Reactions of 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobu tene

Article abstract of DOI:10.1016/j.jorganchem.2006.08.042

Reactions of a sterically protected 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobu tene were investigated. The diphosphinidenecyclobutene reacted with elemental sulfur or transition metal reagents to form a thiaphosphirane derivative or the corresponding transition metal complexes, respectively. Reactions of the di(2-thienyl)diphosphinidenecyclobutene with butyllithium followed by treatment with electrophiles afforded functionalized di(2-thienyl)diphosphinidenecyclobutene derivatives.

Full text of DOI:10.1016/j.jorganchem.2006.08.042

Journal of Organometallic Chemistry 692 (2007) 70–78
www.elsevier.com/locate/jorganchem
Reactions of 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)-
phosphinidene]cyclobutene
,1
*
*
Akitake Nakamura, Subaru Kawasaki, Kozo Toyota , Masaaki Yoshifuji
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
Received 27 February 2006; received in revised form 21 April 2006; accepted 24 April 2006
Available online 30 August 2006
Abstract
Reactions of a sterically protected 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene were investigated.
The diphosphinidenecyclobutene reacted with elemental sulfur or transition metal reagents to form a thiaphosphirane derivative or
the corresponding transition metal complexes, respectively. Reactions of the di(2-thienyl)diphosphinidenecyclobutene with butyllithium
followed by treatment with electrophiles afforded functionalized di(2-thienyl)diphosphinidenecyclobutene derivatives.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Phosphaalkenes; Bidentate ligand; Steric and strain effects
1. Introduction
1A: The straightforward introduction of substituents to
the phenyl rings of (E,E)-1A seems to be difficult, because
phosphorus–carbon p-bonds are relatively reactive. Indeed,
reaction of (E,E)-1A with bromine (1.5 molar amount) in
trimethyl phosphate at room temperature for 30 min led
to the formation of a complex mixture of products contain-
ing (E,Z)-1A [1g] (Chart 2).
On the other hand, compound (E,E)-5a is a promising
building block for construction of more elaborate DPCB
derivatives, because introduction of a functional group
(at the position a to the sulfur atom) is expected to be easy
under mild conditions. Actually, we have prepared (E,E)-
5b and (E,E,E,E)-6 starting from (E,E)-5a [1j]. However,
introduction of synthetically more useful functional groups
is desired from viewpoint of materials science, in order to
construct more sophisticated DPCB derivatives. We report
here the reactions and functionalizations of (E,E)-5a.
Sterically protected 3,4-diphosphinidenecyclobutenes
(hereafter abbreviated to DPCB, Chart 1) [1], bearing an
extremely bulky 2,4,6-tri-t-butylphenyl group (abbreviated
to the Mes group) [2], are unique ligands of interest [3,4],
*
because of their relatively rigid framework containing the
phosphorus–carbon p-bonds [5], as well as their dynamic
behavior such as photo- or iodine-induced E/Z-isomeriza-
tions [1g]. We have prepared various transition metal com-
plexes of DPCB [3] and some of them were used as
homogeneous catalysts [4]. DPCB derivatives 1A–E
[1a,4b,4c,4d] and 2–4 [1c,1d,1e], containing aromatic sub-
stituents at the 1,2-positions, have been reported and we
have recently described preparation of a 1,2-dithienyl
derivative (E,E)-5a [1j].
The compounds (E,E)-1B-E were prepared from the cor-
responding phenylacetylene derivatives and not from
straightforward substitution of the phenyl rings of (E,E)-
2. Results and discussion
*
Corresponding authors. Tel.: +81 22 795 6559; fax: +81 22 795 6562
2.1. Preparation of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene
(K. Toyota), Tel.: +1 205 348 0455; fax: +1 205 348 4704 (M. Yoshifuji).
E-mail addresses: toyota@mail.tains.tohoku.ac.jp (K. Toyota), yoshi-
fuj@mail.tains.tohoku.ac.jp (M. Yoshifuji).
1
First, we prepared (thienylethynyl)phosphine 8 (Scheme 1)
Present address: Department of Chemistry, The University of Ala-
bama, Tuscaloosa, AL 35487-0336, USA.
by the Corey–Fuchs reaction [6] but not by the reported
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.08.042

A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
71
R2
[1j]. Compared with the previous method, the present
method has an advantage: isolation of volatile thienylacet-
ylene is not necessary. The compound obtained here was
subjected to the following reactions (Sections 2.2.1, 2.2.2
and 2.3).
Mes*=2,4,6-t-Bu3C6H2
R1
Mes*
P
(E,E)-1A: R1=R2=H
R2
R2
(E,E)-1B: R1=OMe, R2=H
(E,E)-1C: R1=OOct, R2=H
(E,E)-1D: R1=CF3, R2=H
(E,E)-1E: R1=H, R2=CF3
P
Mes*
R1
2.2. Reactions of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene at the phosphorus atom(s)
R2
2.2.1. Reaction of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene with sulfur
Phosphorus–carbon double bonds are known to react
with elemental sulfur at the phosphorus atoms [9] to give
thiaphosphirane P-sulfides via phosphaethene P-sulfide
Mes*
P
Mes*
P
N
N
P
Mes*
P
Mes*
intermediates. We have studied sulfurization of the Mes -
*
(E,E)-3
(E,E )-2
substituted phosphaethenes Mes P = CR in detail and
*
2
we found a photo-induced isomerization of phosphaethene
P-sulfide as shown in Scheme 2 [10]. A similar sulfurization
reaction of 1-phosphaallene giving methylenethiaphosphi-
rane P-sulfide has also been reported by us (Scheme 2)
[11]. Here we have applied the sulfurization reaction to
(E,E)-5a as follows.
Mes*
P
R1
R2
)-4: Ch=O, R1=R2=H
)-5a: Ch=S, R1=R2=H
)-5b: Ch=S, R1=R2=Me
Ch
Ch
(
E
,
,
,
E
E
E
(E
P
Mes*
(E
Chart 1.
An attempted reaction of (E,E)-5a with elemental sulfur
at room temperature for 3 h resulted in the recovery of
(E,E)-5a. However, in the presence of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU), (E,E)-5a reacted with an
excess amount of sulfur at room temperature for 10 days
to give 11a in 54% yield (Scheme 3). In order to prevent
the photo-induced isomerization however, the reaction
was performed in the dark. 31P NMR spectrum of 11a
showed an AB pattern [dP (C6D6) ꢀ12.4 (d, 3JPP = 4.1 Hz)
Mes*
P
Mes*
P
Ph
Ph
)-1A
S
S
Mes*
Mes*
P
P
(E
,
Z
(E,Z )-5a
3
and 115.7 (d, JPP = 4.1 Hz)], which indicated the unsym-
metrical structure of 11a. 31P NMR monitoring of the reac-
tion mixture suggested a reaction pathway via 9a and 10a
as shown in Scheme 3. Although the compounds 9a and
10a were not isolated in the pure form, signals assignable
to these intermediates were observed during the reaction
Mes*
P
S
S
Mes*
P
P
Mes*
S
S
3
P
Mes*
[9a: dP (C6D6) 107.4 (d, JPP = 5.0 Hz) and 200.5 (d,
3JPP = 5.0 Hz); 10a: dP (C6D6) ꢀ8.8 and 197.9]. The steric
hindrance seems to affect the reaction pathway. For exam-
ple, signals due to bis(mono-sulfurized) derivative 12a
(Chart 3) or tetra-sulfurized derivative 13a were not
(E,E,E,E)-6
Chart 2.
