Osmium porphyrin

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

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... 

SuLiicniD Data tor Structuralia Charactfrizfd Ruthhmlai and Osmium Porphyrin Compi.fxf.s... 

The most significant and widely studied reactivity of the ruthenium and osmium porphyrin carbene complexes is their role in catalyzing both the decomposition of diazoesters to produce alkenes and the cyclopropanation of alkenes by diazoesters. Ethyl diazoacetate is used to prepare the carbene complex 0s(TTP)(=CHC02Et)... 

Both rhodium and osmium porphyrins are active for the cyclopropanation of alkenes. The higher activity of the rhodium porphyrin catalysts can possibly be attributed to a more reactive, cationic carbene intermediate, which so far has defied isolation. The neutral osmium carbene complexes are less active as catalysts but the mono- and bis-carbene complexes can be isolated as a result. 

Trans Effects in Osmium Porphyrins with rr-Acceptor Ligands.108... 

Consequently cis or tram effects mediated by the transmission paths D—F (Fig. 1) should be the largest with the osmium porphyrins. The situation in the latter is therefore treated separately in this chapter. 

Fig. 9. Correlation of the Osn/Osffl redox potentials and the energy of the a-bands of osmium porphyrins Os(OEP)X(L) (ligands X/L indicated in the drawing for further information, see Tables 10 and 11)...

The osmium porphyrins have thus furnished the most coherent series of compounds for investigating cis, trans and metal effects of the origins illustrated in Figures 1 and 8. Additional material from other sources will be presented in the following sections. 

Considerable variation in stereocontrol can also occur, depending on the catalyst employed (equation 125). In general, the various rhodium(II) carboxylates and palladium catalysts show little stereocontrol in intermolecular cyclopropanation162,175. Rhodium(II) acetamides and copper catalysts favour the formation of more stable trans (anti) cyclopropanes162166. The ruthenium bis(oxazolinyl)pyridine catalyst [Ru(pybox-ip)] provides extremely high trans selectivity in the cyclopropanation of styrene with ethyl diazoacetate43. Furthermore, rhodium or osmium porphyrin complexes 140 are selective catalysts... 

The first osmium porphyrins were obtained by Rohbock [46] (Eq. 4) in diethyleneglycol monomethylether (DEGE). 

Scheme 2. Reaction paths a-z of ruthenium and osmium porphyrins starting from carbonylmetal (II) complexes MCO (P) L (M = Ru, Os). For reaction conditions and references, see Table 5...

Photochemically and radiolytically activated oxidations and reductions - A variety of photochemically or radiolytically activated oxidations and reductions of osmium porphyrins were investigated [197]. The only reactions not already covered by Scheme 2 are the radiolytic formation of OsCl2(P) in aerated dichloromethane and the reduction of Os(OR)2(P) to Os(ROH)2(P) in the presence of isopropanol. 

Alkyl and aryl systems - As already mentioned in Sect. 3.2, dialkyl ruthenium and osmium porphyrins have been synthesized according to Eq. (22) by the reaction of metalloporphyrin dianions [M(P)]2 with alkyl iodides [223, 260, 261,307]. These dianions have been obtained by reduction of porphyrin dimers [M(P)]2. 

Instead of adding 4-substituted pyridine ligands trans to the carbene ligand, the complexes Os(CHR XTTP) (R = SiMe3, C02Et) add these donors to the carbene carbon atom with formation of an ylide species. This reaction is not observed for Os(CR2XTTP) with R = Ph [313c]. Nevertheless, the diphenylcar-bene or trimethylsilylmethylene osmium porphyrins crystallize as Os(CRR )-(TTP)THF with a THF molecule in trans position. 

The first silylene complexes of osmium porphyrin, (TTP)Os=SiR2-THF, were prepared by treating K2[Os(TTP)] with Cl2SiR2 or the reaction of [Os(TTP)]2 with hexamethylsilacyclopropane (116). The molecular structure of (TTP)Os=SiEt2-2THF is stabilized by coordination of THF to the silicon, as shown by X-ray crystallography (Fig. 5). The measured Os—Si distance of 2.325(8) A is the shortest ever reported (116). 

Synthesis and structure of ruthenium and osmium porphyrin carbene complexes and their role in the metal-mediated cyclopropanation of alkenes 02CCR(231)151. 

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