Osmium carbon complex

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 chemical reactivity of the organoruthenium and -osmium porphyrin complexes varies considerably, with some complexes (M(Por)R2, M(Por)R and Os(OEP)(NO)R) at least moderately air stable, while most are light sensitive and Stability is improved by handling them in the dark. Chemical transformations directly involving the methyl group have been observed for Ru(TTP) NO)Me, which inserts SO2 to form Ru(TTP)(N0) 0S(0)Me and Ru(OEP)Me which undergoes H- atom abstraction reactions with the radical trap TEMPO in benzene solution to yield Ru(OEP)(CO)(TEMPO). Isotope labeling studies indicate that the carbonyl carbon atom is derived from the methyl carbon atom. "" Reaction of... 

The effect of metal basicity on the mode of reactivity of the metal-carbon bond in carbene complexes toward electrophilic and nucleophilic reagents was emphasized in Section II above. Reactivity studies of alkylidene ligands in d8 and d6 Ru, Os, and Ir complexes reinforce the notion that electrophilic additions to electron-rich compounds and nucleophilic additions to electron-deficient compounds are the expected patterns. Notable exceptions include addition of CO and CNR to the osmium methylene complex 47. These latter reactions can be interpreted in terms of non-innocent participation of the nitrosyl ligand. 

Compound 72 has been crystallographically characterized. The most striking feature of this structure is how little structural reorganization accompanies this adduct formation. The osmium-carbon bond length at 1.90(2) A is not detectably altered from that of the parent complex 47 and the C—Os—C angle is increased by only 8°. 

The X-ray structure determination of 107 reveals that the osmium-carbon bond length is increased by 0.07 A on going from the parent carbyne complex 79 to the silver adduct 107. This may be contrasted with the weaker interaction between the metal-carbon bond and the Aul fragment in Os(CH2AuI)Cl(NO)(PPh3)2 (see Section IV,C,1). 

Vinylidene osmium(O) (187) (Section II,B,3,g) reacts with sulfur, selenium, or copper chloride to give complexes 233 via electrophilic addition to the osmium-carbon bond (116) (Scheme 18). Complex 187 also reacts with benzoylazide to form the five-membered metallacycle 234 (Z) which isomerizes 234 (E) on heating in benzene (141). 

Electrophilic attack at carbyne complexes may ultimately place the electrophile on either the metal or the (former) carbyne carbon, the two possibilities being related in principle by a-elimination/migratory insertion processes (Figure 5.39). The reactions of the osmium carbyne complex are suggestive of an analogy with alkynes. Each of these reactions (hydro-halogenation, chlorination, chalcogen addition, metal complexation see below) have parallels in the chemistry of alkynes. 

Many transition metal carbonyl complexes have been prepared, often inadvertently, by allowing a metal halide or polyhalometallate to react with a ligand in an organic solvent with carbon-oxygen bonds. Indeed, carbonyl abstraction is an important synthetic route to tran5 -[MCl(CO)(PPh3)2] (M = Rh, Ir) or [OsHX(CO)(ZPh3)3] (X = Cl, Br Z = P, As) and related osmium(II) complexes. 

The crystal structure of yellow metallacyclic-osmium(iv) complex 9 was also reported <20030M414>. The distribution of ligands around the osmium atom can be described as a four-legged piano-stool geometry with the carbon atom C-5 of the metallated phenyl group disposed transoid to the hydride ligand. The bidentate carbon donor... 

The trigonal bipyramidal osmium carbyne complex 115 adds HCl across the metal-carbon triple bond to give the octahedral carbene complex 116 [Eq. (101)] (56). Protonation of 115 with aqueous HCIO4 gives the cationic... 

The osmium carbyne complex 115 reacts with elemental sulfur, selenium, and tellurium to afford the complexes 135 in which the element atoms "bridge the metal-carbon triple bond [Eq. (123)] (56). Complex 115 also reacts with transition metal Lewis acids such as AgCl or Cul to give dinuclear compounds with bridging carbyne ligands. Reaction with elemental chlorine results in addition across the metal-carbon triple bond to generate the chlorocarbene osmium complex 136 [Eq. (124)]. 

The dihydride-osmium(IV) complex OsH2Cl2(P Pr3)2 as a precursor for carbon-carbon, carbon-nitrogen, carbon-phosphoms, carbon- germanium, and carbon-silicon coupling reactions... 

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). 

Whereas osmium dithiocarboxylato complexes are very rare, some dithiocar-boxylato iron and ruthenium complexes have been synthesized by substituting into the metal-halogen complex with lithium dithiocarboxylate [77] and by inserting CS2 into the carbon-metal bond [78,79]. The reaction of a vinylidene complex 32 with CS2 and NaOMe has also been reported to undergo a facile loss of HCl, followed by insertion of CS2 to give the dithiocarboxylato complex 33 (Scheme 7) [80]. 

Carbon monoxide is readily oxidized in the coordination sphere of a number of transition metal complexes. In many cases the product of reaction is a carbonate complex which is formed irreversibly, thus precluding the possibility of a catalytic transformation. In Section 5 the reaction between CO and platinum dioxygen complexes was shown to give carbonate complexes. The reaction between iridium, ruthenium and osmium carbonyl complexes and dioxygen to give coordinated carbonate was discussed in Section 6. 

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