Flash photolysis of W

In recent work in collaboration with G.R. Dobson, we have examined the flash photolysis of W(CO) (piperidine)L (L = PPh, ... 

Flash photolysis of W(CO) in CCl results in the formation of the new complex W(CO)5Cl. The crystal structure of W(CO)5(Bu3P) has been determined and as expected, the W—C bond lengths are slightly shorter than found for W(CO). Photolysis of W(CO)g in n-pentane in the presence of HjS has resulted in the isolation of the first complex containing HjS as a ligand, W(CO)jH2S. The H2S is believed to be S-bonded. 

Q Ji, CR Lloyd, EM Eyring, R van Eldik. Probing the solvation properties of liquid versus supercritical fluids with laser flash photolysis of W(CO>6 in the presence of 2,2 -byp5uidine. J Phys Chem 101 243-247, 1997. 

The first two reactions represent the dissociative pathway and the third reaction represents the associative pathway. The authors measured the rate constants for the reaction as function of CO2 pressure without altering the CO concentration. The decrease in k with pressure provided evidence that the reaction was predominantly a dissociative process. The order of reactivity with different metals was found to be Cr Mo > W. Significant shifts observed in the visible absorbance spectrum recorded after 100 ns for flash photolysis of W(CO)e in SCCO2 at 2500 psi and 40°C was attributed to the possibility of ti -0 coordination of CO2 to the metal center. 

Kinetic and thermodynamic studies of organometallics in the gas phase have progressed steadily from systems involving highly unsaturated complexes, often with positively charged metal centers, to systems that are directly relevant to reactions in homogeneous solution. An outstanding example of this involves time-resolved IR spectroscopic studies of [W(CO)5] produced by flash photolysis of [W(CO)6] in the gas phase. Kinetic and equilibrium data for reactions (8) provide equilibrium and rate constants from 300 to... 

The photolyzing light pulse is produced by a dye laser and enters the sample at about 10° to the axis of the sample beam. The observation beam originates from a 75-W xenon arc lamp. The apparatus is supplied by OLIS, Athens, Georgia USA. Reproduced with permission from C. A. Sawicki and R. J. Morris, Flash Photolysis of Hemoglobin, in Methods in Enzymology (E. Antonini, L. R. Bernardi, E. Chiancone eds.), 76, 667 (1981). 

Irradiation of 2,2-dimethyl chromene through Pyrex using a 550-W Hanovia lamp initiates a retro 4 + 2 reaction to form the extended quinone methide 4, which reacts with methanol to form a pair of methyl ethers (Scheme 6A).18 Flash photolysis of coniferyl alcohol 5 generates the quinone methide 6 (Scheme 6B) by elimination of hydroxide ion from the excited-state reaction intermediate.19 The kinetics for the thermal reactions of 6 in water were characterized,20 but not the reaction products. These were assumed to be the starting alcohol 5 from 1,8-addition of water to 6 and the benzylic alcohol from 1,6-addition of water (Scheme 6). A second quinone methide has been proposed to form as a central intermediate in the biosynthesis of several neolignans,21a and chemical synthesis of neolignans has been achieved... 

Basco, N., and R. G. W. Norrish Vibrationally excited nitric oxide produced in the flash photolysis of nitrosyl chloride. Nature [London] 189, 455 (1961). 

Laser flash photolysis of [CpM(CO>3]2 (M = W, Mb, and Cr) provides a convenient source of CpM(CO)3, an organometallic free radical with 17 valence electrons. It is a transient and highly reactive species. Depending on the circumstances and the other reagents present, the radical will dimerize, undergo halogen and hydrogen atom abstraction reactions, and electron transfer reactions. With tetramethyl-phenylenediamine, there is a cyclic process of electron transfer steps, the net result of which is the catalyzed disproportionation of the metal radical. 

Amine radical-cations have been generated by the treatment of para-substituted anilines with ceric ion (Stone and Waters, 1962 Fox and Waters, 1964). When the para position is free, the initial radical-cation can react further for example, the oxidation of triphenylamine with lead tetra-acetate in the presence of boron trifluoride (Allara ei al., 1965) or with iodine (Stamires and Turkevich, 1963) gives the radical cation Ph3N+ , and, when excess of triphenylamine is used, the former oxidant leads to the radical-cation of A(, .A/, W, A -tetraphenylbenzidine. The only radical observed by the oxidation of dimethylanihne either electrochemically (Mzoguchi and Adams, 1962) or with lead tetraacetate and boron trifluoride (Allara et al., 1965) is the radical-cation of iV, .A, .A7, iV -tetramethylbenzidine. The relatively stable (hindered) anilino radical (40) has been generated from the corresponding aniline by flash photolysis audits e.s.r. spectrum has been measured in n-hexane (Land and Porter, 1961). The electronic spectrum of this radical is very similar to that of the unsubstituted anilino radical, detected during flash photolysis of aniline, but this radical is so short-lived that it has not yet been detected by e.s.r. 

Bucher, G., Strehl, A., Sander, W. Laser flash photolysis of disulfonyidiazomethanes Partitioning between hetero-Wolff rearrangement and intramolecular carbene oxidation by a sulfonyl group. Eur. J. Org. Chem. 2003, 2153-2158. 

Among group VIA dimers, [h -CjKjMCCOljJj (M = Cr, Mo, W) and their derivatives receive the bulk of photochemical study. Flash photolysis of the Mo dimer demonstrates the existence of both CO-Ioss and dimer-cleavage intermediates, but the radical-like cleavage intermediates dominate the photochemistry of these species. 

S.-N. Chen, V.W. Cope, M.Z. Hoffman (1973). Behavior of C03 radicals generated in the flash photolysis of carbonatoamine complexes of cobalt(III) in aqueous solution. J. Phys. Chem., 77,1111-1116. 

Intermediates (Alkane) M(CO)s are produced in predominant concentration in solution after flash photolysis of the metal carbonyls M(CO)6 (M = Cr,Mo, W). It has been proposed that the alkane (used as a solvent) is coordinated to the metal via a C-H Magostic interaction [21a,b] ... 

S.P. Pappas, B.C. Pappas, L.R. Gatechair, and W. Schnabel, Photoinitiation of cationic polymer ization, II. laser flash photolysis of diphenyliodonium salts, J. Polym. Sci. Polym. Chem. Ed. 22(1), 69 76 (1984) J.L. DektarandN.P. Hacker, Photochemistry oftriarylsulfoniumsalts, 7. Am. Chem. 

True, M. B. and O. C. Zafiriou. 1987. Reaction of Brj produced by flash photolysis of sea water with components of the dissolved carbonate system. In Zika, R. G. and Cooper, W. J., Eds. Aquatic Photochemistry. Amer. Chem. Soc. Sympos. Ser. 327 106-115. 

Laser flash photolysis of [MCCO) ], M = Cr, Mo, or W, in the presence of phen generates [M(CO)4(phen)]. For M = Cr a transient characterized as [Cr(CO)5(phen)] with a monodentate phen ligand was observed. For M = Mo or W the growth curve for [M(CO)4(phen)] is indicative of a consecutive first-order process. The rates for chelate closure are significantly faster than the rates of substitution of py analogs (Table 10.3), suggesting an interaction between the free... 

W. Schnabel, Laser Flash Photolysis of Polymers, in N. S. Allen (ed.). Developments in Polymer Photochemistry - 3, Applied Science, London (1982), Chapter 7, p. 237. 

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