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.