摘要： After a near 7-year pathway devoted solely to late transition metal systems, my hunt in the world of catalysis drove me progressively towards the very left side of the periodic table. Group 4, then group 3, and now group 2 elements. Rare-earths and alkali-earths are really unique elements. Even though going down those two columns and running through the lanthanide row, physicochemical properties most often vary monotonously, their reactivity remains sometimes quite mysterious: who has ever truly rationalized the “peak activity” of neodymium catalyst systems in diene and ethylene polymerization?! But my favorite element isn’t neodymium: its paramagnetism makes for too nasty an NMR spectra to satisfy a molecular chemist in the search for understanding what’s going on in the coordination sphere… No, my special one is yttrium. This one is diamagnetic, providing beautiful, informative NMR spectra. And, importantly for the single-site polymerization catalysis community, some complexes of this abundant element have proved really unique in the ring-opening polymerization of cyclic esters, featuring high activity and unequaled stereocontrol abilities—not unrelated to its small size, which makes for a crowded, discriminative coordination sphere.