Ru III Complexes

Ruthenium has a considerable propensity to form polynuclear complexes, particularly with carboxylate ligands which as bridging ligands span the Ru centres, sometimes accompanied by a bridging 0x0 ligand. Preparation and properties of bi- and tri-nuclear acetato complexes of Ru have been reviewed [552]. 

W3 (0) j ] were used, as ( Bu N) salts, as complex/aq. Na(lO )7DCE/60°C to effect oxidative cleavage of styrene to benzaldehyde and benzoic acid. Kinetic studies and activation parameters were determined [707]. The system a-( Hx N)j[Ru Si(H30)W,(0)3, ] /TBHP/C H oxidised cyclohexane, n-heptane, n-decane and ethylbenzene to alcohols and ketones [708]. 

Catalytic activities of [Ru PW (H30)(0)3, ] -/03/CH3CN/80°C and of [Ru PMOjj(H30)(0)3, ] /03/CH3CN were compared. The tungsten complex did not catalyse the aerobic oxidation of cumene and 1-octene to cumyl alcohol and 1-octene oxide while the Mo analogue did so the tungsten complex underwent structural change with to an inert form, while its molybdenum analogue did not 

The anhydrous form is rarely if ever used for catalysis, as is the case with anhydrous RuOj. It exists in two modifications. The black a-form is made by heating P-RuClj to 600°C in vacuo, and has the laminar a-TiClj structure also found in CrClj and FeClj with a distorted octahedral structure (Ru-Cl distance 2.40 A). The brown P-form has the P-TiClj structure with linear polymers of RuClj units, the metal atoms having distorted octahedral coordination (Ru-Ru 2.68 A, Ru-Cl 2.30(7) and 2.39(7) A). Infrared spectra and magnetic susceptibility data were recorded for both forms [712]. The toxicological properties of RuClj have been listed it may give off toxic RuO when heated, and is mildly toxic by intraperito-neal routes [238]. 

In the section below on oxidations catalysed by RuClj only those are mentioned which are not likely to involve RuO many examples have been given above (1.2.7) in which RuCyaq. Na(IO ), for example, was used to generate RuO. Such reactions are not repeated here. 

---

The first report on the anticancer properties of ruthenium was published in 1976 when the Ru(III) compound /ac-[RuC13(NH3)3] (Fig. 11) was found to induce filamentous growth of Escherichia coli at concentrations comparable to those at which cisplatin generates similar effects (49). This Ru(III) complex and related compounds such as cis-[RuCl2(NH3)4]Cl illustrated the potential anticancer activity of ruthenium complexes, but insolubility prevented further pharmacological use. Since these initial studies, other Ru(III) complexes have been studied for potential anticancer activity, and two compounds, NAMI-A (50) and KP1019 (51), are currently undergoing clinical trials. Remarkably,... 

In a very special system, the photoelectrochemical regeneration of NAD(P)+ has been performed and applied to the oxidation of the model system cyclohexanol using the enzymes HLADH and TBADH. In this case, tris(2,2 -bipyridyl)ruthenium(II) is photochemically excited by visible light [43]. The excited Ru(II) complex acts as electron donor for AT,AT -dimethyl-4,4 -bipyridinium sulfate (MV2+) forming tris(2,2 -bipyridyl)ruthenium(III) and the MV-cation radical. The Ru(III) complex oxidizes NAD(P)H effectively thus... 

Other metal complexes also have promising anticancer activity. Two Ti(IV) complexes are on clinical trial, an acetylacetonate derivative (budotitane) and titanocene dichloride, and the antimetastic activity of octahedral Ru(III) complexes is attracting attention, one of which is now on clinical trial. Ru(III), like several other metal ions, can be delivered to cells via the iron transport protein transferrin. 

Keppler et al. have shown that the introduction of heterocyclic ligands into Ru(III) complexes such as 28 (163) and 29 (164) can improve the solubility and retain the antitumour activity, especially... 

The Ru(IV)/Ru(III) redox potential is 0.78 V, so that Ru(III) or even Ru(II) species may be present in vivo. Indeed, the related Ru(III) complex 32 is also active (171), and the pendant arms in these octahedral polyaminocarboxylate complexes increase the rate of substitution reactions. Complex 32 binds rapidly to the blood proteins albumin and transferrin (172), and the ruthenium ion appears to remain in the... 

Both Ru(II) and Ru(III) complexes are known to bind DNA preferentially at N7 of G but also to A and C bases (182, 183). Although most ruthenium antitumor agents have two reactive coordination sites, GG intrastrand cross-links on DNA do not appear to form readily. The only example appears to be the adduct of 27 with GpG, which has been structurally characterized by NMR spectroscopy (184). In this complex, the two N7-coordinated guanines adopt a head-to-head conformation and the two bases are strongly destacked. 

The Co(II) complex decomposes rapidly and irreversibly to Co2+, which is so weak a reductant that it is unable to reduce the Ru(III) complex to Ru(II). 

The Co(III)-Ru(III) complexes were synthesized as shown in Scheme I (48, 49). These complexes were purified by chromatography and characterized by HPLC, elemental analysis, UV-Vis spectra, and electrochemical properties. 

One of the very few exceptions to the rule that the acidity of the complexed ligand exceeds that of the free ligands involves the Ru(II) complexes shown in Table 6.5. It is believed that back bonding from the filled iig orbitals of Ru(II) to unoccupied tt-antibonding orbitals of the ligands more than compensates for the usual electrostatic effects of the metal that makes the nitrogen less basic. This tt-bonding is less likely with the Ru(III) complex and its is lower than that for the protonated pyrazine (see also Sec. 6.3.3. for the effects of Ru(II) and Ru(III) on hydrolysis of nitriles). ... 

In the presence of DNA reactions (17) and (18) that generate the excited complex directly or indirectly via reaction (19), become much slower or do not take place, and therefore the ECL disappears. This is due to the fact that the Ru(II) and Ru(III) complexes, physically bound to DNA, are protected by the negatively charged phosphate backbone from the reduction by C02. Thus the ECL titration of the metal complex in the presence of DNA has allowed the determination of the equilibrium constant and binding-site size for association of Ru(phen)3 to DNA [82]. 

Without discussing the relative merits of the two mechanisms it is interesting to point out the information that does not readily fit either mechanism (1) the high reactivity of hydroxide is peculiar to certain Co (III) and Ru (III) complexes and the analogous complexes of Pt (IV), Rh (III), and Ir (III) appear to have little or no excess lability in the presence of hydroxide (2) in many cases, the great reactivity difference between water and hydroxide comes mainly from the activation entropy and not the activation energy (12). 

Electron-transfer pathways In spite of the success of the Marcus theory, rates of electron-transfer from the iron of cytochrome c have been found to vary for different pathways.150 153 155 For example, transfer of an electron from Fe(II) in reduced cytochrome c to an Ru(III) complex on His 33 was fast ( 440 s-1)157 but... 

As well as Pt systems, mixed-valence Ru(II)-Ru(III) complexes have been very widely studied — see C. Creutz,... 

The formation of some Ru(III) complexes upon photodecarbonylation followed by an internal electron transfer can be expressed as follows... 

---