Ruthenium porphyrin

Progress in investigation of ruthenium porphyrin complexes 97MI10. 

High-valent ruthenium oxides (e. g., Ru04) are powerful oxidants and react readily with olefins, mostly resulting in cleavage of the double bond [132]. If reactions are performed with very short reaction times (0.5 min.) at 0 °C it is possible to control the reactivity better and thereby to obtain ds-diols. On the other hand, the use of less reactive, low-valent ruthenium complexes in combination with various terminal oxidants for the preparation of epoxides from simple olefins has been described [133]. In the more successful earlier cases, ruthenium porphyrins were used as catalysts, especially in combination with N-oxides as terminal oxidants [134, 135, 136]. Two examples are shown in Scheme 6.20, terminal olefins being oxidized in the presence of catalytic amounts of Ru-porphyrins 25 and 26 with the sterically hindered 2,6-dichloropyridine N-oxide (2,6-DCPNO) as oxidant. The use... 

Structural data on ruthenium porphyrins shows that the Ru-N (porphyrin) distance is relatively unaffected by changing the oxidation state, as expected for a metal atom inside a fairly rigid macrocyclic ring (Table 1.11). 

A more direct access to the unstable and non isolated sulfonium ylides 58a- c is the reaction of diisopropyl diazomethylphosphonate 57 with allylic sulfides, catalyzed by Cu(II), Rh(II) [39], or ruthenium porphyrins.[40] For example, the a-phosphorylated y,d-unsaturated sulfides 59-61 are obtained through the [2,3] -sigmatropic rearrangement of 58a-c. This method allows the use of a greater variety of starting allylic sulfide substrates, such as 2-vinyl tetrahydrothiophene, or propargylic sulfides (Scheme 15). 

The first ruthenium porphyrin organometallic complexes were reported in 1985... 

Over the last decade a number of high oxidation state ruthenium porphyrin complexes containing 0x0 or imido ligands have been reported and have been thoroughly studied for their role in oxidation and atom-transfer chemistry. Although comparisons can be drawn with organometallic species (carbene, imido. and 0x0 ligands are formally isolobal) the chemistry of the 0x0 and imido complexes is beyond the scope of the review and will not be covered here. 

The first ruthenium porphyrin alkyls to be reported were prepared from the zerovalent dianion, [Ru(Por)] with iodomethane or iodocthane, giving the ruthe-nium(lV) dialkyl complexes Ru(Por)Me2 or Ru(Por)Et2 (Por = OEP, TTP). Alternatively, the Ru(lV) precursors Ru(Por)X2 react with MeLi or ArLi to produce Ru(Por)Mc2 or Ru(Por)Ar2 (Ar = / -C(,H4X where X = H, Me, OMe, F or Cl) 147-149 The osmium analogues can be prepared by both methods, and Os(Por)R2 where R = Me, Ph and CH2SiMe2 have been reported.Some representative structures are shown in Fig. 5, and the preparation and interconversion of ruthenium porphyrin alkyl and aryl complexes are shown in Scheme 10. 

The most recent report of -coordination to a ruthenium porphyrin fragment details the reaction of [Ru(OEP)j2 with C o in benzene/THF (100 1) solution. The UV-visible spectrum of the complex showed a new band at 780 nm, not observed in the spectrum of either Ru(OEP) 2 or C(,o, and H and C NMR data also indicated the presence of a new complex. This has been formulated on the basis of the spectroscopic data as the fullerene complex Ru(OEP)(... 

Ruthenium porphyrin complexes are also active in cyclopropanation reactions, with both stoichiometric and catalytic carbene transfer reactions observed for Ru(TPP)(=C(C02Et)2> with styrene. Ru(Por)(CO)orRu(TMP)(=0)2 catalyzed the cyclopropanation of styrene with ethyidiazoacetate, with aiiti.syn ratios of 13 1... 

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

The coupling reaction of 1 (M=Zn) affords CPO 3 (M=Zn) in 55% yield in the presence of template 2 however, the absence of 2 decreases the yield to 34% [22]. With the increase of yield of 3, template 2 induces the selectivity of the reaction the yield of the by-product (cychc dimer 4 (M=Zn)) was changed from 23% (with no template) to 6% (in the presence of template). A similar CPO formation reaction was reported for the corresponding ruthenium porphyrins (3, M=Ru(CO)), in which the stability constant of the Ru-N coordination bond is 10 larger than that of the Zn-N coordination bond [23]. Although the transition state of the CPO produced by the ruthenium-based substrate is expected to be more stable than that produced by ZnPor, the yield of 3 (M=Ru(CO)) is only... 

