1,2-bis(ferrocenyl)dipnictenes: Bimetallic systems with a Pn=Pn heavy π-spacer (Pn: P, Sb, and Bi)

Article abstract of DOI:10.1246/bcsj.20130174

1,2-Bis(ferrocenyl)dipnictenes bearing a Pn=Pn π-spacer (Pn: P (1), Sb (2), and Bi (3)) between two ferrocenyl units have been synthesized as stable compounds. Not only their molecular structures and fundamental properties but also their redox behavior have been systematically disclosed. Interestingly, in the reduction region, the dipnictenes showed two pseudo-reversible one-electron redox couples at low temperature, suggesting possible generation of the corresponding radical anion and dianion species. On the other hand, they showed three-step one-electron oxidation processes in the oxidation region. The first two oxidation steps would correspond to those of the two ferrocenyl moieties, while the third step would be that of the Pn=Pn π-spacer moiety, respectively. Thus, these 1,2-bis(ferrocenyl)dipnictenes with a Pn=Pn π-spacer should be stable multiredox systems reflecting unique properties of a double bond between heavier 15 group elements. As a result, all Pn=Pn units (Pn: P, Sb, and Bi) were found to work as a more effective π-spacer than those of 2nd row elements such as C=C and N=N.

Full text of DOI:10.1246/bcsj.20130174

1132 Bull. Chem. Soc. Jpn. Vol. 86, No. 10, 1132-1143 (2013)
© 2013 The Chemical Society of Japan
BCSJ Award Article
1,2-Bis(ferrocenyl)dipnictenes: Bimetallic Systems
with a Pn=Pn Heavy ³-Spacer (Pn: P, Sb, and Bi)#
Michiyasu Sakagami,1 Takahiro Sasamori,*1 Heisuke Sakai,2
Yukio Furukawa,2 and Norihiro Tokitoh*1
1Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011
2Department of Chemistry and Biochemistry, School of Advanced Science and Engineering,
Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555
Received June 18, 2013; E-mail: sasamori@boc.kuicr.kyoto-u.ac.jp
1,2-Bis(ferrocenyl)dipnictenes bearing a Pn=Pn ³-spacer (Pn: P (1), Sb (2), and Bi (3)) between two ferrocenyl
units have been synthesized as stable compounds. Not only their molecular structures and fundamental properties but also
their redox behavior have been systematically disclosed. Interestingly, in the reduction region, the dipnictenes showed
two pseudo-reversible one-electron redox couples at low temperature, suggesting possible generation of the corresponding
radical anion and dianion species. On the other hand, they showed three-step one-electron oxidation processes in the
oxidation region. The first two oxidation steps would correspond to those of the two ferrocenyl moieties, while the third
step would be that of the Pn=Pn ³-spacer moiety, respectively. Thus, these 1,2-bis(ferrocenyl)dipnictenes with a Pn=Pn
³-spacer should be stable multiredox systems reflecting unique properties of a double bond between heavier 15 group
elements. As a result, all Pn=Pn units (Pn: P, Sb, and Bi) were found to work as a more effective ³-spacer than those of
2nd row elements such as C=C and N=N.
Organometallic ³-conjugated systems are attracting much
interest from the viewpoint of showing interesting electronic,
optical, and magnetic properties. In this research field, d-³
conjugated systems of bimetallic complexes tethered with a ³-
electron spacer, [M(Ligand)]-(³-electron spacer)-[M(Ligand)]
(M: transition metal), have been actively investigated.1 These
compounds are a unique class of appropriate models of mixed-
valence states giving insight on the ability of the ³-electron
system as a ³-spacer in the context of fundamental organic
electronic materials such as molecular switches and molecular
wires.2 In this background, ferrocene is frequently used as an
effective d-electron moiety in such d-³ conjugated systems,
because it should be a promisingly stable and effective redox
system and amenable to modification with a variety of estab-
lished substituents.3 Thus, ferrocenyl-based bimetallic d-³
electron systems should be a touchstone for investigating
the ability of a ³-electron system as a “³-spacer.” Although
several numbers of d-³ conjugated systems with two ferro-
cenyl groups bridged by a ³-electron spacer have been report-
ed to be investigated, e.g., Ph(Fc)C=C(Fc)Ph,4 FcC¸CFc,5
Fc-N=N-Fc6 (Fc: ferrocenyl), and bis(ferrocenyl)thiophene
derivatives,7 the ³-electron systems in these compounds are
limited to those consisting of 2nd row main group elements.
The advantageous and required properties as a d-³ electron
system toward organometallic electronic materials should be
(i) relatively low redox potential, (ii) stable multistep redox
behavior, and (iii) controllable redox system. Regarding all of
these points, ³-bonds between heavier main group elements
are thought to be superior to those of 2nd row elements as a
³-spacer in d-³ electron systems, because ³-bond compounds
between heavier main group elements are known to exhibit
smaller ³-³* energy gaps than those of 2nd row elements due
to the smaller overlapping of np orbitals.8 In addition, ³-bond
compounds between heavier group 15 elements (P=P, As=As,
Sb=Sb, and Bi=Bi, called dipnictenes) are known to afford
stable anion radical species upon chemical reduction, showing
their lower LUMO level and stable redox behavior.9 From a
standpoint of using a dipnictene moiety as a ³-spacer, the
points of (ii) and (iii) should be clarified and investigated by
the construction of bimetallic systems bearing a dipnictene
moiety as a ³-spacer. Here again, it is expected that ³-bonds
between heavier group 15 elements should be promisingly
more effective ³-electron spacers than those of 2nd row
elements. However, it has been difficult to develop such chem-
istry of heavier ³-electron spacers so far due to the difficulty in
synthesis of the compounds, arising from their extremely high
reactivity toward self-oligomerization and addition reaction
with aerobic oxygen or moisture. On the other hand, it has been
demonstrated that the double-bond compounds between heavier
group 15 elements can be stabilized enough to be treated under
Published on the web August 2, 2013; doi:10.1246/bcsj.20130174

M. Sakagami et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1133
ambient conditions when sterically demanding substituents are
introduced at the reactive ³-bond moiety as steric protection
groups.10 Indeed, a series of heavier dipnictenes have been
synthesized and isolated by taking advantage of very bulky
substituents.9-11 Furthermore, these compounds exhibit unique
electrochemical properties due to their low-lying LUMO. We
have reported that these heavier dipnictenes can be reduced by
lithium metal to give the corresponding anion radical species.9
Thus, it is suggested such ³-bonds between heavier group 15
elements should work as an effective ³-spacer for metal
moieties. Combined with such striking developments in the
field of extended ³-electron systems containing heavier main
group elements and d-³ electron systems,12 this research
background prompted us to investigate the chemistry of a new
type of d-³ electron systems containing a ³-electron system
of heavier group 15 elements. Although the simplest model
compound for 1,2-bis(ferrocenyl)diphosphenes is Fc-P=P-Fc
(Fc: ferrocenyl), the phosphorus analogue of Fc-N=N-Fc, all
of our synthetic attempts to isolate FcP=PFc and those by other
groups have been unsuccessful so far.3b,13 A book3b mentions
the preparation of FcP=PFc from the reductive dehalogena-
tion of FcPCl2, but unfortunately, we were not able to obtain
synthetic and/or characterization details for this reference
(“private communication”), suggesting the instability of FcP=
PFc under ambient conditions and the limited steric demand of
the ferrocenyl groups should however offer only insufficient
protection for the reactive P=P bond.13 As a solution of this
synthetic challenge, we reported the synthesis of a custom-
tailored ferrocenyl unit with an increased ability for steric
protection, and its subsequent implementation in the synthesis
of 1,2-bis(ferrocenyl)diphosphene as a stable crystalline com-
pound.14 Thus, we have recently succeeded in the synthesis of
novel 1,2-bis(ferrocenyl)dipnictene derivatives and developed
two bulky ferrocenyl units, 2,5-Ar2-1-ferrocenyl groups (Fc¤:
Ar = 3,5-dimethylphenyl, Fc*: Ar = Dtp (Dtp: 3,5-di-tert-
butylphenyl), tethered with a Pn=Pn ³-spacer (Pn: P, Sb, and
Bi).14,15 The systematic evaluation of the ³-electron units of
heavier main group elements as a ³-spacer should be of great
interest and importance. In this paper, we describe systematic
studies of the properties of 1,2-bis(ferrocenyl)dipnictenes 1-3
including structural features and redox behavior (Figure 1).
