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Reactivity of R2AlH (R = Me, Bui) and Me3M (M = Al, Ga, In) toward the Silylphosphines P(SiMe3)3 and HP(SiMe3)2

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journal contribution
posted on 17.09.1996 by Larry K. Krannich, Charles L. Watkins, Steven J. Schauer, Charles H. Lake
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 [Me2MP(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[Me2AlH]m species at −80 °C that ultimately produced [Me2AlP(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 [Bui2AlP(SiMe3)2]2 and Bui2AlP(SiMe2)2·Bui2AlP(H)SiMe3 are formed. An X-ray structure analysis of [Bui2AlP(SiMe3)2]2 establishes the planarity of the (AlP)2 core.