Complexes of Osmium O

Within the osmium complexes in oxidation states (II-IV) [11,12] the stability of the +4 oxidation state becomes more important. Ammine and tertiary phosphine complexes have been selected for detailed examination. 

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It seems strange that no hydroxylamine complexes of osmium are established. There is a brief report of a deprotonated complex Os(NO)(NHOH)Cl2(PPh3)2, made from Os(NO)2(PPh3)2 and HCl. The v o band is at 1860cm . ... 

Further variations on the theme have been achieved by anchoring species such as [Ru O-(terpy)(py)] " or complexes of osmium. Iron complexes have also been studied for example, evaporation of a solution containing [Fe(CN)5(H20)] and PYP on to an electrode will inunobilize the pentacyanoferrate as a pyridyl complex, one in three available pyridyl groups being used to avoid precipitation prior to evaporation of solvent. 

Unlike the above example, the majority of five-coordinate complexes appear to undergo oxidative-addition reactions in two separate steps. Additions to the bis phosphine complexes of ruthenium(O) (36) and osmium(O) (39) (XIV) are the most thoroughly studied examples of this generalization (see Section IV). The configurations of these complexes have been established by infrared spectroscopy and, in the case of the osmium complex, by X-ray diffraction (72), Addition of an electrophile A" " (for example H+, HgX+, or Br+ from Br2) to the five-coordinate complexes... 

Fullerene-Organometallics. Also recently investigated are the organo-metallic exohedral complexes of osmium, ruthenium, and platinum which are readily attached to the external framework of the C o molecule by solution chemistry.I X I An osmylated-Ceo compound is shown in Fig. 15.8.P1]... 

The formation of these compounds has been rationalized according to Scheme 6. The reaction of Os (E )-CH=C 11 Ph C1 (C())( P Pr3)2 with n-BuLi involves replacement of the chloride anion by a butyl group to afford the intermediate Os (/i> CH=CHPh ( -Bu)(CO)(P Pr3)2, which by subsequent hydrogen (3 elimination gives OsH ( >CI I=CHPh (CO)( P Pr3)2. The intramolecular reductive elimination of styrene from this compound followed by the C—H activation of the o-aryl proton leads to the hydride-aryl species via the styrene-osmium(O) intermediate Os r 2-CH2=CHPh (CO)(P Pr3)2. In spite of the fact that the hydride-aryl complex is the only species detected in solution, the formation of OsH ( )-CH=CHPh L(CO)(P Pr3)2 and 0s ( )-CH=CHPh (K2-02CH)(C0)(P,Pr3)2 suggests that in solution the hydride-aryl complex is in equilibrium with undetectable concentrations of OsH ( )-CH=CHPh (CO)(P,Pr3)2. This implies that the olehn-osmium(O) intermediate is easily accessible and can give rise to activation reactions at both the olefinic and the ortho phenyl C—H bonds of the... 

Thus the reactivity of transition metal-carbene complexes, that is, whether they behave as electrophiles or nucleophiles, is well explained on the basis of the frontier orbital theory. Studies of carbene complexes of ruthenium and osmium, by providing examples with the metal in either of two oxidation states [Ru(II), Os(II) Ru(0), Os(O)], help clarify this picture, and further illustrations of this will be found in the following sections. 

The olive-green osmium(VI) octaethylporphyrin complex 0s02(0EP) (IR i/(Os—O) 825 cm-1) is representative of a number of osmyl porphyrins [185] they can readily be transformed into a number of osmium porphyrins in lower oxidation states (Figure 1.73). 

Similar reactions of the other group 14 hydrides with ruthenium(O) and osmium(O) complexes have also been described. 

Extensive work on cis- and trans-d o o complexes of ruthenium(VI) and osmium(VI) containing nonlabile, oxidation-resistant nitrogen donor ligands has been reported. 

Oxidative additions are frequently observed with transition metal d8 systems such as iron(0), osmium(O), cobalt(I), rhodium(I), iridium(I), nickel(II), palladium(II) and platinum(II). The reactivity of d8 systems towards oxidative addition increases from right to left in the periodic table and from top to down within a triad. The concerted mechanism is most important and resembles a concerted cycloaddition in organic chemistry (Scheme 1.1). The reactivity of metal complexes is influenced by their... 

IR and EXAFS data representing osmium carbonyls on y-Al203 led to the identification of osmium di- and tricarbonyls and of the conversion of the latter into the former. The loss of one CO ligand from the tricarbonyl complex (indicated by infrared spectroscopy and confirmed approximately by EXAFS spectroscopy) was accompanied by an increase in the Os-O coordination number from2.9 to 3.9 (or nearly from 3 to 4) (Deutsch, Chang, and Gates, 1993), as follows ... 

Peacock AFA, Parsons S, Sadler PJ (2007) Tuning the hydrolytic aqueous chemistry of osmium arene complexes with N,O-chelating ligands to achieve cancer cell cytotoxicity. J Am Chem Soc 129 3348-3357... 

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