3.10 (m, CH2, 16H), 4.36 (A2B2,
1
1JHH ¼ 1:8 Hz, C5H4, 4H), 4.37 (A2B2, JHH ¼ 1:8 Hz, C5H4,
2
4H). 13C{1H} NMR (75 MHz, C6D6, 25 ꢂC) ꢃ 15.00 (d, JCP
¼
1
3:07 Hz, CH3), 42.88 (d, JCP ¼ 17:3 Hz, CH2), 72.29 (s, CH),
72.73 (s, CH), 81.92 (d, JCP ¼ 11:7 Hz, ipso-C5H4). 31P NMR
1

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1897
(120 MHz, C6D6, 25 ꢂC) ꢃ 91.0 (s). HRMS (EI): m=z found
534.2716 ([M]þ), calcd for C26H48FeN4P2: 534.2704.
1:8 Hz, 4H, C5H4), 7.11 (s, 4H, C6H2). 13C{1H} NMR (75 MHz,
C6D6, 50 ꢂC) ꢃ 1.91 (s, CH3), 5.65 (s, CH3), 22.53 (s, C(SiMe3)3),
33.23 (s, CH(SiMe3)2 ꢃ 2), 73.64 (br, C5H4), 75.07 (s, C5H4),
Preparation of 1,10-Bis(dichlorophosphino)ferrocene (6).
To a solution of 1,10-bis[bis(diethylamino)phosphino]ferrocene
(5) (172.0 mg, 0.322 mmol) in ether (3 mL) was added hydrogen
chloride in ether solution (1.0 mol dmꢁ3, 2.60 mL, 2.60 mmol) at
ꢁ78 ꢂC. After the solution was warmed to room temperature for
4 h, the solvent was removed in vacuo. Benzene was added to
the residue and the solution was filtered through Celiteꢁ. The
solvent was removed to afford 1,10-bis(dichlorophosphino)ferro-
cene (6) (105.0 mg, 0.271 mmol, 84%) as waxy orange solids. 6:
1H NMR (300 MHz, C6D6, 25 ꢂC) ꢃ 4.02 (br, 4H, C5H4), 4.19
(br, 4H, C5H4). 13C{1H} NMR (75 MHz, C6D6, 25 ꢂC) ꢃ 72.61 (d,
1
86.30 (d, JPC ¼ 48:7 Hz, ipso-C5H4), 127.42 (br, m-C6H2),
1
135.38 (d, JPC ¼ 30:8 Hz, ipso-C6H2), 146.18 (s, C6H2), 146.49
(br, C6H2). 31P NMR (120 MHz, C6D6, 25 ꢂC) ꢃ 491.1, 496.9
1
(ABq, JPP ¼ 550 Hz). UV–vis (benzene): ꢆmax 389 (" 7400),
485 (sh, " 1300), 553 (" 2200) nm. HRMS (FAB): m=z found
1556.6230 ([M]þ), calcd for C70H142FeP4Si14: 1556.6278. Anal.
Calcd for C70H142FeP4Si14: C, 54.00; H, 9.19%. Found: C, 53.89;
H, 9.37%.
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1a)
with Methanol. In a glovebox filled with argon, 1,10-bis[(E)-di-
phosphenyl]ferrocene ((E,E)-1a) (210.6 mg, 0.149 mmol) was dis-
solved in benzene-d6 (0.8 mL), and the solution was placed in an
NMR tube. After methanol (38 mL, 1.5 mmol) was added to the
solution at room temperature, the tube was degassed and sealed.
Upon standing at room temperature for 24 h, the color of the solu-
tion changed from purple to orange. The tube was opened, and
the solvent was evaporated. Separation of the reaction mixture
by PTLC using hexane and CH2Cl2 as eluents gave H2PTbt (4a)
(172.7 mg, 0.295 mmol, 99%) and [Fe{C5H4PH(O)OMe}2] (9)
(45.9 mg, 0.134 mmol, 90%), respectively. 9: orange solid. mp
1
2JPC ¼ 22:2 Hz, CH), 74.61 (br t, CH), 81.97 (d, JPC ¼ 55:4 Hz,
ipso-C5H4). 31P NMR (120 MHz, C6D6, 25 ꢂC) ꢃ 162.4 (s). HRMS
(EI): m=z found 385.8219 ([M]þ), calcd for C10H835Cl4FeP2:
385.8206.
