Lewis Acid Modification of Binding Modes of bis -Diazophoranimide Ligands at Lithium

The uncatalyzed hydrophosphination of diazoesters with secondary phosphines affords bis-diazophoranimide ligands. Deprotonation provides Li–N2O2-tetradentate complexes with 5,6,5-chelation. These bifunctional ligands coordinate one equivalent of HB(C6F5)2 to a N atom remote from the lithium prompting a geometry change to a 6,5,5 binding mode and dimerization. A second equivalent of HB(C6F5)2 alters chelation, restoring 5,6,5 binding with two B–N bonds adjacent to phosphorus. The energetics of these bonds are examined computationally.