Rhenium complexes, oxo

A remarkable aspect of the rhenium oxo complex chemistry is the ability of terminal oxo functions to act as nucleophiles. This has been used to incorporate dioxo complexes such as [Re02(py)4] or [Re02(CN)4] between the negatively charged interlayers of silicates like hector-ite (pyridine complex) or between the positive layers of a hydrotalcite-like Mg/Al double hydroxide. " The same concept has been applied for the isolation of molecular units containing Re-O-M bridges where M is a Lewis acid. ... 

Although high-valent rhenium-oxo complexes such as perrhenate, Rc207, and ReOjX (X = F, Cl, Br) are widely known, their use as oxidants is rather rare. The stoichiometric oxidation of alkenes to a mixture of ketone and epoxide by Rc207 has been reported in the patent literature. For example, 2-butene is transformed to 2,3-epoxybutane and 2-butanone by Rc207 at 100 °C. A catalytic oxidation was observed in the presence of excess hydrogen peroxide but precise data on this reaction are lacking. 

S. Owens, J. Arias, M. M. Abu-Omar, Rhenium oxo complexes in catalytic oxidations, Catal. Today 55, 317-363 (2000). 

T. R. Cundari, S. C, Critchlow, R. R. Conry, E. Spaltenstein, K. A. Hall, S. Tahmassebi, and J. M. Mayer, Organometallics, 13, 322 (1994). Rhenium-Oxo-Bis(acetylene) Anions Structure, Properties, and Electronic Structure. Comparison of Re—O Bonding with That in Other Rhenium-Oxo Complexes. 

Reaction with Allylic Halides, Alcohols, and their Derivatives. Allylation of allyl and propargyl trimethylsilyl ethers as well as benzyl and propargylic alcohol derivatives proceeds in the presence of a catalytic amount of Lewis acids, such as ZnC, TMS(OTf), and B(C6F5)3. Direct substitutions of the hydroxyl group of allylic, ben-zylic, and propargylic alcohols are catalyzed by HN(S02F)2, a rhenium-oxo complex, and InCls (eq 27). A combination of chlorodimethylsilane and allyltrimethylsilane effectively promotes the deoxygenative allylation of aromatic ketones in the presence of a catalytic amount of an indium compound, such as indium trihalide or metallic indium (eq 28). Allylation of cyclic allylic acetates with allyltrimethylsilane can be catalyzed by molecular iodine. ... 

The reaction of rhenium oxo complexes has provided a new model for the water-gas shift reaction. [LjRe(0)H2] [L3 = (Cy2PCH2)2PPh] reacts... 

Again, fluoro and oxo complexes of rhenium predominate. The reaction of KF and ReFe in an inert PTFE vessel yields pink K2[ReFs], the anion of which has a square-prismatic structure hydrolysis converts it to K[ReOFs]. 

Gable, Kevin P, Rhenium and Technetium Oxo Complexes in the Study of Organic... 

In the bifunctional radiopharmaceuticals, Tc and Re complexes that are suitable for coupling to antibodies are almost square-pyramidal oxo complexes of tetradentate ligands, as mentioned earlier. Spies et al. [65] recently studied the syntheses and structures of rhenium complexes with a tetradentate NS3 tripod ligand 2, 2,, 2"-nitrilotris(ethanethiol) (l in Fig. 9) as an interesting alternative to the oxo complex. Such ligands could lead to weakly polar, trigonal-bipyramidal complexes in which the metal atom is more strongly shielded than in the square-pyramidal oxo complexes. Schemes for the syntheses... 

A rapid reaction between dioxorhenium(VII) and PPh3 was proposed in Eq. (11) for sake of consistency with the kinetic data. For reasons to be presented subsequently, this is shown as the addition of the phosphorus to an oxo oxygen. In effect, this is the reduction of rhenium(VII) with the concomitant creation of a rhenium(V) complex ligated by a phosphine oxide,... 

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). 

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