Electrochemical behavior of nickeladithiolene S,S′-dialkyl adducts: Evidence for the formation of a metalladithiolene radical by electrochemical redox reactions

Article abstract of DOI:10.1021/ic034402u

The electrochemical behavior of nickeladithiolene S,S′-dialkyl adducts (alkyl = benzyl, methyl, tert-butyl) was investigated by using cyclic voltammetry (CV), visible, near-IR, and ESR spectroscopies and bulk electrolyses. The redox potentials of the S,S′-dialkyl adducts were influenced by the electron-donating effect of the functional group on the sulfur atoms. The nickeladithiolene S,S′-dibenzyl adduct [Ni{S(SCH ₂Ph)C₂Ph₂}₂] (2) eliminated one benzyl radical by one-electron reduction, and then the monobenzyl adduct anion [Ni(S₂C₂Ph₂){S₂(CH ₂Ph)C₂Ph₂}]^- (3^-) was formed. Anion 3^- was also formed by the reaction of nickeladithiolene dianion [Ni(S₂C₂Ph₂) ₂]^2- (1^2-) with 1 equiv of benzyl cation. When anion 3^- was oxidized, the long-lived nickeladithiolene radical [Ni(S₂C₂Ph₂){S₂(CH ₂Ph)C₂Ph₂}] (3) was formed. The visible, near-IR, and ESR spectra of radical 3 could be measured and assigned. When radical 3 was further oxidized, the oxidant 3⁺ eliminated one benzyl cation, and then free nickeladithiolene (1) was generated.

Full text of DOI:10.1021/ic034402u

Inorg. Chem. 2003, 42, 6441−6446
Electrochemical Behavior of Nickeladithiolene S,S′-Dialkyl Adducts:
Evidence for the Formation of a Metalladithiolene Radical by
Electrochemical Redox Reactions
Mitsushiro Nomura, Chikako Takayama,† and Masatsugu Kajitani*
Department of Chemistry, Faculty of Science and Technology, Sophia UniVersity,
7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
Received April 16, 2003
The electrochemical behavior of nickeladithiolene S,S′-dialkyl adducts (alkyl ) benzyl, methyl, tert-butyl) was
investigated by using cyclic voltammetry (CV), visible, near-IR, and ESR spectroscopies and bulk electrolyses. The
redox potentials of the S,S′-dialkyl adducts were influenced by the electron-donating effect of the functional group
on the sulfur atoms. The nickeladithiolene S,S′-dibenzyl adduct [Ni{S(SCH Ph)C Ph2}2] (2) eliminated one benzyl
2
2
radical by one-electron reduction, and then the monobenzyl adduct anion [Ni(S C Ph2){S (CH Ph)C Ph2}]- (3-)
2
2
2
2
2
was formed. Anion 3- was also formed by the reaction of nickeladithiolene dianion [Ni(S C Ph2)2]2- (12-) with 1
2
2
equiv of benzyl cation. When anion 3- was oxidized, the long-lived nickeladithiolene radical [Ni(S C Ph2){S (CH -
2
2
2
2
Ph)C Ph2}] (3) was formed. The visible, near-IR, and ESR spectra of radical 3 could be measured and assigned.
2
When radical 3 was further oxidized, the oxidant 3+ eliminated one benzyl cation, and then free nickeladithiolene
(1) was generated.
Introduction
the two sulfur atoms rather than on the center metal. (In this
paper, such adducts are described as S,S′-adducts.)
Recently, Wang and Stiefel have reported that the nickel-
adithiolene complex with electron-withdrawing groups even
reacts with simple olefins to give olefin-bound S,S′-adducts.
