A series of neutral yttrium guanidinates supported by an amine-bridged bis(phenolate) ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of 1,4-dioxan-2-one (p-dioxanone, PDO) were explored. Metathesis reactions of amine-bridged bis(phenolate) yttrium chlorides LLnCl(THF) [L = Me2NCH2CH2N{CH2-(2-OC6H2-tBu2-3,5)}2] with corresponding lithium guanidinates generated in situ in a 1:1 molar ratio in THF gave the neutral yttrium guanidinates LY[R2NC(NR1)2] [R1 = −Cy, R2N = −N(TMS)2 (1), −NiPr2 (2), −N(CH2)5 (3); R1 = −iPr, R2N = −NiPr2 (4) −NPh2 (5))]. These complexes were well characterized by elemental analyses, IR, and NMR spectroscopy. The definitive molecular structures of these complexes were determined by single-crystal X-ray analysis. It was found that these complexes can efficiently initiate the ring-opening polymerization (ROP) of PDO, and the catalytic activity is affected by the nature of the guanidinate groups with the active sequence of 1 > 2 ≈ 3 ≈ 4 > 5. The influences of reaction conditions such as polymerization time, polymerization temperature, and molar ratio of monomer to initiator on the polymerization were also investigated. The polymerization kinetics of PDO catalyzed by complex 1 is first-order with respect to monomer concentration, and the apparent activation energy amounts to 30.8 kJ mol–1. The mechanistic investigations showed that the ROP of PDO proceeded through a coordination–insertion mechanism with a rupture of the acyl–oxygen bond of the monomer. MALDI-TOF mass spectrum analysis of the oligomer revealed that there are two kinds of polymer chains in this catalytic system, e.g., the linear chains H–[OCH2CH2OCH2CO] n –OH and the PPDO macrocycles.

Eight rare-earth metal guanidinates supported by a versatile family of chelating amine-bridged bis(phenolate) ligands were synthesized. Metathesis reactions of rare-earth metal chlorides [LnClL 1 (THF)] stabilized by amine-bridged bis(phenolate) ligand L 1 with in situ generated lithium guanidinates in a 1 : 1 2 ) 5 (2)]. Insertion reactions of the yttrium amides bearing bridged bis(phenolate) ligands with 1 equiv of N,N 0 -diisopropylcarbodiimide (DIC) yielded six yttrium guanidinates 2 ] (8), respectively. The behaviors of complexes 1-8 in the polymerization of rac-lactide (LA) and rac-b-butyrolactone (BBL) were also explored. It was found that complexes 1-8 efficiently initiated the ring-opening polymerization (ROP) of rac-LA and rac-BBL in a controlled manner, providing highly heterotactic polylactide (P r up to 0.99) and highly syndiotactic poly(3-hydroxybutyrate) (P r up to 0.82). The framework of the bridge played a significant role in governing the stereoselectivity, while guanidinate groups work as initiating groups.

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Synthesis and Characterization of Ytterbium Guanidinates Stabilized by Bridged Bis(phenolate) Ligand and Their Application for the Hydrophosphonylation Reaction of Aldehydes. -Ytterbium guanidinates are shown to be highly efficient catalysts for the hydrophosphonylation of various aldehydes (16 examples) under mild conditions. -(ZENG, T.; QIAN, Q.; WANG, Y.; YAO*, Y.; SHEN, Q.; J. Organomet. Chem. 779 (2015) 14-20, http://dx.doi.org/10.1016/j.jorganchem.2014.12.021 ; Coll. Chem., Chem. Eng. Mater. Sci., Soochow Univ., Suzhou 215123, Peop. Rep. China; Eng.) -M. Paetzel 25-230