oxygen room temp.;

in benzene anhydrous and oxygen-free condns., BBr3 in benzene dropped into a soln. of B-compd. in benzene at 0°C with stirring, after 1 h allowed to attain ambient temp. within 30 min; removal of benzene, distn. ((Me2N)2BBr), dissolved in hexane, cooled to -78°C for 9 days, filtered; elem. anal.;

in diethyl ether

in diethyl ether