They proposed that it is reversible olefin binding controlled
electrochemically. When the olefin-bound adduct is reduced,
the reductant dissociates and forms an olefin and the
metalladithiolene anion. When this anion is oxidized, the
oxidant (neutral complex) binds the olefin again. This
reversible olefin binding is proposed as a separation and
purification system of an olefin gas.4 Quite recently, the
cycloaddition of a simple olefin and the structure of the olefin
adduct have also been investigated by theoretical studies.5
Geiger has reinvestigated the electrochemical behavior of
the norbornene-bridged nickeladithiolene S,S′-adduct. This
adduct similarly dissociates norbornene by an electrochemical
reduction.6
Many studies of square planar metalladithiolene complexes
have been reported.1 These complexes are interesting because
of their unique redox and optical properties and “noninno-
cent” properties. The reactivities of metalladithiolene com-
plexes are also well-known. The metalladithiolene ring
undergoes electrophilic and radical substitution reactions due
to its aromaticity.2 The aromaticity can be also explained
by noting that this ring has delocalized 6π electrons and
exhibits π-π* transitions (in the near-IR area). Such a
metalladithiolene complex undergoes cycloaddition by the
reactions with an olefin and a conjugated diene, forming the
metalladithiolene adducts.3 This reaction always occurs on
* 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.
(1) Reviews: (a) Schrauzer, G. N. Acc. Chem. Res. 1969, 2, 72. (b)
McCleverty, J. A. Prog. Inorg. Chem. 1969, 10, 49. (c) Burns, R. P.;
Mcauliffe, C. A. AdV. Inorg. Chem. Radiochem. 1979, 22, 303. (d)
Kisch, H. Coord. Chem. ReV. 1993, 125, 155.
(3) (a) Schrauzer, G. N.; Meyweg, V. P. J. Am. Chem. Soc. 1965, 87,
1483. (b) Wing, R. M.; Tustin, G. C.; Okamura, W. H. J. Am. Chem.
Soc. 1970, 92, 1935. (c) Herman, A.; Wing, R. M. J. Organomet.
Chem. 1973, 63, 441. (d) Clark, G. R.; Waters, J. M.; Whittle, K. R.
J. Chem. Soc., Dalton Trans. 1973, 821.
(4) Wang, K.; Stiefel, E. I. Science 2001, 291, 106.
(5) Fan, Y.; Hall, M. B. J. Am. Chem. Soc. 2002, 124, 12076.
(6) Geiger, W. E. Inorg. Chem. 2002, 41, 136.
(2) (a) Kajitani, M.; Hagino, G.; Tamada, M.; Fujita, T.; Sakurada, M.;
Akiyama, T.; Sugimori, A. J. Am. Chem. Soc. 1996, 118, 489. (b)
Sugimori, A.; Tachiya, N.; Kajitani, M.; Akiyama, T. Organometallics
1996, 15, 5664. (c) Sugimori, A.; Akiyama, T.; Kajitani, M.; Sugiyama,
T. Bull. Chem. Soc. Jpn. 1999, 72, 879.
10.1021/ic034402u CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/05/2003
Inorganic Chemistry, Vol. 42, No. 20, 2003 6441

Nomura et al.
Scheme 1
Many metalladithiolene S,S′-adducts lead to photodisso-
Table 1. Redox Potentials (vs Fc/Fc+)a
ciation. The norbornene-bridged S,S′-adducts of metalla-
dithiolene complexes, [M(S2C2R2)2(C7H8)] (M ) Ni, Pd, Pt;
C7H8 ) norbornene), lead to photodissociation in dichlo-
romethane solution,7 forming free metalladithiolene complex
and norbornadiene. The norbornene-bridged S,S′-adduct of
platinum complex shows emission in benzene solution.8 On
the other hand, the metalladithiolene S,S′-dibenzyl adducts,9
[M{S(SCH2Ph)C2Ph2}2] (M ) Ni, Pd, Pt), eliminate one
benzyl radical by photodissociation, and then the long-lived
metalladithiolene radical10 [M(S2C2Ph2){S2(CH2Ph)C2Ph2}]
is formed (Scheme 1). This unique complex radical has a
lifetime on the order of 103 s; it is further converted to free
nickeladithiolene complex by a thermal dissociation.
complex
temp
rt
rt
rt
rt
rt
1st redn E1/2/V
1st oxidn E1/2/V
1
2
3
4
5
6
-0.51r
-1.74ir
-0.54r
-1.76r
-1.83ir
-1.88r
0.78ir
0.38ir
0.30ir
0.36ir
0.34r
0.34r
-40 °C
a rt: room temperature. r: reversible wave. ir: irreversible wave. E1/2
) (Ep + Ep/2)/2.