1)
n
-BuLi
Mes*
Ph
Ph
Mes*
S
Ph
Ph
Mes*
S
Ph
Ph
CH=CBr2
1/8 S8
1/8 S8
S
P
P
P
P
2) Mes*P(H)Cl
7
cat. DBU
cat. DBU
S
hν
1)
n
-BuLi
2) BrCH2CH2Br
Scheme 1.
(E,E)-5a
Mes*P(H)
Mes*
Ph
Ph
S
8
S
Ph
Ph
Mes*
Mes*
Mes*
method [1j]: 2-(20,20-dibromovinyl)thiophene 7 [7] was pre-
pared from thiophene via thiophene-2-carboxaldehyde.
One pot reaction of 7 using butyllithium and chloro(2,4,6-
tri-t-butylphenyl)phosphine [8] afforded 8. The phosphine
8 was then converted to (E,E)-5a by a reported method
Ph
Ph
Ph
Ph
1/8 S8
1/8 S8
P
P
P
S
S
S
cat. DBU
cat. DBU
DBU = 1,8-diazabicyclo[5.4.0] undec-7-ene
Scheme 2.

72
A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
Mes*
P
Mes*
P
Mes*
P
R
R
R
R
1/8 S8
1/8 S8
M(CO)4
S
S
(OC)4M
S
cat. DBU
cat. DBU
P
Mes*
P
Mes*
P
Mes*
Mes*
P
5aCr: M = Cr
5aMo: M = Mo
5aW: M = W
(E,E)-5a
9a
S
S
P
Mes*
P
Mes*
P
Mes*
R
R
R
1/8 S8
S
S
(E,E)-5a
Mes*
P
S
cat. DBU
P
R
P
S
Mes*
S
S
S
Cl2M
Mes*
Cl2M(RCN)2
P
10a
11a
R = 2-thienyl
Mes*
M=Pd, R=Me
or M=Pt, R=Ph
5aPd: M = Pd
5aPt: M = Pt
Scheme 3.
Mes*
P
Mes*
Mes*
P
S
P
S
S
S
S
S
S
S
S
P
Cr(CO)4
hν
S
S
5aCr
P
Mes*
Mes*
S
P
Mes*
12a
13a
(E,Z)-5a
Chart 3.
Scheme 4.
observed at least as major signals during the 31P NMR
monitoring, even when more or less equivalents of sulfur
were used. Unfortunately, an attempted X-ray crystallo-
graphic analysis of 11a failed due to the lack of single crys-
tal suitable for a diffraction experiment.
Photo-induced isomerization and complex formation of
(E,Z)-5a [12a] were confirmed as follows. The 31P NMR
spectroscopic monitoring of a reaction mixture of (E,Z)-
5a with (bicyclo[2.2.1]hepta-2,5-diene)tetracarbonylchro-
mium(0) in THF-d8 did not show significant change in
the dark at room temperature after 4 h, however, irradia-
tion of the solution with a Xe lamp (300 W) for 24 h led
to the formation of 5aCr. A similar dynamic behavior of
DPCB derivatives has been shown in a previous report [1g].
2.2.2. Reactions of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene with some transition metal
reagents
Next, we studied transition metal complex formation of
5a as follows (Scheme 4). Reaction of (E,E)-5a with
[group(6) transition metal][(bicyclo[2.2.1]hepta-2,5-diene)-
tetracarbonyl] complexes gave the corresponding tetracar-
bonylmetal complexes 5aCr (quant.), 5aMo (quant.), and
5aW (37% yield). When (E,E)-5a was treated with
(MeCN)2PdCl2 at room temperature in THF, complex
5aPd was formed in 75% yield. Reaction of (E,E)-5a with
(PhCN)2PtCl2 under similar conditions resulted in the
recovery of (E,E)-5a. However, when the reaction was car-
ried out at 50 °C for 2 days, complex 5aPt was obtained in
19% yield.
It should be noted that an attempted reaction of (E,E)-
5a with nickel complexes such as NiBr2(dme) has been
unsuccessful (recovery of (E,E)-5a, after 15 h-stirring in
THF-d8 at room temperature followed by an additional
3 h-stirring at 60 °C), probably because coordinating abil-
ity of lone pair of sp2 hybridized phosphorus atom is weak
compared to that of sp3 hybridized phosphorus atom, due
to less p-character of the lone pair.
2.2.3. UV–Vis spectra and cyclic voltammograms of 1,2-
di(2-thienyl)-3,4-diphosphinidenecyclobutene complexes
Fig. 1 shows UV–Vis spectra of compound (E,E)-5a and
its complexes 5aCr,Mo,W,Pd,Pt, while Fig. 2 shows UV–
Vis spectra of compound (E,E)-1A and its complexes
1ACr,Mo,W,Pd,Pt. Compared to the free ligand 5a, bath-
ochromic shifts of 5aPd and 5aPt were observed and wave-
lengths of the absorption bands for 5aPt (ca. 390 and ca.
500 nm) were longer than the corresponding wavelengths
of the bands of 5aPd. A similar tendency was observed in
the case of the complexes 1APd and 1APt. The group(6)
metal complexes of 5a and 1A showed large bathochromic
shifts, compared to the free ligands. As for the MLCT
band at ca. 450 nm, the order of red shift is Cr > Mo ꢁ W
for both 5a-series and 1A-series. This tendency was also
shown in the cases of other DPCB derivatives such as
1,2-trimethylsilyl substituted DPCB [3a], probably because
essentially the same molecular and atomic orbitals are con-
cerned. When we compare the spectra of complexes of 5a

A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
73
Table 1
CV data for 5a and its complexesa
Compound
Eo1x
Eo2x
Er1ed
Er2ed
(E,E)-5a
5aCr
5aMo
5aW
5aPd
5aPt
a
Ep 0.88
E1/2 0.44
E1/2 0.54
E1/2 0.51
Ep 1.22
Ep 1.17
Ep 0.91
Ep 0.88
E1/2 ꢀ1.69
E1/2 ꢀ1.67
Ep ꢀ0.97
Ep ꢀ1.31
Ep ꢀ1.78
Ep ꢀ1.47
Conditions: 1 mM in CH2Cl2 with 0.1 M n-Bu4NClO4 as a support
electrolyte. Working electrode: glassy carbon; counter electrode: Pt wire;
reference electrode: Ag/0.01 M AgNO3 in acetonitrile with 0.1 M n-
Bu4NClO4 [E1/2 (Fc/Fc+) = 0.23 V]; scan rate: 100 mV/s.
oxidation of the metal(0) center, while the second oxidation
(probably due to the phosphorus center) turned out to be
irreversible. The complexes 5aMo and 5aW showed revers-
ible first reduction waves. The reversible redox properties
found here will lead to further investigation of complexes
of the related DPCB ligands, as well as those of DPCB
oligomers and polymers [1h,12].
