Abstract
We describe an experimental study of the reaction mechanism of
phenylacetylene oxidative carbonyl ation to methyl ether of
phenylpropiolic acid catalyzed by Pd(II) and Cu(I), which was closely
guided by recent computational research on the generation of reaction
mechanisms. Our initial mechanistic studies of this reaction were
based on informal (non-computer-generated) mechanistic
hypotheses. When experiments at 20 degrees C and 1 atm led us to
reject four of five mechanistic possibilities for the reaction, we
turned to formulating new hypotheses with the aid of the computer
programs ChemNet, which generated a reaction network consisting of 233
elementary steps, and MECHEM, which uncovered 41 simplest hypothetical
pathways from within the reaction network. Our subsequent analysis of
these 41 hypothetical mechanisms suggested a highly informative
experiment based on the CH3OH/CH3OD kinetic isotope effect. The ratio
between the rates of ester formation in nondeuterated and deuterated
methanol was close to unity, suggesting that O-H bond scission occurs
after the rate-limiting transmetalation step CuCCPh + PdCl2 -->
ClPdCCPh + CuCl. This experiment led to rejecting 32 out of the 41
hypotheses. Four more mechanisms were rejected based on the results of
preliminary experimental studies. Further work is needed to
discriminate among the five remaining mechanisms.
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