H
Fe
Fe
Fe
N
N
C C
H
Fe
Fe
Fe
Fe
replaced by
heavy-atoms
R
Fe
P
P
Si Si
R
1: Pn = P
2: Pn = Sb
3: Pn = Bi
Fe
Dtp
Dtp
Pn Pn
Dtp
Dtp
Fe
Dtp
Figure 1.
The iodoferrocene derivative 5 (Fc*I) as a source of a bulky
ferrocenyl unit was synthesized in 6 steps from ferrocene. It has
two 3,5-di-tert-butylphenyl (Dtp) groups at the 2- and 5-
positions of one of the Cp (cyclopentadienyl) rings (Scheme 1).
Sulfoxide 7 was obtained from a Negishi cross-coupling reac-
tion of ferrocenyl phenyl sulfoxide (6)16 with DtpBr. Reduction
of 7 with NaI and (CF3CO)2O afforded sulfide 8,17 which was
oxidized with mCPBA to give sulfoxide 9, a structural isomer of
7. The inversion of the sulfinyl group at this stage is the key step
for the introduction of another Dtp group to give sulfoxide 10,
which was achieved by the second Negishi cross-coupling
reaction between 9 and DtpBr. Treatment of sulfoxide 10 with
t-BuLi followed by quenching with I2 resulted in the formation
of 5. While the molecular structure of 5 is shown in Figure 2,
one can recognize the effective steric protection ability of the
Fc* group. As precursors for the 1,2-bis(ferrocenyl)dipnictenes,
the corresponding ferrocenyldihalopnictanes, Fc*PCl2 (11),
Fc*SbCl2 (12),15 and Fc*BiBr2 (13),15 were prepared by the
lithiation of iodoferrocene 5 with t-BuLi followed by addition
of PCl3, SbCl3, and BiBr3, respectively. The targeted 1,2-bis-
(ferrocenyl)dipnictenes 1-3 were isolated as stable compounds
by the reductive coupling reactions of the corresponding di-
halopnictanes, 11-13, using magnesium metal in THF at
r.t. (Scheme 2). These compounds are stable under ambient
conditions with strong colors of pink (diphosphene 1), green
(distibene 2), and violet (dibismuthene 3), respectively. In all
Results and Discussion
Synthesis of 1,2-Bis(ferrocenyl)dipnictenes.
We have
reported the synthesis of the first stable 1,2-bis(ferrocenyl)di-
phosphene, Fc¤P=PFc¤ (4, Fc¤: 2,5-bis(3,5-dimethylphenyl)-1-
ferrocenyl).14 Since attempted synthesis of 1,2-bis(ferrocenyl)-
distibene and dibismuthene bearing the same substituents,
Fc¤Sb=SbFc¤ and Fc¤Bi=BiFc¤, have been unsuccessful, we
have developed bulkier ferrocenyl group Fc* (2,5-bis(3,5-
di-tert-butylphenyl)-1-ferrocenyl) and successfully applied it
to the synthesis of Fc*Sb=SbFc* and Fc*Bi=BiFc*, which
exhibit unique electrochemical properties.15 Herein, we have
prepared a series of 1,2-bis(ferrocenyl)dipnictenes bearing the
same ferrocenyl moieties for the systematic comparison of
their redox properties on the basis of the intrinsic nature of
dipnictene ³-bonds. That is, we decided to synthesize a series
of Fc*Pn=PnFc* (Pn = P, Sb, and Bi) to evaluate the char-
acteristics of a Pn=Pn bond as a ³-spacer systematically.
1
of 1-3, their H NMR spectra in C6D6 at r.t. suggested their
symmetric structures in solution. That is, one singlet signal for
the t-Bu protons of Dtp groups and that for unsubstituted Cp
ring were observed, indicating free rotation around the C(Cp)-
C(Dtp) and C(Cp)-E. The 31P NMR spectrum of 1 showed one
resonance for the P nuclei at 471 ppm, which is in a region

1134 Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) BCSJ AWARD ARTICLE
1) LDA
2) ZnCl2
3) DtpBr
cat. [Pd(PPh3)4]
Fe
Fe
Fe
1) NaI
2) (CF3CO)2O
m-CPBA
Dtp
S
Dtp
O S
Ph
O S
Ph
acetone
0 °C
ca. 0.5 h
CH2Cl2
0 °C
THF
–78 °C
ca. 10 h
Ph
6
7
85%
8
90%
ca. 5 h
1) LDA
2) ZnCl2
3) DtpBr
Fe
Fe
Fe
1) t-BuLi
Dtp
Dtp
2) I2
cat. [Pd(PPh3)4]
O
O
Dtp
Dtp
Dtp
S
S
I
THF
–78 °C
ca. 10 h
Et2O
–78 °C
ca. 3 h
Ph
Ph
5 (Fc*I)
9
81%
10
80%
68%
Scheme 1.
1) t-BuLi
2) PnX3
Fe
Fe
Dtp
Dtp
PnX2
solvent
–78 °C
Dtp
Dtp
I
5 (Fc*I)
11 (73%): Pn = P, C = Cl
12 (33%): Pn = Sb, X = Cl
13 (40%): Pn = Bi, X = Br
1: pink
2: green
3: violet
Fe
Dtp
Mg
Dtp
Pn
Pn
Dtp
THF
r.t.
Dtp
Fe
1 (62%): Pn = P
2 (44%): Pn = Sb
3 (52%): Pn = Bi
Scheme 2.
Figure 2. (a) Molecular structure of Fc*I (5) with thermal
displacement ellipsoids at 50% probability. (b) Space-
filling model of 5.
of their Pn=Pn bonds with Ci symmetry.15 The structural
parameters and crystal data are summarized in Tables 1 and 2.
The Pn=Pn bond lengths of 2.0286(6) (1), 2.6700(7)
(2), and 2.8307(3) ¡ (3) are shorter than the corresponding
single-bond lengths [e.g., 2.215 ¡ for Ph2P-PPh2,19 2.837 ¡
for Ph2Sb-SbPh2,20 and 2.990 ¡ for Ph2Bi-BiPh221] and simi-
lar to those of the previously reported dipnictenes (e.g.,
2.043(1) ¡ for BbtP=PBbt (14),18 2.7037(6) ¡ BbtSb=SbBbt
(15),11b 2.8699(6) ¡ for BbtBi=BiBbt (16)11b (Bbt: 2,6-[CH-
(SiMe3)2]2-4-[C(SiMe3)3]-C6H2). Thus, all of the Pn=Pn bonds
of 1-3 were found to exhibit considerable double-bond char-
acter on the basis of the bond lengths. Also, the vibrational
similar to those of the previously reported ferrocenyldiphos-
phenes and diaryldiphosphenes.11,12c-12h,14
Molecular Structures. The structural parameters of 1,2-
bis(ferrocenyl)dipnictenes 1-3 were definitively determined by
X-ray diffraction analysis (Figure 3). While diphosphene 1 was
found to exhibit C1 geometry without any symmetric element
in the independent moiety, both distibene 2 and dibismuthene
3 have the crystallographic center of symmetry at the middle

M. Sakagami et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1135
Table 1. Selected Bond Lengths and Angles of Dipnictenes
1-3 and Related Compounds (Bbt: 2,6-Bis[bis(trimethyl-
silyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl)
(a)
LPn=PnL
Pn=Pn/¡ Pn-C/¡
Pn-Pn-C/°
Fc*P=PFc* (1)
2.0286(6) 1.8080(17) 111.23(5)
1.8454(17) 93.22(5)
BbtP=PBbt (14)18
Fc*Sb=SbFc* (2)15
2.043(1)
1.834(4)
1.845(4)
114.9(1)
97.8(1)
2.6700(7) 2.158(5)
98.28(13)
BbtSb=SbBbt (15)11b 2.7037(6) 2.197(4)
105.38(10)
Fc*Bi=BiFc* (3)15
BbtBi=BiBbt (16)11b
2.8307(3) 2.268(3)
2.8699(6) 2.291(5)
96.17(9)
104.15(12)
¹1
of previously reported dipnictenes (609 cm for TbtP=PTbt
(b)
(17),11a,18 207 cm for TbtSb=SbTbt (18),11a,11b 135 cm for
TbtBi=BiTbt (19);11a,11b Tbt: 2,4,6-[CH(SiMe3)2]3-C6H2), sug-
gesting considerable degrees of double-bond character for the
Pn=Pn bonds in 1, 2, and 3. In attention to the Pn-C(Fc*) in 2
and 3 bond lengths, these are slightly shorter than the Pn-C(Ar)
bond lengths of the corresponding previously reported diaryl-
dipnictenes, i.e., 2.158(5) ¡ for Sb-C(Fc*) of 2 vs. 2.197(4) ¡
for Sb-C(Bbt) of 15,11b 2.268(3) ¡ for Bi-C(Fc*) of 3 vs.
