Photo-Triggered Hydrophosphination of Azoarenes: An Additive-Free Methodology

We report the first hydrophosphination of azoarenes using tunable silylphosphanes under mild conditions. This transformation has been achieved by utilizing UV light, without employing any catalyst or additives. The developed protocol shows very good functional group tolerance, giving good to excellent yields of 1-(diarylphosphaneyl)-1,2-diphenylhydrazine derivatives, P(III) species. Moreover, good regioselectivity was achieved for the unsymmetrically substituted azoarenes. Control experiments and theoretical calculations reveal that the reaction proceeds via a radical pathway.