Different coordination modes of trans-2-{[(2-methoxyphenyl)imino]methyl}phenoxide in rare-earth complexes: influence of the metal cation radius and the number of ligands on steric congestion and ligand coordination modes.

Abstract

A simple and effective synthetic route to homo- and heteroleptic rare-earth (Ln= Y, La and Nd) complexes with a tridentate Schiff base anion has been demonstrated using exchange reactions of rare-earth chlorides with in-situ-generated sodium (E)-2-{[(2-methoxyphenyl)imino]methyl}phenoxide in different molar ratios in absolute methanol. Five crystal structures have been determined and studied, namely tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3O1,N,O2)lanthanum, [La(C14H12NO2)3], (1), tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3O1,N,O2)neodymium tetrahydrofuran disolvate, [La(C14H12NO2)3]·2C4H8O, (2)·2THF, tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-κ3O1,N,O2;κ3O1,N,O2;κ2N,O1-yttrium, [Y(C14H12NO2)3], (3), dichlorido-1κCl,2κCl-μ-methanolato-1:2κ2O:O-methanol-2κO-(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ3O1,N,O2:2κO1)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-1κ3O1,N,O2;2κ3O1,N,O2-diyttrium-tetrahydrofuran-methanol (1/1/1), [Y2(C14H12NO2)3(CH3O)Cl2(CH4O)]·CH4O·C4H8O, (4)·MeOH·THF, and bis(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ3O1,N,O2:2κO1)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato-2κ3O1,N,O2)sodiumyttrium chloroform disolvate, [NaY(C14H12NO2)4]·2CHCl3, (5)·2CHCl3. Structural peculiarities of homoleptic tris(iminophenoxide)s (1)-(3), binuclear tris(iminophenoxide) (4) and homoleptic ate tetrakis(iminophenoxide) (5) are discussed. The nonflat Schiff base ligand displays μ2-κ3O1,N,O2:κO1 bridging, and κ3O1,N,O2 and κ2N,O1 terminal coordination modes, depending on steric congestion, which in turn depends on the ionic radii of the rare-earth metals and the number of coordinated ligands. It has been demonstrated that interligand dihedral angles of the phenoxide ligand are convenient for comparing steric hindrance in complexes. (4)·MeOH has a flat Y2O2 rhomboid core and exhibits both inter- and intramolecular MeO-H...Cl hydrogen bonding. Catalytic systems based on complexes (1)-(3) and (5) have demonstrated medium catalytic performance in acrylonitrile polymerization, providing polyacrylonitrile samples with narrow polydispersity.