Hydroalumination of 1,4-Diazabut-l-enes and 4-Lithio-l,4-diazabut-l-enes: Synthesis of Amidoaluminum Hydride, Lithium Aluminum Hydride, and Lithium Diamidoaluminum Hydride Complexes

Treatment of the dimeric alkyl-substituted (E)4-lithio-l,4-diazabut-l-ene [cis-{Li[μ-N(t-Bu)CH(t-Bu)CHN(t-Bu)]}₂], 1, with 2 equiv of AlH3*NMe₃ results in hydroalumination yielding a tetrameric lithium diamidoaluminum hydride complex [{Li[N(t-Bu)CH(t-Bu)CH2N(t-Bu)]AlH₂}4], 4, which is associated through both mono- and dibridging hydrides forming a complex Li4Al₂H6 12-membered macrocycle. Treatment of the (E)-1,4-diazabut-1-ene HN(t-Bu)CH(t-Bu)CHN(t-Bu), 2, with 2 equiv of AlH₃-NMe₃ in hexane or 1 equiv of AlH3 in Et₂O yields the monomelic internally coordinated secondary amine complexed aminoalane [{HN(t-Bu)CH(t-Bu)CH2N(t-Bu)}-AIH2], 5, which is stable with respect to loss of hydrogen under reflux in benzene. Treatment of 2 with LiAlH4 gives the imine-secondary amine adduct 2·LiAlH₄, 3, which decomposes by hydrometalation and metalation on heating to 120 °C in benzene to give 4. Compound 4 is not accessible via lithiation of 5 by MeLi in Et₂O. Crystals of 4 are triclinic, of space group P1 (No. 2), with a = 15.664(6) Å,b = 15.723(7) Å, c = 16.408(6) Å, ± = 69.65(3)°, β = 84.98(3)°, γ = 84.22(3)°, V = 3763(3) ų, and Z =2. Crystals of 5 are monoclinic, of space group P2₁/n (No. 14), with a = 9.426(9) Å,b= 12.389(1) Å, c = 15.42(1) Å, β = 103.04(4)°, V= 1754(2) ų, and Z = 4.