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 degrees 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: C32H51AlO4, monoclinic, C2/c, a = 21.37(1) Angstrom, b = 9.324(3) Angstrom, c = 15.30(1) Angstrom, beta = 94.16(5)degrees, V-3040(5)Angstrom(3), Z = 4. DMEAA reacted with 2 equiv of triphenylcarbinol, Ph3COH, in THF at -78 degrees C to give (Ph3CO)(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: C42H39AlO3, triclinic, P (1) over bar, a = 8.482(1) Angstrom, b = 9.067(1) Angstrom, c = 23.59(1) Angstrom, alpha = 90.919(1)degrees, beta = 92.624(1)degrees, gamma = 116.093(1)degrees, V = 1626.2(2) Angstrom(3), Z = 2. Three equivalents of DIPH in THF reacted with DMEAA at -78 degrees 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) Angstrom, b = 10.81(1) Angstrom, c = 19.37(1) Angstrom, beta = 122.25(3)degrees, V = 4162(2) Angstrom(3), Z = 4.