Nuclear Ru-complex

Poly-nuclear Ru complexes with pyrazine and 4,4 -bipyridine bridges 03CCR(238-239)127. 

Other bi-, tri-, tetra- or poly-nuclear Ru" complexes mentioned in earlier sections are [(RuClj-CO(PCy3)2)2TCNE] (Section 45.5.4.5.vi), [RuCl2(N2H4)(PMe2Ph)2]2 (Section 45.5.4.6.i),... 

More recently, Adams and coworkers have provided a very interesting case of heteronuclear clusters that are very active for the hydrogenation of alkynes [4, 54, 55]. The high-nuclearity layer-segregated Pt-Ru complex [Pt3Ru6(CO)21(jU3-H)(/ -H)j], consisting of three stacked triangular layers of metal atoms with an... 

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]. 

The photochemical and thermal stabilities of Ru complexes have been investigated in detail [8,153-156]. For example, it has been reported that the NCS ligand of the N3 dye, cri-Ru(II)(dcbpy)2(NCS)2 (dcbpy = 2,2 -bipyridyl-4,4 -dicarboxylic acid), is oxidized to produce a cyano group (—CN) under irradiation in methanol solution. It was measured by both ultraviolet-visible (UV-vis) absorption spectroscopy and nuclear magnetic resonance (NMR) [8,153]. In addition, the intensity of the infrared (IR) absorption peak attributed to the NCS ligand starts to decrease at 135°C, and decarboxylation of N3 dyes occurs at temperatures above 180°C [155]. Desorption of the dye from the 2 surface has been observed at temperatures above 200°C. 

Recently, Ru and Re bi-nuclear (Ru-Re) and tetranuclear (Ru-Re3) complexes for the photoreduction of C02 have been synthesized [32]. Under irradiation at 480 nm, in a DMF/TEOA solution, the complexes were observed to undergo reductive quenching by l-benzyl-l,4-dihydronicohnamide (BNAH). The best bi-nuclear complex yielded a quantum efficiency of 9% for CO production, and a TON of 170. Similarly, the tetranuclear complex yielded a CO quantum efficiency of 12% and a TON of 240. While these marked increases in TONs are encouraging, it should be stated that increases of many more orders of magnitude are required to yield an economically viable system. 

In this way, remarkable complexes have been built up, such as the 22-nuclear [Ru (//-2,3-dpp) [Ru(//-2,3-dpp)Ru (u-2,3-dpp)Ru(bpy)2 2]2 3]44+ (11.7). Compound 11.7 is an excellent example of the fact that metal complexes need to share the same bridging ligand in order to interact, thus the 12 peripheral Ru2+ centres, which are not connected to one another in such a way as to allow electronic interaction between them, are all oxidised at the same potential in one single 12-electron process. 

When the platinum nucleophilicity scale was first proposed it was implied that one np, scale was applicable to all substrates and that plots of logk2 against npt°(Y) were linear, taking the form log 10 2 = S np, (Y) + C, where S is termed the nucleophilic discrimination factor of the substrate and C its intrinsic reactivity. Discussions of mechanism based on a comparison of nucleophilic discrimination factors are frequently encountered. Nucleophiles that do not retain their positions in the nucleophilicity scale, e.g. NO2", SeCN and SC(NH2)2, were termed biphilic by Cattahni since their behaviour could be explained by their n-acceptor properties. When the Pt reaction centre had a greater n-basicity than the standard complex (for example a smaller effective nuclear charge) the substrate was more reactive than predicted and vice versa. This concept had been deduced some years earlier by Bosnich from his work with octahedral Ru complexes... 

Synthesis and properties of mono- and oligo-nuclear Ru(ll) complexes of tridentate ligands 06CCR(250)1763. 

A complication in the interpretation of the distance attenuation of the rates is that both the nuclear and electronic factors decrease with distance. (Inner-shell contributions to the reorganization barriers have been estimated as 0.03 eV and 0.17 eV for Fc and Ru complexes, respectively.) Thus interpretation of the electronic factor requires correction for Aout as a function of n or d. Liu and Newton have modeled Aout for the ferrocene (radius a = 0.34nm) SAM-electrode assembly in terms of three zones (aqueous phase 1 , SAM film 2 , electrode 3 ) of different dielectric properties (see Section 7.12.4.4, Equation (64)). The solvent barrier is considerable and very sensitive to film thickness (L) increasing from 0.75 eV to 0.86 eV when the thickness is increased from 0.5nm to 1.5 nm. For AG°da = 0, variation of Aout with distance contributes 1 nm to j3. The simplified expression... 

Silica immobilized Ru complexes with a different nuclear number as catalysts of the hydrodehalogenation reaction... 

Chelation of (r] -arene) Ru to N7 and deprotonated N6 of adenine derivatives to give a 5-membered ring is facile, giving rise to tri- (or tetra-, when N9 available) nuclear adducts (complexes 24 and 25, Fig. 2.17) [93]. 

Astruc et al. [187] reported a nonairon sandwich complex by treating a nona-ol with [C5H5]Fe(q6-p-MeC6H4F)(PF6). In a subsequent report [188], Astruc and Marvaud reported the synthesis of aromatic star molecules with or without a central Fe(/f-C5H5)+ group. These bipyridine and terpyridine terminated dendrimers were further capped with [Ru(bipy)2Cl2] and [Ru(terpy)Cl3], respectively, to afford the corresponding hexa or hepta nuclear complexes. 

Shore and coworkers—nuclearity studies over Ru carbonyl catalysts. Shore et al.64 studied reactions of K[DRu3(CO)n] + CO + H20 <- HD + Ru3(CO)i2 + KOH. They found that, at room temperature and 1 atm pressure of Pco, HD is rapidly evolved. In the absence of CO, however, the HD was formed only in trace quantities. They proposed two possible mechanisms to account for this behavior, (a) a concerted mechanism where CO promotes hydride decomposition (Scheme 28), or (b) an associative mechanism involving a complex-CO adduct, which decomposes with H20 (Scheme 29). 

A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H20)6 +-Fe(H20)6 +> Ru(NH3)62+-Ru(NH3)63+ and Ru(bpy)32+-Ru(bpy)33+ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted. 

The longer degree of conjugation of the phenanthroline ligands in these complexes causes a bathochromic shift at the ti-ti band and the different nuclearity shows the 1 2 3 ratio of the extinction coefficient of the ti-ti as well as the MLCT bands. To avoid diastereomeric mixtures the authors established the first controlled synthesis of stereochemically defined multinuclear Ru(ll) complexes [59]. 

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