Treatment of the yttrium dialkyl complex Tp(Me2)Y(CH2Ph)(2)(THF) (TpMe(2) = tri(3,5 dimethylpyrazolyl)borate, THF = tetrahydrofuran) with S-8 in a 1:1 molar ratio in THF at room temperature afforded a yttrium pentasulfide Tp(Me2)Y(kappa(4)-S-5) (THF) (1) in 93% yield. The yttrium monoalkyl complex Tp(Me2)CpYCH(2)Ph(THF) reacted with S8 in a 1:0.5 molar ratio under the same conditions to give another yttrium pentasulfide [(Tp(Me2))(2)Y](+)[Cp2Y(kappa(4)-S-5)](-) (10) in low yield. Further investigations indicated that the S-5(2-) anion facilely turned into the corresponding thioethers or organic disulfides, and released the redundant S-8, when it reacted with some electrophilic reagents. The mechanism for the formation of the S-5(2-) ligand has been investigated by the controlling of the reaction stoichiometric ratios and the stepwise reactions.