Kinetic Analysis and Mechanistic Implications

The implications of tins equation are detailed later in the context of the basic three-step catalytic cycle for palladium-catalyzed cross-couphng reactions [llf involving (i) oxidative insertion of palladium(O) into an alkyl hahde (ii) transmetallation of the transferable group from the donor moiety onto palladium and (iii) reductive elimination of the resultant organopaUadium species to give the coupled product and regenerate the palladium(O) catalyst 

The first-order rate-constant dependence on palladium concentration is consistent with a mononuclear palladium entity participating in each turnover of the catalytic cycle. This is similar to the kinetic result obtained for organotin-based cross-couplings [11]. It is noteworthy that the rate dependence on the catalyst concentration, manifested in the rate constant, eliminates the possibility that simple fluoride activation of the silanol (which does not involve palladium) could be turnover limiting. 

The zero-order behavior in 2-iodothiophene also finds analogy in the mechanism of organotin cross-coupling [80]. This is interpreted as a rapid and irreversible oxidative insertion step of the palladium(O) under the reaction conditions. The facility of this process has been well documented, and the predominant use of iodides in many of the early reports of cross-coupling chemistry has its origin in this behavior. 

the remaining possibilities are that either transmetallation or productforming reductive elimination could be the rate-determining step of this reaction. The positive correlation between the rate and silanol concentration strongly supports the conclusion that transmetallation is turnover limiting, as it is in 

It is crucial to note that a rate equation reveals information regarding the mechanistic pathway from the lowest energy species to the highest transition state. Hence, the inverse order dependence of TBAF lends further support to the 

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