Transition metals phenanthroline complexes

Table 1 Excited state properties of transition metal polypyridyi complexes in aqueous solution at room temperature, [M(LL)p] +. dmp = 2,9-dimethyl-1,10-phenanthroline. Data are taken from refs. 10 and 13. ...

Several light-induced electron transfer cycles using transition metal polypyridyl complexes that lead to catalytic fixation of CO2 or CO have been identified [69,70]. Visible light photolysis of C02-saturated aqueous acetonitrile solutions containing Ru(bpy)32+ (as photosensitizer), Co(II) ions (as the catalyst), 4,7-Me2-phenanthroline (as the ligand to complex the Co(II) in situ), triethanolamine (as donor) yields a mixture of CO and H2 (synthetic gas). The syn gas mixture is produced by simultaneous occurrence of two reduction reactions ... 

Technetium-99m coordination compounds are used very widely as noniavasive imaging tools (35) (see Imaging technology Radioactive tracers). Different coordination species concentrate ia different organs. Several of the [Tc O(chelate)2] types have been used. In fact, the large majority of nuclear medicine scans ia the United States are of technetium-99m complexes. Moreover, chiral transition-metal complexes have been used to probe nucleic acid stmcture (see Nucleic acids). For example, the two chiral isomers of tris(1,10-phenanthroline)mthenium (IT) [24162-09-2] (14) iateract differentiy with DNA. These compounds are enantioselective and provide an addition tool for DNA stmctural iaterpretation (36). 

Although the number of applications of olefin metathesis to transition metal complexes is small compared to the number of applications in organic synthesis, this field is becoming increasingly important. Spectacular examples are the double RCM reactions of copper phenanthroline complexes as a synthetic route to catenanes [113] or a recently reported approach to steric shielding of rhenium complex terminated sp-carbon chains [114]. 

What happens if we look at the K2 or Ki, values for didentate ligands In general, the Kj values show stability patterns which closely parallel those for K. However, the values are different. Figure 8-17 presents K, data for transition-metal complexes of 1,10-phenanthroline and 1,2-diaminoethane (Eq. 8.14). 

The Chemistry of Complexes Containing 2.2 -Bipyridy 1, 1,10-Phenanthroline, or 2.2. 6. 2"-Terpyridyl as Ligands W. R. McWhinnie and J. D. Miller Olefin Complexes of the Transition Metals... 

Molecular Metal Complexes Compounds of this type do not form delocalized electronic bands in the sohd state, and their color is due to intramolecular electronic transitions. Many complexes of transition metals with organic ligands belong to this class. complexes with phenanthroline (red/colorless) and Ru + + with 2,2 -... 

A broad range of metal centers have been used for the complexation of functional ligands, including beryllium [37], zinc, transition metals such as iridium [38], and the lanthanide metals introduced by Kido [39], especially europium and terbium. Common ligands are phenanthroline (phen), bathophenanthrolin (bath), 2-phenylpyridine (ppy), acetylacetonate (acac), dibenzoylmethanate (dbm), and 11 thenoyltrifluoroacetonate (TTFA). A frequently used complex is the volatile Eu(TTFA)3(phen), 66 [40]. 

More synthetic interest is generated by the potentially very useful hydration of dienes. As shown on Scheme 9.6, methylethylketone (MEK) can be produced from the relatively cheap and easily available 1,3-butadiene with combined catalysis by an acid and a transition metal catalyst. Ruthenium complexes of several N-N chelating Hgands (mostly of the phenanthroline and bipyridine type) were found active for this transformation in the presence of Bronsted acids with weakly coordinating anions, typically p-toluenesulfonic acid, TsOH [18,19]. In favourable cases 90 % yield of MEK, based on butadiene, could be obtained. 

The free electron pair(s) in the concave pyridines 3 (Table 1), 13 (s. Scheme 3) and 29 (s. Scheme 5) and especially in the concave 1,10-phenanthrolines 11 (s. Scheme 2) and 21 (Structures 3) are not only able to bind a proton, they may also be used to coordinate a metal ion. For concave 1,10-phenanthrolines 11 and 21, transition metal complexes 87 (Structure 11) have already been generated [18, 55]. They form readily in acetonitrile solution with binding constants of 10 10 and larger. Of great importance is the nature of the chains X in the concave 1,10-phenanthrolines 21 (Structures 3). Pure aliphatic chains lead to smaller association constants than polyether chains. 

If the transition metal could exist in two different oxidation states in the complex 87, one would have a concave redox reagent which could be useful for instance in epoxidation reactions [56]. The concave shielding of the metal ion should influence the regio-, stereo- and, if the concave 1,10-phenanthroline 21 is chiral, enantioselectivity of an epoxidation. 

There is abundant evidence that steric hindrance to coordination will decrease the formation constant of any complex formed and may even inhibit complex formation altogether. Numerical data are available for transition metals and substituted ethylenediamines,27 or substituted oxines.-3 for 1,10-phenanthroline and its 2- and 2,9-methyl-substituted derivatives28 and for other systems.29 Since the introduction of a 2-methyl substituent into oxine diminishes 0 while increasing pK2, it is not surprising that the effective concentration [Al(2-MeOxine)3] may not be great enough to cause precipitation, although this is achieved in non-aqueous media such as ethanol. 

Typical OH-scavengers suppress this reaction of (OP)2Cu+ (Que et al. 1980) yet, acetate and benzoate seem to be equally efficient, despite the fact that acetate is nearly two orders of magnitude less reactive towards OH than benzoate (k=7 X 107 dm3 mol-1 s 1 vs k = 5 X 109 dm3 mol-1 s 1 Buxton et al. 1988), and obviously it is not a freely diffusing OH that is responsible for the reaction. The reaction is also suppressed by Cu-complexing compounds and by transition metal ions such as Zn2+, Co2+, Cd2+ and Ni2+ that form stable complexes with 1,10-phenanthroline (Que et al. 1980) and also by competitive intercalators such as ethidium bromide and 2,9-dimethyl-l,10-phenanthroline (Reich et al. 1981). Interestingly, compared to its parent, the latter is inactive. NADH may serve as a reductant, but 02, seems to be a salient intermediate in this cleavage reaction, because cleavage is fully suppressed in the presence of SOD (Reich et al. 1981). 

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