Rhenium complexes cyclopentadienyl

Hydridotris(3,5-dimethyl-l-pyrazolyl)borate]molybdenum-(i72-acyl) complexes, such as 1, are deprotonated by butyllithium or potassium hydride to generate enolate species, such as 488.8> jjie overa]] structure of these chiral complexes is similar to that of the iron and rhenium complexes discussed earlier the hydridotris(3,5-dimethyl-l-pyrazolyl)borate ligand is iso valent to the cyclopentadienyl ligand, occupying three metal coordination sites. However, several important differences must be taken into account when a detailed examination of the stereochemical outcome of deprotonation-alkylation processes is undertaken. 

F,SCH, Methanesulfonic acid, trifluoro-iridium, manganese and rhenium complexes, 26 114, 115, 120 platinum complex, 26 126 OiFeCgH, Iron, acetyl dicarbonyl (if -cyclopentadienyl)-, 26 239 0,FeN2C2 Hll(, Iron, tricarbonylbis(2-isocy-ano-l,3-dimethylbenzene)-, 26 54 0.iMoNaCHH5-2 C4H ,02, Molybdate 1 -), tricarbonyl(T) -cyclopentadienyl)-sodium, compd. with 1,2-dimethoxy-ethane-(l 2), 26 343 0,NaWC H5-2 C4H ,02, Tungstate(l -), tricarbonyl(ris-cyclopentadienyl)-... 

Ethene, molybdenum complex, 26 102 rhenium complex, 26 110 Europium, tetrakis[T) -l, 3-bis(trimethyl-silyl)cyclopentadienyl]di-p.-chloro-di-, 27 171... 

Mull ES, Sattigeri VJ, Rodriguez AL et al (2002) Aryl cyclopentadienyl tricarbonyl rhenium complexes novel ligands for the estrogen receptor with potential use as estrogen radiopharmaceuticals. Bioorg Med Chem 10 1381-1398... 

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... 

HClZrC oH, ), Zirconium, chlorobis(Ti -cyclopentadienyl)hydrido-, 28 259 HF2O2P, Phosphorodifluoridic acid, rhenium complex, 26 83 HFj04P2PtSC 4H34, Platinum(II), hydrido-(methanol)bis(triethylphosphine)-, trans-, trifluoromethanesulfonate, 26 135... 

Despite a common perception that organometallic chemistry essentially belongs in the province of catalysis rather than in vivo applications because of high reactivity of metal carbon bonds, certain organometallic species have very high kinetic stability. Indeed, this point is highlighted by the present wide application of the isonitrile complex Tc(ses-tamibi), [Tc(2-methoxyisobutylisonitrile)6]+, in myocardial imaging. Rhenium tricarbonyl and cyclopentadienyl complexes offer further ex-... 

The chemistry of rhenium(I) is dominated by organometallic compounds which are not covered by this review. Thus, cyclopentadienyl and related compounds, where the organometallic part of the molecule dominate the properties will generally not be considered. Nevertheless, compounds with carbonyl or isocyanide co-ligands will be treated when they can be regarded as constituents of a typical coordination compound or the compounds are of fundamental interest in a radiopharmaceutical context such as the hexakis(isocyanide)rhenium(I) cations. For the same reason a separate section has been included which gives a brief summary of recent attempts to develop synthetic routes to tiicarbonylrhenium(I) complexes for nuclear medical applications. 

Rhenium-acyl complexes, such as 1, are isoelectronic with the iron-acyl complexes discussed above and many reactivity patterns are common to the two groups of compounds. Treatment of complex 1 with strong bases, such as butyllithium or lithium diisopropylamide, results in abstraction of a cyclopentadienyl proton which is followed by rapid migration of the acyl ligand to the cyclopentadienyl ring to produce the metal-centered anion 384. Alkylation of 3generates a metal-alkyl species, such as 4. 

However, the more hindered, less basic lithium hexamethyldisilazamide reacts slowly with 1 at 0 °C to provide chemoselectively the desired enolate species 5. The a-protons of these rhenium-acyl complexes are believed to have a lower pKa than the cyclopentadienyl protons, but unless treated with hulky, selective hases the cyclopentadienyl protons exhibit greater kinetic acidity due to statistical factors and an earlier, reactant-like transition state since minimal rchybridiza-tion is required at the anionic center after cyclopentadienyl deprotonation. Equilibration of the cyclopentadienyl anion to the thermodynamically more stable enolate species cannot compete with the rapid acyl migration84. 

Gillespie, A.M. and White, D.P. (2001) Understanding the steric control of stereoselective olefin binding in cyclopentadienyl complexes of rhenium an application of de novo ligand design. Organometallics, 20, 5149. 

The structures of isomers of complex dibromodicarbonyl cyclopentadienyl-rhenium drawn ... 

The new compounds described in this paper have a rhenium atom incorporated into closo-l,2-dicarba-3-rhenadodecaborane or c/oro-l-carba-2-rhenadodecaboranc structures. However, to avoid a complicated nomenclature for the complexes reported, and to relate them to the many known rhenium species with 77-co-ordinated cyclopentadienyl ligands, we treat the cages as nido- 1 -vertex ligands with numbering as for an icosahedron from which the twelfth vertex has been removed. 

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