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Construction of multinuclear heterobimetallic conjugated complex systems
Synthetic Metals 106 Ž1999. 67–70 www.elsevier.comrlocatersynmet
Short communication
Construction of multinuclear heterobimetallic conjugated complex systems Toshikazu Hirao ) , Satoshi Yamaguchi, Shinya Fukuhara Department of Applied Chemistry, Faculty of Engineering, Osaka UniÕersity, Yamada-oka, Suita, Osaka 565-0871, Japan Received 10 March 1999; received in revised form 6 May 1999; accepted 19 May 1999
Abstract The controlled complexation of the emeraldine base of polyŽ o-toluidine. with two different transition metals, CuŽOAc. 2 and PdŽOAc. 2 , was achieved in organic solvent to afford the multinuclear heterobimetallic conjugated complexes. The complexation was monitored spectroscopically.
The structure was found to depend on the complexation mode. q 1999 Elsevier Science S.A. All rights reserved. Keywords: p-Conjugated complex; Heterobimetallic complex; Polyaniline
1. Introduction Heterobimetallic complexes are of potential in redox reactions and materials synthesis and the intermetallic interaction through a p-conjugated spacer have drawn much attention recently w1–4x. Multicoordination to a pconjugated organic molecule possessing relevant redox function permits the construction of multi-redox systems with electronic communication between metals through the p-conjugated spacer. Complexation with a p-conjugated polymer has been demonstrated to afford the corresponding system in a previous paper w5,6x. Copper salt contributes to the formation of a reversible redox cycle of
undoped polyanilines w7x. Polyanilines or polypyrroles are able to be utilized as a redox-active ligand in the Wacker reaction w8,9x. The controlled complexation of p-conjugated polymers with square-planar palladiumŽII. complexes has been achieved to afford the structurally defined d,p-conjugated complexes w10x. Another subject to be addressed is the introduction of different metals to a p-conjugated polymer, which is considered to allow intermetallic interaction between different metals. We herein report the controlled complexation of polyŽ o-toluidine. in organic solvent to give multinuclear heterobimetallic conjugated complexes ŽScheme 1..
) Corresponding author. Tel.: q81-6879-7413; fax: q81-6879-7415; E-mail: [email protected]
0379-6779r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 1 0 7 - 1
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T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
2. Experimental 2.1. Preparation of poly(o-toluidine) PolyŽ o-toluidine. was prepared by chemical oxidation of o-toluidine with ammonium persulfate according to the reported procedure w11x, followed by deprotonation with 1 N NaOH aq. Although the thus-obtained polymer was mostly soluble in THF, the insoluble polymer was removed by filtration. Reprecipitation from hexane gave the polymer Žnumber average molecular weight, ca. 3000 by GPC. used in this paper. Elemental analysis ŽC 7.00 H 6.72N0.98 . indicated the emeraldine base structure consisting of the amine and imine moieties at ca. 1:1 ratio. 2.2. Preparation of poly(o-toluidine)-copper complex A solution of polyŽ o-toluidine. Ž1.30 mg. in THF Ž250 ml. was treated with a solution of CuŽOAc. 2 in THF at room temperature for 20 min under argon to give the spectra as shown in Fig. 1. The titration curve for plots of absorption vs. copper unitro-toluidine unit is illustrated in Fig. 2. The complex 1 was isolated as follows. To a solution of polyŽ o-toluidine. Ž10.45 mg. in THF Ž10 ml. was dropwise added a solution of CuŽOAc. 2 Ž2.73 mg, 0.015 mmol. in THF Ž10 ml. at room temperature under argon. Stirring was continued for an additional 1 h. The reaction mixture was filtrated and the complex 1 was washed with THF and hexane. 1: IR ŽKBr. 1560, 1475, 1308, 1205, 1156, and 1097 cmy1 .
Fig. 2. The curve for plots of D l versus the ratio of CuŽOAc. 2 and o-toluidine unit.
and an aqueous AgrAgq reference electrode at 100 mV sy1 scan rate. The solution of the complex 1 was obtained by treatment of polyŽ o-toluidine. Ž5.20 mg. with a solution of CuŽOAc. 2 Ž1.25 mM. in THF Ž50 ml. at room temperature for 30 min under argon. Potentials are not corrected for the junction potential. For a 1.0 mM THF solution of ferrocene, the E1r2 value was 0.62 V with 0.26 V peak separation.
