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α,α-Bis(trimethylsilyl)-Substituted Benzyl Complexes of Potassium and Calcium

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posted on 2000-10-27, 00:00 authored by Florian Feil, Sjoerd Harder
The first benzylcalcium complex, (α,α-bis(trimethylsilyl)benzyl)2calcium·(THF)2 (7), has been prepared by reacting CaI2 with α,α-bis(trimethylsilyl)benzylpotassium (6) in THF. The solid state structure of the K precursor shows an interesting Lewis base-free coordination polymer in which the coordination sphere of K is additionally saturated by agostic Si−Me···K interactions. The crystal structure of the Ca product displays a THF-solvated monomeric compound, which shows considerably less delocalization of negative charge into the phenyl ring than the corresponding K compound. NMR investigations as well as ab initio calculations show that the TMS substituents at the benzylic carbon have a charge-localizing influence. Only the more ionic K precursor shows activity in initiating the polymerization of styrene.