Rhenium derivatives

The oxidation of substituted pyridines to iV-oxides was reported by Sharpless and coworkers to proceed with yields between 78 and 99% (Scheme 154). A variety of substituents like electron donor as well as acceptor groups and alkenyl substituents are tolerated. In 1998, Sharpless and coworkers reported an alternative method for the preparation of pyridine-A-oxides in which the MTO/H2O2 catalyst could be replaced by cheaper inorganic rhenium derivatives (ReOs, Re207, HOReOs) in the presence of bis(trimethylsilyl) peroxide (equation 73). Yields of the prepared A-oxides after simple workup (filtration and bulb to bulb distillation) ranged from 70-98%. Molecular sieves slowed down the reaction while small amounts of water (0-15%) were essential for the reaction. Both electron-poor or electron-rich pyridines give high yields of their A-oxides and while para-... 

Oxidation of pyridines with BTSP in the presence of catalytic amounts of inorganic rhenium derivatives gives high yields of their analytically pure N-oxides by simple workups, typically a filtration or a Kugelrohr distillation (equations 59-61). ... 

One of the most important peroxo complexes synthesized after 1983 is the rhenium species formed from methyltrioxorhenium (MTO) precursor. The synthesis of this complex is achieved in the way indicated in equation 2, by reacting hydrogen peroxide with MTO . The isolated peroxo complex 1 contains in the coordination sphere two /7 -peroxide bridges, a direct metal carbon bond and a molecule of water. The crystal structure of the peroxo rhenium derivative, however, was obtained by substitution of the water molecule with other ligands " more details on this aspect are enclosed in the structural characterization paragraph. 

The most active d metal peroxo complexes toward nucleophilic substrates, like amines, phosphines, thioethers, double bonds etc., are molybdenum, tungsten and rhenium derivatives vanadium and titanium catalysis is also important, in particular when... 

Interest in the electrochemistry of rhenium derives in part from its role in nuclear medicine [5], where compounds containing the high-energy, 8 -emitting 186 Re i Re isotopes find use in... 

The rhenium derivative (CH3)3GeRe(COb, can be converted into the carbene complex (CH3)2(jeRe(CO)4C< G )CH ), which in solution is in equilibrium with its dimer. The dimer crystallizes preferentially, and incorporates an eight-membered GeReCO]2 heterocycle (181). 

Rhenium derivatives (entries 10-12) are much less ready to form adducts than their manganese analogs (entries 6, 7, 9). Thus, the adducts in entry 10 dissociate completely at room temperature. 

The molecular structure of the rhenium derivative has been determined by an X-ray diffraction study and is reproduced in Fig. 4 (47). 

Treatment of 2-chloropentaborane (9) with Na[M(CO)s] (M = Mn or Re) in ether solution generated 2-[M(CO)5]B5H8 (5). The rhenium derivative is stable at room temperature for several hours, but the manganese compound develops a yellow color upon melting at -10°C. 

Synthesis of Pyridine-V-Oxides. Methyl isonicotinate was oxidized by (TMSO)2 in the presence of CHsReOs, or other inorganic rhenium derivatives such as ReOs, Re20v and HOReOs, to the V-oxide in high yield (95-98% isolated yields). With ReCls or NaOReOs as catalyst, only trace amounts of oxidation products were obtained (eq 10). The importance of a trace amount of water in this oxidation process was confirmed when the reaction was retarded by the presence of molecular sieves. The optimal water content was found to be between a trace and 15 mol %, with higher proportions leading to lower conversion. A commercial 65-70% solution of perrhenic acid in water was found to be a convenient source of both Re and water. 

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