Synthesis and Isolation of 1,10-Bis[(E)-diphosphenyl]ferro-
cene ((E,E)-1a). In a glovebox filled with argon, butyllithium in
hexane (1.50 mol dmꢁ3, 302 mL, 0.453 mmol) was added to an
ether solution (5 mL) of H2PTbt (4a) (265.0 mg, 0.453 mmol) at
ꢁ40 ꢂC. The solution of LiP(H)Tbt (7a) obtained here was
warmed to room temperature for 30 min and cooled to ꢁ40 ꢂC.
The solution was added to a solution of 1,10-bis(dichlorophos-
phino)ferrocene (6) (87.8 mg, 0.226 mmol) in benzene (30 mL)
at room temperature. After the reaction mixture was stirred for
4 h at room temperature, DBU (67.6 mL, 0.453 mmol) was added
to the reaction mixture at room temperature. After removal of
the solvents, hexane was added to the residue and the reaction
mixture was filtered through Celiteꢁ. The filtrate was cooled to
ꢁ40 ꢂC, the suspension was filtered through a glass filter to afford
(E,E)-1a (217.2 mg, 0.154 mmol, 68%) as purple crystals. (E,E)-
1
3
177–179 ꢂC. H NMR (300 MHz, C6D6, 25 ꢂC) ꢃ 3.35 (d, JPH
¼
¼
1
11:9 Hz, 3H, POCH3), 4.30–4.73 (m, 4H, C5H4), 7.49 (d, JPH
561 Hz, 1H, PH). 13C{1H} NMR (75 MHz, C6D6, 25 ꢂC) ꢃ 51.76
(m, POCH3), 69.95 (d, JPC ¼ 16:1 Hz, ipso-C5H4), 72.22 (d,
JPC ¼ 15:7 Hz, C5H4), 73.56 (m, C5H4). 31P NMR (120 MHz,
C6D6, 25 ꢂC) ꢃ 29.3 (brd, JHP ¼ 561 Hz). HRMS (EI): m=z
1
found 341.9883 ([M]þ), calcd for C12H16FeO4P2: 341.9873. Anal.
Calcd for C12H16FeO4P2: C, 42.14; H, 4.71%. Found: C, 42.48; H,
4.79%.
1
1a: mp 265–266 ꢂC. H NMR (300 MHz, C6D6, 25 ꢂC) ꢃ 0.21 (s,
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b)
with Chromium Pentacarbonyl Acetonitrile Complex. In a
glovebox filled with argon, 1,10-bis[(E)-diphosphenyl]ferrocene
((E,E)-1b) (30.0 mg, 19.3 mmol) and [Cr(CO)5(CH3CN)] (50.0
mg, 215 mmol) in benzene-d6 (0.8 mL) was placed in an NMR
tube. After three freeze–pump–thaw cycles, the NMR tube was
evacuated and sealed. After heating the tube at 50 ꢂC for 2 h,
the signals for (E,E)-1b disappeared in the 31P NMR spectrum.
The tube was opened, and the insoluble materials were removed
by filtering through Celiteꢁ. After removal of the solvent, the
reaction mixture was separated by GPLC to afford the chromium
36H, Si(CH3)3), 0.27 (br, 72H, Si(CH3)3), 1.55 (s, 2H, CH), 2.38
1
(br, 2H, CH), 2.57 (br, 2H, CH), 4.58 (A2B2, JHH ¼ 1:8 Hz, 4H,
1
C5H4), 4.96 (A2B2, JHH ¼ 1:8 Hz, 4H, C5H4), 6.71 (br, 2H,
C6H2), 6.80 (br, 2H, C6H2). 31P NMR (120 MHz, C6D6, 25 ꢂC)
1
ꢃ 488.9, 497.3 (ABq, JPP ¼ 550 Hz). UV–vis (benzene): ꢆmax
384 (" 7300), 480 (sh, " 1800), 539 (" 2200) nm. HRMS (FAB):
m=z found 1411.5419 (½M þ Hꢈþ), calcd for C64H127FeP4Si12:
1411.5409. Anal. Calcd for C64H126FeP4Si12: C, 54.42; H,
8.99%. Found: C, 54.30; H, 9.01%. Satisfactory 13C NMR data
of (E,E)-1a could not be obtained due to its low solubility in
common organic solvents.
