The use of ligands to control the electronic and steric environment around a metal centre is crucial for tuning the properties of metal centres for applications in catalysis, pharmaceutical chemistry, and materials. More sophisticated ligands can also be designed to enable metal-ligand cooperativity, which unlocks reactivity that is not possible at the metal centre alone. Hybrid ligands that feature different donor sites can take advantage of specific binding preferences to give control of coordination chemistry, and allow for these cooperative effects such as hemilability, proton shuttling, and substrate recognition and activation (Figure ). 1,3-P,N ligands are a widely studied class of compounds that can bind selectively through the hard N-atom, the soft P-atom, or both, and can bind to one or multiple metal centres. This ligand class is typified by 2pyridylphosphines and iminophosphines, both of which have a C atom as the bridging centre between the P and the N donors (Figure ). Azophosphines (Figure ) are heavier analogues of triazenes, and are a new member of the family of 1,3-P,N ligands that have a bridging N atom between the donor N and P sites. A limited number of azophosphines were explored in the 1970s and 1980s, but interest in this class of molecules has been renewed with a series of recent publications exploring their synthesis and reactivity. The Cummins group synthesised a P-adamantyl derivative that could serve as a synthetic equivalent of a phosphaazide, and a small family of azophosphines that could undergo cycloaddition chemistry with alkynes to form N-heterocyclic iminophosphoranes. In our own work, we have also demonstrated cycloaddition chemistry of azophosphines to form seven-membered diazaphosphepine heterocycles, and most pertinently to this study, we showed that azophosphines could act as ligands in Ru complexes. The azophosphines initially bound to the ruthenium in a κ 1 -P manner, but the bidentate κ 2 -P,N binding mode could be cleanly accessed by using a halide abstracting agent to free up a coordination site on the metal centre.