Bpy ligands

The most common catalysts for ATRP are complexes based on a copper(T) halide and nitrogen based ligand(s). Various ligands have been employed and those most frequently encountered are summarized in Table 9.5. Typically, four nitrogens coordinate to copper. The bidentate bipyridyl (bpy) ligands 132-133 are known to form a 2 1 complex. The tetradentate ligands are expected to form a 1 1 complex. 

The reaction in Eq. (9.34) is also faster because the bpy ligand is a strong field ligand and there is no longer any need for electronic rearrangement upon change in oxidation state. The process is now comparable to those discussed earlier for low spin iron complexes. 

Dendrimer 1 + is a classical example of a dendrimer containing a luminescent metal complex core. In this dendrimer the 2,2 -bipyridine (bpy) ligands of the [Ru(bpy)3] +-type core carry branches containing 1,2-dimethoxybenzene- and 2-naphthyl-type chromophoric units [15]. 

The synthesis of [Ircp Cl(bpy-cd)]Cl, where bpy-cd is a /3-cyclo-dextrin attached at the 6 position to a bpy ligand, is detailed.138 The complexes [Ircp (diimine)X]+, X = C1, H, diimine = bpy, phen, are active catalysts for the light-driven water-gas-shift reaction.139 The hydride complexes luminesce at 77 K and room temperature, whereas the chloride complexes do not.140 The three-legged piano-stool arrangement of the ligands in [Ircp (bpy)Cl]+ and [Ircp (4,4 -COOFl-bpy)Cl]+ is confirmed by X-ray crystallography.141,142 Further mechanistic studies on the catalytic cycle shown in reaction Scheme 11 indicate that Cl- is substituted by CO and the rate-determining step involves loss of C02 and H+ to leave the Ir1 species, which readily binds Fl+ to yield the lrIH hydride species.143... 

The solution structure of [Ir(bpy)H2(PRPh2)2]X, R = Me, Ph, X = PF6, BF4, CF3S04, BPh4, as determined from NMR studies, is compared to solid-state structure.152 The main difference between the two structures is the location of the counter ion X. In solution, X is positioned on the side of the bpy ligand remote from the Ir, whereas in the solid state X is found close to one of the pyridine rings and one hydride ligand. Theoretical calculations at the QM/MM (B3PW91/ UFF) level support the experimental results. 

The complex [(cp )IrCl(2,2 -bpy-4,4 -COO(CH2)3-pyrrole)]C104 has a typical three-legged piano-stool structure, with short Ir-cp distances due to the strong 7r-acceptor properties of the bpy ligands.540... 

Compound 20 is made of an Os(II)-based core, three Ru(II)-based units in the intermediate positions, and six Os(II)-based units in the peripheral positions. Oxidation should thus first involve the six peripheral Os(II)-based units (which contain the stronger electron-donor bpy ligand in their coordination sphere), followed by the Os(II)-based core, and by the intermediate Ru(II)-based units, according to a 6-1-3 electron-exchange pattern. This is consistent with the 6-1 observed pattern (Fig. 3 a), considering that the oxidation of the intermediate Ru(II)-based units is shifted to inaccessible potentials because of their interaction with the already oxidized core and peripheral units. 

In 19, which is made of an Os(II)-based core and nine Ru(II)-based units, a 1-6-3 oxidation pattern is expected resulting from oxidation of the Os-based core, followed by the six peripheral Ru-based units (which are coordinated to the stronger electron-donor bpy ligand), and by the three intermediate Ru-based... 

Furthermore, it has been demonstrated that the successful electrocatalytic reduction of C02 with [Ru(bpy)2(CO)2]2+ in aqueous MeCN is mainly due to the formation of a polymeric electroactive film, which occurs during the reduction of the complex.91 This film is composed of an open cluster polymer [Ru(bpy)(CO)2]ra (Scheme 6) based upon extended Ru°—Ru° bonds. Electropolymerization of [Ru(bpy)2(CO)2]2+ results from the overall addition of two electrons per mole of [Ru(bpy)2(CO)2]2+ and is associated with the decoordination of one bpy ligand (Equation (33)). 

Furthermore, the utilization of preformed films of polypyrrole functionalized by suitable monomeric ruthenium complexes allows the circumvention of problems due to the moderate stability of these complexes to aerial oxidation when free in solution. A similar CO/HCOO-selectivity with regards to the substitution of the V-pyrrole-bpy ligand by an electron-with-drawing group is retained in those composite materials.98 The related osmium-based redox-active polymer [Os°(bpy)(CO)2] was prepared, and is also an excellent electrocatalyst for the reduction of C02 in aqueous media.99 However, the selectivity toward CO vs. HCOO- production is lower. 

