Rhenium-catalysed reactions

Rhenium The reaction of )3-keto sulfones R COCH2S02R with terminal alkynes R C=CH, catalysed by Re2(CO)io, has been reported to afford the (Z)-configured unsaturated S-keto sulfones R C0CH=C(R )CH2S02R as a result of an unusual insertion of the alkyne into the C-C bond between the a- and )3-positions of the )3-keto sulfone. ... 

Mechanistic insights into the rhenium-catalysed alcohol-to-olefin dehydration reaction have been reported. The experimental studies showed the dependence on water and the intolerance to base, and the involvement of proton transfer in the catalytic cycle. A car-benium ion intermediate has been suggested. Kinetic isotope effect studies, furthermore, ruled out proton loss from the / -position of the alcohol as the rate-determining step. The DFT calculations indicated that the lowest energy pathway most likely proceeds through coordination of the alcohol to the rhenium centre with a subsequent carbon-oxygen breakage that yields a carbenium ion. Proton transfer from the carbenium ion to water. 

A rhenium-catalysed regio- and stereo-selective reaction of terminal alkynes with imines forms A-alkylideneallylamines rather than the expected propargylamines. The 0-carbon of the alkynyl rhenium is believed to attack the imine carbon to give a vinylidene rhenium intermediate (Scheme 6)7 ... 

A study, including computational results, of the role of copper enolate complexes in the a-arylation of enolates has shown that the reaction is likely to occur through oxidative addition of the iodoarene to form an aryl-copper(III) intermediate, (46), followed by reductive elimination to give the product. Copper(III) species are also likely to be involved in the meta-selective C-H arylation of acetanilides by diaryliodonium salts. However, radical species may be involved in the rhenium-catalysed electrophilic triflu-oromethylation of arenes using hypervalent iodine reagents. 

Kuroda and Tarui [498] developed a spectrophotometric method for molybdenum based on the fact that MoVI catalyses the reduction of ferric iron by divalent tin ions. The plot of initial reaction rate constant versus molybdenum concentration is rectilinear in the range 0.01-0.3 mg/1 molybdenum. Several elements interfere, namely, titanium, rhenium, palladium, platinum, gold, arsenic, selenium, and tellurium. 

A rhenium complex, [ReBr(CO)3(thf)]2, has been found able to catalyse the inter-molecular reactions of 1,3-dicarbonyl compounds with terminal alkynes to give the corresponding alkenyl derivatives in excellent yields (Scheme 6).35 These reactions could apply to an intramolecular version and gave the corresponding cyclic compounds quantitatively. Tributylphosphine has been found to be a superior catalyst for the a-C-addition of 1,3-dicarbonyl compounds to electron-deficient alkynes.36... 

Chloride ion catalyses the reaction and has an effect on the final product which is considered to be a dinuclear Ti -Re complex. It is of interest that on preparation of rhenium(v) and reaction with Ti ", there is an instantaneous reduction to yield the same dinuclear product. The use of non-aqueous media for investigating electron-transfer reactions is increasing and a review of solvent effects of systems involving metal complexes in homogeneous and heterogeneous phases has recently been published. ... 

Progress in rhenium chemistry reported in 1991 is reviewed.549 There is much important material in a review of methyltrioxorhenium catalysed alkene metathesis, oxidation and aldehyde alkenation, a review of the insertion of activated alkynes into the metal-metal bond of dinuclear manganese and rhenium carbonyl complexes. i a review of the reactions of [Cp(CO)2Mn=CPh]+ towards electron rich alkynes and nitriles552 and a review of the discovery of tRe(CBu )(CHBu ) OCMe(CF3)2 2l and recent results covering the metathesis of alkenes. s... 

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