The C-C bond formation which occurs when two [PhC=C]- ligands on Cp*2Sm-containing organosamarium complexes are coupled to form the [PhC=C=C=CPh]2- trienediyl ligand in [Cp*2Sm]2(mu-eta2:eta2-PhC=C=C=CPh) (1) has been investigated (Cp* = C5(CH3)5). The generality of the reactions which form 1, namely the reactions of [Cp*2Sm(mu-H)]2 and Cp*2Sm with HC=CPh and the thermolysis of Cp*2Sm(C=CPh)(THF) (2), has been probed by examining the reactivity of a variety of lanthanide alkynide systems. The bis(alkynide) complexes [Cp*2Ln(mu-C=CPh)2K]n (Ln = Ce (3), Nd (4), Sm (5)) do not undergo the coupling reaction, but trienediyl complexes have been obtained by heating Cp*2Ce(C=CPh)(THF) (9) and Cp*2Nd(C=CPh) (THF) (10), which demonstrates that a readily accessible divalent state is not a requirement for the coupling. 9 and 10 are conveniently made from Cp*2Ln[N(SiMe)2] and PhC=CH in a metathesis reaction which succeeds in THF but unexpectedly fails in toluene. Coupled trienediyl products [Cp*2Sm]2[mu-eta2:eta2-Ph(CH2)2-C=C=C=C(CH2)2Ph] (19) and [Cp*2Sm]2[mu-eta2:eta2-Me2CH(CH2)2C=C=C=C(CH2)2CHMe2] (20) have also been obtained from the reaction of Cp*2Sm with HC=C(CH2)2Ph and HC=C(CH2)2CHMe2, respectively. The NMR spectra and X-ray crystal structures of these products show agostic interactions involving methylene groups. The reaction of [Cp*2Sm(mu-H)]2 with HC=CCMe3 generates the loosely joined dimeric alkynide (Cp*2Sm(C=CCMe3)]2 (17) and the unusual insertion product Cp*2Sm[Me3CCH=CC(CMe3)=CH2] (18). The steric and electronic factors responsible for the observed chemistry are discussed, as well as a samarium-based cycle involving trienediyl 1 for the formation of enzynes from alkynes. X-ray crystallography was used to definitively identify several of the products and synthetic precursors. [Cp*2Sm(mu-C=CPh)2K]n (5) crystallizes in space group P2(1)2(1)2(1) with a = 9.8590(15) angstrom, b = 16.251 (3) angstrom, c = 20.242 (4) angstrom, V = 3243(1) angstrom3, and D(calcd) = 1.356 g cm-3 for Z = 4. Least-squares refinement of the model based on 3110 reflections converged to a final R(F) = 2.6%. In 5, the two Cp* ring centroids and the two alkynide alpha-carbon atoms define a distorted tetrahedron around samarium. The potassium atom is bound to both alkynide ligands of one molecular unit and to a Cp* ligand of the adjacent molecule to generate a polymeric species. Cp*2Sm[N(SiMe3)2] (8) crystallizes from toluene in space group R3BAR with a = 17.695(2) angstrom, c = 47.269(5) angstrom, V = 12 818(2) angstrom3, and D(calcd) = 1.355 g cm-1 for Z = 18. Least-squares refinement of the model based on 4940 reflections converged to a final R(F) = 4.1%. The amide ligand in 8 is attached symmetrically to the Cp*2Sm unit such that the two ring centroids, the amide nitrogen, and the Samarium are coplanar to within 0.05 angstrom. [Cp*2Sm(C=CCMe3)]2 (17) crystallizes from toluene in space group Pbca with a = 14.753(2) angstrom, b = 17.682(3) angstrom, c = 22.966(4) angstrom, V = 5991(2) angstrom3, and D(calcd) = 1.297 g cm-1 for Z = 8. Least-squares refinement of the model based on 2917 reflections converged to a final R(F) = 7.3%. Each alkynide ligand in a monomeric unit of 17 is attached asymmetrically to the Cp*2Sm unit such that samarium lies 0.38 angstrom out of the plane defined by the two Cp* ring centroids and the alkynide alpha-carbon atoms. A methyl group from the Cp* ligand of another monomer is oriented toward samarium at a distance of 3.006(7) angstrom to generate a loosely linked dimeric structure. Cp*2Sm[Me3CCH=CC(CMe3)=CH2] (18) crystallizes from toluene in space group Pbca with a = 14.753(2) angstrom, b = 17.682(3) angstrom, c = 22.966(4) angstrom, V = 5991(2) angstrom3, and D(calcd) = 1.297 g cm-3 for Z = 8. Least-squares refinement of the model based on 2917 reflections converged to a final R(F) = 6.0%. In 18, a 1,3-di-tert-butyl-1,3-butadien-2-yl ligand is attached to Cp*2Sm via a 2.484(14) angstrom Sm-C bond. [Cp*2Sm]2[mu-eta2:eta2-Ph(CH2)2C=C=C=C(CH2)2Ph] (19) crystallizes from toluene in space group C2/c with a = 28.589(6) angstrom, b = 10.5209(16) angstrom, c = 22.450(3) angstrom, beta = 110.924(14)degrees, V = 6307(2) angstrom3, and D(calcd) = 1.352 g cm-3 for Z = 4. Least-squares refinement of the model based on 4655 reflections converged to a final R(F) = 5.3%. In 19, the eight-carbon chain of the trienediyl and the two samarium atoms are coplanar to within 0.09 angstrom. The two shortest Sm-C distances connecting a Cp*2Sm unit to the ligand are 2.483(7) and 2.689(6) angstrom. A methylene group is oriented toward each Cp*2Sm unit at a distance of 3.748 angstrom.
