Formation of a bridging planar trimethylenemethane dianion from a neopentyl precursor via sequential beta-alkyl elimination and C-H activation

The reaction of neopentyllithium, Me3CCH2Li, with (C5Me5)2Sm](mu-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]2mu-eta3:eta3-C(CH2)3], 2. Formation of the C4H6]2- trimethylenemethane ligand from the C5H11]1- neopentyl precursor can be explained by a combination of a beta-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)2SmCH2C(Me)CH2], 4.