Effect of Tethered, Axial Thioether Coordination on Rhodium(II)-Catalyzed Silyl-Hydrogen Insertion

Abstract

The effect of tethering a thioether to a rhodium(II) paddlewheel complex are evaluated in Si-H insertion reactions. This study provides further evidence for the benefits of incorporating thioethers into the rhodium paddlewheel motif. When using a tethered complex, the in situ carbenoid formation and Dirhodium paddlewheel complexes [Rh II ] are renowned for being efficient catalysts through the in-situ formation of reactive rhodium carbenoid species from α-diazo carbonyl compounds, which then promote a wide variety of transformations. [1]

Effects of Axial Solvent Coordination to Dirhodium Complexes on Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

“…Darko and coworkers computed similar qualitative trends in the HOMO-LUMO gap for their tethered, axial thioether-coordinated dirhodium catalysts with DFT calculations (M06-2X/def2TZVPP level of theory). 63 Increases to LUMO energies should lead to greater difficulty in forming 6/6-L. The results of our computations support this notion.…”

“…58 As a result of the communication between these three atoms, dirhodium carbene reactivity is potentially "tunable" by axial ligation opposite to the Rh-C bond, a possibility being actively investigated. For instance, many have designed dirhodium complexes with improved catalytic properties 54,[61][62][63][64][65] by incorporating ligands with tethered axial donors (or ligands that shield the Rh core from axial coordination by external molecules 66 ). However, this direction is still in its infancy compared to that of modifying electronic and steric properties of the bridging ligands.…”

“…Further studies from the same group with mixed oxazolidinate/carboxylate dirhodium complexes confirmed the positive effect that the coordination of tethered thioether donors had on the catalytic activity of the complexes in Si-H insertion reactions and cyclopropanation reactions. 63,64 The authors argued that the enhanced selectivity they observed was related to an increase in the energy of the LUMO of the complex upon coordination of the axial ligand. 55 Coordinating Lewis basic additives may also lead to divergent outcomes.…”

“…144 Given the magnitude of our predicted effects, decomposing their origins with current theoretical methods would not be reliable; 77,145 Nonetheless, Darko and co-workers observed an increase in product yield for Si-H insertion reactions when dirhodium catalysts with tethered, axial coordinating ligands were used. 63 Results in Figure 7 suggest that perhaps tethered, axial coordinating ligands might also enhance regioselectivity.…”

Effects of Axial Solvent Coordination to Dirhodium Complexes on the Reactivity and Selectivity in C–H Insertion Reactions: A Computational Study

“…59 As a result of the communication between these three atoms, dirhodium carbene reactivity is potentially "tunable" by axial ligation opposite to the Rh-C bond, a possibility being actively investigated. For instance, many have designed dirhodium complexes with improved catalytic properties 55,[62][63][64][65][66] by incorporating ligands with tethered axial donors (or ligands that shield the Rh core from axial coordination by external molecules 67 ). However, this direction is still in its infancy compared to that of modifying electronic and steric properties of the bridging ligands.…”