Photocatalysis of the Pschorr reaction by tris-(2,2′-bipyridyl)ruthenium( II ) in the phenanthrene series

The photocatalytic conversion of the tetrafluoroborate salt of the stilbenediazonium ion (1) into the corresponding phenanthrene (2)(Pschorr reaction) by Ru(bpy)32+(bpy = 2,2′-bipyridyl) has been investigated. We have shown that this particular Pschorr reaction takes place quantitatively with a high quantum yield (φ > 0.4) upon selective photoexcitation of a catalytic amount of Ru(bpy)32+. Quenching and conventional flash photolysis experiments have revealed that quenching of the excited state of Ru(bpy)32+ probably occurs by an electron-transfer process. In contrast it has been shown that direct photolysis of (1) leads to the Pschorr reaction with a poorer yield (10–20%).