Synthesis and Reactivity of Iminophosphorane Catalysts

Bunmi Adeyiga – Meyer Lab

The focus of our research for the past semester has been on the synthesis of iminophosphoranes. Once made, these compounds can serve as main group catalysts in imine and carbodiimide metathesis reactions.

Scheme 1

It is known that these iminophosphorane compounds can exist in a monomer/dimer equilibrium (Scheme 1). In order to be used as a catalyst, it is necessary that the compound be in the monomer form yet remain sufficiently reactive to interact with substrate. For this reason, iminophosphoranes were synthesized with substituents derived from three different elements of the same group, namely the halogen series: F, Cl, and Br. The size differences in these elements and their differences in electron-withdrawing ability are expected to affect the dimerization and also the propensity of these species to react with imine or carbodiimide substrates.

Scheme 2

We have most recently prepared chlorophenyliminophosphorane 1 (Scheme 2). The new chloro-derivative reacted with diisopropyl carbodiimide, forming phosphetidine compound 2 (Scheme 3). We are currently preparing the bromo-derivative and plan to study the relative reactivities of all of the derivatives with unsaturated substrates containing C=N bonds.

Scheme 3

One long term goal of this research is to prepare biologically innocuous polymers which could be used in such areas as drug delivery agents. The prospect of nontoxic treatments that are capable of slow biodegradation to give slow drug infusion over extended time periods serves as the driving force behind these efforts.

As a senior chemistry major that is soon planning to enter medical school, I have found this research experience to be very valuable. Much of my medical interests are focused on radiology and cancer research. My time spent in this lab has allowed me to recognize the tremendous impact that even the smallest projects can have in the global realm of scientific discovery. Also, I will come away from this experience with improved skills and lab techniques that should help me greatly in my future research endeavors.