10.1021/ja0504441.s001
Daniel T. Nowlan
Daniel T.
Nowlan
Daniel A. Singleton
Daniel A.
Singleton
Mechanism and Origin of Enantioselectivity in the Rh<sub>2</sub>(OAc)(DPTI)<sub>3</sub>-Catalyzed
Cyclopropenation of Alkynes
American Chemical Society
2005
terminal acetylenic carbon
cyclopropenation
OAc
13 C KIE
mechanism
isotope effects
DPTI
Rh 2
canonical variational transition structures
tetrabridged rhodium carbenoids
tribridged rhodium carbenoid
2005-05-04 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Mechanism_and_Origin_of_Enantioselectivity_in_the_Rh_sub_2_sub_OAc_DPTI_sub_3_sub_Catalyzed_Cyclopropenation_of_Alkynes/3288079
The mechanism of cyclopropenations of alkynes with ethyl diazoacetate catalyzed by Rh<sub>2</sub>(OAc)<sub>4</sub> and Rh<sub>2</sub>(OAc)(DPTI)<sub>3</sub> (<b>1</b>) is studied by a combination of kinetic isotope effects and theoretical calculations. With each catalyst, a significant normal <sup>13</sup>C KIE was observed for the terminal acetylenic carbon, while a very small <sup>13</sup>C KIE was observed at the internal acetylenic carbon. These isotope effects are predicted well from canonical variational transition structures for cyclopropenations with intact tetrabridged rhodium carbenoids. A viable mechanism based on the recently proposed importance of a [2 + 2] cycloaddition on a tribridged rhodium carbenoid could not be identified. An explanation for the enantioselectivity with DPTI ligands is described.