Enforcing Metal–Arene Interactions in Bulky p-Terphenyl Bis(anilide) Complexes of Group 2 Metals (Be–Ba): Potential Precursors for Low-Oxidation-State Alkaline Earth Metal Systems

Abstract

An extremely bulky p-terphenyl bis(aniline), p-C 6 H 4 {C 6 H 4 [N(H)TCHP]-2} 2 (TCHP = 2,4,6-tricyclohexylphenyl) TCHP TerphH 2 , has been developed. Deprotonation of a less bulky analogue, Dip TerphH 2 (Dip = 2,6-diisopropylphenyl), with BePh 2 affords the bimetallic system, [(BePh) 2 (μ-Dip Terph)] 1. Treating either TCHP TerphH 2 or Dip TerphH 2 with Mg-{CH 2 (SiMe 3 )} 2 gives the monomeric bis(anilide) complexes [Mg( Ar Terph)] (Ar = Dip 2, TCHP 3) which display rare examples of η 6 -arene coordination to the metal center. Treating 2 with THF leads to partial dissociation of the Mg•••arene interaction and formation of [Mg( Dip Terph)(THF)] 4. Reactions of the bis-(aniline)s with the group 2 metal amides [M{N(SiMe 3 ) 2 } 2 ] afford dimeric, structurally analogous compounds [{M( Ar Terph)} 2 ] (Ar = Dip, M = Ca 5, Sr 6, Ba 7; Ar = TCHP, M = Ca 8, Sr 9, Ba 10) which display intermolecular M•••arene interactions in the solid state. Computational studies have shown that the intramolecular M•••η 6 −arene interactions in models of the ether-free metal bis(anilide) compounds are largely electrostatic in nature. Reductions of these compounds with alkali metals led to mixtures of unidentified products.

Synthesis and Characterization of Bulky 1,3‐Diamidopropane Complexes of Group 2 Metals (Be−Sr)

“…[M( TCHP NON)], which have potential as precursors to low oxidation state group 2 systems. [11] One such ligand candidate we are interested in are 1,3-diamidopropanes, which have previously proven their worth in the stabilization of low oxidation state p-block compounds, e. g. the nucleophilic aluminyl anion IV. [12] Although the 2,6-diisopropylphenyl (Dip) substituted diamide ligand in IV is bulky, we have recently developed a significantly more bulky TCHP adorned diamide, [{(TCHP)NCH 2 } 2 CH 2 ] 2À ( TCHP NCN), which has been used to prepare the N-heterocyclic germylene V. [13] Here, we use this diamide, and its Trip substituted analogue, [{(Trip)NCH 2 } 2 CH 2 ] 2À ( Trip NCN), to prepare a series of diamido complexes of the group 2 metals…”