Hybrid Organometallo-Silica Catalysts for Sustainable Visible-Light Promoted Olefin Isomerization

The use of visible light as a clean and affordable reagent has turned photocatalysis into a green and powerful tool in synthetic chemistry. However, most of these photocatalytic processes are carried out under homogeneous conditions, which requires expensive catalysts that are difficult to recover and recycle. One way to overcome this problem is to incorporate the visible-active species into porous solid matrices. However, integrating these active species into the matrix to achieve a stable and active heterogeneous photocatalyst is not easy, and has usually been done by post-synthetic strategies. Herein, we describe the use of the highly emissive cyclometalated complex [Ir(dfppy)2(dasipy)]PF6 as a building block for the in-situ synthesis of four different silica-based heterogeneous photocatalysts, and a related post-synthetic grafted material. These highly stable materials have been assessed in the energy transfer photo-isomerization reaction of trans- to cis-stilbene under blue light and mild conditions; showing not only high isomerization yields (ca. 80 %), but also easy recovery and excellent recyclability (up to 100 % after 7 cycles).