Rhenium complexes reactions

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] "... 

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. 

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. 

Fig. 21. Comparison of half-lives. [Data from Table VII (equatorial ligand substitution, Table VIII (aqua substitution and related reactions) and Table IX (in vivo reactions of technetium and rhenium radiopharmaceuticals) of the complexes described in Section VII,A. Similar symbols denote similar technetium and rhenium complexes.]...

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 main goals of this research are (1) to characterize polynuclear rhenium complexes which are capable of multielectron transfer reactions (2) to come up with appropriate conclusions on the redox-initiated transformations of this synthetic analog through the use of a new design of spectroelectrochemical cell and (3) propose possible systems or investigations where infrared spectroelectrochemi-stiy can be very useful. 

Grafting on the resin was achieved via a nucleophilic substitution of the benzylic chlorine by the deprotonated OH-linker of 52 (Scheme 29) by using a mixture of KO Bu, 18-crown-6 and CsBr. Determining the nitrogen content of solid phase samples by elemental analyses was accomplished, to verify the functionalization of the polymer. This enables calculation of the degree of functionalization. Usually, an occupancy of more than 20 percent of the theoretical sites was achieved. Saponification of the functionalized Merrifield resin P-52 leads to the monoanionic NJ, 0 functionalized solid phase. Subsequent reaction with [ReBrtCOlsJ afforded the polymer mounted tricarbonyl rhenium complex P-52-Re (Scheme 29). 

---