2.291(5) ¡ for Bi-C(Bbt) of 16,11b indicating slight but appar-
ent conjugative electronic communication between the ferro-
cenyl moieties and the Pn=Pn ³-bond. In the case of 1, the P2-
P1-C1(Fc*) angle (111.23(5)°) is wider than the corresponding
opposite P1-P2-C2(Fc*) angle (93.22(5)°) probably due to
packing effects. In addition, one of the dihedral angles between
the Cp ring vs. P1-P2-C2(Fc*) plane is almost perpendicular
(ca. 88°) and that of the other side (the Cp ring vs. P2-P1-
C1(Fc*)) is nearly parallel (ca. 23°) due to the steric repulsion
between the two 3,5-di-tert-butylphenyl groups.18 Here, the
P1-C1(Fc*) bond (1.8080(17) ¡), where the P2-P1-C1 plane
is almost parallel to the Cp ring, is shorter than the another one
(P2-C2(Fc*) = 1.8454(17) ¡), also suggesting the existence of
conjugative electronic communication between the ferrocenyl
moieties and the P=P ³-bond especially in the case of the P=P
³-plane lying parallel with the Cp plane. The Pn-Pn-C(Cp)
angles of 2 and 3 are 98.28(13) and 96.17(9)°, respectively, i.e.,
Pn-Pn-C(Cp) angles gets smaller and closer to 90° as Pn is gets
heavier from P to Bi, indicating non-hybridized orbitals, one of
the characteristics of heavier main group elements.9,11a,25 The
dihedral angles between the E-E-C(Cp) and the Cp planes of
2 and 3 are 38 (E = Sb) and 37° (E = Bi), respectively, indi-
cating effective conjugation between the Pn=Pn ³-electrons
and ligand moieties of Fc* in 2 and 3 as compared with the
case of ArPn=PnAr, where the aryl rings of the Ar ligands
are almost perpendicular to the Pn=Pn-C plane.11
¹1
¹1
(c)
Figure 3. Molecular structures of (a) diphosphene 1,
(b) distibene 2, and (c) dibismuthene 3 with thermal dis-
placement ellipsoids at 50% probability. Ether molecule in
(a) [1¢Et2O] and all hydrogen atoms in (a)-(c) have been
omitted for clarity.
frequencies of the central Pn=Pn bonds of 1-3 supported
double-bond character. In Raman spectra, strong Raman shifts
were observed at ¯ = 611 (1), 223 (2), and 140 (3) cm
¹1
UV-vis Spectra.
In the UV-vis spectra of these 1,2-
assignable to Pn=Pn (Pn: P, Sb, and Bi) stretching vibrational
frequencies, respectively. These vibrational frequencies were
reasonably reproduced by theoretical calculations (B3PW91,
624 (1), 231 (2), and 162 (3) cm¹1), and these ¯PnPn vibrational
frequencies are larger than those of the corresponding single-
bis(ferrocenyl)dipnictenes 1-3 shown in Figure 4, characteristic
absorptions including that corresponding to d-³* electron
transitions from the filled d-orbitals at the Fe center to the ³*
orbital of the Pn=Pn ³-spacer were observed (Table 3). In the
case of diphosphene 1, three characteristic absorption bands
around 350, 440, and 550 nm were observed in either THF
or hexane solution. The first and second absorptions would
¹1
¹1
bond compounds (530 cm for Ph2P-PPh2,22 141 cm for
Ph2Sb-SbPh2,23 103 cm Ph2Bi-BiPh224) and similar to those
¹1

1136 Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) BCSJ AWARD ARTICLE
Table 2. Crystallographic Data of Dipnictenes 1-3
Compounds
Fc*P=PFc*¢(Et2O)
([1¢Et2O])
Fc*Sb=SbFc* (2)15
Fc*Bi=BiFc* (3)15
Formula
Molecular weight
Temperature/K
C76H98Fe2P2¢C4H10O
1259.30
100
C76H98Fe2Sb2
1366.74
100
C76H98Bi2Fe2
1541.20
100
-/¡
0.71069
0.02 © 0.02 © 0.01
monoclinic
P21/n (#14)
13.8620(1)
34.1010(4)
15.5269(3)
90
104.6656(6)
90
7100.56(17)
4
0.83077
0.71069
Crystal size/mm3
0.04 © 0.03 © 0.02
triclinic
0.10 © 0.08 © 0.02
triclinic
Crystal system
Space group
a/¡
b/¡
c/¡
¡/°
¢/°
£/°
V/¡3
Z
ꢀ
ꢀ
P1 (#2)
P1 (#2)
9.8957(8)
12.2498(10)
16.4043(14)
69.437(3)
74.142(3)
69.623(3)
1719.3(2)
1
9.8783(1)
12.2940(2)
16.4895(2)
69.511(1)
74.0991(8)
69.9873(8)
1735.34(4)
1
®
0.497
1.178
1.855
1.320
5.504
1.475
¹3
Dcalcd/g cm
ªmax
25.5
29.87
26.0
Refl./restr./param.
Completeness
GOF
13188/0/841
99.8%
1.029
6158/36/389
99.1%
1.001
6694/0/398
98.1%
1.114
R1 (I > 2·(I))
wR2 (I > 2·(I))
R1 (all data)
0.0334
0.0824
0.0394
0.0556
0.1291
0.0644
0.0259
0.0669
0.0275
wR2 (all data)
Largest diif. peak and hole/e ¡
CCDC number
0.0869
0.555, ¹0.401
941816
0.1337
1.713, ¹1.006
912009
0.0677
1.685, ¹0.896
912010
¹3
reported 1,2-bis(ferrocenyl)diphosphene, Fc¤P=PFc¤, showing
a little solvent dependency (546 nm in hexane, 556 nm in THF,
¦-max = 9 nm),14 those of diphosphene 1 showed no apparent
solvent dependency in hexane and THF solution. In the UV-vis
spectra of distibene 2 and dibismuthene 3, two characteristic
absorption bands were observed around 500 and 600 nm in
either THF or hexane solution. Similar to the case of diphos-
phene 1, the former absorption can be assigned as symmetry-
allowed ³-³* transitions of Sb=Sb and Bi=Bi chromophores
on the basis of those for the previously reported diaryldistibenes
and dibismuthenes (e.g., TbtSb=SbTbt (18), -max = 466 nm
(¾ 5200, ³-³*) in hexane; TbtBi=BiTbt (19), -max = 525 nm
(¾ 4000, ³-³*) in hexane).11a,11b The latter absorptions at
longer wavelengths are most likely interpreted in terms of
the overlap of several d-³* electron transitions from filled
d-orbitals of the Fe center to the ³* orbitals of the Pn=Pn
³-spacers as in the case of diphosphene 1. Similarly, theoretical
calculations support the assignment of these absorptions (For 2,
497 nm ( f = 0.0787), HOMO(Sb=Sb, ³)-LUMO(Sb=Sb, ³*),
573 nm ( f = 0.0242), HOMO¹4(Fe, d)-LUMO(Sb=Sb, ³*).
For 3, 526 nm ( f = 0.0353), HOMO(Bi=Bi, ³)-LUMO(Bi=
Bi, ³*), 566 nm ( f = 0.0327), HOMO¹3(Fe, d)-LUMO(Bi=
Bi, ³*). Although the absorption due to d-³* electron transi-
tions in dibismuthene 3 showed no apparent solvent dependency
as well as that of diphosphene 1, that of 2 showed only small
solvent dependency in hexane (606 nm) and THF (612 nm)
Fc*
ε (x 104)
Pn Pn
Fc*
1.0
in hexane
1
2
3
Pn = P
Sb
Bi
0.5
0.0
300
400
500
600
700
800
wavelength /nm
Figure 4. UV-vis spectra of dipnictenes 1-3 in hexane.
correspond to symmetry-allowed ³-³* and symmetry-forbid-
den n-³* electron transitions, since these absorptions are
similar to those of the previously reported diaryldiphosphenes.11
The third absorption is assignable to d-³* electron transitions
on the basis of theoretical calculations (TD-B3PW91), where
the electron transitions from HOMO(Fe, d) to LUMO(P=P, ³*)
and those from HOMO¹3(Fe, d) to LUMO(P=P, ³*) would
be estimated as 560 and 551 nm, respectively (Figure 5).
