species of the cobalamin derivative (B12
) 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 (B12
)-titanium oxide (TiO2
) hybrid catalyst in which the B12
complex, cyanoaquacobyrnic acid (CoIII
oxidation state), is immobilized on the surface of TiO2
and the B12
complex is reductively activated to form the CoI
species by electron transfer from TiO2
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 CoI
species by light irradiation, UV light irradiation was required for band gap excitation of TiO2
semiconductor. To overcome this problem, we synthesized new B12
hybrid catalyst (B12
-Cat) composed of interfacial complexation with catechol as shown in Figure 1a
. As a charge transfer band ascribed to catechol to TiO2
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 B12
combination system as shown in Figure 1b
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.