Synthesis and structure of Ti(TADDOLate)(dbm)Cl(THF) and structures of two binuclear Ti(IV) complexes containing a bridging ligand derived from the TADDOL ligand

Treatment of TiCl2(TADDOLate)(THF)2 (1) (TADDOL=α,α,α′,α′-tetraphenyl-1,3-dioxolane-4,5-dimethanol) with 1 molar equiv. of bidentate dibenzoylmethanate (Li+dbm−) afforded the monomeric Ti(TADDOLate)(dbm)Cl(THF) (2). While recrystallization of 1 but without careful exclusion of moisture, an unexpected binuclear Ti(IV) complex 3 containing a bridging (2R,3R)-1,1,4,4-tetraphenyl-1,3-dihydoxy-2,4-dioxobutane (4) was isolated as colorless crystals. The bridging chiral ligand 4 was derived from the TADDOL ligand with loss of the ketal group. When 1 was reacted with lithium acetylacetonate (Li+acac−), another unexpected binuclear Ti(IV) complex 5 containing the same bridging chiral ligand 4 and an acac− ligand was obtained. Complexes 1, 2, 3 and 5 were subjected to X-ray structural analyses and solid state structures show that complexes 1 and 2 are monomeric species with the only difference from the replacement of one Cl− and one THF ligand in 1 by a bidentate dbm− ligand in 2. Complexes 3 and 5 are binuclear species with the replacement of also one Cl− and one THF ligand on one metal center in 3 by the acac− ligand in 5.