Synthesis of Calcium and Ytterbium Complexes Supported by a Tridentate Imino-Amidinate Ligand and Their Application in the Intermolecular Hydrophosphination of Alkenes and Alkynes

Well-defined calcium and ytterbium complexes [{2-NC­(Ph)­NArC6H4CHNAr}­M­{N­(SiMe3)2}­(THF)] (M = Ca, Yb; Ar = 2,6-iPr2C6H3) have been synthesized and characterized. They catalyze the intermolecular hydrophosphination of alkenes, dienes, and alkynes with high activity and selectivity under mild conditions. Highly selective 1,4-additions (94–100%) for the conjugated dienes examined have been observed with both catalysts. The calcium complex exclusively catalyzes anti addition to alkynes, including terminal alkynes, while the ytterbium, in most cases, catalyzes syn addition. The calcium catalyst could promote hydrophosphination of hindered alkenes such as stilbene under relatively mild conditions.