College of Science & Engineering
The long-term goal of this research program is to design new early transition metal-catalyzed reactions for the synthesis of complex molecular architectures from simple precursors. The rationale for using early transition metals (TMs) is that they are earth abundant and generally nontoxic: important factors in the design of sustainable, efficient, and practical synthetic methods. There have been significant recent advances in the utilization of earth abundant late TMs such as Fe, Co, Ni, and Cu in catalysis, but early TMs such as Ti have largely been left behind despite being more abundant and benign than the late TM analogues.
A significant challenge of working with early TMs is that they typically do not undergo facile oxidation state changes due to the thermodynamic stability of their highest oxidation states. In contrast, many late TM-catalyzed reactions require 1- or 2- electron redox changes at the metal center, such as oxidative addition or reductive elimination reactions. As a result, early TM-catalyzed synthetic methods have typically been limited to simple Lewis acid or hydrofunctionalization/insertion-type reactions. However, this limitation is largely borne out of a general lack of reaction development rather than an inherent lack of utility, and my current and future research program is focused on exploiting this disparity and bringing earth-abundant, inexpensive, and nontoxic Ti redox catalysis into the realm of modern synthetic methodology.
The researchers are continuing to capitalize on their recent discovery of the Ti-catalyzed [2+2+1] synthesis of pyrroles from alkynes and diazenes to expand this reaction into a broad suite of useful synthetic methodologies. Their immediate plans within this area are focused in three areas:
- Understanding the mechanism (via computation and experiment) of azobenzene-promoted Ti redox catalytic reactions in order to improve the rate, regioselectivity and scope of catalysis
- Designing related tandem bond forming reactions that incorporate new unsaturated partners
- Probing the viability of accessing new early TM redox strategies for turning over classic stoichiometric reactions such as McMurry or pinacol coupling reactions
The researchers are also carrying out new catalyst design experiments by using a combination of high-throughput computational analysis with statistical analysis (principle component analysis, machine learning) in order to identify new synthetic targets.