Lanthanide borohydrides supported by an ansa-bis(amidinate) ligand with a rigid naphthalene linker: Synthesis, structure and catalytic activity in ring-opening polymerization of lactide

The reactions of Ln(BH4)3(THF)2 with an equimolar amount of the dilithium derivative of a bridged bis(amidine) containing a conformationally rigid naphthalene linker afforded heterobimetallic ansa-bis(amidinate) lanthanide borohydrides [1,8-C10H6{NC(tBu)N-2,6-Me2-C6H3}2]Ln(BH4)(μ-BH4)Li(THF)2 (Ln = Nd, 2; Sm, 3). In the solid state, intermolecular contacts between the lithium atom and the terminal borohydrido groups of these compounds lead to the formation of one-dimensional zigzag coordination polymer chains. Compounds 2 and 3 are active in the ring-opening polymerization (ROP) of racemic lactide at 20 °C, acting as single-site diinitiators with the two borohydride groups operative, and providing polymers with a slight heterotactic bias (Pr = 0.54–0.62), controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.5–1.7).