In most cases,the redox activity of a U^(Ⅵ)O_(2)^(2+) complex is regarded as metal-centered phenomena,because uranium has small energy gaps amongst the 5f/6d/7s subshells,thereby exhibiting a wide range of oxidation ...In most cases,the redox activity of a U^(Ⅵ)O_(2)^(2+) complex is regarded as metal-centered phenomena,because uranium has small energy gaps amongst the 5f/6d/7s subshells,thereby exhibiting a wide range of oxidation states,commonly from+Ⅲ to+Ⅵ or in some cases even+I or+Ⅱ.While a wide variety of redox-active ligands are known for use as transition metal complexes including multi-electron reduction that could facilitate inert bond or small molecule activation,only a few such examples are known for U^(Ⅵ)O_(2)^(2+).In this study,three U^(Ⅵ)O_(2)^(2+)complexes bearing α-diimine-,o-quinonediimine-and 2,6-diiminopyridine-based ligands were synthesized,which exhibited two redox couples in the range of−0.79 V to−2.02 V vs.Fc+/0 to give singly-and doubly-reduced complexes by stepwise reduction.Unique electronic transitions of U^(Ⅵ)O_(2)^(2+) complexes with a variety of low-lying excited states helped us to combine spectroelectrochemistry and time-dependent density functional theory(TD-DFT)calculations which complemented each other to assign the redox-active site in these U^(Ⅵ)O_(2)^(2+) complexes,i.e.,whether or not a ligand of interest becomes redox-active.During all the redox processes observed here,the ligands employed are found to be exclusively redox-active,i.e.,non-innocent,whereas the centered U^(Ⅵ)O_(2)^(2+) is just“spectating”and remains unchanged,i.e.,innocent.Whereas the double reduction of the U^(Ⅵ)O_(2)^(2+) complexes usually involves breaking of strong UuO bonds,in the present examples this is not required and therefore a basis for the synthesis of new types of uranium molecular catalysts and magnetic materials may be found.展开更多
基金supported in part by the Grants-in-Aid for Scientific Research(Grant No.20H02663 to KT,and 21J11942 to TT)of the Japan Society for the Promotion for Science(JSPS)the JAEA Nuclear Energy S&T and the Human Resource Development Project through concentrating wisdom(Grant No.JPJA19P19209861)the International Research Frontiers Initiative(IRFI)of Institute of Innovative Research,Tokyo Institute of Technology.
文摘In most cases,the redox activity of a U^(Ⅵ)O_(2)^(2+) complex is regarded as metal-centered phenomena,because uranium has small energy gaps amongst the 5f/6d/7s subshells,thereby exhibiting a wide range of oxidation states,commonly from+Ⅲ to+Ⅵ or in some cases even+I or+Ⅱ.While a wide variety of redox-active ligands are known for use as transition metal complexes including multi-electron reduction that could facilitate inert bond or small molecule activation,only a few such examples are known for U^(Ⅵ)O_(2)^(2+).In this study,three U^(Ⅵ)O_(2)^(2+)complexes bearing α-diimine-,o-quinonediimine-and 2,6-diiminopyridine-based ligands were synthesized,which exhibited two redox couples in the range of−0.79 V to−2.02 V vs.Fc+/0 to give singly-and doubly-reduced complexes by stepwise reduction.Unique electronic transitions of U^(Ⅵ)O_(2)^(2+) complexes with a variety of low-lying excited states helped us to combine spectroelectrochemistry and time-dependent density functional theory(TD-DFT)calculations which complemented each other to assign the redox-active site in these U^(Ⅵ)O_(2)^(2+) complexes,i.e.,whether or not a ligand of interest becomes redox-active.During all the redox processes observed here,the ligands employed are found to be exclusively redox-active,i.e.,non-innocent,whereas the centered U^(Ⅵ)O_(2)^(2+) is just“spectating”and remains unchanged,i.e.,innocent.Whereas the double reduction of the U^(Ⅵ)O_(2)^(2+) complexes usually involves breaking of strong UuO bonds,in the present examples this is not required and therefore a basis for the synthesis of new types of uranium molecular catalysts and magnetic materials may be found.
