Carbon monoxide, reaction with osmium complexes

Osmium tetroxide reacts with phenyl Grignard reagent to produce a reactive intermediate, serving as a synthetic route to prepare polyphenyl osmium complexes. For example, reaction with o-tolyl magnesium bromide, o-tolMgBr, forms a purple, tetracoordinated osmium ort/io-tolyl complex, Os(o-tol)4, which reacts with trimethylphosphine or carbon monoxide to yield osmium n-aryl complexes. 

Isonitriles are isoelectronic with carbon monoxide bnt homoleptic see Homoleptic Compound) isonitrile complexes are more difficnlt to prepare than carbonyl complexes. The reduction of OsXg with ethanol in the presence of methylisonitrile gives OsX2(CNMe)4. The osmium(II) isonitrile complex [Os(CNMe)6] + results from the alkylation of [Os(CN)6]" with MeOS02CF3. More generally, [Os(CNR)6] + can be prepared by reaction of 0s2(02CMe)4Cl2 with alkyl isonitriles. 

Only a very few compounds have been prepared that contain more than one coordinated N2 molecule. Similarly, there are only one or two complexes known so far in which both N2 and CO are coordinated to the same metal site. Taube (28) prepared the first bis-nitrogen compound, cis-[Os (NH3)4(N2)2] by the reaction of nitrous acid with [Os (NH3)5N2]. Neither of these two osmium-N2 compounds can be prepared using N2 as a reagent, but the carbonyl analogue of one of them, [Os (NH3)sCO] has now been prepared (29) by the careful reduction of an osmium (III) complex with amalgamated zinc in the presence of carbon monoxide. Treatment of this compound with nitrous acid gives cw-[Os(NH3)4CO N2] (29). 

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 only study on the direct reaction of carbon monoxide with osmium pincer complexes was reported by Milstein and coworkers in 2001 [52]. In this case, the pincer (PCP)Os(II) complex (131) was reacted with CO in benzene at room temperature to afford quantitatively the carbon monoxide adduct (132). This species further reacted with an additional equivalent of CO to yield the bis-carbonyl (PCP)Os(II) pincer complex (133) with the elimination of PPhs. Additionally, complex (133) can be directly generated by pressurizing the pincer compound (131) with 3 bar of CO or from the reaction of complex (134) with CO under mild conditions. The structure of... 

Iron, Ruthenium, and Osmium.—Cyclo-octafluorotetramethylenetetra-carbonyliron (100), formed in the thermal reaction of tetrafluoroethylene with iron carbonyls, was one of the earliest reported fluoro-organo-derivatives of a transition metal. It may be more efficiently synthesized in a photochemical reaction. Ligands displace carbon monoxide from complex (100) to form complexes of the types (101) [L = PPhj, AsPhj,... 

---