2.3. Measurement of cyclic Õoltammetry Cyclic voltammograms were obtained in a THF solution containing 0.1 M Bu 4 NClO4 as a supporting electrolyte at room temperature under argon ŽFig. 3.. Potentials were determined with a three-electrode system consisting of a glassy carbon electrode, a platinum auxiliary electrode,
Fig. 1. UV–vis spectra in THF. Ža. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M. Žb. o-Toluidine unit:CuŽOAc. 2 s100:12.
Fig. 3. Cyclic voltammograms in THF under argon. wTBAPx s 0.1 M, scan rate: 100 mV sy1 . Ža. PolyŽ o-toluidine., w o-toluidine unitx s1=10y3 M. Žb. PolyŽ o-toluidine.-CuŽOAc. 2 , w o-toluidine unitx s1=10y3 M. oToluidine unit:CuŽOAc. 2 s100:12.
T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
69
2.4. Preparation of poly(o-toluidine)-bimetallic complexes A solution Ž2.5 ml. of polyŽ o-toluidine. Ž1.05 mg. in THF Ž200 ml. was treated with a solution Ž3.1 ml. of PdŽOAc. 2 Ž2.24 mg, 0.01 mmol. in THF Ž5 ml. at room temperature for 20 min under argon. The spectrum is shown in Fig. 4. Then, a solution Ž11.3 ml. of CuŽOAc. 2 Ž1.82 mg, 0.01 mmol. in THF Ž5 ml. was added to the thus-obtained solution at room temperature. The mixture was kept at the same temperature for 20 min. The resulting spectrum is also shown in Fig. 4. The procedure for the reverse addition of CuŽOAc. 2 and PdŽOAc. 2 was carried out similarly as shown in Fig. 5.
Fig. 5. UV–vis spectra in THF. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M Žsolid.. o-Toluidine unit:CuŽOAc. 2 s100:6 Ždash.. o-Toluidine unit:CuŽOAc. 2 :PdŽOAc. 2 s100:6:45 Ždashrdot..
3. Results and discussion The complexation with copper and palladium compounds was investigated to form the complex mentioned above. For this purpose, the complexation behavior with CuŽOAc. 2 was first monitored spectroscopically, in addition to the reported results of the complexation with palladiumŽII. compounds w10x. Treatment of the emeraldine base Žthe amine and imine moieties at ca. 1:1 ratio. of polyŽ o-toluidine. in THF with a THF solution of CuŽOAc. 2 shifted the broad absorption of polyŽ o-toluidine. around 590 nm, assignable to the CT band between the benzenoid and quinoid, to 545 nm ŽFig. 1.. This blue shift is in sharp contrast to the behavior with the palladiumŽII. species although the difference has not been clear. The titration curve indicated a ratio of 1:0.15 for the o-toluidine unit and copper unit, suggesting more than pentacoordination to copper ŽFig. 2.. The corresponding cross-linked d,p-conjugated complex 1 is considered to be formed. In the cyclic voltammetry of the solution of the thus-obtained polymer complex 1, a new oxidation wave was
detected around 0.65 V vs. AgrAgq with the increase of the current value on repetition of scans ŽFig. 3.. A similar increase was observed only with polyŽ o-toluidine., possibly due to further polymerization of polyŽ o-toluidine. probably on electrode by electrolysis. The heterobimetallic polymer complex was obtained by the following procedure. After treatment of polyŽ o-toluidine. with 5r100 equivalent of PdŽOAc. 2 , 18r100 equivalent of CuŽOAc. 2 were added to the solution of the preformed palladium complex. In these processes, the red shift of the CT absorption of polyŽ o-toluidine. was first observed, followed by the blue shift in UV–vis spectra ŽFig. 4.. These spectral changes are consistent with the individual complexation. The network d,p-conjugated palladiumŽII. complex underwent the above mentioned crosslinking with copperŽII. species, forming the multinuclear heterobimetallic complex consisting of palladium and copper. The reverse addition of CuŽOAc. 2 and PdŽOAc. 2 gave the different spectra as shown in Fig. 5. Of course, these spectral changes do not contradict the results shown in Fig. 4. The coordination number of copper and palladium is different, giving the different structure of the preformed complex in each case. The doubly cross-linked complex appears to be formed in this complexation process. The structure depends on the complexation mode.
