Technetium borate ligands

Several research groups have studied the chemistry of tris(pyrazolyl)borate tricarbonyl complexes of technetium and rhenium. As depicted in Scheme 28, these studies allowed the synthesis of/ac-[M(CO)3Tp ] [M is Tc, Re, Tp is Tp (111/113), Tp (112/114)] complexes, which were all structurally characterized. Complexes 111-114 were synthesized by reaction of the classical starting materials [M(CO)5Br] with the sodium or potassium salts of the correspondent Tp ligands [121-123]. 

In order to introduce lipophilic character into technetium complexes that might be potentially suitable as " Tc radiopharmaceuticals, the hydro-tris(l-pyrazolyl)borate anion (HBpz.3 ) was used as a ligand. Dichloro hydro-lris(Tpyra7olyl)borato)oxotcch-... 

Half-lives for hydrolysis of Tc—Cl to Tc—OH have been determined for four so-called BATO complexes. These contain a semiencapsulating tris-dioxime ligand with a borate cap and the chloride ligand the technetium is seven-coordinate, (21), with Y = OH or Me and either R = Me or pairs of R comprise cyclohexyl rings. Rate constants lie in the range 19 to 1.2 x lO s" for the four complexes examined, at 20 to 37 There is also some very qualitative kinetic information on base hydrolysis and ligand exchange (Cl for Br and vice versa) in this type of complex. These reactions have half-lives of minutes in media such as aqueous acetonitrile. ... 

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