Solid state structures of homo- and hetero-bimetallic alkali metal complexes containing the dianion of (S)-N-(α-methylbenzyl)allylamine

Abstract

Dilithiation of the chiral amine (S)-N-(α-methylbenzyl)allylamine in the absence of a coordinating Lewis donor results in formation of crystals of a cyclic hexamer, {[(S)-α-(PhC(H)Me)(CH₂CHCHLi)N]Li}₆, 1, (rhombohedral, R3) while the addition of tmeda (N,N,N′,N′-tetramethylethylenediamine) leads to deaggregation and formation of the dimer, {[(S)-α-(PhC(H)Me)(CH₂CHCHLi)N]Li·(tmeda)₂}₂, 2 (monoclinic, P2₁). Reaction with ⁿBuLi followed by ⁿBuNa leads to crystals of a cyclic mixed metal tetramer coordinated with thf, {[(S)-α-(PhC(H)Me)(CH₂CHCHNa)N]Li·(thf)}₄, 3 (orthorhombic, P2₁2₁2₁). The three bimetallic complexes have been characterised by single crystal X-ray diffraction, NMR and elemental analysis. The allyl moieties in all three complexes retain the bonding pattern expected in an N-allylamine (–N(M)—CH₂–C(H)C(H)M′, M = Li, M′ = Li or Na) rather than forming a delocalised dianion or an enamide. The anionic amido N and the terminal vinylic C centres form multiple short bonds to all metal centres which in turn form short interactions with all atoms in the allyl groups, and in 1 with the closest Ph carbons.