Reaction with Nondassical Ligands

The approach of using acetylated Cps has one limitation. If the C=0 group and an additional donator in, for example, the biomolecule can form a six-membered chelate, this mode of coordination is preferred and slippage from this if coordination to rf coordination on the Cp takes place, if ever, very slowly. 

Other ligands compatible with aqueous conditions and providing additional M-C bonds are CO and isonitriles. As discussed earlier, at ambient pressure of CO, no more than three COs will coordinate to Tc(I) as a consequence of the trans effect. At elevated pressure, however, it is possible to synthesize the binary carbonyl complex [99mTc(CO)6]+ [42]. This could be shown by Tc NMR spectroscopy and by isolation of the complex. 

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