Lanthanide Borohydride Complexes of Bulky Guanidinate Ligands [(Me_3Si)_2NC(N-Cy)_2]_2Ln(-BH_4)_2Li(THF)_2 (Ln = Nd, Sm, Yb): Synthesis, Structure and Catalytic Activity in Lactide Polymerization

摘要

A series of new lanthanide borohydride complexes supported by bulky guanidinate ligands [(Me_3Si)_2NC(N-Cy)_2]_2Ln(-BH_4)2Li(THF)_2 [Ln = Nd (1), Sm (2), Yb (3)] was synthesized by the reaction of related tris(borohydride)s Ln(BH_4)_3(THF)_2 with a twofold molar excess of [(Me_3Si)_2NC(N-Cy)_2]Li in toluene at 65 . The complexes were isolated after recrystallization from hexane in 66, 64, and 68 % yield, respectively. X-ray diffraction studies revealed that compounds 1-3 are heterodimetallic complexes that have two borohydride ligands -bridging the lanthanide and lithium atoms. Those compounds, especially neodymium complex 1, act as monoinitiators for the ring-opening polymerization of racemic lactide, providing atactic polymers with a good degree of control, that is, controlled molecular weights and relatively narrow polydispersities (1.09 < Mw/Mn < 1.77), provided moderate substrate-to-initiator ratios are used.