N-Heterocyclic Carbene-Ytterbium Amide as a Recyclable Homogeneous Precatalyst for Hydrophosphination of Alkenes and Alkynes

The N-heterocyclic carbene-ytterbium(II) amides (NHC)(2)Yb[N(SiMe3)(2)](2) (1: NHC: 1,3,4,5-tetramethylimidazo-2-ylidene (IMe4); 2: NHC: 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr)) and the NHC-stabilized rare-earth phosphide (IMe4)(3)Yb(PPh2)(2) (3) have been synthesized and fully characterized. Complexes 1-3 are active precatalysts for the hydrophosphination of alkenes, alkynes, and dienes and exhibited much superior catalytic activity to that of the NHC-free amide (THF)(2)Yb[N(SiMe)(2)](2). Complex 1 is the most active precursor among the three complexes. In particular, complex 1 can be recycled and recovered from the reaction media after the catalytic reactions. Furthermore, it was found that complex 3 could catalyze the polymerization of styrene to yield atactic polystyrenes with low molecular weights. To the best of our knowledge, complex 1 represents the first rare-earth complex that can be recovered after catalytic reactions.