Electrochemistry and Reactivity of Cobaltadithiolene Complexes Having Sulfilimine Structures: Effect of Phosphorus Ligand Basicity and Cone Angle on the Electrochemical Behavior and on the Imido Migration to the Cp Ring

Article abstract of DOI:10.1021/om034127j

Various types of cobaltadithiolene complexes having the sulfilimine structure CpCo[S(NTs)SC₂(COOMe)₂](PR₃) were newly synthesized. The lifetimes of the sulfilimine complexes are influenced by the basicities and by the cone angles of PR₃ ligands used. Some of the sulfilimine complexes rapidly eliminate PR₃ ligands by a one-electron reduction (PR₃ = PPh₃, P(OPh)₃, P(p-C₆H₄Me)₃, P(p-C₆H ₄Cl)₃, PCy₃, P(p-C₆H ₄OMe)₃) to give the precursor of the sulfilimine complex, the imido-bridged cobaltadithiolene adduct [CpCo{S₂C ₂(COOMe)₂}(NTs)]. On the other hand, the complexes of PBu₃ and P(OMe)₃ were stable during a one-electron reduction. The elimination of the imido group (NTs) by a second reduction was confirmed in all of the sulfilimine complexes. The investigation of the reactivity of the sulfilimine complexes showed that some of the sulfilimine complexes were the intermediates in the imido migration to the Cp ring (PR ₃ = PPh₃, P(OPh)₃, P(p-C₆H ₄Me)₃, P(p-C₆H₄Cl)₃). The basicities (or nucleophilicities) of PR₃ were important parameters for the imido migration. Sulfilimine complexes containing strongly nucleophilic PR₃ ligands (PR₃ = P(p-C₆H ₄OMe)₃, PBu₃, P(OMe)₃) did not undergo migration of the imido group. In the formation of the disubstituted Cp complex [{C₅H₃(NTs)(PR₃)}Co{S₂C ₂(COOMe)₂}], the basicity (or nucleophilicity) of PR ₃ ligands is also an important parameter (PR₃ = PPh ₃, P(p-C₆H₄Me)₃).

Full text of DOI:10.1021/om034127j

Organometallics 2004, 23, 1305-1312
1305
Electr och em istr y a n d Rea ctivity of Coba lta d ith iolen e
Com p lexes Ha vin g Su lfilim in e Str u ctu r es: Effect of
P h osp h or u s Liga n d Ba sicity a n d Con e An gle on th e
Electr och em ica l Beh a vior a n d on th e Im id o Migr a tion to
th e Cp Rin g
Mitsushiro Nomura, Chikako Takayama,† Toru Sugiyama, Yasuo Yokoyama, and
Masatsugu Kajitani*
Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1, Kioi-cho,
Chiyoda-ku, Tokyo 102-8554, J apan
Received August 25, 2003
Various types of cobaltadithiolene complexes having the sulfilimine structure CpCo[S(NTs)-
SC2(COOMe)2](PR3) were newly synthesized. The lifetimes of the sulfilimine complexes are
influenced by the basicities and by the cone angles of PR3 ligands used. Some of the sulfilimine
complexes rapidly eliminate PR3 ligands by a one-electron reduction (PR3 ) PPh3, P(OPh)3,
P(p-C6H4Me)3, P(p-C6H4Cl)3, PCy3, P(p-C6H4OMe)3) to give the precursor of the sulfilimine
complex, the imido-bridged cobaltadithiolene adduct [CpCo{S2C2(COOMe)2}(NTs)]. On the
other hand, the complexes of PBu3 and P(OMe)3 were stable during a one-electron reduction.
The elimination of the imido group (NTs) by a second reduction was confirmed in all of the
sulfilimine complexes. The investigation of the reactivity of the sulfilimine complexes showed
that some of the sulfilimine complexes were the intermediates in the imido migration to the
Cp ring (PR3 ) PPh3, P(OPh)3, P(p-C6H4Me)3, P(p-C6H4Cl)3). The basicities (or nucleophi-
licities) of PR3 were important parameters for the imido migration. Sulfilimine complexes
containing strongly nucleophilic PR3 ligands (PR3 ) P(p-C6H4OMe)3, PBu3, P(OMe)3) did
not undergo migration of the imido group. In the formation of the disubstituted Cp complex
[{C5H3(NTs)(PR3)}Co{S2C2(COOMe)2}], the basicity (or nucleophilicity) of PR3 ligands is also
an important parameter (PR3 ) PPh3, P(p-C6H4Me)3).
In tr od u ction
complexes [CpM(S2C2Z2)] (M ) Co, Rh).4-7 The reactions
of the Cp metalladithiolene complexes with diazo com-
pounds (R1R2CN2) and tetracyanoethylene oxide (TC-
NEO) yield alkylidene-bridged metalladithiolene ad-
ducts.4 The corresponding alkene-5 and norbornene-
bridged6 adducts can be obtained by reactions with
alkyne and quadricyclane, respectively. Furthermore,
imido-bridged adducts are formed by reaction with (N-
tosylimino)phenyliodinane (PhIdNTs) or sulfonyl azides.7
Recently, o-carboranedithiolato complexes have been
The metalladithiolene ring,1 which consists of one
metal, two sulfur atoms, and two unsaturated carbon
atoms, exhibits both aromaticity and unsaturation.
Electrophilic and radical substitution reactions2 due to
the aromaticity of the metalladithiolene ring have been
reported. This metal chelate ring has six delocalized π
electrons and has π-π* transitions in the visible and
near-IR regions.3
The metalladithiolene ring shows unsaturation when
the metal in the ring is coordinatively unsaturated.
Thus, addition reactions often occur between the metal
and the sulfur bond. We have reported the addition
reactions of cyclopentadienyl (Cp) metalladithiolene
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ki, H. J . Organomet. Chem. 1995, 487, C8.
* To whom correspondence should be addressed. E-mail: kajita-
m@sophia.ac.jp.
