Ruthenium complexes aquation

The pentammine aqua ion [Ru(NH3)j(H20)]2+, best made by zinc amalgam reduction and aquation of [Ru(NH3)5C1]2+, undergoes extensively studied substitution reactions first order in both the ruthenium complex and the incoming ligand (e.g. NH3, py) and is a convenient source of other... 

Kinetics of aquation of [Ru(LLLL)X2], with LLLL = cyclam, 2,3,2-tet, en2, or (NH3)4, and X = Cl or Br, have been followed by cyclic voltammetry. Rate constants, and activation parameters (A// and A5 ) have been evaluated, and compared with kinetic parameters for reactions of analogous compounds of ruthenium(III) and cobalt(III). Similar trends obtain for all three sets of complexes. There is retention of stereochemistry, rates decrease as the extent of chelation in LLLL increases, and trans complexes are less labile than cis analogs. Reactivities are determined by solvation of the initial and transition states, by nephelauxetic effects, and by a-trans effects. A limiting dissociative (D) mechanism is proposed for the ruthenium complexes, with square-pyramidal geometry for the transient intermediate [cf. rhodium(III) photochemistry below. Section 5.8.10]. Differences in isomer lability have also been described for... 

CIO7, or Cl", deposited in a conducting film generated by copolymerization of the ruthenium complex with e.g., pyrrole or 3-methylthiophen, when this film is immersed in acetonitrile. Displacement of chloride is slower when the appropriate film is immersed in water this aquation process is photo-catalyzed." Variable-temperature NMR has given some information on intramolecular conformational changes in the constrained ligands (62) and (63) [X=—CHj— to — (CH2)4—]. The inversion barrier of 44kJmol" ... 

Aquation. The principal reactivity of our family of ruthenium-arene complexes is the exchange of the leaving group Z, usually a... 

Alternatively, arene displacement can also be photo- rather than thermally-induced. In this respect, we studied the photoactivation of the dinuclear ruthenium-arene complex [ RuCl (rj6-indane) 2(p-2,3-dpp)]2+ (2,3-dpp, 2,3-bis(2-pyridyl)pyrazine) (21). The thermal reactivity of this compound is limited to the stepwise double aquation (which shows biexponential kinetics), but irradiation of the sample results in photoinduced loss of the arene. This photoactivation pathway produces ruthenium species that are more active than their ruthenium-arene precursors (Fig. 18). At the same time, free indane fluoresces 40 times more strongly than bound indane, opening up possibilities to use the arene as a fluorescent marker for imaging purposes. The photoactivation pathway is different from those previously discussed for photoactivated Pt(IV) diazido complexes, as it involves photosubstitution rather than photoreduction. Importantly, the photoactivation mechanism is independent of oxygen (see Section II on photoactivatable platinum drugs) (83). 

Dougan SJ, Melchart M, Habtemariam A, Parsons S, Sadler PJ (2006) Phenylazo-pyridine and phenylazo-pyrazole chlorido ruthenium(II) arene complexes arene loss, aquation, and cancer cell cytotoxicity. Inorg Chem 45 10882-10894... 

Zirconium is the principal FP to arise in oxidation state (IV). Where Zircaloy clad fuel is involved, nonradioactive zirconium isotopes may also be present from fuel can residues. As with ruthenium, there may be a variety of nitrato complexes present in the solution including the aquated complexes Zr(N03)s where x = 1-6, and hydroxy nitrato complexes. However, species containing ZrO " " are not expected to be present since this ion is unstable in aqueous media and is rapidly hydrated to Zr(OH)2. The extraction chemistry is further complicated by the formation of inextractable polymeric species when the Zr" concentration exceeds ca. 10 M. An example of such oligomerization is afforded by the [Zr(0H)2(H20)4]4 ion which contains four Zr ions in a square arrangement linked by two /u-OH ligands on each square edge. Four water molecules complete the Zr coordination sphere in an approximately D2d dodecahedral geometry. 

These complexes are prepared by aquation of the corresponding triflato complexes that are prepared in Section C. This is readily accomplished by allowing the hygroscopic solids obtained from the triflic acid/diethyl ether solutions (before vacuum oven drying) to fully aquate in air for 1 day. Storage in a vacuum desiccator over P40,o permits the isolation of the trihydrate and dihydrate complexes for ruthenium and osmium, respectively. The yields are the same as those found for the production of the triflato complexes in Section C. 

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