Rhenium complexes substitution reactions

In inert systems such as technetium and rhenium, ligand substitution reactions-including solvolysis-proceed under virtually irreversible conditions. Thus, the nature of the reaction center, the nature of the leaving group, and the nature and position of the other ligands in the complex affect the rates and activation parameters in a complicated manner. Most substitution reactions take place via interchange mechanisms. This is not too surprising when the solvent is water - or water-like - and where, in order to compete with the solvent,... 

Fig. 21. Comparison of half-lives. [Data from Table VII (equatorial ligand substitution, Table VIII (aqua substitution and related reactions) and Table IX (in vivo reactions of technetium and rhenium radiopharmaceuticals) of the complexes described in Section VII,A. Similar symbols denote similar technetium and rhenium complexes.]...

Grafting on the resin was achieved via a nucleophilic substitution of the benzylic chlorine by the deprotonated OH-linker of 52 (Scheme 29) by using a mixture of KO Bu, 18-crown-6 and CsBr. Determining the nitrogen content of solid phase samples by elemental analyses was accomplished, to verify the functionalization of the polymer. This enables calculation of the degree of functionalization. Usually, an occupancy of more than 20 percent of the theoretical sites was achieved. Saponification of the functionalized Merrifield resin P-52 leads to the monoanionic NJ, 0 functionalized solid phase. Subsequent reaction with [ReBrtCOlsJ afforded the polymer mounted tricarbonyl rhenium complex P-52-Re (Scheme 29). 

In the case of technetum, this is the most practically used element among non-/ radioactive ones for medical and technical purposes [283], so the permanent interest in its coordination chemistry (in particular, the structural aspect of its compounds [547] and kinetics of substitution reactions [548]) is not surprising [549]. The theoretical interest in Tc is provoked, in particular, by the fact that this is a rhenium analogue. This element (Re) forms multiple metal-metal bond complexes and has been studied intensively in order to achieve a better understanding of the physical and chemical properties of multiple bonds between metal atoms [533],... 

Vinyl-substituted benzo[c]furans can be prepared by reaction of n-alkynylbenzaldehydes with chromium Fischer carbene complexes. Initially a benzo[c]furan chromiumtricarbonyl complex is believed to be formed which is converted into an alkylidenephthalan derivative or can be trapped with electron-deficient dienophiles with excellent ( 3 ti-selectivity (Equation 128) <20000L1267>. More elaborate vinylidene Fischer carbene complexes yield dienyl benzo[c]furans that undergo [8-1-2] cycloaddition with DMAD to furnish furanophane derivatives <2003JA12720>. An equilibrium between 7] -(o-ethynylbenzoyl)rhenium complexes and rhenium benzo[f]furyl carbene complexes has been observed. These species behave like other benzo[< ]furans in the reaction with DMAD <20040M4121>. 

An example of a chemically induced substitution reaction is represented by the halide removal in MnCl(CO)5 by AICI3 leading to the hexacarbonylmanganese(I) cation. The driving force of this reaction, carried ont at room temperature, is represented by the high affinity of aluminum for chloride. Similarly, the corresponding rhenium(I) derivative [Re(CO)6]AlCLi can be prepared. This complex has considerable stability in that it can be dissolved in water without prompt decomposition (equation 32). 

The next section about photochemical reactions includes ligand substitution, homolysis, and reactions of the ligand on the rhenium complexes. This section also includes synthesis of emissive multinuclear rhenium(I) complexes using the photochemical ligand substitution. 

Hi) Rhenium(V) complex with NCS (191), thiourea, and other incoming ligands (205). The observed linear free-energy relationship also suggests dissociative activation for the substitution reactions of the rhenium complex (205). 

The 6-substituted cyano bipyridine has been generated in 95% yield from bipyridine A-oxide by reaction with trimethylsilylcyanide and dimethylcarbamylchloride.76 This is an improvement on an earlier method that generated 6-cyano bipyridine from the A-oxide in 62% yield using potassium cyanide and benzoyl chloride.77 This ligand has been used in electrochemical studies of rhenium complexes with sterically hindered bipyridine derivatives, as well as a precursor in the synthesis of 6-carbothioamide-bpy, which showed antitumor activity against P-388 lymphocytic leukemia in mice.77... 

Catalytic oxidation of 239 to the quinone 240 was also effected with H2O2 catalyzed by methyltrioxorhenium(VII) (McRcOb) (Scheme 60)", where a small amount of hydroxy-substituted quinone 280 was produced in addition to 240 (70%). In this reaction, MeRe03 is stepwise converted by H2O2 into the mono- and bis(peroxo)rhenium complex MeRe(02)20-H20 (281). This active oxidant then reacts with the phenol to give the epoxide 282, which is further converted to the two quinones (240 and 280). 

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