Formation of a Bridging Planar Trimethylenemethane Dianion from a Neopentyl Precursor via Sequential β-Alkyl Elimination and C−H Activation

The reaction of neopentyllithium, Me3CCH2Li, with [(C5Me5)2Sm][(μ-Ph)2BPh2], 1, was investigated as a route to the unsolvated alkyl, [(C5Me5)2Sm(CH2CMe3)]x, and found to generate the first f element trimethylenemethane dianion complex, [(C5Me5)2Sm]2[μ-η3:η3-C(CH2)3], 2. Formation of the [C4H6]2- trimethylenemethane ligand from the [C5H11]- neopentyl precursor can be explained by a combination of a β-methyl elimination reaction to form isobutene and [(C5Me5)2SmMe]3, 3, with subsequent C−H activation reactions. This sequence has been modeled in several ways, including the synthesis of 2 from reactions of 3 with CH2CMe2 and 3 with the 2-methylallyl complex, (C5Me5)2Sm[CH2C(Me)CH2], 4.