Abstract:
Rare-earth-metal alkyl complexes are generally well studied for the smaller and intermediate- sized metals. Particularly scandium and yttrium play a special role, since they form diamagnetic trivalent complexes and possess an NMR-active nuclei, which are suitable for systematic studies of heteronuclear NMR chemical shifts. Additionally, ytterbium has been shown to be well suited for these investigations being paramagnetic in the trivalent oxidation state and diamagnetic in the divalent state. This enables the investigation of stabilizing effects of highly reactive alkyl systems and their impact on NMR shifts.
Firstly, the reaction of ScCl3 and Li[CH(SiMe3)2] (“Lappert’s alkyl”) was investigated, from which a series of new scandium complexes emerged, depending on the molar ratio of the alkylating agent employed. Furthermore, all complexes were systematically investigated by 45Sc NMR spectroscopy, and the neosilyl complex [Li(thf)4][Sc(CH2SiMe3)4] showed the maximum downfield shift δ(45Sc) = 933.4 ppm of any scandium complex to date. Afterwards, yttrium tris(trimethylsilylmethyl) donor adduct complexes were synthesized with the aim of grafting them onto monodisperse silica nanoparticles and proving the existence of a reactive Y–C alkyl moiety on the surface via reaction with CO2 and moist air. Then, three up to now unknown types of ate complexes with the formulae [Li(thf)4][LiSc2(CH2SiMe3)8], [Li(thf)4][La(CH2SiMe3)4(thf)] and Li3Y(CH2SiMe3)6 were synthesized. The decomposition products of the latter complex were investigated in depth, wherein strong clues for an alkylidene formation were found.
Moreover, the neutral cyclic ligand Me3TACN was used to synthesize a series of yttrium and ytterbium methyl complexes. Yttrium complexes (Me3TACN)YMe3−nCln could be synthesized and constitute the first featuring where mono-, di and trimethyl complexes of the same type. Trivalent ytterbium complex (Me3TACN)YbMe3 was synthesized and reacted with group 13 methyl compounds, probing its proneness to self-reduction via a reaction with a Lewis acid. Reaction with AlMe3 gave divalent (Me3TACN)Yb(AlMe4)2, presumably via a methyl radical pathway, whereas reaction with GaMe3 only led to 1:1 adduct formation in the form of trivalent (Me3TACN)YbMe2(GaMe4). THF addition and subsequent reduction with potassium graphite led to isolable divalent donor adduct [(Me3TACN)YbMe2]2.
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