Neodymium borohydride complexes supported by diamino-bis(phenoxide) ligands: Diversity of synthetic and structural chemistry, and catalytic activity in ring-opening polymerization of cyclic esters

Abstract

New heterobimetallic borohydrido neodymium complexes {[OONN] 1Nd(BH4)(μ-BH4)Li(THF)}2 (1) and [OONN]3Nd(BH4)(μ-BH4)Li(THF)2 (3) supported by diamino-bis(phenoxide) ligands ([OONN]1 = {CH 2N(Me)CH2-3,5-Me,t-Bu-C6H2O} 2; [OONN]3 = C5H4NCH 2N{CH2-3,5-Me,t-Bu-C6H2O} 2) were synthesized by the reactions of Nd(BH4) 3(THF)2 with equimolar amounts of dilithium derivatives of diamino-bis(phenol)s Li2[OONN]n and isolated in high yields. In the case of Li2[OONN]2 ([OONN]2 = Me2NCH2CH2N{CH2-3,5-t-Bu-C 6H2O}2), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN2]2} (2). The structures of complexes 1-3 were established by X-ray diffraction studies. Compounds 1-3 act as single-site initiators for the ring-opening polymerization (ROP) of racemic lactide and racemic β-butyrolactone under mild conditions (20°C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (Mw/Mn = 1.07-1.82). While 1 and 3 initiate polymerization via their borohydride groups, ROP with 2 proceeds via insertion into the Nd-O(ligand) bond. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011.