CYCLIC ORGANOTIN LEWIS-ACIDS

The Ph3P=O IR frequency shift method has been used to compare the Lewis acid strength of several cyclic organotin dichlorides. Structures 3, 20, and 4 are relatively weak Lewis acids, less potent than Bu2SnCl2, according to the IR criterion. Steric factors appear largely responsible for the decreased Lewis acidity, although bond angle strain may also contribute in the case of 3. Introduction of electronegative substituents into the aromatic ring of structures related to 4 results in stronger Lewis acids 8 and 18, both of which are relatively more potent than Ph2SnCl2. Methods for the preparation of precursors to the fluorinated 8 and 18 are described, based on the deprotonation of tetrafluoroaryl precursors.