[Rh(I)L]-catalyzed cyclotetramerization of 1,3-butadiene: a theoretical investigation of alternative mechanistic paths for the generation of the [Rh(III)(octadienediyl)(PR3)]+ complex.
A detailed theoretical investigation of alternative mechanistic paths for the formation of the [Rh(III)(octadienediyl)(PiPr3)]+ complex is presented, employing a gradient-corrected density functional theory (DFT) method (BP86). This process represents most likely the first step in the recently reported [Rh(I)L]-catalyzed cyclotetramerization of butadiene (M. Bosch, M. S. Brookhart, K. Ilg and H. Werner, Angew. Chem., Int. Ed., 2000, 39, 2304). The favorable route for oxidative addition under C-C-bond formation starts from the prevalent [Rh(I)(butadiene)2(PiPr3)]+ form of the active catalyst through oxidative coupling between two cis-eta4-butadienes. This affords the [Rh(III)(bis-eta3-anti-octadienediyl)(PiPr3)]+ compound as the kinetic coupling product that consecutively undergoes transformation into the thermodynamically favorable bis-eta3-syn-octadienediyl-Rh(III) isomer via facile allylic conversions occurring in the octadienediyl framework. The computationally predicted energy profile is almost in quantitative agreement with the experimentally determined kinetics and allows a consistent rationalization of the experimental observations.
Tobisch
Sven
S
Institut für Anorganische Chemie der Martin-Luther-Universität Halle-Wittenberg, Fachbereich Chemie, Kurt-Mothes-Strasse 2, D-06120, Halle, Germany. tobisch@chemie.uni-halle.de
Werner
Helmut
H