Flip-flap mechanism

In connection with the discussed mechanism of epoxide polymerisation in the presence of associated multinuclear catalysts [65], it is worth noting the flip-flap mechanism proposed by Vandenberg to operate in epoxide coordination polymerisation [18,60,61] as the earliest explanatory attempt involving the formation of an intermediate that could accommodate the essentially linear, three-centred transition state necessary for inversion of the configuration at the epoxide ring carbon atom where cleaved. The flip-flap mechanism assumed... 

The reaction pathway according to scheme (4b) (the flip-flap mechanism) does not take place. 

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