Yttrium Complexes of Arsine, Arsenide, and Arsinidene Ligands**

Deprotonation of the yttrium–arsine complex [Cp′(3)Y{As(H)(2)Mes}] (1) (Cp′=η(5)-C(5)H(4)Me, Mes=mesityl) by nBuLi produces the μ-arsenide complex [{Cp′(2)Y[μ-As(H)Mes]}(3)] (2). Deprotonation of the As–H bonds in 2 by nBuLi produces [Li(thf)(4)](2)[{Cp′(2)Y(μ(3)-AsMes)}(3)Li], [Li(thf)(4)](2)[3], in which the dianion 3 contains the first example of an arsinidene ligand in rare-earth metal chemistry. The molecular structures of the arsine, arsenide, and arsinidene complexes are described, and the yttrium–arsenic bonding is analyzed by density functional theory.