In the second oxidation method, a metalloporphyrin was used to catalyze the carotenoid oxidation by molecular oxygen. Our focus was on the experimental modeling of the eccentric cleavage of carotenoids. We used ruthenium porphyrins as models of cytochrome P450 enzymes for the oxidation studies on lycopene and P-carotene. Ruthenium tetraphenylporphyrin catalyzed lycopene oxidation by molecular oxygen, producing (Z)-isomers, epoxides, apo-lycopenals, and apo-lycopenones. 

Caris-Veyrat, C. et al., Cleavage products of lycopene produced by in vitro oxidations characterization and mechanisms of formation, J. Agric. Food Chem., 51, 7318, 2003. Caris-Veyrat, C. et al., Mild oxidative cleavage of beta, beta-carotene by dioxygen induced by a ruthenium porphyrin catalyst characterization of products and of some possible intermediates, New J. Chem., 25, 203, 2001. 

To substitute the strongly bound axial CO ligand of the ruthenium or osmium center, it is necessary to employ more drastic conditions than simple stirring at room temperature. Imamura (11,20) used photolysis to synthesize porphyrin trimers on the basis of simultaneous coordination of two 4-pyridyl porphyrins to the same ruthenium porphyrin (12, Fig. 3). Some interesting photophysical behavior was observed for these systems. The trimers have an extra UV-Vis absorption band at about 450 nm which is ascribed to metal-ligand charge transfer (MLCT), a d7r(Ru(II))-7r (OEP) transition. This band shows a batho-chromic shift in more polar solvents, and decreased in intensity when... 

The chemically catalyzed oxidation of carotenoids by metalloporphyrins has also been described in the literature. In 2000, French et al. described a central cleavage mimic system (ruthenium porphyrin linked to cyclodextrins) that exhibited a 15,1 S -regiosclectivity of about 40% in the oxidative cleavage of [3-carotene by tert-butyl hydroperoxide in a biphasic system (French et al. 2000). 

Dioxo-ruthenium porphyrin (19) undergoes epoxidation.69 Alternatively, the complex (19) serves as the catalyst for epoxidation in the presence of pyridine A-oxide derivatives.61 It has been proposed that, under these conditions, a nms-A-oxide-coordinated (TMP)Ru(O) intermediate (20) is generated, and it rapidly epoxidizes olefins prior to its conversion to (19) (Scheme 8).61 In accordance with this proposal, the enantioselectivity of chiral dioxo ruthenium-catalyzed epoxidation is dependent on the oxidant used.55,61 In the iron porphyrin-catalyzed oxidation, an iron porphyrin-iodosylbenzene adduct has also been suggested as the active species.70... 

Oxidizing enzymes use molecular oxygen as the oxidant, but epoxidation with synthetic metalloporphyrins needs a chemical oxidant, except for one example Groves and Quinn have reported that dioxo-ruthenium porphyrin (19) catalyzes epoxidation using molecular oxygen.69 An asymmetric version of this aerobic epoxidation has been achieved by using complex (7) as the catalyst, albeit with moderate enantioselectivity (Scheme 9).53... 

Besides ruthenium porphyrins (vide supra), several other ruthenium complexes were used as catalysts for asymmetric epoxidation and showed unique features 114,115 though enantioselectivity is moderate, some reactions are stereospecific and treats-olefins are better substrates for the epoxidation than are m-olcfins (Scheme 20).115 Epoxidation of conjugated olefins with the Ru (salen) (37) as catalyst was also found to proceed stereospecifically, with high enantioselectivity under photo-irradiation, irrespective of the olefmic substitution pattern (Scheme 21).116-118 Complex (37) itself is coordinatively saturated and catalytically inactive, but photo-irradiation promotes the dissociation of the apical nitrosyl ligand and makes the complex catalytically active. The wide scope of this epoxidation has been attributed to the unique structure of (37). Its salen ligand adopts a deeply folded and distorted conformation that allows the approach of an olefin of any substitution pattern to the intermediary oxo-Ru species.118 2,6-Dichloropyridine IV-oxide (DCPO) and tetramethylpyrazine /V. V -dioxide68 (TMPO) are oxidants of choice for this epoxidation. 

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