Fig. 1. UV–Vis spectra for 5a and its complexes in CH2Cl2.
2.3. Reactions of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene on the thiophene ring(s)
2.3.1. Reactions of 1,2-di(2-thienyl)-3,4-
diphosphinidenecyclobutene with some halogenating reagents
We then examined several reactions of 5a on the thio-
phene rings. Iodination of thiophenes by N-iodosuccini-
mide (NIS) at the 2-position is an established method in
the chemistry of thiophenes and oligothiophenes [14].
Thus, we first attempted iodination of (E,E)-5a with NIS.
When a mixture of (E,E)-5a and NIS in chloroform was
stirred in the dark at room temperature for 3 h, (E,Z)-5a
was formed nearly quantitatively, probably because iodine
(formed from NIS) caused the isomerization [1g] of (E,E)-
5a. A similar result was obtained in the reaction of (E,E)-5a
with NIS in the presence of acetic acid (normal conditions
for iodination of thiophenes). In these reactions, iodona-
tion of the thiophene rings of (E,E)-5a did not occur. These
facts suggest that functionalization of the thienyl-DPCB is
more difficult than that of normal thiophene compounds.
In order to keep the (E,E)-geometry of DPCB, introduc-
tion of functional groups should be carried out in the
absence of bromine or iodine molecules (it should be noted
that addition of acetic acid to DPCB did not cause notice-
able E,Z-isomerization at room temperature in 1 d).
Fig. 2. UV–Vis spectra for 1A and its complexes in CH2Cl2.
with those of the corresponding complexes of 1A, com-
plexes of 5a show red shifts, as shown in the cases of the
free ligands. Probably, the coplanarity of the cyclobutene
ring with the 1,2-thiophene rings is better than that of
the cyclobutene ring with the 1,2-phenyl rings.
Redox activity of assembled- or functionalized metal
complexes attracts current interest [13] and reversible redox
steps play an important role in the studies of these mate-
rial-oriented complexes. Redox properties of the complexes
of 5a will give fundamental information about the behavior
of the DPCB-transition metal complexes. Table 1 shows
oxidation potentials of 5a and its complexes. Although
the first oxidation wave of the free ligand 5a was irrevers-
ible, the group(6) metal carbonyl complexes 5aCr,Mo,W
showed reversible first oxidation waves, probably due to
2.3.2. Lithiation and functionalization of 1,2-di(2-thienyl)-
3,4-diphosphinidenecyclobutene
We then investigated introduction of functional groups
via lithiation of the thiophene moiety of 5a. An attempted
introduction of iodine by successive treatment of (E,E)-5a
with butyllithium (2 equiv.) and ICl (2 equiv.) resulted in
the formation of a complex mixture of products including
(E,Z)-5a and some decomposed product. Lithiation of
(E,E)-5a with butyllithium (1 equiv.), followed by reaction
with DMF (1 equiv.), successfully afforded the corresponding

74
A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
4. Experimental
Mes*
P
Mes*
P
1) n-BuLi
2) DMF
S
S
S
S
4.1. General
P
P
CHO
Melting points were measured on a Yanagimoto MP-J3
micro-melting points apparatus and were uncorrected. H
Mes*
Mes*
1
(E,E)-5a
(E,E)-5d
and 13C NMR spectra were recorded on a Bruker
Avance-400 or a Bruker AM-600 spectrometer with TMS
as the internal standard. 31P NMR spectra were collected
on a Bruker Avance-400 spectrometer using 85% H3PO4
as an external standard. UV–Vis spectra were measured
on a Hitachi U-3210 spectrometer. IR spectra were
obtained on a Horiba FT-300 spectrometer. FT-ICR-MS
spectra were measured on a Bruker APEX III spectrome-
ter. Cyclic voltammograms were recorded on a BAS-CV-
50W voltammetric analyzer under nitrogen. Reactions
were performed under an argon atmosphere, while work-
up was carried out in air, unless otherwise specified. Com-
plexes 1ACr, 1AMo, 1AW, and 1APd were prepared
according to the literature [3d,4a] and their UV–Vis spectra
were measured at room temperature in air.
1) n-BuLi
2) DMF
1) n-BuLi, 2) CO2(s), 3) H+
Mes*
P
Mes*
CHO
CHO
P
CO2H
CO2H
S
S
S
S
P
Mes*
P
Mes*
(E,E )-5e
(E,E )-5f
Scheme 5.
formyl derivative (E,E)-5d in 70% yield (Scheme 5). A large
spin–spin coupling constant in the 31P NMR spectrum of
the product (3JPP = 98.4 Hz) is a characteristic of 1,2-
unsymmetrically substituted (E,E)-DPCB [1e,1k]. When 2
equiv. of butyllithium and DMF were used, diformyl com-
pound (E,E)-5e was obtained in 76% yield. Similarly, dicar-
boxylic acid (E,E)-5f was obtained (66% yield) by
successive treatment of (E,E)-5a with butyllithium and
dry ice and water.
These results indicate that the thienyl group is a promis-
ing substituent for introduction of various functional
group near the DPCB center under basic conditions. It
should be emphasized that decomposition or isomerization
of the P@C bond was suppressed under these conditions.
