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.

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-κO,N,O)lanthanum, [La(CHNO)], (1), tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κO,N,O)neodymium tetrahydrofuran disolvate, [La(CHNO)]·2CHO, (2)·2THF, tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-κO,N,O;κO,N,O;κN,O-yttrium, [Y(CHNO)], (3), dichlorido-1κCl,2κCl-μ-methanolato-1:2κO:O-methanol-2κO-(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κO,N,O:2κO)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-1κO,N,O;2κO,N,O-diyttrium-tetrahydrofuran-methanol (1/1/1), [Y(CHNO)(CHO)Cl(CHO)]·CHO·CHO, (4)·MeOH·THF, and bis(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κO,N,O:2κO)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato-2κO,N,O)sodiumyttrium chloroform disolvate, [NaY(CHNO)]·2CHCl, (5)·2CHCl. 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 μ-κO,N,O:κO bridging, and κO,N,O and κN,O 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 YO 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.