Yttrium bis(alkyl) and bis(amido) complexes bearing N,O multidentate ligands. Synthesis and catalytic activity towards ring‐opening polymerization of L ‐lactide

Methoxy‐modified β‐diimines HL1 and HL2 reacted with Y(CH2SiMe3)3(THF)2 to afford the corresponding bis(alkyl)s [L1Y(CH2SiMe3)2] (1) and [L2Y(CH2SiMe3)2] (2), respectively. Amination of 1 with 2,6‐diisopropyl aniline gave the bis(amido) counterpart [L1Y{N(H)(2,6‐iPr2C6H3)}2] (3), selectively. Treatment of Y(CH2SiMe3)3(THF)2 with methoxy‐modified anilido imine HL3 yielded bis(alkyl) complex [L3Y(CH2SiMe3)2(THF)] (4) that sequentially reacted with 2,6‐diisopropyl aniline to give the bis(amido) analogue [L3Y{N(H)(2,6‐iPr2C6H3)}2] (5). Complex 2 was “base‐free” monomer, in which the tetradentate β‐diiminato ligand was meridional with the two alkyl species locating above and below it, generating tetragonal bipyramidal core about the metal center. Complex 3 was asymmetric monomer containing trigonal bipyramidal core with trans‐arrangement of the amido ligands. In contrast, the two cis‐located alkyl species in complex 4 were endo and exo towards the O,N,N tridentate anilido‐imido moiety. The bis(amido) complex 5 was confirmed to be structural analogue to 4 albeit without THF coordination. All these yttrium complexes are highly active initiators for the ring‐opening polymerization of L‐LA at room temperature. The catalytic activity of the complexes and their “single‐site” or “double‐site” behavior depend on the ligand framework and the geometry of the alkyl (amido) species in the corresponding complexes.