4.2. (E,E)-1,2-Di(2-thienyl)-3,4-bis[(2,4,6-tri-t-
butylphenyl)phosphinidene]cyclobutene (5a)
A mixture of (2,4,6-tri-t-butylphenyl)phosphine (7.498 g,
26.93 mmol) [15] and 2,20-azobisisobutyronitrile (AIBN)
(273.0 mg,
1.663 mmol)
in
carbon
tetrachloride
(72 mL) was refluxed for 4 h. The resulting mixture was
concentrated and 50 mL of THF was added to chloro-
(2,4,6-tri-t-butylphenyl)phosphine. To a solution of 2-
(20,20-dibromovinyl)thiophene (7, 26.82 mmol) in THF
(50 mL) was added 53.82 mmol of butyllithium (1.56 M
solution in hexane) at ꢀ78 °C. The resulting solution was
stirred for 1 h, allowed to warm to room temperature,
and stirred for an additional 1 h. The solution was added
to the above THF solution of the chlorophosphine and
the combined mixture was stirred for 1 h and worked up
using hexane and brine, and then the organic phase was
dried over Na2SO4. The solvent was removed under reduced
pressure and the residue was submitted to a silica-gel col-
umn chromatographic treatment (hexane) to give 7.650 g
3. Conclusion
Various reactions of the 1,2-dithienyl-3,4-diphsophinid-
enecyclobutene were curried out and the products were
studied. Carbonyl functional groups such as formyl and
carboxyl groups were successfully introduced to the thio-
phene ring without decomposition or isomerization of the
phosphorus–carbon double bonds. Utilization of the thie-
nyl group turned out to be a fairly useful method for
introduction of functional groups into the proximity of
the DPCB center under mild conditions. The DPCB
derivatives obtained here will become good building
blocks for construction of more elaborate ligands contain-
ing sp2 hybridized phosphorus atoms. The findings
described here will help development of DPCB-transition
metal catalysts [4] and DPCB polymer-transition metal
complexes [1h,12a]. Further investigation is in progress
concerning conversions of the introduced functional
groups of (E,E)-5d-f. These compounds are key building
blocks for construction of DPCB oligomers and will give
fertile chemistry of functionalized DPCB ligands and their
complexes.
of 8 (74% yield based on the starting Mes PH ). The phos-
*
2
phine 8 was converted to (E,E)-5a by a method reported
previously [1j].
4.3. Sulfurization reaction of (E,E)-5a
To a mixture of (E,E)-5a (98.1 mg, 0.128 mmol) and ele-
mental sulfur (25.1 mg, 0.81 mg-atom) in dry benzene
(10 mL) was added 0.03 mmol of DBU. The resulting solu-
tion was stirred in the dark at room temperature. The reac-
tion was monitored by 31P NMR spectroscopy (an
appropriate amount of C6D6 was added to the sample solu-
tion). The reaction mixture was stirred for 2 days and DBU
(0.03 mmol) was added. After additional 3 days-stirring,
DBU (0.03 mmol) was added again, and the resulting

A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
75
mixture was stirred for an additional 5 days. The solution
was then passed through a short alumina column (eluent:
CHCl3) and the solvent was removed under reduced pres-
sure. The residue was then separated by a column chroma-
tography (Al2O3/CCl4) to give 59.2 mg of 11a (54% yield).
Orange solid, m.p. 167–170 °C (dec.); 1H NMR (600 MHz,
CD2Cl2) d = 1.19 (9H, s, p-t-Bu), 1.29 (9H, s, p-t-Bu), 1.62
(9H, s, o-t-Bu), 1.66 (9H, s, o-t-Bu), 1.74 (9H, d,
5JPH = 0.6 Hz, o-t-Bu), 1.82 (9H, s, o-t-Bu), 6.06 (1H,
temperature for 2 h. The solvent was removed under
reduced pressure and the residue was treated with silica-
gel column chromatography (hexane-CHCl3, 5:1) to give
the desired complex 5aCr in nearly quantitative yield.
5aCr. Black solid, m.p. > 125 °C (dec.); 1H NMR
(600 MHz, CDCl3) d = 1.41 (18H, s, p-t-Bu), 1.67 (36H,
3
s, o-t-Bu), 5.95 (2H, d, JHH = 3.6 Hz, thiophene), 6.63
3
(2H, dd, JHH = 4.8, 3.6 Hz, thiophene), 7.11 (2H, d,
3JHH = 4.8 Hz, thiophene), and 7.50 (4H, s, m-Mes );
*
ddd, JHH = 5JPH = 4.2 Hz, JHH = 0.8 Hz, 3-thiophene),
13C{1H} NMR (150 MHz, CDCl3) d = 31.5 (s, p-CMe3),
33.9 (s, o-CMe3), 35.3 (s, p-CMe3), 38.8 (s, o-CMe3),
3
4
3
4
6.45 (1H, dd, JHH = 3.6 Hz, JHH = 1.1 Hz, 3-thiophene),
3
3
6.46 (1H, dd, JHH = 4.9 Hz, JHH = 4.2 Hz, 4-thiophene),
122.7 (s, m-Mes ), 127.4 (s, thiophene), 128.2 (s, thio-
*
3
3
6.66 (1H, dd, JHH = 5.0 Hz, JHH = 3.6 Hz, 4-thiophene),
phene), 129.5 (s, thiophene), 132.4 (s, thiophene), 134.8
6.89 (1H, dd, 4JPH = 7.1 Hz, 4JHH = 1.8 Hz, m-Mes ), 6.93
(d, 1JPC = 178.1 Hz, ipso-Mes ), 143.8 (dd, 2JPC = 55.8 Hz,
*
*
3
6
4
(1H, ddd, JHH = 4.9 Hz, JPH = 1.8 Hz, JHH = 0.8 Hz,
5-thiophene), 7.09 (1H, dd, JHH = 5.0 Hz, JHH = 1.1 Hz,
5-thiophene), 7.38 (1H, dd, JPH = 5.4 Hz, JHH = 1.8 Hz,
m-Mes ), 7.42 (1H, dd, JPH = 5.4 Hz, JHH = 1.8 Hz, m-
3JPC = 34.7 Hz, P@C–C), 152.6 (s, p-Mes ), 157.6 (s, o-
*
4
4
1
2
Mes ), 174.9 (dd, JPC = 28.7 Hz, JPC = 22.6 Hz, P@C),
*
4
4
220.0 (t, 2JPC = 17.4 Hz, CO), and 228.0 (d, 2JPC = 5.1 Hz,
CO); 31P{1H} NMR (162 MHz, CDCl3) d = 189.2; IR
(KBr) 2962, 2910, 2871, 2013, 1957, 1923, 1892, 1593,
1473, 1414, 1404, 1363, 1240, 1211, 1126, 702, 667, 627,
and 474 cmꢀ1; UV–Vis (CH2Cl2) 340 (log e 4.37) and
472 nm (4.28). Found m/z 818.3332. Calc. for
C50H64CrP2S2: M–4CO, 818.3324. Found: C, 63.90; H,
6.85; S, 6.52%. Calc. for C52H64CrO4P2S2 Æ 3H2O: C,
63.40; H, 7.16; S, 6.51.