Techniques for attaching such ruthenium electrocatalysts to the electrode surface, and thereby realizing some of the advantages of the modified electrode devices, have been developed.512-521 The electrocatalytic activity of these films have been evaluated and some preparative scale experiments performed. The modified electrodes are active and selective catalysts for oxidation of alcohols.5 6-521 However, the kinetics of the catalysis is markedly slower with films compared to bulk solution. This is a consequence of the slowness of the access to highest oxidation states of the complex and of the chemical reactions coupled with the electron transfer in films. In compensation, the stability of catalysts is dramatically improved in films, especially with complexes sensitive to bpy ligand loss like [Ru(bpy)2(0)2]2 + 51, 519 521... 

At room temperature thermally activated electron transfer occurs from the bpy ligand to the remote pyridinium site followed by decay of the lower, pyridinium-based CT state. The electron transfer step is the intramolecular analog of the paraquat quenching of Ru(bpy)32+. ... 

These results suggest that the critical factor in the substrate-mediated intermolecular interactions which occur within the close-packed DHT layer is the inherent strong reactivity of the diphenolic moiety with the Pt surface. The interaction of adsorbates with each other through the mediation of the substrate is of fundamental importance in surface science. The theoretical treatment, however, involves complicated many-body potentials which are presently not well-understood (2.). It is instructive to view the present case of Pt-substrate-mediated DHT-DHT interactions in terms of mixed-valence metal complexes (2A) For example, in the binuclear mixed-valence complex, (NH3)5RU(11)-bpy-Ru(111) (NH 3)5 (where bpy is 4,4 -bipyridine), the two metal centers are still able to interact with each other via the delocalized electrons within the bpy ligand. The interaction between the Ru(II) and Ru(III) ions in this mixed-valence complex is therefore ligand-mediated. The Ru(II)-Ru(III) coupling can be written schematically as ... 

More attention has been devoted to aromatic and heteroaromatic substrates since first reported in 1983 [40]. The results are shown in Table 2 [25, 41-51]. All these reactions were run with nickel complexes associated with a phosphane or bpy ligand. Depending on the experimental conditions, the polymers were either precipitated during the electrolysis or deposited as films at the surface of the electrode. The method is also convenient to prepare copolymers from a mixture of two aryl dihalides. A mechanistic investigation on the nickel-bpy catalyzed polymerisation has been reported very recently [52]. 

The ESR spectrum of [(bpy)Cr(C0)4] ion-radical resembles that of the uncoordinated (bpy) anion-radical, indicating clearly that the unpaired electron is localized on the bpy ligand. This conclusion is completely corroborated by the similarity between the electronic spectra of [(bpy)Cr(CO)4] and (bpy) (Vlcek et al. 1998, and references therein). Obviously, the product of one-electron reduction of (bpy)Cr(CO)4 may best be formulated as a formally Cr(0) complex with an anion-radical ligand, (bpy) Cr(CO)4. 

Mononuclear complexes of general formula [Ru(bpy)2L2]" and complexes containing functionalized bpy ligands... 

Complexes of the type [Ru(bpy)2L2L in which L is a simple, monodentate ligand will be surveyed first. The structure of tra 5-[Ru(bpy)2(H20)2][PF6]2 has been determined steric inter actions result in the bpy ligands being bowed .Similar deformations are observed in trans [Ru(bpy)2(MeCN)2] " and tra 5-[Ru(bpy)2(NH3)2]... 

The structural and photophysical properties of [Ru(bp 2(dafo)] PF6]2 (dafo = 93) have been reported the emission lifetime of the complex is 420 ns the study has been extended to the properties of the series of complexes [Ru(bpy) (dafo)3 J +. The nonplanar ligands (94) have been prepared, and form complexes of type [Ru(bpy)2(94)] for = 2, 3 or 4, and l Ru(bpy)2 2(94)]" for = 3 or 4. By using deuterated bpy ligands, more easily interpretable H NMR spectra are obtained. For the diruthenium complexes, there is limited inter-metal communication. ... 

Complexes of the [Ru(bpy)2L] " type in which L is a phen-based ligand are discussed next. Perchlorate salts of [Ru(bpy)2(phen)] + and [Ru(bpy)2(5-Mephen)] + have been prepared and structurally characterized. The steric strain within the coordination sphere is relieved in part by twisting of each bpy ligand. Time-resolved resonance Raman spectroscopy has been used to investigate the localization of the excited electron in the MLCT state of [Ru(bpy)2(4,7-Ph2-phen)] In neutral micelles, the electron is localized on the bpy ligands, but in the presence of DNA and anionic surfactants, it is localized on 4,7-Ph2phen when the complex is in aqueous... 

---