Ruthenium complexes, photolysis

Barrau and coworkers have synthesized a series of iron and ruthenium complexes by irradiation of Me2HGe(CH)KGeMe2H and Me2HGe(CH)K SiMe2H (n = 1, 2) in the presence of Fe(CO)5 and Ru3(CO)i293. In each case irradiation causes CO loss, with the formation of the M(CO)4 species (reaction 43). When n = 2 the products are photostable with n = 1 (65) a mixture of products (66-69) are obtained due to secondary photolysis (reaction 44). The mechanism, outlined in Scheme 23, is presented to explain these observations. 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Research based on time-resolved XAS in an optical pump-x-ray probe scheme has first been implemented at synchrotron radiation sources. Mills et al. [2] used a 20 Hz repetition rate Nd YAG laser to photolyse carbonmonomyoglobin (MbCO) and monitor the photolysis product with time-resolved XAS around the K-edge of the iron atom. Other studies were carried out on different types of photolyzed systems in liquids, by Thiel et al. [3], Clozza et al. [4], Chance et al. [5,6] and Chen et al. [7,8,9]. All these studies were limited to the nanosecond or longer time domain. We recently reported on time-resolved XANES studies of a Ruthenium complex in water solution reaching the picosecond time scale [10]. This work allows us to evaluate the feasibility of future time-resolved XAS experiments, which we present below together with our new results. 

Reduction of [Mo(CO)(Bu C=CH)2Cp] + BF4 with KBHBu3(s) at — 78°C in an atmosphere of carbon monoxide yields a complex of a vinyl substituted y-lactone linked tj3 t]2 (220). The allylidene ruthenium complex 64, obtained by photochemical addition of one alkyne molecule to a /x-carbene derivative, is transformed into pentadienylidene complexes 65 and 66 on photolysis with more alkyne substrate. These reactions show clearly the stepwise growth of chains in alkyne oligomerizations at dimetal centers [Eq. (31)] (221). Similar reactions are also known for dinuclear iron (222), molybdenum (223), and tungsten (224) complexes. 

Photolysis of complex 125 (arene = benzene) in acetonitrile gives a quantitative yield of cyclopentadienyl tris(acetonitrile) ruthenium complex... 

Smface modification with ruthenium complexes has proven valuable in studies of both interprotein and intraprotein electron transfer in systems that are difflcult to stndy by traditional kinetic tools. The choice of ruthenium complexes in these investigations stems from an extensive photochemistry as well as exceptional thermal stability. The photochemistry provides a means of examining reactions over a time range of nanoseconds to seconds by laser-flash photolysis and the thermal stability allows researchers to covalently bind a wide variety of complexes to proteins with... 

The interprotein electron-transfer reactions of Ru-65-cyt bs can be studied using a sacrificial electron donor such as aniline to reduce Ru(III) and prevent the back reaction k2, as described in Scheme 2. Appropriate sacrificial electron donors can also reduce Ru(IB) to Ru(I), which then reduces Fe(III) as shown in the top pathway of Scheme 2. Cyt b is rapidly reduced by either pathway, and is then poised to transfer an electron to another protein. The reaction of cyt bs with Cc using this methodology will be described in the next section. Covalent labelling of Cc with ruthenium complexes and subsequent flash photolysis has provided a... 

Modulation of NO release can be induced by one-electron reduction, which occurs at NO to yield coordinated NO, or by photolysis (41,46). Thus, the ruthenium complexes were studied in search for an ideal system for the site-directed NO delivery from thermally stable precursors which can release NO when triggered by light. A large number of [Ru—NO] nitrosyls release NO upon exposure to UV light and their potential as NO donors under the control of light has been surveyed. In general, the... 

Intramolecular oxidation and reduction in cytochrome c complexes covalently modified was studied by several groups (for review see 190). Histidines (191, 192, 193) and cysteines (194) were used to attach covalently Ruthenium complexes to Fe- or Zn-substituted cytochrome c. Most of the experiments were done using laser lash photolysis. In each series of experiments, the distance was considered as constant and determined by molecular modelling. The free energies span between 0.5 to 1.4V. The L T rate constants do vary with the driving force as expected. However the reactions proceed with rate constants lower than those expected on the basis of results obtained on peptides. Results were all analyzed using Marcus theory. X and Hab were considered as adjustable parameters. Each series of experimental data was fitted separately (3 to 6 points). In all these papers, X values go from 1.15 to 1.22 eV and Hab vary from 0.1 to 0.24 cm l. Activation volumes were also measured (195). It seems that the transition state is more compact than the reactant state in both intra- and inter-molecular steps. 

Table 6 Polypyridine nitrosyl ruthenium complexes quantum yield ( no) A sh photolysis at 355 nm in trifluoroacetate buffer solution, pH 2.01...

Photolysis of [M(PP3)H2] (M = Ru, Os PP3 = P(GH2GH2PPh2)3) in the presence of GO affords [M(PP3)(GO)], the ruthenium complex also being accessible by reduction of the dichloride complex with sodium naphthalenide under an atmosphere of GO. Nanosecond laser flash photolysis studies on [Ru(etp)(GO)H2] 41 (etp = PhP(GH2GH2PPh2)2) generate the expected 16-eleetron Ru(0) species [Ru(etp)(GO)], which back reacts... 

The Water-gas Shift Reaction.—This reaction is catalysed by M(CO) (activity M = W>Mo>Cr) in the presence of base and under phase-transfer conditions these carbonyls, in common with MS(CO)i2 (M =Ru or Os), are also active in the presence of sodium sulphide. The most active catalysts reported are Fe(CO)6 in basic methanol (turnover No. 2000 per day at 180 °C ) and Rh6(CO)i6 with diamine co-catalysts (e.g., en, turnover No. a 25 h at 100 C). Photolysis of [RuCl(CO)(bipy)a]Cl in water under CO produces COa and catalytically the CO2 is produced in a thermal step, whereas the formation of Ha is photo-initiated. Water-gas has also been used to hydroformylate pent-1-ene in the presence of ruthenium complexes similarly, water-gas is used in reaction (9), which is catalysed by a variety of Group VIII metal complexes... 

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