Electron transfer induced

Internal ligand-to-metal electron transfer may be initiated by the action of an external oxidant on the ligand. This phenomenon of induced electron transfer has received rather scant attention. In the complex 3 shown in (5.82) the one-electron oxidizing center of the Co III) and the two-electron reducing ligand 4-pyridylcarbinol can coexist because of their redox incom-patability . The complex is therefore relatively stable. This situation is upset when a strong one-electron oxidant such as Ce(IV) or Co(III) is added to a solution of the Co(III) complex. The oxidant attacks the carbinol function to generate an intermediate or intermediates the intermediate in this case is oxidized internally by the Co(III) center for example. 

one equivalent of an external oxidant and one of the Co(III) complex are consumed in oxidizing one equivalent of the alcohol to the aldehyde. Two-equivalent oxidants, Clj, Cr(VI), give no such radical intermediate, and therefore no Co(II), and only the Co III) complex. 

For more recent examples involving induced electron transfer linked to cobalt(III) complexes of a-hydroxy acids and hydroquinone esters see Refs. 110, 111. 

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The radical cation of 1 (T ) is produced by a photo-induced electron transfer reaction with an excited electron acceptor, chloranil. The major product observed in the CIDNP spectrum is the regenerated electron donor, 1. The parameters for Kaptein s net effect rule in this case are that the RP is from a triplet precursor (p. is +), the recombination product is that which is under consideration (e is +) and Ag is negative. This leaves the sign of the hyperfine coupling constant as the only unknown in the expression for the polarization phase. Roth et aJ [10] used the phase and intensity of each signal to detemiine the relative signs and magnitudes of the... 

Figure C 1.2.9. Schematic representation of photo induced electron transfer events in fullerene based donor-acceptor arrays (i) from a TTF donor moiety to a singlet excited fullerene and (ii) from a mthenium excited MLCT state to the ground state fullerene.

Another example is indium(0)-induced electron transfer to aziridines 270 incorporating allyl iodide moieties (Scheme 2.66). Treatment with indium(O) in MeOH at reflux gave the corresponding chiral (E)-dienylamines 271 in excellent yields [98]. It should be noted that indium was found to be more effective for this transformation than other metals such as zinc, samarium, and yttrium. 

Willner, I and Willner, B. Artifical Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218... 

The low solubility of fullerene (Ceo) in common organic solvents such as THE, MeCN and DCM interferes with its functionalization, which is a key step for its synthetic applications. Solid state photochemistry is a powerful strategy for overcoming this difficulty. Thus a 1 1 mixture of Cgo and 9-methylanthra-cene (Equation 4.10, R = Me) exposed to a high-pressure mercury lamp gives the adduct 72 (R = Me) with 68% conversion [51]. No 9-methylanthracene dimers were detected. Anthracene does not react with Ceo under these conditions this has been correlated to its ionization potential which is lower than that of the 9-methyl derivative. This suggests that the Diels-Alder reaction proceeds via photo-induced electron transfer from 9-methylanthracene to the triplet excited state of Ceo-... 

Ennaoui A, Tributsch H (1986) Light-induced electron transfer and photoelectrocatalysis of... 

Although the correlation between ket and the driving force determined by Eq. (14) has been confirmed by various experimental approaches, the effect of the Galvani potential difference remains to be fully understood. The elegant theoretical description by Schmickler seems to be in conflict with a great deal of experimental results. Even clearer evidence of the k t dependence on A 0 has been presented by Fermin et al. for photo-induced electron-transfer processes involving water-soluble porphyrins [50,83]. As discussed in the next section, the rationalization of the potential dependence of ket iti these systems is complicated by perturbations of the interfacial potential associated with the specific adsorption of the ionic dye. 

Scheme 6 Photo-induced electron transfer and hole transfer in DNA...

The donor-acceptor complexes [Ir(/r-dmpz)(CO)(PPh2 0(CH2)2R )]2 exhibit photo-induced electron-transfer rate constants of 1012s—1 and charge recombination rates slower than 2 x 10los-1 when R = pyridine and 4-phenylpyridine.534 Further studies on these complexes revealed that recombination reactions were temperature dependent and slower for the deuterated acceptors.535... 

Kaim, W. Thermal and Light Induced Electron Transfer Reactions of Main Group Metal Hydrides and Organometallics. 169, 231-252 (1994). 

Fugimori, E. and M. Talva. 1966. Light-induced electron transfer between chlorophyll and hydroquinone and the effect of oxygen and beta-carotene. Photochem. Photobiol. 5 877-887. 

Molecular engineering of ruthenium complexes that can act as panchromatic CT sensitizers for Ti02-based solar cells presents a challenging task as several requirements have to be fulfilled by the dye, which are very difficult to be met simultaneously. The lowest unoccupied molecular orbitals (LUMOs) and the highest occupied molecular orbitals (HOMOs) have to be maintained at levels where photo-induced electron transfer into the Ti02 conduction band and regeneration... 

Warwel, S., Sojka, M., and Riisch, M. Synthesis of Dicarboxylic Acids by Transition-Metal Catalyzed Oxidative Cleavage of Terminal-Unsaturated Fatty Acids. 164, 79-98 (1993). Willner, I., and Willner, B. Artificial Photosynthetic Model Systems Using Light-Induced Electron Transfer Reactions in Catalytic and Biocatalytic Assemblies. 159, 153-218 (1991). 

Figure 5. Effect of vibrational relaxation on photo-induced electron transfer.

These charge-transfer structures have been studied [4] in terms a very limited number of END trajectories to model vibrational induced electron transfer. An electronic 3-21G+ basis for Li [53] and 3-21G for H [54] was used. The equilibrium structure has the geometry with a long Li(2)—H bond (3.45561 a.u.) and a short Li(l)—H bond (3.09017 a.u.). It was first established that only the Li—H bond stretching modes will promote electron transfer, and then initial conditions were chosen such that the long bond was stretched and the short bond compressed by the same (%) amount. The small ensemble of six trajectories with 5.6, 10, 13, 15, 18, and 20% initial change in equilibrium bond lengths are sufficient to illustrate the approach. 

Figure 6. Structural formulae of S-D amphiphilic compounds and other chemicals used for S-D monolayers for comparison of photo-induced electron transfer rates between a single alkyl chain and a triple alkyl chain as the spacers of the S-D dyads with the same length of four-carbons. In these S-D dyads, a naphthalene and a ferrocene moiety are used as an S and a D moiety, respectively. S-D dyads with a rigid spacer consisting of a bicyclo[2.2.2]octane are used as dyads with a triple alkyl chain.

SN P spontaneously releases N O both thermally and photochemically [61-65], but is quite stable in the dark and in aqueous in vitro physiological media [66]. This implies that absorption of heat and light energy induces electron transfer from the Fe2+ center to the N 0+ ligand, resulting in weakening of the Fe-N O bond and subsequent release of NO [65]. SNP also decomposes in an aqueous environment in the presence of biological reductants [65, 66] and some transition metal ions to produce nitric oxide. 

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