Pergamon Tetrahedron Letters 41 (2000) 1015–1018 TETRAHEDRON LETTERS Synthesis of nitronyl- and imino-nitroxide-triradicals interconnected by phenyl ethynyl spacer Laure Catala, a,b Philippe Turek, a,∗ Jacques Le Moigne, b André De Cian c and Nathalie Kyritsakas c a Institut Charles Sadron, 6, rue Boussingault, CNRS, F-67083 Strasbourg, France b Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, 23, rue du Loess, F-67037 Strasbourg, France c Laboratoire de Cristallochimie et Chimie Structurale, associé au CNRS, Université Louis Pasteur, Institut Le Bel, 4, rue Blaise Pascal, F-67000 Strasbourg, France Received 31 August 1999; accepted 18 November 1999 Abstract The design and synthesis, as well as solid state and ESR characterisation of three new triradicals based on phenyl ethynyl backbone bearing nitronyl-nitroxide and imino-nitroxide groups, are reported. The synthesis of these compounds was based on palladium-coupling reactions between alkynyl and bromo derivatives. An ESR study showed magnetic interactions between the radicals through the phenyl ethynyl-coupling unit in solution. © 2000 Published by Elsevier Science Ltd. All rights reserved. In the area of molecular magnetism, purely organic materials based on radicals are still under active investigation. 1 High spin organic molecules may be obtained through interconnection of paramagnetic centres using an active magnetic coupling unit (MCU). In order to achieve ferromagnetic coupling, the positioning of unpaired electrons relatively to the MCU and the nature of the latter must fulfil electronic as well as topological rules. 2 The assessment of the nature and the strength of the magnetic interactions through the MCU units requires model systems based on oligoradicals which may be of interest for understanding more complex polyradicals. 3 Here, we report the design and synthesis, as well as structural determination and ESR characterisation of three new triradicals 1, 2 and 3, based on phenyl ethynyl backbone bearing nitronyl-nitroxide and imino-nitroxide groups. The homotriradical 1 is based on three nitronyl-nitroxide units, whereas the other two hetero systems 2 and 3 are based on a combination of nitronyl-nitroxide and imino-nitroxide moieties. The phenyl ethynyl spacer has been previously used as a connector between two identical radicals. 4 For the synthesis of compounds 1 and 2, three different strategies based on palladium-catalysed co- upling reactions 5 between alkynyl and bromo derivatives were investigated (Scheme 1). The first strategy was based on the Pd-coupling of compounds 8 and 9 both bearing the N,N ′ -dihydroxyimidazoline moiety. ∗ Corresponding author. 0040-4039/00/$ - see front matter © 2000 Published by Elsevier Science Ltd. All rights reserved. PII: S0040-4039(99)02218-2 tetl 16146