Synthesis of Unsupported Ln–Ga Bonds by Salt Metathesis and Ga–Ga Bond Reduction

Three gallyl lanthanide complexes [{(dipp-Bian)­Ga}₂Ln­(thf)₄] (Ln = Sm, Eu, Yb; dipp-Bian = 1,2-bis­[(2,6-diisopropylphenyl)­imino]­acenaphthene), in which the lanthanide atoms are coordinated by only two {(dipp-Bian)­Ga}⁻ ligands and THF, are reported. Two unsupported Ln–Ga bonds are found in each compound. The gallyl lanthanide complexes have been obtained by two synthetic pathways: (1) reductive insertion of the lanthanide metals into the Ga–Ga bond of [{(dipp-Bian)­Ga}]₂ and (2) salt metathesis of [(dipp-Bian)­GaK­(thf)₅] with LnI₂. Moreover, the samarium compound [{(dipp-Bian)­Ga}₂Sm­(thf)₄] was additionally obtained in a reductive pathway from SmI₃ and [(dipp-Bian)­GaK­(thf)₅]. The length of the Ln–Ga bond strongly depends on packing effects. The reaction of TmI₂(thf)₅ and [(dipp-Bian)­GaK­(thf)₅] gave the Tm­(III) complex [{(dipp-Bian)­Ga–Ga­(dipp-Bian)}­(C₄H₈O)­TmI­(thf)₅], in which one THF ring was opened and reduced twice, forming the formal double negative charged anion (O-CH₂-CH₂-CH₂-CH₂)^2–. This thulium compound and its dysprosium analogue [{(dipp-Bian)­Ga–Ga­(dipp-Bian)}­(C₄H₈O)­DyI­(thf)₅] were also obtained in an alternative approach by reacting LnI₂(thf)_x (Ln = Tm, Dy) with [(dipp-Bian)­Ga]₂ in THF. All new compounds were structurally characterized by single-crystal X-ray diffraction. The ytterbium complex shows the shortest Yb­(II)–Ga bond distances reported so far.