Oxo and Nitrido Complexes

Mononuclear oxo and nitrido complexes of Tc can be isolated with a variety of ancillary ligands. These compounds undergo reversible one-electron reactions encompassing oxidation states IV through VI [10-12] (Table 1). 

Photophysical Data of Selected Osmium(VI) Oxo and Nitrido Complexes in Acetonitrile at Room Temperature... 

Bailey, A. J., Griffith, W. P., Mostafa, S. I., Sherwood, P. A. Studies on transition-metal oxo and nitrido complexes. 13. Perruthenate and ruthenate anions as catalytic organic oxidants. Inorg. Chem. 1993, 32, 268-271. 

Table 15 Calculated and Experimental Bond Lengths (A) and Angles (°) of Oxo and Nitrido Complexes... 

A. Neuhaus, A. Veldkamp, and G. Frenking, Inorg. Chem., 33, 5278 (1994). Oxo and Nitrido Complexes of Molybdenum, Tungsten, Rhenium and Osmium. A Theoretical Study. Theoretical Studies of Inorganic Compounds. IV. 

Oxo-complexes, the [Tc=0] core Imido and nitrido complexes Imido complexes... 

Chromium(IV) and chromium(V), previously encountered as the oxides and halides and as unstable intermediates in solution, are now represented by complexes of ligands stabilized by heavy substitution against oxidation by the metal ion, and oxo and nitrido derivatives. These remain unimportant oxidation states compared with molybdenum and tungsten. 

In order to stabilize Os(IV), it is necessary to have either several ligands that are good tt bases (e.g., Cl- or Br-), or one ligand that is a strong7T base (e.g., O2-) (2,5,6). Many Os(IV) complexes contain one or more halo ligands. There is also a growing number of oxo- and nitrido-bridged complexes. 

Since this initial report, NHCs have been used to stabilize a number of additional high-valent metal complexes bearing oxo and nitrido ligands (Chart 1) [26-32]. In contrast to the MTO example, these complexes and the high-valent metal precursors employed in their synthesis are not especially strong oxidants. Consequently, the preparation of these complexes often can be achieved by simple addition of the NHC to an unsaturated metal center or via displacement of a weakly coordinated solvent molecule such... 

Ruthenium(V), (VI), (VII), (VIII) (d3, d2, d, d°) These complexes are restricted to halo, oxo and nitrido species such as [RuNClJ-, [RuNC15]2 and [Ru04]2-, . Oxo complexes of ruthenium have been used as oxidation catalysts. 

Mn corroles have been isolated as Mn(III) [22, 60, 89, 90], Mn(IV) halogenato [91], and Mn(V) oxo [75, 92-94], imido [81, 95], and nitrido complexes [96, 97] (oxidation of (nitrido)Mn(V) correlates to Mn(VI) complexes has been reported as well). Mn(III) corroles represent rare examples of four-coordinate Mn(III) complexes. Mn(IV) corroles are unusually stable in fact, Mn(dpoec)(I) (dpoec = 5,15-diphenyl-2,3,7,8,12,13,17,18-octaethylcorrolate) was the first well-characterized Mn(IV)-I complex reported in the literature [98]. Meanwhile, the high-valent oxo, imido, and nitrido complexes have proven to be competent catalysts for... 

Some recent interest in the technetium chemistry has been focused on complexes possessing a Tc=N3+ core. Tetrachloronitridotechnetate(VI) complexes can easily be synthesized by the reaction of pertechnetate with sodium azide in concentrated hydrochloric acid [34], Although its square-pyramidal structure resembles that of tetrachlorooxotechnetate(V) complexes, stable character of the nitrido complexes in aqueous solution shows a remarkable contrast to the oxo complexes. However, when a strong acid and a coordinating ligand are absent, the interconversion of di(p-oxo)nitridotechnetium(VI) complexes to the monomeric form occurs in the following complicated manner [35]... 

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