Kinetic isotope effects alkyne reactions

A primary hydrogen deuterium kinetic isotope effect of 1.9 was found when Janout and Regen used deuterium oxide in place of water in the hydration of the adduct formed when phenylmercuric hydroxide reacts with terminal alkynes. The first step in this reaction... 

Reactions with aikynes may aiso result in the formation of cyclized products. Thus a ruthenium-catalysed reaction with aromatic amides has been used to give isoquinoline derivatives. On the basis of values of the kinetic isotope effect, A h/ d> proposed that the rate-determining step is a concerted acetate-assisted metalation-deprotonation process to yield the intermediate (30), followed by aikyne insertion and ring closure. The reaction of arylketones with alkynes may yield indenols when catalysed by rhodium cyclopentadienyl in the presence of silver and copper salts. The reaction proceeds regioselectively, so that reaction of acetophenone with 1-phenyl-1-propene... 

Thermolysis of Cp2TiMe2 in the presence of internal alkynes affords the corresponding titanacyclobutenes. The reaction is first order in Cp2TiMe2 and there is a primary kinetic isotope effect. Two equivalents of nitriles RCN react to give the diaza metallacycles... 

A study has been reported regarding the ruthenium-catalysed reaction of benza-mides with alkynes, which yields ort/io-alkenylated derivatives. Here, the mechanism is likely to involve rate-limiting metalation, followed by alkyne insertion to form intermediates such as (63) which on protonolysis yield the alkenylated products. An allylic carbon-carbon double bond has also been used as a coordination site in palladium-catalysed alkenylation reactions, as shown in Scheme 3. Here measurement of kinetic isotope effects suggests that coordination of the palladium with the allylic double bond occurs before palladation to give (64). Insertion of the alkene into the carbon-palladium bond gives (65) and -hydride elimination " leads to the product... 

The formations of dimer 21 or oligomer 22 of tris(thiolato) Zr(IV) complexes were observed by NMR [(12) and (13)]. Kinetic studies on 20-catalyzed reaction of 1-pentanethiol with 1-hexyne showed the empirical rate low expressed as rate = obs[20] l-hexyne] [l-pentanethil] (x = 1 for <0.3 M and x = 0 for >0.3 M) with A// = +18.1(1.2) kcal mol and AS = -20.9(2.5) e.u. In addition, a secondary kinetic isotope effect [kn/kx) = 1.3(0. )] was observed in the reaction of 1-pentanethiol with PhC=C-D catalyzed by 20. These and other findings are consistent with the catalytic cycle shown in Scheme 13, involving alkyne insertion into the Zr-SR bond (i), which is the turnover-limiting process, followed by protonolysis of Zr-C in 23 by thiol (ii). 

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