A series of five-coordinate aluminum complexes supported by o-phenylene-derived amido diphosphine ligands, [N(o-C6H4PR2)(2)](-) ([R-PNP](-); R = Ph, Pr-i) and [N(o- C6H4PPh2)(o-(C6H4PPr2)-Pr-i)](-) ([Ph-PNP-Pr-i](-)), have been prepared and structurally characterized. Alkane elimination reactions of trialkylaluminum with H[Ph-PNP] (1a), H[Pr-i-PNP] (1b), and H[Ph-PNP-Pr-i] (1c) in toluene at -35 degrees C respectively produced the corresponding dialkyl complexes [Ph-PNP]AIR(2), [Pr-i-PNP]AIR(2), and [Ph-PNP-Pr-i]AIR(2) (R = Me (2a-c), Et (3a-c), Bu-i (4a-c)) in high isolated yield. The dihydride complexes [Ph-PNP]AIH(2) (6a), [Pr-i-PNP]AIH(2) (6b), and [Ph-i-PNP-Pr-i]AIH(2) (6c) were prepared in one-pot reactions of in situ prepared clichloride precursors (5a-c) with LiAIH(4) in THF at room temperature. X-ray diffraction studies of 2a-c, 3b-c, 5b, and 6b revealed a distorted trigonal-bipyramidal structure for these molecules in which the two phosphorus donors are mutually trans. The solution structures of these organoaluminum complexes were all characterized by H-1, C-13, and P-31 NMR spectroscopy. The NMR data are indicative of solution C-2 symmetry for [Ph-PNP](-) and [Pr-PNP](-) complexes, whereas they are indicative of C, for [Ph-PNP-Pr-i](-) derivatives. The 1H NMR spectra of 3a-c and 4a-c revealed diastereotopy for the a-hydrogen atoms in these molecules,