4
4
*
4
4
Mes ), and 7.49 (1H, dd, JPH = 5.5 Hz, JHH = 1.8 Hz,
*
m-Mes ); 13C{1H} NMR (150 MHz, CD2Cl2) d = 31.1 (s,
*
p-CMe3), 31.2 (s, p-CMe3), 33.6 (s, o-CMe3), 34.0 (s,
o-CMe3), 34.6 (s,o-CMe3), 34.8 (s, o-CMe3), 35.0 (s, p-
3
CMe3), 35.6 (s, p-CMe3), 39.6 (d, JPC = 2.6 Hz, o-
3
CMe3), 40.1 (d, JPC = 2.3 Hz, o-CMe3), 40.2 (d,
3JPC = 2.6 Hz, o-CMe3), 41.7 (s, o-CMe3), 61.1 (dd,
1JPC = 31.7 Hz,
2JPC = 8.0 Hz,
PSC),
122.6
(d,
3
3JPC = 15.6 Hz, m-Mes ), 124.0 (d, JPC = 13.8 Hz, m-
*
3
Mes ), 124.3 (d, JPC = 13.6 Hz, m-Mes ), 125.4 (d,
4.4.2. [1,2-Di(2-thienyl)-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]-
tetracarbonylmolybdenum(0) (5aMo)
*
*
1JPC = 81.1 Hz, ipso-arom.), 126.7 (d, JPC = 14.3 Hz, m-
3
Mes ), 126.9 (s, thienyl), 127.09 (s, thienyl), 127.13 (s, thi-
*
4
enyl), 127.4 (s, thienyl), 127.5 (d, JPC = 2.7 Hz, thienyl),
A mixture of (E,E)-5a (80.2 mg, 0.104 mmol) and
(bicyclo[2.2.1]hepta-2,5-diene)tetracarbonylmolybdenum(0)
(37.7 mg, 0.126 mmol) in THF (2 mL) was stirred at room
temperature for 3 h. The solvent was removed under
reduced pressure and the residue was treated with silica-
gel column chromatography (hexane-CHCl3, 75:1) to give
the desired complex 5aMo almost quantitatively. 5aMo,
dark brown solid, m.p. > 150 °C; 1H NMR (600 MHz,
CDCl3) d = 1.41 (18H, s, p-t-Bu), 1.66 (36H, s, o-t-Bu),
1
128.7 (s, thienyl), 129.9 (d, JPC = 78.0 Hz, ipso-Mes ),
*
3
131.6 (s, ipso-thienyl), 132.0 (d, JPC = 2.4 Hz, ipso-thie-
nyl), 137.1 (dd, JPC = 55.5 Hz and JPC = 8.2 Hz, P@C–
2
3
1
2
C), 140.2 (dd, JPC = 134.5 Hz and JPC = 3.8 Hz, P@C),
141.9 (dd, JPC = 3JPC = 12.9 Hz, P–C–C), 153.3 (d,
2
4JPC = 3.5 Hz, p-arom.), 154.1 (d, JPC = 12.8 Hz, o-
2
4
arom.), 154.8 (d, JPC = 3.5 Hz, p-arom.), 154.9 (d,
2JPC = 6.0 Hz, o-arom.), 155.0 (d, 2JPC = 7.3 Hz, o-arom.),
2
3
and 156.9 (d, JPC = 7.7 Hz, o-arom.); 31P{1H} NMR
5.98 (2H, d, JHH = 3.6 Hz, thiophene), 6.71 (2H, dd,
(162 MHz, CDCl3) d = ꢀ12.3 (d, JPP = 4.6 Hz) and
3JHH = 5.4, 3.6 Hz, thiophene), 7.11 (2H, d, JHH
=
3
3
115.1 (d, JPP = 4.6 Hz); IR (KBr) 2960, 2908, 2866,
5.4 Hz, thiophene), and 7.49 (4H, s, m-Mes ); 13C{1H}
3
*
1595, 1477, 1400, 1363, 1236, 1213, 1124, 850, 777, and
700 cmꢀ1; UV–Vis (CH2Cl2) 270 (sh, log e 4.39), 344
(3.96), and 430 nm (4.43). Found m/z 885.2975. Calc. for
C48H64NaP2S5: M++Na, 885.2979. Found: C, 66.70; H,
7.53; S, 18.43%. Calc. for C48H64P2S5: C, 66.78; H, 7.47;
S, 18.57.
NMR (150 MHz, CDCl3) d = 31.5 (s, p-CMe3), 34.0 (s,
o-CMe3), 35.3 (s, p-CMe3), 38.9 (s, o-CMe3), 122.7 (s,
m-Mes ), 127.4 (s, thiophene), 128.4 (s, thiophene),
*
1
129.1 (d, JPC = 6.0 Hz, ipso-Mes ), 129.7 (s, thiophene),
*
132.2 (s, thiophene), 144.2 (dd, 2JPC = 55.8 Hz,
3JPC = 34.7 Hz, P@C–C), 152.5 (s, p-Mes ), 157.4 (s, o-
*
1
2
Mes ), 175.3 (dd, JPC = 30.2 Hz, JPC = 22.6 Hz, P@C),
*
4.4. Transition metal complexes of 5a
209.2 (t, 2JPC = 12.1 Hz, CO), and 216.7 (dd,
2JPC = 41.5, 11.4 Hz, CO); 31P{1H} NMR (162 MHz,
CDCl3) d = 173.1; IR (KBr) 2962, 2025, 1928, 1892,
704, 609, and 575 cmꢀ1; UV–Vis (CH2Cl2) 335 (log e
4.43) and 454 nm (4.40). Found m/z 864.3001. Calc. for
C48H64MoP2S2: M–4CO, 864.2977. Found: C, 60.38; H,
6.58; S, 6.15%. Calc. for C52H64MoO4P2S2 Æ 3H2O: C,
60.69; H, 6.86; S, 6.23.
4.4.1. [1,2-Di(2-thienyl)-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]-
tetracarbonylchromium(0) (5aCr)
A mixture of (E,E)-5a (87.0 mg, 0.113 mmol) and
(bicyclo[2.2.1]hepta-2,5-diene)tetracarbonylchromium(0)
(57.4 mg, 0.224 mmol) in THF (2 mL) was stirred at room

76
A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
4.4.3. [1,2-Di(2-thienyl)-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]-
(tetracarbonyl)tungsten(0) (5aW)
6.32%. Calc. for C48H64Cl2P2PdS2 Æ 2H2O: C, 58.80; H,
6.99; Cl, 7.23; S, 6.54.
