Prof Steve Liddle: Zirconium-phosphinidene complex prepared by a Liddle group final year MChem project student published in Angewandte Chemie
Work carried out by Hannah Stafford, a final year MChem project student, which resulted in the synthesis and characterisation of the first example of a transition metal parent phosphinidene complex outside of cryogenic matrix isolation experiments, has been published in Angewandte Chemie International Edition
Phosphinidene complexes were first reported 30 years ago but they still remain a relatively rare class of metal-ligand multiple bond when compared to alkylidenes/carbenes, imidos, and oxos. These complexes are of interest due to the challenges involved in preparing them and also for potential applications in P-atom transfer reactions.
All transition metal phosphinidene complexes have required a sterically demanding P-substituent to be kinetically stable, but this can by definition suppress reactivity and distort equilibrium geometries, so it is of interest to study the parent PH phosphinidene. However, the only examples pertained to spectroscopic studies on microscopic quantities in frozen argon matrices at 5 K.
Working under the supervision of PhD students Liz Wildman and Thomas Rookes, Hanna prepared a zirconium parent phosphanide complex supported by a Tren-ligand tailored to match the steric requirements of zirconium. Hanna was then able to deprotonate this complex to prepare multi-gram quantities of the corresponding zirconium-phosphinidene complex.
Interestingly, the zirconium-phosphinidene complex appears to exhibit an agostic-type Zr···HP interaction, which is, despite very different coordination geometries and states of charge, similar to what has been proposed for matrix isolated Zr=PH species, which suggests that this is an inherent feature of early d-block phosphinidenes. Quantum chemical calculations and bond topological analysis suggest, rather surprisingly, that the Zr=PH bond is about as covalent as U=PH and Th=PH analogues, which runs counter to the generally advanced view that d-block complexes exhibit more covalent bonding than f-block analogues.
Citation: H. Stafford, T. M. Rookes, E. P. Wildman, G. Balázs, A. J. Wooles, M. Scheer, S. T. Liddle, Angew. Chem. Int. Ed., 2017, doi:10.1002/anie.201703870.