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

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.