Rhenium complexes cyanides

Mn is present in K5Mn(CN)g and in Mn(RNC)g+compounds (p. 478). Corresponding rhenium compounds are unknown. The complex cyanide is diamagnetic, indicating that the approach of the cyanide ions causes a large splitting of the d levels (p. 132) and leaves two d orbitals free for bonding in d sp octahedral hybrids. 

The 6-substituted cyano bipyridine has been generated in 95% yield from bipyridine A-oxide by reaction with trimethylsilylcyanide and dimethylcarbamylchloride.76 This is an improvement on an earlier method that generated 6-cyano bipyridine from the A-oxide in 62% yield using potassium cyanide and benzoyl chloride.77 This ligand has been used in electrochemical studies of rhenium complexes with sterically hindered bipyridine derivatives, as well as a precursor in the synthesis of 6-carbothioamide-bpy, which showed antitumor activity against P-388 lymphocytic leukemia in mice.77... 

Notably, as illustrated in Scheme 124, enantiofaces of aldehydes can be differentiated by a chiral rhenium template to result in stereoselective reaction with cyanide ion (297). The rhenium Lewis acid element forms stereoisomeric it complexes with aldehydes, which are convertible via... 

Fig. 6 Photocurrent/potential characteristics for Ti02 ( ), and rhenium ( ) and iron (A) cyanide complexed Ti02 electrodes. The Ti02 was illuminated by UV (380 nm), the others by visible light.

Fig. 7 Photocurrent efficiency (charge transfer/photon flux) of rhenium (ig)and iron (A)cyanide complexed Ti02 photoelectrodes with that of untreated Ti02 ( )for comparison. The extension of the spectral response into the visible is evident.

Complex 376 can be prepared from enantiomerically pure rhenium precursor 381. The former can be deprotonated at low temperatures initiating the [2,3]-sigmatropic rearrangement to diastereomerically pure homoallylic sulfide complex 377. After S-alkylation, cyanide treatment releases the S ligand as product 379. As an extension of this work the authors showed that iron and ruthenium complexes can be used, too [219]. 

In this reaction scheme, the formation of the pentacyano complex is a relatively fast reaction, with rate constants of about 116 and 2.9 Af" sec" for the molybdenum (20°C) and tungsten (25°C) complexes, respectively, whereas the formation of the octacyano complex from the pentacyano complex is a relative slow reaction, with a half-life of several minutes at a cyanide ion concentration of 1 Af for both the molybdenum and the tungsten complexes. The formation of the octacyano complex from the pentacyano complex is third order in the cyanide ion concentration 155,156). This suggests that the rate-determining step is the reaction of the heptacyano complex with cyanide ions. It seems, however, that the pentacyano complex is a necessary intermediate in the synthesis of the octacyano complex. This proposed reaction scheme makes it possible for the first time to explain why the octacyano complex of rhenium(V), which is also a d species, is still unknown in spite of several attempts (and claims of success) by different groups in the past (see Section IIA) to synthesize this complex The reactive complexes [Re0(H20)(CN)4]" and [ReO(OH)(CN)4] do not exist at a pH > 8, at which there are enough free cyanide ions since the values of [Re0(H20)(CN)4]" are only 1.4 and 4.2. The formation ofthe intermediate [ReOtCNlg] (see Scheme 6) is thus not possible. Thus one cannot proceed beyond the tetracyano complex in this way. 

Introduction.—The organometallic chemistry of technetium and rhenium reported during 1974 has been surveyed. The ligand-induced redox reactions of rhenium halides have been reviewed, and the chemistry of cyanide complexes of Group Vila metals has received attention. The electrochemistry of technetium and rhenium has been the subject of two reviews, and a general monograph on the production, uses, and disposal of technetium has appeared. Recently published crystal structures of complexes of technetium and rhenium have been collated. ... 

Rhenium(III) complexes, 143-164 cyanides, 143 alkyl isocyanides, 143 amides, 144 amidines, 146 amines, 144 arsines, 147 aryl isocyanides, 143 cyanates, 145 diazines, 144 diethyidicarbamato, 150 P-diketones, 149 dinitrogen, 144 N heterocycles, 144 nitriles, 146... 

Rhenium(V) complexes, 177 2-aminobenzenethiol, 188, 192 2,2 -bipyridyl, 187 4-chloro-2-aminobenzenethiol, 192 cyanides, 187... 

---