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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
Published on: October 5, 2019
A Lewis-acidic anion enhances energy transfer from excited cationic photocatalysts to basic substrates
Ryo Mandai1, Yuri Oyama2, Takanori Iwasaki1,2
1Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku Tokyo Japan nozaki@chembio.t.u-tokyo.ac.jp.
Abstract:
Anions are inherently basic, and the use of counteranions of photocatalysts in substrate activation relies heavily on the Brønsted-basic nature of the anions. Here we present ion-paired dual catalysis using Ru(bpy)3 2+ with a stable, strongly Lewis-acidic, yet non-nucleophilic anion BBcat. BBcat captures Lewis-basic substrates at the tricoordinated catechol borane (Bcat) centers and keeps them in close proximity to Ru(bpy)3 2+, affording chemoselective and concentration-independent rate enhancement. In [2+2] photocycloaddition of pyridyl enones, Ru(bpy)3(BBcat)2 affords 8.7-times higher yield than Ru(bpy)3(BArF)2, and product selectivity is reversed in competitive reactions with a simple chalcone. Quenching experiments and NMR studies confirmed that BBcat facilitates substrate capture by acid-base interactions and the proximity of the ion pair by electrostatic interactions.
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