in chloroform-d1 allowing soln. of greatest (total tfa)/(total Co) to stand either in diffuse daylight or in the dark at room temp. for 1-2 d; crystals filtered off, washed with cold solvent and hexane, air-dried, dried in vac. at 10-12 mmHg for a few hours;

in dichloromethane N-bromoacetamide (6.9 mmol) slowly added to stirred soln. of but-3-enyl-cobaloxime (3.44 mmol) in CH2Cl2 for 5 min; chromd. on SiO2;