PUB - Publikationen an der Universität Bielefeld

5,11,17,23-Tetrakis(trimethylsilylethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (1) was synthesised in two steps starting from 25,26,27,28-tetra-n-propoxycalix[4]arene, and the structure of 1 was determined by X-ray diffraction. Compound 1 was desilylated (K2CO3) to give 5,11,17,23-tetrakis(ethynyl)-25,26,27,28-tetra-n-propoxycalix[4]arene (2), which was tetra-aurated under basic conditions (NaOEt, THF) with a series of phosphane-gold chlorides (o-Tol(3)PAuCl, Ph3PAuCl, Ph2MePAuCl, PhMe2PAuCl, Me3PAuCl, Cy3PAuCl, t-Bu3PAuCl) to afford in good to excellent yields the tetra-aurated tetraethynylcalix[4]arene species 3-9 in one step [with phosphane ligands o-Tol(3)P (3), Ph3P (4), Ph2MeP (5), PhMe2P (6), Me3P (7), CY3P (8), t-Bu3P (9)1 All compounds were characterised by H-1 NMR and infrared spectroscopy, mass spectrometry and by elemental analyses, additionally 3, 4, 5, 8 and 9 by C-13 {H-1}, and 3-6,8 and 9 by P-31 {H-1} NMR spectroscopy. The molecular structures of complexes 3 and 9 were determined by X-ray diffraction and show pinched-cone conformations, but neither intra- nor intermolecular attractive aurophilic Au center dot center dot center dot Au contacts. The acceptor ability of complexes 3 and 9 was investigated by complexation attempts with various phosphane-gold chlorides and xenon gas under pressure, but interactions could not be determined experimentally. The formation of a complex between xenon and gilded calix[4]arene could, however, be predicted for fluorine-substituted species and with very small phosphane ligands (PH3) on the basis of quantum-chemical calculations; the energy of formation is 9.6 kJ mol(-1). The crystal structure of Ph2MePAuCl was also determined and shows Au center dot center dot center dot Au-bonded dimers.