We focused on the electrochemical behavior of the
nickeladithiolene S,S′-dialkyl adducts [M{S(SR)C2Ph2}2] (R
) benzyl,10 methyl,11 and tert-butyl). Some of these adducts
dissociated by electrochemical redox reactions, and the
metalladithiolene radical was also observed in this work. This
paper describes in detail the electrochemical behavior of S,S′-
dialkyl adducts and the formation mechanisms of long-lived
metalladithiolene radicals by electrochemical redox reactions.
Results and Discussion
The cyclic voltammetry (CV) of the nickeladithiolene S,S′-
dialkyl adducts [Ni{S(SCH2Ph)C2Ph2}2] (2), [Ni{S(SMe)C2-
Ph2}2] (4), and [Ni{S(S-t-Bu)C2Ph2}2] (5) and of the free
nickeladithiolene complex [Ni(S2C2Ph2)2] (1)3a,12 was mea-
sured (Figures 1a-e). The redox potentials of these com-
plexes are shown in Table 1. The reduction potentials of all
adducts were more negative than that of complex 1. Although
free nickeladithiolene complex 1 showed two reversible
reduction waves (E1/2 ) -0.51 and -1.33 V), all of the
adducts showed only one reduction wave in the potential
window of dichloromethane containing TBAP. The redox
potentials of nickeladithiolene S,S′-dialkyl adducts were
influenced by the electron-donating effect of the functional
group on the sulfur atom.
Figure 1. (a-e) Cyclic voltammograms (V ) 100 mV‚s-1, Φ ) 1.6 mm
Pt disk) of 1 mM (a, b) complex 2, (c) complex 4, (d) complex 5, and (e)
complex 1.
(7) Kajitani, M.; Kohara, M.; Kitayama, T.; Akiyama, T.; Sugimori, A.
J. Phys. Org. Chem. 1989, 2, 32.
(8) Kunkely, H.; Vogler, A. Inorg. Chim. Acta 2001, 319, 183.
(9) (a) Schrauzer, G. N.; Rabinowiz, H. N. J. Am. Chem. Soc. 1968, 90,
4297. (b) Zhang, C.; Reddy, H. K.; Schlemper, E. O.; Schrauzer, G.
N. Inorg. Chem. 1990, 29, 4100.
(10) (a) Ohtani, M.; Ohkoshi, S.; Kajitani, M.; Akiyama, T.; Sugimori,
A.; Yamauchi, S.; Ohba, Y.; Iwaizumi, M. Inorg. Chem. 1992, 31,
3873. (b) Ohkoshi, S.; Ohba, Y.; Iwaizumi, M.; Yamauchi, S.;
Ohkoshi, M.; Tokuhisa, K.; Kajitani, M.; Akiyama, T.; Sugimori, A.
Inorg. Chem. 1996, 35, 4569. (c) Sugimori, A. Coord. Chem. ReV.
1997, 159, 397.
(11) (a) Schrauzer, G. N.; Zhang, C.; Schlemper, E. O. Inorg. Chem. 1990,
29, 3371. (b) Schrauzer, G. N.; Rabinowitz, H. N. J. Am. Chem. Soc.
1968, 90, 4297.
The CV of complex 2 showed an irreversible reduction
wave (E1/2 ) -1.74 V) and some irreversible oxidation
waves. The oxidation process of complex 2 was complicated,
and the reaction mechanism has not yet been made clear.
The reductant of complex 2 was unstable on the CV time
scale, and it was converted to an unknown species X- by
the following chemical reaction. When the potential was
scanned to positive after the reduction, a reversible reoxi-
dation wave (X/X-) appeared at -0.54 V (Figure 1b).
Therefore, the unknown redox species X- and X were stable
on the CV time scale. This reoxidation wave does not
correspond to the redox wave of complex 1 (Figure 1e).