† Current address: Department of Chemistry, University of British
Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
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McCleverty, J . A. Prog. Inorg. Chem. 1969, 10, 49. (c) Burns, R. P.;
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10.1021/om034127j CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/19/2004

1306 Organometallics, Vol. 23, No. 6, 2004
Nomura et al.
Sch em e 1
We have found that the sulfilimine complexes 2a and
2b are intermediates in the novel imido migration
reaction to the Cp ring7,12 (Scheme 2). The migration of
a monodentate ligand from the central transition metal
to the Cp ring can be classified into four main catego-
ries: (1) base-induced migration from the metal to the
Cp ring;14-17 (2) migration by ligand(metal)/H(Cp) ex-
change;18 (3) migratory insertion into the C-H bond of
the Cp ring;19 (4) ligand migration to the Cp ring
induced by a photoreaction.20 Our work belongs in the
third category. These four types of migrations may find
use in the generation of functionally substituted Cp
ligands. The effects of the basicities and the cone
angles13 of phosphine and phosphite in the imido
migration reaction shown in Scheme 2 have been
examined.
developed, and various addition and isomerization reac-
tions have been reported by Kang8 and by Herberhold
et al.9
Resu lts a n d Discu ssion
1. P r ep a r a tion s a n d Sp ectr oscop ic P r op er ties of
th e Su lfilim in e Com p lexes. The imido-bridged adduct
1 was prepared from the cobaltadithiolene complex
[CpCo{S2C2(COOMe)2}] (5) by reaction with tosyl azide.7
When complex 1 reacted with 2 equiv of PR3 in dichlo-
romethane at room temperature, the solution color
rapidly changed from green to brown. The sulfilimine
complexes CpCo[S(NTs)SC2(COOMe)2](PR3) (2c-h ) were
We have studied the reactivities of metalladithiolene
adducts: the alkylidene-, alkene-, norbornene-, and
imido-bridged adducts dissociate by thermal, photo-
chemical, and electrochemical redox reactions,4-7 and
the corresponding original metalladithiolene complexes
are regenerated. We have also developed a novel reac-
tion between the metalladithiolene adducts with nu-
cleophiles. For example, the reaction of the alkylidene-
bridged adduct with PR3 undergoes two types of
structural changes10 (Scheme 1). One is the ring expan-
sion of the five-membered metalladithiolene ring to form
a six-membered ring by the nucleophilic attack of PR3
at the metal. The other reaction is metal-carbon bond
cleavage to form a sulfonium ylide structure. In addi-
tion, both complexes undergo redox-induced structural
changes.11
Recently, we have continued the study of the imido-
bridged adduct [CpCo{S2C2(COOMe)2}(NTs)] (1). Com-
plex 1 reacts with PR3 to form complexes having a
sulfilimine structure, CpCo[S(NTs)SC2(COOMe)2](PR3)
(PR3 ) PPh3 (2a ), P(OPh)3 (2b)), by metal-nitrogen
bond cleavage7,12 (Scheme 2). We have new investigated
the effects of the basicities and the cone angles13 of PR3
ligands on the electrochemical behavior of the sulfil-
imine complexes.
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Cobaltadithiolene Complexes
Organometallics, Vol. 23, No. 6, 2004 1307
Sch em e 2
Ta ble 1. Yield s a n d Sp ectr oscop ic Da ta of th e
Su lfilim in e Com p lexes
Cp Co[S(NTs)SC2(COOMe)2](P R3) (2a -h )
31P NMR (δ/ppm)
com-
plex
IR (νS-N
/
com- corresponding
plex free P ligand
PR3
yield/%
cm-1
922
)
2a
2b
2c
2d
2e
2f
PPh3
95a
80b
96
95
90
98
92
95
35.2
126.6
33.2
35.6
32.5
-5.0
128.4b
-7.6
P(OPh)3
932b
920
922
932
935
928
932
P(p-C6H4Me)3
P(p-C6H4Cl)3
PCy3
P(p-C6H4OMe)3
PBu3
-7.9
11.9
32.0
49.4
122.8
-9.7
-30.3
141.5
2g
2h
P(OMe)3
a
b
Reference 7. Reference 12.
F igu r e 1.
separated by column chromatography and obtained as
brown solids in nearly quantitative yield (Table 1).
Complexes 2a ,b have already been characterized.7,12 In
this work, analogous PR3 complexes 2c-h were identi-
fied by spectroscopic data. Although the purities of
F igu r e 2. Cyclic voltammograms (v ) 100 mV s-1, Φ )
1.6 mm Pt disk, concentration of sample 1 mM): (a)
complex 2a ; (b) multiple scan of the one-electron reduction
process of complex 2a ; (c) complex 2g; (d) complex 1.7
cobaltathiaziridine ring.) The 31P NMR signals of com-
plexes 2a -h showed two trends: the δ values of the
phosphine complexes 2a and 2c-g were shifted more
downfield than those of the corresponding free phos-
phines; the δ values of the phosphite complexes 2b12
and 2h were shifted more upfield than those of the
corresponding free phosphites (Table 1). These tenden-
cies have also been found in the PR3 adducts of cobalt-
adithiolene complexes, [CpCo(S2C2X2)(PR3)].22
1
complexes 2c-h were confirmed by H NMR spectra,
the PBu3 complex 2g and the P(OMe)3 complex 2h were
found to exist as isomers (see the Supporting Informa-
tion). We have found two types of isomers in such
complexes. One is that in which the phosphite ligand
and the alkylidene group are located at opposite sides
of the cobaltadithiolene ring (anti form10), and the other
is the complex of syn form.12 Also in this case, we
propose that the two isomers are syn and anti ones
(Figure 1). Our elemental analyses of complexes 2c-h
failed because these complexes were thermally unstable
or air-sensitive. The IR spectra of complexes 2a -h
showed two different signals around 1700 cm-1 at-
tributed to the CdO stretching vibrations of the cobalt-
adithiolene substituents; signals around 920-930 cm-1
attributed to the S+-N- stretching vibrations also
appeared (Table 1). Two different CdO signals indicate
that the imido group is attached to the sulfur atom of
the cobaltadithiolene ring. The latter values are similar
to those for the S+-N- stretching vibration of a typical
sulfilimine compound.21 These results suggest that the
ring opening of the cobaltathiaziridine ring was induced
by the nucleophilic attack of PR3 at the cobalt atom of
complex 1. (In the present paper, the three-membered
ring consisting of Co, N, and S is described as a
2. Electr och em ica l Beh a vior of th e Su lfilim in e
Com p lexes. In situ CV measurements of the reaction
mixtures of complex 1 with PR3 (1 equiv excess) were
performed, because complexes 2a -h were thermally
unstable and air-sensitive. It was confirmed that com-
1
plexes 2a -h were quantitatively formed by in situ H
NMR spectra of the mixtures. The CVs of complexes 2a
and 2g are shown in Figure 2a-c, and the CV of
complex 17 is also shown in Figure 2d for a comparison.