In contrast to the d-³* electron transitions of the previously

M. Sakagami et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1137
Table 3. Absorption Maxima of 1,2-Bis(ferrocenyl)dipnictenes 1-3 and Related Compounds in UV-vis Spectra
-1/nm (¾)
³-³*
-2/nm (¾)
n-³*
-3/nm (¾)
d-³*
Compound
Solvent
Fc*P=PFc* (1)
hexane
THF
hexane
THF
hexane
THF
hexane
THF
hexane
hexane
hexane
hexane
hexane
hexane
CH2Cl2
354 (9800)
351 (9900)
462 (6700)
463 (7700)
522 (3300)
520 (3700)
349 (6100)
351 (9000)
418 (12000)
490 (6000)
537 (6000)
405 (13000)
466 (5200)
525 (4000)
315
436 (1400)
440 (1700)
Overlapped
Overlapped
Overlapped
Overlapped
446 (990)
448 (1400)
532 (1000)
594 (200)
670 (20)
547 (3700)
547 (3500)
606 (3800)
612 (4100)
603 (4000)
602 (4200)
546 (2000)
556 (3000)
®
Fc*Sb=SbFc* (2)15
Fc*Bi=BiFc* (3)15
Fc¤P=PFc¤ (4)14
BbtP=PBbt (14)11a,18
BbtSb=SbBbt (15)11a,11b
BbtBi=BiBbt (16)11a,11b
TbtP=PTbt (17)11a,18
TbtSb=SbTbt (18)11a,11b
TbtBi=BiTbt (19)11a,11b
FcN=NFc1a,6
®
®
530 (2000)
599 (170)
660 (100)
375
®
®
®
510
–2.29 eV, LUMO, π*
–2.59 eV, LUMO, π*
–2.51 eV, LUMO, π*
497 nm
f = 0.0787
526 nm
f = 0.0353
560 nm
f = 0.0086
551 nm
f = 0.0102
573 nm
f = 0.0242
516 nm
–5.39 eV, HOMO, d
–5.22 eV, HOMO, π
–5.00 eV, HOMO, π
566 nm
f = 0.0327
f = 0.0143
–5.47 eV, HOMO-3, d
–5.47 eV, HOMO-4, d
–5.41 eV, HOMO-3, d
Figure 5. TDDFT-calculations of dipnictenes 1-3 with Ci symmetries.
by ¦-max = 6 nm. Such negligible solvent effect of the d-³*
electron transitions in UV-vis spectra of 1,2-bis(ferrocenyl)-
dipnictenes 1-3 would be explained by the symmetric structures
of their excited states symmetric with little polarity due to the
extended d-³ conjugation. At this stage, it is difficult to draw a
clear conclusion on the details of the electron transitions, since
we have some unclear results in the electronic spectra. Although
the HOMO of distibene 2 and dibismuthene 3 are dominantly
composed of their Pn=Pn ³-orbitals and their d-orbital levels
lie on the lower levels (Figure 5) on the basis of theoretical
calculations, the d-³* transitions are computed as the longest
wavelengths. Thus, the structures of the dipnictenes at their
excited states would be different from those at their ground
states. Further theoretical calculations on the excited states
would be necessary in order to understand the electron transi-
tions in detail. In summary, the ³-³* absorptions due to Pn=Pn
chromophores move toward longer wavelengths as the central
elements descend from P to Bi. On the other hand, the absorp-
tion due to the d-³* transitions of 1 is at shorter wavelength
than those of 2 and 3, and those of 2 and 3 are similar to each
other, indicating (i) lower levels of the occupied d- and ³-
orbitals and the higher LUMO (³*) level of 1 than those of 2
and 3 and (ii) slightly higher level of LUMO (³*) of 2 than that
of 3, but the slightly higher occupied d- and ³-orbitals of 2,

1138 Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) BCSJ AWARD ARTICLE
Table 4. Redox Potentials and the Comproportionation
Constants of 1,2-Bis(ferrocenyl)dipnictenes 1-3a)
(a) Fc*P=PFc*
reduction
oxidation
Compound
50 μA
50 μA
Fc*P=PFc* Fc*Sb=SbFc* Fc*Bi=BiFc*
(1)
(2)
(3)
<Reduction>
Epc1/V
¹2.27
¹1.82
-2.05
¹3.33
¹2.71
-3.02
0.97
¹1.33
¹0.92
-1.13
¹2.43
¹1.83
-2.14
1.01
1.21 © 1025
¹1.77
¹1.35
-1.56
¹2.63
¹2.11
-2.37
0.81
8.28 © 1020
Epa1/V
E1/21/V
Epc2/V
Epa2/V
-1.5
-2.0
E/V vs. FcH/FcH+
-2.5
-3.5
-3.0
0.5
1.5
2.0
0.0
1.0
E/V vs. FcH/FcH+
E1/22/V
¦(E1-E2)/V
Kcom (E1-E2) 1.12 © 1025
(b) Fc*Sb=SbFc*
reduction
oxidation
<Oxidation>
Epa1/V
+0.40
+0.06
+0.23
+0.94
+0.61
+0.78
+1.74
®
+0.51
+0.05
+0.28
+0.72
+0.63
+0.70
+1.12
+0.82
+1.00
+0.31
¹0.13
+0.09
+0.75
+0.38
+0.57
+1.02
+0.62
+0.82
50 μA
50 μA
Epc1/V
E1/21/V
Epa2/V
Epc2/V
E1/22/V
Epa3/V
Epc3/V
E1/23/V
¦(E2-E1)/V
®
0.55
0.5
0.0
E/V vs. FcH/FcH+
-0.5
1.0
-3.0
-2.0
-1.0
E/V vs. FcH/FcH+
0.42
0.48
Kcom (E2-E1) 1.60 © 1014
¦(E3-E2)/V
7.02 © 1010
0.30
2.49 © 1012
0.25
Kcom (E3-E2)
5.59 © 107
2.86 © 106
(c) Fc*Bi=BiFc*
a) Conditions: 4.0 mM, 0.1 M n-Bu4NBF4, ¹78 °C, in THF
(reduction), in CH2Cl2 (oxidation).
reduction
oxidation
50 μA
50 μA
FcN=NFc (¹2.32 V),1a and those of the corresponding diaryl
derivatives (E1/2 = ¹1.84 V for BbtP=PBbt (14), ¹1.65 V for
BbtSb=SbBbt (15), ¹1.79 V for BbtBi=BiBbt (16)).9 Such
smaller reduction potentials of 1-3 than those of diaryldipnic-
tenes 14-16 would be due to d-³ conjugation between Fc*
moieties and ³* orbitals of Pn=Pn moiety. Thus, it should be
noted that the bulky ferrocenyl ligand should stabilize the
anionic species, and even the corresponding dianion of the
1,2-bis(ferrocenyl)dipnictenes would be promisingly generated
under these conditions. In the systematic comparison, distibene
2 showed the lowest reduction potential among those of 1,2-
bis(ferrocenyl)dipnictenes, as in the case of reduction potentials
of diaryldipnictenes 14-16 shown in the previously reported
systematic investigation.9 Thus, 1,2-bis(ferrocenyl)distibene 2
should work as an effective electron acceptor of a d-³ electron
system, reflecting the intrinsic nature of the Sb=Sb bond.
In the oxidation region, these dipnictenes showed three one-
electron oxidation steps at ¹78 °C (Table 4). The first two
oxidation potentials should be assignable to the oxidation
processes of two ferrocenyl moieties, whereas the third ones
should be assigned to those of the corresponding Pn=Pn ³-
spacer moiety. Diphosphene 1 showed pseudo-reversible redox
couples for the 1st and 2nd steps at E1/2 = +0.23 and +0.78 V,
0.5
E/V vs. FcH/FcH+
1.0
0.0
-2.0
-3.0
-1.0
E/V vs. FcH/FcH+
Figure 6. Cyclic voltammograms of (a) diphosphene 1,
(b) distibene 2, and (c) dibismuthene 3. Conditions: 4.0
mM, 0.1 M n-Bu4NBF4, ¹78 °C, in THF (reduction), in
CH2Cl2 (oxidation).
which would be affected by the orbital level of Sb=Sb moiety,
relative to those of 3, resulting in similar -max values assignable
to the d-³* electron transitions in 2 and 3.
