SYNTHESIS AND CHARACTERIZATION OF THE MONONUCLEAR COMPOUNDS TERT-BU2MOAR (M = AL OR GA, AR = BULKY ARYL GROUP) - ARE THE SHORT AL-O AND GA-O BONDS A CONSEQUENCE OF PI-INTERACTIONS

The synthesis and characterization of the compounds t-BU2MOAr (Ar = 2,6-t-BU2-4-XC6H2, M = Al, and X = t-Bu, 1; Me, 2; H, 3; X = Me and M = Ga, 4) are described. They were characterized by X-ray crystallography (1, 2, and 4) and H-1 NMR and IR spectroscopy. In the crystal, the structures of 1, 2, and 4 are monomeric with essentially trigonal planar coordinations at the metals and short Al-O and Ga-O bond lengths that are near 1.71 and 1.82 angstrom. The structural data together with VT H-1 NMR studies indicate that there is probably little tau-character in the M-O bonds. The shortness may be explained on the basis of an ionic bonding contribution and the low coordination number of the metal, with M-O tau-interactions playing a relatively minor role. Crystal data with Mo K-alpha (lambda = 0.71069 angstrom) at 130 K: 1, C26H47AlO, a = 11.386 (10), b = 29.11 (2), c = 24.969 (16) angstrom, beta = 102.05 (6)degrees, monoclinic, space group Pn, Z = 12 (six molecules per asymmetric unit), R = 0.105; 2, C23H41AlO, a = 8.200 (2), b = 17.876 (4), c = 15.910 (4) angstrom, beta = 94.47 (2)degrees, monoclinic, space group P2(1)/c, Z = 4, R = 0.047; 4, C23H41GaO, a = 8.215 (1), b = 17.738 (6), c = 15.921 (4) angstrom, beta = 94.73 (2)degrees, monoclinic, space group P2(1)/c, Z = 4, R = 0.051.