Ru II Complexes

-0Ac)3(p-C03) The reagent Ru2(OAc)3(CO3)/O2/water-toluene/80°C oxidised a number of primary alcohols to aldehydes and secondary alcohols to ketones formation of an alkoxyruthenium complex followed by P-hydride elimination was suggested. The reactions were also catalysed by [Ru2(p-OAc) ](OAc) [819]. 

Many Ru(II) complexes function as oxidation catalysts, particularly effective being RuCl3(PPh3)3 and d.t-RuCl3(dmso). In most cases the nature of the active intermediate is not known, but oxo-Ru(IV) species are likely to be involved in many cases. 

RUj(OAc)j(py) is made as orange crystals from Ru3(0)(0C0R) (py)3 and Zn the single-crystal X-ray structure was reported. As Ru3(OAc)2(pyyZn/Oj/(py)/AcOH it oxidised cyclohexane to cyclohexanol and cyclohexanone in low yield [820], 

Ru(NO)Cl(salen = 0 is made by reaction of Ru(N0)Cl3.nH20 with (salen 0, the latter made by condensation of (R)-3-formyl-2-hydroxy-2 -phenyl-1,1 -binaphthyl with (15, 25)-l,2-diamino-cyclohexane. The X-ray crystal structure of the acetonitrile adduct shows the Ru-N-O unit to be essentially linear (Ru-N 1,862(6)A, N-0 0.971(8) A, with the Ru-N-O angle at 176.0(9)°), so that the nitrosyl ligand may be regarded as NO and the formal oxidation state of the Ru as (11) [826]. 

Primary alcohols were oxidised to aldehydes and (less readily) secondary alcohols to ketones by Ru(N0)Cl(salen = )/03//UV (incandescent or halogen lamp), hi competitive experiments between 1- and 2-decanol or benzyl alcohols only the primary alcohol was oxidised [827]. With Ru(NO)Cl(salen )/(Cl2pyNO) or TMPNO or Oj/C H /UV (TMPNO=tetra-methylpyridine-iV,iV -oxide) racemic secondary alcohols were asymmetrically oxidised to ketones [828]. A Ru(NO)(salen ) complex was used as Ru(N0)Cl(salen )/02/UV/CgH3Cl to oxidise racemic secondary alcohols to the ketones in the presence of l,3-bis(p-bromophenyl)propane-l,3-dione e.e. of 55-99% were achieved [829], Chiral Ru(NO)Cl(salen ) complexes were made 

Rh(QI) and Ir(III) Complexes. A number of Rh(III) and some Ir(III) complexes have been investigated thoroughly by CV [78-81]. The values for the electrode potentials for oxidation and for reduction are given in Table 1. The electrochemical behavior of the cyclometallated complexes differs strongly from that of their diimin analogs, but it is completely in line with the spectral and reactivity characteristics. 

Reduction of the tris-diimin complex Rh(bpy) + takes place in a completely irreversible two-electron step, whereas all Rh(CAN)2(NAN)+ and the corresponding Ir complexes show one or more reversible one-electron reductions. In the former case, the reduction is clearly metal centered, 

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Both reactions were carried out under two-phase conditions with the help of an additional organic solvent (such as iPrOH). The catalyst could be reused with the same activity and enantioselectivity after decantation of the hydrogenation products. A more recent example, again by de Souza and Dupont, has been reported. They made a detailed study of the asymmetric hydrogenation of a-acetamidocin-namic acid and the kinetic resolution of methyl ( )-3-hydroxy-2-methylenebu-tanoate with chiral Rh(I) and Ru(II) complexes in [BMIM][BF4] and [BMIM][PFg] [55]. The authors described the remarkable effects of the molecular hydrogen concentration in the ionic catalyst layer on the conversion and enantioselectivity of these reactions. The solubility of hydrogen in [BMIM][BF4] was found to be almost four times higher than in [BMIM][PFg]. 

Tris(2,2 -bipyridine)ruthenium(II) complex (Ru(bpy)3+) has been most commonly employed as a chromophore in the studies of photoinduced ET. Electrostatic effects on the quenching of the emission from the Ru(II) complex covalently bound to polyeletrolytes have been studied by several groups [79-82]. 

