Ruthenium, porphyrins coordinated

The electrochemistry of ruthenium porphyrins coordinated to small molecules, such as CS [118], PF3 [117], NO [69,72,73, 96], or bound by a o-bonded alkyl or aryl group [57, 180-182], has also been documented in the literature. The electroreduction of (T(p-Me)PP)Ru"(CS)(L) where L = EtOH, CN, Im or Py has been studied in THE, DMF or Et2Cl2, and a mechanism involving a two-electron-transfer processes, accompanied by an uptake of protons, has been proposed by Latos-Gra2ynski and coworkers [118]. Kadish and coworkers [117] reported the electrochemistry of (P)Ru(PF3), where P = TPP, T(p-Br)PP, T(p-Me)PP, T(p-Et)PP or OEP. The authors pointed out similarities between the electrochemistry of the CO and PF3 derivatives in CH2CI2, but differences in electrochemical behavior were observed in other nonaqueous solvents. 

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)(... 

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... 

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... 

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... 

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. 

The first HNO complex, Os(PPh3)2(CO)(HNO)Cl2, was reported in 1970 upon exposure of HC1 to Os(PPh3)2(CO)(NO)Cl (173), and the X-ray crystal structure was published in 1979 (174). Recent interest has resulted in isolation of additional examples of HNO complexes, and the structures of three similar complexes have been reported [(Ru(HNO)(2,6-bis(2-mercapto-3,5-di-fert-butyl-phenylthio)dimethylpyridine) (175), ReCl(CO)2(PR3)2(HNO) (176), and IrHCl2 (PPh3)2(FINO) (177)]. Preparative routes generally involve protonation, hydride addition, or reduction of a coordinated nitrosyl (175, 176, 178-186). Farmer and co-workers also described the first synthesis of an HNO complex directly as a result of exposure to a donor compound (187) while Lee and Richter-Addo recently observed the HNO adduct of a heme model complex [ruthenium porphyrin (188)]. 

Thiazyl monomer can be stabihzed by coordination to a metal, and many thionitrosyl complexes with Cr, Mo, Re, Ru, Os, Co, Rh, Ir, and Pt are known. Comparison of the spectroscopic properties and the electronic stmctures of M-NS and M NO complexes indicates that NS is a better a-donor and jr-acceptor ligand than NO. Oxygen transfer from an NO2 to an NS ligand on the same metal center occurs in ruthenium porphyrin complexes. ... 

With respect to the widely investigated metalloporphyrins for catalytic epoxidation, progress was made in the area of polymer-supported ruthenium porphyrins for asymmetric epoxidation. Manganese-porphyrin complexes attached via peptide linkers to organic polymers showed enhanced selectivity and catalyst stability due to donor atoms in the linker that could coordinate to the metal center. This shows that improvement can be achieved not only by optimization of the polymer or metal complex but also by appropriate choice of the linker. Furthermore, electropolymerization by anodic oxidation of suitable manganese-porphyrin complexes proved to be a promising technique for the preparation of efficient immobilized epoxidation catalysts. 

Higuchi, T. and M. Hirobe (1996). Four recent studies in cytochrome P450 modelings A stable iron porphyrin coordinated by a thiolate ligand a robust ruthenium porphyrin-pyridine N-oxide derivatives system polypeptide-bound iron porphyrin application to drug metabolism smdies. J. Mol. Catal A Chem. 113, 403 22. 

These systems can be taken as good examples of the general behavior of free-base porphyrins (Fb), zinc-porphyrins (Zn), and ruthenium-porphyrins (Ru). Minor quantitative changes in the spectroscopic and photophysical behaviors of these chromophores are only expected to occm as a consequence of chemical modifications such as, for example, replacement of peripheral phenyl with pyridyl groups or axial coordination of an additional Ugand (e.g. pyridine) to the metal in the case of Zn. 

Richter-Addo GB, Wheeler RA et al (2001) Unexpected nitrosyl-group bending in six-coordinate[M(NO)] sigma-bonded aryl (iron) and -(ruthenium) porphyrins. J Am Chem Soc 123 6314-6326... 

Structure 5.18. Structural representation of [M(II) — TPyP Ru(bipy)2Cl 4] " complex, TRP. Reprinted from Figure 3 H.E. Toma and K. Araki, Supramolecular assemblies of ruthenium complexes and porphyrins. Coordination Chemical Reviews, 196 (2000) 307-329. Cop5 right 2000, with permission of Elsevier. 

Figure 5.11. Cyclic voltammograms (50 mVs ) of (A) [Ni-TRP](TFMS)4 (1.1 mmoldm ) in DMF, TEA CIO4O.IO moldm , under an argon atmosphere (B) in the presence of 16.2 mmol dm of CH3I (C) of an electroltye solution saturated with CO2 and (D) of the complex solution saturated with CO2. Insert Voltammogram of a 1.1 mmol dm solution of the complex in acetonitrile, TEA CIO4 0.10 mmol dm . Reprinted from Figure 10 H.E. Toma and K. Araki, Supramolecnlar assemblies of ruthenium complexes and porphyrins. Coordination Chemical Reviews, 196 (2000) 307-329. Copyright 2000, with permission o Elsevier.

A nickel-imido complex and a ruthenium-imido complex boimd by an ancillary porphyrin ligand also react with olefins, in this case to generate aziridine products (Equations 13.74 and 13.75). A pathway for the formation of an aziridine that occurs by a [2+2] addition of the olefin across the metal imido unit, followed by reductive elimination of the aziridine, was proposed for the reaction of the nickel complex, although the azametaUacycle was not observed directly. Because of the lack of coordination site cis to the imido group in the ruthenium-porphyrin system, the transfer of the imido group likely occurs by direct reaction of the imido group with the olefin. ... 

Marek D, Narra M, Schneider A, Swavey S (2006) Synthesis, characterization and electrode adsorption studies of porphyrins coordinated to ruthenium(n) pol) pyridyl complexes. Inorg Chim Acta 359(3) 789-799... 

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