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

An extremely bulky p-terphenyl bis(aniline), p-C6H4{C6H4[N(H)TCHP]-2}2 (TCHP = 2,4,6-tricyclohexylphenyl) TCHPTerphH2, has been developed. Deprotonation of a less bulky analogue, DipTerphH2 (Dip = 2,6-diisopropylphenyl), with BePh2 affords the bimetallic system, [(BePh)2(-DipTerph)] 1. Treating either TCHPTerphH2 or DipTerphH2 with Mg{CH2(SiMe3)}2 gives the monomeric bis(anilide) complexes [Mg(ArTerph)] (Ar = Dip 2, TCHP 3) which display rare examples of eta-6-arene coordination to the metal centre. Treating 2 with THF leads to partial dissociation of the Mg···arene interaction, and formation of [Mg(DipTerph)(THF)] 4. Reactions of the bis(aniline)s with the group 2 metal amides [M{N(SiMe3)2}2] affords dimeric, isostructural compounds [{M(ArTerph)}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···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.