Kaneko et al. [80, 81] prepared copolymers of AA (93.9-95.9 mol%) and vinylbipyridine (1.6-3.7 mol%) with pendant Ru(bpy)2+ (2.4-2.5 mol%) (25). The quenching of the excited state of the pendant Ru(II) complex by MV2+ was accelerated in alkaline aqueous solution owing to the electrostatic attraction of the cationic quencher. Interestingly, the quenching efficiency was dependent on the molecular weight of 25. The quenching of the polymer with MW 2100 occurred... 

Sassoon and Rabani [79, 83] constructed an intriguing photoinduced ET system in which the back ET was greatly retarded by the electrostatic repulsion between two different polycations. They prepared poly(3,3-ionene) covalently linked with Ru(bpy)f + (26) and with an iY,Af,/V, Ar -tetraalkyl-/>-phenylenediamine derivative (27). The latter is an electron donor quencher toward the photoexcited Ru(II) complex. 

In an aqueous solution containing 26 and 27 the excited state of the Ru(II) complex in 26 essentially has no chance to be directly quenched by the donor quencher in 27, because a strong electrostatic repulsion acts between 26 and 27. Sassoon and Rabani added methoxydimethylaniline (MDMA, 28) to this system... 

Sheldon et al. have combined a KR catalyzed by CALB with a racemization catalyzed by a Ru(II) complex in combination with TEMPO (2,2,6,6-tetramethylpi-peridine 1-oxyl free radical) [28]. They proposed that racemization involved initial ruthenium-catalyzed oxidation of the alcohol to the corresponding ketone, with TEMPO acting as a stoichiometric oxidant. The ketone was then reduced to racemic alcohol by ruthenium hydrides, which were proposed to be formed under the reaction conditions. Under these conditions, they obtained 76% yield of enantiopure 1-phenylethanol acetate at 70° after 48 hours. 

These ligands were used in protic and biphasic media by modifying their structure using hydroxyalkyl groups [28,29]. The solubihty of the corresponding Ru(II) complexes was significantly increased in protic solvents. Hence, by performing the reaction in mixtures of toluene and water or al-... 

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

Scheme 7.8 Direct arylation of 2-phenylpyiidine with NHC-Ru(II) complexes...

As another successful application of Noyori s TsDPEN ligand, Yan et al. reported the synthesis of antidepressant duloxetine, in 2008. Thus, the key step of this synthesis was the asymmetric transfer hydrogenation of 3-(dime-thylamino)-l-(thiophen-2-yl)propan-l-one performed in the presence of (5,5)-TsDPEN Ru(II) complex and a HCO2H TEA mixture as the hydrogen donor. The reaction afforded the corresponding chiral alcohol in both high yield and enantioselectivity, which was further converted in two steps into expected (5)-duloxetine, as shown in Scheme 9.17. 

Table 24.3, Enantioselective hydrogenation of P-keto esters using Ru(II)-complexes.

The redox active polymer films might bear the mediator group attached either covalently to the polymer backbone (polyvinylferrocene, Ru(II) complexes of polyvinylpyridine, etc.) or electrostatically within the ion-exchange polymer (e.g. in Nation, cf. Section 2.6). 

H-NMR studies of oligocarbene Ru(II) complexes indicate a substantial barrier to rotation about the metal-carbene carbon and nitrogen-R bonds. This restricted rotation is thought to arise as a consequence of intramolecular non-bonding cis interactions of the carbene nitrogen-R substituents, and not because of any significant double bond character in ruthenium-carbene carbon (76). 

Non-luminescent, octahedral Ru(ii) complexes bearing two 4,4 -di(/ r/-butyl)bipyridine and one bibenzimidazole ligand become luminescent upon coordination of diethylzinc to the bibenzimidazole 39, as shown in Scheme 34.85... 

SCHEME 42. Preparation of photoinducible electron-transfer Ru(II)-complexes.279... 

The chiral (R)-bcnzazepine derivative 20 is a key intermediate in the synthesis of a non-peptide AVP V2-agonist. Efficient production of this intermediate was thus required, and this has been achieved by highly enantioselective asymmetric hydrogenation of the easily made acids 18 (E and Z) and 19, using Ru(II) complex catalysts <00CHIR425>. 

Ru-vinylidene complexes can be easily prepared by reaction of low-valent ruthenium complexes with terminal acetylenes. Treatment of the Ru(ii) complex 117 with phenylacetylene gave the Ru(iv)-vinylidene complex 118 in 88% yield (Scheme 41 ).60 The reaction of 118 with C02 in the presence of Et3N afforded selectively the Ru-carboxylate complex 120, probably via the terminal alkynide intermediate 119. 

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