Transition Metal-Carbohydrate Chemistry. Part 2. Homoleptic Diacetoneglucose Complexes of Aluminium and Group 4 Metals

The synthesis of homoleptic 1,2:5,6-di-0-isopropylidene-alpha-D-glucofuranose (HL) complexes of aluminium and Group 4 metals (Ti, Zr or Hf) was achieved by ligand displacement from AlEt3 and [M(PhCH2)4] (M = Ti, Zr or Hf) with HL. The products were characterized by H-1 and C-13 NMR, which showed the sugar ligands to be equivalent and free to rotate about the M-0 bond, even at 1 93 K. Pyridine adducts of all the complexes were obtained and the crystal structures of two of them. [AlL3(py)] and [ZrL4(py)2], determined. The reaction of [AlL3] with two equivalents of 4,4'-bipyridine (4,4'-bipy) led to the formation of the one-to-one adduct [AlL3(4.4'-bipy)]. Complexation of [TiL4] by 1,10-phenanthroline (phen) gave the Lewis-base adduct [TiL4(phen)] which shows a strong steric effect of the base and a clear differentiation of the sugar ligands cis and anti to the N donor atoms. Optical rotatory power values [alpha]D were measured for all the complexes. Crystallographic details: [AlL3(py)], trigonal, space group R3, a = b = c = 10.639(2) angstrom, alpha = beta = gamma = 93.18(2)-degrees, Z = 1 and R = 0.049 for 2154 independent observed reflections; [ZrL4(py)2], triclinic, space group P1, a = 13.843(l), b = 12.682(l), c = 10.942(l) angstrom, alpha = 87.73(l), beta = 73.32(l), gamma = 66.96(l)-degrees, Z = 1 and R = 0.057 for 3336 independent observed reflections.