The reduction potential data for the complexes and the
reversibility of the reaction are shown in Table 2. The
CV of complex 2a showed two irreversible reduction
waves at -0.93 and -1.79 V, respectively (Figure 2a).
The first reduction potential of complex 2a was more
negative than that of complex 1, and the second one was
almost identical with that of complex 1 (Figure 2d). In
(21) (a) Kucsman, A.; Ruff, F.; Kapovits, I. Tetrahedron 1966, 22,
1575. (b) Tsujihara, K.; Furukawa, N.; Oae, S. Bull. Chem. Soc. J pn.
1970, 43, 2153.
(22) Kajitani, M.; Igarashi, A.; Hatano, H.; Akiyama, T.; Sugimori,
A.; Matsumoto, S.; Iguchi, Y.; Boennemann, H.; Shimizu, K.; Satoˆ, G.
P. J . Organomet. Chem. 1995, 485, 31.

1308 Organometallics, Vol. 23, No. 6, 2004
Nomura et al.
Ta ble 2. Red u ction P oten tia ls (vs F c|F c+) of th e
Sch em e 4
Su lfilim in e Com p lexes 2a -h a
first redn
second redn
complex
E
1/2/V
∆E/mV
∆Ep/mV
E1/2/V
∆E/mV
2a
2b
2c
2d
2e
2f
2g
2h
1b
-0.93ir
-0.83ir
-1.04ir
-0.88ir
-1.10ir
-1.04ir
-1.19r
-1.04r
-0.79r
76
118
92
72
80
80
70
74
68
-1.79ir
-1.80ir
-1.83ir
-1.81ir
-1.82ir
-1.80ir
-1.98ir
-1.79ir
-1.80ir
70
82
80
80
70
68
72
82
78
98
134
90
a
behavior of complexes 2b-f was similar to that of
complex 2a .
Definitions: r, reversible wave; ir, irreversible wave; E1/2
)
b
(Ep + Ep/2)/2; ∆E ) |Ep - Ep/2|; ∆Ep ) |Epc - Epa|. Reference 7.
The CV of complex 2g showed a reversible reduction
wave at -1.19 V and an irreversible reduction wave at
-1.81 V (Table 2 and Figure 2c). The first reduction
potential of complex 2g was more negative than that of
complex 1, and the second reduction potential cor-
responded to that of complex 1. The first reduction and
reoxidation responses of complex 2g are different from
those of complexes 2a -f. This result suggests that anion
2g- is stable on the CV time scale; therefore, the PBu3
ligand of complex 2g is difficult to eliminate by a one-
electron reduction. However, the second reduction wave
due to the 1-/12- couple (-1.81 V) indicates the forma-
tion of anion 1- by the elimination of PBu3. Therefore,
anions 2g- and 1- both coexist in an equilibrium state
(Scheme 4). Likewise, after a second reduction, the
reoxidation wave attributed to the wave of the 5/5-
couple appeared around -0.90 V. This result suggests
the elimination of the imido group by a second reduc-
tion. The electrochemical behavior of complex 2g is
summarized in Scheme 4. Complex 2h showed electro-
chemical behavior similar to that of complex 2g. There-
fore, P(OMe)3 of complex 2h is also difficult to eliminate.
Sch em e 3
addition, two reoxidation waves due to a reaction
product appeared around -0.80 and -0.90 V. The
former reoxidation wave appeared after the first reduc-
tion, and the latter reoxidation wave appeared after the
second reduction. These reoxidation waves corresponded
to the waves of 1/1- and 5/5- couples, respectively.
The following reduction behavior can thus be specu-
lated: (1) The electron density of the reduction site of
complex 2a has increased more than that of complex 1.
(2) Anion 1- was formed by the elimination of PPh3 from
the reductant 2a -. Therefore, as soon as PPh3 is
eliminated from the reductant 2a -, the cobaltathiaziri-
dine ring is re-produced by the Co-N bond re-formation.
We have also reported such a reversible Co-N bond
cleavage and re-formation between complex 1 and its
protic acid adduct [CpCo{S2C2(COOMe)2}(Cl)(NHTs)].7
However, the rereduction wave of complex 1 did not
appear in the multiple CV scan (Figure 2b). This result
suggests that complex 2a was re-formed by PPh3
present at close range to the electrode as soon as the
neutral complex 1 was re-formed. These electrode reac-
tions (ECEC reactions) can be described as an electro-
chemical square scheme.23 (3) When anion 1- formed
by the reduction of complex 2a was further reduced, the
imido group was eliminated to form anion 5-. This
behavior has also been observed in the second reduction
of complex 1.7 The electrochemical behavior of complex
2a is summarized in Scheme 3. The electrochemical
The lifetimes of the reductants of complexes 2a -h can
be explained by the basicity and the cone angle13 of the
PR3 ligand. In the case of PR3 having stronger basicity
(or nucleophilicity), the Co-P bond of the sulfilimine
complex becomes stronger and the lifetime of the
reductant becomes longer (e.g. the lifetimes of reduc-
tant: PPh3 complex 2a < PBu3 complex 2g; P(OPh)3
complex 2b < P(OMe)3 complex 2h ). Although PCy3 has
stronger basicity than PBu3, the lifetime of the reduc-
tant of complex 2e is shorter than that of complex 2g.
