methylmagnesium bromide in diethyl ether addn. of CH3MgBr to Fe-complex in diethylether under N2 at -78°C, stirring at -78°C for 7 h, addn. of tert.-BuBr to the dark green mixture at -78°C, allowing to warm to room temp.; filtration, removal of solvent under reduced pressure, sepn. of products by column chromy. (SiO2, light petroleum-diethy ether, 2:1);