Z. Naturforsch. 2014, 69b, 1061 – 1072
Gilded Chalices: Tetra-aurated Calix[4]arenes
Ulf H. Strasser1, Beate Neumann1, Hans-Georg Stammler1, Raphael J. F. Berger2, and Norbert W. Mitzel1
1 Lehrstuhl für Anorganische Chemie und Strukturchemie, Centrum für Molekulare Materialien CM2, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany
2 Materialchemie, Paris-Lodron-Universität Salzburg, Hellbrunner Str. 34, A-5020 Salzburg, Austria
Reprint requests to Prof. Dr. N. W. Mitzel. Fax: +49-521-106-6026. E-mail: mitzel@uni-bielefeld.de
Received July 10, 2014 / published online December 19, 2014
Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday
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-Tol3PAuCl, Ph3PAuCl, Ph2MePAuCl, PhMe2PAuCl, Me3PAuCl, Cy3PAuCl, t-Bu3PAuCl) to afford in good to excellent yields the tetra-aurated tetraethynylcalix[4]arene species 39 in one step [with phosphane ligands o-Tol3P (3), Ph3P (4), Ph2MeP (5), PhMe2P (6), Me3P (7), Cy3P (8), t-Bu3P (9)]. All compounds were characterised by 1H NMR and infrared spectroscopy, mass spectrometry and by elemental analyses, additionally 3, 4, 5, 8 and 9 by 13C{1H}, and 36, 8 and 9 by 31P{1H} 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···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···Au-bonded dimers.
Key words: Gold, Xenon, Calix[4]arenes, Ethynes, Acceptor, Crystal Structure, Quantum-Chemistry
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