Phosphine ligands, technetium complexes

Complexation studies with bidentate phosphine ligands showed that stable cationic complexes of Tc(V), Tc(III), and Tc(I) are easily accessible. The influence of reaction conditions on reaction route and products is well demonstrated by the reaction of pertechnetate with the prototype 1,2-bis(dimethylphosphino)-ethane (dmpe) (Fig. 16). Careful control of reduction conditions allows the synthesis of [Tc02(dmpe)2]+, [TCl2(dmpe)2]+, and [Tc(dmpe)3]+, with the metal in the oxidation states V, III, and I [120,121]. This series illustrates the variety of oxidation states available to technetium and their successive generation by the action of a 2-electron reducing agent. 

In this work, the chemistry of rhenium and technetium complexes anchored by heterofunctionalized phosphines and by scorpionates will be reviewed. Special attention will be given to those chemical aspects that, according to the authors, could enhance the ability of using these ligands in the development of target-specific radiopharmaceuticals. In this context, the chemistry of the novel fac-[M(CO)3]+ and [M(N)PXP]2+ metal fragments will also be mentioned,but to such an extent that minimizes any overlap with other reviews published in this special issue of Topics in Current Chemistry. 

Similar to triphenylphosphine, the tris(2-cyanoethyl)phosphine (cep) forms complexes with technetium in which cep is a monodentatc ligand. Reaction of TcOi in aqueous ethanolic solution containing hydrochloric acid yielded a blue, microcrystal-linc solid of [TcCl4(cep)2]° with a melting point of 175 °C [303]. 

Several technetium(IIl) complexes containing both tetradentate Schiff-base and monodentate tertiary phosphine ligands have been synthesized. [Tcj(acac)2enj (PPh3)2 was obtained by reaction of [TcOCU] with H2(acac)2cn and PPh 3 in methanol ... 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Technetium(V) complexes with /u,v(ohydroxyphenyl)phenylphosphine and (o-hydroxyphenyl)diphenylphosphine ligands were prepared by metathesis reactions with the appropriate Tc(V) precursor and/or by reduction/ligand-exchange reactions with ammonium pertechnetate [530]. It was expected that the combination of one soft phosphine P-donor and two hard phenolate O-donors in the chelate should stabilize Tc centers in intermediate oxidation states. 

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