Cyclam, ruthenium complexes

The mechanism will vary in precise detail according to the metal. In the case of ruthenium complexes, it is quite common to observe a conproportionation and the formation of a ruthenium(iv) intermediate. In other cases, the unavailability of the metal oxidation states precludes reaction. For example, cobalt(m) complexes of cyclam cannot be oxidised to imine species because although a cobalt(ii)/cobalt(m) couple is possible, the cobalt(n) oxidation state is not accessible under oxidative conditions. In the case of metal ions which can undergo two oxidation state changes, alternative mechanisms which do not involve radical species have been suggested. 

Figure 2 Nitrosyl macrocyclic ruthenium complexes structure. (A) frans-[RuCI [15]ane4) NO] " and (B) frans-[RuCI cyclam)NO]. The colored circles represent atoms in the chemical structure (cyan (light gray in the print version) carbon blue (black in the print version) nitrogen green (gray in the print version) chlorine red (dark gray in the print version) oxygen white hydrogen, and gray ruthenium).

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... 

Macrocyclic complexes have also been covalently bound to the periphery of the bpy ligand of a modified Ru(bpy -type complex. Again a quenching of the emission of the MLCT excited state of the ruthenium complex due to interaction of this emissive state with the attached macrocyclic complex is observed. These macrocyclic complexes have been obtained by the covalent attachment of a cyclam moiety onto either the 2- or the 3-position of one of the bipyridyl ligands (Fig. 5.7). The complexes having the metal ions Ni " or Cu " complexed to the cyclam show dramatically reduced emission intensities of the Ru(bpy)3 -type... 

Marcondes FG, Ferro AA, Sousa-Torsoni A, et al. In vivo effects of the controlled NO donor/scavenger ruthenium cyclam complexes on blood pressure. Life Sci 2002 70 2735-52. 

A number of studies have been reported in which a metal atom catalyzes the oxidation of alkenes by PhIO or its derivatives. Three studies have employed iron or manganese model systems for cytochrome P-450 in the oxidation of alkenes. " " [Ru(III) (salen)(X)(Y)] catalyze the oxidation of alkenes by PhIO at room temperature.Similarly, ruthenium(II) complexes of bidentate phosphines may be utilized to promote the epoxidation of alkenes in the presence of iodosylbenzene and in low coordinating media. [Ni(cyclam)] promotes the oxidation of... 

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