Unusually large bite angle of a distally diphosphanylated calix[4]arene chelator

Article abstract of DOI:10.1002/ejic.201000595

5,17-Diphenylphosphanyl-11,23-bis(4-tolyl)-25,26,27,28-tetrapropoxycalix[4] arene (6), a semi-rigid, calixarene-based diphosphane in which the phosphorus atoms are separated by 12 chemical bonds, reacts with [Ni(η⁵- C₅H₅)(1,5-cyclooctadiene)]BF₄ or AgBF ₄ to afford the corresponding chelate complexes [Ni(η ⁵-C₅H₅)(6)]BF₄ and [Ag(6)]BF ₄ quantitatively. These complexes were both characterised by a single-crystal X-ray diffraction study. In the nickel complex the ligand shows a bite angle of 104.5°, which lies in the range expected for this kind of diphosphane with a large P???P separation. In the silver(I) complex the diphosphane displays a much larger bite angle of 138.8°, which was unexpected and reflects the flexilibilty of the calix[4]arene skeleton. Furthermore, in solution the silver complex shows dynamic behaviour. One of the observed motions corresponds to the silver atom switching reversibly from a linear to a bent AgP₂ cordination geometry. An upper-rim, distally diphosphanylated calix[4]arene readily forms a complex with AgBF₄. In the solid state the ligand displays an unexpectedly large bite angle of 138.8°, which reflects the flexibility of the calixarene skeleton. In solution the silver atom moves rapidly between two positions lying on either side of the calixarene axis.