The difference in the value of cone angle means there
is some steric hindrance between the complex and PCy3.
In situ measurements of visible absorption spectra
during electrolysis were performed using an optically
transparent thin-layer electrode cell (OTTLE). When
complex 2a was reduced at -1.40 V, the absorption band
around 490 nm was decreased, and two isosbestic points
appeared around 395 and 435 nm (Figure 3a). Spectral
changes stopped after 2 min, and the final spectrum
corresponded to that of anion 1- previously reported.7
When anion 1- was reoxidized at -0.20 V, the absorp-
tion spectrum reverted to that of complex 2a (Figure
3b). This result also supports the electrochemical square
scheme shown in Scheme 3. In addition, when a second
reduction was performed at -2.20 V (Figure 3c) and the
sample was then reoxidized at -0.90 V, an absorption
band appeared around 550 nm (Figure 3d). This absorp-
(23) (a) Moraczewski, J .; Geiger, W. E. J . Am. Chem. Soc. 1981, 103,
4779. (b) Bernardo, M. M.; Robant, P. V.; Schroeder, R. R.; Rorabacher,
D. B. J . Am. Chem. Soc. 1989, 111, 1224. (c) Bond, A. M.; Colton, R.;
Mann, T. F. Organometallics 1988, 7, 2224. (d) Tsintavis, C.; Li, H.-
L.; Chambers, J . Q. J . Phys. Chem. 1991, 95, 289. (e) Richards, T. C.;
Geiger, W. E. J . Am. Chem. Soc. 1994, 116, 2028. (f) Connelly, N. G.;
Geiger, W. E.; Lagunas, M. C.; Metz, B.; Rieger, A. L.; Rieger, P. H.;
Shaw, M. J . J . Am. Chem. Soc. 1995, 117, 12202.

Cobaltadithiolene Complexes
Organometallics, Vol. 23, No. 6, 2004 1309
F igu r e 3. Visible spectral changes of complex 2a : (a) first reduction (-1.40 V, sampling time 30 s, sampling interval 2
s); (b) reoxidation (-0.20 V, sampling time 30 s, sampling interval 2 s) after first reduction; (c) second reduction (-2.20 V,
sampling time 30 s, sampling interval 2 s) after first reduction; (d) reoxidation (-0.90 V, sampling time 30 s, sampling
interval 2 s) after second reduction.
Ta ble 3. Rea ction s of th e Im id o-Br id ged
Coba lta d ith iolen e Com p lex 1 w ith 2 Equ iv of P R3
in Reflu xin g Ben zen e
Sch em e 5
yield/%
basicityb cone angle/
PR3
(pKa)
deg
time/h
3
2a -h
5
a
PPh3
2.73
3.84
1.03
4.59
8.43
9.70
-2.00
2.60
145
145
145
145
136
170
128
107
5
5
5
5
5
5
45
5
44
36
35
0
0
0
0
0
0
0
95
0
35
34
48
31
0
80
62
55
P(p-C6H4Me)3
P(p-C6H4Cl)3
P(p-C6H4OMe)3
PBu3
isolated in quantitative yield. This result, similar to the
result of the reaction at room temperature (Table 1),
suggests that complex 2g is thermally stable at 80 °C.
In addition, although P(p-C6H4OMe)3 reacted with
complex 1 under the same conditions, only complex 5
was formed (Table 3). P(C6F5)3 did not react with
complex 1 because of its low nucleophilicity.
PCy3
P(OPh)3
P(OMe)3
27
0
0
20
a
b
Reference 7. The Brønsted basicities of the phosphorus(III)
compounds (pKa values of R3PH+).
We assume that the imido migration is also influenced
by the basicities of the PR3 ligands. In the case of PR3
having stronger basicity (or nucleophilicity), the Co-P
bond also becomes thermally stable. As a result, the
imido group is eliminated due to the S-N bond cleavage
before the Co-P bond can cleave. We assume that the
imido elimination from the sulfilimine complex 2 pre-
vents the imido migration to the Cp ring, because this
migration is intramolecular.12 For the imido migration,
the Co-P bond cleavage may conceivably occur before
the S-N bond cleavage, or both bond cleavages may be
simultaneous. In the reaction of complex 2g under
refluxing xylene, this reaction only gave [CpCo{S2C2-
(COOMe)2}(PBu3)] due to the only S-N bond cleavage
in 80% yield (Scheme 5). This reaction also supports that
the Co-P bond cleaves first for the imido migration. The
bond strength of the Co-P bond was also examined by
the electrochemistry of complexes 2a -h in this work.
We conclude that the basicity (or nucleophilicity) of PR3
is one of the important parameters for the imido
migration.
tion band corresponds to that of [CpCo{S2C2(COOMe)2}]
(5).24 The yield of complex 5 based on the spectral
changes was 50%. These spectroelectrochemical data
support our speculation based on the CV data of complex
2a .
3. Rea ctivities of th e Su lfilim in e Com p lexes:
Migr a tion Rea ction s to th e Cp Rin g. The reactions
of complex 1 with 2 equiv of PR3 were attempted with
heating. In these reactions, the sulfilimine complexes
are first formed. The products, yields, basicities, and
cone angles13 of PR3 are shown in Table 3. The reaction
of complex 1 with PPh3 or P(OPh)3 has been previously
reported to give the amide-substituted Cp complex
[(C5H4-NHTs)Co{S2C2(COOMe)2}] (3)7,12 as a migration
product and complex 5 (Scheme 2). In this work,
complex 1 reacted with 2 equiv of P(p-C6H4Me)3 or P(p-
C6H4Cl)3 in refluxing benzene to also give complex 3 in
36% or 35% yield, respectively (Scheme 2 and Table 3).
