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

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posted on 2012-11-05, 00:00 authored by Timothy J. Boyle, Daniel T. Yonemoto, Leigh Anna Steele, Joshua Farrell, Peter Renehan, Taylor Huhta
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 (OBut)] precursors led to the isolation of [(OPri)2Ti]2(μ-OEA-DBP4) (3), [(ONep)2Ti]2(μ-OEA-DBP4) (4), and [(OBut)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 37, 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.