complex, (Z,Z)-1b Cr(CO)4 (27.0 mg, 15.7 mmol; 81%). (Z,Z)-
ꢄ
Synthesis and Isolation of 1,10-Bis[(E)-diphosphenyl]ferro-
cene ((E,E)-1b). In a glovebox filled with argon, butyllithium
in hexane (1.50 mol dmꢁ3, 285 mL, 0.428 mmol) was added to
an ether solution (5 mL) of H2PBbt (4b) (281.3 mg, 0.428 mmol)
at ꢁ40 ꢂC. The solution of LiP(H)Bbt (7b) obtained here was
warmed to room temperature for 1 h and cooled to ꢁ40 ꢂC. The
solution was added to a solution of 1,10-bis(dichlorophosphino)-
ferrocene (6) (83.0 mg, 0.214 mmol) in benzene (30 mL) at room
temperature. After the reaction mixture was stirred for 4 h at room
temperature, DBU (65.0 mL, 0.428 mmol) was added to the reac-
tion mixture at room temperature. After removal of the solvents,
benzene and hexane was added to the residue and the reaction
mixture was filtered through Celiteꢁ. The filtrate was cooled to
ꢁ40 ꢂC, the suspension was filtered through a glass filter to afford
(E,E)-1b (206.6 mg, 0.133 mmol, 62%) as purple crystals. (E,E)-
1b: mp 278–280 ꢂC. 1H NMR (300 MHz, C6D6, 25 ꢂC) ꢃ 0.29
(s, 72H, Si(CH3)3), 0.41 (s, 54H, Si(CH3)3), 2.73 (s, 4H, CH),
1b Cr(CO)4: purple crystals. mp 165 ꢂC (dec.). 1H NMR (400
ꢄ
MHz, C6D6, 20 ꢂC) ꢃ 0.21 (s, 36H, Si(CH3)3), 0.30 (s, 36H,
Si(CH3)3), 0.32 (s, 54H, Si(CH3)3), 2.92 (s, 2H, CH), 2.93 (s,
1
2H, CH), 4.30 (A2B2, JHH ¼ 1:8 Hz, 4H, C5H4), 4.69 (A2B2,
1JHH ¼ 1:8 Hz, 4H, C5H4), 6.92 (brs, 4H, C6H2). 13C{1H} NMR
(100 MHz, C6D6, 20 ꢂC) ꢃ 2.70 (s, Si(CH3)3), 5.48 (s, Si(CH3)3),
22.27 (s, C(SiMe3)3), 31.80 (brs, CH(SiMe3)2 ꢃ 2), 75.40 (s, ꢈ-
C5H4), 78.60 (brs, ꢉ-C5H4), 87.66 (brd, JPC ¼ 28:8 Hz), 127.45
(br, m-C6H2), 137.23 (dd, JPC ¼ 58:0 and 10.7 Hz, ipso-C6H2),
146.29 (s, p-C6H2), 147.35 (br, o-C6H2), 216.91 (brd, JPC
¼
39:1 Hz, CO), 219.24 (brt, CO). 31P NMR (120 MHz, C6D6,
25 ꢂC) ꢃ 386.4, 295.9 (AA0BB0, JPP ¼ ꢅ620:1, JPP ¼ ꢅ37:3,
1
2
4
3JPP ¼ ꢆ18:7, j JPPj < 4:0 Hz). UV–vis (n-hexane): ꢆmax 360
(sh, " 4400), 492 (" 5400), 640 (sh, " 1300) nm. IR (nujol):
ꢅ(CO) 2015, 1954, 1935, 1910 cmꢁ1. HRMS (FAB): m=z found
1721.5421 ([M]þ), calcd for C74H142CrFeO4P4Si14: 1721.5401.
