Porphyrin complexes, osmium

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 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... 

These bis(amido)ruthenium(IV) and bis(amido)osmium(IV) porphyrin complexes show well-resolved H NMR spectra with the signals of the porphyrinato ligands appearing at normal fields, indicating that they are all diamagnetic. 

A number of /.t-oxo-osmium(IV) porphyrin complexes have been prepared by aerial oxidation of [Os OEP)(CO)(MeOH)] in the presence 2,3-dimethylindole in CH2Cl2. " Cyclic voltammetric studies show that [0s2(0)(0EP)2(0Me)2] can undergo reduction to give an Os —O—Os dimer. The X-ray crystal structure of [0s(0EP)(0Me)]2( -0) shows a linear Os—O—Os backbone with Os—O and Os—OCH3 distances of 1.808 A and 1.997 A, respectively. 

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 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. 

Osmium(V) porphyrin complexes, [Osv(P)(OR)2] +, have recently been generated by electrochemical oxidation of the corresponding [Osiv(P)(OR)2] and were characterized by UV-VIS spectroscopy (112). The [Osv(salen)(OR)2]+ complexes have been generated and characterized in a similar manner (152). 

Osmium(VI) nitrido porphyrin complexes trans-[Os(OEP)NX] (X = F, C104, OMe) are made from [Os(OEP)(0)2] and hydrazine hydrate with HF, HCIO4, or MeOH (223). 

Nitrogen is, after oxygen, the most frequently encountered donor atom in the coordination chemistry of osmium. There is a large and growing body of work on the ammine, pyridine, ethylenediamine and porphyrin complexes, but the most popular and rapidly growing field of study at the present time is that of the polypyridyls , the 2,2 -bipyridyl, 1,10-phenanthroline and 2,2,2,6 - terpyridyl complexes of the metal. 

Organometallic osmium(IV) complexes are readily characterized by NMR spectroscopy because they are either diamaguetic or, depeudiug ou their symmetry, paramagnetic but with sharp NMR siguals. Unlike most Os(IV), six-coordinate porphyrin complexes, the dialkylporphyrin complex of osmium(IV) Os(TPP)(CH2SiMc4)2 is diamagnetic... 

Similarly, ra 5-cyclopropanes were obtained from alkenes, such as styrene and 2,5-dimethyl-hexa-2,4-diene, with relative yields > 90% when a diazoacetate bearing a bulky ester group was decomposed by a copper catalyst with bulky salicylaldimato ligands. Several metal complexes with bulky Cj-symmetrlc chiral chelating ligands are also suitable for this purpose, e.g. (metal/ligand type) copper/bis(4,5-dihydro-l,3-oxazol-2-yl)methane copper/ethyl-enediamine ruthenium(II)/l,6-bis(4,5-dihydro-l, 3-oxazol-2-yl)pyridine cobalt(III)/ salen. The same catalysts are also suited for enantioselective reactions vide infra). For the anti selectivity obtained with an osmium-porphyrin complex, see Section 1.2.1.2.4.2.6.3.1. 

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