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.