Selective Transformation of Well-Defined Alkenyllithiums to Alkenylmagnesiums via Transmetalation.

A series of butadienyl organomagnesium complexes, including 1-Li-4-(MgR)-butadienes, 1,4-bis(MgR)-butadienes, and 1-Mg-4-(MgR)-butadiene were synthesized starting with 1,4-dilithio butadienes via the transmetalation reaction between alkenyllithium bond and alkenylmagnesium bond. Single-crystal X-ray structural analysis of these butadienyl organomagnesiates revealed unique bonding modes. Study on their structural transformation demonstrated that 1-Li-4-(MgR)-butadiene is the key intermediate in the reaction process leading to the formation of 1,4-bis(MgR)-butadiene and 1-Mg-4-(MgR)-butadiene.