Rhenium complexes studies

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

In the bifunctional radiopharmaceuticals, Tc and Re complexes that are suitable for coupling to antibodies are almost square-pyramidal oxo complexes of tetradentate ligands, as mentioned earlier. Spies et al. [65] recently studied the syntheses and structures of rhenium complexes with a tetradentate NS3 tripod ligand 2, 2,, 2"-nitrilotris(ethanethiol) (l in Fig. 9) as an interesting alternative to the oxo complex. Such ligands could lead to weakly polar, trigonal-bipyramidal complexes in which the metal atom is more strongly shielded than in the square-pyramidal oxo complexes. Schemes for the syntheses... 

In 1986, Breikss and Abruna reported electrochemical and mechanistic studies on a close analogue of the rhenium complex, (Dmbpy)Re[CO]3Cl, where Dmbpy = 4,4 dimethyl 2,2 bipyridine. The cyclic voltammogram of the complex at platinum in CH3CN/tetrabutylammonium perchlorate is shown in Figure 3.56 for simplicity we will consider only the electrochemistry taking place above c. —2.3V vs. SCE. 

Further evidence came from in situ UV-visible studies by Breikss and Abruna (1986), apparently using external reflectance from a Pt electrode. Figure 3.58(A) shows the absorption spectrum for the rhenium complex in solution in the absence of C02 prior to electrolysis. The potential of the working electrode was then slowly ramped to more cathodic values until it reached —1.7 V, whereupon a reddish material formed with a spectrum labelled B in Figure 3.58, having a Am = 512nm. The potential was then... 

More mechanistic insight into the C-H functionalization process of arenes is provided by theoretical and experimental studies. Multifluorinated, electron poor, aromatic substrates readily undergo CH activation with coordina-tively unsaturated rhenium complexes, attributed to the stronger C-Re bond in the product, whereas with monofluorinated analogs, the if -complex predominates (Equation (60)).61... 

Ma et al. also studied PVK-based PPLEDs using rhenium complex in [28,51], They have prepared the PPLED in configuration ITO/PVK bpyRe (27) DCM (28)/Al (DCM is 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4//-pyran), where the bpyRe... 

Infrared spectroelectrochemical technique proved to be an excellent method to look at time and potential dependent changes of various types of chemical species. The employment of this technique will surely be significant on the mechanistic study of electron-transfer reactions of rhenium complexes. 

The silane o-complexes 11 have been intensively studied as discussed above and in Refs. 2, 4, and 12-14. No examples of such complexes are known for technetium, whereas the related rhenium complex [Re(H)(SiR3)(CO)2Cp] has been concluded to be classical on the grounds of a long-estimated Si-H distance of 2.2 A. Schubert favors a classical description of the latter compound, whereas Kubas noted that this distance may correspond to a stretched a-complex on the verge of oxidative... 

I. Recent review topics include carbon-rich acetylenic materials as molecular scaffolding, studies of luminescent di- and poly-ynyl-rhenium complexes containing Re(CO)3(bpy) groups and Group 4 diynyl tweezer complexes in the context of other tweezer and related molecules. ... 

Structural studies on rhenium complexes containing complexone type ligands are of considerable interest in the light of the application of their technetium analogues in diagnostic nuclear... 

Most photosensitizers, however, are reasonably photostable compounds, and their optical properties have been studied in depth. In particular, there has been much interest in ruthenium-based photosensitizers such as [Ru(bpy)3]2+ and [Ru(phen)3]2+, due to their stability and absorption of visible light. Detailed information on their optical properties, including ground and excited state information in relation to photosensitization, has been reviewed by Creutz et al. [16]. Similarly, the photochemistry and photophysics of rhenium complexes, as discussed here, have been reviewed in detail by Kirgan et al. [7]. 

The rhenium complexes described in Section 11.2 have also been studied as electron mediators for C02 reduction at metal electrodes. Hawecker et al. used the complex Re(bpy)(CO)3Cl in DMF/water (9 1) at glassy carbon electrodes at a potential of-1.44V (versus SCE) to produce CO with 98% faradaic efficiency [15, 87]. Likewise, Sullivan et al. reported the production of CO with similar efficiency at a platinum electrode at -1.5 V (versus SCE) by using the complex fac-Re(bpy) (CO)3Cl [88]. Ruthenium complexes that have been used in photochemical... 

The photochemistry of rhenium complexes occupies a prominent position in the photochemistry of transition metal complexes. Along with early preparative studies on photosubstitution of carbonyl species like Re(CO)sX, the preparation of the remarkably stable yellow complex /ac-Re(CO)3(phen)Cl foreshadowed the discovery of the a large class of related luminescent materials by Wrighton and co-workers in the 1970s [ 1 ]. As pointed out by Vogler and Kunkley, the current photochemistry of rhenium complexes is rich, spanning eight oxidation states from formal Re(0) (for example, Re2(CO)io) to formal Re(VII) (for example MeReOs) [2],... 

---