Dinuclear Tc

Scheme 22. Reaction of homoleptic dinuclear Tc-imido complex 94 with methyl Grignard reagent...

Even though the 13C spectra for the Tc(V) system span a large range of chemical shift there was a rapid formation of the dinuclear [Tc203(CN)g]4 species whenever there were appreciable amounts of the [TcO(OH)(CN)4]2 ion present (13). This excluded the determination of the pKa values for the Tc(V) system by 13C NMR. 

The [TcO(OH2)(CN)4] complex is, as shown by the complex formation constants in Table II, more reactive than the corresponding complexes of either the Re(V) or W(IV). This, coupled with the fact that the dinuclear species [Tc203(CN)8]4 is formed rapidly whenever there are appreciable amounts of the [TcO(OH)(CN)4]2 complex present (71), i.e., below pH ca. 5.5, prohibits any experiment around these acidic conditions. A marked difference in the [H+] dependence for the Tc(V) compared to the above-mentioned Re(V) and W(IV) systems originates from the fact that the Tc(V) is much more reactive and had to be studied at pH values significantly higher than the )Ka2 value of ca. 4. This yielded results similar to the insert (a) in Fig. 16 for the rhenium(V) and only the exchange rate constants and the activation parameters for the hydroxo oxo complex for Tc(V) could thus be obtained (Table V). 

Another example of a Tc nitrido-complex is obtained from the reaction of [TcOCU]" with 1,1-diphenylhydrazine (H2NNPh2) (23) in the presence of thiophenol. Unexpectedly, the dinuclear, formally Tc complex [ TcN(NNPh2)(SAr)(/r-SAr) 2] (24) is formed in good yields. The nitrido-group results from the cleavage of the organohydrazine. This unusual reaction is shown in Scheme 9. 

The Tc complex [TcI(N—Ar)s] (28) (see Section 5.2.2.1.2) can be reduced with Na° in THE to yield the green, nonbridged, dinuclear compound [Tc2(NAr)6] (46), in which three imido-ligands are bound to the Tc center and connected by a single bond to the second technetium. The molecule has a staggered, ethane-like structure and is diamagnetic. Reduction of (28) yields another homoleptic imido-complex of Tc, the imido-bridged, tetrahedral, dinuclear compound [Tc2(/u-NAr )2(NAr )4] (47) (Ar = 2,6-diisopropylphenyl). The conformation could be confirmed by X-ray structure analysis the assumption of a Tc Tc bond is confirmed by the... 

Tc2C14(PR3)4] (R3=Et3, PMe2Ph, PMePh2) ch3cn, hbf4 [Tc (CH3CN)10] [BF4]4 The product is an excellent precursor for the synthesis of other low-valent mono-and dinuclear technetium complexes 541... 

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