Electrochemical Measurements for 1,2-Bis(ferrocenyl)-
dipnictenes 1-3.
The electrochemical properties of 1,2-
bis(ferrocenyl)dipnictenes 1-3 have been investigated by cyclic
and differential potential voltammetries (Figure 6). All of these
dipnictenes showed two-step pseudo-reversible one-electron
redox couples in the reduction region at ¹78 °C, i.e., E1/2
¹2.05 and ¹3.02 V for 1; E1/2 = ¹1.13 and ¹2.14 V for 2;
=
E
1/2 = ¹1.56 and ¹2.37 V for 3 (all potentials referenced
but the 3rd step was an irreversible oxidation wave at Epa =
+1.74 V, which was similar to the 3rd step of the previously
reported ferrocenyldiphosphene (TbtP=PFc, Epa = 1.75 V).12h
vs. FcH/FcH+). As one can see in Table 4, these compounds
showed significantly lower reduction potential than that of

M. Sakagami et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1139
Both distibene 2 and dibismuthene 3 showed pseudo-reversible
redox couples for all steps at E1/2 = +0.28, +0.70, and +1.00 V
for 2, E1/2 = +0.09, +0.57, and 0.82 V for 3, respectively.
While all 1,2-bis(ferrocenyl)dipnictenes 1-3 exhibit higher
oxidation potentials than those of FcN=NFc, which are +0.08
and +0.29 V (r.t. in PhCN),1a the first oxidation potential of
dibismuthene 3 is the lowest oxidation potential among those of
1,2-bis(ferrocenyl)dipnictenes and close to that of FcN=NFc,
suggesting that the Bi=Bi moiety should work as an effective
electron donor, reflecting the intrinsic nature of the Bi=Bi bond.
Although both FcN=NFc and Fc*Bi=BiFc* exhibit such low
oxidation potentials similarly, the reason would be different
for each. That is, the N=N moiety of FcN=NFc would raise
the energy level of the d-electrons in its HOMO orbitals via
mesomeric effect with ³-electron donation, making the oxi-
dation potentials of the ferrocenyl moieties lower. On the
other hand, the Bi=Bi moiety itself should work as an electron
donor, because the Bi=Bi ³-orbital is the HOMO of 3,
exhibiting higher ³-orbital level than the d-orbital levels of the
ferrocenyl moieties. After the oxidation, the electron distri-
butions of the cationic species of 3 would be relaxed through
the d-³ electron conjugation through the [Fc*-Bi=Bi-Fc*]+
unit, because it would have enough time to be relaxed during
adiabatic excitation in the electrochemical measurements. Thus,
the Pn=Pn ³-orbital levels should play important roles in the
case of such d-³ electron systems of the heavier elements
of pnictogens.
Difference between the oxidation potentials is commonly
considered a touchstone of the extent of electronic communi-
cation between two electron-transfer sites.26 It should be noted
that the oxidation processes of both ferrocenyl moieties were
observed as two separate steps with ¦(E1-E2) = 0.55 (1), 0.42
(2), and 0.48 V (3), respectively, which are considerably larger
than the separation observed in FcN=NFc (¦E = 0.21 V)
and (E)-Fc(Ph)C=C(Ph)Fc (¦E = 0.18 V). The separations of
the oxidation potentials [¦(E1-E2)] should be converted to
comproportionation constants Kcom (equilibrium constant be-
tween [Fc*Pn=PnFc*]2+ + [Fc*Pn=PnFc*] and 2 © [Fc*Pn=
PnFc*]+) = 1.60 © 1014 (1), 7.02 © 1010 (2), and 2.49 © 1012
(3) at ¹78 °C, which suggest much stronger electronic com-
munication between the two ferrocenyl moieties through the
Pn=Pn ³-spacers than those in FcN=NFc (Kcom = 3.5 ©
103)1a,6 and (E)-Fc(Ph)C=C(Ph)Fc (Kcom = 1.1 © 103).4 Nota-
bly, ¦(E1-E2) of diphosphene 1 was found to be the largest
among those of the 1,2-bis(ferrocenyl)dipnictenes. Such unique
electrochemical properties of these 1,2-bis(ferrocenyl)dipnic-
tenes as d-³ electron systems should reflect the intrinsic nature
of Pn=Pn double bonds of ³-spacers. In summary, the P=P
moiety works as an effective ³-spacer, suggesting stabilization
of the corresponding mixed-valence state, the Sb=Sb system
should enhanced its electron-accepting ability, and the Bi=Bi
dibismuthene system exhibits the lowest oxidation potential
reflecting the high energy level of the Bi=Bi ³-orbital.
properties allowed us to recognize they should be unique d-³
electron systems with their considerable Pn=Pn double-bond
characters. On the basis of the electrochemical analysis, it
can be concluded that the P=P moiety in 1,2-bis(ferrocenyl)-
diphosphene 1 works as an effective ³-spacer, stabilizing the
corresponding mixed-valence state, the Sb=Sb moiety in 1,2-
bis(ferrocenyl)distibene 2 should be an electron accepter
reflecting the intrinsic nature of a Sb=Sb bond, and the Bi=Bi
moiety in 1,2-bis(ferrocenyl)dibismuthene 3 exhibits low oxi-
dation potential reflecting the high energy level of the Bi=Bi
³-orbital. Thus, these systematic studies on the 1,2-bis(ferro-
cenyl)dipnictenes with a ³-bond of heavier elements are
expected to open new chemistry in d-³ electron systems.
Experimental
General Procedure. Unless otherwise noted, all experi-
ments were performed under dry argon. Prior to use, all
solvents were purified and dried by standard methods and/or
The Ultimate Solvent System (Glass Contour Co.).27 Prepar-
ative column chromatography was performed on Wakogel C-
200. The 1H (300 MHz), 13C (75 Hz), and 31P (120 MHz) NMR
spectra were measured in C6D6 using a JEOL AL-300 spec-
trometer. Chemical shifts were referenced to residual C6HD5
(¤ = 7.15 ppm for 1H NMR) and C6D6 (¤ = 128.0 ppm for
13C NMR) as internal standards or 85% H3PO4 in water (¤ =
0 ppm for 31P NMR) as an external standard. High-resolution
mass spectrometry data were obtained from a JEOL JMS-700
spectrometer (FAB) or a Bruker microTOF (APPI-TOF). Elec-
tronic spectra were recorded on a SHIMADZU-1700 UV-vis
spectrophotometer. Raman spectra were measured on a Raman
spectrometer consisting of a Spex 1877 Triplemate and an
EG&G PARC 1421 intensified photodiode array detector. An
NEC GLG 108 He/Ne laser (633 nm) was used for Raman
excitation. All melting points were determined on a BÜCHI
Melting Point M-565. All elemental analyses were performed
in the Microanalytical Laboratory of the Institute for Chemical
Research, Kyoto University. Ferrocenyl phenyl sulfoxide was
prepared according to the reported procedure.16 1-Bromo-3,5-
di-tert-butylbenzene was received by from MANAC Incorpo-
rated, the cooperation of which is appreciated.
Preparation of 1-(3,5-Di-t-butylphenyl)-2-(phenylsulfin-
yl)ferrocene (7). A solution of diisopropylamine (8.33 mL,
59.5 mmol) in THF (20 mL) was treated with n-BuLi (36.1 mL,
1.65 M in hexane, 59.5 mmol), and the resulting solution of
lithium diisopropylamide (LDA) was added to a solution of
ferrocenyl phenyl sulfoxide (6) (12.3 g, 39.7 mmol) in THF
(100 mL) at ¹78 °C. After stirring at ¹78 °C for 30 min, the
resulting solution was transferred to a suspension of ZnCl2
(16.2 g, 119 mmol) in THF (100 mL) at ¹78 °C. After stirring
at ¹78 °C for 1 h, the reaction mixture was warmed to room
temperature, where stirring was maintained for 1 h. The result-
ing solution was added to a solution of 1-bromo-3,5-di-t-butyl-
benzene (10.7 g, 39.7 mmol) and [Pd(PPh3)4] (2.30 g, 1.99
mmol) in THF (50 mL). The reaction mixture was heated at
60 °C for 10 h, and then the reaction was quenched with a
saturated aqueous sodium hydrogen carbonate solution. The
reaction mixture was extracted with Et2O, and the combined
organic phases were washed with water and dried over MgSO4.
