[PhC(H)NC(H)Ph]Na · PMDETA (1) (PMDETA = (Me2NCH2CH2)2NMe), exhibits a contact ion-pair arrangement in the crystal, with the complexed metal cation bound to the nitrogen centre of the aza-allyl fragment (NNa bond length, 2.384(2) Å). Further close contacts exist between the sodium and one ortho-C from each phenyl ring (distances 3.133(4) and 3.166(4) Å). Variable-temperature 1H NMR spectroscopic studies indicate that 1 adopts a remarkably similar structure in tetrahydrofuran-d8 solution. Thus, at −50°C the restricted rotation about each C(ipso)C(benzylic) bond results in the appearance of two distinct resonances each for both the ortho- and meta-H's. From their coalescence temperatures the energy barrier to rotation has been estimated (12.8 kcal mol−1). Evidence that this rigid solution conformation mimics the crystal structure in having short ortho-CH ··· Na distances comes from the exceptionally large chemical shift difference (1.05 ppm) associated with the dual ortho-H signals.
- crystallographic studies
- crystal structures