Selective lithiation and crystal structures of G1-carbosilane dendrimers with dimethoxybenzene functionalities.
Synthetic routes for the following dendrimers are described: Si[CH2CH2Si(Me)2CH2-3,5-(MeO)2C6H3]4 (2) and Si[CH2CH2Si(Me)2-2,4-(MeO)2-C6H3]4 (4). The crystal structures of these dendrimers were detd. by single crystal x-ray diffraction. One of the dendrimers (2) shows crystallog. S4-symmetry and intramol. C-H...O bonding, whereas the other (4) shows crystallog. C2-symmetry and is imbedded in a zipper-like network of intermol. C-H...O bonds. Direct lithiation of these dendrimers with BuLi in Et2O yields complete and selective lithiation in the aryl ring between the methoxy substituents. However, dendrimer 2 is also partially lithiated in the benzylic group. For the solid state structure of such lithiated dendrimers, a diamond-type assembly is predicted.
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