Reversible Carbon-Carbon Bond Formation in Organolanthanide Systems. Preparation and Properties of Lanthanide Acetylides [Cp*2LnC≡CR], and Their Rearrangement Products [Cp*2Ln]2(μ-η2: η2-RC4R) (Ln = La, Ce, R = Alkyl)

H.J. Heeres, J. Nijhoff, J.H. Teuben, R. D. Rogers

OnderzoeksoutputAcademic

109 Citaten (Scopus)

Samenvatting

The early lanthanide carbyls Cp*2LnCH(SiMe3)2 (1, Ln = Ce; 2, Ln = La) react with terminal alkynes HC≡CR (R = Me, t-Bu) to produce oligomeric acetylides [Cp*2LnC≡CR]n (3, Ln = Ce, R = Me; 4, Ln = La, R = Me; 5, Ln = Ce, R = t-Bu). The acetylides are not stable in solution and rearrange to give the carbon-carbon coupled products, [Cp*2Ln]2(μ-η2:η2-RC4R) (6, Ln = Ce, R = Me; 7, Ln = La, R = Me; 8, Ln = Ce, R = t-Bu). The acetylide carbon-carbon coupling reaction is reversible in solution. Thermodynamic and kinetic parameters for this process were determined for the [Cp*2LaC≡CMe]n/[Cp*2La]2(μ-η2:η2-MeC4Me) couple: ΔG⊖ = 4.5 ± 0.4 kJ/mol; k1 = 8.3(±0.4) × 10-5 s-1; k-1 = 1.1(±0.7) × 10-5 s-1, and ΔG‡ = 96.3(±0.1) kJ/mol (298 K). The molecular structures of 6 and 8 were determined by single-crystal X-ray diffraction and shown to consist of two Cp*2Ce units bridged by a conjugated RC4R group. Cell data for 6: monoclinic, P21/n, a = 10.670(8) Å, b = 25.081(9) Å, c = 16.706(9) Å, β = 102.41(7)°, Dcalcd(Z = 4) = 1.37 g·cm-3. Least-squares refinement based on 4179 reflections converged to R = 0.046 and Rw = 0.053. Cell data for 8: monoclinic, P21/n, a = 11.376(6) Å, b = 14.151(5) Å, c = 15.541(4) Å, β = 103.92(4)°, Dcalcd(Z = 2) = 1.34 g·cm-3. Least-squares refinement based on 3502 reflections converged to R = 0.031 and Rw = 0.040. Protolysis of 6 and 7 with 2,6-di-tertbutyl-4-methylphenol affords (E)-2-hexen-4-yne, exclusively. Contrastingly, a mixture of enynes and butatrienes is formed upon protolysis of 8. Both 5 and 8 catalyze the dimerization of tert-butylacetylene to 2,4-di-tert-butyl-1-buten-3-yne.
Originele taal-2English
Aantal pagina's9
TijdschriftOrganometallics
Volume12
Nummer van het tijdschrift7
DOI's
StatusPublished - 1993

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