Synthesis, Reactivity, and Structural Characterization of Sodium and Ytterbium Complexes Containing New Imidazolidine-Bridged Bis(phenolato) Ligands

A new imidazolidine-bridged bis(phenol) [ONNO]H2 ([ONNO]H2 = 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)imidazolidine) was prepared in relatively high yield by Mannish reaction of 2,4-di-tert-butylphenol, formaldehyde,
and ethylenediamine in a 2:3:1 molar ratio. Reaction of the bis(phenol) with NaH in THF, after workup, afforded the
sodium bis(phenolate) {[ONNO]Na2(THF)2}2·2THF (1) as a dimeric tetranuclear complex in an almost quantitative
yield. Reaction of YbCl3 with complex 1 in a 2:1 molar ratio in THF, in the presence of HMPA, produced the
desired bis(phenolate) ytterbium dichloride as bimetallic complex [ONNO]{YbCl2(HMPA)}2·2.5C7H8 (2). Complex 2
can be used as a precursor for the synthesis of ytterbium derivatives by salt metathesis reactions. Reaction of
complex 2 with NaOiPr in a 1:2 molar ratio in THF led to the formation of bimetallic alkoxide [ONNO]{Yb(μ-OiPr)Cl(HMPA)}2·THF (3). However, the residual chlorine atoms in complex 3 are inactive for the further substituted
reaction. Further study revealed that the bulkiness of the reagent has profound effect on the outcome of the
reaction. Complex 2 reacted with bulky NaOAr (ArO = 2,6-di-tert-butyl-4-methylphenoxo) or NaNPh2 in a 1:2 molar
ratio under the same reaction conditions, after workup, to give the ligand redistributed products, (ArO)2YbCl(HMPA)2 (4) and [ONNO]YbCl(HMPA)2 (5) for the former and complexes 5 and (Ph2N)2YbCl(HMPA)2 (6) for the
latter. If the molar ratio of complex 2 to NaNPh2 decreased to 1:4, the expected ligand redistributed products
[ONNO]YbNPh2(HMPA) (7) and (Ph2N)3Yb(HMPA)2·C7H8 (8) can be isolated in high yields. All of the complexes
were well characterized, and the definitive molecular structures of complexes 1−4, 7, and 8 were provided by
single-crystal X-ray analysis.