Copper complex with, 1,10-phenanthroline

Special features strongly related to the compactness of the phenylene-bridged knots were also observed during the photophysical studies. All die compounds, as usual for copper complexes with phenanthroline-type ligands [116, 117], exhibit MLCT luminescence in CH2C12 at room temperature. Only one emission band, assigned to the lowest MLCT excited state, is observed even for the complexes con-... 

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]. 

Phenanthroline and 2,2 -bipyridyl form complexes, although not intensely coloured, with Ru, Os, and Cu(I). Many metals e.g., Zn and Cd) can form colourless complexes with phenanthroline and bipyridyl, which are more stable than the corresponding Fe(II) complexes. When determining Fe in the presence of Zn or Cd, EDTA should be used as a masking agent [31]. Copper can be masked with triethylenetetramine [32]. 

The most effective catalysts were found to be the 1 1 copper complexes with a,a -dipyridyl, L-histidine, o-phenanthroline, imidazole, and ethylene-diamine. Because of the apparent requirement that the metal be incompletely coordinated, it was suggested that the reactive positions of the metal are those occupied by water or hydroxide ion. Three such species have been reported by Fowkes et al. (9) from a study of aqueous equilibria involving the 1 1 dipyridyl chelate, according to the following reaction scheme ... 

Hydroquinone has been used " to probe the reactivity of copper complexes with substituted phenanthroline ligands where it is thought that... 

Interestingly, the rate constants for Diels-Alder reaction of the ternary complexes with 3.9 are remarkably similar. Only with 2,2 -bipyridine and 1,10-phenanthroline as ligands, a significant change in reactivity is observed. It might well be that the inability of these complexes to adopt a planar geometry hampers the interaction between the copper ion and the dienophile, resulting in a decrease of the rate of the catalysed Diels-Alder reaction. 

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

Synthesis and Characterization of N-[l,10-Phenanthroline]-N -[(Benzo-15-Crown-5)yl] Thionrea and Its Complex with Copper(I)... 

Figure 17.29 Structure of distorted tetrahedral copper complexes. SP is sparteine-TV./V, mint is maleonitriledithiolate, dmp is 2,9-dimethyl-1,10-phenanthroline, and phen is 1,10-phenan-throline. Reprinted with permission from Ref. 67. Copyright 2005 American Chemical Society.

Dithio-oxamide (LH2) and its dimethyl and dicyclohexyl derivatives form polymeric [CuL]n probably with S2N2 co-ordinated copper.405 The copper complexes of l,10-phenanthroline-2-carbothiamide, CuLX2 (X = Cl, Br, or NCS), are six-co-ordinate with X-bridges. The N-phenyl-l,10-phenanthroline-2-carbothiamide complexes of copper are similar to those of Co111, in that only species containing the deprotonated ligand can be obtained, Cu(L - H)X (X = Cl, Br, or N03). 

Not many reduction potentials are known for copper complexes. That of the Cu2+/Cu+ couple is 0.16 V Since lo(Cu+/Cu°) is 0.52 V, the disproportionation of Cu+ to Cu° and Cu2+ is favourable. This reaction does indeed occur, which makes is impossible to study stable copper(I) solutions. Reduction potentials of copper(II)-/copper(I)-(l,10-phenanthroline)2 and a few derivatives have been calculated from a kinetic analysis of appropriate rate constants values range from 108 mV for the 5-methyl-l, 10-phenanthroline complex to 219 mV for the complex with a nitro group at the 5 position [52], Values of 0.17 V and 0.12 V are given by Phillips and Williams [53] for the phenanthroline and bipyridine complexes, respectively. Such complexes can thermodynamically catalyse both the superoxide dismutation and the one-electron reduction of hydrogen peroxide (see below). 

There are several excellent photosensitizers one of them is [Ru(bpy)3]2+ [6]. There are two optical isomers in this complex one is A [Ru(bpy)3]2+ and the other is A-[Ru(bpy)3]2 +, as shown in Scheme 1. Thus one can expect to perform the stereoselective electron transfer reaction with A- and A-[Ru(bpy)3]2 +. Unfortunately, however, the racemization of [Ru(bpy)3]2+ is induced photochemically [7]. The reasonable way to suppress the photoracemiza-tion of this complex is to introduce the optically active organic functional group into the transition metal complexes, as will be discussed in Sec. II.B. The other photosensitizer that is useful for the photoinduced electron transfer reaction is the copper(I) complexes with 1,10-phenanthroline and their derivatives [8,9]. Zinc(II) porphyrin is also an excellent photosensitizer for photoinduced electron transfer reaction [10]. In these complexes, molecular chirality does not exist, unlike in [Ru(bpy)3]2 +. Thus one must introduce some chiral functional group into these compounds, to use these complexes as chiral photosensitizers. 

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. 

Many attempts with various linkers were carried out before it was found that 1,10-phenanthroline moieties, connected via their 2-positions by a butyl chain, form a double helix when complexed with two copper ions. In addition, by introducing appropriate functions at the 9-positions, the strategy of Fig. 9 could be followed to achieve the synthesis of a molecular knot. The route to the knot, showing the... 

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