A mixture of (E,E)-5a (83.0 mg, 0.108 mmol) and (bicy-
clo[2.2.1]hepta-2,5-diene)tetracarbonyltungsten(0) (83.9 mg,
0.216 mmol) in THF (2 mL) was stirred at 50 °C for 1
day. The solvent was removed under reduced pressure
and the residue was treated with silica-gel column chroma-
tography (hexane-CHCl3, 5:1) to give the desired complex
5aW (42.7 mg, 37% yield). Black solid, m.p. > 180 °C
4.4.5. Dichloro[1,2-di(2-thienyl)-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]platinum(II)
(5aPt)
A mixture of (E,E)-5a (85.2 mg, 0.111 mmol) and bis-
(benzonitrile)dichloroplatinum(II) (104.6 mg, 0.222 mmol)
in THF (2 mL) was stirred at 50 °C for 2 days. The solvent
was removed under reduced pressure and the residue was
treated with silica-gel column chromatography (hexane–
AcOEt, 4:1) to give the desired complex 5aPt (22.0 mg,
19% yield). Red solid, m.p. > 300 °C; 1H NMR (600 MHz,
CDCl3) d = 1.41 (18H, s, p-t-Bu), 1.74 (36H, s, o-t-Bu),
6.30 (2H, br s, thiophene), 6.69 (2H, t, 3JHH = 4.2 Hz, thio-
1
(dec.); H NMR (600 MHz, CDCl3) d = 1.42 (18H, s, p-
3
t-Bu), 1.67 (36H, s, o-t-Bu), 5.99 (2H, d, JHH = 3.6 Hz,
3
thiophene), 6.63 (2H, dd, JHH = 4.8, 3.6 Hz, thiophene),
3
7.13 (2H, d, JHH = 4.8 Hz, thiophene), and 7.51 (4H, s,
m-Mes ); 13C{1H} NMR (150 MHz, CDCl3) d = 31.5 (s,
*
3
p-CMe3), 34.1 (s, o-CMe3), 35.3 (s, p-CMe3), 39.0 (s, o-
phene), 7.37 (2H, d, JHH = 4.8 Hz, thiophene), and 7.67
3
CMe3), 122.8 (t, JPC = 3.0 Hz, m-Mes ), 127.5 (s, thio-
(4H, s, m-Mes ); 13C{1H} NMR (150 MHz, CDCl3)
*
*
phene), 128.2 (s, ipso-Mes ), 128.2 (s, thiophene), 129.6
(s, thiophene), 132.2 (s, thiophene), 142.8 (m, P@C–C),
d = 31.2 (s, p-CMe3), 34.6 (s, o-CMe3), 35.5 (s, p-CMe3),
*
1
39.6 (s, o-CMe3), 119.1 (d, JPC = 31.7 Hz, ipso-Mes ),
*
3
152.7 (s, p-Mes ), 157.6 (s, o-Mes ), 174.9 (dd,
124.2 (t, JPC = 5.3 Hz, m-Mes ), 128.2 (s, thiophene),
*
*
*
1JPC = 36.2 Hz, 2JPC = 24.1 Hz, P@C), 203.4 (t,
130.5 (s, thiophene), 131.4 (pseudo t, thiophene), 132.2
2JPC = 11.3 Hz, CO), and 206.9 (m, CO); 31P{1H} NMR
(s, thiophene), 139.1 (dd, JPC = 63.4 Hz, JPC = 33.2 Hz,
2
3
(162 MHz,
CDCl3)
d = 152.2
(satellite
d,
P@C–C), 155.4 (s, p-Mes ), 158.1 (s, o-Mes ), and 161.0
* *
1 2
1JPW = 259.2 Hz); IR (KBr) 2962, 2908, 2871, 2019, 1919,
1888, 1593, 1473, 1414, 1402, 1365, 1240, 1211, 1126,
704, 584, and 573 cmꢀ1; UV–Vis (CH2Cl2) 335 (log e
4.27) and 455 nm (4.31). Found m/z 950.3413. Calc. for
C48H64P2S2W: M–4CO, 950.3434. Found: C, 58.02; H,
6.33; S, 5.54%. Calc. for C52H64O4P2S2W Æ H2O: C, 57.78;
H, 6.15; S, 5.93.
(dd, JPC = 86.0 Hz, JPC = 13.6 Hz, P@C); 31P{1H}
1
NMR (162 MHz, CDCl3) d = 126.6 (satellite d, JPtP
=
4497.0 Hz); IR (KBr) 2962, 2871, 1593, 1473, 1414, 1367,
1265, 1240, 710, and 650 cmꢀ1; UV–Vis (CH2Cl2) 268 (log e
4.49) and 394 nm (4.47). Found m/z 959.3438. Calc. for
C48H62P2PtS2: M–2Cl–2H, 959.3416. Found: C, 55.15; H,
6.54; Cl, 6.23; S, 5.58%. Calc. for C48H64Cl2P2PtS2 Æ H2O:
C, 54.85; H, 6.33; Cl, 6.75; S, 6.10.
4.4.4. Dichloro[1,2-di(2-thienyl)-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]-palladium(II)
(5aPd)
4.4.6. Formation of 5aCr from (E,Z)-5a
A mixture of (E,Z)-5a (35.2 mg, 0.046 mmol) and
(bicyclo[2.2.1]hepta-2,5-diene)tetracarbonylchromium(0)
(22.1 mg, 0.086 mmol) in THF-d8 (0.74 mL) in an NMR
sample tube was stored in the dark at room temperature
for 4 h. The 31P NMR spectrum of the solution showed
that most of the starting (E,Z)-5a remained unchanged
and that formation of 5aCr was trace (probably due to
room light during the operation). This solution was then
irradiated with a Xe lamp (300 W) in an ice-bath for 2 h.
Apparent formation of (E,E)-5a and 5aCr was confirmed
by 31P NMR spectroscopy. After irradiation for an addi-
tional 22 h, the ratio of (E,Z)-5a:5aCr became 4:1.
