Complexes rhenium

These ketophosphine complexes all exhibit reversible one-electron oxidation of the ferrocene fragment. In addition, as shown in Fig. 7-21, [( -C5H5)Fe ( -C5H4C(0)CHPPh2)Re(C0)3Br ][NMe4] also displays a subsequent two-electron oxidation. Access to such a rhenium-centered process is likely to be electrostatically favored because of the anionic nature of the complex [77]. 

Hori et al., when using the photocatalyst Re(bpy)(CO)3[P(OEt)3] SbFs, achieved a quantum yield of 38% for CO in a C02-saturated DMF/TEOA solution illuminated with 365 nm light [27]. Under the same conditions, the quantum yield for CO using Re(CO)3(bpy)Cl was only 16%, but comparable to that in previous reports. 

Hori et al. studied the photocatalysts Re(bpy)(CO)3Cl and [Re(bpy)(CO)3(PO Pr)3]+ in a high-pressure DMF/amine system for the production of CO under 356nm illumination [30, 31], The high-pressure system (2.45 Pa C02) resulted in a 5.1-fold higher turnover number (TON) than was achieved under normal pressure (0.1 Pa) for the Re(bpy)(CO)3Cl catalyst. The [Re(bpy)(CO)3(PO Pr)3]+ photocatalyst showed a 3.8-fold increase at 3.8 Pa. The TONs for CO production peaked at 42 and 16 for each catalyst, respectively. 

Recently, Ru and Re bi-nuclear (Ru-Re) and tetranuclear (Ru-Re3) complexes for the photoreduction of C02 have been synthesized [32]. Under irradiation at 480 nm, in a DMF/TEOA solution, the complexes were observed to undergo reductive quenching by l-benzyl-l,4-dihydronicohnamide (BNAH). The best bi-nuclear complex yielded a quantum efficiency of 9% for CO production, and a TON of 170. Similarly, the tetranuclear complex yielded a CO quantum efficiency of 12% and a TON of 240. While these marked increases in TONs are encouraging, it should be stated that increases of many more orders of magnitude are required to yield an economically viable system. 

Also called a nitrogen flow adapter. (See Kontes Glassware cat. no. K-211300.) 

Submitted by FRANCINE AGBOSSOl), EDWARD J. O CONNOR, CHARLES M. GARNER, N. QUIROS MENDEZ, JESGS M. FERNANDEZ, ALAN T. PATTON, JAMES A. RAMSDEN, and J. A. GLADYSZ  

Checked by JOSEPH M. O CONNORf and TRACY TAJIMAf (Sections A-G), and KEYIN P. GABLED (Section H) 

Chiral, pseudotetrahedral cyclopentadienyl rhenium complexes of formulas Re(ij -C5H5)(NO)(PPh3)(X) and [Reft/ -CjHsKNOKPPhjKLll X- have proved to be of broad utility in synthetic and mechanistic organometallic chemistry. As described in the procedures that follow, they are readily available in optically active form. This provides a valuable stereochemical probe for mechanistic 

Furthermore, the Re(t/ -C5H5)(NO)(PPh3) moiety can function as an efficient chiral auxiliary for the stereospecific introduction of new ligand-based chiral Organic compounds of high 

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The parent ligand forms complexes of the type [M(CO)5(HNSO)][AsF6] (M = Mn, Re) (Eq. 9.11). ° The rhenium complex can also be prepared by nucleophilic displacement of F from coordinated NSF using MesSnOH as the source of... 

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]. 

When alkenes are treated with certain catalysts (most often tungsten, molybdenum, or rhenium complexes), they are converted to other alkenes in a reaction in which the alkylidene groups (R RX=) have become interchanged by a process schematically illustrated by the equation ... 

Scheme 21 Synthesis of rhenium complexes by the reaction of the rhenium chlorides with polysulfide dianions...

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

The potentially versatile ligating ability of trisimidometaphosphate anions is manifested in the formation of either dispirocyclic (13) or heterocubane (14) rhenium complexes from the reaction of [(Me3Si)2NP(=NSiMe3)2] with RefCOljCl [18, 19]. Both (13) and (14) contain the dianionic [(RN)2P(fi-NR)2P(NR)2] "... 

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. 

Finally, (7 5-heterolyl)Mn(CO)3 complexes, the heterocymantrenes, have been prepared for the complete family of group 15 elements from N to Bi. As shown in Scheme 10, 2,5-dimethylarsacymantrene (71) is obtained directly from l-phenyl-2,5-dimethylarsole (25) in 50% yield by heating with Mn2(CO)10.26 The tetraphenylarsacymantrene (74) is obtained by pyrolysis of the corresponding cr-complex 72. Rhenium complex 75 is obtained by an analogous reaction. The 2,5-dimethylstibacymantrene (76)8 and 2,5-dimethylbismacymantrene (78)27 were obtained by similar routes. 

Rhenium Complexes Labeled with l 6/l88Re for Nuclear Medicine... 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

Another type of mixed ligand technetium or rhenium complexes in the above sense contains two or more monodentate ligands (Fig. 26b). The six-coordinated polypyridyl-thiolato complexes of rhenium(V) [ReO(terpy)(SR)2] + [186] are an example. Further representatives are a variety of mixed-ligand complexes, combining tetramethylthiourea with dimethyldithiocarbamate [TcO(tu)2-((CH3)2NCSS)]2+ [194],... 

Although these complicated features of the redox reactions of technetium are important topics, the present article is limited to the susbtitution kinetics of technetium complexes. Some redox kinetics of technetium complexes have been discussed by Koltunov and Gomonova [6], The redox potentials for analogous technetium and rhenium complexes, based on their differences, have been compiled by Deutsch et al. [7],... 

The results show that the technetium complexes are more labile than the rhenium complexes. The overall reaction rate depended on the concentrations of both hexachlororhenate and hydrogen ion, but was independent of the chloride concentration. 

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