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Download file# Amine Elimination Reactions between Homoleptic Silylamide Lanthanide Complexes and an Isopropylidene-Bridged Cyclopentadiene−Fluorene System

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posted on 19.06.2002, 00:00 authored by Aswini K. Dash, Abbas Razavi, André Mortreux, Christian W. Lehmann, Jean-François CarpentierThis contribution describes the amine elimination process as an alternative synthetic route
to traditional salt metathesis for introducing the isopropylidene-bridged unsymmetrical
ligand C

_{5}H_{5}-CMe_{2}-C_{13}H_{9}(CpH-CMe_{2}-FluH) onto group III-metal centers (Y, La, Nd) to give in turn the neutral, ate-complex-free*ansa*-lanthanidocenes. The reactions of homoleptic Ln[N(SiMe_{3})_{2}]_{3}(Ln = Y (**1**), La (**2**), Nd (**3**)) with CpH-CMe_{2}-FluH (**4**) in THF under mild conditions lead to the formation of*ansa*-complexes (η^{5},η^{5}-Cp-CMe_{2}-Flu)Ln(η^{5}-Cp-CMe_{2}-FluH) (Ln = Y (**8**), La (**12**), Nd (**13**)) in 70−84% isolated yields (based on**4**). These reactions proceed via the rapidly formed bis(amido)lanthanide intermediates (η^{5}-Cp-CMe_{2}-FluH)Ln[N(SiMe_{3})_{2}]_{2}(Ln = Y (**5**), La (**9**)), which undergo readily disproportionation/ligand redistribution reactions at 5−23 °C to give either a mono(amido)lanthanide complex (η^{5}-Cp-CMe_{2}-FluH)_{2}Ln[N(SiMe_{3})_{2}] (Ln = Y (**6**)) or another species assumed to be the binuclear complex (η^{5}-Cp-CMe_{2}-FluH)_{2}Ln[μ-N(SiMe_{3})_{2}]_{2}Ln[N(SiMe_{3})_{2}]_{2}(Ln = La (**10**)), respectively. Complexes**6**and**10**undergo an intramolecular amine elimination reaction under THF reflux to yield the corresponding*ansa*-complexes**8**and**12**, respectively. The reversibility of the process has been investigated in the yttrium case: complex**8**converts back to**6**in the presence of (SiMe_{3})_{2}NH in toluene at 90 °C with 50% conversion after 12 h. The effect of a noncoordinating apolar solvent on the reaction outcome of tris(amido) complexes**1**−**3**with**4**has been also studied using toluene, in which the low solubility presumably shifts the disproportionation equilibria and leads to the isolation of another class of compounds Ln(η^{5}-Cp-CMe_{2}-FluH)_{3}(Ln = Y (**7**), La (**11**)) in reasonable yields. Compounds**5**−**12**have been characterized in solution by 1D and 2D NMR techniques (^{1}H,^{13}C,^{1}H−^{1}H COSY, and^{1}H−^{13}C HETCOR), and the solid state structures of**6**and of the mono(THF) adducts of*ansa*-lanthanidocenes**12**and**13**have been established by X-ray diffraction studies. The latter*ansa*-complexes feature very narrow Cp(centroid)−Ln−Flu(centroid) bite angles (Ln = La, 103.67(1)°; Ln = Nd, 105.08(1)°).## History

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2 NHcomplexes featureTHF refluxintramolecular amine elimination reactioncomplexes 8Complexes 62 D NMR techniques8 convertsreaction outcomeCOSYCMe 2LnHomoleptic Silylamide Lanthanide Complexes1 Hsalt metathesis1 D12 hamine elimination processC 13 H 9SiMe 3noncoordinating apolardisproportionation equilibriastate structureslatter ansa13 CAmine Elimination ReactionsFluHHETCORlanthanidocenes 12