A new convenient preparation of monocyclooctatetraenyl-lanthanide complexes from metallic lanthanides and oxidants

Treatment of lanthanide metals with cyclooctatetraene in the presence of an equimolar amount of iodine afforded cyclooctatetraenyl-iodolanthanide(III) complexes, LnI(η8-cot)(thf)n. (cot = cyclooctatetraenyl; 1a: Ln  La, n = 3; 1b: Ln  Ce, n = 3; 1c: Ln  Pr, n = 3; 1d: Ln  Nd, n = 2; 1e: Ln  Sm, n = 1), in modest yields. Bromo and chloro-bridged dinuclear complexes of samarium, [Sm(μ-X)(cot)(thf)]2 (2: X  Br; 3: X  Cl), are also prepared by the reaction of samarium metal with cyclooctatetraene in the presence of 1,2-dibromoethane or Ph3PCl2, respectively. The reaction of metallic samarium with cyclooctatetraene and diaryl disulfide or diphenyl diselenide in THF afforded cyclooctatetraenyl-thiolate or -selenolate complexes of samarium(III), [Sm(μ-EAr)(η8-cot)(thf)n]2 (4a: EAr  SPh, n = 2; 4b: SC6H2Me3-2,4,6,n = 2; 4c: SC6H2iPr3-2,4,6, n = 1; 5: SePh, n = 2). The dimeric structure of 5 was revealed by X-ray. crystallography [monoclinic, space group P21/n with a = 8.500(5), b = 21.805(6), c = 12.042(5) Å, β = 105.98(4)°, V= 2145(1) Å3, Z = 2, R = 0.055 for 2061 reflections with I > 3σ-(I) and 235 parameters].A samarium (II) complex, [Sm(η8-cot)(thf)]n, (6), was also obtained by the direct reaction of samarium metal with cyclooctatetraene in THF with a catalytic amount of iodine. Reaction of 6 with iodine and diphenyl disulfide afforded 1e and 4a, respectively.