Capturing HBCy 2 : Using N,O‐Chelated Complexes of Rhodium(I) and Iridium(I) for Chemoselective Hydroboration

1,3‐N,O‐chelated complexes of Rh I and Ir I cooperatively and reversibly stabilized the B−H bond of HBCy 2 to afford six‐membered metallaheterocycles (M=Rh ( 7 ) or Ir ( 8 )) having a δ‐[M]⋅⋅⋅H‐B agostic interaction. Treatment of these Shimoi‐type borane adducts 7 or 8 with both an aldehyde and an alkene resulted in chemoselective aldehyde hydroboration and reformation of the 1,3‐N,O‐chelated starting material. The observed chemoselectivity is inverted from that of free HBCy 2 , which is selective for alkene hydroboration.