After filtration, the filtrate was evaporated to remove the
Conclusion
We have synthesized a series of 1,2-bis(ferrocenyl)dipnic-
tenes with a Pn=Pn (Pn = P, Sb, and Bi) ³-spacer by utilizing
the originally developed bulky ferrocenyl group. The system-
atic comparison of their structural parameters and physical

1140 Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) BCSJ AWARD ARTICLE
solvent under reduced pressure. The obtained residue was
purified by column chromatography on silica gel (hexane/ethyl
acetate 1:1) to give 7 (16.8 g, 33.7 mmol, 85%). 7: yellow
was dissolved in THF (100 mL) and cooled to ¹78 °C. To this
solution was added at ¹78 °C a freshly prepared solution of
LDA from diisopropylamine (5.15 mL, 36.7 mmol) and n-BuLi
(22.2 mL, 1.65 M, 36.7 mmol) in THF (50 mL). After stirring
at ¹78 °C for 30 min, the resulting solution was added to a
suspension of ZnCl2 (12.1 g, 89.1 mmol) in THF (100 mL) at
¹78 °C. The reaction mixture was stirred at ¹78 °C for 1 h and
warmed to room temperature, where stirring was continued for
1 h. The resulting solution was added to a solution of 1-bromo-
3,5-di-t-butylbenzene (6.60 g, 24.5 mmol) and [Pd(PPh3)4]
(1.42 g, 1.22 mmol) in THF (50 mL). The resulting solution
was heated at 60 °C for 10 h, before the reaction was quenched
by addition of saturated aqueous sodium hydrogen carbonate.
The reaction mixture was extracted with Et2O and the com-
bined organic phases were washed with water and dried over
MgSO4. After filtration and evaporation of all volatiles under
reduced pressure, the obtained residue was purified by column
chromatography on silica gel (hexane/ethyl acetate 1:1) to give
10 (13.5 g, 19.7 mmol, 80%). 10; orange crystals; mp 84-85 °C;
1H NMR (300 MHz, C6D6): ¤ 1.37 (s, 18H), 1.39 (s, 18H), 4.42
1
crystals; mp 139-140 °C; H NMR (300 MHz, C6D6): ¤ 1.40
3
(s, 18H), 3.97 (pt, JHH = 2.6 Hz, 1H), 4.08 (s, 5H), 4.11 (dd,
3JHH = 2.6 Hz, 4JHH = 1.4 Hz, 1H), 4.45 (dd, 3JHH = 2.6 Hz,
4JHH = 1.4 Hz, 1H), 6.88-6.91 (m, 3H), 7.43 (t, 3JHH = 1.8 Hz,
1H), 7.60-7.63 (m, 2H), 7.92 (d, 3JHH = 1.8 Hz, 2H); 13C NMR
(75 MHz, C6D6): ¤ 31.8 (q), 35.1 (s), 68.8 (d), 71.0 (d), 71.5
(d), 72.5 (d), 91.6 (s), 94.2 (s), 121.2 (d), 125.5 (d), 125.6 (d),
128.3 (d), 130.0 (d), 135.6 (s), 145.4 (s), 150.4 (s); HRMS
(FAB), m/z 498.1676 ([M+]), Calcd for C30H3456FeO32S:
498.1680; Anal. Calcd for C30H34FeOS: C, 72.28; H, 6.87%.
Found: C, 72.47; H, 6.97%.
Preparation of 1-(3,5-Di-t-butylphenyl)-2-(phenylsulfan-
yl)ferrocene (8). To a solution of compound 7 (16.8 g, 33.7
mmol) and NaI (11.1 g, 74.1 mmol) in acetone (100 mL) at
0 °C was added to a solution of trifluoroacetic anhydride (10.3
mL, 74.1 mmol) in acetone (50 mL). After stirring for 30 min
at 0 °C, the reaction mixture was extracted with Et2O. The
combined organic phases were washed with 10% sodium
thiosulfate solution and dried over MgSO4. After filtration, the
filtrate was evaporated under reduced pressure. The obtained
residue was purified by column chromatography on silica gel
(hexane/ethyl acetate 1:1) to give 8 (14.6 g, 30.3 mmol, 90%).
8: yellow crystals; mp 151-152 °C; 1H NMR (300 MHz, C6D6):
¤ 1.28 (s, 18H), 4.06 (s, 5H), 4.12 (pt, 3JHH = 2.6 Hz, 1H), 4.45
3
3
(s, 5H), 4.52 (d, JHH = 2.5 Hz, 1H), 4.65 (d, JHH = 2.5 Hz,
1H), 6.61-6.62 (m, 3H), 7.20-7.22 (m, 2H), 7.27 (s, 1H), 7.54
4
4
(s, 1H), 7.70 (d, JHH = 1.5 Hz, 2H), 7.92 (d, JHH = 1.5 Hz,
2H); 13C NMR (75 MHz, C6D6): ¤ 31.7 (q), 31.8 (q), 34.9 (s),
35.1 (s), 69.5 (d), 70.5 (d), 73.3 (d), 92.3 (s), 94.9 (s), 95.1 (s),
121.1 (d), 121.6 (d), 124.9 (d), 125.7 (d), 126.5 (d), 127.6 (d),
128.6 (d), 135.7 (s), 136.0 (s), 145.8 (s), 149.3 (s), 150.7 (s);
HRMS (FAB), m/z 686.3268 ([M+]), Calcd for C44H54-
56FeO32S: 686.3246; Anal. Calcd for C44H54FeOS: C, 76.95;
H, 7.92%. Found: C, 77.12; H, 8.05%.
3
4
3
(dd, JHH = 2.6 Hz, JHH = 1.4 Hz, 1H), 4.58 (dd, JHH = 2.6
Hz, 4JHH = 1.4 Hz, 1H), 6.78-6.83 (m, 1H), 6.92-6.97 (m, 2H),
7.18-7.21 (m, 2H), 7.42 (t, 3JHH = 1.8 Hz, 1H), 7.71 (d, 3JHH
=
1.8 Hz, 2H); 13C NMR (75 MHz, C6D6): ¤ 31.7 (q), 34.9 (s),
69.4 (d), 71.5 (d), 72.2 (d), 73.6 (d), 77.2 (s), 82.6 (s), 120.7
(d), 124.1 (d), 124.7 (d), 125.6 (d), 129.1 (d), 136.7 (s), 142.2
(s), 150.3 (s); HRMS (FAB), m/z 482.1729 ([M+]), Calcd
for C30H3456Fe32S: 482.1731; Anal. Calcd for C30H34FeS: C,
74.68; H, 7.10%. Found: C, 74.86; H, 7.22%.
Preparation of 1,3-Bis(3,5-di-t-butylphenyl)-2-iodoferro-
cene (5). A solution of compound 10 (13.5 g, 19.7 mmol) in
Et2O (100 mL) was treated with t-BuLi in pentane (27.0 mL,
1.61 M, 43.3 mmol) at ¹78 °C. After stirring for 5 min, iodine
(12.4 g, 98.5 mmol) was added to the reaction mixture, and the
reaction mixture was allowed to warm to room temperature.
After stirring for 3 h, the reaction mixture was extracted with
Et2O. The combined organic phases were washed with 10%
sodium thiosulfate solution and dried over MgSO4. After
filtration and evaporation of all volatiles under reduced pres-
sure, the obtained residue was purified by column chromatog-
raphy on silica gel (hexane/ethyl acetate 1:1). The obtained
solid was precipitated from Et2O to afford iodide 5 (9.31 g,
13.5 mmol, 68%). 5: yellow crystals; mp 218-219 °C; 1H NMR
(300 MHz, C6D6): ¤ 1.41 (s, 36H), 4.05 (s, 5H), 4.63 (s, 2H),
7.54 (s, 2H), 7.89 (s, 4H); 13C NMR (75 MHz, C6D6): ¤ 31.5
(q), 34.9 (s), 49.4 (s), 69.0 (d), 74.0 (d), 92.1 (s), 120.9 (d),
125.3 (d), 137.0 (s), 149.9 (s); HRMS (FAB), m/z 688.2240
([M+]), Calcd for C38H4956FeI: 688.2229; Anal. Calcd for
C38H49FeI: C, 66.29; H, 7.17%. Found: C, 66.19; H, 7.17%.
