Toward Organic Synthesis of a Magnetic Particle: Dendritic Polyradicals with 15 and 31 Centers for Unpaired Electrons

Starting from a bromo triether derivative 1, we prepared a homologous pentadecaether, which is a precursor for the title pentadecaradical, by repeating twice the following two-step procedure (total of four steps): (1) Br/Li exchange followed by the addition of the organolithium to a benzoic acid ester derivative and (2) conversion of the triarylmethyl alcohol to methyl ether. Similarly, a 31-ether precursor was prepared by repeating three times the above sequence (total of six steps). The polyethers were converted with lithium metal in THF to the corresponding carbopolyanions and, subsequently, oxidized with iodine at 180 K to give the polyradicals. The polyradicals were studied in frozen THF and 2-MeTHF solutions by SQUID magnetometry in the 2–80 K temperature range and the 0–5.5-T magnetic field range; spin values, which are lower than expected for strong ferromagnetic coupling, were obtained. One of the possible explanations is the presence of defects, which disrupt ferromagnetic coupling between the triarylmethyl sites in these single-path π-conjugated systems; relationship of the current work to the percolation problem is discussed.