Ruthenium and Osmium Porphyrins

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)... 

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...

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. 

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

Despite uncertainties concerning the site of the first one-electron oxidation of Fe P, the second oxidation is thought to form a ferry 1 species, 0 = Fe P, which can oxidize or hydroxylate various organic compounds. In parallel with this chemistry of iron porphyrins, the oxidation of ruthenium and osmium porphyrins was studied by radiation chemical methods. 

Table 3 X-ray structural data for carbene and carbide complexes of ruthenium and osmium porphyrin carbenes...

Ruthenium and osmium porphyrin carbonyl complexes have been excluded from this review readers arc referred to the following leading references for further details. " ... 

Xie J, Huang J-S, Zhu N, Zhou Z-Y, Che C-M (2005) Primary and secondary phosphane complexes of metalloporphyrins isolation, spectroscopy, and X-ray crystal structures of ruthenium and osmium porphyrins binding phenyl- or diphenylphosphane. Chem Eur J 11 2405-2416... 

Diazoalkanes are u.seful is precursors to ruthenium and osmium alkylidene porphyrin complexes, and have also been investigated in iron porphyrin chemistry. In an attempt to prepare iron porphyrin carbene complexes containing an oxygen atom on the /(-carbon atom of the carbene, the reaction of the diazoketone PhC(0)C(Ni)CH3 with Fe(TpCIPP) was undertaken. A low spin, diamagnetic carbene complex formulated as Fe(TpCIPP)(=C(CH3)C(0)Ph) was identified by U V-visible and fI NMR spectroscopy and elemental analysis. Addition of CF3CO2H to this rapidly produced the protonated N-alkyl porphyrin, and Bit oxidation in the presence of sodium dithionitc gave the iron(II) N-alkyl porphyrin, both reactions evidence for Fe-to-N migration processes. ... 

The bulky ruthenium TMP complex Ru(TMP) is very electron deficient in the absence of any coordinating ligand, and a tt-complex with benzene has been proposed. In fact, it readily coordinates dinitrogen, forming the mono- and bis-N adducts Ru(TMP)(N2)(THF) and Ru(TMP)(N2)2, - As a result, the use of the TMP ligand for careful stereochemical control of the chemistry at the metal center, which has been very successful for the isolation of elusive rhodium porphyrin complexes, is less useful for ruthenium (and osmium) because of the requirement to exclude all potential ligands, including even N2,... 

The porphyrin ligands in the diamagnetic ruthenium and osmium carbene complexes generally exhibit four-fold symmetry by NMR, indicating that the barrier to rotation about the M=C bond is low. The carbenoid protons appear shifted down-field in the H NMR spectra, for example appearing for Ru(TTP)=CHC02Et and Ru(TTP)=CHSiMc3 at 13.43 and 19.44 ppm, respectively, and for the osmium... 

While metalloporphyrin carbene complexes are well established for ruthenium and osmium, they are less well known for rhodium. Cationic rhodium porphyrin carbene intermediates were implicated in a report by Callot et al. in w- hich... 

The group homologues of iron, ruthenium and osmium, are expected to show a much stronger metal-to-porphyrin backbonding in their + II-oxidation states than iron. This has been discussed in Section 4.2 and is further exemplified in Section 7. 

There have also been significant advances in the imido chemistry of ruthenium and osmium. A variety of imido complexes in oxidation states +8 to +6 have been reported. Notably, osmium (VIII) imido complexes are active intermediates in osmium-catalyzed asymmetric aminohydroxyl-ations of alkenes. Ruthenium(VI) imido complexes with porphyrin ligands can effect stoichiometric and catalytic aziridination of alkenes. With chiral porphyrins, asymmetric aziridination of alkenes has also been achieved. Some of these imido species may also serve as models for biological processes. An imido species has been postulated as an intermediate in the nitrite reductase cycle. " ... 

Ruthenium and Osmium High Oxidation States S.6.4.4.9 Porphyrins and related complexes... 

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The porphyrin complexes of ruthenium and osmium display a rich oxidation-reduction chemistry. Oxidation states +2, +3 +4, and + 6 are well documented. The scope of states that can be realised at the metal is restricted by the fact that the tetrapyrrole ligands (P)2 themselves can be oxidized or reduced to radicals (P )-1 or (P )-3, respectively, at potentials about + 0.7 or - 2.0 V. 

Double bonded ruthenium and osmium homodimers have been synthesized by Coil-man . These two metals are inserted into the porphyrin free base by using the corresponding metal chlorocarbonyl dimer [MCl2(CO)3]2- Irradiation of the resulting carbonyl metal(II) porphyrin irradiated in pyridine solutions yields the bis(pyridine) metal(II) porphyrin and leads to the expected dimers by heating under vacuum. This is shown in Scheme 16. 

Not considered within this review are the wide range of porphyrin and other nitrogen macrocycle-stabilized ruthenium and osmium hydrocarbyl complexes. Readers should see the following as a starting point for information on this type of alkyl/aryl, alkynyl, vinylidene, allenylidene, and carbene complexes. 

Ruthenium and Osmium - NMR spectroscopy has been used to analyse the effect of halides on paramagnetic /ra -X2Ru and Os porphyrins NMR data have also been reported for [M(NH3)5(OH2)] , M = Ru, [RuCl2 (02CCH2)2NCH2CH2N(CH2C02)2 ] " d and tm 25-[Os(terpy)Cl2-(NPPh3)] di ... 

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