Titanium Lewis Acids for Asymmetric Catalysis: Synthesis and Structural Characterization of Dichloro[diolato(2−)-κO,κO′]bis(solvent)titanium ([TiCl2(diolato)(solvent)2]) Complexes
✍ Scribed by Lukas Hintermann; Diego Broggini; Antonio Togni
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- German
- Weight
- 321 KB
- Volume
- 85
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
The complexes [TiCl 2 {(R,R)-TADDOLato}(DME)] ¥ MeCN (3), and [TiCl 2 {(R,R)-1-Nph-TADDOL-ato} (MeCN)
(R,R)-1-Nph-TADDOLato (4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanolato(2 À)-kO,kO') were prepared and isolated in high yield as stable crystalline materials (Scheme 1). They constitute ideally suited and easyto-handle catalyst precursors for a large number of Ti-catalyzed asymmetric reactions, for which they have been previously generated in situ. The X-ray crystal structures of 3 and 4b show a distorted octahedral geometry around Ti with the chloro ligands in mutual trans positions (Figs. 5 and6). The new chiral diols a-(1S,3R)-3hydroxy-2,2,3-trimethylcyclopentyl]-a-phenylbenzenemethanol (13a), derived from camphoric acid (5), and (M)-6,6'-dimethyl-a,a,a',a'-tetraphenyl[1,1'-biphenyl]-2,2'-dimethanol (15) were prepared (Schemes 3 and 4). These new ligands are able to form mononuclear complexes with the Ti IV Cl 2 fragment. The corresponding complex 14 derived from 13a was characterized by X-ray as a mixed THF/MeCN adduct.