文摘
The kinetics for the cobalt-catalyzed intermolecular Pauson-Khand reaction (PKR) between (trimethylsilyl)acetylene and norbornadiene (NBD) at a constant CO pressure has been studied by means ofin situ FT-IR. The rate dependence on catalyst and substrate concentrations was examined, and it wasfound that the process is -1.9 order with respect to CO pressure, zero order with respect to acetylene,0.3-1.2 order with respect to NBD, and 1.3 order with respect to the Co2(CO)8 catalyst. Catalytic reactionintermediates were examined by their corresponding metal carbonyl IR frequencies. By a one-potconsecutive Pauson-Khand experiment, the NBD-dicobalt hexacarbonyl complex was identified as acatalytically active complex. Co4(CO)12 was also studied as a catalyst source in the PKR. Analysis of thecorresponding reaction intermediates by IR demonstrated that Co2(CO)8 and Co4(CO)12 provide identicalintermediate profiles upon reaction with TMSC2H. The experimental measured kinetics are consistentwith the alkene insertion being the rate-limiting step in the catalytic PKR. Finally, the effect of phosphinesubstitution on the catalyst and the use of Lewis acid additives were shown to have a deleterious effecton the reaction rate.