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Four chiral dinuclear rare-earth metal complexes [REL1]2(RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H3L1(H3L1= (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe3)2]3with Trost proligand H3L1in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.

Highly efficient and selective hydroboration of aldehydes and ketones with HBpin is achieved by using the simple and convenient n-BuLi as a catalyst. The reaction proceeds rapidly with low catalyst loading (0.1–0.5 mol %) under mild conditions. Key features include the high catalytic efficiency, exceptional functional group compatibility, ample substrate scope, and high selectivity for aldehydes over ketones. Computational studies were carried out to provide a mechanistic insight into the n-BuLi catalyzed hydroboration of aldehydes/ketones with HBpin.

Attempted synthesis of tris(β‐diketiminato)lanthanide complexes [Ln(L2,6‐Me2)3] (L2,6‐Me2= [{N(C6H3Me2‐2,6)C(Me)}2CH]) resulted in ligand deprotonation, and different outcomes depending on the central metal used were observed. Reaction of YbCl3with NaL2,6‐Me2(3 equiv.) afforded the five‐membered cyclometalated ytterbium β‐diketiminate complex [Yb(L2,6‐Me2)(L2,6‐Me2)dep] (1). The same reaction with LnCl3(Ln = Nd, Sm, and Er) gave the new complexes composed of one normal L2,6‐Me2and one deprotonated neighboring benzazacyclopentane ligand derived from deprotonation of the 2‐methyl group followed by an attack of thecarbon atom on the β‐diketiminate backbone, [Ln(L2,6‐Me2)(L2,6‐Me2)dep′(thf)] [Ln = Nd (2), Sm (3), and Er (4)]. The bonding mode in the {Ln(L2,6‐Me2)dep′} moiety was also found to depend on the central metal ions.

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

Ring‐opening polymerization of ɛ‐caprolactone (ɛ‐CL) was carried out using β‐diketiminato‐supported monoaryloxo ytterbium chlorides L1Yb(OAr)Cl(THF) (1) [L1 = N,N′‐bis(2,6‐dimethylphenyl)‐2,4‐pentanediiminato, OAr = 2,6‐di‐tert‐butylphenoxo‐], and L2Yb(OAr′)Cl(THF) (2) [L2 = N,N′‐bis(2,6‐diisopropylphenyl)‐2,4‐pentanediiminato, OAr′ = 2,6‐di‐tert‐butyl‐4‐methylphenoxo‐], respectively, as single‐component initiator. The influence of reaction conditions, such as polymerization temperature, polymerization time, initiator, and initiator concentration, on the monomer conversion, molecular weight, and molecular weight distribution of the resulting polymers was investigated. Complex 1 was well characterized and its crystal structure was determined. Some features and kinetic behaviors of the CL polymerization initiated by these two complexes were studied. The polymerization rate is first order with respect to monomer. The Mn of the polymer increases linearly with the increase of the polymer yield, while polydispersity remained narrow and unchanged throughout the polymerization in a broad range of temperatures from 0 to 50 °C. The results indicated that the present system has a “living character”. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1147–1152, 2006

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)