When the potential was scanned to positive after the
(12) Electrochemical data for complex 1 have been reported: (a) Davison,
A.; Edelstein, N.; Holm, R. H.; Maki, A. H. Inorg. Chem. 1963, 2,
1227. (b) Olson, D. C.; Mayweg, V. P.; Schrauzer, G. N. J. Am. Chem.
Soc. 1966, 88, 4876.
6442 Inorganic Chemistry, Vol. 42, No. 20, 2003

Nickeladithiolene S,S′-Dialkyl Adducts
Scheme 2
Scheme 3
The bulk electrolysis of complex 2 was performed. The
coulometry of complex 2 revealed 1.1 as the number of
electrons/molecule passed in reduction. The bulk electrolysis
of complex 2 in the presence of TEMPO at the same
condition (1.0 F/mol) was also examined. We confirmed the
generation of TEMPO-CH2Ph (Scheme 3). Complex 2 did
not react with TEMPO at all. These results suggest that the
benzyl radical generates by the reduction process of complex
2. In addition, complex 2 was reduced by the bulk electrolysis
at -1.93 V (0.87 F/mol), and then methyl iodide was added
to the solution. The nickeladithiolene adduct [Ni{S2(CH2-
Ph)C2Ph2}{S2(Me)C2Ph2}] was formed. This adduct had one
benzyl group and one methyl group on the sulfur atoms of
the dithiolene ring (Scheme 3). On the other hand, complex
2 did not react with methyl iodide at room temperature. We
assumed that when complex 2 was reduced, the monobenzyl
adduct anion [Ni(S2C2Ph2){S2(CH2Ph)C2Ph2}]- (3-) was
formed. We identified the unknown species X- as anion 3-.
The oxidant of anion 3-, namely, the monobenzyl adduct
[Ni(S2C2Ph2){S2(CH2Ph)C2Ph2}] (3), has already been re-
ported and is known as a long-lived metalladithiolene
radical.10 It can also be formed by the photodissociation of
complex 2.
Figure 2. (a-c) Visible and near-IR spectral changes of complex 2 during
(a) one-electron reduction (-1.90 V, sampling time 2 min, sampling interval
4 s), (b) reoxidation (-0.30 V, sampling time 1 min, sampling interval 2
s), and (c) reoxidation (+0.50 V, sampling time 1 min, sampling interval
2 s) using an OTTLE cell.
formation of X, the irreversible oxidation wave corresponding
to X+/X couple appeared at +0.30 V (Figure 1b). The
unknown species X+ was unstable on the CV time scale.
We attempted in situ measurements of the visible and near-
IR absorption spectra following an electrochemical redox
reaction using an optically transparent thin-layer electrode
(OTTLE) cell. The spectral changes were not remarkable
during the reduction of complex 2. The spectrum of X- was
similar to that of complex 2 (Figure 2a). When the potential
was jumped at -0.30 V, absorption appeared around 950
nm (Figure 2b), and this absorption was assumed to be that
of X as an oxidant of X-. The absorption of X is similar to
that of nickeladithiolene anion 1-. However, the two redox
potentials are different (Figure 1a,e). When the potential was
jumped at +0.50 V, these spectral changes showed more
blue shift than that of X and did not show an isosbestic point
(Figure 2c). The maximum absorption was around 850 nm,
and this absorption corresponds to free nickeladithiolene
complex 1.3a We assume the oxidant X+ was converted to
complex 1 by elimination of the benzyl cation. This
electrochemical behavior is summarized in Scheme 2.
The visible and near-IR absorptions of dithiolene com-
plexes can be distinguished from the π-electron numbers of
the dithiolene ring. The π-electron numbers of the dithiolene
ring in complexes 2 and 3- are same. Furthermore, com-
plexes 1- and 3 have the same number of π-electrons in
dithiolene rings. We have reported the electron counting in
the metalladithiolene rings of complex 3.10b These support
the spectra observed using the OTTLE (Figures 2a-c). The
Inorganic Chemistry, Vol. 42, No. 20, 2003 6443

Nomura et al.
Scheme 4
Scheme 5
Figure 3. ESR spectra after electrolysis of complex 2: (a) observed
spectrum; (b) simulated spectrum of 3.
redox states and the π-electron numbers of dithiolene rings
are shown in Scheme 4.
