P- and N‑Coordination of the Ambidentate Ligand HN[P(i‑Pr)2]2 with Group 13 Trihalides

Five different coordination motifs were observed upon reaction of the simple group 13 Lewis acids MCl3 (M = In, Ga, Al, B) or BF3·Et2O with the ambidentate bis­(diisopropylphosphino)­amine ligand HN­[P­(i-Pr)2]2. In a 1:1 reaction mixture, the softer Lewis acids InCl3, GaCl3 and BCl3 coordinate to one of the two P atoms of the ligand. In contrast, AlCl3 and BF3 prefer coordination to the harder N atom. In all cases, the acidic N–H proton is shifted to P upon complexation with a metal. By altering the reaction stoichiometry, 2:1 metal–ligand complexes could be isolated for three of the combinations. BCl3 gives a bis-adduct via the two P atoms. GaCl3 produces a salt consisting of a [GaCl4]− anion and a P,P-chelated [LGaCl2]+ cation. Most unexpectedly, the reaction with InCl3 in methanol resulted in solvent deprotonation by the ligand to give two symmetric [(i-Pr2PH)2N]+ cations in which all the basic P sites are coordinated to H rather than the group 13 Lewis acid. These cations are balanced by the unique complex dianion [(MeO)6In4Cl8·2MeOH]2–. All complexes were characterized with a combination of multinuclear NMR spectroscopy and single-crystal X-ray diffraction.