Metathesis reaction between hydroxo(tetraphenylporphinato)indium and tetraphenylborate by two-phase reaction: Implication to liquid membrane anion selective electrode

Article abstract of DOI:10.1246/cl.2007.946

The two-phase reaction of [In(OH)(tpp)] (tpp^2-: tetraphenylporphine) with sodium tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate (NaTFPB) gave ion-pairs of a cationic dimer, [In₂(OH)(tpp) ₂]TFPB, and a cationic monomer, [In(tpp)]TFPB. In contrast, a stoichiometric metathesis was observed by the two-phase reaction with sodium tetraphenylborate (NaTPB) giving [In(Ph)(tPP)] and PhB(OH)₂. Copyright

Full text of DOI:10.1246/cl.2007.946

946
Chemistry Letters Vol.36, No.7 (2007)
Metathesis Reaction between Hydroxo(tetraphenylporphinato)indium
and Tetraphenylborate by Two-phase Reaction:
Implication to Liquid Membrane Anion Selective Electrode
Toshiyuki Baba, Yoshio Kanegawa, Takashi Yasui, Kazutake Takada, and Akio Yuchiꢀ
Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555
(Received May 10, 2007; CL-070509; E-mail: yuchi.akio@nitech.ac.jp)
The two-phase reaction of [In(OH)(tpp)] (tpp2ꢁ: tetra-
phenylporphine) with sodium tetrakis[3,5-bis(trifluoromethyl)-
phenyl]borate (NaTFPB) gave ion-pairs of a cationic dimer,
[In2(OH)(tpp)2]TFPB, and a cationic monomer, [In(tpp)]TFPB.
In contrast, a stoichiometric metathesis was observed by the
two-phase reaction with sodium tetraphenylborate (NaTPB)
giving [In(Ph)(tpp)] and PhB(OH)2.
6
5
4
3
2
1
(a)
0.0
0.5
1.0
CTFPB/CIn
1.5
2.0
In preparation of liquid membrane anion-selective elec-
trodes using charged carriers, addition of a lipophilic anion to
the membrane reduces the response induced by the purely elec-
trostatic interaction, while highlighting some other interactions
like hydrogen-bonding and Lewis acid–base reactions.1 The ef-
fects of such ionic additives on the performances of ion-selective
electrodes were discussed in detail.2,3 With some metal–porphy-
rin complexes as the carrier, however, the addition induced an
unexpectedly large potential response or super-Nernstian re-
sponse. Recently, the super-Nernstian response of a gallium
complex to fluoride or an indium complex to chloride was suc-
cessfully explained by the spontaneous formation of a cationic
dimer in the presence of a lipophilic counter anion in the mem-
brane phase and its cleavage by a sample anion.4 The cationic
dimers of gallium and indium have been isolated and structurally
characterized.5 The same phenomena have been reported in oth-
er metal–porphyrin complexes.6–10 The spectral characteristics
of the dimers were appreciably different from the monomeric
species and were effectively utilized for optical sensing of
anions.11,12 These have been reviewed and fully discussed.13
Commonly used as anionic additives are the derivatives of
sodium tetraphenylborate (NaTPB), such as sodium tetra-
kis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB) and potas-
sium tetrakis(p-chlorophenyl)borate (KTCPB).1 Especially,
NaTFPB having high chemical stability and lipophilicity14,15
has almost exclusively been used for porphyrin complexes.9
In this paper, we have examined the two-phase reactions of
[In(OH)(tpp)] (tpp2ꢁ: tetraphenylporphine) complex with sever-
al lipophilic anions as the model for their interactions in the
membrane phase of anion selective electrodes and have found
completely different reaction patterns including an unusual
metathesis reaction.
0
6
(b)
5
4
3
2
1
0.0
0.5
1.0
CDS/CIn
1.5
2.0
ε
0
6
(c)
5
4
3
2
1
0
0.0
0.5
1.0
CTPB/CIn
1.5
2.0
Examination of UV–vis spectra for a series of chloroben-
zene solutions of [In(OH)(tpp)] in a concentration range of
2 ꢂ 10ꢁ5–2 ꢂ 10ꢁ4 mol dmꢁ3 indicated no intermolecular inter-
actions as found for [Zr(OH)2(tpp)].9,16,17 A portion of 2:5 ꢂ
10ꢁ5 mol dmꢁ3 chlorobenzene solution of [In(OH)(tpp)] was
equilibrated with a series of aqueous solutions containing lipo-
philic anions (NaTFPB, NaTPB, and sodium dodecyl sulfate
(NaDS)) at various concentrations and at pH 6.0 buffered by
390 400 410 420 430 440 450 460
wavelength/nm
Figure 1. UV–vis spectral changes by two-phase reactions of
[In(OH)(tpp)] with NaTFPB (a), NaDS (b), and NaTPB (c)
and a molar ratio plot at 428 nm. Organic phase: chlorobenzene
containing 2:5 ꢂ 10ꢁ5 mol dmꢁ3 [In(OH)(tpp)]; aqueous phase:
0{4 ꢂ 10ꢁ5 mol dmꢁ3 lipophilic anion and MES buffer at pH 6.0.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.7 (2007)
947
10ꢁ3 mol dmꢁ3 4-morpholinoethanesulfonate solution. Changes
of absorption spectra are shown in Figure 1, where the apparent
molar absorption coefficients at 428 nm are plotted against the
