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A series of trisβdiketiminate ytterbium complexes with the general formula [YbL3] L = [NC6H5CMe]2CH–, LH1; [N4MeC6H4CMe]2CH–, L4Me2, and [N2MeC6H4CMe]2CH–, L2Me3 were synthesized and structurally characterized. All complexes have longer Yb–N bond lengths than other YbLcontaining derivatives, and complex 3has the longest average Yb–N bond length. A comparative study on the reactivity of complexes 1–3revealed that complex 3was a highly active catalyst for the polymerization of caprolactone and Llactide, as well as for the addition of amines to carbodiimides, whereas both complexes 1and 2were almost inactive under the same conditions. The active sequence is consistent with the distance of the Yb–N bond, which is reflected in the sterically induced activation of the bulky trisβdiketiminate ytterbium complexes.

Metathesis of {[4–XC6H4NCMe]2CH}Li with anhydrous lanthanide trichlorides LnCl3 in a 3:1 molar ratio yielded a series of trisβdiketiminate complexes with the general formula [LnLX3] [X = Cl, LCl: Ln = Pr 1, Nd 2, Sm 3; X = H, L: Ln = Nd 4; X = Me, LMe: Ln = Nd 5]. Reaction of sodium salt of βdiketiminate with anhydrous LnCl3in a 1:1 molar ratio in thf afforded the corresponding βdiketiminate lanthanide dichlorides [LClPrCl2thf2] 6, [LMeNdCl2thf2] 7, and [LiPr2NdCl2thf2] {LiPr2= [2,6iPr2C6H3NCMe]2CH–} 8, respectively. Each of these complexes was characterized, and the molecular structures of complexes 1–5and 8were determined by Xray singlecrystal structure analysis. Complexes 1–5were found to be very active singlecomponent initiators for the ringopening polymerization of caprolactone CL and Llactide LLA under mild conditions, giving polymers with high molecular weight and moderate polydispersities, whereas complexes 6–8displayed no activity under the same polymerization conditions. The high catalytic activity shown by trisβdiketiminate lanthanide complexes may be attributed to the activated Ln–βdiketiminate bond caused by the crowded coordination sphere around the central metal.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009

Two methods to synthesize homoleptic guanidinate lanthanide complex are described. The samarium guanidinate complex [Sm{Ph2NC(NCy)2}3]·2C7H8 (1) can be synthesized by the metathesis reaction of lithium guanidinate with anhydrous samarium trichloride in a 3:1 molar ratio. The analogous complexes [Ln{Ph2NC(NCy)2}3]·2C7H8 [Ln = Yb (2), Nd (3)] can also be synthesized by the insertion reaction of N,N'-dicyclohexylcarbodiimide into the Ln−N bond of [(THF)4Li][Ln(NPh2)4] in a 3:1 molar ratio in good yield. Complexes 1−3 were characterized by elemental analysis, IR and ¹H NMR spectroscopy. The molecular structures of complexes 1 and 3 were further determined by X-ray diffraction techniques. These complexes showed high activity for the ring-opening polymerization of trimethylene carbonate (TMC), giving polymers with Mw/Mn ranging from 1.41−1.73. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)