Copper complexes photoreduction

Copper complexes, 5,533-750 acetylacetone hydrolysis, 2,379 photoreduction, 2.384 amidines... 

Because the copper complexes with 2,2/-bipyridine, 1,10-phenanthroline, and their derivatives have a triplet MLCT excited state like that of [Ru(bpy)3]2+, the copper complexes exhibit similar photocatalyses to those of [Ru(bpy)3]2 + for instance, the trans-cis isomerization of stylbene through energy transfer [48] and the photoreduction of viologen compounds [9b,c,e,49,50] were successfully carried out with the copper complexes. Also, a Gratzel-type solar cell was constructed with the copper complexes, recently [51,52]. 

Since the copper complexes, [Cu(NN)2]+ and [Cu(NN)(PR3)2]+ (NN = 1,10-phenanthroline, 2,2 -bipyridine, and their derivatives) were applied to stoichiometric and catalytic photoreduction of cobalt(III) complexes [8a,b,e,9a,d], one can expect to perform the asymmetric photoreduction system with the similar copper(l) complexes if the optically active center is introduced into the copper(I) complex. To construct such an asymmetric photoreaction system, we need chiral copper(I) complex. Copper complex, however, takes a four-coordinate structure. This means that the molecular asymmetry around the metal center cannot exist in the copper complex, unlike in six-coordinate octahedral ruthenium(II) complexes. Thus we need to synthesize some chiral ligand in the copper complexes. 

The first example of a chiral copper photosensitizer is [Cu(dmp)((R,R-diop))]+ [R,R-diop = (R,R)-2,3-0-isopropylidene-2,3-dihydroxy-1,4-bis(diphe-nylphosphino)-butane dmp = 2,9-dimethyl-1,10-phenanthroline], in which two chiral centers are introduced in the (R,R)-diop ligand. This complex was applied to the stereoselective photoreduction of [Co(edta)]- [25]. After the reaction, the CD spectrum exhibits a positive peak at 590 nm and a negative one at 515 nm, which indicates the presence of excess A-fCo(edta)]. This means that A-[Co(edta)] more rapidly reacts with the photoexcited copper complex than does the A-enantiomer, where the stereoselectivity, defined as the ratio of the conversion rate, is 1.17. However, the photoreduction of Co(acac)3 and [Co(bpy)3]3+ occurs without stereoselectivity. This is probably because the electrostatic attraction between [Cu(dmp)((R,R-diop))]+ and [Co(edta)] is favorable for the stereoselection, but such interaction does not exist between [Cu(dmp)((R,R-diop))]+ and the other cobalt(III) complexes. 

Involving copper complexes,and photoreduction of aromatic species. ... 

Cyclopentenes behave differently and often act through radical mechanisms this can lead to photoreduction to cyclopentanes, or photoaddition of the kind exemplified by norborneneand propan-2-ol 12.57). The photoadduct in this process is linked through the carbon atom of the alcohol, and not the oxygen atom. A related addition to acetonitrile 12.58) takes place when norbornene is irradiated in the presence of a silver(i) compound. It is likely thal a metal complex of the alkene is the real irradiation substrate, and the same may be true for copper(i)-promoted additions of haloalkanes to electron-deficient alkenes (2.59). When dichloromelhane is used in such a reaction the product can be reduced electrochemically to a cyclopropane (2.60), which is of value because the related thermal addition of CH.I, to alkenes in the presence of copper does not succeed with electron-poor compounds. 

Metal acetylacetonates quench triplet species generated by flash photolysis of aromatic ketones and hydrocarbons.330-333 More recently, these reactions have been studied from a synthetic standpoint. Triplet state benzophenone sensitizes photoreduction of Cu(MeCOCHCOMe)2 by alcohols to give black, presumably polymeric, [Cu(MeCOCHCOMe)] . This reacts with Lewis bases to provide complexes of the type CuL2(MeCOCHCOMe) (L = bipyridyl/2, ethylenediamine/2, carbon monoxide, Ph3P). Disubstituted alkynes yield Cu(C2 R2 XMeCOCHCOMe) but terminal alkynes form CuQR acetylides.334 The bipyridyl complex of copper(I) acetylacetonate catalyzes the reduction of oxygen to water and the oxidation of primary and secondary alcohols to aldehydes and ketones.335... 

Cu11 complexes undergo photoreduction to the Cu1 species and may be the photocatalyst in photo-oxidation cycles of organic environmental matter, quite similar to the Fem species [20, 81] (see Figure 9.11). Dissolved copper compounds are important to transformation reactions, because they react with hydroperoxyl (H02) and superoxide (02 ) radicals much faster than other species present in the solution. Oxidation of Cu1 and Fe11 by H202 is a source of the OH radicals in oceans comparable with nitrite photolysis, whereas photochemistry of Cu11 chlorocom-plexes provides Cl radicals [81] ... 

Keywords Environmental homogeneous photocatalysis Photoreduction of transition metal complexes NO-carriers Photodegradation of organic pollutants Photocatalytic cycles stimulated by iron, copper and chromimn complexes. 

Table 13. Quantum Yields for the Photoreduction of Copper(II) Chloro Complexes ...

The presence of chlorine atoms can be detected by their reaction with alkanes (RH) to give alkyl chlorides. The quantum yields for the photoreduction of copper(II) halide complexes in acetonitrile solution are given in Table 2.13. These values show that the neutral complex has a significantly larger quantum yield than the anionic complexes. 

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