Dibromobis l, 2-ethanediamine cobalt III Bromide

Werner prepared cis- and tazns-dibromobis(l, 2-ethanediamine)cobalt(III) bromide by reacting the carbonato bromide with concentrated hydrobromic acid.2 In the cold, the cis isomer resulted the trans isomer was obtained by heating the mixture. The reaction proceeds via ds-aquabromobis(l, 2-ethanedi-amine)cobalt(III) dibromide which can be isolated by this route. In our hands, the preparations, as originally described, are not reproducible. The reaction times and yields are variable, depending too critically on the conditions for one not intuitively skilled in the art to consistently obtain the desired cis or trans form. However, the syntheses described here for the cis and trans dibromo complexes and based on this reaction are reproducible if one adheres closely to the procedures. 

Other preparative methods have been reported. cis-Dibromobis(l,2-ethane-diamine )cobalt(III) bromide is obtained in reasonable yield by evaporating a neutral aqueous solution of the trans isomer to dryness. The reaction between ds-diazidobis(l,2-ethanediamine)cobalt(III) perchlorate and hydrobromic acid proceeds rapidly and quantitatively at ambient temperature, largely with retention of the cis configuration to yield the dibromo bromide. The diazido starting complex can be made within 1 hour in greater than 90% yield. 

BrjCoN4C4H,g, Cobalt(III), dibromobis(l,2-ethanediamine)-, bromide, trans-, 21 120... 

CoBrN407S2C4Hi8 HjO, Cobalt(III), aqua-bromobis(l, 2-ethanediamine)-, dithio-nate, trans-, monohydrate, 21 124 CoBrsNgCgHie, Cobalt(III), dibromobis(l,2-ethanediamine)-, bromide, trans-, 21 120... 

CoBrN403C3Ht6, Cobalt(III), (carbonato)bis-(1,2-ethanediamine)-, bromide, 21 120 CoBrN407S2C4Hi8 H20, Cobalt(III), aqua-bromobis(l, 2-ethanediamine)-, dithionate, trans-, monohydrate, 21 124 CoBr3N4C4Hi , Cobalt(III), dibromobis( 1,2-ethanediamine)-,bromide, trans-, 21 120 CoBr CaHit - H20, Cobalt(IIl), dibromo-bis(l,2-ethanediamine)-, bromide, cis-, monohydrate, 21 121... 

---