1,2-Ethanediyl bis[(1,2,3,3a,7a-h)-4,5,6,7-tetrahydro-1H-inden-1-ylidene] difluorotitanium
· (MW 350.27)
(precatalyst for the hydrosilation of carbon-heteroatom double bonds)
Alternate Name: [(EBTHI)TiF2]1.
Physical Data: yellow solid, mp 226-229 °C.
Solubility: THF, dichloromethane.
Preparative Methods: (EBTHI)TiF2 can be synthesized in one step from [1,2-ethanediyl bis[(1,2,3,3a,7a-h)-4,5,6,7-tetrahydro-1H-inden-1-ylidene] titanium dichloride (EBTHITiCl2) and sodium fluoride2 or by treatment of EBTHITi(binaphth-1,1´-diol) with methyl lithium and HF·pyridine adduct.3
Handling, Storage, and Precautions: no special handling is required. (EBTHI)TiF2 can be crystallized from toluene/hexane or from methylene chloride/heptane.
Asymmetric hydrosilation of imines derived from ketones is a challenging problem.4 The difficulty stems from the presence of E/Z mixtures of the imines and the varying reactivity of different N-substituents. Treatment of EBTHITiF2 with PhSiH3 in the presence of pyrrolidine and methanol forms an active catalyst which hydrosilates N-methyl and cyclic imines2 or N-aryl imines5 derived from non-aromatic ketones in excellent yields and high enantioselectivities (1). An important feature of the reaction is that the enantiomeric excesses are independent of the starting E/Z ratio of the imine.6 Also, the use of a primary amine additive allows the use of polymethylhydrosiloxane (PHMS), an inexpensive silating reagent, rather than the typically employed PhSiH3. Unlike the hydrogenation of imines, which require elevated temperatures and pressures, hydrosilations proceed at room temperature under an inert atmosphere. Application of this methodology to the reduction of aromatic and a, b-unsaturated ketones proceeds through a similar pathway, as described above, to produce the corresponding alcohol.7
- 1. Hoveyda, A. H.; Morken, J. P., Angew. Chem., Int. Ed. Engl. 1996, 35, 1263.
- 2. Verdaguer, X.; Lange, U. E. W.; Reding, M. T.; Buchwald, S. L., J. Am. Chem. Soc. 1996, 118, 6784.
- 3. Reding, M. T.; Buchwald, S. L., J. Org. Chem. 1998, 63, 6344.
- 4. Kobayashi, S.; Ishitani, H., Chem. Rev. 1999, 99, 1069.
- 5. Hansen, M.C.; Buchwald, S. L., Org. Lett. 2000, 2, 713.
- 6. Verdaguer, X.; Lange, U. E. W.; Buchwald, S. L., Angew. Chem., Int. Ed. Engl. 1998, 37, 1103.
- 7. Yun, J.; Buchwald, S. L., J. Am. Chem. Soc. 1999, 121, 5640.
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