Charge‐Separated and Molecular Heterobimetallic Rare Earth–Rare Earth and Alkaline Earth–Rare Earth Aryloxo Complexes Featuring Intramolecular Metal–π‐arene Interactions

Abstract

Treatment of a rare earth metal (Ln) and a potential divalent rare earth metal (Ln') or an alkaline earth metal (Ae) with 2,6-diphenylphenol (HOdpp) at elevated temperatures (200-250 degrees C) afforded heterobimetallic aryloxo complexes, which were structurally characterised. A charge-separated species [(Ln'/Ae)(2)(Odpp)(3)][Ln(Odpp)(4)] was obtained for a range of metals, demonstrating the similarities between the chemistry of the divalent rare earth metals and the alkaline earth metals. The [(Ln'/Ae)(2)(Odpp)(3)](+) cation in the heterobimetallic structures is unusual in that it consists solely of bridging aryloxide ligands. A molecular heterobimetallic species [AeEu(Odpp)(4)] (Ae = Ca, Sr, Ba) was obtained by treating an alkaline earth metal and Eu metal with HOdpp at elevated temperatures. Similarly, [BaSr(Odpp)(4)] was prepared by treating Ba metal and Sr metal with HOdpp. Treatment of [Ba(2)(Odpp)(4)] with [Mg(Odpp)(2)(thf)(2)] in toluene afforded [Ba(2)(Odpp)(3)][Mg(Odpp)(3)(thf)]. Analogous solution-based syntheses were not possible for [(Ln'/Ae)(2)(Odpp)(3)][Ln(Odpp)(4)] complexes, for which the free-metal route was essential. As a result of the absence of additional donor ligands, the crystal structures of the heterobimetallic complexes feature extensive pi-Ph-metal interactions involving the pendant phenyl groups of the Odpp ligands, thus enabling the large electropositive metal atoms to attain coordination saturation. The charge-separated heterobimetallic species were purified by extraction with toluene/thf mixtures at ambient temperature (Ba-containing compounds) or by extraction with toluene under pressure above the boiling point of the solvent (other products). In donor solvents, heterobimetallic complexes other than those containing barium were found to fragment into homometallic species.

Advances in alkaline earth-nitrogen chemistry

“…Metal· · ·C() interactions are a prevalent stabilizing force in alkaline earth metal chemistry [13][14][15][16], as summarized in Table 1. However, less is known about the role that agostic interactions of the type M· · ·H-C play in stabilizing these metal centers.…”

Developments in the Coordination Chemistry of Europium(II)

“…The Eu 2+ centers in [Eu 2 -(Odpp) 3 ] + are bridged by aryloxide ligands and have coordination modes of η 4 :η 2 :η 1 and η 1 :η 6 :η 3 with π-arene–Eu interactions. [50] In contrast to the charge-separated complexes, heterobimetallic complexes [CaEu(Oddp 4 )] ( 35 ), [SrEu(Oddp) 4 ] ( 36 ), and [BaEu(Oddp) 4 ] ( 37 ) were produced upon reaction of Eu 0 and an alkaline-earth metal (Ca 0 , Sr 0 , or Ba 0 ) with OHdpp at high temperatures (210–235 °C). However, when Eu 0 was treated with HOdpp in the presence of MOdpp (M = Na 0 , K 0 , and Li 0 ) at elevated temperature (210 °C), heterobimetallic Eu 2+ -containing complexes [NaEu(Oddp) 3 ]·PhCH 3 ( 38 ) and [KEu(Oddp) 3 ]·2.5PhCH 3 ( 39 ) and the mixed-valent complex [Eu 2 (Oddp) 3 ]-[Eu(Oddp) 4 ] ( 40 ) were obtained.…”

π-Coordination as a structure determining principle: structural characterization of [K(Odpp)]∞, and {[K2(Odpp)2H2O]2}∞

“…In an attempt to expand this work to combinations of two alkali metals, identical reaction conditions were utilized to those used previously [1][2][3]. In analogy to prior work, a distinct sensitivity toward solvents was detected; the use of polar THF has previously resulted in the isolation of homometallic species [2].…”

“…This route had been used successfully to prepare aryloxide based heterobimetallic species containing combinations of alkali-alkaline earth metals [1][2][3], two different alkaline earth metals [3], and alkali-lanthanide metal combinations [3,4,11].…”

“…The capacity of steric saturation of metal centers through secondary interactions, such as MÀ ÀCp interactions, has been recently demonstrated by a series of monoand heterobimetallic compounds based on the 2,6-diphenylphenol (HOdpp) ligand [1][2][3][4][5][6]. In these complexes, extensive metal-Cp interactions support the low metal coordination numbers.…”