In the reaction of complex 1 with PBu3 in refluxing
benzene, the corresponding sulfilimine complex 2g was
Werner et al. have proposed a mechanism for the
migratory insertion of a carbene ligand into the C-H
(24) Kajitani, M.; Suetsugu, T.; Wakabayashi, R.; Igarashi, A.;
Akiyama, T.; Sugimori, A. J . Organomet. Chem. 1985, 293, C15.

1310 Organometallics, Vol. 23, No. 6, 2004
Nomura et al.
Sch em e 6
Ta ble 4. Rea ction s of Im id o-Br id ged
Coba lta d ith iolen e Com p lex 1 w ith Va r iou s
Am ou n ts of P R3 in Reflu xin g Ben zen e
bond of the Cp ring.18d Their report says that the
reaction of [CpRh(dCPh2)(PiPr3)] with PF3 gives [(C5H4-
CHPh2)Rh(PiPr3)(PF3)] as a migration product. Ligand
displacement reactions of [CpRhL2] with Lewis bases
L′ are known to follow second-order kinetics.25 A rea-
sonable assumption is that a labile 1:1 adduct is formed
from [CpRh(dCPh2)(PiPr3)] and PF3. A slippage of the
carbene ligand to the temporarily generated η3-C5H5
unit affords the migration product [(C5H4-CHPh2)Rh(Pi-
Pr3)(PF3)]. We assume that the mechanism of the imido
migration is similar to that of this carbene migration
via a η3-C5H5 intermediate.
The reaction of complex 1 with PCy3 under refluxing
benzene gave only complex 5 in good yield (Table 3).
Although PCy3 is as basic as PBu3, the cone angle of
PCy3 (θ ) 170°) is larger than that of PBu3 (θ ) 136°).
The cone angle of a phosphorus ligand is related to the
stability of the sulfilimine complex rather than to the
imido migration. On the other hand, trimesitylphos-
phine, P(C6H2Me3)3, which has a larger cone angle (θ )
212°) than that of PCy3, did not react with complex 1
due to steric hindrance.
yield/%
PR3
amt/equiv time/h
4
3
2a ,c,d
5
a
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
2
1
5
5
5
18
5
18
5
trace 44
0
0
28
0
20
0
0
35
31
29
47
trace
58
34
34
34
0
0
0
0
44
31
36
trace
3
0.5
0.5
0.2
0.2
5
0
12
17
42
29
10
5
0
P(p-C6H4Me)3
P(p-C6H4Me)3
P(p-C6H4Cl)3
P(p-C6H4Cl)3
2
10
2
5
5
5
5
trace 36
0
0
0
0
18
0
34
35
37
15
48
38
10
0
a
Reference 7.
slower and a lower yield of complex 3 was obtained.
Therefore, 1 equiv of PPh3 is necessary to obtain
complex 3 efficiently, and a large excess of PPh3 ef-
ficiently gives complex 4a .
The effects of various phosphines were examined in
the formation of the disubstituted Cp complex 4. The
reactions of complex 1 with a large excess of P(p-C6H4-
OMe)3 or PBu3 did not form complexes 3 and 4, and
finally results similar to those shown in Table 3 were
obtained. The reaction of complex 1 with 10 equiv of
P(p-C6H4Me)3 gave complex 3 and the corresponding
disubstituted Cp complex [{C5H3(NTs)(P(p-C6H4Me)3)}-
Co{S2C2(COOMe)2}] (4c). However, a large excess of
P(p-C6H4Cl)3 only gave complex 3, and the disubstituted
Cp complex was not formed (Table 4). These results
suggest that the basicity (or nucleophilicity) of phos-
phine is also one of the important parameters in the
formation of the disubstituted Cp complex. According
to a similar procedure, the NMs- and PPh3-substituted
Cp complex [{C5H3(NMs)(PPh3)}Co{S2C2(COOMe)2}]
(4a ′) was synthesized by the reaction of the imido adduct
[CpCo{S2C2(COOMe)2}(NMs)]7 with a large excess of
PPh3. The 31P NMR signals of complexes 4a ′ and 4c
appeared at 23.0 and 23.3 ppm, respectively. These 31P
NMR signals are similar to those of a typical phospho-
nium salt (PPh4+I-, 22.0 ppm) and complex 4a (23.4
ppm) previously reported.12 This result suggests that
complexes 4a ′ and 4c also have a triarylphosphonium
cyclopentadienyl ligand.26
We also attempted the reactions of complex 1 with
other trivalent ligands, such as phosphite, amine, ar-
sine, and stibine. Although the reaction of complex 1
with P(OMe)3 did not form the migration product 3
under refluxing benzene, the sulfilimine complexes 2h
and 5 were obtained (Table 3). The sulfilimine complex
2h was thermally more stable than complex 2a , al-
though P(OMe)3 has a basicity similar to that of PPh3.
We assume that the bond pattern of a phosphite ligand
with the cobalt is different from that of a phosphine
ligand. This suggestion is supported by the δ value shifts
of 31P NMR spectra of complexes 2a -h (see Table 1).
The difference can be explained by the difference in
back-donation from cobalt to the phosphorus ligand. On
the other hand, NEt3, NPh3, AsPh3, and SbPh3 did not
react with complex 1. These results indicate that
complex 1 only reacts with a trivalent phosphorus
compound.
According to our previous report, the reaction of
complex 1 with a large excess of PPh3 with heating gave
not only complex 3 but also the disubstituted Cp
complex [{C5H3(NTs)(PPh3)}Co{S2C2(COOMe)2} (4a )12
(Scheme 6). The reactions of complex 1 with various
amounts of PPh3 were examined (Table 4). Although a
larger amount of PPh3 gave a higher yield of complex
4a than did 1 equiv of PPh3, a lower yield of complex 3
was obtained than when 1 equiv of PPh3 was used. The
reaction of complex 1 with 1 equiv of PPh3 gave complex
3 and did not give complex 4a . In the reaction of complex
1 with 0.5 equiv of PPh3, the reaction rate became
Con clu sion s
The imido-bridged cobaltadithiolene adduct 1 reacts
with PPh3 and P(OPh)3 to give the sulfilimine complexes
(26) (a) Tresoldi, G.; Recca, A. Finocchiaro, P.; Faraone, F. Inorg.
