Visible-Light-Induced trans -Hydroboration of Diaryl Alkynes Utilizing Excited State of Borate Complexes.

We have developed visible-light-induced trans -hydroboration of diaryl alkynes via direct photoexcitation of in-situ-generated diboron complexes, affording previously elusive ( E )-1,2-diaryl-vinylboronates with high stereoselectivity. Experimental, spectroscopic, and theoretical mechanistic studies revealed that the triplet-state borate complex facilitates B-B bond cleavage and the desired C-B bond formation. This methodology does not require any catalyst and is operationally simple. The highly borylated 1,2-diaryl alkenes [1-(2-borylphenyl)vinyl)boronates] are shown to be useful as building blocks.