4. Conclusion
Fig. 4. UV–vis spectra in THF. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M Žsolid.. o-Toluidine unit:PdŽOAc. 2 s100:5 Ždash.. o-Toluidine unit:PdŽOAc. 2 :CuŽOAc. 2 s100:5:18 Ždashrdot..
The multinuclear heterobimetallic conjugated complexes are allowed to be constructed by successive complexation of a p-conjugated polymer with different transition metals. These complexes are expected to be of potential utility as catalysts and materials.
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T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
Acknowledgements The use of the facilities of the Analytical Center, Faculty of Engineering, Osaka University is acknowledged. This work was partially supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture, Japan, and the Japan Securities Scholarship Foundation.
References w1x F. Garnier, Angew. Chem., Int. Ed. Engl. 28 Ž1989. 513. w2x J.-P. Sauvage, J.-P. Collin, J.-C. Chambron, S. Guillerez, C. Coudret,
w3x w4x w5x w6x w7x w8x w9x w10x w11x
V. Balzani, F. Barigelletti, L. De Cola, L. Flamigni, Chem. Rev. 94 Ž1994. 993. M.-a. Haga, M. Ali, R. Arakawa, Angew. Chem., Int. Ed. Engl. 35 Ž1996. 76. A. Harriman, R. Ziessel, Chem. Commun. 1996, 1707. T. Hirao, M. Higuchi, I. Isao, Y. Ohshiro, J. Chem. Soc., Chem. Commun., 1993, 194. M. Higuchi, I. Ikeda, T. Hirao, J. Org. Chem. 62 Ž1997. 1072. M. Higuchi, D. Imoda, T. Hirao, Macromolecules 29 Ž1996. 8277. T. Hirao, M. Higuchi, B. Hatano, I. Ikeda, Tetrahedron Lett. 36 Ž1995. 5925. M. Higuchi, S. Yamaguchi, T. Hirao, Synlett, 1996, 1213. T. Hirao, S. Yamaguchi, S. Fukuhara, Tetrahedron Lett. 40 Ž1999. 3009. A.G. MacDiarmid, J.C. Chiang, A.F. Richter, N.D.L. Somasiri, in: L. Alcacer ŽEd.., Conducting Polymers, Reidel Publ., 1987, 105.
Short communication
Construction of multinuclear heterobimetallic conjugated complex systems Toshikazu Hirao ) , Satoshi Yamaguchi, Shinya Fukuhara Department of Applied Chemistry, Faculty of Engineering, Osaka UniÕersity, Yamada-oka, Suita, Osaka 565-0871, Japan Received 10 March 1999; received in revised form 6 May 1999; accepted 19 May 1999
Abstract The controlled complexation of the emeraldine base of polyŽ o-toluidine. with two different transition metals, CuŽOAc. 2 and PdŽOAc. 2 , was achieved in organic solvent to afford the multinuclear heterobimetallic conjugated complexes. The complexation was monitored spectroscopically.
The structure was found to depend on the complexation mode. q 1999 Elsevier Science S.A. All rights reserved. Keywords: p-Conjugated complex; Heterobimetallic complex; Polyaniline
1. Introduction Heterobimetallic complexes are of potential in redox reactions and materials synthesis and the intermetallic interaction through a p-conjugated spacer have drawn much attention recently w1–4x. Multicoordination to a pconjugated organic molecule possessing relevant redox function permits the construction of multi-redox systems with electronic communication between metals through the p-conjugated spacer. Complexation with a p-conjugated polymer has been demonstrated to afford the corresponding system in a previous paper w5,6x. Copper salt contributes to the formation of a reversible redox cycle of
undoped polyanilines w7x. Polyanilines or polypyrroles are able to be utilized as a redox-active ligand in the Wacker reaction w8,9x. The controlled complexation of p-conjugated polymers with square-planar palladiumŽII. complexes has been achieved to afford the structurally defined d,p-conjugated complexes w10x. Another subject to be addressed is the introduction of different metals to a p-conjugated polymer, which is considered to allow intermetallic interaction between different metals. We herein report the controlled complexation of polyŽ o-toluidine. in organic solvent to give multinuclear heterobimetallic conjugated complexes ŽScheme 1..
