in tetrahydrofuran soln. of MesMgBr added to suspn. of anhyd. AgCl (-25°C), mixt. stirred (18 h); filtered, filtrate evapd., dried (high vac., 2 h), redissolved in toluene (40°C), filtered, concd., allowed to stand (room temp.), mother liqor concd.; elem. anal. (all operations in absence of light);