We have previously shown 2-MCP interacts with a surface −OH predominantly by H2O elimination, forming a monodentate surface chlorophenoxy species.
Instead, base-mediated C H activation occurs to form palladacycle (C), which may follow one of two pathways: Oxidative addition to alkyl halide 6 can produce PdIV intermediate D-I, which upon reductive elimination forms intermediate E. 9 Another plausible sequence is a transmetalation between two different PdII centers (D-II), which forms E following reductive elimination.
The resulting product, Im3, is a stable hexacoordinate octahedral complex, in which the calculated distance between Rh and the O atom of THF is 2.343 Å. Reductive elimination forms the pinB C bond, leading to release of the γ-borylated product.
Hydroxyl dissociation generates a short-lived retinylic cation that can undergo proton elimination to form anhydroretinol.
The final step in the two-point binding mechanism is reductive elimination to form the pinB Cγ bond.
In contrast, with alkenes, insertion into a cyclometallated intermediate is usually followed by β-H elimination to form a vinyl species that dissociates from the metal.
In contrast, hydroxylation at a position carrying a leaving group leads to an intermediate that undergoes gem elimination to form a benzoquinone.
Furthermore, intermediate D is kinetically stabilized as the final E2 elimination to form 6 requires an s- trans arrangement of the vinyl lone pair and the phosphate leaving group.
Upon a migratory insertion, complex 11 is converted into π-allyl Pd species 12, which undergoes a reductive elimination to form diamination product 9 and regenerate the Pd(0) catalyst.
Reaction proceeds via migratory insertion of the alkene bond into the Rh H or Rh B bond with subsequent reductive elimination to form the B C or C H bond, respectively.
