Synthesis of titanium-TADDOLate complexes containing bidentate nitrogen donors and the asymmetric ethylation of benzaldehyde

Reaction of TiCl2(TADDOLate)L-2 (L = THF (1) or AcOEt (2)) with a bidentate nitrogen-containing ligand such as 2,2'-bipyridine (bipy) or 1,10-phenanthroline(phen) affords six-coordinate complexes TiCl2(TADDOLate)(L-2)(L-2 =bipy(3) or phen(4)). Complexes 3 and 4 can also be obtained from reaction of 1.3 eq. of TiCl4 with a TADDOL (alpha,alpha,alpha',alpha'-tetraphenyl-1,3-dioxolane-4,5-dimethanol) ligand in diethyl ether followed by the addition of the bidentate ligand. The complex 3 reacts further with 2.2 eq. of MeLi in toluene to give the mono-methyl complex TiCl(Me)(TADDOLate)(bipy) (5). Complexes 3 and 4 were subjected to X-ray structural analyses and both structures reveal the same C, molecular symmetry with the bidentate bipy or phen ligand trans to the TADDOLate ligand. In the asymmetric reaction of diethylzinc addition to benzaldehyde, the monomeric metal complex 3 or 4 alone shows good catalytic reactivities with low to moderate enantioselectivities of 31% or 52% ee, respectively. However, with the addition of excess Ti(O-i-Pr)(4), the reaction gives nearly quantitative yields of the desired product with good enantioselectivities up to 88% ee. (C) 2004 Elsevier B.V. All rights reserved

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 = alpha,alpha,alpha',alpha'-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(TV) complex 3 containing a bridging (2R,3R)-1,1,4,4-trtraphrnyl-1,3-dihydoxy-2,4-dioxo (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(TV) 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. (C) 2001 Elsevier Science B.V. All rights reserved

Synthesis and characterizations of Ti(O-i-Pr)Cl-3(THF)(PhCOR) (R = H, Me, Ph) and Ti(O-i-Pr)Cl-3(PhCOR)(2) (R = Me, Ph). The molecular structure of Ti(O-i-Pr)Cl-3(PhCOPh)(2)

A series of titanium(IV) complexes Ti(O-i-Pr)Cl-3(THF)(PhCOR) (R = H (1), CH3 (2), or Ph (3)) is prepared quantitatively from reactions of [Ti(O-i-Pr)Cl-2(THF)(mu-Cl)](2) with 2 molar equiv. PhCOR. Treatment of Ti(O-i-Pr)Cl-3 with 2 molar equiv. of PhCOR affords the disubstituted complexes Ti(O-i-Pr)Cl-3(PbCOR)(2) (R = CH3 (4) or Ph (5)). The C-13 NMR study of these complexes shows that the relative bonding abilities are in the order of PhCOCH3 > PhCHO > PhCOPh. The molecular structure of 5 reveals that one of the benzophenone ligands is trans to the strongest 2-propoxide ligand with a long Ti-O(carbonyl) distance of 2.193(5) Angstrom which is much longer than the other Ti-O(carbonyl) distance of 2.097(4) Angstrom by similar to0.1 Angstrom. All ligands cis to the alkoxide ligand are bending away from the alkoxide ligand with the RO-Ti-L angles ranging from 93.6(2) to 99.0(2)degrees