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Alkylyttrium Complexes of Amidine–Amidopyridinate Ligands. Intramolecular C(sp3)–H Activation and Reactivity Studies

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journal contribution
posted on 11.03.2013, 00:00 by Vasily Rad’kov, Vincent Dorcet, Jean-François Carpentier, Alexander Trifonov, Evgeny Kirillov
The new multidentate amidine–aminopyridine proligand {NMe2NNMe2CMeNMe2}H (1) was used in σ-bond metathesis reactions with the trialkyl precursors Y­(CH2­SiMe3)3(THF)2 and Y­(CH2C6H4-o-NMe2)3. These reactions generate the dialkyl complexes {NMe2NNMe2CMeNMe2}­Y­(CH2SiMe3)2(THF) (2a) and {NMe2NNMe2CMeNMe2}­Y­(CH2C6H4-o-NMe2)2 (2b), respectively, which were characterized by NMR spectroscopy and microanalysis (for 2b). Complex 2a is unstable at −30 °C in toluene and selectively undergoes intramolecular C­(sp3)–H activation to give {NMe2NNMe2CMeNMe–CH2}­Y­(CH2SiMe3)­(THF) (2a′), authenticated by X-ray crystallography, NMR spectroscopy, and elemental analysis. The reactivity of 2a′ toward a number of Lewis and Brønsted acids and bases as well as oxidants and reductants was explored. In the course of these studies, the new complexes {NMe2NNMe2CMeNMeCH2B­(C6F5)3}­Y­(CH2SiMe3)­(THF) (3), [{NMe2NNMe2CMeNMeCH2}­Y­(CH2SiMe3)­(THF)x]+[BPh4] (4), {NMe2NNMe2CMeNMeCH2}­Y­(iPrNC­(PPh2)­NiPr) (5), [{NMe2NNMe2CMeNMe2}­Y­{(μ2-BH3)­(μ2-NH)}]2 (6), and [{NMe2NNMe2CMeNMeCH2(μ-O)}­Y­(CH2SiMe3)]2 (7) were isolated and characterized by NMR spectroscopy and X-ray crystallography and microanalysis (for 6 and 7). Complex 6 was found to be active in the ROP of rac-lactide, affording slightly heterotactic-enriched PLAs.