Preparation of [1,3-Bis(3,5-di-t-butylphenyl)ferrocen-2-
yl]dichlorophosphine (11). Iodoferrocene 5 (211 mg, 0.306
mmol) was dissolved in Et2O (10.0 mL) and cooled to ¹78 °C,
and then t-BuLi (0.42 mL, 1.61 M in pentane, 0.67 mmol) was
added dropwise to the solution. After stirring for 1 h, the
reaction mixture was warmed to room temperature for 30 min
and then cooled down to ¹78 °C again. The resulting solution
was added to a solution of PCl3 (54 ¯L, 0.620 mmol) in Et2O
(2.0 mL) at ¹78 °C. After stirring for 1 h, the reaction mixture
Preparation of 1-(3,5-Di-t-butylphenyl)-2-(phenylsulfin-
yl)ferrocene (9). A solution of compound 8 (14.6 g, 30.3
mmol) in CH2Cl2 (100 mL) was cooled to 0 °C, and a solution
of m-CPBA (6.27 g, 36.4 mmol) in CH2Cl2 (150 mL) was
added dropwise. The reaction mixture was stirred at 0 °C for
5 h before being extracted with CH2Cl2. The combined organic
phases were consecutively washed with NaOH(aq) and water.
After drying over MgSO4, filtration and evaporation of the sol-
vent under reduced pressure, the resulting residue was purified
by column chromatography on silica gel (hexane/ethyl acetate
1:1) to give 9 (12.2 g, 24.5 mmol, 81%). 9: yellow crystals; mp
1
49-50 °C; H NMR (300 MHz, C6D6): ¤ 1.33 (s, 18H), 4.06
3
3
(pt, JHH = 2.6 Hz, 1H), 4.31 (s, 5H), 4.43 (dd, JHH = 2.6 Hz,
4JHH = 1.4 Hz, 1H), 4.75 (dd, 3JHH = 2.6 Hz, 4JHH = 1.4 Hz,
1H), 6.62-6.90 (m, 3H), 7.47-7.52 (m, 3H), 7.74 (d, JHH
3
=
1.8 Hz, 2H); 13C NMR (75 MHz, C6D6): ¤ 31.7 (q), 35.0 (s),
65.9 (d), 68.9 (d), 70.4 (d), 71.8 (d), 90.5 (s), 96.0 (s), 121.3
(d), 124.5 (d), 124.7 (d), 128.9 (d), 130.1 (d), 136.3 (s), 148.5
(s), 151.1 (s); HRMS (FAB), m/z 498.1677 ([M+]), Calcd
for C30H3456FeO32S: 498.1680; Anal. Calcd for C30H34FeOS:
C, 72.28; H, 6.87%. Found: C, 72.26; H, 6.93%.
Preparation of 1,3-Bis(3,5-di-t-butylphenyl)-2-(phenyl-
sulfinyl)ferrocene (10). Compound 9 (12.2 g, 24.5 mmol)

M. Sakagami et al.
Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) 1141
was warmed to room temperature and stirred for 1 h. The
solvent was removed under reduced pressure and the residue
was extracted with hexane (50 mL). All insoluble inorganic
salts were removed by filtration through a pad of Celite. After
removal of the solvent from the filtrate, the residue was recrys-
tallized from Et2O/hexane to afford dichloro(ferrocenyl)phos-
phine 11 (148 mg, 0.223 ¯mol, 73%). 11: orange crystals; mp
Anal. Calcd for C38H49BiBr2Fe: C, 49.05; H, 5.31%. Found:
C, 48.81; H, 5.29%.
Preparation of 1,2-Bis[1,3-bis(3,5-di-t-butylphenyl)ferro-
cen-2-yl]diphosphene (1). To a THF solution (2.0 mL) of
dichloro(ferrocenyl)phosphine 11 (82.7 mg, 0.125 ¯mol) was
added magnesium metal (15.1 mg, 0.617 mmol) at room tem-
perature. After the reaction mixture was stirred for 30 min, the
color of the solution changed to red. The solvent was evaporated
under reduced pressure and 20 mL of hexane was added to the
residue. Insoluble inorganic salts and the residual magnesium
metal were removed by filtration through Celite. After removal
of the solvent from the filtrate, the residue was recrystallized
from Et2O/hexane to afford diphosphene 1 (46.1 mg, 38.8
1
193 °C (decomp); H NMR (300 MHz, C6D6): ¤ 1.42 (s, 36H),
4.16 (s, 5H), 4.63 (s, 2H), 7.53 (s, 2H), 7.83 (s, 4H); 13C NMR
(75 MHz, C6D6): ¤ 31.8 (q), 35.2 (s), 75.4 (d), 74.2 (d), 75.5 (s),
97.6 (s), 122 (d), 125 (d), 136 (s), 151 (s); 31P NMR (120
MHz, C6D6): ¤ 156 (s); HRMS (FAB), m/z Found: 662.2286
([M+]), Calcd for C38H4935Cl37Cl54FeP: 662.2300; Anal. Calcd
for C38H49Cl2FeP: C, 68.79; H, 7.44%. Found: C, 68.75; H,
7.58%.
1
¯mol, 62%). 1: red crystals; mp 178 °C (decomp); H NMR
(300 MHz, C6D6): ¤ 1.35 (s, 72H), 4.04 (s, 10H), 4.72 (s, 4H),
7.40 (s, 4H), 7.75 (s, 8H); 13C NMR (75 MHz, C6D6): ¤ 31.9
(q), 35.0 (s), 65.9 (s), 73.0 (d), 73.4 (d), 95.7 (s), 121 (d), 127
(d), 138 (s), 150 (s); 31P NMR (120 MHz, C6D6): ¤ 471 (s);
HRMS (FAB), m/z Found: 1184.5853 ([M+]), Calcd for
C76H9856Fe2P2: 1184.5848; Anal. Calcd for C76H98Fe2P2: C,
77.02; H, 8.33%. Found: C, 76.87; H, 8.53%.
Preparation of [1,3-Bis(3,5-di-t-butylphenyl)ferrocen-2-
yl]dichlorostibine (12).
Iodoferrocene 5 (164 mg, 0.238
mmol) was dissolved in Et2O (5.0 mL) and cooled to ¹78 °C,
and then t-BuLi (0.33 mL, 1.61 M in pentane, 0.52 mmol) was
added dropwise to the solution. After stirring for 1 h, the
reaction mixture was warmed to room temperature for 30 min
and then cooled to ¹78 °C again. The resulting solution was
added to a solution of SbCl3 (138 mg, 0.606 mmol) in Et2O
(2.0 mL) at ¹78 °C. After 1 h, the reaction mixture was warmed
up to room temperature and stirred for 12 h. The solvent was
removed under reduced pressure and the residue was extracted
with hexane (50 mL), while all insoluble inorganic salts were
removed by filtration through a pad of Celite. After removal of
the solvent from the filtrate, the residue was recrystallized from
Et2O/hexane to afford dichloroferrocenylstibine 12 (59.3 mg,
78.6 ¯mol, 33%). 12: orange crystals; mp 170 (decomp) °C;
1H NMR (300 MHz, C6D6): ¤ 1.41 (s, 36H), 4.14 (s, 5H), 4.70
(s, 2H), 7.51 (t, 4JHH = 3.0 Hz, 2H), 7.70 (d, 4JHH = 3.0
Hz, 4H); 13C NMR (75 MHz, C6D6): ¤ 31.8 (q), 35.2 (s), 71.2
(s), 72.4 (d), 75.5 (d), 98.9 (s), 122.9 (d), 124.7 (d), 136.3
(s), 151.3 (s); HRMS (FAB), m/z 754.1604 ([M+]), Calcd for
C38H4937Cl254Fe121Sb: 754.1593; Anal. Calcd for C38H49Cl2-
FeSb: C, 60.51; H, 6.55%. Found: C, 60.36; H, 6.55%.
Preparation of 1,2-Bis[1,3-bis(3,5-di-t-butylphenyl)ferro-
cen-2-yl]distibene (2).
