Copper quenching, formation

Quenching Studies. The solvated electron component at 675 nm was studied under conditions of oxygen and copper quenching (FIGURE 5)> It appears that in our (concentrated) solutions of fulvic acid (200 mg/1), and at elevated laser power (3-30 m.j), it is formed by a one photon process. Conditions for observation of these spectra with excitation at 355 nm and on the nanosecond scale match those cited by previous authors (6 ). Moreover, we were able to observe the solvated electron formation at reduced power (2-3 m.j) on the picosecond scale in (concentrated) solution (200 mg/1), suggesting, at least for our material, that there is no intensity threshold for formation of e solv. 

The enantioselective lithiation of anisolechromium tricarbonyl was used by Schmalz and Schellhaas in a route towards the natural product (+)-ptilocaulin . In situ hthi-ation and silylation of 410 with ent-h M gave ewf-411 in an optimized 91% ee (reaction carried ont at — 100°C over 10 min, see Scheme 169). A second, substrate-directed lithiation with BuLi alone, formation of the copper derivative and a quench with crotyl bromide gave 420. The planar chirality and reactivity of the chromium complex was then exploited in a nucleophilic addition of dithiane, which generated ptilocaulin precnrsor 421 (Scheme 172). The stereochemistry of componnd 421 has also been used to direct dearomatizing additions, yielding other classes of enones. ... 

Normant and coworkers demonstrated that the intermolecular carbomagnesiation across acetylene (HC=CH) could be catalyzed by a copper salt . The treatment of w-heptylmag-nesium bromide with acetylene in the presence of a catalytic amount of CuBr (5 mol%) in EtgO at —20 °C followed by the reaction with C2H5CHO and quenching with H2O results in the formation of allylic alcohol 12 in 31% yield (Scheme 9) . The carbomagnesiation takes place in a yw-addition manner. 

On the basis of the strong photo-oxidising behaviour of [Re(phen)(CO)3(imidazole)]+ (9) (Re(I) /Re(0) = ca. +1.3 V vs. NHE in CH3CN), Gray and co-workers reacted [Re(phen)(C0)3(H20)]+ with azurin, resulting in the formation of [Re(phen) (CO)3(His83)]+-AzCu+, and studied the electron-transfer in this mutant [28], Excitation of the rhenium(I) complex leads to direct oxidation of the copper centre of the protein to copper(II). Using the flash-quench technique with... 

Perfluorophenyl)copper exhibits high reactivity towards organic substrates. and reacts with fluorinated or nonfluorinated aryl iodides (e.g., formation of 5), fluorinated vinyl iodides, al-kynyl bromides and iodides, allyl halides, alkanoyl halides, and iodomethane to afford the corresponding coupled products in good yields. (Perfluorophenyl)copper readily undergoes addition in a syn fashion to perfluorobut-2-yne to form a perfluorovinylcoppcr reagent 6, which can be quenched by electrophiles (e.g. formation of 7). Recall that (per-fluorophcnyl)coppcr reacts with (trifluoromethyl)copper to form (perfluorophenethyl)copper (Section 2.1.1.3.3.). 

The effect of oxygen exposure during the quenching process has nicely been demonstrated by Guczi and coworkers [4.17,18], who studied the structural and chemical properties of Fe-B alloys prepared by melt spinning under atmospheric conditions. They found drastic differences in the chemical and structural properties between the dull (in contact with copper wheel) and shiny side (exposed to air) of as-prepared ribbons. Such a behavior is likely to occur with alloys containing constituents with largely different heat of formation. 

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