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b)
with Molybdenum Tetracarbonyl Norbornadiene Complex.
1
1
4.58 (A2B2, JHH ¼ 1:8 Hz, 4H, C5H4), 4.93 (A2B2, JHH
¼

1898 Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) BCSJ AWARD ARTICLE
1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b) (32.0 mg, 20.6
mmol) and [Mo(CO)4(nbd)] (57.0 mg, 206 mmol) in benzene-d6
(0.8 mL) was placed in an NMR tube. After three freeze–pump–
thaw cycles, the NMR tube was evacuated and sealed. When
the NMR tube was heated at 50 ꢂC for 2 h, the signals for (E,E)-
1b disappeared in the 31P NMR spectrum. The tube was opened,
and the insoluble materials were removed by filtering through
Celiteꢁ. After removal of the solvent, the reaction mixture was
separated by GPLC to afford the molybdenum complex, (Z,Z)-
1b Mo(CO)4 (27.0 mg, 15.3 mmol; 74%). (Z,Z)-1b Mo(CO)4:
vis (n-hexane): ꢆmax 363 (sh, " 4400), 492 (" 5700), 620 (sh, "
1500) nm. IR (nujol): ꢅ(CO) 2024, 1951, 1932, 1896 cmꢁ1. LRMS
(FAB): m=z found 1852 (½M þ Hꢈþ), calcd for C74H143FeO4-
P4Si14W: 1852. Anal. Calcd for C74H142FeO4P4Si14W: C, 47.97;
H, 7.73%. Found: C, 47.57; H, 7.51%.
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b)
with Tungsten Pentacarbonyl Acetonitrile Complex. 1,10-Bis-
[(E)-diphosphenyl]ferrocene ((E,E)-1b) (31.1 mg, 20.0 mmol) and
[W(CO)5(CH3CN)] (73.0 mg, 200 mmol) in benzene-d6 (0.8 mL)
was placed in an NMR tube. After three freeze–pump–thaw cy-
cles, the NMR tube was evacuated and sealed. The solution was
heated at 50 ꢂC for 2.5 h, during which time the original purple
color changed to dark red, and the signals for (E,E)-1b disap-
peared in the 31P NMR spectrum. The tube was opened, and the
insoluble materials were removed by filtering through Celiteꢁ.
After removal of the solvent, the reaction mixture was separated
ꢄ
ꢄ
1
purple crystals. mp 132 ꢂC (dec.). H NMR (300 MHz, C6D6, 25
ꢂC) ꢃ 0.21 (s, 36H, Si(CH3)3), 0.29 (s, 36H, Si(CH3)3), 0.32 (s,
54H, Si(CH3)3), 2.87 (s, 2H, CH), 2.90 (s, 2H, CH), 4.32 (A2B2,
1
1JHH ¼ 1:8 Hz, 4H, C5H4), 4.62 (A2B2, JHH ¼ 1:8 Hz, 4H,
C5H4), 6.92 (brs, 4H, C6H2). 13C{1H} NMR (75 MHz, C6D6, 23
ꢂC) ꢃ 2.55 (s, Si(CH3)3), 5.34 (s, Si(CH3)3), 22.11 (s, C(SiMe3)3),
31.77 (brs, CH(SiMe3)2), 31.84 (brs, CH(SiMe3)2), 75.02 (s, ꢈ-
C5H4), 78.69 (brd, JPC ¼ 6:1 Hz, ꢉ-C5H4), 87.42 (m, ipso-C5H4),
127.62 (br, m-C6H2), 137.13 (m, ipso-C6H2), 146.21 (s, p-C6H2),
147.05 (br, o-C6H2), 214.85 (m, CO), 223.14 (br, CO). 31P NMR
(120 MHz, C6D6, 25 ꢂC) ꢃ 358.7, 304.3 (AA0BB0, 1JPP ¼ ꢅ606:7,
by GPLC to afford (Z,Z)-1b W(CO)4 (35.3 mg, 19.1 mmol; 96%).
ꢄ
Theoretical Calculations. All theoretical calculations were
carried out using the Gaussian 98 program35 with density function
theory at the B3LYP method. The geometries of (E,E)-8a, (E,E)-
8b, and (Z,Z)-14 were optimized by using the 6-31G(d) basis sets.
