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Highly reactive and yet isolable! The bis(benzophenone ketyl)calcium complex 1 was isolated as blue crystals from the reaction of calcium chips with benzophenone and hexamethylphosphoric acid triamide (HMPA) in THF (see below). Its X-ray crystal structure explains why benzophenone ketyl is much more reactive than fluorenone ketyl.
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Hou et al. (1997) studied this question.
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