1,3-Cyclopentadiene complexes

MetaHacarborane dicarboUide complexes are generaUy more robust than the corresponding cyclopentadiene complexes. The bis-dicarboUide sandwich complexes of general formula [M(C2Bg)H )2] , where M is Fe ", Co ", and exhibit great thermal, chemical, redox, and radiolytic stabUity. 

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

Examples with a skeletal electron count of 8 pairs, and with structures formally based on a pentagonal bipyramid, include the cloao-ferra-cyclopentadiene complex Fe3(CO)8C4Ph4 (55) and the related nido... 

The chromium tricarbonyl derivative 252 ° and the cyclopentadiene complexes 253 and 254 ° have been prepared. 

Blacker, A.J. and MeUor, B. J. Preparation of Chiral Arylalkanols by Transfer Hydrogenation using Chiral Metal Cyclopentadiene Complex Catalysts. PCT Int. Appl. 1998, WO 9842643 Al. 

Cobaltacyclobutene 39 reacts with alkynes in a net insertion/reductive elimination process to yield stereoisomeric cobalt-77-cyclopentadiene complexes 55 (Equation 17) <1995JA8029>. 

Only with 1,3-cyclopentadiene (lh) does 73 give two r -1,3-cyclopentadiene complexes [Eq. (41)]. The two products are the thermo- and photolabile ace-... 

Samarium iodide catalyzes the reduction of halides in damp THF120-122 and yields may be significantly improved if HMPA is added to the reaction mixture121,123. a-Halocarbonyl compounds are readily hydrodehalogenated by the use of this and similar methods124-126. Bis-cyclopentadiene complexes of samarium catalyze the reduction of benzylic and ally-lie halides via an organosamarium complex intermediate127-129. This reaction may be controlled so that monodeuteration occurs if the reaction is carried out under dry aprotic conditions followed by addition of D20 (equation 12). 

The linear coupling reaction of acetylene and acrylonitrile afforded 2,4,6-hep-tatrienenitrile by dimerization of acetylene and insertion of one molecule of acrylonitrile [88] (Eq. 66). The reaction involves the formation of a ruthena-cyclopentadiene complex, which also catalyzed the reaction. 

Apart from providing direct spectroscopic evidence for the various catalytic steps, experiments with 6.15 and other lanthanide cyclopentadiene complexes also established that paramagnetic metal ions do not have any special effect on the oligomerization reaction. The mechanism proposed on the basis of these studies is as shown in Fig. 6.5. 

The synthesis of the mixed sulfur-selenium donor BEDS-TTF (BEST) via the tetralithiation of TTF was mentioned above [53]. Bis(ethylenedithio) tetraselenafulvalene (BEDT-TSF, BETS) is obtained in good yield following the sequence outlined in Scheme 14. The synthesis makes use of a titanium-cyclopentadiene complex to stabilize a problematic, unstable synthetic intermediate (35) [7]. 

Other 7t-bonded cyclopentadiene complexes to be mercurated include (h -C5H5)2Ru ° h=-C5H5M(CO)3 (M = Mn ° or Rei° ), h -C5H5M(CO)2PPh3... 

Metal carbonyl complexes of steroids have been synthesized by the groups of Jo-hannsen and Katzenellenbogen (Arterburn et al. 2003 Bigott et al. 2005 Luyt et al. 2003 Wust et al. 1998, 1999). Various 17j -progesterone and 7a-estradiole dithioether and cyclopentadiene complexes of technetium/rhenium(I) tricarbonyl have been pre-... 

Cyclopentadienylthallium is a superior reagent for many syntheses. It is easily prepared and stored, it may be handled in air, and the insolubility of thallium halide leads to high yields of product that may be filtered easily and worked up. The reagent has been used for preparing a variety of actinide, lanthanide, and transition metal cyclopentadiene complexes. 

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