The Determination of Bond Cleavage

Obtaining definite evidence regarding the occurrence of bond cleavage is helped considerably by using isotopes. The following two examples illustrate different approaches. 

Reactions of Co(NHj)50H or Co(NH3)5H20 + with certain ligands are unusually rapid (Chap. 8. Co(III)). This suggests that Co-O bond breakage does not occur during the substitution, else it likely would be very much slower. This can be verified by using isotopes e.g.  

The nmr signal due to bound OH2 is unchanged after the cycle (2.104) is completed (Fig. 2.2). This observation also rules out linkage rotation (2.105) 

Such a rearrangement, although seemingly unlikely, does occur with the nitrito complex as demonstrated by 0-nmr experiments  

The formation of a double-bridged Co(III) complex from a single peroxo-bridged complex can take place by either (2.107) or (2.108), L = CHjNHj, 

---