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-κ ³ O ¹ ,N,O ² )lanthanum, [La(C ₁₄ H ₁₂ NO ₂ ) ₃ ], (1), tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ ³ O ¹ ,N,O ² )neodymium tetrahydrofuran disolvate, [La(C ₁₄ H ₁₂ NO ₂ ) ₃ ]·2C ₄ H ₈ O, (2)·2THF, tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-κ ³ O ¹ ,N,O ² ;κ ³ O ¹ ,N,O ² ;κ ² N,O ¹ -yttrium, [Y(C ₁₄ H ₁₂ NO ₂ ) ₃ ], (3), dichlorido-1κCl,2κCl-μ-methanolato-1:2κ ² O:O-methanol-2κO-(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ ³ O ¹ ,N,O ² :2κO ¹ )bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-1κ ³ O ¹ ,N,O ² ;2κ ³ O ¹ ,N,O ² -diyttrium-tetrahydrofuran-methanol (1/1/1), [Y ₂ (C ₁₄ H ₁₂ NO ₂ ) ₃ (CH ₃ O)Cl ₂ (CH ₄ O)]·CH ₄ O·C ₄ H ₈ O, (4)·MeOH·THF, and bis(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ ³ O ¹ ,N,O ² :2κO ¹ )bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato-2κ ³ O ¹ ,N,O ² )sodiumyttrium chloroform disolvate, [NaY(C ₁₄ H ₁₂ NO ₂ ) ₄ ]·2CHCl ₃ , (5)·2CHCl ₃ . 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 ₂ -κ ³ O ¹ ,N,O ² :κO ¹ bridging, and κ ³ O ¹ ,N,O ² and κ ² N,O ¹ 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 Y ₂ O ₂ 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.