Chem. 1981, 20, 3103. (b) Watanabe, M.; Sato, M.; Takayama, T.
Organometallics 1999, 18, 5201.
(25) (a) Basolo, F. Inorg. Chim. Acta 1985, 100, 33. (b) Rerek, M.
E.; Basolo, F. J . Am. Chem. Soc. 1984, 106, 5908.

Cobaltadithiolene Complexes
Organometallics, Vol. 23, No. 6, 2004 1311
atmosphere. Cyclic voltammograms were measured on a CV-
50W instrument by BAS Co. Visible absorption spectra during
electrolysis were measured on MCPD-7000 and MC-2530
instruments by Otsuka Electronics Co., Ltd.
Rea ction s of Com p lex 1 w ith P R 3 a t Room Tem p er a -
tu r e. A solution of complex 1 (50 mg, 0.1 mmol) and PR3 (0.2
mmol, PR3 ) P(p-C6H4Me)3, P(p-C6H4Cl)3, PCy3, P(p-C6H4-
OMe)3, PBu3, P(OMe)3) in dichloromethane (10 mL) was stirred
at room temperature for 5 min. After the solvent was removed
under reduced pressure, the residue was separated by column
chromatography. Products 2c-h were obtained as brown solids
in quantitative yields. The yields of products are summarized
in Table 1.
R ea ct ion s of Com p lex 1 w it h 2 E q u iv of P R 3 w it h
Hea tin g. A solution of complex 1 (50 mg, 0.1 mmol) and PR3
(0.2 mmol, PR3 ) P(p-C6H4Me)3, P(p-C6H4Cl)3, PCy3, P(p-C6H4-
OMe)3, PBu3, P(OMe)3) in benzene (10 mL) was refluxed for 5
h. After the solvent was removed under reduced pressure, the
residue was separated by column chromatography. Product
37,12 was obtained as a purple solid, and products 2f-h were
obtained as brown solids. The yields of products are sum-
marized in Table 3.
CpCo[S(NTs)SC2(COOMe)2](PR3) (PR3 ) PPh3 (2a ),
P(OPh)3 (2b)) at room temperature, and these complexes
undergo the imido migration to the Cp ring when
heated.7,12 In this work, the reactions of complex 1 with
other PR3 species quantitatively gave the corresponding
sulfilimine complexes 2c-h at room temperature. How-
ever, these sulfilimine complexes 2c-h were not always
intermediates in the imido migration. The imido migra-
tion was influenced by the basicities (nucleophilicities)
of PR3 ligands. Sulfilimine complexes containing strongly
nucleophilic PR3 ligands (e.g. PR3 ) PBu3) were ther-
mally stable because of the strong Co-P bond, and the
nonelimination of PR3 ligands prevents the imido mi-
gration. In the case of PR3 having weaker basicity (e.g.
PR3 ) P(C6F5)3), the sulfilimine complex was not
formed, due to its low nucleophilicity. The phosphines
having pKa ) 1.03-3.84 (PR3 ) PPh3, P(p-C6H4Me)3,
P(p-C6H4Cl)3) were required in the imido migration. In
addition, the cone angles of phosphines were only
correlated with the thermal stability of the sulfilimine
complex.
Rea ction s of Com p lex 1 w ith Va r iou s Am ou n ts of P R3.
A solution of complex 1 (50 mg, 0.1 mmol) and PR3 (PR3
)
The elimination of PR3 was confirmed by the inves-
tigation of the electrochemical behavior of the sulfil-
imine complexes 2a -h . The sulfilimine complexes 2a -h
showed two opposite trends in a first reduction process.
One is the elimination of a PR3 ligand by the first
reduction of the sulfilimine complexes (PR3 ) PPh3,
P(OPh)3, P(p-C6H4Me)3, P(p-C6H4Cl)3, PCy3, P(p-C6H4-
OMe)3), and the other is the nonelimination of the PR3
ligand; that is, the reductants of the sulfilimine com-
plexes (PR3 ) PBu3, P(OMe)3) are stable. These trends
revealed the different strengths of the Co-P bonds of
the sulfilimine complexes. The basicities and the cone
angles of PR3 ligands also influenced the electrochemical
behavior of the sulfilimine complexes.
In the formation of the disubstituted Cp complex, the
amounts and the basicity values of phosphines were
important parameters. A large excess of phosphine
efficiently gave the disubstituted Cp complex. Only
phosphines having pKa ) 2.73-3.84 (PR3 ) PPh3, P(p-
C6H4Me)3) were required.
PPh3, P(p-C6H4Me)3, P(p-C6H4Cl)3) in benzene (10 mL) was
refluxed for 5 h. After the solvent was removed under reduced
pressure, the residue was separated by thin-layer chromatog-
raphy (silica gel 60) and then the product was further
separated by HPLC. Products 4a and 4c were obtained as blue
crystalline solids. In these reactions, complex 37,12 was formed
as a migration product and complex 5 was also formed. The
yields of products are summarized in Table 4.
Complex 4a ′ was synthesized by the reaction of [CpCo{S2C2-
(COOMe)2}(NMs)]7 with 10 equiv of PPh3 under the same
reaction conditions. The separation of complex 4a ′ was also
achieved by the same method, and product 4a ′ was obtained
as a blue crystalline solid in 25% yield. The amide-substituted
Cp complex [(C5H4-NHMs)Co{S2C2(COOMe)2}]7 as a migration
product and complex 5 were also obtained in 23% and 31%
yields, respectively.
CV Mea su r em en ts. CV measurements were done in 1
mmol dm-3 acetonitrile solutions of complexes containing 0.1
mol dm-3 tetraethylammonium perchlorate (TEAP) at 25 °C.
