in toluene recrystd. from pentane at 20--78°C, elem. anal.;

n-butyl lithium in tetrahydrofuran; hexane treating C5Me5H (30 mmol) in THF with 12.5 ml n-BuLi (2.4 M in hexane) for 15 h and then addition of 45 mmol of Tl2SO4; (by the method of G. A. Rupprecht et al. J. Am. Chem. Soc., 102 (1980) 6236;;

in toluene prepared by the method of H. Werner, H. Otto, H.J. Kraus, J. Organomet. Chem., 315 (1986) C57;;