Diimine Ru

There are more examples of a second type in which the chirality of the metal center is the result of the coordination of polydentate ligands. The easiest case is that of octahedral complexes with at least two achiral bidentate ligands coordinated to the metal ion. The prototype complex with chirality exclusively at the metal site is the octahedral tris-diimine ruthenium complex [Ru(diimine)3 with diimine = bipyridine or phenanthroline. As shown in Fig. 2 such a complex can exist in two enantiomeric forms named A and A [6,7]. The bidentate ligands are achiral and the stereoisomery results from the hehcal chirality of the coordination and the propeller shape of the complex. The absolute configuration is related to the handness of the hehx formed by the hgands when rotated... 

Ru(CN)jNO reactions with OH , SH and SOj" resemble those of the nitroprusside ion, with attack at the coordinated nitrosyl to give analogous transients and similar second-order rate constants. Ruthenium(II) complexes of the general type Ru(N2), Nj = biden-tate hgands, are important reactants. The relative inertness of Ru(NH3) + and Ru(diimine)f+ towards substitution makes these complexes definite, although weak, outer-sphere reductants (Tables 5.4, 5.5, 5.6 and 5.1). Ruthenium(ll) complexes of the general type Ru(diimine)f +, and particularly the complex Ru(bpy)j+, have unique excited state properties. They can be used as photosensitizers in the photochemical conversion of solar energy. Scheme 8.1 ... 

Fig. 8 Rigidly bridged Ru diimine donor/Os diimine acceptor [47]...

Light-driven Unthreading Reaction in Rotaxane with a [Ru(diimine)3]2+ Core... 

We have recently reported the synthesis of a [2]rotaxane constructed around a Ru(diimine)2+ core [95]. The ring was a derivative of dmbp, and, in the course of the threading reaction, we noticed that both exo- and endo-coordination to the ruthenium(II) centre of the rod-like fragment take place, as schematically represented in Fig. 17. 

From a band centered at 465 nm, typical of a Ru(diimine)2+ complex [96], a new spectrum is obtained by irradiation, which corresponds to a RuC12 (diimine)2 complex (/.max = 562 nm). As expected, the MLCT band for the photochemical product is strongly bathochromically shifted from that of the tris-diimine complex. The presence of a clean isosbestic point at 485 nm indicates that the photochemical reaction is selective and quantitative. This has been confirmed by JH NMR spectroscopy and by thin-layer chromatography. Only one photochemical product was detected and the starting complex 342+ has completely disappeared. Similar experiments have been performed with the rotaxane 352+. The reaction is represented in a schematic fashion in Fig. 20. 

Inspection of the literature reveals rate data for two Ru(diimine) + based type 2 dyads. As part of a larger study, Elliott determined the rate of photoinduced forward ET in 32 (Scheme 14) which consists of a fm-dimethylbipyridine... 

Schanze and Sauer were the first to report a detailed study of long-range photoinduced ET in a series of metal-organic dyads [94]. These authors synthesized dyads 50a-e (Scheme 22 and Table 4) that comprise a Ru(diimine) + chromophore covalently linked to a p-benzoquinone acceptor using a series of oligo-L-proline peptide spacers. Oligo-proline peptide spacers are used because previous studies suggest that these peptides are conformationally restricted and... 

Schmehl, Elliott, and co-workers reported an extensive study of the spacer dependence of photoinduced ET in several series of metal-organic dyads consisting of a Ru(diimine) + chromophore covalently linked to a diquat electron acceptor [128]. In the present review we list only results for the series of poly-methylene linked dyads 52a-f (Scheme 23 and Table 4) the reader is directed to the original... 

Dunn AR, Dmochowski H, Winkler JR, Gray HB. Nanosecond photoreduction of cytochrome P450cam by channel-specific ru-diimine electron tunneling wires. J. Am. Chem. Soc. 2003 125 12450-12456. 

Recent studies have shown that coordinated ammonia and amine ligands under basic conditions may effect nucleophilic attack at carbonyl centres in organic compounds, " These reactions occur due to formation of deprotonated amido species which can act as nucleophiles. For example, reaction of cobalt(III) and platinum(IV)ammines with ketones gives the corresponding Co and Pt imine complexes. A similar reaction between [Ru(NH3)6] and diones produces the corresponding Ru diimine (108). It has also been found that nitrilepentaammineruthenium(II)... 

The rates of high-driving-force ET reactions have been measured for more than 30 Ru(diimine)-labeled metalloproteins.Only modest corrections are required to scale these rates to driving-force-optimized values, permitting comparisons of ET in different proteins. The results are summarized in the electron tunneling timetable of Fig. 1-2. 

Figure 1-4. Ru-wires. Variation of the linkage connecting the Ru-diimine to the enzyme substrate or heme ligand modifies the electronic coupling and hence the rate of electron transfer. The tetramethylated ancillary bipyridine ligands in tmRu-Fsbp-Im and tmRu-Fpbp decrease the reduction potential of the excited Ru-diimine by 130 mV. See ref. 91.

Interestingly, neither adamantyl nor imidazole is necessary for binding Ru-wires terminating in either an alkyl chain or a perfluorobiphenyl bind to the enzyme. This observation suggests that interactions of the protein with the Ru-diimine and linker moieties provide the bulk of the binding energy. 

Ru-wires allow the ET pathway between the Ru-diimine and the heme to be altered while retaining the surroimding protein matrix. Ru-wire P450cam conjugates thus serve as a useful complement to synthetic and protein ET systems. 

Ayman, A., Abdel Shah, A. A., Ward, M. D., Schmidt, R., Mechanism of Quenching by Oxygen of the Excited States of Ruthenium(II) Complexes in Aqueous Media. Solvent Isotope Effect and Photosensitized Generation of Singlet Oxygen, 02( Ag), by [Ru(diimine)(CN)4 2 Complex Ions, Dalton Trans. 2007, 2517 2527. 

More recently MacDonnell, Armstrong and coworkers reported a highly efficient method for the resolution of [Ru(diimine)3] complexes using HPLC with cyclodextrin chiral stationary phase. This technique allowed the separation of several monomeric and also dinuclear ruthenium polypyridyl compounds. 

The second more common approach to the preparation of enantiopure assemblies consists of using the A- or A- cA-[Ru(diimine)2L2] (5.96-5.98) as chiral building blocks. Then, when the latter is treated with multidentate ligands and subsequent displacement of monodentate labile ligands L occurs, the related supramolecualr assemblies are formed. It should be pointed out that such reactions often occur at relatively high temperatures in order to displace the monodentate ligands in some cases this results in low yields of the polynuclear products. 

I21CATENANE CONSTRUCTED AROUND A Ru(DIIMINE)3 DERIVATIVE USED AS A TEMPLATE... 

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