Carboxylates cyclopentadienyl compounds

Covalently bonded chiral auxiliaries readily induce high stereoselectivity for propionate enolates, while the case of acetate enolates has proved to be difficult. Alkylation of carbonyl compound with a novel cyclopentadienyl titanium carbohydrate complex has been found to give high stereoselectivity,44 and a variety of ft-hydroxyl carboxylic acids are accessible with 90-95% optical yields. This compound was also tested in enantioselective aldol reactions. Transmetalation of the relatively stable lithium enolate of t-butyl acetate with chloro(cyclopentadienyl)-bis(l,2 5,6-di-<9-isopropylidene-a-D-glucofuranose-3-0-yl)titanate provided the titanium enolate 66. Reaction of 66 with aldehydes gave -hydroxy esters in high ee (Scheme 3-23). 

Figures 5 and 6 show one of the first examples of organo-metallic compounds adsorbed on the alumina of a metal-insulator-metal junction. The carboxyl groups on the benzene ring and cyclopentadienyl rings are most likely coordinated to the alumina. The arrangement of the carbonyl groups with respect to the surface would then be as shown below ...

In scientific and patent literature on diene polymerization the following Nd(III)-salts are most often cited as catalyst precursors halides, carboxylates, alcoholates, phosphates, phosphonates, allyl compounds, cyclopentadienyl derivatives, amides, boranes and acetylacetonates. The catalyst systems based on these Nd-sources are reviewed in the following subsections. 

The bridging chloride ligands in these [Ir(olefin)2Cl]2 compounds are susceptible to metathesis reactions, yielding new dimeric compounds of the form [Ir(olefin)2B]2 where B represents a new bridging ligand. AUcoxides, thiolates, and carboxylates have all been employed successfully in the replacement of chloride. The complexes with B = Br, I have also been prepared, both by metathesis reactions and by direct reaction of cyclooctene or cyclooctadiene with IrBrs or Iris The olefin complexes also provide excellent starting materials for the syntheses of arene and cyclopentadienyl iridium complexes, a subject that will be discussed in the next section. 

Chlorobis(cyclopentadienyl)tetnihydrobor8tozirconiuni(IV), Cp2Zr(CI)BH4. Mol. wt. 271.70. An early preparation has been reported without details. A convenient preparation involves reaction of Cp2Zr(H)Cl and BHi-S(CHj)2 yield 70-80%. Reduction of carbonyl groups Aldehydes and ketones are reduced by this complex in high yield esters, carboxylic acids, nitriles, and nitro compounds are reduced very slowly. The reagent thus resembles NaBH4, but can be used for reductions in benzene. 

ABSTRACT. Dicarbonyl(t 5-cyclopentadienyl)carbyne complexes of molybdenum and tungsten prove to be a valuable synthetic tool Reaction with phosphines provides substituted carbyne complexes and leads via an intramolecular CC-coupling to t 1- or Tj -ketenyl complexes respectively. Electrophiles attack the metal carbyne triple bond forming hetero- and acyclic carbene complexes, r 2-acyl compounds, T -ketene complexes and metalla-dithia-bicyclobutane cations. Dithio-carboxylates are formed in reaction of these dicarbonyl(Ti5 cyclo-pentadienyl)carbyne complexes with sulfur or cyclohexene sulfide. 

Spiro[3,4]octa-l,5,7-triene (249) has been prepared by modification of the carboxylic acid (250). The triene was characterized chemically by reduction to the saturated hydrocarbon and by its Diels-Alder reaction with JV-phenyltriazoline-3,5-dione. Any spiroconjugative interaction in the triene is not shown on its u.v. spectrum, which has at 262 nm, the same as observed for the diene (251). The triene is unstable, rearranging at — 5°C (t = 90 min) to 6-vinylfulvene and a dihydropentalene derivative. The ring-opening of (249) to 6-vinylfulvene is unusually rapid for a 3,3-disubstituted cyclobutene derivative, and other similarly strained compounds do not show this reactivity. The ring-opening may well proceed via a biradical intermediate with stabilization of the zwitterionic form of the biradical by formation of the aromatic cyclopentadienyl anion. 

CO2, as a small molecule, is inserted into Cp2Ti(7r-allyl) and the carboxylic aid is isolated by adding hydrochloric acid as shown in eq. (12.22). In the synthetic reaction of carboxylic acid, as shown in eq. (12.23), with chiral cyclopentadienyl titanium compounds having an asymmetric carbon bonded to the cyclopentadienyl ring, the optically active carboxylic acid yields [72]. 

In addition to being a component of tetrahedral chiral centres, ferrocene compounds with two different substituents on the same cyclopentadienyl ring display planar chirality. For example, the generalised structure 17 where X and Y represent two different substituents is non-superimposible upon its mirror image ent-17 such that compounds of this sort may be separated into, or synthesised as, their constituent enantiomers. Separation may be achieved through classical resolution where X or Y is a suitable functionality, typically a carboxylic acid. 

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