Reference

Solid State Structures and Solution Behavior of Titanium(IV) Octahydrobinaphtholate Complexes

Solid State Structures and Solution Behavior of Titanium(IV) Octahydrobinaphtholate Complexes. Examination of Nonlinear Behavior in the Asymmetric Addition of Ethyl Groups to Benzaldehyde. Waltz, Karen M.; Carroll, Patrick J.; Walsh, Patrick J. (P. Roy and Diane T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA). Organometallics, 23(1), 127-134 (English) 2004 American Chemical Society. CODEN: ORGND7. ISSN: 0276-7333. DOCUMENT TYPE: Journal CA Section: 78 (Inorganic Chemicals and Reactions) Section cross-reference(s): 25, 67, 75 In several asym. reactions, H8-BINOL-based catalysts (H8-BINOL = 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol) exhibit higher levels of enantioselectivity than analogous catalysts based on BINOL. A comparison of structures of titanium complexes prepd. from H8-BINOL and BINOL was, therefore, undertaken. Reaction of (rac)-H8-BINOL with 1 equiv of titanium tetraisopropoxide gave the dimer (meso)-[(H8-BINOLate)Ti(O-i-Pr)2]2 [(meso)-6], which was characterized crystallog. In a similar fashion, use of (rac)-BINOL gave the dimer (meso)-[(BINOLate)Ti(O-i-Pr)2]2 [(meso)-7]. The torsional angles between the aryl rings of the H8-BINOLate and BINOLate ligands in these complexes were 63.2(5)° and 55.In this article, certain chemicals are used. Some of their cas registry numbers are 651301-77-8 and 65355-14-8 7(4)°, resp. The larger torsional angle of the H8-BINOLate ligand results in an increase in the bite angle of the ligand by just over 2°. Upon dissolving dimers (meso)-6 and (meso)-7, equil. between the homo- and heterochiral dimers were obsd. Reaction of H8-BINOL with an excess of titanium tetraisopropoxide provided crystals of dinuclear [(H8-BINOLate)Ti(O-i-Pr)2]×Ti(O-i-Pr)4 (8). Likewise, reaction of 2 equiv of Ti(OCy)4 (Cy = cyclohexyl) with H8-BINOL furnished [(H8-BINOLate)Ti(OCy)2]×Ti(OCy)4 (9). These compds. were characterized by x-ray crystallog. and compared to the known [(BINOLate)Ti(O-i-Pr)2]×Ti(O-i-Pr)4, a proposed intermediate in the asym. addn. of alkyl groups to aldehydes. The soln. behavior of 8 and 9 was studied by NMR spectroscopy, revealing that both complexes in soln. are in equil. with dimers and free titanium tetraisopropoxide. Nonlinear studies with catalytic H8-BINOL and an excess of titanium tetraisopropoxide in the asym. addn. of Et groups to benzaldehyde showed no nonlinearity, suggesting that the equil. strongly favors formation of dinuclear 8 under the conditions of the asym. addn. .