The zwitterionic complex [Cp*IrCl{(MeIm)2CHCOO}] (1) efficiently catalyzes the selective hydrosilylation of CO2 to afford the corresponding silylformate. The best reaction performance has been achieved in acetonitrile at 348 K using HSiMe2Ph. The 1‐catalyzed reaction of pyrrolidine with CO2 and HSiMe2Ph strongly depends on the CO2 pressure. At low concentration of CO2 (1 bar) formation of the corresponding silylcarbamate, by insertion of CO2 into the Si−N bond of the in situ generated silylamine was observed, while at higher pressure (3 bar) the formamide derivative was obtained as major reaction product. The unexpected formation of pyrrolidin‐1‐ium formate as intermediate of the reaction the 1‐catalyzed of CO2 with pyrrolidine and HSiMe2Ph has been observed, and its role in the formation of 1‐formylpyrrolidine rationalized. Moreover, a mechanism for the reaction of CO2 with hydrosilanes, in the presence and in the absence of amines, based on theoretical calculations has been proposed.
Enhancing catalytic activity through synergic effects
is a current
challenge in homogeneous catalysis. In addition to the well-established
metal–metal and metal–ligand cooperation, we showcase
here an example of self-activation by the substrate
in controlling the catalytic activity of the two-coordinate iron complex
[Fe(2,6-Xyl2C6H3)2] (1, Xyl = 2,6-Me2C6H3). This
behavior was observed for aryl acetylenes in their regioselective
cyclotrimerization to 1,2,4-(aryl)-benzenes. Two kinetically distinct
regimes are observed dependent upon the substrate-to-catalyst ratio
([RC≡CH]0/[1]0), referred
to as the low ([RC≡CH]0/[1]0 < 40) and high ([RC≡CH]0/[1]0 > 40) regimes. Both showed
sigmoidal
kinetic response, with positive Hill indices of 1.85 and 3.62, respectively,
and nonlinear Lineweaver–Burk replots with an upward curvature,
which supports positive substrate cooperativity. Moreover, two alkyne
molecules participate in the low regime, whereas
up to four are involved in the high regime. The second-order
rate dependence on 1 indicates that binuclear complexes
are the catalytically competent species in both regimes, with that
in the high one being 6 times faster than that involved
in the low one. Moreover, Eyring plot analyses revealed
two different catalytic cycles, with a rate-determining step more
endergonic in the low regime than in the high one, but with a more ordered transition state in the high regime than in the low one.
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