A stationary platinum disk (1.6 mm in diameter) was used as
a working electrode. A coiled platinum wire served as a counter
electrode. The reference electrode is Ag|AgNO3 corrected for
junction potentials by being referenced internally to the
ferrocene/ferrocenium (Fc|Fc+) couple.
Exp er im en ta l Section
All reactions were carried out under an argon atmosphere
by means of standard Schlenk techniques. Solvents were
purified by ketyl distillation before use. The phosphines and
phosphites were used without further purification. The cobalt-
adithiolene complexes [CpCo{S2C2(COOMe)2}] (5) were pre-
pared by literature methods.27 Silica gel (Wakogel C-300) was
obtained from Wako Pure Chemical Industries, Ltd. Thin-layer
chromatography plates filled with silica gel 60 (20 × 20 cm,
0.25 mm thick) were obtained from Merck J apan Ltd. HPLC
was performed on an LC-908 instrument produced by J apan
Analytical Industry Co. Mass and IR spectra were recorded
on J EOL J MS-D300 and Shimadzu FTIR 8600PC instruments,
respectively. NMR spectra were measured with a J EOL LA500
spectrometer. UV-vis spectra were recorded on a Hitachi UV-
2500PC instrument. Elemental analyses were determined by
using a Shimadzu PE2400-II instrument. Melting points were
measured on a Yanaco Micro melting point apparatus. All
electrochemical measurements were performed under an argon
Visible Absor p tion Sp ectr a l Mea su r em en ts d u r in g
Electr olysis. Visible absorption spectra during electrolysis
were obtained for 1 mmol dm-3 acetonitrile solutions of
complexes containing 0.1 mol dm-3 TEAP at 25 °C in an
optically transparent thin-layer electrode cell (OTTLE, thin-
layer thickness 0.4 mm) by using a Photal MCPD-7000 rapid
scan spectrometer. The working electrode was stationary
platinum mesh. A coiled platinum wire served as a counter
electrode. The reference electrode is Ag|AgNO3 corrected for
junction potentials by being referenced internally to the
ferrocene/ferrocenium (Fc|Fc+) couple.
Cp Co[S(NTs)SC2(COOMe)2][P (p -C6H 4Me)3] (2c). Mp:
134-135 °C dec. Mass (FAB+, 70 eV): m/z 804 (M+ + 1), 500
(M+ - P(p-C6H4Me)3 + 1). 1H NMR (500 MHz, CDCl3, vs
TMS): δ 7.78 (d, J ) 8.43 Hz, 2H, Ar), 7.56 (broad, 6H, Ar),
7.25 (broad, 6H, Ar), 7.18 (d, J ) 8.43 Hz, 2H, Ar), 5.36 (s,
5H, Cp), 3.67 (s, 3H, OMe), 2.71 (s, 3H, OMe), 2.38 (s, 9H,
Me), 2.37 (s, 3H, Me). 31P NMR (200 MHz, CDCl3, vs 85% H3-
PO4): δ 33.2 (P(p-C6H4Me)3). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1
cm-1)): 495 (3400), 369 (11 000). IR (KBr disk; cm-1): 1734,
1699, 1528, 1431, 1252, 1130, 1082, 920.
(27) Boennemann, H.; Bogdanovic, B.; Brijoux W.; Brinkmann, R.;
Kajitani, M.; Mynott, R.; Natarajan, G. S.; Samson, M. G. Y. Transition
Metal-Catalyzed Synthesis of Heterocyclic Compounds. In Catalysis
in Organic Reactions; Kosak, J . R., Ed.; Marcel Dekker: New York,
1984; pp 31-62.
Cp Co[S(NTs)SC2(COOMe)2][P (p -C6H 4Cl)3] (2d ). Mp:
121-122 °C dec. Mass (FAB+, 70 eV; m/z): 866 (M+(37Cl) +

1312 Organometallics, Vol. 23, No. 6, 2004
Nomura et al.
1), 864 (M+(35Cl) + 1), 500 (M+ - P(p-C6H4Cl)3 + 1). H NMR
(500 MHz, CDCl3, vs TMS): δ 7.73 (d, J ) 8.28 Hz, 2H, Ar),
7.60 (broad, 6H, Ar), 7.46 (broad, 6H, Ar), 7.20 (d, J ) 8.28
Hz, 2H, Ar), 5.41 (s, 5H, Cp), 3.68 (s, 3H, OMe), 2.79 (s, 3H,
OMe), 2.38 (s, 3H, Me). 31P NMR (200 MHz, CDCl3, vs 85%
H3PO4): δ 35.6 (P(p-C6H4Cl)3). UV-vis (CH2Cl2; λmax, nm (ꢀ,
M-1 cm-1)): 475 (2600), 369 (8300). IR (KBr disk; cm-1): 1732,
1701, 1531, 1431, 1252, 1130, 1082, 922.
M-1 cm-1)): 471 (2900), 371 (11 000). IR (KBr disk; cm-1):
1734, 1699, 1433, 1254, 1132, 1020, 932.
1
[{C5H3(NMs)(P P h 3)}Co{S2C2(COOMe)2}] (4a′). Mp: 219-
1
220 °C dec. Mass (FAB+, 70 eV, NBA; m/z): 684 (M+ + 1). H
NMR (500 MHz, CDCl3, vs TMS): δ 7.62-7.93 (m, 15H, Ph),
6.50 (1H, Cp), 5.31 (1H, Cp), 5.02 (1H, Cp), 3.80 (s, 6H, OMe),
2.55 (s, 3H, Me). 13C NMR (125 MHz, CDCl3, vs TMS): δ 165.6,
154.1, 140.5, 140.4, 134.91, 134.88, 134.76, 134.68, 130.0,
129.9, 119.1, 118.4, 78.1, 78.0, 77.9, 68.1, 68.0, 57.5, 52.6, 36.5.
