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Organolanthanide-Induced C-C Bond Formation. Preparation and Properties of Monomeric Lanthanide Aldolates and Enolates

By J.H. Teuben, M. Maters, H.J. Heeres, G. Helgesson and S. Jagner


The reactivity of early-lanthanide carbyls Cp*2LnCH(SiMe3)2 (1, Ln = La; 2, Ln = Ce) toward ketones has been studied. No reaction was observed with the bulky di-tert-butyl ketone. The corresponding lanthanum hydride [Cp*2LaH]2 (3) is more reactive and afforded the addition product Cp*2LaOCH(t-Bu)2·O=C(t-Bu)2 (4). Hydrogen transfer and formation of lanthanide aldolates Cp*2LnOCMe2CH2C(=O)Me (5, Ln = Ce; 6, Ln = La) together with the protonated carbyl CH2(SiMe3)2 were observed when 1 or 2 was treated with acetone. The molecular structure of the cerium analogue 5 was determined by X-ray diffraction and was found to be a monomeric bent metallocene compound with a η2-coordinated aldol fragment. Cell data: monoclinic, P21/n, a = 10.386 (5) Å, b = 17.32 (1) Å, c = 14.488 (3) Å, β = 99.33 (3)°, Dcalcd (Z = 4) = 1.36 g·cm-3. Least-squares refinement based on 3343 reflections converged to R = 0.035 and Rw = 0.041. Addition of 3-pentanone to the carbyls 1 and 2 did not result in C-C coupling but provided enolate-ketone adducts Cp*2LnOC(Et)=C(H)Me·O=CEt2 (7, Ln = La; 8, Ln = Ce). Reactions of the carbyls 1 and 2 with 4-methyl-5-hydroxy-5-ethyl-3-heptanone yielded the enolate-ketone adducts as well and suggest that the differences in reactivity between acetone and 3-pentanone are thermodynamic and not kinetic in origin.

Year: 1992
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