The reactivities of Me2AlH with P(SiMe3)3 and of Me3M (M = Al, Ga, In) and Bui2AlH with P(SiMe3)3 and HP(SiMe3)2 were monitored with multinuclear NMR to determine the trend for adduct formation and establish the role that the Me and Bui moieties and M play in influencing the nature of the possible 1,2-elimination product. 1:1 adducts were obtained in the Me3M/P(SiMe3)3 systems with no tendency toward room-temperature, 1,2-elimination reactivity. Thermolysis at 100 °C gave the following order of reactivity for SiMe4 elimination: Me3In·P(SiMe3)3 > Me3Ga·P(SiMe3)3 > > Me3Al·P(SiMe3)3. With the Me3M/ HP(SiMe3)2 systems, only Me3Al gave an isolable adduct, which eliminated CH4 upon heating to form [Me2AlP(SiMe3)2]2. Although NMR spectral data indicated adduct formation in the Me3Ga and Me3In systems, these underwent CH4 elimination to yield the respective [Me2-MP(SiMe3)2]2 species. The variable-temperature, multinuclear NMR study of the Me2AlH/ P(SiMe3]3 system indicated adduct formation at -90 °C and subsequent conversion to cyclic oligomeric [Me2AlP(SiMe3]2]n[Me 2AlH]m species at -80 °C that ultimately produced [Me2-AlP(SiMe3)2]2. The reactivity of Bui2AlH toward P(SiMe3)3 and HP(SiMe3)2 is much slower then that of Me2AlH. In the Bui2AlH/HP(SiMe3)2 system, H2 elimination is favored and [Bui2-AlP(SiMe3)2]2 and Bui2AlP(SiMe2)2·Bu i2AlP(H)SiMe3 are formed. An X-ray structure analysis of [Bui2AlP(SiMe3)2]2 establishes the planarity of the (AlP)2 core.