We also measured the ESR spectrum of radical 3, after
radical 3 was formed by electrolysis. The two signal mixture
of the isotropic spectra appeared (Figure 3). A smaller signal
corresponds to the isotropic spectrum of anion 1- (g )
2.057),12a,13 and a larger signal corresponds to the isotropic
spectrum of radical 3. The g value of radical 3 (2.044) was
the same as that previously reported10 (2.042). This result
also suggests that X is monobenzyl adduct 3, as did the
results of visible and near-IR spectra. We assume that anion
1- was formed by the decomposition of complex 3.
The CVs of complexes 4 and 5 are shown in Figure 1c,d.
The CV of S,S′-dimethyl adduct 4 showed a reversible
reduction wave and three irreversible oxidation waves. The
reductant of complex 4 was stable on the CV time scale.
The oxidation process of complex 4 was complicated.
Complex 5 showed three irreversible oxidation waves. The
second and third oxidation waves corresponded to the
oxidation waves of complex 1. Therefore, when complex 5
was oxidized, the oxidant rapidly eliminated two tert-butyl
groups, and complex 1 was generated. On the other hand,
though the CV of adduct 5 showed a slightly irreversible
reduction wave, a reoxidation wave appeared at -0.55 V.
Therefore, since the electrochemical behavior of complex 5
is similar to that of complex 2, we assumed the formation
of the corresponding metalladithiolene radical [Ni(S2C2-
Ph2){S2(t-Bu)C2Ph2}]. In the CV of complex 5 at -40 °C, a
reversible reduction wave was confirmed. On the other hand,
the reduction wave of complex 2 was irreversible even at
-40 °C. The reductant of complex 5 was stable at low
temperature on the CV time scale. Therefore, the reductant
of complex 5 is more stable than that of complex 2 and less
Figure 4. Cyclic voltammograms (V ) 100 mV‚s-1, Φ ) 1.6 mm Pt
disk) of complex 1 in the presence of benzyl bromide: (a) in two-electron
reduction and reoxidation processes; (b) until measurement limit in a
negative potential window.
stable than that of complex 4. We assumed that the lifetime
of the reductant relates to the stability of an eliminated radical
(stability: benzyl radical > tert-butyl radical > methyl
radical). If a reductant becomes less stable, the radical
eliminated from a reductant becomes more stable (stability:
4- > 5- > 2-).
The CV of complex 1 in the presence of benzyl bromide
(10 equiv) was measured. Although the first reduction wave
(-0.51 V) was reversible, the second reduction wave (-1.33
V) was irreversible (Figure 4a). These results suggest that
dianion 12- reacted with benzyl bromide on the CV time
scale. However, the reduction wave of dibenzyl adduct 2
was not observed (Figure 4b). When the potential was
scanned to positive after the two-electron reduction of
complex 1, two reoxidation waves appeared around -0.54
and +0.3 V. (The former reoxidation wave could be
confirmed as the shoulder of the wave of 1/1-.) These
reoxidation waves correspond to the waves of the redox
couples of 3-/3 and 3/3+. These results suggest that dianion
12- reacts with one benzyl cation to give the anion of
monobenzyl adduct 3- on the CV time scale (Scheme 5).
(13) (a) Bowmaker, G. A.; Boyd, P. D. W.; Campbell, G. K. Inorg. Chem.
1983, 22, 1208. (b) Davison, A.; Edelstein, N.; Holm, R. H.; Maki,
A. H. J. Am. Chem. Soc. 1963, 85, 2029.
6444 Inorganic Chemistry, Vol. 42, No. 20, 2003

Nickeladithiolene S,S′-Dialkyl Adducts
Scheme 6
dianion 12- and complex 2 are also conceivable. However,
the spectra of three species could not be distinguished,
because these complexes contain the same numbers of
π-electrons in the dithiolene ring (see Scheme 4). When the
potential was jumped at -0.10 V, maximum absorptions
appeared around 850 and 950 nm (Figure 5c). These spectra
correspond to those of complexes 1 and 3, respectively. In
this potential, although anion 3- is oxidized to neutral adduct
3, dianion 12- should be also oxidized to neutral complex 1.
