Coordination of allenyl/propargyl group to samarium(III): the first crystal structures of η3-allenyl and η1-propargyl lanthanide complexes

The synthesis and crystal structures of samarium complexes incorporating bridged Cp′SiMe2allenyl/propargyl ligands [Cp′=(Me3Si)2(C5H2)] are described. The reaction of a dilithium salt of [(Me3Si)2(C5H3)]SiMe2CH2CCSiMe3 (1a) with SmCl3 yielded an η3-allenyl complex {[(Me3Si)2(C5H2)]SiMe2(η3-CCC[H]SiMe3)}SmCl3Li2(TMEDA)2 (2a) (TMEDA=N,N,N′,N′-tetramethylethylenediamine). On the other hand, the reaction of a dilithium salt of a Ph3Si substituted ligand [(Me3Si)2(C5H3)]SiMe2CH2CCSiPh3 (1b) with SmCl3 yielded an η1-propargyl complex {[(Me3Si)2(C5H2)]SiMe2(η1-CHCCSiPh3)}Sm(TMEDA)[Cl2Li(TMEDA)] (2b). A conversion of bonding mode from η1-propargyl to η3-allenyl was observed when 2b was treated with (Me3Si)3CLi/LiI to give an η3-allenyl complex {[(Me3Si)2(C5H2)]SiMe2(η3-CHCCSiPh3)}SmI2Li(TMEDA) (3b). The same structural conversion was also observed when 2b was treated with (Me3Si)2CHLi to give an anionic ate complex ({[(Me3Si)2(C5H2)]SiMe2(η3-CHCCSiPh3)}SmCl[CH(SiMe3)2])[Li(TMEDA)2] (4b), which had the η3-allenyl bonding structure. The structures of these four complexes (2a, 2b, 3b, and 4b) were revealed by X-ray crystallography. These are the first examples of the structural characterization of η3-allenyl and η1-propargyl lanthanide complexes.