Lithiated α-cyanophosphonates: self-assembly of two-dimensional molecular sheets composed of interconnected twenty-four membered rings

Abstract

Reaction of the phosphonates (RO)₂P(O)CH₂CN (R = Et I or PrⁱII) with one molar equivalent of LiNPrⁱ₂ in THF gave the metallated complexes [(RO)₂P(O)CHCNLi·THF]_∞ (R = Et 1 or Prⁱ2). Crystallographic analyses of them reveal that they form dimeric Li₂(O=P)₂ units, which further aggregate through inter-dimer association via the nitrile of the phosphonate to form cross-linked, polymeric network structures. These sheets align in the crystals to form a ‘patchwork’ arrangement of molecular channels. The carbanionic centres of the phosphonates are devoid of Li–C contacts and almost perfectly planar. In solution, the dimeric units most likely remain intact but the nitrile is involved in chelation to a metal centre via intra-dimer association. Theoretical calculations show that chelation of the nitrile unit is a viable mode of bonding.