molar ratio of the lipophilic anion to indium in insertion.
In the reaction with NaTFPB (Figure 1a), a Soret band
of [In(OH)(tpp)] at 428 nm was shifted to a shorter wavelength
of 411.5 nm up to the molar ratio of 0.5 and then to a longer
wavelength of 422.5 nm up to the molar ratio of 1.0. The first
reaction is assigned to the formation of a cationic dimer, based
on the reaction stoichiometry and on the resemblance to the
spectral shift (from 406 to 387 nm) induced by the formation
with water, the same products were obtained immediately. So-
dium hydroxide, phenylboronic acid, or sodium phenylborate
is expected to precipitate or to dissolve into water saturated
in chlorobenzene.
From the viewpoint of sensor development, we suggest the
possibility of undesirable reactions of NaTPB as ionic additives
with metal porphyrin complexes. In this respect, NaDS that
causes neither ion-pair formation nor metathesis is a promising
additive, although the lipophilicity is not so high. From the
viewpoint of organic chemistry, such stoichiometric M–C bond
formation under mild conditions has not been found in literature
by our survey.21 Further studies on the essential factors of this
reaction are in progress in our institute.
of [In2(OH)(oep)2]TFPB (oep2ꢁ
[InCl(oep)].4–6,11–13
: octaethylporphine) from
2½In(OH)(tpp)ꢃo þ NaTFPB
¼ ð[In2(OH)(tpp)2]TFPBÞo þ NaOH
We thank to Prof. Shuki Araki and Dr. Tunehisa Hirashita
for the helpful discussion on the metathesis reaction.
ð1Þ
The hydroxide expelled from the organic phase was accommo-
dated in the aqueous buffer. In contrast, the product of the second
reaction is assigned to the 1:1 ion-pair of [In(tpp)]TFPB.
References and Notes
1
2
3
4
5
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ð[In2(OH)(tpp)2]TFPBÞo þ NaTFPB
¼ 2ð½In(tpp)TFPBꢃÞo þ NaOH
ð2Þ
In the reaction with NaDS (Figure 1b), a Soret band was
shifted only slightly to a shorter wavelength of 424 nm up to
the molar ratio of 1.0. The reaction stoichiometry indicates for-
mation of the 1:1 ion-pair.
P. G. Parzuchowski, J. W. Kamph, E. Rozniecka, Y.
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Chim. Acta 2003, 355, 302.
½In(OH)(tpp)ꢃo þ NaDS ¼ ð[In(tpp)]DSÞo þ NaOH ð3Þ
The absence of a cationic dimer is not clearly reasoned at
this stage but may be related to the less lipophilicity of DSꢁ
than that of TFPBꢁ. The less spectral shift of [In(tpp)]DS from
[In(OH)(tpp)] than [In(tpp)]TFPB suggests a stronger interaction
of [In(tpp)]þ with DSꢁ than with TFPBꢁ.
In contrast to these systems, the reaction with NaTPB
showed a shift of a Soret band to a longer wavelength of
438.5 nm up to the molar ratio of 0.33 (Figure 1c). Unlike the re-
action with NaTFPB, further addition of NaTPB or the reaction
in more acidic media caused no changes. Based on the compar-
ison of the spectrum with those in literature, the product has
been identified as [In(Ph)(tpp)] (ꢀmax ¼ 439 nm, CHCl3).18,19
By taking the reaction stoichiometry, the following metathesis
is expected:
6
7
8
9
E. Malinowska, J. Niedziolka, M. E. Meyerhoff, Anal. Chim.
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´
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16 Use of aliphatic chlorohydrocarbons such as chloroform and
1,2-dichloroethane was avoided because of possible occur-
ring chlorination as found for niobium(V)–tpp complex.10
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3½In(OH)(tpp)ꢃ þ NaB(Ph)4
¼ 3½In(Ph)(tpp)ꢃ þ PhB(OH)2 þ NaOH
ð4Þ
This reaction is confirmed by two more evidences. First, the
same reaction was observed in chloroform; the aqueous phase
showed a series of absorption maxima at 260.5, 265, and
271.5 nm characteristic of phenylboronic acid; tetraphenylborate
1
had no peak in this region.20 Second, H NMR spectral charac-
teristics of the product containing porphyrin [(300 MHz, CDCl3,
ꢁ) 8.99 (s, pyrrole), 8.14 (s, m-ph(py)), 7.77 (br, o-, p-ph(py)),
6.03 (t, p-ph), 5.72 (t, m-ph), 2.98 (d, o-ph)] agreed well with
those of [In(Ph)(tpp)] in literature.18,20
19 K. M. Kadish, B. Boisselier-Cocolios, P. Cocolios, R.
Guilard, Inorg. Chem. 1985, 24, 2139.
The reaction with KTCPB is more complicated. Both 1:1
ion-pair formation and metathesis reactions were observed, but
neither of these reactions proceeded quantitatively at any molar
ratios.20 When these salts of lipophilic anions were directly
added to a solution of [In(OH)(tpp)] in chlorobenzene saturated
20 Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/.
21 Comprehensive Organometallic Chemistry I and II, ed. by
G. Wilkinson, F. G. A. Stone, E. W. Abel, Elsevier Ltd.,
1982 and 1995.
Published on the web (Advance View) June 27, 2007; doi:10.1246/cl.2007.946