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 AlH·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: C 32 H 51 AlO 4, monoclinic, C 2/ c, a = 21.37(1) Å, b = 9.324(3) Å, c = 15.30(1) Å, β = 94.16(5)°, V = 3040(5)Å 3, Z = 4. DMEAA reacted with 2 equiv of triphenylcarbinol, Ph 3 COH, in THF at −78 °C to give (Ph 3 CO) 2 AlH·THF ( 2 ) in 42% yield. The lower coordination number was attributed to the larger cone angle of the ligand. Crystal data for 2: C 42 H 39 AlO 3, triclinic, P 1̄, a = 8.482(1) Å, b = 9.067(1) Å, c = 23.59(1) Å, α = 90.919(1)°, β = 92.624(1)°, γ = 116.093(1)°, V = 1626.2(2) Å 3, Z = 2. Three equivalents of DIPH in THF reacted with DMEAA at −78 °C to form the unexpected compound (DIP) 3 (THF)(NMe 2 Et)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: C 44 H 70 AlNO 4, 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 3, Z = 4.