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

Abstract

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.