A mixture of (E,E)-5a (89.7 mg, 0.117 mmol) and bis(ace-
tonitrile)dichloropalladium(II) (36.4 mg, 0.140 mmol) in
THF (2 mL) was stirred at room temperature for 3 h. The
solvent was removed under reduced pressure and the residue
was treated with silica-gel column chromatography (hex-
ane–AcOEt, 2:1) to give the desired complex 5aPd
(83.0 mg, 75% yield). Brown solid, m.p. > 265 °C (dec.);
1H NMR (600 MHz, CDCl3) d = 1.40 (18H, s, p-t-Bu),
1.71 (36H, s, o-t-Bu), 6.26 (2H, br s, thiophene), 6.71 (2H,
3
3
t, JHH = 4.2 Hz, thiophene), 7.39 (2H, d, JHH = 4.8 Hz,
thiophene), and 7.63 (4H, s, m-Mes ); 13C{1H} NMR
*
(150 MHz, CDCl3) d = 31.2 (s, p-CMe3), 34.7 (s, o-CMe3),
35.5 (s, p-CMe3), 39.5 (s, o-CMe3), 121.4 (pseudo t,
4.5. Introduction of functional groups to the thiophene ring
3
JPC = 4.5 Hz, ipso-Mes ), 124.1 (t, JPC = 4.5 Hz, m-
*
Mes ), 128.2 (s, thiophene), 131.5 (s, thiophene), 131.7 (s,
4.5.1. (E,E)-1-(5-Formyl-2-thienyl)-2-(2-thienyl)-3,4-
bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene
(5d)
To a solution of (E,E)-5a (94.3 mg, 0.123 mmol) in THF
(2 mL) was added 0.133 mmol of butyllithium (1.56 M
solution in hexane) at ꢀ78 °C. The resulting solution was
stirred at ꢀ78 °C for 30 min and 0.050 mL (0.643 mmol)
of DMF was added. The mixture was stirred at ꢀ78 °C
for 1 h, allowed to warm to room temperature, and the
*
thiophene), 132.1 (s, thiophene), 140.4 (m, P@C–C), 155.5
1
(s, p-Mes ), 157.5 (s, o-Mes ), and 163.2 (dd, JPC
=
*
*
46.0 Hz, 3JPC = 41.5 Hz, P@C); 31P{1H} NMR (162 MHz,
CDCl3) d = 149.4; IR (KBr) 2962, 2906, 2870, 1589, 1473,
1412, 1369, 1267, 1240, 1213, 1124, 710, and 648 cmꢀ1
;
UV–Vis (CH2Cl2) 303 (log e 4.39), 382 (4.57), and 461 nm
(4.07). Found m/z 871.2879. Calc. for C48H63P2PdS2: M–
2Cl–H, 871.2894. Found: C, 59.23; H, 6.91; Cl, 7.47; S,

A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
77
solvent was evaporated under reduced pressure. The resi-
due was treated with column chromatography (SiO2/hex-
ane-EtOAc) to give 69.6 mg (70% yield) of (E,E)-5d. Red
solid, m.p. 189–192 °C (dec.); 1H NMR (600 MHz, CDCl3)
d = 1.38 (9H, s, p-t-Bu), 1.38 (9H, s, p-t-Bu), 1.54 (18H, s,
(CH2Cl2) 357 (log e 4.46) and 441 nm (4.13). Found m/z
821.3761. Calc. for C50H63O2P2S2: M–H, 821.3744. Found:
C, 71.55; H, 7.97; S, 7.32%. Calc. for C50H64O2P2S2 Æ H2O:
C, 71.40; H, 7.91; S, 7.62.
3
o-t-Bu), 1.56 (18H, s, o-t-Bu), 5.72 (1H, d, JHH = 4.1 Hz,
4.5.3. (E,E)-1,2-Bis(5-carboxy-2-thienyl)-3,4-bis[(2,4,6-
tri-t-butylphenyl)phosphinidene]cyclobutene (5f)
3
thiophene), 5.99 (1H, d, JHH = 3.8 Hz, thiophene0), 6.58
3
3
(1H, dd, JHH = 4.9 Hz, JHH = 3.8 Hz, thiophene0), 7.09
To a solution of (E,E)-5a (81.0 mg, 0.106 mmol) in THF
(1 mL) was added 0.23 mmol of butyllithium (1.58 M solu-
tion in hexane) at ꢀ78 °C. The resulting solution was stir-
red at ꢀ78 °C for 30 min, and an excess amount of dryice
was added. The mixture was stirred at ꢀ78 °C for 1 h,
allowed to warm to room temperature, and then the sol-
vent was evaporated under reduced pressure. The residue
was treated with column chromatography (SiO2/hex-
ane:EtOAc:HCO2H = 100:20:1) to give 59.9 mg (66%
3
(1H, d, JHH = 4.9 Hz, thiophene0), 7.12 (1H, d,
3JHH = 4.1 Hz, thiophene), 7.40 (2H, s, m-Mes ), 7.42
*
(2H, s, m-Mes ), and 9.69 (1H, s, CHO); 13C{1H} NMR
*
(100 MHz, CDCl3) d = 32.0 (s, CMe3), 32.0 (s, CMe3),
33.5 (s, CMe3), 33.6 (s, CMe3), 35.5 (s, CMe3), 35.6 (s,
CMe3), 38.7 (s, CMe3), 38.8 (s, CMe3), 122.4 (s, m-
Mes ), 122.6 (s, m-Mes ), 127.7 (s, thiophene), 129.4 (d,
*
*
JPC = 3.0 Hz, thiophene), 130.7 (d, JPC = 5.1 Hz, thio-
1
phene), 130.8 (d, JPC = 4.9 Hz, thiophene), 132.4 (s, thio-
yield) of (E,E)-5f. Red solid, m.p. 158–161 °C (dec.); H
1
phene), 134.3 (d, JPC = 43.1 Hz, ipso-Mes ), 134.9 (d,
NMR (400 MHz, CDCl3) d = 1.39 (18H, s, p-t-Bu), 1.57
*
1JPC = 44.2 Hz, ipso-Mes ), 135.9 (s, thiophene), 142.6 (s,
(36H, s, o-t-Bu), 5.66 (2H, d, JHH = 4.0 Hz, thiophene),
3
*
3
thiophene), 143.7 (d, JPC = 3.0 Hz, thiophene), 145.8 (dd,
7.24 (2H, d, JHH = 4.0 Hz, thiophene), and 7.42 (4H, s,
3
2JPC = 40.7 Hz, JPC = 27.7 Hz, P@C–C), 149.1 (dd,
m-Mes ); 13C{1H} NMR (100 MHz, DMSO-d6) d = 32.0
*
3
2JPC = 39.3 Hz, JPC = 27.1 Hz, P@C–C), 151.2 (s, p-
(s, CMe3), 33.7 (s, CMe3), 35.4 (s, CMe3), 38.7 (s, CMe3),
Mes ), 151.2 (s, p-Mes ), 155.6 (s, o-Mes ), 155.7 (s, o-
122.5 (s, m-Mes ), 131.0 (s, thiophene), 133.3 (s, thio-
*
*
*
*
1
2
Mes ), 174.3 (dd, JPC = 22.8 Hz, JPC = 12.5 Hz, P@C),
phene), 133.7 (pseudo t, JPC = 27.5 Hz, ipso-Mes ), 137.3
*
*
1
2
174.8 (dd, JPC = 23.0 Hz, JPC = 12.5 Hz, P@C), and
(s, thiophene), 137.7 (s, thiophene), 147.3 (pseudo t,
183.0 (s, CHO); 31P{1H} NMR (162 MHz, CDCl3)
P@C–C), 151.4 (s, p-Mes ), 155.3 (s, o-Mes ), 163.1 (s,
*
*
d = 173.2
(d,
3JPP = 98.4 Hz)
and
187.2
(d,
CO2H), and 173.8 (m, P@C); 31P{1H} NMR (162 MHz,
CDCl3) d = 185.3; IR (KBr) 13500 (br), 2951, 2921, 2871,
1678, 1518, 1454, 1425, 1398, 1284, and 1244 cmꢀ1; UV–
Vis (DMF) 361 (log e 4.44) and 450 nm (4.03). Found m/
z 797.3031. Calc. for C46H55O4P2S2: M–t-Bu, 787.3017.
Found: C, 68.45; H, 7.73; S, 6.90%. Calc. for C50H64O4-
P2S2 Æ H2O: C, 68.78; H, 7.62; S, 7.34.