It was confirmed that the optimized structures of (E,E)-8a, (E,E)-
8b, and (Z,Z)-14 have minimum energies by frequency calcula-
tions. The TDDFT calculations of (E,E)-8a, (E,E)-8b, and (Z,Z)-
14 were performed at TZ(2d) for Fe, 6-311+G(2d) for P, and
6-31G(d) for C and H (for (E,E)-8a and (E,E)-8b) or 6-31G(d)
(for (Z,Z)-14) basis sets. Theoretically optimized coordinations
of (E,E)-8a, (E,E)-8b, and (Z,Z)-14 are shown in Table S1, S2,
and S4, respectively.
4
3
2JPP ¼ ꢅ29:7, JPP ¼ ꢆ14:9, j JPPj < 4:0 Hz). UV–vis (n-hex-
ane): ꢆmax 362 (sh, " 5400), 488 (" 4100), 627 (sh, " 640) nm.
IR (nujol): ꢅ(CO) 2028, 1958, 1942, 1906 cmꢁ1. HRMS (FAB):
m=z found 1764.5075 ([M]þ), calcd for C74H142Fe98MoO4P4Si14:
1764.5046.
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b)
with Molybdenum Pentacarbonyl Acetonitrile Complex. 1,10-
Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b) (23.1 mg, 14.8 mmol)
and [Mo(CO)5(CH3CN)] (40.8 mg, 148 mmol) in benzene-d6 (0.7
mL) was placed in an NMR tube. After three freeze–pump–thaw
cycles, the NMR tube was evacuated and sealed. After heating
of the tube at 50 ꢂC for 3 h, the signals for (E,E)-1b disappeared
in the 31P NMR spectrum. The tube was opened, and the insoluble
materials were removed by filtering through Celiteꢁ. After re-
moval of the solvent, the reaction mixture was separated by GPLC
X-ray Crystallographic Analyses of (E,E)-1a, (E,E)-1b, and
(Z,Z)-1b W(CO) . Single crystals of (E,E)-1a, (E,E)-1b, and
ꢀ
benzene solution at room temperature in a degassed and sealed
4
(Z,Z)-1b W(CO)4 were obtained by slow recrystallization from
ꢄ
tube (for (E,E)-1a and (E,E)-1b) or in a glovebox filled with argon
(for (Z,Z)-1b W(CO)4). The intensity data were collected on a
ꢄ
Rigaku Mercury CCD diffractometer with graphite-monochromat-
˚
to afford (Z,Z)-1b Mo(CO)4 (18.2 mg, 10.3 mmol; 70%).
ed Mo Kꢉ radiation (ꢆ ¼ 0:71070 A) (for (E,E)-1a and (E,E)-1b)
ꢄ
Reaction of 1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b)
with Tungsten Tetracarbonyl 1,5-Cyclooctadiene Complex.
1,10-Bis[(E)-diphosphenyl]ferrocene ((E,E)-1b) (48.0 mg, 31.0
mmol) and [W(CO)4(cod)] (125.1 mg, 310 mmol) in benzene-d6
(0.7 mL) was placed in an NMR tube. After three freeze–pump–
thaw cycles, the NMR tube was evacuated and sealed. When the
NMR tube was heated at 50 ꢂC for 3 h, the signals for (E,E)-1b
disappeared in the 31P NMR spectrum. The tube was opened,
and the insoluble materials were removed by filtering through
Celiteꢁ. After removal of the solvent, the reaction mixture was
separated by GPLC to afford the tungsten complex, (Z,Z)-
1b W(CO)4 (51.2 mg, 27.6 mmol; 89%). (Z,Z)-1b W(CO)4: dark
or on a Rigaku Saturn70 CCD system with VariMax Mo Optic
˚
using Mo Kꢉ radiation (ꢆ ¼ 0:71070 A) (for (Z,Z)-1b W(CO)4).