It is conceivable that dianion 12- did not completely react
with benzyl cation. In addition, when the potential was
jumped at +0.50 V, the absorption of complex 3 decreased
and the absorption of complex 1 increased (Figure 5d). This
can be explained by the fact that cation 3+ was converted to
complex 1 by the elimination of benzyl cation (Scheme 5).
Conclusion
We investigated the electrochemical behavior of the
nickeladithiolene S,S′-dialkyl adducts (alkyl ) benzyl, meth-
yl, and tert-butyl) using various electrochemical measure-
ments. The S,S′-dibenzyl adduct 2 eliminated one benzyl
radical by one-electron reduction, and then the monobenzyl
adduct anion 3- was formed. Anion 3- was also generated
by the reaction of dianion 12- with one benzyl cation.
Complex 2 can be synthesized by dianion 12- with two
benzyl cations.10 Therefore, anion 3- reacts with another
benzyl cation, and then nickeladithiolene S,S′-dibenzyl adduct
2 is formed. The stepwise formation of complex 2 via
monobenzyl adduct was revealed for the first time in this
work.
When anion 3- was oxidized, the long-lived metalladithi-
olene radical 3 was formed by electrochemical redox
reactions. This complex radical also forms in the photodis-
sociation of S,S′-dibenzyl adduct.10 In addition, when radical
3 was further oxidized, the corresponding cation 3+ became
unstable, and then free nickeladithiolene complex 1 was
formed by the elimination of benzyl cation. Therefore, the
dissociation mechanism of complex 2 was revealed to be a
stepwise process for the first time. The lifetime of the
reductant of S,S′-adduct is influenced by the group on the
sulfur atoms of the dithiolene ring; therefore, if the radical
eliminated from sulfur becomes more stable, the reductant
of the S,S′-dialkyl adduct becomes less stable. Such elec-
trochemical behavior of the nickeladithiolene S,S′-dialkyl
adducts is summarized in Scheme 6.
Figure 5. (a-d) Visible and near-IR spectral changes of complex 1 in
the presence of benzyl bromide during (a) one-electron reduction (-0.90
V, sampling time 1 min, sampling interval 2 s), (b) two-electron reduction
(-1.50 V, sampling time 5 min, sampling interval 2 s), (c) reoxidation
(-0.10 V, sampling time 1 min, sampling interval 2 s) after two-electron
reduction, and (d) reoxidation (+0.50 V, sampling time 1 min, sampling
interval 2 s) after two-electron reduction.
The visible and near-IR absorption spectra of the mixture
of complex 1 with benzyl bromide (10 equiv) were measured
using the OTTLE cell. The spectrum changed to that of anion
1- at -0.90 V, and the spectral changes showed an isosbestic
point around 930 nm (Figure 5a). This result suggests no
reaction of anion 1- with benzyl cation. In a second reduction
at -1.50 V, the absorption based on π-π* transition
disappeared, and then the analogue spectra of anion 3-
appeared (Figure 5b). At this potential, the formations of
Experimental Section
All synthetic reactions were carried out under argon atmosphere
by means of standard Schlenk techniques. Complexes 1, 2, 4, and
Inorganic Chemistry, Vol. 42, No. 20, 2003 6445

Nomura et al.
5 were prepared by literature methods.3a,10b Solvents for chemical
synthesis were dried by CaH2 and distilled before use. Solvents
for electrochemical measurements were dried by molecular sieve
4A before use. The reagents were used without further treatment.