) Corresponding author. Tel.: q81-6879-7413; fax: q81-6879-7415; E-mail: [email protected]
0379-6779r99r$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 1 0 7 - 1
68
T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
2. Experimental 2.1. Preparation of poly(o-toluidine) PolyŽ o-toluidine. was prepared by chemical oxidation of o-toluidine with ammonium persulfate according to the reported procedure w11x, followed by deprotonation with 1 N NaOH aq. Although the thus-obtained polymer was mostly soluble in THF, the insoluble polymer was removed by filtration. Reprecipitation from hexane gave the polymer Žnumber average molecular weight, ca. 3000 by GPC. used in this paper. Elemental analysis ŽC 7.00 H 6.72N0.98 . indicated the emeraldine base structure consisting of the amine and imine moieties at ca. 1:1 ratio. 2.2. Preparation of poly(o-toluidine)-copper complex A solution of polyŽ o-toluidine. Ž1.30 mg. in THF Ž250 ml. was treated with a solution of CuŽOAc. 2 in THF at room temperature for 20 min under argon to give the spectra as shown in Fig. 1. The titration curve for plots of absorption vs. copper unitro-toluidine unit is illustrated in Fig. 2. The complex 1 was isolated as follows. To a solution of polyŽ o-toluidine. Ž10.45 mg. in THF Ž10 ml. was dropwise added a solution of CuŽOAc. 2 Ž2.73 mg, 0.015 mmol. in THF Ž10 ml. at room temperature under argon. Stirring was continued for an additional 1 h. The reaction mixture was filtrated and the complex 1 was washed with THF and hexane. 1: IR ŽKBr. 1560, 1475, 1308, 1205, 1156, and 1097 cmy1 .
Fig. 2. The curve for plots of D l versus the ratio of CuŽOAc. 2 and o-toluidine unit.
and an aqueous AgrAgq reference electrode at 100 mV sy1 scan rate. The solution of the complex 1 was obtained by treatment of polyŽ o-toluidine. Ž5.20 mg. with a solution of CuŽOAc. 2 Ž1.25 mM. in THF Ž50 ml. at room temperature for 30 min under argon. Potentials are not corrected for the junction potential. For a 1.0 mM THF solution of ferrocene, the E1r2 value was 0.62 V with 0.26 V peak separation.
2.3. Measurement of cyclic Õoltammetry Cyclic voltammograms were obtained in a THF solution containing 0.1 M Bu 4 NClO4 as a supporting electrolyte at room temperature under argon ŽFig. 3.. Potentials were determined with a three-electrode system consisting of a glassy carbon electrode, a platinum auxiliary electrode,
Fig. 1. UV–vis spectra in THF. Ža. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M. Žb. o-Toluidine unit:CuŽOAc. 2 s100:12.
Fig. 3. Cyclic voltammograms in THF under argon. wTBAPx s 0.1 M, scan rate: 100 mV sy1 . Ža. PolyŽ o-toluidine., w o-toluidine unitx s1=10y3 M. Žb. PolyŽ o-toluidine.-CuŽOAc. 2 , w o-toluidine unitx s1=10y3 M. oToluidine unit:CuŽOAc. 2 s100:12.
T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
69
2.4. Preparation of poly(o-toluidine)-bimetallic complexes A solution Ž2.5 ml. of polyŽ o-toluidine. Ž1.05 mg. in THF Ž200 ml. was treated with a solution Ž3.1 ml. of PdŽOAc. 2 Ž2.24 mg, 0.01 mmol. in THF Ž5 ml. at room temperature for 20 min under argon. The spectrum is shown in Fig. 4. Then, a solution Ž11.3 ml. of CuŽOAc. 2 Ž1.82 mg, 0.01 mmol. in THF Ž5 ml. was added to the thus-obtained solution at room temperature. The mixture was kept at the same temperature for 20 min. The resulting spectrum is also shown in Fig. 4. The procedure for the reverse addition of CuŽOAc. 2 and PdŽOAc. 2 was carried out similarly as shown in Fig. 5.
Fig. 5. UV–vis spectra in THF. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M Žsolid.. o-Toluidine unit:CuŽOAc. 2 s100:6 Ždash.. o-Toluidine unit:CuŽOAc. 2 :PdŽOAc. 2 s100:6:45 Ždashrdot..
