10.1021/om4002389.s001 Nikolaos Tsoureas Nikolaos Tsoureas Alex Hamilton Alex Hamilton Mairi F. Haddow Mairi F. Haddow Jeremy N. Harvey Jeremy N. Harvey A. Guy Orpen A. Guy Orpen Gareth R. Owen Gareth R. Owen Insight into the Hydrogen Migration Processes Involved in the Formation of Metal–Borane Complexes: Importance of the Third Arm of the Scorpionate Ligand American Chemical Society 2013 Third Arm Computational studies PhBai HB Scorpionate LigandThe reactions reaction step formation Hydrogen Migration Processes energy barrier Tai borohydride group carbon monoxide result reaction mixtures coordination properties iridium center migration species NMR spectroscopy borohydride hydrogen atom borohydride units Ir metallaboratrane complexes 2013-05-13 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Insight_into_the_Hydrogen_Migration_Processes_Involved_in_the_Formation_of_Metal_Borane_Complexes_Importance_of_the_Third_Arm_of_the_Scorpionate_Ligand/2416078 The reactions of [Ir­(κ<sup>3</sup><i>N</i>,<i>N</i>,<i>H</i>-<b>Tai</b>)­(COD)] and [Ir­(κ<sup>3</sup><i>N</i>,<i>N</i>,<i>H</i>-<sup><b>Ph</b></sup><b>Bai</b>)­(COD)] (where <b>Tai</b> = HB­(azaindolyl)<sub>3</sub> and <sup><b>Ph</b></sup><b>Bai</b> = Ph­(H)­B­(azaindolyl)<sub>2</sub>) with carbon monoxide result in the formation of Z-type iridium–borane complexes supported by 7-azaindole units. Analysis of the reaction mixtures involving the former complex revealed the formation of a single species in solution, [Ir­(η<sup>1</sup>-C<sub>8</sub>H<sub>13</sub>)­{κ<sup>3</sup><i>N</i>,<i>N</i>,<i>B</i>-B­(azaindolyl)<sub>3</sub>}­(CO)<sub>2</sub>], as confirmed by NMR spectroscopy. In the case of the <sup><b>Ph</b></sup><b>Bai</b> complex, a mixture of species was observed. A postulated mechanism for the formation of the new complexes has been provided, supported by computational studies. Computational studies have also focused on the reaction step involving the migration of hydrogen from boron (in the borohydride group) to the iridium center. These investigations have demonstrated a small energy barrier for the hydrogen migration step (Δ<i>G</i><sub>298</sub> = 10.3 kcal mol<sup>–1</sup>). Additionally, deuterium labeling of the borohydride units in <b>Tai</b> and <sup><b>Ph</b></sup><b>Bai</b> confirmed the final position of the former borohydride hydrogen atom in the resulting complexes. The importance of the “third azaindolyl” unit within these transformations and the difference in reactivity between the two ligands are discussed. The selective coordination properties of this family of metallaboratrane complexes have also been investigated and are discussed herein.