Modeling catalytic reactions can give perhaps the most useful information for catalyst development; namely, how changing the ancillary ligands affects the catalytic reaction. The most intuitive methods for such modeling can give direct information about how ancillary ligand donor properties and sterics affect characteristics like the rate or regioselectivity. While methods for measuring the donor abilities of phosphines have been known for decades, e.g., the Tolman electronic parameter, methods for measuring donor abilities of common ligands for high oxidation state catalysis were far less explored. Recently, our group published a method for quantifying the donor abilities of anionic ligands for high oxidation state systems, which we name Ligand Donor Parameters (LDPs). These LDPs correlate with a variety of different data from the literature. Interestingly, we can apply these donor abilities to the modeling of titanium-catalyzed reactions. In this presentation, we will describe a general model for understanding the rate of titanium-catalyzed hydroamination applicable to virtually any catalyst with a bidentate ligand. The model gives some mechanistic information regarding the nature of the rate determining steps for the catalysis. In addition, it provides some insight into when a mechanism change occurs; and as a result, we discovered an indolyl-effect, where 3-unsubstituted indolyl groups lead to greatly enhanced catalytic rates over and above the rate expected from simple electronic and steric perturbations.

New methods for modeling high oxidation state catalysis

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