Further exploring the “Sting of the Scorpion” : hydride migration and subsequent rearrangement of Norbornadiene to Nortricyclyl on Rhodium(I)

A new boron-based flexible scorpionate ligand based upon 7-azaindole, Li[Ph(H)B(azaindolyl)2] (Li[PhBai]), has been prepared. This ligand, together with the previously reported ligand K[HB(azaindolyl)3] (K[Tai]), have been used to prepare a range of monovalent group 9 transition-metal complexes. The complexes [M(COD){κ3N,N,H-Ph(H)B(azaindolyl)2}] (where M = rhodium, iridium and COD = 1,5-cyclooctadiene) and [Rh(NBD){κ3N,N,H-HB(R)(azaindolyl)2}] (where NBD = 2,5-norbornadiene and R = Ph, azaindolyl) have been prepared. Structural characterization of [M(COD){κ3NNH-Ph(H)B(azaindolyl)2}] (where M = rhodium, iridium) and [Rh(NBD){κ3N,N,H-HB(azaindolyl)3}] reveal strong interactions of the B−H functional group with the metal centers, particularly in the case of [Ir(COD){κ3N,N,H-Ph(H)B(azaindolyl)2}]. The complex [Rh(NBD){κ3N,N,H-HB(azaindolyl)3}] undergoes a further reaction, resulting from hydride migration from boron to the norbornadiene group. Subsequent rearrangement results in the formation of the rhodium−nortricyclyl complex [Rh(nortricyclyl){κ4N,N,B,N-B(azaindolyl)3}], providing the first nitrogen-based metallaboratrane complex to contain the tetradentate (κ4N,N,B,N) coordination mode.