To a THF solution (2.0 mL) of
dichlorostibine 12 (35.4 mg, 46.9 ¯mol) was added magnesium
metal (5.70 mg, 0.235 mmol) at room temperature. After the
reaction mixture was stirred for 30 min, the color of the solu-
tion changed to deep green. The solvent was evaporated under
reduced pressure and 20 mL of hexane was added to the
residue. Insoluble inorganic salts and the residual magnesium
metal were removed by filtration through Celite. After the
removal of the solvent from the filtrate, the residue was
recrystallized from Et2O/hexane to give green crystals of
distibene 2 (14.1 mg, 10.3 ¯mol, 44%). 2: green crystals, mp
1
231-232 °C. H NMR (300 MHz, C6D6): ¤ 1.33 (s, 72H), 4.17
(s, 10H), 4.76 (s, 4H), 7.41 (s, 4H), 7.69 (s, 8H). 13C NMR
(125 MHz, C6D6): ¤ 32.0 (q), 35.1 (s), 71.9 (s), 72.4 (d), 73.9
(d), 99.1 (s), 121.3 (d), 126.8 (d), 139.0 (s), 150.1 (s). HRMS
(FAB), m/z 1366.4440 ([M]+), Calcd for C76H9856Fe2121Sb2:
1366.4465; Anal. Calcd for C76H98Fe2Sb2: C, 66.78; H, 7.23%.
Found: C, 67.20; H, 7.35%.
Preparation of Dibromo[1,3-bis(3,5-di-t-butylphenyl)-
ferrocen-2-yl]bismuthine (13).
Iodoferrocene 5 (171 mg,
0.248 mmol) was dissolved in THF (5.0 mL) and cooled to
¹78 °C, and then t-BuLi (0.34 mL, 1.61 M, 0.55 mmol) was
added dropwise to the solution. The reaction mixture was stirred
at room temperature for 30 min and then cooled to ¹78 °C.
The resulting solution was added to a solution of BiBr3 (278
mg, 0.620 mmol) in THF (2.0 mL) at ¹78 °C. After stirring for
1 h, the reaction mixture was warmed up to room temperature
and stirred for 12 h. The solvent was removed under reduced
pressure and extracted with hexane (50 mL). All insoluble
inorganic salts were removed by filtration through a pad of
Celite. After removal of the solvent from the filtrate, the residue
was recrystallized from Et2O/hexane to afford dibromoferro-
cenylbismuthine 13 (92.3 mg, 99.2 ¯mol, 40%). 13: purple
crystals; mp 180 °C (decomp); 1H NMR (300 MHz, C6D6):
Preparation of 1,2-Bis[1,3-bis(3,5-di-t-butylphenyl)ferro-
cen-2-yl]dibismuthene (3). To a THF solution (2.0 mL) of
dibromobismuthine 13 (52.3 mg, 56.2 ¯mol) was added mag-
nesium metal (6.83 mg, 0.281 mmol) at room temperature.
After the reaction mixture was stirred for 15 min, the color of
the solution changed to deep purple. The solvent was evapo-
rated under reduced pressure and 20 mL of hexane was added
to the residue. Insoluble inorganic salts and the residual
magnesium metal were removed by filtration through Celite.
After removal of the solvent from the filtrate, the residue was
recrystallized from Et2O/hexane to afford dibismuthene 3
(22.5 mg, 14.6 ¯mol, 52%), 3: violet crystals; mp 121 °C
(decomp); 1H NMR (300 MHz, C6D6): ¤ 1.37 (s, 72H), 4.13 (s,
10H), 4.81 (s, 4H), 7.44 (t, 4JHH = 3.0 Hz, 4H), 7.76 (d, 4JHH
=
4
¤ 1.44 (s, 36H), 4.20 (s, 5H), 4.76 (s, 2H), 7.54 (t, JHH = 3.0
3.0 Hz, 8H); 13C NMR (75 MHz, C6D6): ¤ 32.3 (q), 35.0 (s),
65.9 (s), 72.8 (d), 74.1 (d), 103.7 (s), 121.2 (d), 127.0 (d), 140.5
(s), 150.2 (s); HRMS (FAB), m/z 1540.5957 ([M+]), Calcd
for C76H98Bi256Fe2: 1540.5980; Anal. Calcd for C76H98Bi2Fe2:
C, 59.23; H, 6.41%. Found: C, 59.35; H, 6.64%.
Hz, 2H), 7.71 (d, 4JHH = 3.0 Hz, 4H); 13C NMR (75 MHz,
C6D6): ¤ 31.9 (q), 35.3 (s), 65.9 (s), 68.6 (d), 72.1 (d), 77.7 (s),
122.1 (d), 124.4 (d), 136.5 (s), 151.5 (s); HRMS (FAB), m/z
930.1342 ([M+]), Calcd for C38H49Bi81Br256Fe: 930.1339;

1142 Bull. Chem. Soc. Jpn. Vol. 86, No. 10 (2013) BCSJ AWARD ARTICLE
Theoretical Calculations. All calculations were conducted
with the Gaussian 09 series28 of electronic structure programs.
Geometries were optimized using density functional theory at
Pt electrodes
flange
glass
screw
cap
the B3PW91 level, with the basis sets of 6-31G(d) (C, H),
TZ(2d) (P, Sb, Bi) and Lanl2DZ (Fe), and the TDDFT calcu-
lations were performed at the same level of theory and basis
sets. Frequency (Raman) calculations confirmed the optimized
structures to have minimum energies at the same level. Com-
putational time was generously provided by the Supercomputer
Laboratory at the Institute for Chemical Research of Kyoto
University.
joint
10φ
10φ
10φ
J-Young
J-Young
X-ray Crystallographic Analysis of 1, 2, and 3. The
intensity data for compound 2 were collected at BL40XU in
Spring-8 (JASRI, 2011B1545) on a Rigaku Saturn 724 CCD
system with synchrotron radiation (- = 0.83077 ¡), and those
for compound 1, 3, and 5 were collected on a RIGAKU
Saturn70 CCD(system) with VariMax Mo Optic using Mo K¡
radiation (- = 0.71070 ¡). Single crystals suitable for X-ray
analysis were obtained by slow recrystallization from Et2O or
hexane at ¹40 °C. A single crystal was mounted on a glass
fiber. The structures were solved by direct methods (SHELXS-
97)29 and refined by full-matrix least-squares procedures on F2
for all reflections (SHELXL-97).29 All hydrogen atoms were
placed using AFIX instructions, while all other atoms were
refined anisotropically. Crystal data for 1-3 were summarized
in Table 2. Crystal data for 5: Formula C38H49FeI, Mw =
688.52; T = ¹170 °C; monoclinic; space group C2 (#5); a =
32.689(2) ¡, b = 9.6693(9) ¡, c = 10.7948(10) ¡; Z = 4; V =
25 mm
50 mm
sample solution
degassed and sealed
12φ
Figure 7. Custom-tailored glassware for electrochemical
measurements for reactive species.
Areas, “Stimuli-responsive Chemical Species for the Creation
of Functional Molecules” [#2408] (No. 24109013), and MEXT
Project of Integrated Research on Chemical Synthesis from
Ministry of Education, Culture, Sports, Science and Technol-
ogy (MEXT), Japan. We would like to thank Mr. Toshiaki
Noda and Ms. Hideko Natsume in Nagoya Univ. for their kind
manufacturing of custom-tailored glassware. We appreciate the
kind gift of 1-bromo-3,5-di-tert-butylbenzene from MANAC
Incorporated. The X-ray diffraction data of 2 was collected
at the BL40XU in Spring-8 (JASRI, 2011B1545). We thank
Dr. Nobuhiro Yasuda (Spring-8/JASRI) and Dr. Daisuke
Hashizume (RIKEN) for their kind assistance in measuring
X-ray diffraction for compound 2.
3409.1(5) ¡3; ® = 1.371 mm¹1; Dcalcd = 1.341 g cm¹3; ªmax
=
25.5°; 13199 measured reflections, 5932 independent reflec-
tions [Rint = 0.0911], 373 refined parameters; GOF = 1.028;
R1 (I > 2·(I)) = 0.0782; wR2 (all data) = 0.1965; largest diff.
peak and hole 3.400 (around I atom) and ¹0.783 e ¡¹3. Cif
files containing all crystallographic data for 1, 2, 3, and 5 have
been deposited at the Cambridge Crystallographic Data Centre
(CCDC-941816 for 1, CCDC-912009 for 2, CCDC-912010 for
3, and CCDC-942572 for 5). The data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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