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 -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.