3JPP = 98.4 Hz); IR (KBr) 2966, 2877, 2864, 1670, 1439,
1398, 1361, and 1215 cmꢀ1; UV–Vis (CH2Cl2) 345 (log e
4.44) and 445 nm (4.10). Found m/z 793.3808. Calc. for
C49H63OP2S2, M–H, 793.3795.
4.5.2. (E,E)-1,2-Bis(5-formyl-2-thienyl)-3,4-bis[(2,4,6-tri-
t-butylphenyl)phosphinidene]cyclobutene (5e)
To a solution of (E,E)-5a (134.8 mg, 0.176 mmol) in
THF (2 mL) was added 0.38 mmol of butyllithium
(1.58 M solution in hexane) at ꢀ78 °C. The resulting solu-
tion was stirred at ꢀ78 °C for 30 min and 0.070 mL
(0.90 mmol) of DMF was added. The mixture was stirred
at ꢀ78 °C for 1 h, allowed to warm to room temperature,
and the solvent was evaporated under reduced pressure.
The residue was then treated with column chromatography
(SiO2/hexane:EtOAc = 10:1) to give 110.0 mg (76% yield)
of (E,E)-5e. Red solid, m.p. ca. 170 °C; 1H NMR
(400 MHz, CDCl3) d = 1.42 (18H, s, p-t-Bu), 1.59 (36H,
4.6. Dichloro[1,2-diphenyl-3,4-bis{(2,4,6-tri-t-
butylphenyl)phosphinidene}cyclobutene]platinum(II)
(1APt)
A mixture of (E,E)-1A (103.5 mg, 0.137 mmol) and bis-
(benzonitrile)dichloroplatinum(II) (129.5 mg, 0.274 mmol)
in THF (2.0 mL) was stirred at 50 °C for 2 days. The sol-
vent was then removed under reduced pressure and the res-
idue was treated with silica-gel column chromatography
(hexane-EtOAc) to give 1APt (75.9 mg, 54% yield). Orange
1
solid, m.p. > 300 °C (dec.); H NMR (400 MHz, CDCl3)
3
s, o-t-Bu), 5.85 (2H, d, JHH = 4.0 Hz, thiophene), 7.20
d = 1.42 (18H, s, p-t-Bu), 1.72 (36H, s, o-t-Bu), 6.89 (4H,
3
3
3
(2H, d, JHH = 4.0 Hz, thiophene), 7.46 (4H, s, m-Mes ),
d, JHH = 8.4 Hz, o-Ph), 6.93 (4H, t, JHH = 7.8 Hz, m-
*
and 9.74 (2H, s, CHO); 13C{1H} NMR (100 MHz, CDCl3)
Ph), 7.21 (2H, t, JHH = 7.5 Hz, p-Ph), and 7.64 (4H, d,
3
d = 32.0 (s, CMe3), 33.6 (s, CMe3), 35.6 (s, CMe3), 38.8 (s,
4JPH = 3.6 Hz, m-Mes ); 13C{1H} NMR (100 MHz,
*
CMe ), 122.6 (s, m-Mes ), 131.0 (s, thiophene), 134.1
CDCl3) d = 31.5 (s, p-CMe3), 34.6 (s, o-CMe3), 35.5 (s, p-
*
3
(pseudo t, JPC = 27.6 Hz, ipso-Mes ), 135.9 (s, thiophene),
CMe ), 39.5 (s, p-CMe ), 119.4 (m, ipso-Mes ), 124.2 (m,
*
3 3
*
141.4 (s, thiophene), 144.7 (s, thiophene), 146.9 (pseudo t,
m-Mes ), 127.6 (s, Ph), 128.5 (s, Ph), 130.0 (s, Ph), 130.5
(s, Ph), 148.9 (dd, JPC = 61.2 Hz, JPC = 31.0 Hz, P@C–
*
2
3
JPC = 6.6 Hz, P@C–C), 151.6 (s, p-Mes ), 155.6 (s, o-
*
1
2
Mes ), 173.8 (dd, JPC = 17.6 Hz, JPC = 9.6 Hz, P@C),
C), 155.1 (s, p-Mes ), 157.5 (s, o-Mes ), and 162.5 (m,
*
* *
and 182.9 (s, CHO); 31P{1H} NMR (162 MHz, CDCl3)
d = 189.4; IR (KBr) 2966, 2924, 2900, 2866, 1674, 1471,
1452, 1415, 1396, 1362, 1215, and 810 cmꢀ1; UV–Vis
P@C); 31P {1H} NMR (162 MHz, CDCl3) d = 129.2 (satel-
lite d, 1JPtP = 4499.2 Hz); IR (KBr) 2962, 2908, 2871, 1595,
1473, 1448, 1400, 1362, 1240, 1211, 1126, 748, 690, and

78
A. Nakamura et al. / Journal of Organometallic Chemistry 692 (2007) 70–78
677 cmꢀ1; UV–Vis (CH2Cl2) 265 (4.60) and 369 nm (4.55).
Found: m/z 947.4264. Calc. for C52H66P2Pt: M–2Cl–2H,
947.4284. Found: C, 59.99; H, 6.77; Cl, 7.14%. Calc. for
C52H68Cl2P2Pt Æ H2O:C, 60.11; H, 6.79; Cl, 6.82.
(e) M. Yoshifuji, Y. Ichikawa, N. Yamada, K. Toyota, Chem.
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(f) K. Toyota, N. Yamada, M. Yoshifuji, Phosphorus Sulfur Silicon
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[4] (a) K. Toyota, K. Masaki, T. Abe, M. Yoshifuji, Chem. Lett. (1995)
221;
(b) S. Ikeda, F. Ohhata, M. Miyoshi, R. Tanaka, T. Minami, F.
Ozawa, M. Yoshifuji, Angew. Chem., Int. Ed. 39 (2000) 4512;
(c) F. Ozawa, S. Kawagishi, T. Ishiyama, M. Yoshifuji, Organomet-
allics 23 (2004) 1325;
Acknowledgements
This work was supported in part by the Grants-in-Aid
for Scientific Research (Nos. 13304049, 14044012,
16033207, and 50217569) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
(d) F. Ozawa, T. Ishiyama, S. Yamamoto, S. Kawagishi, H.
Murakami, M. Yoshifuji, Organometallics 23 (2004) 1698;
(e) F. Ozawa, S. Yamamoto, S. Kawagishi, M. Hiraoka, S. Ikeda, T.
Minami, S. Ito, M. Yoshifuji, Chem. Lett. (2001) 972;
(f) T. Minami, H. Okamoto, S. Ikeda, R. Tanaka, F. Ozawa, M.
Yoshifuji, Angew. Chem., Int. Ed. 40 (2001) 4501;
(g) F. Ozawa, H. Okamoto, S. Kawagishi, S. Yamamoto, T. Minami,
M. Yoshifuji, J. Am. Chem. Soc. 124 (2002) 10968.
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