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

New heterobimetallic borohydrido neodymium complexes {[OONN]Nd-1(BH4)(mu-BH4)Li(THF)}(2) (1) and [OONN]Nd-3(BH4)(mu-BH4)Li(THF)(2) (3) supported by diamino-bis(phenoxide) ligands ([OONN](1) = {CH2N(Me)CH2-3,5-Me,t-Bu-C6H2O}(2); [OONN](3) = C5H4NCH2N-{ 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 Li-2[OONN](n) and isolated in high yields. In the case of Li-2[OONN](2) ([OONN](2) = Me2NCH2CH2N{CH2-3,5-t-Bu-C6H2O}(2)), the same synthetic procedure afforded the heterobimetallic bis(phenoxide) complex Li{Nd[OONN 2] 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 beta-butyrolactone under mild conditions (20 degrees C), providing atactic polymers with controlled molecular weights and relatively narrow polydispersities (M-w/M-n = 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.