ꢄ
Selected structural parameters and crystal data of (E,E)-1a, (E,E)-
1a, and (Z,Z)-1b W(CO)4 are shown in Tables 3, 12, and 13, re-
ꢄ
spectively. The structure was solved by direct method (SHELXS-
97)36 and refined by full-matrix least-squares procedures on F2 for
all reflections (SHELXL-97).37 All non-hydrogen atoms were re-
fined anisotropically. All hydrogen atoms were placed using AFIX
instructions. All atoms of (E,E)-1a except for the benzene ring of
the Tbt group were disordered and their occupancies were refined
(0.62:0.38). The cyclopentadienyl ring and phosphorus atoms of
(E,E)-1b were disordered, and their occupancies were refined
(0.89:0.11). The cyclopentadienyl ring of the minor part of the
disordered carbon atoms of (E,E)-1b are restrained using SADI
instructions and refined isotropically. One of the CH(SiMe3)2
groups at the ortho-position and the C(SiMe3)3 group at the
para-position of the Bbt group of (E,E)-1b were disordered, and
the occupancies were refined (0.57:0.43). One of the CH(SiMe3)2
groups at the ortho-position and two C(SiMe3)3 groups at the
ꢄ
ꢄ
red crystals. mp 144 ꢂC (dec.). 1H NMR (400 MHz, C6D6, 24 ꢂC) ꢃ
0.20 (s, 36H, Si(CH3)3), 0.29 (s, 36H, Si(CH3)3), 0.32 (s, 54H,
Si(CH3)3), 2.90 (s, 2H, CH), 2.91 (s, 2H, CH), 4.32 (A2B2, 1JHH
¼
1
1:8 Hz, 4H, C5H4), 4.62 (A2B2, JHH ¼ 1:8 Hz, 4H, C5H4), 6.92
(brs, 4H, C6H2). 13C{1H} NMR (100 MHz, C6D6, 20 ꢂC) ꢃ 2.57
(s, Si(CH3)3), 5.37 (s, Si(CH3)3), 22.17 (s, C(SiMe3)3), 31.82
(s, CH(SiMe3)2), 31.89 (s, CH(SiMe3)2), 75.11 (s, ꢈ-C5H4), 78.90
(brd, JPC ¼ 6:2 Hz, ꢉ-C5H4), 87.80 (m, ipso-C5H4), 127.75 (br,
m-C6H2), 137.74 (dd, JPC ¼ 12:3, 60.5 Hz, ipso-C6H2), 146.29 (s,
p-C6H2), 147.15 (brs, o-C6H2), 199.08 (brt, CO), 205.19 (brd,
J ¼ 33:2 Hz, CO). 31P NMR (120 MHz, C6D6, 24 ꢂC) ꢃ 307.2
para-position of the Bbt group of (Z,Z)-1b W(CO)4 were disor-
ꢄ
dered, and the occupancies were refined (The final ratios were
0.52:0.48, 0.56:0.44, and 0.73:0.27). Crystallographic data re-
ported in this manuscript have been deposited with Cambridge
Crystallographic Data Centre as supplementary publication
Nos. CCDC-287252 ((E,E)-1a), 287251 ((E,E)-1a), and 617389
(the satellite signals of 1JWP ¼ 245:1 Hz), 283.7 (AA0BB0, 1JPP
¼
4
3
ꢅ604:6 Hz, 2JPP ¼ ꢅ29:0, JPP ¼ ꢆ14:5, j JPPj < 4:0 Hz). UV–

N. Nagahora et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 10 (2007) 1899
Table 13. Crystallographic Data and Experimental Parameters for the Crystal Structure Analyses of
(E,E)-1a, (E,E)-1b, and (Z,Z)-1b W(CO)4
ꢄ
(E,E)-1a
(E,E)-1b
(Z,Z)-1b W(CO)4
ꢄ
Formula
C64H126FeP4Si12
1412.46
0:30 ꢃ 0:20 ꢃ 0:10
103(2)
triclinic
C70H142FeP4Si14
1556.83
0:40 ꢃ 0:30 ꢃ 0:15
103(2)
monoclinic
C2=c (#15)
22.9804(5)
11.6477(3)
34.7151(8)
90
96.8190(9)
90
9226.4(4)
4
1.121
C74H142FeO4P4Si14W
