H. Shimakoshi, S. Yonemura, and Y. Hisaeda (Kyushu University)
The Co
I species of the cobalamin derivative (B
12) is widely known as a supernucleophile that forms an alkylated complex by reaction with an alkyl halide. The alkylated complex is a useful reagent for forming radical species as the cobalt-carbon bond is readily cleaved homolytically.
1 Our research interest is focused on the application of this catalytic system to various molecular transformations.
2 Recently, we have reported the unique catalysis of the cobalamin derivative (B
12)-titanium oxide (TiO
2) hybrid catalyst in which the B
12 complex, cyanoaquacobyrnic acid (Co
III oxidation state), is immobilized on the surface of TiO
2 and the B
12 complex is reductively activated to form the Co
I species by electron transfer from TiO
2 under UV-light irradiation.
3 The hybrid catalyst mediated the dehalogenation of various organic halides and was applied to the radical-mediated organic reaction via an alkylated complex as a catalytic intermediate. Though the great advantage of the catalyst is the facile and efficent formation of Co
I species by light irradiation, UV light irradiation was required for band gap excitation of TiO
2 semiconductor. To overcome this problem, we synthesized new B
12-TiO
2 hybrid catalyst (B
12-TiO
2-Cat) composed of interfacial complexation with catechol as shown in
Figure 1a. As a charge transfer band ascribed to catechol to TiO
2 appear in visible region,
4 this new hybrid catalyst is expected to work under visible light irradiation. Futhermore, exploiting the interparticle electron transfer process in the B
12-TiO
2 and Cat-TiO
2 combination system as shown in
Figure 1b was investigated.
References:
1. (a) Brown, K. L. Chem. Rev., 2005, 105, 2075; (b) Hisaeda, Y.; Shimakoshi, H., in Handbook of Porphyrin Science, Kadish, K. M.; Smith, K. M.; Guilard, R., Eds. World Scientific: Singapore, 2010; Vol. 10, pp 313-370.
2. (a) Jing, X.; Shimakoshi, H.; Hisaeda, Y. J. Organomet. Chem., 2015, in press; (b) Zhang, W.; Shimakoshi, H.; Houfuku, N.; Song, M.; Hisaeda, Y. Dalton Trans., 2014, 2014, 43, 13972.
3. Shimakoshi, H.; and Hisaeda, Y. et al, (a) ChemPlusChem, 2014, 79, 1250-1253 (Back cover article); (b) Chem. Commun., 2011, 6427-6429; (c) Dalton Trans, 2010, 39, 3302-3307; (d) Chem. Lett., 2009, 38, 468-469; (e) Bull. Chem. Soc. Jpn., 2010, 83, 170-172.
4. (a) Ikeda, S.; Abe, C.; Torimoto, T.; Ohtani, B. J. Photochem. Photobiol. A: Chem. 2003, 160, 61; (b) Tae, E. L.; Lee, S. H.; Lee, J. K.; Yoo. S. S.; Kang, E. J.; Yoon, K. B. J. Phys. Chem. B 2005, 109, 22513; (c) Varaganti, S.; Ramakrishna G. J. Phys. Chem. C 2010, 114, 13917; (d) Kamegawa, T. Seto, H.; Matsuura, S.; Yamashita, H. ACS Appl. Mater. Interfaces, 2012, 4, 6635.