31P NMR (200 MHz, CDCl3, vs 85% H3PO4): δ 23.0 (PPh3). IR
(KBr disk; cm-1): 1701, 1497, 1246, 1109. UV-vis (CH2Cl2;
Cp Co[S(NTs)SC2(COOMe)2](P Cy3) (2e). Mp: 114-115 °C
1
dec. H NMR (500 MHz, CDCl3, vs TMS): δ 7.78 (d, J ) 8.07
Hz, 2H, Ar), 7.19 (d, J ) 8.07 Hz, 2H, Ar), 5.64 (s, 5H, Cp),
3.83 (s, 3H, OMe), 2.95 (s, 3H, OMe), 2.36 (s, 3H, Me), 1.22-
2.09 (m, 33H, Cy). 31P NMR (200 MHz, CDCl3, vs 85%
H3PO4): δ 32.5 (PCy3). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1
cm-1)): 516 (2700), 367 (11 000). IR (KBr disk; cm-1): 2926,
2851, 1734, 1699, 1526, 1431, 1248, 1132, 1084, 932.
λ
max, nm (ꢀ, M-1 cm-1)): 745 (1500), 578 (5800), 294 (22 000).
Anal. Calcd for C30H27NO6PS3Co‚CH2Cl2: C, 48.44; H, 3.80.
Found: C, 48.80; H, 3.82.
[{C5H 3(NTs)(P (p -C6H 4Me)3)}Co{S2C2(COOMe)2}] (4c).
Mp: 140-141 °C; 228-229 °C dec. Mass (FAB+, 70 eV, NBA;
m/z): 802 (M+ + 1). 1H NMR (500 MHz CDCl3, vs TMS): δ
7.75 (d, J ) 5.19 Hz, 6H, Ar), 7.36 (d, J ) 5.19 Hz, 6H, Ar),
7.41 (d, J ) 8.24 Hz, 2H, Ar), 6.94 (d, J ) 8.24 Hz, 2H, Ar),
6.20 (1H, Cp), 5.25 (1H, Cp), 4.81 (1H, Cp), 3.80 (s, 6H, OMe),
2.48 (s, 9H, Me), 2.23 (s, 3H, Me). 31P NMR (200 MHz, CDCl3,
vs 85% H3PO4): δ 23.3 (P(p-C6H4Me)3). IR (KBr disk; cm-1):
1701, 1477, 1234, 1140. UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1
cm-1)): 772 (1500), 585 (5900), 294 (23 000). Anal. Calcd for
Cp Co[S(NTs)SC2(COOMe)2][P (p-C6H4OMe)3] (2f). Mp:
124-125 °C dec. Mass (FAB+, 70 eV; m/z): 851 (M+), 500 (M+
1
- P(p-C6H4OMe)3 + 1). H NMR (500 MHz, CDCl3, vs TMS):
δ 7.79 (d, J ) 8.28 Hz, 2H, Ar), 7.60 (broad, 6H, Ar), 7.19 (d,
J ) 8.28 Hz, 2H, Ar), 6.95 (broad, 6H, Ar), 5.37 (s, 5H, Cp),
3.84 (s, 9H, OMe), 3.67 (s, 3H, OMe), 2.71 (s, 3H, OMe), 2.37
(s, 3H, Me). 31P NMR (200 MHz, CDCl3, vs 85% H3PO4): δ
32.0 (P(p-C6H4OMe)3). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)):
489 (3400), 369 (16 000). IR (KBr disk; cm-1): 1732, 1697,
1593, 1431, 1259, 1126, 1022, 935.
C
39H37NO6PS3Co‚CH2Cl2: C, 54.18; H, 4.43. Found: C, 53.94;
H, 4.80.
Cp Co[S(NTs)SC2(COOMe)2](P Bu 3) (2g). Mp: 50-51 °C.
1
Mass (FAB+, 70 eV; m/z): 702 (M+ + 1). H NMR (500 MHz,
Ack n ow led gm en t. The present work was supported
CDCl3, vs TMS): δ 7.86 (d, J ) 8.14 Hz, 2H, Ar), 7.24 (d, J )
8.14 Hz, 2H, Ar), 5.35 (s, 5H, Cp), 3.75 (s, 3H, OMe), 2.95 (s,
3H, OMe), 2.39 (s, 3H, Me), 1.40-1.62 (m, 18H, Bu), 0.97 (t, J
) 7.39 Hz, 9H, Bu). 31P NMR (200 MHz, CDCl3, vs 85% H3-
PO4): δ 49.4 (PBu3). UV-vis (CH2Cl2; λmax, nm (ꢀ, M-1 cm-1)):
378 (12 000). IR (KBr disk; cm-1): 2957, 2932, 2872, 1734,
1701, 1526, 1431, 1252, 1130, 1084, 928.
by the Sasakawa Scientific Research Grant, by the
grant-in-aid for Scientific Research No. 14740369, and
by the grants-in-aid on Priority Area-Researches on
‘Interelements’ Nos. 09239246 and 11120251 from the
Ministry of Education, Science, Sports and Culture,
J apan.
Cp Co[S(NTs)SC2(COOMe)2][P (OMe)3] (2h ). Mp: 69-70
°C dec. Mass (FAB+, 70 eV; m/z): 624 (M+ + 1), 500 (M+
-
Su p p or tin g In for m a tion Ava ila ble: Figures giving 1H
NMR spectra as evidence of the purity of complexes 2c-h . This
material is available free of charge via the Internet at
http://pubs.acs.org.
P(OMe)3 + 1). 1H NMR (500 MHz, CDCl3, vs TMS): δ 7.87 (d,
J ) 8.39 Hz, 2H, Ar), 7.25 (d, J ) 8.39 Hz, 2H, Ar), 5.44 (s,
5H, Cp), 4.02 (d, J ) 10 Hz, 9H, Me), 3.76 (s, 3H, OMe), 2.99
(s, 3H, OMe), 2.40 (s, 3H, Me). 31P NMR (200 MHz, CDCl3, vs
85% H3PO4): δ 122.8 (P(OMe)3). UV-vis (CH2Cl2; λmax, nm (ꢀ,
OM034127J