Which future for stereogenic phosphorus? Lessons from P* pincer complexes of iron(ii).

PNP pincer ligands stabilise diamagnetic base metal catalysts, and much effort has been invested in the development of chiral analogues for asymmetric catalysis. Starting from the conformational issues that affect P-stereogenic diphosphines, we extend the analysis to our recently prepared P-stereogenic PNP pincer ligands, which we used in the iron(ii)-catalysed hydrogenation of ketones. Backbone rigidity and size (and shape) of the substituents at phosphorus are pivotal in both bi- and tridentate P-stereogenic ligands, and their interplay is discussed, as well as the contribution (and shortcomings) of DFT calculations to the understanding of the conformational flexibility and enantiodiscrimination.

Highly enantioselective transfer hydrogenation of ketones with chiral (NH)2 P2 macrocyclic iron(II) complexes.

Bis(isonitrile) iron(II) complexes bearing a C2 -symmetric diamino (NH)2 P2 macrocyclic ligand efficiently catalyze the hydrogenation of polar bonds of a broad scope of substrates (ketones, enones, and imines) in high yield (up to 99.5 %), excellent enantioselectivity (up to 99 % ee), and with low catalyst loading (generally 0.1 mol %).