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Iridium Double Clutch Produces Triborylalkenes

Catalysis: Adding carbon monoxide mid-reaction switches gears for the catalyst, leading to a two-step, one-pot alkyne borylation/boronation

by Stephen K. Ritter
October 12, 2015 | APPEARED IN VOLUME 93, ISSUE 40

Tetrasubstituted olefins are important structural motifs in drugs and functional materials. Chemists have many ways to make them, including using polyborylated alkenes as intermediates. In exploring alternative routes to the borylated compounds, Oleg V. Ozerov of Texas A&M University and his colleagues previously reported the first example of dehydrogenative borylation of terminal alkynes, in which they used an iridium catalyst with a polydentate SiNN ligand and pinacolborane to make an alkynylboronate. Now they report that they can take the reaction a step further and add two more pinacolborane groups to produce triborylalkenes (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201507372). The second step is new, Ozerov says, in that diboration of a triple bond is accomplished not by insertion of the alkyne triple bond into a B–B bond, but rather by a second dehydrogenative process involving two B–H bonds. The other thing that is “strange” in this second step, Ozerov adds, is that it requires a different catalyst, but that catalyst can be made directly from the first one. The researchers found they could easily change gears in route by blanketing the reaction with carbon monoxide, which adds CO ligands to the original catalyst. With new triborylalkenes in hand, the team next plans to explore what they can do with them.



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