Ruthenium high oxidation states

High oxidation states are accessible a f-butylimide of ruthenium(VI) can be made by oxidative deprotonation... 

There is a vigorously expanding chemistry of compounds of ruthenium and osmium in high oxidation states [3, 4, 11, 12], particularly of dioxo and nitrido compounds, though recently some striking developments have taken place in imide chemistry. 

Ruthenium and osmium form some remarkably stable alkyls and aryls compounds, often in unusually high oxidation states. 

Several complexes with cobalt in the unusually high oxidation state of (-(- 4) were reported (198,202,280) in 1974. All of the complexes reported were prepared by reaction of [Codlidtcls] with BF3 or Et20BF3 in the presence of air. The complexes were formulated (202, 280) as [Co(R2dtc)3]BF4 (R = Me, Et, Pr, or cyclohexyl), but Hendrickson and Martin (198) suggested that dimeric [Co2(R2dtc)5]BF4 (Rj = Me2, Et2 pyrrolidyl, MeBu", or Bzj), Co(III) complexes, form that are analogous with the ruthenium(III) complex discussed earlier. 

Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing 0x0 or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the 0x0 and imido complexes is beyond the scope of the review and will not be covered here. 

Further improvements in activity of the imidazol-2-ylidene Ru complexes might be attained by the incorporation of a better a-donor substituents with larger steric requirements. The ligands that most efficiently promote catalytic activity are those that stabilize the high-oxidation state (14 e") of the ruthenium metallacyclobutane intermediate [7]. Both ligand-to-metal a-donation and bulkiness of the NHC force the active orientation of the carbene moiety and thus contribute to the rapid transformation into metallacyclobutane species [7b]. Both can be realized by incorporation of alkyl groups in 3,4-position of imidazol-2-ylidene moiety, lyie Me. Me... 

Among the metal complexes used in electrocatalytic oxidation of organic compounds, polypyridyl oxo-ruthenium complexes have attracted special attention,494"508 especially [RuIV(terpy)(bpy)0]2+.495 197,499,500,502,504 This high oxidation state is reached from the corresponding Run-aqua complex by sequential oxidation and proton loss (Equations (75) and (76)). 

High oxidation state alkylidene complexes in which a heteroatom is bound to the alkylidene carbon atom are extremely rare [41]. Since the approach shown in Eq. 43 failed, the related approach shown in Eq. 44 was taken to prepare the medium-sized ring subunits [222]. The latter product was formed in good yield when n=2, R H, R2=Et, but only poor yield when n=2, R =Et, R2=H, possibly due to unfavorable interactions between the ethyl substituent and transannular groups in the transition state for cyclization of the allyl ether [222]. Ruthenium catalysts either failed or gave low yields, presumably because of the steric hindrance associated with ring-closing dienes of this type. 

Ruthenium and Osmium High Oxidation States S.6.2.3 Oxo Complexes... 

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