Dr. Paul G. Hayes, University of Lethbridge

Phosphazides: A New Functional Group for Ligand Design

The Staudinger reaction,1 wherein a tertiary phosphine is reacted with an organic azide, is a commonly utilized process to generate an iminophosphorane (RN=PR3). Because they are prone to facile loss of N2, the rarely observed phosphazide (RN3=PR3) intermediate is generally considered a fleeting species with no synthetic value. However, various stabilization methods (e.g., hydrogen bonding, steric hindrance and metal coordination)2 have been employed to isolate several phosphazides. In an effort to glean a deeper understanding of these functional groups, we developed several families of thermally robust mono- and diphosphazides that have been characterized by multinuclear NMR spectroscopy and X-ray crystallography. The synthesis, characterization and reaction chemistry of group 1 (Li, Na and K) and actinide (U3a and Th3b,3c) complexes supported by phosphazide ligands will be presented. Notably, divergent chemistry has been observed for complexes supported by these phosphazide-containing ancillary ligands compared to their phosphinimine counterparts, thereby suggesting that with judicious design phosphazides represent a viable functional group for coordination chemistry and homogenous catalysis. As proof of concept, a synthetic cycle of actinide-mediated CO2 functionalization was established. All aspects of these unqiue phosphazide-containing compounds will be discussed in detail.

All are welcome.