Substrate-Rhodium Cooperativity in Photoinduced ortho-Alkynylation of Arenes

In the realm of metallaphotocatalytic C-H activation strategy, the direct excitation of the transition metal which plays the dual role of light energy harnessing alongside performing the bond breaking and forming is a rare phenomenon. In this context we have developed the first photo-induced Rh-catalyzed ortho-alkynylation under ambient conditions without the requirement of silver salt, photocatalyst (PC) or any engineered substrate or catalyst. The transformation functions by the specific cooperative effect of a six-membered rhodacycle which is the photo-responsive species. The catalytic system allows the conjugation of arenes with sp(3)-rich pharmacophoric fragments. The control experiments as well as the computational studies resolve the mechanistic intricacies for this transformation. An outer sphere electron transfer process from Rh to alkynyl radical is operative for the present photoinduced transformation over the more common oxidative addition or 1,2-migratory insertion pathways.