3. Results and discussion The complexation with copper and palladium compounds was investigated to form the complex mentioned above. For this purpose, the complexation behavior with CuŽOAc. 2 was first monitored spectroscopically, in addition to the reported results of the complexation with palladiumŽII. compounds w10x. Treatment of the emeraldine base Žthe amine and imine moieties at ca. 1:1 ratio. of polyŽ o-toluidine. in THF with a THF solution of CuŽOAc. 2 shifted the broad absorption of polyŽ o-toluidine. around 590 nm, assignable to the CT band between the benzenoid and quinoid, to 545 nm ŽFig. 1.. This blue shift is in sharp contrast to the behavior with the palladiumŽII. species although the difference has not been clear. The titration curve indicated a ratio of 1:0.15 for the o-toluidine unit and copper unit, suggesting more than pentacoordination to copper ŽFig. 2.. The corresponding cross-linked d,p-conjugated complex 1 is considered to be formed. In the cyclic voltammetry of the solution of the thus-obtained polymer complex 1, a new oxidation wave was
detected around 0.65 V vs. AgrAgq with the increase of the current value on repetition of scans ŽFig. 3.. A similar increase was observed only with polyŽ o-toluidine., possibly due to further polymerization of polyŽ o-toluidine. probably on electrode by electrolysis. The heterobimetallic polymer complex was obtained by the following procedure. After treatment of polyŽ o-toluidine. with 5r100 equivalent of PdŽOAc. 2 , 18r100 equivalent of CuŽOAc. 2 were added to the solution of the preformed palladium complex. In these processes, the red shift of the CT absorption of polyŽ o-toluidine. was first observed, followed by the blue shift in UV–vis spectra ŽFig. 4.. These spectral changes are consistent with the individual complexation. The network d,p-conjugated palladiumŽII. complex underwent the above mentioned crosslinking with copperŽII. species, forming the multinuclear heterobimetallic complex consisting of palladium and copper. The reverse addition of CuŽOAc. 2 and PdŽOAc. 2 gave the different spectra as shown in Fig. 5. Of course, these spectral changes do not contradict the results shown in Fig. 4. The coordination number of copper and palladium is different, giving the different structure of the preformed complex in each case. The doubly cross-linked complex appears to be formed in this complexation process. The structure depends on the complexation mode.
4. Conclusion
Fig. 4. UV–vis spectra in THF. Undoped polyŽ o-toluidine., w o-toluidine unitx s 5.0=10y5 M Žsolid.. o-Toluidine unit:PdŽOAc. 2 s100:5 Ždash.. o-Toluidine unit:PdŽOAc. 2 :CuŽOAc. 2 s100:5:18 Ždashrdot..
The multinuclear heterobimetallic conjugated complexes are allowed to be constructed by successive complexation of a p-conjugated polymer with different transition metals. These complexes are expected to be of potential utility as catalysts and materials.
70
T. Hirao et al.r Synthetic Metals 106 (1999) 67–70
Acknowledgements The use of the facilities of the Analytical Center, Faculty of Engineering, Osaka University is acknowledged. This work was partially supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture, Japan, and the Japan Securities Scholarship Foundation.
References w1x F. Garnier, Angew. Chem., Int. Ed. Engl. 28 Ž1989. 513. w2x J.-P. Sauvage, J.-P. Collin, J.-C. Chambron, S. Guillerez, C. Coudret,
w3x w4x w5x w6x w7x w8x w9x w10x w11x
V. Balzani, F. Barigelletti, L. De Cola, L. Flamigni, Chem. Rev. 94 Ž1994. 993. M.-a. Haga, M. Ali, R. Arakawa, Angew. Chem., Int. Ed. Engl. 35 Ž1996. 76. A. Harriman, R. Ziessel, Chem. Commun. 1996, 1707. T. Hirao, M. Higuchi, I. Isao, Y. Ohshiro, J. Chem. Soc., Chem. Commun., 1993, 194. M. Higuchi, I. Ikeda, T. Hirao, J. Org. Chem. 62 Ž1997. 1072. M. Higuchi, D. Imoda, T. Hirao, Macromolecules 29 Ž1996. 8277. T. Hirao, M. Higuchi, B. Hatano, I. Ikeda, Tetrahedron Lett. 36 Ž1995. 5925. M. Higuchi, S. Yamaguchi, T. Hirao, Synlett, 1996, 1213. T. Hirao, S. Yamaguchi, S. Fukuhara, Tetrahedron Lett. 40 Ž1999. 3009. A.G. MacDiarmid, J.C. Chiang, A.F. Richter, N.D.L. Somasiri, in: L. Alcacer ŽEd.., Conducting Polymers, Reidel Publ., 1987, 105.