Trimethyltin-tetraphenylcyclopentadiene as a Precursor to Group VB Transition Metal Lewis Acid Catalysts
Danielle Barrios, J. Bernardo Lepe, and Pamela Lee, and Wayne Tikkanen, PhD
Department of Chemistry and Biochemistry, CSULA
The development of catalysts that facilitate stereoselective carbon-carbon bond-forming reactions has great practical importance; one particularly important application is the development of single enantiomers that can be used as precursors to drugs and other bioactive molecules. Trimethyltin-tetraphenylcyclopentadiene (C5H(C6H5)4)Sn(CH3)3; TMSnD) was successfully synthesized in 85% crude yield and has been characterized by 1H and 13C-NMR. Its expected cleaner reactivity has been exploited to yield the Lewis acid catalyst candidate, η5-C5H(C6H5)4)TaCl4 , which has also been characterized by 1H and 13C NMR. Conversely, the transmetallation of TMSnD with niobium pentachloride to yield the corresponding η5-C5H(C6H5)4)NbCl4 has proven to be more difficult, and further work must be done to optimize the reaction. The catalytic efficacy and versatility of the tantalum complex was tested in the silylcyanations of butyraldehyde and benzaldehyde. The Ta complex efficiently catalyzed the silylcyanation of butyraldehyde: the reaction proceeded to completion in 3 hours in comparison to the control, which showed no activity after 18 hours. However, this complex is not an efficient catalyst for the silylcyanation of benzaldehyde, which suggests that a more Lewis acidic complex is necessary for effective catalysis. Future work includes forming chiral derivatives of and testing the catalytic selectivities of the niobium and tantalum complexes.