Coordination Chemistry of N,N,N′,N′‑Tetrakis(3,5-substituted benzyl-2-oxide)-2,2′-(ethylenedioxy)diethanamine Modified Group 4 Metal Alkoxides

The coordination behavior of a set of (ethylenedioxy)­diethanamine-based tetraphenol ligands with a series of Group 4 metal alkoxides ([M­(OR)₄]) was determined. The ligands were synthesized from a modified Mannich reaction and fully characterized as N,N,N′,N′-tetrakis­(3,5-tert-butyl-benzyl-2-hydroxy)-2,2′-(ethylenedioxy)­diethanamine, termed H₄-OEA-DBP₄ (1), and N,N,N′,N′-tetrakis­(3,5-chloro-benzyl-2-hydroxy)-2,2′-(ethylenedioxy)­diethanamine, termed H₄-OEA-DCP₄ (2). The reaction of 1 with a set of [M­(OR)₄] [M = Ti, Zr, or Hf; OR = iso-propoxide (OPrⁱ), neo-pentoxide (ONep), or tert-butoxide (OBu^t)] precursors led to the isolation of [(OPrⁱ)₂Ti]₂(μ-OEA-DBP₄) (3), [(ONep)₂Ti]₂(μ-OEA-DBP₄) (4), and [(OBu^t)₂M]₂(μ-OEA-DBP₄) where M = Ti (5), Zr (6), or Hf (7). In addition, the [(ONep)₂Ti]₂(μ-OEA-DCP₄) (4a) derivative was isolated from the reaction of 2 and [Ti­(ONep)₄], demonstrating the similarity of coordination behavior between the two OEA-R₄ ligands. For 3–7, the metal center adopts a slightly distorted octahedral geometry by binding the two O atoms of the phenoxide moiety, as well as one N and one O atom from the OEA moieties, while retaining two of the original OR ligands. Solution NMR demonstrates inequivalent protons for the majority of the bound OEA ligands, which argues for retention of structure in solution. The synthesis and characterization of these compounds are presented in detail.