DFT calculations revealed the effects of N-heterocyclic carbene (NHC) ligands on reaction mechanism and bridged between ground state ligand properties and reaction outcomes. The rate determining step (RDS) for Rh-NHC catalyzed hydroboration of styrene is boryl migration for linear regio-isomer and hydride migration for branched regio-isomer. Due to different geometries of these RDS, following designing principles were concluded for rational catalyst design: 1). Better doner ancillary ligands, evidenced by smaller tolman electronic parameter (TEP) promote activity of both linear and branched products; 2). Bulky NHC ligands with larger cone angle suppresses sterically sensitive hydride migration making linear selective boryl migration more accessible; 3). Smaller NHC and PPh3 ligands with smaller cone angle lead to branched product. These summarized designing principles of Rh-NHC catalysts aim to achieve enhanced reactivity, and the ability to perform switchable catalysis in hydroboration even other hydrofunctionalization reactions.

Control of reaction mechanism and reactivity and by photoswitchable N-heterocyclic carbene ligands in Rh-catalyzed hydroboration of styrene: A computational investigation

2019 Spring National Meeting

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