5114 Organometallics, Vol. 24, No. 21, 2005
Nomura et al.
son.19 One reduction and one oxidation wave were found
in the potential window of the TBAP-CH2Cl2 solution.
This result is similar to the CV data of [CpNi(dmit)] and
its analogues. From the redox potentials, the substituent
effect of an electron-withdrawing or -donating group was
confirmed. In complexes 2-4, the potential gap (∆E1/2
) |E1/2(ox) - E1/2(red)|) between the first oxidation and
reduction waves is analogous to that of the square-
planar complex 1a (∆E1/2 ) 1.29 V in TBAP-CH2Cl2).
This result explains why the electronic absorption
wavelengths of complexes 2-4 (835-846 nm described
in Table 5) are similar to that of complex 1a (858 nm in
CH2Cl2). These are low-energy electronic absorptions in
the near-IR region. A blue shift of the absorption was
confirmed in complexes 5 (695 nm) and 6 (698 nm) as
compared with complexes 2-4. The redox waves of
complexes 2-5 were reversible, and this result suggests
that the reduced or oxidized species of complexes 2-5
were stable on the CV time scale, but only the oxidation
wave of complex 6 exhibited an irreversible response (v
) 100 mV‚s-1).
The ESR data of the CpNi dithiolene complexes are
shown in Table 5. In toluene solution at room temper-
ature, isotropic ESR signals (g ) 2.041-2.048) were
observed in complexes 2-6. These g values are similar
to that of [CpNi(S2C2(CF3)2)] (g ) 2.0479) previously
reported.32 However, the g values of CpNi dithiolene
complexes are very different from those of the one-
electron-reduced species of CpCo dithiolene complexes,
[CpCoII(S2C2(CF3)2)]- (g ) 2.454)32 and [CpCoII(S2C2-
(CN)2)]- (g ) ca. 2.5).33 The DFT theoretical calculations
of CpNi dithiolene complexes have been reported: the
SOMO (singly occupied molecular orbital) of [CpNi-
(dmit)] is essentially localized on the dithiolene moiety
with little metal contribution.19 In contrast, a strong
spin localization on the central metal is given in
[CpCo(dithiolene)]- complexes.
vs Fc/Fc+). When the oxidation potential is more nega-
tive than -0.42 V, the monoanions [M(S2C2(R1)(R2))2]-
(e.g., M ) Ni; R1, R2 ) Ph) are oxidized by nickeloce-
nium, and then the reaction is not efficient in a polar
solvent. In such cases, the reactions of the neutral
complexes can be performed in a nonpolar solvent (e.g.,
dichloromethane or benzene).
The nickelocene reacts with a 1,2-dithioketone ligand
or with a highly reactive free 1,2-dithioketone. In this
work, we found that the hexacoordinated platinum
complex [Pt(S2C2Ph2)2(dppe)] (1f) is the most efficient
dithioketone source for the synthesis of the CpNi
dithiolene complex (96% yield). In this paper, we
reported a novel dithiolene transfer reaction that uses
complex 1f.
Experimental Section
General Remarks. All reactions were carried out under
an argon atmosphere by means of standard Schlenk tech-
niques. All solvents were dried and distilled by Na-benzophe-
none (for benzene, toluene, and xylene) or CaH2 (for dichlo-
romethane and methanol) before use. The neutral complexes
[M(S2C2Ph2)2] (M ) Ni (1a), Pd (1b), and Pt (1c)),34 [Ni(S2C2-
(Ph)(H))2] (1d),5b and [Ni(S2C2Me2)2] (1e),35 [Pt(S2C2Ph2)2(dppe)]
(1f),36 the monoanions (NBu4)[Ni(S2C2Ph2)2] (1a-),37 (NBu4)-
[Ni(S2C2(Ph)(H))2] (1d-),37 (PPh4)2[Ni(S2C2(COOMe)2)2](I) (1g-),38
and (NBu4)[Ni(S2C2(CN)2)2] (1h-),37 and [Cp2Ni](BF4)39 were
synthesized by literature methods. The monoanion 1d- was a
novel product, and its tetrabutylammonium salt ((NBu4+)[1d-])
was identified by elemental analysis (Anal. Calcd for C32H48N1-
Ni1S4: C, 60.65; H, 7.63; N, 2.21; Found: C, 60.66; H, 7.78; N,
2.27). Nickelocene, which was stored in an inert gas, was
obtained from Strem Chemicals. Dimethyl 1,3-dithiol-2-one-
4,5-dicarboxylate [OdC(S2C2(COOMe)2)]40 and 4-phenyl-1,3-
dithiol-2-one [OdC(S2C2(Ph)(H))]41 were obtained by literature
methods. Dimethyl 1,3-dithiol-2-thione-4,5-dicarboxylate [Sd
C(S2C2(COOMe)2)] was produced by Tokyo Kasei Kogyo Co.,
Ltd. Silica gel (Wakogel C-300) was obtained from Wako Pure
Chemical Industries, Ltd. Mass and IR spectra were recorded
on a JEOL JMS-D300 and a Shimadzu Model FTIR 8600PC
instrument, respectively. UV-vis spectra were recorded on a
Hitachi Model UV-2500PC spectrometer. Elemental analyses
were determined by using a Shimadzu PE2400-II instrument.
Reaction of Nickelocene with the Neutral Square-
Planar Metal Dithiolene Complexes [M(S2C2(R1)(R2))2].
A dichloromethane solution of nickelocene (100 mg, 0.53 mmol)
and the square-planar dithiolene complex [M(S2C2Ph2)2] (M
) Ni (1a), Pd (1b), or Pt (1c), 0.53 mmol) was reacted at room
temperature. After the solvent was removed under reduced
pressure, the residue was separated by column chromatogra-
phy (silica gel, eluent ) dichloromethane). The greenish-brown
residue was purified by recrystallization (n-hexane/dichlo-
romethane). Complex 2 was obtained as a greenish-brown
crystal in 62% (from 1a), 36% (from 1b), or 13% (from 1c) yield,
Conclusion
We developed the convenient syntheses of the CpNi
dithiolene complexes by the reactions of nickelocene
with the neutral square-planar metal dithiolene com-
plexes [M(S2C2(R1)(R2))2] (M ) Ni, Pd, Pt). In the
previous method reported by Faulmann et al., the ionic
complexes (nickelocenium and [Ni(dmit)2]-) have been
used (Scheme 2(a)),18 and Fourmigue´ et al. have used
nickelocenium and [PhSb(dmit)] or [PhSb(dsit)] (Scheme
2(b)),19 but our procedures represent a novel synthetic
method. Since we use only neutral species, syntheses
are also available in a nonpolar solvent.
On the other hand, if we use the square-planar
dithiolene complex having electron-withdrawing sub-
stituents (e.g., R1, R2 ) CN, COOMe), the monoanion
[M(S2C2(R1)(R2))2]- reacts with nickelocenium to pro-
duce the CpNi dithiolene complexes, because this type
of neutral square-planar dithiolene complex is unstable
or is difficult to synthesize.30 This ionic reaction can be
applied when the oxidation potentials of the monoanion
[M(S2C2(R1)(R2))2]- (Table 3) are more positive than the
potential of nickelocene/nickelocenium (E1/2 ) -0.42 V
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