1852.72
Formula weight
Crystal dimensions/mm3
Collection temperature/K
Crystal system
0:15 ꢃ 0:10 ꢃ 0:05
103(2)
triclinic
ꢀ
ꢀ
Space group
˚
P1 (#2)
P1 (#2)
a/A
˚
10.834(3)
10.640(3)
19.972(6)
75.001(10)
87.417(12)
71.851(9)
2111.7(11)
1
1.111
7272
668
0.0780
9.9493(8)
12.7337(11)
42.806(5)
97.960(4)
91.607(4)
112.083(8)
4957.9(8)
2
1.241
17117
1005
0.1063
b/A
˚
c/A
ꢉ/ꢂ
ꢈ/ꢂ
ꢊ/ꢂ
3
˚
Volume/A
Z
Density/g cmꢁ3
Independent reflections
No. of parameters
R1 [I > 2ꢇðIÞ]
8118
510
0.0765
0.2095
0.0995
0.2281
1.049
wR2 [I > 2ꢇðIÞ]
R1 (all data)
wR2 (all data)
0.1619
0.1298
0.1963
1.096
0.2446
0.1855
0.2957
1.138
Goodness of fit
((Z,Z)-1b W(CO)4). Copies of the data can be obtained free of
Chem. Soc. 1986, 108, 3130. e) S. Shah, S. C. Burdette, S.
Swavey, F. L. Urbach, J. D. Protasiewicz, Organometallics
1997, 16, 3395.
ꢄ
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK; fax: +44 1223 336033; or deposit@
ccdc.cam.ac.uk).
4
a) N. Tokitoh, Y. Arai, R. Okazaki, S. Nagase, Science
1997, 277, 78. b) N. Tokitoh, Y. Arai, T. Sasamori, R. Okazaki,
S. Nagase, H. Uekusa, Y. Ohashi, J. Am. Chem. Soc. 1998, 120,
433. c) T. Sasamori, N. Takeda, N. Tokitoh, Chem. Commun.
2000, 1353. d) T. Sasamori, Y. Arai, N. Takeda, R. Okazaki, Y.
Furukawa, M. Kimura, S. Nagase, N. Tokitoh, Bull. Chem. Soc.
Jpn. 2002, 75, 661. e) T. Sasamori, N. Takeda, M. Fujio, M.
Kimura, S. Nagase, N. Tokitoh, Angew. Chem., Int. Ed. 2002,
41, 139. f) T. Sasamori, N. Takeda, N. Tokitoh, J. Phys. Org.
Chem. 2003, 16, 450. g) T. Sasamori, E. Mieda, N. Takeda, N.
Tokitoh, Chem. Lett. 2004, 33, 104. h) N. Nagahora, T. Sasamori,
N. Takeda, N. Tokitoh, Chem. Eur. J. 2004, 10, 6146. i) T.
Sasamori, E. Mieda, N. Nagahora, N. Takeda, N. Takagi, S.
Nagase, N. Tokitoh, Chem. Lett. 2005, 34, 166. j) T. Sasamori,
E. Mieda, N. Takeda, N. Tokitoh, Angew. Chem., Int. Ed. 2005,
44, 3717. k) T. Sasamori, E. Mieda, N. Nagahora, K. Sato, D.
Shiomi, T. Takui, Y. Hosoi, Y. Furukawa, N. Takagi, S. Nagase,
N. Tokitoh, J. Am. Chem. Soc. 2006, 128, 12582. l) T. Sasamori,
A. Tsurusaki, N. Nagahora, K. Matsuda, Y. Kanemitsu, Y.
Watanabe, Y. Furukawa, N. Tokitoh, Chem. Lett. 2006, 35, 1382.
This work was supported in part by Grants-in-Aid for Cre-
ative Scientific Research (No. 17GS0207), Scientific Research
(No. 18750030), and the 21st Century COE, Kyoto University
Alliance for Chemistry from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. N. N. thanks
for the general support from the Kyoto Sustainability Initiative
and the Institute of Sustainability Science, Kyoto University.
Supporting Information
Tables S1–S6 are in PDF format. This material is available free
of charge on the web at http://www.csj.jp/journals/bcsj/.
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