Mono complexes tungsten

In the latter case, the red anionic vinylidene complex is formed at — 78°C quenching with DzO gives a 1 1 mixture of the mono- and dideuterocar-byne complexes, as a result of a primary kinetic isotope effect by which the anion selectively abstracts a proton from the monodeuterocarbyne complex before quenching is complete. Similar observations were made in the tungsten series (55). 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

Phosphinocarbenes, with tungsten carbonyls, 5, 678 Phosphino ligands, on Ti(IV) mono-Cp complexes, 4, 393 Phosphinomethanides, with Zr(IV), 4, 789 Phosphinooxazolines, in allylic ester alkylations, 11, 83—86 0-Phosphinophenoxo ligands, on mono-Cp Ti(IV) complexes, 4, 487... 

The bis(l,2-enedithiolate) complexes discussed closely resemble the metal centers found in the dmso reductase family of Mo enzymes and in the tungsten enzymes. The reactivity of mono(l,2-enedithiolate) complexes remains a continuing challenge as synthetic chemists pursue accurate models for the xanthine oxidase and sulfite oxidase families of metal sites. New 1,2-dithiolate ligands [70,71] and complexes are needed to demonstrate ligand effects to help elucidation reaction mechanism. 

Figure 11. Scheme showing synthetic routes to mono- and binuclear bis(dithiolene)tungsten(IV) and (V) complexes from [W(CO)2(S2C2R2)2] (R = Me or Ph) (83, 85-87). 

H4O)], and [ W (0)Tp Cl 2(0C6H2Cl20)]. The tungsten atom in each of these species has pseudo-octahedral geometry. The mononuclear species could be electrochemically oxidized and reduced in reversible one-electron steps to and species, but none of these was isolated. The din-uclear complexes exhibited more complex redox behavior, oxidation occurring in discrete one-electron steps, generating mono and dications. Reduction occurred, at least for the species containing OC6H4O, in two clearly separate one-electron processes, but for the other species reduction appeared to occur in two nearly or actually coincident one-electron steps. From simple molecular orbital calculations, supported by detailed spectroelectrochemical and EPR spectral measurements, it was clear that for most of the complexes, the first one-electron oxidation resulted in the formation first of mixed-valence species (W W ) and the second process resulted in formation of the dication. Reduction... 

These complexes are excellent models for theoretical studies. The octacyano complexes of molybdenum and tungsten are stable and inert toward substitution reactions and therefore very suitable for theoretical studies of redox reactions and application of the Marcus theory. The photoreactivity of these systems is also proving to be important. The 0X0- and nitridocyano complexes of Mo(IV), W(IV), Tc(V), Re(V), and Os(VI) are very good candidates for kinetic studies of substitution reactions with both mono- and bidentate ligands and are of interest especially in view of the large variations in the observed reactivity. 

The reactions of the molybdenum(IV) and tungsten(IV) complexes with cyanide ions proceed via the same scheme as those of other mono-dentate ligands (see Scheme 3) with the formation of the pentacyano complex (155,156). This very fast reaction is followed by a much slower reaction with the production of the octacyano complex in the presence of an excess of cyanide ions. 

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