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 eta (3)-allenyl complex ([(Me3Si)(2)(C5H2)]SiMe2(eta (3)-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 Ph,Si substituted ligand [(Me3Si)(2)(C5H3)]SiMe2CH2C=CSiPh3 (Ib) with SmCl3 yielded an eta (1)-propargyl complex ([(Me3Si)(2)(C5H2)]SiMe2(eta (1)-CHC=CSiPh3)}-Sm(TMEDA)[Cl2Li(TMEDA)] (2b). A conversion of bonding mode from eta (1)-propargyl to eta (3)-allenyl was observed when 2b was treated with (Me3Si)(3)CLi/LiI to give an eta (3)-allenyl complex ([(Me3Si)(2)(C5H2)]SiMe2(eta (3)-CH=C=CSiPh3)} SmI2Li(TMEDA) (3b). The same structural conversion was also observed when 2b was treated with (Me3Si)(2)CHLi to give an anionic ate complex ({[(Me3Si)(2)(C5H2)]SiMe2(eta (3)-CH=C=CSiPh3)}SMCl[CH(SiMe3)(2)])[Li(TMEDA)(2)] (4b), which had the eta (3)-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 eta (3)-allenyl and eta (1)-propargyl lanthanide complexes. (C) 2000 Elsevier Science B.V. All rights reserved.