Silica gel and Wakogel C-300 were obtained from Wako Pure
Chemical Industries, Ltd. Mass spectra were recorded on a JEOL
JMS-D300. NMR spectra were measured with a JEOL LA500
spectrometer. All electrochemical measurements were performed
under argon atmosphere. In all electrochemical measurements and
syntheses, a coiled platinum wire served as a counter electrode,
and the reference electrode was Ag|AgCl corrected for junction
potentials by being referenced internally to the ferrocene/ferroce-
nium (Fc|Fc+) couple. Cyclic voltammetry were measured with a
CV-50W of BAS Co. Visible and near-IR absorption spectra during
electrolysis were measured with MCPD-7000 and MC-2530 of
Otsuka Electronics Co., Ltd. ESR spectra were recorded on a JEOL
X-band JES-3X ESR spectrometer. Microwave frequencies and the
magnetic field were directly determined by using a microwave
counter, ADVANTEST TR5212, and a field measurement unit,
JEOL NMR field meter ES-FC-5, respectively.
CV Measurements. CV measurements were done in 1 mmol‚
dm-3 dichloromethane solutions of complexes containing 0.1
mol‚dm-3 tetrabutylammonium perchlorate (TBAP) at 25 °C. A
stationary platinum disk (1.6 mm in diameter) was used as a
working electrode.
Visible Absorption and Near-IR Spectral Measurements
during Electrolysis. The visible and near-IR absorption spectra
during electrolysis were obtained for 1 mmol‚dm-3 dichloromethane
solutions of complexes containing 0.1 mol‚dm-3 TBAP at 25 °C
in an optically transparent thin-layer electrode (OTTLE) cell by
using a Photal MCPD-7000 rapid scan spectrometer. The working
electrode was stationary platinum mesh.
Coulometry Measurement. Coulometry measurements were
done in ca. 0.12 mmol‚dm-3 dichloromethane solutions of com-
plexes containing 0.1 mol‚dm-3 TBAP at 25 °C. A stationary
platinum plate was used as a working electrode.
Radical Trapping by 2,2,6,6-Tetramethylpiperidine N-Oxyl
(TEMPO). The mixture of complex 2 and 100 equiv of TEMPO
as a radical scavenger in dichloromethane solutions containing 0.1
mol‚dm-3 TBAP was subjected to bulk electrolysis (-1.93 V, 1.0
F/mol). A stationary platinum plate was used as a working electrode.
The product was separated by column chromatography on silica
gel. Spectroscopic data for TEMPO-CH2Ph were as follows: GC-
mass (EI+, 1.3 kV) m/z 156 (TEMPO+), 91 (CH2Ph+); mass (FAB+,
70 eV, NBA) m/z 248 (TEMPO - CH2Ph+ + 1), 156 (TEMPO+),
1
91 (CH2Ph+); H NMR (500 MHz, CDCl3) δ 7.26-7.39 (m, 5H,
Ph), 4.83 (s, 2H, CH2), 1.36-1.68 (m, 6H, CH2), 1.26 (s, 6H, Me),
1.15 (s, 6H, Me).
Reaction of Anion 3- with Methyl Iodide. Complex 2 in
dichloromethane solution containing 0.1 mol‚dm-3 TBAP was
subjected to bulk electrolysis. A stationary platinum plate was used
as a working electrode. After the bulk electrolysis (-1.93 V, 0.87
F/mol), 10 equiv of methyl iodide was added to this solution and
the mixture was stirred at room temperature for 20 h. The product
was separated by column chromatography on silica gel and HPLC.
Spectroscopic data for complex [Ni{S2(CH2Ph)C2Ph2}{S2(Me)C2-
Ph2}] were as follows: mass (FAB+, 70 eV, NBA) m/z 649 (M+
1
+ 1); H NMR (500 MHz, CDCl3) δ 6.95-7.49 (m, 25H, Ph),
4.04 (s, 2H, CH2), 2.34 (s, 3H, Me).
Acknowledgment. This work was supported by Grant-
in-Aid for Scientific Research No. 14740369 and by Grants-
in-Aid on Priority Area-Researches on “Interelements” Nos.
09239246 and 11120251 from the Ministry of Education,
Science, Sports, and Culture of Japan.
ESR Spectral Measurements during Electrolysis. ESR spectra
were obtained for ca. 5 mmol‚dm-3 dichloromethane solutions of
complexes containing 0.1 mol‚dm-3 TBAP at 293 K by electrolysis.
IC034402U
6446 Inorganic Chemistry, Vol. 42, No. 20, 2003