Chemical properties of the coordinatively unsaturated sites

The different grade of saturation defining the two species A and B is of course reflected by their chemical reactivity. 

It should be mentioned that organic rr-systems, like the double bond in olefins, benzene, or the cyclopentadienyl rings are added as well. The formation of 1 1 or 1 2 complexes is obviously the first step of all interactions of olefins with the catalytic centre [55]. 

Not all of the additions are completely reversible. The temperatures necessary to volatilize the ligand are often too high to keep the system redox inert. Some of the ligands, e.g. NO, are irreversibly added, others as N2O are decomposed at moderate temperatures under vacuum conditions (here to N2 and surface Cr(IV)=0) [38]. Siuface Cr(II)(H20)2 undergoes a redox reaction at 600 to 800 °C to form surface Cr(IIl) and hydrogen [38, 56]. 

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