Osmium complexes hydroxo

Schemes 6-14 Reactions of osmium hydrido (hydroxo) complex 2 with several substrates...

There has also been little work on osmium hydroxo complexes apart from the now well-characterized czs-[0s04(0H)2]2 (p. 592), tra j-[0s02(0H)4]2 (p. 581) and the two /i-hydroxo species structurally characterized, M[0s2(0H)08] (M = Rb, Cs) (p. 596). The [Os(OH)6]2- species should certainly exist but does not seem to have been mentioned in the literature even [Os(OH)6]3 might be expected to be stable in the absence of oxygen. Other hydroxo (and aqua) complexes are considered in sections dealing with the other ligands present. 

Similarly, reference is made to another more recent review (41) of the author s contributions to the chemistry of rhodium, iridium, rhenium, osmium and ruthenium alkoxo, and hydroxo complexes, following a similar earlier publication (40) on the alkoxo derivatives of platinum metals. Reference may also be made to the first X-ray structural study (265, 266) of a siloxy derivative, [(cod)Rh(/i-OSiMe)3]2. 

As many carbonate complexes are synthesized usually in aqueous solution under fairly alkaline conditions, the possibility of contamination by hydroxy species is often a problem. To circumvent this, the use of bicarbonate ion (via saturation of sodium carbonate solution with COj) rather than the carbonate ion can often avoid the precipitation of these contaminants. Many other synthetic methods use carbon dioxide as their starting point. Transition metal hydroxo complexes are, in general, capable of reacting with CO2 to produce the corresponding carbonate complex. The rate of CO2 uptake, which depends upon the nucleophilicity of the OH entity, proceeds by a mechanism that can be regarded as hydroxide addition across the unsaturated C02. There are few non-aqueous routes to carbonate complexes but one reaction (3), illustrative of a synthetic pathway of great potential, is that used to prepare platinum and copper complexes. Ruthenium and osmium carbonate complexes result from the oxidation of coordinated carbon monoxide by dioxygen insertion (4). ... 

The inert hydroxo-bridged species were also a product of (very fast) hydrolysis of p-cymene osmium complexes with glycinate, L-alaninate, a-aminobutyrate and p-alaninate. However, complexes with picolinate as the chelating ligand, [Os(r 6-/> cym)Cl(pic)] 8 and [Os(r 6-biph)Cl(pic)] 9, with pyridine as /V-donor and carboxy-late as O-donor, hydrolyzed with half-lives of 0.20 and 0.52 h (298 K), and aqua adduct pKa values (pk L value for solutions in D20) of 6.67 and 6.33, respectively. Complexes 8 and 9 were cytotoxic towards A2780 human ovarian cancer cells, with IC50 values of 8 and 4.2 pM, respectively [64],... 

Osmium and ruthenium in high oxidation states (III, IV, or V) form polypyridine (bpy, phen or tpy) hydroxo and 0x0 complexes, which have a rich redox chemistry [166, 167]. Redox changes are metal-localized and accompanied by reactions of M=0 or M-OH bonds. These complexes are active as electrocatalysts of the oxidation of water to O2, or of CF to CI2, or they can transfer oxygen atoms and oxidize organic substrates like (CH3)2CHOH or C6H5-CH(CH3)2. 

The 0x0 (0 ) ligand is dominant in the coordination chemistry of osmium, participating in the VIII to IV oxidation states inclusive. The tetroxide OSO4 is the single most important compound of osmium OSO4 and the recently discovered [0s04] ion arc tetrahedral. The /ra 5-[0=0s —O] osmyl moiety displays an extensive chemistry, comparable with that of the uranyl 0=U=0 unit, and there is an extensive and unique cyclic oxo-ester chemistry (p. 584). There is surprisingly little information on hydroxo, aqua, sulfato, nitrato or phosphato complexes, but much recent work has been carried out on carboxylato species, and clearly much work remains to be done on the O-donor chemistry of the element. There are a reasonable number of sulfur-donor complexes but few with selenium or tellurium. 

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