Synthesis and Structure of Alkoxy- and (Aryloxy)alanes. Observation of a Ring-Opening Reaction Involving Tetrahydrofuran

Dihydrogen elimination from aluminum hydrides and alcohols was used to produce new alkoxide and aryloxide complexes. Dimethylethylamine-alane (DMEAA) reacted with 2 equiv of 2,6-diisopropylphenol (DIPH) in THF at -78 °C to give (DIP)₂:A1H·2THF (1) in 94% yield. It was characterized by NMR, IR, MS. and X-ray crystallography and found to be trigonal bipyramidal with both axial sites occupied by THF. Crystal data for 1: C₃₂H₅₁AlO₄, monoclinic, C2/c, a = 21.37(1) Å, b = 9.324(3) Å, c = 15.30(1) Å, β = 94.16(5)°, V = 3040(5)ų, Z = 4. DMEAA reacted with 2 equiv of triphenylcarbinol, Ph₃COH, in THF at -78 °C to give (Ph₃CO)₂AIH· THF (2) in 42% yield. The lower coordination number was attributed to the larger cone angle of the ligand. Crystal data for 2: C₄₂H₃₉AlO₃, triclinic, P1̄, a = 8.482(1) Å, b = 9.067(1) Å, c = 23.59(1)°, α = 90.919(1)°, β = 92.624(1)°, γ = 116.093(1)°, V = 1626.2(2) ų, Z = 2. Three equivalents of DIPH in THF reacted with DMEAA at -78 °C to form the unexpected compound (DIP)₃(THF)(NMe₂Et)Al (3) in 89% yield. Both solution spectroscopic and X-ray crystallographic data established that THF underwent a ring-opening reaction. Crystal data for 3: C₄₄H₇₀AlNO₄, monoclinic, Cc, a = 23.50(1) Å, b = 10.81(1) Å, c= 19.37(1) Å, β= 122.25(3)°, V = 4162(2) Å, Z = 4.