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Cobalt complexes photolysis

Bis(aryl)cobalt(II) compounds have been prepared by reaction of R MgX (where R = C6H6 Cl n = 2-4) with Co(PR3)2Cl2.203 They undergo both thermally and oxidatively induced decomposition, with the corresponding biphenyl a product. The reactions of alkyl-cobalt complexes have been reviewed recently, and include thermolysis, photolysis, oxidation, and reduction reactions.25 Homolysis of the Co—C bond is a feature of reactions. [Pg.21]

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. [Pg.41]

Because such alkylation proceeds by S l mechanism, even cobalt complexes derived from unreactive (in an SN2 sense) halides can be formed. The cobalt complexes are air-stable compounds, but are affected by direct daylight. The incorporated Co—C bond is weak and, therefore, photolysis of 33 sets free the anomeric radical 11. In the presence of olefins 12 this radical adds to the double bond, followed by subsequent combination to give the insertion product 35 (Scheme 9). [Pg.513]

Quite a range of P-lactams have been made by methodologies following disconnection a with carbamoyl radicals (aminoacyls) as intermediates. Pattenden and co-workers made carbamoyl cobalt salophen complexes and showed that on photolysis carbamoyl radicals were released and underwent 4-exo cyclisations [75-77]. For example, carbamyl chloride derivative 59 was converted to cobalt complex 60, which on photolysis yielded the cyclised cobalt-azetidinone complex 61. The free azetidinone 62 was released by heating the cobalt complex in toluene and was transformed into thienamycin in several subsequent steps (Scheme 15). [Pg.176]

Stable, isolable metallacycles are also obtained from reaction of complexes that serve as sources of the CpCo fragment (e.g. CpCo(PPh3)2) and alkynes. Upon carbonylation diese typically give high yields of cobalt-complexed cyclopentadienones. Direct reaction of CpCo(CO)2 with alkynes is similarly useful. The cycloaddition of di(t-butoxy)acetylene upon photolysis with CpCo(CO)2 is an example (Scheme 5). In all these systems the final complexes lack coordinated CO, and therefore amine oxides are not suitable reagents for liberating the stable cyclopentadienones. Tetra(t-butoxy)cyclopentadienone is accessible on a preparative scale via controlled electrochemical oxidation. Other oxidants such as Cr have been used as well in other systems. [Pg.1133]

The dependence of the decay rate of TP on [CO2], measured for solutions containing CO2 with no cobalt macrocycle is not linear in CO2 concentration [28]. A rate constant of <10 s is estimated for the TP -C02 reaction. This sluggish rate constant is consistent with the large reorganization of the C02/C02 couple and modest driving force for the reaction (0.5 V). Under photocatalytic conditions (continuous photolysis) the TP reacts much faster with the cobalt complex than with CO2 and >90 % the photochemically generated reducing equivalents are captured by the cobalt macrocycle. [Pg.2476]

In contrast to the cobalt-based system, small amounts of H2 and no CO are produced when nickel cyclam or other saturated 14-membered tetraazamacrocycles (L) in Figure 3 are used to replace the cobalt complex in the above system [22]. Flash photolysis studies indicate that the electron-transfer rate constant (kn) for the reaction of the />-terphenyl radical anion with Nil (cyclam)2 is 4.3 x 10 M s. However, when CO2 is added to the solution, the decay of the TP anion becomes slower Flash photolysis studies of the acetonitrile solutions... [Pg.101]

Photolysis of the dinuclear cobalt complex (59) in low-temperature matrices has been investigated using IR spectroscopy. The primary process is loss of CO... [Pg.331]

However, the similarity in bond strengths of the peroxide linkage to molecular 02, the ease with which the known -peroxo Cobalt complexes liberate 02 (in contrast to /x-oxo bipyridyl Mn dimers) on photolysis, kinetic barriers on ju-oxo to peroxo dimer conversions led Sawyer et al.47 -49) to suggest peroxo binuclear complexes as the most probable intermediates. More studies with model compounds are needed to elucidate this point. Various mechanisms proposed for water oxidations are variations of these two principal types. [Pg.49]

Tin(II) bis(jS-ketonolates), Sn[0CRCHCR (=0)]2 (R, R = Me, CFj, Ph), are also excellent donor molecules to transition metal carbonyl residues, readily forming the type D structure chromium, molybdemun and tungsten complexes (8) under photolysis in tetrahydrofuran, as well as the manganese complexes (9). The cobalt complexes (10) and (11) prepared by the same method are somewhat different, and in these the stannylene functions as a bridging group. The two platinum(0) complexes (12) and (13) have been obtained from the reaction of tin(II) bis(pentane-2,4-dionate) and Pt(C2H4)(PPhj)2 under different conditions. ... [Pg.664]

In contrast to these results, low-temperature methane and argon matrix photolysis of [Cp M(CO)2] (Cp = Cp, Cp, 7/ -indenyl, M = Ir, Rh) gave indications of initial CO dissociation. No difference was seen in the behavior of 17 -indenyl and Cp. No evidence was found for C—H bond activation by [Cp Co(CO)2]. However, carbonyl exchange was the most rapid with the cobalt complex. Such compounds have also been studied in Nujol mull matrix at temperatures as low as 12 Similar studies have been undertaken to elucidate C—H activation... [Pg.293]

Cobalt complexes are the specific area of interest for a paper dealing with the technology of spinning-cell Fourier transform Raman spectroscopy. The technique uses near-IR light and, because of the rapidly spinning cell, avoids the problems of sample burning and should be most useful for the study of delicate carbonyl species. Clusters are studied somewhat differently, following UV laser photolysis, in a paper published by Belyaev et. ... [Pg.147]

The phosphine complex Ru(dmpe)2 has been studied in matrices [62], Ru(diphos)2 (diphos = depe, dppe, (QFs P F P Fs ) has similarly been formed by photolysis of Ru(diphos)2H2 in low-temperature matrices. They probably have square planar structures and undergo oxidative addition with cobalt, C2H4 and hydrogen [63]. [Pg.20]


See other pages where Cobalt complexes photolysis is mentioned: [Pg.161]    [Pg.153]    [Pg.140]    [Pg.18]    [Pg.510]    [Pg.25]    [Pg.183]    [Pg.178]    [Pg.510]    [Pg.535]    [Pg.322]    [Pg.602]    [Pg.425]    [Pg.390]    [Pg.6655]    [Pg.161]    [Pg.68]    [Pg.163]    [Pg.97]    [Pg.286]    [Pg.814]    [Pg.162]    [Pg.777]    [Pg.22]    [Pg.109]    [Pg.156]    [Pg.403]    [Pg.405]   
See also in sourсe #XX -- [ Pg.251 ]




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Complex photolysis

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