Synthesis, structure, and significance for MOCVD of intramolecularly base-stabilized monomeric cyclopentadienylaluminum and -gallium dihydrides

The (N,N-dialkylaminoethyl)cyclopentadienyl group 13 element dichlorides 3 and 4 of the type [(R2NCH2CH2)C5H4]MCl2 {M = Al, R = Me (3); M = Ga, R = i-Pr (4)} were prepared via salt elimination reactions of [(R2NCH2CH2)C5H4]K {R = Me (1), i-Pr (2)} with the respective group 13 element trichlorides. The reaction of 3 with LiAlH4 afforded the cyclopentadienylaluminum dihydride [(Me2NCH2CH2)C5H4]AlH2 (5) in nearly quantitative yield. Treatment of the organogallium dichlorides [(R2NCH2CH2)C5H4]GaCl2 {R = i-Pr (4), Me (6)} with LiAlH4 led via transmetalation to the organoaluminum dihydrides [(R2NCH2-CH2)C5H4]AlH2 {R =Me (5), i-Pr (7)} in good yields. The reaction of 6 with LiGaH4 resulted in the formation of the organogallium dihydride [(Me2NCH2CH2)C5H4]GaH2 (8). The novel compounds 3-5, 7, and 8 were characterized by elemental analysis, NMR spectroscopy, mass spectrometry, and X-ray crystallography. In the solid state and also in solution, all compounds feature a monomeric structure with an intramolecularly coordinated dialkylamino group. The coordinative and electronic saturation of the metal center in these compounds leads to a drastically decreased reactivity toward moisture and air in comparison to nondonor-stabilized Cp-group 13 element compounds. The dynamic behavior observed in solution is based on fast haptotropic shifts in a "windshield-wiper" type process. Sufficient volatility makes the organodihydrido compounds 5 and 8 suitable precursors for the deposition of aluminum and gallium, respectively, in the MOCVD process. Ex-situ characterization with sputter auger electron spectroscopy (SAES) provides information about the chemical composition of the aluminum and gallium layers. Irradiation of 5 and 8 in solution is followed by decomposition into the respective metal and into the hydrogen-functionalized ligand [C5H5(CH2CH2NMe2)].