Synthesis, structure, and coordination chemistry of a neutral pyrrolyl-functionalized amidinate ligand

Abstract

A new o-phenylene-bridged ligand incorporating neutral pyrrolyl and amidino moieties with the formula 2-(2,5-Me₂C₄H₂N)C₆H₄NHC(Ph)NDipp (HL, Dipp = 2,6-ⁱPr₂C₆H₃) was prepared via the reaction of 2-(2,5-dimethylpyrrolyl)aniline with 2,6-ⁱPr₂C₆H₃NC(Cl)C₆H₅. Metalation of the ligand with an equivalent of alkali-metal bis(trimethylsilyl)amide produced the corresponding alkali-metal salts ML(thf)₂ (M = Na, 1; M = K, 2) and the ligand bonds to the alkali-metal center in κ²:η⁵ (for 1) and κ¹:η⁵:η⁶ (for 2) fashions, respectively. The alkali-metal salts 1 and 2 could be employed as synthons for generating rare-earth metal dichlorides LRECl₂(thf)₃ (RE = Y, 3; Er, 4; Yb, 5) by the metathesis reaction of 1 or 2 with RECl₃ in THF and the ligand coordinates to the rare-earth metal center by only the amidinate fragment in classic κ²-chelating mode. Furthermore, these rare-earth metal dichlorides could react with two equiv. of LiCH₂SiMe₃ and rare-earth metal dialkyl complexes LRE(CH₂SiMe₃)₂ (RE = Y, 6; Er, 7; Yb, 8) were obtained in good yields. In contrast to rare-earth metal dichlorides 3–5, complexes 6–8 are solvent-free and the ligand coordinates to the central ions through both the neutral pyrrolyl ring and amidinate moieties, thus forming a constrained geometry configuration. All complexes were characterized by spectroscopic methods, and their structures were determined by X-ray diffraction study.