Ligand design elements for iron catalysts

1 Strong field ligands on iron(II) keep it diamagnetic 

2 Strong field ligands promote hydride formation 

Hundreds of iron hydride complexes with phosphine ligands have been isolated and characterized. These complexes are almost always diamagnetic. For example, a spectacularly active electrocatalyst for dihydrogen oxidation is the cyclopentadienyl iron 

Strategy, allowing the ready exploration of catalyst structure to find the one that yields the highest activity and selectivity for a particular substrate. 

2 First generation iron catalysts with symmetrical [6.5.6]-P-N-N-P ligands 

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